Structure of Heart, Cardiac Muscle, Conduction System Flashcards
What is the cardiovascular system composed of?
Heart (creates oressure head to push blood through vessels) , blood vessels, blood
What are the functions of the cardiovascular system?
-Transportation- respiratory, nutritive, excretory
-Regulation- hormonal, temperature, protection (clotting), immune
What are the 2 circuits present?
-Pulomonary circuit - supplied by right side heart, blood vessels from heart to lungs and lungs to heart
-Systemic circuit - supplied by left heart, blood vessels from heart to systemic tissues and tissues to heart
What happens in the pulomary capillaries?
Blood entering the lungs is deoxygenated blood
Oxygen diffuses from tissues to blood
Blood leaving lungs is oxygenated
What happens in systematic capillaries?
Blood entering tissues is oxygenated blood
Oxygen diffuses from blood to tissues
Blood leaving tissues is deoxygenated
What drives blood flow?
Contraction increases pressure while relaxation decreases pressure - this pressure difference drives blood flow (pressure gradient) - blood moves from an area of higher pressure to an area of lower pressure
Which is greater atria pressure or ventrical pressure?
Atrial pressure
What are atria and ventricles separated by?
A sheet of connective tissue containing one way atrioventricular valves
-open during atrial contraction and allow blood flow only from atria into the ventricles
Where are the semilunar valves?
At the origin of the pulmonary artery and aorta
-ope during ventricular contraction and allow blood to flow only from ventricles into arteries
Whta is cardiac muscle composed of?
Contain actin and myosin arranged in sarcomeres similar to skeletal muscle cells
-contract via sliding-filament mechanism
What are myocardial ceöös?
Short branching and join neighbouring cells to create a complex network
-Adjacent myocardial cells joined by intercalated discs containing gap junctions
Why do myocardial cells contract almost simulatneously?
Gap junctions are fluid filled channels that allow action potentials to spread rapidly from cell to cell
Extracellular Ca2+ is used to initiate contraction in myocardial cells rather than intracellular stores
Are extracellular or intracellular stores of Ca2+ used to initiate myocardial cells contraction?
Extracellular
What causes contraction of skeletal muscle?
External stimulation by somatic motor nerves
What triggers the contraction of cardiac muscle?
-Specialized noncontractile myocardial cells, autorhythmic or pacemaker cells are responsible for triggering the contraction of cardiac muscle
-Cell membranes spontaneously depolarize and generate APs which spread into surrounding contractile myocardial cells
What is the Sinoatrial Node?
-Autorhythmic cells are concentrated in the sinoatrial node
-Located in the right atrium near the opening of the superior vena cava
-Spontaneous depolarizations generated here pass into surrounding myocardial cells and generate contraction
What happens the ion channels in the myocardial autorhythmic cells?
-Membrane potential (Vm) is unstable due to slow Na+ and Ca2+ channeöls (HCN) which remain open at -60mV - slow influx of Na+ and Ca2+ ions and slow drift in Vm from -60 to -50mV
-At -50mV (threshold) fast Ca2+ and Na+ channels open - spontaneous depolarization - action potential generated
-At +20mV, K+ channels open and membrane repolarization occurs - fast Ca2+ and Na+ channels close, rapid efflux of K+ ions
Breakdown of myocardial contraction due to ions
- Arrival of AP at cells opens voltage-gated Na+ channels - RAPID DEPOLARIZATION
- Voltage-gated Ca2+ channels also open morr slowly
- At +20mV, Na+ channels close and K+ channels open, repolarization begins
-Slow inward diffusion of Ca2+ then balances outward diffusion of K+ - plateau phase
-Ca2+ channels close and K+ channels complete repolarization
When is the plateau phase?
Slow inward diffusion of Ca2+ balances the outward diffusion of K+
How does Ca2+ influx affect muscle contraction?
-Inward movement of extracellular Ca2+ during depolarization also opens Ca2+ channels on the sarcoplasmic reticulum - triggers identical mechanism to skeletal muscle
(AP travels along plasma membrane and T tubules)
-Ca2+ induces Ca2+ release from sarcoplasmic reticulum
-Ca2+ binds to troponin, exposing myosin-binding sites
-Crossbridge cycle begins (muscle fiber contracts)
-Ca2+ is actively transported back to SR and ECF
-Tropomyosin blocks myosin-binding sites - muscle fiber relaxes
-During repolarization - Ca2+ is transported out pof the cell and relaxation occurs
What is present in skeletal muscle contraction?
-AP in skeletal muscle is fast (20msec)- no plateau phase
-Cell has repolarised before associated contraction has begun
-Cell is responsive to further stimuli during contraction - summation of contraction, tetany
Time for myocardial cell contraction
-Length of action potential in myocardial cell (250msec) is much longer due to plateau phase
-Duration of AP is almost as long as associated contraction
-Myocardial cells are refractory during almost entire contraction
-Summation of contraction and tetany cannot happen in cardiac muscle
What does the SA node affect?
-Rate of depolarization in SA node sets the rate of depolarization of the contractile myocardial cells
-Sets rate of contraction
-Determines heart rate
What causes the contraction of atrial muscle?
-Action potentials generated in SA node spread through adjacent myocardial cells via gap junctions in right and left atrium
