Special Circulatioms

Question 1

What are the two types of blood supplies going to the lungs ?

Answer 1

1. Bronchial circulation

2. Pulmonary circulation

Question 2

What is the bronchial circulation ?

Answer 2

The metabolic requirement of the lungs is supplied by the bronchial circulation which is part of the systemic circulation.

Question 3

What is the pulmonary circulation ?

Answer 3

It is required for gas exchange between the alveolar air and the blood.

Question 4

What are two features of the pulmonary circulation?

Answer 4

1. Low pressure -

2. Low resistance due to lots of capillaries , short and wide vessels and arterioles have little smooth muscle.

Question 5

What are adaptations of the pulmonary circulation that promote efficient gas exchange?

Answer 5

1. Very High density of capillaries in the alveolar wall ( a high number of capillaries very close together ). This means that the surface of the alveoli in the lungs are covered in capillaries , providing a large surface area over which gas exchange can take place.
2. Very short diffusion distance
3. Low pressure due to large number of capillaries.

Question 6

What is the ventilation- perfusion ratio ?

Answer 6

The ratio between the volume of air coming in and out of the lungs and the volume of blood flowing past the lungs into the pulmonary circulation.

Question 7

For efficient oxygenation of the alveoli of the lungs , what needs to happen with the V/Q ratio ?

Answer 7

The ventilation must match the perfusion of the alveoli. The optimal ratio is 0.8. Eg 4L/min : 5L/min.

Question 8

How is the V/Q ratio maintained ?

Answer 8

The body must be able to divert blood away from the poorly ventilated alveoli and towards better ventilated alveoli. This is done via hypoxia pulmonary vasoconstriction.

Question 9

What is hypoxic pulmonary vasoconstriction?

Answer 9

When the alveoli are poorly ventilated , the air in them isn’t being refreshed leading to a low partial pressure or oxygen and a high partial pressure of Carbon dioxide. The body responds by causing vasoconstriction of the pulmonary vessels to direct blood away from the poorly ventilated alveoli and towards the better ventilated alveoli to maintain V;Q.

Question 10

How can chronic hypoxic vasoconstriction occur ?

Answer 10

Due to chronic lung disease such as emphysema or if at high altitudes for long periods of time.

Question 11

What are the consequences of chronic hypoxic vasoconstriction?

Answer 11

Right ventricular failure

This is because due to vasoconstriction of the pulmonary vessels , there would be a chronic increase in vascular resistance. This would lead to chronic pulmonary hypertension.

There would be a high afterload on the right ventricle which can lead to right ventricle heart failure

Question 12

What are the effects of exercise on pulmonary blood flow ?

Answer 12

1. increased cardiac output
2. Small increase in arterial pulmonary pressure
3. Opens apical capillaries ( at the top of the lungs )
4. Increased o2 uptake by lungs
5. Capillary transit time is reduced

Question 13

How is tissue fluid formed ?

Answer 13

High hydrostatic pressure of blood within the capillary which pushes fluid out of the capillary.

And oncotic pressure in the capillary is pressure exerted by large molecules such as plasma proteins which draws fluid into the capillary.

The balance between these two is what determines how much fluid leaves the capillary into the interstitium
.

Question 14

Is capillary hydrostatic pressure more influenced by arterial pressure or venous pressure ?

Answer 14

VENOUS pressure in the systemic circulation

Question 15

What is the difference between oncotic / hydrostatic pressures in the lungs compared to other parts of the body ?

Answer 15

Oncotic pressure of tissue fluid in lungs is greater than in periphery

Capillary hydrostatic pressure in the lungs is lower than in the systemic capillaries

Plasma Oncotic pressure is the same

Filtration and reabsorption of fluid in the lungs is more or less the same so much less formation of lung fluid occurs.

Question 16

What are benefits of there being low capillary pressure in the lungs ?

Answer 16

Pulmonary capillary pressure is normally low which means only a small amount of fluid leaves the capillaries.

Question 17

How can pulmonary oedema arise ?

Answer 17

When capillary pressure is increased
Due to left atrial pressure increase . This could be the case in mitral valve stenosis or left ventricular heart failure.

Question 18

What are the consequences of pulmonary oedema ?

Answer 18

It impairs gas exchange and is affected by posture.

When the patient is standing , the fluid in the lungs pools at the base. When the patient is lying down , the fluid spreads out throughout the lungs. This fills the alveoli with fluid and causes impairment of gas exchange leading to breathlessness.

Question 19

What percentage of cardiac output does the cerebral circulation receive ?

Answer 19

15% of cardiac output.

But only accounts for 2% of body mass.

Question 20

How does the cerebral circulation meet the high demand for O2 ?

Answer 20

1. High capillary density : large surface area for gas exchange. And reduced diffusion distance.
2. High basal flow rate
3. High o2 extraction

Question 21

Why is O2 supply to the brain vital ?

Answer 21

Neurones are very sensitive to hypoxia. Loss of consciousness after a few seconds of cerebral ischameia. And you begin to get irreversible damage to neurones in 4 minutes.

Question 22

How is a secure blood supply ensured to the cerebral circulation ?

Answer 22

1. Structural features : anastomoses between basilar and internal carotid arteries.
2. Function features : myogenic autoregulation maintains perfusion during hypotension.

Metabolic factors control blood flow

Brain stem regulates other circulations

Question 23

What is myogenic autoregulation ?

Answer 23

This is where cerebral arteries will change their diameter in response to changes in systemic pressure . This ensures cerebral, blood flow remains at the same rate even where there are increases and decreases in systemic pressure.

For example , if the blood pressure is increased , there is vasoconstriction of the arteries to prevent too much blood flowing to the brain,

If blood pressure is decreased , the. Vasodilation occurs so enough blood enters cerebral circulation.

Question 24

Give an example of how metabolic factors help to ensure blood flow to cerebral circulation ?

Answer 24

At high levels of Co2 ( hyper cap is) in the brain : vasculature in the brain results in vasodilation to increase blood flow to restore to the normal co2 levels.

Hypocapnia ( low Co2 levels ) : brain vasculature results in vasoconstriction to decrease the blood flow and increase PCo2 in the brain.

Question 25

What are other vasodilators in the brain that help to increase the blood to the cerebral circulation ?

Answer 25

1. Co2
2. Potassium
3. Adenosine
4. Decreased o2

Question 26

What is the Cushing reflex ?

Answer 26

As the skull is a rigid structure , it will not allow for volume expansion of the brain. Any expansion eg due to a tumour or haemorrhage will result in an increased intracranial presssure which impairs cerebral blood flow by compressing the blood vessels.

Impaired blood flow to the vasomotor control regions of the brain stem will increase the sympathetic vasomotor activity which increases arterial BP and maintains cerebral blood flow.

Question 27

Why are coronary arteries prone to atheroma’s?

Answer 27

Few arteriosus-arterial anastomoses

They are also end arteries

Question 28

The blood supply to the myocardium is mainly through which coronary artery ?

Answer 28

Left coronary artery

Question 29

When does blood flow through the coronary artery mainly occur ? And why

Answer 29

During diastole , this is because it is harder for blood to flow through thr coronary circulation during systole due to the increased pressure on the arteries caused by the contraction of the ventricles.

Question 30

Would coronary blood flow increase or decrease with myocardial O2 demand ?

Answer 30

Increases because extra O2 is supplied mainly by increased blood flow. There is almost a linear relationship until high O2 demand.

Question 31

Is capillary density across all muscles the same ?

Answer 31

No , it depends on the muscle type. For example postural muscles have a higher capillary density.

Question 32

Do skeletal muscles have a low or high vascular tone ?

Answer 32

Very high vascular tone - they can permit lots of dilation. Flow can increase > 20 times in active muscle.

Question 33

What percentage of adult body mass does skeletal muscles take up ?

Answer 33

40%

Question 34

What agents are thought to act as vasodilators in skeletal muscle ?

Answer 34

Increase is K+

Increase in osmolarity

Increase is inorganic phosphates

Adenosine

Increase H+

And adrenaline

Question 35

What is the main function of cutaneous regulation ?

Answer 35

Regulate temperature - the skin is the main dissipating surface of the body.

Question 36

What are ateriovenous anastomoses?

Answer 36

Apical skin contains these. - these open to increase blood flow to veins where heat can then be lost.

AVA are under neuronal control and are not regulated by local metabolites

Question 37

If there is a decreasein body temperature , what will occur to the arteriovenous anastomoses?

Answer 37

There will be an increased sympathetic tone in the AVA. , causing them to constrict and decrease heat loss.

Question 38

If there is an increase in body temperature , what will happen to thr AVA ?

Answer 38

There will be a decreased sympathetic tone in the aaa a causing them to dilate and increase heat loss

Question 39

In non-apical skin , sweat glands release what local vasodilator ?

Answer 39

Bradykinin which acts as a local vasodilator for dilate veins and arterioles to increase heat loss from thr body.