The pituitary gland Flashcards
What is a hormone?
A messenger
Carried from the organ which they’re produced in to target organ
2 types: peptide hormone and steroid hormone
How is a peptide hormone synthesised, where is it stored and what’s its receptor?
Synthesis: synthesised as pro hormones- need further processing to activate
Storage: Stored in vesicles (regulatory secretion)
Receptor: Bind on cell membrane and transduce signal using 2nd messenger systems
How is a steroid hormone synthesised, where is it stored and what’s its receptor?
Synthesis: synthesised in series of reactions from cholesterol
Storage: released immediately (constitutive secretion)
Receptor: Bind to intracellular receptors to change gene expression directly
What is the pituitary gland also known as?
The master gland
What structures make up the anterior pituitary?
Pars tubercles
Pars intermedia
Pars distalis
What structures make up the posterior pituitary?
Pars nervosa
What regulates anterior pituitary function?
Hypothalamic parvocellular neurones
They’re short- terminate on median eminence
Release hypothalamic releasing/ inhibitory hormones (RH/IH) into capillary plexus in median eminence
Where are hypothalamic regulatory factors (IH/ RH) carried to and how?
Carried by portal circulation to anterior pathways
What is the pituitary stalk also known as?
Infundibulum
What cells make up the anterior pituitary?
Made up of endocrine cells: (GoTh CoLaS) Gonadotrophs Thyrotrophs Corticotrophs Lactotrophs Somatotrophs
What is the hypothalamus- pituitary portal system?
- Axon terminals of hypothalamic neurosecretory cells release hormones (IHs and RHs) into hypothalamus- pituitary portal system
- The RHs and IHs travel in portal system to anterior pituitary
- RHs and IHs stimulate or inhibit the release of hormones from anterior pituitary cells
- Anterior pituitary hormones leave the gland via the blood
What do somatotrophs release and what stimulates them and what’s their target?
Release: Growth Hormone (somatotrophin)
Stimulated by: Growth hormone releasing hormone/ somatostatin (inhibits)
Target: Hepatocytes/Liver, bone, muscles
What do lactotrophs release and what stimulates them and what’s their target?
Release: Prolactin
Stimulated by: Dopamine (inhibits)
Target: Mammary glands
What do thyrotrophs release and what stimulates them and what’s their target and what’s their target?
Release: Thyroid Stimulating Hormone (thyrotrophin)
Stimulated by: Thyrotrophin releasing hormone
Target: Thyroid gland
What do gonadotrophs release and what stimulates them and what’s their target?
Release: Luitenising Hormone (LH) and Follicle Stimulating Hormone (FSH)
Stimulated by: gonadotrophin releasing hormone
Target: Gonads
What do corticotrophs release and what stimulates them and what’s their target?
Release: Adrenocorticotrophic hormone (ACTH, corticotrophin)
Stimulated by: Corticotrophin releasing hormone
Target: Adrenal cortex
What does a pituitary tumour compressing the optic chiasm cause?
Bitemporal Hemianopia
Fibres from nasal retinae cross at optic chiasm
Compression of optic chasm by a pituitary tumour/ suprasellar tumour prevents transmission of sensory information from lateral visual fields to occipital lobes
What is the neuroendocrine reflex arc (prolactin) and how does it cause milk production?
- mechanical stimulation of nipple and surrounding area activates afferent 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
What are mechanisms of growth hormone action?
2 mechanisms of growth:
- GH binds to GH receptors on bones and muscles
- … and binds to liver to form insulin-like growth factor (IGF-1 in post-natal growth) which stimulates growth
What is acromegaly?
A disorder where theres excess growth hormone - too much somatotrophin
Does not result in increased height
Known as gigantism in children
What are symptoms of acromegaly?
Coarseing of facial features Macroglossia (big tongue) Prominent nose Large jaw- prognathism Increased hand and feet size Sweatiness Headache
What are the posterior pituitary gland hormones?
Arginine Vasopressin (AVP) aka. anti-dietetic hormone Oxytocin
What are hypothalamic magnocellular neurones?
Long and originate in supraoptic (AVP) and paraventricular (Oxytocin) hypothalamic nuclei
Nuclei -> stalk -> pituitary
How is the posterior pituitary regulated?
- Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport them to posterior pituitary
- Excitation of these hypothalamic magnocellular neurones stimulate release of AVP or oxytocin into the posterior pituitary where they diffuse into blood capillaries
- Then they leave the posterior pituitary via blood
