A&P 2 - Introduction and Endocrine System

Homeostasis

The condition of maintaining the body’s internal environmental in a relative constant state (Same, stable conditions).

Homeostatic Imbalance

Anything that disturbs or alters the balance of the internal environment.

Positive Feedback

A change in one direction that accelerates a change in the same direction (Blood clotting, labor contractions, orgasms).

Negative Feedback

A change in one direction that results in feedback that causes a change or adjustment in the opposite direction (Similar to a thermostat).

Nervous System and Feedback Mechanism

Uses “electrical” impulses delivered by neurons to specific target cells. Nerve impulses are quick and not as lasting; Neural control is brief, quick, and generally results in either muscle contraction or gland secretion.

Endocrine System and Feedback Mechanism

Affects cell activity by releasing chemical messengers (hormones) directly into the blood system. More slow but longer lasting; target cells are varied (might be all over the body); Hormonal control takes from minutes to hours and the changes are long lasting (Slow, long lasting).

Endocrine Gland

A gland that secretes their products into extra-cellular (outside cell) spaces where they’re picked up and transported by the circulatory system (Blood stream).

Exocrine Gland

A gland that produces non-hormonal substances and secretes products the way of a duct (tube), onto a surface.

Hormone

A secretion that is transported in the blood (or lymph) and alters the physiological activity of a target cell(s).

Chemical Messenger

Produced by one type of cell which has a specific effect on the metabolic activity of another type of cell.

Hormones affecting cells

Hormones can alter plasma membrane permeability (or membrane potential) by opening or closing ion channels; Hormones stimulate the synthesis of enzymes and other proteins within the cells (starts/stops protein synthesis); Hormones can activate/deactivate enzymes; Hormones can induce secretory activity (glands secreting); Hormones can stimulate mitosis.

Hormonal Stimuli

Hormones stimulate other endocrine organs to release their hormones; Hormones from final target organs inhibit release of anterior pituitary hormones.

Humoral Stimuli

Changing blood levels of ions and nutrients directly stimulate secretion of hormones.

Neural Stimuli

Nerve fibers stimulate hormone release.

Plasma Proteins

Steroids and thyroid hormones are attached to these proteins.

Concentration of circulating hormones

Rate of release and speed at which it’s inactivated and removed from the body,

Removing hormones

Can be removed from the body by degrading enzymes, kidneys, or liver.

Permissiveness

A situation in which one hormone cannot exert its full effects without another hormone being present.

Synergism

Occurs when more than one hormone produces the same effects at the target cell and their combined effects are amplified.

Antagonism

Occurs when one hormone opposes the action of another.

Hypothalamus and Pituitary Gland

Secretes oxytocin, ADH (Antidiuretic hormone), releasing and inhibiting hormones, GH (Growth hormone), TSH (Thyroid-stimulating hormone), ACTH (Adrenocorticotropic hormone), FSH (Follicle-stimulating hormone), LH (Luteinizing hormone), and PRL (Prolactin)

Oxytocin

Strong stimulant of uterine contractions released during childbirth; Neural secretion.

ADH (Antidiuretic Hormone)

Hypothalamus contains osmoreceptors that monitor solute concentrations; Targets kidney tubules to reabsorb more water to inhibit or prevent urine formation; Humoral secretion.

GH (Growth Hormone)

Produced by somatropic cells; Has direct actions on metabolism and indirect growth-promoting actions (stimulating production of IGFs); Causes glycogen breakdown in liver and decreases the rate of glucose uptake and metabolism, conserving glucose; Hormonal secretion.

TSH (Thyroid-Stimulating Hormone)

Produced by thyrotropic cells; stimulates normal development and secretory activity of thyroid; release triggered by thyrotropin-releasing hormone from hypothalamus; Hormonal secretion.

ACTH (Adrenocorticotropic Hormone)

Secreted by corticotropic cells; Stimulates adrenal cortex to release corticosteroids; Hormonal secretion.

Gonadotropins (FSH and LH)

Secreted by gonadotropic cells; FSH stimulates production of gametes (egg or sperm), LH promotes production of gonadal hormones; LH helps mature follicles of egg in females and triggers ovulation, LH stimulates production of testosterone in males; Both hormonal secretion.

PRL (Prolactin)

Secreted by prolactic cells; Stimulates milk production in females, role in males not well understood; Hormonal secretion.

Thyroid Gland

Secretes TH (Thyroid hormone), T4 (Thyroxine), T3 (Triiodothyronine), and Calcitonin.

TH (Thyroid Hormone)

Body’s major metabolic hormone; Found in 2 forms being T4 (Thyroxine) and T3 (Triiodothyronine), both are iodine-containing amine hormones; Vitually affects every cell in the body; Increases basal metabolic rate and heat production; Regulates tissue growth and development, and maintains blood pressure; Hormonal Secretion.

Calcitonin

Produced by parafollicular cells; Antagonist to PTH (Parathyroid hormone); Increases calcium in the blood; At higher-than-normal levels it inhibits osteoclast activity and prevents release of Ca2+ from bone matrix, stimulates Ca2+ uptake and incorporation into bone matrix, and 1-5% of minerals in bone are exchanged with extracellular fluid; Humoral secretion.

Parathyroid Gland

Secretes PTH (Parathyroid hormone) (Parathormone)

PTH (Parathyroid Hormone)

Stimulates osteoclasts to digest bone matrix and release Ca2+ to blood, enhances reabsorption of Ca2+ and secretion of phosphate (PO43-) by kidneys, and promotes activation of vitamin D by kidneys, leading to increased absorption of Ca2+ by intestinal mucosa.

Adrenal Gland

Two glands in one: Adrenal Cortex and Adrenal Medulla; Secretes corticosteroids, mineralocorticoids (Aldosterone), glucocorticoids (Cortisol), and gonadocorticoids.

Mineralocorticoids

Regulates electrolyte concentrations (primarily Na+ and K+) in extracellular fluid.

Aldosterone

Most potent mineralocorticoid; Stimulates Na+ reabsorption by kidneys; stimulates K+ elimination by kidneys; ADH converse H2O, water follows the solutes, so it’s also reabsorbed.

Glucocorticoids

Influence metabolism of most cells and help us resist stressors; keeps blood glucose levels relatively constant; maintains blood pressure by increasing action of vasoconstrictors.

Cortisol

Only glucocorticoid in significant amounts in humans; prime metabolic effect is gluconeogenesis, formation of glucose from fats and proteins (Making new glucose); regulated hormonally (ACTH).

Gonadocorticoids

Adrenal sex hormones produced by Zona Reticularis.

Androgens

Weak, male sex hormones converted to testosterone in tissue cells, some to estrogens; may contribute to onset of puberty an appearance of secondary sex characteristics, sex drive in women, and source of estrogens in postmenopausal women; regulated hormonally (ACTH).

Adrenal Medulla

Medullary chromaffin cells synthesize catecholamines epinephrine (80%) and norepinephrine (20%) (fight or flight response); effects include vasoconstriction, increased heart rate, increased blood glucose levels, blood diverted to brain, heart, and skeletal muscle; regulated neurally.

Pineal Gland

Secretes melatonin, derived from serotonin.

Melatonin

May affect timing of sexual maturation and puberty, day/night cycles, physiological processes that show rhythmic variations (body temp., sleep, appetite), production of antioxidant and detoxification molecules in cells.

Pancreas

Secretes glucagon and insulin; has both endocrine and exocrine cells; acinar cells produce enzyme-rich juice for digestion; pancreatic islets contain endocrine cells.

Glucagon

Triggered by decreased blood glucose levels, risking amino acid levels, or sympathetic nervous system; raises blood glucose levels by targeting liver to break down glycogen into glucose, synthesize glucose from lactic acid and other noncarbohydrates, and release glucose into blood.

Insulin

Secreted when blood glucose levels increase; lowers blood glucose levels by enhancing membrane transport of glucose into fat and muscle cells, inhibits breakdown of glycogen to glucose, and inhibits conversion of amino acids or fats to glucose.

Gonads

Ovaries produce estrogens and progesterone; estrogen is the maturation of reproductive organs, appearance of secondary sexual characteristics, and causes breast development and cyclic changes in uterine mucosa; testes produce testosterone which initiates maturation of male reproductive organs, causes appearance of male secondary sexual characteristics and sex drive, necessary for sperm production, and maintains reproductive organs in functional state.

Thymus Gland

Secretes thymosins, which seem to be essential for the normal production and programming of T-cells (which are a type of white blood cell involved in immunity).