Endocrine Physiology: Pituitary & Adrenals Flashcards Preview

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Flashcards in Endocrine Physiology: Pituitary & Adrenals Deck (64):

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

  1. amine hormones (tyrosine derivatives)
  2. peptide hormones
  3. steroid hormones


describe solubility/polarity classifications for hormones

  1. lipophilic (nonpolar) = fat-soluble
    1. steroid hormones and thyroid hormones
    2. usually bind to intracellular receptors
  2. hydrophilic (polar) = water-soluble
    1. peptide hormones and catecholamines
    2. 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

  1. genes code for mRNA, which undergoes translation into protein precursors
  2. preprohormone is formed in ER before getting broken down to prophormone in golgi apparatus
  3. 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

  1. mineralocorticoids (ex. aldosterone)
    1. secreted by the zona glomerulosa
  2. glucocorticoids (ex. cortisol)
    1. secreted by the zona fasciculata
  3. adrenal androgens (ex. dehydroepiandrosterone)
    1. 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