Endocrinology Overview

Endocrinology Overview

• Definition: Study of hormones and structures that produce them

• Role of Endocrinologists: Physicians specializing in treating endocrine issues

• Functions of the Endocrine System: Growth, metabolism, maintenance of electrolytes and water balance, immune responses, etc.

Endocrine vs. Exocrine Glands

• Endocrine Glands: Produce hormones directly into the bloodstream

• Exocrine Glands: Secrete substances through ducts.

• Pancreas: Functions as both exocrine (produces digestive enzymes) and endocrine (releases insulin and glucagon)

Key Hormones and Glands

• Pineal Gland: Produces melatonin

• Hypothalamus: Controls several endocrine functions

• Gonads:

• Ovaries produce estrogen and progesterone

• Testes produce testosterone

Types of Hormones

• Water-soluble:

• Examples: Amino acid derivatives and small peptides, which have receptors on plasma membranes

• Mechanism: Bind to receptors on target cell membranes, activate G proteins, and increase cyclic AMP, leading to cellular responses

• Lipid-soluble:

• Examples: Steroid hormones (derived from cholesterol) and thyroid hormones, which can pass through cell membranes

• Mechanism: Bind to intracellular receptors, leading to direct activation of gene transcription.

Cellular Responses to Hormones

• Responsiveness can change based on hormone levels and receptor availability.

• Example: Type 2 Diabetes - Insulin resistance leads to ineffective glucose metabolism.

Hormonal Regulation Mechanisms

• Humoral Stimuli: Hormones released in response to changes in blood levels of ions/nutrients (e.g., calcium affecting the parathyroid hormone)

• Neural Stimuli: Release of hormones in response to nerve impulses (e.g., adrenal medulla releasing epinephrine)

• Hormonal Stimuli: Hormones stimulate other hormone releases (e.g., TSH from anterior pituitary stimulates the thyroid gland).

Hormone Interaction Types

• Permissiveness: One hormone requires another to have effect (e.g., thyroid hormones facilitating growth hormone action)

• Antagonism: One hormone opposes action of another (e.g., parathyroid hormone vs. calcitonin)

• Tropic Hormones: Hormones that stimulate other hormones through a cascade (e.g., hypothalamus to pituitary to other glands)

Feedback Mechanisms

• Negative Feedback: Most common, where a hormone's release is inhibited by its effects on target organs (e.g., thyroid hormone levels inhibiting TSH production)

• Positive Feedback: Enhances the original stimulus (e.g., oxytocin during childbirth)

Thyroid Hormone Feedback

• Iodine deficiency leading to low T3/T4 production can result in excess TSH and goiter formation (swelling in the thyroid)

Calcium Regulation

• When calcium levels decline, parathyroid hormone is released to increase calcium levels through bone resorption and kidney reabsorption.

Pancreas Functions

• Produces hormones in the islets of Langerhans:

• Insulin: Decreases blood glucose

• Glucagon: Increases blood glucose

• Cortisol: Secreted from the adrenal cortex, involved in stress response and glucose metabolism regulation.