Endocrine Physiology: Pituitary & Adrenals Flashcards
feedback mechanisms generally involve what 4 features?
- system variable
- set point
- detector
- corrective mechanism
what are hormones?
- chemical messengers secreted into the blood by specialized cells
- control long-term homeostatic processes: growth, development, metabolism, reproduction, and internal environmental regulation
what is endocrinology?
the study of the endocrine system and hormone action
hormones act by binding receptors on or in target cells, controlling what 3 things?
- the rates of enzymatic reactions
- the movement of ions or molecules across membranes
- gene expression and protein synthesis
hormones are produced by ___ and ___, and are released from ___.
- endocrine cells
- organs
- endocrine glands
name the 6 major hormonal contributors to homeostasis
- thyroid hormone
- cortisol
- mineralocorticoids
- vasopressin
- parathyroid hormone
- insulin
name the hormone and its source responsible for the following action:
controls basal metabolism
- hormone: thyroid hormone
- source: thyroid gland
name the hormone and its source responsible for the following action:
energy metabolism; stress response
- hormone: cortisol
- source: adrenal cortex
name the hormone and its source responsible for the following action:
regulate plasma volume via effects on serum electrolytes
- hormone: mineralocorticoids
- source: adrenal cortex
name the hormone and its source responsible for the following action:
regulate plasma osmolarity via effects on water excretion
- hormone: vasopressin
- source: posterior pituitary
name the hormone and its source responsible for the following action:
regulates calcium and phosphorus levels
- hormone: parathyroid hormone
- source: parathyroid glands
name the hormone and its source responsible for the following action:
regulates plasma glucose concentration
- hormone: insulin
- source: pancreas
describe the 4 methods of hormonal communication
- neurocrine: secretion of hormones into the bloodstream by neurons
- endocrine: secretion of hormones into the bloodstream by endocrine glands
- paracrine: hormone molecule secreted by one cell affects adjacent cells
- autocrine: hormone molecule secreted by a cell affects the secreting cell
what are the two major hormone classifications?
chemical and solubility/polarity
describe chemical classifications for hormones
- amine hormones (tyrosine derivatives)
- peptide hormones
- steroid hormones
describe solubility/polarity classifications for hormones
- lipophilic (nonpolar) = fat-soluble
- steroid hormones and thyroid hormones
- usually bind to intracellular receptors
- hydrophilic (polar) = water-soluble
- peptide hormones and catecholamines
- usually bind to extracellular cell membrane receptors
___ hormones cannot diffuse through the cell membrane lipid bilayer, and instead pass on their message to a ___ located on the cell surface.
- hydrophilic (water soluble) hormones
- receptor
which hormones bind to cell membrane receptors on the extracellular surface of the cell?
- all amino acid-derived hormones
- peptides and amine-derived
- the EXCEPTION is thyroid hormones
do water soluble hormones directly affect the transcription of target genes? explain
- no
- they initiate a signaling cascade carried out by 2nd messenger molecules
- the hormone itself is called the 1st messenger
describe signal transduction
- occurs when hormones (chemical signal) bind to receptors on the surface of the membrane coupled to a G-protein which activates an intracellular second messenger cascade
what is the second messenger used by most water soluble hormones?
cyclic adenosine monophosphate (cAMP)
what does it mean if a hormone is in its bound form?
- it is inactive
- it can, however, become unbound (and thus, active), so it is put into a hormone reservoir
there are 2 groups of amine hormones derived from which amino acid? what are the 2 groups?
- tyrosine
- thyroid hormones
- catecholamines
describe thyroid hormones
- amine hormones derived from tyrosine
- lipophilic
- binds to nuclear receptor
- long half life
describe catecholamines
- amine hormones derived from tyrosine
- hydrophilic
- binds to cell surface receptor
- short half life
what are the most numerous class of hormones?
peptide (protein) hormones
describe peptide (protein) hormones
- water-soluble
- often produced as preprohormones (precursor)
- must be transported in the blood bound to carrier proteins (bound = inactive)
- only the free/unbound fraction binds to cell surface receptors
- 2nd messenger systems exert actions
what are preprohormones?
- hormone precursors
- large, inactive
- the include:
- signal sequence
- one or more copies of the hormone
- many additional peptide fragments
describe the 3 steps to produce peptide hormones
- genes code for mRNA, which undergoes translation into protein precursors
- preprohormone is formed in ER before getting broken down to prophormone in golgi apparatus
- after post-translational modifications in the golig, the peptide hormone gets secreted but may still undergo post-secretory processing
describe steroid hormones
- derived from cholesterol
- lipid-soluble
- carried in plasma by plasma-binding globulins (ex. albumin, testosterone binding globulin, thyroxine binding globulin)
- bound steroid hormones serve as reservoir for rapid release as needed
intracellular hormone receptor pathway:
only ___ hormones cross the cell membrane to bind intracellular receptors. which 2 hormones?
- lipid-soluble
- steroid and thyroid hormones
describe the intracellular hormone receptor pathway
- lipid soluble hormones bind to intracellular receptors
- hormone receptor complexes are generated and bind to a segment of the cell’s DNA
- once bound, the complex acts as a transcription factor
- mRNA then moves to the cytosol to direct protein synthesis by ribosomes
in postemenopausal women, ___ is the primary source of estrogens
adipose tissue
what is the clinical significance of the aromatase enzyme?
coversion of androgens to esterogens by the aromatase enzyme is performed by both trophoblastic tumors and by some nromal cells in adipose tissue, liver, and brain
describe negative feedback loops
- hormone shuts down either the stimulating or the releasing factors terminating the hormone action
describe positive feedback loops
- hormones enhance releasing and stimulating factors thus perpetuating additional hormone action
- much less common than negative feedback
describe the anterior pituitary
- adenohypophysis
- secretes protein hormones that stimulate/inhibit target organs and may feedback to hypothalamus
- utilizes hypophyseal portal system
describe the posterior pituitary
- neurohypophysis
- extension of the hypothalamus
- infundibular stalk connects the anterior gland to the hypothalamus
what is the hypothalamic-pituitary-adrenal (HPA) axis?
- responsible for the adaptation component of the stress response
- involves the anterior pituitary
what is osmolality?
a measure of how much of one substance has been dissolved in another substance
how is serum osmolality regulated?
- via systems that add/remove water from the system
- vasopressin (ADH) is secreted at the neurohypophysis (posterior pituitary)
- increases water reabsorption at the renal level by inserting aquaporins in the collecting duct
- vasopressin secretion is controlled by hypothalamic osmoreceptors
describe feedback control of serum osmolality
- with ADH/vasopressin:
- water is reabsorbed into the blood
- urine is hypertonic (concentrated)
- without ADH/vasopressin:
- water is not reabsorbed in the blood
- urine is dilute, and its volume is increased
all adrenocortical hormones are ____
steroid hormones
*adrenocortical hormones are produced in the adrenal cortex (3 zones)
the adrenal medulla secretes ___
- catecholamines
- for example, epinephrine and norepinephrine
- *these hormones are produced in the medulla
describe the 3 adrenocortical hormones
- mineralocorticoids (ex. aldosterone)
- secreted by the zona glomerulosa
- glucocorticoids (ex. cortisol)
- secreted by the zona fasciculata
- adrenal androgens (ex. dehydroepiandrosterone)
- secreted by the zona reticularis
describe the function of aldosterone
promotes sodium reabsorption and potassium excretion by the renal tubular epithelial cells of the collecting and distal tubules
what is aldosterone escape?
pressure diuresis in the kidney caused by persistently elevated extracellular fluid volumes
describe what happens if aldosterone levels increase vs decrease
- increase
- hypokalemia and muscle weakness are observed
- decrease
- may lead to hyperkalemia with cardiac toxicity
cortisol stimulates ___ in the liver while simultaneously decreasing glucose use by extrahepatic cells in the body. describe the overall result.
- gluconeogenesis
- the overall results is an increase in serum glucose and increased glycogen stores in the liver
describe the clinically significant anti-inflammatory effects of cortisol
- blocks the early stages of inflammation
- immunity is adversely affected
- eosinophil and lymphocyte counts in the blood decrease with atrophy of lymphoid tissue
the adrenal cortex continually secretes which male sex hormones?
- DHEA, DHEA sulfate (DHEAS), androstenedione, and 11-hydroxyandrostenedione
- small quantities of the female sex hormones progesterone and estrogen are secreted via aromatization
the adrenal medulla secretes ___ (80%) and ___ (20%) into the bloodstream due to direct stimulation by ___ release from sympathetic nerves
- epinephrine
- norepinephrine
- acetylcholine
epinephrine and norepinephrine secreted from the adrenal medulla are responsible for what?
- all the physiologic characteristics of the short term stress response
- aka acute stress: fight or flight
what is the response initiated by the release of steroid hormones from the adrenal cortex?
- long-term stress response
- metabolic changes and immune suppression
name the 3 main endocrine disorders
- endocrine gland hyposecretion (hormone deficiency)
- hormone resistance
- hormone excess
describe endocrine gland hyposecretion (hormone deficiency)
Due to destruction of the gland responsible for production, as in autoimmune disease (i.e., destruction of pancreatic islets cells in Type I Diabetes Myelitis), or a defect in the enzymatic machinery or precursors needed (i.e., iodine deficiency leads to hypothyroidism)
describe hormone resistance
Target tissues become resistant to to hormone effects either due to signal transduction uncoupling (i.e., Type II Diabetes Myelitis)
describe hormone excess
- tumors of endocrine glands produce hormone in an excessive/uncontrolled manner, often no longer subject to feedback regulation
- acromegaly
- graves disease
describe acromegaly
- gigantism
- pituitary gland produces excess growth hormone
- therapy is the use of somatostatin analogues that inhibit the secretion of growth hormone
describe diabetes
- most common endocrine disorder in the US
- type I - immune system destroys beta cells that make insulin
- type II - insulin is produced, but the body is insulin resistant
describe adrenal insufficiency
- addison’s disease is an example
- the adrenal gland releases too little cortisol and sometimes, aldosterone
- symptoms include fatigue, stomach upset, dehydration, and skin changes
describe cuching’s syndrome
- caused by prolonged exposure to elevated levels of either endogenous glucocorticoids or exocenous glucocorticoids
- excess ACTH results in overproduction of cortisol
describe hypothyroidism
- insufficient thyroid hormone leads to fatigue, constipation, dry skin, and depression
- hashimoto’s disease: autoimmune hypothyroidism
describe hyperthyroidism
- thyroid gland produces too much thyroid hormone
- results in weight loss, fast heart rate, sweating, nervousness disorder, and bulging eyes
- most common cause for hyperthyroidism is graves disease
