The Urinary System Functions: Excretion of wastes from the blood (kidneys) Elimination of wastes into environment (ureters, bladder, urethra) Regulation of volume and solute concentration of blood plasma

Organs of the Urinary Tract Kidneys reddish brown, bean shaped, located just below the ribs on posterior wall of abdominal cavity regulate volume, composition, and pH of body fluids (remove metabolic wastes in the process) secrete hormone erythropoetin (controls rate of RBC formation) secrete enzyme renin (regulates blood pressure) functional unit is the nephron (will discuss later)

Organs cont. Ureters transport urine from kidneys to bladder 25 cm long tubes muscular walls help move urine by peristalsis kidney stones can block this tube

Organs cont. Urinary bladder temporarily stores urine hollow, muscular organ composed of transitional epithelium (stretches) internal urethral sphincter - muscle that surrounds the neck of the bladder; remains contracted to prevent the bladder from emptying until pressure increases to a certain level – autonomic controlled External urethral sphincter – voluntarily controlled, ring of muscles where urethra exits body. How you control when you use the restroom.

Female Male

Organs cont. Urethra conveys urine out of body about 4 cm long in females about 19 cm long in males

Urethral Sphincters

Micturition bladder can hold as much as 600 ml of urine urge to urinate occurs when it contains 200 ml the reflex to urinate is inhibited by the conscious control of the external urethral sphincter Urine leaves the bladder by micturition (a.k.a. urination)

Micturition Reflex bladder distends as it fills with urine and stimulates stretch receptors in bladder wall when stretch receptors are triggered, they stimulate muscular bladder wall to contract external urethral sphincter is relaxed voluntarily, and the internal urethral sphincter relaxes also urination occurs if ext. urethral sphincter does not relax, int. urethral sphincter remains closed

Micturition Reflex cont. What happens if you “hold it” too long? Once volume exceeds 500 ml, pressure may force open internal sphincter which causes reflexive relaxation of external sphincter, and urination occurs

Urinary Diseases and Disorders UTI - urinary tract infection more common in women than men b/c the urethra is shorter in females symptoms – burning pain during urination cause – bacteria spread from rectum to urethra Kidney Stones (a.k.a. renal calculi) result from chronically concentrated urine which causes uric acid to clump and form “stones” Possible causes: oxalate – found in green, leafy vegetables, coffee, and chocolate Gout – uric acid build up in joints

Gout Kidney Stones

World’s Largest Kidney Stone 22 oz. 5.5 in across

The Nephron each kidney contains ~ 1 million nephrons they filter 7.5 liters of plasma each hour each nephron consists of a renal corpuscle (blood vessels) and a renal tubule (tube) the renal corpuscle is divided into 3 parts. Renal artery, glomerulus, and peritubular capillary. renal artery becomes a cluster of capillaries called a glomerulus (surrounded by Bowman’s capsule) Then goes to a network of capillaries called peritubular capillaries which surround the renal tubule the renal tubule is divided into 4 parts; Bowman’s capsule, the proximal convoluted tubule, loop of Henle, and the distal convoluted tubule

Urine Formation Urine formation occurs in the nephrons Consists of 3 processes: 1. glomerular filtration (collects good and bad stuff) 2. tubular reabsorption (removes good stuff from filtrate and put back into body) 3. tubular secretion (puts in extra bad stuff into filtrate which is going to the toilet)

1. Glomerular Filtration (collecting good and bad stuff) Occurs when the renal artery delivers blood to the glomerulus blood pressure forces water and small molecules from blood plasma into the Bowman's’ capsule this fluid is now known as filtrate and moves into the renal tubule ex. of molecules in filtrate: water, glucose, amino acids, sodium, urea, uric acid, other minerals Filters both good and bad stuff for example; water and toxic substances

2. Tubular Reabsorption (removes good stuff from filtrate) occurs in the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct molecules from the filtrate (in the tubule) are returned by diffusion and active transport to the blood in the peritubular capillaries ex. of molecules that are reabsorbed: glucose, amino acids, and almost all of the water and sodium that enters the tubule is reabsorbed Make a really salty place so that on the next pass by we can remove almost all the water. (good stuff)

3. Tubular Secretion (Puts in extra bad stuff into filtrate) occurs mainly at the distal convoluted tubule molecules from the peritubular capillaries (blood vessels) are actively transported into the renal tubule (tubes) ex. of molecules that are secreted: uric acid, hydrogen ions, ammonia, penicillin (and other drugs)

Notice hormones in orange and green on right 3 1 2

Urine Formation cont. the distal convoluted tubule empties the fluid (urine) into a collecting duct which carries it away from the nephron Each collecting duct empties many nephrons Many collecting ducts empty the medullas into the funnel-shaped central chamber of the kidney (renal pelvis) the ureters drain this chamber the peritubular capillaries merge to form venules that carry the filtered blood away from the nephron and eventually out of the kidney

Urine Physical characteristics pH – slightly acidic (6.0) The yellow color in urine is due to chemicals called urobilins. These are the breakdown products of the bile pigment bilirubin. Bilirubin is itself a breakdown product of the heme part of hemoglobin from worn-out red blood cells. Most bilirubin is partly broken down in the liver, stored in the gall bladder, broken down some more in the intestines, and excreted in the feces (its metabolites are what make feces brown), but some remains in the bloodstream to be extracted by the kidneys where, converted to urobilins, it gives urine that familiar yellow tint. pH – slightly acidic (6.0) Chemical composition 95% water, 5% solutes

Urine Components Urea is the body’s main waste product - formed when amino acids are broken down into energy; is toxic to cells in high levels Uric acid – a by-product of the breakdown of nucleic acids (RNA & DNA) Creatinine – a by-product of muscle metabolism Ammonia – waste formed when bacteria break down proteins Ketones – waste produced when fats are digested (diabetes and Atkin’s diet)

Urine Composition affected by lifestyle and diet Volume varies from 0.6 to 2.5 liters/day Diuretics – inhibit reabsorption of water so increase urine volume – ex. coffee, tea, alcoholic beverages

Hormonal Regulation Aldosterone stimulates both reabsorption of Na+ and the secretion of K+ Na+ reabsorption increases water reabsorption, leading to a rise in blood volume and therefore a rise in blood pressure

Hormonal Regulation ADH (antidiuretic hormone) causes increased water absorption high solute conc. in blood  increased ADH secretion alcohol and caffeine inhibit ADH secretion causing excess excretion of dilute urine and dehydration

Diuretics in orange