d) Cardiovascular System

Higher Human Biology

What can you

remember about the heart and

blood vessels?

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.

Heart Revision

Learning Intention

• Describe the path of blood flow through the heart including the heart valves

The heart is a DOUBLE PUMP:1st - blood is pumped to the lungs & returns to the heart,2nd - blood is pumped to the body & back to the heart again.

1. Deoxygenated blood from the body is pumped from the heart to the lungs

2. The blood receives oxygen in the lungs and is pumped back to the heart

4. The oxygen leaves the blood to be used by the body and the blood goes back to the heart

3. The oxygenated blood is then pumped by the heart to the body

The Structure of the Heart

• The heart is has 4 chamber

• The upper chambers are called atria (atrium singular)

• The lower chambers are called ventricles

Heart Valves• Valves prevent

back flow of blood • Between the atria

and ventricles are atrioventricular (AV) valves

• Between the ventricles and arteries leaving the heart are semilunar (SL) valves

LA

RV

RA

LV

Right AV Valve

Right SL Valve

Left AV Valve

Left SL Valve

Heart Rap

Oxygenated blood flows

back from the lungs via the PULMONARY

VEIN

LEFT ATRIUM

LEFT VENTRICLE

From left ventricle out through the aorta to the body

Left AV valve

Left SL valve

Deoxygenated blood flows from the body into the heart via the VENA CAVA

RIGHT

ATRIUM

Right AV valve

RIGHT

VENTRICLE

Out via the pulmonary artery to the lungsRight SL valve

Pig heart dissectionParts of heart musical quiz

Who Am I?1. I leave the right ventricle and go to the lungs

2. I take deoxygenated blood to the heart

3. I prevent backflow of blood into the left atrium

4. I come from the lungs and go back to the heart

5. I prevent backflow of blood into the right ventricle

6. I leave the left ventricle of the heart

Pulmonary Artery

Vena Cava

Left AV Valve

Pulmonary Vein

Right SL Valve

Aorta

Learning Intentions

• State what is meant by the terms cardiac output, heart rate and stroke volume

• Explain the calculation of cardiac output

Learning Intention

• Compare the structure and function of arteries, capillaries and veins

Blood Vessels• Blood leaves the

heart in arteries • It then flows

through capillaries in the tissues and organs

• And returns to the heart in veins

• There is a decrease in blood pressure as the blood moves away from the heart.

Layers in Blood Vessels

• The endothelium lining the central lumen of the blood vessels is surrounded by layers of tissue.

• These surroundings layer differ in each type of blood vessel

endothelium

Arteries

EndotheliumConnective tissue

Muscle tissue

• Arteries have an outer layer of connective tissue containing elastic fibres which stretch

• They have a middle layer containing smooth muscle with more elastic fibres

• Endothelium lines the central lumen where the blood flows through

• The elastic walls of the arteries stretch and recoil to accommodate the surge of blood that enters them after each contraction of the heart.

• The smooth muscle can contract causing vasoconstriction and less blood to flow

• The smooth muscle can relax causing vasodilation and more blood to flow

Arteries

Capillaries

• Transport blood between arteries and veins

• Exchange of materials between blood and cells

• Their walls are only one cell thick, allowing nutrients and waste to diffuse through with ease

Veins• Veins have an outer layer of connective tissue containing

elastic fibres but a much thinner muscular wall than arteries.

• Endothelium lines the central lumen where the blood flows through

• They contain valves which prevent the backflow of blood.

EndotheliumConnective tissue

Muscle tissue

Learning Intentions

• Describe the exchange of materials between tissue fluid and cells

• State how lymph is formed and what happens to it

Blood

• Blood consists of red and white blood cells, platelets and plasma

• Plasma is a watery yellow liquid containing dissolved substances such as glucose, amino acids, respiratory gases, plasma proteins and useful ions

Tissue Fluid

• Blood arriving at the arteriole end of a capillary bed is at a higher pressure than blood in the capillaries

• As blood is forced into the narrow capillaries, it undergoes pressure filtration and much of the plasma is squeezed out through the thin walls

Blood at high pressure

Blood at low pressure

Fluid squeezed out

Tissue Fluid

Tissue Fluid

Tissue Fluid

• This plasma which has been squeezed out through the thin walls of the capillaries into the surrounding tissues is called tissue fluid

• The only difference between plasma and tissue fluid is that plasma has proteins and tissue fluids do not

Tissue Fluid• The cells exchange molecules with the tissue fluid by

diffusion down a concentration gradient • Useful molecules such as food and oxygen diffuse into

the cells from the tissue fluid• Carbon dioxide and other metabolic wastes diffuse out

of the cells and into the tissue fluid to be excreted

Lymph

• Most of the tissue fluid goes back by into the blood capillary by osmosis

• The fluid that does not return to the blood is now referred to as lymph and is collected by the lymphatic system

Blood arriving in

the arteriole high

pressure

Blood leaving in

venule

low pressure

Lymph vessel

capillary

Tissue fluidSome tissue fluid enters lymphatic system

Some plasma forced out of capillary

Some tissue fluid enters capillary by osmosis

Lymph passes into lymphatic system

Lymph

• Lymph is collected by a vast network of lymph vessels

• These vessels eventually return their contents to the main circulation near the heart via osmosis

• The lymphatic system has no pump- the contraction of skeletal muscles squeezes lymph along the vessels

Try these questions . . .

1. What is tissue fluid?2. Name a substance that passes from body cells into tissue

fluid3. Tissue fluid surrounds the muscle cells. Some of this fluid is

reabsorbed into the bloodstream. How else is tissue fluid removed from around the cells?

4. Describe the means by which lymph is forced along through the lymphatic system

Answers . . .

1. It is the liquid consisting of plasma and small, dissolved molecules that is squeezed out of capillaries during pressure filtration

2. Carbon dioxide3. It is absorbed into the lymphatic system via thin-walled

lymphatic vessels and returned to blood capillaries by osmosis

4. When the vessels are pressed during muscular contraction, the lymph is pushed along the lymph vessels

Heart Rate (HR)

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

What is your HR?

Stroke Volume (SV)

• Volume of blood pumped out by each ventricle during contraction

• Normal values are around 70ml

Cardiac Output (CO)

• Cardiac output is the volume of blood pumped out of a ventricle per minute

• It is calculated by the following equation –

CO = HR X SV

• Normal values are around 5 litres/min

a) At rest: HR = 72bpmSV = 70ml

What is the CO of this individual?

CO = 72 x 70 = 5040 ml/min

= 5 litres/min

b) During exercise: HR = 200bpm SV = 150ml

What is the CO of this individual?

CO = 200 x 150 = 30000ml/min

= 30 litres/min

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:

Learning Intention

• Describe the events of the cardiac cycle

The Cardiac Cycle• The cardiac cycle refers to the pattern of contraction

and relaxation of the heart during one complete heartbeat.

• Contraction of the heart muscle is known as systole while relaxation is known as diastole.

• This lasts about 0.8 secs (0.3s systole,0.5s diastole)

Two Phases of the Cardiac Cycle

• Systole: contraction of the heart (atrial first, the ventricular). Blood forced out of chambers

• Diastole: relaxation of all chambers of the heart. The chambers fill with blood

The Cardiac Cycle

1. Atrial & ventricular diastole

2. Atrial systole (ventricular diastole)

3. Ventricular systole (atrial diastole)

Animation

Atrial and Ventriclar Diastole

• The atria fill with blood from the vena cava and pulmonary vein, and some of the blood flows into the ventricles.

• AV valves open

Atrial Systole

• Both atria contract and transfer the remainder of the blood through the open AV valves to the ventricles

Ventricular Systole• About 0.1s after atrial systole the

ventricles contract

• Ventricular systole closes the AV valves and pumps the blood out through the open semi lunar (SL) valves to the aorta and pulmonary artery.

• Semi-lunar valves close when pressure in arteries exceeds pressure in ventricles and the cardiac cycle begins again!

Cardiac Cycle Summary

Cardiac Cycle Summary

Ventricular Volume Graph

Atrial systoleVentricular systole

Heart Sounds

• The opening and closing of the AV and SL valves are responsible for the heart sounds heard with a stethoscope (lubb dubb)

Learning Intention

• Describe the structure of the cardiac conducting system

• The heart beat starts in the heart itself

• Heart muscle cells are self-contractile. This means they are able to contract and produce an electrochemical signal, which is passed on to other cardiac muscle cells, causing them to contract.

• It is regulated by the nervous system and hormones which ensures that it beats in a co-ordinated manner.

Conducting System of Heart

Inside human body

SA Node• The SAN is found at the top of the right atrium.

• It sends out a electrical impulses which are carried through the muscular walls of both atria

• This ensures that both atria contract simultaneously and results in atrial systole

• The electrical impulse is thenpassed to the atrioventricular node (AVN)

Bundle of HIs

AV Node• The AVN is found lower part of the right atrium

• When the impulse reaches the AVN it is passed into a bundle of conducting fibres.

• These fibres split left and right into the ventricles. This causes the ventricles to contract at the same time.

Pathway

(1) Impulse is generated in the SA node(2)The AVN then picks up the impulse from SAN(3)Passes to bundle of conducting fibers and travels down the septum(4)Passes to the bundle branches (right & left)(5)Passes to the ventricles contract from bottom up

SAN

AVN

Bundle of conducting fibers

septum

Learning Intention

• Describe the autonomic and hormonal regulation of the cardiac conducting system

Regulation of Heart Rate• The SAN alone initiates

each heartbeat, and the timing of each is controlled by the impulse from the SAN travelling to the AVN and then through the ventricles.

• However, heart rate is not fixed as it is altered by nervous and hormonal activity

Autonomic Nervous System Regulation

• The medulla regulates the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS)

• The autonomic nervous system consists of 2 opposing (antagonistic) branches– Sympathetic pathway– Parasympathetic pathway

Sympathetic Nerve• An increase in the

number of nerve impulses at the SAN via the sympathetic nerve increases heart rate

• Sympathetic accelerator nerves release norepinephrine (noradrenaline)

Parasympathetic Nerve

• An increase in the number of nerve impulses at the SAN via the parasympathetic nerve decreases heart rate

• Parasympathetic nerves release acetylcholine

Hormonal Regulation of the Heart

• Under certain circumstances e.g. stress or exercise the sympathetic nervous system causes the adrenal glands to produce the hormone adrenaline

• This travels in the blood to act on the SAN, which generates impulses at a higher rate, increasing heart rate

Autonomic Nervous System & Hormonal Regulation

Control centre in medulla

adrenalin

1. What structure initiates the heartbeat?2. Name the two parts to the autonomic nervous

system.3. Which nerve in the autonomic nervous system

speeds up heart rate?4. Which nerve in the autonomic nervous system slows

down heart rate?5. Which part of the brain sends messages to via the

sympathetic nerve to speed up heart rate and the parasympathetic nerve to slow down heart rate?

6. Name the hormone secreted by the adrenal glands.7. Under what circumstances is adrenaline released by

the adrenal glands?8. What neurotransmitter is released by the

sympathetic nerve?9. What neurotransmitter is released by the

parasympathetic nerve?

Starter Questions

Electrocardiogram• In an ECG(electrocardiogram)

test, the electrical impulses made while the heart is beating are recorded and shown on a piece of paper

• It can show any problems with the heart's rhythm, and the conduction of the heart beat through the heart which may be affected by underlying heart disease

Animation

• The P wave = the wave of excitation spreading over the atria from the SAN

• The QRS Complex = the wave of excitation passing through the ventricles.

The T wave = the recovery of the ventricles towards the end of ventricular systole

Abnormal Heart Rhythms

• Some forms of heart disease can be detected and diagnosed using ECGs because they produce unusual but identifiable patterns such as:

– Ventricular Tachycardia– Ventricular fibrillation– Atrial Flutter

Abnormal ECG - Ventricular Tachycardia

Abnormal cells in the ventricle walls act

like pacemakers and beat rapidly and

independently of the atria

• Uncoordinated electrical activity• Coordinated pumping of the chambers cannot

take place• Fatal if not corrected by defibrillation

(Defibrillation consists of delivering a therapeutic dose of electrical energy to the heart with a device called a defibrillator).

Abnormal ECG - Ventricular fibrillation

Abnormal ECG - Atrial Flutter

• Rapid rates of electrical excitation occur which leads to an increase in the contraction of either the atrium or ventricles.

• The contractions remain coordinated

Learning Intention

• Discuss the measurement and typical readings for blood pressure

Blood Pressure • This is the force exerted by blood against

the walls of the blood vessels. It is measured in millimetres of mercury (mmHg)

Blood Pressure• The blood needs to be under

pressure to travel round the body and for pressure filtration (as mentioned at the capillaries)

• As the heart contracts and relaxes blood pressure rises and falls.

• Measure 2 values – systolic BP (pressure during ventricular contraction) and diastolic BP (pressure during ventricular relaxation)

Measurement of BP

Both systolic and diastolic BP can be measured by an inflatable instrument called a sphygmomanometer which is wrapped around the upper arm.

• Normal values are around 120mmHg for systolic pressure and 70mmHg for diastolic pressure (120/70)

Hypertension

• High blood pressure is called hypertension

• Hypertension is a major risk factor for many diseases including coronary heart disease.