VASCULAR: SPECIAL CIRCULATION

Question 1

What is the myogenic response that assist with autoregulation

Answer 1

Increased blood flow leads to increased stretch and reflexive constriction

Question 2

What is the metabolic response that assist with autoregulation

Answer 2

Decreased blood flow leads to metabolic build up and a decrease in O2 pressure → leads to local vasodilation

Question 3

How does autonomic nervous control assist with autoregulation

Answer 3

Sympathetic stimulation → vasoconstriction

parasympathetic stimulation → vasodilation

Question 4

Where can you find the B1 adrenergic receptors and how do they assist with autoregulation?

Answer 4

located at cardiac muscle; greater affinity for norepinephrine than epinephrine; increases contractility

Question 5

Where can you find the B2 adrenergic receptors and how do they assist with autoregulation?

Answer 5

located at bronchioles and has a much greater affinity for epinephrine than norepinephrine; results in bronchodilation

located at the large skeletal muscle vasculature and coronary arteries; also greater affinity for epinephrine; results in vasodilation and increased blood supply during exercise

Question 6

Where can you find the A1 adrenergic receptors and how do they assist with autoregulation?

Answer 6

located at vascular smooth muscle; greater affinity for norepinephrine than epinephrine; results in profound vasoconstriction and increase in blood pressure

Question 7

In the skeletal muscle during rest, what is the response for autoregulation?

Answer 7

Sympathetic tone predominantes

Norepinephrine binds to a1 and a2 adrenoceptors → vasoconstriction

Adrenaline levels are so low so there is little B2 adrenergic stimulation

Question 8

In the skeletal muscle during exercise, what is the response for autoregulation?

Answer 8

Vasodilator metabolites (especially adenosine) → dilation

Dilation predominates despite increased sympathetic tone

Adrenaline levels rise → B2 adrenergic stimulation → dilation

Question 9

Define: reactive hyperemia

Answer 9

Reactive hyperemia: increased flow in response to ischemia; K+ release → hyperpolarizes VSM → vasodilation

Question 10

Define: active hyperemia

Answer 10

Active hyperemia: metabolite induced vasodilation and therefore increased blood flow; can take a few seconds to initiate

Question 11

How does % blood flow change from rest to exercise?
- brain
- heart
- muscle
- skin
- kidney
- abdominal organs
- others

Answer 11

At rest vs during exercise % blood flow
Brain: 13% → 4%
Heart: 4% → 4%
Muscle: 20% → 73%
Skin: 9% → 11%
Kidney: 20% → 3%
Abdominal organs: 24% → 3%
Other: 10% → 2%

Question 12

What type of dilation occurs in the muscle, heart, and skin during exercise?

Answer 12

Metabolic dilation predominates in exercising muscle and heart

Thermoregulatory dilation occurs in skin vasculature

Question 13

What decreases flow to non-essential regions during exercise?

Answer 13

Adrenergic constriction

Question 14

Describe the skeletal muscle pump action that enhances venous return

Answer 14

Blood enters the vein, the upper valve opens further when muscle contracts but the lower valve closes so that contracting muscle pushes blood upwards. After muscle relaxes, upper valve closes to prevent backflow and lower valve opens allowing veins to fill

Question 15

define: apical skin

Answer 15

Apical skin: skin to the face, hands, and feet; typically poorly insulated

Question 16

Describe how apical skin blood flow occurs

Answer 16

arteriovenous anastomoses: direct connections between small arteries and veins; arteriole to venule shunting

This is a low resistance pathway which allows a high flow of blood

Sympathetic regulated

Insensitive to metabolic vasodilators

Question 17

What is apical skin important for?

Answer 17

• Important area for heat dissipation
• Increased core temperature causes decreased sympathetic output, less vasoconstriction, more flow through anastomoses, and heat dissipation

Question 18

Describe how non apical skin blood flow differs from apical skin

Answer 18

• fewer A-V anastomoses

Question 19

How does the non apical skin assist with returning the body to normal core temp after hyperthermia

Answer 19

Hyperthermia (elevated core temp): hypothalamic cholinergic fibre activates and sweat glands release bradykinin and other local mediators which lead to vasodilation and increased heat dissipation

Question 20

How much of the cardiac output goes to the brain? How much does it weigh?

Answer 20

10-15% cardiac output yet only 2% body weight

Question 21

Why is the brain considered intolerant of ischemia (reduced blood flow)

Answer 21

Interruption of flow for just a few seconds causes loss of consciousness (syncope)

depends on oxidative metabolism of glucose

Question 22

What is cerebral blood flow dependent on?

Answer 22

Autoregulation is critical (pressure and metabolic regulation > neural control)

Question 23

Describe the blood brain barrier
- what is it gated by
- what types of molecules can pass through

Answer 23

• Gated by continuous tight junctions and limited transcytosis
• few select breaches e.g. posterior pituitary
• highly lipid soluble molecules can pass e.g. CO2, alcohol, caffeine, nicotine, heroine, methadone (not H+, not adrenaline)
• permits water through endothelial water channels

Question 24

What arteries supply the brain?
Internal carotid arteries (2)
Vertebral arteries (2)

Question 25

What is the circle of Willis

Answer 25

Receives blood through internal carotid and vertebral arteries and distributes blood to the rest of the brain.

Circle shape blood vessel which maintains effective flow even if flow in one artery is reduced

Question 26

Why are some people more prone to syncope (fainting)? (4)

Answer 26

1. Their cerebral autoregulation is less effective; when they stand up, they have more pronounced reduction in flow as cerebral pressure falls
2. Their cerebral circulation is abnormally sensitive to carbon dioxide
   When you stand up there is increased ventilation and decreased carbon dioxide which leads to vasoconstriction. In fainters, this is more pronounced
3. Baroreflex blood pressure is impaired; decreased systemic pressures with standing further reduce cerebral pressure
4. Upon standing, decreases in blood pressure and CO2 cause marked decreases in cerebral blood flow and loss of consciousness

Question 27

Describe Ficks principle applied to whole body O2 consumption

Answer 27

O2 consumption = Q* (arterial-venous O2 difference)

If assuming a cardiac output of 5 l/min, O2 consumption is 200 mL O2/min in the whole body.

Question 28

Describe the a-vO2 difference of the whole body when the body is at rest

Answer 28

At rest (whole body)
Arterial O2 content = 20 ml O2 per 100 ml of blood
Venous O2 content = 16 ml O2 per 100 ml of blood
↳ a-v O2 difference = 4 ml O2 / 100 ml

Question 29

Describe the a-vO2 difference of the coronary circulation when the body is at rest

Answer 29

Cardiac arterial O2 content = 20 ml O2 per 100 ml blood

Cardiac venous O2 content = 4 ml O2 per 100 ml blood

↳ a-v O2 difference = 16 ml O2 / 100 ml
→ near maximal oxygen extraction at rest

Question 30

How does coronary blood flow differ in terms of O2 extraction?

Answer 30

Cardiac muscle cannot increase O2 extraction to meet increased demand thus flow must increase to meet demand.

Question 31

What type of dependence does myocardial O2 consumption have on coronary blood flow (i.e. delivery)

Answer 31

linear

Question 32

How does a-vO2 difference differ between the whole body and the coronary circulation

Answer 32

coronary circulation extracts near maximal oxygen at rest

(16 ml O2/ 100 ml vs 4 ml O2 / 100 ml)

Question 33

During exercise, how does the heart increase O2 consumption if there is already maximal oxygen extraction in the coronary circulation at rest?

Answer 33

since oxygen extraction can’t increase, blood flow must increase

Question 34

Describe coronary blood flow starting from the aorta

Answer 34

• Aorta splits into two branches which are the left and right conary artery
• Right coronary artery supplies the right ventricle, atrioventricular node and sino-atrial node
• Left coronary artery supplies the left anterior descending artery and circumflex artery
• Left anterior descending artery supplies the left ventricle, bundle of his, and conducting tissue
• Coronary circulation drains into right atrium via the coronary sinus

Question 35

Describe the mechanical regulation (ventricular compression) of coronary blood flow

Answer 35

Ventricular compression caused by the cardiac muscles contracting that squeeze the arteries and prevent their flow. Decreases arteriole radius and increases their radius. Results in decreased flow during systole

There is more flow during diastole

Question 36

What type of myocardial tissue is most susceptible to myocardial infarction?

Answer 36

Endocardium tissue is most susceptible to myocardial infarction as the arteries must travel through the epicardium and myocardium first (more road ahead that can get blocked)

Question 37

Describe the neurological regulation of coronary blood flow

Answer 37

High intrinsic vasomotor tone: there is always resting sympathetic vasoconstriction

Vasodilator reserve: describes the reserved capacity to dilate due to high intrinsic vasomotor tone

Question 38

Describe the metabolic regulation of coronary blood flow

Answer 38

Metabolic dilators in the coronary circulation:
- decreased O2
- increased Co2
- increased adenosine
- decreased pH
- Increased K+
- Decreased ATP (opens KATP channels)
- NO is a potent coronary artery dilater
- Medications: GTN and nitroprusside are used in the treatment of angina

Question 39

Describe the myogenic regulation of coronary blood flow

Answer 39

sense stretch –> constriction to maintain pressure

Question 40

Describe coronary artery disease

Answer 40

• Collateral vessels will develop with slow onset ischemia (reduced blood flow)

– vascular endothelial growth factor and hypoxia inducible factor are upregulated and induce angiogenesis/proliferation.