BLOOD PHYSIOLOGY

Dr. Majid Hameed

1

Lecture One

Lecture One

Blood: It is a moving tissue circulates in a closed system of blood vessels. It consists of cellular elements {erythrocytes, leukocytes, and platelets} suspended in a liquid medium (plasma).

Functions of blood:•Transportation of O2, CO2, nutrients, heat, wastes, and hormones, enzymes & vitamins.•Regulation of pH, body temperature, arterial BP. •Prevention of blood loss; clotting factors•Protection against pathogens via WBCs.

Blood volume:

In Adult male ≈ 5 liters (equal to 8% of the total body weight)

In newborn baby ≈ 300 ml blood

It reaches the adult range at the time of puberty.

Mechanisms of regulation of blood volume

1. Capillary fluid shift mechanism. blood volume capillary pressure leakage of fluid from capillary to interstitial fluid blood volume back to normal, and vise versa.

2. Reflex mechanisms (Baroreceptor reflex).

blood volume stretching and stimulation of baroreceptors reflex inhibition of sympathetic nervous system dilatation of renal arteries allowing excess urinary output.

3. Hormonal mechanism a) Atrial natriuretic factor (ANF).

blood volume release of ANF (from atria of heart) sodium and water excretion through kidneys blood volume back to normal

b) Aldosterone. blood volume stimulates aldosterone secretion from adrenal cortex absorption of sodium and water from kidney tubules blood volume

c) Angiotensin. It is released when blood volume is decreased. It causes retention of water and salt.

d) ADH (Anti-diuretic hormone). blood volume release of ADH and allows water loss through kidneys and vice versa.

4. Thirst mechanism: it is stimulated when blood volume decreases.

When blood volume falls below normal, exactly reverse events occur.

5. Renal mechanism.

Conditions leading to increased blood volume:Physiological conditions Age: o infants > adults when compared to body weight o infants < adults compared to surface area. o 80 ml/kg in infants and 70 ml/kg in adults.

Sex: o males > females because of more

erythropoietin activity, more body weight and greater surface area (cyclical loss of blood during menstruation).

Exposure to warm environment: the blood volume.

Conditions leading to increased blood volume:Physiological conditions (cont.)Pregnancy: blood volume 20 to 30%.

Exercise: due to contraction of spleen and release of stored blood in circulation.

High altitude: Due to hypoxia there is increased erythropoietin secretion at high altitude. This in turn increases the production of RBC blood volume.

Emotional disturbance: Sympathetic stimulation causes contraction of spleen which releases stored blood in circulation.

Pathological conditions with high blood volume

Congestive cardiac failure:

Hyperthyroidism:

Hyperaldosteronism.

Cirrhosis of liver.

Polycythaemia vera.

Conditions which reduce blood volume Physiological conditions

Acute exposure to cold.

Posture. erect < recumbent state

Obesity. Blood volume per kilogram of body weight in an obese person is lower

Conditions which reduce blood volume Pathological conditions

• Haemorrhage or blood loss.

• Fluid loss.

• Reduction in red blood cells.

• Hypothyroidsim.

Blood components:

Properties of Blood

Heavier, thicker, and 3-4 X more viscous than water

temperature: 38 °C

pH : 7.38-7.42 pH < 7.38 ….. Acidosis pH > 7.42 ….. Alkalosis

Plasma: • It is the straw-colored fluid portion of the blood

(intravascular fluid) in which the cells are suspended.

• Its quantity = 3,500 ml = 5% of the total body weight.

• It consists of 91.5% water 8.5% solutes (70% plasma proteins, 20% low-molecular-weight substances, 10% electrolytes).

Proteins (7 – 7.5 g/dl).

•Albumins: 4.5 g/dl, synthesized in liver.

• Globulins: 2.7 g/dl, synthesized in liver, lymphoid tissue, (α, β, γ)

•Fibrinogen: 0.3 g/dl, synthesized in liver

• Normal albumin-globulin ratio is about 2:1.

• Change of this ratio occur mainly in liver diseases because only albumin synthesis is reduced.

Functions of plasma proteins1. Colloid osmotic pressure. • plays important role in exchange of water

between tissue fluid and blood. • It is normally 25 to 30 mmHg. • Albumin contributes 70 to 80% of osmotic pr.

2. Viscosity. Fibrinogen and globulins due to their

asymmetrical shape. It provides resistance to flow of blood in blood

vessels, & to maintain blood pr. in the normal range.

3. Buffering action. Plasma proteins can combine with acids and bases. They are responsible for about 15% of buffering capacity of blood.

Functions of plasma proteins4. Binding and transport function. CO2 (carbamino compound), hormones (thyroxine binding protein (TBP) Cortisol (transcortin); drugs, electrolyte (calcium), iron (transferrin), Cu (Ceruloplasmin); lipids and fat soluble vitamins (A, D and E) (HDL and LDL).

5. Immunity. Gamma globulins in plasma are antibodies and they protect body against bacterial infections.

6. Clotting of blood. Whenever there is injury to the blood vessel fibrinogen is converted to fibrin which forms blood clot. This clot seals the hole in the vessel and therefore prevents blood loss.