Physiology Flashcards
what is stroke volume?
the volume of blood ejected by each ventricle per heart beat
SV = EDV-ESV
what is edv determined by?
venous return
what does edv determine?
preload
what is afterload?
the resistance into which the heart is pumping
what is the CO?
the volume of blood pumped by each ventricle per minute
CO=SVxHR
what is MAP?
the average bp during a single cardiac cycle, which involves contraction and relaxation of the heart (minimum 60mmHg)
3 MAP equations
- MAP = 2/3 DBP-SBP
- MAP = DBP +1/3 (SBP-DBP)
- MAP = TPR x CO
what is TPR?
this is the sum of resistance of all peripheral vasculature in the systemic circulation
what is the major vessel or resistance?
arterioles
what does increased venomotor tone do?
increases venous return, SV, MAP
what does increased vasomotor tone do?
increases TPR and MAP
humoral agents that cause vasoconstriction?
Leukotrines, thromboxane A2, serotonin, endothelin
humoral agents that cause vasodilatation?
histamine, bradykinin, nitric oxide
local metabolite changes which cause vasodilatation in an organ?
decreased PO2 increased PCO2 increased local [H+] increased extra cellular K+ increased osmolarity of ECF adenosine (from ATP)
excitation in SA node cells
- decrease in K efflux, superimposed on slow Na+ influx until threshold is reached
- when this is reached, rising phase of AP is caused by Ca2+ influx
- falling phase is caused by K+ efflux
AP in contractile myocytes
- rising phase caused by fast Na+ influx
- plateau phase by Ca2+ influx
- falling action caused by inactivation of Ca2+ channels and K+ efflux
parasympathetic neurotransmitter?
acetylcholine acting through M2
sympathetic neurotransmitter?
noradrenaline, acting through B1
what allows the refractory period to occur?
in the plateau phase, Na+ channels are depolarised (closed)
and in descending phase, K+ channels are open so membrane cannot be depolarised
valves on LHS of heart?
mitral, aortic
valves on RHS of heart?
tricuspid, pulmonary
baroreceptor reflex
- correction of a fall in MAP, due to gravity
- sympathetic constrictor tone increases (increased TPR, venous return, SV, HR)
what does ANP do?
- released by muscle cells in response to atrial distension
- reduced blood volume, plasma volume and increases excretion of Na and H2O by kidneys
what does ADH do?
- release stimulated by decreased ECFV and increased osmolarity
- increases water reabsorption (concentrates urine), increasing CO and BP
- causes vasoconstriction of blood vessels
extrinsic control of vascular smooth muscle?
- vasomotor tone
- hormones (adrenaline - alpha dilate, beta constrict, angiotensin II and ADH)
intrinsic control of vascular smooth muscle?
- local metabolites
- local humoral agents
- physical (e.g temp, stress, myogenic response)
