• 2 The cardiovascular system • (a) The structure and function of arteries, capillaries

and veins to include endothelium, central lumen, connective tissue, elastic fibres, smooth muscle and valves. The role of vasoconstriction and vasodilation in controlling blood flow.

Structure of the Cardiovascular System

What is the Cardiovascular system?• The cardiovascular system, also

known as the circulatory system, is composed of blood, blood vessels and the heart.

• The heart functions as a pump to move blood through the blood vessels of the body.

• A circulatory system is essential for large, multi-cellular organisms, such as humans and animals, and provide at least five major functions that are necessary for life.

The five major functions of the cardiovascular system are:

• Transporting oxygen and removing carbon dioxide

• Transporting nutrients and removing wastes

• Fighting disease• Transporting hormones• Regulating body temperature

Cardiovascular system

• http://www.youtube.com/watch?v=CjNKbL_-cwA

Components of the CVS

• The CVS consists of a double pump (the heart) and a complex system of blood vessels.

The cardiovascular system

•The cardiovascular system is made up of the heart along with the blood vessels.

Blood vessels

A layer of cells called the endothelium lines the central lumen of all blood vessels. It is surrounded by layers of tissue. These surrounding layers differ in each type of blood vessel.

The middle of the vessel is called the central lumen.

ARTERIES• Carry blood away from

the heart• Endothelium

• One cell thick

• Elastic tissues & smooth muscles• Rebounds• Evens flow

• Fibrous tissue• Tough• Resists stretch

Contraction of the smooth muscle: vasodilation and vasoconstriction

Arteries • Arteries carry blood away from the heart. The further the blood

travels away from the heart, the lower the blood pressure gets.

• They have an outer layer of connective tissue containing elastic fibres and a middle layer containing smooth muscle with more elastic fibres. The elastic walls of the arteries stretch and recoil to accommodate the surge of blood after each contraction of the heart.

• The smooth muscle can contract, called vasoconstriction. This decreases the blood flow. It can also relax, causing vasodilation. This increases blood flow. Movement of these muscles controls blood flow.

VEINS• Carry blood towards the

heart• Endothelium • Larger lumen than

arteries• Thinner muscle layer &

few elastic fibres• Blood at lower pressure

• Fibrous tissue

VEINS• Contain valves

• Prevents backflow of blood

• Situated between skeletal muscles

• Muscle compresses vein when contracted

• Blood “squirted” towards heart

Veins• Veins have an outer layer of connective

tissue containing elastic fibres but a much thinner muscular wall than arteries. They contain valves to prevent back flow of blood as blood is at a lower pressure in veins than arteries.

CAPILLARIES• Transport blood between

arteries and veins• Form large networks

(capillary beds)• Exchange of materials

between blood and cells• Their walls are only one cell

thick, allowing nutrients and waste to diffuse through with ease.

Capillaries

Arteriole Capillaries

(capillary bed)

Venule

Capillaries • Capillaries are only one cell thick to allow

exchange of substances with tissues.

• (i) The exchange of materials between tissue fluid and cells through pressure filtration and the role of lymph vessels.

• Similarity of tissue fluid and blood plasma with the exception of plasma proteins.

Tissue Fluid and the Lymphatic system

Lymphatic system

• http://www.youtube.com/watch?v=Q530H1WxtOw

Plasma Tissue fluid

Protein e.g. red blood cells No protein

Oxygen and carbon dioxide Oxygen and carbon dioxide

glucose, amino acids glucose, amino acids

water water

Comparison of contents of plasma and tissue fluid

Tissue fluid

• Dissolved substances move out through the capillary walls by pressure filtration, forming tissue fluid. Tissue fluid is similar to blood plasma except it does not contain plasma proteins e.g. red blood cells. Tissue fluid surrounds cells and supplies them with glucose, amino acids, oxygen and other useful substances. Carbon dioxide and other metabolic waste (waste produced by chemical reactions in the cell) diffuse out of the cells and into the tissue fluid to be excreted.

Blood arriving in

the arteriole high

pressure

Blood leaving in

venule

low pressure

Lymph vessel

capillary

Respiring cell

Tissue fluid

Some tissue fluid enters lymphatic system

Some plasma forced out of capillary

Some tissue fluid enters capillary by osmosis

Lymph passes into lymphatic system

Summary Tissue Fluid and Lymphatic System

• Case study on disorders of the lymphatic system. Suitable examples include the effect of kwashiorkor on fluid balance and elephantiasis.

Lymphatic system

• Excess tissue fluid is absorbed by lymphatic vessels which are found around cells in each tissue, forming lymph fluid. The lymph fluid eventually returns to the blood.

• (b) The structure and function of the heart. • (i) Cardiac function and cardiac output. • Definition of cardiac output and its calculation.

Cardiac Function and Cardiac Output

Heart Rate (HR)

• Number of times heart beats in one minute• Normal values around 72bpm • Normal range is between 60-90

Stroke Volume (SV)• Volume of blood ejected by each ventricle during

contraction• The heart pumps the same volume of blood through

the ventricles during each beat.• ~ 70ml

Cardiac OutputCardiac Output is the volume of blood pumped by

each ventricle per minute and is the function of two factors:

• Heart rate (beats per minute)• Stroke volume (the volume of blood ejected by

each ventricle during each contraction)

CO = HR x SV

• Measuring pulse rate in arteries using pulsometer. Calculate cardiac output under different conditions.

Activity Level

Heart rate (bpm)

Stroke Volume (ml)

Cardiac Output (l/min)

Rest 72 70 5

Mild 100 110 11

Moderate 120 112 13.4

Heavy (athlete)

200 150 30

Some typical values for cardiac output at varying levels of activity

Cardiac output• Heart rate (HR) = number of beats of the

heart per minute (bpm)• Stroke volume (SV) = volume of blood

ejected by each ventricle during contraction (ml). The left and right ventricles pump the same volume of blood through their arteries each time.

• Cardiac output (CO) measures the volume of blood pumped out by each ventricle per minute. To calculate this:

CO = HR x SV

• http://www.phschool.com/science/biology_place/labbench/lab10/intro.html

Cardiac function

The Heart

Semi-lunar valve

Atrioventicular valve

Semi-lunar valve

Atrioventricular valve

• The opening and closing of the AV and SL valves are responsible for the heart sounds which can be heard with a stethoscope.

• (ii) The cardiac cycle to include the functions atrial systole, ventricular systole, diastole. Effect of pressure changes on atrio-ventricular (AV) and semi lunar (SL) valves.

THE CONDUCTING SYSTEM OF THE HEART

Stuart brown – stooibrown@yahoo.com

• Cardiology. As a youngster I had a cardiac pacemaker. Two, actually. I still have one of them, plus the x-ray of the damn thing in my chest. So I can talk a bit about what it did for me (and what it didn't do) and the sorts of tests which were done on me to examine my heart's performance.

Cardiac cycle• The cardiac cycle consists of three

stages:1. Atrial systole2. Ventricular systole3. Diastole

Cardiac cycle

1. Atrial systole

Pressure in the atria builds up as muscles of the atria walls contract,

forcing blood through the AV valves into the ventricles. AV valves open, SL

valves shut.

2. Ventricular systole

Pressure in the ventricles build up as muscles of the ventricle walls

contract, forcing blood through the SL valves into the arteries. SL valves

open, AV valves shut.

3. Diastole

Pressure decreases in both atria and ventricles as muscles relax.

Blood flows back into the atria and starts to flow into the ventricles. The

higher pressure in the arteries closes the SL valves. AV valves open, SL

valves shut.

Pure Science Specials - Of Hearts and Minds • https://www.youtube.com/watch?v=Xwx5fbElMfk • 50 mins

• (iii) The structure and function of cardiac conducting system including nervous and hormonal control.

• Control of contraction and timing by cells of the sino-atrial node (SAN) and atrio-ventricular node (AVN). Interpretation of electrocardiograms (ECG).

• The medulla regulates the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS). Sympathetic accelerator nerves release adrenaline (epinephrine) and slowing parasympathetic nerves release acetylcholine.

Regulation of the Cardiac Cycle

Sino-atrial node (SAN) and Atrial Ventricular node (AVN)

Electrical activity of the heart

• http://www.youtube.com/watch?v=v3b-YhZmQu8&feature=related

Cardiac conducting system• The heart beat is regulated by both nervous

and hormonal control. • Nervous control:• Cells of the sino atrial node (SAN), also

known as the pacemaker, in the right atrium set the pace at which cardiac cells contract without conscious thought. They are called autorhythmic.

• The SAN generates an electrical impulse which spreads throughout the atria, causing atrial systole. The impulse reaches the AVN which then carries the impulse across the ventricles, causing ventricular systole.

Autonomic Nervous System

• The autonomic nervous system (ANS) consists of 2 antagonistic (opposing) branches

• Sympathetic nerve

• Parasympathetic nerve

Sympathetic

Sympathetic accelerator nerves

Release adrenaline (epinephrine)

Increases heart rate

Parasympathetic

Parasympathetic slowing nerves

Release acetylcholine

Decreases heart rate

The medulla region in the brain regulates the rate of

the SAN through the Autonomic Nervous System(ANS). It contains two branches which work inAntagonistic (opposing) ways.

Sympathetic accelerator nerves releaseadrenaline (epinephrine) which increases heart

rate.Slowing parasympathetic nerves releaseacetylcholine which decreases heart rate.

ABPI schools

• Adrenaline animation:

• http://www.abpischools.org.uk/page/modules/hormones/horm8.cfm?coSiteNavigation_allTopic=1

Hormonal Regulation of the Heart

• Under certain circumstances e.g. stress or exercise the sympathetic nervous system causes the adrenal glands to produce adrenaline which travels in the blood to act on the SAN, which generates impulses at a higher rate, increasing heart rate

Hormonal Regulation of the Heart

• Under certain circumstances e.g. stress or exercise the sympathetic nervous system causes the adrenal glands to produce adrenaline which travels in the blood to act on the SAN, which generates impulses at a higher rate, increasing heart rate

• Hormonal control: • Under circumstances such as stress and exercise, the

sympathetic nervous system causes the adrenal glands to produce the hormone adrenaline which acts on the SAN to increase heart rate.

• The impulses generated by the SAN creates currents that can be detected by an electrocardiogram (ECG).

• P wave – atrial systole• QRS waves – ventricular systole• S wave - diastole

ABNORMAL ECG’S

• Atrial flutter• Rapid contraction of the atria• Atria contract 3 times for every

ventricular contraction

ABNORMAL ECG

• Ventricular tachycardia• Ventricles beat rapidly and

independently of the atria

ABNORMAL ECG’S

• Ventricular fibrillation• Unco-ordinated electrical activity• Pumping cannot take place• Fatal if not corrected• Defibrillation

• (iv) Blood pressure changes, in response to cardiac cycle, and its measurement.

• Blood pressure changes in the aorta during the cardiac cycle. Measurement of blood pressure using a sphygmomanometer. A typical reading for a young adult is 120/70 mmHg. Hypertension is a major risk factor for many diseases including coronary heart disease.

blood pressure measurement

• http://www.youtube.com/watch?v=ElCbQMiBC6A&NR=1

Blood pressure

• Blood pressure changes in the aorta during the cardiac cycle. It can be measured using a sphygmomanometer.

• An inflatable cuff stops blood flow and deflates gradually. The blood starts to flow (detected by a pulse) at systolic pressure. The blood flows freely through the artery (and a pulse is not detected) at diastolic pressure.

• A typical reading for a young adult is 120/70 mmHg.

High blood pressure, known as hypertension, is a major risk factor for many diseases including coronary heart disease.