# 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.

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-   **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.

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-   **Organelles:** That perform the metabolic activity of the cell.

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-   **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.

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-   **Endoplasmic reticulum (ER) :** They are fluid-filled tubules for
    carrying substances. There are two types of ER :

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-   **Rough endoplasmic reticulum :** They carry ribosomes that
    represent sites of protein synthesis.

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-   **Smooth endoplasmic reticulum :** They function in cholesterol
    synthesis and breakdown, fat metabolism, and detoxification of
    drugs.

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-   **Golgi apparatus :** It modifies and packages proteins, secretes
    vesicles, plasma membrane components and lysosomes.

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-   **Lysosomes :** They contain enzymes that digest non-usable
    materials within the cell.

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-   **Peroxisomes :** These are membranous sacs of oxidase enzymes. They
    detoxify harmful substances and break down free
    radicals.

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-   **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.

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-   **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.

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-   **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.

