1.&Glomerular/Pressure&Filtration&

Transcription

1 Urine&Formation& Overall&Process&! Urine gets rid of wastes (NH 3, urea, uric acid, creatinine) and other substances (vitamins, penicillin, histamines) found in excess in the blood!! blood is filtered using pressure good and bad stuff enters nephron as filtrate!! good stuff is reabsorbed from filtrate into blood!! extra stuff and wastes fine tuning occurs to make urine! 1.&Glomerular/Pressure&Filtration& STEPS%OF%URINE%FORMATION% =movementfrombloodtonephron*! Blood enters the afferent arteriole and then the glomerulus 1.&Glomerular/Pressure&Filtration& =movementfrombloodtonephron*! Blood enters the afferent arteriole and then the glomerulus this increases BP into the glomerulus because capillaries are smaller than arterioles. increased BP forces water & small substances out of the blood and into the Bowman s capsule (start of nephron) fluid is now called filtrate.!

2 1.&cont d&! The filtrate contains: H 2 O, glucose, AA, salts, nitrogenous wastes!! Larger molecules remain in the now thicker capillaries they are taken away by the efferent arteriole which is narrower to keep pressure up in the glomerulus for filtration! 1.&cont d&! GlomerularFiltration Filterable Blood Components Water Nitrogenous wastes Nutrients Salts Nonfilterable Blood Components Blood cells and platelets Plasma proteins 1.&cont d&! Both filtrate and blood are isotonic! 2.&Tubular/Selective&Reabsorption& =movement from nephron to blood (peritubular capillary network PCN) - Occurs mainly in the proximal convoluted tubule!

3 2.&Tubular/Selective&Reabsorption& =movement from nephron to blood (peritubular capillary network PCN) - Occurs mainly in the proximal convoluted tubule! o Cells contain lots of protein carriers and mitochondria for active transport o microvilli for surface area for absorption! 2.&cont d&! Glucose, AA, some salts, little H 2 O return to blood by active transport (carrier proteins)! o Na + is actively reabsorbed and Cl - passively follows!! reabsorption of salts increases osmolarity of blood compared to filtrate water moves passively from tubule into blood.! 2.&cont d& At the proximal convoluted tubule: &Reabsorbed*filtrate* Non3reabsorbed* components* filtrate*components*! Most!water!! Nutrients!! Required!salts!! All!AA!&!glucose!!! Somewater! Mostnitrogenous wastes! Excesssalts(ions) 2.&cont The descending (down) limb of the Loop of Henle passively reabsorbs water.! 2.&cont d&(descending&loop&of&henle)&! water moves out for 2 reasons:! i. As solute is reabsorbed, water follows by osmosis (into PCN)! ii. Loop of Henle is in the renal medulla which is very salty (ECF full of NaCl and urea) water moves to establish equilibrium!

4 2.&cont d&(descending&loop&of&henle)&! By end of descending loop, much water has been reabsorbed filtrate is very concentrated (hypertonic to blood)! 2.&cont d&(ascending%loop&of&henle)& # The ascending (up) limb of the Loop of Henle reabsorbs salts (e.g. NaCl) first passively then actively # (permeable to salts only NOT water)# 2.&cont d&(ascending&loop&of&henle)& # The ascending (up) tubule of the Loop of Henle reabsorbs salt (e.g. NaCl) # (permeable to salts only NOT water)# o by the time filtrate reaches distal convoluted tubule it is isotonic to blood again! 3.&Tubular&Secretion& =movement from blood to nephron! Occurs in distal convoluted tubule by active transport

5 3.&cont d& excess substances in blood enter the filtrate (i.e. Creatinine, drugs, penicillin, H + )!! ph of blood is maintained by adjusting H + levels! 3.&cont d& 3.&cont d&! Now into the Collecting Duct some urea slips out and adds to solute concentration of renal medulla! causes more H 2 O to diffuse out of collecting duct into renal medulla if ADH is present!! Urine = filtered substances + substances not reabsorbed+ secreted substances Brought to urinary bladder via the ureter! Urination&! Stretchreceptorsin wallofbladder Sendimpulseswhen bladderfillsto250ml Motorimpulsesfrom spinalcord! Bladdercontraction! Sphinctersrelax END&of&Urine&Formation&

6 Regulation&of&Urine&Formation&! ADH = Antidiuretic hormone! Diuresis= increase urine formation! Antidiuresis= decreases urine volume when ADH present! Released from the posterior pituitary gland; made by hypothalamus! Cont d& Regulates reabsorption of water by increased permeability of collecting duct!! So, more water into blood! increases BP! Cont d&! If a person does not drink much water in a given day, posterior pituitary releases ADH, causing more water to be reabsorbed and less urine to form!! osmoreceptors in hypothalamus detect changes in osmotic pressure (amount of water) Cont d&&! alcohol inhibits ADH so need to urinate frequently water loss leads to dehydration (causes hangover symptoms)! if low, ADH is released water reabsorbed blood volume increases no more ADH!! =NEGATIVE FEEDBACK LOOP! Cont d&regulation& ALDOSTERONE:* =hormone produced by adrenal cortex of adrenal glands (on top of kidneys)

7 Cont d&regulation& ALDOSTERONE:* =hormone produced by adrenal cortex of adrenal glands (on top of kidneys) Regulates BP by adjusted blood volume! Increases Na + reabsorption at distal convoluted tubule this causes water to move out by osmosis so blood volume (BP) increases! BP sensors in the juxtaglomerular apparatus,=( region of contact between afferent arteriole and distal convoluted tubule)! Juxtaglomerular&Apparatus& BP sensors in the juxtaglomerular apparatus,=( region of contact between afferent arteriole and distal convoluted tubule)! o Detects low BP at glomerulus (BP too low to promote filtration)! Juxtaglomerular apparatus secretes renin (hormone) due to low BP! Causes constriction of blood vessels and release of Aldosterone from adrenal cortex! Aldosterone increases Na + reabsorption followed by reabsorption of water out of the nephron and into the blood! effects: 1 st distal convoluted tubule, 2 nd loop of Henle, 3 rd proximal convoluted tubule! Increases BP and blood volume