The Hypothalamus and the Pituitary Flashcards
Which glands coordinate the majority of the glands in the endocrine system?
Pituitary and Hypothalamus
Where does the pituitary gland sit in relation to the hypothalamus?
Immediately below
What is the function of the hypothalamus?
Neuroendocrine function- releases chemicals into blood to act at distal sites
In which bone in there a depression in which the anterior pituitary sits?
Sphenoid bone
Which part of the pituitary is an extension of the hypothalamus?
Posterior pituitary- extension of neural tissue
->anterior pituitary gland is a true endocrine gland but is still linked to hypothalamus
What is the name given to the stalk which connects the hypothalamus to the pituitary?
Infundibulum
What provides the connection between the anterior pituitary and the hypothalamus?
Capillary portal system
Which part of the pituitary gland is a true endocrine gland?
Anterior pituitary gland
Which part of the pituitary makes up the majority of it?
Anterior- 2/3
Posterior- 1/3
The posterior pituitary is neuroendocrine. What role does it have?
Consists of axons and nerve terminals of hypothalamic neurons and secretes neurohormones which are made in the hypothalamus
List some of the stimuli which create an input to the hypothalamus in which the hypothalamus then responds to.
Cold
Stress
Puberty
Sleep
Pregnancy
Metabolic demand
What is the goal of the hypothalamus?
To maintain homeostasis
After the hypothalamus receives input from stimuli, how is a response generated to maintain homeostasis?
Via the pituitary gland
Both the hypothalamus and the anterior pituitary release tropic and non-tropic hormones.
What is meant by a tropic hormone?
A hormone which alters the release of another hormone
Which type of hormones are all hormones released from the hypothalamus?
Neurohormones
Which type of hormones are all hormones released from the posterior pituitary?
Neurohormones
Which type of hormones are all hormones released from the anterior pituitary?
Classic endocrine hormones
Name the two forms of hypothalamic neurohormones.
Tropic
Non-tropic
Where are non-tropic hormones produced and where do they travel to?
Non tropic hormones are produced in the hypothalamus and travel to the posterior pituitary.
They are then released into the blood
Where are all the tropic hormones secreted?
Into capillaries leading into the anterior the anterior pituitary.
Therefore:
a. which type of hormone are all the hormones of posterior pituitary gland?
b. which type of hormone are all the hormones of anterior pituitary gland?
a. Posterior= non-tropic
b. Anterior= tropic
Where are the non-tropic hormones of the posterior pituitary derived from?
Magnocellular neurons
Where do the magnocellular neurons have their cell bodies?
Hypothalamus
The posterior pituitary releases two non-tropic neuroendocrine hormones.
Name them.
Vasopressin
Oxytocin
What role does vasopressin have?
Maintains water balance
What role does oxytocin have?
Stimulates uterine contraction at parturition (giving birth)
Aids expression of milk in lactating breast
What can vasopressin also be known as?
ADH- anti-diuretic hormone
Name the five types of hypothalamic ‘releasing hormones’ which are tropic hormones.
TRH- thyrotropin releasing hormone
CRH- corticotropin releasing hormone
GHRH- growth hormone releasing hormone
GnRH- gonadotropin releasing hormone
PRH- prolactin releasing hormone
Name the two types of hypothalamic ‘inhibiting hormones’ which are tropic hormones.
GHIH- growth hormone inhibiting hormone
PIH- prolactin inhibiting hormone
What is GHIH also known as?
Somatostatin
What is PIH also known as?
Dopamine
Dopamine most commonly acts as a neurotransmitter but what is it’s endocrine role?
Inhibits the release of prolactin from the anterior pituitary gland
All tropic hormones are peptide hormones except dopamine. Which type of hormone is dopamine?
Amine hormone
What is the hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer tropic hormones from the hypothalamus to the anterior pituitary
Name the five tropic hormones released from the anterior pituitary gland.
TSH- thyroid stimulating hormone
ACTH- adrenocorticotropic hormone
FSH- follicle stimulating hormone
LH- luteinising hormone
GH- growth hormone
RECAP- what do tropic hormones do?
Control the secretion of other hormones
Prolactin is another hormone produced by the anterior pituitary gland and is the only hormone produced here that is not a tropic hormone. What does prolactin do?
Directly stimulates milk production from the breast during lactation
In terms of anterior pituitary feedback control, there are three integration centres. List them.
- Hypothalamus
- Anterior pituitary
- Target endocrine cell e.g. thyroid gland, adrenal cortex etc.
Hormones themselves act as negative feedback signals- each hormones feeds back to inhibit hormone secretion by integration centres earlier in the reflex.
What is meant by long-loop feedback?
Feedback from the endocrine target
(last integration centre in the loop hence long loop)
Hormones themselves act as negative feedback signals- each hormones feeds back to inhibit hormone secretion by integration centres earlier in the reflex.
What is meant by short-loop feedback?
Feedback from the anterior pituitary to the hypothalamus
Endocrine disorders can be described as hyposecretion. What does this mean?
Too little hormone secreted.
Endocrine disorders can be described as hypersecretion. What does this mean?
Too much hormone secreted
Hypo or hypersecretion can be as a result of primary, secondary and tertiary endocrine disorders.
What happens in primary endocrine disorders?
There is a defect in the cells that secrete the hormone
Hypo or hypersecretion can be as a result of primary, secondary and tertiary endocrine disorders.
What happens in secondary endocrine disorders?
Too much or too little tropic hormone is released from the pituitary
Hypo or hypersecretion can be as a result of primary, secondary and tertiary endocrine disorders.
What happens in tertiary endocrine disorders?
There are hypothalamic defects releasing too much or too little hormone from the hypothalamus
What can cause hyporesponsiveness?
-Alterations in receptors for hormones
-Disordered post-receptor events
-Failure of metabolic activation or hormone
-Antagonistic effects
What can cause hyperresponsiveness?
Permissive effects- when one hormone enhances the activity of another hormone
What happens if there is prolonged exposure to low hormone concentration?
Up-regulation of receptor for that hormone
->this is so any hormone in plasma is more likely to bump into a receptor
What happens if there is prolonged exposure to high hormone concentration?
Down-regulation of receptor for that hormone
What is meant by antagonistic effects?
Presence of one hormone reduces the effect of another
Give an example of permissive effects.
Epinephrine causes modest lipolysis but when thyroid hormones are also present, greatly increases lipolysis
Give an example of antagonistic effects.
Growth hormone impairs glucose uptake