Chapter 44 Campbell Reece

Front 1

Function of excretory system

Back 1

1. Rids body of waste
2. Regulates amounts of ions and water that are present in body fluids

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Marine Bony Fishes

Back 2

Hypoosmotic to seawater – lose water and gain salt by diffusion and osmosis

Gain water by drinking lots of seawater

Salt and solutes discarded by gills, skin, and kidneys

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Marine Cartilaginous Animals and Sharks

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Slightly hyperosmotic to seawater – gain water

Have low internal salt concentration, but high urea concentration

Salt discarded by kidneys and rectal gland

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Freshwater Fish

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Hyperosmotic to environment – gain water and lose salt

Do not drink water

Secrete lots of dilute urine to get rid of water

Gain salt through food and by active transport across gills

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Birds and Reptiles Living Near the Sea

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Consume lots of salt in their diets

Nasal salt glands remove excess salt from body by secreting a concentrated salt solution

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sea mammals

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Kidneys can maintain a constant salt concentration in body by producing urine that has a high concentration of salt.

Can drink seawater because the salt concentration of urine is higher than that of sea water

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Terrestrial Mammals

Back 7

Dessication a big problem for land animals

Have many structures to protect against water loss – skin, exoskeleton, waxy cuticle, fur, etc.

Most terrestrial animals drink water, but some are so highly adapted that they get enough water from metabolic waste water and food (e.g. kangaroo rat)

Front 8

Contractile vacuoles

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Mostly seen in paramecia

Live in fresh water – water always entering the cell through osmosis

Water is expelled through 2 contractile vacuoles

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Protonephridia

Back 9

– seen in freshwater flatworms
Interstitial fluid passes through a flame cell, propelled by a tuft of cilia along the branched system of tubules.
Fluid drains into excretory ducts that empty out of the body through numerous nephridiopores
Transport epithelium lining the tubules function in osmoregulation by absorbing salts before the fluid exits the body

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Metanephridia

Back 10

seen in annelids (earthworms)
Earthworms have two nephridia per segment
Tubule with ciliated opening (nephridiostome) on one end and an excretory pore (nephridiopore) that opens to the outside of the body
Fluid is moved in by cilia. Some substances and water are reabsorbed in a network of capillaries that surround the tubule.
This system produces large amount of urine (60% of body wt./day).

Front 11

Malphigian Tubules

Back 11

- Excretory organs of insects and other terrestrial arthropods
Remove nitrogenous wastes from the hemolymph and function in osmoregulation
Are outpocketings of the gut that open into the digestive tract.
They collect water and uric acid from surrounding hemolymph (blood) and empty it into the gut. Water and useful materials are reabsorbed by the intestine but wastes remain in the intestine

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Vertebrate Kidneys

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Function in the removal of nitrogenous and other wastes and in osmotic regulation of the body fluids

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Nitrogenous Wastes

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1. Ammonia
2. Urea
3. Uric acid

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Ammonia

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highly soluble in water but very toxic. Aquatic animals such as bony fishes, aquatic invertebrates, and amphibians excrete ammonia because it is easily eliminated in the water.

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Urea

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terrestrial amphibians and mammals excrete urea because it is less toxic than ammonia and can be moderately concentrated to conserve water

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Uric Acid

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not very toxic and is not very soluble in water. Conserves water because it can be produced in a concentrated form due to its low toxicity. Insects, reptiles, birds, and some dogs (Dalmatians) excrete uric acid. Because it is relatively insoluble and nontoxic, it can accumulate in eggs without damaging the embryos

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mammalian kidney

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consists of an outer cortex and an inner medulla and is composed of units called nephrons

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Nephrons

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1. Gomerulus
2. Loop of Henle
3. Bowman’s Capsule

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Glomerulus

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a ball of capillaries situated in the cortex of the kidney

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Loop of Henle

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- long U-shaped tubule that extends into the medulla of the kidney and connects to collecting tubules which eventually merge to join the ureter.

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Bowman’s Capsule

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cup-shaped swelling at the blind end of the tubule that surrounds the glomerulus

Front 22

Filtration of blood

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Blood pressure forces plasma out of the capillaries of glomerulus and into the Bowman’s capsule and down the tube of the nephron
Small solutes are also forced out of the bloodstream with the plasma.
Larger proteins, and cells remain in the capillaries, creating a very hypertonic solution.

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Reabsorption in Proximal Tubule

Back 23

Filtrate passes through the proximal tubule – first part of nephron
Lumen wall of the epithelial cells of the proximal tubule is like the lumen wall of the small intestine - both are bordered with millions of microvilli to increase surface area.
Epithelial cells reabsorb ions, nutrients, and water and transport them to the blood vessels nearby

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Descending limb of the loop of heple

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is highly permeable to water but impermeable to solutes. Water flows from the loop into the surrounding medium via osmosis.

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Ascending limb of the loop of heple

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is highly permeable to salt but impermeable to water. Salt removed from filtrate by both passive and active transport.

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Vasa recta

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a network of capillaries that surround the loop of Henle and reabsorb water and solutes filtered from the blood

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Distal Tubule

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last part of nephron which absorbs variable amounts of water, Na+, Cl-, and electrolytes.

Front 28

Tubular secretion

Back 28

process by which some wastes are actively secreted into the fluid in the distal tubule. Examples of secreted wastes are H+, K+, NH4+ toxic substances and foreign substances (drugs, penicillin, uric acid, creatine).
Secretion of H+ adjusts the pH of the blood.

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Aldosterone (a hormone) .

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is released if the Na+ levels in the blood are low - leads to reabsorption of Na+ and Cl-. Water will also flow into the tubule via osmosis

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ADH (antidiuretic hormone)

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is released if a person is dehydrated. This causes aquaporin channels to be inserted in the membrane of the collecting duct so that large quantities of water can be reabsorbed.