2 Ionic and osmotic balance 2/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Tabin multicellular organisms the interstitial fluid is the internal environment – composition resembles that of the ancient sea: high Na+, low K+, low Ca++ and Mg++osmoregulatory organs maintain this environment isovolumic, isotonic, isoionic, isohydric, etc.further task: removal of poisonous end products of metabolism (mostly NH3 from proteins)marine invertebrates: osmotic pressure and ionic constitution in equilibrium with seawatermarine vertebrates: ion concentration is one third of seawater except in hagfish (Eptatretus - Cyclostomata), MgSO4, Cl- much lower; in sharks-rays ion concentration is lower, but osmotic pressure is maintained by ureafresh water, terrestrial: ion concentration is one third; hyperosmotic to freshwater, hyposmotic to seawater
3 Osmotic exchange3/21plasma membrane separates fluids with different ionic composition, but equal osmotic pressureepithelium separates fluids that are different in both respectsanimals cannot isolate themselves from the environment: exchange of gases, absorption of nutritients; exception: Artemia salinaobligate and regulated osmotic exchangeobligate exchange depends on physical factors, that animals cannot readily regulateregulated exchange compensates for changes caused by the obligateonly some parts of the epithelium participate in osmoregulation: gill, kidney, salt gland, enteric systemArtemia salina tengeri sóféreg, rákocska. Him és nőstény órákig úsznak együtt, 4-5 percenként kopulálnak, petesejt petezsákban fejlődésnek indul, szárazra kerülve héjat választ ki, évekig életképes, vízbe rakva naupliusz lárva, majd igen gyorsan rákocska; újság promóciós anyag anthrax előtt
4 Obligate osmotic exchange 4/21occurs through the skin, respiratory epithelium and other epithelia in contact with environmentinfluencing factors:gradient: determines direction of exchange; a frog sitting in a pond takes up water through the skin; a marine fish is loosing water in the sea, but gains NaCl; a freshwater fish is taking up water, but loosing salt through the gillsurface: small animal – relatively larger surface, faster exchange, e.g. dehydrationpermeability:transcellular and paracellular exchange (but: tight junction);skin of amphibians, gill of fish have high permeabilityskin of reptiles, desert amphibians, birds, mammals are much less permeable (leather containers), but mammals loose water through sweatingeating, metabolism, excretes: metabolic water is very important for desert animals, but also for marine mammals (seals put on weight eating fish, but loose weight burning fat when is feeding on invertebrates)respiration: function of nose – condense water during exhalation – dropping nose in winter
5 Osmotic regulation I.5/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figmost vertebrates are strict osmoregulators - exception: shark, ray and hagfishmarine invertebrates are in equilibrium, other invertebrates, similar to vertebrates, are hyperosmotic in freshwater, hyposmotic in seawatersome of the invertebrates is conformer, others are osmoregulatorsfreshwater animals breathing from waterthey are hyperosmotic: mOsm; freshwater in general below 50 mOsm – water inflow, salt outflowto compensate, they produce dilute urine, take up salt with food and through active transport (fish, frog), decrease the permeability of their skinthey do not drink freshwater
6 Osmotic regulation II. marine animals breathing from water 6/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figmarine animals breathing from waterinvertebrates are in equilibriumhagfish: Ca++, Mg++, SO42- regulation onlyshark-ray osmotic equilibrium due to urea accumulation, excess salt removed by rectal glandsfish are loosing water, drinking seawater; excess salt removed through the gill (chloride cells) marine animals breathing airloosing water through respiratory epithelium and other epitheliamarine reptiles and birds are drinking seawater – cannot produce strongly hyperosmotic urine (just as fish) – excess salt removed through salt glandsmarine mammals do not drink seawater, water is taken in with food and produced metabolically, urine is hyperosmoticlion seal males spend 3 months on the beach without eating or drinking; seal pups do similarly for 8-10 weeks while mother is on the sea
7 Osmotic regulation III. 7/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figterrestrial animals breathing airif freshwater is available then water lost through breathing can be replenished by drinking, salt loss (urine, faces, sweating) compensated from food – sparing is importantproblem of shipwrecked sailors: kidney can remove 6 g Na+/l urine, seawater contains 12 g Na +/l – drinking of seawater leads to salt gaindesert animals have two problems: heat and lack of waterkangaroo rat: remains in cool burrow during daytime, active only during the night; gaining water metabolically, water condensation in nosecamel: cannot hide in burrow; when dehydrated do not sweat, body temperature raises changing between 35-41° C; hyperosmotic or no urine, urea stored in tissues; faces dry
9 Water compartments9/21human body contains 60% water on average, differences between male-female, young-olddistributed in different compartmentsintracellularly 2/3, extracellularly 1/3of the extracellular water: 3/4 interstitially, 1/4 in blood plasmabarriers and, transport rules are already knownmeasurement of volumes applying dilution principle: Evans-blue, inulin, tritiated waterhomeostasis is very important . cholera, diarrhea - dehydration, working by a furnace in tropical areas – water poisoning, severe burns – dehydration due to loss of skinthe most important regulator in humans is the kidney, behavioral regulation is also important – metabolic water is limited
10 Human kidney10/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figosmoregulatory organs always contain transport epithelium (skin, gill, kidney, gut) : polarized - apical (luminal, mucosal) and basal (serosal) surfaces are differentcapacity of the transport epithelium is increased by its special structure: tubular organizationfunctioning of the mammalian kidney is well known – though it does not represent all types of vertebrate kidneys0,5% of body weight, 20-25% of cardiac outputcortex, medulla, renal pyramid, renal pelvis, ureter, urinary bladder, urethra volume of urine is 1 l daily, slightly acidic (pH 6), composition, volume changes with the food and the requirements of the water homeostasis - beer, Amidazophen, etc.
11 The nephron functional unit of human kidney is the nephron 11/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figfunctional unit of human kidney is the nephronafferent and efferent arterioles, in between glomerulus; Bowman capsule, proximal tubule, loop of Henle, distal tubule, collecting duct most of the nephrons (85%) are cortical, the rest juxtamedullary (15%) nephronsteps in the formation of urine:ultrafiltrationreabsorptionsecretionthe kidney is very important in pH regulationthe kidney removes ammonia formed during the decomposition of proteins
12 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 14-19. Ultrafiltration12/21in the kidney 15-25% of water and solutes is filtrated, 180 l daily – proteins and blood cells remainfiltration depends on:the hydrostatic pressure between the capillaries and the lumen of the Bowman capsule: = 40 mmHgthe colloid osmotic pressure of the blood: 30 mmHg – effective filtration pressure = 10 mmHg the permeability of the filter: fenestrated capillaries, basal membrane (collagen + negative glycoproteins), podocytes (filtration slits between pedicels) voluminous blood supply due to the relatively low resistance – afferent arteriole is thick and short – high pressure in the glomerulusregulation of the blood flow: basal miogenic tone, paracrine effect of juxtaglomerular apparatus, sympathetic effect (afferent arteriole, glomerulus, podocyte) Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, FigBerne and Levy, Mosby Year Book Inc, 1993, Fig. 41-7Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
13 Clearance13/21clearance of a substance is the volume of plasma that is completely cleaned from the given substance in the kidney in every minuteVU CP = VU that is C = PC - clearance, P – concentration in plasma, V – volume of urine in 1 minute, U – concentration in urineclearance of a substance that is neither reabsorbed nor secreted (e.g. inulin) equals the glomerulus filtration rate : GFRclearance of a substance that is not only filtrated, but completely secreted as well (e.g. PAH) equals the renal plasma flow : RPFknowing the hematocrit, renal blood flow (RBF) can be calculated
14 Tubular reabsorption I. 14/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig180 l primary filtrate is produced every day, but only 1 l is excreted, of 1800 g filtrated NaCl only 10 g remains in the urinethe process of reabsorption has been successfully examined since the 1920’s using the method of micropuncturerole played by the subsequent sections of the tubules:proximal tubule70% of Na+ is reabsorbed by active transport, Cl- and water follow passively, obligate reabsorption filtrate is isosmotic, but concentration of substances that are not reabsorbed increases 4-foldon the apical membrane of epithelial cells microvillivirtually all filtrated glucose and amino acids are reabsorbed using Na+ dependent symportertubular maximum for glucose: below 1.8 mg/ml complete reabsorption (normal value: 1.0 mg/ml), above 3.0 mg/ml linear increase – sugar in urine in diabetesCa++, phosphate and other electrolytes are reabsorbed as needed – see later
15 Tubular reabsorption II. 15/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figdescending part of Henle’s loopno microvilli, few mitochondria – no active transportlow permeability for NaCl and urea, high for waterthin ascending part of Henle’s looplow permeability for water, high for NaClthick ascending part of Henle’s loopactive reabsorption of Na+low water permeabilitydistal tubuleactive reabsorption of Na+, and passive reabsorption of waterK+, H+ and NH3 transport as needed – see later (pH regulation)transport is regulated by hormones – facultative reabsorptioncollecting ductactive reabsorption of Na+ at the cortical part, high urea permeability in the internal medullary partregulated water permeability (ADH)
16 Tubular secretion16/21several substances are secreted from the plasma to the tubule in the nephron – best examined: different electrolytes (K+, H+, NH3) organic acids and basesactive transport – recognizes substances conjugated with glucuronic acid in the liverK+ is reabsorbed in the proximal tubule and Henle’s loop (Na/2Cl/K transporter)if K+ concentration is too high, secretion in the distal tubule depending on aldosterone and coupled to Na+ reabsorption - K+ acts directly on aldosterone, Na+ through renin-angiotensin conflicting demands: insulin secretion is induced by high K+ - excess K+ is taken up by adipose tissuesecretion of H+ and NH3 serves pH regulationEckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, FigAz uronsavakban a cukor végálló CH2OH-ja oxidálódik COOH-vá. a legismertebb a glükózból képződő glükuronsav.
17 pH regulation I. normal pH 7.4 – 7.35 acidosis, 7.45 alkalosis 17/21normal pH 7.4 – 7.35 acidosis, 7.45 alkalosisnormal functioning is possible betweenregulation: buffer systems, respiration, kidneyHenderson-Hasselbalch equation: [A-] pH = pK + log [HA]for CO2 two equations; following rearrangement:[HCO3-] pH = pK’ + log [αCO2] - solubility of CO2pK’ = 6.08, i.e. not good buffer at normal pH – as CO2 and HCO3- can be easily modified (respiration, kidney)plasma proteins (14-15% Hgb, 6-8% other) pK is same as blood pH – good buffersphosphate concentration low, negligible effect
18 pH regulation II.18/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figrespiratory alkalosis and acidosis: caused by hyper-, or hypoventilationmetabolic alkalosis – e.g. Cl- loss because of vomitingmetabolic acidosis – anaerobic energy production, ketosis in diabetes mellitusin the first case: kidney compensates, in the second: breathing (short-term) and the kidney (long-term)proximal tubule, Henle’s loop: Na+/H+ exchanger, distal tubule, collecting duct: HCO3- uptake through A-cellsin distal tubule and collecting duct: HCO3- secretion through B-cells in acidosis HCO3- level is low in the filtrate: NH3 secretion – binds to H+, NH4+ cannot go back, H+ secretion increases Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
19 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 14-32. Hyperosmotic urine19/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, SLbirds and mammals can produce hyperosmotic urine - water reabsorption in the collecting duct due to osmotic pressure differencescommon characteristic: Henle’s loop, the longer the loop, the more concentrated the urine – very long in kangaroo ratpressure difference is achieved through the counter-current principle Na+ transport in the ascending part of the Henle’s loop – do not enter the descending part, but attracts water leading to the same resultin addition, urea present in high concentration because of the reabsorption of water, can only leave the tubule in the internal medulla osmotic pressure increases from the cortex to the medulla blood supply to the tubules (vasa recta) is running in parallel to the Henle’s loop , does not decrease the osmotic gradientEckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
20 Regulation of the kidney Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, FigRegulation of the kidney20/21Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Figgranular cells in the juxtaglomerular apparatus produce renin in response to a decrease in blood pressure or NaCl delivery to the distal tubulerenin cuts off angiotensin I (10 amino acids) from angiotensinogen (glycoprotein)converting enzyme (mostly in the lung) cuts off 2 amino acids from angiotensin I – angiotensin IIangiotensin II enhances aldosterone secretion in the adrenal gland, increases blood pressure through vasoconstriction and increases ADH production aldosterone increase Na+ reabsorption through 3 different ways: facilitation of the pump, ATP production, increased apical Na+ permeability ADH producing cells detect blood pressure and osmolality and are sensitive to alcohol atrial natriuretic peptide (ANP) – released in the atria when venous pressure increases - inhibits renin, aldosterone, ADH productionEckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
21 Nitrogen removal21/21part of the digested amino acids are reused, amino groups from the others have to be removed as NH3 and NH4+ are poisonousthree forms: ammonia, urea, uric acid ammoniapoisonous – huge volume is needed to provide low concentration in the cell and high outward gradient0.5 l water/1 g nitrogenfish, aquatic invertebrates, mammals in low amounttransport in the form of glutamine from the liver to the kidneyurealess poisonous, 0.05 l water/1 g nitrogensynthesis requires ATPvertebrates, except fish, synthesize urea in the ornithine-urea cycle, fish and invertebrates from uric acidhominoids cannot metabolize uric acid (from nucleic acids) – can accumulate and lead to gouturic acidlow solubility: l water/1 g nitrogenwhite precipitate - guano in birds (uric acid, guanine)fish, reptiles, terrestrial arthropodsEckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig , 50.
22 Extracellular ion concentrations Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Tab
23 Osmoregulation in animals Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
24 Structure of mammalian kidney Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
25 Structure of a nephronEckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig
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