The Urinary System Chapter 20

Introduction A major part of homeostasis is maintaining the composition, pH, and volume of body fluids within normal limits The urinary system removes metabolic wastes, substances in excess, and toxic foreign materials (e.g., drugs)

Urinary system anatomy

Kidneys Paired structures Main functions: regulate volume, composition, and pH of body fluids Removes metabolic wastes from blood, excretes to outside of body

Kidney anatomy One million nephrons per kidney

Nephron functioning Four processes: – Filtration- movement of substances from blood to nephron – Reabsorption- moving substances back into blood – Secretion- removing select molecules from blood to tubule – Excretion- filtrate into the bladder

Nephrons Each kidney contains about 1 million Composed of two parts – Renal corpuscle (glomerulus, Bowman’s (glomerular) capsule) – Renal tubules (from Bowman’s to collecting duct) Distal tubules of several nephrons empty into one collecting duct, many collecting ducts merge

Renal corpuscle - Capsule - Glomerulus

Glomerular filtration Blood from afferent arteriole into glomerular capillaries Capillaries are very permeable Large volume of water, ions, sugars are filtered out of the blood stream and into the renal tubule

Capillary pressure Drives filtration from capillary to glomerulus Primarily due to blood pressure

Glomerular filtration Only 20% filters through, 19% reabsorbed

x 90, per day Only 1.5L leaves body

Reabsorption Concentration gradients Along Loop of Henle Descending loop- permeable to water, as solute concentration increases in medulla, water moves to try to equalize Ascending loop- permeable to solutes, as solute concentration decreases, solutes move Allows for reabsorption of water and solutes as needed

Reabsorption- why bother? Clears out foreign material quickly Quicker way to regulate water and ions, if needed just reabsorb

Reabsorption can reach saturation point Too many solutes in blood stream, can’t reabsorb What’s not reabsorbed is excreted into the bladder

Diabetes mellitus Excess glucose in urine

Secretion If a substance isn’t caught during filtration, capillaries can secrete into nephron Usually an active transport process Organic compounds and foreign materials

Several nephrons dump into collecting duct, into ureters

Micturition- peeing Bladder can hold 500 mL

Urethra Tube through which urine leaves body

Urine 95% water Urea, chloride, sodium, other organic and inorganic substances

Dialysis Diabetes, high blood pressure End stage renal failure- lost 85-90% function Permanent, can get transplant

Gout Metabolism of purine, uric acid crystalizes Causes immune reaction Kidneys can’t excrete enough uric acid (decreased filtration, secretion, increased reabsorption)

Kidney stones Chemicals in the urine become concentrated, most common is calcium Leads to crystallization Can get lodged in urinary tract