Urinary system Chapter 25

Excretory System The main organs of the excretory system are the bladder, kidneys, liver, lungs, and skin. The excretory system is like the sewage system because it gets rid of waste that the body does not need. The body also gets rid of natural gases which can be fatal if not released.

Functions of Urinary System Kidneys carry out four functions –Filter nitrogenous wastes, toxins, ions, etc. from blood to be excreted as urine. –Regulate volume and chemical composition of blood (water, salts, acids, bases). –Produce regulatory enzymes. Renin – regulates BP/ kidney function Erthropoeitin – stimulates RBC production from marrow. –Metabolism of Vitamin D to active form.

Urinary System Two Kidneys –Perform all functions except actual excretion. Two Ureters –Convey urine from Kidneys to Urinary Bladder Urinary Bladder –Holds Urine until excretion Urethra –Conveys urine from bladder to outside of body

Kidney general info Lie against posterior abdominal wall at level of T12-L3. Right kidney is lower than left kidney due to the shape of the liver. Lateral surface of kidney is convex while medial is concave.

Kidney External Anatomy Average size – 12cm x 6cm x 3 cm Weights 150 grams or 5 oz Filters blood almost 400x times a day!

Human Kidney

Kidney Internal Anatomy I Renal arteries and veins –Bring blood in and out of kidney Renal cortex –Outer layer of Kidney Renal medulla –Inner layer of Kidney Nephron

Kidney Internal Anatomy II Renal Pyramids Renal Columns –Space between pyramids within the medula Renal Papilla –Narrow end of pyramid Calyx (ces) –Collecting tubes Renal Pelvis –Collecting vessel prior to ureter

Purpose of Nephron Millions of nephrons located inside of each kidneys Responsible for filtration and purification of blood Creates urine

Parts of a Nephron

Urine Formation Urine is formed through a combination of four basic processes: 1) glomerular filtration, 2) tubular reabsorption, 3) tubular secretion, and 4) water conservation.

Glomular Filtration Pressure of heart contractions filters blood by forcing water, ions and solutes from glomular capillaries into Bowman's capsule Leaves behind blood cells and proteins First step in urine formation Osmosis and active filtration Substances that passes through become filtrate 3. Starr, Cecie. Biology: the unity and diversity of life. 11th ed. Australia: Thomson Brooks/Cole, Print.

Tubular Reabsorption Variety of substances (water, ions, and selected solutes) leak out of the nephron, diffuse through interstitial fluid, and then enter a capillaries Occurs along a nephron's tubular parts Returns most of filtrate back to blood Water is transported via osmosis o High to low concentration 3. Starr, Cecie. Biology: the unity and diversity of life. 11th ed. Australia: Thomson Brooks/Cole, Print.

Tubular Secretion & Water Conservation Transporters move urea, H+, and K+, (wastes) from the capillaries into the nephron for excretion Continues along nephron's tubular parts Active transportation (capillary → collecting tubules) Once the fluid moves into the collecting duct it is called urine. While in the collecting duct, additional water is removed from the urine, concentrating the wastes. 3. Starr, Cecie. Biology: the unity and diversity of life. 11th ed. Australia: Thomson Brooks/Cole, Print.

Micturition (Urination) Ureters –25 cm long –Enters on the floor of bladder Urinary Bladder –Muscular sac on floor of pelvic cavity –Average bladder volume is 500 ml –Max capacity is ml

Micturition Reflex Bladder with >= 200 ml of urine Sensory input to parasympathetic system Contraction of detrusor muscle and relaxation of internal urethral sphincter Relaxation of external urethral sphincter

Micturition

Urethra –Conveys urine out of body –Female urethra – cm –Opens into external urethral oriface –Lies between vaginal oriface and clitoris –Male urethra – 18 cm

Kidney stones A hard granule of calcium, phosphate, uric acid and protein. Form in renal pelvis and get lodged in pelvis or ureter. Caused by urinary tract infections, dehydration, pH imbalances, or an enlarged prostate gland. Treated with stone dissolving drugs, surgical removal, or lithotripsy (ultrasonic vibrations)

Kidney Stones