Talk:2009 Lecture 20

Introduction

The endocrine system resides within specific endocrine organs and both organs and tissues with other specific functions. Epithelia (ectoderm and endoderm) form the majority of the “ductless” endocrine glands like gastrointestinal and skin associated “ducted” glands. Differentiation of several also organs involves a epithelial/mesenchye interaction, seen in repeated in many differentiation of many different tissues. The endocrine glands produce hormones, which are distributed by the vascular system to the many body tissues, subsequently these organs are richly vascularized.

Thyroid and Pituitary

Hormones are recognised by either cell surface receptors (modified amino acids, peptides, proteins) or cytoplasmic/nuclear receptors (steroids). Hormones “orchestrate” responses in other tissues, including other endocrine organs, and these overall effects can be similar or different in different tissues. In addition, these hormone effects (like music) can be rapid, slow, brief, diurnal, or long-term. Hormone effects can be mimicked, stimulated, and blocked by therapeutic drugs, nutritional and environmental chemicals.

[endocrine7.htm Pituitary Development]

The human fetus is dependent upon endocrine development for hormones, which support normal development. Peripheral endocrine glands (thyroid, pancreas, adrenals, gonads) form early in the second month from epithelial/mesenchye interactions and differentiate into the third month. The fetus also has a unique hormonal system that combines not only its own developing endocrine system, but also that of the placenta (More? see [placenta.htm Placenta notes]) and maternal hormones.

Abnormal endocrine development/function can impact on many different systems. For example, insufficient maternal dietary iodine impacts on fetal thyroid gland thyroid hormone production, which in turn can lead to abnormal neural development. Alternatively, we now know many environmental and therapeutic chemicals have a wide range of effects on the endocrine system.

Sex hormones from the gonads have significant effects prenatally and postnatally, specifically at puberty with a role to play in male/female biological maturity and have wide actions throughout the body.

Page Links: [#Intro Introduction] | [#Recent Some Recent Findings] | [#Reading Reading] | [#Overview Development Overview] | [#SerialImages Serial Images] | [#Abnormalities Abnormalities] |[#WWWLinks WWW Links] | [#References References] | [#Glossary Glossary]

Some Recent Findings

File:Podcasticon.jpg Podcast - Listen ABC Radio Ockham's Razor 2005-07-31 Centenary of the word 'hormone', Sydney medical scientist and writer Dr John Carmody commemorates the centenary of the entry of the word 'hormone' into the English language. Slip this MP3 into your player and listen! [../Podcast/OckhamRazor/CentenaryofHormone.mp3 13 minutes 32seconds 6.2 Mb mp3] | ABC Radio Ockham's Razor | ABC Radio Ockham's Razor Transcript | [../Podcast/podcast.htm About UNSW Embryology Podcasts]

Reading

In general, not dealt with as a “system” in many textbooks, so various chapters: nervous system, head, gastrointestinal tract, reproductive organs, etc.

• Human Embryology (3rd ed.) Larson
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch10: p230-233, Ch12: p280-282, Ch13: p319-347
• Before We Are Born (5th ed.) Moore and Persaud
• Essentials of Human Embryology Larson
• Human Embryology Fitzgerald and Fitzgerald Ch24: p166-167
• Search PubMed- Medline

Online Texbooks

External links to online textbooks at NCBI Bookshelf

Developmental Biology (6th ed) by Gilbert Part 3. Later embryonic development, 15. Endoderm

Endocrinology: An Integrated Approach table of Contents

NIH Genes & Disease Chapter 41

Objectives

• Understand the main steps in the development of the thyroid, parathyroid, adrenal, pituitary, pineal glands, thymus and gonads.
• Have a general understanding of the chief functions of these endocrine organs.
• Understand the endocrine contribution to embryo development.
• Understand the endocrine role of the placenta during development.
• Have a general understanding of different types of hormones and their signaling actions.

Learning Activities

• Examine the developing thyroid, adrenal and pituitary glands in the stage 13/14 and stage 22 embryos.
• Review the vascular and nerve supply of the above glands.
• Review the development of the parathyroid and pineal glands.
• Review the endocrine role of the placenta.([#Endocrine Placenta see below])
• Review the development and endocrinefunction of the gonads.

Computer Activities

UNSW Embryology:

• [endocrine3.htm Stage 13/14 Embryo]
• [endocrine4.htm Stage 22 Embryo]
• [endocrine4.htm Selected Sections Stage 22 Embryo]
• [endocrine2.htm Abnormal Endocrine Development]
• [endocrine7.htm Overview Pituitary Development]
• [endocrine8.htm Overview Thyroid Development]
• [endocrine9.htm Overview Adrenal Development]
• [endocrine10.htm Overview of Pancreas Development] See also [git9.htm GIT Notes- Pancreas]
• [endocrine14.htm Overview of Endocrine Placenta]
• [endocrine16.htm Overview of Hypothalmus]
• [endocrine17.htm Overview of Parathyroid]
• [endocrine18.htm Overview of Endocrine Adipose Tissue]
• [endocrine19.htm Overview of Other Endocrine Tissues]

Human Embryology Movies:

Embryo Images Unit:

Requires Internet connection

• Pituitary Gland

Development Overview

Links: [#hypothalamus hypothalamus] | [#Pineal Pineal] | [#Pituitary Pituitary] | [#Thyroid Thyroid] | [#Parathyroid Parathyroid] | [#Thymus Thymus] |[#Pancreas Pancreas] | [#Pancreas Pancreas] | [#Gonads Gonads] | [#EndocrinePlacenta Placenta] | [#Maternal Maternal] | [#OtherCells Other Cells]

hypothalamus [endocrine16.htm hypothalamus Development Notes]

• Neuroectoderm ‚Äì prosenecephalon
• Diencephalon ‚Äì ventro-lateral wall intermediate zone proliferation
• Mamillary bodies - form pea-sized swellings ventral wall of hypothalamus

Pineal - [endocrine12.htm Pineal Development Notes]

• Neuroectoderm ‚Äì prosenecephalon
• Diencephalon ‚Äì caudal roof, median diverticulum, epiphysis
• Hollow diverticulum - cell proliferation to solid, pinealocytes (neuroglia), cone-shaped gland, innervated by epithalmus
• Melatonin- diurnal cycle, inhibits pituitary-gonad axis

Pituitary - [endocrine7.htm Pituitary Development Notes]

• Ectoderm- ectoderm roof of stomodeum, neuroectoderm of diencephalon
• Adenohypophysis ‚Äì anterior pituitary, glandular (pars anterior, pars intermedia, pars tuberalis)
• Neurohypophysis ‚Äì posterior pituitary, nervous (pars nervosa)
• Week 4 ‚Äì hypophysial pouch, Rathke‚Äôs pouch, diverticulum from roof
• Week 5 ‚Äì elongation, contacts infundibulum, diverticulum of diencephalon
• Week 6 ‚Äì connecting stalk between pouch and oral cavity degenerates
• Adenohypophysis
• Anterior wall proliferates - pars distalis
• Posterior wall little growth ‚Äì pars intermedia
• Rostral growth around infundibular stem ‚Äì pars tuberalis
• Neurohypophysis
• Infundibulum ‚Äì median eminence, infundibulum, pars nervosa
• Week 10 ‚Äì growth hormone and ACTH detectable
• Week 16 ‚Äì adenohypophysis fully differentiated
• Week 20 to 24 ‚Äì growth hormone levels peak, then decline

Thyroid - [endocrine8.htm Thyroid Development Notes]

• 24 days ‚Äì thyroid median endodermal thickening in the floor of pharynx
• outpouch ‚Äì thyroid diverticulum
• tongue grows, descend in neck ‚Äì thryoglossal duct (proximal end foramen cecum of tongue)
• thyroid diverticulum ‚Äì hollow then solid, right and left lobes, central isthmus
• pyramidal lobe ‚Äì from isthmus (50% of people) attached to hyoid bone (distal end of thryoglossal duct)
• Week 11 ‚Äì colloid appearance in thyroid follicles, iodine and thyroid hormone (TH) synthesis
• growth factors (insulin-like, epidermal) stimulates follicular growth
• Fetal TH - Initial secreted biologically inactivated by modification, late fetal secretion develops brown fat
• Iodine deficiency- during this period, leads to neurological defects
• Birth ‚Äì TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels

Parathyroid [endocrine17.htm Parathyroid]

• Third and Fourth Pharyngeal Pouches- endoderm (could also have ectoderm and neural crest)
• 3rd Pharyngeal Pouch ‚Äì inferior parathyroid, initially descends with thymus
• 4th Pharyngeal Pouch ‚Äì superior parathyroid
• Week 6 - diverticulum elongate, hollow then solid, dorsal cell proliferation
• Fetal parathyroids- respond to calcium levels, fetal calcium levels higher than maternal

Thymus - [endocrine13.htm Thymus]

• Third Pharyngeal Pouch- endoderm
• Week 6 - diverticulum elongate, hollow then solid, ventral cell proliferation
• Thymic primordia- surrounded by neural crest mesenchyme
• Thymus development - epithelia/mesenchye interaction

Pancreas - [endocrine10.htm Pancreas Development Notes]

• Functions- exocrine (amylase, alpha-fetoprotein) and endocrine (pancreatic islets)
• Pancreatic buds- endoderm, covered in splanchnic mesoderm
• Pancreatic bud formation ‚Äì duodenal level endoderm, splanchnic mesoderm forms dorsal and ventral mesentery, dorsal bud (larger, first), ventral bud (smaller, later)
• Duodenum growth/rotation ‚Äì brings ventral and dorsal buds together, fusion of buds
• Pancreatic duct ‚Äì ventral bud duct and distal part of dorsal bud, exocrine function
• Islet cells- cords of endodermal cells form ducts, which cells bud off to form islets
• Week 7 to 20 ‚Äì pancreatic hormones secretion increases, small amount maternal insulin
• Week 10 ‚Äì glucagon (alpha) differentiate first, somatostatin (delta), insulin (beta) cells differentiate, insulin secretion begins
• Week 15 ‚Äì glucagon detectable in fetal plasma
• Beta cells - stimulate fetal growth, continue to proliferate through to postnatal in infancy, most abundant
• Maternal diabetes mellitus ‚Äì hypertrophy of fetal beta cells

Adrenal (Suprarenal) - [endocrine9.htm Adrenal Development Notes]

• Cortex mesoderm, medulla neural crest
• Fetal and adult cortex
• Week 6 ‚Äì fetal cortex forms from mesothelium adjacent to dorsal mesentery, medulla neural crest cells from adjacent sympathetic ganglia
• ‚Äì adult cortex mesothelium mesenchyme encloses fetal cortex
• Late Fetal Period- differentiates to form cortical zones
• Birth - zona glomerulosa, zona fasiculata present
• Year 3 ‚Äì zona reticularis present
• Fetal Cortex produces- a steriod precursor (DEA) converted by placenta into estrogen
• Adult Cortex produces ‚Äì cortisol, ‚Ķ‚Ķ..
• Adult Medulla produces ‚Äì adrenalin (epinephrine), noradrenalin (norepinephrine)
• Fetal adrenal hormones - influence lung maturation

Gonads (Covered in Sexual Differentiation) - [endocrine15.htm Endocrine Gonad Notes] | [genital.htm Genital Development]

• Gonad- mesoderm (mesothelium and underlying mesenchyme) and primordial germ cells
• Gonadal ridge ‚Äì mesothelium thickening, medial mesonephros
• Primordial Germ cells- yolk sac, to mesentery of hindgut, to genital ridge of developing kidney
• Gonad differentiation - dependent on presence (testes) or absence (ovaries) of expression of testis-determining factor (TDF) from Y chromosome
• Testis
• 8 Weeks ‚Äì mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione
• 8 to 12 Weeks - hCG stimulates testosterone production
• Sustentacular cells- produce anti-mullerian hormone to puberty
• Ovary
• X chromosome genes regulate ovary development

Placenta - [endocrine14.htm Endocrine Placenta Notes] | [placenta.htm Placenta Development]

• Maternal (decidua) and Fetal (trophoblastic cells, extraembryonic mesoderm) components
• Endocrine function- maternal and fetal precursors, synthesis and secretion
• Hormones- protein and steroidal
• Protein Hormones- chorionic gonadotropin (hCG), chorionic somatomammotropin (hCS) or placental lactogen (hPL), chorionic thyrotropin (hCT), chorionic corticotropin (hCACTH)
• Steroid Hormones- progesterone (maintains pregnancy), estrogens (fetal adrenal/placenta)
• hCG - up to 20 weeks, fetal adrenal cortex growth and maintenance
• hCS ‚Äì rise through pregnancy, stimulates maternal metabolic processes, breast growth

Maternal

Maternal hormones - can cross the placental barrier, contribute precursors to placental hormone production.

Other Cells - [endocrine18.htm Endocrine Other Cells Notes]

Selected cells within the following organs also contribute to endocrine regulation.

• Digestive Tract -
• Heart -
• Kidney -

Glossary of Terms

[Index/A.htm A] |[Index/B.htm B] | [Index/C.htm C] | [Index/D.htm D] | [Index/E.htm E] | [Index/F.htm F] | [Index/G.htm G] | [Index/H.htm H] | [Index/I.htm I] | [Index/J.htm J] | [Index/K.htm K] | [Index/L.htm L] | [Index/M.htm M] | [Index/N.htm N] | [Index/O.htm O] | [Index/P.htm P] | [Index/Q.htm Q] | [Index/R.htm R] | [Index/S.htm S] | [Index/T.htm T] | [Index/U.htm U] | [Index/V.htm V] | [Index/W.htm W] |[Index/X.htm X] | [Index/Y.htm Y] | [Index/Z.htm Z]

Quick Links

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G

Navigation

[../embryo.htm Home Page][../wwwhuman/Stages/Stages.htm Embryo stages][../wwwhuman/Fetus.htm Fetal Dev][../devnote.htm Dev Notes 1][../devnote2.htm Dev Notes 2][../sysnote.htm System Notes][../People.htm Acknowledgements]

Internal LinksEndocrine

Introduction[endocrine2.htm Abnormalities][endocrine3.htm Stage 13/14][endocrine4.htm Stage 22][endocrine5.htm Selected Stage 22][endocrine8.htm Thyroid][endocrine7.htm Pituitary][endocrine9.htm Adrenal][endocrine10.htm Pancreas][endocrine12.htm Pineal][endocrine13.htm Thymus][endocrine15.htm Gonad][endocrine14.htm Placenta][endocrine16.htm Hypothalmus][endocrine17.htm Parathyroid][endocrine18.htm Adipose Tissue][endocrine19.htm Other Tissues][endocrine11.htm Molecular][endocrinelink.htm Web Links]

Internal Links

[../Movies/Movies.htm Movies][../Podcast/podcast.htm Audio][../News/news.htm News][../class.htm Class Notes][../Series.htm Serial Images][../K12/embryo.htm K12 Students][../Defect/page1.htm Abnormal][../histo.htm Histology][../sitemap.htm Site Map][Index/Index.htm Glossary][../Refer/refer.htm References][../Refer/search.htm Search]

External Links

School of Med SciUNSW MedicineUniversity of NSWUNSW Cell BiologyNCBI BooksDev Biol (Gilbert)2009-10-01T10:41:14Search Google

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Comments

This section of notes covers the endocrine system organs, development and function.

This first page introduces the system and gives a general [#Overview Development Overview]. Subsequent linked pages focus on specific organs.

Each organ in the endocrine system has an important role to play during embryonic development and postnatally.

Interestingly, many endocrine organs have different fetal roles than those found in the adult organs. ©M.A. Hill, 2007