Lecture 37 Introduction to Circulation

BY DR QAZI IMTIAZ RASOOL

1. Identify the two divisions of circulation and track the pathway of the blood through both circulations.

2. Outline the various parts of circulation and identify the differences in structure, function, pressure and velocity of blood in different vessels.

3. Describe the physiological anatomy of the heart and identify its various specialized functional parts.

OBJECTIVES

Functions of the Heart

1. Generating blood pressure

2. Routing blood: separates pulmonary and systemic

circulations

3. Ensuring one-way blood flow: valves

4. Regulating blood supply

1.Changes in contraction rate and force match

blood delivery to changing metabolic needs

Circulatory System Function

Move circulatory fluid (blood) around body1. Gas Transport2. Nutrient Transport3. Excretory Product Transport4. Cell Signal Transport 5. Distribute secretions of endocrine glands,6. Production/Synthesis7. Hydraulic Force8. Heat Conductance9. Immunity

Overview of the Cardiovascular System

1. Heart- circulates blood through vessels2. Vascular System /Blood vessels3. Arteries- away from heart

4. Veins- towards heart

5. Capillaries- location of internal respiration, are tiny, thin-walled blood vessels that connect arteries to veins and are located in all body tissues.

- in diameter that blood cells pass through in a single file.

3. Blood- transport medium

Path of Blood

Pulmonary Circuit

Blood flow between the lungs and heart

Supplied by the Right side of the heart

Systemic Circuit

Blood flow between the rest of the body and heart

Supplied by the Left side of the heart

Pulmonary circulation

Systemic circulation /greater circulation / peripheral circulation.

Venous return

is aided by both structural modifications and functional adaptations.1. Structural

-Large lumen-Valves - present mostly in

extremities, none in ventral body cavity2. Functional

-Respiratory Pump-Muscular Pump-Smooth muscle layer under

sympathetic control

Physiological- anatomy

Structure of Blood Vessel Walls

except the smallest consist of three layers:1.Tunica intima reduces friction between the vessel walls and blood;

2. Tunica media controls vasoconstriction and vasodilation of the vessel;

3. Tunica externa protects, reinforces, and anchors the vessel to surrounding structures

1.Blood flow is the volume of blood flowing

through a vessel, organ, or the entire circulation

ml/min (controlled in relation to the tissue need)

2. Blood pressure is the force per unit area exerted by the blood against a vessel wall (mm Hg). (by the tension at the end of the arterioles)

3. Resistance is friction between blood and the vessel wall,.

Systemic Blood Pressure

Functional Anatomy of the HeartChambers

1. 4 chambers1. 2 Atria2. 2 Ventricles

2. 2 systems1. Pulmonary 2. Systemic

Functional Anatomy of the HeartCardiac Muscle

1. Characteristics1. Striated2. Short branched cells3. Uninucleate4. Intercalated discs5. T-tubules larger and

over z-discs

Functional Anatomy of the HeartValves

1. Function is to prevent backflow1. Atrioventricular Valves

1. Prevent backflow to the atria2. Prolapse is prevented by the

chordae tendinae1. Tensioned by the papillary

muscles2. Semilunar Valves

1. Prevent backflow into ventricles

The Conduction System of the Heart

1. Conduction pathways 2. Depolarization spreads

throughout the heart very rapidly facilitating a coordinated contraction pattern

3. Intercalated disks 1. Form junctions between

adjacent cardiac muscle fibers

2. Contain a high concentration of gap junctions for rapid transmission of the action potential

Myocardial PhysiologyContractile Cells

1. Plateau phase prevents summation due to the elongated refractory period

2. No summation capacity = no tetanus (Which would be fatal)

Myocardial PhysiologyAutorhythmic Cells (Pacemaker Cells)

1. Altering Activity of Pacemaker Cells1. Sympathetic activity

1. NE and E increase If channel activity1. Binds to β1 adrenergic receptors which activate cAMP

and increase If channel open time2. Causes more rapid pacemaker potential and faster

rate of action potentials

Sympathetic Activity Summary:

increased chronotropic effectsheart rate

increased dromotropic effectsconduction of APs

increased inotropic effectscontractility

Sympathetic Activity Summary:

increased chronotropic effectsheart rate

increased dromotropic effectsconduction of APs

increased inotropic effectscontractility

Myocardial PhysiologyAutorhythmic Cells (Pacemaker Cells)

1. Altering Activity of Pacemaker Cells1. Parasympathetic activity

1. ACh binds to muscarinic receptors1. Increases K+ permeability and decreases Ca2+

permeability = hyperpolarizing the membrane1. Longer time to threshold = slower rate of action

potentials

Parasympathetic Activity Summary:

decreased chronotropic effectsheart rate

decreased dromotropic effects conduction of APs

decreased inotropic effects contractility

Parasympathetic Activity Summary:

decreased chronotropic effectsheart rate

decreased dromotropic effects conduction of APs

decreased inotropic effects contractility

Aging and the CVSChanges occur in the blood, heart, and BVs1.Blood changes – HCT; thrombi and emboli form more easily; blood pools in leg2.Heart changes – efficiency and elasticity; atherosclerosis of coronary vessels; scar tissue forms3.Blood vessel changes – loss of elasticity; calcium deposits damage vessel walls4.Gradual changes in heart function, minor under resting condition, more significant during exercise5.Hypertrophy of L ventricle6.Maximum heart rate decreases7. tendency for valves to function abnormally and arrhythmias to occur8. O2 consumption required to pump same amount of blood