Integration of Cardiovascular System

Question 1

describe veins

Answer 1

capacitance vessels (contain most of blood volume during rest);
passageways of blood from tissues to heart 
venous return must provide heart with sufficient blood to pump

Question 2

describe preload

Answer 2

initial stretching of myocytes prior to contraciton

Question 3

describe afterload

Answer 3

force against which the heart has to contract to eject blood

Question 4

how is systemic vascular resistance controlled

Answer 4

regulated by vascular smooth muscles (supplied by sympathetic nerves, noradrenaline acts on alpha receptors) through changes in the radius of arterioles
vasoconstriction - increased BP
vasodilation - decreased BP

no significant parasympathetic innervation of arterial smooth muscles

Question 5

describe vasomotor tone

Answer 5

determinant of BP, modulated by sympathetic system (partially constricted at rest)
caused by discharge of sympathetic nerves resulting in continuous release of noradrenaline
increase sympathetic discharge = increased vasomotor tone = vasocontriction

increased vasomotor tone increases systolic ventricular resistance and MAP

Question 6

describe hormonal control of vascular smooth muscles

Answer 6

adrenaline acts on alpha receptors (skin, gut, kidney arterioles) = vasoconstriction
adrenaline acts on beta receptors (cardiac and skeletal muscle arterioles) = vasodilation
helps with strategic redistribution of blood (exercise)

angiotensin II = vasoconstriction

antidiuretic hormones = vasoconstriction

Question 7

describe intrinsic control of vascular smooth muscles

Answer 7

matches blood flow of different tissues to their metabolic needs
they can over ride extrinsic control mechanism
includes chemical and physical factors

Question 8

describe intrinsic control of vascular smooth muscles - chemical: local metabolites

Answer 8

local metabolites within an organ influences the contraction of arteriolar smooth muscles
the following factors causes relaxation of arteriolar smooth muscles resulting in vasodilation and metabolic hyperaemia;
decreased local PO2
increased local PCO2
increased local [H+] (decreased pH)

increased extra-cellular [K+]
increased osmolality of extracellular fluid
adenosine release (from ATP)

Question 9

describe intrinsic control of vascular smooth muscles - chemical: local humoral agents

Answer 9

influences contraction of arterial and arteriolar smooth muscles
released in response to tissue injury or inflammation

endothelium is important in maintenance of vascular health
endothelium damage/dysfunction can be caused by;
high BP
high cholesterol
diabetes
smoking

endothelium produced vasodilators;
anti-thrombotic
anti-inflammatroy
anti-oxidants

endothelial produced vasoconstrictors;
pro-thrombotic
pro-inflammatory
pro-oxidants

Question 10

describe nitric oxide

Answer 10

continuously produced by vascular endothelium from amino acid L-arginine through enzymatic action of nitric oxide synthase (NOS)
potent vasodilator (short half life) which is important in regulation of blood flow and maintenance of vascular health
shear stress on vascular endothelium, as a result of increased flow, causes release of calcium in vascular endothelium cells and subsequent activation of NOS - flow dependent NO formation
chemical stimuli can also induce NO formation - receptor stimulated NO formation - many vasoactive substances act through stimulation of NO formation 
NO diffuses from vascular endothelium into adjacent smooth muscle cells where it activates the formation of cGMP that serves as a second messenger for signalling smooth muscle relaxation

Question 11

list examples of local humoral agents causing vasodilation

Answer 11

histamine
bradykinin
nitric oxide - continuously released by endothelial cells of arteries and arterioles

Question 12

list examples of humoral agents causing vasoconstriction

Answer 12

serotonin
thromboxane A2
leukotrienes
endothelin - potent vasoconstrictor released from endothelial cells. Its production is stimulated by various agents which cause vasoconstriction

Question 13

describe intrinsic control of vascular smooth muscles - phyiscal

Answer 13

temperature;
cold - vasoconstriction
warmth - -vasodilation

myogenic response to stretch;
important in tissue like brain => autoregulation of blood flow (keeps cerebral blood flow constant over a wide range of mean arterial pressure) and kidneys - helps with regulation of local blood flow;
increase MAP - resistance vessels automatically constrict to limit flow
decrease MAP - resistance vessels automatically dilate to increase flow

sheer stress;
dilation of arterioles causes sheer stress in the arteries upstream to make them dilate
this increases blood flow to metabolically active tissues

Question 14

describe factors influencing venous return

Answer 14

increase in venous return;
increase venomotor tone 
increase blood volume
increase skeletal muscle pump
increase respiratory pump

increasing venous return results in increased atria pressure –> increased end diastolic volume –> increase stroke volume (starling law)

Question 15

describe venomotor tone

Answer 15

venous smooth muscles are supplied with sympathetic nerve fibres
stimulation gives venous constriction
on account of venous valves, blood driven to right atrium
increased venomotor tone increases venous return, stroke volume and MAP

Question 16

describe respiratory pump and venous return

Answer 16

during inspiration, intra-thoracic pressure decreases and intra-abdominal pressure increases
this increases pressure gradient for venous return and creates a suction effects that moves blood from the veins towards the heart
increasing rate and depth of breathing increases venous return to the heart

Question 17

explain skeletal muscle pump and venous return

Answer 17

large veins in limbs lie between skeletal muscles
contraction of muscle aids venous return
one-way venous valves allow blood to move forward towards the heart
muscle activity increases venous return to the heart

Question 18

describe acute cardiovascular responses to exercise

Answer 18

increased cardiac out and increased sympathetic nerve activity
sympathetic vasomotor nerve reduces flow to kidney and gut - vasoconstriction
in skeletal and cardiac muscle, metabolic hyperaemia overcomes vasomotor drive- vasodilation
blood flow to skeletal and cardiac muscles increase in proportion to metabolic activity
the increases in CO increases systolic BP
the metabolic hyperaemia decreases systolic ventricular resistance and decreases diastolic bP (pulse pressure increases)
post exercise hypotensive response

Question 19

describe chronic cardiovascular responses to exercise

Answer 19

regular aerobic exercise helps reduce blood pressure
multifactorial
reduction in sympathetic tone and noradrenaline levels
increases parasympathetic tone to the heart
cardiac remodelling
reduction in plasma renin levels
improved endothelial function - increased vasodilators, decreased vasoconstrictors
decreased arterial stiffening