Chapter 18 Flashcards
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
Hormones
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
- stimulate enzyme or protein synthesis
- alter transcription or translation to increase or decrease rate of protein & enzyme synthesis
- turn on or off channel or membrane enzyme by altering shape
- alter cellular activities of several tissues at the same time
- coordinate cell, tissue & organ activities on a long term basis
Synaptic Communication
4 facts
- chemical communication using neurotransmitters across synaptic clefts (not in blood stream)
- target cells are close to the synapse and have specific receptors
- carries high speed messages which are quick/short lived (adrenaline)
- crisis management (fight or flight)
3 Classes of Hormones
Amino Acid Derivatives
Peptide
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
peptides
- 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)
- diffuse out of blood stream and bind to target cell receptor
- absorbed and broken down by liver or kidneys
- 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
- Is a protein molecule to which particular molecules bind strongly
- can respond to several different hormones
- different tissues have different combos of receptors
- 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
Eicosanoids
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
- activated G protein activates adenylate cyclase
- adenylate cyclase converts ATP to cAMP
- cAMP is now a 2ed messenger and activates kinase causing phosphorylation
- phosphodiesterase inactivates cAMP to AMP making increased levels of cAMP short lived
Decreasing cAMP
4 steps
- G protein activates phospholipase C (PLC)
- triggers a receptor cascade allowing ca2+ release from intracellular reserve (SER)
- phosphorylation of calcium channel proteins opens the channel and permits extracellular calcium to center the cell
- calcium, acting as 2ed messenger, can bind to calmodulin which ativates other enzymes
Hormones and intracellular receptors
(fig. 18-4)
4 facts
- alter rate of DNA transcription in nucleus
- change patterns of protein synthesis
- directly affect metabolic activity and structure of target cell
- 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
- releases 9 important peptide hormones
- hormones bind to receptors
- 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
- 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
7 hormones of the anterior lobe
thyroid stimulating adrenocorticotropic gonadotropins follicle stimulating luteinizing prolactin 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?
testosterone
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
vasopressin
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)
