3.3 Hormonal Controls

Nervous system

Regulates quick responses to abrupt environmental change by sending fast electrical or chemical signals through neurons.

Endocrine system

Regulates more defined and time-consuming processes such as development by sending chemical signals via the circulatory system to target cells.

Paracrine signaling

Communication between adjacent cells using local regulators such as growth factors, prostaglandins, and nitric oxide (NO).

Synaptic signaling

Communication between nerve cells by sending neurotransmitters across synapses.

Endocrine gland

A ductless gland that secretes hormones directly into the circulatory system.

Hormone

A chemical signal that travels via the circulatory system to target cells with specific receptors.

Small, lipid-soluble hormones

Hormones that penetrate through the cell membrane, bind to intracellular receptors, and initiate transcription and translation (e.g., sex hormones like testosterone).

Large, water-soluble hormones

Hormones that cannot penetrate the cell membrane, bind to membrane receptors, and use second messengers to trigger rapid cellular responses (most hormones act this way).

Antidiuretic hormone (ADH)

Released from the posterior pituitary in response to increased blood osmolarity, leading to increased water reabsorption in the kidneys to prevent dehydration.

Insulin

A protein hormone from the β-cells of the pancreas that lowers blood glucose level by driving glucose uptake by body cells and encouraging storage as glycogen.

Glucagon

A protein hormone from the α-cells of the pancreas that raises blood glucose level by stimulating the liver to break down glycogen to glucose.

Type I Diabetes Mellitus

An autoimmune disorder, usually appearing in childhood, where the body cannot produce insulin, often requiring insulin injections.

Type II Diabetes Mellitus

A condition characterized by decreased responsiveness to insulin, usually occurring after age 40, accounting for over 90% of diabetes cases.

Calcitonin

A peptide hormone from the thyroid gland that reduces blood calcium levels by increasing Ca$^{2+}$ deposition in bones and increasing Ca$^{2+}$ uptake in kidneys.

Parathyroid hormone (PTH)

A peptide hormone from the parathyroid glands that raises blood calcium levels by increasing Ca$^{2+}$ release from bones, reducing Ca$^{2+}$ excretion in kidneys, and increasing Ca$^{2+}$ absorption from the gut.

Negative feedback

A regulatory mechanism in endocrine axes (e.g., thyroid axis) where high levels of hormones like T3, T4, and TSH inhibit the secretion of upstream hormones like TRH from the hypothalamus.

Ren