Scenario 16: Patrick's Pituitary Flashcards
Describe the axis which leads to cortisol secretion and the feedback loops in place to control this
Trauma/stress causes CRH release which causes anterior pituitary feedback causing ACTH release causing cortisol release. Cortisol acts on the anterior pituitary and CRH release in a negative feedback loop
What are some classic signs of Grave’s disease?
Goitre, exophthalmos, upper eyelid retraction, pretibial myxoedema, thickening of skin due to glycosaminoglycan deposition and the classic signs of hyperthyroidism
What are Herring bodies?
Accumulation of hormones within an axon
What is the main hormone released by the thyroid gland?
T4 which is converted to T3 in the periphery
What is the blood supply to the thyroid gland?
Superior and inferior arteries arising from external carotid and subclavian artery
What kind of receptors do peptide hormones bind to?
Cell membrane receptors
What controls growth hormone release?
Hypothalamic hormones- somatostatin and negative feedback from growth hormone releasing hormone
What is the inactive version of cortisol?
Cortisone
What are the symptoms of hypothyroidism?
Cold intolerance, dry skin, weight gain, constipation, hoarse voice, slow reflexes, coarse hair and skin, hypercholesterolemia, puffiness
What are the symptoms of diabetes insipidus?
Polyuria, polydipsia, with no change in urinary glucose
How are steroid hormones synthesised?
ACTh acts on a G-protein coupled receptor (MC2R) to activate adenylate cyclase which increases cAMP levels. This in turn activates PKA which activates cholesterol ester hydrolase (CEH) which liberates cholesterol from lipid droplets. There is also a stimulation of cholesterol 2022 hydroxylase also referred to as desmolase, the rate limiting enzyme. Steroid hormones are then formed from cholesterol
What are the shapes of left and right adrenal glands respectively?
Right: pyramidal, Left: crescent shaped
How can we test for growth hormone function?
GH stimulation test- fast for 12 hours then give insulin or arginine which should cause an increase in GH secretion.
GH suppression test- fast for 12 hours then give glucose drink which should suppress GH stimulation
What is the histological appearance of cells which secrete steriod hormones?
Lots of sER, mitochondria and lipid droplets
How can we assess hormone levels?
Bioassays of biologically active hormone, radioimmunoassay of hormone
What stimulates the gonads to produce testosterone/estradiol?
LH/FSH (lutenising hormone/follicle stimulating hormone)
Which cells regulate the secretion of the anterior pituitary?
Neuroendocrine cells of the hypothalamus whose axons project to the median eminence
What is the shape of thyroid gland?
2 pear shaped lateral lobes connected by an isthmus in the midline
What do glucocorticoids increase the production of?
Annexin-1, which inhibits PLA
How are T4 levels controlled?
Feedback, tissue action, hormone metabolism and fecal excretion
How does thyroid hormone interact with it’s receptors?
Interacts with nuclear receptors, enters cells by diffusion or by specific carrier. T3 enters nucleus and binds to thyroid receptor. Hormone receptor complex binds to thyroid hormone responsive element on DNA
What do the parathyroid glands secrete?
Secretes parathyroid hormone stimulates Ca2+ mobilisation
Describe the shape of a glycoprotein hormone and give some examples
A & B chains with carbohydrate e.g. lutenizing hormone, FSH, TSH, hCG
What forms the posterior pituitary in development?
The neurohypophysis (posterior pituitary) is a downgrowth from the floor of dicencephalon of the brain
What is the appearance of the adrenal medulla?
Modified sympathetic ganglion, large polyhelical cells in clumps or cords
What are the weak androgens secreted by the adrenal gland?
Dehydroepiandrosterone and it’s sulphate and androsteredione
What does the thyroid release in the thyroid axis?
Thyroxine and tridothyronine (T4 and T3)
What does the hypothalamus release in the thyroid axis?
Thyrotrophin releasing hormone
What do thyroid hormones cause?
Increase O2 and heat production, cardiac contractility, sensitivity to catecholamines, maintain hypoxia and hypercapnia drive in respiratory centre, increase gut motility, erythropoiesis, bone turnover, protein turnover and increase muscles mass, cholesterol degradation, metabolic turnover of hormones and drugs
What does oxytocin do?
Uterus contraction, milk ejection from mammary gland
What activates vasopressin receptor V2 where is it found and what does it do?
Adenyl cyclase, DCT/collecting duct, insert aquaporins to increase H2O permeability
What are the main cell types of the islet of Langerhans and what do each of them secrete?
A cells: glucagon
B cells: insulin
D cells: somatostatin
F or PP cells: pancreatic polypeptide
What is the treatment for Hashimoto’s thyroditis?
T4 or liothyronine (T3)
What stimulates secretions from the posterior pituitary?
For AVP it is changes in body water, hypoosmolarity, hypothalamic osmoreceptors, plasma volume, baroreceptors.
For oxytocin- it is parturition and lactation
What does AVP do?
Maintains blood pressure via actions on blood vessels, fluid balance, water absorption, vasoconstriciton
Give an example of a autocrine hormone
Interleukins
How can we treat acromegaly?
Treated by trans sphenoidal surgery, D2 agonists (cabergoline and bromocriptine) octrestride (long acting somatostatin) lanreotide (analogues SSTR2 agonists) pasineotide (SSTR5 agonist)/
What is myxoedema and how is it treated?
Iodine deficiency causing non-toxic goitre which should be treated with iodine supplements
Give an example of a neurocrine hormone
Neurotransmitters e.g. acetylcholine
What kind of receptors do steroid hormones bind to?
Intracellular receptors
What are amine hormones derived from?
Tyrosine or tryptophan derived
What does the adrenal medulla secrete and what stimulates this?
Secretes NA and adrenaline after stimulation from cholinergic preganglionic sympathetic input from greater and lesser splanchnic nerves via coeliac ganglion
How does growth hormone act?
Via GH receptor and insulun-like-growth factor synthesis in the liver
What is a hormone?
A biactive molecule which is secreted and travels in the blood to the target cell
What is Grave’s disease?
An autoimmune disorder where TSAb produce prolonged stimulation of TSH receptors
What is the cellular organisation of the parathyroid glands?
Densely packed small chief or principal cells arranged in irregular chords around blood vessels
How does a G protein coupled receptor work?
The G protein binds and increases cAMP, switches on gene transcription, adrenaline binds and PKA catalyses
What causes goitre?
Increased TSH secretion caused by goitrogens such as kelp, cabbage, cassava, lithium, local waters and cough mixtures
What activates vasopressin receptor V1b (V3) where is it found and what does it do?
Phospholipase C, corticotrophs, increase ACTH release
What is Hashimoto’s thyroditis?
Autoimmune disease, antibodies to thyroglobulin or thyroid peroxidase formed by body
What are the actions of growth hormone?
Growth of long bones at epiphyses, increase size of viscera, anti-insulin effects, anabolic for protein growth, catabolic for fat and carbohydrate growth
Where do the cell bodies of the neurones of the posterior pituitary lie?
In the supraoptic and paraventricular nuclei of the hypothalamus
What are the parts of the posterior pituitary?
Pars nervosa and the infundibulum
What stimulates the adrenals to produce cortisol?
ACTH (adrenocorticotropic hormone)
How does thyroglobulin accumulate in the follicles of thyroid epithelium?
Accumulates as collid, follicular cells take up iodide which is oxidised to iodine. The iodine is convalently attached to the tyrosines of thyroglobulin within the lumen of the follicle
What is the histological appearance of the adrenal cortex?
Loads of sER, lipid droplets, pale and frothy
What are the symptoms of hyperthyroidism?
Anxiety, tachycardia, sweating, tremor, heat intolerance, palpitations, eye signs, fatigue, atrial fibrillation, weight loss
What do thyroid hormones control?
Control heart rate, heat production, calorie control, metabolism, digestion, bone turnover, critical to brain development
What is the manifestation of hypersecretion of growth hormone?
Gigantism if before epiphyses fusion, acromegaly if after fusion
What controls the release of adrenocorticotrophic hormone (ACTH)?
Corticotrophin from hypothalamus and cortisol via negative feedback