# Human Physiology/Physiology Introduction

Physiology The word physiology is from the Ancient Greek φυσιολογία (phusiología, "natural philosophy") and it is the study of how organisms perform their vital functions. An example is the study of how a muscle contracts or the force contracting muscles exert on the skeleton. It was introduced by French physician Jean Fernery in 1552. Physiology is built upon a tripod of sciences: physics, chemistry, and anatomy.

## Types of human physiology

Human physiology is the study of functions of the human body that can be divided into the following types:
Cell physiology.
This is the cornerstone of human physiology; it is the study of the functions of cells.
Special physiology
This is the study of the functions of specific organs. For example, renal physiology is the study of kidney function.
Systemic physiology
It includes all aspects of the function of the body systems, such as cardiovascular physiology, respiratory physiology, reproductive physiology etc..
Pathophysiology
It is the study of the effects of diseases on organ or system functions (pathos is the Greek word for disease).

## Levels of organization

Atom: An atom is the smallest particle of an element or a molecule. [carbon (C), Hydrogen (H), Oxygen (O), etc.].
Molecule: A molecule is a particle composed of two or more joined atoms (carbon dioxide CO2, water H2O).
Macromolecule: A macromolecule is a large molecule (carbohydrates, lipids, proteins, nucleic acids).
Organelles: An organelle is a small organ of a cell, which performs a particular function (cell membrane, cytoplasm and nucleus)
Cell: The cell is the basic unit of structure and function of living organisms.
Tissue: A tissue is a group of similar cells that perform a specialized function (epithelia, connective, muscle and nervous).
Organ: An organ is a structure consisting of a group of tissues that perform a specialized function (skin, heart, brain, etc.).
System: A system is a group of organs that act together to perform a specialized function. 1 . cardiovascular system 2 . respiratory system 3 . urinary system 4 . digestive system 5.nervous system 6.reproductive system 7.endocrine system 8 . musculoskeletal system 9.integument system.
Human body: A living organism is the most complex level of organization. It consists of all the systems arranged in a discrete manner so as to facilitate functioning of the various organ systems in synchronicity.
The seven characteristics of life
1. Cells: All living organisms have cells; cells are the building blocks of life.
2. Metabolism: All living organisms eat, drink, breathe and excrete.
3. Growth: All living organisms take in material from the environment to enlarge and sustain.
4. Reproduction: All living organisms are able to produce a copy of themselves.
5. Irritability: All living organisms are able to react to a change in their environment.
6. Adaptation: All living organisms are able to compete with each other for food and space to survive.
7. Movement: All living organisms are able to move.

## Cell physiology

The cell is the basic unit of all living organisms.
The cell is the functional unit of an organism.
Cells are not all the same but all cells share general structures.
Cells are organized into three main regions: Nucleus, cytoplasm and plasma membrane.
1) The nucleus : It is the center of the cell because it contains genetic material (DNA). It consists of three main regions: the nuclear membrane, the nucleolus and chromatin.
* Nuclear membrane : Nuclear membrane serves as a barrier of nucleus. It consists of a double phospholipid membrane and contains nuclear pores that allow for the exchange of material with the rest of the cell.
* Nucleolus : Nucleus contains one or more nucleoli. It functions as a site of ribosome production. Ribosomes then migrate to the cytoplasm through nuclear pores.
* Chromatin : It is composed of DNA and protein scattered throughout the nucleus. Chromatin condenses to form chromosomes when the cell divides.
2) Plasma membrane : It is the barrier for cell contents. It consists of double phospholipid layer and monolayer of protein scattered around phospholipid layer. Other materials in the plasma membrane include cholesterol and glycoproteins.
3) Cytoplasm : It is a thick, jelly-like fluid. It represents the material outside the nucleus and inside the plasma membrane. It consists of Cytosol.
* Cytosol: It is a fluid that suspends other elements - organelles.
* Organelles: That perform the metabolic activity of the cell.
* Cytoplasmic organelles : These are the organelles which are present scattered into the cytoplasm and performs specific functions.
These are as follows:-
* Ribosomes : They represent sites of protein synthesis in the cell. They are found at two locations : Free in the cytoplasm and attached to endoplasmic reticulum.
* Endoplasmic reticulum (ER) : They are fluid-filled tubules for carrying substances. There are two types of ER :
* Rough endoplasmic reticulum : They carry ribosomes that represent sites of protein synthesis.
* Smooth endoplasmic reticulum : They function in cholesterol synthesis and breakdown, fat metabolism, and detoxification of drugs.
* Golgi apparatus : It modifies and packages proteins, secretes vesicles, plasma membrane components and lysosomes.
* Lysosomes : They contain enzymes that digest non-usable materials within the cell.
* Peroxisomes : These are membranous sacs of oxidase enzymes. They detoxify harmful substances and break down free radicals.
* Mitochondria : The powerhouse of the cell (cells often have multiple mitochondria). They can change shape continuously. They also carry out reactions where oxygen is used to break down food to provide ATP for cellular activities.
* Centrosome : The centrosome is composed of two centrioles surrounded by an amorphous mass of protein. Centrosomes are associated with the nuclear membrane during prophase of the cell cycle. In mitosis the nuclear membrane breaks down and the centrosome can interact with the chromosomes to build the mitotic spindles.
* Centrioles : These are self-replicating organelles made up of nine bundles of microtubules. They appear to help in organizing cell division, but aren't essential to the process.
* Cytoskeleton : It's a network of protein structures that extend throughout the cytoplasm. It provides the cell with an internal framework. For example,
microfilaments and microtubules.
* a-Microfilaments : Microfilaments are solid rods made of proteins called actin. These filaments are important supports of the cytoskeleton.
* b-Microtubules : These straight, hollow cylinders are found throughout the cytoplasm of all human cells and carry out a variety of functions, ranging from transport to structural support.
Cell membrane is made up of lipids, proteins and carbohydrates.