Lecture 12 - Control of Blood Flow I Flashcards
What are the different phases of control of blood pressure?
Acute control:
- rapid changes in local vasodilation/constriction
- minutes to seconds
Long-term control:
- increase in size/number of vessels
- days, weeks, or months
What are the different theories of acute local blood flow control?
Vasodilator theory:
- increased metabolism results in decrease oxygen availability
- decreased oxygen availability results in the formation of vasodilators
Oxygen (nutrient) lack theory:
-decreased oxygen availability leads to relaxation of blood vessels (vasodilation)
What is vasomotion and what regulates it?
L12 S7
- cyclic opening and closing of precapillary sphincters
- number of sphincters open is roughly proportional to nutrient requirement of tissues (primarily influenced by oxygen)
What is autoregulation of blood flow?
- increase in arterial pressure leads to temporary increase in blood flow
- blood flow eventually returns to normal even with elevated pressure
What are the theories explaining autoregulation?
L12 S13
Metabolic theory:
-increase in blood flow washes out vasodilator
Myogenic theory:
-stretching of vessels causes a reactive vascular constriction
What special acute blood flow control mechanisms are present in other organs?
Kidneys:
-tubuloglomerular feedback (macula dense/juxtaglomerular apparatus)
Brain:
-increased [CO2] or [H+] results in cerebral vessel dilation which washes out the CO2/H+
Skin:
- flow linked to body temp
- regulated by sympathetic nerves
- 3mL/min/100g of tissue in cold weather
- 7-8L/min in body in hot weather
What is the endothelial derived mechanism for blood flow control?
Healthy tissue:
- cGTP is converted to cGMP
- cGMP activates kinases
- kinases trigger vasodilation
Damaged tissue:
- endothelin is produced which prevents conversion of cGTP to cGMP
- lack of cGMP results in vasoconstriction
What substance result in vasoconstriction?
- norepinephrine
- epinephrine
- angiotensin II
- vasopressin
What substances result in vasodilation?
- bradykinins (also increases capillary permeability)
- histamine (derived from MAST cells and basophils)
The sympathetic nervous system innervates all vessels except __________ and primarily result in _________.
Capillaries; vasoconstriction
Describe the vasomotor center in the brain.
L12 S22
Vasoconstrictor area:
- anterolateral upper medulla
- continuous signal through sympathetic nerves to blood vessels resulting in vasoconstriction
Vasodilator area:
- anterolateral lower medulla
- inhibits vasoconstrictor area
Sensory area:
- posterolateral medulla
- receives signals through vagus and glossopharynngeal nerve
What higher nervous centers indirectly regulate the vasomotor center?
(L12 S22)
- reticular substance
- hypothalamus
- cerebral cortex
What neural mechanism can be used to rapidly increase arterial pressure?
- constriction of systemic arteries
- constriction of veins
- increased heart rate
What are baroreceptors?
L12 S28-29
- pressure sensors located in the carotid and aortic sinuses
- stimulated by pressure >60mmHg (carotid) or >80mmHg (aortic)
- carotid baroreceptors stimulate glossopharyngeal nerve (CN IX) via Herring’s nerves
- aortic baroreceptors stimulate the vagus nerve (CN X)
- inhibit vasoconstrictor center and stimulates vasodilator center
What are chemoreceptors?
L12 S34
- located in carotid bodies and aortic bodies
- sensitive to lack of O2, excess of CO2, or excess of H+
- stimulate Herring’s nerve and vagus nerve
- more important in respiratory control
