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*USMLE Step 1, Organ Systems > Endocrine > Flashcards

Endocrine Flashcards

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USMLE® Step 1 flashcards
1
Q

Thyroid gland

- Embryologic origin

A

The thyroid gland develops from an ENDODERMAL thickening in the FLOOR of the PRIMORDIAL PHARYNX, which soon thereafter forms a small outpouching called the THYROID PRIMORDIUM.

Recall - The primordium of the esophagus and oropharynx develops from the dorsal aspect of the cranial/upper foregut.

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2
Q

During development, the thyroid gland is connected to the tongue by what structure?

A

Thyroglossal duct

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3
Q

By ___ weeks gestation, the thyroglossal duct has normally degenerated and disappeared.

What is the embryologic remnant of the thyroglossal duct?

A

By SEVEN weeks gestation, the thyroglossal duct has normally degenerated and disappeared.

Foramen cecum - Posterosuperior surface of the tongue

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4
Q

What TWO embryologic processes are essential in the development of the thyroid gland?

A
  1. Migration - The developing thyroid migrates/descends down the neck to its final anatomical location.
  2. Fusion - Fusion is a process when 2 cells from different embryologic origins fuse to form an organ system. Thyroid gland development involves fusion of THYROID FOLLICLES and PARAFOLLICULAR C-CELLS
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5
Q

What TWO embryologic processes are essential in the development of the thyroid gland?

A
  1. Migration - The developing thyroid migrates/descends down the neck to its final anatomical location.
  2. Fusion - Fusion is a process when 2 cells from different embryologic origins fuse to form an organ system. Thyroid gland development involves fusion of THYROID FOLLICLES and PARAFOLLICULAR C-CELLS.
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6
Q

Embryologic derivation:

  • Thyroid follicles
  • Parafollicular C-cells
A

Thyroid follicles - Endodermal thickening in the floor of the primordial esophagus/pharynx (dorsal aspect of the cranial foregut)

Parafollicular C-cells - 4th branchial pouch

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7
Q

Thyroglossal duct cyst develops 2/2 persistent ___ that presents clinically as:

Branchial cleft cyst develops 2/2 persistent ___ that presents clinically as:

A

Thyroglossal duct cyst develops 2/2 persistent thyroglossal duct - Presents as painless, progressively enlarging, MOVEABLE mass that usually moves with swallowing or protrusion of tongue.

Branchial cleft cyst develops 2/2 persistant cervical sinus - Presents as a LATERAL NECK mass.

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8
Q

Thyroglossal duct cyst develops 2/2 persistent ___ that presents clinically as:

Branchial cleft cyst develops 2/2 persistent ___ that presents clinically as:

A

Thyroglossal duct cyst develops 2/2 persistent thyroglossal duct - Presents as painless, progressively enlarging, MOVEABLE mass that usually moves with swallowing or protrusion of tongue.

Branchial cleft cyst develops 2/2 persistant cervical sinus - Presents as a LATERAL NECK mass.

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9
Q

What are the 2 components of the fetal adrenal gland?

A
  1. Inner active fetal zone

2. Outer dormant/inactive adult zone

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10
Q

Part of adrenal gland immature when baby born? When functional?

A

Zona reticularis of adrenal cortex is immature at birth and not fully developed until 3 years after birth.

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11
Q

Mechanism by which fetus produces androgens in utero?

A

Fetus requires PLACENTAL 3β-hydroxysteroid dehydrogenase enzyme to convert pregnenolone to progesterone for synthesis of androgens.

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12
Q

Adrenal gland

  • Embryologic derivation of cortex
  • Embryologic derivation of medulla
A

Cortex - Mesenchyme/mesoderm

Medulla - Neuroectoderm (neural crest cells)

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13
Q

ADRENAL CORTEX

- 3 layers and corresponding secretory products

A

Zona glomerulosa
- Mineralocorticoids (ALDOSTERONE)

Zona fasciculata
- Glucocorticoids (CORTISOL)

Zona reticularis
- Androgens

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14
Q

ADRENAL CORTEX

- 3 layers and corresponding secretory products

A

Zona glomerulosa
- Mineralocorticoids (ALDOSTERONE)

Zona fasciculata
- Glucocorticoids (CORTISOL)

Zona reticularis
- Androgens

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15
Q

ADRENAL MEDULLA

- Cell type and corresponding secretory product

A

Chromaffin cells
- Catecholamines (epinephrine, NE)

Chromaffin cells are modified postganglionic sympathetic neurons that receive sympathetic input (neuroendocrine cells).

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16
Q

Adrenal tumors

  • MCC in children
  • MCC in adults
A

Children - Neuroblastoma (medulla)

Adults - Pheochromocytoma (medulla)
–> Episodic HTN

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17
Q

Venous drainage

  • Left adrenal
  • Right adrenal
A

Left: Left adrenal vein to left renal vein to IVC

Right: Right adrenal vein to IVC

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18
Q

SYMPATHETIC PREGANGLIONIC NEURONS release [?], which activates [?] receptors on postganglionic neurons.These postganglionic neurons release [?] to activate [?] receptors on target tissues. What are 2 exceptions to this principle?

A

Sympathetic preganglionic neurons release ACh, which activates AChR receptors on postganglionic neurons.These postganglionic neurons release NE to activate ADRENERGIC receptors on target tissues.

Exceptions:

1) Postganglionic neurons that innervate sweat glands release ACh, not NE.
2) Chromaffin cells of adrenal medulla - Innervated by preganglionic sympathetic nerons that release ACh and bind AChRs on chromaffin cell surface. However, these cells are MODIFIED postganglionic neurons. They release catecholamines (80% epi, 20% NE) directly into blood stream to activate adrenergic receptors in target tissues.

19
Q

PREGANGLIONIC SYMPATHETIC NEURONS release [?], which activates [?] receptors on postganglionic sympathetic neurons, which subsequently release [?] to activate [?] receptors on target tissues.

What are the 2 exceptions to this principle?

A

Preganglionic sympathetic neurons release ACh, which activates AChR receptors on postganglionic sympathetic neurons, which subsequently release NE to activate ADRENERGIC receptors on target tissues.

Exceptions:

1) Postganglionic neurons that innervate sweat glands release ACh, not NE.
2) Chromaffin cells of adrenal medulla - Innervated by preganglionic sympathetic nerons that release ACh and bind AChRs on chromaffin cell surface. However, these cells are MODIFIED postganglionic neurons. They release catecholamines (80% epi, 20% NE) directly into blood stream to activate adrenergic receptors in target tissues.

20
Q

Adrenal medulla releases catecholamines (epi, NE) that bind adrenergic receptors in what 4 locations in body to mediate acute stress response?

A

Heart, lungs, liver, and skeletal muscle

21
Q

Adrenal medulla releases catecholamines (epi, NE) that bind adrenergic receptors in what 4 locations in body to mediate acute stress response?

A

Heart, lungs, liver, and skeletal muscle

22
Q

Anterior pituitary gland

  • Embryologic origin
  • Hormones
A

Anterior pituitary gland = Adenohypophysis

Embryology - Derived from an UPGROWTH of oral ectoderm (Rathke’s pouch)

FLAT PiG

FSH, LH, ACTH, TSH, prolactin, GH

23
Q

Chromophils are anterior pituitary cells containing granules that react with acidophilic/basophilic stains.

Acidophilic cells

  • Hormones present in granules
  • Color staining
A

ACIDOPHILS = PiG hormones

Prolactin, GH

ACIDOPHILS stain pink/red

24
Q

Chromophils are anterior pituitary cells containing granules that react with acidophilic/basophilic stains.

Basophilic cells

  • Hormones present in granules
  • Color staining
A

BASOPHILS = FLAT hormones

FSH, LH, ACTH, TSH

BASOPHILS stain BLUE (blue/purple = PAS+)

“B-FLAT”

BASOPHILS - FSH, LH, ACTH, TSH

25
Q

Chromophobes aree anterior pituitary cells lacking granules that react with acidophilic/basophilic stains.

Chromophobic cells

A
  1. Stromal cells

2. DEGRANULATED CHROMOPHILS

26
Q

Posterior pituitary gland

  • Embryologic origin
  • Hormones
A

Posterior pituitary gland = Neurohypophysis

Embryology - Derived from a DOWNGROWTH of neuroectoderm

ADH/vasopressin, oxytocin

27
Q

ADH/vasopressin

  • Site of synthesis
  • Secretory granule co-product
A

ADH/vasopressin

SUPRAOPTIC (and paraventricular) nucleus of the hypothalamus

Pro-hormone contains ADH/vasopressin and NEUROPHYSIN II

ADH - 2 names, hypothalamic nuclei has 2 syllables, neurophysin 2

28
Q

Oxytocin

  • Site of synthesis
  • Secretory granule co-product
A

Oxytocin

PARAVENTRICULAR (and supraoptic) nucleus of the hypothalamus

Pro-hormone contains oxytocin and NEUROPHYSIN I

29
Q

Oxytocin

  • Site of synthesis
  • Secretory granule co-product
A

Oxytocin

PARAVENTRICULAR (and supraoptic) nucleus of the hypothalamus

Pro-hormone contains oxytocin and NEUROPHYSIN I

30
Q

CRH

- Function

A

Hypothalamus releases corticotropin releasing hormone (CRH), which stimulates ACTH

POMC = ACTH pro-hormone

POMC - ACTH, beta-lipotropin, alpha- and beta-MSH, beta-endorphin, met-enkephalin

31
Q

GHRH

- Function

A

Hypothalamus releases growth hormone releasing hormone (GHRH), which stimulates GH

32
Q

GnRH

- Function

A

Hypothalamus releases gonadotropin releasing hormone (GnRH), which stimulates FSH, LH

33
Q

CRH

- Function

A

Hypothalamus releases corticotropin releasing hormone (CRH), which STIMULATES ACTH

POMC = ACTH pro-hormone

POMC - ACTH, beta-lipotropin, alpha- and beta-MSH, beta-endorphin, met-enkephalin

34
Q

GHRH

- Function

A

Hypothalamus releases growth hormone releasing hormone (GHRH), which STIMULATES GH

35
Q

GnRH

- Function

A

Hypothalamus releases gonadotropin releasing hormone (GnRH), which STIMULATES FSH, LH

36
Q

TRH

- Function

A

Hypothalamus releases thyroid releasing hormone (TRH), which STIMULATES TSH AND PROLACTIN (!)

37
Q

Dopamine

- Function

A

Hypothalamus releases dopamine, which INHIBITS prolactin

Dopamine = prolactin inhibiting factor (PIF)

38
Q

Somatostatin

- Function

A

Hypothalamus releases somatostatin, which INHIBITS GH and TSH

39
Q

Somatostatin

- Function

A

Hypothalamus releases somatostatin, which INHIBITS GH and TSH

Somatostatin = somatotropin release inhibiting factor (SRIF)

GH = somatotropin

[GH and TSH work synergistically in bone development]

40
Q

Somatostatin

- Function

A

Hypothalamus releases somatostatin, which INHIBITS GH and TSH

Somatostatin = somatotropin release inhibiting factor (SRIF)

GH = somatotropin

[GH and TSH work synergistically in bone development]

41
Q

Anterior pituitary

  • Glycoprotein hormones (3)
  • Hormone subunits
A

LH, FSH, TSH

Alpha- and beta-subunits

Alpha subunit is common to all glycoproteins, whereas beta subunit confers hormone specificity

LH, FSH, TSH SHARE ALPHA SUBUNIT WITH hCG (!)

42
Q

Anterior pituitary

  • Glycoprotein hormones (3)
  • Hormone subunits
A

LH, FSH, TSH

Alpha- and beta-subunits

Alpha subunit is common to all glycoproteins, whereas beta subunit confers hormone specificity

LH, FSH, TSH SHARE ALPHA SUBUNIT WITH hCG (!)

43
Q

CRH stimulates anterior pituitary to release ACTH

- Additional site of action

A

CRH also stimulates INTERMEDIATE LOBE of the pituitary gland to release MSH

*USMLE Step 1, Organ Systems (3 decks)

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