Download AP Notes Excretion 09

Functions of the Excretory System
 Remove nitrogenous wastes caused by metabolism
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Protein  amino acids
Nucleic acids  nitrogenous groups
o Ammonia:* very toxic can be transported if very diluted
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Aquatic animals: excrete directly
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Terrestrial animals: make a less toxic form in the liver & concentrated in kidneys
▫ Urea:* nontoxic, water soluble. Mammals, amphibians & some marine
▫ Uric Acid:* nontoxic, water insoluble paste. Insects, bird & some reptiles
 Regulate water loss and gain
Systems
 Flatworms: Protonephridia
o Flame cells collect interstitial fluid of body, Cilia move fluid through the tube, Water and salt adjusted
 Earthworms: Metanephridia
o Tubes with internal openings to collect fluids, Salts/water adjusted in capillary area, Urine is hypoosmotic to
body fluid
 Insects: Malphighian tubules
o Dead end tubes dangle in the hemolymph in body cavity, Salts, wastes pumped into tube, rectum restores salts
to blood, Nitrogenous wastes are dry and excreted with feces
 Vertebrates: Kidney with Nephrons
o Overviews:
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Filtration:* water and solutes enter nephron
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Reabsorption:* water and valuable solutes are reabsorbed into the blood
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Secretion:* substances in blood are transported to the filtrate
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Excretion:* urine leaves the body
o Kidney:* excretory organ, basic unit is a nephron
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Filtrate:* water, urea & solute (glucose, AA, ions & vitamins), extracted by kidneys
o Two parts: renal cortex & renal medulla
o Renal artery & vein supply blood for cleaning
o Nephron:* functional unit of kidney, starts & ends in the cortex
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Bowman’s Capsule:* cup shaped, receives the filtrate
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Glomerulus:* ball of capillaries
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Combined form a filtration unit
st
 1 – Blood pressure forces plasma out & into tube: all solutes
 2nd – Glomerulus & Bowman’s capsule: filtrate is processed
Out of blood  salt sugar urea water
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3rd – Proximal Tubule:* Secretion into & reabsorption out of tube through active & passive transport
o 75% of salts, water, nutrients, glucose, AA are reabsorbed
Out of blood  ammonia drugs poison
Into blood  salts, water, nutrients, glucose, amino acids

4th – Descending Loop of Henle:* carries filtrate into the medulla, length varies in animals, depends on
environment – dryer = longer
Into blood/interstitial  water
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5th – Ascending Loop of Henle:* carries filtrate into the cortex.
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6th – Distal tubule:* Cortex, pH regulation (helps buffer blood) by absorbing bicarbonate and secreting H+. Farthest
away from Bowman’s capsule.
Into tube  K+, H+
Into blood/interstitial  Na+, Cl-, bicarbonate
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7th – Collecting Duct: in medulla. Urine is collected & disposed of. Water & salt is reabsorbed
o Only 20% of nephrons go through the medulla, rest stay in cortex
8th – Urine travels to renal pelvis
9th – Ureters carry urine to bladder
10th – Bladder stores urine
11th – Urethra:* tube through which urine exits the body
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Into blood/interstitial  salt
Control
 Water intake sets off hormones
o Lots of water: very dilute urine, remove water without losing salts
o Little water: slightly hyperosmotic urine to remove wastes with as little water as possible
 Antidiuretic Hormone (ADH)* – need water/volume
o Made in hypothalamus, released from pituitary
o Receive impulses from osmoreceptor cells when osmolarity (solute concentration) increases
o Increases permeability to water in distal convoluted tubule and collecting duct
o Increase reabsorption of water decreases osmolarity and shuts off ADH = negative feedback
 Aldosterone – need water/volume and salt
o Released by tissue near glomerulus
o Causes the tubules to retain sodium and water, increases the volume of fluid in the body, and drives blood
pressure up.