Endocrine System Overview

The endocrine system is a network of glands that secrete hormones directly into the bloodstream, acting as a second messenger system within the body.

Hormones are chemical messengers produced by specialized cells, secreted into the bloodstream, and carrying signals to target cells or organs.

Target cells or organs possess specific protein receptors that bind to hormones, triggering a response within the cell.

Amino acid-based hormones include proteins, peptides, and amines. Steroid hormones are derived from cholesterol. Prostaglandins are highly active lipids.

Hormones can affect various aspects of the body, including reproduction, growth and development, immune response, homeostasis, and metabolism.

Negative feedback loops control hormone levels in the blood. When hormone levels rise, a signal is sent to stop further hormone production. When hormone levels fall, production is stimulated.

Hormonal stimuli occur when one hormone triggers the release of another hormone from a different endocrine gland.

Humoral stimuli involve changes in blood levels of certain ions or nutrients, which, in turn, trigger hormone release.

The pituitary gland, located at the base of the brain, is a small, pea-sized gland that controls many other endocrine glands through its hormones.

The anterior pituitary (adenohypophysis) is the glandular portion, producing hormones that affect non-endocrine targets and stimulate other glands.

The posterior pituitary (neurohypophysis) is the nervous tissue portion, which stores and releases hormones produced by the hypothalamus.

Growth hormone (GH) affects skeletal muscle and bone growth, increases protein synthesis, and promotes fat breakdown for energy.

Prolactin (PRL) stimulates and maintains milk production in females after childbirth. Its function in males is less understood.

Adrenocorticotropic hormone (ACTH) regulates the activity of the adrenal cortex, particularly the production of hormones like cortisol.

Thyroid-stimulating hormone (TSH) influences the growth and activity of the thyroid gland, ensuring proper thyroid hormone production.

Gonadotropic hormones regulate the activity of the reproductive glands (gonads), affecting both male and female reproductive functions.

Follicle-stimulating hormone (FSH) stimulates follicle development in the ovaries and sperm development in the testes.

Luteinizing hormone (LH) triggers ovulation in females and stimulates testosterone production in males.

Oxytocin stimulates uterine contractions during labor and milk ejection after childbirth.

Antidiuretic hormone (ADH) prevents excess water loss by reducing urine production and can also constrict blood vessels to increase blood pressure.

The thyroid gland, located in the neck, produces thyroid hormone and calcitonin, both involved in calcium regulation and metabolism.

Thyroid hormone, consisting of thyroxine (T4) and triiodothyronine (T3), is a major metabolic hormone that regulates energy production and utilization.

Calcitonin, produced by the thyroid gland, lowers blood calcium levels by promoting calcium deposition in bone.

The parathyroid glands, located on the back of the thyroid, secrete parathyroid hormone, which increases blood calcium levels.

The adrenal glands, located on top of the kidneys, produce a variety of hormones, including corticosteroids and catecholamines.

Mineralocorticoids, particularly aldosterone, regulate mineral content in the blood, especially sodium and potassium.

Glucocorticoids, like cortisol, are involved in stress response, energy metabolism, and inflammation control.

The adrenal medulla produces catecholamines, mainly epinephrine and norepinephrine, which prepare the body for 'fight or flight' responses.

The pancreas, an organ with both digestive and endocrine functions, produces insulin and glucagon, which regulate blood sugar levels.

Insulin, produced by beta cells in the pancreas, lowers blood sugar levels by allowing glucose to enter cells.

Glucagon, produced by alpha cells in the pancreas, raises blood sugar levels by releasing stored glucose from the liver.

The pineal gland, located in the brain, produces melatonin, which regulates sleep-wake cycles and may have other functions.

The thymus, located in the chest, is important for immune system development, particularly in children.

The ovaries, the female reproductive organs, produce estrogens and progesterone, involved in the menstrual cycle, pregnancy, and development of female characteristics.

Estrogens, produced by ovaries, are responsible for development of female secondary sex characteristics and play a role in pregnancy and breast development.

Progesterone, produced by ovaries, helps prepare the uterus for pregnancy, maintains pregnancy, and contributes to the menstrual cycle.

The testes, the male reproductive organs, produce testosterone, responsible for development of male secondary sex characteristics, sperm production, and reproductive system maturation.

Testosterone is the primary male sex hormone, responsible for male secondary sex characteristics and promoting sperm production.

The placenta, a temporary organ during pregnancy, produces hormones that support pregnancy and prepare the body for childbirth.