From Blood Filtrate to Urine: A Closer Look

Transcription

1 Blood Vessels Associated with the Nephrons Each nephron supplied with blood by an afferent arteriole branch of renal artery divides into glomerular capillaries capillaries converge as they leave glomerulus forming an efferent arteriole The vessels divide again Forming the peritubular capillaries surround the PCT and DCT Blood Vessels Associated with the Nephrons Vasa recta Capillaries that serve the loop of Henle vasa recta and loop of Henle funcbon as countercurrent system Blood flows in opposite direcbon of filtrate From Blood Filtrate to Urine: A Closer Look Proximal Convoluted Tubule (PCT) ReabsorpBon of ions, water, and nutrients Molecules ed acbvely and passively From filtrate into intersbbal then capillaries Some toxic materials secreted into the filtrate filtrate volume decreases 1

2 From Blood Filtrate to Urine: A Closer Look Descending Limb of the Loop of Henle ReabsorpBon of water conbnues through aquaporin proteins Movement is driven by High osmolarity of the intersbbal HyperosmoBc to the filtrate filtrate becomes increasingly concentrated From Blood Filtrate to Urine: A Closer Look Ascending Limb of the Loop of Henle Salt diffuses from tubule into intersbbal but not water No aquaporins present Completely impervious to water Filtrate becomes increasingly dilute From Blood Filtrate to Urine: A Closer Look Distal Convoluted Tubule (DCT) Regulates K + and concentrabons of body s controlled movement of ions contributes to ph regulabon 2

3 From Blood Filtrate to Urine: A Closer Look CollecCng Duct Carries filtrate through medulla to renal pelvis Water reabsorbed from filtrate some salt and urea Filtrate becomes more concentrated Urine hyperosmobc to body s Fig Proximal tubule Nutrients HCO K + 3 Distal tubule HCO 3 H + NH 3 K + H + Filtrate Loop of Henle Collecting duct Solute Gradients and Water ConservaBon Summary Urine Much more concentrated than blood loops of Henle and collecbng ducts Proximal tubule NaC Nutrient HCO l K + s 3 H + NH 3 Distal tubule HCO 3 K + H+ responsible for osmobc gradient Filtrate and urea concentrates urine Contribute to osmolarity of intersbbal causes reabsorpbon of water Loop of Henle Collecting duct concentrates the urine 3

4 PCT The Two- Solute Model ( & ) Filtrate volume decreases osmolarity remains same Countercurrent mulcplier system loop of Henle Maintains high salt concentrabon in kidney acbve of In thick ascending limb of LoH Thin limb loses by diffusion Allows formabon of concentrated urine allows vasa recta to supply nutrients to kidney without interfering with osmolarity gradient Due to counter flow of blood in vasa recta The Two- Solute Model collecbng duct Conducts filtrate through osmolarity gradient Cortex to outer medulla to inner medulla 200 More water exits filtrate by osmosis diffuses out of collecbng duct 700 In inner medulla Fig

5 Fig Fig PLAY 700 Mammals The juxtamedullary nephron Contributes to water conservabon in terrestrial animals Mammals that inhabit dry environments Have long loops of Henle While those in fresh water have relabvely short loops 5

6 Birds Birds and Other RepBles shorter loops of Henle Even in juxtamedullary nephrons conserve water by excrebng uric acid instead of urea excreted as a paste Fairly non- water soluble Other repbles have only corbcal nephrons No juxtamedullary nephrons But also excrete uric acid Freshwater Fishes and Amphibians Freshwater fish Conserve salt in DCT s Excrete large volumes of dilute urine Uptake of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Amphibian kidney funcbon similar to freshwater fish Excretion of large amounts of water in dilute urine from kidneys conserve water on land (b) Osmoregulation in a freshwater fish by reabsorbing water from the urinary bladder Marine bony fish Marine Bony Fishes HypoosmoBc compared with their environment excrete very lible urine Gain of water and salt ions from food Excretion of salt ions from gills Osmotic water loss through gills and other parts of body surface lost through skin and gills Fewer and smaller nephrons than fresh water fish No DCT Gain of water and salt ions from drinking seawater Excretion of salt ions and small amounts of water in scanty urine from kidneys Divalent ions secreted to proximal tubule (a) Osmoregulation in a saltwater fish Ca 2+, Mg 2+, SO 4 2-6

7 Thirst Drinking reduces blood osmolarity to set point. (a) prevent further osmolarity increase. Increased permeability Collecting duct Osmoreceptors in hypothalamus trigger release of ADH. Hypothalamus ADH ( mosm/l) osmolarity (b) COLLECTING DUCT LUMEN Exocytosis Second messenger signaling molecule camp channels ADH urine AnBdiureBc Hormone Regulated by nervous and hormonal control INTERSTITIAL FLUID of water and salt reabsorpbon COLLECTING DUCT CELL AnCdiureCc hormone (ADH) (vasopressin) Distal tubule Pituitary gland Storage vesicle ADH receptor Increases water reabsorpbon in Aquaporin water DCT and collecbng ducts reabsorption helps STIMULUS: Increase in blood An increase in osmolarity triggers the release of ADH Homeostasis: Blood osmolarity to conserve water When above mosm/l AnBdiureBc Hormone MutaBon in ADH producbon causes severe dehydrabon Results in diabetes insipidus Large volumes of dilute urine Alcohol is a diurebc inhibits the release of ADH PLAY The Renin- Angiotensin- Aldosterone System Renin- angiotensin- aldosterone system (RAAS) Part of complex feedback circuit funcbons in homeostasis drop in blood pressure near glomerulus Causes juxtaglomerular apparatus (JGA) to release the enzyme renin triggers the formabon of angiotensin II 7

8 The Renin- Angiotensin- Aldosterone System Angiotensin II Raises blood pressure and decreases blood flow to kidneys Through vasoconstricbon SBmulates release of the hormone aldosterone Causes retenbon of salt Increases blood volume and pressure As water follows salt Fig Distal tubule Renin Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure Homeostasis: Blood pressure, volume Fig Liver Angiotensinogen Distal tubule Renin Angiotensin I ACE Juxtaglomerular apparatus (JGA) Angiotensin II STIMULUS: Low blood volume or blood pressure Homeostasis: Blood pressure, volume 8

9 Fig Liver Angiotensinogen Distal tubule Renin Angiotensin I ACE Juxtaglomerular apparatus (JGA) Angiotensin II Adrenal gland STIMULUS: Low blood volume or blood pressure Aldosterone Increased Na + and reabsorption in distal tubules Arteriole constriction Homeostasis: Blood pressure, volume HomeostaBc RegulaBon of the Kidney ADH and RAAS Both increase water reabsorpbon But only RAAS will respond to a decrease in blood volume Atrial natriurecc pepcde (ANP) Opposes the RAAS released in response to increase in blood volume and pressure Inhibits the release of renin You should now be able to: 1. DisBnguish between the following terms: isoosmobc, hyperosmobc, and hypoosmobc; osmoregulators and osmoconformers; stenohaline and euryhaline animals 2. Define osmoregulabon, excrebon, anhydrobiosis 3. Compare the osmoregulatory challenges of freshwater and marine animals 4. Describe some of the factors that affect the energebc cost of osmoregulabon 9

10 You should now be able to: 5. Describe and compare the protonephridial, metanephridial, and Malpighian tubule excretory systems 6. Using a diagram, idenbfy and describe the funcbon of each region of the nephron 7. Explain how the loop of Henle enhances water conservabon 8. Describe the nervous and hormonal controls involved in the regulabon of kidney funcbon 10