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Excretion Continued. Composition of Urine. The kidneys remove waste from the plasma and concentrate them in the urine Ratio of the concentration of substances in urine to concentration of substances in plasma on next slide (ratios, not amounts):. Urination. - PowerPoint PPT Presentation
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Excretion Continued
Composition of Urine
The kidneys remove waste from the plasma and concentrate them in the urine
Ratio of the concentration of substances in urine to concentration of substances in plasma on next slide (ratios, not amounts):
Urine Plasma
Na+ 1 1K+ 12 1CA2+ 1 1Mg2+ 5 1H2PO4-HPO4
2-25 1
glucose 0 1urea 70 1uric acid 14 1
Urination
As bladder fills, stretch receptors send impulses to spinal cord
Impulses from spinal cord cause bladder to contract and urine is released
Usually this reflex is controlled by the brain
Regulatory functions of the kidney 1: water balance
Blood volume (Water balance) Blood volume is directly controlled by kidneys Increased reabsorption of water, increased
blood volume Decreased reabsorption of water, decreased
blood volume Combination of hormones and nervous system
Hormonal control
ADH = anti-diuretic hormone Released by posterior pituitary gland Causes upper DCT and collecting duct
to be more permeable to water at the DCT (more water is reabsorbed, which can increase or maintain blood volume)
Changes in OP detected by osmoreceptors in hypothalamus
Alcohol inhibits release of ADH because it is a diuretic
Brain break!!!
Hormonal control cont’d
Aldosterone (hormone) Released by adrenal gland (on
top of kidney) Causes increased reabsorption
of Na+ from DCT This causes blood to be
hypertonic, causing more water to be reabsorbed into blood from the nephron
Juxtaglomerular Apparatus and BP
Region of afferent arteriole that monitors BP Increase in fluid loss will result in lowered BP If BP is too low for glomerular filtration, the
juxtaglomerular cells release renin (enzyme) Renin stimulates the conversion of
Angiotensinogen (from liver) to Angiotensin
Angiotensin causes vasoconstriction and stimulates the release of aldosterone from the adrenal cortex
Vasoconstriction will help increase BP Aldosterone causes increase in Na+
Increased Na+ retention results in increased blood volume which will also increase BP
Juxtaglomerular Apparatus and BPCont’d
Regulatory functions of the kidney 2: Maintenance of
pH Chemoreceptors in the carotid and aortic
bodies stimulate the respiratory centre when blood pH decrease
But resp. centre can only deal with minor fluctuations in pH
Kidneys help maintain the blood’s constant pH If blood pH decreases, H+ ions are excreted
with ammoniaNH3 + H+ NH4
+ (excreted)
And bicarbonate ions are reabsorbed:
HCO3- + H+ H2CO3
If blood is too basic (alkaline), less NH4
+ will be excreted and less HCO3
- will be reabsorbed Phosphate will also buffer blood