THE URINARY SYSTEM AND HOMEOSTASISACHMAD AMIUDDIN

THE URINARY SYSTEM AND HOMEOSTASISThe urinary system contributes to homeostasis by altering blood composition, Ph, volume and pressure ; maintaining blood osmolarity ;ing hormon excreting wastes and foreign substances ; and produc

FUNCTINS OF THE URINARY SYSTEMThe kidney regulate blood volume and composition, help regulate blood pressure, synthesize glucose, release erythropoietin, participate in vitamin D synthesis, and excrete wastes in the urine.The ureters transport urine from the kidneys to the urinary bladder.The urinary bladder stores urine.The urethra discharges urine from the body.

FUNCTIONS OF THE KIDNEYSRegulation of blood ionic composition

Help regulate the blood level of Na+ , K+, Ca2+ , Cl- and PO4 2-Regulation of blood Ph

The kidney excrete H+, and conserve HCO3- , which are an important buffer of H+ in the bloodRegulation of blood volume.

The kidney adjust blood volume by conserving or eliminating water in the urine.

FUNCTIONS OF THE KIDNEYRegulation of blood pressure

Secreting the enzyme renin, which activates the renin angiotensin aldosteron pathwayMaintenance of blood osmolarity

By separately regulating loss of water and loos of solutes in the urine, the kidney maintain a relatively costant blood osmolarity close to 300 milliosmoles perliter.Production of hormone

FUNCTIONS OF THE KIDNEYSProduction of hormone

Calcitrol, the active form of vitamin D, help regulate calcium homeostasis, Erythropoietin, stimulates production of RBCRegulation of blood glucose level

The kidney can use the amono acid glutamine in gluconeogenesis, and then release glucose into the bloodExcretion of wastes and foreign substances

FUNCTION OF THE KIDNEYSExcretion of wastesand foreign substances

- By forming urine, the kidney help excrete wastes. - Ammonia and urea from the deamination of amino acid. - Bilirubin from the catabolism of haemoglobin - Creatinin from the break down of creatin phosphate in muscle fibers. - Uric acid from the catabolism of nucleic acid. - Foreign substances from the diet.

THREE BASIC FUNCTIONS OF THE NEPHRONGLOMERULAR FILTRATION

Water and most solutes in blood plasma move across the wall of glomerular cappilaries into the glomerular capsule and then into the renal tubule.TUBULAR REABSORPTION

Tubule cells reabsorb about 99 % of the filtered water and many useful solutes. The water and solutes return to the blood as it flow through the peritubular cappilaries and vasa recta. Proximal convoluted tubu le cells make the largest contribution.

THE THREE BASIC FUNCTIONS OF THE NEPHRONSTUBULAR SECRETION

The tubule and duct cells secrete other material such as hydrogen ion ( H ),K , ammonium ion ( NH4+ ), creatinin and certain drugs. Tubular secretion has twoimportant out comes 1. The secretion of H+ help control Ph. 2. Help elimination.

GLOMERULAR FILTRATIONThe daily volume of glomerular filtrate in adult is about 150 lters in females and 180 liters in males.More than 99 % of the glomeular filtrate return to the blood stream via tubular reabsorption, so only 1 2 liters are excreted as urine.

THE FILTRATION MEMBRANEPermits filtration of water and small solutes but prevents filtration of most plasma protein, blood cells and platelets 1. Glomerular endothelial cells.

2. The basal lamina. 3. Podocyte and pedicels

GLOMERULAR ENDOTHELIAL CELLSLarge fenestrations ( 70 100 nm ).Permits all solutes in blood plasma to exit glomerular cappilary, but prevents filtration of blood cells and platelets.In the cleft between afferent and efferent arterioles are mesangial cells , help regulate glomerular filtration

THE BASAL LAMINA AND PODOCYTEBASAL LAMINA

Consists of minute collagen figer and proteoglycans in a glycoprotein matrix. Prevents filtration of large plasma proteins.PODOCYTES AND PEDICELS

The space between pedicells are are the filtration slits. The slit membrane, extends acros each filtration slit; it permits the passage of molecules having diameter smaller than 6 7 nm , including water, glucose, vitamins , amino acid,very small plasma proteins, ammonia, urea and ions

THE GLOMERULAR FILRATE IS MUCH LARGEGlomerular cappilaries present a large surface area for filtration. The mesangial cells regulate how much of this surface is afailable.The filtration membrane is thin and porous.Glomerular cappilary blood pressure is high.

NET FILTRATI0N PRESSURE Fig 26,9

GLOMERULAR FILTRATION RATEThe amount of filtrate formed in all the renal corpuscles of both kidneys each minute.The mechanisms that regulate the glomerular filtration rate operate in two main ways ;

1. by adjusting blood flow into and outthe of the glomerulus. 2. by altering the glomerular capillary surface area available for filtration. Three mechanisms control GFR : renal autoregulation,renal regulation and hormonal regulation

RENAL AUTOREGULATION OF GFR.The kidneys help maintain a constant renal blood flow and GFR despite normal, everyday changes in blood pressure, like those that occur during exercise.Renal autoregulation consists of two mechanisms

- myogenic mechanism. - tubuloglomerular feed back.

TEH MYOGENIK MECHANISMMajor stimulus

Increased streching of smooth muscle fibers in affrent arteriole wall due to increased b.p.Mechanism and site of action

Stretched smooth muscel fibers contract, thereby narrowing the lumen of the afferent arteriolesEffect on GFR : decreased

Fig 26.10

NEURAL REGULATIONMajor stimulus

Increase in level of activity of renal sympathetic nerves releases norepinephrineMechanism and site of action

Constrict of afferent arteriles through activation of 1 receptors and increased release of renin.Effect on GFR : decrease.

Angiotensin II regulationMajor stimulus

Decreased blood volume or blood preesure stimulates production of angiotensin IIMechanismm and site of action

Constriction of both afferent and efferent ateriolesEffect on GFR : decrease.

Atral natriuretic peptide regulationMajor stiulus

Stretching of the atria of the heart stimulates secretion of ANPMechanism and site of action

Relaxation of mesangial cells in glomerulus increases capillary surface area andavailable for filtrationEffect on GFR : increase

TUBULAR REABSORPTION table 26.3

Fig 26.11

Fig 26.12

Fig 26.13 a

26.13 b

Fig 26.14

fig 26.15

Fig 26.16

Fig 26.17

ANGIOTENSIN IIStimuli

Low blood volume,or low blood pressure stimulates renin-induced production of angiotensin IIMechanism and site of action

Stimulates activity of Na+/H+ antipoters in proximal tubulus cellsEffects

Increases reabsorption of Na+, other solutes, and water, which increase blood volume

ALDOSTERONMajor stimul.

Increase angiotensin II level and increaselevel of plasma K+ promote release of aldosteron.Mechanism and site of action

Enhaces activity of sodium-potassium pumps in basolateral membrane and Na+ chanels in apical membrane of principal cellsEffects

Increases secretion of K+ and secretion of Na+, Cl ; increase reabsorption of water, which increase blood volume.

ADH or vasopressinMajor stimuli

Increased osmolarity of extracellular fluid or decreased blood volume promote release of ADH from the posterior pituitary glandMechnism and site of action

Stimulates of insertion of water-channel proteins into the apical membrane of principal cellsEffects

Increases facultative reabsorption of water, which decreases osmolarity of body fluids

ATRIAL NATRIURETIC PEPTIDEMajor stimuli

Stretching of atriaof heart stimulates secretion of ANPMechanism and site of action

Suppresses reabsorption of Na+ and water in proximal tubule and collecting duct, also inhibits secretion of aldosteron and ADHEffects

Increases excretion of Na+ in urine; increases urine output and thus decreases blood volume