Railway Science (Biology – Excretory System)

The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH₂)₂CO from ammonia (NH₃). It converts highly toxic ammonia to urea for excretion. The liver is the largest solid organ in the body.
Kidney- It filters out a variety of water-soluble waste products and environmental toxins into the urine for excretion. Other excretory organsUreter, Urinary bladder and Urethra.

Human Urine Contains- water (95%), urea (2%), creatinine (0.1%), uric acid (0.03%), chloride, sodium, etc. Fish excrete ammonia directly into the water. Cows Urine- Contains 95% water, 2.5% urea, minerals, 24 types of salts, hormones, and 2.5% enzymes.

Squamous epithelial cells are large, flattened cells filled with cytoplasm possessing a small round nucleus at the centre. Squamous epithelium is found in the outer layer of the skin.
Some areas where non-keratinized stratified squamous epithelium is found are conjunctiva of the eye, rectum, parts of oesophagus, lining of the oral cavity, external female genitalia etc.
Kidney tubules are very essential organs for blood clearance mechanism, and filtration by active transport, recover essential metabolites from glomerular.

Other excretory products of plants - Gums are used in the manufacture of medicines and in cosmetic products. Resins are used in the production of adhesives and food glazing agents. Oxygen is one of the excretory products produced by plants which are useful to humans, they can not survive without oxygen.

About 99% of the glomerulus filtrate reabsorbed by renal tubules. Out of 180 liters of the filtrate, only 1.5 liters excreted as urine. This reabsorption of materials or substances performed by the active or passive mechanism. The amount of reabsorbed filtrate depends on the amount of additional water and the amount of dissolved waste to be excreted.

The gaseous wastes, oxygen, carbon dioxide, and water vapor are removed through the stomata of leaves and lenticels of stems. Some waste products collect in the leaves and bark of trees.
When the leaves and bark are shed, the wastes are eliminated. Some waste products are rendered harmless and then stored in the plant body as solid bodies.
Raphides, tannins, resins, gum, rubber, and essential oils are some such wastes. Oxygen is a waste product of photosynthesis.

Each of our kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.

The large intestine (or colon, or large bowel) is the last structure to process food, taking the indigestible matter from the small intestine, absorbing water from it and leaving the waste product called feces. Feces are expelled from the body through the rectum and the anus.

Kidneys- It is the main organ of the human excretory system. It cleans the blood and transforms waste into urine. Ureter- It is a thin muscular tube that carries urine from the kidneys to the bladder. The bladder- It receives urine from the ureters and expelled it from the body by micturition (urination). Urethra- It acts as the common route for sperms and urine.

Bowman capsule:- It is a double-walled cup-shaped structure present before and with continuity with the PCT (proximal convoluted tubule). Inside this, there lies the glomerulus which is a tuft of leaky blood vessels.
Function:- The bowman's capsule helps the glomerulus to filter the blood to form urine. Glomerulus:- It is the main filtering unit of the kidney composed of a network of capillaries and epithelial cells, the podocytes.
Loop of Henle or nephron loop in the kidney is a tubule that opens from the proximal convoluted tubule (PCT) and leads to the distal convoluted tubule.