Excretie (BOOK)
44.1
Osmolarity is the number of moles of solute per liter of solution. Two solutions with the
same osmolarity are isoosmotic, when they differ, one is hyperosmotic, and the other is
hypoosmotic.
Osmoconformer: to be isoosmotic with its surrounding, it are all marine animals.
Osmoregulator: to control internal osmolarity independent of that of the external
environment.
Stenohaline animals can’t handle big changes, whereas euryhaline animals can.
Marine fish
Marine fish constantly lose water by osmosis, so they drink lots of seawater. The salt is
eliminated through the gills and kidneys.
Sharks have a high concentration of urea in their blood, this isn’t toxic for them because they
have an organic molecule called trimethylamine N-oxide (TMAO) which protects proteins
from the denaturing effect of urea. TMAO regulates osmoses as well.
Freshwater animals
The problems of marine animals are the opposite of freshwater animals. They face the
problem of gaining water by osmosis. Water balance relies on excreting large amounts of
very dilute urine and drinking almost no water.
Animals that live in temporary waters
Desiccation is extreme dehydration and is fatal for most animals. However, a few aquatic
invertebrates that live in temporary ponds and films of water around soil particles can lose
almost all their body water and survive, these animals enter a dormant state, an adaptation
called anyhydrobiosis.
Osmoregulation accounts for 5% or more of the resting metabolic rate of many fishes.
In animals with a closed circulatory system the cells are bathed in an interstitial fluid, in an
open circulatory system it is called hemolymph.
44.2
Forms of nitrogenous waste
- Ammonia
o Need access to a lot of water, because ammonia can only be tolerated at very
low concentrations marine animals
- Urea
o In most land animals (they don’t have enough water to transport ammonia
safely)
o Combination of ammonia and CO2 in liver
o Low toxicity
, - Uric acid
o Insects, land snails, many reptiles (including birds)
o Nontoxic and does not readily dissolve in water
44.3
Urine is produced through a couple of basic steps:
1. Filtration
a. Water and solute are forced by blood pressure into excretory tubules
2. Reabsorption
a. Transport epithelium reclaims valuable substances
3. Secretion
a. Other substances are extracted from body fluids and added
4. Excretion
a. Leaves the system and body
Protonephridia
Protonephridia (flatworms, rotifers, annelids, larvae and lancelets) consist of a network of
dead-end tubules that branch throughout the body, flame bulbs cap the branches and
consist of a cap cell and a tubule cell has a tuft of cilia projecting into the tubule. The beating
of cilia draws water and solutes form the interstitial fluid through the flame bulb, releasing
filtrate into the tubule network where it is excreted.
Metanephridia
Metanephridia are excretory organs that collect fluid directly from the coelom. A ciliated
funnels surrounds the internal opening and pushes fluid into the collecting tubule.
Malpighian tubules
Malpighian tubules (insects) remove nitrogenous wastes and function in osmoregulation.
Malpighian tubules extend form dead-end tips immersed in hemolymph to openings into the
digestive tract.
In humans kidneys function in both osmoregulation and excretion and they consist of
tubules. Urine produced by each kidney exits through the ureter and they drain into the
urinary bladder and leaves the body through the urethra.
The renal cortex and renal medulla are both supplied with blood. Within them, tightly
packed excretory tubules carry and process a filtrate produced from the blood, nearly all of
the fluid is reabsorbed, the remaining leaves the tubules as urine and is collected in the
renal pelvis.
Cortical nephrons reach a short distance into the medulla and juxtamedullary nephrons
further and are essential for production of urine that is hyperosmotic to body fluids.
The glomerulus is a ball of capillaries and is surrounded by Bowman’s capsule. Filtrate is
formed when blood pressure forces fluid from the blood in the glomerulus into the lumen of
Bowman’s capsule.
44.1
Osmolarity is the number of moles of solute per liter of solution. Two solutions with the
same osmolarity are isoosmotic, when they differ, one is hyperosmotic, and the other is
hypoosmotic.
Osmoconformer: to be isoosmotic with its surrounding, it are all marine animals.
Osmoregulator: to control internal osmolarity independent of that of the external
environment.
Stenohaline animals can’t handle big changes, whereas euryhaline animals can.
Marine fish
Marine fish constantly lose water by osmosis, so they drink lots of seawater. The salt is
eliminated through the gills and kidneys.
Sharks have a high concentration of urea in their blood, this isn’t toxic for them because they
have an organic molecule called trimethylamine N-oxide (TMAO) which protects proteins
from the denaturing effect of urea. TMAO regulates osmoses as well.
Freshwater animals
The problems of marine animals are the opposite of freshwater animals. They face the
problem of gaining water by osmosis. Water balance relies on excreting large amounts of
very dilute urine and drinking almost no water.
Animals that live in temporary waters
Desiccation is extreme dehydration and is fatal for most animals. However, a few aquatic
invertebrates that live in temporary ponds and films of water around soil particles can lose
almost all their body water and survive, these animals enter a dormant state, an adaptation
called anyhydrobiosis.
Osmoregulation accounts for 5% or more of the resting metabolic rate of many fishes.
In animals with a closed circulatory system the cells are bathed in an interstitial fluid, in an
open circulatory system it is called hemolymph.
44.2
Forms of nitrogenous waste
- Ammonia
o Need access to a lot of water, because ammonia can only be tolerated at very
low concentrations marine animals
- Urea
o In most land animals (they don’t have enough water to transport ammonia
safely)
o Combination of ammonia and CO2 in liver
o Low toxicity
, - Uric acid
o Insects, land snails, many reptiles (including birds)
o Nontoxic and does not readily dissolve in water
44.3
Urine is produced through a couple of basic steps:
1. Filtration
a. Water and solute are forced by blood pressure into excretory tubules
2. Reabsorption
a. Transport epithelium reclaims valuable substances
3. Secretion
a. Other substances are extracted from body fluids and added
4. Excretion
a. Leaves the system and body
Protonephridia
Protonephridia (flatworms, rotifers, annelids, larvae and lancelets) consist of a network of
dead-end tubules that branch throughout the body, flame bulbs cap the branches and
consist of a cap cell and a tubule cell has a tuft of cilia projecting into the tubule. The beating
of cilia draws water and solutes form the interstitial fluid through the flame bulb, releasing
filtrate into the tubule network where it is excreted.
Metanephridia
Metanephridia are excretory organs that collect fluid directly from the coelom. A ciliated
funnels surrounds the internal opening and pushes fluid into the collecting tubule.
Malpighian tubules
Malpighian tubules (insects) remove nitrogenous wastes and function in osmoregulation.
Malpighian tubules extend form dead-end tips immersed in hemolymph to openings into the
digestive tract.
In humans kidneys function in both osmoregulation and excretion and they consist of
tubules. Urine produced by each kidney exits through the ureter and they drain into the
urinary bladder and leaves the body through the urethra.
The renal cortex and renal medulla are both supplied with blood. Within them, tightly
packed excretory tubules carry and process a filtrate produced from the blood, nearly all of
the fluid is reabsorbed, the remaining leaves the tubules as urine and is collected in the
renal pelvis.
Cortical nephrons reach a short distance into the medulla and juxtamedullary nephrons
further and are essential for production of urine that is hyperosmotic to body fluids.
The glomerulus is a ball of capillaries and is surrounded by Bowman’s capsule. Filtrate is
formed when blood pressure forces fluid from the blood in the glomerulus into the lumen of
Bowman’s capsule.
