Endocrine glands and hormones secreted by them

The Endocrine system (along with the nervous system) controls and regulates the complex activities of the body. The Endocrine system regulates the activities of the body by secreting complex chemical substances (hormones) into the blood stream. These secretions come from a variety of glands which control various organs of the body. The key functions are:

• To regulate the metabolic functions of the body.
• To regulate the rate of chemical reactions in various cells.
• To influence the ability of substances to transport themselves through cell membranes.

About Hormones

Hormones are secreted from the glands of the endocrine system, they are specific in that each hormone causes a response in a specific target organ or group of cells, rather than on the body as a whole. Exocrine hormones are secreted via a duct into the blood and usually effect a distant organ or tissue. Endocrine hormones are secreted within the tissue (rather than via a duct) and enter the blood stream via capillaries.

Hormones can be grouped into three main types:

1. amines , these are simple molecules
2. proteins and peptides which are made from chains of amino acids
3. steroids which are derived from cholesterol.

The Pituitary Gland

• ACTH (Adrenocorticotrophic hormone) stimulates the adrenal glands to secrete its hormones.
• hGH (Human growth hormone) also known as somatotrophic hormone is responsible for the growth of long bones, muscles and viscera.
• TSH (Thyroid stimulating hormone) influences the structure of the thyroid and causes it to secrete thyroid hormone.
• FSH (Follicle stimulating hormone) stimulates female egg production or male sperm production.
• PRL (Prolactin) in females causes the corpus luteum the area around the mature follicle to produce two important hormones: Oestrogen and Progesterone. During pregnancy PRL is also responsible for the development of the glandular tissues of the breast which produce milk.
• LH (Luteinzing hormone) works in conjunction with FSH in females to cause ovulation and prepares the uterus for pregnancy, in males the testes to secrete testosterone.

The Posterior Lobe of the Pituitary Gland (or neurophpophysis) stores and releases hormones secreted by the hypothalamus section of the brain including:

• ADH (Antidiuretic hormone) stimulates the smooth muscles, blood vessels and the intestine. ADH increases the kidney’s permeability to water allowing the body to re-absorb water that would otherwise escape in urine.
• OT (Oxytocin) stimulates the smooth muscles of the uterus during pregnancy, causing it to contract during labour. It also stimulates the lacteals (milk ducts) in the breast.

The Thyroid gland

The thyroid is a butterfly shaped gland which is located at the base of the throat . It has two lobes separated in the middle by a strip of tissue (the isthmus). The Thyroid itself secretes three main hormones:

• Thyroxine contains iodine which is essential for the body’s normal growth, and metabolism. Thyroxine helps control body size, regulating not only the growth of tissues but also the differentiation or specialisation of tissues.
• Triiodothyronine has similar functions to thyroxine.
• Calcitonin causes a decrease in the concentration of calcium in the blood. Calcitonin works with secretions from the parathyroid glands to maintain the balance of calcium necessary for the body to function.

People who have surgery to remove the thyroid gland (thyroidectomy) for cancer or other thyroid problems usually need to take thyroxine supplements in order to maintain normal weigh and body functions.

The Parathyroids

There are four Parathyroid glands which are small and rounded, arranged in two pairs usually located above and below the thyroid. Each Parathyroid is small, yellow and smooth, sometimes they imbed themselves in the thyroid itself.

Parathyroid hormone increases the blood concentrations of calcium and phosphorous, working to balance the Calcitonin which is secreted by the thyroid to maintain the body’s balance of calcium.

The Pancreas

The pancreas is a long, narrow, lobed gland located behind the stomach. The Pancreas has two types of cells: exocrine and endocrine cells. The exocrine cells secrete Pancreatic juices which are used in the duodenum as an important part in the digestive system. The endocrine cells are arranged in clusters throughout the Pancreas, these known as Islets of Langerhans . There are three types of endocrine cells; alpha cells which secrete glucagon, beta cells which secrete insulin, and delta cells which inhibit the secretion on glucagon and insulin:

• Glucagon increases the blood glucose level by stimulating the liver causing convert Glycogen into Glucose (sugar).
• Insulin increases the cells permeability to glucose, which the cells use for energy. By promoting the utilisation of glucose by the tissue cells, insulin causes a decrease in the concentration of glucose in the blood. Insulin also promotes the storage of glycogen in the liver.

The Adrenal Glands

The adrenal glands resemble small caps perched on top of each kidney. The Adrenal is actually a combination of two glands the adrenal cortex and the adrenal medulla.

The adrenal cortex is essential for life, as opposed to the adrenal medulla which is important but not indispensable. The anterior pituitary controls the adrenal cortex by secreting the hormone ACTH. All of the secretions of the adrenal cortex are known as steroids, many of which can now be manufactured synthetically. The adrenal cortex is made up of three layers associated with three classes of hormones:

• Mineralocorticoids are produced by the outer layer of the adrenal cortex, the most important of which is aldosterone. Aldosterone promotes the retention of sodium (Na+) and the excretion of potassium (K+). This helps to maintain both the electrolyte and water content of the body.
• Glucocorticoids are produced by the middle cortex. These affect almost every cell in the body regulating the metabolism of fats, proteins, and carbohydrates. Cortisone is one such glucocorticoid.
• Gonadal hormones are produced by the inner cortex, there are roughly even amounts of two types of hormones secreted: Androgen (male) and Estrogen (female). The adrenal gland is not the only gland to secrete sex hormones.

The Adrenal Medulla is the inner part of the adrenal gland. The hormones secreted effect the structures in the body that are under the control of the sympathetic nervous system, aiding the body to deal with stressful situations such as fright, attack or pursuit. They are both associated with an increased heart beat, higher blood pressure, and higher blood glucose levels, thus preparing the body for quick action.

• Adrenalin (or epinephrine) affects both alpha and beta receptors in the nervous system.
• Noradrenalin (Norepinephrine) affects only the alpha receptors of the nervous system.

The Gonads

The gonads consist of ovaries in the female and testes in the male. These glands produce hormones important in the development and functioning of the reproductive organs. they are under the control of the pituitary gland, and produce the secondary sexual traits.

Male testes are egg shaped glands located in the sac like scrotum, and serve two main functions: (i) The production of sperm cells, and (ii) The secretion of testosterone. Testosterone is the masculizing hormone inducing male secondary sexual characteristics after puberty.

Female ovaries are two almond shaped glands on each side of the uterus. They have three main functions; (i) Containing immature ova (eggs), (ii) The secretion of oestrogen, and (ii) the secretion of progesterone. Ostrogen is secreted by the adrenal cortex as well as the ovaries, and is present in the blood of all females from puberty through to the menopause. oestrogen acts on the structure of the reproductive organs, especially during the menstrual cycle. This induces and maintains female secondary sexual characteristics. Progesterone works on the uterus to prepare it for the implantation of a fertilised ovum (egg). It causes the development of the breasts, and is essential for the complete development of the maternal proportion of the placenta.

Giantism too much HGH is secreted before puberty.
Dwarfism is caused by a lack of HGH before puberty.

Diabetes Mellitus is a condition with under-secretion of insulin, causing the cells to loose their permeability to glucose preventing them from getting sugar needed for energy. Sugar remains in the blood and often the body will try and remove this leading to a high sugar content in the urine, causing polyuria (passing of large volumes of urine) and polydipsia (excessive thirst).

Roots, suffixes, and prefixes

Most medical terms are comprised of a root word plus a suffix (word ending) and/or a prefix (beginning of the word). Here are some examples related to the Endocrine System. For more details see Chapter 4: Understanding the Components of Medical Terminology

Cancer Focus

Overview of Endocrine System Cancers Tumours can arise in the endocrine system, e.g. pituitary tumours, thyroid cancers and neuroendocrine tumours of the pancreas. As a consequence of the position of these tumours, they may cause destruction of the normal gland and subsequent hormonal deficiency. Occasionally these tumours can also lead to an overproduction or secretion of hormone e.g. some pituitary tumours may lead to precocious puberty. The adrenal medulla is a common site for the development of neuroblastoma.Neuroblastoma may be associated with hypertension as a result of the oversecretion of catecholamines.

Internet Resources for Endocrine Cancers Adrenocortical Cancer Internet Resources for Adrenocortical Ca. Pancreas Cancer Pancreatic cancer is a disease in which the cells of the pancreas become malignant. The pancreas has two main functions; (i) it makes juices that help digest food and (ii) produces hormones (including insulin) that conrol how food is used and stored in the body. The vast majority of pancreatic cancers are associated with the part of the pancreas that makes digestive juices – these are known as “exocrine” pancreatic cancers. Only about 1/20 pancreatic cancers start in the hormone producing part of the pancreas ; these are known as “endocrine” pancreatic cancer or “islet cell cancer”. There are several types of exocrine pancreatic cancers (based on how the cells appear under the microsope), most are classed as “ductal adenocarcinomas”. Pancreatic cancer is rare before the age of 40 years, incidence increases sharply with increasing age.

Internet Resources for Pancreas Cancer Pituitary Cancer Internet Resources for Pituitary Cancer Thyroid Cancer Cancer of the thyroid is a disease in which malignant (cancerous) cells are found in the tissues of the thyroid gland. The thyroid gland is located at the base of the throat and produces hormones that help the body function normally. Most patients are between 25 and 65 years old, thyroid cancer is more common in women than in men. It is the most common malignancy of the endocrine (hormone) system. There are four main types of thyroid cancer (depending on the type of cell that the cancer developed in); papillary carcinoma, follicular carcinoma, medullary carcinoma and anaplastic carcinoma. Occasionally other type of cancer (lymphoma, sarcoma and carcinosarcoma) can be found in the thyroid gland. Some thyroid cancers are caused by exposure to radiation and some medullary carcinomas are associated with an inherited condition (multiple endocrine neoplasia). However, in the large majority of cases the cause is unknown.

Internet Resources for Thyroid Cancer Parathyroid Cancer The parathyroid gland is located at the base of the neck near the thyroid gland. It produces a hormone called parathyroid hormone (PTH), which controls how the body stores and uses calcium. Parathyroid cancer is a condition where the cells of the parathyroid gland become malignant (cancerous). Parathyroid cancers are rare; while problems with the parathyroid gland are common, these are not usually cancer related.

Internet Resources for Parathyroid Cancer Thymus cancer Internet Resources for Thymus Cancer Potential Endocrine Side Effects of Treatment for Childhood Cancers Chemotherapy can sometimes affect future fertility, and in children it can have the potential to affect growth in a few cases. In such cases the patient may receive hormone therapy, for example testosterone to stimulate growth for patients with hypogonadism (under developed genitals). Cranial irradiation, particularly in the treatment of brain tumours, frequently causes endocrine abnormalities. The pituitary is particularly sensitive and growth hormone deficiency with short stature can arise. Both delayed and early puberty can also occur and therefore close endocrine monitoring is required. Early intervention with hormone replacement therapy can minimise the side effects.

Radiation therapy given to children may lead to reduced growth in the bones and muscles in the affected area, for example when the patient reaches adulthood one limb might be slightly shorter than the other.

OncoLink manuscript: Effects of Therapeutic Irradiation on Skeletal Growth in Children Rickets -vitamin D deficiency in childhood where the body does not absorb calcium and the bones may soften and bend.

Related Abbreviations and Acronyms

Further Resources (3 links)

SEER, National Cancer Institute
Part of a SEER training module for cancer registry staff.

WebAnatomy, University of Minnesota
Test your anatomy knowledge with these interactive questions. Includes different question types and answers.

Paul Andersen
Paul Andersen explains the major elements in the endocrine system. He explains how glands produce hormones which target cells. He differentiates between water soluble and lipid soluble hormones. He then describes the hormones and actions of ten glands; pineal, anterior pituitary, posterior pituitary, thyroid, parathyroid, pancreas, adrenal cortex, adrenal medulla, testes and ovaries.

First created 4th March 1996
Last modified: 1st February 2014