VASCULAR: SPECIAL CIRCULATION Flashcards
What is the myogenic response that assist with autoregulation
Increased blood flow leads to increased stretch and reflexive constriction
What is the metabolic response that assist with autoregulation
Decreased blood flow leads to metabolic build up and a decrease in O2 pressure → leads to local vasodilation
How does autonomic nervous control assist with autoregulation
Sympathetic stimulation → vasoconstriction
parasympathetic stimulation → vasodilation
Where can you find the B1 adrenergic receptors and how do they assist with autoregulation?
located at cardiac muscle; greater affinity for norepinephrine than epinephrine; increases contractility
Where can you find the B2 adrenergic receptors and how do they assist with autoregulation?
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
Where can you find the A1 adrenergic receptors and how do they assist with autoregulation?
located at vascular smooth muscle; greater affinity for norepinephrine than epinephrine; results in profound vasoconstriction and increase in blood pressure
In the skeletal muscle during rest, what is the response for autoregulation?
Sympathetic tone predominantes
Norepinephrine binds to a1 and a2 adrenoceptors → vasoconstriction
Adrenaline levels are so low so there is little B2 adrenergic stimulation
In the skeletal muscle during exercise, what is the response for autoregulation?
Vasodilator metabolites (especially adenosine) → dilation
Dilation predominates despite increased sympathetic tone
Adrenaline levels rise → B2 adrenergic stimulation → dilation
Define: reactive hyperemia
Reactive hyperemia: increased flow in response to ischemia; K+ release → hyperpolarizes VSM → vasodilation
Define: active hyperemia
Active hyperemia: metabolite induced vasodilation and therefore increased blood flow; can take a few seconds to initiate
How does % blood flow change from rest to exercise?
- brain
- heart
- muscle
- skin
- kidney
- abdominal organs
- others
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%
What type of dilation occurs in the muscle, heart, and skin during exercise?
Metabolic dilation predominates in exercising muscle and heart
Thermoregulatory dilation occurs in skin vasculature
What decreases flow to non-essential regions during exercise?
Adrenergic constriction
Describe the skeletal muscle pump action that enhances venous return
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
define: apical skin
Apical skin: skin to the face, hands, and feet; typically poorly insulated
Describe how apical skin blood flow occurs
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
What is apical skin important for?
- Important area for heat dissipation
- Increased core temperature causes decreased sympathetic output, less vasoconstriction, more flow through anastomoses, and heat dissipation
Describe how non apical skin blood flow differs from apical skin
- fewer A-V anastomoses
How does the non apical skin assist with returning the body to normal core temp after hyperthermia
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
How much of the cardiac output goes to the brain? How much does it weigh?
10-15% cardiac output yet only 2% body weight
Why is the brain considered intolerant of ischemia (reduced blood flow)
Interruption of flow for just a few seconds causes loss of consciousness (syncope)
depends on oxidative metabolism of glucose
What is cerebral blood flow dependent on?
Autoregulation is critical (pressure and metabolic regulation > neural control)
Describe the blood brain barrier
- what is it gated by
- what types of molecules can pass through
- 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
What arteries supply the brain?
Internal carotid arteries (2)
Vertebral arteries (2)