Passive Transport

Distinguish between active and passive transport and define the role of each with in the mammalian kidney.

Passive transport is the diffusing of molecules from areas of high concentration to low concentration across a cell membrane without the use of energy. There are four types of passive transport;

Diffusion: The movement of molecules from high to low concentration.

Facilitated diffusion: The movement of of molecules using carrier protein molecules to transport them across the cell membrane from high to low concentration.

Osmosis: The movement of water molecules across a cell membrane from a less concentrated to more concentrated solution.

Filtration: The movement of water and other molecules across a cell membrane caused by blood pressure.

Both active and passive transport are used in the processes of filtration, reabsorption and secretion, which are used to process enormous volumes of blood into a small volume of urine.

Filtration takes place in the glomerlus. About 20% of the plasma that passes through the kidney gets filtered into the nephron. Filtration is commonly a passive process as it does not require energy, driven by the hydrostatic pressure of the blood. This causes water and small molecules to be filtered, while blood cells and large molecules like proteins do not pass through the filter.

Reabsorption takes the the useful substances for the body from the tubules and places them back into the blood filled capillaries. This happens through the process of active transport. Reabsorption materials include: glucose, amino acids, vitamins, minerals, bicarbonate ions and some water.

Secretion is the process the kidney uses to transport substances from the blood to the nephron that occurs in the tubules and uses active