AP chap 18 Endocrine system

cellular communication

-direct communication
-paracrine communction
-hotmones

direct communication

occurs between two cells of the same type; exchange of ions and molecules between gap junction; must be in contact with each other *
ex; heart muscle, cillia
*

paracrine communication

use of chemical messangers to transfer informationf rom cell to cell within a single tissue ; chemicals are called paracrine factor or local hormoes;primary effects occur within tissue of origin; when paracrine factors have a secondary effect in other tis

hormones

chemical messengers that are released in one tissue and transported in the bloodstream to alter activities of cells in another tissue; a substance with effects outside its tissue of origin

target cells

specific cells that can read the message of a hormone and alter its activity accordingly; need specialized receptors for that hormone message

function of a hormone

-stimulate enzyme or protein synthesis
-alter transcription or translation to increase or decrease rate of protein and enzyme synthesis
-altering channel or membrane enzyme shapes thereby turning it on or off
-alter cellular activities of several tissues

synaptic communication

-chemical communication using neurotransmitters across synaptic clefts (not in bloodstream)
-target cells are close to the synapse and have specific receptors
-carries high speed messages which are quick but short-lived
-crisis management (fight or flight

classes of hormones

-amino acid derivative
-peptide hormones
-lipid derivatives

amino acid derivatives

-small structures related to amino acids
-thyroid hormone, and catecholamines (E, NE and dopamine) are derived from the amino acide, tyrosin
-melatonin derived from the amino acid, tryptophan

peptide hormones

-thyroid stimulating hormone, LH and FSH are glycoproteins that consist of long chains of amino acids
-all hormones from the hypothalamus, heart, digestive tract, thymus, pancreas and posterior pituitary gland are short polypeptides

lipid derivatives

-eicosanoids commonly have paracrine effects; prostaglandins, leukotrines, thromboxanes and prostacyclins
-steroid hormones resemble cholesteral; secreated by reproductive glands (androgens, estrogens and progestins), by the adrenal glands (corticosteroid

distribution of hormones

-hormones can circulate freely or bind to transport proteins
-freely circulating hormones are active from only a few minutes up to an hour
-freely circulating hormones are inactivated when; they diffuse out of the blood stream and bind to the target cell

thyroid and steroid homrones

lst in the blood longer because they attach to a transport protein this is how hormones maintain equilibrium in the blood stream, free circulating hormones being replaced by bound hormones to a reserve of several weeks supply.

hormone receptor

-is a protein molecule to which a particular molecule binds strongly
-can respond to several different hormones
-different tissues have different combination of receptors
-presence or absence of specific receptor determines hormonal sensitivity

catecholamines and peptide hormones

not lipid soluable and cannot penetrate the plasmamembrane; bind to receptor on outersurface of plasma membrane called extracellular receptors

eicosanoids

are lipid soluable so they can diffuse across plasma membrane to reach receptor proteins ont he inner surface of the plasma membrane called intracellular receptors

first and second messengers

hormones that vbind to receptors in the plasma membrane cannot have direct effect on activities inside target cell; they have to use intracellular intermediary to exert effects

first messenger

the hormone that binds to the plasma membrane; leads to a second messenger

second messengers

act as enzyme activators, inhibitors, or cofactors resulting in change in rates of metabolic reactions; important second messengers; cyclic AMP cAMP derivative of atp
cyclic GMP cGMP derivative of gtp

The process of amplification

the binding of a small number of hormone molecules to membrane receptors which leads to thousands of second messangers in cell; magnifies effect of hormone on target cell

down-regulation

the presence of a hormone triggers a decrease in number of hormone receptors; when levels of particular hormone are high, cells become less sensitive to it

up-regulation

the absence of a hormone triggers an increase in the number of hormone receptors; when levels of particular hormone are low, cells become more sensitive to it

g protein

middle man between 1st and 2nd messenger. these proteins bind to GTP and are activated when a hormone binds to its receptro at the membrane surface

g proteins and camp

g proteins increase or decrease camp (second messenger) levels in response to peptide hormones, catecholamines, and eicosanoids

increasing cAMP

1-activated g protein activates the enzyme adenylate cyclase
2. adenylate cyclase converts ATP to cAMP
3.cAMP is no a 2nd messenger and activates kinase causing phosphorylation (attaching of a high energy phosphate group to another molecule)
4.phosphodies

decreasing cAMP

1. activated g protein stimulates phosphodiesterase activity
2. adenylate cyclase activity is inhibited
3.cAMP levels decline
4. witout phosphorylation, key enzymes remain inactive

g proteins and calcium ions

activated g proteins trigger the opening of calcium ion channels in the membrane or the release of calcium ions from intracellular strone
1. g protein activates the enzyme phospholipase
2. triggers a receptor cascade allowing calcium release from intracel

hormones and intracellular receptors

-alter rate of DNA transcription in cucleus
-change patterns of protein synthesis
-directly affect metabolic activity and structure of target cell
-include steroids and thyroid hormones

steroid hormones

diffuse through the plasma membrane and bind to receptors in the cytoplasm or nucleus; the hormone then binds to DNA in the nucleus to activate certain genes

thyroid hormones

enter the cytoplasm and bind to receptors on the mitochondria or in the mucleus; activates genes or accelerates ATP production

the pituitary gland

also called the hypophysis; lies within sella turcica isolated from cranial cavity; hangs inferior to the hypothalmus and is connected by the infundibulum
*
facts to know, releases 9 important peptide hormones, hormones bind to membrane receptors, use cam

Anterior lobe of the pituitary gland

also called adenoypophysis; hormones turn on endocrine glands or support other organs

hypothalamic control of the anterior lobe

two classes of hypothalamic regulatory hormones; rate of secreation is controlled by negative feedback

releasing hormones (RH)

stimulate synthesis and secretion of one or more hormones at anterior lobe

inhibiting hormones (IH)

prevent synthesis and secretion of hormones from the anterior lobe

the thyroid gland

lies anterior to thyroid cartilage of larynx; consists of two lobes connected by narrow isthmus

thyroid follicles

hollow spheres linned by cuboidal epithelium

thyroxine t4

also called teraiodothyronine contains 4 iodide ions

triiodothyronine t3

contains 3 iodide ions

absence of thyroid stimulating hormone tsh

causes thyroid follicles to become inactive

points to note thyroid gland

bind to receptors in cytoplasm (for storage) surfaces of mitochondria (atp production), and the nucleus (gene activation)
-t4 can be converted to t3 in the liver when needed
-thyroid gland contains most of the iodide reserves in the body; needed to synthe

function of thyroid hormones t3 and t4

thyroid hormones enter target cells by transport system and affect most cells in body not lipid soluable
-in children they are essential to normal development of skeletal, muscular and nervous systems
-responsible for calorigenic where the cell consumes m

the c cells fo the thyroid gland and calcitonin

-c(clear)cells also called parafollicular cells
-produce calcitonin (ct)
-helps regulate concentration of calcium in body fluids
-inhibits osteoblast which slows the rate of calcium release form bone
-stimulates calcium excretion by the kidney
-most impor

parathyroid glands

four parathyroid glands embeddd in the posterior surface of the thyroid gland