Thought to be antigen-free, the thymus is a primary lymphoid organ with two major functions: differentiation of T cells; and recognition of self from non-self. The thymus differs from lymph nodes and bone marrow in that no immune reactions occur, except in certain diseases. Pre-thymocytes arrive into the thymus via blood, move into subcapsular space [...]

The average adult contains 2-3 liters of bone marrow, a primary lymphoid organ located in the core of long bones. Bone marrow is composed of myeloid tissue (tissue capable of hematopoiesis) and has three major functions: production and support of stem cells; B cell maturation; and antibody production. Bone marrow has a definite architecture, with [...]

Although not a gland, it is important to note that the stomach lining secretes gastrin, a pepide, into the stomach. Gastrin promotes digestion by stimulating release of digestive juices and stimulates stomach movements that mix food and digestive fluids. The stomach lining is part of the exocrine system, which operates via ducts like sweat and [...]

The pineal Gland secretes melatonin and is one of the brain’s only unitary structures. The pineal gland is located near the center of the human brain, and is stimulated by nerves from the eyes. In some other animals, the pineal gland is close to the surface of the skin and is directly stimulated by light. [...]

The pancreas contains exocrine cells and endocrine cell clusters. Exocrine cells secrete digestive enzymes into the small intestines. Endocrine cell clusters (aka pancreatic islets or islets of Langerhans) secrete insulin and glucagon. Insulin and glucagon regulate blood glucose levels. After a meal, when blood glucose levels rise, insulin is released so that cells can uptake [...]

Thyroid Gland is located in the neck. Thyroid follicles secret thryoglobulin, a storage form of thyroid hormone. Thyroid stimulating hormone (TSH) from anterior pituitary causes conversion of thyroglobulin into thyroid hormones T4 and T3. Almost all body cells are targets of thyroid hormones. Thyroid hormones increase overall metabolic rate, regulate growth and development, and influence [...]

Adrenal Glands are located one above each kidney. The adrenal gland is divided into an inner medula and an outer cortex. The medulla synthesizes 2 hormones, epinephrine (adrenaline) and norepinephrine. When the sympathetic nervous system stimulates the cortex causes hormones related to fight-or-flight to get secreted into the blood. The adrenal cortex produces several steroid [...]

Sex Organs, which not only produce gametes but also secrete sex hormones. Sex hormone secretion is controlled by the pituitary gland hormones such as FSH and LH. While both sexes make some of each of the hormones, typically male testes secrete primarily androgens including testosterone. Female ovaries make estrogen and progesterone in varying amounts depending [...]

Hypothalamus releases gonadotropin Releasing hormone (GnRH), causing pituitary to release LH (stiumalting ovulaiton) The hypothalamus contains neurons that control releases from the anterior pituitary. Seven hypothalamic hormones are released into a portal system connecting the hypothalamus and pituitary, and cause targets in the pituitary to release eight hormones. Hypothalamus receptors monitor blood levels of thyroid [...]

Pituitary Gland consists of a stalk linking the pituitary to the hypothalamus, which controls release of pituitary hormones. The pituitary gland has two lobes: the anterior and posterior lobes. The anterior pituitary is a glandular structure under contorl of the hypothalamus. Together, the pituitary gland and hypothalamus control many endocrine functions. They secrete many hormones, [...]

A differentiated part of an organism, such as an eye, wing, or leaf, that performs a specific function. It is composed of a tissue or tissues which function together.