Talk:2009 Lecture 20

Endocrine 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.

Some Recent Findings

• Endocrine activity of extraembryonic membranes extends beyond placental amniotes. Albergotti LC, Hamlin HJ, McCoy MW, Guillette LJ Jr. PLoS One. 2009;4(5):e5452. Epub 2009 May 8. PMID: 19424488 PLOS

• Beta cells within single human islets originate from multiple progenitors. Scharfmann R, Xiao X, Heimberg H, Mallet J, Ravassard P. PLoS One. 2008;3(10):e3559. Epub 2008 Oct 29. PMID: 18958289

• All beta cells contribute equally to islet growth and maintenance. Brennand K, Huangfu D, Melton D. PLoS Biol. 2007 Jul;5(7):e163. Epub 2007 May 29. PMID: 17535113 PLOS

In healthy adult mice, the beta cell population is not maintained by stem cells but instead by the replication of differentiated beta cells. It is not known, however, whether all beta cells contribute equally to growth and maintenance, as it may be that some cells replicate while others do not. Understanding precisely which cells are responsible for beta cell replication will inform attempts to expand beta cells in vitro, a potential source for cell replacement therapy to treat diabetes. Two experiments were performed to address this issue. First, the level of fluorescence generated by a pulse of histone 2B–green fluorescent protein (H2BGFP) expression was followed over time to determine how this marker is diluted with cell division; a uniform loss of label across the entire beta cell population was observed. Second, clonal analysis of dividing beta cells was completed; all clones were of comparable size. These results support the conclusion that the beta cell pool is homogeneous with respect to replicative capacity and suggest that all beta cells are candidates for in vitro expansion. Given similar observations in the hepatocyte population, we speculate that for tissues lacking an adult stem cell, they are replenished equally by replication of all differentiated cells.

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: Stage 13/14 Embryo | Stage 22 Embryo | Selected Sections Stage 22 Embryo | Abnormal Endocrine Development | Pituitary Development | Thyroid Development | Adrenal Development | Pancreas Development See also [git9.htm GIT Notes- Pancreas] | Endocrine Placenta | Hypothalmus | Parathyroid | Endocrine Adipose Tissue | 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 -

Quick Links

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G

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]

Classification by structure of the major human hormones

Hormone	Peptide/protein	Steroid	Amino acid or fatty acid derived
Hypothalamic hormones	Thyrotrophin releasing hormone (TRH)
	Corticotrophin releasing hormone (CRH)
	Arginine vasopressin (AVP)
	Gonadotrophin releasing hormone (GnRH)
	Growth hormone releasing hormone (GHRH)
	Somatostatin
	Prolactin relasing factor (PRF)
	Dopamine
Anterior pituitary hormones	Thyroid-stimulating hormone (TSH)
	Adrenocorticotrophic hormone (ACTH)
	Luteinizing hormone (LH)
	Follicle-stimulating hormone (FSH)
	Somatotrophin/growth hormone (GH)
	Prolactin (PRL)
	Melanocyte-stimulating hormone (MSH)
Posterior pituitary hormones	Oxytocin
	Arginine vasopressin
Thyroid hormones			Thyroxine (T4)
			Triiodothyronine (T3)
Pancreatic hormones	Insulin
	Glucagon
	Somatostatin
	Pancreatic polypeptide
Calcium regulating hormones	Parathyroid hormone (PTH)	1,25-dihydroxyvitamin D
	Calcitonin (CT)
	Parathyroid hormone-related peptide (PTHrp)
Adrenal cortical steroids		Cortisol
		Aldosterone
		Dehydroepiandrosterone
Adrenal medullary hormones			Epinephrine
			Norepinephrine
Male reproductive hormones	Inhibin	Testosterone
		Dihydrotestosterone
Female reproductive hormones	Inhibin	Estradiol
	Oxytocin	Progesterone
	Human chorionic gonadotropin (hCG)
	Human chorionic somatotrophin
Plasma volume and sodium regulating hormones	Atrial natriuretic peptide (ANP)
	Arginine vasopressin
	Renin/angiotensin	Aldosterone
Cardiovascular hormones	Atrial natriuretic peptide (ANP)		Nitric oxide
	Endothelins
	Erythropoietin
	Bradykinin
Pineal hormones			Melatonin
			Serotonin
Growth factors or cytokines	Insulin-like growth factors (IGFs)
	Epidermal growth factor (EGF)
	Interleukins (ILs)
	Tumor necrosis factor (TNF)-alpha
Eicosanoids			Prostaglandins
			Thromboxanes
			Prostacyclin
			Leucotrienes
			Lipoxins

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