What is the smallest blood vessel in the body? | Reference.com What is the smallest blood vessel in the body? A: Quick Answer The smallest blood vessels in the human body are capillaries, which connect arteries and veins. Capillaries can be as small as 5 micrometers wide. The average adult body has about 10 billion capillaries. Full Answer Capillaries are part of the circulation system in the human body. They help move oxygen, water, carbon dioxide and other nutrients throughout the body. Arteries transfer blood out of the heart. Arteries narrow into capillaries, then widen into venules and veins. The veins transport blood back into the heart. Capillaries work as a group and not individually. During exercise, capillaries assist the lungs with meeting the need for increased blood flow. What are tiny blood vessels called? | Reference.com What are tiny blood vessels called? A: Quick Answer Tiny blood vessels are called capillaries. The capillaries main function is to work as a bridge between the larger arteries. Full Answer As the blood passes through the capillaries, the oxygen is passed on to the tissue.

The blood enters and leaves the capillaries through venules which are very small veins. After passing through the venules, the blood enters the body's main veins that lead to the heart. Arteries contain thick muscular walls as they have a higher blood pressure. Veins and venules, on the other hand, have thin muscular walls as they contain a much lower amount of blood pressure within them. The Cardiovascular System: Blood Vessels The Cardiovascular System: Blood Vessels Part 1: Overview of Blood Vessel Structure and Function Structure of Blood Vessel Walls The walls of all blood vessels except the smallest consist of three layers: the tunica intima, tunica media, and tunica externa. The tunica intima reduces friction between the vessel walls and blood; the tunica media controls vasoconstriction and vasodilation of the vessel; and the tunica externa protects, reinforces, and anchors the vessel to surrounding structures. Arterial System Elastic, or conducting, arteries contain large amounts of elastin, which enables these vessels to withstand and smooth out pressure fluctuations due to heart action.

Muscular, or distributing, arteries deliver blood to specific body organs, and have the greatest proportion of tunica media of all vessels, making them more active in vasoconstriction. Arterioles are the smallest arteries and regulate blood flow into capillary beds through vasoconstriction and vasodilation. Capillaries are the smallest vessels and allow for exchange of substances between the blood and interstitial fluid. Continuous capillaries are most common and allow passage of fluids and small solutes. Fenestrated capillaries are more permeable to fluids and solutes than continuous capillaries. Sinusoidal capillaries are leaky capillaries that allow large molecules to pass between the blood and surrounding tissues. Capillary beds are microcirculatory networks consisting of a vascular shunt and true capillaries, which function as the exchange vessels. A cuff of smooth muscle, called a precapillary sphincter, surrounds each capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary. Venous System Venules are formed where capillaries converge and allow fluid and white blood cells to move easily between the blood and tissues.

Venules join to form veins, which are relatively thin-walled vessels with large lumens containing about 65% of the total blood volume. Vascular anastomoses form where vascular channels unite, allowing blood to be supplied to and drained from an area even if one channel is blocked . Part 2: Physiology of Circulation Introduction to Blood Flow, Blood Pressure, and Resistance Blood flow is the volume of blood flowing through a vessel, organ, or the entire circulation in a given period and may be expressed as ml/min (blood flow of the entire circulation is equal to cardiac output). Blood pressure is the force per unit area exerted by the blood against a vessel wall and is expressed in millimeters of mercury (mm Hg). Resistance is a measure of the friction between blood and the vessel wall, and arises from three sources: blood viscosity, blood vessel length, and blood vessel diameter. The variable with the greatest effect on resistance is the diameter (or radius, 1/2 the diameter) of a particular vessel - resistance drops exponentially as the radius increases. TPR is total peripheral resistance - resistance throughout the entire systemic circulation.

Relationship Between Flow, Pressure, and Resistance If blood pressure increases, blood flow increases; if peripheral resistance increases, blood flow decreases. Peripheral resistance is the most important factor influencing local blood flow, because vasoconstriction or vasodilation can dramatically alter local resistance while systemic blood pressure remains unchanged (due to homeostatic mechanisms that maintain systemic BP at a constant value, see below). Systemic Blood Pressure The pumping action of the heart generates blood flow; pressure results when blood flow is opposed by resistance. Systemic blood pressure is highest in the aorta, and declines throughout the pathway until it reaches 0 mm Hg in the right atrium. Arterial blood pressure reflects how much the arteries close to the heart can be stretched (compliance, or distensibility), and the volume forced into them at a given time. When the left ventricle contracts, blood is forced into the aorta, producing a peak in pressure called systolic pressure (120 mm Hg). Diastolic pressure occurs when blood is prevented from flowing back into the ventricles by the closed semilunar valve, and the aorta recoils (70–80 mm Hg).

The difference between diastolic and systolic pressure is called the pulse presssure. The mean arterial pressure (MAP) represents the pressure that propels blood to the tissues. Capillary blood pressure is low, ranging from 40–20 mm Hg, which protects the capillaries from rupture, but is still adequate to ensure exchange between blood and tissues. Venous blood pressure changes very little during the cardiac cycle, and is low, reflecting cumulative effects of peripheral resistance (17 mm Hg in venules dropping to almost 0 mm Hg at the termini of the venae cavae). Venous return is aided by both structural modifications and functional adaptations. Structural Smooth muscle layer under sympathetic control Maintaining Blood Pressure Blood pressure varies with changes in blood volume, TPR, and cardiac output, which are determined primarily by venous return and neural and hormonal controls. Short-term mechanisms include both (1) neural and (2) hormonal controls, which alter blood pressure by changing peripheral resistance and CO. Long-term mechanisms alter blood pressure by using renal controls to alter blood volume.

Short-term Mechanisms Neural controls of peripheral resistance alter blood distribution to (1) meet specific tissue demands and (2) maintain adequate MAP by altering blood vessel diameter. The vasomotor center is a cluster of sympathetic neurons in the medulla, lying close to the cardioacceleratory and cardioinhibitory centers, that controls changes in the diameter of blood vessels. It constantly sends impulses to vascular smooth muscle to maintain a state of partial contraction (remember "tone"?) Most neural controls work through reflex arcs that send information on stretch to effectors (muscle) that respond accordingly. Chemoreceptors and input from higher brain centers can also influence neural controls. Baroreceptors If mean arterial pressure rises, baroreceptors in the carotid sinus and aortic arch detect stretch and send impulses to the vasomotor center, inhibiting its activity and promoting vasodilation of arterioles and veins. They also stimulate the cardioinhibitory center and inhibit the cardioacceleratory center when stretched, reducing cardiac output. A drop in mean arterial pressure causes vasocontriction and increased cardiac ouput. The carotid sinus reflex protects blood flow to the brain, while the aortic reflex maintains blood pressure throughout the systemic circuit.

Chemoreceptors located near the baroreceptors in the carotid sinus and aortic arch detect a rise in carbon dioxide levels, a drop in oxygen levels, and drops in pH of the blood, and stimulate the cardioacceleratory and vasomotor centers, which increases cardiac output and vasoconstriction. The cortex and hypothalamus can modify arterial pressure by signaling the medullary centers. Hormonal Controls Chemicals, both endocrine and paracrine, influence blood pressure by acting on vascular smooth muscle or the vasomotor center. Norepinephrine and epinephrine promote an increase in cardiac output and generalized vasoconstriction when acting on alpha receptors (will promote vasodilation at beta receptors, which are present in skeletal and cardiac muscle). Atrial natriuretic peptide acts as a vasodilator and an antagonist to aldosterone, resulting in a drop in blood volume. Antidiuretic hormone promotes vasoconstriction and water conservation by the kidneys, resulting in an increase in blood volume. Angiotensin II acts as a vasoconstrictor, as well as promoting the release of aldosterone and antidiuretic hormone.

Endothelium-derived factors promote vasoconstriction, and are released in response to low blood flow. Nitric oxide is produced in response to high blood flow or other signaling molecules, and promotes systemic and localized vasodilation. Inflammatory chemicals, such as histamine, prostacyclin, and kinins, are potent vasodilators. Alcohol inhibits antidiuretic hormone release and the vasomotor center, resulting in vasodilation. Long-Term Mechanisms: Renal Mechanisms The direct renal mechanism counteracts changes in blood pressure or volume by altering blood volume independently of hormones. The direct mechanism works best to counteract an increase in blood pressure Increased blood pressure or volume increases the rate of kidney filtration, causing filtrate to be formed faster than water can be reabsorbed back into circulation. The result is an increased volume of dilute urine and a decrease in blood volume. When faced with a decrease in blood pressure it does nothing to increase blood volume, it just decreases the amount of filtrate formed, increases reabsorption from filtrate to blood, and decreases the amount of water lost in urine.

The indirect renal mechanism is the renin-angiotensin mechanism, which counteracts a decline in arterial blood pressure by causing systemic vasoconstriction. Monitoring circulatory efficiency is accomplished by measuring pulse and blood pressure; these values together with respiratory rate and body temperature are called vital signs. A pulse is generated by the alternating stretch and recoil of elastic arteries during each cardiac cycle. Systemic blood pressure is measured indirectly using the ascultatory method, which relies on the use of a blood pressure cuff to alternately stop and reopen blood flow into the brachial artery of the arm. Alterations in blood pressure may result in hypotension (low blood pressure) or transient or persistent hypertension (high blood pressure). Blood Flow Through Body Tissues: Tissue Perfusion Tissue perfusion is involved in delivery of oxygen and nutrients to, and removal of wastes from, tissue cells; gas exchange in the lungs; absorption of nutrients from the digestive tract; and urine formation in the kidneys. Velocity of Blood Flow Velocity or speed of blood flow changes as it passes through the systemic circulation; it is fastest in the aorta, and declines in velocity as vessel diameter decreases (and then increases on the venous side as vessel diameter increases again).

Autoregulation: Local Regulation of Blood Flow Autoregulation is the automatic adjustment of blood flow to each tissue in proportion to its needs, and is controlled intrinsically by modifying the diameter of local arterioles. (Extrinsic influences control MAP.) Metabolic controls of autoregulation are most strongly stimulated by a shortage of oxygen at the tissues. Vasodilators: Endothelins Thromboxane A2 Myogenic control involves the localized response of vascular smooth muscle to passive stretch - reflex contraction when stretched to decrease flow, reflex relaxation when stretch is reduced to vasodilate and increase flow. This maintains a relatively constant flow locally when pressure fluctuates. Long-term autoregulation develops over weeks or months, and involves an increase in the size of existing blood vessels and an increase in the number of vessels in a specific area, a process called angiogenesis. Blood Flow in Special Areas Blood flow to skeletal muscles varies with level of activity and fiber type. Muscular autoregulation occurs almost entirely in response to decreased oxygen concentrations. Cerebral blood flow is tightly regulated to meet neuronal needs, since neurons cannot tolerate periods of ischemia, and increased blood carbon dioxide causes marked vasodilation.

In the skin, local autoregulatory events control oxygen and nutrient delivery to the cells, while neural mechanisms control the body temperature regulation function. Autoregulatory controls of blood flow to the lungs are the opposite of what happens in most tissues: low pulmonary oxygen causes vasoconstriction, while higher oxygen causes vasodilation. Movement of blood through the coronary circulation of the heart is influenced by aortic pressure and the pumping of the ventricles. Blood Flow Through Capillaries and Capillary Dynamics Vasomotion, the slow, intermittent flow of blood through the capillaries, reflects the action of the precapillary sphincters in response to local autoregulatory controls. Capillary exchange of nutrients, gases, and metabolic wastes occurs between the blood and interstitial space through diffusion. Routes: Fluid Movements: Bulk Flow (Starlings Law of the Capillary) Hydrostatic pressure (HP) is the force of a fluid against a membrane. Colloid osmotic pressure (OP), the force opposing hydrostatic pressure, is created by the presence of large, nondiffusible molecules that are prevented from moving through the capillary membrane.

Fluids will leave the capillaries if net HP exceeds net OP, but fluids will enter the capillaries if net OP exceeds net HP. Circulatory shock is any condition in which blood volume is inadequate and cannot circulate normally, resulting in blood flow that cannot meet the needs of a tissue. Hypovolemic shock results from a large-scale loss of blood, and may be characterized by an elevated heart rate and intense vasoconstriction. Vascular shock is characterized by a normal blood volume, but extreme vasodilation, often related to a loss of vasomotor tone, resulting in poor circulation and a rapid drop in blood pressure. Anaphylactic shock is an example of vascular shock Neurogenic shock - failure of autonomic controls Septic shock - bacterial toxins, some increase vascular permeability and lower blood volume and others stimulate vasodilation. Transient vascular shock is due to prolonged exposure to heat, such as while sunbathing, resulting in vasodilation of cutaneous blood vessels. Cardiogenic shock occurs when the heart is too inefficient to sustain normal blood flow, and is usually related to myocardial damage, such as repeated myocardial infarcts.

Part 3: Circulatory Pathways: Blood Vessels of the Body Two distinct pathways travel to and from the heart: pulmonary circulation runs from the heart to the lungs and back to the heart; systemic circulation runs to all parts of the body before returning to the heart. There are some important differences between arteries and veins. There is one terminal systemic artery, the aorta, but two terminal systemic veins: the superior and inferior vena cava. Arteries run deep and are well protected, but veins are both deep, running parallel to the arteries, and superficial, running just beneath the skin. Arterial pathways tend to be clear, but there are often many interconnections in venous pathways, making them difficult to follow. There are at least two areas where venous drainage does not parallel the arterial supply: the dural sinuses draining the brain, and the hepatic portal system draining from the digestive organs to the liver before entering the main systemic circulation. Four paired arteries supply the head and neck (common carotid arteries and three branches from the subclavian arteries; the vertebral arteries, the thyrocervical trunks, and the costocervical trunks.

The upper limbs are supplied entirely by arteries arising from the subclavian arteries. The arterial supply to the abdomen arises from the aorta. The internal iliac arteries serve mostly the pelvic region; the external iliacs supply blood to the lower limb and abdominal wall. The venae cavae are the major tributaries of the venous circulation. Blood drained from the head and neck is collected by three pairs of veins (internal jugular veins, external jugular veins, and the vertebral veins). The deep veins of the upper limbs follow the paths of the companion arteries. Blood draining from the abdominopelvic viscera and abdominal walls is returned to the heart by the inferior vena cava. Most deep veins of the lower limb have the same names as the arteries they accompany. Developmental Aspects of the Blood Vessels The vascular endothelium is formed by mesodermal cells that collect throughout the embryo in blood islands, which give rise to extensions that form rudimentary vascular tubes. By the fourth week of development, the rudimentary heart and vessels are circulating blood.

Fetal vascular modifications include shunts to bypass fetal lungs (the foramen ovale and ductus arteriosus), the ductus venosus that bypasses the liver, and the umbilical arteries and veins, which carry blood to and from the placenta. At birth, the fetal shunts and bypasses close and become occluded. Congenital vascular problems are rare, but the incidence of vascular disease increases with age, leading to varicose veins, tingling in fingers and toes, and muscle cramping. Atherosclerosis begins in youth, but rarely causes problems until old age. Blood pressure changes with age: the arterial pressure of infants is about 90/55, but rises steadily during childhood to an average 120/80, and tends to increase to somewhere around 150/90 in old age. Depending on how you live. It's an average but it's also a choice, so workout, eat right, and don't smoke and old age might look better than "young age". What is the Smallest Blood Vessel in the Human Body? | Were You Wondering… Home Anatomy What is the Smallest Blood Vessel in the Human Body?

What is the Smallest Blood Vessel in the Human Body? Posted By: Katrina Cain on: June 25, 2008 Tweet The smallest blood vessels in the human body are capillaries. They are responsible for the absorption of oxygen into the blood stream and for removing the deoxygenated red blood cells for return to the heart and lungs for reoxygenation. To understand capillaries, you need to understand what happens to a red blood cell as it’s being circulated around the body. A red blood cell both brings oxygen to the body’s tissues and carries away the carbon dioxide byproduct from cellular metabolism to ultimately be breathed out as we exhale. First, a deoxygenated red blood cell enters the heart through the superior and inferior vena cava. The deoxygenated blood traveled there by way of capillaries to veins to reach the vena cava. Next, the heart forces these red blood cells through the pulmonary artery into the lungs. When we breathe in, oxygen is attached to the red blood cells. The lungs send this reoxygenated blood back to the heart. The heart via the ascending and descending aorta sends the blood to the rest of the body for use.

Capillaries are the site at which oxygen is diffused into the tissues of the body, such as skeletal muscles. All of the cells of all of the tissues in our body need oxygen to perform normal metabolic function. Once they are finished with the oxygen, carbon dioxide is the byproduct which the capillaries take up and funnel into the veins for circulation back to the heart to repeat the cycle. In summary, capillaries are the site of oxygen exchange between the body’s tissues and the blood stream. Capillaries and arteries carry oxygenated red blood cells, and venules and veins carry the deoxygenated blood cells. The smallest capillaries in the body are in the brain. The brain uses an incredible amount of oxygen and therefore needs many blood vessels to bring in this oxygen and carry away the waste. About one liter of blood flows through the brain every minute, carrying with it nutrients and oxygen to fuel the neurons and support cells. The brain uses 20% of the food energy that we consume. Consider that we have neurons that are over one meter long. These are the ones that send impulses from the brain via the spine to our feet.

Imagine how much energy it takes to conduct nerve signals to the ends of those neurons, and you can understand why the brain requires so many resources. Related Posts Blood Vessels - Heart and Blood Vessel Disorders - Merck Manuals Consumer Version Heart and Blood Vessel Disorders Find information on medical topics, symptoms, drugs, procedures, news and more, written in everyday language. * This is the Consumer Version. * Effects of Aging on the Heart and Blood Vessels The blood vessels consist of arteries, arterioles, capillaries, venules, and veins. All blood is carried in these vessels. The arteries, which are strong, flexible, and resilient, carry blood away from the heart and bear the highest blood pressures. Because arteries are elastic, they narrow (recoil) passively when the heart is relaxing between beats and thus help maintain blood pressure. The arteries branch into smaller and smaller vessels, eventually becoming very small vessels called arterioles. Arteries and arterioles have muscular walls that can adjust their diameter to increase or decrease blood flow to a particular part of the body.

Capillaries are tiny, extremely thin-walled vessels that act as a bridge between arteries (which carry blood away from the heart) and veins (which carry blood back to the heart). The thin walls of the capillaries allow oxygen and nutrients to pass from the blood into tissues and allow waste products to pass from tissues into the blood. Blood flows from the capillaries into very small veins called venules, then into the veins that lead back to the heart. Veins have much thinner walls than do arteries, largely because the pressure in veins is so much lower. Veins can widen (dilate) as the amount of fluid in them increases. Some veins, particularly veins in the legs, have valves in them, to prevent blood from flowing backward. When these valves leak, the backflow of blood can cause the veins to stretch and become elongated and convoluted (tortuous). Stretched, tortuous veins near the body's surface are called varicose veins (see Varicose Veins ). Blood Vessels: Circulating the Blood Blood travels from the heart in arteries, which branch into smaller and smaller vessels, eventually becoming arterioles. Arterioles connect with even smaller blood vessels called capillaries.

Through the thin walls of the capillaries, oxygen and nutrients pass from blood into tissues, and waste products pass from tissues into blood. From the capillaries, blood passes into venules, then into veins to return to the heart. Arteries and arterioles have relatively thick muscular walls because blood pressure in them is high and because they must adjust their diameter to maintain blood pressure and to control blood flow. Veins and venules have much thinner, less muscular walls than arteries and arterioles, largely because the pressure in veins and venules is much lower. Veins may dilate to accommodate increased blood volume. If a blood vessel breaks, tears, or is cut, blood leaks out, causing bleeding. Blood may flow out of the body, as external bleeding, or it may flow into the spaces around organs or directly into organs, as internal bleeding. Resources In This Article What Are the Human Body's Smallest Parts? - Kids Discover by KIDS DISCOVER Share The human body is a marvel of engineering, with thousands of interrelated parts. Some are tiny but still very important.

Let’s look at four of the smallest parts of the human body: the smallest muscle, the smallest bone, the smallest organ, and the smallest blood vessel. What’s the smallest muscle in the human body? The stapedius, in your middle ear, measures about 1mm in size (or 1/26 of an inch). Connected to the stapes bone, it contracts to pull back the stapes and help protect your inner ear from loud noises. The stapedius also contracts to keep your own voice from sounding too loud in your head. What’s the smallest bone in the human body? Conveniently, that would be the stapes. It is one of three tiny bones in the middle ear that convey sound from the outer ear to the inner ear. Collectively called the ossicles, these bones are individually known as the malleus, incus, and stapes. Those are Latin words for the shapes the bones resemble: a hammer, anvil, and stirrup. What’s the smallest organ in the human body? You’ll find the pineal gland near the center of the brain, in a groove between the hemispheres. It’s not an organ like those in the abdominal cavity.

It’s the human body’s smallest endocrine gland, and it produces melatonin, a hormone (derived from serotonin) that affects how we sleep, wake up, and react to seasonal changes. It’s called pineal because it’s shaped like a little pinecone. What’s the smallest blood vessel in the human body? Capillaries, the smallest, thinnest-walled blood vessels in the body, connect veins and arteries. They can be as small as 5-10 micrometers wide — or 50 times thinner than a baby’s hair. Each of us contains about 10 billion of them, with the average adult body containing about 25,000 miles of capillaries. About the author KIDS DISCOVER For over 25 years, we’ve been creating beautifully crafted nonfiction products for kids. With a specialty in science and social studies, our team of talented writers, award-winning designers and illustrators, and subject-experts from leading institutions is committed to a single mission: to get children excited about reading and learning. You May Also Like I'm a Homeschooler Newsletter Sign Up Sign up for our email list and gain access to free content, special promotions, sales and more.

The Cardiovascular System (Blood Vessels) The Cardiovascular System (Blood Vessels) I. Blood Vessels: Overview Blood vessels of the body form a closed delivery system that begins and ends at the heart. Three major types of blood vessels: arteries, veins, and capillaries 60,000 miles of blood vessels in body A. Structure of Blood Vessel Walls Diagram Diagram Diagram Arteries and Veins are composed of three distinct layers called tunics which surround the blood-containing space (lumen) Tunica intima (interna) - contains epithelium (simple squamal) Tunica media - circularly arranged smooth muscle cells and elastic fibers (in arteries); tunica media has myogenic activity (vasoconstriction and vasodilation) Tunica adventitia (externa) - loosely woven collagen fibers and in large blood vessels contain tiny blood vessel, vasa vasorum, that supplies blood to nourish tunica adventitia B. Arterial System - arteries are vessels that transport blood away from the heart and consists of three groups: Elastic (conducting) arteries - large, thick-walled arteries near to the heart (ex: aorta).

Their large diameter lumens allows elastic arteries to serve as low-resistance conduits for conducting blood from heart to medium-sized arteries. Elastic arteries expand and recoil passively to accommodate changes in blood volume, keeping blood under continuous pressure. Blood flows continuously rather than directed by pulsatile rhythm of the heartbeat. Muscular (distributing) arteries - arteries composed proportionately more smooth muscle and less elastic tissue and delivers blood to specific body organs. Arterioles - smallest of arterial vessels; smallest arterioles have single layer of smooth muscle cells spiralling around endothelial lining Arterial Pulse - alternating expansion & recoil of elastic arteries during each cardiac cycle creates a pressure wave = pulse Pulse point (also referred to as compression/pressure points) arteries: Temporal, femoral, facial, popliteal, common carotid, posterior tibial, brachial, dorsalis pedis, and radial C. Venous System - blood is carried from the capillary beds toward the heart by veins Venules - are formed when capillaries unit Veins - have thin tunics and larger lumens than arteries, therefore can accommodate larger blood volumes.

Due to the fact that 65% of the blood supply is always in veins, veins are referred to as capacitance vessels or blood reservoirs. Blood Pressure is low in veins - adaptations to help return blood the heart at the same rate it was pumped into circulation: Large diameter lumen Presence of valves (in limbs) that prevent blood from flowing backward (therefore unidirectional flow) Valves found in veins of limbs not ventral cavity because upward flow of blood is opposed by gravity. D. Capillaries - smallest blood vessels with thin walls consisting of only a tunica intima; Capillary Types : Continuous capillaries - abundant in skin and muscle and are continuous because their endothelial cells provide an uninterrupted lining. Adjacent cells are joined laterally by tight junctions but usually incomplete and leave gaps of unjoined membranes called intercellular clefts. Fenestrated capillaries - endothelial cells have many oval pores (fenestrations) that are covered by a membrane and therefore has greater permeability to fluids and small solutes.

Sinusoids - are capillaries connecting arterioles and venuoles in liver and have large irregular shaped lumens, are fenestrated, and have fewer tight junctions but larger intercellular clefts Capillary Beds - interweaving networks of capillaries consisting of two types of vessels: A vascular shunt (interarteriole-thoroughfare channel) which is a short vessel that directly connects the arteriole and venule at opposite ends of the bed True capillaries Note: The terminal arteriole feeding the bed leads into a metarteriol (a vessel structurally intermediate between an artery and a capillary) , which is directly continuous with the thoroughfare channel (intermediate between a venule and a capillary). The thoroughfare channel, in turn, joins the postcapillary venule that drains the bed. E.

Capillary Exchange Vesicular Transport (exocytosis and endocytosis) Bulk Flow Bulk Flow --> regulation of the relative volumes of blood and interstitial fluid Filtration and reabsorption of fluids due to pressure ( ) differences Balance of pressures = net filtration pressure (NFP) Starling's Law of the Capillaries - movement of fluid between plasma and the interstitial fluid is in a state of near equilibrium at the arterial and venous ends of a capillary NFP = (Blood Hydrostatic Pressure + Interstitial Fluid Osmotic Pressure) - (Blood Colloid Osmotic Pressure + Interstitial Fluid Hydrostatic Pressure) blood hydrostatic pressure = pressure of blood acting against the capillary walls forcing fluids out of capillaries interstitial fluid hydrostatic pressure = pressure acting outside the capillaries pushing fluid in blood colloid osmotic pressure = pressure as a result of moving fluid into cappillaries due to attraction to non diffusable solutes interstitial fluid osmotic pressure = pressure of blood acting against the cappillary walls forcing fluids into capillaries Edema - filtration exceeds reabsorption resulting in increased interstitial fluid volume; causes include: Increased blood hydrostatic pressure in capillaries Decreased concentration of plasma proteins

 Increased permeability of capillaries 2.

Output- vagus (X) nerve - decreases heart rate Cardiac accelerator nerves - increase heart rate and contractility Vasomotor nerves - vasodilation and vasoconstriction Hormonal Regulation Renin-angiotensin mechanism: renin released by kidneys leads to the formation of angiotensin II angiotensin II - causes vasoconstriction of arterioles and increases blood pressure aldosterone - angiotenisn II stimulates release of aldosterone which promotes sodium/water reabsorption in kidney; therefore aldosterone increases blood volume and pressure Epinephrine/norepinephrine - increases heart rate and contraction thereby increasing cardia output and BP Antidiuretic hormone, ADH - released by the hypothalamus increases water retention in the kidney; increases BP causes intense vasoconstriction of arterioles and increases BP Atrial natriuretic peptide, ANP - protein produced by the heart and causes vasodilation of arterioles and promotes loss of salt and water in urine; decreases BP PTH (vasodilator) and Calcitrol (vasoconstrictor) - regulates calcium and phosphate ions, in turn regulates smooth muscle contraction other chemical but non hormonal factors: Nitric oxide (vasodil

ator) Frog anatomy part 1 - Body parts - The World of Frogs The World of Frogs Frog Anatomy part 1 Body parts External Anatomy Pupil - The opening through which light enters an eye.

Iris - The colored part of the eye which forms and regulates the size of the pupil. Cornea - The transparent anterior part of the external layer of the eye (transparent outer covering of the eye). Nictitating Membrane - A transparent part of a frog’s lower eyelid that moves over the eye to clean it and protect it. Lens - The transparent structure within an eye that focuses light rays. External nares or nostrils - Anterior openings for the entry or exit of air. Tympanic Membrane - The eardrum - receives sound waves Flexors - Muscles which contract to move a part toward the body. Extensors - Muscles which contract to move a part away from the body. Mucous Glands - Structures in the skin of a frog that secrete mucous which keeps the skin moist. Poison Glands - Structures in the skin of the frog which secrete a whitish fluid that is highly irritating to enemies. Epidermis - The outer layer of the skin. Dermis - The inner layer of skin which contains blood vessels and pigment cells. Glottis - The opening from the mouth into the respiratory system. Larynx - The voice box (contains vocal cords).

Bronchi - The short tubes of a frog’s breathing system that leads from the larynx to the lungs. Lungs - Exchange point where CO2 leaves and O2 enters the blood Alveoli - Air sacs in the lungs where the movement of gases occurs. Red Blood Cells - Blood cells which carry O2 and CO2. Hemoglobin - The red pigment in red blood cells which combine with and carry gases. Cold-blooded - Condition or designation of an animal’s body temperature being the same as the external temperature. Hibernation - A state of dormancy during which life processes and activities are greatly slowed and reduced. Arteries - Thick-walled blood vessels that carry blood under high pressure away from the heart. Arterioles - Small arteries which branch out into capillaries. Capillaries - Smallest blood vessels with thinnest walls through which substances move into and out of the blood. Venules - Small blood vessels which carry blood away from capillaries. Veins - Thin walled blood vessels that carry blood under low pressure to the heart. Neurotransmitters - Chemical substances produced by an animal that influence parts of the body (“chemical messengers”).

Tongue - Muscular structure attached to the front of the mouth which is extended to catch insects (its food). Maxilla - The upper jaw. Maxillary Teeth - Sharp teeth in the maxilla of a frogs mouth that function in holding captured prey. Mandible - The lower jaw. Vomerine Teeth - Small projections in the top of a frog’s mouth that function in holding and captured prey. Eustachian tube openings - Openings in the mouth that lead to tubes that connect to the middle ear to equalize air pressure. Internal Anatomy Skeletal muscles - Muscles of the body which control voluntary movements. Tendons - Strands of tissue which attach skeletal muscles to bones. Smooth Muscle - Muscle tissue of inner organs which control involuntary muscles. Gullet - Posterior part of the mouth cavity in a frog. Food enters the esophagus here. Esophagus - Tube that connects the mouth and the stomach in a frog. Stomach - Stores food and mixes it with enzymes to begin digestion. Digestive Enzymes - Function in the chemical part of breaking down food. Mucous - Lines the digestive system and protects it from acid and enzymes. Mucous Cells - Special cells which secrete the mucous.

Pylorus - The opening between the stomach and the small intestine. Small Intestine - The principal organ of digestion and absorption of digested food. Duodenum - The anterior (front) part of the small intestine into which food passes from the stomach. Peristaltic Waves - Automatic muscular contractions of the smooth muscle tissue in the walls of organs of the digestive system to move food. Pancreas - Gland which secretes digestive enzymes into the duodenum. Bile - Fluid produced by the liver that aids in the digestion of fats. Gall Bladder - Sac which stores bile. Common Bile Duct - Tube which carries bile from the gall bladder and digestive juice from the pancreas into the duodenum. Ileum - The posterior part of the small intestine. Site of absorption of digested food. Large Intestine - Posterior organ of the digestive system which stores undigested food. Rectum - Posterior part of the large intestine Cloaca - Organ through which the products of the frogs digestive and urogenital system pass when discharged from the body. Cloacal Opening - Opening of cloaca through which undigested food, urine, eggs, and sperm are passed.

Liver - Secretes bile and processes digested food molecules carries in the blood from the ileum. Veins - Blood vessels that carry blood to the heart. Arteries - Blood vessels which carry blood away from the heart. Capillaries - Blood vessels through which substances enter and leave the bloodstream. Anterior Vena Cava - Large vein that carries blood from the anterior part of the body toward the heart. Posterior Vena Cava - Large vein that carries blood from the posterior part of the body towards the heart. Sinus Venosus - Sac that receives blood from the vena cava Heart - Pumping organ of the circulatory system (has 3 chambers). Right Atrium - Chamber of the frogs heart which receives blood from the sinus venosus. Left Atrium - The chamber of the heart that receives blood from the lungs. Pulmonary Veins - The blood vessels that carry blood form the lungs to the left atrium. Ventricle - Chamber of a frog’s heart that pumps blood out of the heart to the lungs and other parts of the body. Truncus Arteriosis - Large artery in a frog that carries blood away from the ventricle into branches that lead to all parts of the body.

Spleen - Organ in the frog’s circulatory system that makes, stores, and destroys blood cells. Kidneys - Organs in the frog’s excretory or urogenital system that filter the blood and remove the wastes to make urine. Urinary Ducts - Tubes in a frog that carry urine from the kidneys to the cloaca Urinary Bladder - The organ that collects and stores urine until released. Adrenal Glands - Organs located near the kidneys which secrete hormones. Ova or Eggs - Female sex cell or gametes Ovaries - Organs of the female reproductive system that produce the eggs. Oviducts - Tubes of a female frog’s reproductive system that carry eggs from the ovaries to the cloaca. Testes - Male sex organs that produce sex cells (sperm). Sperm - Male sex cell or gametes. Seminal Vesicles - Enlarged distal sections of the male frog’s urinary ducts that collect sperm prior to entry into the cloaca. Fat Bodies - Masses of fat in the body cavities of frogs. Needed for hibernating and mating Central Nervous System - Brain and spinal cord.

Peripheral Nervous System - Part of the nervous system which branches out from the CNS to all parts of the frog’s body Neurons - Cells which make up the nervous system. Each is made up of a cell body and fibers of varying lengths. Nerves - Bundles of neurons fibers which transmit messages. Brain - Main organ of the nervous system. The “control center”. Olfactory Lobe - Part of the frog’s brain associated with the sense of smell Cerebrum - Part of the brain that is associated with memory, pain, and voluntary muscle control. Optic Lobes - Part of the brain associated with vision. Cerebellum - Part of a brain that influences balance and equilibrium. Medulla Oblongata - Part of a brain that is the center for some involuntary functions. Cranial Nerves - Nerves that lead to and from the brain. Spinal Cord - Main pathway to and from the brain Spinal Nerves - Nerves that lead to and from the spinal cord. © 2014 D.Knight Your Body's Systems Your Body's Systems Circulatory System The circulatory system is the body's transport system. It is made up of a group of organs that transport blood throughout the body.

The heart pumps the blood and the arteries and veins transport it. Oxygen-rich blood leaves the left side of the heart and enters the biggest artery, called the aorta. The aorta branches into smaller arteries, which then branch into even smaller vessels that travel all over the body. When blood enters the smallest blood vessels, which are called capillaries, and are found in body tissue, it gives nutrients and oxygen to the cells and takes in carbon dioxide, water, and waste. The blood, which no longer contains oxygen and nutrients, then goes back to the heart through veins. Veins carry waste products away from cells and bring blood back to the heart , which pumps it to the lungs to pick up oxygen and eliminate waste carbon dioxide. Digestive System The digestive system is made up of organs that break down food into protein, vitamins, minerals, carbohydrates, and fats, which the body needs for energy, growth, and repair. After food is chewed and swallowed, it goes down the esophagus and enters the stomach, where it is further broken down by powerful stomach acids. From the stomach the food travels into the small intestine. This is where your food is broken down into nutrients that can enter the bloodstream through tiny hair-like projections.

The excess food that the body doesn't need or can't digest is turned into waste and is eliminated from the body. Endocrine System The endocrine system is made up of a group of glands that produce the body's long-distance messengers, or hormones. Hormones are chemicals that control body functions, such as metabolism, growth, and sexual development. The glands, which include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, thymus gland, pineal body, pancreas, ovaries, and testes, release hormones directly into the bloodstream, which transports the hormones to organs and tissues throughout the body. Immune System The immune system is our body's defense system against infections and diseases. Organs, tissues, cells, and cell products work together to respond to dangerous organisms (like viruses or bacteria) and substances that may enter the body from the environment. There are three types of response systems in the immune system: the anatomic response, the inflammatory response, and the immune response. The anatomic response physically prevents threatening substances from entering your body. Examples of the anatomic system include the mucous membranes and the skin. If substances do get by, the inflammatory response goes on attack.

The inflammatory system works by excreting the invaders from your body. Sneezing, runny noses, and fever are examples of the inflammatory system at work. Sometimes, even though you don't feel well while it's happening, your body is fighting illness. When the inflammatory response fails, the immune response goes to work. This is the central part of the immune system and is made up of white blood cells, which fight infection by gobbling up antigens . About a quarter of white blood cells, called the lymphocytes, migrate to the lymph nodes and produce antibodies, which fight disease. Lymphatic System The lymphatic system is also a defense system for the body. It filters out organisms that cause disease, produces white blood cells, and generates disease-fighting antibodies. It also distributes fluids and nutrients in the body and drains excess fluids and protein so that tissues do not swell. The lymphatic system is made up of a network of vessels that help circulate body fluids. These vessels carry excess fluid away from the spaces between tissues and organs and return it to the bloodstream. Muscular System The muscular system is made up of tissues that work with the skeletal system to control movement of the body.

Some muscles—like the ones in your arms and legs—are voluntary, meaning that you decide when to move them. Other muscles, like the ones in your stomach, heart, intestines and other organs, are involuntary. This means that they are controlled automatically by the nervous system and hormones—you often don't even realize they're at work. The body is made up of three types of muscle tissue: skeletal, smooth and cardiac. Each of these has the ability to contract and expand, which allows the body to move and function. . Skeletal muscles help the body move. Smooth muscles, which are involuntary, are located inside organs, such as the stomach and intestines. Cardiac muscle is found only in the heart. Its motion is involuntary Nervous System The nervous system is made up of the brain, the spinal cord, and nerves. One of the most important systems in your body, the nervous system is your body's control system. It sends, receives, and processes nerve impulses throughout the body. These nerve impulses tell your muscles and organs what to do and how to respond to the environment. There are three parts of your nervous system that work together: the central nervous system, the peripheral nervous system, and the autonomic nervous system.

The central nervous system consists of the brain and spinal cord. It sends out nerve impulses and analyzes information from the sense organs, which tell your brain about things you see, hear, smell, taste and feel. The peripheral nervous system includes the craniospinal nerves that branch off from the brain and the spinal cord. It carries the nerve impulses from the central nervous system to the muscles and glands. The autonomic nervous system regulates involuntary action, such as heart beat and digestion. Reproductive System The reproductive system allows humans to produce children. Sperm from the male fertilizes the female's egg, or ovum, in the fallopian tube. The fertilized egg travels from the fallopian tube to the uterus, where the fetus develops over a period of nine months. Respiratory System The respiratory system brings air into the body and removes carbon dioxide. It includes the nose, trachea, and lungs. When you breathe in, air enters your nose or mouth and goes down a long tube called the trachea. The trachea branches into two bronchial tubes, or primary bronchi, which go to the lungs. The primary bronchi branch off into even smaller bronchial tubes, or bronchioles.

The bronchioles end in the alveoli, or air sacs. Oxygen follows this path and passes through the walls of the air sacs and blood vessels and enters the blood stream. At the same time, carbon dioxide passes into the lungs and is exhaled. Skeletal System The skeletal system is made up of bones, ligaments and tendons. It shapes the body and protects organs. The skeletal system works with the muscular system to help the body move. Marrow, which is soft, fatty tissue that produces red blood cells, many white blood cells, and other immune system cells, is found inside bones. Urinary System The urinary system eliminates waste from the body, in the form of urine. The kidneys remove waste from the blood. The waste combines with water to form urine. From the kidneys, urine travels down two thin tubes called ureters to the bladder. When the bladder is full, urine is discharged through the urethra.

Question: What are the smallest blood vessels of a body called?
Answer: Capillary