Pituitary And Adrenal Glands Flashcards
Explain how the separate pituitary lobes are formed in the embryo
- Anterior lobe formed by up growth of ectodermal cells from the roof of the primitive pharynx
- Posterior lobe formed from down growth of neural tissue from hypothalamus
Name the 6 main hormones that are produced in the anterior pituitary gland
- TSH (thyrotropes)
- ACTH (corticotropes)
- Growth hormone (somatotropes)
- LH (gonadotropes)
- FSH (gonadotropes)
- Prolactin (lactotropes)
Where are the adrenal glands located?
Sit on top of the kidneys (cap the upper poles)
What are the two sections of the adrenal gland?
- Adrenal Cortex
- Adrenal Medulla
How is the adrenal cortex layered?
- Outermost layer is the ZONA GLOMERULOSA
- Middle layer is the ZONA FASICULATA
- Innermost layer is the ZONA RETICULARIS
What is secreted from the zona glomerulosa?
Mineralocorticoids e.g. ALDOSTERONE
What is the role of Mineralocorticoids?
Regulation of Na+ and K+ levels in blood
Where exactly is cortisol secreted from?
Zona fasiculata of the adrenal cortex of the adrenal gland
What is secreted from the adrenal medulla?
Adrenaline
Describe the properties of cortisol and how it is synthesised
- Steroid hormone
- Lipophillic
- Hydrophobic
- Synthesised from cholesterol via progesterone
Describe the arterial blood supply to the pituitary gland
From superior and inferior hypophyseal arteries, arising from internal carotid artery
What are the main effects of cortisol?
- Increase glycogenolysis in liver and muscle
- Increase gluconeogenesis in the liver
- Increase β oxidation of fatty acids in adipose
- Increase proteolysis in skeletal muscle
Explain how secretion of cortisol is stimulated
- Decrease in cortisol in blood detected by the hypothalamus and stimulates secretion of CRH from corticotropes into the hypophyseal portal system
- CRH travels to anterior pituitary and binds to specific receptors and stimulates secretion of ACTH into bloodstream
- ACTH binds to G protein coupled receptors on zona fasciculata of adrenal cortex stimulating the secretion of cortisol
What kind of feedback mechanism controls the secretion of cortisol?
Negative feedback
What is the nature of the hormone ACTH?
- Peptide hormone
- Water soluble
- Single polypeptide chain of 39 amino acids
What is the name of the precursor of ACTH?
Pro-opiomelanocortin POMC
Explain why ACTH can have some α-MSH properties when present in excess
- Both are derived from POMC
- α-MSH sequence is contained within the ACTH sequence
- ACTH has α-MSH receptor complementarity
ACTH follows a circadian rhythm. What is meant by this?
- Low plasma levels late in the evening
- High plasma levels early in the morning
Explain how the binding of ACTH stimulates the synthesis and secretion of cortisol
- ACTH binds to complementary type 2 melanocortin receptors on the zona fasciculata of the adrenal cortex
- Activation of the enzyme CHOLESTEROL ESTERASE which converts cholesterol esters into free cholesterol
- Free cholesterol is used in the synthesis of cortisol via progesterone
What are the clinical consequences of an over-secretion of ACTH?
- Increased stimulation of adrenal cortex resulting in adrenal hyperplasia and overproduction of cortisol
- Increased stimulation of melanocytes (as ACTH can bind to α-MSH receptors) resulting in increased pigmentation of skin
How is cortisol transported in the blood?
- Cortisol is lipophilic
- ~90% bound to plasma proteins such as TRANSCORTIN (corticosteroid binding globulin CBG)
- ~10% remains free in blood and is biologically active
Explain the action of cortisol on target cells
- Enters cell through diffusion across plasma membrane (lipophilic) and enters nucleus
- Binds to specific receptors on DNA and changes the rate of transcription of specific genes coding for proteins
- THIS MAY TAKE TIME TO COME INTO EFFECT
What are the main effects of cortisol?
- Mainly CATABOLIC
- Decrease amino acid uptake and protein synthesis
- Increase proteolysis (not liver)
- Increase glycogenolysis (liver), lipolysis (adipose) and gluconeogenesis (liver)
- Decrease peripheral uptake of glucose (ANTI-INSULIN)
- Increase lipogenesis in abdomen, face and neck
What is the nature of adrenaline?
- Water soluble hormone
- Neurotransmitter
- Amino acid derived (TYROSINE)
Describe the effects of adrenaline in the fight or flight response
- Increase cardiac output
- Increase blood supply to heart, brain and skeletal muscles
- Increase sweat production
- Pupils dilate
- Increase stimulation of CNS
- Increase lipid metabolism (lipolysis)
Describe how adrenaline is synthesised from amino acids
TYROSINE –> Dopamine –> Noradrenaline –> Adrenaline
What are the signs and symptoms associated with increased adrenaline secretion?
- Hypertension
- Pallor
- Sweating
- Anxiety
- Palpitations
- Glucose intolerance
What is the half life of ACTH?
Short half life of ~8mins
