The Excretory System SBI 4U

The Importance of Excreting Wastes to maintain life processes, the body must eliminate harmful waste products excess proteins are converted into carbohydrates  amino group must be removed (deamination) byproduct is ammonia – extremely toxic! fish are able to avoid ammonia build-up, but land animals must store wastes in the form of urea or uric acid (less toxic)

Excretion: From Simple to More Complex Animals unicellular & primitive multicellular organisms – wastes released directly from cells amoeba & paramecium – contractile vacuoles expel excess water worms – wastes collected and stored in a series of tubules grasshopper – wastes released into gut and eliminated with solid wastes

The Importance of Excreting Wastes

The Urinary System Functions: remove wastes balance blood pH maintain water balance Major organs: kidneys, ureters, bladder

The Urinary System Nephron: functional unit of the kidneys ~1 million per kidney afferent arterioles bring blood in blood reaches a capillary bed called a glomerulus where filtration occurs efferent arterioles carry blood out wastes (fluids & solutes) collect in the kidney to be reabsorbed and secreted

Renal Bloodflow H_yesYhttps:// H_yesY

Formation of Urine 1.Filtration – pressure in glomerulus is high so some solutes (e.g. NaCl, glucose) and fluids move out

Formation of Urine 2.Reabsorption – selective reabsorption of Na +, Cl - and HCO 3 - occurs by both active and passive transport 3.Secretion – wastes (water, salt, urea, uric acid, minerals) move from blood into nephron to be released as urine

Water Balance osmoregulation – the control of water and ion balance in the body. osmoreceptors – specialized nerve cells in the hypothalamus that detect changes in the osmotic pressure of the blood and surrounding extracellular fluids. antidiuretic hormone (ADH) – causes the kidneys to increase water absorption; helps to conserve body water. aldosterone – hormone that increases Na+ reabsorption; helps to regulate blood pressure and blood volume.

Regulating ADH

Kidneys & Blood Pressure

pH Balance kidneys maintain pH balance of body fluids ( ) acid-base balance is maintained by buffer systems that absorb excess H + ions or ions that act as bases restore buffers by excreting excess H + ions or restoring more HCO 3 - ions:

pH Balance

Kidney Disease Can be diagnosed from a urinalysis = analysis of urine colour, clarity and components could also be an indicator of diet Possible disorders (see handout): –diabetes mellitus –diabetes insipidus –Bright’s disease –kidney stones

Kidney Disease Normal urine: colour: yellow clarity: clear glucose: negative specific gravity: – blood (heme): neg pH: ~7 protein: neg nitrite: negative leukocytes: negative