Basic principles and concepts Flashcards
Define: hormone
Chemical substance produced by an endocrine cell in response to a certain stimuli to cause an effect on a target cell which in turn causes a change or adjustment in various organ systems of the body.
; 3 classes- steroids, protein/peptide, amino acid analogues and derivatives
Describe the major chemical classes to which hormones belong, with examples
steroid- originate from cholesterol precursor, organs that secrete ex.- ovaries, testis, adrenal cortex, specific hormone ex.- mineralcorticoids, glucocorticois, testosterone and estradiol
protein/peptide- name indicates structure, organs that secrete ex.- pancreas, thyroid, parathyroid, anterior pituitary, specific hormone ex.- insulin, prolactin, parathormone
amino acid analogues/derivatives- name indicates chemical structure, organs that secrete ex.- thyroid, adrenl medulla, specific hormones ex.- thyroxine (T4), epinephrine and norepinephrine (catecholamines)
Describe the 2 major classes of hormone receptors and their functions
membrane receptors- used by hormones that cannot diffuse through plasma membrane (amines, peptides, proteins)
does not directly alter gene expression
G proteins in cell membrane are activated
1st messenger is hormone, 2nd messenger may be cAMP, cGMP, Ca++
cytoplasmic/nuclear receptors- characteristic of steroid/thyroid hormones
diffuse through plasma membrane
bind to receptor; receptor-hormone complex binds specific DNA sequences
directly alters gene expression
new mRNA and proteins made, new proteins change cell function
Describe the role of cyclic AMP in mediating actions of some protein hormones
cAMP may act as a secondary messenger once G proteins in the cell membrane are activated; hormone binds to a receptor which then leads to activation of G proteins, altering cell function and causing multiple biological effects
Give examples of endocrine “glands” that are part of the nervous system
Hypothalamus, pituitary
Describe how steroid hormones act
diffues through plasma, act on nuclear receptors, bind to receptor, receptor/hormone complex binds to DNA sequence particularly in the promoter region, directly alters gene expression, leads to new protein and a biological response
Describe negative feedback, and the role of negative feedback systems in the control of endocrine organs
increase of concentration in system leads to down-regulation of production of hormone; ex.- T3 and T4 levels will signal increase or decrease of TRH (hypothalamus) or TSH (anterior pituitary/adenohypophysis)
Describe autocrine, paracrine and endocrine
autocrine- acts on same cell that produced it
paracrine- acts locally by diffusing from its source to target cells in the neighborhood
endocrine- secreted into blood; binds distant target cells
Define and give examples of diseases that arise from hormone deficiency
Deficiency- lack of sufficient hormone production, can be caused by destructive process in the gland or genetic defect in hormone production
Ex.- Hypothyroidism (T4), Dwarfism (GH), Diabetes (Insulin)
Define and give examples of diseases that arise from hormone excess
Excess- overproduction of hormone either by the gland itself or tissue not normally active as an endocrine gland (tumor)
Ex.- Cushing’s, Primary hyperthyroidism
List clinical approaches to treating diseases that arise from hormone excesses
surgery, irradiation, hormone suppression through medication
List clinical approaches to treating diseases that arise from hormone deficiency
supplementation; hormone replacement therapy
Define: receptor
specific binding site; can have affinity for one or more type of molecule depending on conformation
Define: second messenger
activated by primary messenger; seen in cells that cannot permeate cell membrane, activation of G cells cause initiation of these secondary messengers; use membrane receptors
Define: feedback
mechanism of controlling production of a substance, including hormones; ex. - negative feedback loop involving T3/T4 and the hypothalamus and pituitary
