4.1: The pituitary gland Flashcards
What is a hormone?
A messenger carried by the blood stream
Two main hormone classifications
Peptide and Steroid
Synthesis of Peptide hormones
synthesised as prohormones (long inactive chain) requiring further processes to activate
Storage of Peptide hormones
Stored in vesicles, released by stimulus
Receptors of peptide hormones
On cell membrane, then transducer signal using 2nd messenger (intracellular signal cascade)
Synthesis of steroid hormones
Synthesised in series of reactions from cholesterol
Storage of steroid hormones
Released immediately (constitutive secretion)
Receptors of steroid hormones
Bind to intracellular receptors, change gene expression directly
What bone does the pituitary gland sit in
Stella turcica of sphenoid bone
Another name for anterior pituitary gland, and cell type
Adenohypophysis
Epithelial
Origin of anterior pituitary gland
Upgrowth from oral ectoderm of primitive oral cavity - Rathkes pouch (in embryo)
Another name of posterior pituitary gland and cell type
Neurohypophysis
Neural origin
Where is the posterior pituitary gland derived from
Down growth of diencephalon that forms floor of the third ventricle (in embryo)
What regulates anterior pituitary function
Hypothalamic-pituitary portal system
How is the anterior pituitary gland regulated
Parvocellular neurones in the hypothalamus release signals which terminate at the median eminence.
Median eminence released hypothalamic releasing/inhibiting factors into capillary plexus in median eminence.
Factors carried by portal circulation to anterior pituitary.
5 endocrine cells making up anterior pituitary
Somatotrophs
Lactotrophs
Corticotrophs
Thyrotrophs
Gonadotrophs
Hypothalamo-pituitary portal system
Hypothalamic neurosecretory cells release hormones into hypothalamo-pituitary portal system
RHS and IHs travel in portal system to anterior pituitary
Stimulate or inhibit hormone release from anterior pituitary cells
Anterior pituitary hormones leave gland via blood
Somatotrophs release
Growth hormone
Lactotrophs release
Prolactin
Thyrotrophs release
Thyroid stimulating hormone (TSH)
Gonadotropins release
Luteinising hormone (LH)
Follicle stimulating hormone (FSH)
Corticotrophs release
Adrenocorticotrophic hormone (ACTH)
What regulates growth hormone
Releasing - growth hormone releasing hormone
Inhibiting - somatostatin
What regulates prolactin
Inhibiting- dopamine
What regulates thyroid stimulating hormone (TSH)
Releasing - thyrotrophin releasing hormone
What regulates LH and FSH
Gonadotrophin releasing hormone
What regulates Adrenocorticotrophic hormone (ACTH)
Release - corticotrophin releasing hormone
Target of GH
General body tissues (liver)
Target of prolactin
Breasts (lactating women)
Target of TSH
Thyroid
Target of Gonadotrophins (LH & FSH)
Testes and ovaries
Target of ACTH
Adrenal cortex
What sits above the pituitary gland
Optic chiasm
What happens if a pituitary tumour compresses the optic chiasm
- bitemporal hemianopia
Fibres from nasal retinae which cross at optic chiasm are compressed, preventing transmission of sensory information from lateral (temporal) visual fields to occipital lobe
Mechanism of growth hormone action
Acts directly on body tissues but also stimulates insulin-like growth factor (IGF-1 and 2) which also acts
Excess growth hormone can lead to
(ADULTS) - ACROMEGALY Coarsening of facial features (macroglossia and prominent nose)
Prognathism: large jaw
Increased hand and feet size
Sweatiness
Headache
(CHILDREN) GIGANTISM
2 posterior pituitary hormones
Arginine vasopressin (AVP) : Anti-diuretic hormone
Oxytocin
(Produced by hypothalamus put stored in posterior pituitary)
Anatomy of posterior pituitary
Continuous with hypothalamus
What is controlled in posterior pituitary regulation
Hypothalamic magnicellular neurons
Supraoptic - AVP
Paraventicular - oxytocin
Regulation of posterior pituitary gland
Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport them to posterior pituitary
Excitation of hypothalamic magnocellular neurones stimulates release of AVP or oxytocin, they diffuse into blood
Physiological action of vasopressin (AVP / ADH)
Stimulation of water reabsorption in renal collecting duct, concentrating urine
Vasoconstrictor, stimulating ACHT release from anterior pituitary
How does vasopressin concentrate urine
AVP from blood binds to V2 receptor on cells lining lumen of collecting duct,
Triggers intracellular signalling cascade
Allows insertion of aquaporin-2 to membrane
Water reabsorbed unit lumen
Aquaporin-3 added to membrane to allow water to be reabsorbed into blood stream
2 physiological actions of oxytocin
Uterus at parturition - myometrial cells - contraction - baby delivery
Breast during lactation - myoepithelial cells - contraction- milk ejection
2 physiological actions of oxytocin
Uterus at parturition - myometrial cells - contraction - baby delivery
Breast during lactation - myoepithelial cells - contraction- milk ejection
Role of anterior pituitary in lactation
Mechanical stimulation activates afferent pathways
Signals integrated in hypothalamus and inhibit dopamine release from dopaminergic neurons
Less dopamine = less inhibition of anterior pituitary Lactotrophs
Increased plasma prolactin increases milk SECRETION in mammary glands
Role of posterior pituitary in lactation
Mechanical stimulation activates afferent pathways
Stimulate oxytocin in hypothalamus releasing neuron activity
Action potentials travel down oxytocin neurons and oxytocin into blood
Increased plasma oxytocin increases milk ejection in mammary glands
