Physiology

Question 1

what is stroke volume?

Answer 1

the volume of blood ejected by each ventricle per heart beat

SV = EDV-ESV

Question 2

what is edv determined by?

Answer 2

venous return

Question 3

what does edv determine?

Answer 3

preload

Question 4

what is afterload?

Answer 4

the resistance into which the heart is pumping

Question 5

what is the CO?

Answer 5

the volume of blood pumped by each ventricle per minute

CO=SVxHR

Question 6

what is MAP?

Answer 6

the average bp during a single cardiac cycle, which involves contraction and relaxation of the heart (minimum 60mmHg)

Question 7

3 MAP equations

Answer 7

1. MAP = 2/3 DBP-SBP
2. MAP = DBP +1/3 (SBP-DBP)
3. MAP = TPR x CO

Question 8

what is TPR?

Answer 8

this is the sum of resistance of all peripheral vasculature in the systemic circulation

Question 9

what is the major vessel or resistance?

Answer 9

arterioles

Question 10

what does increased venomotor tone do?

Answer 10

increases venous return, SV, MAP

Question 11

what does increased vasomotor tone do?

Answer 11

increases TPR and MAP

Question 12

humoral agents that cause vasoconstriction?

Answer 12

Leukotrines, thromboxane A2, serotonin, endothelin

Question 13

humoral agents that cause vasodilatation?

Answer 13

histamine, bradykinin, nitric oxide

Question 14

local metabolite changes which cause vasodilatation in an organ?

Answer 14

decreased PO2
increased PCO2
increased local [H+]
increased extra cellular K+
increased osmolarity of ECF
adenosine (from ATP)

Question 15

excitation in SA node cells

Answer 15

1. decrease in K efflux, superimposed on slow Na+ influx until threshold is reached
2. when this is reached, rising phase of AP is caused by Ca2+ influx
3. falling phase is caused by K+ efflux

Question 16

AP in contractile myocytes

Answer 16

1. rising phase caused by fast Na+ influx
2. plateau phase by Ca2+ influx
3. falling action caused by inactivation of Ca2+ channels and K+ efflux

Question 17

parasympathetic neurotransmitter?

Answer 17

acetylcholine acting through M2

Question 18

sympathetic neurotransmitter?

Answer 18

noradrenaline, acting through B1

Question 19

what allows the refractory period to occur?

Answer 19

in the plateau phase, Na+ channels are depolarised (closed)

and in descending phase, K+ channels are open so membrane cannot be depolarised

Question 20

valves on LHS of heart?

Answer 20

mitral, aortic

Question 21

valves on RHS of heart?

Answer 21

tricuspid, pulmonary

Question 22

baroreceptor reflex

Answer 22

• correction of a fall in MAP, due to gravity

- sympathetic constrictor tone increases (increased TPR, venous return, SV, HR)

Question 23

what does ANP do?

Answer 23

• released by muscle cells in response to atrial distension

- reduced blood volume, plasma volume and increases excretion of Na and H2O by kidneys

Question 24

what does ADH do?

Answer 24

• release stimulated by decreased ECFV and increased osmolarity
• increases water reabsorption (concentrates urine), increasing CO and BP
• causes vasoconstriction of blood vessels

Question 25

extrinsic control of vascular smooth muscle?

Answer 25

• vasomotor tone

- hormones (adrenaline - alpha dilate, beta constrict, angiotensin II and ADH)

Question 26

intrinsic control of vascular smooth muscle?

Answer 26

• local metabolites
• local humoral agents
• physical (e.g temp, stress, myogenic response)