Endocrine Gland Functions and Hormones

Study Notes

Primary Functions of the Endocrine System: Hormone secretion regulates physiological processes, including maintaining homeostasis, regulating growth and development, controlling metabolic activities, and coordinating stress responses.
Insulin and its Function: Produced by the pancreas, insulin regulates glucose metabolism by helping cells absorb glucose, lowering blood glucose levels.
Hormones Produced by the Thyroid Gland: Thyroxine (T4) and Triiodothyronine (T3) regulate metabolism, energy production, and growth/development.
Endocrine vs. Exocrine Glands: Endocrine glands secrete hormones directly into the bloodstream (e.g., pancreas), while exocrine glands secrete substances through ducts (e.g., pancreas also secretes digestive enzymes).
Hormone Stimulating Uterine Contractions: Oxytocin stimulates uterine contractions during childbirth, targeting smooth muscle cells in the uterus.
Negative Feedback in Hormone Regulation: Negative feedback prevents excessive hormone production by inhibiting the process that caused the hormone release. Insulin release decreases as glucose levels normalize, illustrating this process.
Example of Hormone-Regulated Feedback Loop: Parathyroid Hormone (PTH) regulates blood calcium levels.

Steroid Hormones: Derived from cholesterol, enter cells, bind to intracellular receptors, and affect gene expression (e.g., cortisol).
Peptide Hormones: Bind to cell membrane receptors, activating second messenger systems (e.g., insulin).

Steroid Hormone (Cortisol): Regulates metabolism and immune responses.
Peptide Hormone (Insulin): Regulates glucose metabolism by promoting glucose uptake into cells.

Hormones: Thyroxine (T4) and Triiodothyronine (T3).
Target: Various body tissues.
Action: Regulate metabolism, energy production, and growth.
Regulation: Stimulated by Thyroid-Stimulating Hormone (TSH) from the pituitary gland. Negative feedback loop controls release.

Hormone: Growth Hormone (GH).
Target: Bones, muscles, and other tissues.
Action: Stimulates growth and cell reproduction.
Regulation: Controlled by Growth Hormone-Releasing Hormone (GHRH) and Growth Hormone-Inhibiting Hormone (GHIH) from the hypothalamus.

Hormone: Insulin.
Target: Liver, muscle, and adipose tissue.
Action: Promotes glucose uptake, storage, and inhibits glucose production.
Regulation: Released in response to high blood glucose levels and inhibited by low glucose levels.

Hormone: Cortisol.
Target: Liver, muscle, and adipose tissue.
Action: Regulates metabolism, reduces inflammation, and affects immune response.
Regulation: Controlled by the hypothalamus-pituitary-adrenal (HPA) axis; regulated by Corticotropin-Releasing Hormone (CRH) and ACTH.

Estrogen (Female): Regulates menstrual cycle, secondary sexual characteristics. Regulated by FSH and LH from pituitary.
Testosterone (Male): Stimulates sperm production, secondary sexual characteristics, and influences muscle mass. Regulated by LH from pituitary.

Hormone: Parathyroid Hormone (PTH).
Target: Bones and kidneys.
Action: Increases blood calcium levels by stimulating calcium release from bones and enhancing calcium reabsorption in kidneys.
Regulation: Triggered by low blood calcium levels, inhibited by high levels.

Hormone: Melatonin
Target: Various tissues, especially the brain.
Action: Regulates sleep-wake cycles (circadian rhythms).
Regulation: Controlled by light-dark cycles; secretion increases in darkness and decreases in light.