Endocrine System Overview

Study Notes

The endocrine system is a network of glands that produce hormones.
Hormones are chemical messengers that regulate various bodily functions.
Hormones act on specific target cells or organs.
Glands secrete hormones directly into the bloodstream or surrounding fluids.
The endocrine system works in conjunction with other body systems to maintain homeostasis.

Glands are organs that secrete materials (hormones) through ducts or directly into the bloodstream.
Ducts are tube-like structures that carry secretions to different parts of the body.
Some glands release secretions via ducts (exocrine glands), others release hormones directly into the blood (endocrine glands).

Hormones are chemical messengers that carry instructions to cells affecting activities.
Hormones can last for hours, days, weeks, or even years.
The effect or duration of a hormone's action varies.
The correct hormonal amount is critical for good bodily function.
Different types of hormones exist with varied effects.
Hormones are produced by endocrine glands to regulate various processes.

Various organs also have endocrine tissue like brain, stomach, small intestine, kidney, liver, and heart.
These organs produce hormones.
Major endocrine glands include: hypothalamus, pituitary, thyroid, parathyroids, adrenals, pancreas, ovaries (in females), testes (in males), and pineal gland.

Hypothalamus: Located at the base of the brain, it helps regulate other endocrine glands.
Pituitary gland: Often called the "master gland," it controls other endocrine functions, using hypothalamic hormones. Consists of an anterior and posterior part having different hormone secretions.
Thyroid gland: Secretes hormones (T3, T4, calcitonin) regulating metabolism, heart rate, blood pressure, and growth/development. Iodine is essential for thyroid function.
Parathyroid glands: Four small glands embedded in the thyroid. Produce parathyroid hormone (regulates blood calcium levels). Works with calcitonin to maintain calcium balance.
Adrenal glands: Located atop the kidneys. Outer part (cortex) produces corticosteroids regulating metabolism, electrolyte balance, and long-term stress. Inner part (medulla) produces adrenaline for short-term stress response.
Pancreas: Produces insulin (lowers blood sugar) and glucagon (increases blood sugar) to regulate blood glucose levels.
Gonads (ovaries and testes): Responsible for sexual development and reproduction, producing sex hormones like estrogen and progesterone (in ovaries), and testosterone (in testes).
Pineal gland: Produces melatonin regulating sleep-wake cycles and synchronizing bodily rhythms.

Some endocrine glands function until the organism reaches a specific age/stage.
Hormones must be produced in the right amounts to support function.
Hormones trigger changes; different hormones have different durations of effect.

Hyperthyroidism: Excess thyroid hormone (T3 & T4) leading to symptoms like irritability, sweating, weight loss, etc.
Hypothyroidism: Insufficient thyroid hormone (T3 & T4) leading to lethargy, weight gain, intolerance to cold, etc.