Hormones

• 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