Pituitary Gland Flashcards
(25 cards)
What is a hormone
A message carried from the organ where they are produced to the organ which they affect by means of bloodstream
Types of hormones
Peptide and steroid
Peptide hormones:
Synthesis, storage and receptors
Synthesised as prohormones requiring further processing to activate
Stored in vesicles (regulatory secretion)
Bind receptors in cell membrane and transducer signal using 2nd messenger systems
Steroid hormones:
Synthesis, storage and receptors
Synthesised in a series of reactions from cholesterol Released immediately (constitutive secretion) Bind to intracellular receptors to change gene expression directly
Describe function and pathway of Hypothalamic parvocellular neurons
Regulate anterior pituitary function
Neurones are short and terminate on median eminence
Release hypothalamic releasing/inhibitory factors into capillary plexus in median eminence
These hypothalamic regulatory factors carried by portal circulation to anterior pituitary
Anterior Pituitary - adenohypophysis
Anatomically distinct from hypothalamus
Made up of endocrine cells:
Somatotrphs, Lactotrophs, Corticotrophs, Thyrotrophs and Gonadotrophs
Regulated by hypothalamic releasing/inhibiting factors via hypophyseal-pituitary portal system
How does the Hypothalamo-pituitary portal system work?
Axon terminals of hypothalamic neurosecretory cells release hormones into the system
The RHs and IHs travel in the portal system to the anterior pituitary
The RHs and IHs stimulate or inhibit the release of hormones from anterior pituitary cells
Anterior pituitary hormones leave the gland via the blood
These blood vessels constitute the hypothalamic-pituitary portal system
Describe regulation of thyroid hormone production
Axon terminals of hypothalamic neurosecretory cells release Thyrotrophin Releasing Hormone (TRH) into hypothalamo-hypophysial portal system
TRH travels in the portal system to the anterior pituitary
TRH stimulates the release of Thyroid Stimulating Horomone (Thyrotrophin) from anterior pituitary thyrotrophs
TSH leaves the gland via the blood to travel to the thyroid gland to stimulate thyroid hormone release (thyroxine)
Somatotrophs
Growth hormone (somatotrophin) - releasing
Somatostatin- inhibiting
Receptor: general body tissues (particularly liver)
Lactotrophs
Prolactin (dopamine) - inhibiting
Receptor: breasts (lactating women)
Thyrotrophs
Thyroid stimulating hormone (TSH)
Thyrotrophin
-releasing
Receptor: thyroid
Gonadotrophs
Luteinising hormone (LH) [receptor: testes] Follicle Stimulating Hormone (FSH) [receptor: ovaries] - releasing
Corticotrophs
Adrenocorticotrophic hormone (ACTH, corticotrophin)
-releasing
Receptor: adrenal cortex
Assessing a bitemporal hemianopia
Normal vision - full view
Pituitary tumour - only see middle section of normal view
Describe bitemporal hemianopia
Fibres from the nasal retinae cross at the optic chiasm
Compression of the optic chiasm by a pituitary/ suprasellar tumour prevents transmission of sensory information from lateral visual fields to the occipital lobe
Name bony dish the pituitary gland sits in
Sella turcica of sphenoid bone
Describe the neuroendocrine reflex arc: milk production
Mechanical stimulation of nipple and surrounding area activated afferent pathways
Afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurons
Less dopamine in the hypothalamic-pituitary portal system causes less inhibition of anterior pituitary lactotrophs
Increased plasma prolactin increases milk secretion in mammary glands
Mechanism of growth hormone action
Growth hormone (somatotrophin) released from anterior pituitary
Travels directly to body tissues causing metabolic actions that increase growth and development
Also reaches the liver which releases insulin like growth factor (somatomedin) which then travels to body tissues causing growth and development
Acromegaly
Excess growth hormone Coarsening of facial features (macroglossia/ prominent nose) Large jaw - prognathism Increased hand and feet size Sweatiness Headache Does not result in increased height
The posterior pituitary gland (neurohypophysis) hormones
Arginine vasopressin (anti-diuretic hormone) Oxytocin
Describe the hypothalamic magnocellular neurons
Posterior pituitary is anatomically continuous with hypothalamus
Neurons are long, originating in supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei
From Nuclei down the stalk into the posterior pituitary
Regulation of the posterior pituitary gland
Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport the. To the posterior pituitary
Excitation of these hypothalamic magnocellular neurons stimulates release of AVP or oxytocin into the posterior pituitary where they leave via blood and diffuse into blood capillaries
Physiological action of vasopressin
Diuresis= production of urine
Main physiological action is stimulation of water reabsorption in the renal collecting duct, this concentrates urine. Acts through the V2 receptor in the kidneys
Also a vasoconstrictor via V1 receptor stimulating ACTH release from anterior pituitary
Physiological actions of oxytocin
- Uterus at parturition, myometrial cells - Contraction for delivery of baby
- Great during lactation, myoepithelial cells - Contraction for milk ejection
