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direct communication

two cells of the same type, in contact with each other, exchange ions and molecules between gap junction


Examples of direct communication

cilliary movement, contraction of cardiac muscles, propagation of action potential


Paracrine communication

"local", chemical messengers transfer info from cell to cell within a single tissue. Primary effects occur within the tissue of origin. It is acting as a HORMONE when it has a secondary effect in other tissues beside the original


Example of Paracrine communication

prostaglandis, various growth factors



chemical messengers transported in the blood stream to alter activities in cells in another tissue; effects substance outside its tissue of origin


Target cells

cells with specialized receptors for specific hormones that reads it message and alters its activity accordingly


5 Functions of a hormone

1. stimulate enzyme or protein synthesis
2. alter transcription or translation to increase or decrease rate of protein & enzyme synthesis
3. turn on or off channel or membrane enzyme by altering shape
4. alter cellular activities of several tissues at the same time
5. coordinate cell, tissue & organ activities on a long term basis


Synaptic Communication
4 facts

1. chemical communication using neurotransmitters across synaptic clefts (not in blood stream)
2. target cells are close to the synapse and have specific receptors
3. carries high speed messages which are quick/short lived (adrenaline)
4. crisis management (fight or flight)


3 Classes of Hormones

Amino Acid Derivatives
lipid derivatives


amino acid derivatives

*small, related to amino acids
*thyroid hormone and CATECHOLAMINES (E, NE & DOPAMINE) are derived from the amino acid tyrosine
*melatonin derived from the amino acid tryptophan



*THYROID stimulating hormone, LH and FSH are glycol proteins 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 have paracrine effects, prostaglandins, leukotrines, thomboxanes and prostacyclins
*steroid hormones resemble cholesterol; secreted by repo glands, adrenal glands and the kidneys


Distribution of hormones

pass through bloodstream
circulate freely or bound to transport proteins


Freely circulating hormones

*short lived (few minutes - 1 hr)


Freely circulating hormones are inactive when (3)

1. diffuse out of blood stream and bind to target cell receptor
2. absorbed and broken down by liver or kidneys
3. enzymes in the cell plasma break it down


Why do thyroid and steroid hormones circulate/last longer?

they attach to a transport protein, the blood stream can have a 2 wk supply at any given time, maintaining equilibrium in the blood stream


Hormone receptor
4 facts

1. Is a protein molecule to which particular molecules bind strongly
2. can respond to several different hormones
3. different tissues have different combos of receptors
4. presence or absence of specific receptor determines hormonal sensitivity


Hormones do not affect all tissues with their receptors the same

cells have dif. combos. of receptors so hormones can have dif. effects on dif. target organs


Catecholamines and peptide hormones

NOT lipid soluble and cannot penetrate the plasma membrane, it has to bind to an extracellular receptor to get in



ARE lipid soluble, they diffuse through membrane to reach receptor proteins on the INNER surface called the INTRAcellular receptor


1st and 2ed messengers

hormones that bind to receptors in the plasma membrane cannot have direct effect on activities inside taget cell; they have to cue intracellular intermediary to exert effects


First messenger

the hormone that binds to the plasma membrane; leads to second messanger


Second messenger

act as enzyme activator, inhibitor or cofactor resulting in change in rates of metabolic reactions


Important second messengers:

Cyclic-AMP (cAMP) - derivative of ATP
Cyclic-GMP (cGMP) - derivative of GTP
Calcium ions


The process of amplification

binding of a smaller number of hormone molecules to membrane receptors which leads to thousands of 2ed messengers in cell; magnifies effect of hormone on target cell


down regulation

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


Up regulation

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


G protein

middle man between 1st and 2ed messenger, they bind to GTP and are activated when a hormone binds to its receptor at the membrane surface


G Proteins and cAMP (fig 18-3)

G proteins increase or decrease the 2ed messenger cAMP levels in response to peptides, catecholamines and eicosanoids


Increasing cAMP
4 steps

1. activated G protein activates adenylate cyclase
2.adenylate cyclase converts ATP to cAMP
3. cAMP is now a 2ed messenger and activates kinase causing phosphorylation
4. phosphodiesterase inactivates cAMP to AMP making increased levels of cAMP short lived


Decreasing cAMP
4 steps

1. G protein activates phospholipase C (PLC)
2. triggers a receptor cascade allowing ca2+ release from intracellular reserve (SER)
3. phosphorylation of calcium channel proteins opens the channel and permits extracellular calcium to center the cell
4. calcium, acting as 2ed messenger, can bind to calmodulin which ativates other enzymes


Hormones and intracellular receptors
(fig. 18-4)
4 facts

1. alter rate of DNA transcription in nucleus
2. change patterns of protein synthesis
3. directly affect metabolic activity and structure of target cell
4. include steroid and thyroid hormones


steroid hormones

diffuse through the plasma membrane and bind to receptor 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 of the mitochondria or in the nucleus; activates genes or accelerates ATP production


The pituitary gland (fig 18-6)

also called the hypophysis; lies within cella tucica isolated from cranial cavity; hangs inferior to hypothalamus and is connected by the infundibulum


Pituitary gland
3 facts

1. releases 9 important peptide hormones
2. hormones bind to receptors
3. use cAMP as 2ed messenger


Anterior lobe of pituitary gland

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


hypothalamic control of the anterior lobe

two classes of hypothalamic regulatory hormones; rate of secretion is controlled by negative feedback
1. releasing hormones (RH)- stimulate synthesis and secretion of one or more hormones at anterior lobe
2. inhibiting hormones (IH)- prevent synthesis and secretion of hormones from the anterior lobe


7 hormones of the anterior lobe

thyroid stimulating
follicle stimulating
growth hormone


ACTH targets

glucocorticoids (effect glucose metabolism)


Low levels of gonadotropins causes

hpogonadism; children can't mature sexually, adults sterile


Luteinizing prepares the body for

pregnancy, stimulates testosterone in males


prolactin is found in males and might help regulate ______ production?



Growth hormone stimulates growth indirectly

liver cells respond to GH by producing compounds that stimulate growth tissue; these peptides bind to receptors on membrane to increase uptake of amino acids for new protein synthesis


Growth hormones stimulate growth directly

stem cell division and differentiation of epithelial and connective tissues, in adipose tissue; glucose-sparing effect where fatty acids are released from adipose tissue for energy, and in the liver; stimulates the break down of glycogen into glucose from the liver increasing blood glucose levels


Posterior lobe of pituitary

contains unmyelinated axons of hypothaamic neurons; secretes antidiuretic hormone and oxytocin


antidiuretic hormone also referred to as



Thyroid gland

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


thyroid follicles

hollow spheres lined by cuboidal epithelium


Thyroxine (t4)

contains 4 iodide ions
T4 can be converted to T3 in the liver when needs


Triiodonthyronine (t3)

contains 3 iodide ions


Causes thyroid follicles to become inactive?

the absence of thyroid stimulating hormone


Functions of thyroid hormone

*essential to development of skeletal, muscular and nervous system in children
*responsible for calorigenic effect where the cell consumes more energy resulting in increased heat generation and


The C cells of the thyroid gland and calcitonin

*c (clear) cells also called parafollicular cells
*produce calcitonin (ct)