Human Excretory System Function and Anatomy
Elimination of Cellular Waste Products
Elimination involves removing waste excretions from our cells. Urine has a composition similar to blood plasma, although it has a higher concentration of waste substances such as urea.
Components of the Urinary System
Kidneys
Kidneys: Two bean-shaped organs located on both sides of the spine. They form urine. Three parts can be differentiated within them: the medulla or central mass (divided into pyramid-shaped zones), blood vessels, and the cortex.
Bladder
Bladder: Urine collects here, arriving continuously through the ureters. It is extensible and can contain a varying amount of urine (250 to 500 cm³). When full, it contracts, and the need to urinate arises.
Ureter
Ureter: Two thin tubes that collect the urine produced in each kidney and carry it to the bladder.
Urethra
Urethra: A tube that carries urine from the bladder to the outside.
Urine Formation
Each kidney contains over a million cells called nephrons. The nephron, the basic functional unit, is formed by:
- A capsule surrounding a hollow ball of blood capillaries.
- A tubule, or thin tube-shaped handle.
Tubules from several nephrons lead to thicker tubes which collect the urine formed in each of them.
Filtration Process
As urine is formed, the blood is filtered toward the capsule surrounding them. The thin wall acts as a filter, allowing only small molecules such as water, mineral salts, glucose, and urea to pass through the membrane.
The filtered liquids pass along the tubule. Through the walls, the liquid returns within the capillaries surrounding them. 99% of the water is returned to the blood.
Regulatory Role of the Kidneys
Regulatory role of the kidneys: The kidneys perform a double function:
- Help cleanse the blood of waste.
- Control the amount of water and minerals it contains.
Homeostasis
Homeostasis (homeo - equal; stasis - still) refers to the mechanisms all living things tend to achieve stability in the properties of their internal environment. The organs that maintain the stability of our internal environment are:
- Kidneys
- Lungs
- Liver (regulates glucose)
- Skin (excretory organ and regulates body temperature)
- Brain (works as a controller of homeostatic processes. This process detects the composition and temperature of the blood passing through it and sets up the appropriate mechanisms to control changes.)
Transplants
Transplants: A complex medical treatment based on allowing organs, tissues, or cells from a healthy person to help a sick person by replacing damaged parts. Types of transplants include:
- Autotransplants (when the donor and recipient are the same person)
- Isotransplants (when they are identical twins)
- Allotransplants (when they are of the same species)
- Xenotransplantation (when they are from different species)
- Autotopic (removal of the organ and substitution)
Compatibility and Rejection
When our body detects something that is not 'good,' such as bacteria, viruses, or organisms that can harm us, white blood cells destroy them. However, they can act this way with other organs. Therefore, it is important that the donor be as compatible as possible. If rejection occurs...