Excretory System

How to make pee …

Renal Artery Renal Vein

Adrenal GlandRenal Cortex

Renal Pelvis

KidneyRenal Medulla

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

Urea

• H2N ---C---NH2

//

O

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