circulation 2 Flashcards
heart
myogenic heartbeat=initiates their own heartbeat; all chordate animals
chambered heart: fish, mammals, birds
cardiac muscles contract without external stimuli, why?
-excitation contraction coupling
-heartbeat generated inside the cell via an UNSTABLE MEMBRANE POTENTIAL
1/. voltage activation of ion channels
2. changes in ion permeability
3. action potentials
4. increase in intracellular Ca2+
pacemaker potential
begins with hyperpolarization, causing slow Na+ leak
- once reaches threshold potential Na+ open fast, potential rises quickly
- SLOPE of pacemaker potential sets INTRINSIC HEART RATE
action potential
relative timing for opening and closing of voltage-gated, ion-specific protein channels in cell membrane
key voltage-gated ion channels
Na+=’funny’ channel; PRODUCES SA NODE’S PACEMAKER POTENTIAL
Ca2+=t-type channel; fast opening, slow closing;
K+ channel=inside to outside; fast opening, slow closing
cardiomyocytes
-similar to striated muscle cells aside from diff in excitation-contraction coupling
how does electrical activity pass rapidly from heart cell to heart cell
INTERCALATED DISCS/GAP JUNCTIONS electrically couple cardiomyocytes
-elec coupling->syncitial contraction: once one cell contract, ALL CARDIOMYOCYTES in chamber contact simultaneously
simple fish heart design
-two muscular chambers, one atrium one ventricle
-must pump through resistance of GILL AND SYSTEMIC VESSELS, and enough pressure in veins to refill the heart
two other chambers: sinus venosus and bulbus/conus arteriosus
venosus and arteriosus
sinus venosus=collecting chamber for venous blood and SITE OF CARDIAC PACEMAKER
-bulbus/cjonus arteriousus=outflow vessel, helps ventricle increase bp
single circulation
most fishes have blood go from heart the two primary vessel beds: respiratory/gills, and systemic/body tissue vessels
double circulation
- one pump for pulmonary circuit, another for systemic vessels
- rbc therefore see heart TWICE per circuit
- seen in birds and mammals
- right=pulmonary and deoxygentated, left=systemic and oxygenated
cardiac O2 supply
cardiomyocytes needs O2 for muscle contractions
- some spongy myocardium receive venous O2 supply
- only spongy tissue in AMPHS and most fish hearts; if any COMPACT myocardium present, it is 5-50% of ventricle mass in fish and reptiles
- all vertebrate hearts start development as spongy myocardium
spongy vs compact myocardium
spongy for receiving venous O2 supply, large SA
- compact dominates developed mammal and avian hearts, and therefore requires CORONARY CIRCULATION to supply O2
- 99% of mammal/avian ventricle is supplied with coronary circulation
variety of AP among cardiomyocytes
SA node>atrium>AV node>bundle of His>ventricular cardiomyo
- differences due to different ion channels
- AP in order of contraction order
mammalian ventricular myocytes
few funny channels
FAST Na+ channels
SLOW L-type Ca2+ channels
