Flashcards in BIOL 0800 Reading- Chapter 11 Deck (162):
What are hormones?
Chemical messengers that enter the blood, which carries them, from their site of secretion to the cells upon which they act
What is the difference between exocrine and endocrine?
Exocrine glands secret products into ducts to exit the body; whereas endocrine glands are ductless and release their secretory products into the interstitial fluid to diffuse into the blood
What are amine hormones?
Derivatives of the amino acid tyrosine
What are the two classes of hormones encompassed by "amine hormones?"
Thyroid hormones and catecholamines
What are the three catecholamines?
Epinephrine, norepinephrine, and dopamine
What are the two parts of the adrenal gland?
Inner adrenal medulla and outer adrenal cortex
What does the adrenal medulla secret more of, epinephrine or norepinephrine?
Where is dopamine synthesized?
In thy hypothalamus, and released by a portal system to inhibit pituitary gland activity
What are prohormones?
The precursor to peptide hormones, which are cleaved from preprohormone by proteolytic enzymes in the RER, to be packaged in the Golgi to yield the active peptide hormones
Does a single prohormone create one kind of peptide hormone?
Nope, can create a whole bunch that are all released together
What are the three classes of hormones?
Amine hormones, peptide hormones, and steroid hormones
What are steroid hormones?
Primarily produced in the adrenal cortex and gonads
What is the general process of steroid hormones synthesis?
Anterior pituitary gland hormone binds to receptors in adrenal cortex/gonads, which are linked to G proteins for cAMP production, activating protein kinase A to facilitate the process through phosphorylation
What is the precursor to all steroid hormones?
How is cholesterol introduced into and used by cells?
Enters as LDLs, which centers cells by receptor-mediated endocytosis and is stored in a liquid droplet until released by the enzyme cholesterol esterase, activated by a protein kinase; then carried to the mitochondria and processed into steroid hormones by cytochrome P450s
What are cytochrome P450s?
Attach hydroxyl groups to carbon atoms and cleave carbon-carbon bonds, to modify cholesterol into steroid hormones
What happens to steroid hormones after synthesis? Where are they stored?
Diffuse across plasma membrane into interstitial fluid and into circulation; not highly soluble in the blood, so primarily transported in plasma bound to carrier proteins like albumin
What are the five major hormones secreted by the adrenal cortex?
Aldosterone, cortisol, corticosterone, DHEA, and androstenedione
What is aldosterone?
A mineralocorticoid, since it affects kidneys' mineral balances (potassium, sodium, hydrogen)
What hormone controls aldosterone production?
What steroid hormones are glucocorticoids?
Cortisol and corticosterone
What steroid hormone is a mineralcorticoid?
What are cortisol and corticosterone?
Glucocorticoids because they affect glucose metabolism
What steroid hormones are androgens?
DHEA and androstenedione
What are DHEA and androstenedione?
Androgens, which includes testosterone
What are the three layers of the adrenal cortex?
Zona glomerulosa, zona fasciculata, and zona reticularis
What is the zona glomerulosa?
Outer layer of the adrenal cortex; only synthesizes/secretes aldosterone; coverts corticosterone to aldosterone, but do NOT code for genes that form cortisol and androgens
What is the zona fasciculata?
Middle layer of the adrenal cortex; secretes cortisol, primarily
What is the zona reticularis?
Inner layer of the adrenal cortex; secretes primarily androgens
What are the two hormones that make up the category "estrogens?"
Estradiol and estrone
Which estrogen is the major hormone secreted by the ovaries?
What gonadal hormone is secreted by the corpus luteum (ovarian structure after ovulation)?
How are most hormones transported in the blood?
Dissolved in plasma
How are steroid and thyroid hormones transported in the blood?
Bound to large proteins in the plasma, but a small concentration exists dissolved in the plasma as well
Why is the concentration of free hormone in the plasma more important than the total concentration of hormone-protein complex?
Because only the free hormones can diffuse out of capillaries to target cells
What are the two major organs that metabolize or excrete hormones?
Liver and kidneys
What kinds of hormone are removed from the bloodstream quickest? Why?
Peptide and catecholamine hormones are removed quickly because there are enzymes in the bloodstream that break them down quickly; steroid and thyroid hormones take longer because enzymes won't break them down if they're bound to proteins
What are the receptors for peptide and catecholamine hormones?
In the plasma membranes of target cells
Where are the receptors for thyroid and steroid hormones?
Inside the target cells
What is up-regulation?
An increase in the number of a hormone's receptors in a cell, resulting from prolonged exposure to a low concentration of the hormone; temporarily increases target-cell responsiveness
What is down-regulation?
A decrease in receptor number, often from exposure to high concentrations of the hormone; temporarily decreases target-cell responsiveness and prevents overstimulation
How do up and down regulation affect responsiveness to hormones?
Up regulation increases, down regulation decreases
What is permissiveness?
When hormone A must be present for the full strength of hormone B's effect
What are the three main controls of inputs to endocrine cells?
Changes in plasma concentrations of mineral ions or organic nutrients; neurotransmitters released from the neurons ending on the endocrine cells; or another hormone or paracrine substance on the endocrine cell
What is an example of input to endocrine cell controlled by plasma concentrations of mineral ions of organic nutrients?
Insulin secretion stimulated by high plasma glucose levels; PTH secretion stimulated by low plasma calcium ion levels
What is an example of input to endocrine cell controlled by neurons?
Insulin and gastrointestinal hormone secretion, stimulated by neurons of the parasympathetic nervous system and inhibited by sympathetic nervous system
How does the adrenal medulla relate to the sympathetic nervous system?
It's a modified sympathetic ganglion, so it's stimulated by sympathetic preganglionic fibers
Which group of hormones is under direct control of brain neurons themselves, rather than autonomic neurons?
Those secreted by the hypothalamus and co.
What is an example of input to endocrine cells controlled by other hormones?
Tropic hormone, which often stimulates secretion of other hormones as well as the growth of the gland itself
What are three causes of primary hyposecretion?
Partial gland destruction, enzyme deficiency, and dietary iodine deficiency
What is secondary hyposecretion?
Endocrine gland isn't damaged, but is receiving too little of its topic hormone
What is primary hyposecretion?
When the endocrine gland can't function normally
How does one diagnose primary or secondary hyposecretion?
Measure the level of tropic hormone in the blood; if elevated, then primary; if lowere, then secondary
What is the difference between primary and secondary hypersecretion?
Primary is when the gland is secreting too much hormone, and secondary is when the tropic hormone excessively stimulates the gland
How does one diagnose primary vs secondary hypersecretion?
Primary if decreased concentration of the tropic hormone because of negative feedback trying to turn off excessive hormone secretion; Secondary if both concentrations of hormone and tropic hormone are elevated.
What is an important example of hyporesponsiveness?
Diabetes mellitus, when target cells of insulin are hyporesponsive
What is one cause of hyporesponsiveness?
Lack of receptors, or defective receptor behavior, or deficiency in enzymes needed to catalyze the steps of the reaction
What is an example of hyperresponsiveness?
Hypersecretion of thyroid hormones causes hyperresponsiveness of epinephrine, which results in elevated heart rate
What is the infundibulum?
The pituitary stalk that connects the pituitary gland to the hypothalamus
Is the posterior pituitary actually a gland?
Nope, it's technically an extension of the neural components of the hypothalamus
What happens to the axons in the infundibulum? Where do their terminals end up?
Directly on capillaries to release hormones into circulation
What is the median eminence?
The junction of the hypothalamus and infundibulum, where capillaries recombine to form the hypothalamo-pituitary portal vessels
What is a portal vessel?
A vessel that connects two capillary beds
Where are posterior pituitary hormones synthesized?
In the hypothalamus itself
What are the two posterior pituitary gland hormones?
Oxytocin and vasopressin (ADH)
What are hypophysiotropic hormones?
The hypothalamic hormones that regulate anterior pituitary gland function
What is the standard three-hormone sequence of the hypophysiotropic hormones? Which hormones doesn't follow that route?
Dopamine doesn’t follow: 1) hypophysiotropic hormone controls secretion of 2) anterior pituitary gland hormone to control secretion of 3) other endocrine gland hormone to act on target cells
What are the six most common anterior pituitary hormones?
FSH, LH, GH, TSH, prolactin, ACTH
What is the main function of the TSH and ACTH?
To stimulate target cells to synthesize and secret other hormones
What does growth hormone do?
Stimulates the liver to secret a growth-promoting peptide hormones known as IGF-1 (insulin like growth factor 1)
What controls anterior pituitary hormone activity?
Hypothalamus hormones, or hypophysiotropic hormones
How do hypophysiotropic hormones work?
Secreted by neurons originating in the hypothalamus, terminate in the median eminence around the capillaries of the hypothalamo-pituitary portal vessels to release the hormones into the capillaries
What is the difference in the secretion of posterior pituitary hormones and hypophysiotropic hormones?
For posterior pituitary hormones, the hypothalamic neurons end in the posterior pituitary gland and enter the general bloodstream; For hypophysiotropic hormones, the hypothalamic neurons stay in the hypothalamus and end in the median eminence and enter median eminence capillaries and hypothalamo-pituitary portal vessels to the cells of the anterior pituitary gland
What is the primary function of the hypothalamo-pituitary portal vessels?
To ensure that the hypophysiotropic hormones can reach the anterior pituitary glands quickly
What are the two hypophysiotropic hormones that inhibit the secretion of anterior pituitary gland hormones?
Somatostatin and dopamine
What does somatostatin inhibit?
Secretion of growth hormone
What does dopamine inhibit?
Secretion of prolactin
What anterior pituitary hormone is controlled by two hypophysiotropic hormones?
Growth hormones, inhibited by somatostatin and stimulated by GHRH
What are the two mechanisms by which secretion of hypophysiotropic hormones are released?
Neural and hormonal controls
How do neurons control secretion of hypophysiotropic hormones?
Neurotransmitters (like catecholamines and serotonin) are at the synapses of hormone-secreting hypothalamic neurons
What is one example of neuronal control of hypophysiotropic hormone secretion?
CRH from the hypothalamus stimulates ACTH in the anterior pituitary which stimulates the adrenal cortex to secrete cortisol; BUT release of CRH is regulated by complex neural pathways based on stress levels, circadian rhythms, etc.
What is one example of hormonal control of hypophysiotropic hormone secretion?
When the CRH-ACTH pathway stimulates the adrenal cortex to produce cortisol, the cortisol itself acts as negative feedback for secretion of CRH; also acts on anterior pituitary to reduce response to CRH
What is a long-loop negative feedback?
When the third hormone in the three-hormone sequence acts as negative feedback effect over the other two steps
What is short-loop negative feedback?
When the prolactin hormone acts on the hypothalamus to stimulate dopamine to inhibit secretion of prolactin; influence of an anterior pituitary gland hormone on the hypothalamus
What are the two iodine-containing thyroid hormones?
Thryoxine, and triiodothyrozxine (T4 and T3)
What is the "main" iodine-containing thyroid hormone?
T3, because T4 is generally converted into T3 by deiodinase enzymes
What is iodide trapping?
When the iodide ion is trapped into the follicular cell in the thyroid, after being cotransported in with sodium ions
What does thyroid peroxidase do?
Oxidizes iodides and attaches them to tyrosines on thyroglobulin in the colloid
What is unique about the thyroid gland?
Large storage capacity of iodinated thyroglobulin stored in the follicles to provide enough thyroid hormone for several weeks
Essentially all follicular cell actions are stimulated by what hormone?
TSH, which is stimulated by TRH
What is the basic control mechanism of TSH production?
Negative feedback action of T3 and T4 on the anterior pituitary gland and sometimes hypothalamus
What does TSH do in the follicular cells?
Stimulates T3 and T4 production, increases protein synthesis, increases DNA replication and cell division, increases amount of RER
What is different about receptor location for thyroid hormones from other hormones?
Located in the nuceli of most cells in the body, whereas others are usually more limited
Thyroid hormones have a greater affinity for which compound, T3 or T4?
T3 (but this is okay because T4 is usually deiodinized to T3 anyway)
How do T3 and T4 act?
By inducing gene transcription and protein synthesis
How do T3 and T4 affect carbohydrate and lipid metabolism?
Increase carb absorption from the small intestine; increase fatty acid release from adipocytes
What pump's activity is highly dependent on thyroid hormones?
The Na/K pump
What effect does a decrease in cellular ATP (used up by the Na/K pump stimulated by thyroid hormones) stores have on glycolysis?
Increase in glycolysis: burns additional glucose that restores ATP levels, which requires heat and increased metabolism of fuels: calorigenic action of T3 and T4
How do thyroid hormones contribute a significant fraction of body heat?
Stimulate use of ATP to fuel Na/K-ATPase pump; increases use of glycolysis to provide more ATP for cellular function, which generates heat
What does it mean that T3 and T4 are permissive on catecholamines?
Up-regulate beta-adrenergic receptors in many tissues (esp. heart and nervous)
Excess thyroid hormone symptoms look like excess of what other hormones? Why?
Epi/norepi because they upregulate beta-adrenergic receptors for catecholamines
Epi and norepi are associated with which nervous system?
Why are T3 and T4 crucial for nervous system development?
Forms axon terminals and production of synapses, growth of dendrites and dendritic extensions, formation of myelin
What disorder is a result of T3/4 deficit in infancy?
Congenital hypothyroidism: poorly developed nervous system and compromised intellectual function
What happens during hypothyroidism?
Increase in TRH and TSH levels (lack of negative feedback to hypothalamus and pituitary due to lack of T3/4); increase thyroid gland, goiters
What is the most common cause of hypothyroidism in the US?
Autoimmune thryoiditis, often Hashimoto's disease when the immune system T cells attack thyroid tissue
Why are two symptoms of hypothyroidism weight gain and sensitivity to cold?
Lack of T3/4 stimulation of Na/K pump leads to decreased calorigenic actions
What is Graves' disease?
Hyperthyroid disorder: autoimmune disease, overstimulation and growth and activity of the thyroid gland
What are some symptoms of thyrotoxicosis?
Heat intolerance, weight loss, increased appetite, increased sympathetic nervous system activity
What hormone is released during stress?
Cortisol (glucocorticoid hormone); and sometimes epi from the adrenal medulla
Where is cortisol secreted from, and what kind of hormone is it?
Glucocorticoid hormone secreted from the adrenal cortex
What system mediates increased cortisol secretion during stress?
Hypothalamo-anterior pituitary gland system
How does the HPA axis increase cortisol secretion?
Neural input to H induces CRH secretion, through HP portal vessels to anterior P to stimulate ACTH secretion, which circulates in the blood to reach the adrenal cortex and stimulate cortisol release
What biological molecule helps stimulate ACTH secretion directly and by stimulating secretion of CRH as a way to elicit endocrine stress response?
Cytokines: secretions from immune system cells
Why do basal levels of cortisol help maintain normal blood pressure?
Because even under nonstressed conditions, they're permissive for epi/norepi that controls smooth muscle cells around arterioles
What are the two important main systemic actions of cortisol?
Anti-inflammatory and anti-immune functions
How does cortisol inhibit the immune system?
Inhibits leukotrine and prostaglandin production (involved in inflammation); stabilizes lysosomal membranes in damaged cells tp prevent release of contents; reduces capillary permeability in injured areas (reduces fluid leakage)
What are the five main effects of increased cortisol?
1) effects on organic metabolism (protein catabolism up, liver gluconeogenesis up, plasma glucose maintenance, triglyceride catabolism up), 2) enhanced vascular reactivity; 3) unidentified protective effects against damaging stress, 4) inhibits inflammation and specific immune responses; 5) inhibition of nonessential functions
What is a summary of cortisol's effect on organic metabolism?
Increases plasma concentrations of amino acids, glucose, glycerol, and free fatty acids
Why do certain cytokines stimulate secretion of ACTH and thus cortisol?
To dampen the body's immune response and protect against damage from excessive inflammation during infection or trauma
What is primary adrenal insufficiency?
Due to loss of adrenal cortical function as in TB or tumors, but most often an autoimmune attack of the adrenal cells as foreign
What indicates primary adrenal insufficiency?
Low levels of cortisol and aldosterone, but increased ACTH levels (no negative feedback)
What is the effect of low levels of aldosterone, as caused by primary adrenal insufficiency?
Imbalance in Na/K/water, leading to hypotension
What is Addison's disease?
Primary adrenal insufficiency
What is secondary adrenal insufficiency?
Due to ACTH deficiency, as with pituitary disease
Which has more drastic symptoms, primary or secondary adrenal insufficiency?
Primary, because secondary doesn't affect aldosterone levels
What is Cushing's syndrome?
Excess cortisol in the blood even when unstressed
What are five other hormones besides cortisol that are released during stress?
Aldosterone, vasopression (ADH), GH, glucagon, and beta-endorphin (coreleased with ACTH from anterior pituitary)
What are five actions of the sympathetic NC during stress?
1) increased hepatic and muscle gluconeogenesis; 2) increased adipose triglyceride breakdown; 3) increased cardiac function; 4) diversion of blood to skeletal muscles (vasocon in visceral, vasodil in skeletal); 5) increased lung ventilation
What is epiphyses vs shaft?
The ends vs rest of bones
What is the epiphyseal growth plate?
The portion of each epiphysis in contact with the shaft; plate of actively proliferating cartilage
What are osteoblasts?
Bone-forming cells at the shaft edge of epiphyseal growth plates
What are chondrocytes?
Cells that lay down new cartilage in the interior of the epiphyseal growth plate
What is a mitogen?
A chemical that stimulates cell division
How does GH affect epiphyseal growth plates?
Stimulates maturation and cell division of chondrocytes in epiphyseal plates
How does GH accomplish its mitogenic effects?
Indirectly through mediation of mitogenic hormone IGF-1
How do GH and IGF-1 interact on epiphyseal plates?
GH stimulates prechondrocytes, which begin to differentiate and secrete and become response to IGF-1, which acts as a paracrine/autocrine substance to stimulate differentiating chondrocytes to undergo cell division
How does IGF-1 directly stimulate protein synthesis, especially in muscle?
Increases amino acid uptake and synthesis/activity of ribosomes
What hormones stimulate and inhibit GH?
GHRH and somatostatin
What is IGF-2?
Secreted independent of GH, crucial mitogen during prenatal period
Why are thyroid hormones necessary for growth?
Required for synthesis and growth-promoting effects of GH
What is insulin?
Anabolic hormone that promotes glucose and AA transport from ECF into adipose/skeletal/cardiac cells; stimulates fat storage, inhibits protein degradation
What effect do sex hormones have on growth?
Stimulate bone growth AND stop it by inducing epiphyseal closure
What hormone has antigrowth effects?
Cortisol: inhibits DNA synthesis and stimulates protein catabolism and inhibits bone growth, in high concentrations
What three areas does Ca homeostasis depend on?
Bones, kidneys, and GI tract
What is the osteoid?
Collagen matrix in bones upon which minerals and calcium/phosphate/hydroxyapatite are deposited
What are the three types of bone cells?
Osteoblasts, osteocytes, osteoclasts
What are osteoblasts?
Bone-forming cells; secret collagen into the matrix, which becomes calcified during mineralization
What are osteocytes
Osteoblasts that have been surrounded by a calcified matric: long cytoplasmic processes through the bone, form tight junctions
What are osteoclasts?
Large multinucleated cells that break down previously formed bone by secreting hydrogen ions to dissolve the crystals and hydrolytic enzymes to digest the osteoid
Of the hormones that affect bone calcium, which is the only one regulated by plasma calcium concentration?
How do kidneys affect plasma calcium concentration?
Control Ca excretion and reabsorption; also regulates phosphate ion balance
How does the GI tract affect plasma calcium concentration?
Controls large regulated increases or decreases of amount of Ca absorbed from the diet, since the GI tract usually doesn't absorb much calcium
What are the two major hormones that regulate plasma calcium concentration?
PTH and 1,25 dihydroxyvitamin D
How does plasma calcium concentration affect PTH secretion?
Decreased concentration stimulates PTH secretion
How does PTH increase extracellular calcium?
Directly increases osteoclast bone resorption to move calcium ions from bone to Ecf; directly stimulates 1,25dhv D formation to increase intestinal absorption of Ca and phosphate; directly increases Ca reabsorption in kidneys; reduces absorption of phosphate ions in kidneys (increases urinary excretion) which keeps plasma phosphate from increasing, since the Gi tract and bone are increasing phosphate concentration
What is 1,25- (OH)2D?
Calcitriol: active form of vitamin D
What is the major action of calcitriol?
Stimulate intestinal absorption of calcium ions
What is calcitonin?
Peptide hormone secreted by parafollicular cells in the thyroid gland
What does calcitonin do?
Decreases plasma calcium concentration by inhibit osteoclasts
What is the most common cause of hypercalcemia?