Hypothalamic-pituitary Axis (week 1) Flashcards
What is the hypothalamic-pituitary axis and what does it do
It is the most dominant part of the entire endocrine system system
The HPA regulated function of the thyroid, adrenal gland and reproductive glands and controls somatic growth, lactation, milk secretion and water metabolism
How is the pituitary gland sat in the brain
It is sat in a depression
What is the infundibular recess
Commonly illustrated as a v-shaped hollow in the sagital view is recognised as a small a extension of the third ventricle into the pituitary stalk
What are the 2 main compartments of the pituitary gland
Posterior and anterior pituitary gland
Explain the primary and secondary plexus
Blood supply and lymphatics
The superior hypophseal portal system form the primary plexus
This plexus supplies blood to the median eminence. The blood from the median eminence would then drain via the hypophyseal portal veins in a secondary plexus.
What is the name of the stalk between the hypothalamus and the posterior pituitary gland
Infundibulum
Which pituitary gland is directly connected to the hypothalamus
The posterior
How does the hypothalamus communicate with the anterior pituitary gland
Hypophyseal system
How does the hypothalamus communicate with the posterior pituitary gland
Nerve impulses
Which hormones are secreted from the (neurohypophysis) posterior pituitary gland
ADH
Oxytocin
Which hormones are secreted from the (adenohypophysis) anterior pituitary gland
FSH
LH
ACTH
Prolactin
GH
And ANT and POST pituitary gland develop from the same tissue or not
No they don’t
What is neuropophysis
Downgrowth of the forebrain - posterior
What is adenohypophysis
Oral ectoderm of the roof of stomatodeum
What is the primary plexus important for
Anterior pituitary gland
What is the secondary plexus important for
It is important for both anterior and posterior pituitary gland
adenohypophysis cells
endocrine tissue with distinct cell types responsible for releasing different hormones
- somatotropes - produces growth hormone
- Corticotropes - secrete adrenocorticotropic hormone (ACTH), stimulates adrenal gland to release cortisol
- Thyrotropes - produces thyroid stimulating hormone
- Gonadotropes - produces Luteinizing hormone (LH) and follicle- stimulating hormone (FSH)
- Lactotropes - secretes prolactin
neurohypophysis cells
neural tissue which is responsible for transport and storage of secretory granules of hormones in the hypothalamus
what is ADH secretion stimulated by
increased plasma osmolality
decrease in blood pressure
stress
pain
physiological effects of ADH
increases permeability of the collecting ducts and distal convoluted tubule allowing for better water reabsorption from the urine back into the blood stream
in presence of ADH urine flow decreases and urine osmolality increases where as in the absence of ADH urine flow increases and urine osmolality decreases.
maintaining blood pressure: can cause vasoconstriction, can cause narrowing of the blood vessels. In conditions where blood volume is reduced, such as during dehydration, ADH secretion is increased to help maintain blood pressure.
what can abnormally high ADH lead to
high urine osmolality
oedema (due to high plasma volume
low plasma osmolality
what can abnormally low ADH lead to
diabetes insipidus - inability of the kidneys to concentrate urine properly, can result in excretion of high volumes of dilute urine leading to dehydration.
what does oxytocin do
stimulates secretion of breast milk from lactating females
may also contribute to parturition of a foetus
oxytocin secretion
secretion of oxytocin is stimulated by
-suckling
-vaginal/ cervical stimulation
-crying
-during social event
-during hugging, kissing
oxytocin physiological effects
It stimulates the contraction of the cells around the mammary glands, causing the milk to be ejected from the breasts. This helps ensure an adequate milk supply for nursing infants.
reduction in stress
summary of the adenohypophysis hormones
parvicellular neuronal cell bodies in the hypothalamus –> adenohypophysis (anterior pituitary gland) —-> end organ or peripheral endocrine gland
TSH
regulates thyroid function via the TSH receptor in the thyroid epithelial cells.
stimulates the release of T3 and T4 to support tropic effects on growth and metabolism
FSH and LH
regulate the function of the gonads in both males and females via the FSH and LH receptors on the gonads
ACTH
adrenocorticotropic hormone, responsible for stimulating the adrenal cortex via the MC2R receptor. This induces upregulation of circulating cortisol and adrenal androgen. The released cortisol negatively feeds back to inhibit ACTH secretion in the anterior pituitary
GH
regulates metabolism via the GH receptor in the liver. The resulting insulin like growth factor 1 (IGF-1) produced negatively feeds back on the production and secretion of GH. This negative feedback is due to the direct effects of IGF-1 and release of somatostatin from the hypophysiotropic hormone somatostatin
prolactin
stimulates manufacture of breast milk via the reduced release of dopamine from the parvicellular hypothalamic neurons
what is a key feature of HPA
the ability of tropic hormones to provide negative feedback upon the system thanks to the hormones they induce release of in their target organs/ endocrine glands.
