Pituitary and Adrenals Flashcards
Where is the pituitary gland located?
In the base of brain
How is the pituitary gland associated with the hypothalamus?
It’s suspended from the hypothalamus by a stalk
What surrounds the pituitary gland?
Lies in a deep recess of sphenoid bone (the pituitary fossa), surrounded by a small bony cavity (sella turcia)
How much does the pituitary gland weigh?
0.5-0.9g
Who is the pituitary gland larger in?
Females
Why is the pituitary gland larger in females?
Due to the effect of oestrogen on Lactotropes
Why is the blood flow to the pituitary gland unusual?
It has a portal system
What is meant by a portal system?
A vessel connecting to capillary beds located in separate tissues
Where do the capillary beds making up the pituitary glands portal system lie?
One in hypothalamus, one in anterior pathway
Where does the pituitary get its arterial blood supply from?
The superior and inferior hypothyseal arteries arising from internal carotid arteries
What do pituitary glands develop as?
A fusion between up growth of ectodermal cells from the roof of the primitive pharynx (buccal cavity), and a down growth of neural tissue from the hypothalamus
What is formed from the up growth of ectodermal cells from the roof of the buccal cavity?
The anterior lobe
What is the anterior lobe of the pituitary gland also known as?
Adenohypophysis
What is formed from the down-growth of neural tissue from the hypothalamus?
The posterior lobe
What is the posterior lobe of the pituitary gland also known as?
Neurohypophysis
How are the posterior and anterior lobes of the pituitary gland different?
Histologically different, have different functins
Where are hormones produced in the anterior pituitary?
In distinct cell types
What hormones are produced in the anterior pituitary?
- TSH
- ACTH
- Growth hormone
- LH and FSH
- Prolactin
Where is TSH produced?
Thyrotropes
Where is ACTH produced?
Corticotropes
Where is growth hormone produced?
Somatotropes
What do somatotropes constitute?
The largest cell group in the anterior pituitary
Where is LH and FSH produced?
Gonadotropes
Where is prolactin produced?
Lactotropes
What are the adrenal glands?
A pair of multifunctional endocrine glands
Where are the adrenal glands found?
Capping the upper roles of the kidneys, and lie against the diaphragm
How much to the adrenal glands weigh?
6-8kg
How do the adrenal glands differ in females?
They weigh slightly less
What do the adrenal glands consist of?
2 regions
What are the 2 regions of the adrenal glands?
NAME?
What hormones does the adrenal cortex produce?
- Mineralocorticoids
- Glucocorticoids
- Androgens
Give an example of of a mineralocorticoid
Aldosterone
Give 2 examples of glucocorticoids
- Cortisol
- Costerone
Give an example of an androgen
Dehydroepiandrosterone
How much androgen is produced by the adrenal gland?
Only small amounts
What hormone does the adrenal medulla produce?
Adrenaline
What can be recognised in the adrenal cortex?
3 zones
What do the 3 zones of the adrenal cortex lie under?
A connective tissue capsule
What does the connective tissue capsule of the adrenal cortex have?
A plexus of blood vessel
How can the 3 zones of the adrenal cortex be identified?
By the different arrangement of the secretory cells
What does each zone of the adrenal cortex have?
An associated network of capillaries and sinusoids
What are the 3 zones of the adrenal cortex?
- Zona Glomerulosa
- Zona Fasciculata
- Zona Reticularis
What do the cells of the zona glomerulosa do?
Secrete mineralocorticoids
What is the purpose of the zona glomerulosa’s secretions?
Regulate body Na + and K + levels
What do the cells in the zona fasciculata do?
Produce glucocorticoids
What is the purpose of the secretions of the zona fasciculata?
Number of functions, including regulation of carbohydrate metabolism
What do the cells of the zona reticularis do?
Secrete glucocorticoids and small amount of androgens
What is cortisol a member of?
The C 21 steroid family
How does cortisol differ form other steroids?
- The number of C atoms
- Presence of functional groups
- Distribution of C=C double bonds
What is true of all steroid hormones?
NAME?
How are steroid hormones synthesised from cholesterol?
Via progesterone, in a series of enzyme catalysed reactions
What is the main factor in controlling the release of cortisol?
ACTH (or corticotropin)
What is ACTH secreted by?
The cortiotropes of the anterior pituitary
How is secretion of ACTH controlled by?
Corticotropin releasing factor (CRF)
What is CRF?
A 41 amino acid polypeptide
Where is CRF produced?
In hypothalamus
What is CRF secreted in response to?
Physical, chemical and emotional stressors
Give 2 examples of physical stressors?
- Temperature
- Pain
Give an example of a chemical stressor
Hypoglycaemia
How do glucocorticoids have an impact on cortisol secretion?
They exert negative feedback on both the hypothalamus and pituitary
What is ACTH?
A 39 amino acid, single chain polypeptide hormone
What is the initial biosynthetic precursor of ACTH?
A large protein, of ~250 amino acids, called proopiomelanocortin (POMC)
What happens to POMC?
Post-translational processing of POMC at different sites
What does post-translational processing of POMC produce?
A range of biologically active peptides
Give 3 peptides produced by POMC?
NAME?
What is α-MSH?
Melanocyte stimulating hormone
Where is the α-MSH sequence contained?
Within the ACTH sequence
What is the result of the α-MSH sequence being contained within the ACTH sequence?
It gives ACTH some α-MSH-like activity when present in excess
How long is the ACTH half life in circulation?
Short- ~8mins
In what manner in ACTH released into the circulation?
In pulses that follow a cardiac rhythm
When do peak plasma levels of ACTH occur?
Early morning
Is ACTH hydrophilic or hydrophobic?
Hydrophilic
What does ACTH interact with?
High affinity receptors on the surface of the cells in zona fasciculata and reticularis
What does the binding of ACTH to receptors lead to?
Activation of cholesterol esterase
What does the activation of cholesterol esterase do?
NAME?
What do the clinical consequences of over-secretion of ACTH relate to?
Direct effects of ACTH on tissues and the adrenal cortex
What are the effects of over-secretion of ACTH on the tissues?
Increased pigmentation
What causes increased pigmentation?
Partial MSH activity
What is the result of over-secretion of ACTH on the adrenal cortex?
Adrenal hyperplasia and over-production of cortisol
What are the clinical consequences of under-secretion of ACTH related to?
Lack of glucocorticoids
Why is under-secretion of ACTH not related to lack of lack of mineralocorticoids?
As aldosterone secretion is normal, because it’s not controlled by ACTH
What kind of hormone is ACTH?
Peptide
What does ACTH act on?
G-protein coupled receptors on plasma membrane of target cells
What is the specific GPCR for ACTH?
A type of melanocortin receptor (type 2), known as MC 2
What does the MC 2 receptor use?
cAMP
What does the MC 2 receptor use cAMP for?
As the second messenger
How must cortisol be transported?
Bound to plasma proteins
What is the major transport protein for cortisol?
Transcortin
What is transcortin also known as?
Corticosteroid binding globulin (CBG)
How much of the plasma cortisol is carried by transcortin?
90%
What happens to the 10% or cortisol not bound to transcortin?
It is free and biologically active
What is cortisol an important component of?
The stress response
When do the major metabolic effects of cortisol act?
In the stressed/starved states
What does cortisol affect regarding metabolism?
The availability of all major metabolic substrates
How does cortisol affect the availability of major metabolic substrates?
Increasing proteolysis, gluconeogenesis and lipolysis
What do the metabolic actions of cortisol include?
- Decreased amino acid uptake
- Decreased protein synthesis
- Increased proteolysis in most tissues
- Increased hepatic gluconeogenesis and glycogenolysis
- Increased lipolysis in adipose tissue
- Decreased peripheral uptake of glucose
Where does cortisol not increase proteolysis?
In the liver
What is the effect of high cortisol levels in adipose tissue?
Increases lipogenesis
What does cortisol do in additional to its metabolic actions?
Has direct effects on cardiac muscle, bone and immune system
What is the adrenal medulla in essence?
A modified sympathetic ganglia
What does the adrenal medulla do?
Synthesises catecholamines, including the hormone adrenaline and the neurotransmitters noradrenaline and dopamine
How are catecholamines synthesised?
- In a series of enzyme catalysed steps that convert the amino acid tyrosine into dopamine.
- Dopamine then converted to noradrenaline
- Noradrenaline converted to adrenaline
Where are the catecholamines stored?
In the medullary cells in membrane-limited vesicles
What is adrenaline released as part of?
The fright, flight or fight response
What is adrenaline released in response to?
Stressful situations
What does adrenaline have effects on?
- Cardiovascular system
- CNS
- Carbohydrate metabolism
- Lipid metabolism
What is the effect of adrenaline on the cardiovascular system?
NAME?
What is the effect of adrenaline on the CNS?
Increased mental alertness
What is the effect of adrenaline on carbohydrate metabolism?
Increased gluconeogenesis in liver and muscle
What is the effect of adrenaline on lipid metabolism?
Increased lipolysis in adipose tissue
What usually causes overproduction of adrenaline?
A tumour- pheochromocytoma
What are the clinical consequences of over-secretion of adrenaline?
- Hypertension
- Anxiety
- Palpitations
- Pallor
- Sweating
- Glucose intolerance
