The Urinary System

Objectives: Describe the functions of the Urinary SystemDescribe the functions of the Urinary System Describe the major organs of the urinary systemDescribe the major organs of the urinary system Describe the structure of a nephronDescribe the structure of a nephron Describe filtration, re-absorption, and formation of urine by the nephronDescribe filtration, re-absorption, and formation of urine by the nephron Describe diseases and disorders of the urinary systemDescribe diseases and disorders of the urinary system

Functions Elimination of waste productsElimination of waste products –Nitrogenous wastes from the metabolism of proteins –Toxins –Drugs Regulate aspects of homeostasisRegulate aspects of homeostasis –Water balance –Electrolytes –Acid-base balance in the blood –Blood pressure –Red blood cell production –Activation of vitamin D

Major Organs of the Urinary System KidneysKidneys UretersUreters Urinary bladderUrinary bladder UrethraUrethra

Kidneys Against the dorsal body wallAgainst the dorsal body wall At the level of vertebrae T12 to L3At the level of vertebrae T12 to L3 The right kidney is slightly lower than the leftThe right kidney is slightly lower than the left Attached to ureters, renal blood vessels, and nerves at renal hilusAttached to ureters, renal blood vessels, and nerves at renal hilus Atop each kidney is an adrenal glandAtop each kidney is an adrenal gland Renal capsuleRenal capsule –Surrounds each kidney Adipose capsuleAdipose capsule –Surrounds the kidney –Provides protection to the kidney –Helps keep the kidney in its correct location

Kidney Internal Structure Renal cortex – outer regionRenal cortex – outer region Renal medulla – inside the cortexRenal medulla – inside the cortex Renal pelvis – inner collecting tubeRenal pelvis – inner collecting tube Medullary pyramids – triangular regions of tissue in the medullaMedullary pyramids – triangular regions of tissue in the medulla Renal columns – extensions of cortex-like material inwardRenal columns – extensions of cortex-like material inward Calyces – cup-shaped structures that funnel urine towards the renal pelvisCalyces – cup-shaped structures that funnel urine towards the renal pelvis

Nephron Nephrons are the structural and functional filtration units of the kidneysNephrons are the structural and functional filtration units of the kidneys Responsible for forming urineResponsible for forming urine Main structures of the nephronsMain structures of the nephrons –Glomerulus –Renal tubule

Nephron: Glomerulus A specialized capillary bedA specialized capillary bed Attached to arterioles on both sides (maintains high blood pressure)Attached to arterioles on both sides (maintains high blood pressure) –Large afferent arteriole –Narrow efferent arteriole Capillaries are covered with podocytes from the renal tubuleCapillaries are covered with podocytes from the renal tubule The glomerulus sits within a glomerular capsule (the first part of the renal tubule)The glomerulus sits within a glomerular capsule (the first part of the renal tubule)

Nephron: Renal Tubule Glomerular (Bowman’s) capsuleGlomerular (Bowman’s) capsule Proximal convoluted tubuleProximal convoluted tubule Loop of HenleLoop of Henle Distal convoluted tubuleDistal convoluted tubule

Peritubular Capillaries Arise from efferent arteriole of the glomerulusArise from efferent arteriole of the glomerulus Normal, low pressure capillariesNormal, low pressure capillaries Attached to a venuleAttached to a venule Cling close to the renal tubuleCling close to the renal tubule Reabsorb (reclaim) some substances from collecting tubesReabsorb (reclaim) some substances from collecting tubes

Urine Formation a. Filtrationa. Filtration b. Reabsorptionb. Reabsorption c. Secretionc. Secretion

Filtration Nonselective passive processNonselective passive process Water and solutes smaller than proteins are forced through capillary wallsWater and solutes smaller than proteins are forced through capillary walls Blood cells cannot pass out to the capillariesBlood cells cannot pass out to the capillaries Filtrate is collected in the glomerular capsule and leaves via the renal tubuleFiltrate is collected in the glomerular capsule and leaves via the renal tubule

Reabsorption The peritubular capillaries reabsorb several materialsThe peritubular capillaries reabsorb several materials –Some water –Glucose –Amino acids –Ions ( sodium) Some reabsorption is passive, most is activeSome reabsorption is passive, most is active Most reabsorption occurs in the proximal convoluted tubuleMost reabsorption occurs in the proximal convoluted tubule Materials not reabsorbed:Materials not reabsorbed: Nitrogenous waste products UreaUrea Uric acidUric acid CreatinineCreatinine Excess water

Secretion Some materials move from the peritubular capillaries into the renal tubulesSome materials move from the peritubular capillaries into the renal tubules –Hydrogen and potassium ions –Creatinine Materials left in the renal tubule move toward the ureterMaterials left in the renal tubule move toward the ureter

Urine Formation

Characteristics of Normal Urine Colored somewhat yellow due to the pigment urochrome (from the destruction of hemoglobin) and solutesColored somewhat yellow due to the pigment urochrome (from the destruction of hemoglobin) and solutes SterileSterile Slightly aromatic (has an odor)Slightly aromatic (has an odor) Normal pH of around 6Normal pH of around 6 Specific gravity of to 1.035Specific gravity of to 1.035

Ureters Slender tubes attaching the kidney to the bladderSlender tubes attaching the kidney to the bladder –Continuous with the renal pelvis –Enter the posterior aspect of the bladder Runs behind the peritoneumRuns behind the peritoneum Peristalsis aids gravity in urine transportPeristalsis aids gravity in urine transport

Urinary Bladder Smooth, collapsible, muscular sacSmooth, collapsible, muscular sac Temporarily stores urineTemporarily stores urine Trigone – three openingsTrigone – three openings –Two from the ureters –One to the urethra Three layers of smooth muscle (detrusor muscle)Three layers of smooth muscle (detrusor muscle) Mucosa made of transitional epitheliumMucosa made of transitional epithelium Walls are thick and folded in an empty bladderWalls are thick and folded in an empty bladder Bladder can expand significantly without increasing internal pressureBladder can expand significantly without increasing internal pressure

Urethra Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsisThin-walled tube that carries urine from the bladder to the outside of the body by peristalsis Release of urine is controlled by two sphincter muscles:Release of urine is controlled by two sphincter muscles: –Internal urethral sphincter (involuntary) –External urethral sphincter (voluntary) LengthLength –Females – 3–4 cm (1 inch) –Males – 20 cm (8 inches) LocationLocation –Females – along wall of the vagina –Males – through the prostate and penis FunctionFunction –Females – only carries urine –Males – carries urine and is a passageway for sperm cells

Micturition (Voiding) Both sphincter muscles must open to allow voidingBoth sphincter muscles must open to allow voiding –The internal urethral sphincter is relaxed after stretching of the bladder –Activation is from an impulse sent to the spinal cord and then back via the pelvic splanchnic nerves –The external urethral sphincter must be voluntarily relaxed

Water Balance Water intake must equal water outputWater intake must equal water output Sources for water intakeSources for water intake –Ingested foods and fluids –Water produced from metabolic processes Sources for water outputSources for water output –Vaporization out of the lungs –Lost in perspiration –Leaves the body in the feces –Urine production Dilute urine is produced if water intake is excessiveDilute urine is produced if water intake is excessive Less urine (concentrated) is produced if large amounts of water are lostLess urine (concentrated) is produced if large amounts of water are lost Proper concentrations of various electrolytes must be presentProper concentrations of various electrolytes must be present Regulation is primarily by hormonesRegulation is primarily by hormones –Antidiuretic hormone (ADH) prevents excessive water loss in urine –Diuretics are substances which block the production (alcohol) or inhibit the action of ADH on the collecting tubules (caffeine) in either event they increase urine output.

Diseases and Disorders of the Urinary System Cystitis: Bladder infection due to yeast or bacteria which irritate the lining of the bladder resulting in inflammation, often producing a feeling of a need to void constantly, more common in females than males due to anatomical differences.Cystitis: Bladder infection due to yeast or bacteria which irritate the lining of the bladder resulting in inflammation, often producing a feeling of a need to void constantly, more common in females than males due to anatomical differences. Glomerular nephritis: Destruction of the nephron of the kidney, genetic, hypertension, or renal infections can result in this disorder. Can lead to renal failure and the necessity for dialysis by a kidney machine to function as the kidney.Glomerular nephritis: Destruction of the nephron of the kidney, genetic, hypertension, or renal infections can result in this disorder. Can lead to renal failure and the necessity for dialysis by a kidney machine to function as the kidney.

Diseases and Disorders of the Urinary System Kidney and Bladder Stones: These are solid particles formed in urine usually from calcium carbonate crystals. Kidney stones dislodge from the kidney and as they travel through the ureters result in severe pain, sometimes accompanied by bleeding. Bladder stones form in the bladder and cause problems due to blocking of the urethral opening preventing voiding of the bladder.Kidney and Bladder Stones: These are solid particles formed in urine usually from calcium carbonate crystals. Kidney stones dislodge from the kidney and as they travel through the ureters result in severe pain, sometimes accompanied by bleeding. Bladder stones form in the bladder and cause problems due to blocking of the urethral opening preventing voiding of the bladder.