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my phase 1 > Endocrine > Flashcards

Endocrine Flashcards

1
Q

describe the structure of the thyroid gland

A

2 lobes connected via the isthmus

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2
Q

where is the thyroid gland located

A

in the anterior of the neck between C5 and T1
wrapped around the cricoid cartilage and the superior rings of the trachea

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3
Q

describe the blood supply and drainage around the thyroid

A
  • arterial supply =
    • superior thyroid artery
      • 1st branch of the external carotid artery
      • supplies superior and anterior porteions of the gland
    • inferior thyroid artery
      • arises from the subclavian artery
      • supplies the inferior portion of the gland
  • venous drainage
    • drained by the superior, middle and inferior thyroid veins
    • The superior and middle veins drain into the internal jugular vein and the inferior empties directly into the brachiocephalic vein.
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4
Q

how is the thyroid gland innervated

A

via the sympathetic trunk in the cervical ganglion BUT do not control secretion of hormones

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5
Q

why is the thyroid gland highly vascularised

A

it secretes hormones directly into the blood

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6
Q

what controls hormone release from the thyroid

A

the HPT axis

the anterior pituitary gland via TSH, which is stimulated by TRH from the hypothalamus

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7
Q

label

A
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8
Q

what are the major hormones of the thyroid

A
  • T3 - triiodothyronine
  • T4 - thyroxine
    • 3 and 4 indicate the number of iodine molecules in each hormone
  • Calcitonin
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9
Q

where are thyroid hormones produced

A

in the follicle cells which are arranged in lobules with a lumen called colloid

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10
Q

how do thyroid hormones take effect

A

via nuclear receptors in target tissues to increase metabolic rate

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11
Q

give examples of processes affected by thyroid hormones

A
  • Basal Metabolic Rate
  • Gluconeogenesis
  • Glycogenolysis
  • Protein synthesis
  • Lipogenesis
  • Thermogenesis
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12
Q

describe the process of thyroid hormone synthesis

A

ATE ICE

  1. Active transport
    • the sodium-iodide symporter [NIS] actively transports iodide into the follicular cell
    • the iodide molecules pass into the colloid by pendrin
  2. Thyroglobulin production
    • the RER of the follicular cells produce thyroglobulin and it’s packaged by the golgi body
  3. Exocytosis
    • the packaged thyroglobulin is transported out of the cell by exocytosis into the follicular lumen = colloid
  4. Iodination
    • the iodide molecules are converted → iodine by thyroid peroxidase.
    • the tyrosine molecules on the thyroglobulin have 1 or 2 iodine molecules attached to them → monoiodotyrosine MIT or diiodotyrosine DIT.
  5. Coupling
    • MIT + DIT = T3
    • DIT + DIT =T4
    • this occurs while still attached to thyroglobulin
  6. Endocytosis
    • the iodinated thyroglobulin molecules are endocytosed back into the follicular cells
    • thyroglobulin then undergoes proteolysis → free T3 and T4.
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13
Q

which is more active?

which is more abundant?

T3 or T4

A

T3 is 10 times more active than T4

T4 is more abundant as it is more stable and has a longer half-life than T3.

T4 is converted into T3 at the target tissue

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14
Q

how is T4 converted to T3

A

via deiodinase

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15
Q

describe the HPT axis [hypothalamic-pituitary-thyoid axis]

A
  1. the hypothalamus releases TRH
  2. TRH stimulates the anterior pituitary to release TSH
  3. TSH acts on the thyroid gland to synthesise and secrete T3 and T4
  4. T4 is converted to T3 at target tissue
  5. T3 inhibits the hypothalamus and stops the release of TRH
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16
Q

when do the thyroid thyroid glands start producing thyroxine in utero

A

18-20 weeks

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17
Q

overall actions of the thyroid hormones

A

increases metabolic rate

important in brain maturation

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18
Q

how many parathyroid glands are there

where are they located

A

4

2 superior and 2 inferior

posterior lateral aspect of the thyroid glands

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19
Q

how are the parathyroid glands innervated

A

by the sympathetic trunk

this does not control hormone secretion

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20
Q

describe the blood supply to the parathyroid glands

A

the inferior thyroid artery - branch of the subclavian

drained by the thyroid plexus

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21
Q

what hormone does the parathyroid secrete

what does it do

A

parathyroid hormone

it regulates phosphate and calcium levels

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22
Q

what triggers release of PTH

A
  • low calcium
  • high phosphate
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23
Q

function of calcitonin and which gland releases it

A
  • regulates calcium levels, when present in large amounts it decreases calcium and vice versa
  • released by the thyroid gland
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24
Q

the anterior and posterior pituitary glands develop from the same tissue

T/F

A

False

they develop from different tissues grow next to each other then join together

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25
Q

what is the anterior pituitary gland formed from

A

the upward protrusion of ectoderm from Rathke’s pouch = adenohypophysis

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26
Q

what is the posterior pituitary form from

A

it is a neuronal extension of the neural components of the hypothalamus

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27
Q

how does the hypothalamus communicate with the anterior pituitary

A
  • using hypophysiotropic hormones
  • these hormones reach the anterior pituitary via the hypothalamo-hypophyseal portal vessels
    • their action in the anterior pituitary is to stimulate or inhibit release of 6 hormones
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28
Q

how many hypophysiotropic hormones are there,

what are they

what do they do

A

5

  1. corticotropin releasing hormone [CRH]
    • stimulates release of adenocorticotropic hormone ACTH → increased cortisol produced in the adrenal cortex - zona fasiculata
  2. Growth hormone releasing hormone [GHRH]
    • stimulates release of growth hormone → growth and protein synthesis
    • inhibited by somatostatin [which is produced in the hypothalamus and pancreas]
  3. thyrotropin-releasing hormone [TRH]
    • stimulates release of TSH from the anterior pituitary → stimulates synthesis and secretion of T3 and T4
  4. Gonadotropin-releasing hormone [GnRH]
    • stimulates release of LH and FSH → production of oestrogen, progesterone and testosterone in the gonads
  5. dopamine
    • inhibits release of prolactin
      6.
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29
Q

how does the hypothalamus communicate with the anterior pit gland

A

via the hypothalamo-hypophyseal portal vessels

they share a blood network which allows the hormones released by the hypothalamus to reach and affect the APG

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30
Q

function of hypophysiotropic hormones

A

control the secretion of anterior pituitary hormones hormones

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31
Q

general role of the hypothalamus

A
  • Important for homeostasis + primitive functions :–
    • appetite, thirst, sleep, temperature regulation
  • Control of autonomic function via brainstem autonomic centres
  • Control of endocrine function via pituitary gland
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32
Q

how many hormone producing cell types are there in the APG

and how many hormones are produced

A
  • 5 cell types
    1. gonadotropes cells → FSH and LH
    2. corticotropes cells → adrenocorticotropic hormone ACTH
    3. somatotropes → growth hormone (GH);
    4. Lactotropes → prolactin (PRL)
    5. thyrotropes → TSH
  • 6 hormones in total
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33
Q

which APG hormones have a negative feedback loop

A

all of them except for prolactin feedback negatively

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34
Q

which hypothalamic hormone is not involved in the 1st step of the 3 hormone sequence

A

dopamine

it is an inhibitory regulator of prolactin

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35
Q

what is short loop negative feedback

which hormones exhibit this

A
  • where the anterior pituitary hormone act on the hypothalamus for negative feedback
  • prolactin acts on hypothalamus → secretion of dopamine which inhibits the release of prolactin from APG
  • GH acts directly on the APG and hypothalamus to inhibit GH and GHRH
  • IGF stimulates somatostatin which acts on the APG to inhibit release of GH from the APG
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36
Q

what is long loop -ve feedback

which hormones exhibit this

A
  • where the endocrine gland hormone → negative feedback on the hypothalamus or the APG
  • all but PRL and GH
    • cortisol
    • T3, T4
    • oestrogen, progesterone, testosterone
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37
Q

function of growth hormone

A

stimulates growth and protein synthesis

released in a pulsatile manner throughout life

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38
Q

effect of cortisol

A
  • regulates stress response
  • increased energy mobilisation
  • salt/water balance
  • reduced immune response
  • reduced growth
39
Q

function of prolactin

A
  • lactation
  • breast development
  • increased testosterone production
40
Q

whaich hormones are produced by the posterior pituitary gland

A
  • oxytocin
  • vasopressin
41
Q

where is vasopressin synthesised

A

in the supraoptic nucleus

42
Q

what stimulates release of vasopressin

A
  1. increased osmotic pressure in the blood
  2. decreased blood volume
  3. trauma/ stress
  4. increased PCO2
  5. decreased PO2
43
Q

what effects does vasopressin have

A
  • it increases the expression of aquaporin 2 on the apical membrane of the primary cells in the collecting ducts of the kidney
  1. vasopressin binds to V2 receptors in primary cells of renal collecting duct
  2. triggers an intracellular cascade →
  3. upregulation of aquaporin 2 proteins which are inserted on the apical membrane → increased permeability of collecting duct cells
  4. Water is reabsorbed from the renal collecting duct and returned to the blood stream, decreasing the plasma osmolality
44
Q

describe the -ve feedback system in high blood volume and low plasma osmolality

define osmolality

A

osmolality = the amount of solutes per kilo of solvent

45
Q

describe the -ve feedback system in high plasma osmolality

define osmolality

A

osmolality = the amount of solutes per kilo of solvent

46
Q

where is oxytocin produced

A

in the paraventricular nucleus

47
Q

what triggers oxytocin release

A

triggered by nipple stimulation

48
Q

what are the effects of oxytocin

A
  • milk let down = constriction of muscles of the breast to promote milk ejection
  • uterine smooth muscle contraction
  • promotion of labour
49
Q

describe the feedback mechanism of oxytocin

A

positive feedback

  • uterine contraction stimulates the paraventricular nucleus further until labour
  • suckling stimulates the paraventricular nucleus further until milk ejection
50
Q

what is the bodies response to high calcium levels

A

releases calcitonin from the thyroid gland

51
Q

where is calcitonin produced

A

in the parafollicular cells [c cells]

52
Q

how does T3 and T4 travel in the blood

A

they are insoluble therefore they travel via transport proteins:

  • albumin
  • TBG
  • tranthyretin
53
Q

where are the adrenal glands located

A

supramedial aspect of the kidneys

retroperitoneal

54
Q

describe the arterial blood supply of the adrenal glands

A
  • Superior adrenal artery – arises from the inferior phrenic artery
  • Middle adrenal artery – arises from the abdominal aorta.
  • Inferior adrenal artery – arises from the renal arteries.
55
Q

describe the venous drainage of the adrenal glands

A
  • right kidney drains directly into the IVC
  • left kidney drains into the left renal vein then into the IVC
56
Q

what is the innervation of the adrenal glands

A

splanchnic nerve [sympathetic]

57
Q

what are the hormones produced by the anterior pituitary gland

A

FLAGTOP

  • Follicle stimulating hormone
  • Leutenising hormone
  • Adrenocorticotropic hormone
  • Growth hormone releasing hormone
  • Thyroid stimulating hormone
  • O- melanocyte stimulating hormone
  • Prolactin
58
Q

describe the anatomy of the adrenal glands

A
  • capsule
  • cortex
    • zona Glomerulosa
      • mineraolcorticoids synthesis
    • Zona Fascicularis
      • Glucocorticoids synthesis
    • Zona Reticularis
      • androgens synthesis
  • medulla
    • catecholamine synthesis
59
Q

describe adrenal gland vasculature

A
  • arteries x3
    • superior artery = branch of the inferior phrenic artery
    • middle artery = branch of the abdominal aorta
    • inferior artery = branch of the renal artery
  • one vein drains the gland = the adrenal vein
    • the right adrenal vein drains directly into the IVC as its is in close proximity
    • the left adrenal vein drains into the left renal vein first
60
Q

give examples of catecholamines

A

adrenaline and noradrenaline

61
Q

how is the adrenal gland innervated

A

the splanchnic nerve

62
Q

where is ADH produced

A

hypothalamus

63
Q

which cells does ADH take effect in

A

principal cells of the collecting duct

64
Q

what effect does ADH have

A
  1. it binds to the V2R receptors of the principal cells →
  2. upregulation of aquaporin channels in the collecting tubule walls →
  3. increased H2O reabsorption and less urine produced
65
Q

where is erythropoietin produced

what is its function

A

in the kidneys

increases production of RBCs in the bone marrow

66
Q

what hormones are produced in the adrenal glands

A
  1. Aldosterone
  2. cortisol
  3. corticosterone
  4. DHEA
  5. androstenedione

1= glomerulosa

2+3=fasciculata

4+5 = reticularis

67
Q

what is the role of the adrenal medulla

A
  • part of the autonomic nervous system
  • production of catecholamines
    • adrenaline 80% and noradrenaline20%
    • main site for adrenaline synthesis
  • production of catecholamines is dependent on cortisol levels [permissive effect]
68
Q

what is the effect of catecholamine release

A
  1. lipolysis in adipocytes
  2. gluconeogenesis in liver and muscles
  3. tachycardia and increased cardiac contractility
  4. redistribution of circulatory volume
69
Q

where are corticosteroids produced

A

in the adrenal cortex

70
Q

how do corticosteroids work

A
  • they are lipid soluble so can pass through the lipid membrane and:
    • act on intracellular receptors
    • alter gene transcription directly or indirectly
71
Q

what are steroids and steroid hormones made from

A

cholesterol

72
Q

role of ACTH

A

ACTH stimulates the synthesis of corticosteroids and cortisol acutely

73
Q

where are glucocorticoids produced

A

in the zona fasciculata and reticularis

(more-so in fascicularis)

74
Q

glucocorticoids are essential to life

T/F

A

true

  • glucocorticoids are essential to life
75
Q

what stimulates the production of glucocorticoids

A
  • hypothalamus releasing CRH - corticotropin releasing hormone
  • CRH→ APG causing release of ACTH
  • ACTH acts on the zona fasciculata in the adrenal cortex to produce cortisol
76
Q

what are the effects of cortisol and glucocorticoids

A
  • Increase glucose mobilisation
    • Augment gluconeogenesis
    • Amino acid generation
    • Increased lipolysis Important during “stress”
  • Maintenance of circulation
    • Vascular tone
    • Salt and water balance
  • Immunomodulation
    • Dampen immune response
77
Q

how are glucocorticoids transported

A
  • In the circulation glucocorticoids are mostly bound to proteins –
    • 90% bound to Corticosteroid-Binding Globulin (CBG)
    • 5% bound to albumin
    • 5% “free”
78
Q

what fraction of glucocorticoids in blood are bioavailable

A

the free glucocorticoids are bioavailable thus ~5%

when stressed level of binding reduces so there is more free cortisol as CBG is cleaved

79
Q

how is cortisol production regulated

A

via negative feedback

80
Q

cortisol has a diurnal rhythm - what does this mean

A

the the secretion follows a daily cycle

cortisol secretion is higher in the morning and early afternoon

81
Q

what factors stimulate cortisol secretion

A

stress

diurnal / circadian rhythm

cytokines

82
Q

what is calssified as stress

A
  • “The sum of the bodies responses to adverse stimuli”
    • Infection
    • Trauma
    • Haemorrhage
    • Medical illness
    • Psychological
    • Exercise/exhaustion
83
Q

how does the HPA axis change in acute illness

A
  1. there is less negative feedback so more cortisol is produced
  2. less CBG synthesised and more broken down → more free cortisol
84
Q

what are mineralocorticoid -give example

where are they produced

A

aldosterone

produced in the zona glomerulosa

85
Q

function of aldosterone

A
  • critical for salt and water balance in the:
    • kidneys
    • pancreas
    • colon
    • salivary glands
    • sweat glands
86
Q

what triggers aldosterone secretion

A

renin from the juxtaglomerular cells

87
Q

effects of aldosterone secretion

A
  • salt balance in th kidneys, colon, pancreas, salivary glands and sweat glands.
  • in the kidneys it acts on the distal convoluted tubule and collecting duct
    • increases epithelial Na+ channels and Na/K ATPase expression
88
Q

where are adrenal androgens produced

A

in the zona reticularis

89
Q

what androgens are produced in the adrenal glands

A
  • DHEA
  • androstenadione
90
Q

what is the most abundant adrenal steroid

A

DHEA

91
Q

which androgen has 1/10th adrongenic activty as testosterone

A

androstenedione

92
Q

what is a major source of androgens in women

A

androstenedione and DHEA

93
Q

what stimulates production of DHEA anandrostenedione

A

ACTH [not ghrh]

94
Q

effect of high cortisol on sex hormones

A
  • High cortisol levels inhibit the gonadotropin releasing hormone (GnRH) leading to
    • decreased progesterone and oestrogen in females.
    • Decreased testosterone and sperm count in males

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