4 Cell plasma membrane maintains ionic, but not osmotic difference between intracellular and extracellular fluids.Epithelium surrounding the body often maintains both ionic and osmotic difference between animal and their environments.Gills, salty gland and kidney are primary organs of osmoregulation in vertebratesAppropriate solute concentrations and water are maintained by osomregulation
5 Exchange of water and salts depends on The size of gradientSurface area of the animalPermeability of the animal’s surface
6 The surface-to-volume ratio is greater for small animals than large animals. A small animal will dehydrate or hydrate more rapidly than a larger animal
8 Various Strategies for Preserving Body Water Amphibians have moist, highly permeable skinsTo avoid desiccation, stay in cool, damp microenvironment, stay close to waterwater and slats are stored in a large-volume lymphatic system and an oversized urinary bladder.Insect’s waxy cuticleBurning fat to produce water in seal
9 Seals became fat when eating fish but get thin eating marine invertebrate
10 The respiratory loss of water is minimized by temporal countercurrent system
11 Water loss via respiration depends on Difference between body temperature and air temperatureHumidity of inhaled air
13 Euryhaline aquatic animal can tolerate a wide range of salinities Stenohaline animals can tolerate only narrow osmotic range
14 Freshwater animals face two kinds of osmoregulatory problems: gain of waterloss of saltTo prevent the net gain of water and net loss of salts, freshwater animalsDrink no waterProduce a dilute urineReplace lost salts from ingested foodActive transport salt from external environment
15 Marine invertebrates and hagfish (vertebrate) are iso-osmotic to seawater, and have similar osmolarity and ionic concentrations to seawaterElasmobranch (e.g. shark, rays and skates, Latimeria) is iso-osmotic to seawater by maintaining low concentration of electrolytes and high concentration of urea and TMAO (trimethylamine oxide)Marine teleost, bird and mammals are hypo-osmotic to seawater
16 Marine teleosts face two kinds of osmoregulatory problems: loss of watergain of saltTo prevent the net loss of water and net gain of salts, marine teleostsDrink waterActive transport Na+, Cl- and K+ from gill to seawater.Secretion of divalent salts (Ca2+, Mg2+, SO42-) by kidney to urine
17 Marine reptiles and marine birds Drink seawaterKidney is unable to excrete the saltsSalt gland (near eyes, nose and in the tongue) secrete concentrated salt solution
18 Most mammals lack salt gland and will become dehydrated if they drink seawater
20 Camel strategies:Change body temperatureProduce dry feces & concentrated urineStore high levels of ureaCamel do not sweat and has large body mass and thick fur
21 Marine mammals:Drink no waterProduce hypertonic ureaAbsorb water from metabolic activity and ingested foodTerrestrial arthropodsCreate high concentrated solutions in the rectum to absorb water from the airSalivary glands secrete highly concentrated KCl
22 Structure of the Kidney 2 distinct regions:Outer cortex:Many capillaries.Medulla:Renal pyramids separated by renal columns.Nephron is functional unit of the kidney
23 Kidney FunctionsPrimarily on regulation of ECF through formation of urine.Regulate volume of blood plasma and BP.Regulate concentration of waste products in the blood.Regulate concentration of electrolytes as Na+, K+, and HC03-.Regulate pH.Secrete erythropoietin.
24 Nephron Functional unit of the kidney. Consists of: Blood vessels vasa rectaperitubular capillariesUrinary tubulesProximal tubeLoop of HenleDistal tubeCollecting tube
33 Juxtaglomerular Apparatus Region in each nephron where the afferent arteriole comes in contact the the thick ascending limb of the loop. Two types of cellsMacula densa:Monitor the osmolarity and flowInhibit renin secretion when blood [Na+] in blood increasesGranular cells:Secrete renin.Converts angiotensinogen to angiotensin I.Initiates the renin-angiotensin-aldosterone system.
35 Arterial blood pressure Driving pressure into glomerulusGlomerular capillary pressureGFRRate of fluid flowthrough tubulesStimulation of macula densa cellsto release vasoactive chemicalsChemicals released that induceafferent arteriolar vasoconstrictionBlood flow into glomerulusGlomerular capillary pressureto normalGFR to normalFig , p.538
36 Arterial blood pressure Short-term adjustment for Long-term Detection by aortic arch andcarotid sinus baroreceptorsArterialblood pressureCardiacoutputSympathetic activityTotalperipheralresistanceGeneralizedarteriolar vasoconstrictionAfferent arteriolarvasoconstrictionGlomerular capillaryblood pressureGFRUrine volumeConservation offluid and saltArterial blood pressureFig , p.539
37 Tubular re-absorption Return of most of the filtered solutes and H20 from the urine filtrate back into the peritubular capillaries.About 180 L/day of ultrafiltrate produced, however only 1 – 2 L of urine excreted (>99%).Minimum of 400 ml/day urine necessary to excrete metabolic wastes (obligatory water loss).
43 Proximal tube70% Na+, Cl- and H20 reabsorbed across the PT into the blood. 90% K+ reabsorbed.Fluid reduced to ¼ original volume but still iso-osmatic 300 mOsm/LNa+/K+ ATPase pump located in basal and lateral sides of cell membrane creates gradient for diffusion of Na+ across the apical membrane.Na+/K+ ATPase pump extrudes Na+.Cl- follows electrical gradient into the interstitial fluid.H20 follows by osmosis.Reabsorption is constant, not subject to hormonal regulation.
47 Descending Limb Loop of Henle Deeper regions of medulla reach 1200 mOsm/L.Impermeable to passive diffusion of NaCl & ureaPermeable to H20.Hypertonic interstitial fluid causes H20 movement out of the descending limb via osmosis.Fluid volume decreases in tubule, causing higher [Na+] in the ascending limb.
48 Ascending Limb Loop of Henle Na+ actively transported across the basolateral membrane by Na+ / K+ ATPase pump.Cl- passively follows Na+ down electrical gradient.K+ passively diffuses back into filtrate.Walls are impermeable to H20.
49 Distal tubule Transport K+, H+, and NH3 into the lumen Reabsorption of Na+, Cl-, and HCO3-H20 follows passivelysubject to hormonal regulation.
50 Collecting DuctMedullary area impermeable to high [NaCl] that surrounds it.The walls of the CD are permeable to H20.H20 is drawn out of the CD by osmosis.Rate of osmotic movement is determined by the # of aquaporins in the cell membrane.Permeable to H20 depends upon the presence of ADH.ADH binds to its membrane receptors on CD, incorporating water channels into cell membrane.
51 Kidney Secretion Secretion of substances from the blood to the urine. Allows the kidneys to rapidly eliminate certain potential toxins.Substances (foreign & normal metabolites) conjugated with glucuronic acid or its sulfate, removed by organic anionic and cationic transport system
52 Renin-angiotensin system Cells of macula densa senses blood pressure decrease, they stimulate releasing of renin from the granular cells, leads to an increase in angiotensin II and aldosterone, promotes Na+ and water reabsorption
53 Role of Aldosterone 90% K+ reabsorbed in early part of the nephron. When aldosterone is absent, no K+ is excreted in the urine.Final [K+] controlled in distal tube by aldosterone.High [K+] or low [Na+] stimulates the secretion of aldosterone.Only means by which K+ is secreted.Control of plasma of K+ important in proper function of cardiac and skeletal muscles
54 Na+ ReabsorptionIn the absence of aldosterone, 80% remaining Na+ is reabsorbed.2% is excreted (30 g/day).Final [Na+] controlled in distal tube by aldosterone.Control of Na+ important in regulation of blood volume and pressure.
55 (Antidiuretic hormone) ADH increase number of water channels (aquaporins) and thereby promotes water reabsorption
56 Atrial natriuretic peptide (ANP) Produced by atria due to stretching of walls.Antagonist to aldosterone.Inhibits release ADH, renin and aldosteroneIncreases [Na+] excretion and urine production
57 Two factors control pH in mammals: Excretion of CO2 via the lung (short term)Excretion of acid via kidney (mainly)
58 Renal Acid-Base Regulation Kidneys help regulate blood pH by excreting H+ and reabsorbing HC03-.Most of the H+ secretion occurs across the walls of the proximal tube in exchange for Na+.Antiport mechanism.Normal urine normally is slightly acidic because the kidneys reabsorb almost all HC03- and excrete H+.Returns blood pH back to normal range.
62 Urinary Buffers Nephron cannot produce a urine pH < 4.5. IN order to excrete more H+, the acid must be buffered.H+ secreted into the urine tubule and combines with HPO4-2 or NH3.HPO4-2 + H H2PO4-NH3 + H NH4+
63 Buffering of the renal filtrate by H2PO4- and NH4- permits greater secretion of protons.
64 Kidney in vertebratesHagfish: possess glomeruli, no tubules, excrete divalent ions (Ca2+, Mg2+ , and SO42- ), carry out little osmoregulation,Freshwater teleost: larger glomeruli, produce dilute urineMarine teleost: produce little urine, excrete NH3 from gillsAmphibians and reptiles: lack of loop of Henle, can’t produce concentrated urineMammals and birds: produce concentrated urine