Endocrine System

Endocrine System

Network of specialized glands and organs producing hormones released into the bloodstream to affect target cells

Exocrine Glands

Have ducts that carry secretions to specific locations

Endocrine Glands

Ductless glands that secrete hormones directly into the bloodstream

Hormones

Chemical messengers secreted into the bloodstream that influence cells or organs in another area

Target Cells

Cells with receptor sites specific to a hormone; follow a lock-and-key mechanism

Receptor

The site on a target cell where a hormone binds to exert its effect

Humoral Stimulation

Triggered by changes in ion or nutrient concentration in blood (e.g., pancreas releases insulin when glucose rises)

Hormonal Stimulation

One hormone stimulates another gland to release its hormone (e.g., CRH → ACTH → Adrenal gland)

Neural Stimulation

Nervous system directly triggers hormone release (e.g., sympathetic nerves trigger epinephrine release)

Hypothalamus

Control center of the endocrine system located in the diencephalon; regulates hunger, thirst, temperature, and controls the pituitary gland

Hypophyseal Portal System

Delivers hypothalamic hormones to the anterior pituitary

Hypothalamo-Hypophyseal Tract

Sends hormones to the posterior pituitary

Neurohormones of Hypothalamus

CRH, GHRH, GHIH, GnRH, PRH

CRH, GHRH, GHIH, GnRH, PRH

Neurohormones of Hypothalamus

Pituitary Gland

Known as the “master gland”; controls other endocrine glands

Anterior Pituitary (Adenohypophysis)

Produces and secretes its own hormones

Posterior Pituitary (Neurohypophysis)

Stores and releases hormones made by the hypothalamus

Anterior Pituitary Hormones

GH, TSH, ACTH, FSH, LH, PRL, MSH

GH, TSH, ACTH, FSH, LH, PRL, MSH

Anterior Pituitary Hormones

Growth Hormone (GH)

Stimulates tissue growth, repair, and maintenance (liver, bone, muscle, fat).

Thyroid-Stimulating Hormone (TSH)

Stimulates thyroid to release T3 and T4 for metabolism.

Adrenocorticotropic Hormone (ACTH)

Stimulates adrenal cortex to release cortisol for stress response and immune regulation.

Follicle-Stimulating Hormone (FSH)

Stimulates sperm production and follicle growth.

Luteinizing Hormone (LH)

Triggers ovulation, corpus luteum formation, and testosterone secretion.

Prolactin (PRL)

Stimulates milk production; in males, increases testes sensitivity to LH.

Melanocyte-Stimulating Hormone (MSH)

Produces skin pigmentation; may suppress appetite and influence aldosterone.

Posterior Pituitary Hormones

ADH/Vasopressin, Oxytocin

ADH/Vasopressin, Oxytocin

Posterior Pituitary Hormones

Antidiuretic Hormone (ADH / Vasopressin)

Kidneys; promotes water retention and maintains blood pressure.

Oxytocin

Causes uterine contractions, milk ejection, and sperm transport; follows positive feedback.

Pineal Gland

Located in the diencephalon; secretes melatonin.

Melatonin

Controls sleep-wake cycle; more light = less melatonin, less light = more melatonin.

Circadian rhythm

Controls sleep-wake cycle

Thyroid Gland

Produces T3, T4 (increase metabolism), and Calcitonin (lowers blood calcium by promoting bone formation).

Parathyroid Glands

Produce PTH, which raises blood calcium by stimulating osteoclasts and increasing calcium absorption.

High Blood Calcium Response

Thyroid releases Calcitonin to lower calcium.

Low Blood Calcium Response

Parathyroids release PTH to raise calcium.

Adrenal Glands

Located above kidneys; consist of adrenal cortex and adrenal medulla.

Zona glomerulosa, zona fasciculata, zona reticularis

Adrenal Cortex Zones

Zona Glomerulosa

Produces Aldosterone (regulates sodium and water balance, BP).

Zona Fasciculata

Produces Cortisol (stress resistance, metabolism, immune suppression).

Zona Reticularis

Produces Androgens (sex hormones for secondary traits).

Adrenal Medulla

Inner region; releases Epinephrine (adrenaline) and Norepinephrine during fight-or-flight.

Epinephrine, Norepinephrine

Adrenal Medulla

Pancreas

Both endocrine and exocrine gland.

Insulin

Lowers blood glucose by promoting glucose uptake.

Glucagon

Raises blood glucose by promoting glycogen breakdown.

Somatostatin

Balances insulin and glucagon levels.

Skin

Produces Vitamin D (first step in calcitriol synthesis).

Liver

Produces EPO, Angiotensin II, Calcitriol, IGF-I, and Hepcidin (blood and calcium regulation).

Kidneys

Produce EPO (RBCs), Renin (BP control), and Calcitriol (calcium absorption).

Heart

Produces ANP, which lowers blood pressure by promoting salt and water excretion.

Thymus

Produces Thymosin, which matures T-cells for immunity.

Stomach

Produces Gastrin, which stimulates gastric juice secretion.

Small Intestine

Produces Secretin and CCK, which stimulate pancreatic juice and bile.

Placenta

Produces hCG to maintain pregnancy.

Negative Feedback

Hormone release stops once the desired effect is achieved (most hormones).

Positive Feedback

Hormone release increases to enhance its effect (e.g., Oxytocin during childbirth).