circulation 2

Question 1

heart

Answer 1

myogenic heartbeat=initiates their own heartbeat; all chordate animals
chambered heart: fish, mammals, birds

Question 2

cardiac muscles contract without external stimuli, why?

Answer 2

-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+

Question 3

pacemaker potential

Answer 3

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

Question 4

action potential

Answer 4

relative timing for opening and closing of voltage-gated, ion-specific protein channels in cell membrane

Question 5

key voltage-gated ion channels

Answer 5

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

Question 6

cardiomyocytes

Answer 6

-similar to striated muscle cells aside from diff in excitation-contraction coupling

Question 7

how does electrical activity pass rapidly from heart cell to heart cell

Answer 7

INTERCALATED DISCS/GAP JUNCTIONS electrically couple cardiomyocytes
-elec coupling->syncitial contraction: once one cell contract, ALL CARDIOMYOCYTES in chamber contact simultaneously

Question 8

simple fish heart design

Answer 8

-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

Question 9

venosus and arteriosus

Answer 9

sinus venosus=collecting chamber for venous blood and SITE OF CARDIAC PACEMAKER
-bulbus/cjonus arteriousus=outflow vessel, helps ventricle increase bp

Question 10

single circulation

Answer 10

most fishes have blood go from heart the two primary vessel beds: respiratory/gills, and systemic/body tissue vessels

Question 11

double circulation

Answer 11

• 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

Question 12

cardiac O2 supply

Answer 12

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

Question 13

spongy vs compact myocardium

Answer 13

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

Question 14

variety of AP among cardiomyocytes

Answer 14

SA node>atrium>AV node>bundle of His>ventricular cardiomyo

• differences due to different ion channels
• AP in order of contraction order

Question 15

mammalian ventricular myocytes

Answer 15

few funny channels
FAST Na+ channels
SLOW L-type Ca2+ channels

Question 16

pacemaker cells:

Answer 16

• located in sa node of right atrium
• determine contraction rate of heart
• few myofibrils or mitochondria
• UNSTABLE RESTING MEMBRANE POTENTIAL
• mp slowly drifts upward from starting pot at -60mv due to SLOW INWARD MOVEMENT of FUNNY CURRENT CHANNELS (If), until reaches threshold at -40 where initiates AP

Question 17

funny channels

Answer 17

non-selective cation channels that open when cell is hyperpolarized, allowing Na+ to enter the cell, and closes as membrane gradually depolarises

Question 18

atrium-ventricular contractions

Answer 18

atrium and ventricle must contract SEQUENTIALLY, to give time for blood to move from atrium to ventricle
-accomplished via AV DELAY

Question 19

conduction pathways

av delay

Answer 19

-they assist in coordinated spread of electrical activity throughout the heart
av delay allows blood to move from atriume before ventricle contracts, seen as PAUSE BETWEEN P AND Q OF ELECTRO CARDIOGRAM

Question 20

syncitial contraction

Answer 20

-single cell contaction initiates other cells to contract; aka pacemaker cells in sa node through electric coupling with other cardiomyocytes