TOPIC 5 - The circulatory system

Question 1

How is the heart organised into 3 functional parts?

Answer 1

1. Pump (heart)
2. Fluid (blood)
3. Set of containers (blood vessels)

Question 2

Why is the heart a dual pump?

Answer 2

Because the heart pumps blood in two serial circuits:

Left heart - Systemic circulation:
- Parallel pathways from left to right

Right heart - Pulmonary circulation:
- Single pathway from right to left side of heart

Question 3

What is the role of arteries, microcirculation and veins?

Answer 3

• Arteries - the distribution system
• Microcirculation - diffusion and filtration systems
• Veins - collection system (reservoir)

Question 4

What are the 4 ‘building blocks’ in vascular wall?

Answer 4

1) Endothelial cells
2) Elastic fibres
3) Collagen fibres
4) Smooth-muscle cells

Question 5

What are the 3 layers in the blood vessel walls?

Answer 5

Blood vessel walls - 3 layers:

1. intima (Tunica Interna)
2. media (Tunica Media)
3. adventitia (Tunica Externa)

Capillaries - only intimal layer resting on a basement membrane

Question 6

Describe the structure of Elastic arteries (large arteries)?

Answer 6

• High compliance - walls stretch easily without tearing in response to pressure increase –> Enables vessels (e.g. aorta) to cope with peak ejection pressures.
• Elastic fibres - Recoil of elastic fibres forces blood to move even when the ventricles are relaxed

Question 7

What is the function if muscular arteries?

Describe the structure of MUSCULAR
arteries (medium sized arteries)

Answer 7

Muscular arteries control blood flow and pressure.

• Smooth muscle cells are arranged circumferentially
• Capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow
• Vascular tone – state of partial contraction maintains vessel pressure and efficient flow.

Question 8

Describe the structure of arterioles.

Answer 8

• Arterioles have smooth muscle enabling regulation of blood flow into capillary networks regulated microcirculation
• Terminal regions of arterioles are known as metarterioles
• Precapillary sphincters monitor blood flow into the capillary

Question 9

Describe the structure of Venules.

Answer 9

• Postcapillary venules are porous - act as exchange sites for nutrients and waste
• Muscular venules have a thin smooth muscle cell layer (less muscular than arterioles)
• Thin walls allow expansion - excellent reservoirs for blood

Question 10

Describe the structure of veins

Answer 10

• Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
• Like venules, veins can “store” blood
• Veins have valves (prevent backflow)

Question 11

Describe the structure of veins

Answer 11

• Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
• Like venules, veins can “store” blood

Question 12

Describe the structure of large veins.

Answer 12

• More muscular than venules and smaller veins
• Possess valves to prevent backflow
• Defective, leaky valves allow backflow and can lead to varicose veins

Question 13

What is the function of the capillary?

Answer 13

Capillary – principal exchange site:

• Gases
• Water
• Nutrients
• Waste products

Most tissues capillaries serve -nutritional needs, in addition:

• Glomerular filtrate
• Skin temperature regulation
• Hormone delivery
• Platelet delivery

Question 14

Describe the structure of capillaries.

Answer 14

• Small vessels composed only of endothelial cells and basement membrane
• Exchange of substances between blood and interstitial fluid
• Three groups based on their degree of ‘leakiness’

Question 15

Describe the structure of capillaries.

Answer 15

• Small vessels composed only of endothelial cells and basement membrane
• Exchange of substances between blood and interstitial fluid
• Three groups based on their degree of ‘leakiness’

Question 16

Who’s equation is used for fluid transfer in capillaries and what is fluid transfer?

Answer 16

Starling’s Forces

• Fluid transfer across capillary walls driven by sum of hydrostatic and osmotic pressures

Question 17

What is oncotic pressure?

Answer 17

Oncotic pressure (colloid osmotic pressure) due to serum proteins (albumin)

Question 18

What is hydraulic conductance?

Answer 18

Kf hydraulic conductance (water permeability of capillary wall) varies with tissue

Question 19

If there is a blockage in the lymphatic system?

Answer 19

Blockage leads to Oedema.

Question 20

What is the function of the lymphatic system?

Answer 20

• Drains excess interstitial fluid
• Transport of dietary lipids
• Lymph nodes/organs - immunology

Question 21

How do the Starling forces change across the capillary wall?

Answer 21

Pc (capillary hydrostatic pressure) declines along length of capillary.

Net filtration becomes net absorption.

Question 22

What are the key components of blood?

Answer 22

• plasma
• erthrocytes
• Leukocytes
• platelets

Question 23

What is plasma?

Answer 23

Watery solution of electrolyres, plasma proteins, carbs and lipids.

Question 24

What are erythrocytes?

Answer 24

• most abundant element in blood (haematocrit).
• non-nucleated biconcave disc = maximises SA: vol ratio.
• carries O2 from lungs to systematic system
• C02 carriage from tissues to lungs

Question 25

What are leucocytes?

Answer 25

Are white blood cells... can be granulocytes - neurtrophils, eosinophils and basophils. or non-granular - lymphocytes and monocytes.

Question 26

What are platelets and how do they form?

Answer 26

Platelets are nucleus free fragments. | They bud-off from megakaryocytes in bone marrow.

Question 27

What does blood viscosity measure? How does blood flow viscosity change with increasing haematocrit?

Answer 27

Viscosity measures resistance to sliding of shearing fluid layers. Blood flow decreases with increasing haematocrit.

Question 28

How is blood flow affected by velocity?

Answer 28

Velocity increases from wall to centre - RBC moves faster in the centre of the arteriole. In a cylindrical blood vessel, laminae of blood are concentric cylinders.

Question 29

how does blood flow turbulence occur?

Answer 29

At high flow rate, blood flow is no lionger laminar - but turbulent. Turbulent flow when radius is large, velocity is hight or local stenosis. laminar flow = silent turbulent flow = murmurs.

Question 30

What is haemostasis and how does it occur (4 ways)?

Answer 30

It is the prevention of a haemorrhage (blood clotting that stops excessive blood loss). Haemostasis from.... 1. Vasoconstriction 2. Increased tissue pressure 3. Platelet plug (adhesion, activation and aggregation) 4. Coagulation/clot formation

Question 31

What is a thrombus?

Answer 31

an intravascualr clot

Question 32

How is a blood clot prevented?

Answer 32

- homeostatic mechanisms prevent haemostasis. | - endothelial cells - maintain normal blood fluidity through paracrine and anticoagulant factors.

Question 33

What 3 layers does the heart wall contain?

Answer 33

Epicardium Myocardium Endocardium

Question 34

Describe the sequence of depolarisation through the heart.

Answer 34

1 ) cells of SA node depolarise to fire action potentials at regular rate. 2) Cardiac cells electrically coupled through gao junctions conduct cell to cell through right and left atrial muscle - atrial systole 3) Signal arrives at atrioventricular node. 4) impulse spread prevented by fibrous atrioventricualr ring (non-conducting tissue) so impulse spreads from AV to His-purkinje within ventricles so leads to ventricular systole.

Question 35

What are the steps A-G of the cardiac cycle?

Answer 35

A - atrial systole B - Isovolumetric ventricular contraction C - Rapid ventricular ejection D - Reduced ventricular ejection E - Isovolumetric ventricular relaxation F - Rapid ventricular filling G - Reduced ventricular filling

Question 36

What does an an ECG electrocardiogram detect?

Answer 36

ECG records the summed electrical activity of the heart - the depolarisation and repolarisation events of the cardiac cycle.

Question 37

What does the P wave show in an ECG?

Answer 37

Depolarisation of atria P wave duration = atrial conduction time

Question 38

What does the PR interval show in ECG?

Answer 38

AV node conduction - shows initial depolarisation of atria to that of ventricles.

Question 39

What does QRS complex show in ECG?

Answer 39

depolarisation of ventricles

Question 40

What does T wave show on ECG?

Answer 40

Repolarisation of ventricles.

Question 41

What is the equation for velocity of blood flow?

Answer 41

V = Q/A velocity = flow / area

Question 42

What is the relationship between blood flow, resistance and pressure?

Answer 42

Blood flow is determined by the pressure difference between vessel inlet and outlet and resistance to blood flow.

Question 43

Why is there resistance to blood flow?

Answer 43

Poiseuille’s Law ``` Resistance due to: • Blood vessel diameter • Vessel length • Series/parallel arrangement • Blood viscosity ```

Question 44

How does blood pressure vary in the cardiovascular system?

Answer 44

Blood pressure decreases as blood flows as energy is consumed by frictional resistance.

Question 45

What is the equation for pulse pressure?

Answer 45

pulse pressure = systolic - diastolic pressure

Question 46

What is the equation for the mean arterial pressure?

Answer 46

mean arterial pressure = diastolic pressure + 1/3 pulse pressure

Question 47

How is blood pressure regulated in both short and long term?

Answer 47

Short term = baroreceptors, chemoreceptors, ADH Long term = renin - angiotensin - aldosterone (RAAs) system regulates blood volume. - angiotension -> angiotensin 1 -> angiotensin 2 (acts on adrenal cortex to make and secrete aldosterone)

Question 48

What is hypertension and how can it be treated?

Answer 48

a long term elevation of blood pressure --> Chronic hypertension can desensitise baroreceptors treated with ACE inhibitors, ARBs, diuretics, alpha blockers, renin inhibitors.