Download the excretory system

THE EXCRETORY SYSTEM
Excretory System- how animals get rid of the nitrogen-containing waste products of
metabolism
Nitrogenous Waste:
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Ammonia -very soluble; can only be tolerated at very low concentrations (highly toxic)
-can easily pass through membranes and are readily lost by diffusion to the
surround water
-most aquatic animals, including most bony fishes
Urea -substance produced in the vertebrate liver by a metabolic cycle that combines
ammonia with carbon dioxide
-low toxicity allows animals to transport and store urea safely at high
concentrations
-the circulatory system carries urea to the excretory organs, the kidneys
-mammals, most amphibians, sharks, some bony fishes, turtles
Uric Acid -relatively nontoxic; largely insoluble in water and can be excreted as a semisolid paste with very little water loss
-great advantage for animals with little access to water: many reptiles, birds,
insects, land snails
Other Excretory Systems (Invertebrates):
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Nepridia- found in earthworms
Malpighian- found in anthropods
Osmoregulation- the general process by which animals control solute concentrations and
balance water gain and loss
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Osmolarity
- Used to measure osmotic pressure in a solution
- Expressed as moles of solute per liter of solution
Osmoconformers- animals are isoosmotic (the same osmolarity) with their surroundings
-because their internal osmolarity is the same as their environment, there
is no tendency to gain or lose water
-often live in water that has a very stable composition and hence have a
very constant internal osmolarity (saltwater fish)
Osmoregulators- an animal that must control its internal osmolarity because its body
fluids are not isoosmotic with the outside environment
-an animal must discharge excess water if it lives in a hypoosmotic
environment
-an animal must take in water to offset osmotic loss if it inhabits a
hyperosmotic environment
-enables animals to live in freshwater and terrestrial environment, allows
many marine animals to maintain internal osmolarities different from that of seawater
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Stenohaline- animals that cannot tolerate substantial changes in external osmolarity
(goldfish)
Euryhaline-animals that can survivelarge fluctuations in external osmolarity (white
barnacles, Mozambique tilapia)
Fish use their gills in order to perform osmoregulation
Saltwater Fish: salt ions are excreted from the gills, lose water through their gills
Freshwater Fish: salt is taken in through the gills, gain water through their gills
ORGANS
The kidney gets rid of nitrogenous wastes and reabsorbs water and salt.
The skin gets rid of excess salt.
Kidney- the major organ that regulates excretion; each kidney is made up of a million tiny
structures called nephrons
Hormones of the Kidney: Vasopression (antidiuretic hormone) & Aldosterone
Nephrons- functional units of the kidney; consists of a single long tubule and ball of capillaries
called the glomerulus
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Bowman’s Capsule: cup-shaped swelling at blind end of tubule which surrounds
the glomerulus
Three Regions of Nephron:
Proximal Convoluted Tubule
Loop of Henle: a hairpin turn with a descending limb and an ascending
limb
Distal Convolute Tubule
Collecting Duct: receives processed filtrate from many nephrons
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Renal Artery: blood vessel which leads to the kidney and branches into arterioles,
then tiny capillaries
Glomerulus: ball of capillaries “sits” within Bowman’s Capsule
Filtrate: blood is filtered as it passed from glomerulus to bowman’s capsule
How Nephrons Work
1. Blood enters the nephron at the Bowman’s capsule.
2. Blood is filtered as it passes from the glomerulus to the Bowman’s capsulefluid now
called filtrate
3. Filtrate travels from bowman’s capsule, passes through proximal convoluted tubule,
then the loop of henle, distal convoluted tubule, then received by the collecting duct
4. Concentrated urine moves from the kidneys into the ureters, then into the bladder, and
finally out through the urethra.
How Urine is Made
Filtration- blood is filtered as it passed from glomerulus to the bowman’s capsule. Small
substances such as ions, water, glucose, and amino acids, easily pass through capillary walls.
Large substances, such as proteins and blood cells, cannot pass through.
Reabsorption- as the filtrate moves through the proximal convoluted tubule, some materials
are reabsorbed. The small solutes, such as water, nutrients, and salts, leave the proximal
convoluted tubule and are reabsorbed by a network of capillaries, the peritubular capillaries
that surround the tubules. The material remaining in t he tubule is urine.
Secretion- as the filtrate moves through the convoluted tubules, some substances, such as H+,
potassium, and ammonium ions, are secreted from the surrounding capillaries into the tubule
Skin
- largest organ in the body; contains 2.5 million sweat glands that secrete water and ions
in warm weather
- sweat glands maintain an optimal salt balance in the body and maintain the body’s
temperature
Three Layers:
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Epidermis- covered by a layer of dead cells called the stratum corneum
-stratum corneum form a barrier against invading microorganisms
Dermis- sweat glands are found here along with blood vessels, nerves, and sebaceous
(oil) glands
Subcutaneous tissue- mostly fats
Multiple Choice Questions:
1. The urinary system (also known as the excretory system) is the principal system
responsible for _______.
A. removal of carbon dioxide
B. water and electrolyte balance
C. excretion of toxic nitrogenous compounds
D. both "A" and B"
E. both "B" and "C"
F. "A", "B", and "C"
2. Each kidney is made up of a milllion tiny structures. They are also the
functional units of the kidney. What are these structures called?
A. nephridia
B. malpighian
C. renal artery
D. nephron
3. The Excretory System includes a lot of organs. What is the major organ(s)?
A. urethra
B. kidneys
C. skin
D. "B" and "C"
Free Response Question:
1. How does a nephron work? Describe how blood flows through a nephron. Be
sure to include where the blood goes after it leaves the nephron.
THE EXCRETORY SYSTEM