Cardiovascular Physiology

Question 1

what is the role of the heart

Answer 1

• delivers O2 to respiring tissues
• removes CO2 and waste products of metabolism
• deliver hormones to sight of action
• central to homeostasis

Question 2

How much oxygen and carbon dioxide does the heart transport /min

Answer 2

• delivers 250 ml O2 /min
• removes 200 ml CO2 / min

Question 3

• weight of heart
• how man beats / day
• how much blood pumped / day

Answer 3

• 200-425g
• 100,000 beats /day
• 7,000 litres blood /day

Question 4

how does number of heart beats a day relate to size of an organism

Answer 4

• the smaller the organism the larger the number of heartbeats s day

Question 5

where does the apex (base) of the heart sit

Answer 5

the top of the 5th rib down
(5th intercostal space)

Question 6

name the heart valves and the arteries/ veins, describe where they are

Answer 6

• superior vena cava (top left)
• aorta (top right)
• pulmonary artery (under aorta)
• pulmonary veins (under pulmonary artery)
• inferior vena cava (bottom left)
• pulmonary valve (top left)
• tricuspid valve (bottom left)
• aortic valve (next to pulmonary valve)
• mitral valve (right)

Question 7

describe the details of a systole and diastole

Answer 7

SYSTOLE
- 70 ml blood leaves each ventricle
- 300 ms

DIASTOLE
- lasts 550 ms
- filling occurs in first 100-200 ms

Question 8

what is normal:
- heart rate
- stroke volume
- cardiac output

Answer 8

• 70 bpm
• 70 mL /beat
• 5 L /min

Question 9

how do you calculate cardiac output

Answer 9

cardiac output = stroke volume X heart rate

Question 10

what is Starlings law of the heart?

Answer 10

energy of contraction is s function of the length of the cardiac muscle fibres

the larger the blood volume, the larger the stretch of the muscle, therefore the larger the force

Question 11

how is the heart stimulated to beat

Answer 11

• the heartbeat is myogenic - initiated within itself
• signal from SA node (pacemaker cells)
• travels through atrial muscle to AV notes
• travels through Purkinje fibres of Bundle of His
• then spreads through myocardium

Question 12

what causes depolarisation in the heart

Answer 12

• reduced K+ concentration and increased Na+ permeability
• increased Ca2+ permeability

Question 13

what happens to induce the ionic pacemaker potential

Answer 13

• depolarisation occurs due to influx of calcium ions through T-type Ca2+ channels
• sodium influx through non-selective cation channels
• exiting of K+ ions through K+ channels

Question 14

what causes depolarisation of SAN

Answer 14

• slow influx of Na+ up to the threshold (-40mV)
• then rapid influx of Ca2+ ions up to +20mV
• influx of K+ for repolarisation

Question 15

what does ventricular myocyte refractory period depend on

Answer 15

• rapid depolarisation due to Na+ influx
• short repolarisation due to K+ efflux
• delay in repolarisation
  (Ca2+ entry via L-type channels)
• rapid repolarisation due to K+ efflux
• slow depolarisation

Question 16

what is the effect of the long refractory period of cardiac muscle

Answer 16

• prevents tetanus (sustained contraction) by ensuring the muscle cannot be re-excited before it is fully relaxed

Question 17

how are myocytes connected and what causes them to contract

Answer 17

• myocytes are connected through connexins
• contract due to entry of Ca2+

Question 18

what are the layers of the blood vessel from the inside out

Answer 18

• lumen
• tunica intima (interna)
• tunica media
• tunica adventitia

Question 19

what is blood flow/ resistance dependent on

Answer 19

1. length of blood vessels
   longer blood vessels means greater resistance
2. viscosity of blood
   blood with more solute provides more resistance
3. radius of blood vessels

Question 20

what is Ohms law (how to calculate blood flor)

Answer 20

blood flow (Q) = (P1 - P2) / R
P1 = pressure at the beginning
P2 = pressure at the end
R = resistance of the vessel

Question 21

what happens to blood flow at high velocities

Answer 21

• the layers of flow break up and become disordered
• the resistance of flow is raised
• leads to endothelial damage then arterial heart disease

Question 22

what types of molecules can travel through capillaries

Answer 22

• lipid soluble molecules e.g. O2 and CO2
• hydrophilic molecules via paracellular route
• Molecules < 60 kd

Question 23

describe the equilibrium of the extracellular fluid around capillaries
what determines the equilibrium?

Answer 23

• 3 litres plasma
• 10.5 litres intestinal fluid
• equilibrium determined by hydrostatic pressure and oncotic pressure

Question 24

how do you calculate filtration pressure

Answer 24

hydrostatic pressure - oncotic pressure

Question 25

why are veins referred to as capacitance vessels

Answer 25

- around 60-70% of the body's total blood volume is held in the venous system - they have high compliance (stretchy) - help regulate cardiac output by adjusting how much blood returns to the heart (venous return)

Question 26

what is the autonomic nervous system split into

Answer 26

- sympathetic - parasympathetic

Question 27

how does each branch of the ANS control the heart

Answer 27

sympathetic - increases heart rate - speeds up signal conduction - increases heart muscle strength parasympathetic - slows heart rate - slows signal conduction - no effect on contractility

Question 28

define the following: 1. chronotropic 2. dromotropic 3. inotropic

Answer 28

1. affects heart rate 2. affects signal conduction 3. affects heart contractility

Question 29

how does ANS affect the heartbeat

Answer 29

- sympathetic input makes the cells reach threshold faster - parasympathetic slows down this process

Question 30

how does the sympathetic nervous system affect blood vessels

Answer 30

- it releases noradrenaline which causes vasoconstriction, therefore increasing resistance and venous return

Question 31

how do you calculate blood pressure and what is it controlled by?

Answer 31

BP = cardiac output X total peripheral resistance controlled by: heart rate, stroke volume, vessel diameter, blood volume

Question 32

how is blood pressure regulated in the long term

Answer 32

- low blood pressure causes renin to be released by kidneys - makes angiotensin II - causes vasoconstriction, increased retention of salt and water

Question 33

how is blood flow controlled locally (and extra quickly)

Answer 33

tissues can produce metabolites that override sympathetic signals and cause vasodilation to increase blood flow to wherever it is needed most

Question 34

what is the short term fix of a haemorrhage

Answer 34

baroreceptor reflex - BR sense drop in pressure, tell brain to increate heart rate and contractility, constrict arterioles to increase resistance, constrict veins to increase venous return

Question 35

what is the intermediate fix of a haemorrhage

Answer 35

- capillaries cause reabsorption of intestinal fluid - restores blood volume, makes blood more dilute

Question 36

what is the hormonal response to a haemorrhage

Answer 36

- renin makes angiotensin II - causes vasoconstriction, aldosterone release (kidneys retain salt and water) - stimulates thirst

Question 37

what is the long term fix of a haemorrhage

Answer 37

- erythropoietin made by kidneys, stimulates production of new red blood cells - ADH and ANP help control fluid balance

Question 38

what are the different classes of haemorrhage and their symptoms

Answer 38

I. <15%, no visible symptoms II. 15-30%, fast heart rate, pale skin III. 30-40%, low BP, shock, confusion IV. >40% life threatening, urgent resuscitation needed

Question 39

how does the body protect the heart during exercise

Answer 39

- limits filling time (reducing diastole) so the heart doesn't stretch too much, reduce efficiency and cause fluid fluid in lungs (pulmonary oedema)