Session 8 - Special Circulations

Question 1

How does the pulmonary circulation ensure a low resistance?

Answer 1

• short, wide vessels
• lots capillary networks in parallel
• arterioles with little smooth muscle

Question 2

Name the mean pressures in the pulmonary artery, capillaries and veins.

Answer 2

Artery: 12-15mmHg
Capillaries: 9-12mmHg
Veins: 5mmHg

Question 3

What is ventilation perfusion matching?

Answer 3

For efficient oxygenation of blood the amount of blood that is perfumed to the lungs much match the oxygen that is ventilated into the lungs

Question 4

How is ventilation perfusion matching maintained?

Answer 4

Hypoxic pulmonary vasoconstriction- region of lungs that are not being well ventilated cause the arterioles supplying them to constrict thus reducing blood blow tot these areas

Question 5

What does chronic hypoxic vasoconstriction cause and how?

Answer 5

RV failure - chronic increase in vascular resistance puts an increasing after load on the right ventricle leading to its eventual failure

Question 6

How do oncotic and hydrostatic forces effect fluid levels in capillaries?

Answer 6

Oncotic - draws fluid in

Hydrostatic - forces fluid out

Question 7

What has the biggest effect on capillary hydrostatic forces?

Answer 7

Venous pressure

Question 8

How does the location of pulmonary Oedemma depend on posture?

Answer 8

Determined by gravity
Therefore;
- when stood, will be mainly in base of lungs
- when lying down, will be spread throughout

Question 9

What is the relationship between myocardial oxygen demand and coronary blood flow?

Answer 9

Linear

Question 10

How do coronary arteries ensure constant vasodilation?

Answer 10

The endothelial cells produce Nitrous Oxide which is a vasodilator

Question 11

Which of diastole or systole can coronary arteries fill?

Answer 11

Diastole

Question 12

How can stress and cold effect coronary arteries?

Answer 12

Can cause them to have greater sympathetic vasoconstriction + angina

Question 13

How is cerebral oxygen demand met?

Answer 13

• High capillary density
• Large surface area for gas exchange + low diffusion distance
• High basal flow
• High oxygen extraction

Question 14

What can panic hyperventilation cause, in terms of cerebral blood flow?

Answer 14

• Decreased carbon dioxide conc in blood
• Vasoconstriction in cerebral arterioles
• Leads to dizziness and fainting

Question 15

How does regional activity ensure efficient cerebral blood flow?

Answer 15

Areas of the brain that have increased neuronal activity release adenosine which is a powerful vasodilator

Question 16

What is Cushing’s reflex?

Answer 16

• cerebral BP rises due to a haemorrhage of tumour
• Peripheral vasoconstriction is stimulated
• more blood flow to brain

Question 17

How can heat be lost using the cutaneous circulation?

Answer 17

• core temp rises
• vas motor tone of arterio-venous anastomoses is decreased
• they vasodilation allowing more blood through them
• now more blood flows closer to skin
• heat is lost

Question 18

How is the massive increase in demand for blood in skeletal muscle catered for?

Answer 18

• at rest most capillaries are not perfused

- upon exertion the pre-capillary Sphincters can open massively increasing the blood flow to the muscle

Question 19

What is the bronchial circulation?

Answer 19

This is the circulation of blood that supplies the metabolic requirements of the lungs, it is part of the systemic circulation