The Endocrine System Overview

A system of glands that secrete hormones directly into the bloodstream to regulate body functions.

A chemical messenger produced by endocrine glands that travels through the bloodstream to target organs, influencing their activity.

The 'master gland' of the endocrine system, located at the base of the brain, that controls the secretion of hormones from other endocrine glands.

The front lobe of the pituitary gland, responsible for producing hormones that regulate growth, metabolism, and other vital functions.

A network of blood vessels that connects the hypothalamus to the anterior pituitary, allowing for the exchange of hormones and regulatory signals.

Stimulates the growth and activity of the thyroid gland.

Stimulates and controls the growth and hormonal output of the adrenal cortex.

Stimulates lactation (milk production). Release is stimulated by suckling.

Stimulates the development and ripening of ovarian follicles (female) and the testes to produce sperm (male).

Stimulates the final maturation of ovarian follicle and ovulation (female). Promotes formation of the Corpus luteum which secretes progesterone. Stimulates testes to produce testosterone (male).

Stimulates the production of melanin in the basal cell layer of the epidermis.

Promotes uterine contraction during childbirth and milk expression from the breast.

Contracts smooth muscle in blood vessels, increasing blood pressure. Increases permeability of kidney tubules so that more water is absorbed.

The thyroid gland is located in the neck, situated in front of the larynx and trachea. It is a butterfly-shaped gland with two lobes.

The thyroid gland produces three main hormones: T3 (tri-iodothyronine), T4 (thyroxine), and calcitonin.

Calcitonin, produced by the thyroid gland, helps reduce calcium levels in the blood by inhibiting its absorption from bones and kidneys.

The parathyroid glands, located behind the thyroid, secrete parathyroid hormone (PTH). PTH increases blood calcium levels by promoting its absorption from bones, intestines, and kidneys.

Thyroid and parathyroid hormones work together to maintain blood calcium levels, which are essential for muscle contraction, blood clotting, and nerve impulse transmission.

A physiological state characterized by decreased heart rate, lowered blood pressure, and relaxed muscles, promoting relaxation and digestion.

Vasconstriction, the narrowing of blood vessels, increases blood pressure by creating resistance to blood flow.

The ovaries are located in the lower abdomen of females, below the kidneys, one on each side of the uterus.

FSH stimulates the development of eggs, while LH triggers ovulation and the production of progesterone.

The testes produce sperm cells and the hormone testosterone, both essential for male reproduction and sexual development.

A period of rapid physical and hormonal changes leading to sexual maturity, marked by the development of secondary sex characteristics.

Androgens, primarily produced by the adrenal glands, contribute to the development of secondary sex characteristics in females, like pubic hair growth, but in excess can cause hirsutism (excess hair growth).

A monthly cycle in females involving the shedding of the uterine lining if pregnancy doesn't occur, regulated by hormones and marked by menstruation.

The thymus gland is responsible for the maturation of T-lymphocytes, a crucial type of white blood cell responsible for immune responses.

The thymus gland secretes thymosin and thymic factor, which stimulate the maturation and development of T-lymphocytes.

The Islets of Langerhans are groups of cells within the pancreas that secrete hormones vital for regulating blood glucose levels.

The Islets of Langerhans secrete glucagon and insulin, both essential for maintaining blood glucose levels.

The adrenal glands are located atop each kidney, one on each side of the body.

The outer layer of the adrenal gland, the adrenal cortex, produces hormones like glucocorticoids, mineralocorticoids, and androgens.

The inner layer of the adrenal gland, the adrenal medulla, releases adrenaline and noradrenaline, hormones crucial for stress response.

Adrenaline, released by the adrenal medulla during stress, triggers a range of physiological changes, including increased heart rate, dilated pupils, and the conversion of glycogen to glucose.

The first stage of the menstrual cycle where the lining of the uterus, known as the endometrium, is shed in the form of menstrual bleeding. This occurs due to the decline in progesterone levels at the end of the previous cycle.

The second stage of the menstrual cycle where the endometrium starts to thicken again due to the release of estrogen from the ovaries. This is the stage where the egg matures within the follicle and gets released (ovulation) due to the release of FSH and LH from the pituitary gland.

The final stage of the menstrual cycle where the thickened endometrium prepares for potential pregnancy. The released egg is captured by the fallopian tube, and the Corpus Luteum, a temporary endocrine gland, releases progesterone to further thicken the endometrium. If fertilization occurs, the Corpus Luteum continues to release progesterone until the 4th month of pregnancy.

A temporary endocrine gland that develops from the ruptured ovarian follicle after ovulation. It releases progesterone to further thicken the endometrium and prepare for potential pregnancy.

The natural cessation of menstruation and ovarian activity in a woman's life, usually occurring between 45 and 55 years of age. This is marked by a decline in estrogen levels, causing various physical and emotional symptoms.

Symptoms of menopause include hot flashes, palpitations, anxiety, irritability, fatigue, lack of concentration, and osteoporosis. These are caused by the decline in estrogen levels, which disrupt the hormonal balance in the body.

Normally, the ovaries and the anterior pituitary (master gland) have a feedback mechanism to regulate hormone levels. However, in menopause, the ovaries stop working, causing confusion for the pituitary gland. This can lead to over-stimulation of the adrenal cortex, resulting in excess androgens and sometimes excess facial and body hair.

Progesterone is the hormone responsible for maintaining the uterus lining during pregnancy. It also plays a vital role in the development of the placenta and prepares the breasts for lactation.