Endocrine System - Abnormalities

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Introduction

Human adrenal gland (Week 10)

The endocrine system has an ongoing important role in embryonic, fetal and postnatal development as well as maintainance of homeostasis and reproductive function. There exists a complex interaction between the maternal and fetal endocrine system during development and failure for fetal endocrine development has a cascading effect on many other developing systems. There are additional pages covering abnormalities of specific endocrine organs.

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 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.

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 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 also 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. Finally, each endocrine organ page listed below has additional abnormalities information specific to that organ.

Endocrine Links: Introduction | BGD Lecture | Science Lecture | Pineal | Hypothalamus‎ | Pituitary | Thyroid | Parathyroid | Thymus‎ | Pancreas‎ | Adrenal‎ | Gonad‎ | Placenta‎ | Other Tissues | Stage 22 | Abnormalities | Hormones | Category:Endocrine
Links: Endocrine - Pineal Development‎

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).
Links: Endocrine - Pituitary Development‎

Thyroid

Thyroid pyramidal lobe
Thyroid uptake scans
  • 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. Image - 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
Links: Endocrine - Thyroid Development‎

Parathyroid

  • Usually four glands are present (2 on each side), but three to six glands have been found in human.
  • Lower parathyroid glands arise from the third pharyngeal pouch and descend with the thymus. Variable descent can lead to a range of adult locations, from just beneath the mandible to the anterior mediastinum.

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)
Links: Endocrine - Pancreas Development‎ | Abnormal Development - Maternal Diabetes

Adrenal

  • Congenital Adrenal Hyperplasia (CAH) - family of inherited disorders of adrenal steroidogenesis enzymes which impairs cortisol production by the adrenal cortex. Androgen excess leads newborn females with external genital ambiguity and postnatal progressive virilization in both sexes.
    • Enzymes most commonly affected: 21-hydroxylase (21-OH), 11beta-hydroxylase, 3beta-hydroxysteroid dehydrogenase.
    • Enzymes less commonly affected: 17alpha-hydroxylase/17,20-lyase and cholesterol desmolase.
  • Pheochromocytomas (PCC) - Catecholamine-producing (neuro)endocrine tumor located in the adrenal medulla. Similar catecholamine-producing tumors outside the adrenal gland are called paragangliomas (PGL).
Links: Endocrine - Adrenal Development

Endocrine Disruptors

Diethylstilbestrol
Finasteride
Vinclozoline

Exogenous chemicals that interfere with the function of hormones. There are 3 main mechanisms: mimic, block or interfere.

Mimic

Replicate the effects of natural hormones by binding receptors.

  • Diethylstilbestrol - (DES or diethylstilbetrol) a drug prescribed to women from 1938-1971 to prevent miscarriage in high-risk pregnancies. Acts as a potent estrogen (mimics natural hormone) and therefore a potential endocrine disruptor. Female fetus, increased risk abnormal reproductive tract and cancer. Male fetus, abnormal genitalia. Banned by USA FDA in 1979 as a teratogen, previously used as livestock growth promoter.

Block

Inhibit the binding of a hormone to receptor or hormone synthesis.

  • Finasteride - chemical used to prevent male pattern baldness and enlargement of prostate glands. An anti-androgen (blocks synthesis of dihydrotestosterone) and therefore a potential endocrine disruptor, exposed pregnant women can impact on male fetus genetial development.
  • Vinclozolin - a dicarboximide fungicide, perinatal exposure in rats inhibits morphological sex differentiation. In adult rats, shown to cause gonad tumours (Leydig cell) and atrophy. Chemical has androgen-antagonist (antiandrogenic) activity, metabolies compete with natural androgen

Interfere

Compromise with the hormone transport or elimination.

  • Polychlorinated biphenyl pollutants - (PCBs) Rats exposed to PCBs have low levels of thyroid hormone. Compete for binding sites of thyroid hormone transport protein. Without being bound to this protein, thyroid hormones are excreted from the body (McKinney et al. 1985; Morse et al. 1996)

References

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Cite this page: Hill, M.A. (2014) Embryology Endocrine System - Abnormalities. Retrieved September 16, 2014, from https://php.med.unsw.edu.au/embryology/index.php?title=Endocrine_System_-_Abnormalities

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© Dr Mark Hill 2014, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G