Blood pressure and the kidneys Flashcards
What is the major electrolyte of ECFV?
→ Na
If you add Na+ to the blood why doesn’t hypernatremia happen (Increase in Na+ concentration)?
→ If Na+ increases
→ an equivalent amount of water is drawn with it
Equation for BP?
→ CO x TPR
What does an increase in blood volume lead to?
→ ventricular filling and increased stroke volume (Starlings law)
→ Increase cardiac output
→ Increase blood pressure
What is long term control of blood pressure?
→ regulating Na levels
What is short term control of blood pressure?
→ Baroreceptors
Flow chart for changes in Na balance
Changes in Na balance ↓ Changes in osmolarity ↓ ADH release ↓ H2O moves through ADH stimulated aquaporin channels in collecting duct
Why does resuscitation fluid not cause hypernatremia?
→ It is isotonic
→ Na+ cannot cross cell membranes
→ fluid will expand the ECFV
What is the effect of retained sodium the same as?
→ adding isotonic fluid
→ It draws an equivalent amount of water with it
→ Increase in blood pressure
How is Na+ sensed in the body?
→ Indirectly
→ A change in ECFV occurs (up or down)
→ Stretch and pressure receptors in CVS detect this
What are the afferent pathways for detecting indirect changes in Na+?
→ Cardiac volume receptord
→ Baroreceptors
→ Renal arterial pressure
What are the efferent pathways for responding to changes in Na+?
→ Neuronal : sympathetic nervous system
→ Hormonal : RAAS, ANP
→ Haemodynamic : + or - GFR, pressure natriuresis
How is sodium taken in the body?
→ Diet 10 to > 400 mMol a day
How is sodium removed from the body?
→ Sweat/faeces
→ Regulated renal excretion
What are mammals designed to do with Na+?
→ Conserve sodium
What is the Na+ conserving system called?
→ RAAS
How does RAAS work?
1) A loss of blood pressure stimulates the secretion of renin
2) Renin acts on a liver substrate called angiotensinogen and converts it to angiotensin I
3) Angiotensin I is converted to angiotensin II by angiotensin converting enzyme ( epithelial cells of the lung)
4) Angiotensin II acts on the AT1R receptor on the adrenal cortex and stimulates it to release aldosterone
5) Increases Na+ reabsorption in the nephron and increases K+ secretion
6) vascular smooth muscle contracts (vasoconstriction and BP increases)
Where is the macula densa?
→ The region of contact between the afferent arteriole and the distal tubule of the same nephron
What are renin secreting juxtaglomerular cells?
→ Modified smooth muscle cells along the afferent arteriole
What is renin secreted in response to?
1) decrease in BP and blood volume and renal blood flow detected by afferent arteriole mechanoreceptors
2) decrease Na levels at the macula densa
3) Sympathetic nerve activation of beta 1 adrenoceptors