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.
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.
2008: Lecture - Endocrine Development | lecture 1 slide/page PDF | lecture 4 slides/page PDF |
2009: Medicine Lecture - Endocrine Development | lecture 1 slide/page PDF
Lecture Objectives
- Understanding of hormone types
- Understanding of endocrine gland development
- Understanding of endocrine developmental functions
- Brief understanding of endocrine abnormalities
Textbooks
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 Chapters 10: p230-233; Ch12: p280-282; Ch13: p319-347
Hormones
Hormone Types
- Amino acid derivatives - noradrenaline (norepinepherine), adrenalin (epinepherine) , thyroid hormone
- Proteins, peptides - thyroid stimulating hormone, leutenising hormone, follicle stimulating hormone
- Steroids - androgens, glucocorticoids, mineralocorticoids
Hormone Actions
- Autocrine - acts on self (extracellular fluid)
- Paracrine - acts locally (extracellular fluid)
- Endocrine - acts by secretion into blood stream (endocrine organs are richly vascularized)
Hormone Receptors
Hormones are recognised by either cell surface receptors (modified amino acids, peptides, proteins) or cytoplasmic/nuclear receptors (steroids).
MH - Interested in hormone history? Listen ABC Radio Ockham's Razor 2005-07-31 6.2 Mb mp3 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.
Endocrine Origins
- Derived from epithelia - covering embryo, lining gastrointestinal tract, lining coelomic cavity
- Also mesenchymal contribution
Pineal Gland
UNSW Embryology - Pineal Development
- part of epithalmus - neurons, glia and pinealocytes
- pinealocytes secrete melatonin - cyclic nature of activity, melatonin lowest during daylight
- inhibit hypothalamic secretion of GnRH until puberty, pineal gland then rapidly regresses.
- other activities - possibly gamete maturation, antioxidant effect, protect neurons?
Pineal Development
- Neuroectoderm - prosenecephalon then diencephalon
- caudal roof, median diverticulum, epiphysis
- Initially a hollow diverticulum, cell proliferation to solid, pinealocytes (neuroglia), cone-shaped gland innervated by epithalmus
Hypothalmus
UNSW Embryology - Hypothalmus Development
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
Hypothalmus Development
- Neuroectoderm - prosenecephalon then diencephalon
- ventro-lateral wall intermediate zone proliferation
- Mamillary bodies - form pea-sized swellings ventral wall of hypothalamus
Pituitary
UNSW Embryology - Pituitary Development
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
Pituitary Development
- Dual ectoderm origins
- Ectoderm - ectoderm roof of stomodeum, Rathke's pouch, adenohypophysis
- Neuroectoderm - prosenecephalon then diencephalon, neurohypophysis
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
Pituitary Timeline
- Week 4 - hypophysial pouch, Rathke’s pouch, diverticulum from roof
- Week 5 - elongation, contacts infundibulum, diverticulum of diencephalon
- Week 6 - connecting stalk between pouch and oral cavity degenerates
- Week 10 - growth hormone and ACTH detectable
- Week 16 - adenohypophysis fully differentiated
- Week 20 to 24 - growth hormone levels peak, then decline
Thyroid
UNSW Embryology - Thyroid Development
- Functions from wk10, required for neural development, stimulates metabolism (protein, carbohydrate, lipid), reduced/absence = cretinism (see abnormalities)
Hormones - (amino acid derivatives) Thyroxine (T4), Triiodothyronine (T3)
Thyroid Development
- thyroid median endodermal thickening in the floor of pharynx, outpouch – thyroid diverticulum
- tongue grows, cells descend in neck
- thyroglossal duct - proximal end at the foramen cecum of tongue
- thyroid diverticulum - hollow then solid, right and left lobes, central isthmus
Thyroid Timeline
- 24 days - thyroid median endodermal thickening in the floor of pharynx, outpouch – thyroid diverticulum
- Week 11 - colloid appearance in thyroid follicles, iodine and thyroid hormone (TH) synthesis
growth factors (insulin-like, epidermal) stimulates follicular growth
Fetal Thyroid Hormone
- Initial secreted biologically inactivated by modification, late fetal secretion develops brown fat
- Iodine deficiency- during this period, leads to neurological defects (cretinism)
- Birth - TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels
Parathyroid
- Parathyroid Hormone - Increase calcium ions [Ca2+], stimulates osteoclasts, increase Ca GIT absorption (opposite effect to calcitonin)
- Adult Calcium and Phosphate - Daily turnover in human with dietary intake of 1000 mg/day
- secreted by chief cells
Principal cells cords of cells
Parathyroid Development
- Endoderm - third and fourth pharyngeal pouches, 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
UNSW Embryology - Thymus Development
- Thymus - bone-marrow lymphocyte precursors become thymocytes, and subsequently mature into T lymphocytes (T cells)
- Thymus hormones - thymosins stimulate the development and differentiation of T lymphocytes
Thymus Development
- Endoderm - third pharyngeal pouch
- Week 6 - diverticulum elongates, hollow then solid, ventral cell proliferation
- Thymic primordia - surrounded by neural crest mesenchyme, epithelia/mesenchyme interaction
Pancreas
Lecture- Gastrointestinal Tract Development | UNSW Embryology - Pancreas Development see also GIT Notes- Pancreas
- Functions - exocrine (amylase, alpha-fetoprotein), 99% by volume; endocrine (pancreatic islets) 1% by volume
- Exocrine function - begins after birth
- Endocrine function - from 10 to 15 weeks onward hormone release
- exact roles of hormones in regulating fetal growth?
Pancreas Development
- Pancreatic buds - duodenal level endoderm, splanchnic mesoderm forms dorsal and ventral mesentery, dorsal bud (larger, first), ventral bud (smaller, later)
- Pancreas Endoderm - pancreas may be opposite of liver
- Heart cells promote/notochord prevents liver formation
- Notochord may promote pancreas formation
- Heart may block pancreas formation
- 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, from which cells bud off to form islets
Pancreatic Islets
- Islets of Langerhans - 4 endocrine cell types
- Alpha - glucagon, mobilizes lipid
- Beta - insulin, increase glucose uptake
- Beta cells, stimulate fetal growth, continue to proliferate to postnatal, in infancy most abundant
- Delta - somatostatin, inhibits glucagon, insulin secretion
- F-cells - pancreatic polypeptide
Pancreas Timeline
- 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
Adrenal
UNSW Embryology - Adrenal Development
- Richly vascularized - arterioles passing through cortex, capillaries from cortex to medulla, portal-like circulation
- Fetal Cortex - produces a steroid precursor (DEA), converted by placenta into estrogen
- Adult Medulla - produces adrenalin (epinephrine), noradrenaline (norepinephrine)
- Fetal adrenal hormones - influence lung maturation
Adrenal cortical hormones - (steroids) Cortisol, Aldosterone, Dehydroepiandrosterone
- zona glomerulosa - regulated by renin-angiotensin-aldosterone system controlled by the juxtaglomerular apparatus of the kidney.
- zona fasciculata - regulated by hypothalamo-pituitary axis with the release of CRH and ACTH respectively.
Adrenal medullary hormones - (amino acid derivatives) Epinephrine, Norepinephrine
Adrenal Development
- Fetal Adrenals - fetal cortex later replaced by adult cortex
- Week 6 - fetal cortex, from mesothelium adjacent to dorsal mesentery; Medulla, neural crest cells from adjacent sympathetic ganglia
- Adult cortex - mesothelium mesenchyme encloses fetal cortex
Adrenal Cortex
- Late Fetal Period - differentiates to form cortical zones
- Birth - zona glomerulosa, zona fasiculata present
- Year 3 - zona reticularis present
Adrenal Medulla
- neural crest origin, migrate adjacent to coelomic cavity, neuron-like morphology
- 2 cell types- secrete epinepherine (adrenaline) 80%; secrete norepinepherine (noradrenaline* 20%
Gonad
Lecture - Genital Development | UNSW Embryology - Gonads see also previous Sexual Differentiation Lecture/Practical
Gonad Development
- mesoderm - mesothelium and underlying mesenchyme, primordial germ cells
- Gonadal ridge - mesothelium thickening, medial mesonephros
- Primordial Germ cells - yolk sac, to mesentery of hindgut, to genital ridge of developing kidney
Differentiation
- testis-determining factor (TDF) from Y chromosome: presence (testes), absence (ovaries)
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
Lecture - Placenta Development | UNSW Embryology - Endocrine Placenta
- Human chorionic gonadotrophin (hCG) - like leutenizing hormone, supports corpus luteum in ovary, pregnant state rather than menstrual, maternal urine in some pregnancy testing
- Human chorionic somatommotropin (hCS) - or placental lactogen stimulate (maternal) mammary development
- Human chorionic thyrotropin (hCT)
- Human chorionic corticotropin (hCACTH)
- progesterone and estrogens - support maternal endometrium
- Relaxin
- Placenta - Maternal (decidua) and Fetal (trophoblastic cells, extraembryonic mesoderm) components
- Endocrine function - maternal and fetal precursors, synthesis and secretion
- Protein Hormones - chorionic gonadotropin (hCG), chorionic somatomammotropin (hCS) or placental lactogen (hPL), chorionic thyrotropin (hCT), chorionic corticotropin (hCACTH)
- hCG - up to 20 weeks, fetal adrenal cortex growth and maintenance
- hCS – rise through pregnancy, stimulates maternal metabolic processes, breast growth
- Steroid Hormones - progesterone (maintains pregnancy), estrogens (fetal adrenal/placenta)
- Protein Hormones - chorionic gonadotropin (hCG), chorionic somatomammotropin (hCS) or placental lactogen (hPL), chorionic thyrotropin (hCT), chorionic corticotropin (hCACTH)
Other Endocrine
UNSW Embryology - Other Endocrine Tissues
Endocrine Heart
- Atrial natriuretic peptide (ANP) - Increase Filtration rate / decrease Na+ reabsorption
- Endothelins - ET-1, ET-2, ET-3, Vasoconstriction / Increase NO
- Nitric oxide (NO) - Vasodilatation
Endocrine Kidney
- Renin - Increase Angiotensin-aldosterone system
- Prostaglandins - decrease Na+ reabsorption
- Erythropoietin - Increase Erythrocyte (rbc) production
- 1,25 (OH)2 vitamin D - calcium homeostasis
- Prekallikreins - Increase Kinin production
GIT Endocrine
Enteric control of digestive function
- Gastrin - Secreted from stomach (G cells), role in control of gastric acid secretion
- Cholecystokinin - small intestine hormone, stimulates secretion of pancreatic enzymes and bile
- Secretin - small intestine hormone (epithelial cells), stimulates secretion of bicarbonate-rich fluids from pancreas and liver
Adipose Tissue
UNSW Embryology - Endocrine Adipose Tissue
- Leptin - polypeptide hormone produced in adipose and many other tissues with also many different roles
- Adiponectin - regulation of energy homeostasis and glucose and lipid metabolism, as well as acting as an anti-inflammatory on the cellular vascular wall
- Resistin - (for resistance to insulin, RETN) a 108 amino acid polypeptide and the related resistin-like protein-beta (Resistin-like molecule-beta, RELMbeta) stimulate endogenous glucose production
Endocrine Functional Changes
- Puberty- Increased activity
- Menopause- Decreased activity
- Disease (diabetes, thyroid, kidney) suggested trends that genetics, health, nutrition, lifestyle may influence time that these events occur
- Pharmaceutical impact - birth control, steroids, Hormone Replacement Therapy (HRT)
Abnormalities
Pineal
- hypoplasia - associated with retinal disease.
- tumours - in children are associated with abnormal puberty development.
Pituitary
- craniopharyngeal canal - Rathke's pouch abnormality, from the anterior part of the fossa hypophyseos of the sphenoid bone to the under surface of the skull.
- pituitary tumours (adenomas) - several abnormalities associated with abnormal levels of the hormonal output of the pituitary.
- Growth hormone (GH) adenomas - benign pituitary tumors lead to chronic high GH output levels, that may lead to acromegaly.
- Cushing's disease - caused either by a pituitary adenoma produces excess adrenocorticotropic hormone (ACTH, corticotropin) or due to ectopic tumors secreting ACTH or corticotropin-releasing hormone (CRH).
Thyroid
- Pyramidal lobe - from isthmus (50% of people) attached to hyoid bone distal end of thryoglossal duct.
- Congenital hypothyroidism - approximately 1 in 3000 births, associated with neurological abnormalities.
- Lingual thyroid gland - failure of thyroid descent.
- Thyroglossal cyst - persistance of thyroglossal duct.
- Thyroglossal fistula - partial degeneration of the thyroglossal duct.
- Abnormal development of the thyroid - incomplete or excessive descent.
- Childhood hypothyroidism delays ossification and bone mineralization.
Iodine Deficiency
- A teaspoon of iodine, total lifetime requirement, cannot be stored for long periods by our body, tiny amounts are needed regularly
- Areas of endemic iodine deficiency, where soil and therefore crops and grazing animals do not provide sufficient dietary iodine to the populace
- food fortification and supplementation - Iodized salt programs and iodized oil supplements are the most common tools in fight against IDD
Pancreas
- Type 1 Diabetes - juvenile onset diabetes, more severe form of illness, increases risk of blindness, heart disease, kidney failure, neurological disease, T-lymphocyte-dependent autoimmune disease, infiltration and destruction of the islets of Langerhans, Approx 16 million Americans
- Type 2 Diabetes - loosely defined as "adult onset" diabetes, becoming more common cases of type 2 diabetes seen in younger people
- Risk of developing diabetes - environmental factors (food intake and exercise play an important role, either overweight or obese), Inherited factors (genes involved remain poorly defined)
Adrenal
Links
- 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 GIT Notes- Pancreas | Endocrine Placenta | Hypothalmus | Parathyroid | Endocrine Adipose Tissue | Other Endocrine Tissues
- Embryo Images: Pituitary Development
References
- Endocrinology: An Integrated Approach Nussey, S.S. and Whitehead, S.A. London:Taylor & Francis; c2001 Major hormone types
Histology
Adult
Embryonic
Terms
adrenocorticotropin - (ACTH or corticotropin) anterior pituitary, peptide hormone
antidiuretic hormone - (ADH) hypothalamus, peptide hormone
atrial natriuretic factor - (ANP) heart, , peptide hormone
calcitonin - (CT) C cells of thyroid, peptide hormone
follicle stimulating hormone - (FSH) pituitary, protein hormone
growth hormone - (GH) pituitary, peptide hormone
human chorionic gonadotropin - (hCG) pancreas glycoprotein hormone with 2 subunits (alpha and beta joined non covalently). Similar in structure to luteinizing hormone (LH), hCG exists in multiple hormonal and non-endocrine agents (regular hCG, hyperglycosylated hCG and the free beta-subunit of hyperglycosylated hCG). PMID: 19171054
lutenizing hormone - (LH) pituitary, protein hormone
melaocyte stimulating hormone - (MSH) pituitary, peptide hormone
prolactin - (PRL) pituitary, peptide hormone
parathyroid hormone - (PTH) parathyroid, peptide hormone
thyroid hormone - (TH) thyroid,amino acid derivative
thyroid stimulating hormone - (TSH) pituitary, protein hormone
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Course Content 2009
Embryology Introduction | Cell Division/Fertilization | Cell Division/Fertilization | Week 1&2 Development | Week 3 Development | Lab 2 | Mesoderm Development | Ectoderm, Early Neural, Neural Crest | Lab 3 | Early Vascular Development | Placenta | Lab 4 | Endoderm, Early Gastrointestinal | Respiratory Development | Lab 5 | Head Development | Neural Crest Development | Lab 6 | Musculoskeletal Development | Limb Development | Lab 7 | Kidney | Genital | Lab 8 | Sensory - Ear | Integumentary | Lab 9 | Sensory - Eye | Endocrine | Lab 10 | Late Vascular Development | Fetal | Lab 11 | Birth, Postnatal | Revision | Lab 12 | Lecture Audio | Course Timetable
Cite this page: Hill, M.A. (2024, June 14) Embryology 2009 Lecture 20. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_20
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G