BM3 - Intro to hormones

rate of metabolic inactivation:

all hormones are eventually inactivated by enzymes in the liver, kidneys, blood or target cells.

example of diurnal rhythm mechanism:

cortisol secretion rises during the night, reaching its peak in the morning, then falls throughout the day

t/f: a single endocrine gland may not produce multiple hormones

false, anterior pituitary gland secretes six different hormones

t/f: endocrine glands secrete their hormones at a constant rate

false, secretion rate of all hormones vary and each rate is highly regulated in order to keep the hormone concentration at a desired set point that will allow our system to maintain its homeostasis

lipophilic hormones

-steroid hormones -thyroid hormone

non-tropic hormone secreted by anterior pituitary

prolactin (PRL)

primary hyposecretion:

too little hormone secreted due to abnormality within the gland

hormones that regulate the production and secretion of another endocrine gland and also maintain the structure of their target endocrine tissue:

tropic hormone

t/f: responsiveness of a target cell to a specific hormone can be adjusted by regulating the number of target-cell receptors for that particular hormone

true

t/f: a single hormone may have multiple target-cell types which allows coordination of the activities of various tissues toward a common end

true, for example insulin on muscle, liver and fat act in concerto to store nutrients after absorption of a meal

t/f: a single target cell may be influenced by more than one hormone

true, insulin and glucagon both stimulate liver enzymes for different functions

rate of metabolic activation (peripheral conversion):

when hormones are modified in other peripheral organs resulting in a more active form after being secreted into the blood by the endocrine gland

example of hormone synergism

-FSH and testosterone, both needed to maintain the normal rate of sperm production -growth hormone and thyroxine on skeletal growth

lipophylic hormones characteristics

-cannot dissolve in plasma -> circulate in blood by specific binding to plasma proteins - cross PM and bind to intracellular receptors -> activation of specific genes expression -> synthesis of new proteins inside target cell that carry out the desired physiological response

hormone categories based on solubility

-hydrophilic -lipophilic

explain neuroendocrine reflexes mechanism:

-it includes neural and hormonal components - purpose is to increase hormone secretion after exposure to a specific stimulus, usually a stimulus external to the body

growth hormone excess

-most often caused by tumor of GH-producing cells of AP -symptoms depend on age of individual when abnormal secretion begins (gigantism - caused by overproduction in childhood before epiphyseal plates close// acromegaly - when GH hypersecretion occurs after adolescence)

hydrophilic hormones

-peptide hormones -catecholamines

in what ways can a hormone influence the activity of another hormone at a given target cell?

-permissiveness -synergism -antagonism

fetal growth

-promoted by hormones from placenta -no role of GH -after birth GH and other non-placental hormones begin to play an important tole in regulating growth

effective plasma concentration of a hormone can also be influenced by:

-rate of metabolic activation (peripheral conversion) -rate of metabolic inactivation

endocrine system functions:

-regulate organic metabolism, H2O, and electrolyte balance -induce adaptive changes to help body cope w.stressful situations -promote smooth, sequential growth and development - control reproduction -regulate red blood cell production -w/ANS control and integrate both circulation, digestion, and absorption of food

tropic hormones secreted by anterior pituitary

-thyroid stimulating hormone (TSH) -adrenocorticotropic hormone (ACTH) -follicle stimulating hormone (FSH) -luteinizing hormone (LH) -growth hormone (GH)

what are the three general mechanisms for controlling hormones secretion?

1- negative feedback control 2- neuroendocrine reflexes 3- diurnal (day-night, circadian) rhythms

vasopressin action:

ADH -conserves water during urine formation and causes arterioles vasoconstriction

GH secretion is regulated by:

GHRH and GHIH

hormones that directly regulate the secretion of growth hormone:

Growth hormone releasing hormone and somatostatin

the hypothalamic-hypophyseal portal system:

It is a vascular system which links the hypothalamus to the anterior lobe of the pituitary

prolactin release is stimulated by:

TRH and PRH

TSH is stimulated by:

TRH and somatostatin

example of tropic hormone:

Thyroid-stimulating hormone (TSH) secreted from A. Pituitary stimulates thyroid hormone secretion by thyroid gland and maintains the structural integrity of thyroid gland

endocrine dysfunction is most commonly caused by:

abnormal plasma concentrations of a hormone, caused by inappropriate rates of secretion

ACTH function:

adrenocorticotropic hormone -stimulates secretion of cortisol by adrenal cortex

what part of pituitary synthesizes and releases hormones?

anterior lobe

the effective plasma concentration of a hormone is mainly regulated by:

appropriate changes in the rate of its secretion

hypothalamic-hypophyseal portal system

capillary-to-capillary connection between anterior pituitary and hypothalamus -all blood supplied to AP must first pass through hypothalamus that way all hypophysiotropic releasing/inhibiting hormones are delivered to AP immediately

hormones derived from AA tyrosine:

catecholamines thyroid hormones

peptide hormones consist of:

chains of AA of varying length

secondary hypersecretion:

excessive stimulation form outside the gland causes oversecretion -example: immunologic factors, such as excessive stimulation of the thyroid gland by an abnormal antibody that mimics the action of TSH

t/f: target cells can respond to all hormones

false, specific target cells respond to each hormone because only target cells have receptors for binding w/that particular hormone

FSH function:

follicle stimulating hormone -in females, stimulates growth and development of ovarian follicles; promotes secretion of estrogen by ovaries -in males required for sperm production

causes of primary hyposecretion:

genetic, dietary, chemical or toxic, immunologic, other diseases such as cancer, iatrogenic, idiopathic

secondary hyposecretion:

gland is normal but too little hormone is secreted due to deficiency of its tropic hormone

GH function:

growth hormone -primary hormone responsible for regulating overall body growth; important in intermediary metabolism

functions of pineal gland:

helps maintain body's circardian rhythms in synchrony with light-dark cycle -promotes sleep -influences onset of puberty -acts as antioxidant to remove free radicals -enhances immunity

explain negative feedback control:

hormone B stimulated by hormone A will inhibit hormone A when levels of B are achieved

act through 2nd msg system to alter the specific activity of preexisting proteins

hydrophilic hormones

difference between hydrophilic and lipophilic hormones regarding metabolic inactivation

hydrophilic hormones remain in the blood briefly since they are easy targets for the inactivation enzymes whereas lipophilic hormones can last longer in the blood because they are less vulnerable to the inactivating enzymes

how does down regulation work?

it is a physiologic protective mechanism that prevents the target cells from overreacting to a prolonged high concentrations of a hormone

how does synergism affect the hormonal interactions at target cells?

it occurs when actions of several hormones are complimentary and their combined effect is greater than the sum of their separate effects

bind to intracellular receptors -> activation of specific genes expression -> synthesis of new proteins inside target cell that carry out the desired physiological response

lipophylic hormones

LH function:

luteinizing hormone -in females: responsible for ovulation and luteinization; regulates ovarian secretion of female sex hormones -in males stimulates testosterone secretion

overall function of endocrine system are directed towards:

maintaining homeostasis

vasopressin and oxytocin are produced by:

neurosecretory neurons in paraventricular and supraoptic nuclei in hypothalamus

how does antagonism affect the hormonal interactions at target cells?

occurs when one hormone causes loss of another hormone's receptors, reducing the effectiveness of second hormone

what is permissiveness?

one hormone must be present in adequate amounts to permit another hormone to exert its full effect

most abundant chemical category of hormones

peptide hormones

periods of rapid growth:

postnatal - during the first two years of lie pubertal - during adolescence

catecholamines produced by: derived by:

produced by adrenal medula derived from: AA tyrosine

steroid hormone, produced by: derived by:

produced by: adrenal CORTEX & reproductive endocrine glands derived from: cholesterol

thyroid hormones produced by: derived by:

produced by: thyroid gland derived from: AA tyrosine

example of hormones antagonism

progesterone (secreted during pregnancy, decreases contractions of uterus) inhibits uterine responsiveness to estrogen (which inc uterine contractions during pregnancy), that way the uterus is kept quiet and noncontracting environment for the development of fetus

PRL function:

prolactin -enhances breast development and milk production in females

explain diurnal rhythm mechanism:

secretion rates of many hormones fluctuates up and down as a function of time

oxytocin action:

stimulates uterine contraction during childbirth and milk ejection during breast-feeding

example of target-cell receptor down regulation

sustained elevation of insuline leads to gradual reduction in the number of target-cell receptors for insulin

difference between the hypothalamic hypophysiotropic hormones and the hypothalamic hormones stored in posterior pituitary:

the hypothalamic hypophysiotropic hormones are released into portal vessels, delivering them to AP. the hypothalamic hormones stored in PP are released into the general circulation

what happens to the thyroid gland in the absence of TSH:

thyroid gland atrophies (shrinks) and produces very low levels of its hormones

example of hormones permissiveness:

thyroid hormone increases number of receptors for epinephrine = increasing effectiveness of epinephrine in the absence of thyroid hormone, epinephrine is only marginally effective

other hormones besides GH are essential for normal growth: ** know

thyroid hormone: growth stunted in hypothyroid children/ hypersecretion doesnt cause excessive growth -insulin: def often blocks growth/hyperinsulinism often spurs excessive growth -androgen: play role in pubertal growth spurt, stimulate protein synthesis in many organs -estrogens: effects of estrogen on growth prior to bone maturation are not well understood

TSH function:

thyroid stimulating hormone -stimulates secretion of thyroid hormone

major hypophysiotropic hormones:

thyrotropin-releasing hormone (TRH) corticotropin-releasing hormone (CRH gonadotropin-releasing hormone (GnRH) growth hormone-releasing hormone (GHRH) somatostatin - growth hormone inhibiting hormone (GHIH) prolactin-releasing hormone (PRH) dopamine - prolactin-inhibiting hormone (PIH)

primary hypersecretion:

too much hormone is secreted due to abnormality within gland. -example: cancer in gland ignore normal regulatory input and continuously secrete excess hormone

t/f: single hormone may be secreted by more than one endocrine gland.

true example: somatostatin, secreted by both hypothalamus and pancreas

besides growth hormone, what are other factors that influence growth?

-genetic determination of an individual's max growth capacity -adequate diet -freedom from chronic disease and stressful environment conditions -normal levels of growth-influencing hormones

hydrophilic hormones characteristics

- circulate in blood, dissolved in plasma - cannot cross PM, bind to specific receptors on surface of PM -primarily act through 2nd msg system to alter the specific activity of preexisting proteins w.in target cell to produce their desired physiological response

growth hormone deficiency:

- due to pituitary defect or hypothalamic dysfunction -hyposecretion of GH in child is one cause of dwarfism -deficiency in adults produces relatively few symptoms