HEMODYNAMICS

Physics of Blood flow in the circulation

Dr. Kamla ChoudharyAssistant Professor

Heart• Heart:(Left, Right)

2 collecting chambers – Atria2 Pumping chambers - Ventricles

Heart ValvesAtrioventricular (A-V) valves - separate Atria from Ventricles

Bicuspid (Mitral) - Left SideTricuspid - Right Side

Semi-Lunar Valves – separate ventricles from Arteries

Opening, Closing of Valves - Depends on Pressure differences between blood in adjacent areas

Dynamics of Circulation is concerned with flow of blood, lymph and also the pressure in the various segment of the vascular system.

Dynamics of Circulation will be discussed

under following heading:-1.Functional organization and structure of Vascular System

2. Blood Flow and Pressure in different segments of circulatory system

3.Hemodynamic

4. Blood pressure

1.Functional organization and structure of Vascular System

The circulatory system forms two circuits in series with each other:-- Systemic circulation (greater circulation)- Pulmonary circulation (lesser circulation)

In addition to these,circulation of lymph present parallel.

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Parts of the circulatory system

Circulation Schematic

Lungs Tissues

Left Side of Heart

Right Side of Heart

A V

V A

Pulmonary Vein

Pulmonary Artery

Aorta

Sup. & Inf. Vena Cava

Mitral Valve

Pulmonary Valve

Aortic Valve

Tricuspid Valve

General Pathway of Blood Flow

heart -> arteries -> arterioles -> capillaries -> venules -> veins ->

heart

Systemic Vascular tree:-Major Types of Blood Vessels found with in circulation

Arteries are strong, elastic vessels adapted for carrying blood away from the heart under high pressure

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1-Types Of Arteries

ELASTIC ARTERIES (LARGE-SIZED)Also called as Windkessel vessels including Aorta and its main branches carotid, iliac and axillary arteries.

MUSCULAR ARTERIES (MEDIUM-SIZED)Distribution vessels includes most of arteries of the body.

RESISTANCE ARTERIES (SMALL-SIZED)Arterioles and pre capillary sphincters

2-Meta – Arterioles And Capillaries Exchange vessels

3. Types of VeinsVeins –capacitance vesselsVenules- Post capillary resistance vessels

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.

Three distinct layers:

Tunica interna

Tunica media

Tunica externa.

Endothelium – Inner most layer, Rich in elastic fibres and collagen also.Tunica media Middle layer –. Smooth muscle fibers, thick layer of elastic connective tissue.

Outer layer – Tunica externa. Connective tissue layers with collagen fibres are prominent.

Structure of Blood vessels

Media

Elastic Arteries• Largest-diameter arteries have lot of elastic fibers

in tunica media• Help propel blood onward despite ventricular

relaxation (stretch and recoil)

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Windkessel Effect

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In old age elasticity of these vessels is lost due to degenerative & atherosclerotic changes. So SBP rises,DBP falls, Pulse Pressure Rises resulting in defective perfusion in periphery

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Muscular Arteries• Medium-sized arteries with more

muscle than elastic fibers in tunica media

• Capable of greater vasoconstriction and vasodilation to adjust rate of flow– walls are relatively thick

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RESISTANCE ARTERIES

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Types of Capillaries

Continuous capillaries gaps between neighboring cells muscle and lungs

Fenestrated capillariesplasma membranes have many holes kidneys, small intestine & endocrine glands

Sinusoids very large fenestrations incomplete basement membrane liver, bone marrow, & spleen

Hydraulic conductivity of capillaries in various parts of the body

(Ganong, Medical Physiology 2001)

Organ Conductivity Type of Endothelium

Brain (except CVO) 3 Skin 100 Skeletal muscle 250 Continuous Lungs 340 Heart 860 GIT (intestinal mucosae) 13,000 Fenestrated Kidney (glomerulus) Liver Bone marrow Endocrine glands Sinusoidal Lymphoid tissue (Marieb, Human Anatomy and Physiology)05/03/23 25

Copyright 2009, John Wiley & Sons, Inc.

Dynamics of Capillary Exchange

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Fluid movement in the capillary• Arteriole side: fluid moves

toward the tissues

• Venous side: fluid reenters the capillary

• Overall: for every 1 liter of fluid entering the tissues, only 0.85 l reenter the capillary

• The remaining 0.15 l is reabsorbed as lymph by lymphatic capillaries and eventually returned back to blood circulation

• When this system fails: Edema

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Causes of edema

• Increased hydrostatic blood pressure

- heart failure (left or right),- excess fluid in the blood

• Decreased blood osmotic pressure– Liver, kidney diseases,

malnutrition (kwashiorkor), burn injuries

• Increased interstitial hydrostatic pressure (lymphatic capillary blockage)- breast cancer surgery, elephantiasis

• Leaking capillary wall- histamine release during allergic reaction

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VEINS Transport blood under low pressure. 8x more distensible than arteries transport blood towards the heart carry deoxygenated blood.

Great veins no valves, thin and easily distended

Venules no valves, walls slightly thicker than capillaries

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Characteristics of various types of blood vessels

Windkessel vessels: large arteries

Resistance vessels: small arteries

Exchange vessels: formed by a single layer of endothelial cells

Capacitance vessels: veins

Shunt vessels: Meta-arterioles

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