Endocrinology Overview and Hormone Mechanisms

Study Notes

Endocrinology is the study of hormones and glandular abnormalities, including diabetes and thyroid problems.
Hormones are biologically active substances secreted by glands.
Endocrine hormones have a biological effect far away from their source.
Paracrine hormones have a biological effect nearby.
Autocrine hormones have a local effect.

Hormones circulate in the bloodstream, either bound to transporter proteins or free.
Free hormones are the active form.
Hormones enter cells to alter biological activity.

The diagram shows various glands in the body, including the pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries (female), and testes (male).

Causes of endocrine hypofunction include congenital defects in hormone biosynthesis, autoimmune destruction of glands, surgery or trauma to glands, and infiltration by tumors or infection.

Body functions are coordinated through various systems, including the nervous system (neurotransmitters), the endocrine system (hormones), neuroendocrine (neurohormones), paracrines (secreted into extracellular fluid), autocrines (affecting the same cells), and cytokines (peptides like interleukins, lymphokines, and adipokines).

High blood sugar requires communication to stimulate body cells to take up sugar
This is achieved primarily through endocrine communication

Growth and development: Thyroid, growth hormone (GH), sex steroids, cortisol
Reproduction: Estrogen, testosterone, follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid
Homeostasis: Thyroid, cortisol, insulin
Environmental changes: Cortisol, thyroid, aldosterone

Examples of homeostasis regulated by hormones include thyroid and temperature control; thyroid, parathyroid, and calcium regulation; and pancreas and glucose control.

Combination organ: exocrine tissues (acini) secrete digestive enzymes into the small intestine, while endocrine tissues secrete hormones (e.g., insulin, glucagon, somatostatin)
Processes associated with the pancreas include glycogenolysis and gluconeogenesis.

A table lists pancreatic hormones and their target tissues along, with their major effects:
Insulin: targets all cells (particularly in liver, muscle, and fat); effects: stimulates cellular glucose uptake, increased glycogen synthesis, protein and fat synthesis, and decreases blood glucose.
Glucagon: targets alpha cells in the pancreas; effect: stimulates hepatic glycogenolysis (breakdown) and gluconeogenesis(production of glucose from other sources), increasing blood glucose.
Somatostatin: targets alpha and beta cells in the pancreas; effect: suppresses secretion of glucagon and insulin.

Diabetes Mellitus is a disorder of glucose metabolism.
Type I: Insulin deficiency (juvenile onset, closely related to heredity)
Type II: Insulin resistance (adult onset, related to heredity and obesity).
Symptoms of untreated type I and II diabetes include polydipsia, polyuria, polyphagia, weight loss, and weakness.
Severe cases may lead to ketosis or diabetic ketoacidosis

Hormones are vital for normal growth, development, metabolism, energy, and reproduction
Hormones are tightly regulated by various systems.
Hormone imbalances (over or underproduction) cause clinical problems.