2009 Lecture 20

Introduction

Pituitary

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).

Endocrine Origins

Derived from epithelia - covering embryo, lining gastrointestinal tract, lining coelomic cavity
Also mesenchymal contribution

Pineal Gland

part of epithalmus - neurons, glia and pinealocytes
pinealocytes secrete melatonin - cyclic nature of activity, melatonin lowest during daylight
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

Hypothalmus Development

Neuroectoderm - prosenecephalon then diencephalon
ventro-lateral wall intermediate zone proliferation
Mamillary bodies - form pea-sized swellings ventral wall of hypothalamus

Pituitary

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

Fetal Thyroiud 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

Thyroid

Functions from wk10, required for neural development, stimulates metabolism (protein, carbohydrate, lipid), reduced/absence = cretinism (see abnormalities)

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

Parathyroid

Parathyroid Hormone Increase calcium ions [Ca2+] stimulates osteoclasts increase Ca GIT absorption opposite effect to calcitonin secreted by chief cells Principal cells cords of cells 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

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

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

Cite this page: Hill, M.A. (2024, May 3) Embryology 2009 Lecture 20. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_20

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