Properties of special circulations

Question 1

Describe Coronary circulation? (2pts)

Answer 1

1. 2 Coronary arteries originate from the left side of the heart at the begging of the aorta just after it exists the left ventricle
2. Cardiac veins carry blood with a poor level of oxygen from the myocardium to the right atrium. Most of the blood of the coronary veins returns through the coronary arteries.

Question 2

What are the special requirements for coronary circulation? (2pts)

Answer 2

1. Needs a high basal supply of oxygen

2. Increases O2 supply in proportion to increased demand/ cardiac otuput

Question 3

Describe structural features of coronary circulation?

Answer 3

1. High capillary density- short diffusion distance which means oxygen is transported quickly
2. Large surface area for O2 transfer- reduces diffusion distance to myocytes . Diffusion time is proportional to the distance squared.
3. Cardiac muscle contains high numbers of fibres and capillaries giving ride to shorter diffusion distances thus meaning oxygen is transported quickly.

Question 4

What happens during normal activity? (4pts)

Answer 4

1. There is a higher blood flow to the heart. 10x the flow per weight of the rest of the body
2. Very low sympathetic innervation which lowers heart rate
3. There is high levels of nitric oxide released which leads to vasodilation.
4. There is high oxygen extraction- 75% of oxygen is extracted whilst there os 25% oxygen in the rest of the body

Question 5

What happens during increased demand? (3pts)

Answer 5

1. Coronary blood flow increases in the heart in proportion to demands
2. Production of blood vasodilators ( adenosine, K+ and acidosis) will outcompete relaivetly low sympathetic vasoconstriction
3. Circulating adrenaline dilates coronary vessels due to the abundance of B2-adrenoreeptors.

Question 6

What happens as the amount of oxygen in the plasma increases? (2pts)

Answer 6

1. As the amount of oxygen in the plasma increased the percentage saturation of haemoglobin binding to oxygen slightly increases. Once there is 15% of 02. in the plasma the percentage increases rapidly in a linear way till it reaches 80-90% oxygen saturation
2. The amount of 02 in the plasma falls.

Question 7

What happens to tissues that are metabolising

Answer 7

In tissues that are metabolizing there is an increase in carbon dioxide, an increase in hydrogen ions, increase in temperature and an increase in 2,3-biphopshoglycerate.

Question 8

How does increased 02 requirement produce increased blood flow?

Answer 8

1. Extraction of oxygen is near max during normal activity
2. . Therefore to provide more oxygen during demand metabolic hyperemia occurs and we must increase blood flow
3. Myocardium metabolism generates metabolites to produce vasodialation and increase blood flow in metabolic hyperaemia. Adenosine produced by ATP metabolsim and is released from cardiac myoctyes, It also increases pC02, H+ and K+ levels

Question 9

What happens during Ischaemic heart disease? (4pts)

Answer 9

1. Coronary arteries are functional end arteries and therefore the decreased perfusion produces major problems
2. The arteries are therefore packed very closely together which means there is not much room to have branches between them.
3. Heart is very susceptible to sudden and slow obstruction

sudden= acute thrombosis which produces myocardial infraction
slow= atheroma which is chronic narrowing of the lumen which will produce angina. 

4. Systole obstructs coronary blood flow. It is only during diastole that blood flows freely.

Question 10

What is thrombosis?

Answer 10

Occlusion of the left anterior descending coronary artery

Question 11

Describe Thrombosis? (5pts)

Answer 11

1. Occlusion leading to the obstruction of blood flow to anterior ( front) left ventricle- myocardial infraction
2. Side effects:
3. Ischemic tissue area- without blood. This causes pain e.g in the shoulder and the stimulation of c fibres.
4. Causes impaired contractility
5. Causes sympathetic activation
6. Causes arrhythmia
7. Causes cell death- necrosis

Question 12

What is stenosis?

Answer 12

Partial occlusion due to plaque formation

Question 13

What occurs during exercise?

Answer 13

During exercise, metabolic vasodilation of the arterioles will reduce total resistance. There will be increased blood flow ( vasodilation) to meet the increased oxygen demand.

Question 14

What occurs during stenosis? (2pts)

Answer 14

1. Stenosis in the large coronary artery will increase resistance
2. Metabolic hyperemia occurs at rest so blood flow meets needs

Question 15

How does Angina develop? (3pts)

Answer 15

1. During exercise arterioles further dialate to reduce resistance but total resistance is still too high due to dominance of stenosis
2. O2 demand cannot be met, so angina develops
3. The total resistance is not reduced enough.

Question 16

Name the

What are the mechanical factors which reduce Coronary flow? (3pts)

Answer 16

1. Shortening diastole- causes a high heart rate. The window for coronary flow which is the diastolic window gets shorter as heart rate increases
2. Increased ventricular end diastolic pressure- heart failure, during aortic stenosis which is narrowing of the aorta and stiffening of the ventricles
3. Reduced diastolic arterial pressure e.g hypotension, aortic regurgitation.

Question 17

Describe the properties of cutaneous circulation?

Answer 17

1. The skin is defence against the environment
2. Lewis triple response to trauma-if the skin is damaged it will responds by causing increased blood flow to the area. There will be an increase in immune cells to the area and growth factors
3. Temperature regulation:
4. Blood flow delivers heat from the body core
5. Radiation- proportional to the skin temperature
6. Conduction to the skin- convection from the skin 4
7. Sweating- sweat evaporates from the body and as it does so it takes heat away with it.

• the skin is an organ and temperature can range from 0 to 40 degrees without damage.

Question 18

What does skin temperature depend on? (2pts)

Answer 18

1. Skin blood flow

2. Ambient temperature

Question 19

What is arterio-venous anastomoses (AVA)

Answer 19

1. The direct connections of arterioles and venules expose blood to regions of high surface area.
2. This causes convection, conduction, radiation and evaporation.

Question 20

What are sympathetic vasoconstrictor nerves? (2pts)

Answer 20

1. Release noradrenaline acting on alpha 1 receptors
2. Arterioles constrict so blood doesn’t go through the capillary route and instead it goes through the arteriovenous anastomosis.

• this occurs during the cold to conserve body heat

Question 21

What are sudomotor vasodilator fibres?

Answer 21

1. Causes vasodilators to dilate the arterioles that lead to the capillary loops
2. Acetylcholine acts on the endothelium to produce nitric oxide
3. It is driven by temperature regulation nerves in the hypothalamus,.

Question 22

Describe features of the skin? (3pts)

Answer 22

1. The skin is responsive to ambient and core temperature
2. The skin helps heat loss- this increases ambient temperature as it causes vasodilation and venodialation.
3. The skin helps to conserve heat:
4. Vasoconstriction and venoconsitrction decreases ambient temperature
5. Severe cold causes paradoxical cold vasodilatation
6. Core temperature receptors in the hypothalamus control sympathetic activity to the skin

Question 23

What does increased cutaneous perfusion do? (3pts)

Answer 23

1. Increased cutaneous perfusion with increased core body temperatyre
2. This increases core temperature
3. It stimulates temperature receptors in the anterior hypothalamus.

Question 24

What does increased cutaneous pressure cause? (2pts)

Answer 24

1. Sweating- increased sympathetic activity to sweat glands mediated by acetylcholine
2. Vasodilation- increased sympathetic sudomotor activity such that acetylcholine acts on the endothelium to produce nitric oxide which dilates arterioles in extremities.

Question 25

Describe functionalist specialisations of the skin? (3pts)

Answer 25

1. Baroreflex- vasoconstriction of skin blood vessels
2. Blood is directed to more important organs/ tissues during the loss of blood pressure following haemorrhage, sepsis and acute cardiac failure
3. This is mediated by sympathetic vasoconstriction fibres, adenaine, vasopressin and angiotensin II. It is responsive for pale cold skin of a patient in shock.
4. During hemorrhage warming up the body too quickly reduces cutanoues vasoconstriction and is potentially dangerous- blood flow to the skin is not vital for organs and tissues.
5. Emotional communication- blushing due to symapthetic sudomtor nerves
6. Response to skin injury- Lewis triple response

Question 26

Describe the Lewis triple response of skin to trauma?

RFW

Answer 26

1. Redness- which is caused by capillary vasodilation
2. Flare- a redness in the surrounding area due to anterior dilation mediated by a axon reflex
3. Wheal- exudation of extracellular fluid from capillaries and venules.

• increased delivery of immune cells and antibodies to the site of damage occurs to deal with invading pathogens

Question 27

Name problems with the skin?

Answer 27

1. Prolonged obstruction of flow by compression
2. Severe tissue necrosis
3. Bed sores- heels, buttocks, weight bearing areas

• this is avoided by shifting position/ turning causing reactive hyperaemia on the removal of compression
• there is high skin tolerance to ischemia

2. Postural hypotension/ oedema due to gravity
3. often standing up for long periods of time in hot weather will decrease central venous pressure ( hypotension) increased capillary permeability (oedmea)
4. Feel faint, rings of finger can be tighter

Question 28

What occurs during pressure sores? (3pts)

Answer 28

1. O2 and nutrients are close but diffusion is too slow
2. Compression has not been released
3. This causes necrosis of the tissue