Ch 18 endocrine system Flashcards
Explain importance of intercellular communication
Maintains homeostasis, provides communication within the body by coordinating chemical messages.
Describe mechanism involved and compare the modes of intercellular communication that occur in the Endocrine/Nervous system
Direct communication: occur between two cells of the same type and must be in extensive physical contact. (ei. gap junctions: coordinate ciliary movement among epithelial cells, coordinate contractions of cardiac muscles cells, facilitate propagation of action potentials from one neuron to the next electrical synapses.)
Paracrine Communication: when messages occur between cells within a single tissue, communicate by releasing chemicals into the extracellular fluid to tell cells around it what’s going on. (ei. somatostatin/Growth hormone-inhibiting hormone (GHIH) released by some pancreatic cells to inhibit release of insulin by other pancreatic cells.)
Autocrine communication/ Neuronal are specialized paracrine communicates but autocrine occurs when the chemical message affects the same cells that secrete them (ei. prostaglandins are secreted by smooth muscle cells but also cause contractions of those very own cells)
Endocrine communication: when endocrine system uses chemical messengers called hormones to relay info and instructions between cells in body. Travel through blood stream. each hormone has target cells with receptors to determine if that the right hormone for the job. Hormones can modify structure, type, and activity of enzymes/structural proteins and target cells. Can affect multiple tissues and organs at the same time.
Synaptic communication: neurons release neurotransmitters at a synapse close to target cells with right receptors. The signal travels from one location to the other in the form of action potentials propagated along axons. Fast messaging thus best for crisis management.
Compare cellular components of endocrine system with other systems
Contrast major structural classes of hormones
What major processes are affected by hormone actions
- Growth and development
- reproduction
- Regulation of metabolism and energy
- Regulation of water content, electrolytes, and nutrients
- Mobilization of body defense
Define endocrine cells
glandular secretory cells that release secretions into extracellular fluid (internal)
Define exocrine cells
secrete onto epithelial surfaces generally though ducts (external)
organs of the endocrine system:
hypothalamus, pituitary gland (anterior and posterior lobe), pineal gland, Thyroid gland, Parathyroid gland (posterior surface of thyroid gland small dimples), Adrenal gland (medulla and cortex), pancreas and gonads
define Hypothalamus and explain three mechanisms of hypthalmic control over endocrine function
connected to pituitary gland by
infundibulum and secretes regulatory hormones and ADH. hypothalamic neurons synthesize hormones and transport them along axons to posterior lobe in pituitary.(drawing in class) Releasing or storing antidiuretic hormone (ADH), oxytocin (OXT) which can then go to target organs.
Hypothalamus also release regulator hormones that control secretion of endocrine cells in anterior lobe of pituitary which then can go to target organs.
uses (ANS) autonomic nervous system (involuntary) control over endocrine cells in adrenal medulla. when sympathetic division is activated sends output through preganglionic motor fibers medulla releases epinephrine (E) and norepinephrine (NE) into blood. (part of stress response)
Pituitary gland
Anterior lobe or adrenohypophysis: has 3 regions pars distalis (secretes ACTH, TSH, GH, PRL, FSH,LH) , pars tuberalis, and pars intermedia (secretes MSH). Adrenocorticotropic (ACTH), thyroid-stimulating hormone (TSH), Growth hormone (GH), Prolactin (PRL), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), Melanocyte-stimulating hormone (MSH). All seven hormones bind to extracellular receptors and use cAMP as a second messenger
Posterior lobe: Doesn’t make just stores oxytocin (OXT), and antidiuretic (ADH)
Pineal Gland
Melatonin
Thyroid gland
Thyroxine (T4), Triiodothyronine (T3), Calcitonin (CT)
Adrenal Gland
Medulla: Epinephrine (E), Norepinephrine (NE)
Cortex: Cortisol, corticosterone, cortisone, aldosterone, androgens.
Pancreas
Insulin and glucagon
Parathyroid glands
Parathyroid Hormone (PTH)
Testes
Testosterone, Inhibin
Ovaries
Estrogen, Progesterone, inhibin
What are the hormone classes
Amino acid derivatives: relatively small, synthesized by amino acids tyrosine (thyroid hormone, epinephrine, norepinephrine, and dopamine) and tryptophan (melatonin).
Pepetide hormones: Divided into two groups glycoproteins and short peptides/small proteins.
lipid derivatives: Divided into two groups eicosanoid and steroid hormones.
Hormone Travel
typically release where capillaries are abundant, can circulate freely or attached to special carrier proteins. If freely circulating can remain functional for less than an hour and sometimes as little as two minutes. Its inactive when it diffuses out the blood to bind to receptors on target cells, its broken down by liver or kidney cells, or broken down by enzymes in blood/interstitial fluid.
How do thyroid and steroid hormones differ from other hormones?
remain function much longer due to 99% of them attaching to special transport proteins because they are hydrophobic and cannot dissolve thus can’t travel in the blood by themselves. Also attaching increases their half-life thus stays active in body longer.
Down-regulation
hormone triggers a decrease in number of hormone receptors, so cell becomes less sensitive to high levels of a particular hormone.
Up-regulation
absence of a hormone triggers an increase in number of hormones receptors, so cell becomes more sensitive to low levels of a particular hormone.
Where are hormone receptors located?
Either in the plasma membrane (extracellular receptors: receive info from outside of cell) or target cells (intracellular receptors: receive info from things entering the cell)
How do plasma membranes affect hormones communication?
Catecholamines (E, NE, dopamine) and peptide hormones are extracellular receptors as they aren’t lipid soluble and cant enter plasma membrane thus bind to outer surface.
Define a first and second messenger
First messenger: hormone that binds to extracellular receptors
Second messenger: appears due to hormone receptor interactions. important second messengers are cyclic AMP (cAMP), cyclic GMP (cGMP) and calcium ions.
Define amplification
when a small number of hormone molecules bind to extracellular receptors thousands of second messengers may appear in cell magnifying hormone effect on target cell.
Define receptor cascade
production of linked sequences of enzymic reactions
whats a G protein
is an enzyme complex thats couples to a membrane receptor, links first and second messengers, most prescription drugs target this protein. to exert affects G protein typically change concentration of cAMP or calcium ions (typically acts as second messengers).
How does intracellular receptors affect communication?
typically affect steroid or thyroid hormones as they can diffuse through lipid part of plasma membrane and bind to receptors in cytoplasm or nucleus. Then hormone receptors can turn on or off for specific genes this can alter DNA transcriptions and change protein synthesis patterns. (ei. testosterone stimulates production of enzymes and structural proteins in skeletal muscle fibers, causing increased muscle size and strength)
Explain the process of thyroid hormones in hormone binding. (Intracellular receptors)
1) cross plasma membrane by transport mechanism
2) In cytoplasm they bind to receptors in nucleus/mitochondria
3) hormone receptors in nucleus activate specific genes/ change transcription rate.
4) this rate change affects metabolism in cell due to the concentrations increasing or decreasing.
5) thus, thyroid hormones bound to mitochondria increase mitochondrial rates of ATP production.
define neuroendocrine response
pathways where both neural and endocrine components are activated (ei. adrenal medulla secreting E and NE in response to aciton potentials rather than hormones.
Hypophyseal portal system
ensures all hypothalmis hormones entering portal blood vessels reach target cells in anterior lobe before bieng diluted though mixing with circulation; stricly moves one way
what are the classes of hypothalmic regulatory hormones
releasing hormones (RH): stimulate synthesis/secretion of one or more hormones
inhibiting hormones (IH): prevents synthesis/secretion of hormones
TSH
draw out chart for this
thyroid stimulating hormone; targets thyroid gland ans triggers release of thyroid hormone. Thyrotropin-releasing hormone (TRH) is released from hypothalmus and causes TSH to release in response. varying concentrations called T3 or T4 circulate and if they rise rates of TRH and TSH decline.
ACTH
draw out chart for this
Adrenocorticotropic hormone; stimulates release of steroid hormones in adrenal cortex (outer portion of adrenal gland).
Target glucocorticoids (affect glucose metabolism like cortisol).
Stimulated by corticotropic-releasing hormone (CRH) from hypothalmus. As glucocorticoid levels increase CRH and ACTh rates decline
