Special Circulations Flashcards
Compare the functions of the 2 circulations of the lungs
Bronchial circulation;
- Meets the metabolic requirements of lung
- Part of systemic circulation
Pulmonary circulation;
- Blood supply to alveoli
- Required for gas exchange
What are the mean pressures of the pulmonary vessels?
Mean Pulmonary Arterial Pressure: 12-15mmHg
Mean Pulmonary Capillary Pressure: 9-12mmHg
Mean Pulmonary Venous Pressure: 5mmHg
What is the Ventilation-Perfusion ratio
what is it represented as?
What is it optimally?
Represented as “ V/Q ratio”, Optimal=0.8
The matching of Ventilation of Alveoli to Perfusion of Alveoli
Name and explain the primary mechanism that regulates pulmonary vascular tone?
Hypoxia Pulmonary Vasoconstriction
Alveolar hypoxia results in vasoconstriction of pulmonary vessels
(Ensures that perfusion matches ventilation)
Explain 1 downside of Chronic Hypoxic Vasoconstriction
Chronic Hypoxia (Altitude/ lung disease)
- Increase in vascular resistance-> Pulmonary hypertension
- High aterload on RV-> RV heart failure
Compare the hydrostatic pressure of vessels in different parts of lung?
Explain the difference?
Thus, explain how they differ during inspiration?
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
How does exercise affect pulmonary blood flow and O2 uptake?
- Increased cardiac output-> Small increase in arterial pressure
- Opens apical capillaries-> increased O2 uptake
Explain the forces that determine tissue fluid formation
Starling forces
Hydrostatic pressure pushes fluid out of capillary
Oncotic pressure draws fluid into capillary
Is hydrostatic pressure affected more by arterial or venous pressure?
Using this knowledge, would hypertension usually cause oedema
Venous pressure
No, as hypertension is influenced by arterial pressure
Where do pulmonary oedemas form when upright and when lying down
Explain this
Upright: At base as hydrostatic pressure here is highest due to gravity
Lying down: Throughout lung
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
Few seconds: Syncope (Fainting)
3-4 mins: (Permanent brain damage or death)
Headaches
How much of the cardiac output goes to brain
15%
What are 4 factors that allow the cerebral circulation to meet its high demand for O2
- High capillary density
- High basal flow rate
- High O2 extraction
- Secure O2 supply
What are 4 ways the secure blood supply to the brain is maintained
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
Explain Myogenic Autoregulation in brain
Below what blood pressure, does this process fail?
Increase in BP-> Vasoconstriction to reduce blood flow to brain
Decrease in BP-> Vasodilation to increase blood flow to brain
50mmHg
Explain Metabolic Regulation in brain
What can panic ventilation cause? What does this present as
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
How is blood flow affected in areas of brain with increased neuronal activity?
Name 1 substance that is a strong vasodilator of cerebral arterioles
Increased blood flow
Adenosine
Describe Cushing’s Reflex
- 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
Where to the right and left coronary arteries arise from
Right Coronary Artery- Right Aortic Sinus
Left Coronary Artery- Left Aortic Sinus
Identify 3 features of Coronary circulation that improve blood flow+O2 supply
- High capillary density
- Short diffusion distance
- Continuous production of NO by coronary endothelium (Vasodilator)
Describe the relationship between Myocardial O2 demand and Coronary Blood Flow
What are coronary arteries prone to
Linear relationship until O2 demand is very high
Prone to atheroma
Why is coronary blood flow mostly during diastole?
Explain why angina is more likely to occur during exercise
During systole, tension of ventricle walls compresses the coronary vessels
During exercise, less time spent in diastole, so less O2 supply
How is the rate of flow through the myocardium controlled?
By the action of metabolites that cause vasodilation of coronary arterioles
(Adenosine, K+, Low pH)
Name 1 important role of the skeletal muscle circulation
How does it do this?
Regulation of Arterial BP
Via resistance vessels innervated by sympathetic vasoconstrictor fibres
Pre-capillary sphincters are opened to allow perfusion of more capillaries
In skeletal muscle, flow can be increased by vasodilation of capillaries.
What are 2 ways this can be done
Via metabolites;
- K+
- Inorganic phosphates
- Adenosine
- H+
Via nervous activity;
- Adrenaline acts at arterioles
- through B2 receptors
What is the main role of cutaneous circulation
What is another role?
Temp. regulation
Maintaining blood pressure (Vasoconstriction to maintain BP)
What are the specilaised structures in the skin that regulate temperature?
How are they controlled?
Artereovenous anastomose, under neuronal control via sympathetic vasoconstrictor fibres
Outline how Artereovenous anastomoses regulate temperature in apical skin
- Decreased core temp-> Increased sympathetic tone in AVAs-> Vasoconstriction of AVAs
- Increased core temp-> reduced vasomotor drive-> Dilation of AVAs
