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.
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 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
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! 13 minutes 32seconds 6.2 Mb mp3 | ABC Radio Ockham's Razor | ABC Radio Ockham's Razor Transcript
| 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
Development Overview
Links: hypothalamus | Pineal | Pituitary | Thyroid |
Parathyroid | Thymus |Pancreas |
Pancreas | Gonads | Placenta | Maternal | Other Cells
hypothalamus hypothalamus Development Notes
- Neuroectoderm prosenecephalon
- Diencephalon ventro-lateral wall intermediate zone proliferation
- Mamillary bodies - form pea-sized swellings ventral wall of hypothalamus
Pineal - Pineal Development Notes
- Neuroectoderm prosenecephalon
- Diencephalon 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 - Pituitary Development Notes
- Ectoderm- ectoderm roof of stomodeum, neuroectoderm of diencephalon
- Adenohypophysis anterior pituitary, glandular (pars anterior, pars intermedia, pars tuberalis)
- Neurohypophysis posterior pituitary, nervous (pars nervosa)
- Week 4 hypophysial pouch, Rathkes pouch, diverticulum from roof
- Week 5 elongation, contacts infundibulum, diverticulum of diencephalon
- Week 6 connecting stalk between pouch and oral cavity degenerates
- Adenohypophysis
- Anterior wall proliferates - pars distalis
- Posterior wall little growth pars intermedia
- Rostral growth around infundibular stem pars tuberalis
- Neurohypophysis
- Infundibulum median eminence, infundibulum, pars nervosa
- Week 10 growth hormone and ACTH detectable
- Week 16 adenohypophysis fully differentiated
- Week 20 to 24 growth hormone levels peak, then decline
Thyroid - Thyroid Development Notes
- 24 days thyroid median endodermal thickening in the floor of pharynx
- outpouch thyroid diverticulum
- tongue grows, descend in neck thryoglossal duct (proximal end foramen cecum of tongue)
- thyroid diverticulum hollow then solid, right and left lobes, central isthmus
- pyramidal lobe from isthmus (50% of people) attached to hyoid bone (distal end of thryoglossal duct)
- Week 11 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 TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels
Parathyroid Parathyroid
- Third and Fourth Pharyngeal Pouches- endoderm (could also have ectoderm and neural crest)
- 3rd Pharyngeal Pouch inferior parathyroid, initially descends with thymus
- 4th Pharyngeal Pouch 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 - 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 - Pancreas Development Notes
- Functions- exocrine (amylase, alpha-fetoprotein) and endocrine (pancreatic islets)
- Pancreatic buds- endoderm, covered in splanchnic mesoderm
- Pancreatic bud formation duodenal level endoderm, splanchnic mesoderm forms dorsal and ventral mesentery, dorsal bud (larger, first), ventral bud (smaller, later)
- Duodenum growth/rotation brings ventral and dorsal buds together, fusion of buds
- Pancreatic duct 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 pancreatic hormones secretion increases, small amount maternal insulin
- Week 10 glucagon (alpha) differentiate first, somatostatin (delta), insulin (beta) cells differentiate, insulin secretion begins
- Week 15 glucagon detectable in fetal plasma
- Beta cells - stimulate fetal growth, continue to proliferate through to postnatal in infancy, most abundant
- Maternal diabetes mellitus hypertrophy of fetal beta cells
Adrenal (Suprarenal) - Adrenal Development Notes
- Cortex mesoderm, medulla neural crest
- Fetal and adult cortex
- Week 6 fetal cortex forms from mesothelium adjacent to dorsal mesentery, medulla neural crest cells from adjacent sympathetic ganglia
- adult cortex mesothelium mesenchyme encloses fetal cortex
- Late Fetal Period- differentiates to form cortical zones
- Birth - zona glomerulosa, zona fasiculata present
- Year 3 zona reticularis present
- Fetal Cortex produces- a steriod precursor (DEA) converted by placenta into estrogen
- Adult Cortex produces cortisol,
..
- Adult Medulla produces adrenalin (epinephrine), noradrenalin (norepinephrine)
- Fetal adrenal hormones - influence lung maturation
Gonads (Covered in Sexual Differentiation) - Endocrine Gonad Notes | Genital Development
- Gonad- mesoderm (mesothelium and underlying mesenchyme) and primordial germ cells
- Gonadal ridge 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 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 - Endocrine Placenta Notes | 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 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 - Endocrine Other Cells Notes
Selected cells within the following organs also contribute to endocrine regulation.
- Digestive Tract -
- Heart -
- Kidney -
Glossary of Terms
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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 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.
Something old, something new....listen to where the term "hormone" came from in the linked podcast.
Please email Dr Mark Hill if you wish to make a comment about this current project.
