Glands and Tissues that produce Hormones

Hormones are chemicals (sometimes called ‘chemical messengers‘) that are produced (‘synthesized’) and released (‘secreted’) by the endocrine system.

In many cases hormones are secreted by the main endocrine glands in the human body.

Some other organs and tissues also include cells called endocrinocytes that synthesize and secrete specific hormones.

In many cases hormones secreted by these endocrinocytes affect the body system of which the organ or tissue that secreted the hormones is a part.

i.e. the “main endocrine” glands, meaning those glands whose main function is to synthesize and/or secrete hormones

1. Pineal gland
2. Hypothalamus
3. Pituitary gland
4. Parathyroid glands
5. Thyroid gland
6. Thymus gland (also part of the immune system)
7. Adrenal Glands
8. Pancreas (also part of the digestive system)
9. Ovaries (female only)
10. Testes (male only)

* Lists of endocrine glands vary slightly. Most sources list 8-10 endocrine glands. Sometimes the thyroid and parathyroid glands are listed together, sometimes the thymus and/or pancreas are not included due to them also being part of other body systems.

List of other organs and tissues that produce hormones

i.e. that contain some cells ( endocrinocytes ) that synthesize and secrete hormones – even though that is not the main function of the organ or tissues of which those cells are part

1. Heart (part of the cardiovascular system)
2. Stomach (also part of the digestive system)
3. Parts of the Gastrointestinal Tract (GT)
   including the stomach, duodenum and colon.
4. Duodenum
5. Liver (also part of the digestive system)
6. Kidneys (part of the urinary system)
7. Skin (also known as the integumentary system)
8. Adipose Tissue

Hormones secreted by the main endocrine glands (indicated above-left) are listed together with their functions beneath the diagram of the locations of the main endocrine glands. Hormones secreted by the other organs and tissues (indicated above-right) are listed in the following table.

Hormones Secreted by Hormone-Producing Tissues not classified as Endocrine Glands:

The following are common examples, although not a complete list.

Atrial natriuretic hormone (ANH)

• Powerful vasodilator.
• Contributes to homeostatic control of water in the body
• Also helps control of levels of sodium, potassium (i.e. to control electrolyte homeostasis).

Main overall effect: Helps reduce blood pressure.

3. Parts of Gastrointestinal Tract incl. the stomach, duodenum and colon

secreted from mucosa of the proximal small intestine

a group of gastrointestinal hormones, incl. GLP-1 & GIP

Stimulate increase in insulin after eating. Slows rate of absorption of nutrients into the blood stream by reducing gastric emptying, may directly reduce food intake, i.e. suppress appetite.

• Regulates the environment within the duodenum (esp. its pH) via secretions from the stomach and pancreas
• Helps regulate homeostatic control of water throughout the body
• Has been used as a medicine – hormone products coming from animal sources or synthesized artificially.

Cholecystokinin (CCK)

The main hormone controlling gallbladder contraction and pancreatic enzyme secretion, CCK stimulates delivery of digestive enzymes from the pancreas and bile from the gallbladder into the small intestine.

(Mainly by interstitial fibroblasts in the kidney, to a lesser extent also secreted by the perisinusoidal cells of the liver)

Erythropoietin (EPO)

also known as erythropoetin, erthropoyetin, hematopoietin and hemopoietin

• Main Role: Controls production of red blood cells (erythropoiesis) which takes place in bone marrow and is esp. useful for athletes.
• Involved in the brain’s response to neuronal injury and helps with wound healing.
• Can also increase iron absorption (by suppressing the hormone hepcidin) among other functions

Renin is an enzyme that regulates mean arterial blood pressure by adjusting extracellular volume (i.e. of the blood plasma, lymph and interstitial fluid), and arterial vasoconstriction.

Functions of Calcitriol**:

Functions of Calcitriol**:

• Increases blood calcium levels (Ca 2+ ) by increasing absorption of dietary calcium.
• Contributes to reduction of loss of calcium via urine.
• Contributes to stimulation of release of calcium from bone (via action on osteoblasts that leads to activation of osteoclasts).

** Cholecalciferol is sometimes referred to as a biologically inactive form of vitamin D3. It is synthesized when skin is exposed to UV radiation e.g. sunlight. Then it is metabolized into the active form of vitamind (calcitriol), which is a steroid hormone. Cholecalciferol itself is a secosteroid hormone that is structurally similar to testosterone and cholesterol.

Regulates intake and expenditure of energy, including appetite/hunger and metabolism. (Acts on receptors in the hypothalamus of the brain, where it inhibits appetite.)

Note: The numbers 1-8 listed above-left are only for ease of reference to and discussion of this information. They do not indicate e.g. sequence or quantity of secretion of hormones from cells in these structures of the body.

• Although secretion of hormones is the main function of endocrine glands, many other organs and tissues also contain endocrinocytes (cells that secrete specific hormones) and therefore release hormones into the body.
• There are many different hormones that, individually, have one or more specific tasks.
• Hormones in general are responsible for controlling a huge range of different functions that affect all of the systems of the body. This is achieved by a many different hormones, each controlling very specific conditions or processes, often via biochemical cycles or ‘pathways’ involving various other biochemicals within the body.