Biology Assessment

Part A:

2) Background information:

Kidneys are located on the right and left side at the back of the abdomen (the middle part of the body) just below the chest and rib cage. The kidneys clean all blood in the body every two minutes. They do this by filtering the blood with small groups of blood vessels. There are about 1 million glomeruli in each kidney. Blood is filtered in the glomerulus, and water and wastes are passed out as urine. Urine collects in the middle of each kidney. The kidneys make more urine when there is too much fluid in the body, and less urine when the body needs fluids.

The water passing from the body as urine passes through the ureters (two thin-walled tubes of around 30 centimetres in length) into the bladder (a muscular container with a capacity of around 500 millilitres). This urine is stored in the bladder and then leaves the body through the urethra (a small passage from the bladder to the outside of the body).

Part B:

a) Function of a kidney:

1. Kidneys regulate water: remove excess water from the body or to retain water when the body needs more.

2. Kidneys remove waste products and help to balance the body's minerals
the kidneys are working properly, extra minerals and adjust the levels of other minerals. Also it helps remove waste

3. Kidneys produce hormones
these hormones circulate in the bloodstream like “messengers” and regulate blood pressure, red blood cell production and the calcium balance in the body.

b) There are four primary components to a kidney:  

1. Renal Capsule: A smooth semitransparent membrane that adheres tightly to the outer surface of the kidney.  

2. Renal Cortex: The region of the kidney just below the capsule. In a fresh kidney the colour of the cortex will be reddish brown.

 3. Renal Medulla: The region deeper into the kidney, beneath the cortex layer. It is segregated  into  triangular  and  columnar  regions. The  triangular regions are the renal pyramids. The renal  medulla  contains  the structures  of  the  nephron. The columnar regions between the pyramids a the renal columns. These renal columns are where  the interloper arteries are located.

 4.  Renal  Pelvis: A  cavity  within  the  kidney  that  is  continuous  with  the  ureter. The  primary extensions are the major calyces and the smaller extensions are the minor calyces.

Part C:

1) The role of the kidney in the excretory system of a fish and mammal:

• Marine Fish – converse water, excrete excess salts and nitrogenous wastes: Marine fish urinate less. They tend to lose body water (by osmosis), across the body surface and gills, into their salty surroundings. Excess salt tends to accumulate in their bodies, moving in by diffusion from the surrounding sea water. The main function of the kidneys is therefore, to remove excess salt. Marine fish drink the sea water, extract the salt, use the water for metabolism, then excrete the extracted salt to keep their bodies salt levels at a minimum. The kidneys also tend to conserve water rather than excrete it – and as a result the kidneys of marine fish have small glomeruli as well as a mechanism for removing excess salt from sea water. The kidney is also responsible for removing nitrogenous wastes.

• Freshwater fish – excrete excess water and nitrogenous wastes (produce large amounts of dilute urine), conserve salt: live in rivers and lakes, where the water potential is very high (water potential is the tendency of a solution to lose water by osmosis, generally these solutions have high water concentrations) – these habitats contain few dissolved salts and hence water is freely available. Freshwater fish tend to urinate frequently, as water tends to accumulate in their tissues as a result of passive movement by osmosis (water moves from high concentrations to lower concentrations inside the fish). These fish are face with the problem of there being too much water in their bodies – as a result their kidneys excrete excess water, as well as nitrogenous wastes. Their kidneys are structurally suited to this as they have large glomeruli for the filtration of blood in large volumes. Their kidneys are not involved in salt balance, as there is no salt accumulation in freshwater fish.

• Mammals – conserve water and salts when required and excrete excess

nitrogenous wastes: lose water and solutes as a result of evaporation from the lung surface during respiration. The kidneys of mammals excrete urine, which is composed mainly of water and nitrogenous wastes as well as some excess salts. The mammalian kidney can adjust the reabsorption of nitrogenous wastes, water and salts – varying the concentration of urine produced. Mammals have a complex control mechanism to ensure that a balance is maintained between the amounts of sweat and urine excreted. For example in hot weather, more water is excreted as sweat (since sweat is evaporative cooling, lowering the bodies temperature) and as a result less urine is produced. In colder weather, more water is lost in urine and very little as sweat. A relatively large quantity of salts is also lost during sweating and needs to be replaced, in order to maintain a stable osmotic pressure. Any adjustment to the water or salt concentration in body fluids is brought about by the hormone ADH and aldosterone. Urine may be dilute or concentrated depending on the needs of the body.