Urinalysis and Body Fluids CRg Unit 1 EPhysiology of the Urinary SystemPhysiology of the Urinary System• Functions of the kidney• Elimination of excess water• Elimination of waste products of metabolism. such as Urea & Creatinine• Elimination of foreign substances (such as drugs that have been detoxified by the liver)• Retention of substances necessary for normal body function (glucose, electrolytes, minerals, amino acids, etc)Physiology of the Urinary System• Functions of the kidney, continued • Regulation of electrolyte balance and osmotic pressure of body fluids (BP)• Maintenance of body acid / base balance• Hormone production • Erythropoietin – RBC stimulus• Renin – long term regulation and maintenance of blood pressure.• Physiology of the Urinary System• Kidney accomplishes these tasks by: • Filtering• Reabsorbing• Secreting• Concentrating• To accomplish these tasks, needed are:• Renal blood flow• Glomerular filtration• Tubular reabsorption• Tubular secretionPhysiology of the Urinary SystemUrine Formation - Filtration • Glomerular filtration• @ 120 ml/minute of renal plasma is filtered through the glomeruli • (Glomerular filtration rate / GFR – chemistry test• Blood enters glomerular capillary system• Very high pressure created by arterioles• Special capillaries allowing filtration• Selected components of the blood plasma to pass through the semi-permeable membrane into the capsular space of Bowman's capsule Urine Formation - Filtration • Glomerular filtration continued• Ultrafiltrate• *Composition similar to blood plasma• Contains substances up to @ 70,000 daltons.• Water, glucose, amino acids, urea, creatinine, ammonia,electrolytes - Na, Cl, , etc. • NOT blood cells, fats, & proteins. • Recap• GFR – glomerular filtration rate - @ 120 mL/min, varies with age and sex, used to monitor kidney disease progression• Ultrafiltrate –• substances < 70,000 daltons• No blood cells, fats, higher mol wt. proteins, etc.Urine Formation  Anatomy review Modified blood leaving through efferent arteriole pass through vessels (peritubular capillaries) that participate in reabsorption process. These vessels eventually become the renal vein.• Physiology of the Urinary System• Kidney accomplishes these tasks by: • Filtering• Reabsorbing• Secreting• ConcentratingUrine Formation –Reabsorption• Selected substances removed during ultrafiltration are returned to circulation.• Those things (small enough to filter) that the body cannot afford to lose.• Proximal tubules reabsorb water, sodium chloride, bicarbonate, potassium, calcium, amino acids, phosphate, protein, glucose, and other substances.• Varying proportions are reabsorbed • proteins and glucose almost completely reabsorbed• sodium chloride is only partly reabsorbed• no reabsorption of creatinineUrine Formation –Reabsorption• Tubular processing of the glomerular ultrafiltrateUrine Formation –Reabsorption• Both active and passive transport processes are used.Urine Formation –Reabsorption• Renal tubular function• Failure to reabsorb unwanted substances• Urea• Creatinine• phosphates, sulfates, uric acid• Such substances not actively transported, but some may be passively returned.Urine Formation - Secretion • Secretion of unwanted substances• drugs, & some waste products• Acid – base balance through the• reabsorption of filtered bicarbonate ion • secretion of H+ions attached to bicarbonate• secretion of H+ions attached to phosphate• secretion of H+ions attached ammoniaUrine Formation – Concentration • Endocrine influence – hormones affecting excretion/reabsorption of electrolytes and water.Urine Formation – endocrine influence • Antidiuretic hormone (ADH) (also known as vasopressin)• secreted by the posterior pituitary gland. • Controlled by body hydration, ADH regulates absorption of water in the distal portion of the nephron• By making the walls of the distal and collecting tubules permeable to water.Urine Formation – endocrine influence • Antidiuretic hormone (ADH) • insufficient ADH results in diabetes insipidus• Effects• Excess urine production , increased urine volume• Decreased plasma volume• Excess results in SIADH• Results in o high plasma volume,o low serum osmolarityo high urine osmolarityo low plasma sodiumo higher than normal urine sodium.Urine Formation – Concentration • Endocrine influence • Aldosterone• From adrenal cortex• Acts on distal and collecting tubules• Promotes active reabsorption of sodium from the glomerular filtrate (and concurrent secretion of potassium). • Increases water retention• Raises blood pressureRenal Functions • Hormones produced by the Kidney• Erythropoietin / EPO• Also called hematopoietin / hemopoietin • Produced and released by peritubular capillary endothelial cells in the kidney • Stimulates bone marrow to produce and release RBCs Renal Functions • Hormones produced by the Kidney• Renin• Enzyme –like acting substance • Released from the juxtaglomerular cells • Released in response to decreased blood pressure.• Acts on plasma substrate (angiotensinogen) changing it to Angiotensin I. When it passes through the lungs it is then changed into the active form, Angiotension II.• causes dilation of afferent arteriolesand vasoconstriction of efferent arterioles• promotes reabsorption of sodium in the proximal tubules• promotes secretion of the sodium retaining hormone, aldosterone.• (all of which cause increase in BP)Renal Functions • Electrolyte balance • Sodium & Potassium• Renin-angiotensin-aldosterone system (reabsorption of sodium and secretion of potassium)• Calcium reabsorbed in proximal tubule under influence of parathyroid hormone (PTH)• Magnesium regulation parallels calcium• Phosphorus reabsorption in proximal tubule is suppressed by PTH.Renal Functions • Renal threshold /Threshold substances• When plasma concentration of a substance is so high that it can no longer be reabsorbed. The substance will then be detectable in the urine.Renal Functions • Renal threshold /Threshold substances• Glucose - high threshold substance • appears in the urine when plasma concentration exceeds about 160 to 180 mg/dl. • Other threshold substances:• amino acids• ascorbic acid • creatine• potassium• sodium chlorideRenal Functions