Lecture 15 - Anatomy (Development of Endocrine Organs) PDF

DEVELOPMENT OF THE ENDOCRINE SYSTEM Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of...

DEVELOPMENT OF THE ENDOCRINE SYSTEM Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atlas & Textbook [email protected] Goal: To understand how development of endocrine glands influences their adult structure and function Outline: Outcomes: Origins & development of endocrine Understand and describe the developmental origins of the endocrine organs organs shown in this lecture. Pituitary gland Describe how the development of an endocrine organ effects its function and possible pathological presentations. Pineal gland Pharyngeal arch glands Adrenal gland Endocrine pancreas How embryonic endocrine organs differ Endocrine system overview Endocrine organs produce hormones and/or molecules that travel from their site of synthesis to a target cell, via the blood stream usually ① Hormonal postal service Organs: Hypothalamus Pituitary gland Pineal gland Thyroid Parathyroid gland Thymus (?) not this lecture Adrenal gland Pancreas Gonads Placenta ✗ notthis lecture PART 1: Development Carnegie stage 13: 28-32 days GA https://www.3dembryoatlas.com/blank Pituitary Gland: Rathke’s pouch ← develops with surface ectoderm Stomodeum and the oro Stomodeum: invagination of surface ectoderm Lining of the mouth is derived from both ectoderm & membrane ( aµ Pituitary gland (aka cerebral Hypophysis, Hypo: Under, Phusis: growth) B Found at anterior part of 3rd ventricle → invaginates.in (lining mouth) closes off to what will become the Posterior pituitary: Derived from forebrain pharyx Thus, neural tube ectoderm looks like the rest of the brain in appearance Full of neurons connected to hypothalamic neurons (infvndibulum) A e becoming anterior Anterior pituitary : Surface ectoderm of Rathke’s pouch pituitary gland Glandular appearance, more similar to what you’d expect from surface ectoderm ☐ " adenohypophysis " - like skin glands ztt E placodes roof of nasal cavity F- 0 8 weeks very thin cerebrum / / pituitary :¥÷¥µ - remnant of Rathke's Pouch neural tissue of the developing brain :* ↓nF surface ectoderm - mandible - maxillary - chin → mouth (base of tongue) → nasal cavity endoderm tongue junction -. - nasopharyx - oral pharyx  Pineal Gland: The ‘3rd eye’? possible connection to circada in rhythm & seasonal mood disorders in lizards ' lol  Pineal Gland: The ‘3rd eye’? Pineal gland: means pine cone gland AKA Cerebral epiphysis 3rd Ventricle Common evolutionary origin with the photoreceptor genes of the retina No longer photoreceptive in mammals But neurologically linked to the retina’s photoreceptors… Suprachiasmatic nucleus  Paraventricular nuclei  Spinal cord  Sup cervical ganglion  Pineal gland ↳ no need to learn this pathway What does it do? Secretes melatonin Why? Helps set circadian rhythm (~12hr Light/dark cycle)? Commonly becomes calcified (can occur from 2yoa) 40% of 17yo Americans have calcified Pineal glands pineal gland Insomnia? Corpora arenacea (Means body sandy, or brain sand), show up on X-ray Secretions begin to regress from puberty Melatonin can inhibit hypothalamic GnRH secretion (Gonadotrophic Releasing Hormone) Possibly via GnIH sensitivity to melatonin? (Gonadotrophic Inhibiting Hormone) Precocious puberty associated with pineal tumours ?⃝ Calcified Pineal Glands ~65% of people in SA between the ages of 2-87 have calcification in their pineal gland Correlates strongest with age and is more common in females Radiopaedia.org  Visualising the pharyngeal arches Used to form gill arches Fusion of gills creates ‘clefts & pouches’ Clefts: Exterior  surface ectoderm Most notable is the external ear (1st cleft) Pouches: Interior  Origin of: Palatine tonsils ~ Parathyroid - arm Thymus tongue C-cells of Thyroid Not the actual thyroid itself develops from the tongue Development of the thyroid Origin: Foramen caecum of the tongue where tongue develops from Migrates through the tongue & into the neck ‘Thyroid diverticulum’  ‘thyroglossal duct’ (closes off) I. Arrests just inferior to thyroid cartilage (thyroid: shield) 74ᵗʰ ↳ develops towards thorax Importance of migration: Extra ‘Pyramidal’ lobe (?), aligned with the thyroglossal duct remnant Thyroid cancer in the tongue? thyroidglandcellsthatremaininthetong.ve Orin some component of the thyroid gland cell duct becoming cancerous Thyroid follicles functional at 10-11wk GA Essential in maturation of the lungs to a mature state ¥ thyroid hormone ↓ TH accelerates alveolar septation & ↑ compliance ↓ ↓ Low maternal iodine  impacts fetal thyroid  abnormal neural hormone development ↑TH in late fetal period stimulates development of brown fat Mechanism for non-shivering thermogenesis fullof mitochondria TH assisting lung development is ancient Axolotls: Mexican salamanders who live(d) in areas of seasonal rain, which fluctuates water quality and availability. They have external gills, can breathe through their skin, and can develop lungs! failure ofthe duct to completely close They usually eat worms, insects and small fish (all low in iodine). Unless…  Feotus Adult Gland of the neck & upper thorax I r,drum clefts Pouches -- ' """ =. surface ectoderm endoderm F ⇐ * ÷ É: ÷ : ÷ ; % ÷ É ; ÷ É ;É " "" """ "" " 1st 1st [email protected]. * *¥É¥H ÷H÷÷÷÷÷::÷:÷÷÷÷ 2nd "÷, ". ¥↳*" -.." CNVII Palatine 2nd (2 3rd iii. non - pathological : É ! £ É : ÷ ÷÷ cN☒ " """ " "" 3rd in neck go.no, bulge ¥%%¥%¥m p, ÷ :*. , p, , µ, ,,, ÷÷:: ÷;÷É÷÷ ::** 4th L I # pyr%mjdal ' gq superior c 4th ↳ '. (4 " ' glands 6th § y s←. 5th ?;§ - body ↓ " """ of the release calcitonin 6th L thyroid (↓µ◦◦d[calcium]) Migrated thymus ?⃝ ?⃝ ?⃝ Pharyngeal arch contributions Parathyroid: 4 rice grain sized cell condensations 2 Inferior: From 3rd pouch (not a mistake) 2 Superior: From 4th pouch (not a mistake) P1 P2 Thymus: From 3rd pouch C-cells of thyroid: From 4th pouch (Aka from Ultimobranchial body) ¥q. Development of Adrenal Glands Develop from urogenital ridge & only cleaved from the gonad once primordial germ cells enter the gonad Dual origin: Neural crest cells & Lateral plate mesoderm °°°°° Neural crest cells: Become the medullary cells AKA chromaffin cells go.gg @ ;÷o. 008 go :&:&:&:& &¥:&:& They stained yellow with chromium salts ; They are specialised ‘post-synaptic autonomic nerve cells’ "" Pre-synaptic sympathetic nerve release ACh directly on chromaffin cells %:* Synthesise & secrete adrenaline & Nor Adrenaline.gg 0%8%0 *: LP-mesoderm: Cortex, via 2 waves of mesothelial cells 1st: Mesothelial cells of the coelom differentiate, proliferate & migrate ← % to form the fetal cortex (4-5th week) 0 disappears _ a couple months after birth É% 00£ 2nd wave: Same again, but this time forming tissues that become the definitive adult cortex (6-7th week) Fetal cortex ≠ Adult cortex  Why is it important to consider fetal vs adult cortex? Fetal adrenal gland is developmentally critical → most important Cortex secretes DHEA (dehydroepiandrosterone)  converted to oestradiol by the placenta (endocrine organ!) Regulates maturation of the lungs, GIT & regulate parturition and other perinatal maternal adaptations Corpus luteum  placenta  fetal adrenal glands ↳ eg. progesterone estrogen , Definitive cortical cells encapsulate the fetal cortex & developing medulla (8-10th week) 1. Zona Glomerulosa (‘ball of thread’): 3rd trimester  aldosterone is critical in postnatal salt preservation 2. Zona Fasciculata (‘small bundle’): 2nd trimester (parallel to another) → secretes primarily cortisol one → not in feotus / neonate only in adult a ~ 3. Zona reticularis (‘net-like’): not definitively present until 3yoa Fetal cortex regresses in the first 2 months of life, whilst the adult cortex continues to grow Development of the ENDOCRINE pancreas ↳ is active in a foetus Develop from foregut epithelium Proliferate and form masses of stratified cells Creates microlumens that coalesce to form branched lumens Common embryonic tube forming mechanism Some cells didn’t coalesce into lumen rtb from delaminating endocrine cells Differentiate  Islet cells → from maternal blood Functional from wk10 to maintain glucose homeostasis Influenced by very common issues of pregnancy! poor placental vasculature  Intrauterine growth restriction Maternal diabetes Fetal malnutrition µ pancreatic peptide Islet cells: Alpha, Beta, Delta, PP-cells (aka Epsilon) Formed into ~1 million islet structures (only 1-2% of pancreas) Why is this important? Because the number of islet cells is (basically) set during fetal development