Cardiac Muscle Flashcards
How long and wide are cardiac muscle cells in comparison with smooth muscle cells and skeletal muscle cells
Skeletal - 1mm-20cm long, 10-100μm wide
Cardiac - 50-100μm long 10-20μm wide
Smooth - 20-200μm long 5-10μm wide
What shape are they and do they branch?
short branched cylinders
How many nuclei and where placed
1 central
What are intercalated discs? What are they useful for?
3 types of junction that hold cardiac myocytes together - skeletal muscle doesn’t have this on histology (have Z lines)
Gap
Desmosomes
Adherens type - adhere to actin
They are useful for synchronised contraction of cardiac tissue (electrical and mechanical)
Which NS controls cardiac rhythm and is it voluntary or involuntary
Involuntary intrinsic rhythm - controlled by ANS
Do cardiac myocytes have sarcomeres? How are they arranged?
Yes have sarcomeres - gives striations
Not arranged in strict myofibrils as skeletal - arranged in continuous masses in cytoplasm
Do cardiac myocytes have triads or diads
Diads - 1 T tubule to 1 terminal cisternae of SR
What are purkinje fibres and what are they useful for? What 3 things to they have to help their role?
Modified cardiac myocytes that enable rapid conduction of impulse to allow synchrony of ventricular contraction. Have lots of gap junctions, glycogen and sparse filaments
What peptide hormone can be measured to diagnose HF? How?
BNP or NT-Pro-BNP in an immunoassay
What is ANP, when is it release, and what hormone does it work exactly in the opposite way to?
ANP is a potent vasodilator released by atria in response to increased blood volume (atrial distension). Acts to reduce BP by this and also works in the kidney to excrete Na+ (opposite to aldosterone)
When does ANP increase?
in CHF
What is BNP? Is it similar or different to ANP?
BNP is similar to ANP but is released by ventricular myocytes in response to distension. Acts to reduce peripheral resistance and also stimulates natriuresis
Can cardiac muscle regenerate?
No post damage e.g. infarction fibroblasts lay down scar tissue
How does the RAAS system work? (Renin-Angiotensin-Aldosterone- System). How is it different to ANP/BNP?
Renin is secreted by kidneys in response to reduced plasma Na+ or reduced renal blood flow, it’s enzyme activity convert angiotensinogen to angiotensin I. Angiotensin I is converted to Angiotensin II by ACE. Angiotensin II is a potent vasoconstrictor and also acts to stimulate Aldosterone release from Adrenal cortex. Aldosterone increased Na+ reabsorption at kindness = increased BP and Na+ retention. Works in the opposite way to ANP/BNP which act to reduce BP and increase Na+ excretion.
What are the junctions present in cardiac intercalated discs? What do they do?
Desmosomes - anchor to next cell and prevent separation in contraction
Adheres - adhere to actin in nearest sarcomere
Gap junctions allow action potentials between cardiac myocytes
