Excretory System

How to make pee …

Renal Artery Renal Cortex Renal Vein Adrenal Gland Renal Pelvis Renal Medulla Kidney Ureter Urinary Bladder Urethra

• Every Cell in your body produces wastes • Metabolic waste, not feces (undigested material)

• Skin excretes water and salts in perspiration • Lungs excrete CO2 as a gas • Liver excretes bile pigments • Kidneys excrete nitrogeneous wastes in urine

Role of Kidneys

• Important in protein breakdown (proteins are amino acid based which is nitrogen based) • Nucleotides (metabolic products) are metabolized to form uric acid • Uric acid is not very soluble - if it precipitates out of solution, you have

gout

• H2N ---C---NH2 // O

Urea

What do kidneys do?

• 2 kidneys located high up in the abdomal cavity • Purposes • filter blood • maintain blood volume • remove waste products • recover vital substances • Maintains homeostasis in the body

• Little bit of protection by rib cage • Covered by tough fibrous cap of connective tissue - surrounded by adipose tissue (inside fibrous tissue)

Ureters

• Ureters connect bladder to kidney smooth muscle • Ureters and bladder made of transitional epithelium

• Urinary bladder can stretch to accommodate up to 600 ml or more (sometimes in excess of 1000ml) (600 ml is conservative) • has folds - rugae (like folds of stomach) running throughout is smooth muscle fibers • Urethra extends from bladder to outside the body

• Females urethra is about 1-2” - this leads to more frequent urinary tract infections • Male urethra is about 6” - prostate in later years can enlarge (very often does) which causes an obstruction in urine flow •

Histology of Kidney

• Bean shaped

3 regions

• Cortex • Medulla which contains renal pyramids (appear striated) • Renal Pelvis (or inner space) - continuous with ureter

Nephron

• Plasma minus the proteins pass through filtration cells, then you need to recover vital molecules - glucose, water, etc. • over 1 million nephrons • Nephron is the filtration unit of the kidney made of cells that are specialized for active transport, diffusion, moving substances across membranes

Nephron

• Structure of nephron • cup shaped structure - Bowman’s capsule • Parts of nephron beyond Bowman’s capsule • specialized tube

Bowman’s Capsule Renal Arteriole Glomerulus Capillaries Loop of Henle Collecting Tubule

Nephron

• part closest to glomerulus is the

proximal convoluted tubule

(closest to renal corpuscle • Loop of Henley or Henley’s Loop - descending and ascending limb with a hairpin turn • Distal convoluted tubule - farthest away from renal corpuscle • each has a role in recovery of nutrients and leads away from nephron to collecting duct and away

Formation of Urine

• Pressure Filtration • Blood from arteriole is flowing into glomerulus, due to bp, filtration • Everything from plasma that is filterable leaves through glomerulus - water, glucose, amino acids, salts, urea, uric acid and creatinine (nitrogen wastes) • blood cells, platelets and proteins are not filtered

• Concentration of water is same as plasma • Body needs to recover water and nutrients • Selective Reabsorption

• Almost 180 L of filtrate pass into collecting tubules per day. 90 - 2L bottles!

• Diffusion and active transport (passive and active processes) • water glucose amino acids and salts are reabsorbed. About 99% of the water is reabsorbed.

• Region most highly specialized for selective reabsorption is the proximal convoluted tubule • Many mitochondria needed - produce atp for active transport

• Reabsorption of water • happens in loop of Henle • Lower part of ascending limb - dealing with passive diffusion of NaCl • Regulate pH of blood by regulating particular ions • Beside filtration, keeping good stuff and getting rid of waste

• Maintaining blood volume • ADH - Produced in Hypothalamus by neurosecratory cells, stored and secreted from posterior pituitary gland • ADH increases the permeability of the collecting duct to water so more water can be reabsorbed.

• • Increase Blood Pressure and Blood Volume •

Diuresis

- increases amount of water in urine • Alcohol is a diuretic - decreases production of ADH • Believed after effects of alcohol (hangover) is due to dehydration

Kidney stones

- calcium salts or uric acid precipitate and form kidney stone