Pituitary gland physiology Flashcards
What are the main functions of the endocrine system?
integrate body functions via secretion of biologically active neuroendocrine peptides into body
What is a hormone?
substance released in one tissue
travels in blood stream (usually)
to have action in alternative tissue
(although autocrine effects also occur)
What are the 3 modes of action of hormones?
autocrine (acting on cell which released hormone)
paracrine (acts on cell adjacent to the secretory cell)
endocrine (hormone travels via bloodstream to act on cell type in distant location to secretory cell)
What are the main physical properties of hormones?
peptides (charged)
steroid (aliphatic)
amino acid derivatives (this is variable)
Hormones act at surface or nuclear receptors
What are the main features of the endocrine system?
mesoderm origin transmission of signals via body fluids (mostly blood) generalised circulation chemical signals effects can take minutes to days
What is the anatomical position of the pituitary?
Immediately inferior to the hypothalamus
Lies in the Sella Turcica
What are the main structures that make up the pituitary?
2 lobes: Anterior pituitary (in front) Posterior pituitary (at back)
How is the anterior pituitary lobe derived?
invagination of Rathke’s pouch
= this is the roof of the embryonic oropharynx
What structure connects the 2 lobes of the pituitary? What are its embryonic origins?
pituitary stalk
also connects the broad gland to the brain
Originates from a notochordal projection
What is are alternative names for the 2 lobes of the pituitary?
anterior lobe: adenohypophysis
posterior lobe: neurohypophysis
What is the blood supply of the pituitary gland?
long and short pituitary arteries
hypophyseal portal circulation. Begins as a capillary plexus around the arc
How were pituitary cell types originally defined histologically?
acidic dyes: orange-G
basic dyes: aldehyde fuscin
What are the 5 main hormones produced in the anterior pituitary?
ACTH: regulates adrenal cortex TSH: thyroid hormone regulation GH: growth regulation LH/FSH: reproductive control PRL: breast milk production
Which cell type in the pituitary produces LH/FSH?
gonadotroph cells
basophyllic staining
central distribution in gland
pleomorphic granules
Which cell type in the pituitary produces prolactin?
lactotroph cells
acidophyllic staining
peripheral distribution in gland
ovoid dense granules
Which cell type in the pituitary produces GH?
somatotroph cells
acidophyllic or chromophobic staining
peripheral distribution in gland
spherical granules
Which cell type in the pituitary produces ACTH?
corticotroph cells
acidophyllic or basophyllic staining
central distribution
stellate granules
Which cell type in the pituitary produces TSH?
thyrotroph cells
basophyllic staining
central and Pas Intermedia distribution
Irregular granules
What are the main posterior pituitary hormones?
ADH: water regulation
Oxytocin: breast milk expression
What hypothalamic mediators are released to stimulate hormone release from the pituitary?
gonadotrophin releasing hormone: releases FSH/LH
GH releasing hormone: releases GH
thyrotrophin releasing hormone: releases TSH
Corticotrophin releasing hormone: releases ACTH
In endocrinology, where are primary, secondary and tertiary pathologies?
Primary: end organ
Secondary: pituitary
Tertiary: hypothalamus
How do hormones and fluid travel between the hypothalamus and pituitary?
via portal circulation
In general, what is the function of hypothalamic factor?
Released from hypothalamus (tertiary source)
Acts on pituitary (secondary source)
Stimulates release release of pituitary hormone
Which then acts on the end organ (primary source)
What organs does the end organ hormone have a negative feedback loop on?
Secondary and Tertiary organs
e.g. pituitary and hypothalamus
What is the outcome in a negative feedback loop?
stopping of that hormone release for eg.
usually mediated by elevated secretion and or levels of that hormone in the system
What are the main clinical presentations of pituitary tumours?
Hormone hypersecretion
Space occupying lesion (headaches, visual loss, cavernous sinus invasion - this is lateral to the sella tunica)
Hormone hypo secretion/deficiency
(interference with remaining normal pituitary function)
What are the names of the illnesses that are caused by pituitary hormone hypersecretion?
GH: acromegaly ACTH: Cushing's disease TSH: Secondary thyrotoxicosis LH/FSH: non-functioning pituitary tumour PRL: prolactinoma
These are often caused by pituitary tumours
What is IGF-1?
Insulin-Like GF
Produced primarily by liver
Release is stimulated by GF
works in conjunction with GF to stimulate cell growth and proliferation
What are some of the clinical systemic effects of GH/IGF excess?
acromegaly acanthosis nigricans fasting hyperglycaemia insulin resistance + DM (increased) nitrogen retention high triglycerides reduced total cholesterol increased skin thickness
What are complications of excess GH/IGF?
Cardiomyopathy + hypertension
bowel polyps + colonic cancer
multimodal goitre + hypogonadism
arthropathy + obstructive sleep apnoea (OSA)
What are the actions of cortisol?
increased plasma glucose levels:
increased gluconeogenesis, glycogenesis, glycogen storage
decreased glucose utilisation
increased lipolysis
Protein catabolism:
free aa are released
Na+ and H2O retention: maintains BP
Anti-inflammatory
Increased gastric acid production
How does Cushing’s syndrome present clinically?
changes in sex hormones:
excess hair growth (e.g. hirtuism), irregular periods, infertility, impotence)
salt and water retention:
high BP, fluid retention
changes in protein and fat metabolism: central obesity moon face buffalo hump think skin, easy bruising osteoporosis DM
What are the main features of prolactinomas?
fairly common
PRL is under different regulation to all other pituitary hormones
Dopamine inhibits PRL release
Positive feedback loop
Which drugs interfere with dopamine and prolactin (PRL) release and signalling?
anti-emetics
anti-psychotics
HRT
oral contraceptives
What are the clinical features of PRL excess caused by prolactinoma? What illness does this cause?
known as Hypogonadism
Causes: infertility oligomenorrhoea amenorrhoea galactorrhea reduced libido impotence
What is the treatment for prolactinomas?
dopamine agonists
e.g. bromocriptine, cabergoline
NOT SURGERY
What are non-functioning pituitary tumours?
30% of all pituitary tumours
Hormone excess does not occur with these tumours
Symptoms associated more with space-occupying nature of lesion:
headaches, visual loss, nerve palsies, interference with remaining pituitary function (compression) causing hormone deficiency
What is the treatment for non-functioning tumours?
transsphenoidal surgery ± radiotherapy
no effective medical therapy
What is the order of hormones that are lost (due to impaired pituitary function) when there is an expanding pituitary tumour? Why? (think of biological importance)
earliest loss: LH/FSH (sex) GH (growth) TSH (metabolism) ACTH (survival) PRL (stalk compression, brain survival) last to be lost
What is the treatment for pituitary adenomas?
Surgery: transsphenoidal, or adrenalectomy if Nelson’s syndrome)
Radiotherapy: SLOW
Drugs: block hormone action, or stop hormone release
What are the main causes of pituitary failure?
Tumour (benign/malignant)
Trauma
Infection
Inflammation (sarcoidosis, histiocytosis)
Apoplexy (bleeding within organs, akin to a stroke)
Iatrogenic
What is sarcoidosis?
formation of granulomas
Granulomas are abnormal collections of inflammatory cells
Can affect multiple and any organs
but most commonly, lymph nodes, lungs, skin etc
Cause is not well understood. May be triggered by infection or auto-immune reaction
What is histiocytosis?
Histiocyte = dendritic cell or macrophage
(antigen presenting cell)
Histiocytosis is an elevated or abnormal number/level of histiocytes
Treated by chemotherapy
What are the main clinical features of hypopituitarism?
Thyroid: bradycardia, weight gain, cold intolerance, hypothermia, constipation
Reduced cortisol: tiredness, weakness, anorexia, postural hypotension, myalgia
Sex steroids: oligomenorrhoea, reduced libido, hot flushes, reduced body hair
Reduced GH: tired, central weight gain
What are the treatment options for hypopituitarism?
Depends on which end organ (primary) tissues are affected. But is usually hormone replacement.
Thyroid: thyroxine
Sex steroids: testosterone, oestrogen
Reduced cortisol: hydrocortisone
Reduced GH: growth hormone
What is secreted from the posterior pituitary?
ADH
Oxytocin
Where are ADH and oxytocin made and how are they transported to the posterior pituitary?
- made in hypothalamus
- transported by the hypothalamo-hypophyseal portal system
