Physiology Flashcards
Why does pulse pressure increase during acute exercise?
increased CO - increased systolic BP, vasodilation - decreased systemic vascular resistance - decreases diastolic BP
Cerebral perfusion pressure = ?
MAP - intracranial pressure
What is the role of atrial contraction?
complete end diastolic volume
What is a negative chronotropic effect?
decreases HR
What decreases resistance to blood flow?
increased radius of blood vessel
Why is a long refractory period important in cardiac muscle?
prevents tetanic contraction (sustained muscle contraction) - would cause cardiac arrest
How is the brain protected from fluctuating ion levels in the blood?
blood brain barrier impermeable to ions
Where is ADH/vasopressin stored?
posterior pituitary gland
What forces favour transcapillary filtration?
capillary hydrostatic pressure and interstitial fluid osmotic pressure
How do baroreceptors prevent postural hypotension?
decreased MAP - reduces rate of firing in baroreceptors - sympathetic tone to the heart increases - increases HR and SV - sympathetic constrictor tone increases - increases systemic vascular resistance - increases venous return - increases SV
What happens when systolic press > cuff pressure > diastolic pressure?
blood flow becomes turbulent - recorded systolic BP = 1st Korotkoff sound - recorded diastolic BP = 5th Korotkoff sound
What is the treatment for shock?
ABCDE, high flow oxygen - 15L/min in a non-rebreather mask, volume replacement -bloods or fluid, inotropes for cardiogenic shock - increase force of contraction, immediate chest drain for a tension pneumothorax, adrenaline for anaphylactic shock, vasopressors for septic shock
What is obstructive shock?
increased intra-thoracic pressure - decreased venous return - decreased EDV - decreased SV - decreased CO - decreased BP
What causes vasomotor tone?
tonic discharge of sympathetic nerves
What happens during isovolumetric ventricular relaxation?
ventricles relax around a certain volume of blood (ESV) atrial pressure > ventricular pressure - AV valves open
What stimulates secretion of ADH?
reduced extracellular fluid volume, increased extracellular fluid osmolarity (monitored by osmoreceptors)
What is the role of aldosterone?
acts on the kidneys - increase sodium and water retention - increases plasma volume - increases BP
What covers the actin binding site on the myosin head
troponin-tropomyosin
What causes vasodilation of skeletal and cardiac arterioles during acute exercise?
adrenaline released, decreased local PO2 and increased local PCO2 which overrides sympathetic stimulation - to match supply to demand
How is the cerebral blood flow autoregulated?
MAP rises = vasoconstriction to limit blood flow
MAP falls = vasodilation to maintain blood flow
What triggers the power stroke?
cross bridge formation pulls actin filaments over myosin filaments
What causes the dicrotic notch in the aortic pressure curve?
valve vibration as aortic and pulmonary valves close
What are the effects of endothelial produced vasoconstrictors?
pro-thrombotic, pro-inflammatory, pro-oxidants
What is a positive chronotropic effect?
increases HR
How does adrenaline causes vasoconstriction?
acts on alpha adrenoceptors
What occurs during isovolumetric contraction?
ventricular pressure > atrial pressure - AV valves shut - first heart sound - lub - beginning of systole. aortic and pulmonary valves still shut - ventricles contracting around a certain volume of blood (EDV) - ventricular pressure rises steeply
What is the function of renin?
stimulates the formation of angiotensin I in the blood from angiotensinogen which is released from the liver
What arterioles have beta 2 adrenoceptors?
cardiac and skeletal muscle
What is neurogenic shock?
loss of sympathetic tone - massive venous and arterial dilation - decreased venous return and total peripheral resistance - decreased CO - decreased BP
What forces oppose transcapillary filtration?
capillary osmotic pressure and interstitial fluid hydrostatic pressure
What are the endothelial produced vasodilators?
histamine, bradykinin, nitric oxide
How does the sympathetic system increase HR?
increases rate of firing of SA node - slope of pacemaker potential increases - pacemaker potential reaches threshold quicker - frequency of APs increases – positive chronotropic effect (also decreases AV nodal delay)
What happens during passive filling?
atrial pressure > ventricular pressure - AV valves open - blood flows into ventricles
What is the aldosterone?
steroid hormone
What is hypovolemic shock?
loos of blood volume - decreased venous return - decreased EDV - decreased CO - decreased BP
What is tachycardia?
resting HR > 110
What is the result of increased sympathetic discharge on vascular smooth muscle?
vasoconstriction
What causes increased CO during acute exercise?
sympathetic nerve active increases - HR and SV increases
What causes adrenaline release?
sympathetic stimulation
What causes an increased resistance to blood flow?
increased blood vessel length, increased blood viscosity
What are the endothelial produced vasoconstrictors?
serotonin, thromboxane A2, leukotrienes and endothelin
What happens if cardiac myocytes are stretched too much?
stroke volume falls, doesn’t happen in a normal heart
What is cardiogenic shock?
sustained hypotension caused by decreased cardiac contractility - decreased SV - decreased CO - decreased BP
What is the role of the nitric oxide?
vasodilator - diffuses into smooth muscle cells - cGMP acts as a second messenger for signalling smooth muscle relaxation
Which arterioles have alpha adrenoceptors?
skin, gut and kidney
What is Starling’s Law of the Heart/Frank-Starling mechanism?
greater venous return = greater end diastolic volume = greater stretch in myocytes = greater stroke volume
What is a positive inotropic effect?
increases force of contraction
What is the function of ADH?
acts in kidney tubules to increase reabsorption of water - increases extracellular plasma volume - increases CO - increases BP causes vasoconstriction - increased SVR - increased BP - small effect in normal people - important in hypovolemic shock/haemorrhage
What is stroke volume?
volume of blood ejected by each ventricle per heart beat
What is the result of increase intracranial pressure?
decreases cerebral perfusion pressure - decreases cerebral blood flow
What causes vasoconstriction in kidneys, gut and skin during acute exercise?
sympathetic stimulation and adrenaline released
What is the role of the AV node?
slows conduction velocity to delay impulse slightly to allow atrial systole to precede ventricular systole
What is the effect on increased local PCO2 on vascular smooth muscle?
vasodilation
What is the effect of sympathetic stimulation on ventricular muscle?
positive inotropic effect - activation of calcium channels - greater calcium influx, reduces duration of systole, increases duration of diastole
What is cardiac output?
volume of blood pumped by each ventricle per minute
What is vasoactive shock?
release of vasoactive mediators - massive venous and arterial dilation and increased capillary permeability - decreased venous return and total peripheral resistance - decreased CO - decreased BP
What are the special adaptations of the coronary circulation?
oxygen demand of the cardiac muscle is high, high capillary density, high basal blood flow, high oxygen extraction at rest
How does adrenaline cause vasodilation?
acts on beta 2 adrenoceptors
What is the jugular venous pulse?
occurs after right atrial pressure waves - no valves from inferior jugular vein to right atrium
What is the role of the Renin-Angiotensin-Aldosterone system?
regulation of plasma volume and SVR and hence MAP
What is shock?
inadequate tissue perfusion and oxygenation - anaerobic metabolism and accumulation of metabolic waste products - cellular failure
What areas of the heart are supplied by the parasympathetic nervous system?
SA node and AV node
How does parasympathetic stimulation decrease HR?
cell hyperpolarises and the slope of the pacemaker potential decreases - longer to reach threshold - AP frequency decreases - negative chronotropic effect
Where is the SA node located?
upper right atrium close to where the superior vena cava enters
What type of shock is caused by a tension pneumothorax?
obstructive shock
Where is ACE (angiotensin converting enzyme) produced?
vascular endothelium
What is the result of decreased local PO2 on vascular smooth muscle?
vasodilation
What is the role of angiotensin II?
causes systemic vasoconstriction - increases SVR - increases BP stimulates thirst and ADH release - increases plasma volume - increases BP stimulates aldosterone release from the kidneys
How is renin released?
from the kidneys, stimulated by renal artery hypotension, stimulation of renal sympathetic nerves, decreased sodium concentration in renal fluid
What tone dominates in the heart under resting conditions?
vagal/parasympathetic
What is the effect of sympathetic stimulation on the heart?
increases heart rate, decreases AV nodal delay, increases force of contraction
What is bradycardia?
resting HR < 60
What happens when cuff pressure is greater than systolic pressure?
flow blocked - no sound
What areas of the heart are supplied by the sympathetic nervous system?
SA node, AV node and myocardium
What are the chronic CVS responses to exercise?
reduces BP, reduces sympathetic tone, increased parasympathetic tone to the heart, cardiac remodelling, reduction in plasma renin levels, improved endothelial functions - increased vasodilators and decreased vasoconstrictors, decreased arterial stiffening
What are the compensatory mechanisms to maintain BP in response to haemorrhage?
tachycardia via baroreceptor reflex - small volume pulse due to decreased SV - cool peripheries due to increased SVR via baroreceptor reflex
How can vomiting, diarrhoea and excessive sweating cause hypovolemic shock?
decreased extracellular fluid - decreased plasma volume
Where is the AV node located?
at the base of the right atrium
What is the Circle of Willis?
basilar (formed by two vertebral arteries) and carotid arteries anastomose together to form the circle of Willis, major cerebral arteries arise from the circle of Willis
What are the effect of endothelial produced vasodilators?
anti-thrombotic, anti-inflammatory, anti-oxidants
What is afterload?
resistance into which the heart is pumping
What provides mechanical adhesion between cardiac myocytes?
desmosomes within intercalated discs
What happens after acute exercise?
post exercise hypotensive response
CO = ?
SV x HR
What is the function of ACE (angiotensin converting enzyme)?
converts angiotensin I to angiotensin II
What is the result of decreased sympathetic discharge on vascular smooth muscle?
vasodilation
What could a raised jugular venous pulse indicate?
heart failure
How does the electrical impulse spread between cardiac myocytes?
via gap junctions at intercalated discs through low resistance protein channels
What is the result of sheer stress on blood vessels?
dilatation of arterioles - sheer stress in arteries upstream due to increased flow - sheer stress on vascular endothelium activates nitric oxide synthase - produces nitric oxide from L-arginine - vasodilation upstream
What is the effect of myogenic response to stretch on vascular smooth muscle?
MAP rises = vasoconstriction to decrease blood flow
MAP falls = vasodilation to maintain blood flow
What happens if the afterload increases?
fall in stroke volume initially until end diastolic volume increases
What is metabolic hyperaemia?
increased local H+ concentration/decreased pH, increased extracellular fluid K+ concentration, increased osmolality of ECF , increased adenosine released from ATP
What happens during ventricular ejection?
ventricular pressure > arterial pressure - aortic and pulmonary valves open arterial pressure > ventricular pressure - aortic and pulmonary valves shut - second heart sound - dub - beginning of diastole
Why is arterial pressure not zero during diastole?
walls of major arteries have elastic fibres - recoil when heart relaxes - keeps blood moving forward
What neurotransmitter is released by the parasympathetic system and what does it act on?
acetylcholine acting on muscarinic 2 receptors
What is the result of chronic increased afterload?
ventricular hypertrophy
How does blood flow increase to active regions of the brain?
rise in K+ concentration - efflux from neurones
What is the effect of temperature on vascular smooth muscle
cold = vasoconstriction warm = vasodilation
What is the effect of metabolic hyperaemia on vascular smooth muscle?
vasodilation
How is the actin binding site on the myosin head exposed?
calcium influx occurs during the plateau phase of AP during systole - calcium is released from sarcoplasmic reticulum in presence of extracellular calcium - calcium binding causes a conformational change - binding site exposed
Where is antidiuretic hormone (ADH)/vasopressin produce?
hypothalamus
What is the function of natriuretic peptides?
cause excretion of salt and water from the kidneys - reduces blood volume - reduces BP decreases renin release act as vasodilators - decreased SVR - decreased BP
What causes release of natriuretic peptides?
cardiac distension or neurohormonal stimuli
stoke volume = ?
end diastolic volume - end systolic volume
What neurotransmitter is released by the sympathetic system and what does it act on?
noradrenaline acting on beta 1 adrenoceptors
What is the role of calcium ATPase?
return calcium to sarcoplasmic reticulum during diastole
What are the 5 stages of the cardiac cycle?
- passive filling 2. atrial contraction 3. isovolumetric contraction 4. ventricular ejection 5. isovolumetric ventricular relaxation
