CVS S8 - Special circulations Flashcards
How does the pulmonary circulation differ from the systemic circulation?
Pulmonary circulation is at lower pressure and lower resistance and must accept the entire cardiac output so is supply driven
How is this low resistance pulmonary circulation created?
Wide vessels, high capillary density so lots of vessels connected in parallel and the arterioles present have very little smooth muscle
List the pressures of the RA, RV, LA, LV, PA and Aorta
RA- 0-8 mmHg
RV- 15-30/0-8 mmHg
LA- 1-10 mmHg
LV- 100-140/1-10 mmHg
PA- 15-30/ 4-12 mmHg
Aorta- 100-140/60-90 mmHg
List the mean arterial, venous and capillary pressures in the pulmonary circulation
Arterial- 12-15 mmHg
Venous- 5 mmHg
Capillary- 9-12 mmHg
What is ventilation perfusion matching and how would a deviation from the optimum 0.8 be corrected?
Ensures efficient oxygenation of blood as the ventilation of the alveoli is matched with the perfusion of the alveoli
Blood must be diverted from alveoli which are not well ventilated by hypoxic pulmonary vasoconstriction
What is bronchial circulation?
Part of systemic circulation, serves to meet metabolic requirements of the lungs
When might a chronic defect in ventilation perfusion matching occur and what would be the effects of this?
High altitudes or lung diseases
- Resistance increases
- Creates pulmonary hypertension
- Increase after load on the right ventricle as must work harder to pump blood out into lungs
- Results in right ventricular heart failure
Which forces are involved in the formation of tissue fluid?
Hydrostatic pressure of blood in the capillaries forces fluid out
Colloid osmotic pressure of large molecules such as plasma proteins draws fluid into the capillary
How do hydrostatic and colloid osmotic pressure forces differ between the lungs and systemic circulation?
Oncotic pressure of the tissue fluid in the lungs is greater than the systemic circulation
Capillary hydrostatic pressure in lungs is less than the systemic circulation
Plasma oncotic pressure remains the same in the two circulations
What is the combined overall effect of colloid and hydrostatic pressure in the lungs?
Minimises the formation of lung lymph which would decrease the efficiency of gas exchange
How does posture effect formation of oedema?
When upright, oedema will only form at the base of the lungs where vessels are distended due to high hydrostatic pressure
When laying down oedema forms in all parts of the lungs (apex, level of heart and base)
Outline the relationship between demand and oxygen supply to the myocardium
Under increased mechanical demand, oxygen supply increases mainly by increasing blood flow
This is a linear relationship until very high oxygen demands are reached
When is the myocardium perfused with oxygenated blood and why is this a problem in exercise?
- Coronary arteries fill during diastole
- When heart rate increases during exercise the length of diastole shortens
Describe the features of the coronary circulation and how is a high blood flow maintained?
- High capillary density (3000mm2- greater than skeletal muscle at just 400mm2)
- Low diffusion distance of less than 9 micrometres
- NO production by coronary endothelium maintains high basal flow
How is blood supply to the brain secured structurally?
Anastomoses between basilar and internal carotid arteries
How is blood supply to the brain secured functionally?
- Brainstem regulates other circulations
- Myogenic auto-regulation maintains perfusion during hypotension
- Metabolic factors
What is myogenic auto-regulation?
Responds to changes in transmural pressure
Increase in blood pressure-vasoconstriction
Decrease in blood pressure-vasodilation
What are cerebral vessels particularly sensitive to in metabolic regulation and what is the effects of this?
Respond to changes in carbon dioxide
High carbon dioxide (hypercapnia)- vasodilation
Low carbon dioxide (hypocapnia)- vasoconstriction
What are the potential consequences of panic hyperventilation on cerebral circulation?
Hypocapnia
Cerebral vasoconstriction causes syncope and dizziness
What is the primary role of cutaneous circulation and how is this achieved?
- Temperature regulation arteriovenous anastomoses (AVAs) in the apical skin are controlled by sympathetic vasoconstrictor fibres
- Increase temp- opens AVAs, increases blood flow
- Decrease temp- increases sympathetic tone, decreases blood flow
List the functions of skeletal muscle circulation
- Must increase oxygen and nutrient delivery and remove waste metabolites in exercise
- Regulates arterial blood pressure
Which skeletal muscle type has high capillary density?
Muscles involved in posture
What is the Cushing’s reflex?
- Rigid cranium protects brain but does not allow for volume expansion
- Increase in intracranial pressure due to blockage
- Impairs central blood flow
- Decreased blood flow to vasomotor control centres
- Increased sympathetic vasomotor activity
- Causes increase in arterial pressure
- Ensures cerebral blood flow is maintained
