E3- Random Flashcards
Thyroid deficiency during gestation leads to what?
cretinism
In a hyperthyroid state is colloid is reabsorbed more or less?
More
What type of cells release calcitonin?
Parafollicular
What 2 things inhibit the Na/I symporter?
Perchlorate and thiocyanate inhibit
What are the effects of a low iodide diet?
NIS is increased to compensate for deficiency
Lack of iodide in the diet –> cannot make iodine –> cannot T3 or T4 –> hypothyroidism
A lack of thyroid hormones –> lack of negative feedback on the HPA –> ↑ TRH and ↑ TSH –> ↑ TSH causes goiter
What are the effects of Graves’ disease
Autoantibodies that mimic TSH
Leads to hyperthyroidism
Excessive thyroid hormones –> increased negative feedback on HPA –> ↓ TRH and ↓ TSH –> stimulation of growth causes goiter
What does iodide bind to for transport to/across the apical membrane
Pendrin
What is Pendred Syndrome
Goiter and hearing loss develop during childhood
If iodide intake is scarce, pts develop goiter and hypothyroidism
Iodide efflux from the cell into the colloid occurs through the what channel?
Iodide channel anoctamin-1
On the colloid side of the apical membrane, iodide is oxidized to iodine by what?
thyroid peroxidase (TPO)
What inhibits thyroid peroxidase (TPO)?
Propylthiouracil
What is the Wolff-chikoff effect?
Iodine metabolism can also be regulated independently of TSH
Occurs when plasma iodide levels are elevated
Elevated iodide levels inhibit organification to prevent excess thyroid hormone production
Iodinated tyrosine molecules fuse together to form thyroid hormones, this fusion is catalyzed by what?
thyroid peroxidase (TPO)
Following stimulation by TSH, what induces the follicular cell to engulf the colloid containing Tg, T3 and T4?
Megalin
Lysosomes target the engulfed colloid and what splits the iodinated products from thyroglobulin?
Proteases
In the plasma T3 and T4 bind to what?
Thyoxine-binding globulin (TBG)
T3 and T4 have a very high binding affinity for proteins; very little free circulating hormone
In the follicular cell, MIT and DIT are diiodinated by what?
Deiodinases
What is associated with higher Tg levels in the plasma?
Hyperthyroidism
T4 is converted to active __ by ___ ring deiodination via deiodinases type __
T4 is converted to active T3 by outer ring deiodination via deiodinases type 1 and 2
T4 is converted to inactive __ by ___ ring deiodination via deiodinase type __
T4 is converted to inactive rT3 by inner ring deiodination via deiodinase type 3
T3 and T4 enter cells by transporters.
OATP transporter has preference for which hormone?
T4
T3 and T4 enter cells by transporters.
MCT transporter has preference for which hormone?
T3
Mutations in this which thyroid hormone transporter class are associated with psychomotor retardation and thyroid hormone resistance?
MCT
Which thyroid hormone has a greater blinding affinity for thyroid receptors?
T3
T3 is 10x more potent for all actions!!
What are some calorigenic actions of thyroid hormones?
Increased oxygen consumption resulting in:
Increased basal metabolic rate (BMR)
Increased body temperature
Occurs in all tissues except the brain, gonads, and spleen
What are some metabolism actions of thyroid hormones?
Increases: -Glucose absorption from gut -Gluconeogenesis -Lipolysis -Protein synthesis and proteolysis (catabolic effect)
What are some CV actions of thyroid hormones?
T3 increases CO and ventilation
T3 is chronotropic and inotropic
T3 reduces vascular resistance
What are some SNS actions of thyroid hormones?
Increased synthesis of B-adrenergic receptors in cardiac/skeletal muscles and adipocytes (heterologous up-regulation)
What are some SNS actions of thyroid hormones?
Acts synergistically with GH and growth factors to promote bone formation
Stimulates protein synthesis
Maturation of CNS, axonal growth, and myelination
(anabolic effect)
What layer produces mineralocorticoids (aldosterone)?
Zona glomerulosa
What layer produces glucocorticoids (cortisol)?
Zona fasciculata
What layer produces androgens (DHEA)?
Zona reticularis
What layer produces EPI and NE?
Adrenal medulla
The production of steroids is controlled by what?
ACTH
The production of catecholamines is controlled by what?
SNS
Precursor for all adrenocortical steroids is what?
Cholesterol
Free cholesterol is transferred to the mitochondria, and then to the inner mitochondrial membrane by what?
STaR
Cholesterol is converted to pregnenolone by what enzyme? (rate-limiting step and is dependent on STaR)
Desmolase
What stimulates desmolase?
ATCH
Cells in the zona glomerulosa are lacking what enzyme?
17a-hydrozylase; therefore, this zone does not produce glucocorticoids or androgens
What is a type of primary hyperaldosteronism?
Conn’s syndrome
What are the effects of Conn’s syndrome?
Increased Na reabsorption –> hypernatremia, fluid retention and HTN
Increased K secretion –> hypokalemia
Increased H secretion –> metabolic alkalosis
Low renin levels
What are the effects of o 17a-hydroxylase deficiency?
Glucocorticoids and androgens are not produced
Steroid intermediates in the aldosterone pathway build up resulting in overproduction of 11-deoxycorticosterone and corticosterone
Corticosterone produces aldosterone-like effects (fluid retention, ↑ BP); the HTN inhibits renin secretion, causing aldosterone levels to be low
Leads to the same outcomes as with Conn’s syndrome
HTN
Hypokalemia
Metabolic alkalosis
Cells in the zona fasiculate are lacking what enzymes?
17,20-lyase; therefore, this zone does not produce androgens
Aldosterone synthase; therefore, the synthesis of aldosterone cannot be completed
Corticotrophin releasing hormone (CRH) stimulates corticotrophs to release ACTH. What are the effects of ACTH?
Stimulates adrenal gland growth
Transfers cholesterol into the mitochondria
Activates desmolase
What inhibits CRH?
Cortisol
Cortisol levels reflect a circadian and pulsatile release of ACTH. Greatest cortisol secretion occurs in the morning
In periods of stress, ACTH secretion is enhanced as a result of what?
Increased amplitude of CRH burst, rather than frequency
What are the effects of cortisol?
Increase blood glucose by enhancing gluconeogenesis (essential for survival during fasting and stress)
- Increases protein catabolism and lipolysis
- Decreases glucose uptake by the tissues
What hormone enhances responsiveness to alpha 1 receptors, inhibits bone formation, increases proteolysis in muscle, and has anti-inflammatory and immunosuppressive effects?
Cortisol
Cells in the zona reticularis are lacking what enzyme?
Cells in this zone do not have 21B-hydroxylase; therefore, this zone does not produce aldosterone or cortisol
What are adrenal androgens called?
17-ketosteroids
What enzyme converts Progesterone to 11-Deoxycorticosterone?
21B-hydroxylase
What enzyme converts corticosterone to aldosterone?
Aldosterone synthase
What enzyme converts Pregnenolone to 17-hydroxypregnelone?
17a-hydroxylase
What enzyme converts Progesterone to 17-hydroxypregnelone?
17a-hydroxylase
What enzyme converts 17-hydroxypregnelone to DHEA?
17,20-lyase
What enzyme converts 17-hydroxypregnelone to androstenedione?
17,20-lyase
What enzyme converts 17-hydroxypregnelone to 11-Deoxycortisol?
21B-hydroxylase
What are the effects of a 21B-hydroxylase deficiency?
Cortex does not produce glucocorticoids or mineralocorticoids, resulting in Na loss and hypoglycemia
Steroid intermediates build-up in the androgen pathway
ACTH levels are high because of a lack of feedback control of cortisol on the pituitary
Trophic effect of ATCH is seen
Increased levels of DHEA and androstenedione result in masculinization of female
Penis-like clitoris Scrotum-like labia Ovaries are present Deepening of voice Increased muscle mass Amenorrhea and hirsutism Are seen with what?
21B-hydroxylase deficiency
Knowing that cortisol levels are higher than aldosterone and that cortisol binds with a higher affinity to produce mineralocorticoid activity, why does this not occur in normal conditions?
- Cortisol circulates bound to albumin and CBG, allowing only a small fraction of free hormone to cross cell membranes
- Aldosterone target cells have the enzyme 11B-hydroxysteroid dehydrogenase type II which converts cortisol into its inactive form (cortisone), which has less affinity to the MR
- Aldosterone dissociates from the MR more slowly than cortisol
What type of MR and GR are predominant in the kidney and are specific for aldosterone?
Type I receptors
What type of MR and GR are expressed in all cells and are specific for glucocorticoids?
Type II receptors
11B-hydroxysteroid dehydrogenase type I (11B-HSD1)
promotes what conversion?
Cortisone to cortisol
11B-hydroxysteroid dehydrogenase type II (11B-HSD2) promotes what conversion?
Cortisol to cortisone