Pituitary gland physiology

Question 1

What are the main functions of the endocrine system?

Answer 1

integrate body functions via secretion of biologically active neuroendocrine peptides into body

Question 2

What is a hormone?

Answer 2

substance released in one tissue
travels in blood stream (usually)
to have action in alternative tissue
(although autocrine effects also occur)

Question 3

What are the 3 modes of action of hormones?

Answer 3

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)

Question 4

What are the main physical properties of hormones?

Answer 4

peptides (charged)
steroid (aliphatic)
amino acid derivatives (this is variable)

Hormones act at surface or nuclear receptors

Question 5

What are the main features of the endocrine system?

Answer 5

mesoderm origin
transmission of signals via body fluids (mostly blood)
generalised circulation 
chemical signals
effects can take minutes to days

Question 6

What is the anatomical position of the pituitary?

Answer 6

Immediately inferior to the hypothalamus

Lies in the Sella Turcica

Question 7

What are the main structures that make up the pituitary?

Answer 7

2 lobes:
Anterior pituitary (in front)
Posterior pituitary (at back)

Question 8

How is the anterior pituitary lobe derived?

Answer 8

invagination of Rathke’s pouch

= this is the roof of the embryonic oropharynx

Question 9

What structure connects the 2 lobes of the pituitary? What are its embryonic origins?

Answer 9

pituitary stalk
also connects the broad gland to the brain
Originates from a notochordal projection

Question 10

What is are alternative names for the 2 lobes of the pituitary?

Answer 10

anterior lobe: adenohypophysis

posterior lobe: neurohypophysis

Question 11

What is the blood supply of the pituitary gland?

Answer 11

long and short pituitary arteries

hypophyseal portal circulation. Begins as a capillary plexus around the arc

Question 12

How were pituitary cell types originally defined histologically?

Answer 12

acidic dyes: orange-G

basic dyes: aldehyde fuscin

Question 13

What are the 5 main hormones produced in the anterior pituitary?

Answer 13

ACTH: regulates adrenal cortex
TSH: thyroid hormone regulation
GH: growth regulation
LH/FSH: reproductive control 
PRL: breast milk production

Question 14

Which cell type in the pituitary produces LH/FSH?

Answer 14

gonadotroph cells
basophyllic staining
central distribution in gland
pleomorphic granules

Question 15

Which cell type in the pituitary produces prolactin?

Answer 15

lactotroph cells
acidophyllic staining
peripheral distribution in gland
ovoid dense granules

Question 16

Which cell type in the pituitary produces GH?

Answer 16

somatotroph cells
acidophyllic or chromophobic staining
peripheral distribution in gland
spherical granules

Question 17

Which cell type in the pituitary produces ACTH?

Answer 17

corticotroph cells
acidophyllic or basophyllic staining
central distribution
stellate granules

Question 18

Which cell type in the pituitary produces TSH?

Answer 18

thyrotroph cells
basophyllic staining
central and Pas Intermedia distribution
Irregular granules

Question 19

What are the main posterior pituitary hormones?

Answer 19

ADH: water regulation
Oxytocin: breast milk expression

Question 20

What hypothalamic mediators are released to stimulate hormone release from the pituitary?

Answer 20

gonadotrophin releasing hormone: releases FSH/LH

GH releasing hormone: releases GH

thyrotrophin releasing hormone: releases TSH

Corticotrophin releasing hormone: releases ACTH

Question 21

In endocrinology, where are primary, secondary and tertiary pathologies?

Answer 21

Primary: end organ
Secondary: pituitary
Tertiary: hypothalamus

Question 22

How do hormones and fluid travel between the hypothalamus and pituitary?

Answer 22

via portal circulation

Question 23

In general, what is the function of hypothalamic factor?

Answer 23

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)

Question 24

What organs does the end organ hormone have a negative feedback loop on?

Answer 24

Secondary and Tertiary organs

e.g. pituitary and hypothalamus

Question 25

What is the outcome in a negative feedback loop?

Answer 25

stopping of that hormone release for eg. | usually mediated by elevated secretion and or levels of that hormone in the system

Question 26

What are the main clinical presentations of pituitary tumours?

Answer 26

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)

Question 27

What are the names of the illnesses that are caused by pituitary hormone hypersecretion?

Answer 27

``` GH: acromegaly ACTH: Cushing's disease TSH: Secondary thyrotoxicosis LH/FSH: non-functioning pituitary tumour PRL: prolactinoma ``` These are often caused by pituitary tumours

Question 28

What is IGF-1?

Answer 28

Insulin-Like GF Produced primarily by liver Release is stimulated by GF works in conjunction with GF to stimulate cell growth and proliferation

Question 29

What are some of the clinical systemic effects of GH/IGF excess?

Answer 29

``` acromegaly acanthosis nigricans fasting hyperglycaemia insulin resistance + DM (increased) nitrogen retention high triglycerides reduced total cholesterol increased skin thickness ```

Question 30

What are complications of excess GH/IGF?

Answer 30

Cardiomyopathy + hypertension bowel polyps + colonic cancer multimodal goitre + hypogonadism arthropathy + obstructive sleep apnoea (OSA)

Question 31

What are the actions of cortisol?

Answer 31

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

Question 32

How does Cushing's syndrome present clinically?

Answer 32

[increased ACTH]: sustained effects of cortisol on systemic receptors 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 ```

Question 33

What are the main features of prolactinomas?

Answer 33

fairly common PRL is under different regulation to all other pituitary hormones Dopamine inhibits PRL release Positive feedback loop

Question 34

Which drugs interfere with dopamine and prolactin (PRL) release and signalling?

Answer 34

anti-emetics anti-psychotics HRT oral contraceptives

Question 35

What are the clinical features of PRL excess caused by prolactinoma? What illness does this cause?

Answer 35

known as Hypogonadism ``` Causes: infertility oligomenorrhoea amenorrhoea galactorrhea reduced libido impotence ```

Question 36

What is the treatment for prolactinomas?

Answer 36

dopamine agonists e.g. bromocriptine, cabergoline NOT SURGERY

Question 37

What are non-functioning pituitary tumours?

Answer 37

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

Question 38

What is the treatment for non-functioning tumours?

Answer 38

transsphenoidal surgery ± radiotherapy | no effective medical therapy

Question 39

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)

Answer 39

``` earliest loss: LH/FSH (sex) GH (growth) TSH (metabolism) ACTH (survival) PRL (stalk compression, brain survival) last to be lost ```

Question 40

What is the treatment for pituitary adenomas?

Answer 40

Surgery: transsphenoidal, or adrenalectomy if Nelson's syndrome) Radiotherapy: SLOW Drugs: block hormone action, or stop hormone release

Question 41

What are the main causes of pituitary failure?

Answer 41

Tumour (benign/malignant) Trauma Infection Inflammation (sarcoidosis, histiocytosis) Apoplexy (bleeding within organs, akin to a stroke) Iatrogenic

Question 42

What is sarcoidosis?

Answer 42

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

Question 43

What is histiocytosis?

Answer 43

Histiocyte = dendritic cell or macrophage (antigen presenting cell) Histiocytosis is an elevated or abnormal number/level of histiocytes Treated by chemotherapy

Question 44

What are the main clinical features of hypopituitarism?

Answer 44

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

Question 45

What are the treatment options for hypopituitarism?

Answer 45

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

Question 46

What is secreted from the posterior pituitary?

Answer 46

ADH | Oxytocin

Question 47

Where are ADH and oxytocin made and how are they transported to the posterior pituitary?

Answer 47

- made in hypothalamus | - transported by the hypothalamo-hypophyseal portal system