Anatomy Chapter 17

Gap Junctions

openings between adjacent cells that allow direct passage from one cytoplasm to another- eg cardiomyocyte

Neurotransmitters

communicate at the synapse, eg neuromuscular junction

paracrines

chemicals that diffuse from one cell to affect nearby cells of the same tissue- eg histamine from a basophil

hormones

chemicals secreted by cells into the blood stream that affect cells far away in different tissues and organs - eg testosterone causing facial beard growth

Glands, tissues, cells (which synthesize and secrete the hormones)

The endocrine system is composed of

exocrine glands

glands that have ducts that secrete chemicals onto an epithelial surface, have extracellular effects

endocrine glands

do not have ducts, secrete chemicals (hormones) into the bloodstream. these chemicals have intracellular effects

fenestrated

have large pores, as in the endocrine glands are served by capillaries that have large pores in their walls to allow easy circulatory hormone uptake

target tissue

hormone only effects this because it has the appropriate receptor for it

hypothalamus

critical center for endocrine control, located underneath the 3rd ventricle of the brain and is composed of bervous tissue. part of the central nervous system

The Pituitary Gland

Hangs off the bottom of the hypothalamus and sits in the bony sella turcica (“Turk’s saddle”) of the skull, just posterior to the optic chasm.

infundibulum

pituitary gland is connected to the hypothalamus by this, has separate anterior and posterior components, dervived from different embryological tissues

Anterior Pituitary Gland

accounts for 3/4ths of the gland, not directly connected to hypothalamus but there is an extensive vascular connection between the two called the “portal” system. veins leaving the hypothalamus carry blood to the antieror pituitary. produces and secretes hormones under the direct control of the hypothalamus

Posterior Pituitary

¼ of the gland, direct downward extension of the hypothalamus and is composed of nervous tissue. hromones released by the posterior pituitary are made in hypothalamus and carried down to the posterior pituitary by hypothalamic axons

neuroendocrine cells

specialized neurons that release hormones into the bloodstream instead of neurotransmitters into a synapse.

Thyrotropin-releasing hormone (TRH)

hypothalamic, causes release of thyroid-stimulating hormone (TSH) by the anterior pituitary

Corticotropin-releasing hormone (CRH)

hypothalamic, causes release of adrenocorticotropic hormone (ACTH) by the anterior pituitary

Gonadotropin-releasing hormone (GnRH)

hypothalamic, causes release of follicle-stimulating hormone (FSH) and (LH) by the anterior pituitary gland

Growth hormone-releasing hormone (GHRH)

hypothalamic, causes release of growth hormone by the anterior pituitary

prolactin-inhibiting hormone (PIH)

hypothalamic, suppresses prolaction release from the antieror pituiatr

somatostatin

hypothalamic, suppresses secretinon of growth hromone from the anterior pituitary

Follicle-stimulating hormone (FSH)

anterior pituitary, Causes the ovary to produce sex hormones (estrogen and progesterone) and the testicle to produce sperm

Luteinizing hormone (LH)

anterior pituitary, stimulates ovulation (egg release) mid cycle and causes the testicle to produce testosterone

Thyroid-stimulating hormone (TSH)

anterior pituitary, stimulates the thyroid gland

Adrenocorticotropic hormone (ACTH)

anterior pituitary, stimulates the adrenal cortex to release cortisol

prolactin

anterior pituitary, stimulates milk synthesis after birth

Growth Hormone (GH)

anterior pituitary, promotes tissue growth

Antidiuretic hormone (ADH)

is released in response to dehydration and causes the kidneys to retain water (to not" “diverse”)

Oxytocin

posterior pituiatry, stimulates the “letting down” of milk during nursing and stimulates the uterus during labor

Cortisol is released at __ and slows down at __

4pm, 4am

target organ feedback

the process where hormones released by a target gland regulate and inhibit the secretion of upstream hormones from the hypothalamus and pituitary to maintain balance.

posterior pituitary neuroendocrine reflex

a feedback mechanism where rising blood osmolarity triggers ADH release to conserve water, and secretion stops once osmolarity returns to normal.

Growth hormone

promotes bone and muscle growth and so has its main effects prior to adulthood and is epecially active during the adolescent growth spurt. Has short half life but does cause the liver to secrete growth factors which have similar effects but much longer half lives. These levels rise when we are asleep, GH levels fall as we age.

The Pineal Gland

located in the brian just below the posterior corpus callosum, activity peaks between ages 1-5, closely connected to visual input, some neuronal input runs directly from the retina to this gland. likely plays an important role in establishing the circadian rhythm. Produces melatonin at night which supports sleep.

Thymus Gland

Located just behind the upper sternum, activity peaks about age 6, This is where a particular type of white blood cell called a T-lymphoctye (or just T-cell) matures. These cells direct the entire immune system. In adults, the gland usually nearly fully involutes or disappears

The Parathyroid Glands

usually 4 of these glands- tiny glands located one each at each corner of the posterior thyroid gland. These secrete paraythroid hormone, helps support adequate calcium levels by promoting bone resorption by osteoclasts

The thyroid Gland

located in the anterior neck just below the larynx, composed of two lobes- one either side

isthmus

connects the two lobes of the thyroid gland

thryoid follicles

microscopic pools of liquid thyroid hormone surrounded by follicular cells which make and secrete thyroid hormone for storage in the follicles. follicular cells surround these follicles and are stimulated by thyroid stimulating hormone from the anterior pituiatry

Thyroid hormone

he thyroid gland is the only organ that uses iodine to produce the hormones T3 and T4, which are released in response to TSH and act mainly to increase metabolic rate.

Calcitonin

A clear cell randomly scattered in the thryoid gland, causs blood calcium to fall in resposne to elevated blood calcium levels

Adrenal Glands

triangular shaped glands that sit on top of the kidneys, each gland consists of two layers: the outer cortex and the inner medula

adrenal medullary cells are

post-ganglionic sympathetic neurons, an ecample of neuroendocrine cells because they are neurons that release chemicals into the bloodstream and not the synaptic cleft

primary hormone released by the adrenal medulla

epinephrine

corticosteroids

the adrenal cortex synthesizes and releases

3 glomerulosa, fasciculata, reticularis

three layers of the adrenal cortex

aldosterone

cortical steroid that causes sodium retention, which holds water by osmosis

cortisol

adrenal cortical steroid, our body’s natural form of cortisone, this is the hormone that helps us deal with stress- it is released in response to ACTH- release occurs daily about 4am and wanes throughout the day- it is also released in response to any stress at any time

androgens

these are masculinizing hormones and adrenal androgens are much more important for women (very little effect in amels as the testes release much higher amounts) important for libido in women

estradiol

a form of the feminizing hormone estrogen- this is the primary source for this hormone after menopause in women when the ovaries shut down

Pancreatic Islets

these are 1-2mm collections of endocrine cells scattered throughout the pancreas, 2 major types of islet cells

alpha

secrete glucagon which raises blood sugar via glycogenolysis (breakdwon of gylycogen stored in the liver) and gluconeogenesis (the creatino of glucose from fats or protein)

beta

secrete insulin in response to elevated blood sugar- and insulin stimulates the absorption of glucose by liver cells (for storage as glycogen) and muscle cells (for energy) the lack of an insulin effect is the cause of diabetes mellitus

Gonads

glands that produce hormoneshave exocrine functions, release of eggs by the ovary, release of sperm by the testivle, they become active at puberty in response to increased FSH and LH levels

follicles

a small sac-like structure in the ovary that contains an immature egg (oocyte). As the egg matures, the follicle grows larger and its surrounding cells produce hormones.

estrogen

secreted by the peripherry cells in the follicle, primarily in the form of estradiol, which is the main feminizing hormone

ovulation

the release of a mature egg from the ovary, usually in the middle of the menstrual cycle.

Testicles

have microscopic tubules (seminiferous tubules) which produce sperm

seminiferous tubules

microscopic tubules which produces sperm

interstitial cells

cells located between the tubules produce testosterone

testosterone

the main source of libido in both sexes, causes male secondary sex characterstics to develop

Steroid Hormones

all made from cholesterol and include estrogen, progesterone, testosterone, cortisol and aldosterone. high in fat and hydrophobic, insoluable in water but easily dissolved in fat . only come from the adrenal cortex or gonads

Peptide Hormones

class of hormones that are composed of short chains of amino acids, may be up to 200 amino acids

thyroglobin

thyroid hormone begins as a percursor called ___

Iodine

What is added to thyroglobulin

Circadian rythm

he natural, internal biological cycle that repeats about every 24 hours, regulating processes like the sleep–wake cycle, hormone release, body temperature, and metabolism, in response to light and dark in the environment.

signal amplification

the process by which a single hormone–receptor interaction triggers a cascade of events inside the cell, producing thousands of second messengers and activating many enzymes, so that one hormone molecule causes a very large cellular response.

Target sensitivity modulation

the ability of a target cell to adjust how strongly it responds to a hormone by changing the number of receptors on its surface.

up-regulation

occurs when a target cell increases the number of membrane receptors to increase sensitivity

down-regulation

occurs when the target cell instead reduces the number of membrane receptors so that it becomes less sensitive

synergistic

if the