Hormones are chemical messengers produced by endocrine glands that are secreted into the bloodstream to regulate various physiological processes in the body.
Hormones play a crucial role in maintaining homeostasis, growth and development, metabolism, reproduction, and stress response.
They act on target cells or organs that have specific receptors for these hormones.
Functions of hormones:
1. Growth and development:
Hormones like growth hormone (GH), insulin-like growth factor (IGF), and thyroid hormones promote cell growth, differentiation, and tissue repair.
2. Metabolism:
Hormones like insulin, glucagon, and thyroid hormones regulate the metabolism of carbohydrates, proteins, and lipids.
3. Reproduction:
Sex hormones like Estrogen, progesterone, and testosterone regulate reproductive functions, such as the menstrual cycle, pregnancy, and the development of secondary sexual characteristics.
4. Stress response:
Hormones like cortisol, epinephrine, and norepinephrine help the body respond to stress by mobilizing energy reserves and increasing heart rate and blood pressure.
5. Water and electrolyte balance:
Hormones like aldosterone and antidiuretic hormone (ADH) regulate the balance of water and electrolytes in the body.
6. Sleep-wake cycles:
Melatonin, produced by the pineal gland, regulates sleep-wake cycles and circadian rhythms.
Classification of hormones:
Hormones can be classified based on their chemical structure:
1. Amino acid derivatives:
These hormones are derived from amino acids, such as tyrosine and tryptophan.
Examples include thyroid hormones (T3 and T4), catecholamines (epinephrine, norepinephrine, and dopamine), and melatonin.
2. Peptide hormones:
These hormones are composed of short chains of amino acids. Examples include insulin, glucagon, growth hormone, and antidiuretic hormone.
3. Protein hormones:
These hormones are composed of long chains of amino acids.
Examples include follicle-stimulating hormone (FSH), luteinizing hormone (LH), and human chorionic gonadotropin (hCG).
4. Steroid hormones:
These hormones are derived from cholesterol and have a distinct four-ring structure.
Examples include cortisol, aldosterone, testosterone, oestrogen, and progesterone.
Hormones can also be classified based on their function or the system they act upon:
1. Growth and developmental hormones:
Growth hormone, insulin-like growth factor, and thyroid hormones.
2. Metabolic hormones:
Insulin, glucagon, and thyroid hormones.
3. Stress response hormones:
Cortisol, epinephrine, and norepinephrine.
4. Reproductive hormones:
Estrogen, progesterone, testosterone, follicle-stimulating hormone, and luteinizing hormone.
5. Water and electrolyte balance hormones:
Aldosterone and antidiuretic hormone.
6. Sleep-wake cycle hormones:
Melatonin.
Here is a table summarizing the primary endocrine glands, their locations, hormones, and functions in the context of the endocrine system:
Gland | Location | Hormone(s) | Function |
Hypothalamus | Brain | Various releasing and inhibiting hormones | Regulate the release of hormones from the pituitary gland |
Pituitary gland | Base of the brain | Growth hormone (GH) | Stimulate growth, cell reproduction, and regeneration |
Adrenocorticotropic hormone (ACTH) | Stimulate the adrenal cortex to produce cortisol | ||
Thyroid-stimulating hormone (TSH) | Stimulate the thyroid gland to produce thyroid hormones | ||
Luteinizing hormone (LH) | Stimulate ovulation and testosterone production | ||
Follicle-stimulating hormone (FSH) | Stimulate the growth of ovarian follicles and sperm production | ||
Prolactin (PRL) | Stimulate milk production | ||
Antidiuretic hormone (ADH) | Regulate water balance by reducing urine output | ||
Oxytocin | Stimulate uterine contractions during childbirth and milk ejection during breastfeeding | ||
Thyroid gland | Neck | Thyroxine (T4) and triiodothyronine (T3) | Regulate metabolism, growth, and development |
Calcitonin | Regulate calcium levels in the blood | ||
Parathyroid glands | Back of the thyroid gland | Parathyroid hormone (PTH) | Regulate calcium and phosphorus levels in the blood |
Adrenal glands | Above the kidneys | Cortisol | Regulate stress response, metabolism, and immune function |
Aldosterone | Regulate sodium and potassium balance and blood pressure | ||
Epinephrine and norepinephrine | Mediate the fight-or-flight response | ||
Androgens | Contribute to the development of secondary sexual characteristics | ||
Pancreas | Abdomen | Insulin | Lower blood glucose levels by promoting glucose uptake into cells |
Glucagon | Raise blood glucose levels by promoting the breakdown of glycogen | ||
Gonads | Testes (males) | Testosterone | Regulate male sexual development, sperm production, and secondary sexual characteristics |
Ovaries (females) | Estrogen and progesterone | Regulate female sexual development, menstrual cycle, pregnancy, and secondary sexual characteristics | |
Pineal gland | Brain | Melatonin | Regulate sleep-wake cycles and circadian rhythms |