The heart

Question 1

Describe how the structure of cardiac muscle cells allows them to transmit impulses.

Answer 1

• branched (faster signal propagation )
• short cylindrical cells
• intercalated discs join cells together preventing them from pulling apart
• gap junctions (at intercalated discs) - enable rapid transmission of «electrical» impulses «between cells»
• myogenic- trigger action potentials without nervous input
• more mitochondria than skeletal muscles (does not become fatigued allowing for life long contractions)

Question 2

what causes heart sounds? lubb dubb

Answer 2

• first sound caused by the closing of atrioventricular valves during ventricular systole
• second sound casued by closing of semilunar valves during ventricular diastole

Question 3

signal initiation and propagation

Answer 3

• SA node acts as a pacemaker
• causes atrial contraction
• signal passed on to AV node with a delay
• the delay allows blood to flow into ventricules before atrioventricular valve closes
  -AV node sends a signal through Bundle of His and Purkinjee fibers which ensure coordinated contraction of the entire ventricular wall

Question 4

what letters and traces appear on an alectrocardiogram? What do they mean?

Answer 4

P - atrial systole
QRS - ventricular systole
T - repolarization of ventricles

Question 5

heart rate
what affects it?

Answer 5

• number of contractions per minute,
• temperature, age, weight, emotional state
• sympathetic nervous system
• adrenaline

Question 6

normal blood pressure?

Answer 6

120/80 mmHg

Question 7

What increases the risk of coronary heart disease?

Answer 7

sedentary life style
age
diet rich in fats
nicotine
high LDL levels
atherosclerosis

Question 8

thrombosis

Answer 8

Thrombosis is the formation of a clot within a blood vessel
- plaques develop in the arteries, reduce the diameter of the vessel
- high blood pressure damages the arterial wall, forming lesions
- plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
- in the coronary arteries leads to heart attacks, while thrombosis in the brain causes strokes

Question 9

explain the action of a defibrillator.

Answer 9

a. defibrillator is electrodes/a metal paddle/pad that is placed on the
patient’s chest ✔
3 max
b. the device determines whether fibrillation is happening ✔
c. a series of electrical shocks are delivered through the electrodes ✔
d. electrical impulse is used to depolarize the heart muscle ✔
e. to re-establish the function of the SA node/natural pacemaker/natural
rhythm «of the heart»

Question 10

Explain how the pH of blood is kept constant during exercise

Answer 10

pH of blood is regulated to stay within a narrow range/7.35 to 7.45 ✔ If values provided, both required
6 max
b. increase in CO2 produced during aerobic respiration «during exercise» ✔
c. CO2 reacts with water to form carbonic acid ✔
d. chemoreceptors detect drop in blood pH «when CO2 concentration rises»
OR
«increase in» CO2 lowers blood pH ✔
e. carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions ✔ Allow formula
f. hydrogencarbonate is alkaline/increases pH/neutralizes H+ ions ✔ OWTTE
g. hydrogen ions bind to plasma proteins/hemoglobin ✔
h. stimulation of breathing centre/medulla oblongata
OR
ventilation rate increased ✔
i. faster diffusion/removal of CO2 «in alveoli/lungs»