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Physiology



Lec. (1) Dr.Abeer Mansoor

Physiology: is the scientific study of the normal function in living systems , sub-discipline of biology, its focus is in how organisms, organ systems, organs, cells, and biomolecules carry out the chemical or physical functions that exist in a living system.
Composition and functions of Blood:-  SHAPE \* MERGEFORMAT 
Blood is a fluid, which circulates in the vascular channels of human body due to the pumping action of heart. It is red in colour and consists of a liquid portion called plasma in which various types of cells are present. The cells which are suspended in plasma are of three different types.
Erythrocytes or Red Blood Cells:- 
The colour of these cells is red due to the presence of an iron containing pigment known as haemoglobin.

Leucocytes or White Blood Cells:-They are of different types as will be described later.


Thrombocytes or Platelets:-These cells help in the coagulation of blood.



Functions of blood:-

Blood performs various important functions, which could be summarised as " follows:
1- Respiratory function: Tissues and organs require a constant supply of oxygen to maintain their activity and simultaneously they form carbon dioxide and other waste products. Blood and particularly the red cells are responsible for transport of oxygen from lungs to the tissues. This is due to the presence of haemoglobin, which combines with oxygen to form oxy-haemoglobin. Carbon dioxide from tissues is taken up by the blood and released in the lungs.
2-Excretory function:- As a result of metabolic activity there is a constant production of waste products. Blood transports them to kidney, lungs, skin and gastrointestinal tract for excretion.
3-Nutritive function: - Food is digested into simpler end products in the digestive tract. These substances are absorbed from the intestine and transported to all parts of the body by blood.
4-Defensive function:- Blood protects the body against infections. This is achieved in two different ways. Leucocytes have the ability to engulf and destroy invading organisms and this property of white cells is termed as phagocytosis. These cells form the defence force of body and during infection their count increases. Plasma proteins (gamma globulin) can form antibodies against specific organisms. This virtue forms the basis of immunization against diseases.
5-Coagulation:- It is a mechanism by which various factors present in blood form a clot and thus prevent blood loss.
6-Acid base equilibrium:- Celland enzyme activity require maintenance of a constant acid-base equilibrium. Blood contains buffers which maintain the pH constant.
7-Body temperature:- The water content of blood is 90%. It has got a high specific heat and high latent heat of evaporation, which help blood to maintain the body temperature.
8-Transport of substances:- Blood is in rapid circulation and as such substances like hormones , vitamins and drugs are easily transported all over the body. Protein reserve Plasma proteins to a certain extent act as protein reserve and are used in extreme protein deficiency to form cell proteins.
PLASMA:
It is the fluid part of blood in which formed elements are suspended. The relative quantity of plasma and cells is in the ratio of 55:45. If blood mixed with an anticoagulant is taken in a graduated tube and centrifuged for about half an hour, the cells being heavier, settle at the bottom of the tube and constitute about 45% of the blood volume. This is known as packed cell volume (PCV).
Composition:-
Plasma contains 91-92% water and 8-9% of solid substances, which are both organic and inorganic in nature.
Inorganic constituents are less than 1% and are mostly chlorides, carbonates and phosphates of sodium, potassium and calcium. Small amounts of iron, copper and iodide are also present. Sodium bicarbonate present in the plasma helps in the maintenance of blood pH during Co2 transport.
Organic sub stances "form the major bulk of solids present in plasma and they are:


Plasma proteins (6.5 to 8 gms%)
Glucose (80-120 mgm%)
Cholesterol and lipids (150-250 mgm%)
Non-protein nitrogenous (NPN) substances like urea, uric acid, creatine, creatinine, etc.
Hormones, enzymes and blood pigments.
Plasma Proteins:-
They are specific proteins present in plasma and are of three different types.
1-Albumin:- it forms the major bulk of plasma proteins and has a molecular weight of 69,000. content of plasma is 4 to 4.5 gms%
2-Globulin:- it constitutes about 2.5 gm of plasma proteins and it has a relatively higher molecular weight of 1,30,000. Various types of globulins have been identified like alpha, beta and gamma globulin. The latter plays an important role in antibody formation. Prothrombin which helps in the coagulation is a beta globulin and its content is 0.1 gm%..
3-Fibrinogen:-blood coagulation requires this protein. The chemical nature of clot is fibrin which is formed from fibrinogen. About 0.25 gm% of fibrinogen is present in plasma.
Fibrinogen and Prothrombin are utilized in the clotting and plasma devoid of these two proteins is called serum. It only contains albumin and globulin. There :are various methods by which plasma proteins can be isolated, like half or full saturation' with ammonium sulphate or by electrophoresis.

Functions:-

1-Colloidal osmotic pressure:- It is 25 mmHg. Albumin being the major plasma protein primarily influences the colloidal osmotic pressure. This is responsible for preventing fluid exit from the capillaries.
2-Antibody formation:- As mentioned earlier, antibodies form an essential defense mechanism. This virtue is attributed to the gamma globulin.
3-Coagulation:- Fibrinogen and prothrombin are involved in the clotting of blood. Various other clotting factors also belong to globulin.
4-Transport media:- Certain substances bind themself with albumin, alpha and beta globulins and are transported. The transport of hormones, metals, drugs, dyes etc are examples of this function.
5-Erythrocyte sedimentation rate ESR:- is influenced by the fibrinogen content of plasma.
6-Viscosity:- Fibrinogen and Globulins, due to their high molecular weight and irregular shape contribute to blood viscosity.
7-Buffer mechanism:- Plasma proteins act as buffers and maintain acid base balance.
Protein reserve:- Plasma proteins constitute protein reserve of the body. During emergency, cells of the reticuloendothelial system break them into amino acids. Subsequently these are used for the synthesis of cell protein.

ERYTHROCYTES:-

They are commonly known as red blood cells because of their colour. These cells are circular, biconcave, non-nucleated and contain haemoglobin. They have a thin cell membrane, which shows selective permeability and allows exchange of crystalloids and anions between'the plasma and the cell.
The normal erythrocyte count in healthy adult ranges from 4.5 million to 5.5 million cells/cu mm of blood. It is slightly lower in females. In the newborn, the cell count is higher and ranges from 6 to 7 million/cu mm. Erythrocyte count shows certain physiological variations.
Age: It is higher in the newborn.
Sex Cell count: is relatively less in females.
Exercis:- During muscular exercise there is a slight temporary elevation of cell count.
Diurnal variation:- It is slightly reduced during sleep.
Altitude:- At higher altitudes the count is increased due to hypoxic state, which stimulates cell production.
Emotional state:-
There is increased secretion of adrenaline during excitement, which raises the erythrocyte count.
Normal erythrocytes have a mean diameter of 7.2 microns and an average thickness of 2.2 microns. They contain about 65% water and the rest is made up of solid substances, out of which the haemoglobin constitutes 33%.
The main function- of red blood cell is to transport oxygen and carbon-dioxide.
Life period:-
The average life of an RBC is 120 days. The old cells are destroyed in the spleen and liver.
The physiological rise in RBC.count is called polycythaemia. This can be observed in high altitudes.


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