Special Circulations

Question 1

Compare the functions of the 2 circulations of the lungs

Answer 1

Bronchial circulation;

• Meets the metabolic requirements of lung
• Part of systemic circulation

Pulmonary circulation;

• Blood supply to alveoli
• Required for gas exchange

Question 2

What are the mean pressures of the pulmonary vessels?

Answer 2

Mean Pulmonary Arterial Pressure: 12-15mmHg

Mean Pulmonary Capillary Pressure: 9-12mmHg

Mean Pulmonary Venous Pressure: 5mmHg

Question 3

What is the Ventilation-Perfusion ratio

what is it represented as?
What is it optimally?

Answer 3

Represented as “ V/Q ratio”, Optimal=0.8

The matching of Ventilation of Alveoli to Perfusion of Alveoli

Question 4

Name and explain the primary mechanism that regulates pulmonary vascular tone?

Answer 4

Hypoxia Pulmonary Vasoconstriction

Alveolar hypoxia results in vasoconstriction of pulmonary vessels

(Ensures that perfusion matches ventilation)

Question 5

Explain 1 downside of Chronic Hypoxic Vasoconstriction

Answer 5

Chronic Hypoxia (Altitude/ lung disease)

• Increase in vascular resistance-> Pulmonary hypertension
• High aterload on RV-> RV heart failure

Question 6

Compare the hydrostatic pressure of vessels in different parts of lung?

Explain the difference?

Thus, explain how they differ during inspiration?

Answer 6

Apex;

• Low hydrostatic pressure (< Alveolar pressure)
• Vessels collapse during inspiration

Level of Heart;

• Higher H pressure (> Alveolar pressure)
• Vessels continuously patent

Base;

• Highest H pressure (> Alveolar pressure)
• Vessels distended

Question 7

How does exercise affect pulmonary blood flow and O2 uptake?

Answer 7

• Increased cardiac output-> Small increase in arterial pressure
• Opens apical capillaries-> increased O2 uptake

Question 8

Explain the forces that determine tissue fluid formation

Answer 8

Starling forces

Hydrostatic pressure pushes fluid out of capillary
Oncotic pressure draws fluid into capillary

Question 9

Is hydrostatic pressure affected more by arterial or venous pressure?

Using this knowledge, would hypertension usually cause oedema

Answer 9

Venous pressure

No, as hypertension is influenced by arterial pressure

Question 10

Where do pulmonary oedemas form when upright and when lying down

Explain this

Answer 10

Upright: At base as hydrostatic pressure here is highest due to gravity

Lying down: Throughout lung

Question 11

Compare the patient outcomes of blood flow to brain being reduced;

For a few seconds
3-4 minutes

Name 1 outcome of a small alteration to cerebral blood flow

Answer 11

Few seconds: Syncope (Fainting)
3-4 mins: (Permanent brain damage or death)

Headaches

Question 12

How much of the cardiac output goes to brain

Answer 12

15%

Question 13

What are 4 factors that allow the cerebral circulation to meet its high demand for O2

Answer 13

• High capillary density
• High basal flow rate
• High O2 extraction
• Secure O2 supply

Question 14

What are 4 ways the secure blood supply to the brain is maintained

Answer 14

Structurally;
- Anastomoses between basilar and internal carotid arteries

Functionally;

• Metabolic factors that control blood flow
• Brainstem regulates other circulations
• Myogenic autoregulation maintains perfusion during hypotension

Question 15

Explain Myogenic Autoregulation in brain

Below what blood pressure, does this process fail?

Answer 15

Increase in BP-> Vasoconstriction to reduce blood flow to brain

Decrease in BP-> Vasodilation to increase blood flow to brain

50mmHg

Question 16

Explain Metabolic Regulation in brain

What can panic ventilation cause? What does this present as

Answer 16

Hypercapnia: Vasodilation increases blood flow to brain

Hypocapnia: Vasoconstriction decreased blood flow to brain

(Hypercapnia= High partial pressure of CO2)

Panic hyperventilation can cause hypocapnia-> cerebral vasoconstriction, leading to dizziness and syncope

Question 17

How is blood flow affected in areas of brain with increased neuronal activity?

Name 1 substance that is a strong vasodilator of cerebral arterioles

Answer 17

Increased blood flow

Adenosine

Question 18

Describe Cushing’s Reflex

Answer 18

• Cranium doesn’t allow for volume expansion
• Increased intercranial pressure-> Impaired cerebral blood flow
• Impaired flow to vasmotor control region of Brainstem increased sympathetic vasomotor activity-> Increased arterial BP

Question 19

Where to the right and left coronary arteries arise from

Answer 19

Right Coronary Artery- Right Aortic Sinus

Left Coronary Artery- Left Aortic Sinus

Question 20

Identify 3 features of Coronary circulation that improve blood flow+O2 supply

Answer 20

• High capillary density
• Short diffusion distance
• Continuous production of NO by coronary endothelium (Vasodilator)

Question 21

Describe the relationship between Myocardial O2 demand and Coronary Blood Flow

What are coronary arteries prone to

Answer 21

Linear relationship until O2 demand is very high

Prone to atheroma

Question 22

Why is coronary blood flow mostly during diastole?

Explain why angina is more likely to occur during exercise

Answer 22

During systole, tension of ventricle walls compresses the coronary vessels

During exercise, less time spent in diastole, so less O2 supply

Question 23

How is the rate of flow through the myocardium controlled?

Answer 23

By the action of metabolites that cause vasodilation of coronary arterioles

(Adenosine, K+, Low pH)

Question 24

Name 1 important role of the skeletal muscle circulation

How does it do this?

Answer 24

Regulation of Arterial BP

Via resistance vessels innervated by sympathetic vasoconstrictor fibres

Pre-capillary sphincters are opened to allow perfusion of more capillaries

Question 25

In skeletal muscle, flow can be increased by vasodilation of capillaries. What are 2 ways this can be done

Answer 25

Via metabolites; - K+ - Inorganic phosphates - Adenosine - H+ Via nervous activity; - Adrenaline acts at arterioles - through B2 receptors

Question 26

What is the main role of cutaneous circulation What is another role?

Answer 26

Temp. regulation Maintaining blood pressure (Vasoconstriction to maintain BP)

Question 27

What are the specilaised structures in the skin that regulate temperature? How are they controlled?

Answer 27

Artereovenous anastomose, under neuronal control via sympathetic vasoconstrictor fibres

Question 28

Outline how Artereovenous anastomoses regulate temperature in apical skin

Answer 28

- Decreased core temp-> Increased sympathetic tone in AVAs-> Vasoconstriction of AVAs - Increased core temp-> reduced vasomotor drive-> Dilation of AVAs