Chapter 45: Hormones and the Endocrine System Flashcards
Water-soluble hormones
Secreted by exocytosis and travel freely in bloodstream
Cannot diffuse through cell membrane, bind to cell-surface receptors
Binding of a hormone to its receptor initiates a signal transduction pathway leading to changes in the cytoskeleton, enzyme activation, or gene expression
Lipid soluble hormones
Exit secreting cells by diffusing out across the membrane
Bind to transport proteins in the bloodstream to keep them soluble
When a steroid hormone binds to its cytosolic receptor a hormone-receptor complex forms that moves into the nucleus
The response to a lipid-soluble hormone is usually a change in gene expression
Paracrine and autocrine signaling
Secrete local regulators that act over short distances and reach target cells solely by diffussion
Prostaglandins are modified fatty acids; have diverse functions such as reproduction, the immune system, and blood clotting
Nitric oxide is a gas that functions in the body as both a local regulator and a neurotransmitter
- When the level of oxygen in blood falls endothelial cells release NO which activates an enzyme that results in vasodilation, thus increasing blood flow to tissues
Endocrine glands
Endocrine cells are often grouped in ductless organs secrete hormones directly into the surrounding fluid
E.g., thyroid and parathyroid glands, testes, and ovaries
Exocrine glands
Have ducts that carry secreted enzymes or bicarbonate carry secreted substances onto body surfaces or into body cavities
E.g., sweat or salivary glands
Nervous and endocrine coordination
The hypothalamus receives information from the nervous system to initiate a response
Signals from the hypothalmus travel to the pituitary gland located at the base of the hypothalmus
The posterior pituitary is an extension of the neural tissue of the hypthalmus
- Stores and secretes hormones that are synthesized in the hypothalamus
The anterior pituitary is an endocrine gland that synthesizes and secretes hormones in response to hormones from the hypothalmus
Posterior pituitary hormones
Neurosecretory cells of the hypothalamus synthesize the two posterior pituitary hormones
They are then stored in the posterior pituitary and released into the bloodstream in response to nerve impulses from the hypothalmus
- Antidiuretic hormone regulates kidney function and behavior
- Oxytocin regulates milk secretion by the mammary glands and influences behaviors related to maternal care and pair bonding
Anterior pituitary hormones
Regulate other endocrine glands or tissues
Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones secreted by the hypothalamus
Hypothalamic hormones are secreted near capillaries at the base of the hypothalamus that drain into short blood vessels called portal vessels which subdivide into a second capillary bed within the anterior pituitary
Anterior pituitary hormones are called tropic hormones and are said to have tropic effects
Thyroid hormones
Thyroid hormones regulate bioenergetics such as blood pressure, heart rate, muscle tone, digestive, and reproductive functions
If the thyroid hormone level drops in the blood the hypothalamus secretes thyrotropin-releasing hormone (TRH)
TRH causes the anterior pituitary to secrete thyroid-stimulating hormone (TSH)
TSH stimulates release of triiodothyronine (T3) and thyroxine T4) by follicular cells in the thyroid gland
Calcitonin
Is secreted by C-cells
Decreases blood calcium levels by inhibiting bone breakdown and enhancing calcium excretion by the kidneys
Growth hormone regulation
Growth hormone (GH) is secreted by the anterior pituitary gland
Promotes growth directly by targeting insulin-like growth factors (IGFs) which circulate in the blood and directly stimulate bone and cartilage growth
Also exerts diverse metabolic effects that tend to raise blood glucose levels and oppose the effects of insulin
Stimulates production of growth factors
Parathyroid hormones
The parathyroid glands are a set of four small structures imbedded in the posterior surface of the thyroid
Regulate blood calcium levels through the release of parathyroid hormone (PTH)
PTH raises blood calcium through direct effects in bones and the kidneys and indirect effects on the intestines
- Bones- causes mineralized matrix to breakdown releasing calcium into the blood
- Kidneys- stimulates reabsorption of calcium through the renal tubules
- Intestines- promotes production of vitamin D in the liver and kidneys which acts on the intestines to stimulate the uptake of calcium from food
Adrenal medulla hormones
The adrenal medulla is the inner portion comprised of cells derived from neural tissue
Secretes catecholamines epinephrine and norepinephrine which increase the amount of chemical energy available for immediate use
Adrenal cortex hormones
The adrenal cortex is the outer portion of the adrenal gland comprised of true endocrine tissue
Releases a family of steroids called corticosteroids in response to stress
Glucorticoids such as cortisol make glucose more available as fuel by promoting glucose synthesis from non carbohydrate sources
- Can also suppress certain components of the immune system when present at higher than normal levels
Mineralocorticoids such as aldosterone affect salt and water balance
Sex hormones
Sex hormones are controlled by two gonadotropins from the anterior pituitary; follicle stimulating hormone (FSH) and luteinizing hormone (LH)
Gonadotropin secretion is in turn controlled by gonadotropin-releasing hormone (GnRH) from the hypothalamus
- The testes primarily synthesize androgens, the main one being testosterone
- Estrogens, mainly estradiol, are responsible for maintenance of the female reproductive system
- Progestins, mainly progesterone, are involved in preparing and maintaining tissues of the uterus
