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Excretion Continued

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.

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Excretion Continued

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  1. Excretion Continued

  2. 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):

  3. 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

  4. 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

  5. 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

  6. Brain break!!!

  7. 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

  8. 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

  9. Juxtaglomerular Apparatus and BP Cont’d • 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

  10. 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 ammonia NH3 + H+ NH4+ (excreted)

  11. 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

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