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IBLSModule

2nd year Medicine

Phase II, MBBS2nd year Medicine- IBLS Module

May 2008

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Lecture 1: Introduction to Blood PhysiologyObjectives

By the end of this lecture the student should be able to:

1. Describe the composition of blood.2. State normal values of blood and plasma volume.3. Define hematocrit and state its normal value.4. Describe the functions of blood as a tissue.5. Describe the composition of plasma.6. List types of plasma proteins.7. State the normal plasma protein concentration.8. Describe the functions of plasma proteins.9. Outline the different causes of low plasma protein concentration.

2nd year Medicine- IBLS Module May 2008

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Blood• Blood is the only liquid tissue.

• It represents about 8% of total body weight.

• Average blood volume is 5 L in women and 5.5 L in men.

• Blood is composed of cellular elements suspended in liquid plasma.

• Average plasma volume is 3 L.

• 99% of cellular elements are RBCs.

2nd year Medicine- IBLS Module May 2008

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Composition of the blood

• Plasma: fluid part, 55% of total blood volume, mainly water, organic and inorganic substances.

Cellular elements: 45% of total blood volume.• RBC or erythrocytes (5x106/mm3)• WBC or leukocytes (3-10x103/mm3 )• Platelets or thrombocytes (150-400x103/mm3)

2nd year Medicine- IBLS Module May 2008

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Hematocrit or packed cell volume

• Definition: % of total blood volume occupied by RBCs.

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Normal value:

Adult male: 47 %

Adult females: 42 %

2nd year Medicine- IBLS Module May 2008

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Functions of Blood• Transport function:

• O2 and nutrients to cells

• CO2 and metabolic waste products away from cells

• Hormones, drugs, etc… • Defensive function:

• WBC and antibodies• Hemostatic function:

• Stop bleeding (platelets and clotting factors) • Homeostatic function:

– pH

– Temperature

– Plasma volume2nd year Medicine- IBLS Module

May 2008

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Plasma• Composition

• Water: 90%

• Solids: 10%

– Organic substances 9.1%:

» Plasma proteins 6-8% of plasma’s total weight

» Nutrients (a.a., glucose, lipids, vitamins)

» Waste products (creatinine, bilirubin, urea)

» Dissolved gases (O2 and CO2)

» hormones

– Inorganic substances: 0.9% (Na, Cl, others)

2nd year Medicine- IBLS Module May 2008

Plasma proteins• Normal concentration 7-7.5 g/dl

• Plasma proteins are:• Albumins (3.5-5 g/dl)

• Globulins α1, α2, β1, β2, γ

• Fibrinogen

• Most of the plasma proteins are synthesized in the liver.

• Circulating antibodies (γ globulins) are synthesized by plasma cells (activated B-lymphocytes).

92nd year Medicine- IBLS Module

May 2008

Functions of Plasma proteins• Osmotic function:

• plasma proteins (mostly albumin) exert an osmotic pressure across the capillary wall (colloid osmotic pressure or oncotic pressure).

•Plasma volume regulation

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Arterial end of capillary

cap. pressure 35 mm Hg 25 mm Hg

absorbing force

filtration force

Net: filtration = 10 mm Hg

Venous end of capillary

cap. pressure 15 mm Hg 25 mm Hg

absorbing force

filtration force

Absorbing = 10 mm Hg

2nd year Medicine- IBLS Module May 2008

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•Buffer action:• help in keeping pH of blood constant.• plasma proteins act as acids (due to COOH) and act as alkali (due to NH2 group).

• Defensive function: -globulins defend the body against microorganisms and their toxins.

2nd year Medicine- IBLS Module May 2008

• Blood clotting: prothrombin and fibrinogen are essential for blood clotting.

• Contributes to blood viscosity: blood viscosity prevents the rapid flow of blood from arterial to venous system. Viscosity of blood contributes to the peripheral resistance which maintains diastolic BP.

• Transport: carrier proteins for small molecules such as vitamins, hormones, trace elements and drugs.

• Nutritive: used by the tissue during prolonged starvation.

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• Hypoproteinema: low plasma protein concentration.

– Causes:»Liver diseases

»Renal diseases

»Prolonged starvation

»Congenital deficiency (e.g. afibrinogenemia

2nd year Medicine- IBLS Module May 2008

Summary

• What is the composition of the blood?

• What is the normal blood volume, plasma volume?

• What is hematocrit value? Normal value?

• What are the general functions of blood?

• What is the composition of plasma?

• Describe plasma proteins in terms of their:

• Types

• Normal concentration

• Sites of formation

• Functions

• What are the causes of hypoproteinemia? 15