the renin-angiotensin-aldosterone system Flashcards
the kidneys
- Represent 1% of body mass, but receive 20-25% of total resting cardiac output
- Around 180 litres of filtrate are processed per day
- Regulation of pH
- Production of hormones
- Removing of metabolic waste products
- Activation of vit D
- Regulation of osmolarity
- Regulation of salt concentrations
- Regulation of extracellular fluid volume
- The functional unit of the kidney is the nephron
juxtaglomerular apparatus
- structure where afferent arteriole makes contact with DCT
- involved in blood pressure regulation
- found at vascular pole of each renal corpuscle
- made up of: Macula Densa (DCT), juxtaglomerular cells, extraglomerular mesangial cells
Macula Densa
- accumulation of columnar calls within DCT.
- monitor Na+ concentration in the forming of urine, regulate Glomerular Filtration Rate GFR and release of renin from juxtaglomerular cells
renin
- a proteolytic enzyme synthesised by granular cells (aka juxtaglomerular cells) in the wall of glomerular afferent arterioles.
- renin cleaves angiotensinogen to angiotensin I
why is renin released
function is to raise BP via other mediators.
1) in response to decreased arterial pressure (body acts like low BP is caused by fluid loss)- there are baroreceptors in the afferent arteriole.
2) decrease in sodium load to distal tubule- macula densa responds to sodium concentration
3) direct stimulation by SNS- mediated by the B1 adrenergic receptors
Angiotensin Converting Enzyme
- function is to produce angiotensin II
- ACE is expressed in many tissues, including kidney but conversion largely occurs during transit through the lungs
- ACE inhibitors stop its function
angiotensin II (Ang II)
Ang II constricts resistance vessels, stimulates ADH release from the posterior pituitary, stimulates thirst, and promotes aldosterone release from the adrenal cortex.
aldoterone (Aldo)
- targets mostly principal cells in the renal tubule distal segments. promotes recovery of Na+ and osmotically obligated water from the tubule.
takes up to 48 hrs to work.
vasopressin is Anti diuretic hormone (ADH)
ADH is released from the posterior pituitary when tissue osmolarity rises or blood volume decreases.
its principal role is in ECF volume regulation through control of renal water retention.
if circulating levels are sufficiently high, it can vasoconstrict also
pathologies associated with high RRA
- can occur both chronically and acutely in response to decreases in blood flow to kidney. can occur physiologically but can also from pathological causes
what is hypertension HTN
- abnormal elevation of systolic/ diastolic blood pressure.
- BP>140/90mmHg.
generally asymptomatic for years - secondary hypertension is when a specific cause for HTN is found, hence secondary to an underlying disease process. e.g. renal disease 5%, Conn’s syndrome.
what is essential HTN
Primary (Essential) Hypertension
- cause unknown 95% cases
- can be benign (slowly progressive) or malignant (rapid onset, above 180/110)
activation of the Renin-Angiotensin- Aldosterone System (RAAS) as a cause of HTN
- this hormonal system is key regulator of BP, its activation promotes vasoconstriction through angiotensin II and sodium and water retention through aldosterone.
blood renin concentrations can be elevated in hypertensive patients who are white and aged under 55
hypotensive shock
a condition in which blood pressure is below the autoregulatory range for maintenance of cerebral and renal perfusion, such that consciousness is lost and vital organ perfusion critically impaired
shock (definition)
reduced perfusion of tissue, which results in impaired oxygenation of tissue.
