Hypothalamus and the Pituitary Flashcards
What are the principal organisers to the endocrine system?
Hypothalamus and pituitary
Where is the hypothalamus?
-Located at the base of the brain, below the thalamus
Where is the pituitary gland?
Located in a pocket in the sphenoid bone, directly below the hypothalamus
What type of communication exists between the hypothalamus and pituitary?
neuroendocrine
- neural to the posterior pituitary
- endocrine to the anterior pituitary
What is the pituitary stalk called?
Infundibulum
What is the pituitary gland?
Bean-shaped and bean-sized endocrine gland (~14mm diameter)
What are the 2 distinct types of tissue of the pituitary?
- anterior pituitary: endocrine tissue
- posterior pituitary: neural tissue
What is the hypothalamus?
Integration centre for endocrine systems
What inputs does the hypothalamus receive?
- Cold
- Stress
- Metabolic demand
- Hydration status
- Exercise
- Day/night
- Menstrual cycle
- Sleep
- Breastfeeding
- Pregnancy
- Puberty
What is the pituitary involved in regulating?
- Adrenal function
- Thyroid function
- Gonadal function
- Lactation
- Parturition
- Growth
- Water balance
- Metabolism
What do the hypothalamus and anterior pituitary release?
tropic and non-tropic hormones
The hormones released by the hypothalamus are all….
Neurohormones
The hormones released by the posterior pituitary are all…
Neurohormones (from the hypothalamus)
The hormones released by the anterior pituitary are all…
Classic endocrine hormones
What are the 2 forms of hypothalamic neurohormones?
- Tropic
- Non-tropic
Tropic neurohormones
Neurohormones secreted into capillaries travelling to anterior pituitary. Govern release of anterior pituitary hormones
describe nootropic neurohormones
produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood
What do all hypothalamic tropic hormones bind to?
Receptors on anterior pituitary and stimulate/inhibit release of AP hormones
Name 5 hypothalamic ‘releasing hormones’.
- Thyrotropin Releasing Hormone (TRH)
- Corticotropin Releasing Hormone (CRH)
- Growth Hormone Releasing Hormone (GHRH)
- Gonadotropin Releasing Hormone (GnRH)
- Prolactin Releasing Hormone (PRH
Name 2 hypothalamic ‘inhibiting hormones’
- somatostatin: growth hormone inhibiting hormone (GHIH)
2. dopamine: prolactin inhibiting hormone (PIH)
What is the only hypothalamic tropic hormone which isn’t a peptide?
Dopamine
What is the hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer tropic hormones from hypothalamus to anterior pituitary
What is sufficient for control of the hypothalmo-hypophyseal portal system?
Small numbers of neurosecretory neurons sufficient for control
Where are hormones released from in the hypothalamo-hypophyseal portal system?
neurosecretory neurons at the median eminence
What are the benefits of the hypothalamo-hypophyseal portal system?
- Short distance
- Very rapid and dynamic
What type of tissue is the anterior pituitary?
True endocrine tissue
What type of tissue is the posterior pituitary?
Neuroendocrine tissue
What is the origin of the anterior pituitary?
Epithelial origin
What is the origin of the posterior pituitary?
Neural tissue origin
How is the anterior pituitary connected to the hypothalamus?
Connected to hypothalamus via capillary portal system
How is the posterior pituitary connected to the hypothalamus?
Neural connection
What is the anterior pituitary also known as?
Adenohypophysis
What is the posterior pituitary also known as?
Neurohypophysis
How is the pituitary gland split into the posterior and anterior aspects?
- Anterior 2/3rds
- Posterior 1/3rd
What controls the production of anterior pituitary hormones?
Hypothalamus
How does the hypothalamus control the production of anterior pituitary hormones?
by producing “releasing” or “inhibiting” tropic hormones that stimulate or inhibit hormone production from the anterior pituitary
How many hormones are released from the anterior pituitary?
- 6 hormones released
- All are peptides
- 5 are tropic hormones
Name the 6 hormones released by the anterior pituitary.
- Thyroid Stimulating Hormone (TSH) aka thyrotropin
- Adrenocorticotropic Hormone (ACTH) aka corticotropin
- Follicle Stimulating Hormone (FSH) aka gonadotropin
- Luteinising Hormone (LH) aka gonadotropin
- Growth Hormone (GH)
- Prolactin
What does prolactin directly stimulate?
Milk production for the breast during lactation
What are the trophic hormones released by the anterior pituitary?
- thyroid stimulating hormone (TSH) aka thyrotropin
- adrenocorticotropic hormone (ACTH) aka corticotropin
- follicle stimulating hormone (FSH) aka gonadotropins
- lutenising hormone (LH)
- growth hormone (GH)
- prolactin
What does prolactin act on and stimulate?
Breast to stimulate lactation (direct)
What does GH act on and stimulate
- Liver to stimulate IGF-1 release (trophic)
- MSK system to stimulate tissue metabolism (direct)
What does TSH act on and stimulate?
Thyroid to stimulate TH release (trophic)
What does ACTH act on and stimulate?
Adrenal cortex to stimulate cortisol release (trophic)
What do LH and FSH act on and stimulate?
Gonads to stimulate regulation of reproductive function (direct) and sex hormone release (trophic)
What are the 3 integration centres in anterior pituitary feedback control?
- hypothalamus
- anterior pituitary
- target endocrine cell
What act as negative feedback signals?
Hormones
Where does feedback come from in long-loop feedback?
Endocrine target
Where does feedback come from in short-loop feedback?
Anterior pituitary
How does negative feedback loops keep hormones within limits?
Links levels of sequential hormones together and tightly maintains plasma levels within the correct range
What are the 2 peptide neurohormones which the posterior pituitary stores and releases?
- Vasopressin (aka anti-diuretic hormone; ADH)
- Oxytocin
Where are vasopressin and oxytocin synthesised?
Magnocellular neurons which have their cell bodies in specific areas of the hypothalamus
What project down the infundibulum to the posterior pituitary?
Axons
Where do the axons in the infundibulum terminate?
Do not synapse with other neurons, their terminals end directly on capillaries
What does activity in the neurons in the infundibulum result in?
release of vasopressin or oxytocin into the blood stream at the posterior pituitary
What do oxytocin and vasopressin behave as?
Typical peptide hormones
-i.e. synthesis and storage in vesicles, cell surface receptors etc
What is the main function of vasopressin?
Regulates water balance
What is vasopressin release triggered by?
- Increase in plasma osmolarity
- Decrease in plasma volume/blood pressure
What is the site/mode of action of vasopressin?
- Kidney collecting ducts to increase water reabsorption
- Vascular smooth muscle to increase blood pressure
What is the main function of oxytocin?
Milk ejection and uterine contraction
What is oxytocin release triggered by
- Labour (baby’s head against cervix)
- Suckling
What is the site/mode of action of oxytocin?
- Milk duct smooth muscle to contract muscle, ejecting milk
- Uterine smooth muscle for child birth
How can endocrine disorders be classified?
- Hyposecretion
- Hypersecretion
- Hyporesponsiveness
- Hyperesponsiveness
- Primary disorders
- Secondary disorders
- Tertiary disorders
