Lecture 2 The Pituitary Gland Flashcards
Name the principal organisers of the endocrine system
Hypothalamus and Pituitary
Name the structure that connects the hypothalamus to the pituitary gland
Infundibulum
What is the posterior portion of the pituitary gland
An extension of the neural tissue
What is the anterior portion of the pituitary gland
True endocrine gland of epithelial origin
What is the function of the Hypothalamus
Integration centre for endocrine systems
Where is the Hypothalamus located
Base of the brain, below the thalamus
Where is the pituitary gland loctaed
In a pocket in the sphenoid bone, directly below the hypothalamus
Name external stimuli that effects the hypothalamus
Cold Stress Metabolic demand Hydration status Exercise Day/Night Menstrual cycle Sleep Breastfeeding Pregnancy Puberty
Name functions affected by the pituitary gland
Adrenal Thyroid Gonadal Lactation Parturition Growth Water balance Metabolism
What type of hormones do both the anterior and posterior pituitary release
Trophic and non-trophic
All hormones released by the hypothalamus are____
Neurohormones
All hormones released by the posterior pituitary gland are ____
Neurohormones (from hypothalamus)
All hormones released by the anterior pituitary gland are ___
Endocrine hotmones
Define Trophic Hormones
Neurohormones secreted into capillaries traveling to anterior pituitary and govern the release of secondary hormones
Define Non-trophic Hormones
Neurohormones produced in the hypothalamus and travel to posterior pituitary via axons where they are released into the blood
Name 5 hypothalamic “releasing hormones”
– Thyrotropin Releasing Hormone (TRH)/(TSH)
– Corticotropin Releasing Hormone (CRH)
– Growth Hormone Releasing Hormone (GHRH)
– Gonadotropin Releasing Hormone (GnRH)
– Prolactin Releasing Hormone (PRH)
Name 2 hypothalamic “inhibiting hormones”
– Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
– Dopamine aka Prolactin Inhibiting Hormone (PIH)
All hypothalamic hormones are peptides except_____
Dopamine
PRH causes the release of what anterior pituitary hormone
Prolactin–> Breast
TRH causes the release of what anterior pituitary hormone
TSH–> Thyroid gland
CRH causes the release of what anterior pituitary hormone
ACTH–> Adrenal Cortex
GHRH causes the release of what anterior pituitary hormone
GH
GHIH inhibits what anterior pituitary hormone
GH
GnRH causes the release of what anterior pituitary hormone(s)
FSH and lSG (Gonadotropins)–> endocrine cells of gonads
PIH inhibits the release of what anterior pituitary hormone
Prolactin
What is the Hypothalamus-hypophyseal portal system
Network of tiny vessels which transfer trophy hormones from hypothalamus to anterior pituitary
The anterior pituitary is connected to the hypothalamus via
Capillary portal system (hypothalamic-hypophyseal portal system)
What is the anterior pituitary sometimes called
Adenohypophysis
Makes up 2/3rds of the gland
What is the posterior pituitary gland sometimes called
Neurohypophysis
Makes up 1/3rd of the gland
What is the function of the Pars intermedia
- Stimulates production of melanin (MSH)
* Sits between anterior and posterior pituitary
Describe the short feedback loop
Trophic hormone has negative feedback on Hypothalamus
Describe long feedback loop
End hormone from endocrine gland acts on anterior pituitary gland and hypothalamus
Name the 2 peptide neurohormones released from the posterior pituitary
Vasopressin (aka anti-diuretic hormone; ADH)- maintains water balance, increase water retention
Oxytocin- uterine contraction and lactation
Where are the posterior pituitary peptide neurohormones synthesised
Magnocellular neurons
What is the main function of vasopression
Regulates water balance
What triggers vasopressin
Increase in plasma osmolarity
Decrease in plasma volume/blood pressure
Site/mode of action of vasopression
Kidney collecting ducts- water reabsorption
Vascular smooth muscle- increase blood pressure
What is the main function of oxytocin
Milk ejection and uterine contraction
What triggers the release of oxytocin
Labour (baby’s head against cervix), Suckling
Site/mode of action of oxytocin
Milk duct smooth muscle- contracts muscle, ejecting milk
Uterine smooth muscle- child birth
Define hyposecretion
too little hormone secreted- disorders at any level of pituitary access
Define hypersecretion
too much hormone secreted
Define hypo responsiveness
reduced response of the target cell
Define hyperresponsiveness
increased response of the target cell
What are primary disorders
those in which the defect is in the cells that secrete the hormone (end hormone)- most common
What are secondary disorders
those in which there is too little or too much trophic hormone from pituitary
Wha are tertiary disorders
relate to hypothalamic defects
What does hyporesponsiveness relate to
alterations in receptor for hormone, disordered post-receptor events or failure of metabolic activation of hormone, (where this is required for function).
What could be the cause of hyper responsiveness
: could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis
prolonged exposure to low hormone plasma leads to
Up-regulation of receptor number (increase tissue sensitivity)
Prolonged exposure to high hormone plasma leads to
Down regulation of receptor umber (decrease tissue sensitivity)
Define permissive effects
the presence of one hormone enhances the effect of another eg epinephrine causes only modest lipolysis in adipose tissue, but when thyroid hormones are also present, greatly increased lipolysis occurs.
TH synthesis of receptors for epinephrine on adipocytes. TH itself has no effect on lipolysis but is permissive to epinephrine.
Define Antagonistic effects
The presence of one hormone reduces the effect of another e.g. Growth hormone impairs glucose uptake in response to insulin by decreasing the number of insulin receptors on muscle and adipose tissue.
