Cardiac Output 2

Question 1

how will the parasympathetic nervous system impact the heart at rest

Answer 1

decrease heart rate but not effect on stroke volume

decrease Na+ current by inhibiting HCN channels

Question 2

intrinsic regulation

Answer 2

CVS is a closed system
amount of blood returning must = vol. blood ejected
Venous return = Cardiac Output

Question 3

frank-Starling law

Answer 3

hearts intrinsic ability to adapt to changes in blood volume

greater degree of stretch = greater force of contraction of myocytes

Question 4

how did otto frank and Ernest H Starling investigate the law

Answer 4

independent experiments investigating effects of filling pressure on stroke volume

Question 5

mechanics of starling law

Answer 5

Actin and myosin are brought together as myocardium is stretched
– increased filling increases the stretch
increased overlap = more cross bridges formed -> more force made

Question 6

the muscle stretch relationship with cross bridge relationship is similar to

Answer 6

force-length

Question 7

preload

Answer 7

umbrella term to describe ventricular filling during diastole
– it is a catch term all to describe the end diastolic volume

Question 8

what is ventricular filling affected by

Answer 8

the pressure in the atria, venous pressure, gravity and the volume of blood in the circulation

Question 9

what will ventricular filling impact

Answer 9

stroke volume and cardiac output

Question 10

great veins function

Answer 10

capacitance vessels for the storage of blood

– veins contain 60-70% of total blood volume at any given time

Question 11

how does increased blood volume change venous pressure and preload

Answer 11

increased central venous
pressure and hence increased preload
– equally an increased venous tone will also increase the central venous pressure

Question 12

how does gravity affect the blood returning to the heart

Answer 12

blood returning to the heart has to work against gravity

e.g. arterial blood to the brain

Question 13

when upright, what factor is gravity for venous return and what is it the basis for

Answer 13

this is negative factor for venous return

– this is the basis for postural hypotension on standing

Question 14

how is venous return affected in supine position

Answer 14

In the supine position venous return is increased
– this can contribute to pulmonary congestion and orthopoea (breathlessness when
lying flat) in heart failure

Question 15

where do large veins pass through in limbs

Answer 15

• In limbs large veins pass between muscle blocks and are compressed as the muscle contracts
– to a lesser extent this happens as an adjacent artery pulsates

Question 16

how does compression in veins affect blood distribution

Answer 16

This compression displaces the blood and the presence of the valves
mean it must go back toward the heart
– think of squeezing a tube of toothpaste

Question 17

how does the thoracic and abdominal pressure change during inspiration

Answer 17

diaphragm flatten
raises abdominal pressure
lowers thoracic pressure
blood from abs to thorax

Question 18

how does the thoracic and abdominal pressure change during inspiration

Answer 18

thoracic pressure increases
abdominal pressure decreases
stays below abdomen in legs

Question 19

how do muscle and thoracic pump contribute to cardiac output in exercise

Answer 19

increase cardiac output in exercise

Question 20

The Starling Law of the heart increases stroke volume by

Answer 20

changing the orientation of the fibres

Question 21

what do iontropes increase and how

Answer 21

increase contractility by changing

Ca2+ signalling

Question 22

what do changes in preload effect

Answer 22

the filling of the ventricle

– as preload increases so does filling

Question 23

how will increased afterload affect the cardiac output

Answer 23

decrease cardiac output short term

Question 24

as the stroke volume drops …

Answer 24

the end systolic volume rises
– atrial filling remains unchanged
– the end diastolic volume is increased

Question 25

Increased end diastolic pressure, increases …

Answer 25

increases stretch of the ventricles
leading to a more forceful contraction
– cardiac output is maintained at greater work

Question 26

typical daily water intake

Answer 26

~2.5 L most lost via kidney

Question 27

how is water intake categorised

Answer 27

body water compartments
intracellular - 67%
extracellular 33%

Question 28

Physiological control of blood volume

Answer 28

renin-angiotensin system
Antri-diuretic hormone
Atrial Natriuretic Peptide

Question 29

RAS

Answer 29

Ang II - potent vasoconstrictor (increases resistance)
– stimulates aldosterone, increasing Na+ and water reabsorption from urine.
– net effect is expansion of blood volume and increase in blood pressure

Question 30

ADH

Answer 30

released in response to high osmolality and/or low blood volume
– drives water reabsorption from kidney (decreases diuresis)

Question 31

Atrial Natriuretic Peptide (ANP)

Answer 31

one of many natriuretic peptides (includes brain or BNP)

– opposite of the other two, inhibits salt reabsorption so promotes salt and water loss

Question 32

heart failure

Answer 32

inability to maintain cardiac output
decrease cardiac output = decreased blood pressure
activate baroreceptor reflex
SNS induced increase in renin-angiotensin system

Question 33

when there is heart failure how does the problem try to be address by activating SNS induced ATS

Answer 33

maintain stroke volume by volume expansion

will be a point where no further volume expansion can maintain stroke volume

Question 34

excess blood volume

Answer 34

increased blood volume stretches atria activating sensory afferents to medulla
decrease SNS = less RAS, ADH greater filtration in kidney
also triggers release of ANP and BNP