Nuts and bolts of the endocrine system - part 2 Flashcards
Endocrine glands
No duct system
Hormones are released at specific times in small amounts into the tissue fluids or blood vessels
Endocrine definition
Action of the hormone on a target organ away from the secreting cell
Autocrine definition
Action of the hormone on the secreting cell
Paracrine definition
Action of the hormone on the adjacent cell
Neuroendocrine definition
Neural stimulation of endocrine cells to secrete hormones
Overall structure of endocrine glands
Functional unit consist of cuboidal secretory cells with a lumen at the centre
Secretory cells supported by myoepithelial cells
Clinical manifestations of endocrine diseases
Hormone overproduction
Hormone underproduction
Tumour/ mass lesion which can be
- non-functional so has pressure effect
- associated with over production of hormones
Pituitary gland divided into
Adenohypophysis/ anterior lobe
Neurohypophysis/ posterior lobe
Cells of the anterior pituitary gland
Acidophils
Basophils
Chromophobe
Acidophils
Take up acidic dyes
Basophils
Take up basic dyes
Chromophobe
No specific staining feature
Somatotroph
Secretes growth hormone
Target organ: bones
Lactotroph
Secretes prolactin
Target organ: breasts
Corticotroph
Secretes adrenocorticotrophic hormone
Target organ: adrenal glands
Gonadotroph
Secretes follicle stimulating hormone and luteinising hormone
Target organ: ovary and testis
Thydrotroph
Secretes thyroid stimulating hormone
Target organ: thyroid gland
Hormones from the posterior pituitary
Antidiuretic hormone
- facilitates absorption of water in kidneys
Oxytocin
- promotes contraction of smooth muscle in the uterus during childbirth and myoepithelial cells in the breast during breast feeding
Pathology of the pituitary gland
Pituitary adenomas (benign tumours)
- arise from anterior lobe
- can be functional or non-functional
- constitute 10% of intra cranial neoplasms
- productive adenomas cause hyperpituitarism
- pressure effect causing hypopituitarism
Space occupying effect of functional or non-functional adenomas
- headaches, vomiting, nausea and diplopia, impaired vision
Thyroid gland
Synthesises T4 (thyroxine) and T3 (triiodothyronine) which stimulates metabolic rate
Synthesis of T4 and T3 requires iodine
Lack of iodine leads to an enlarged thyroid gland termed goitre
Gland expands to absorb maximum concentration of iodine
Normal thyroid gland
Weight = 35-45g
2 lobes and isthmus
Thyroid tissue is composed of follicles with variable sized lumina
Follicles contain colloid with eosinophilic or pink appearance
Features of the thyroid gland
Very vascular
Endothelial cells lining the capillaries are fenestrated
Fenestration allows passage of hormones into the circulation
Para- follicular cells or clear (C) cells are found between the follicles
C cells secrete calcitonin which promotes reduction of calcium concentration in the blood
Pathology of the thyroid gland
Goitre- euthyroid
Grave’s disease- hyperthyroid
Hashimoto’s disease- hypothyroid
Adenoma- euthyroid
Cancer- euthyroid
Multi-nodular goitre
Lack of iodine leads to an enlarged thyroid gland
Due to hyperplasia and hypertrophy of thyroid cells
Gland enlarges to maximise amount of iodine absorbed
The increase in size overcomes the hormone deficiency and the patients are euthyroid
Grave’s disease
Auto-antibodies stimulate TSH receptors
Diffuse enlargement of the thyroid due to hyperplasia of thyroid cells
Infiltrative opthalmopathy
Infiltrative dermopathy
Infiltrative opthalmopathy
Accumulation of soft tissue and inflammatory cells behind the eye leading to proptosis
Infiltrative dermopathy
Thickening and induration of the skin on the anterior shin
Pre-tibial myxoedema
Hashimoto’s thyroiditis
Most common cause of hypothyroidism in areas where iodine is readily available
An auto-immune disease- immune system destroys its own thyroid tissue
Progressive depletion of thyroid cells by inflammation and replaced by fibrosis
- decreased T3 and T4
- increased TSH
Thyroid tumours
Follicular adenoma- benign tumour of the thyroid follicular cells
Four main types of carcinoma
- pappilary (75-85%): increased risk of lymph node metastasis
- follicular (10-20%): increased mets to bone, lung and liver
- medullary (5%): arise from C cells
- anaplastic (<5%): older patients, poor prognosis
Para-follicular cells
C cells secrete calcitonin which promotes reduction of calcium concentration in the blood
Para- follicular cells (C cells) are found between the follicles
C cells are the origin of medullary carcinoma of the thyroid
Parathyroid glands
Secrete parathyroid hormone
Controls the levels of calcium in the blood
Decrease in blood calcium stimulates PTH secretion
Chief cells with no lumen
Pathology of parathyroid glands
Adenoma- involves one gland
Hyperplasia- involves all four glands
Both cause hypercalcaemia
Adrenal glands
Paired glands
Upper poles of the kidneys
Consist of adrenal cortex and adrenal medulla which are embryologically, morphologically and functionally distinct
Adrenal cortex derived from
The mesoderm
Adrenal medulla derived from
The neural crest
Normal adrenal gland
Characteristically orange/ yellow in colour because cells are rich in lipids
Adrenal cortex
Divided into three distinct zones
- zona glomerulose
- zona fasciculata
- zona reticularis
Cells appear pale on histology becuase the lipids are cleared by chemicals during processing
Functional zonation of the adrenal cortex (salt, sugar, sex)
Zona glomerulosa
- minerlocorticoid
- aldosterone
- for absorption of sodium
Zona fasciculata
- glucocorticoids
- cortisol and corticosterone
- sex hormones
Zona reticularis
- 17 ketosteroids
- sex hormones
Pathology of the adrenal glands
Adrenocortical hyperactivity
Adrenocortical insufficiency
Adrenocortical hyperactivity
Due to hyperplasia, adenoma or cancer
Cushing’s syndrome (excess cortisol)
Conn’s syndrome (excess aldosterone)
Adrenogenital syndrome (excess androgens)
Adrenocortical insufficiency
Addision’s disease
Adrenal cortex adenoma
Non-functional cortical adenoma
Incidental finding on abdominal imaging
Functional adenomas can cause Cushing’s or Conn’s syndrome
Adrenal medulla
Compact cells which secrete adrenaline and noradrenaline
Fight or flight hormones
Secretion results in vasoconstriction, increased heart rate, increased blood sugar levels
Adrenal medulla cells
Neuroendocrine
Darker staining than the adrenal cortex cells
Phaechromocytoma
Tumour of the adrenal medulla
0.1-0.3% cause of treatable hypertension
10% tumour
- familial as part of MEN2
- extra adrenal
- bilateral
- malignant
- arise in childhood
Cause of phaechromocytoma
Due to high levels of catecholamines
Phaechromocytoma leads to
Precipitois increase BP and tachycardia
Palpitations
Headache
Sweating
Tremor
Sense of apprehension
