Module 2: Cardiovascular system

anatomy of the heart

Two components of the cardiovascular system

Blood vascular system and lymphatic vascular system

Structures which make up the blood vascular system

Heart, arteries, arterioles, capillaries, venules, veins

Blood vascular system

A closed-loop circulatory system which transport oxygen, nutrients, hormones and remove carbon dioxide and metabolic wastes

Lymphatic vascular system

One-way open ended drainage network which drains excess interstitual fluid and slowly returns it to the venous circulation

Interstitial fluid becoming lymph

Excess tissue fluid enters lymphatic capillaries through porous finger-like openings

Function of arteries

Carry blood away from the heart to supply tissues

Location of major arteries

Deep within the body to reduce the risk of injury because they carry blood under high pressure

Collateral circulation

Organs receive blood from two arteries to maintain blood supply if one becomes blocked

Capillaries

Microscopic vessels connecting arteries to veins

Function of capillaries

Exchange gasses, nutrients, wastes, hormones and tissue fluid between blood and tissues

Three types of capillaries

Continuous, fenestrated, sinsoidal

Continuous capillaries

Least permeable capillaries found in muscle, skin and brain

Fenestrated capillaries

Capillaries which contain pores found in kidneys and endocrine glands

Sinusoidal capillaries

Most permeable capillaries found in the liver, spleen and bone marrow

Veins

Blood vessels which return blood towards the heart

Three venous drainage pathways

Deep veins, superficial veins, lymphatic vessels

Deep veins

Veins located alongside arteries which drain muscles and deep tissues

Superficial veins

Veins located beneath the skin which drain superficial tissues

Lymphatic vessels

Tubes which drain excess interstitial fluid

Tissues which make up blood vessel walls

Connective tissue, smooth tissue, endothelium

Connective tissue in blood vessels

Provides strength, support and elasticity

Smooth muscle in blood vessels

Controls vessel diameter and blood flow

Endothelial cells in blood vessels

Provide a smooth lining that reduces friction and helps prevent blood clotting

Two circulatory circuits

Pulmonary circulation and systemic circulation

Pulmonary circulation

Carry deoxygenated blood to the lungs for oxygenation

Pulmonary circulation pathway

Right atrium → right ventricle → pulmonary arteries → lungs → pulmonary veins → left atrium

Systemic circulation

Deliver oxygenated blood to the body and return deoxygenated blood to the heart

Systemic circulation pathway

Left atrium → left ventricle → aorta → body tissues → superior and inferior vena cava → right atrium

Coronary artery disease

Heart attack

Cerebrovascular disease

Stroke

Shape of the heart

A blunt cone-shaped muscular organ

Location of the heart

In the thorax, between the lungs, slightly left of the midline

Apex

The pointed inferior tip formed mainly by the left ventricle

Location of the apex

Around the 5th intercostal space near the midclavicular line

PMI

The point where the apex beat can be felt during ventricular contraction

Base

The broad superior portion formed mainly by the atria and great vessels

Location of the base

Around the level of the 2nd and 3rd ribs

Chambers of the heart

Right atrium, right ventricle, left atrium, left ventricle

Three vessels which drain into the right atrium

Superior vena cava, inferior vena cava, coronary sinus

Superior vena cava

Drains the head, neck, upper limbs and thorax

Inferior vena cava

Drains the lower body

Right ventricle

Pumps deoxygenated blood through the pulmonary semilunar valve into the pulmonary arteries and lungs

Left atrium

Receives oxygenated blood from right pulmonary veins and left pulmonary veins

Left ventricle

Pumps oxygenated blood into the aorta for distribution throughout the body

Interatrial septum

Separates the right and left atria

Interventricular septum

Separates the right and left ventricles

Septa

Prevent the mixing of deoxygenated and oxygenated blood

Three layers of the heart wall

Endocardium, myocaridum, epicardium

Endocardium

The thin inner lining of the heart chambers and valves

Tissues which form the endocardium

Simple squamous epithelium and loose irregular fibrous connective tissue

Functions of endocardium

Produces a smooth blood-contacting surface, reduces friction, prevents activation of blood clotting

Myocardium

Thick, muscular middle layer of the heart wall

Tissue which makes up the myocardium

Cardiac muscle

Function of myocardium

Generates the force required to pump blood

Epicardium

The outer layer of the heart wall

Tissues which make up the epicardium

Mesothelium, loose irregular connective tissue, adipose tissue, coronary blood vessels

Functions of epicardium

Protects the heart, supports coronary vessels, stores fat, reduces friction during heart movement

Pericardium

A double-layered sac surrounding the heart

Layers of the pericardium

Fibrous pericardium, parietal serous pericardium, pericardial cavity, epicardium

Pericardial cavity

Contains serous fluid which reduces friction as the heart beats

Fibrous pericardium

Tough outer connective tissue preventing over expansion

Two types of heart valves

AV valves and semilunar valves

Function of heart valves

They prevent the backflow of blood ensuring blood flows in one direction through the heart during the cardiac cycle

Systole

The contraction phase of the heart when the ventricles contract and pump blood into the arteries

Diastole

The relaxation phase of the heart when the ventricles relax and fill with blood

Atrioventricular valves

Located between the atria and ventricles

Right AV valve

Tricuspid valve (three leaflets/cusps)

Left AV valve

Mitral (bicuspid) valve (two leaflets/cusps)

Function of the AV valves

Allow blood to flow from atria to ventricles during diastole and prevent blood returning to the atria during ventricular systole

AV valves open

During ventricular diastole when ventricular pressure is lower than atrial pressure

AV valves closed

During ventricular systole when ventricular pressure exceeds atrial pressure

Papillary muscles

Finger-like projections of ventricular muscle attached to the chordae tendineae

Chordae tendineae

Tough fibrous cords connecting papillary muscles to the free edges of the AV valve leaflets

Function of papillary muscles

They contract early during ventricular systole to place tension on the chordae tendineae and stabilise the AV valves

Function of chordae tendineae

Prevent valve leaflets from folding back into the atria and valve prolapse, reduce stress on the valve leaflets, help coordinate valve closure

Semilunar valves

Located between the ventricles and their output arteries

Right semilunar valve

Pulmonary valve

Left semilunar valve

Aortic valve

Function of the semilunar valves

Prevent blood flowing back into the ventricles after ventricular contraction

Semilunar valves open

During ventricular systole when ventricular pressure exceeds arterial pressure

Semilunar valves close

During ventricular diastole when blood begins to flow backwards filling the cusps and sealing the valve

Supports all four heart valves

The fibrous skeleton (septum/ring) of dense connective tissue

Coronary circulation

Supply oxygen and nutrients to the myocardium and remove metabolic wastes

Coronary arteries origin

From the ascending aorta immediately above the aortic valve

Left coronary artery

Artery which runs behind the pulmonary trunk before branching

Two major branches of the left coronary artery

Anterior interventricular artery and circumflex artery