OPTION D.4-Heart Flashcards
What are the shape of cardiac muscles?
Y-shaped
→ joined end-to-end in a complex network of interconnected cells
Intercalated disc
Specialised junction where the end of one muscle cell comes in contact with the end of another muscle cell
The difference between cardiac muscle and skeletal muscle?
+ Cardiac muscles are shorted and wider
+ commonly they only have one nucleus per cell
+ many contract even w/ absence of stimulus from nerves
What does the intercalated disc consist of?
Double membrane containing gap junctions = provide channels of connected cytoplasm betw/ the cells
What does the connected cytoplasms betw/ the cells of the heart muscle allow for?
Rapid movement of ions and a low electrical resistance.
What does being interconnected cuz of Y-shape and being electrically connected cuz of gap junctions allow the heart muscles to do?
Allows for a wave of depolarisation to pass easily from one cell to a network of other cells
→ leading to the synchronisation of the contractions
How does the contraction from the SA node travel really rapidly through the heart muscles?
+ The gap junctions allow electric charges to flow freely betw/ the cells = contractions that originate in the SA node spreads really rapidly through the heart muscles
What is the mechanism that staggers the contraction of the atria and the ventricles?
+ The fibres which connect the SA node to the AV node carry the action potential relatively slow
How long is the delay between the arrival of the stimulus from the SA node and the initiation of the impulse with the ventricles?
0.12 sec
Which cells take longer to become excited, the SA node or the AV node?
AV node
What are the 4 features of the AV node that lead to a delayed initiation of contraction of the ventricles by the AV node?
1) AV node cells hv. smaller diameter and don’t conduct as quickly
2) There are less Na+ channels in the membrane of AV node cells
→ more negative resting potential and a prolonged refractory period within the cells of AV node
3) Fewer gap junctions betw/ cells of AV node
4) More non-conductive connective tissue in the node
Why is the delay in contraction caused by the AV node important?
It ensures that the atria contracts and empty the blood into the ventricles before the ventricles contract.
→ contraction of ventricles too early = lead to too small vol. of blood entering the ventricle.
What is the route of the signal from the AV node?
+ Atrioventricular bundle receives impulse
+ conducts signal rapidly until pt. where splits into left and right bundle
+ At apex (base) branches connect to Perkinje fibres = conduct signal even more rapidly to the ventricle
Modifications of the Perkinje fibres that facilitate the conduction of signals at such a high speed (4)
+ hv. relatively fewer myofibrils
+ Bigger diameter
+ Higher densities of voltage-gated Na channels
+ High #’s of mitochondria and High glycogen stores
Where does the contraction of the ventricles begin?
At the Apex
→ it pushes upwards
What causes the “lub” sound?
Atrioventricular valves ‘Shut’
What causes the “dub” sound?
Semilunar valves shut
What are the 2 options of help that the artificial pacemaker can provide to a patient?
1) regular impulse
2) discharge only when a heartbeat is missed
→ it monitors the heart’s rhythm and when it doesn’t beat the ventricle is stimulated w/ a low voltage pulse.
What is cardiac arrest?
When the blood supply to the heart becomes reduced and the heart tissues are deprived of oxygen.
How are the 2 paddles of a defibrillator applied to a patient’s chest?
The 2 paddles are aligned setting up a diagonal line betw/ the 2 paddles with the heart in the middle.
How does a defibrillator work?
+ it will first detect whether or not there is fibrillation happening in the heart
→ then if there is, an electrical charge is given off to restore normal heart rhythm
What is Atherosclerosis?
The hardening of the arteries caused by the formation of plaque on the inner lining of the arteries
What is a thrombosis?
A blood clot
What is Myocardial infarction?
Heart attack
What causes hypertension?
The greater resistance to the flow of blood = slow down the blood = greater pressure on the walls of the arteries
What is one of the consequence of hypertension?
1) Damage of the cells that line the arteries
→ lead to arteries becoming narrower and stiff
What can constant high blood pressure cause?
weaken the arteries causing a section in the wall to enlarge and form a bulge = aneurysm = can burst = internal bleeding
What can chronic high blood pressure cause? (2)
1) lead to stroke
→ by weakening blood vessels in the brain causing them to narrow, leak, rupture
→ can lead to blood clot in arteries leading to brain = cause strokes
2) Kidney failure
→ damages both arteries leading to the kidney and capillaries within the glomerulus
Factors that correlate to the greater incidence of thrombosis and hypertension (4)
1) Genetic precondition = having parents who hv experienced heart attack
2) Smoking causes high bp cuz nicotine causes vasoconstriction
3) Sedentary lifestyle = lack of exercise correl. w/ obesity and prevents the return of venous blood from extremities = lead to greater risk of clot formation
4) Lower levels of oestrogen
→ males and females after menopause = have higher risk
Blood pressure measured in?
mm Hg
What does the higher number represent in bp?
Pressure in the artery caused by ventricular systole
What does the lower number represent in bp?
Pressure in the artery due to ventricular diastole
What is the instrument used to measure bp called?
Sphygmomanometer
What is a normal bp?
Systolic = less than 120 Diastolic = less than 80
The Cardiac cycle (6)
1) Isometric Relaxation
2) Rapid Filling
3) Diastasis
4) Atrial Systole
5) Isometric contraction
6) Ejection
