Diseases of Endocrine System Flashcards
Endocrine system
What is an endocrine organ?
Secretes products directly into blood stream to reach a distant target e.g. Islets of Langerhan cells secrete hormones into blood vessels
What is an exocrine organ?
Secretes products into ducts that lead to target e.g. acinar cells secrete pancreatic enzymes into pancreatic duct
What are the 4 types of hormones?
- Neurocrine
- Endocrine
- Paracrine
- Autocrine
What are neurocrine hormones?
Secretion of hormones into the bloodstream by neurons
What are endocrine hormones?
Secretion of hormones into the bloodstream by endocrine glands
What are paracrine hormones?
Hormone molecule secreted by one cell affects adjacent cells
What are autocrine hormones?
Hormone molecule secreted by a cell affects the secreting cell
Pituitary gland
Where is the pituitary gland located?
In sella turcica; saddle shaped depression) in body of sphenoid bone of skull just beneath hypothalamus
What does the pituitary gland consist of?
2 lobes; anterior and posterior
What is the ‘adenohypophysos’?
Another name for anterior lobe of pituitary gland
What is the ‘neurohypophysis’?
Another name for posterior lobe of pituitary
What is the anterior pituitary lobe under control of?
Hypothalamus
Function of hypothalamus?
Produces and secretes the majority of pituitary hormones:
- TSH
- FSH & LH
- ACTH
- GH
- Prolactin
- Endorphins
Function of the hormones secreted by the anterior pituitary?
- TSH –> stimulates thyroid to produce T3 and T4
- GH –> skeletal muscle growth and function
- Prolactin –> acts on mammary glands (lactation)
- FSH and LH –> sex hormones
- ACTH –> stimulates adrenal cortex to release cortisol
- Endorphins –> acts on pain receptors in brain
Function of posterior pituitary lobe?
Stores hormones that are initially produced by hypothalamus:
- ADH
- Oxytocin
Function of hormones stored by posterior pituitary?
- Oxytocin; stimulation of mamillary glands (provokes milk ejection) and uterine muscles (childbirth)
- ADH (vasopressin); increases water reabsorption
Pituitary lobe hormones overview
What is an ‘adenoma’?
a type of non-cancerous tumor or benign that may affect various organs
Are pituitary tumours normally benign or malignant?
Almost always benign - ‘adenoma’
If a pituitary adenoma is ‘functional’, what does this mean?
- Adenoma is producing hormones - the hormone produced depends on the cell type that is proliferating e.g. prolactinoma, GH secreting, ACTH secreting
- If functional, the clinical effects of the tumour reflect the effects of excess hormone production
What are local effects of pituitary tumours?
- Pressure on the optic chiasm anteriorly (bitemporal hemianopia)
- Pressure on adjacent pituitary cells (hypofunction of other cells)
- Stretching of meningeal cover of brain due to tumour –> pain
What is a prolactinoma? What does it result from?
- A noncancerous tumor of the pituitary gland that causes the pituitary to make too much prolactin.
- Result from mutation in lactotroph cells of anterior pituitary which are responsible for producing prolactin –> results in uncontrollable division of lactotrophs
Prolactinomas cause an increase in prolactin. What are the symptoms of this?
- Infertility
- Amenorrhea
- Gynecomastia
- Galactorrhea
What measurements define a:
- microprolactinoma?
- macroprolactinoma?
- microprolactinoma <10mm
- macroprolactinoma >10mm
What is bitemporal hemianopia?
‘Tunnel vision’ –> impaired peripheral vision in outer temporal halves of visual field of each eye (i.e. partial blindness affecting lateral halves of vision due to compression/lesions of optic chiasm)
What does bilateral hemianopia result from?
Prolactinoma compresses optic nerve/chiasm
What is a growth hormone–secreting pituitary adenoma? What does it result from?
- Benign pituitary tumour that releases GH
- Mutation of somatotropic cells; responsible for releasing GH
Clinical presentation of growth hormone–secreting pituitary adenoma in:
a) adults
b) children
- Adults: acromegaly
- Excessive growth of the hands, feet, jaw, and internal organs
- MRI shows that a pituitary tumour in 90% of acromegalic patients
- Children: gigantism__
- Abnormally high linear growth due to the excessive action of growth hormone before the closure of the epiphyseal growth plates in childhood
Why does growth hormone–secreting pituitary adenoma present differently in adults and children?
Excessive action of growth hormone before the closure of the epiphyseal growth plates in childhood
Which test is used to diagnose a growth hormone–secreting pituitary adenoma?
Oral glucose suppression test;
- Normally glucose suppresses GH
- In acromegaly glucose does not suppress GH (due to tumour)
Thyroid gland anatomy
What 3 hormones does the thyroid gland produce?
- T3 (active); triiodothyronine
- T4; thyroxine
- Calcitonin
Describe stimulation from hypothalamus to thyroid gland
- Hypothalamus secretes TRH
- Stimulates thyrotrophs of pituitary gland to secrete TSH
- Stimulates thyroid gland to produce T3 and T4
This then is under a negative feedback loop.
Which cells of the pituitary gland secrete TSH?
Thyrotrophs
Which cells of the pituitary gland secrete GH?
Somatotropic cells
Which cells of the pituitary gland secrete prolactin?
Lactotrophs
What is thyroglobulin?
- protein produced by follicle cells and stored in thyroid gland
- is the main precursor to thyroid hormones; thyroglobulin’s tyrosine residues + iodine –> thyroid hormones
Regulation of thyroid hormones
What is hypothyroidism?
Overall insufficiency of circulating T3 and T4 hormones