Transport of Wastes and Urinary System

Comparison of Transport Systems

Comparison of Excretory System

The main structures and functions of the kidney

Materials that pass through the Bowman's capsule

• Kidneys filter wastes from the blood. They maintain a correct balance of ions in our blood by excreting the excess ones. This then helps the pH of the blood.
• A thin layer of cells called the capsule, surrounds each of the kidneys. The dent in the side of the kidney is where the blood vessels enter and leave the kidney.
• The outer layer of the kidney tissue is the cortex, which extends into the second layer, the medulla.

• Plasma proteins, blood cells and the platelets are held back. Pressure forces the phosphate ion, water, sodium and chloride ions, glucose and amino acids and the urea into the Bowman's capsule.
• The nutrients and the ions are reabsorbed by active transport, but the water follows by diffusion from the tubule into blood.
• Ions are then reabsorbed by active transport in the ascending loop of Henle.
• The left over then goes in the collecting duct, which is the urine.

• Each kidney contains about one million functional units or nephrons. This is the process of filtration and reabsorption of the nephrons that regulates the body fluid. The artery that enters the kidney, branches into arterioles and then those branch into capillaries. These capillaries then form small clusters which are called a glomerulus. This is the first stage of the filtering process in the kidneys.
• Each glomerulus is surrounded by a double-walled cup called the Bowman’s capsule.
• The tubule is a part of the nephron containing tubular fluid that is filtered through the glomerulus. The remainder fluid joins up in a collecting tubule, called a duct.
• The loop of Henle, is U-shaped and extends into the medulla.

The Kidney

The main function of the loop of Henle is to recovery water and salt from the urine before it is excreted from the body. The animals that have a small loop of Henle or don’t have any at all, would have a large water and salt intake, because they wont be needing to recover them. This then means that this animal will most likely be living in an environment where there is lots of water, and not a hot and dry environment.

What is Ammonia?

Transport of Wastes and Urinary System

Ammonia is a nitrogen containing compound which is produced when protein is metabolised in cells. Ammonia must be excreted immediately in water or converted to some other nontoxic compound as it is toxic to cells.

Aquatic animals are most expected to excrete ammonia. This is due to ammonia diffusing easily through membranes and being more water-soluble than other types of nitrogenous waste. Ammonia is excreted in large volumes as dilute urine due to the need to maintain the water balance in their bodies.

Key Structures of the Urinary System

• Two ureters: transports urine from the kidney to the bladder

• Bladder: stores the urine

• Urethra: transports the urine from the bladder to outside body

• Two kidneys: filters the blood and produces urine

Transport of the Urine

• The urine is carried away from each kidney by the ureters. Each of these tubes is 25-30 cm.

• Two ureters, one from each kidney, transport the urine to the bladder.

• The urine us transported from the bladder to outside of the body by the urethra

This act of getting rid of urine from the body is called micturition, which is known as urinating or voiding.

How urine is formed

Urine is formed when waste materials are filtered from the blood in the glomerulus. The blood is under pressure as the arteriole leaving a glomerulus are smaller in diameter than the arteriole entering a glomerulus, therefore substances are forced through the ‘holes’ in the capillary walls and the inner wall of the Bowman’s capsule. Only large compounds such as protein and blood cells do not pass through.

As fluid moves along the nephron tubule, some things that were filtered out in the glomerulus are reabsorbed into the capillaries. Some materials are diffused back into the bloodstream where as others are actively transported. Some materials are secreted into the tubules by the tubule cells. This includes drugs like penicillin and ion which are secreted to control the acidity of the blood and other tissues.

The fluid that reaches the end of the nephron tubule is urine. The composition of a person’s urine depends on how much urine is produced and its pH.

Hypertonic urine

hypertonic urine is produced by mammals. It contains a higher concentration of solutes than body fluid, of the same animal.

Hypotonic urine

Animals such as freshwater bony fish and amphibians, produce hypotonic urine. Hypotonic urine contains a lower concentration of salts than the body fluids of the same animal.

Isotonic urine.

Isotonic urine is produced by marine fish. Isotonic urine carries magnesium sulfate salts and urea out of the body.