Bowman's Capsule - Kidney Blood Filtering Home > Cardiovascular System > Cardiovascular System of the Lower Torso > Blood Supply to the Kidneys > Bowman's Capsule Bowman's Capsule The Bowman's capsule is an expansion at the closed end of a renal tubule. A kidney's renal corpuscle is composed of tangled clusters of blood capillaries, called a glomerulus, and a thin-walled, saclike structure called the Bowman's capsule, which surrounds the glomerulus. The Bowman's capsule is composed of two layers of cells: an inner layer that closely covers the glomerulus, and an outer layer that is continuous with the inner layer and with the wall of the renal tubule. The renal tubule ...

Inside Your Kidneys - How Your Kidneys Work | HowStuffWorks How Your Kidneys Work Diagram showing the parts of the kidney and the nephron If you were to cut a kidney in half, you would see the following parts: Renal capsule - a thin, outer membrane that helps protect the kidney Cortex - a lightly colored outer region Medulla - a darker, reddish-brown, inner region Renal pelvis - a flat, funnel-shaped cavity that collects the urine into the ureters If you look closely at the cortex and medulla, you can see many tiny, tubular structures that stretch across both regions perpendicular to the surface of the kidney. In each kidney, there are one million of these structures, called nephrons. The nephron is the basic unit of the kidney. It's a long, thin tube that is closed at one end, has two twisted regions interspaced with a long hairpin loop, ends in a long straight portion and is surrounded by capillaries. Up Next The parts of the nephron are as follows: Bowman's capsule - This closed end at the beginning of the nephron is located in the cortex.

Proximal convoluted tubule or proximal tubule - The first twisted region after the Bowman's capsule; it's in the cortex. Loop of Henle - A long, hairpin loop after the proximal tubule, it extends from the cortex down into the medulla and back. Distal convoluted tubule or distal tubule - This second twisted portion of the nephron after the loop of Henle is located in the cortex. Collecting duct - This long straight portion after the distal tubule that is the open end of the nephron extends from the cortex down through the medulla. Each part of the nephron has different types of cells with different properties -- this is important in understanding how the kidney regulates the composition of the blood.

The nephron has a unique blood supply compared to other organs: Afferent arteriole - connects the renal artery with the glomerular capillaries Glomerular capillaries - coiled capillaries that are inside the Bowman's capsule Efferent arteriole - connects the glomerular capillaries with the peritubular capillaries Peritubular capillaries - located after the glomerular capillaries and surrounding the proximal tubule, loop of Henle, and distal tubule Interlobular veins - drain the peritubular capillaries into the renal vein The kidney is the only organ of the body in which two capillary beds, in series, connect arteries with veins. This arrangement is important for maintaining a constant blood flow through and around the nephron despite fluctuations in systemic blood pressure.

Regulating the composition of the blood involves the following: Keeping the concentrations of various ions and other important substances constant Keeping the volume of water in your body constant Removing wastes from your body Keeping the acid/base concentration of your blood constant The kidney does this by a combination of three processes: It filters 20 percent of the plasma and non-cell elements from the blood into the inside of the nephron (the lumen). It reabsorbs the components that the body needs from the lumen back into the blood. It secretes some unwanted components from the blood into the lumen of the nephron. Anything (fluid, ions, small molecules) that has not been reabsorbed from the lumen gets swept away to form the urine, which ultimately leaves the body. Through these processes, the blood is maintained with the proper composition, and excess or unwanted substances are removed from the blood into the urine.

Next, we'll look at how the kidneys regulate blood composition by three main processes: Filtration The Nephron: The Glomerulus's Major Structures and Functions - Video & Lesson Transcript | Study.com The Nephron: The Glomerulus's Major Structures and Functions Watch short & fun videos Start Your Free Trial Today An error occurred trying to load this video. Try refreshing the page, or contact customer support. You must create an account to continue watching Register for a free trial Are you a student or a teacher? I am a student Start Your Free Trial To Continue Watching As a member, you'll also get unlimited access to over lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed. Coming up next: Supportive Structures of the Nephron: Functions and Definitions You're on a roll. Keep up the good work! Your next lesson will play in 10 seconds 0:40 The Glomerulus Add to Add to Add to Want to watch this again later? Log in or sign up to add this lesson to a Custom Course. Custom Courses are courses that you create from Study.com lessons.

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Create an account to start this course today Try it free for 5 days! Lesson Transcript Instructor: Artem Cheprasov Artem is a doctor of veterinary medicine and has taught science and medicine at the college level. Together, the glomerulus and Bowman's capsule make up the renal corpuscle of the nephron. These parts of the nephron filter blood and are vital to our body's survival. In this lesson, you'll explore the major corpuscular structures and their functions. Cardiac Output to the Kidneys About 25% of your cardiac output goes to your kidneys. Without a doubt, I'm sure you know that your kidneys are critical for life. In fact, they are so important that every minute about 25% of your heart's output, known as cardiac output, goes to your kidneys. This is because your kidneys are essential in the filtration of blood and the maintenance of water balance throughout your entire body. In this lesson, we'll get into the very first part of your blood's transit through the nephrons, which are the functional units of the kidneys. The Glomerulus As blood is pumped out of the heart, it will pass through the aorta before reaching the kidney.

Once this blood enters the kidneys, it will eventually enter the first part of each nephron. This part is a network of capillaries responsible for the filtration of blood that is called a glomerulus. The Bowman's Capsule Each glomerulus is surrounded by a single layer of epithelium called the Bowman's capsule. If you can imagine inserting your fist into a large water balloon, your fist would be the glomerulus, and the balloon would be the Bowman's capsule enveloping your fist. The space between the sides of the balloon would be called the Bowman's space. The Renal Corpuscle Together, the glomerulus and its surrounding Bowman's capsule are called a renal corpuscle. This structure is located in the renal cortex. You should also be aware that the nephron is composed of two main parts: the renal tubule and the renal corpuscle. The renal corpuscle, in essence, is the first structure involved in the nephron's formation of urine, while the renal tubule takes over thereafter. In addition, the renal corpuscle's role is often referred to as the ultrafiltration of blood. The renal corpuscle is the first structure involved in the formation of urine.

The Afferent and Efferent Arteriole At this point, you're probably wondering how the process of ultrafiltration occurs. In essence, blood enters the glomerulus through a small artery supplying the glomerulus with unfiltered blood called the afferent arteriole. Another vessel, a small artery carrying filtered blood away from the glomerulus, is called the efferent arteriole. These two arterioles play a key role in helping the glomeruli's capillaries perform the process of ultrafiltration. Ultrafiltration Here's what I mean. If you were to go outside and connect a hose to a faucet and turn the faucet on, water would flow freely out the open end of the hose. If you were to take the open end and close off half of the opening with your finger without adjusting the faucet's output, the pressure inside the hose would increase since the water is being held back from coming out freely and you haven't decreased the amount of water coming into the hose from the faucet. Likewise, thanks to a pressure difference between the afferent and efferent arterioles, your blood can be filtered by the glomerulus.

Normally, the efferent arteriole's lumen, which is the central space where blood flows, is a smaller diameter than the afferent arteriole's lumen. This means that the 'open' end of the hose, the efferent arteriole, is smaller than the faucet's end, the afferent arteriole. This difference creates a sort of back-up of blood in the glomerulus itself, and this back-up of blood means the pressure rises within the glomerulus as it did in our hose. × What is Bowman's Capsule? (with pictures) What is Bowman's Capsule? Last Modified Date: 14 December 2016 Copyright Protected: These 10 facts about space will blow your mind A Bowman's capsule is part of the filtration system in the kidneys. When blood reaches the kidneys for filtration, it hits this area first, with the capsule separating the blood into two components: a cleaned blood product, and a filtrate that is moved through the nephron , another structure in the kidneys. As the filtrate travels along the nephron, additional impurities are removed, and the filtrate is concentrated into urine for the purpose of expressing waste products and excess water.

Each nephron in the kidneys is attached to its own capsule, and there are hundreds of thousands of nephrons. Functioning kidneys can move the blood around the body about 20 times each day, illustrating just how important these structures are. The system within the kidneys is also very complex, with a number of interconnected structures that work together to filter the blood effectively. The kidneys are truly a marvelous feat of natural engineering, and despite the medical community's best efforts, it has proved impossible to build a fully artificial kidney . Blood enters the Bowman's capsule through an afferent arteriole , which connects to the glomerulus , a tangled array of tubes. The glomerulus and capsule are often collectively referred to as the renal corpuscle. As the blood is forced through these tubes, impurities and water filter out into the Bowman's capsule. The cleaned blood exits at the vascular pole, while the impurities are moved through the urinary pole so that they can connect with the nephron and start working their way to the ureter .

The blood that leaves the vascular pole connects with the efferent arteriole, a capillary which enters the kidney and wraps around the loop of Henle so that it can reabsorb water and the correct concentration of solutes. At this point, the blood can be sent up to the heart via a network of veins for recirculation. Red blood cells are not filtered through the nephrons, which is why blood in the urine is a concern, because it means that the kidneys or urinary tract are damaged. Astute observers may note that the composition of urine also changes, depending on dietary factors and the amount of water being consumed. When the kidneys identify impurities that need to be removed, they will express them, and they will also conserve water and minerals that may be useful for the body to have, through the process of osmosis along the nephrons. Ad Glomerular Filtration About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account.

There, you can easily access this resource later when you’re ready to customize it or assign it to your students. Glomerular Filtration Glomerular filtration is the renal process whereby fluid in the blood is filtered across the capillaries of the glomerulus. Learning Objective Explain the process of glomerular filtration in the kidneys Key Points The formation of urine begins with the process of filtration . Fluid and small solutes are forced under pressure to flow from the glomerulus into the capsular space of the glomerular capsule . The Bowman's capsule is the filtration unit of the glomerulus and has tiny slits in which filtrate may pass through into the nephron . Blood entering the glomerulus has filterable and non-filterable components. Filterable blood components include water, nitrogenous waste, and nutrients that will be transferred into the glomerulus to form the glomerular filtrate. Non-filterable blood components include blood cells , albumins , and platelets , that will leave the glomerulus through the efferent arteriole . Glomerular filtration is caused by the force of the difference between hydrostatic and osmotic pressure (though the glomerular filtration rate includes other variables as well).

Terms Register for FREE to remove ads and unlock more features! Learn more Full Text Glomerular filtration is the first step in urine formation and constitutes the basic physiologic function of the kidneys . It describes the process of blood filtration in the kidney, in which fluid, ions , glucose , and waste products are removed from the glomerular capillaries . Many of these materials are reabsorbed by the body as the fluid travels through the various parts of the nephron, but those that are not reabsorbed leave the body in the form of urine. Glomerulus Structure Blood plasma enters the afferent arteriole and flows into the glomerulus, a cluster of intertwined capillaries. The Bowman's capsule (also called the glomerular capsule) surrounds the glomerulus and is composed of visceral (simple squamous epithelial cells—inner) and parietal (simple squamous epithelial cells—outer) layers. The visceral layer lies just beneath the thickened glomerular basement membrane and is made of podocytes that form small slits in which the fluid passes through into the nephron.

The size of the filtration slits restricts the passage of large molecules (such as albumin) and cells (such as red blood cells and platelets) that are the non-filterable components of blood. These then leave the glomerulus through the efferent arteriole, which becomes capillaries meant for kidney–oxygen exchange and reabsorption before becoming venous circulation. The positively charged podocytes will impede the filtration of negatively charged particles as well (such as albumins). Kidney Filtration - How Your Kidneys Work | HowStuffWorks How Your Kidneys Work Prev Next The glomerular capillaries, peritubular capillaries and the Bowman's capsule are all integral to the filtration process. In the nephron, approximately 20 percent of the blood gets filtered under pressure through the walls of the glomerular capillaries and Bowman's capsule. The filtrate is composed of water, ions (sodium, potassium, chloride), glucose and small proteins (less than 30,000 daltons -- a dalton is a unit of molecular weight). The rate of filtration is approximately 125 ml/min or 45 gallons (180 liters) each day.

Considering that you have 7 to 8 liters of blood in your body, this means that your entire blood volume gets filtered approximately 20 to 25 times each day! Also, the amount of any substance that gets filtered is the product of the concentration of that substance in the blood and the rate of filtration. So the higher the concentration, the greater the amount filtered or the greater the filtration rate, the more substance gets filtered. This filtration process is much like the making of espresso or cappuccino. In a cappuccino machine, water is forced under pressure through a fine sieve containing ground coffee; the filtrate is the brewed coffee. The arrangement of the glomerular capillaries in series with the peritubular capillaries is important to maintain a constant pressure in the glomerular capillaries, and thus a constant rate of filtration, despite momentary fluctuations in blood pressure. Once the filtrate has entered the Bowman's capsule, it flows through the lumen of the nephron into the proximal tubule. Up Next BBC - GCSE Bitesize Science - The urinary system : Revision, Page 3 Next The nephron Urine is produced in microscopic structures in the kidney called nephrons.

There are approximately 1 million nephrons in each kidney. The glomerulus filters blood and produces glomerular filtrate. This filtrate contains water, glucose [glucose: A simple sugar made by the body from food, which is used by cells to make energy in respiration.] , salts and urea [urea: A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine.] . Large molecules such as protein [protein: Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.] are too large to fit through the blood capillary [capillaries: Extremely narrow tubes, which carry blood around a body's tissues.] walls. The Bowman's capsule collects the filtrate and it enters the tubules. All glucose is reabsorbed immediately into the blood capillaries. As the rest of the filtrate travels through the tubules, water and salts needed by the body are reabsorbed into the blood capillaries. The loop of Henlé helps maintain the correct water balance in the body by filtering out salts. The waste, consisting of excess water, excess salts and urea, is urine.

The collecting duct collects the urine, which is then transported in the ureter to the bladder. The bladder stores urine until the body is ready to expel it through the urethra. This process can be summarised in three important steps: Filtration - where lots of water, ions [ion: The charged particle formed when an atom, or a group of atoms, lose or gain electrons. Ion charge helps determine a substance's acidity or alkalinity.] , urea [urea: A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine.] and sugar are squeezed from the blood into the tubules. Selective reabsorption – the useful substances (ions and sugars) are reabsorbed back into the blood from the tubules. The amount of water in the blood is regulated here to maintain it at a constant rate. This is known as ‘osmoregulation’. Excretion of waste - urea and excess water and ions travel to the bladder as urine, to be released from the body. For more information about the kidney visit the Human Body and Mind section of the BBC website. Read on if you're taking the higher paper.

Page Human Physiology/The Urinary System - Wikibooks, open books for an open world Human Physiology/The Urinary System This is the latest reviewed version , checked on 6 September 2014. (+) Quality: minimal 12 References Introduction The Urinary System is a group of organs in the body concerned with filtering out excess fluid and other substances from the bloodstream. The substances are filtered out from the body in the form of urine. Urine is a liquid produced by the kidneys, collected in the bladder and excreted through the urethra. Urine is used to extract excess minerals or vitamins as well as blood corpuscles from the body. The Urinary organs include the kidneys, ureters, bladder, and urethra. The Urinary system works with the other systems of the body to help maintain homeostasis. The kidneys are the main organs of homeostasis because they maintain the acid base balance and the water salt balance of the blood. Functions of the Urinary System One of the major functions of the Urinary system is the process of excretion. Excretion is the process of eliminating, from an organism, waste products of metabolism and other materials that are of no use.

The urinary system maintains an appropriate fluid volume by regulating the amount of water that is excreted in the urine. Other aspects of its function include regulating the concentrations of various electrolytes in the body fluids and maintaining normal pH of the blood. Several body organs carry out excretion, but the kidneys are the most important excretory organ. The primary function of the kidneys is to maintain a stable internal environment (homeostasis) for optimal cell and tissue metabolism. They do this by separating urea, mineral salts, toxins, and other waste products from the blood. They also do the job of conserving water, salts, and electrolytes. At least one kidney must function properly for life to be maintained. Six important roles of the kidneys are: Regulation of plasma ionic composition. Ions such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphates are regulated by the amount that the kidney excretes. Regulation of plasma osmolarity. The kidneys regulate osmolarity because they have direct control over how many ions and how much water a person excretes. Regulation of plasma volume. Your kidneys are so important they even have an effect on your blood pressure.

The kidneys control plasma volume by controlling how much water a person excretes. The plasma volume has a direct effect on the total blood volume, which has a direct effect on your blood pressure. Salt(NaCl)will cause osmosis to happen; the diffusion of water into the blood. Regulation of plasma hydrogen ion concentration (pH). The kidneys partner up with the lungs and they together control the pH. The kidneys have a major role because they control the amount of bicarbonate excreted or held onto. The kidneys help maintain the blood Ph mainly by excreting hydrogen ions and reabsorbing bicarbonate ions as needed. Removal of metabolic waste products and foreign substances from the plasma. One of the most important things the kidneys excrete is nitrogenous waste. As the liver breaks down amino acids it also releases ammonia. The liver then quickly combines that ammonia with carbon dioxide, creating urea which is the primary nitrogenous end product of metabolism in humans. The liver turns the ammonia into urea because it is much less toxic. We can also excrete some ammonia, creatinine and uric acid. The creatinine comes from the metabolic breakdown of creatine phospate (a high-energy phosphate in muscles).

Uric acid comes from the break down of nucleotides. Uric acid is insoluble and too much uric acid in the blood will build up and form crystals that can collect in the joints and cause gout. Secretion of Hormones The endocrine system has assistance from the kidney's when releasing hormones. Renin is released by the kidneys. Renin leads to the secretion of aldosterone which is released from the adrenal cortex. Aldosterone promotes the kidneys to reabsorb the sodium (Na+) ions. The kidneys also secrete erythropoietin when the blood doesn't have the capacity to carry oxygen. Erythropoietin stimulates red blood cell production. The Vitamin D from the skin is also activated with help from the kidneys. Calcium (Ca+) absorption from the digestive tract is promoted by vitamin D. CC: Chapter Check: Name the role of the kidneys and how they work? Organs in the Urinary System Kidneys And Their Structure 1. Renal pyramid 2. Interlobar artery 3. Renal artery 4. Renal vein 5. Renal hylum 6. Renal pelvis 7. Ureter 8. Minor calyx 9.

Renal capsule 10. Inferior renal capsule 11. Superior renal capsule 12. Interlobar vein 13. Nephron 14. Minor calyx 15. Major calyx 16. Renal papilla 17. Renal column The kidneys are a pair of bean shaped, brown organs about the size of your fist.It measures 10-12 cm long. They are covered by the renal capsule, which is a tough capsule of fibrous connective tissue. Adhering to the surface of each kidney is two layers of fat to help cushion them. There is a concaved side of the kidney that has a depression where a renal artery enters, and a renal vein and a ureter exit the kidney. The kidneys are located at the rear wall of the abdominal cavity just above the waistline, and are protected by the ribcage. They are considered retroperitoneal, which means they lie behind the peritoneum. There are three major regions of the kidney, renal cortex, renal medulla and the renal pelvis. The outer, granulated layer is the renal cortex. The cortex stretches down in between a radially striated inner layer.

The inner radially striated layer is the renal medulla. This contains pyramid shaped tissue called the renal pyramids, separated by renal columns. The ureters are continuous with the renal pelvis and is the very center of the kidney. Renal Vein The renal veins are veins that drain the kidney. They connect the kidney to the inferior vena cava. Because the inferior vena cava is on the right half of the body, the left renal vein is generally the longer of the two. Unlike the right renal vein, the left renal vein often receives the left gonadal vein (left testicular vein in males, left ovarian vein in females). It frequently receives the left suprarenal vein as well. Renal Artery The renal arteries normally arise off the abdominal aorta and supply the kidneys with blood. The arterial supply of the kidneys are variable and there may be one or more renal arteries supplying each kidney. Due to the position of the aorta, the inferior vena cava and the kidneys in the body, the right renal artery is normally longer than the left renal artery. The right renal artery normally crosses posteriorly to the inferior vena cava. The renal arteries carry a large portion of the total blood flow to the kidneys.

Up to a third of the total cardiac output can pass through the renal arteries to be filtered by the kidneys. Ureters The ureters are two tubes that drain urine from the kidneys to the bladder. Each ureter is a muscular tube about 10 inches (25 cm) long. Muscles in the walls of the ureters send the urine in small spurts into the bladder, (a collapsible sac found on the forward part of the cavity of the bony pelvis that allows temporary storage of urine). After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine. The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allow release of the urine. However, relaxation of the sphincter is also in part a learned response under voluntary control. The released urine enters the urethra. Urinary Bladder The urinary bladder is a hollow, muscular and distendible or elastic organ that sits on the pelvic floor (superior to the prostate in males).

On its anterior border lies the pubic symphysis and, on its posterior border, the vagina (in females) and rectum (in males). The urinary bladder can hold approximately 17 to 18 ounces (500 to 530 ml) of urine, however the desire to micturate is usually experienced when it contains about 150 to 200 ml. When the bladder fills with urine (about half full), stretch receptors send nerve impulses to the spinal cord, which then sends a reflex nerve impulse back to the sphincter (muscular valve) at the neck of the bladder, causing it to relax and allow the flow of urine into the urethra. The Internal urethral sphincter is involuntary. The ureters enter the bladder diagonally from its dorsolateral floor in an area called the trigone. The trigone is a triangular shaped area on the postero-inferior wall of the bladder. The urethra exits at the lowest point of the triangle of the trigone. The urine in the bladder also helps regulate body temperature.

A bladder when operating normally empties completely upon a complete discharge, otherwise it is a sign that its elasticity is compromised, when it becomes completely void of fluid, it may cause a chilling sensation due to the rapid change of body temperature. Urethra Female urethra (labeled at bottom right.) Male Sphincter urethrae muscle - The male urethra laid open on its anterior (upper) surface. (Region visible, but muscle not labeled.) The urethra is a muscular tube that connects the bladder with the outside of the body. The function of the urethra is to remove urine from the body. It measures about 1.5 inches (3.8 cm) in a woman but up to 8 inches (20 cm) in a man. Because the urethra is so much shorter in a woman it makes it much easier for a woman to get harmful bacteria in her bladder this is commonly called a bladder infection or a UTI. The most common bacteria of a UTI is E-coli from the large intestines that have been excreted in fecal matter.

Female urethra In the human female, the urethra is about 1-2 inches long and opens in the vulva between the clitoris and the vaginal opening. Men have a longer urethra than women. This means that women tend to be more susceptible to infections of the bladder (cystitis) and the urinary tract. Male urethra In the human male, the urethra is about 8 inches long and opens at the end of the head of the penis. The length of a male's urethra, and the fact it contains a number of bends, makes catheterisation more difficult. The urethral sphincter is a collective name for the muscles used to control the flow of urine from the urinary bladder. These muscles surround the urethra, so that when they contract, the urethra is closed. There are two distinct areas of muscle: the internal sphincter, at the bladder neck and the external, or distal, sphincter. Human males have much stronger sphincter muscles than females, meaning that they can retain a large amount of urine for twice as long, as much as 800mL, i.e. "hold it".

Nephrons A nephron is the basic structural and functional unit of the kidney. The name nephron comes from the Greek word (nephros) meaning kidney. Its chief function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Nephrons eliminate wastes from the body, regulate blood volume and pressure, control levels of electrolytes and metabolites, and regulate blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. Each nephron has its own supply of blood from two capillary regions from the renal artery. Each nephron is composed of an initial filtering component (the renal corpuscle) and a tubule specialized for reabsorption and secretion (the renal tubule). The renal corpuscle filters out large solutes from the blood, delivering water and small solutes to the renal tubule for modification. Glomerulus The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation.

The glomerular blood pressure provides the driving force for fluid and solutes to be filtered out of the blood and into the space made by Bowman's capsule. The remainder of the blood not filtered into the glomerulus passes into the narrower efferent arteriole. It then moves into the vasa recta, which are collecting capillaries intertwined with the convoluted tubules through the interstitial space, where the reabsorbed substances will also enter. This then combines with efferent venules from other nephrons into the renal vein, and rejoins with the main bloodstream. Afferent/Efferent Arterioles The afferent arteriole supplies blood to the glomerulus. A group of specialized cells known as juxtaglomerular cells are located around the afferent arteriole where it enters the renal corpuscle. The efferent arteriole drains the glomerulus. Between the two arterioles lies specialized cells called the macula densa. The juxtaglomerular cells and the macula densa collectively form the juxtaglomerular apparatus. It is in the juxtaglomerular apparatus cells that the enzyme renin is formed and stored.

Renin is released in response to decreased blood pressure in the afferent arterioles, decreased sodium chloride in the distal convoluted tubule and sympathetic nerve stimulation of receptors (beta-adrenic) on the juxtaglomerular cells. Renin is needed to form Angiotensin I and Angiotensin II which stimulate the secretion of aldosterone by the adrenal cortex. Glomerular Capsule or Bowman's Capsule Bowman's capsule (also called the glomerular capsule) surrounds the glomerulus and is composed of visceral (simple squamous epithelial cells) (inner) and parietal (simple squamous epithelial cells) (outer) layers. The visceral layer lies just beneath the thickened glomerular basement membrane and is made of podocytes which send foot processes over the length of the glomerulus. Foot processes interdigitate with one another forming filtration slits that, in contrast to those in the glomeruluar endothelium, are spanned by diaphragms. The size of the filtration slits restricts the passage of large molecules (eg, albumin) and cells (eg, red blood cells and platelets).

In addition, foot processes have a negatively-charged coat (glycocalyx) that limits the filtration of negatively-charged molecules, such as albumin. This action is called electrostatic repulsion. The parietal layer of Bowman's capsule is lined by a single layer of squamous epithelium. Between the visceral and parietal layers is Bowman's space, into which the filtrate enters after passing through the podocytes' filtration slits. It is here that smooth muscle cells and macrophages lie between the capillaries and provide support for them. Unlike the visceral layer, the parietal layer does not function in filtration. Rather, the filtration barrier is formed by three components: the diaphragms of the filtration slits, the thick glomerular basement membrane, and the glycocalyx secreted by podocytes. 99% of glomerular filtrate will ultimately be reabsorbed. The process of filtration of the blood in the Bowman's capsule is ultrafiltration (or glomerular filtration), and the normal rate of filtration is 125 ml/min, equivalent to ten times the blood volume daily. Measuring the glomerular filtration rate (GFR) is a diagnostic test of kidney function.

A decreased GFR may be a sign of renal failure. Conditions that can affect GFR include: arterial pressure, afferent arteriole constriction, efferent arteriole constriction, plasma protein concentration and colloid osmotic pressure. Any proteins that are roughly 30 kilodaltons or under can pass freely through the membrane. Although, there is some extra hindrance for negatively charged molecules due to the negative charge of the basement membrane and the podocytes. Any small molecules such as water, glucose, salt (NaCl), amino acids, and urea pass freely into Bowman's space, but cells, platelets and large proteins do not. As a result, the filtrate leaving the Bowman's capsule is very similar to blood plasma in composition as it passes into the proximal convoluted tubule. Together, the glomerulus and Bowman's capsule are called the renal corpuscle. Proximal Convoluted Tubule (PCT) The proximal tubule can be anatomically divided into two segments: the proximal convoluted tubule and the proximal straight tubule.

The proximal convoluted tubule can be divided further into S1 and S2 segments based on the histological appearance of it's cells. Following this naming convention, the proximal straight tubule is commonly called the S3 segment. The proximal convoluted tubule has one layer of cuboidal cells in the lumen. This is the only place in the nephron that contains cuboidal cells. These cells are covered with millions of microvilli. The microvilli serve to increase surface area for reabsorption. Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries, including approximately two-thirds of the filtered salt and water and all filtered organic solutes (primarily glucose and amino acids). This is driven by sodium transport from the lumen into the blood by the Na+/K+ ATPase in the basolateral membrane of the epithelial cells. Much of the mass movement of water and solutes occurs in between the cells through the tight junctions, which in this case are not selective.

The solutes are absorbed isotonically, in that the osmotic potential of the fluid leaving the proximal tubule is the same as that of the initial glomerular filtrate. However, glucose, amino acids, inorganic phosphate, and some other solutes are reabsorbed via secondary active transport through cotransport channels driven by the sodium gradient out of the nephron. Loop of the Nephron or Loop of Henle The Nephron Loop or Loop of Henle. The loop of Henle (sometimes known as the nephron loop) is a U-shaped tube that consists of a descending limb and ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla, and then returns to the cortex to empty into the distal convoluted tubule. Its primary role is to concentrate the salt in the interstitium, the tissue surrounding the loop. Descending limb Its descending limb is permeable to water but completely impermeable to salt, and thus only indirectly contributes to the concentration of the interstitium.

As the filtrate descends deeper into the hypertonic interstitium of the renal medulla, water flows freely out of the descending limb by osmosis until the tonicity of the filtrate and interstitium equilibrate. Longer descending limbs allow more time for water to flow out of the filtrate, so longer limbs make the filtrate more hypertonic than shorter limbs. Ascending limb Unlike the descending limb, the ascending limb of Henle's loop is impermeable to water, a critical feature of the countercurrent exchange mechanism employed by the loop. The ascending limb actively pumps sodium out of the filtrate, generating the hypertonic interstitium that drives countercurrent exchange. In passing through the ascending limb, the filtrate grows hypotonic since it has lost much of its sodium content. This hypotonic filtrate is passed to the distal convoluted tubule in the renal cortex. Distal Convoluted Tubule (DCT) The distal convoluted tubule is similar to the proximal convoluted tubule in structure and function. Cells lining the tubule have numerous mitochondria, enabling active transport to take place by the energy supplied by ATP.

Much of the ion transport taking place in the distal convoluted tubule is regulated by the endocrine system. In the presence of parathyroid hormone, the distal convoluted tubule reabsorbs more calcium and excretes more phosphate. When aldosterone is present, more sodium is reabsorbed and more potassium excreted. Atrial natriuretic peptide causes the distal convoluted tubule to excrete more sodium. In addition, the tubule also secretes hydrogen and ammonium to regulate pH. After traveling the length of the distal convoluted tubule, only 3% of water remains, and the remaining salt content is negligible. 97.9% of the water in the glomerular filtrate enters the convoluted tubules and collecting ducts by osmosis. Collecting ducts Each distal convoluted tubule delivers its filtrate to a system of collecting ducts, the first segment of which is the connecting tubule. The collecting duct system begins in the renal cortex and extends deep into the medulla.

As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system. Though the collecting duct is normally impermeable to water, it becomes permeable in the presence of antidiuretic hormone (ADH). As much as three-fourths of the water from urine can be reabsorbed as it leaves the collecting duct by osmosis. Thus the levels of ADH determine whether urine will be concentrated or dilute. Dehydration results in an increase in ADH, while water sufficiency results in low ADH allowing for diluted urine. Lower portions of the collecting duct are also permeable to urea, allowing some of it to enter the medulla of the kidney, thus maintaining its high ion concentration (which is very important for the nephron). Urine leaves the medullary collecting ducts through the renal papilla, emptying into the renal calyces, the renal pelvis, and finally into the bladder via the ureter.

Because it has a different embryonic origin than the rest of the nephron (the collecting duct is from endoderm whereas the nephron is from mesoderm), the collecting duct is usually not considered a part of the nephron proper. Renal Hormones 1. Vitamin D- Becomes metabolically active in the kidney. Patients with renal disease have symptoms of disturbed calcium and phosphate balance. 2. Erythropoietin- Released by the kidneys in response to decreased tissue oxygen levels (hypoxia). 3. Natriuretic Hormone- Released from cardiocyte granules located in the right atria of the heart in response to increased atrial stretch. It inhibits ADH secretions which can contribute to the loss of sodium and water. Formation of Urine Urine is formed in three steps: Filtration, Reabsorption, and Secretion. Filtration Blood enters the afferent arteriole and flows into the glomerulus. Blood in the glomerulus has both filterable blood components and non-filterable blood components. Filterable blood components move toward the inside of the glomerulus while non-filterable blood components bypass the filtration process by exiting through the efferent arteriole.

Filterable Blood components will then take a plasma like form called glomerular filtrate. A few of the filterable blood components are water, nitrogenous waste, nutrients and salts (ions). Nonfilterable blood components include formed elements such as blood cells and platelets along with plasma proteins. The glomerular filtrate is not the same consistency as urine, as much of it is reabsorbed into the blood as the filtrate passes through the tubules of the nephron. Reabsorption Within the peritubular capillary network, molecules and ions are reabsorbed back into the blood. Sodium Chloride reabsorbed into the system increases the osmolarity of blood in comparison to the glomerular filtrate. This reabsorption process allows water (H2O) to pass from the glomerular filtrate back into the circulatory system. Glucose and various amino acids also are reabsorbed into the circulatory system. These nutrients have carrier molecules that claim the glomerular molecule and release it back into the circulatory system. If all of the carrier molecules are used up, excess glucose or amino acids are set free into the urine.

A complication of diabetes is the inability of the body to reabsorb glucose. If too much glucose appears in the glomerular filtrate it increases the osmolarity of the filtrate, causing water to be released into the urine rather than reabsorbed by the circulatory system. Frequent urination and unexplained thirst are warning signs of diabetes, due to water not being reabsorbed. Glomerular filtrate has now been separated into two forms: Reabsorbed Filtrate and Non-reabsorbed Filtrate. Non-reabsorbed filtrate is now known as tubular fluid as it passes through the collecting duct to be processed into urine. Secretion Some substances are removed from blood through the peritubular capillary network into the distal convoluted tubule or collecting duct. These substances are Hydrogen ions, creatinine, and drugs. Urine is a collection of substances that have not been reabsorbed during glomerular filtration or tubular reabsorbtion. Maintaining Water-Salt Balance It is the job of the kidneys to maintain the water-salt balance of the blood. They also maintain blood volume as well as blood pressure.

Simple examples of ways that this balance can be changed include ingestion of water, dehydration, blood loss and salt ingestion. Reabsorption of water Direct control of water excretion in the kidneys is exercised by the anti-diuretic hormone (ADH), released by the posterior lobe of the pituitary gland. ADH causes the insertion of water channels into the membranes of cells lining the collecting ducts, allowing water reabsorption to occur. Without ADH, little water is reabsorbed in the collecting ducts and dilute urine is excreted. There are several factors that influence the secretion of ADH. The first of these happen when the blood plasma gets too concentrated. When this occurs, special receptors in the hypothalamus release ADH. When blood pressure falls, stretch receptors in the aorta and carotid arteries stimulate ADH secretion to increase volume of the blood. Reabsorption of Salt The Kidneys also regulate the salt balance in the blood by controlling the excretion and the reabsorption of various ions. As noted above, ADH plays a role in increasing water reabsorption in the kidneys, thus helping to dilute bodily fluids.

The kidneys also have a regulated mechanism for reabsorbing sodium in the distal nephron. This mechanism is controlled by aldosterone, a steroid hormone produced by the adrenal cortex. Aldosterone promotes the excretion of potassium ions and the reabsorption of sodium ions. The release of Aldosterone is initiated by the kidneys. The juxtaglomerular apparatus is a renal structure consisting of the macula densa, mesangial cells, and juxtaglomerular cells. Juxtaglomerular cells (JG cells, also known as granular cells) are the site of renin secretion. Renin is an enzyme that converts angiotensinogen (a large plasma protein produced by the liver) into Angiotensin I and eventually into Angiotensin II which stimulates the adrenal cortex to produce aldosterone. The reabsorption of sodium ions is followed by the reapsorption of water. This causes blood pressure as well as blood volume to increase. Atrial natriuretic hormone (ANH) is released by the atria of the heart when cardiac cells are stretched due to increased blood volume.

ANH inhibits the secretion of renin by the juxtaglomerular apparatus and the secretion of the aldosterone by the adrenal cortex. This promotes the excretion of sodium. When sodium is excreted so is water. This causes blood pressure and volume to decrease. Hypernatremia An increase in plasma sodium levels above normal is hypernatremia. Sodium is the primary solute in the extracellular fluid. Sodium levels have a major role in osmolarity regulation. For excitable cells the electrochemical gradient for sodium across the plasma membrane is critical for life. Water retention and an increased blood pressure usually are signs of hypernatremia. If the plasma sodium levels are below normal it is called hyponatremia. Signs of this are low plasma volume and hypotension. Diuretics A diuretic (colloquially called a water pill) is any drug that elevates the rate of bodily urine excretion (diuresis). Diuretics also decrease the extracellular fluid (ECF) volume, and are primarily used to produce a negative extracellular fluid balance. Caffeine, cranberry juice and alcohol are all weak diuretics.

In medicine, diuretics are used to treat heart failure, liver cirrhosis, hypertension and certain kidney diseases. Diuretics alleviate the symptoms of these diseases by causing sodium and water loss through the urine. As urine is produced by the kidney, sodium and water – which cause edema related to the disease – move into the blood to replace the volume lost as urine, thereby reducing the pathological edema. Some diuretics, such as acetazolamide, help to make the urine more alkaline and are helpful in increasing excretion of substances such as aspirin in cases of overdose or poisoning. The antihypertensive actions of some diuretics (thiazides and loop diuretics in particular) are independent of their diuretic effect. That is, the reduction in blood pressure is not due to decreased blood volume resulting from increased urine production, but occurs through other mechanisms and at lower doses than that required to produce diuresis. Indapamide was specifically designed with this is mind, and has a larger therapeutic window for hypertension (without pronounced diuresis) than most other diuretics.

Chemically, diuretics are a diverse group of compounds that either stimulate or inhibit various hormones that naturally occur in the body to regulate urine production by the kidneys. Alcohol produces diuresis through modulation of the vasopressin system. Diseases of the Kidney Diabetic nephropathy (nephropatia diabetica), also known as Kimmelstiel-Wilson syndrome and intercapillary glomerulonephritis, is a progressive kidney disease caused by angiopathy of capillaries in the kidney glomeruli. It is characterized by nodular glomerulosclerosis. It is due to longstanding diabetes mellitus, and is a prime cause for dialysis in many Western countries. An image of a kidney stone. In medicine, hematuria (or "haematuria") is the presence of blood in the urine. It is a sign of a large number of diseases of the kidneys and the urinary tract, ranging from trivial to lethal. Kidney stones, also known as nephrolithiases, urolithiases or renal calculi, are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters.

They vary in size from as small as a grain of sand to as large as a golf ball. Kidney stones typically leave the body in the urine stream; if they grow relatively large before passing (on the order of millimeters), obstruction of a ureter and distention with urine can cause severe pain most commonly felt in the flank, lower abdomen and groin. Kidney stones are unrelated to gallstones. Case Study I was 34 weeks pregnant when I noticed blood in my urine. I immediately went to my OBGYN where I was told that I had a bladder infection and given an antibiotic. The next morning I experienced the most intense pain. I was rushed to the ER where I was told that I had kidney stones. The doctors explained that there was nothing they could do as long as I was pregnant. The next 3 weeks of my life were filled with intense pain and multiple painkillers. After I delivered my baby, CAT scans were done and I was informed that I had 6 kidney stones. It took three more weeks for me to pass all of the stones the largest measuring 5 mm. The stones were tested and I was informed that my body had been building up calcium due to my pregnancy and this was the cause of the kidney stones.

I continued to have kidney pain for 6 months after passing the stones. I now live my life on a low calcium diet and the hope that my body will not develop more kidney stones. Pyelonephritis When an infection of the renal pelvis and calices, called pyelitis, spreads to involve the rest of the kidney as well, the result is pyelonephritis. It usually results from the spread of fecal bacterium Escherichia coli from the anal region superiorly through the urinary tract. In severe cases, the kidney swells and scars, abscesses form, and the renal pelvis fills with pus. Left untreated, the infected kidney may be severely damaged, but administration of antibiotics usually achieve a total cure. glomerulonephritis Inflammation of the glomerular can be caused by immunologic abnormalities, drugs or toxins, vascular disorders, and systemic diseases. Glomerulonephritis can be acute, chronic or progressive. Two major changes in the urine are distinctive of glomerulonephritis: hematuria and proteinuria with albumin as the major protein. There is also a decrease in urine as there is a decrease in GFR (glomerular filtration rate).

Renal failure is associated with oliguria (less than 400 ml of urine output per day). Renal Failure Uremia is a syndrome of renal failure and includes elevated blood urea and creatinine levels. Acute renal failure can be reversed if diagnosed early. Acute renal failure can be caused by severe hypotension or severe glomerular disease. Diagnostic tests include BUN and plasma creatinine level tests. It is considered to be chronic renal failure if the decline of renal function to less than 25%. Diabetes Insipidus This is caused by the deficiency of or decrease of ADH. The person with (DI) has the inability to concentrate their urine in water restriction, in turn they will void up 3 to 20 liters/day. There are two forms of (DI), neurogenic, and nephrogenic. In nephrogenic (DI) the kidneys do not respond to ADH. Usually the nephrogenic (DI) is characterized by the impairment of the urine concentrating capability of the kidney along with concentration of water. The cause may be a genetic trait, electrolyte disorder, or side effect of drugs such as lithium.

In the neurogenic (DI), it is usually caused by head injury near the hypophysisal tract. Urinary tract infections (UTI's) The second most common type of bacterial infections seen by health care providers is UTI's. Out of all the bacterias that colonize and cause urinary tract infections the big gun is Escherichia coli. In the hospital indwelling catheters and straight catheterizing predispose the opportunity for urinary tract infections. In females there are three stages in life that predispose urinary tract infections, that is menarche, manipulation between intercourse, and menopause. However, a small percentage of men and children will get urinary tract infections. In men it is usually due to the prostate gland growth which usually occurs in older age men. In children it can occur 3% to 5% in girls and 1% in boys, uncircumcised boys it is more common than circumcised ones to have a urinary tract infection, in girls it may be the result of onset of toilet training, some predispositions for getting urinary tract infection include family history and urinary tract anomalies. In neonates urinary tract infections is most common when bacteremia is present.

Dialysis and Kidney Transplant Plugged into dialysis Generally, humans can live normally with just one kidney. Only when the amount of functioning kidney tissue is greatly diminished will renal failure develop. If renal function is impaired, various forms of medications are used, while others are contraindicated. Provided that treatment is begun early, it may be possible to reverse chronic kidney failure due to diabetes or high blood pressure. If creatinine clearance (a measure of renal function) has fallen very low ("end-stage renal failure"), or if the renal dysfunction leads to severe symptoms, dialysis is commenced. Dialysis is a medical procedure, performed in various different forms, where the blood is filtered outside of the body. Kidney transplantation is the only cure for end stage renal failure; dialysis, is a supportive treatment; a form of "buying time" to bridge the inevitable wait for a suitable organ. The first successful kidney transplant was announced on March 4, 1954 at Peter Bent Brigham Hospital in Boston. The surgery was performed by Dr. Joseph E. Murray, who was awarded the Nobel Prize in Medicine in 1990 for this feat.

There are two types of kidney transplants: living donor transplant and a cadaveric (dead donor) transplant. When a kidney from a living donor, usually a blood relative, is transplanted into the patient's body, the donor's blood group and tissue type must be judged compatible with the patient's, and extensive medical tests are done to determine the health of the donor. Before a cadaveric donor's organs can be transplanted, a series of medical tests have to be done to determine if the organs are healthy. Also, in some countries, the family of the donor must give its consent for the organ donation. In both cases, the recipient of the new organ needs to take drugs to suppress their immune system to help prevent their body from rejecting the new kidney.

Review Questions Answers for these questions can be found here 1.While reading a blood test I notice a high level of creatinine, I could assume from this that A) There is a possibility of a UTI B) There is a possibility of diabetes C) There is a possibility of kidney failure D) There is nothing wrong, this is normal 2.Direct control of water excretion in the kidneys is controlled by A) Anti-diuretic hormone E ) all of the above 7. Why do substances in the glomerulus enter the Bowman's capsule? A ) the magnetic charge of the Bowman's capsule attracts the substances B ) the substances are actively transported into the Bowman's capsule C ) blood pressure of the glomerulus is so great that most substances in blood move into capsule D ) little green men force it in with their ray guns 8. What happens in tubular excretion? A ) urine bonds are formed between the wastes B ) wastes are diffused from the tubule C ) wastes move into the distal convoluted tubule from the blood D ) blood pressure forces wastes away from the kidney 9. The countercurrent exchange system includes_________and_________.

A ) glomerulus and macula densa B ) proximal convoluted tubule and distal convoluted tubule C ) loop of Henle and collecting tubule D ) afferent arteriole and efferent arteriole E ) ureters and bladder 10. The function of the loop of the nephron in the process of urine formation is: A ) reabsorption of water 11. Name the six important roles of the kidneys. Glossary Antidiuretic: lessening or decreasing of urine production or an agent that decreases the release of urine. Catheterisation: a catheter is a tube that can be inserted into a body cavity, duct or vessel. Catheters thereby allow drainage or injection of fluids or access by surgical instruments. The process of inserting a catheter is catheterisation. In most uses a catheter is a thin, flexible tube: a "soft" catheter; in some uses, it is a larger, solid tube: a "hard" catheter. Dehydration: condition resulting from excessive loss of body fluid. Diabetes: a general term for a disease characterized by the begining stages and onset of renal failure.

It is derived from the Greek word diabaínein, that literally means "passing through," or "siphon", a reference to one of diabetes' major symptoms—excessive urine production. Diuresis: secretion and passage of large amounts of urine. Diuretic: increasing of urine production, or an agent that increases the production of urine. Erythropoietin: hormone that stimulates stem cells in the bone marrow to produce red blood cells Fibrous Capsule: the kidney's loose connective tissue Glomerulus: capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation. Gluconeogenesis: the cycle of producing a glucose form fat or protein; preformed by the kidney in times of long fasting, initially gluconeogenesis is preformed by the liver Juxtaglomerular (JG) cells: Renin-secreting cells that are in contact with the macula densa and the afferent arterioles of the renal nephron.

Juxtaglomerular apparatus (JGA): A site of juxtaglomerular cells connecting with the macula densa where renin is secreted and sensor for control of secretion of golmerular filtration rate.

Loop of Henle/ Nephron Loop: u-shaped tube that consists of a descending limb and ascending limb; primary role is to concentrate the salt in the interstitium, the tissue surrounding the loop Medullary Pyramids or Renal Pyramids: the cone shaped masses in the kidney Micturition: another name for excretions Nephron: basic structural and functional unit of the kidney; chief function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine Podocytes: filtration membrane, in the visceral layer of the bowman's capsule Renal Calculi: kidney stones, solid crystals of dissolved minerals in urine found inside the kidneys Renal Cortex: outer portion of the kidney Renal Lobe: each pyramid together with the associated overlying cortex Renal Pelvis: a central space, or cavity that transmits urine to the urinary bladder via the ureter Renin: hormone released by the Juxtaglomerular (JG) cells of the kidneys when blood pressure falls TURP: transurethral resection of the prostate.

During TURP, an instrument is inserted up the urethra to remove the section of the prostate that is blocking urine flow. This is most commonly caused by benign prostatic hyperplasia (BPH). A TURP usually requires hospitalization and is done using a general or spinal anesthetic. It is now the most common surgery used to remove part of an enlarged prostate. Urethra: a muscular tube that connects the bladder with the outside of the body Ureters: two tubes that drain urine from the kidneys to the bladder Urine: liquid produced by the kidneys, collected in the bladder and excreted through the urethra Urinary Bladder: a hollow, muscular and distensible or elastic organ that sits on the pelvic floor Urinary System: a group of organs in the body concerned with filtering out excess fluid and other substances from the bloodstream References Kidneys Filter Blood : Processes of Glomerular Filtration, Tubular Reabsorption and Tubular Secretion Blood Cleaning by the Kidneys This page is about processes performed by the kidneys in order to filter (clean) blood.

These are: Glomerular Filtration also called "Ultra-filtration", Tubular Reabsorption also called "Selective Re-Absorption" and Tubular Secretion. As these occur in the kidney nephrons, it is best to read this page after viewing the page about the structure of a kidney nephron . (1) Glomerular Filtration Blood enters the kidney via the renal artery. This seperates many times (Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries -> Afferent Arterioles), eventually forming many afferent arterioles, each of which delivers blood to an individual kidney nephron. The diameter of the afferent (incoming) arteriole is greater than the diameter of the efferent arteriole (by which blood leaves the glomerulus). The pressure of the blood inside the glomerulus is increased due to the difference in diameter of the incoming and out-going arterioles. This increased blood pressure helps to force the following components of the blood out of the glomerular capillaries: Most of the water; Most/all of the glucose; Most/all of the urea.

The above are filtered in preference to other components of blood based on particle size. (Water and solutes of relative molecular mass less than 68,000 form the filtrate.) Blood cells and plasma proteins are not filtered through the glomerular capillaries because they are relatively larger in physical size. The water and salts that have been forced out of the glomerular capillaries pass into the Bowman's Capsule and are called the glomerular filtrate. This glomerular filtrate is formed at a rate of above 125 cm3 per minute in humans. This volume is approx. 20% of the plasma delivered during that time. (Again: It contains all the materials present in the blood except blood cells and most proteins - which are too large to cross the basement membrane of the glomerulus.) Click here to read more about the Glomerular Filtration Rate (GFR) - link coming soon.

The glomerular filtrate passes from the renal corpuscle to the renal tubule: (2) Tubular Reabsorption Only about 1% of the glomerular fitrate actually leaves the body because the rest (the other 99%) is reabsorbed into the blood while it passes through the renal tubules and ducts. This is called tubular reabsorption and occurs via three mechanisms. They are: Osmosis Diffusion, and Active Transport. Reabsorption varies according to the body's needs, enabling the body to retain most of its nutrients. The processes of tubular reabsorption occur in the following order (see also the diagram of a kidney nephron to trace the flow of fluid through the 3 stages outlined below): In the PCT Most of the volume of the fitrate solution is reabsobed in the proximal convoluted tubule (PCT). This includes some water and most/all of the glucose (except in the case of diabetics). Most of the energy consumed by the kidneys is used in the reabsorption of sodium ions (Na+), which are solutes - that is, they are dissolved in the water component of the fitrate solution.

As the concentration of Na+ in the filtrate solution is high (about the same as the concentration of Na+ in blood plasma), Na+ moves from the tubular fluid into the cells of the PCT. In the cases of many Na+ ions this occurs with the help of symporters . Symporters simultaneously facilitate passage through the PCT membrane of both Na+ and another substances/solutes. Other such substances that are reabsorbed with Na+ in this way include glucose (an important type of sugar), amino acids , lactic acid, and bicarbonate ions (HCO3-). These then move on through cells via diffusion and/or other transport processes. A short way to summarize the above is to say that solutes are selectively moved from the glomular filtrate to the plasma by active transport. (However, almost all glucose and amino acids, and high but variable amounts of ions, are reabsorbed again later - see the next section, below). Following the movement of solutes (including Na+ ), water is then also reabsorbed by osmosis. About 80% of the filtrate volume is reabsorbed in this way.

As this part of the reabsorption process is not controlled by the proximal tubule itself, it is sometimes called obligatory water reabsorption. In the Loop of Henle The remaining water (together with the dissolved salts and urea) passes from the PCT into the descending limb of Henle. It then passes along the Loop of Henle, and up the ascending limb of Henle. The different permeability properties of the two limbs of the Loop of Henle, together with their counterflow arrangement, allows a countercurrent multiplication to generate a high solute concentration in the tissue fluid of the medulla (that is, outside of the tubules). The highest solute concentrations are generated deep in the medulla. This is explained as follows: Descending Limb of Loop of Henle The epithelium lining of the descending limb of Henle is relatively permeable to water - but much much less permeable to the salts Na+ and Cl-, and to urea. Therefore water gradually moves from the descending limb and into the interstitium (surrounding the tubules) as fluid flows through this part of the system of renal tubules.

Thin Ascending Limb of Loop of Henle The thin ascending limb of Henle differs from the descending limb in that it is impermeable to water (so the water that is inside the tubule at this stage generally remains inside it), but is highly permeable to Na+ and Cl-, and somewhat permeable to urea. Therefore while the tubular fluid flows back towards the renal cortex, Na+ and Cl- (which are more concentrated in the tubular fluid than in the interstital fluid) diffuse from the tubules into the interstitium. Some urea also enters the tubules at this stage - but the loss of NaCl from the tubular fluid greatly exceeds the gain in urea. Thick Ascending Limb of Loop of Henle The thick ascending limb of Henle (and its continuation into the first part of the DCT), reabsorbs NaCl from the tubular fluid via a different transport process from that of the thin ascending limb of Henle. The overall effect of the processes outlined above is that the concentation of the fluid inside the renal tubules that form the Loop of Henle is highest at the deepest part of the renal medulla, and is less concentrated in the renal cortex.

This is what is meant by the "concentration gradient" of the Loop of Henle. The term "counter-current" is also used in descriptions of the Loop of Henle - and refers to the tubular fluid flowing in opposite directions along the descending and ascending limbs (as indicated by the thin red arrows in the diagram above. In the DCT The water, urea, and salts contained within the ascending limb of Henle eventually pass into the distal convoluted tubule (DCT). The DCT reacts to the amount of anti-diuretic hormone (ADH) in the blood: The more ADH is present in the blood, the more water is re-absorbed into it. This happens because the presence of ADH in the blood causes the cells in the last section of the DCT (and associated tubules and collecting ducts) to become more permeable to water, therefore they allow more water to pass from the tubular fluid back into the blood. This results in more concentrated urine. The opposite is also true, i.e.

if the level of ADH in the blood is reduced then the cells in the latter sections of the DCT (and associated tubules and collecting ducts) becomes less permeable to water therefore less water is able to pass from the tubular fluid back into the blood - which results in less concentrated urine. The amount of ADH in the blood may be affected by conditions such as diabetes insipidus, or by consumption of diuretics* in the diet (*substances that occur in some foods and drinks). (3) Tubular Secretion The third process by which the kidneys clean blood (regulating its composition and volume) is called tubular secretion and involves substances being added to the tubular fluid. This removes excessive quantities of certain dissolved substances from the body, and also maintains the blood at a normal healthy pH (which is typically in the range pH 7.35 to pH 7.45). The substances that are secreted into the tubular fluid (for removal from the body) include: Potassium ions (K+), some drugs (e.g. penicillin). Tubular secretion occurs from the epithelial cells that line the renal tubules and collecting ducts.

It is the tubular secretion of H+ and NH4+ from the blood into the tubular fluid (i.e. urine - which is then excreted from the body via the ureter, bladder, and urethra) that helps to keep blood pH at its normal level. The movement of these ions also helps to conserve sodium bicarbonate (NaHCO3). The typical pH of urine is about 6. ... and finally Urine formed via the three processes outlined above trickles into the kidney pelvis. At this final stage it is only approx. 1% of the originally filtered volume but includes high concentrations of urea and creatinine, and variable concentrations of ions. The typical volume of urine produced by an average adult is around 1.5 - 2.0 dm3 per day. Quick Summary: The Processes of Blood Filtration by the Kidneys What Is the Function of Bowman's Capsule? (with pictures) What Is the Function of Bowman's Capsule?

Last Modified Date: 02 January 2017 Copyright Protected: These 10 animal facts will amaze you Bowman's capsule, also known as a glomerular capsule or capsula glomeruli, is a double-walled, cup-shaped structure inside the kidney. The kidney contains up to two million units called nephrons. Each consists of a tube, one closed end of which is swollen to form Bowman's capsule while the other opens into the renal pelvis , the space from which urine leaves the kidney. A knot of tiny blood vessels called a glomerulus sits inside the capsule. Blood entering the kidney passes through the glomerulus and is filtered through blood vessel walls and the outer wall of Bowman's capsule, before the resulting filtrate collects inside the capsule. The function of the kidney involves removing waste and harmful products from the blood, while conserving useful substances and water. In order to achieve this, different parts of the kidney act together to filter out and then reabsorb different factors from the blood. Eventually, the correct composition is achieved to maintain the body's fluid and electrolyte balance. Urine is formed at the end of the process. It contains waste material and fluid which is expelled from the body during urination.

Bowman's capsule and the glomerulus form a unit called the renal corpuscle , in which the initial process of filtration occurs. A small artery carries blood into the glomerulus, where it is filtered at high pressure through two layers of cells before the remaining blood leaves through another artery. The first layer of cells, the lining of the glomerular blood vessels, is full of holes that are too small to allow blood cells and proteins to pass out, but which allow smaller molecules through. Substances leaving the blood then pass through a second cell layer, formed by the outer wall of Bowman's capsule. The outer layer of Bowman's capsule consists of specialized cells called podocytes , which have long thin projections. These are arranged to interlink with the projections from other podocytes like interlocked fingers, leaving narrow slits between them. Small particles which have filtered through the holes in glomerular blood vessels must pass through these slits before entering the space inside Bowman's capsule. The composition of the filtrate at this point is the same as blood, apart from the lack of blood cells and proteins. Next, the filtrate passes through a series of tubes in which some factors are absorbed back into the blood and others are secreted out.

The body actively controls many of these processes so that the composition of body fluids can be regulated. Finally, the remaining urine drains through a tube called the collecting duct into the renal pelvis, ureter and bladder. Ad

Question: Where in the human body would you find Bowman's Capsule?
Answer: Kidney