8. Circulations Flashcards
Bronchial circulation - purpose
• Bronchial: supplies O2 and nutrients to the lungs
Pulmonary circulation - purpose
• Pulmonary: Carries deoxygenated blood away from the RV and oxygenated blood back to LA
Bronchial circulation
- what does it do
- Perfuses the respiratory tract to the level of terminal bronchioles
- Bronchial arteries arise from the aorta
- Bronchial veins anastomose and brings deoxygenated blood to pulmonary veins
- Pressure in bronchial arteries is equal to systemic pressure
Co - ra and lv
• Remember, the right and left ventricles have the same CO – cardiac output
- So the entire CO need to be oxygenated in the lungs
- Special adaptations to facilitate the high volume of blood and to prom
Pulmonary circulation: special adaptations
—> To facilitate high volume of blood:
- Low pressure system
* Low resistance
• Low pressure system
– mean arterial pressure:12-15mmHg
– mean capillary pressure: 9-12mmHg
– mean venous pressure: 5mmHg
– maintain low pressure with Thin vascular walls, high compliance (stretching of walls- very stretchy)
• Low resistance
–Pulmonary vessels are shorter and wider
–Capillaries run in parallel – lower resistance
–Relatively less SMC - smooth muscle cells on arterioles
Pulmonary circulation: special adaptations
–> To promote efficient gas exchange (oxygenate entire blood supply):
- Branching structure provide large surface area
- Short diffusion distance
- High density of capillaries
- Hypoxic vasoconstriction
• Branching structure provide large surface area
– 300 million alveoli in the lungs
• Short diffusion distance
– Alveoli and capillaries consist of one layer of epithelium ~0.3μm thickness
• High density of capillaries
– Alveoli always close to capillaries
• Hypoxic vasoconstriction
– Optimal Ventilation/Perfusion (V/Q) ratio: ~0.8-1.0
Perfusion = blood going into vessel (pulmonary vessels) = Q
Ventilation = V
4-5/5 = 0.8-1.0
– If poorly ventilated, blood re-directed to well ventilated areas and alveoli
Problems due to hypoxic vasoconstriction
• Chronic hypoxia→ Widespread vasoconstriction of pulmonary vessels→ Increase in pulmonary resistance→ chronic pulmonary hypertension
• Reasons for chronic hypoxia:
– Altitude
– Lung disease (e.g. Emphysema)
Chronic hypoxia - effect on heart
○ So when there is hypoxia in some alveoli, blood vessels around that alveoli constrict and divert that blood to other alveoli to be oxygenated
○ = vasoconstriction = increase pressure in pulmonary arteries= pulmonary hypertension = impact right side of heart = increase afterload of right ventricle (as there is more strain to push blood out) = right ventricle hypertrophy = right ventricular heart failure.
○ Blood can also push septal wall between left and right ventricle towards left ventricle
○ Decreased left ventricle preload – not enough blood in pulmonary veins – not enough blood in left ventricle
2 forces affecting fluid as it moves through vessel
- Hydrostatic pressure – pushes fluid out
- Osmotic/oncotic pressure – keeps fluid in the vessel
- For blood to remain in vesel –> HP = OP
Hydrostatic pressure in lungs - normal
In the lungs = HP>OP hydrostatic pressure is slightly higher so some fluid leaks
• The mean filtration pressure at the pulmonary capillaries is +1mm Hg
Lymphatic system prevents fluid build up in lungs
- Lymphatic system drain the leaked excess fluid in interstitial space preventing fluid build up
- Any imbalance in hydrostatic pressure or oncotic pressure will lead to accumulation fo fluid = pulmonary edema
• Left ventricular heart failure or mitral valve stenosis can cause pulmonary edema
○ due to decrease in pressure on the left side of the heart, blood backs up into left atrium and then back into pulmonary veins, blood backs up as left ventricle can’t pump it out = excess fluid accumulation
Low pressure pulmonary vesseks strongly influenced by gravity
In the upright position (orthostasis) there is greater hydrostatic pressure on vessels in the lower part of the lung
Apex of lung - vessels
- Vessels collapse during diastole
- When we exercise vessels in apex open up
- Apical capillaries open during increased CO (e.g. exercise)
Level of the heart in the lung -vessels
• Vessels continuously patent
Base of lungs - vessels
• Vessels distended (increased hydrostatic pressure)
Coronary circulation - figures
- Rest 70-80 ml min-1 gram-1
* Heavy exercise 300-400 ml min-1 gram-1
Intramural arteries
• Coronary arteries are intramural: compressed during systole, perfusion occurs during diastole
Intramural artery = within muscles
Coronary circulation
• Structural adaptations:
– High capillary density: Low diffusion distance (a lot of blood vessels)
– Continuous production of NO (nitric oxide) : potent vasodilator
– Reactive hyperaemia: Increase in metabolite production→ can trigger local vasodilation
• More metabolically active = more vasodilation
Coronary circulation - vessel problems
- These are end arteries (few or no anastomosis)→ prone to atheromas (tissue can infarct)
- Obstruction→ Ischemia and infarction
Cerebral circulation
Basic facts
—> very intolerant to oxygen insufficiency
• Brain has very high oxygen demand
• Brain is very intolerant to reduced blood supply
Interruption to Cerebral circulation
Interruptions: unconscious within 5 seconds, irreversible damage after 4 minutes
Cerebral circulation
Adaptations
– High capillary density
– Short diffusion distance (~10um)
– High basal flow rate = always constant blood flow rate to brain
– High oxygen extraction from the blood
Cerebral circulation: how secure blood flow is maintained?
• Structural adaptations:
–> to ensure constant blood flow to brain
– Circle of Willis: Anastomoses between basilar (from the base) and internal carotid arteries
• If one branch is cut off there is always another branch supplying sufficient blood
Cerebral circulation: how secure blood flow is maintained?
• Functional adaptations
– Myogenic autoregulation: Change in blood pressure leads to change in vessel diameter
– Metabolic autoregulation: Change in pCO2 (biproduct of metabolic activity) leads to change in vessel diameter
Myogenic autoregulation
– Myogenic autoregulation: Change in blood pressure leads to change in vessel diameter
• Vessels constrict to decrease blood supply when bp is high
• Vessels dilate to increase blood supply to the brain when bp is low
Metabolic autoregulation
– Metabolic autoregulation: Change in pCO2 (biproduct of metabolic activity) leads to change in vessel diameter
• Co2 high means oxygen is low = vasodilation to increase oxygen supply to brain
• Co2 low means oxygen is high = vasoconstriction
Cushing’s reflex
- Pathological increase in intracranial pressure ICP (due to tumor or fluid accumulation etc.)→ compress brain
- Increase in ICP→ Impair blood flow to brain stem→ Increase in sympathetic activity→ Increase in BP→ Increase blood flow
If Cushing’s reflex fails: Cushing’s triad:
– Triad consisting of bradycardia, irregular respiration and systolic hypertension = increased ICP
○ Bradycardia = due to increased bp, this activates baroreceptors which try to decrease bp by activating parasympathetic supply which causes decrease in heart rate
○ Systolic hypertension – local production of nitric oxygen in the brain tries to maintain and promote vasodilation esp. In brain so systolic pressure remains high
○ Irregular respiration = compression of brainstem
Bradycardia - Cushing triad
○ Bradycardia = due to increased bp, this activates baroreceptors which try to decrease bp by activating parasympathetic supply which causes decrease in heart rate
Systolic hypertension - Cushing tried
○ Systolic hypertension – local production of nitric oxygen in the brain tries to maintain and promote vasodilation esp. In brain so systolic pressure remains high
Irregular respiration - Cushing triad
○ Irregular respiration = compression of brainstem
Skeletal muscle circulation
• Functions:
– Meet metabolic need during exercise
– Many of the capillaries are closed off from the rest of the circulation due to the contraction of pre-capillary sphincters
Skeletal muscle circulation
In exercise
• In exercise the precapillary sphincters open
– This results in a higher vascular tone and the constriction of vessels
– This allows to cope with the increased workload during exercise
– Metabolic hyperaemia
Cutaneous circulation
—-> Relatively less metabolically active, main role in temperature regulation
- Blood supply different from other tissues
- Skin has arteriovenous anastomoses (AVAs) - arteries come and connect direct to the veins without using capillaries
- AVAs play a role in temperature regulation
- Sympathetic nervous system influence blood flow through AVAs
Cutaneous circulation
Changes in body temp
Increase core body temp
• Vasodilation, reduced sympathetic activity, more heat disapated to reduce temp
Opposite happens when there is a decrease in core body temp.
