8. Circulations

Question 1

Bronchial circulation - purpose

Answer 1

• Bronchial: supplies O2 and nutrients to the lungs

Question 2

Pulmonary circulation - purpose

Answer 2

• Pulmonary: Carries deoxygenated blood away from the RV and oxygenated blood back to LA

Question 3

Bronchial circulation

• what does it do

Answer 3

• 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

Question 4

Co - ra and lv

Answer 4

• 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

Question 5

Pulmonary circulation: special adaptations

—> To facilitate high volume of blood:

Answer 5

• Low pressure system

* Low resistance

Question 6

• Low pressure system

Answer 6

– 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)

Question 7

• Low resistance

Answer 7

–Pulmonary vessels are shorter and wider
–Capillaries run in parallel – lower resistance
–Relatively less SMC - smooth muscle cells on arterioles

Question 8

Pulmonary circulation: special adaptations

–> To promote efficient gas exchange (oxygenate entire blood supply):

Answer 8

• Branching structure provide large surface area
• Short diffusion distance
• High density of capillaries
• Hypoxic vasoconstriction

Question 9

• Branching structure provide large surface area

Answer 9

– 300 million alveoli in the lungs

Question 10

• Short diffusion distance

Answer 10

– Alveoli and capillaries consist of one layer of epithelium ~0.3μm thickness

Question 11

• High density of capillaries

Answer 11

– Alveoli always close to capillaries

Question 12

• Hypoxic vasoconstriction

Answer 12

– 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

Question 13

Problems due to hypoxic vasoconstriction

Answer 13

• Chronic hypoxia→ Widespread vasoconstriction of pulmonary vessels→ Increase in pulmonary resistance→ chronic pulmonary hypertension

Question 14

• Reasons for chronic hypoxia:

Answer 14

– Altitude

– Lung disease (e.g. Emphysema)

Question 15

Chronic hypoxia - effect on heart

Answer 15

○ 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

Question 16

2 forces affecting fluid as it moves through vessel

Answer 16

• Hydrostatic pressure – pushes fluid out
  
  • Osmotic/oncotic pressure – keeps fluid in the vessel
  • For blood to remain in vesel –> HP = OP

Question 17

Hydrostatic pressure in lungs - normal

Answer 17

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

Question 18

Lymphatic system prevents fluid build up in lungs

Answer 18

• 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

Question 19

• Left ventricular heart failure or mitral valve stenosis can cause pulmonary edema

Answer 19

○ 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

Question 20

Low pressure pulmonary vesseks strongly influenced by gravity

Answer 20

In the upright position (orthostasis) there is greater hydrostatic pressure on vessels in the lower part of the lung

Question 21

Apex of lung - vessels

Answer 21

• Vessels collapse during diastole
  
  • When we exercise vessels in apex open up
• Apical capillaries open during increased CO (e.g. exercise)

Question 22

Level of the heart in the lung -vessels

Answer 22

• Vessels continuously patent

Question 23

Base of lungs - vessels

Answer 23

• Vessels distended (increased hydrostatic pressure)

Question 24

Coronary circulation - figures

Answer 24

• Rest 70-80 ml min-1 gram-1

* Heavy exercise 300-400 ml min-1 gram-1

Question 25

Intramural arteries

Answer 25

• Coronary arteries are intramural: compressed during systole, perfusion occurs during diastole Intramural artery = within muscles

Question 26

Coronary circulation • Structural adaptations:

Answer 26

– 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

Question 27

Coronary circulation - vessel problems

Answer 27

* These are end arteries (few or no anastomosis)→ prone to atheromas (tissue can infarct) * Obstruction→ Ischemia and infarction

Question 28

Cerebral circulation Basic facts

Answer 28

---> very intolerant to oxygen insufficiency • Brain has very high oxygen demand • Brain is very intolerant to reduced blood supply

Question 29

Interruption to Cerebral circulation

Answer 29

Interruptions: unconscious within 5 seconds, irreversible damage after 4 minutes

Question 30

Cerebral circulation Adaptations

Answer 30

– High capillary density – Short diffusion distance (~10um) – High basal flow rate = always constant blood flow rate to brain – High oxygen extraction from the blood

Question 31

Cerebral circulation: how secure blood flow is maintained? • Structural adaptations:

Answer 31

--> 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

Question 32

Cerebral circulation: how secure blood flow is maintained? • Functional adaptations

Answer 32

– 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

Question 33

Myogenic autoregulation

Answer 33

– 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

Question 34

Metabolic autoregulation

Answer 34

– 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

Question 35

Cushing’s reflex

Answer 35

* 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

Question 36

If Cushing’s reflex fails: Cushing’s triad:

Answer 36

– 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

Question 37

Bradycardia - Cushing triad

Answer 37

○ Bradycardia = due to increased bp, this activates baroreceptors which try to decrease bp by activating parasympathetic supply which causes decrease in heart rate

Question 38

Systolic hypertension - Cushing tried

Answer 38

○ Systolic hypertension – local production of nitric oxygen in the brain tries to maintain and promote vasodilation esp. In brain so systolic pressure remains high

Question 39

Irregular respiration - Cushing triad

Answer 39

○ Irregular respiration = compression of brainstem

Question 40

Skeletal muscle circulation • Functions:

Answer 40

– 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

Question 41

Skeletal muscle circulation In exercise

Answer 41

• 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

Question 42

Cutaneous circulation

Answer 42

----> 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

Question 43

Cutaneous circulation Changes in body temp

Answer 43

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.