Hypothalamic Pituitary Axis Flashcards
What is the hypothalamic pituitary axis?
A functional unit composing of the hypothalamus and pituitary gland
What is the sella turcica?
The socket of bone protecting the pituitary
What are the 2 parts of the pituitary gland?
Anterior
Posterior
Why is the posterior pituitary not actually a gland?
It does not produce hormones it only stores them and secretes them
What embryolicggal origin did the anterior pituitary originate from
Oral/epithelial ectoderm
What did posterior pituitary originate from
Neuroectoderm
What a nuclei in the brain?
A collection of neurones
What are the names of the nuclei which produce Oxytocni and ADH in the hypothalamus?
Supraoptic
Paraventricular
What is the type of secretion which hormones travel down axons, stored and released?
Nerocrine secretion
Where are hormones made in the Hypothalamus stored before release into the hypophyseal portal system?
The median eminence
What is the function of the hormones made in the hypothalamus and stored in the median eminence?
Target endocrine cells in the anterior pituitary (neurocrine)
What affects do hormones made in the anterior pituitary have?
Endocrine (released into blood and affect distant cells)
Autocrine
Paracrine
What is a tropic hormone?
A hormone which targets and affects release of other hormones
What is a trophic hormone?
Hormones that regulate growth
What are the 6 tropic hormones made in the hypothalamus?
TRH Thyrotropin releasing hormone
PRH Prolactin releasing hormone (not important)
PIH Prolactin release-inhibiting hormone (dopamine)
CRH Corticotropin releasing hormone
GnRH Gonadotropin releasing hormne
GHRH GGrowth hormone releasing hormone
GHIH Growth hormone-inhibiting hormone (Somatostatin
What dos the RH part of the hormone name mean
Releasing hormone
Hormones made by the anterior pituitary
TSH Thhroid stimulating hormone
ACTH Adrenocorticotropic hormone
LH Luteinidisingg hormone
FSH Follicle stimulating hormone
PRL Prolactin
GH Growth hormone
What are the factors affecting ggrowth
Hormones (GGrowth hormne is most important)
Nutrition
Environment
Genetics
What is necrosis?
Cell death by damage
What is apoptosis?
Programmed cel death
Atrophy
Decrease in cell size or decrease in cell number
Hyperplasia
Increase in cell number
HYpertrophy
Increase in cell size (e.g muscle fibres get bigger when trained)
Where is GGrowth hormone produced?
Anterior pituitary
What are the hormones which stimulate and inhibit production of GH
GHRH made in hypothalamus STIMULATES
Somatostatin made in hypothalamus INHIBITS
What type of hormone is GH
Protein/peptide hormone (191 amino acids)
What are 2 types of affects GH
Direct
Indirect (promotes Insulin-like growth factors (IGF1 and IGF2)
Where does GH cause IGFs to be produced?
Liver
Skeletal muscle
WHy is GH essential for normal growth during childhood and teenage years? (when epiphyseal plates have not sealed)
GH directly stimulates long bone Growth
IGFs stimulate bone growth and cartilage growth
What do GH and IGFs do in adults? (So once epiphyseal plates in bone close)?
Maintain bone and muscle mass
Promote healing and tissue repair
What affects production of GH
Deep sleep increases
REM sleep decreases
Stress Increase
Excersie increases
Dedcresased glucose/fatty acids decreases
Increase glucose/fatty acids decreases
Fasting increase
Obesity decreases
What is the long loop negative feedback regulation of GH?
IGFs:
inhibits release of GHRH
Stimulates release of somatostatin = GHIH
Inhibits release of GH from anterior pituitary
Short loop negative feeback regulation of GH secretion
GH regulates itself by stimulating release of somatostatin which inhibits GH releases
Short loop negative feeback regulation of GH secretion
GH regulates itself by stimulating release of somatostatin which inhibits GH releases
Somatostatin = GHIH
What does GH deficiency in childhood causes? (Before epiphyseal plates close)
Pituitary dwarfism
(Slow ggrowth, delayed/no sexual development)
What does excess GH cause in childhood and adults?
Childhood = Gigantism
Adulthood = Acromegaly
What is Gigantism normally caused by
Pituitary adenoma (Benign Tumor in pituitary)
What is acromegaly?
Large extremities
(Hands, greet and lower jaw)
What 2 neurocrine pathways do the hormones produced by the hypothalamus act in?
Oxytocin and ADH travels down axons from the hypothalamus to the posterior pituitary where it is stored it’s later released to act on distant target tissues
Tropic hormones secreted into hypophyseal portal system affect endocrine cells in anterior pituitary
What are the functions of the 2 hormones made in the hypothalamus and stored in the posterior pituitary?
Oxytocin (Milk let down and uterus contractions in childbirth)
Anti-diuretic hormone (ADH/Vasopressin) Regulates body water volume by causing body to absorb more water so less released in urine
How does GH exert its affect on cells?
Binds to receptor activating Janus Kinases (JAKs)
These JAKs Phosphorylates themselves
This activates a transcription factor causing production of IGFs
What does IGF stand for?
Insulin like Growth factors
What is the role of IGF1 and IGF2
IGF1 major growth factor in adults
IGF2 mainly Fetal growth
What are the 3 types of action IGFs can work by?
Autocrine (act on cell that made them)
Paracrine (act on adjacent cells by diffusing through gap junctions)
Endocrine (release in blood to distant tissues)
What do IGFs modulate?
Hypertrophy (cell growth)
Hyperplasia (Cell number)
Increase rate of protein synthesis
Increase rate of lipolysis
Where is TRH (Thyrotropin Releasing Hormone) synthesised, where does it affect and what effect does it have?
TRH made in Hypothalamus
Stimulates anterior pituitary to produce TSH (Thyroid Stimulating Hormone)
TSH stimulates Thyroid gland to produce Thyroid hormone (T3 and T4)
Thyroid hormones affect metabolic rate
Where is CRH (Corticotropin Releasing Hormone) synthesised, where does it affect and what effect does it have?
CRH made in the hypothalamus
Stimulates the anterior pituitary to produce ACTH (Adrenocorticotropic hormone)
ACTH stimulates adrenal cortex to produce hormones like Cortisol
Cortisol is important in stress response metabolic actions
Where is PIH (Prolactin release-inhibiting Hormone) synthesised, where does it affect and what effect does it have?
Name a type of Prolcatin-release inhibiting hormone
PIH made in the Hypothalamus
PIH inhibits anterior pituitary from producing prolactin
Lack of prolactin causes lack of breast growth and milk secretion (mammary glands affected)
Dopamine inhibits production of prolactin so is a PIH
TRH can also a stimulate production of which hormone?
Prolactin
Where is GHRH (Growth Hormone Releasing Hormone) synthesised, where does it affect and what effect does it have?
Made in hypothalamus
Stimulates anterior pituitary to produce GH (Growth Hormone)
GH stimulates liver to produce IGFs which stimulate growth or stimulate growth by acting on tissues directly
GH needed for growth and energy metabolism
Where is GHIH (Growth Hormone Inhibiting Hormone) synthesised, where does it affect and what effect does it have?
What is the other name for Growth Hormone Inhibiting Hormone?
Made in hypothalamus
Inhibits anterior pituitarys production of GH (Growth Hormone)
No GH to stimulate liver to produce IGFs which stimulate growth or No GH to stimulate growth by acting on tissues directly
GH needed for growth and energy metabolism
GHIH also called Somatostatin
Where is GnRH (Gonadotropin Releasing Hormone) synthesised, where does it affect and what effect does it have?
GnRH made in the hypothalamus
GnRH stimulates anterior pituitary to make LH and FSH
Stimulates Ogaries in females and Testes in males
What is the function of LH (Luteinising Hormone)?
Stimulates ovulation in females
Stimulates release of sex hormones in males and females
What is the function of FSH (Follicle Stimulating Hormone)?
Stimulates production of gametes
Stimulates egg production in the ovaries
Stimulates sperm production in the testes
