Starter - reviewUsing these key words write 3 sentences

about the human circulatory system.

What are the parts of the circulatory system?What is its function (job)?

How is it designed to do this function ?

Words: Closed, transport, pump, blood, double, pressure, oxygenated, deoxygenated, blood vessels

Lesson Aims

How is the structure of the heart related to its function?

5.6 litre

s

How much blood does the human body contain?

The Heart

• Between the two lungs• Enclosed by the

PERICARDIUM• Pericardial fluid is secreted

between them to aid movement• The pericardium protects the

heart from over expansion

Where is it?

• The walls of the heart are made of cardiac muscle (MYOCARDIUM)

• Only found in heart• Never tires but can’t tolerate lack of O2.

Hold your hand in front of you and make a fist. Squeeze and relax. How long can you do this for?

Activity Drag the labels to the right place to complete the

diagram and the key

(bicuspid valve)

Septum

Pericardial membranes

Semi-lunar valves

Internal Features

Internal Structure

Task: Add labels to

the diagram

Watch this Video

• Blood flow through the heart

nearly 12,000 miles

How far does your blood travel

in one day?

Blood flow through the heart

• Blood comes into the heart from the body• It then has to pass to the lungs to collect

oxygen• This is called a double circulatory system• After it returns to the heart it leave again to

be transported to the body.

Task: Draw a flow diagram to show the flow of blood through the heart. You should start and finish with the body.

Atrium- receives blood from veinsVentricle- pumps blood into arteries

Right

Left

Deoxygenated blood

atrium

Tricuspid valve

Right ventricle

Pulmonary artery

lungs

Pulm

onar

y ve

in

Oxygenated blood

atrium

Bicuspid valve

Left ventricle

body

aorta

Vena cava

Body

External Features

External StructureTask: Add labels to your

diagram

Heart Dissection

around 35 million times

How many times does the heart beat

in a lifetime?

Your sheep’s heart

What external features can you identify?

A

CB

D

F

Ea million barrels of

blood

How much blood does the heart

pump in a lifetime?

External Features

FRONT BACKApex

Intact Heart…This shows the heart from

the front, with the portion on the right of the picture being the left side of the heart and vice versa.

The aorta is clearly visible at the top, with an atrium on either side, while the ventricles are in the bottom left.

The first incision…… is along the right ventricle. The right ventricle can be

identified by squeezing the heart, since the myocardium on the right side is much less rigid than that of the left ventricle.

This allows us to see the tricuspid valve and the right ventricular outflow tract which includes the pulmonary valve.

Longitudinal Cut…The right ventricle has been

cut open from the bottom towards the top.

In this picture, the myocardium is being held back. My finger is stuck underneath one leaflet of the tricuspid valve, which leads to the pulmonary valve.

The Tricuspid Valve up close…The tricuspid

valve allows blood to flow from the right atrium into the right ventricle.

Pulmonary Valve…When the heart is

contracting, the pulmonary valve is open because the blood pushes the cusps out of the way.

After contracting, the ventricles begin to relax and the pulmonary valve closes and prevents back-flow (called regurgitation) of blood into the ventricle.

The Left Ventricle…This longitudinal incision

extends from the bottom to the top of the left ventricle, then continues up into the atrium to allow us to view the entire left heart.

The Mitral (bicuspid) valve…The mitral valve prevents

blood from flowing back into the left atrium

The mitral valve is positioned between the atrium (at top) and ventricle (at bottom).

Left Ventricular Outflow…Blood flows into the

ventricles by passing through the mitral valve, but can you see where it flows out? This is a bit of a trick question because the outflow tract is hidden behind the mitral valves

What to do next!

• Answer the questions on the worksheet

• Match the keywords and their definitions

1. Why are pig or sheep hearts used to study the anatomy of the human heart?

2. How can you tell which side of the heart is the ventral surface?3. How many chambers are found in the mammalian heart? What

other group of organisms would have this same number of chambers?

4. What is the advantage in having this number of chambers compared to organisms with a fewer number of chambers?

5. Which chambers are the pumping chambers of the heart?6. Which chambers are the receiving chambers of the heart?7. How do the walls of the atria compare with the walls of the

ventricles and why are they different?8. What is the purpose of heart valves?9. Name & compare the heart valves found between the upper &

lower chambers of the right and left sides of the heart.10. Vessels that carry blood away from the heart are called

__________, while __________ carry blood toward the heart.11. Which artery is the largest and why?12. What is the purpose of the coronary artery and what results if

there is blockage in this vessel?13. Use the diagram of the heart below to trace blood flow

through the heart:

Questions to answer after the dissection

Oxygenated Relating to the lungsDeoxygenated

The valve which prevents backflow from the pulmonary artery to the right ventricle

Pulmonary vein Separates the two sides of the heart, keeping oxygenated and deoxygenated blood apart.

Pulmonary arteryBlood vessels on the surface of the heart which supply the heart itself with blood.

Aorta Blood without oxygen (usually coloured blue on a diagram)Vena cava

The valve which prevents backflow from the right ventricle to the right atrium

VentricleThe major blood vessel which carries oxygenated blood from the heart to the body.

Atrium Relating to the bodyMitral valve One of the bottom two chambers of the heartTricuspid valve

Blood with oxygen (usually coloured red on a diagram)

Pulmonary valve

One of the top two chambers of the heart

Aortic valveBlood vessel which returns with oxygenated blood from the lungs to the left atrium

SeptumThe muscle of the heart, cardiac muscle which never fatigues (gets tired)

Myocardium Blood vessel which leaves the right ventricle transporting deoxygenated blood to the lungs

PulmonaryValve which prevents backflow from the aorta to the left ventricle

SystemicThe valve which prevents backflow from the left ventricle to the left atrium

Coronary arteryThe major blood vessel which returns deoxygenated blood to the heart from the body

Activity Drag the labels to the correct numbered boxeson the diagram of the blood system

The Circulatory System

• Valves prevent backflow• When pressure in ventricles exceeds that in

the atrium the bicuspid/tricuspid valves shut

• This makes the first noise we hear with a stethoscope.

• Tendinous chords attached to Papillary Muscles prevent valves turning inside out.

• Semi-lunar valves prevent backflow in the pulmonary artery and dorsal aorta.

• Closure of these makes the second noise of the heart beat. (hence lub-dub)

• The heart requires a lot of oxygen and nutrients

• Some oxygenated blood leaving the left ventricle goes directly to the heart through the coronary Arteries.

• These branch many times to supply oxygen and nutrients throughout the cardiac muscle.

• When these get blocked a heart attack is likely and by-pass surgery required.

Task: Label the diagram of the

circulatory system

• Follow the red blood cell through the circulatory system

The Cardiac Cycle

• Cardiac muscle contracts without nervous or hormonal stimulation these are MYOGENIC contractions.

• The muscle cells work together to produce the heartbeat (cardiac cycle)

• Heart beat animation

• The cycle starts at the Sinoatrial node (SA node)

• A small piece of tissue with a inherent rhythm of contraction.

• The rhythm can be slowed or sped by nervous impulses and hormones.

• The SA node is also known as the pacemaker

• The SA node generates waves of electrical impulses called cardiac impulses.

• The electrical impulses pass over the atria until they hit the Atrioventricular septum

• This is non-conductive with only one gap in it called the Atrioventricular Node (AV node)

• This is the only route for cardiac impulse transmission.

• This is the second pacemaker and can take over if the SA node malfunctions

• Conducting sytem of the heart animation

Cardiac Cycle• Cardiac Cycle animation

Systole (contraction)

a) Atrial systole• Atria contract• Semi-lunar valves closed• Blood forced from the atria into the

ventricle

b) Ventricular systole• Ventricle contracts• Blood is forced into arteries• Bicuspid and tricuspid valves closed

Systole (contraction)• Cardiac impulse relayed from AV node over the

ventricles through the Bundle of His (atrioventricular bundle)

• Bundle branches into Purkinje (Purkyne) Fibres• The cardiac impulse passing through the fibres causes

a wave of contraction.• It starts at the apex of the heart and rapidly passes

over the ventricles (ventricular systole)• Regions close to the AV node have thin fibres

therefore slow the impulse so all ventricle contracts at once.

Diastole (relaxation)

• Heart relaxes and fills with blood from the veins.

• Semi-lunar valves closed to blood entering through arteries.

• Cardiac Cycle Tutorial• Task: Order the diagrams of

the cardiac cycle and annotate.

Pressure Changes

• You need to be able to explain the pressure changes in the heart in. terms of what is happening inside the heart

• You also need to be able to identify where the valves open and close and explain why in terms of pressure

• Task: Label this diagram of pressure changes in the heart. What is happening at A, B, C and D?

Answer these questions:

• Explain the difference in pressure between the atria and the ventricles.

• What causes the valves to open and close?

Pressure changes in the heart• Atrium has lower max pressure as only pumps

blood into the ventricle; ventricle pumps to the whole body.

• Closure of the valves is a passive process; it depends on the relative pressures on either side of the valve.

• The Atrioventricular valves close when the pressure in the ventricles is higher than in the atrium.

• They open when the pressure is higher in the atrium than the ventricle.

• Cardiac Cycle Overview

An Electrocardiogram - ECG

R

P Q S

T

• Cardiac muscle contracts as a result of electrical stimulation, this is detected with recording electrodes.• Electrical signals are shown on a cathode ray oscilloscope or a chart recorder; this is an ECG.

A single cardiac cycle: P = atrial systole; QRS = wave of ventricular systole; T = ventricular diastole

ECG changes in a diseased heart are used by doctors for diagnosis

• heart rate calculated from interval between P waves

P

Interpreting an ECG Trace

• Electrocardiogram animation

Cardiac output

• Average resting for a man is 75cm3 (stroke) and 70 beats per minute (rate)

• When exercising both stroke and rate increase• The fitter a person is the lower the resting rate

and higher stroke volume.

Cardiac Output = Stroke Volume X Heart rate( Volume of blood

leaving left ventricle with each beat)

(beats per minute)

As the heart beats, it releases regular surges (increased volumes) of blood. As these pass along the arteries, the vessel must stretch to allow it to pass. This stretching

pushes on the skin, which we sense as a pulse.

Skin surface

Blood flow Blood flow

Heart rate is measured by the pulse

• Although the heart has its own rhythm it is also regulated by the nervous and hormonal systems.

• Sensory receptors in the walls of heart and blood vessels are sensitive to changes in blood pressure

• These send impulses to the CARDIORESPIRATORY CENTRE in the medulla oblongata

• A vagus nerve branch leads to the SA node. • The vagus nerve is part of the Parasympathetic

Nervous System and so is an inhibitory nerve, impulses slow the heart rate.

Control of the heart beat

• Branches of a sympathetic nerve also lead to the heart, these impulses will speed up the heart rate.

• When excited or in danger the sympathetic nervous system also stimulates the release of Adrenaline from the adrenal glands.

• Adrenaline increase the strength (stroke) and speed (rate) of the heart.

The cardiac output is therefore modified by the parasympathetic and sympathetic nervous

systems.

• The cardiac output also varies with the Venous Return (volume of blood returning to heart)

• If venous return is high, walls of atrium are stretched, which is detected by stretch receptors.

• The effect of this is that the heart beats faster; this is called the Bainbridge reflex.

• High venous return also stretches the ventricle wall, this results in the ventricle contracting stronger, giving a greater stroke volume; this is called the Frank-Starling Effect.