 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):

UrinePlasma Na + 11 K+K+ 121 CA Mg H 2 PO 4- HPO glucose01 urea701 uric acid141

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

Endocrine Control (use your handout)  Hormones speed up or slow down certain body functions – long term adjustments as opposed to the the nervous system which makes short term adjustments.

Posterior Pituitary: below hypothalamus  Connected to hypothalamus by nerve tracts  Secretes hormones that were produced in the hypothalamus and stored here.

Anterior Pituitary:  Not connected to posterior pituitary  Produces its own hormones but is controlled by hypothalamus  Hypothalamus produces releasing hormones which cause the anterior pituitary to secrete specific hormones  These hormones may affect body tissues or other endocrine glands  Thus, the anterior pituitary and the hypothalamus are considered the neuro-endocrine control center  Anterior pituitary considered the master gland

Adrenal: on top of kidneys  No connection exists between the adrenal cortex and adrenal medulla  Adrenal glands are controlled by both nervous system and endocrine system  Ultimate control is by hypothalamus (nervous)

adrenal medulla: inner portion  secretes adrenalin and noradrenalin (epinephrine and norepinephrine)  initiates “Fight or Flight” response  metabolic rate  heart and breathing rate  blood flow to digestive system  blood flow to muscles

adrenal cortex: outer portion  Secretes cortisol (promotes healing)  Secretes aldosterone for Na + reabsorption

Brain break!!!

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

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 BP Cont’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 ammonia NH 3 + H +  NH 4 + (excreted)

 And bicarbonate ions are reabsorbed: HCO H +  H 2 CO 3  If blood is too basic (alkaline), less NH 4 + will be excreted and less HCO 3 - will be reabsorbed  Phosphate will also buffer blood