Lecture 4 Flashcards
Functions of cardiac skeleton (3)
- electrphysiological discontinuity(allow for total filling/ insulation)
- attachments for atrial and ventricular myocardium
- strong yet flexible support for vavular openings
Cardiac skeleton
fibrous plate- 3 triangular areas- trigones
reinforced by cartilage or bone- ox (2 bones), sheep (1 bone- os cordis), cat, dog pig, horse (cartilage)
The heart wall- 3 layers
- endocardium (inside)- endothelium
-myocardium (largest and thickest)- bundles of cardiac muscle cells
-epicardium (outside)- mesothelial cells of visceral pericardium
THERE IS FAT ON THE OUTSIDE (under epicardium)
What is special about cardiac myocytes? 2
- Abundant mitochondria
- dependent on aerobic respiration- no rest periods-no o2 debt possible
cardiac muscle has (4)
intercalated discs
central nuclei (usually 1) with perinuclear space
good blood supply
branched fibers
intercalated discs (2)
structurally attached at desmosomes
electrically connected at gap juncitons
what are t tubules
cell membrane invaginations to get AP closer to SR
what are purkinje fibers and histo look
specialized conducting cells, pale staining (lots of glycogen) large cells
What links AP and contraction
all about Ca
- Ca enters vell in respose to AP, stimulates release of Ca from SR-> contraction
- Ca sensitive Ca release
- 20% of rise in intracellualr Ca thorugh VO channels
- 80% from SR
Excititation- contraction coupling
AP conducted across myocyte membrane and down t tubule->
- opening of VO Ca channels
- entry of Ca into cell
- inc in intracellular Ca that:
- stimulates release of Ca from SR (ryanodine receptor channels)->initiates contraction
generation of tension- regulatory protein complex
tropomyosin
troponin
these prevent interaction betwen actin and myosin
generation of tension- ca switch
in intracellualr Ca
Ca causes tropomyosin to move aside
myosin-actin crossbridges from: contraction
generation of tension- contraction
(powerstroke)
energy supplied by ATP bound to myosin
generation of tension- Ca release from SR
contributes to the plateau phase of the AP (phase 2) and therefor to the refractory period
Relaxation (4)
Active pumps return Ca to: -SR - extracelluar fluid
Ca exchanged for extracellular Na
intracellular Ca [ ] falls
myocyte relaxes
Generation of tension round 2 (3)
- amount of Ca release (and therefor force of contraction) depends on…
- -tension generally directly related to…
- tension generated also depends on…
amount of Ca release (and therefor force of contraction) depends on how much Ca stored in SR and #of release channels activated
- tension generally directly related to intrcellular Ca levels
- tension generated also depends on length of myocyte prior to contraction
Isotonic contraction
(muscle gets shorter)
activating an unrestrained muscle causes it to shorten without force development (maximal velocity)(like when valves open)
isometric contraction
(stays same length but creates tension)
measure of the muscles maximal ability to create tension
-like cardiac contraction before the valves open
Effect of cell length (2)
cell length determines overlap of thick and thin filaments
length of relaxed cells is determined by amount of blood in ventricle
optimal and normal cell length
normal cell length is less than maximal
length tension relationship
tension (CO) inc as length (EDV) inc. to a point and then plateau
contractility
the amount of tension that can be developed at any given stretch of cardiac muscle
inotropes
agents that alter contractility
contractility is inc by…
and inc in intracellular Ca[ ]
intracelluar Ca can be modualted by… (2)
receptor operated Ca chanels on cell membrane
ryanodine channels on SR
2 ways to inc strength of contraction
inc length by inc cardiac filling
agent (inotrope) that inc excitation of a cell
