1 Flashcards
(96 cards)
Describe the baroreceptors reflex with high blood pressure
Baroreceptors are activated by stretch, increased firing rate causes increased parasympathetic output via vagus nerve to lower heart rate and blood pressure
Where are baroreceptors located?
Aortic arch and carotid sinus
Describe the baroreceptors reflex with low blood pressure
Decreased firing rate causes increased sympathetic outflow (and inactivated vagal neurones) causing increased CO and SV to raise BP
Where is ANP released from and what is its purpose?
Released from Atrial myocytes in response to stretch and high blood volume. Has opposing effect of aldosterone;
Dilate afferent and constrict efferent arteriole to increase GFR
Increase blood flow through vasa recta to wash out Na and urea
Decrease Na reabsorption in DCT
Define sepsis
SIRS + documented/presumed infection
Describe SIRS
Systemic inflammation, organ dysfunction and failure
On examination: pale, cold extremities, temperature, high HR and RR, low BP
Characterised by;
HR greater than 90
Resp rate greater than 20
WBC less than 4x10^9 or greater than 12x10^9
Temperature greater than 38 or less than 36
Where are peripheral and central chemoreceptors located?
Carotid and aortic bodies
Ventral surface of the medulla
What is the function of central chemoreceptors
Respond to changes in H+ concentration and CO2 in brain ECF
When local H+ rises central chemoreceptors stimulate the respiratory centre to increase ventilation
NB: CO2 can cross BBB but bicarbonate cannot as easily
What is the function of peripheral chemoreceptors
Respond to changes in O2, CO2 and pH.
In metabolic acidosis causes hyperventilation
In respiratory acidosis CSF pH is corrected quickly so stimulus for breathing relies entirely on peripheral chemoreceptors until renal compensation is complete (3-5 days)
What is the main action of ACE inhibitors?
Inhibit the conversion of angiotensin I to angiotensin II
What are the normal actions of angiotensin II
Causes aldosterone release from adrenal cortex
Vasoconstriction to increase blood pressure
Acts at NHE in PCT to stimulate Na reabsorption
Stimulate posterior pituitary to release ADH
Discuss the common side effects of ACE inhibitors
A persistent dry cough, thought to be as a result of increased bradykinin (angiotensin 2 normally breaks this down)
Cough caused by pro inflammatory mechanisms
Increased bradykinin may also cause angiooedema
Explain how hyperkalaemia may result from use of ACE inhibitors
ACE inhibitors reduce production of aldosterone. Normally aldosterone increases Na+ reabsorption and so K+ excretion. Reduced levels of aldosterone mean k+ may be retained
Describe afterload
Load that heart must eject blood against, related to aortic pressure and ventricular wall stress
In what situations will after load be increased
Aortic stenosis
High systemic vascular resistance
What changes as a result of increased afterload
Increased end systolic volume and decreased stroke volume
Define preload
Initial stretching of cardiac myocytes prior to contraction, related to sarcomere lengths
In what situations would you get increased preload
High CVP
High ventricular compliance
Low HR (increased ventricular filling time)
How do you work out CO
HR x SV
How do you calculate SV
EDV-ESV
How do you calculate BP
CO x TPR
What is EDV
Volume of blood in R/L ventricle at end if diastole just before systole
What is ESV
Volume of blood left in ventricle at end of systole
Define systolic pressure
Maximal pressure in aorta at end of contraction
