Pituitary Gland Flashcards
What is a hormone
A messenger that is carried from the organ where they are produced to the organ where they affected by means of bloodstream
What are the two types of hormone
Peptide and steroid
Peptide hormone synthesis
Synthesised as pro hormones requiring further processing for example cleavage to activate. So pro hormones are basically long peptide chains for example Insulin
Steroid hormone synthesis
Synthesising a series of reactions from cholesterol
Stores with peptide hormones
They are stored in vesicles just beneath the membrane of cells and these are only released when the vesicles fuse with the cell membrane
Steroid home storage
Released immediately so it’s constitutive secretion
Peptide hormone receptors
Find receptors on the cell membrane and transducer signal using second messenger system
Steroid hormone receptors
Bind to intracellular receptors to change gene expression directly
What is the name of the neurons that regulate anterior pituitary function
Parvocellular neurons
Characteristics of hypothalamic parvocellular neurons
Short and terminate on median eminence
Release hypothalamic releasing – factors into capillary plexus and median Eminence
These hypothalamic regulatory factors are carried by portal circulation to anterior pituitary
Name the anterior pituitary
Adenohypophysis
Why is the anterior pituitary anatomically distinct from the hypothalamus
It’s not neuronal instead it has endocrine cells
Five types of endocrine cells (cells which contain hormones)
Somatotrophs Lactotrophs Corticotrophs Thyrotrophs Gonadotrophs
What are the endocrine cells in the anterior pituitary gland controlled by
Regulated by hypothalamic releasing – inhibiting factors via hypophyseal- pituitary portal system
Hypothalamus-pituitary portal system
) axon terminals of hypothalamic neurosecretory cells release hormones ( Releasing hormones and inhibitory hormones ) into the hypothalamo-pituitary portal system ( diffuse in as there are lots of fenestrations in the blood vessels)
These travel in the portal system to the anterior pituitary
The releasing hormones and inhibitory hormones stimulate or inhibit the release of hormones from the anterior pituitary cells
The anterior pituitary hormones leave the gland via the blood
Thyroid hormone production
Axon terminals of hypothalamic neurosecretory cells release TRH into hypothalamic-hypophysial portal system
TRH travels in the portal system to the anterior pituitary
TRH stimulates the release of the Thyroid Stimulating Hormone ( 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 )
Lactotrophs
Prolactin
Thyrotrophs
Thyroid stimulating hormone ( TSH) Thyrotrophin
Gonadotrophs
LH
FSH
Corticotrophs
Adrenocorticotrophic hormone ( ACTH, corticotrophin )
Growth hormone regulators
Growth hormone releasing hormone - on switch
Somatostatin - off switch
Prolactin
Dopamine ( inhibitory )
TSH ( thyrotrophin)
Thyrotrophin releasing hormone
LH , FSH
Gonadotropin releasing hormone
Adrenocorticotrophic hormone ( ACTH, corriocotrophin )
Corticotrophin releasing hormone
Target cells of growth hormone
General body tissues in particular liver
Prolactin target
BreastS of lactating women
TSH target
Thyroid
Gonadotrophs ( LH and FSH) target
Testes and ovaries
Adrenocorticotrophic hormone target
Adrenal cortex
What may cause a bitemporal hemianopia
Cannot see temporal aspects of visual field / outer aspects due to pituitary tumour which has grown out of sella tursica and onto optic chiasm ( supra sella)
Fibres from the nasal ( medial) retinae cross at the optic chiasm and compression of the optic chiasm by a pituitary tumour prevents the transmission of sensory information from lateral visual fields to the occipital lobe
Milk production ( reflex arc)
Mechanical stimulation of nipple and surrounding area activates afferent sensory pathways
Afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurones
Less dopamine in the hypothalamic pituitary portal system causes less inhibition of anterior pituitary lactotrophs
Increased plasma prolactin increases milk secretion in mammary glands which travels by blood to nipple
Mechanisms of growth hormone action
Direct secretion of somatotrophin onto body tissues
Indirectly somatotrophin travels to liver where it stimulates Insulin like Growth factor ( somatomedin )
IGF-1 then binds to receptors on muscle and bone and can also stimulate growth
Gigantism
Too much growth hormone release before puberty ends leads to gigantism as the femur / epiphyseal plates only fuse together after puberty has finished
But if too much growth hormone happens after puberty has fished once the growth plates have fused , you can’t grow taller and this is called acromegaly. But get other physiological changes
Physiological features of acromegaly
Coarsening of facial features
Macroglossia ( increased size of tongue )
Prominent nose
Large jaw - prognathism
Increased hand and feet size and spade like hands
Sweatiness
Headache
What is the posterior pituitary gland called
Neurohypophysis
Hormones associated with the posterior pituitary gland
Arginine vasopressin ( AVP)/ ADH Oxytocin
Why is the posterior pituitary gland anatomically continuous with the hypothalamus
Posterior pituitary gland is made of neuronal tissues and has hypothalamic magnocellular neurons
These are long and originate in super optic ( AVP) and paraventricular (oxytocin ) hypothalamic nuclei
Nuclei -> stalk -> posterior pituitary
Regulation of the posterior pituitary gland
Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport them to the posterior pituitary
Excitation of these hypothalamic magnocellular neurones stimulates the release of AVP or oxytocin onto the posterior pituitary where they diffuse into blood capillaries and then leave the posterior pituitary via the b
Pod
Physiological action of vaspressin
Stimulation of water reabsorption in the renal collecting duct
This concentrates the urine
Acts through the V2 receptor in the kidney
Also a vasoconstrictor ( V1)
Stimulates ACTH release from anterior pituitary
Actions of oxytocin when delivering baby
Acts on uterus at parturition
Causes myometrial cells to contract
Delivery of baby
Can use oxytocin analogue for women who need biological encouragement to contracts
Oxytocin and lactation
Milk ejection is controlled by the posterior pituitary gland
Oxytocin acts on breast during lactation
Which causes myoepothelial cells to contract
Milk ejection
Milk ejection reflect arc
Mechanical stimulation of nipple and surrounding area causes afferent pathways
Afferent signals integrated in the hypothalamus and stimulate oxytocin releasing neurone activity
Action potentials travel down oxytocin neurones and oxytocin is secreted into the bloodstream
Incradrf plasma oxytocin increases milk ejection in mammary glands
