CVS 4 Flashcards
(31 cards)
What is MAP
DPB + 1/3 Pulse pressure
What is normal MAP at rest
93mmHg
Why is a balance between a MAP that is too high (above 115mmHg) or too low (below 60mmHg) needed?
- Pressure must be high enough to perfuse the internal organs
- Pressure must not be too high to damage the blood vessels or place an extra strain on the heart
What is the equation for MAP (physiological factors)
MAP = CO x TPR
What is TPR?
The sum of resistance of all peripheral vasculature in the systemic circulation
-arteries are the major resistance vessels (50% TPR)
What controls TPR?
Vascular smooth muscles (supplied by sympathetic nerve fibres). The neurotransmitter is norAd acting on a-adrenergic receptors
What is vasomotor tone?
Vascular smooth muscle is partially contracted at rest
What causes vasomotor tone?
A tonic discharge of sympathetic nerves resulting in continuous release or norAd
Describe the relationship between vasomotor tone and the autonomic nervous system
Increased sympathetic discharge will increase the vasomotor tone resulting in vasoconstriction = increase TPR and MAP
-No significant parasympathetic innervation of arterial smooth muscle, exceptions are the penis and clirtoris
What is the Baroreceptor reflex?
Immediate short term regulation of MABP
Where are baroreceptors located?
- Brainstem
- Glossopharyngeal nerve IX
- Hering’s nerve
- Vagus
- Carotid sinus
- Aorta
What type of mechanism are baroreceptors involved in?
Negative feedback: They act to minimise any disturbance to MAP (the controlled variable)
What is the effect baroreceptors have on decreased ABP?
-Decreased baroreceptor discharge
-Detected CV integrating centre in medulla of brain
- Decreased vagal activity, Increases HR, increases CO
-Increased cardiac sympathetic activity, increase SV, increase CO
-Increase in sympathetic constrictor tone= venoconstriction, increase SV (increase CO) vasoconstriction =increase TPR
ALL = INCREASE IN ABP
What is the effect baroreceptors have on decreased ABP?
-Increased baroreceptor discharge
-Detected CV integrating centre in medulla of brain
-increased vagal activity, decreases HR, decreases CO
-Decreased cardiac sympathetic activity, decreases SV, decreases CO
-Decreased in sympathetic constrictor tone, venodilation= decrease SV (decrease CO) vasoconstriction, vasodilation = decrease TPR
ALL = DECREASE IN ABP
When does baroreceptor firing decrease?
If high BP is sustained as they only respond to acute changes in BP
- Then baroreceptors ‘reset’ and will only fire again if there is an acute change above the new higher steady state level
- Therefore they cannot provide information about prevailing steady state blood pressure
What percent of body weight is water?
roughly 60%
What is total body fluid?
Total body fluid = ICF + ECF
what is ECFV?
Plasma volume (PV) + Interstitial Fluid Volume (IFV)
What is vasopressin?
(ADH) is a polypeptide hormone synthesised by the hypothalamus, stored in the posterior pituitary gland
What stimulated vasopressin secretion?
- Reduced extracellular fluid volume
- Increased extracellular fluid osmolarity
What is the normal osmolarity of ECF?
280milli-osmoles/L
What monitors plasma osmolarity?
Osmoreceptors (close to the hypothalamus)
-increased plasma osmolarity stimulates the release of ADH
What is ANP?
Atrial Natriuretic Peptide
- A 28 aa peptide synthesised and stored y atrial muscle cells
When in ANP released?
in response to atrial distension
