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COT Part II > Lecture 20: Endocrinology > Flashcards

Lecture 20: Endocrinology Flashcards

1
Q

What is an endocrine axis?

A

A chain of hormones regulating a system, typically contained in the hypothalamus, pituitary, and target organ.

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2
Q

Primary endocrine disease

A

Originates in the target organ of an endocrine axis

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3
Q

Secondary endocrine disease

A

Originates the the hypothalamus or pituitary, or is caused off-axis.

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4
Q

General pharmacological endocrine axis features.

A
  1. Hypothalamic hormones
  2. Trophic hormones from pituitary
  3. Action at target organ(s)
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5
Q

Protein vs steroid hormones

A

Proteins: actively stored and secreted into fenestrated capillaries, target surface receptors
Steroids: require carrier proteins in the blood, synthesized from cholesterol. Target surface, intracell., or nuclear receptors

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6
Q

How does adipose tissue act as a hormone source?

A

Adipose tissue itself produces many hormones, primarily leptin and adiponectin which are satiating/anorexigenic, inflammatory/anti-inflammatory.

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7
Q

Parts of the pituitary gland

A
  1. Neurohypophysis (posterior)
  2. Adenohypophysis (anterior)
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8
Q

Neurohypophysis

A

Neuroectoderm origin. Made of descending axons from supraoptic/paraventricular hypothalamic nuclei. Releases ADH, oxytocin.

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9
Q

Pituicytes

A

Resident glia of the neurohypophysis. Control hormone release to surrounding capillaries.

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10
Q

Structures of the neurohypophysis

A
  1. Median eminence
  2. Infundibular stalk
  3. Pars nervosa
  4. Herring bodies (axonal endings dilated with NTs)
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11
Q

Adenohypophysis

A

Originates from oral ectoderm. Responds to hypothalamic hormones released to the hypophyseal portal system.

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12
Q

Cells of the adenohypophysis

A

Pars distalis
1. Acidophils -> somatotropin, prolactin
2. Basophils -> ACTH, TSH, FSH, LH, β-endorphin
3. Chromophobes

Pars intermedia cells -> melanocyte-stimulating hormone

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13
Q

Structures of the adenohypophysis

A
  • Pars tuberalis
  • Pars intermedia
  • Pars distalis
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14
Q

Where is the pituitary located?

A

The pituitary is at the base of the brain, encapsulated by sphenoid bone in the sella turcica cavity with an apical stalk to the hypothalamus.

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15
Q

Thyroid gland

A

Composed of many thyroid follicles, which are epithelial-enclosed accumulations of colloid. Uptakes iodine from blood, sequesters with thyroglobulin (colloid, Tyr-containing). Mono-iodin. Tyr + di-iodin. Tyr (MIT/DIT) sum for T3, T4.

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16
Q

Cells of the thyroid gland

A

Majority: follicular cells containing thyroglobulin -> T3, T4
Minority: parafollicular cells aka C-cells -> calcitonin

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17
Q

Parathyroid gland

A

Primarily made of chief cells -> PTH, also contains oxyphil cells

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18
Q

Pineal gland

A

Gland in brain with pinealocytes producing melatonin. Regulates circadian sleep/wakefulness. Accumulates concretions of corpora arenacea (brain sand)

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19
Q

Endocrine pancreas

A

Islets of Langerhans. In order of decreasing frequency, cells include:
β cells -> insulin
α cells -> glucagon
γ cells aka PP cells -> pancreatic polypeptide
δ cells -> somatostatin
Other cells -> ghrelin (hunger)

20
Q

Adrenal glands

A

Consists of 2 embryological parts: cortex + medulla (mesenchyme + NCCs aka ectoderm). Produces corticosteroids, epi, and NE

21
Q

Adrenal cortex layers

A

Outer to inner:
1. Zona glomerulosa -> mineralocorticoids (aldosterone)
2. Zona fasciculata -> glucocorticoids (cortisol)
3. Zona reticularis -> androgens

22
Q

Adrenal medulla

A

Derived from neural crest cells. Contains 2 types of chromaffin cells producing epi and NE. Has dual blood supply from cortical capillaries and long cortical aka medullary arteries (arterioles).

23
Q

DNES

A

Diffuse Neuroendocrine System. Refers to scattered cells in other organs that release endocrine hormones, especially in the GI system.

24
Q

APUD cells

A

Amine Precursor Uptake + Decarboxylation cells. Part of DNES, produce polypeptide hormones from amine precursors via decarboxylases.

25
Q

Sex hormones

A

Includes estrogen, progesterone, testosterone. Can be free or carrier bound; primarily produced by Leydig cells in testis or ovarian follicle granulosa cells/corpus luteum.

26
Q

Sex hormone carriers

A
  1. Sex Hormone Binding Globulin (SHBG)
  2. Albumin
  3. Corticosteroid Binding Globulin (CBG) aka transcortin
27
Q

Estrogens

A

4 significant types:
1. E1 (estrone)
2. E2 (estradiol)
3. E3 (estriol)
4. E4 (estetrol)

28
Q

Sex hormone receptors

A
  1. Estrogen Receptors (ERs, α/β = nuclear receptors)
  2. Androgen receptors (for t-sterone)
  3. Nuclear progesterone receptors (for progesterone, types A/B/C)
29
Q

How is sex hormone production controlled?

A

Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates FSH/LH secretion by ant. pituitary basophils. Inhibin-B inhibits FSH/LH release (negative feedback).

30
Q

Menstrual cycle

A

Cyclical hormone variation due to temporary loss of inhibin-B negative feedback.

31
Q

Major endocrine axes

A
  1. HPA (adrenal)
  2. HPT (thyroid)
  3. HPG (gonads)
  4. HPS (somatic)
  5. HPP (prolactin)
32
Q

Characteristics of endocrine cells

A

Endocrine cells secrete hormones basally, i.e. into the blood, in order to act at a distance.

33
Q

Common endocrine features

A
  1. Fenestrated capillaries (even in pituitary despite BBB)
  2. Disturbed polarity (lack of apical domain due to no lumen)
  3. Carrier proteins for blood transmission
34
Q

Hormone types by gland origin

A

Protein hormones come from epithelial origin glands
Steroid hormones come from mesenchymal origin glands

35
Q

Releasing/inhibiting factors

A

Positive/negative feedback in the endocrine system

36
Q

HPA axis

A

H: Corticotropin releasing hormone
P: adrenocorticotropic hormone (ACTH), corticotrophs
A: cortisol, etc., adrenals

37
Q

HPT axis

A

H: Thyroid Releasing Hormone (TRH)
P: Thyroid Stimulating Hormone (TSH), thyrotrophs
T: T3/T4 from thyroid.

38
Q

HPG axis

A

H: GnRH
P: LH/FSH, gonadotrophs
G: estrogen/estradiol/progesterone from ovaries, testosterone from testes; inhibin from both.

39
Q

HPS axis

A

H: GnRH
P: Growth Hormone from somatotrophs
S: Various target organs e.g. liver; somatostatin inhibits GnRH

40
Q

HPP axis

A

H: Dopamine
P: Prolactin from lactotrophs
P: Lactation by mammary glands

41
Q

Hypothalamus

A

Major parts: supraoptic + paraventricular nuclei (SON, PVN)
2 projections to the pituitary:
1. Magnocellular (axons to neurohypophysis)
2. Parvocellular (releasing hormone secretion to adenohypophysis via pituitary portal circulation)

42
Q

Goiter

A

Enlarged thyroid due to iodine deficiency

43
Q

Graves’ disease

A

Autoimmunity to TSH receptors.

44
Q

Endocrine organ aging

A

Fibrosis normally occurs with age from collagens and other ECM molecules.

45
Q

Testis

A

FSH -> Sertoli cells -> inhibin-B, Androgen Binding Protein (ABG), Anti-Müllerian Hormone

LH -> Leydig cells -> t-sterone

46
Q

Sex endocrine organ development

A

Ovary/testis develop from bipotential mesonephric mesenchyme. Testis req. testis-determining factor (TDF) from SRY.

Mesonephric (Wolffian) duct -> epididymis, vas deferens
Paramesonephric (Müllerian) duct -> oviduct, uterus
DHT drives external male pattern genitalia.

47
Q

Endocrine organs embryonic origins

A

Surface ectoderm -> ant. pituit.
Neural ectoderm -> hypothal., post. pituit., pineal
Endoderm -> pancreas, thyroid, parathyroid
Mesoderm -> ovary/testis, adrenal cortex
Ectomesenchyme (NCCs) -> adrenal medulla

COT Part II (12 decks)

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