Lecture 15- Special Circulations

Question 1

What are the two blood supplies to the lungs?

Answer 1

Pulmonary which is formgaseous exchange

Bronchial which supplies the lungs with its metabolic requirements and is part of the systemic circulation

Question 2

Why does the pulmonary circulation operate at low pressure?

Answer 2

Lots of short capillaries
Short and wide vessels
Arterioles have little smooth muscle

Question 3

Lung adaptions for gas exchange?

Answer 3

High capillary density

Short diffusion distance

Large surface area

Question 4

What is the ventilation perfusion ratio (V/Q)

Answer 4

Optimal ratio of ventilation to blood flow to the alveoli for efficient gas exchange.
Should ideally be 0.8 meaning that 4/5 of blood that goes to alveoli undergoes gaseous exchange.
Maintaining ratio involves vasoconstriction of vessels leading to alveoli that are not well ventilated

Question 5

What can decrease the ventilation perfusion ratio?

Answer 5

Chronic altitude an emphysema reduce ventilation and cause chronic pulmonary hypertension leading to right ventricular hypertrophy and right sided heart failure.

Question 6

Right sided heart failure without left sided heart failure cause?

Answer 6

Will always be some sort of lung problem

Question 7

Effects of exercise on pulmonary blood flow?

Answer 7

Capillary transit time reduced
Increased perfusion of lungs due to increased cardiac output but also increased pressure of apical capillaries means they don’t collapse in diastole and so are perfuse better

Question 8

Hydrostatic pressure in pulmonary and systemic circulations?

Answer 8

In systemic venous pressure greater influence as high VP prevents blood from leaving capillaries.

Pulmonary both arterial and venous pressure have influence

Question 9

What can cause lung oedema?

Answer 9

Left sided heart failure and mitral valve stenosis.

Leads to pulmonary venous pressure increase and so increased hydrostatic pressure and more fluid enters lungs

Question 10

How can you treat pulmonary oedema?

Answer 10

Treat underlying condition and give diuretics to reduce blood volume and so hydrostatic pressure

Question 11

How does cerebral circulation meet the high O2 demand?

Answer 11

High capillary density

High basal flow rate

High O2 extraction 35% above average

Question 12

What happens if blood supply stopped to brain?

Answer 12

Loss of consciousness after a few seconds.

Irreversible neuronal death after 4 minutes

Question 13

How is secure blood supply to brain ensured?

Answer 13

Structurally- many anastomoses between arteries

Functional- myogenic autoregulation maintains perfusion during hypotension

Metabolic factors eg pCO2

brainstem regulates circulations eg Cushings reflex

Question 14

How does myogenic autoregulation work?

Answer 14

Control comes from muscle.

Increased BP leads to vasoconstriction to reduce blood flow etc

Fails below 50mmHg

Question 15

How does metabolic regulation work?

Answer 15

Hypercapnia or high PCO2 causes vasodilation to remove it and hypocapnia does the opposite

Question 16

Why does hyperventilating after fright etc make dizzy and faint?

Answer 16

Induces hypocapnia which causes vasoconstriction and reduced cerebral blood flow

Question 17

What is cushing’s reflex?

Answer 17

Rigid cranium means that increased intracranial pressure will impair blood flow to vasomotor regions of brain stem. This will increase sympathetic vasomotor activity and cause vasoconstriction increasing BP and cerebral blood flow

Question 18

Where do right and left coronary arteries come from?

Answer 18

Right and left aortic sinuses

Question 19

Comparing coronary and skeletal muscle circulation

Answer 19

Not all skeletal capillaries perfused at rest but all coronaries are. Short diffusion distance etc and production of NO maintains high basal flow

Question 20

Why does angina occur?

Answer 20

Heart requires more blood during exercise. Also coronary arteries fill during diastole but this is reduced during exercise. Stress and cold can cause sympathetic coronary vasoconstriction and angina also.

Question 21

Why is it good that during rest only half of skeletal muscle capillaries are perfused?

Answer 21

It allows for increased recruitment during exercise. Probably why feel pumped during exercise.

Precapillary sphincters open

Question 22

What are arterovenous anastomoses.

Answer 22

Present in apical skin they carry blood from artery to veins located close to the surface to dissipate heat. Increased sympathetic activity causes vasoconstriction and blood flow is diverted to vital organs