Endocrine Histology

Question 1

Embryological development of pituitary gland

Answer 1

• Anterior pituitary
  
  • Derived from outgrowth of oral ectoderm called Rathke’s pouch (pharyngeal ectoderm)
• Posterior pituitary
  
  • Extension of brain and hypothalamus (neuroectoderm)
  • No nuclei found here, only axons

Question 2

Basic structure of pituitary gland

Answer 2

• Anterior pituitary - 3 subunits
  
  • Pars distalis: composed of hormone secreting cells
  • Pars tuberalis: forms sheath around infundibulum
  • Pars intermedia: remnant of Rathke’s pouch, divides pars distalis and pars nervosa
• Posterior pituitary - 3 subunits
  
  • Pars nervosa (infundibular process): extension of hypothalamus
  • Infundibulum (stalk): contains portal vessels connecting hypothalamus to pars distalis
  • Median eminence: contains axons on the way to pars nervosa

Question 3

Blood supply to hypothalmus/pituitary

Answer 3

• Vital to the function of the hypothalamic-pituitary system
• Superior hypophyseal artery supplies:
  
  • Median eminence
  • Pars tuberalis
  • Infundibulum
• Inferior hypophyseal artery supplies:
  
  • Pars nervosa
• Pars distalis: no dedicated arterial blood supply
  
  • Superior hypophyseal artery –> primary capillary plexus in median eminence/infundibulum –> hypophyseal portal veins –> pars distalis
  • Drained by hypophyseal veins
• Allows releasing factors secreted by hypothalamic nerves (in median eminence, infundibulum) to be delivered to pars distalis, allowing them to act on AP cells
• AP is most richly vascularized of all mammalian tissues
• Retrograde flow exists between pituitary and hypothalamus (direct feedback between pit hormones and neuroendocrine control centers)

Question 4

AP cells and hormones released

Answer 4

• Somatotrophs: growth hormone (GH)
• Lactotrophs: prolactin (PH)
• Gonadotrophs: follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Corticotrophs: adrenocorticotropic hormone (ACTH)
• Thyrotrophs: thyroid-stimulating hormone (TSH)

Question 5

Histologic classification of AP cells (3 classes)

Answer 5

• Acidophils: acid dye staining
  
  • Somatotrophs and lactotrophs
• Basophils: basic staining cells
  
  • Gonadotrophs, corticotrophs, thyrotrophs
  • B-FLAT: basophils secrete FSH, LH, ACTH, TSH
• Chromophobes: non-staining, lack secretory granules

Question 6

Structure and function of adrenal gland (2 main areas)

Answer 6

• Cortex: derived from mesenchymal tissues; made up of 3 regions, each releases specific kind of steroid hormone
  
  • Zona glomerulosa: mineralocorticoids (aldosterone)
  • Zona fasciculata: glucocorticoids
  • Zona reticularis: androgens
  • GFR: Salt –> sugar –> sex
• Medulla: releases AA hormones (epi and norepi), controlled by sympathetic and parasympathetic NS
  
  • Derived from neural crest
  • Also regulated by levels of steroid hormones from cortex (hormones migrate to medulla via capillary system)

Question 7

Blood supply to adrenal glands

Answer 7

• Enters via capsular arteries, heads to medulla (through cortex) via medullary arteries and branches into capillaries
• Capsular arteries also give rise to subcapsular arterial plexus –> feeds cortex
• All blood drained from adrenal gland via suprarenal vein

Question 8

Basic structure/function of thyroid gland

Answer 8

• Thyroid produces 2 types of hormones
  
  • Thyroid hormone: produced by majority of the cells
  • Calcitonin: decreases Ca2+ (“tones down calcium”), thought to fine-tune Ca levels (PTH is critical)
• Gland made up of follicles –> single layer of epithelium surrounds colloid
• Colloid droplet: hormone storage (fatty treasure chest)

Question 9

Synthesis of thyroid hormone

Answer 9

• Tyrosine amino acid taken up by cell –> thyroglobulin synthesized
• Iodide taken up by cell –> iodine, secreted to colloid with thyroglobulin
• In colloid: thyroglobulin tyrosine molecules iodinated, put back into cell, modified to final form and secreted into blood

Question 10

Structure/function of parathyroid gland

Answer 10

• Made up of 4 separate glands on posterior aspect of thyroid
• Secrete parathyroid hormone (PTH): helps to regulate blood calcium levels (increases)
• Works at bone, gut, and kidney

Question 11

Cell types (2) in thyroid gland and hormones they produce

Answer 11

• C-Cells: produce calcitonin
  
  • Minority of cells in thyroid gland
• Follicular cells: produce T4 (tetraiodothyronine/thyroxine) and T3 (triiodothyronine)
  
  • Majority of cells

Question 12

Structure and function of pineal gland

Answer 12

• Sits towards the back of corpus callosum
• Made up of pinealocytes (neurons that produce melatonin)
• Accumulated calcium salts in pineal gland appear as “brain sand” on plain films and CTs
• Melatonin increases at night, decreases during the day
• Pineal gland linked to visual system and hypothalamus
  
  • Thought to be involved in diurnal cycle