The Pituitary Gland Flashcards
where is the pituitary gland?
Sits in a bony cavity at the base of the brain called the Sella Turcica
what components is the pituitary gland made of?
Consists of two lobes:
anterior and posterior
what is the name of the stalk that connects the pituitary to the hypothalamus?
the infundibular stalk
what is the difference between the anterior and posterior pituitary gland?
The anterior lobe produces and releases hormones.
The posterior lobe does not produce hormones —this is done by nerve cells in the hypothalamus—but it does release them into the circulation
they also have different embryological origin
what hormones are in the anterior pituitary gland?
○ TSH – thyroid hormone synthesis & secretion
○ ACTH – adrenal corticosteroid synthesis
○ FSH/LH – egg/sperm development
○ GH – longitudinal growth
○ prolactin – breast milk production
what hormones are in the posterior pituitary gland?
○ ADH – water balance/osmolality
○ oxytocin – parturition (delivery of foetus/lactation)
what does the hypothalamus do?
The hypothalamus is the final common pathway by which signals from multiple systems reach the anterior pituitary gland
what 3 nuclei does the hypothalamus consist of?
Its endocrine functions are mainly regulated by paraventricular, supraoptic and ventromedial nuclei.
what hormone does the supraoptic nucleus produce?
Antidiuretic hormone (ADH)
what hormone does the paraventricular nucleus produce?
oxytocin
what non-endocrine functions does the hypothalamus have?
regulation of body temp, thirst and food intake, and blood pressure
what is the hypothalamuses functions regulated by?
- hormone-mediated signals- (like negative feedback)
- neural inputs- (mediated by neurotransmitters like acetylcholine, dopamine, norepinephrine, epinephrine, serotonin, GABA)
where in the body does the hypothalamus send signals to?
It sends signals to other parts of nervous system (eg. in brain stem, vasopressinergic neurons involved in autonomic regulation of BP – similar neurons project to gray matter, implicated in higher cortical functions)
how many nerve cells does the hypothalamus- pituitary consist of?
2 sets
what do the 2 sets of nerve cells in the hypothalamus- pituitary do?
1) One set sends hormones it produces down its axon, through the infundibular stalk- enters posterior lobe and goes to its axon terminal
2) The other set produce stimulating and inhibiting hormones that flow down blood vessels in the infundibular stalk and reach the anterior lobe.
what regulates the GH in the hypothalamus?
GH releasing hormone (GHRH) -stimulates the secretion
somatostatin & dopamine- inhibits the secretion
what regulates the FSH and LH in the hypothalamus?
Gonadotropin releasing hormone (GnRH)- stimulates the secretion
Prolactin - inhibits the secretion
how does prolactin inhibit FSH and LH?
Inhibits gonadal activity through central GnRH suppression which results in decreased FSH/LH- acts as natural contraceptive
what are common pituitary diseases?
what are their most common outcomes?
Sellar or Parasellar lesions cause mass effects.
Mass effects: When brain structures are compressed and injured due to the degree of space that leaking blood, cerebrospinal fluid, or edema (swelling) takes up within the restricted skull space.
The most common outcomes of these mass effects are:
Neurological effects
Visual effects
Hypopituitarism (defective secretion of pituitary hormones)
Hormone hypersecretion caused by an adenoma (benign tumour)
NB: pituitary adenoma can be non-function as well.
what are the neurological and visual mass effects of pituitary diseases?
Visual effects are caused because the optic chiasm is located right above the pituitary gland
Neurological effects are caused as lateral to the pituitary gland we have various cranial nerves.
Pressure effects on these can cause optic nerve damage or cranial nerve damage:
CNIII, IV, V, VI compression/damage (contained within cavernous sinus)
CNII damage - compression of optic chiasm causes bitemporal heterogenous hemianopia (vision is missing in the outer half of both the right and left visual field)
If the lesion exerts pressure in any direction you will get a head ache
If the lesion exerts pressure downward to sinusoid sinus - you get CSF leak
If the lesion is large enough to exert pressure up to the hypothalamus you get hypothalamic damage or brain damage
what is Hypopituitarism?
major causes?
defective secretion of pituitary hormones
Major Causes:
Hypothalamic releasing hormone deficiency (e.g Kallmann’s syndrome)
Trauma
Pituitary/Para-pituitary tumours
Radiotherapy of the pituitary or brain due to a tumour can cause the pituitary itself to be affected by radiation
Pituitary apoplexy (bleeding or impaired blood supply of the pituitary) caused by death of an infarction or Sheehan’s syndrome
Infiltration of the pituitary by inflammatory cells (sarcoidosis) or iron(haemochromatosis)
what are functioning pituitary adenomas?
Benign tumour at pituitary gland which hyper-secretes one or more hormones
If these adenomas are large enough, they will exert pressure effects e.g. on the optic pathway causing vision problems.
what is GH?
stimulated/ supressed by?
what does it cause/ stimulate?
released throughout your life
stimulated by hypoglycaemia, exercise, sleep
Supressed by Hyperglycaemia
has a pulsatile manner of secretion (see graph) - levels are usually undetectable throughout the day
It causes secretion of insulin-like growth factors (IGFs) in the liver
Its effects are controlled/carried out by these IGF-1:
Cause cartilage growth
tissue growth
Bone growth
Action on bone growth plates causes linear growth in children
Stimulates:
protein synthesis
lipolysis
increase in blood glucose
Important for Psychological well-being
what are GH deficiency manifestations?
manifestations:
children: poor growth - dwarfism
adults:
increased abdominal fat and decreased lean body mass
decreased muscle strength & exercise capacity
impaired cardiac function
impaired lipid profile
impaired psychological well-being