Hypothalamus and Pituitary Gland Flashcards
Describe the hypothalamo-pituitary axis
Hypothalamus connected to pituitary gland - releases chemicals into blood to act on distal sites as neuroendocrine function
What does the hypothalamus secrete?
Neurohormones
Describe the connection of hypothalamus and pituitary gland
Connected via stalk
Connects to anterior via neurohormones in capillary portal system
Connects to posterior by hypothalamic axons and nerve terminals
Describe the anterior pituitary
True endocrine tissue and epithelial origin
Adenohypophysis
2/3rd of gland
Describe the posterior pituitary
Continuation of hypothalamus
Axons and nerve terminals
Secretes neurohormones made in hypothalamus
Neuroendocrine
Neural in origin
Neurohypophysis
What are some key integrate functions of the pituitary and hypothalamus?
Adrenal, thyroid, gonadal function, lactation, parturition, growth, water balance and metabolism
What are hypothalamic-pituitary hormones?
Both hypothalamus and anterior pituitary gland release tropic and non-tropic hormones
Posterior and hypothalamus - neuroendocrine hormones
Anterior - endocrine hormones
What are non-tropic neurohormones?
Produced in hypothalamus and travel to posterior pituitary where released into blood
What are tropic neurohormones?
Neurohormones secreted into capillaries travelling to anterior pituitary
Govern the release of anterior pituitary hormones
What 2 peptide neurohormones does magnocellular neurons in posterior pituitary store and release?
Vasopressin - maintaining water balance
Oxytocin - stimulates uterine contraction at parturition and aids expression of milk in lactating breasts
Different subsets of neurons make either one or other
Where are the nerve terminals in hypothalamus for non-tropic hormones?
End terminals in posterior pituitary which end directly on capillaries
What does the posterior pituitary gland release?
Neurohormones -activity in magnocellular neurons
Oxytocin and vasopressin behave as typical peptide hormones
Where is the cell bodies of magnocellular neurons?
Hypothalamus
What are 5 hypothalamic releasing hormones acting on anterior pituitary?
Thyrotropin releasing hormone
Corticotropin releasing hormone
Growth hormone releasing hormone
Prolactin releasing hormone
Gonadotropin releasing hormone
What are 2 hypothalamic inhibiting hormones acting on anterior pituitary?
Growth hormone inhibiting hormone - somatostatin
Dopamine - prolactin inhibiting hormone
What type of hormones are hypothalamic tropic hormones?
All peptide except dopamine
Describe the hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer tropic hormones from hypothalamus to anterior pituitary
Released from neurones at median eminence
Small amounts of hormone required
Short distance so rapid
Describe pathway of TRH (thyroid releasing hormone)
TRH from hypothalamus stimulates release of thyroid stimulating hormone (TSH) from anterior pituitary
What type of hormones are hormones from anterior pituitary gland?
All peptides
5 are also tropic
What is trophic action?
Control secretion of other endocrine glands and have direct or indirect effects in promoting growth
What are the 6 anterior pituitary hormones?
Thyroid stimulating hormone
Adenocrticotropic
Follicle stimulating
Lutenising hormone
Growth hormone
Prolactin
What is the function of prolactin?
Stimulates milk production from breasts during lactation
What are the 3 integrating centres of anterior pituitary feedback control?
Hypothalamus
Anterior pituitary
Target endocrine cell
Describe anterior pituitary feedback control
Hormones themselves act as negative feedback control
Feedback from endocrine target - long-loop feedback
From anterior pituitary to hypothalamus - short-loop feedback
What is short loop and long loop feedback control?
Short - Anterior pituitary to hypothalamus
Long - endocrine target cell upwards
What can endocrine disorders be classified as?
Hyposecretion - too little hormone secreted
Hypersecretion - too much hormone secreted
What are primary disorders?
Defect is in cells that secrete the hormone
What are secondary disorders?
There is too little or much tropic hormone from pituitary
Either over or under stimulating
What are tertiary disorders?
Relate to hypothalamic disorders
Rare
Describe hyporepsonsiveness
May be due to alterations in receptor for hormone disordered post receptor events, failure of metabolic activation of hormone, or antagonistic effects
Describe hyperresponsiveness
Due to permissive effects like thyroid hormone causing more adrenaline mediated lipolysis
What does prolonged exposure to low hormone level in plasma lead to?
Up regulation of receptor number - increases tissue sensitivity/ response to hormones
What does prolonged exposure to high hormone level in plasma lead to?
Down regulation of receptor number - decreases tissue sensitivity/ response to hormone
What happens if plasma hormone conc. is disrupted?
Homeostatic responses
Effects not only the hormones own receptors but also receptors for other hormones
Permissive or antagonistic
Describe permissive effects
Presence of one hormone enhances effects of another
What is an example of permissive effects?
Thyroid hormone increases synthesis of receptors for epinephrine on adipocytes
TH itself has no effect on lipolysis but is permissive to epinephrine
Describe antagonist effects
Presence of one hormone reduces effect of another
Ex. growth hormone impairs glucose uptake in response to insulin - decreasing number of insulin receptors on muscle and adipose tissue
