It is the stress hormone produced by adrenal cortex gland at the time of stress.

The cells develop in the bone marrow and circulate for about 100-120 days in the body before their components are recycled by macrophages. Each circulation takes about 20 seconds. Approximately a quarter of the cells in the human body are red blood cells.

There are 31 pairs of spinal nerves in the human body. The spinal nerves are grouped according to where they leave the vertebral column. There are eight pairs of cervical nerves (C1-C8), twelve pairs of thoracic nerves (T1-T12), five pairs of lumbar nerves (L1-L5), five pairs of sacral nerves (S1-S1) and one pair of coccygeal nerves (Co1).

The liver is central to the regulation of cholesterol levels in the body. Not only does it synthesize cholesterol for export to other cells, but it also removes cholesterol from the body by converting it to bile salts and putting it into the bile where it can be eliminated in the feces.

The thymus gland, located behind your sternum and between your lungs, is only active until puberty. After puberty, the thymus starts to slowly shrink and become replaced by fat.

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Islets of Langerhans are present as a part of the pancreas. The islets of Langerhans are the regions of the pancreas that contain its endocrine cells. Discovered in 1869 by German pathological anatomist Paul Langerhans at the age of 22, the islets of Langerhans constitute approximately 1 to 2% of the mass of the pancreas.

Skin consists of two main layers: The outer layer, known as the epidermis and the inner layer, known as the dermis.

 Suckling by the baby stimulates the paraventricular nuclei and supraoptic nucleus in the hypothalamus, which signals to the posterior pituitary gland to produce oxytocin. Oxytocin stimulates contraction of the myoepithelial cells surrounding the alveoli, which already hold milk. The increased pressure causes milk to flow through the duct system and be released through the nipple.