cardiovascular system - regulation of blood flow

Question 1

blood flow is controlled by…

Answer 1

arterioles

Question 2

widespread constriction leads to…

Answer 2

increase in peripheral resistance and BP

Question 3

types of blood flow control

Answer 3

-intrinsic
-extrinsic

Question 4

intrinsic

Answer 4

blood flow control due to LOCAL factors

Question 5

extrinsic

Answer 5

blood flow control by factors OUTSIDE the organ, often capable of overriding intrinsic system

Question 6

intrinsic blood flow control

Answer 6

-myogenic response (response to stretching)
-vasodilator metabolites
-endothelial factors
-autocoids (local hormones)
-in skin: temperature

Question 7

metabolic hyperaemia

Answer 7

-CO2
-lactic acid
-adenosine
-K+
-phosphate
-osmolarity
= all increase blood flow

Question 8

intrinsic hyperaemia

Answer 8

-after exercise, blood flow to muscle remains elevated considerably for a few minutes
-this is due to built up vasodilator metabolites, prostaglandins and nitric oxide (NO)

Question 9

structure/nature of NO

Answer 9

N=O
-nitric oxide is a diatomic free radical
-lipid soluble + very small, so easy passage between cell membranes
-short lived, usually degrades or reacts within seconds
-natural form is a gas

Question 10

synthesis of NO

Answer 10

-synthesised from L-arginine
-reaction catalysed by eNOS (nitric oxide synthase)

Question 11

endothelium-dependent vascular relaxation

Answer 11

-endothelium-relaxing derived factor (ERDF) stimulates guanylate cyclase (GC) of the smooth muscle
-resulting in cyclic GMP activating relaxation
-strong evidence suggests ERDF is nitric oxide and its precursor is L-arginine

Question 12

smooth muscle relaxation by NO

Answer 12

-shear stress stimulates endothelial NO production
-oestrogen up-regulates endothelial NO synthase
-inflammatory mediators (e.g. cytokines, bradykinin) increase NO synthesis

Question 13

extrinsic blood flow control

Answer 13

-hormones
-nerves
=mostly vasoconstrictory (e.g. sympathetic)
=vasodilatory nerves found in few tissues
(e.g. cerebral + coronary arteries, salivary
glands, GI tract, genitalia, bladder etc.)
=vasodilatory nerves are parasympathetic

Question 14

smooth muscle contraction

Answer 14

-mechanical stretching
-electrical depolarisation
=L-type + Ca^2+ channels
-hormones
=noradrenaline
=vasopressin
=angiotensin II
=endothelin-1 (autocoid)
=thromboxane A2 (autocoid)
=serotonin (autocoid)
=leukotrienes (autocoid)

Question 15

smooth muscle characteristics

Answer 15

-actin + myosin loosely arranged around periphery of cell (held in place by protein dense bodies)
-arrangement of fibres cause cell to become globular when contracting
-myosin can slide along actin for long distances w/o encountering the end of a sarcomere
-smooth muscle myosin has hinged heads all along its length

Question 16

smooth muscle CONTRACTION mechanism

Answer 16

-intracellular Ca2+ conc. increase when Ca2+ enters cell and is released from sarcoplasmic reticulum (SR)
-Ca2+ binds to calmodulin (CaM)
-Ca2+-CaM activates myosin light chain kinase (MLCK)
-MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
-active myosin crossbridges slide along actin and create muscle tension

Question 17

smooth muscle RELAXATION mechanism

Answer 17

-free Ca2+ in cytosol decreases when Ca2+ is pumped out of the cell or back into the SR
-Ca2+ unbinds from CaM
-myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity
-less myosin ATPase results in decreased muscle tension