physiology and pathology, Exercises of Physiology

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INTRODUCTION TO HUMAN

PHYSIOLOGY

Definition of Human Physiology:

It is the science which deals with the functions

of the human body under different external

and internal environmental conditions to

maintain life (How organs work).

Organization of the human body

• The unit of structure is the cell.
• Cells of the same shape and function form

tissue.

• The organ is formed of more than one tissue

performing a special function; the stomach

digest and kidney excretes…

• A system is formed of more than one organ

having a complementary functions.

• The human body is a group of systems.

Digestive system

The body Fluids The total body water about 60 % of total body weight, distributed as follow: 1 - Intracellular fluid (ICF): this constitutes about 2 / 3 of the total body water. 40 % of total body weight 2 - Extracellular fluid (ECF) : this constitutes about 1 / 3 of the total body water. 20 % of total body weight It includes the following subdivisions:

• Intravascular fluid (i .e. the plasma): This is normally about 1 / 4 of the ECF volume.
• Extravascular fluid : This is normally about 3 / 4 of the ECF volume, it includes: - Interstitial fluid: the fluid in spaces between the tissue cells - Transcellular fluids: fluid present in closed spaces surrounded by epithelium as cerebrospinal fluid

Components of Human Cell

1. The cell membrane.

2. The nucleus.

3. The cytoplasm ----- organelles

Membranous

A. Endoplasmic reticulum B. Mitochondria C. Lysosomes D. Golgi apparatus

Non-membranous

A. Ribosomes B. Centrosome C. Microfilaments and microtubules D. Storage granules and pigments

1 - The cell membrane

Its functions are: 1 - a boundary to surround the cell 2 - Selective permeability allowing certain substances to pass and preventing others It is very thin ( 75 angstrom thick). Chemically it is formed of phospholipids and proteins: The phospholipid molecule is formed of water soluble hydrophilic phosphate and fat soluble hydrophobic lipid part containing cholesterol. The plasma membrane is formed of two layers of phospholipid molecules with their hydrophilic ends directed outwards and inwards and their hydrophobic parts directed to the interior of the membrane. Proteins of the cell membrane are peptide chains of amino acids. They are either pure proteins or conjugated with carbohydrates (glycoproteins) or with lipids (lipoproteins). Proteins are either surface (peripheral) proteins on the outer or inner surfaces, or through and through proteins (transmembrane or integral proteins).

Functions of membrane proteins

❑ Structural part of cell membrane. ❑ Pumps e.g. Na

• K
  • pump ❑ Receptors for hormones and chemical transmitters. Receptors can determine self from non self and play important role in immunity and protection against autoimmune diseases. ❑ Enzymes e.g. adenyl cyclase which forms cyclic AMP (cAMP) from ATP. ❑ Carriers : helping transport of substances through the cell membrane. They may be: Uniport: transport one substance in one direction. Symport: cotransport more than one substance at a time in only one direction. Antiport: transport one substance in one direction in exchange for another in opposite direction e.g. Na

• K

pump carrier which transport 3 Na to the exterior in exchange with 2 K to the cell interior. .

❑ Channels: through which water soluble substances can pass through the cell membrane. These may be: Non gated channels: they are channels that are open all the time allowing passage of ions all the time. Sometimes they are called “leak channels” Gated channels : these channels are classified into: Voltage gated channels: that open or close in response to membrane potential changes. Ligand gated channels: that open or close in response to binding to a chemical substance (ligands). Ligands may be: External ligands; binds to the outer surface as neurotransmitters and hormones. Internal ligands; binds to the inner surface as ca

• 2 and cAMP. Mechanical gated channels: that open or close in response to mechanical stretch or pressure. The cell membrane is dynamic; molecules are continuously degraded and resynthesized

Transport Mechanisms

through Cell Membrane

I. Passive

i.e. Doesn’t need energy ( no ATP ) Examples: 1 - Diffusion 2 - Osmosis 3 - Filtration

II. Active

i.e. needs energy ( ATP is required ) Examples: 1 - Primary active transport 2 - Secondary active transport 3 - Endocytosis 4 - Exocytosis

Transport across

cell membrane