Excretion

• Homeostasis is the maintenance of a

stable internal environment– in cells– in the tissue fluid around the cells – in the blood plasma

• For example:– Temperature– Water– Glucose

negative feedback mechanisms

• Excretion is the removal, from the body, of unwanted waste from metabolic reactions

• For example:– CO2 from respiration in all body cells is

carried by the blood to the lungs and excreted– Urea from the deamination of excess

Deamination

Excretory System

Kidney: external view

Adrenal gland

Cortex

Renal artery – brings blood in

Pelvis – continues into ureter

Renal vein – removes bloodUreter – urine to bladder

Kidney: section

Capsule – tough outer layer

Renal sinus – continues to pelvisRenal pelvis – continuous with

ureter

Renal pyramid – part of medulla

Medulla – mostly collecting ductsCortex – glomeruli are found here

Renal Cortex

This is where the kidney nephrons are foundThere is a rich supply of capillaries

Detail of nephron

Nephrons are long tubes that start at a Bowman’s capsule and finally flow into the pelvis of the kidney

Nephron

Renal Arteryblood comes in rich in urea

GlomerulusThis is a knot of capillaries Water and solutes are forced out

Bowman’s capsuleThe filtrate flows into this capsule

Proximal Convoluted TubuleAll the glucose, amino acids and some water and salts move back into the blood here

Peritubular capillariesThese surround the tubules and pick up substances from the filtrate

Loop of HenleThis is important in re-absorption of water

Distal covoluted tubulesNa+ is reabsorbed here

Collecting ductMore water is reabsorbed and osmoregulation happens here

Urine Leaves the kidney,Removing urea and excess salt and water

Renal Veinblood leaving the kidney has very little urea and some of the salts and water removed