Cardiovascular system

r.watson@hull.ac.ukTwitter: @rwatson1955

Cardiovascular system

The cardiovascular system is comprised of the heart and the blood vessels. It is the primary means of transport around the body and it distributes blood to all regions of the body. Blood is the means of transport of oxygen, nutrients, hormones and waste products. The cardiovascular system is controlled, primarily, by the cardiac centre in the medulla of the brain.

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The circulatory system

The heart

Gross anatomical structure:

• Fist sized muscular organ located in the thorax

Heart valves

Prevent backflow of blood into atria and ventricles:

• Atrioventricular valves (bicuspid and tricuspid)• Pulmonary valve• Aortic valve

Circulation through heart

• Vena cava• Right atrium• Right ventricle• Pulmonary artery• Pulmonary vein• Left atrium• Left ventricle• Aorta

Pulses

Pulses are located where an artery runs close to the surface of the body and over a bony prominence.

radialcarotid

femoral

Electrical activity in heart

Pacemaker:

• Generated at sinoatrial node

• Travels to atrioventricular node and spreads across atria

• Travels through septum along Purkinje fibres

• Spreads across ventricles

Electrocardiogram (ecg)

At rest this picks up the electrical activity in the heart.

Cardiac cycle

Systole:• When heart contracts and pumps blood into the arteries

Diastole:• When the heart relaxes and the ventricles fill with blood

Cardiac muscle

One of three types of muscle:

• Skeletal• Smooth• Cardiac

Skeletal muscle

Cardiac muscle

• Structure allows rapid conduction of electrical activity across heart

• Acts as a functional syncytium – ie as one cell

Coronary circulation

The heart has its own blood supply

Control of the heart

The heart responds to different situations, eg

• Walking• Resting• Running up stairs

Cardiac output (CO)

This needs to change in different situations, eg

• Need more CO when running than when walking

Cardiac output (CO)

Composed of:

• Stroke volume (approx 70ml/beat)• Heart rate (approx 70 bpm at rest)

70 x 70ml = 4900ml

Therefore: CO = approx 5 litres per minute at rest

Cardiac output (CO)

Mainly controlled by changing heart rate

Heart rate is controlled by:

• Sympathetic stimulation• Circulating levels of catecholamines (adrenaline and noradrenaline)

Hard to separate control of heart rate from control of blood pressure

• Many factors involved

Vascular system

System of vessels through which the heart pumps blood to all regions of the body.

Comprised of:

• Arteries• Veins• Capillaries

Arteries

Carry blood away from the heart under pressure from the ventricles

Structure:

• Mainly composed of smooth muscle

Veins

Carry blood to the heart using skeletal and respiratory muscle pumps

Structure:

• Mainly composed of smooth muscle• Similar to artery but less smooth muscle• Contain valves

Capillaries

• No smooth muscle• Composed of epithelial cells• Single cell layer• Transport blood to tissues• Enable diffusion of substances across capillary wall• Diameter is same as a red blood cell (7μm)

Blood circulation

Achieved by blood pressure:

• Generated by the heart• Maintained by the arteries

Blood pressure (BP)

Composed of:

• Cardiac output (CO)• Peripheral resistance (PR)

Therefore:

BP = CO x PR

Peripheral resistance

Provided by the resistance to blood flow in the arterial system

Therefore BP can be controlled by changing

• cardiac output• peripheral resistance

Peripheral resistance

Altered by changing the diameter of the arteries through:

• sympathetic stimulation (↓ diameter)• parasympathetic stimulation (↑diameter)

NB: ↓ diameter → ↑ resistance → ↑ Blood pressure

Blood pressure and circulation

Blood circulation is achieved by the gradient of pressure from:

• The left ventricle to

• The right atrium

‘Normal’ blood pressure

Measured in mmHg:

• Systolic = 120 mmHg

• Diastolic = 80 mmHg

Mean arterial blood pressure (MAP)

MAP = diastolic + (1/3 systolic – diastolic)

MAP is the blood pressure which maintains blood flow in the peripheral arteries and the coronary arteries

Capillary exchange

Enabled by the difference between:

• Capillary blood pressure

• Capillary osmotic pressure

Lymphatic system

Serves two purposes:• Maintenance of fluid balance• Immune system function

Control of blood pressure

Achieved by changing cardiac output and peripheral resistance

Mediated via the medulla:• Alters heart rate and• Peripheral resistance

Control of blood pressure

Achieved by changing cardiac output and peripheral resistance

Mediated via the medulla:• Alters heart rate and• Peripheral resistance

And the kidneys:• Alter blood volume (aldosterone)• peripheral resistance (renin angiotensin system)

Blood

Blood is a tissue composed of:

• Plasma• Blood cells

The red blood cell (erythrocyte)

Highly specialised cell designed primarily to carry oxygen

• No nucleus• No mitochondria

Oxygen is carried mainly bound to haemoglobin

ABO blood grouping

This is due to the existence of antigen like molecules on the surface of red blood cells:

• Agglutinogens

These bind antibody type molecules in the plasma:• Agglutinins

ABO blood grouping

This is due to the existence of antigen like molecules on the surface of red blood cells:

• Agglutinogens

These bind antibody type molecules in the plasma:• Agglutinins

If the wrong combination of the above meet – as can happen in blood transfusion:

• Agglutination

This is VERY dangerous and can lead to DEATH

Blood transfusion

People with blood type Are know as

0 Universal donors

AB Universal recipients

Cardiovascular system

The cardiovascular system is comprised of the heart and the blood vessels. It is the primary means of transport around the body and it distributes blood to all regions of the body. Blood is the means of transport of oxygen, nutrients, hormones and waste products. The cardiovascular system is controlled, primarily, by the cardiac centres in the medulla of the brain.

Questions

1. What is the cardiovascular system comprised of and what are the three types of blood vessel?

2. Describe the heart.

3. In addition to oxygen name four things that the blood transports.

4. What are the four chambers of the heart?

5. What are the four blood vessels attached to the heart?

6. What are the four valves in the heart?

Questions

7. Which blood vessels attached to the heart carry oxygenated blood and deoxygented blood, resepectively?

8. Describe the flow of blood through the heart.

9. In addition to the radial pulse, name 8 other sites on the body where a pulse can be felt.

10. Describe the generation and spead of electrical activity in the heart.

11. What is a trace of electrical activity in the heart called: what are the three sets of patterns observed?

Questions

12. What is happening at the three wave patterns on the electrocardiogram? What can happen to the T-wave in a myocardial infarction?

13. What are the two stages of the cardiac cycle and what is happening at each stage?

14. Describe the cardiac output; what are its components and how is it calculated?

15. What effect do: sympathetic stimulation, parasympathetic stimulation and increased end diastolic volume have, respectively, on the cardiac output? What happens to resting heart rate in athletes?

Questions

16. What type of muscle is found in arteries and veins? How does this differ between arteries and veins? What do veins have that arteries lack? What is the space in the middle of a blood vessel called?

17. What are the two factors that determine blood pressure? What is the equation for bood pressuer based on these factors?

18. What two factors determine capillary exchange? Which is larger at the arterial end of the capillary bed; what is the fluid in the tissues called?

Questions

19. How are the medulla and the kidneys, respectively, involved in control of blood pressure?

20. What are the three formed elements in the blood?  How is one of these formed elements further subdivided into two main types?

21. Describe four unique things about the specialisation of the erythrocyte.

22. What are the four main blood types?

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The cardiovascular system