The Cardio-Vascular System - Part 2 (week 8)

Question 1

state 2 facts about cardiac muscle

Answer 1

1. have 1-2 nuclei centrally located
2. sliding filament mechanism
3. branching cells with gap junctions crucial to being stimulated
4. have large mitochondria
5. autorhythmicity/automaticity - node cells have the ability to generate their own AP’s

Question 2

what percentage of cardiac muscle cells are replaced yearly

Answer 2

the heart has a limited ability to replace its muscle cells. only about 1% of heart muscle cells are replaced yearly

Question 3

what percentage of muscle cells do not function in contraction (2 things)

Answer 3

1. about 1% of muscle cells do not function in contraction

2. these cells form the conduction system and are in electrical contact with the cardiac muscle via gap junctions

Question 4

state the effect of the sympathetic nervous system on the heart

Answer 4

the sympathetic nervous system innervates the entire heart muscle and node cells by the release of norepinephrine

Question 5

state the effect of the parasympathetic nervous system on the heart

Answer 5

the parasympathetic nervous system innervates the node cells and releases primarily acetyl choline

Question 6

1. what type of receptors are on cardiac muscle for norepinephrine
2. state another hormone which exerts the same effects

Answer 6

1. beta-adrenergic receptors
2. the hormone epinephrine (from the adrenal medulla) binds to the same receptors as norepinephrine and exerts the same actions on the heart

Question 7

what type of receptors are on the cardiac muscle for acetyl choline

Answer 7

muscarinic receptors

Question 8

state the 4 steps of the conduction pathway

Answer 8

1. signal starts at the SA node (approx. 75 signals/min)
2. wave of depolarisation travels through inter-nodal pathway via gap junctions to the AV node
3. signal has a 0.1s delay to allow atria to contract and totally fill the ventricles before they contract
4. the purkinje fibres also supply the papillary muscles and tell them to contract before the rest of the atria to help prevent back flow through the valves

Question 9

state what it is meant by the key term - electrocardiogram (ECG)

Answer 9

an ECG shows a graphic record of the heart’s electrical activity. the reading is a composite of the electrical activity, not a single action potential

Question 10

state what it is meant by the key term - P wave

Answer 10

the result of the depolarisation wave from the SA node to the AV node. atria contract 0.1s after P wave

Question 11

state what it is meant by the key term - QRS complex

Answer 11

the result of ventricular depolarisation and precedes ventricular contraction. the atria repolarisation is also observed by the QRS complex

Question 12

state what it is meant by the key term - T wave

Answer 12

caused by ventricular repolarisation

Question 13

state what it is meant by the key term - cardiac output (Q)

Answer 13

the volume of blood ejected from the left ventricle per minute (Q = HR x SV)

Question 14

state what it is meant by the key term - stroke volume (SV)

Answer 14

the difference between end diastole volume (EDV) and end systolic volume (ESV) - (SV = EDV - ESV)

Question 15

state what it is meant by the key term - positive chronotropic factors

Answer 15

positive chronotropic factors are factors which cause the HR to increase

Question 16

state what it is meant by the key term - negative chronotropic factors

Answer 16

negative chronotropic factors are factors which cause the HR to decrease

Question 17

state what it is meant by the key term - Frank Starling mechanism

Answer 17

concept: the ventricles contract more forcefully when it has been filled to a greater degree during diastole (this is due to the length-tension relationship)

Question 18

state 2 facts about the Frank Starling mechanism

Answer 18

1. EDV is determined by how stretched the ventricular sarcomeres are before contraction
2. the greater the EDV, the more the muscles are stretched, and thus the greater the contraction

Question 19

state what it is meant by the key term - contractility (in relation to VR)

Answer 19

concept: norepinephrine acts on beta-adrenergic receptors to increase ventricular contractility (the strength of contraction at any given EDV)

Question 20

state 2 facts about contractility

Answer 20

1. plasma epinephrine also increases contractility

2. increased contractility results in increased SV due to a more complete ejection of the EDV

Question 21

state the calculation to work out - mean arterial pressure

Answer 21

diastolic pressure + 1/3(systolic pressure - diastolic pressure)

Question 22

mean arterial pressure is dependent upon what

Answer 22

cardiac output (Q) x total peripheral resistance (TPR)

Question 23

state 3 facts about arterial baroreceptors

Answer 23

1. respond to changes in arterial pressure as nerve endings are highly sensitive to stretch/distortion
2. degree of stretching is directly proportional to BP
3. at normal mean arterial pressure (MAP) there is already a steady rate of neuronal discharge

Question 24

talk about arteriole baroreceptors ST and LT adaptation

Answer 24

ST - respond to changes in BP

LT - adapt to BP and only way to adjust BP is by changing blood volume

Question 25

state what it is meant by the key term - medullary cardio-vascular centre

Answer 25

located in the medulla oblongata and is the primary integrating centre for the baroreceptor reflex in a network of connected neurones

Question 26

state 3 facts about the medullary cardio-vascular centre

Answer 26

1. the neurones receive input from the various baroreceptors
2. input determines AP frequency from the CV centre
3. not just neural, but also alters angiotensin 2 generation and vasopressin secretion

Question 27

state the physiological responses to hypertension (high BP) - 9 steps

Answer 27

1. increased atrial pressure
2. kidneys increase urinary loss of Na+ and H2O
3. decreased plasma volume
4. decreased blood volume
5. decreased venous pressure
6. decreased venous return
7. decreased EDV
8. cardiac muscle decreases SV
9. decreased Q

Question 28

state 4 methods of treating hypertension

Answer 28

1. diuretics
2. beta-adrenergic receptor blockers
3. calcium channel blockers
4. angiotensin-converting enzyme (ACE) inhibitors

Question 29

explain how diuretics can be used to treat hypertension

Answer 29

increase the excretion of sodium and water, decreasing Q with no peripheral resistance

Question 30

explain how beta-adrenergic receptor blockers can be used to treat hypertension

Answer 30

reduce Q

Question 31

explain how calcium channel blockers can be used to treat hypertension

Answer 31

reduce the entry of calcium in vascular smooth muscle cells = weaker contractions = lower peripheral resistance

Question 32

explain how angiotensin-converting enzyme (ACE) inhibitors can be used to treat hypertension

Answer 32

final step in the formation of angiotensin 2 (a vasoconstrictor) is mediated by an ACE. blocking this enzyme causes vasodilation lowering peripheral resistance

Question 33

state the action of aldosterone in the renin-angiotensin system

Answer 33

slow acting steroid hormone that stimulates sodium re-absorption by kidney tubercles

Question 34

state the action of vasopressin (anti-diuretic hormone) in the renin-angiotensin system

Answer 34

rapid acting peptide produced by the pituitary gland which stimulates water re-absorption

Question 35

explain how the kidneys regulate blood pressure

Answer 35

intra-renal baroreceptors detect changes in stretching due to lower blood volumes which stimulates an increase in the production of Renin

Question 36

cardiac cells produce what to help with the renin-angiotensin system

Answer 36

atrial natriuretic peptide (ANP)

Question 37

atrial natriuretic peptide (ANP) has what 3 effects

Answer 37

1. inhibits Na+ reabsorption by kidney tubercle cells
2. acts on renal blood vessels to increase filtration rate causing sodium excretion
3. inhibits aldosterone action

Question 38

what 4 things happen within hours of blood loss ?

Answer 38

1. compensatory movement of interstitial fluid into capillaries to increase plasma volume
2. redistribution not replacement
3. slower effects: increase in thirst, decrease in Na+ and H2O secretion
4. mediated by hormone and kidney function (renin, angiotensin, and aldosterone)

Question 39

what happens within days of blood loss

Answer 39

1. erythropoiesis

2. haematopoiesis

Question 40

state the 4 steps (in order) of the cardiac cycle

Answer 40

1. isovolumetric ventricular contraction
2. ventricular ejection
3. isovolumetric ventricular relaxation
4. ventricular filling

Question 41

state 3 characteristic about the stage of the cardiac cycle - isovolumetric ventricular contraction (step 1)

Answer 41

1. during 1st part of systole, ventricles are contracting, but all valves are closed so no blood is ejected
2. ventricle walls develop tension + squeeze blood they enclose raising BP
3. as blood is incompressible, ventricle fibres can’t shorten so is termed isometric

Question 42

state 2 characteristic about the stage of the cardiac cycle - ventricular ejection (step 2)

Answer 42

1. once pressure in ventricles exceeds that in aorta and pulmonary trunk, SL valves open
2. blood is forced out aorta + pulmonary trunk as the contracting ventricle muscles shorten

Question 43

state 2 characteristic about the stage of the cardiac cycle - isovolumetric ventricular relaxation (step 3)

Answer 43

1. during 1st part of diastole, ventricles begin to relax and the SL valves close
2. at the same time, AV valves are closed so no blood is entering or leaving the ventricles

Question 44

state 3 characteristic about the stage of the cardiac cycle - ventricular filling (step 4)

Answer 44

1. AV valves open and ventricular filling occurs as blood flows in from atria
2. atria contraction occurs at end of diastole, after most ventricular filling has occurred
3. ventricles receive approx 80% throughout diastole before the atria contract