Endocrine Devo

Question 1

2 most common problems of abnormal thyroid gland embryologic genesis?

Answer 1

1. Thyroglossal duct cyst–cyst can grow if the thyroglossal duct does not disappear
   - presents as anterior midline mass on neck
2. Lingual thyroid–thyroid did not migrate down thyroglossal duct
   - presents as mass at base of tongue

Question 1

Pharyngeal hypophysis

Answer 1

Congenital abnormality:

Remnants of Rathke’s pouch that remain in roof of pharynx after birth.

Question 2

Foramen cecum

Answer 2

This is the midline fold at the base of the tongue. In the embryo, this is where thyroid tissue first develops before traveling via the thyroglossal duct to its mature position.

Lingual thyroid (congenital abnormality) is found here.

Question 2

Adrenal cortex development:

-describe, from embryo to post-birth

Answer 2

1. Fetal Adrenal Cortex
   - formed by initial wave of epithelial cells, and is 20 times larger than definitive cortex. Relies on placenta to produce progesterone and androstenedione b/c it lacks 3-beta HSD dehydrogenase.
   - involutes starting at birth and completely regresses by months 6-12.
2. Definitive Adrenal Cortex
   - formed by 2nd wave of proliferating epithelial cells, after birth.

Question 3

Thymus:

-arises from what pharyngeal pouch?

Answer 3

• inferior portion of pharyngeal pouch 3.
• The thymus tissue migrates inferiorly from original location

Question 4

Neural crest cells:

-What do they form in the endocrine system? (2)

Answer 4

1. Adrenal medulla
2. Parafollicular C cells in the thyroid (secrete calcitonin)

Question 5

Adrenal gland cortex vs medulla

-what are the origin embryonic tissues?

Answer 5

1. Cortex–mesoderm
2. medulla–ectoderm (neural crest cells–chromaffin cells)

Question 5

Ecto, meso, or endoderm? (may contain more than 1)

1. pituitary
2. thyroid
3. parathyroid
4. adrenal

Answer 5

1. ectoderm (anterior–oral ectoderm, posterior–neuroectoderm)
2. endoderm (parafollicular C cells are neural crest ectoderm)
3. endoderm
4. mesoderm (cortex), ectoderm neural crest (medulla)

Question 5

Embryo does not develop 3rd and 4th pharyngeal pouches

• what’s this called
• how are parathyroid and thyroid affected?

Answer 5

DiGeorge syndrome

• parathyroid missing (develops from pouches 3/4)
• thyroid normal b/c not developed from pouches 3/4 (except for parafollicular C cells from pouch 4, which serve no real function secreting calcitonin)

CATCH 22

Cardiac abnormalieis

Abnormal facies

Thymic aplasia (thymus from pouch 3)

Cleft palate

Hypocalcemia (no PTH)

22p11

Question 7

Origin of thyroid gland components:

1. thyroid follicular cells
2. parafollicular cells
3. parathyroid gland prinicipal cells

Answer 7

1. endoderm (thyroid diverticulum)
2. neural crest cells from ultimopharyngeal body
3. Endoderm (dorsal wing of pharyngeal pouches 3, 4)

Question 8

Craniopharyngeoma

-formed from what tissue

Answer 8

Formed from oral surface ectoderm of Rathke’s pouch.

aka “Rathke’s pouch tumors”

Question 9

Pineal gland

• what does it secrete
• how does this hormone affect other hormones?

Answer 9

• Melatonin
• It has inhibitory effect on anterior pituitary secretion of LH, FSH

Question 10

Parathyroid glands:

-describe embryogenesis (superior vs inferior glands)

Answer 10

• Derived from endoderm and migrate downwards
• Superior: migrates from 4th pharyngeal pouch
• Inferior: migrates from 3rd pharyngeal pouch

Question 11

Rathke’s pouch:

-abnormal growth can cause what 2 problems?

Answer 11

1. Pharyngeal hypophysis–remnants of pouch remain in roof of pharynx
2. craniopharyngeoma–tumor of Rathke’s pouch tissue

Question 12

Rathke’s pouch

• what is it
• aka what

Answer 12

1. Diverticulum formed from oral suface ectoderm. This joins with the neuroectoderm and eventually becomes the anterior pituitary.
2. aka Hypophyseal Diverticulum

Question 14

Anterior and posterior pituitary gland

-what are their tissue precursors and the structures they arise from

Answer 14

Anterior: Oral surface ectoderm, formed from Rathke’s pouch (hypophyseal diverticulum)

Posterior: neuroectoderm (infundibulum)

Question 15

Congenital Adrenal Hyperplasia

Answer 15

• Group of hereditary disorders in which an enzyme in the steroidogenesis pathway is missing in adrenal cortex.
• 21 alpha hydroxylase deficiency is most common. results in lack of glucocorticoid and mineralocorticoid activity and excess androgens.
• classic form: baby born with hypotension, hyponatremia, ambiguous genitalia (females)

Question 17

Exocrine vs endocrine glands

-how do they develop differently

Answer 17

-Both start as epithelial cells that bud into underlying mesenchyme.

Exocrine: Duct remains

Endocrine: Duct disappears and blood vessels connect with glandular cells

Question 18

Ultimopharyngeal bodies

Answer 18

• precursors of parafollicular C cells in thyroid
• they are neural crest cells that arise from the inferior portion of pharyngeal pouch 4

Question 20

How would a craniopharyngeoma cause these problems?

1. anosmia
2. diabetes insipidus
3. facial paralysis
4. growth hormone deficiency
5. visual problems

Answer 20

Mass effect, pushing against local structures:

1. olfactory nerve
2. hypothalamus/posterior pit–loss of ADH secretion
3. Facial nerve
4. anterior pit
5. optic chiasm

Question 21

What is derived from:

1. 3rd pharyngeal pouch, dorsal
2. 3rd pharyngeal pouch, ventral
3. 4th pharyngeal pouch, dorsal
4. 4th pharyngeal pouch, ventral

Answer 21

1. parathyroid glands, inferior
2. Thymus
3. parathyroid glands, superior
4. parafollicular C cells (secrete calcitonin)–neural crest cells

Question 22

describe Thyroid gland embryogenesis

Answer 22

Endoderm forms a midline diverticulum at the pharyngeal floor (at pharyngeal pouch 2), which descends inferiorly, with cells migrating towards final thyroid gland location.

This diverticulum becomes the thyroglossal duct, which typically disappears by birth

Question 23

What does the infundibulum give rise to?

(3)

Answer 23

1. median eminence
2. pituitary stalk
3. neural lobe (post pituitary)

Question 24

What does the Hypophyseal diverticulum (Rathke’s pouch) give rise to?

1. anterior wall
2. superior extension
3. posterior wall

Answer 24

1. Distal lobe (anterior pituitary)
2. Tuberal lobe
3. intermediate lobe

Question 25

What week of embryo does thyroid tissue start migrating from base of tongue?

Answer 25

week 4

Question 26

Chromaffin cells - what are they - appearance on histology

Answer 26

Neural crest cells that migrate to form the adrenal medulla -They stain brown because of presence of catecholamines. ("chromium affinity" cells)