Unit 2: The continuation of life

Chapter 20:

Transport Mechanisms: The cardiac cycle

Higher Human Biology

21/04/23 1Mrs Smith Ch19 The need for transport

Learning Intentions

To understand the anatomy of the heart, to find out how the heartbeat is controlled and to look at differences in blood pressure in the circulatory system.

Success Criteria1. Describe the cardiac cycle

of the heart

2. Explain the cardiac cycle of the heart in relationship to pressure changes

21/04/23 2Mrs Smith Ch19 The need for transport

Cardiac CycleCardiac CycleThe cardiac cycle is the pattern of contraction and relaxation of the heart during one heartbeat.

Diastole = relaxation

The average heart rate is 75 beats/min with a cardiac cycle of 0.8 secs.

Image source: www.classes.kumc.edu

Systole = contraction

Heartbeat animation

The average human heart rate at rest is 75 beats a minute

Each heart beat lasts for approximately 0.8 of a second at rest

Each heart beat involves a series of Events referred to as THE CARDIAC CYCLE

Heartbeat: Atria & Ventricular diastole

Stage 1: A heartbeat begins with the heart muscle relaxed and valves closed.

Blood flows into the two atria and both sides fill up with blood.

This blood has to be pushed through the valves to get into the ventricles. How does this happen?

Heartbeat: Atrial systole

Stage 2: The atria contract and the blood is squeezed which causes the AV valves leading to the ventricles to open.

Blood then flows from the atria into the ventricles.

What happens to the open valves when the atria are empty?

Stage 2 (continued): The AV valves between the atria and the ventricles close.

This prevents any backflow.

What happens next to the blood in the ventricles?

Heartbeat: Atrial systole

Heartbeat: Ventricular Systole

Stage 3: Almost immediately, the ventricles contract and the blood is squeezed again.

The pressure of the blood forces open the SL valves leading out of the heart.

Blood is pumped outof the heart.

What happens to the open valves when the ventricles are empty?

Heartbeat: Ventricular Systole

Stage 3 (continued): When the ventricles are empty, the SL valves leading out of the heart close and the heart muscle relaxes.

This completes the sequence of contraction and relaxation in one heartbeat.

What will happen next?

Stages of a heartbeat

Stage 1 (again): The atria fill up with blood as the heartbeat sequence begins again.

Why are the walls of the atria thinner than the walls of the ventricles?

Why is the wall of the left ventricle thicker than the right ventricle?

Try this Scholar Animation Fig.3.9 http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=dfaf24ad-0021-9d39-4277-e967e919c79f

2. Heart Valves & Sounds2. Heart Valves & Sounds

Throughout the cardiac cycle, pressure changes take placein the atria, ventricles and arteries

Pressures in the right and left atrium, right and left ventricle, aortaand pulmonary arteries can be recorded and illustrated in

graphical form

The graph on the next slide shows pressure changes in the left side of the heart and the aorta

A similar graph can be drawn for the right side of the heart and thepulmonary arteries

Such a graph is similar in shape to that obtained for the left sideof the heart but all the pressures readings are of a lower value

0

20

40

60

80

100

120

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

pre

ssure

(m

m H

g)

tim e (s)

= systole = diastole

SLvalveopens

SL valve closes

aorticpressure

left ventricularpressure

AVvalve

closes

AVvalveopens

left atrialpressure

ATRIA

VENTRICLES

Pressure Changes in the Heart

0

20

40

60

80

100

120

pre

ssu

re (

mm

Hg

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

tim e (s)

Pressure Changes in the Left Side of the Heart During One

Cardiac Cycle

aorticpressure

left ventricularpressure

left atrialpressure

The pressure changesin the left ventricle,left atrium and aortacan be related to thephases of the cardiac

cycle

0

20

40

60

80

100

120

pre

ssu

re (

mm

Hg

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

tim e (s)

Pressure Changes in theLeft Side of the Heart YX AZWA

aorticpressure

left ventricularpressure

left atrialpressure

Period Z to A representsthe phase of Passive Fillingof the ventricles when theAV valves are open and

the semi-lunar valves are closed

Period A to W representsthe phase of Atrial Systole

when the atria contractand the ventricles arefilled to full capacity

Period W to X representsthe first phase of

Ventricular Systole whenthe ventricles contract in an

isometric fashion; thegreatest rise in ventricular

pressure occurs during thisphase and the ventricularvolume remains constantPeriod X to Y represents thesecond phase of Ventricular

Systole when ejection of blood takes place and pressure in the

aorta risesPeriod Y to Z represents relaxation of the ventricles (diastole) when the ventricular pressure drops sharply

LUB

DUB

Heart MurmurHeart MurmurAbnormal cardiac blood flow causes abnormal heart sounds known as heart murmurs.

This is often caused by faulty valves that fail to open or close fully.This is often an inherited condition but can be caused by illness e.g. rheumatic fever.

Learning Intentions

To understand the anatomy of the

heart, to find out how the heartbeat is controlled and to

look at differences in blood pressure in the circulatory system.

Success Criteria3. Describe the structures

involved in the conducting system of the heart

4. Describe the role of the sino-atrio node in the conductivity of the heart

5. State the sequence of electrical conductivity of the heart.

3. Conducting System of the Heart3. Conducting System of the Heart

• The heart is special in that the electrical stimulation necessary for contraction of its muscles originates from within the heart itself

• The sequence of events which occurs during each heartbeat is brought about by the activity of the PACEMAKER and the CONDUCTING SYSTEM of the heart

Pace maker (Sino-atrial node (SAN))

As well as the Pacemaker the conduction system consists of... • Atrio-ventricular node or AV node• Bundle of conducting fibres, which divides into left &

right branches (Bundle of His)• Dense network of Conduction fibres in the ventricle

walls (Purkinje fibres)

• The above cells are specialised muscle cells which join in a network called the CONDUCTION SYSTEM

• http://www.bbc.co.uk/learningzone/clips/the-human-heart/12225.html

The PACEMAKER The PACEMAKER

AKA – Sino-atrial Node (SANAKA – Sino-atrial Node (SAN))• The pacemaker is located in the wall of the right atrium.• The pacemaker is specialised tissue which exhibits

spontaneous excitation.• This means that it initiates electrical impulses which

make the heart contract at a certain rate. • This rate can then be regulated by other factors to suit

the bodies requirements.• The pacemaker works automatically and would continue

to function in the absence of nerve connections from the rest of the body.

http://www.youtube.com/watch?v=te_SY3MeWys&feature=related

Conduction system of the Heart

Understanding these DEFINITION will help with the following slides:

SYSTOLE; The phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries. (the chambers empty).

DIASTOLE; The phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood

Conduction of the heart: step by step!

1.The electrical signal originates from the pacemaker (sino-atrial node) this makes heart muscle cells contract at a certain rate.

2. A wave of excitation (from the SA node) spreads across the muscle cells of the two atria making them contract (atrial systole).

3.The impulse is picked up by the atrio-ventricular node (AV node) located near the base of the atria.

Conducting System of the Heart

4. The impulse passes from the AV node to the bundle of His. This bundle of conducting fibres divides into right and left branches which are continuous with the Purkinjie fibres in the ventricular walls.

5. Stimulation of these fibres causes contraction of the two ventricles (Ventricular systole). The contraction of the ventricles spreads upwards from the apex.

6.The muscle cells contract in unison, and then relax awaiting the next signal.

Summary: Conduction of the heart with an ECG.

Such coordination of the heartbeat ensures each type of systole recieves the combined effect of many muscle cells contracting and that the ventricular systole occurs slightly later the atrial systole allowing time for the ventricles to fill completely before they contract.

The origin of the heartbeat isfrom within a specialised patch

of cardiac muscle tissue, locatedin the wall of the right atrium,and known as the sino-atrial

node or SA node

Another node ofspecialised tissue known

as the AV node islocated in the right

portion of the septumbetween the atriaand close to the

AV valves

The AV node connectswith a bundle of large

fibres called the bundleof His, which divides into

left and right bundle branches

The left andright bundle

branches divideinto smaller

branchescalled Purkinje

fibres that spread

throughout theventricular muscle

SA nodein wall of

right atrium Bundle of Hiswith left and rightbundle branches

AV node

& AGAIN Conducting System of the Heart: Explained a little differently.& AGAIN Conducting System of the Heart: Explained a little differently.

When the SA node emits spontaneous electrical impulses, they spread rapidly

across both atria due to the inter-connecting nature of the cardiac muscle cells

As the impulses spreadacross the atria, they stimulate a wave of

contraction within theatrial walls andatrial systole is

triggeredWhen the electricalimpulses reach theborder between theatria and ventriclesthey are blocked by

a band of non-conducting

fibrous tissue

Fibrous Tissue

In order to reach the ventricles,

electrical impulses must pass through

the AV node, which slows down the

speed of electrical transmission

This delay, called the AV delay,is extremely important as it

allows the atria to complete theircontraction before the ventricles

begin to contract

Impulses areconducted from AV node along

the bundle of His

The bundle fibresdivide intonumerous

Purkinje fibres that permeatethroughout the

ventricular muscles

The spread ofelectrical impulses

throughout theventricles triggersventricular systole

AVNode

CON’T: Conducting System of the Heart: Explained a little differently.CON’T: Conducting System of the Heart: Explained a little differently.

Electrocardiogram (ECG)Electrocardiogram (ECG)The electrical signals of the heart can be detected by electrodes on the skins surface. They are displayed on an oscilloscope screen to produce a pattern called an electrocardiogram (ECG).

The ECG trace for each heartbeat displays 3 distinct waves: A P wave, a QRS complex

and a T wave

The diagram below shows a normal ECGThe diagram below shows a normal ECG

Q

R

S

P wave T wave

The waves of an ECGThe waves of an ECG

• P wave - Electrical impulses spreading across the atria from the SAN; it coincides with atrial contraction or systole.

• QRS complex - Wave of excitation passing through ventricles; coincides with ventricular systole.

• T wave - Electrical recovery of the ventricles at the end of ventricular systole.

Q

R

S

P wave T wave

P – Rinterval

T – Pinterval

• The P – R interval time between the events of atrial systole and ventricular systole. This period represents the time taken for the impulse to spread from the SA node through the atria, plus the delay in transmission to the AV node, together with the conduction time through the bundle of His and Purkinje fibres.

• The T – P interval is the time spent by the heart in diastole before the next atrial systole begins

ECG waves : The intervalsECG waves : The intervals

A

Abnormal ECGsAbnormal ECGsHeart disease and unusual heart rhythms can be detected by ECG patterns. The diagrams below show identifiable patterns for some common heart conditions.

http://www.youtube.com/watch?v=x67vRkooZDc&feature=related

Normal ECG

Abnormal ECG: Arterial Flutter

• In an arterial flutter the contractions occur much too rapidly than normal but do remain coordinated.

• The example shown in the diagram shows several P waves for ever QRS complex.

• In a fibrillation, contractions of different groups of muscle cells occurs at different times making it impossible for coordinated pumping of the heart chambers to take place.

• Ventricular fibrillation, for example produces an ECG with an irregular pattern.

• This condition is lethal if not corrected.

Abnormal ECG: Fibrillation

• During ventricular tachycardia, abnormal cells in the ventricle walls act like pacemakers and make these chambers beat rapidly and independently of the atria.

• The P (atrial) waves are absent and the wide QRS waves are abnormal.

Abnormal ECG: tachycardia.

PacemakersPacemakers

Abnormal heart rhythms can be controlled by fitting an artificial pacemaker. This stimulator regulates the heart beat by sending out small electrical impulses to the heart making it beat normally.

Task: Torrance-TYK pg152 Qu’s 1&4

21/04/23 41Mrs Smith Ch18 Birth & Post-natal development

Essay Questions:SQA 2010

Discuss the conducting system of the heart and how it is controlled.

(10)

21/04/23 Mrs Smith Ch19 The need for transport

42

Learning Intentions

To understand the anatomy of the heart, to find out how the heartbeat is controlled and to look at differences in blood pressure in the circulatory system.

Success Criteria6. Describe the changes in

blood pressure as blood flows through the circulatory system.

7. Explain these changes in blood pressure in reference to peripheral resistance.

8. Explain the role of elastic walls of the main arteries.

21/04/23 43Mrs Smith Ch19 The need for transport

4. Blood Pressure4. Blood PressureContraction of the ventricles creates pressure which causes the blood to flow. The pressure in the arteries rises and falls as the heart goes through systole & diastole.

Ventricular systole = maximum ~120 mm Hg

Ventricular diastole = minimum ~80 mm Hg

Blood Pressure Con’t

• During ventricular systole (contraction) the pressure of the blood in the aorta rises to a maximum e.g. 120 mmHg

• During ventricular diastole (relaxing) it drops to a minimum e.g. 80 mm Hg

Systolic and diastolic blood pressures are measured using a sphygmomanometer

and varies widely from person to person.

Try the Scholar Animation 3.4.7

Measuring Blood Pressure

http://courses.scholar.hw.ac.uk/vle/

scholar/session.controll

er?action=viewContent&content

GUID=06fbef35-8105-5747-

fc89-55365ca328af

Measurement of the blood pressure

The graph below shows arterial blood pressure trace

The graph below shows arterial blood pressure trace

5. Role of Elastic walls5. Role of Elastic wallsLarge arteries are elastic

They conduct blood from the heart to medium sized arteries

When the heart contracts and ejects blood, the walls stretch to accommodate the surge of blood.

The stretched fibres store some of the energy.

During the diastole phase the arteries recoil, causing the blood to move forward in a continuous flow.

Diagram of the Elastic wallsDiagram of the Elastic walls

6. Decreasing Blood Pressure6. Decreasing Blood Pressure• Although the pumping

action of the heart causes fluctuations in aortic blood pressure (e.g. Systolic 120mm Hg and diastolic 80mm Hg), the average pressure in the aorta remains fairly constant at 100mm Hg.

• The diagram shows how a progressive decrease in pressure occurs as blood travels round the circulatory system dropping to almost zero by the time it reaches the right atrium again

Why does the Blood Pressure Why does the Blood Pressure decrease?decrease?

• The pressure of the blood decreases as the blood moves away from the heart.

• Changes are due to the peripheral resistance as the vessels become narrower.

• Blood pressure is also related to the volume of blood present.

• e.g

increase in volume

increase in blood pressure

Peripheral Resistance

• Peripheral resistance means the resistance to the blood flow caused by friction between the blood and the walls of the vessels.

• This friction occurs because blood is sticky and the arterioles and capillaries through which it passes are narrower in diameter and present a large surface area of wall in contact with blood.

Peripheral resistance: Peripheral resistance: Greatest in the arteriolesGreatest in the arterioles

The arterioles present the greatest resistance to blood flow and bring about the largest drop in pressure (around 50mm Hg). LARGE DROP IN

THE ARTERIOLES

 Changes in blood pressure, velocity, and the area of the arteries, capillaries, and veins of the

circulatory system

Changes in blood pressure

• Blood pressure is also directly related to volume of blood present in the arteries. An increased arterial volume leads to an increase in arterial pressure.

High Blood PressureHigh Blood Pressure

For example•High levels of stress •Excessive salt in the diet.

Caused by: • Any factor that increases the rate and force of contraction of the heart tend to increase the arterial blood pressure

Dangers of High Blood Pressure

Prolonged high blood pressure is dangerous because it•Requires the ventricles to work harder (in order to eject the blood into the arteries).•Makes arterial walls more prone to atherosclerosis.•May damage blood vessels (e.g. In cerebrum leading to a ‘stroke’).

Image source: www.healthygoodies.ca

Task: Torrance-TYK pg156 Qu’s 1&2

21/04/23 59Mrs Smith Ch18 Birth & Post-natal development

Learning Intentions

To understand how the various vessels involved in the transport are related and how materials are exchanged between these vessels, tissue fluid and body cells.

Success Criteria

9. Describe the structure and function of the vessels in the lymphatic system

10. Describe the method of movement of lymph through the lymphatic circulation

11. Describe the absorption of lipid in relation to the lymphatic circulation

12. Describe the structure and function of lymph nodes

Image source: http://trc.ucdavis.edu

9. Lymphatic System9. Lymphatic System

Tiny lymphatic vessels have porous walls that lets them absorb excess tissue fluid (lymph) filtered from the bloodstream at the capillary beds. This is collected by lymph capillaries which join to form larger lymphatic vessels.

The lymphatic system is considered a specialised part of the circulatory system because lymph fluid is derived from blood and lymph vessels return lymph to the bloodstream.

9. Lymphatic Vessels9. Lymphatic Vessels

10. Lymphatic Circulation 10. Lymphatic Circulation • Flow of lymph is dependent

upon the vessels becoming periodically compressed when muscles contract during breathing and movement

• Backflow of lymph is prevented by valves

• Lymph fluid is returned to the bloodstream by 2 lymphatic ducts in the veins of the arms

11. Absorption of lipids11. Absorption of lipids

The epithelial cells on the surface of the villus absorb the products of fat digestion (lipids). Droplets of lipid then pass to the lacteal and to the lymphatic system where they become part of the lymph.

Each finger-like villus in the small intestine has a tiny lymphatic vessel called a lacteal.

12. Lymph Nodes12. Lymph NodesLymph nodes are oval or bean-shaped structures found in the lymphatic system, particularly where lymph vessels meet.

They are usually found in groups (glands) at the neck, armpit and groin.

The Lymphatic System

Task label the diagram from page 155 - Torrence

Answer: Are your labels correct?

Summary: Function of Lymph NodesSummary: Function of Lymph Nodes• Engulf microbes by phagocytosis.•Filter unwanted debris and toxins from lymph.• Produce lymphocytes which make antibodies

Swollen Lymph NodesSwollen Lymph NodesDuring illness, if many micro-organisms

enter the nodes they swell up and can even become infected.

OedemaOedemaThis occurs when tissue fluid gathers in the spaces between cells and blood capillaries causing tissues to swell. This can be caused by

e.g. kwashiorkor

• Malnutrition

Low levels of plasma proteins result in the tissue fluid and blood water concentration being equal, therefore, no net movement of water

• High Blood Pressure

Tissue fluid produced at a faster rate than it can be drained away.

OedemaOedemaOedema can also be caused by parasites e.g. larvae of the filarial worm, transmitted by mosquitoes, which invade the lymphatic system then when they mature, blocking lymph vessels.

This causes excessive growth of tissue – a

condition called elephantiasis.

http://www.youtube.com/watch?v=pwfdTndbNfA&feature=related

Task: Torrance-TYK pg156 Qu 3

21/04/23 73Mrs Smith Ch18 Birth & Post-natal development

Testing Your Knowledge….• Pg 156 Q 3

• 3a i) Describe the means by which lymph in a lymph vessel is forced along through the lymphatic system

• ii) what structures prevent backflow of lymph?

• iii) which structures along lymph to return to the blood circulatory system?

• 3b) which type of food is absorbed into the body via the lymphatic system?

• 3c i) which type of white blood cell is produced in the germinal centre of the lymph nodes?

• ii) Which type of white blood cell removes micro-organisms from lymph as it passes through the spaces in a lymph node?