Putting It Together: The Endocrine System

This video fills us in on the endocrine system—the system of glands which produce and secrete different types of hormones directly into the bloodstream to regulate the body’s growth, metabolism, and sexual development & function.

Table 1 summarizes the major hormones, their target and their function.

Table 1. Major Horomes
Endocrine Gland Hormone Released Chemical Class Target Tissue/Organ Major Function of Hormone
Hypothalamus Hypothalamic releasing and inhibiting hormones Peptide Anterior pituitary Regulate anterior pituitary hormone
Posterior Pituitary Antidiuretic (ADH) Peptide Kidneys Stimulates water reabsorption by kidneys
Oxytocin Peptide Uterus, mammary glands Stimulates uterine muscle contractions and release of milk by mammary glands
Anterior Pituitary Thyroid stimulating (TSH) Glycoprotein Thyroid Stimulates thyroid
Adrenocorticotropic (ACTH) Peptide Adrenal cortex Stimulates adrenal cortex
Gonadotropic (FSH, LH) Glycoprotein Gonads Egg and sperm production, sex hormone production
Prolactin (PRL) Protein Mammary glands Milk production
Growth (GH) Protein Soft tissue, bones Cell division, protein synthesis and bone growth
Thyroid Thyroxine (T4) and Triiodothyronie (T3) Iodinated amino acid All tissue Increase metabolic rate, regulates growth and development
Calcitonin Peptide Bones, kidneys and intestine Lowers blood calcium level
Parathyroids Parathyroid (PTH) Peptide Bones, kidneys and intestine Raises blood calcium level
Adrenal Cortex Glucocorticoids (cortisol) Steroid All tissue Raise blood glucose level, stimulates breakdown of protein
Mineralocorticoids (aldosterone) Steroid Kidneys Reabsorb sodium and excrete potassium
Sex Hormones Steroid Gonads, skin, muscles and bones Stimulates reproductive organs and brings on sex characteristics
Adrenal Medulla Epinephrine and norepinephrine Modified amino acid Cardiac and other muscles Released in emergency situations, raises blood glucose level, “fight or flight” response
Pancreas Insulin Protein Liver, muscles, adipose tissue Lowers blood glucose levels, promotes formation of glycogen
Glucagon Protein Liver, muscles, adipose tissue Raises blood glucose levels
Testes Androgens (testosterone) Steroid Gonads, skin, muscles and bone Stimulates male sex characteristics
Ovaries Estrogen and progesterone Steroid Gonads, skin, muscles and bones Stimulates female sex characteristics
Thymus Thymosins Peptide T lymphocytes Stimulates production and maturation of T lymphocytes
Pineal Gland Melatonin Modified amino acid Brain Controls circadian and circannual rhythms, possibly involved in maturation of sexual organs

Career Connection

Fittingly, the profession that works closely with the endocrine system is known as endocrinology. If you found this body system interesting, you may want to look into this field.

Endocrinologist

An endocrinologist is a medical doctor who specializes in treating disorders of the endocrine glands, hormone systems, and glucose and lipid metabolic pathways. An endocrine surgeon specializes in the surgical treatment of endocrine diseases and glands. Some of the diseases that are managed by endocrinologists: disorders of the pancreas (diabetes mellitus), disorders of the pituitary (gigantism, acromegaly, and pituitary dwarfism), disorders of the thyroid gland (goiter and Graves’ disease), and disorders of the adrenal glands (Cushing’s disease and Addison’s disease).

Endocrinologists are required to assess patients and diagnose endocrine disorders through extensive use of laboratory tests. Many endocrine diseases are diagnosed using tests that stimulate or suppress endocrine organ functioning. Blood samples are then drawn to determine the effect of stimulating or suppressing an endocrine organ on the production of hormones. For example, to diagnose diabetes mellitus, patients are required to fast for 12 to 24 hours. They are then given a sugary drink, which stimulates the pancreas to produce insulin to decrease blood glucose levels. A blood sample is taken one to two hours after the sugar drink is consumed. If the pancreas is functioning properly, the blood glucose level will be within a normal range. Another example is the A1C test, which can be performed during blood screening. The A1C test measures average blood glucose levels over the past two to three months by examining how well the blood glucose is being managed over a long time.

Once a disease has been diagnosed, endocrinologists can prescribe lifestyle changes and/or medications to treat the disease. Some cases of diabetes mellitus can be managed by exercise, weight loss, and a healthy diet; in other cases, medications may be required to enhance insulin release. If the disease cannot be controlled by these means, the endocrinologist may prescribe insulin injections.

In addition to clinical practice, endocrinologists may also be involved in primary research and development activities. For example, ongoing islet transplant research is investigating how healthy pancreas islet cells may be transplanted into diabetic patients. Successful islet transplants may allow patients to stop taking insulin injections.