Presentation on theme: "Cell plasma membrane maintains ionic, but not osmotic difference between intracellular and extracellular fluids. Epithelium surrounding the body often."— Presentation transcript:
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 vertebrates Appropriate solute concentrations and water are maintained by osomregulation
Exchange of water and salts depends on The size of gradient Surface area of the animal Permeability of the animal’s surface
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
Amphibians have moist, highly permeable skins To avoid desiccation, stay in cool, damp microenvironment, stay close to water water and slats are stored in a large-volume lymphatic system and an oversized urinary bladder. Insect’s waxy cuticle Burning fat to produce water in seal Various Strategies for Preserving Body Water
Seals became fat when eating fish but get thin eating marine invertebrate
The respiratory loss of water is minimized by temporal countercurrent system
Water loss via respiration depends on Difference between body temperature and air temperature Humidity of inhaled air
Osomoregulatory in Various Classes of Animals
Euryhaline aquatic animal can tolerate a wide range of salinities Stenohaline animals can tolerate only narrow osmotic range
Freshwater animals face two kinds of osmoregulatory problems: gain of water loss of salt To prevent the net gain of water and net loss of salts, freshwater animals Drink no water Produce a dilute urine Replace lost salts from ingested food Active transport salt from external environment
Marine invertebrates and hagfish (vertebrate) are iso- osmotic to seawater, and have similar osmolarity and ionic concentrations to seawater Elasmobranch (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
Marine teleosts face two kinds of osmoregulatory problems: loss of water gain of salt To prevent the net loss of water and net gain of salts, marine teleosts Drink water Active transport Na +, Cl - and K + from gill to seawater. Secretion of divalent salts (Ca 2+, Mg 2+, SO 4 2-) by kidney to urine
Marine reptiles and marine birds Drink seawater Kidney is unable to excrete the salts Salt gland (near eyes, nose and in the tongue) secrete concentrated salt solution
Most mammals lack salt gland and will become dehydrated if they drink seawater
Camel strategies: Change body temperature Produce dry feces & concentrated urine Store high levels of urea Camel do not sweat and has large body mass and thick fur
Marine mammals: Drink no water Produce hypertonic urea Absorb water from metabolic activity and ingested food Terrestrial arthropods Create high concentrated solutions in the rectum to absorb water from the air Salivary glands secrete highly concentrated KCl
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
Kidney Functions Primarily 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 HC Regulate pH. Secrete erythropoietin.
Nephron Functional unit of the kidney. Consists of: Blood vessels –vasa recta –peritubular capillaries Urinary tubules –Proximal tube –Loop of Henle –Distal tube –Collecting tube
Three main processes for urine production 1.Filtration 2.Reabsorption 3.Secretion
Glomerular filteration Ultrafiltration in glomerulus depends on 1.pressure difference 2.Membrane permeability
Fig. 12-9, p.534
Juxtaglomerular Apparatus Region in each nephron where the afferent arteriole comes in contact the the thick ascending limb of the loop. Two types of cells Macula densa: –Monitor the osmolarity and flow –Inhibit renin secretion when blood [Na + ] in blood increases Granular cells: –Secrete renin. –Converts angiotensinogen to angiotensin I. –Initiates the renin-angiotensin- aldosterone system.
Stimulation of macula densa cells to release vasoactive chemicals Chemicals released that induce afferent arteriolar vasoconstriction Arterial blood pressureDriving pressure into glomerulusGlomerular capillary pressureGFR Rate of fluid flow through tubules Blood flow into glomerulus Glomerular capillary pressure to normal GFR to normal Fig , p.538
Detection by aortic arch and carotid sinus baroreceptors Sympathetic activity Generalized arteriolar vasoconstriction Afferent arteriolar vasoconstriction GFR Glomerular capillary blood pressure Cardiac output Total peripheral resistance Short-term adjustment for Arterial blood pressure Long-term adjustment for Urine volume Conservation of fluid and salt Arterial blood pressure Fig , p.539
Tubular re-absorption Return of most of the filtered solutes and H 2 0 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).
Filtered glucose and amino acids are normally reabsorbed by the nephrons. –Carrier mediated transport: Saturation. Exhibit T m. (320 mg min -1, 3mgml -1 ) Glucose re-absorption
Solute concentrations in the interstitial fluid increase from the cortex to the depths of the medulla. Urea increases most in the inner medulla. NaCl increases most in outer medulla
Proximal tube 70% Na +, Cl - and H 2 0 reabsorbed across the PT into the blood. 90% K + reabsorbed. Fluid reduced to ¼ original volume but still iso-osmatic 300 mOsm/L Na + /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. H 2 0 follows by osmosis. Reabsorption is constant, not subject to hormonal regulation.
Fig , p.541
Fig , p.541
Descending Limb Loop of Henle Deeper regions of medulla reach 1200 mOsm/L. Impermeable to passive diffusion of NaCl & urea Permeable to H 2 0. Hypertonic interstitial fluid causes H 2 0 movement out of the descending limb via osmosis. Fluid volume decreases in tubule, causing higher [Na+] in the ascending limb.
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 H 2 0.
Distal tubule Transport K +, H +, and NH 3 into the lumen Reabsorption of Na +, Cl -, and HCO 3 - H 2 0 follows passively subject to hormonal regulation.
Collecting Duct Medullary area impermeable to high [NaCl] that surrounds it. The walls of the CD are permeable to H 2 0. H 2 0 is drawn out of the CD by osmosis. Rate of osmotic movement is determined by the # of aquaporins in the cell membrane. Permeable to H 2 0 depends upon the presence of ADH. ADH binds to its membrane receptors on CD, incorporating water channels into cell membrane.
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
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
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
Na + Reabsorption In 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.
(Antidiuretic hormone) ADH increase number of water channels (aquaporins) and thereby promotes water reabsorption
Atrial natriuretic peptide (ANP) Produced by atria due to stretching of walls. Antagonist to aldosterone. Inhibits release ADH, renin and aldosterone Increases [Na + ] excretion and urine production
Two factors control pH in mammals: Excretion of CO2 via the lung (short term) Excretion of acid via kidney (mainly)
Renal Acid-Base Regulation Kidneys help regulate blood pH by excreting H + and reabsorbing HC 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 HC0 3 - and excrete H +. Returns blood pH back to normal range.
A type cell: acid secreting cell
B type cell: base secreting cell
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 HPO 4 -2 or NH 3. HPO H + H 2 PO 4 - NH 3 + H + NH 4 +
Buffering of the renal filtrate by H 2 PO 4 - and NH 4 - permits greater secretion of protons.
Kidney in vertebrates Hagfish: possess glomeruli, no tubules, excrete divalent ions (Ca 2+, Mg 2+, and SO 4 2- ), carry out little osmoregulation, Freshwater teleost: larger glomeruli, produce dilute urine Marine teleost: produce little urine, excrete NH 3 from gills Amphibians and reptiles: lack of loop of Henle, can’t produce concentrated urine Mammals and birds: produce concentrated urine