Pituitary And Adrenal Glands

Question 1

Explain how the separate pituitary lobes are formed in the embryo

Answer 1

• 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

Question 2

Name the 6 main hormones that are produced in the anterior pituitary gland

Answer 2

• TSH (thyrotropes)
• ACTH (corticotropes)
• Growth hormone (somatotropes)
• LH (gonadotropes)
• FSH (gonadotropes)
• Prolactin (lactotropes)

Question 3

Where are the adrenal glands located?

Answer 3

Sit on top of the kidneys (cap the upper poles)

Question 4

What are the two sections of the adrenal gland?

Answer 4

• Adrenal Cortex

- Adrenal Medulla

Question 5

How is the adrenal cortex layered?

Answer 5

• Outermost layer is the ZONA GLOMERULOSA
• Middle layer is the ZONA FASICULATA
• Innermost layer is the ZONA RETICULARIS

Question 6

What is secreted from the zona glomerulosa?

Answer 6

Mineralocorticoids e.g. ALDOSTERONE

Question 7

What is the role of Mineralocorticoids?

Answer 7

Regulation of Na+ and K+ levels in blood

Question 8

Where exactly is cortisol secreted from?

Answer 8

Zona fasiculata of the adrenal cortex of the adrenal gland

Question 9

What is secreted from the adrenal medulla?

Answer 9

Adrenaline

Question 10

Describe the properties of cortisol and how it is synthesised

Answer 10

• Steroid hormone
• Lipophillic
• Hydrophobic
• Synthesised from cholesterol via progesterone

Question 11

Describe the arterial blood supply to the pituitary gland

Answer 11

From superior and inferior hypophyseal arteries, arising from internal carotid artery

Question 12

What are the main effects of cortisol?

Answer 12

• Increase glycogenolysis in liver and muscle
• Increase gluconeogenesis in the liver
• Increase β oxidation of fatty acids in adipose
• Increase proteolysis in skeletal muscle

Question 13

Explain how secretion of cortisol is stimulated

Answer 13

• 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

Question 14

What kind of feedback mechanism controls the secretion of cortisol?

Answer 14

Negative feedback

Question 15

What is the nature of the hormone ACTH?

Answer 15

• Peptide hormone
• Water soluble
• Single polypeptide chain of 39 amino acids

Question 16

What is the name of the precursor of ACTH?

Answer 16

Pro-opiomelanocortin POMC

Question 17

Explain why ACTH can have some α-MSH properties when present in excess

Answer 17

• Both are derived from POMC
• α-MSH sequence is contained within the ACTH sequence
• ACTH has α-MSH receptor complementarity

Question 18

ACTH follows a circadian rhythm. What is meant by this?

Answer 18

• Low plasma levels late in the evening

- High plasma levels early in the morning

Question 19

Explain how the binding of ACTH stimulates the synthesis and secretion of cortisol

Answer 19

• 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

Question 20

What are the clinical consequences of an over-secretion of ACTH?

Answer 20

• 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

Question 21

How is cortisol transported in the blood?

Answer 21

• Cortisol is lipophilic
• ~90% bound to plasma proteins such as TRANSCORTIN (corticosteroid binding globulin CBG)
• ~10% remains free in blood and is biologically active

Question 22

Explain the action of cortisol on target cells

Answer 22

• 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

Question 23

What are the main effects of cortisol?

Answer 23

• 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

Question 24

What is the nature of adrenaline?

Answer 24

• Water soluble hormone
• Neurotransmitter
• Amino acid derived (TYROSINE)

Question 25

Describe the effects of adrenaline in the fight or flight response

Answer 25

• 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)

Question 26

Describe how adrenaline is synthesised from amino acids

Answer 26

TYROSINE –> Dopamine –> Noradrenaline –> Adrenaline

Question 27

What are the signs and symptoms associated with increased adrenaline secretion?

Answer 27

• Hypertension
• Pallor
• Sweating
• Anxiety
• Palpitations
• Glucose intolerance

Question 28

What is the half life of ACTH?

Answer 28

Short half life of ~8mins