Physiology of the Endocrine System - Week 2

Lipid-Soluble Hormones

Derived from cholesterol, transported by transport proteins, and pass through cell membranes to bind internal receptors.

Water-Soluble Hormones

Derived from amino acids and peptides, dissolve in plasma, and bind to surface receptors activating G proteins and cAMP.

Mechanism of Lipid-Soluble Hormones

Diffuse through membrane, bind cytoplasmic/nuclear receptor, alter gene expression, form new mRNA, and synthesize new protein.

Mechanism of Water-Soluble Hormones

Bind surface receptors, activate G protein and adenylate cyclase, convert ATP to cAMP, and activate protein kinases.

Thyroid Hormones (T3 and T4) Classification Exception

Derived from amino acids and classified as water-soluble, but act as lipid-soluble hormones.

Neural Control of Hormone Release

Stimulation by the nervous system, such as electrical impulses regulating epinephrine release from the adrenal medulla.

Humoral Control of Hormone Release

Stimulation by chemical changes in the blood, such as blood calcium levels regulating parathyroid hormone.

Hormonal Control of Hormone Release

Stimulation by the presence of other hormones, such as ACTH regulating the release of cortisol.

Human Growth Hormone (hGH)

Released from anterior pituitary; promotes insulin-like growth factors to stimulate tissue growth. Regulated by growth hormone-releasing hormone and growth

hormone-inhibiting hormone from hypothalamus (hormonal).

Thyroid Stimulating Hormone (TSH)

Released from anterior pituitary; stimulates thyroid gland to produce T3 and T4. Produced and released in response to thyroid-releasing hormone

from the hypothalamus (hormonal).

Follicle Stimulating Hormone (FSH)

Released from anterior pituitary; stimulates ovarian follicle maturation in females and sperm production in males. Regulated by the release of gonadotrophin-releasing hormone from the hypothalamus (hormonal).

Luteinizing Hormone (LH)

Released from anterior pituitary; stimulates ovulation in females and testosterone production in males. Regulated by the release of gonadotrophin-releasing hormone from the hypothalamus (hormonal).

Prolactin

Released from anterior pituitary; stimulates milk production by mammary glands in response to suckling. Secretion increased by the release of prolactin releasing hormone from the hypothalamus in response to the baby suckling at the breast (hormonal).

Adrenocorticotropic Hormone (ACTH)

Released from anterior pituitary; stimulates production and release of cortisol, androgens, and aldosterone. Secreted in response to corticotropin-releasing hormone from the hypothalamus (hormonal).

Oxytocin

Released from posterior pituitary; increases uterine contractions and is responsible for milk let-down. Receptors in the cervix and nipple send signals to hypothalamus that results in the release of oxytocin from the posterior pituitary gland (neural)

Antidiuretic Hormone (ADH)

Released from posterior pituitary; increases water reabsorption in the nephrons of the kidneys. Stimulated by increased plasma osmolality and decreased blood volume (humoral)

Melatonin

Released from pineal gland; induces drowsiness and has concentrations that peak at night (suppressed by light). Suppressed by bright light (neural)

Thyroid Hormones (T3 and T4)

Released from thyroid gland; increase metabolic rate, cell growth, and body heat production. Regulated by the release of thyroid stimulating hormone from the

anterior pituitary gland (hormonal)

Calcitonin

Released from thyroid gland; decreases blood calcium by promoting storage in bone and inhibiting intestinal absorption. Regulated by blood calcium concentration (humoral)

Parathyroid Hormone (PTH)

Released from parathyroid gland; increases blood calcium by stimulating osteoclast activity and bone reabsorption. Regulated by blood calcium concentration (humoral)

Aldosterone (Mineralocorticoid)

Released from adrenal cortex; increases sodium reabsorption and potassium secretion, raising blood volume. Primary control mechanism is the production of angiotensin II in response to reduced blood pressure (hormonal)

Cortisol (Glucocorticoid)

Released from adrenal cortex; increases protein breakdown and glucose formation while depressing immune response. Stimulated by the release of adrenocorticotropic hormone from the anterior pituitary gland (hormonal)

Androgens (Sex Hormones)

Released from adrenal cortex; promote libido in women and convert to oestrogens in body tissues. Not fully understood. But the main hormone that stimulates its secretion is adrenocorticotropic hormone. Therefore, hormonal regulation.

Epinephrine and Norepinephrine

Released from adrenal medulla; produce effects associated with the fight-or-flight response. Innervated by the sympathetic nervous system (neural)

Glucagon

Released from pancreas; increases blood glucose by stimulating glycogen breakdown in the liver. Regulated by blood glucose concentration (humoral)

Insulin

Released from pancreas; reduces blood glucose by facilitating cellular uptake and glycogen storage. Regulated by blood glucose concentration (humoral)

Oestrogen and Progesterone

Released from ovaries; regulate menstrual cycle, maintain pregnancy, and prepare mammary glands for lactation. Regulated by follicle stimulating hormone and luteinizing hormone (hormonal)

Testosterone

Released from testes; regulates sperm production and stimulates development of male sexual characteristics. Regulated by luteinizing hormone (hormonal)