Session 8-Hypothalamic Pituitary Axis And Growth Hormone Flashcards
Where does the pituitary gland sit?
Beneath hypothalamus in a socket of bone called the sella turcica
What is the embryological origin of the anterior pituitary gland?
Evagination of oral ectoderm (Rathke’s pouch) - primitive gut tissue
What is the embryological origin of the posterior pituitary gland?
Neuroectoderm - primitive brain tissue
Complete the sentence:
The posterior pituitary gland is physically connected to the hypothalamus since the hypothalamus drops down through the __________________ to form the posterior pituitary
Infundibulum
Where are oxytocin and antidiuretic hormone produced?
Neurosecretory cells in supraoptic and paraventricular nuclei of hypothalamus
What transports oxytocin and antidiuretic hormone to the posterior pituitary to be released?
Nerve cell axons
Where are hormones synthesised in the hypothalamus stored?
Median eminence before release into hypophyseal portal system
What do hormones synthesised in the hypothalamus stimulate/inhibit?
Target endocrine cells in anterior pituitary gland (neurocrine function)
What transport functions do anterior pituitary hormones have?
Endocrine
Autocrine
Paracrine
Via which two distinct neurocrine pathways do hormones produced by nerve cells in the hypothalamus act?
1) direct effects on distant target tissues via oxytocin and antidiuretic hormone from posterior pituitary
2) tropic hormones secreted exclusively into hypophyseal portal system affect endocrine cells within anterior pituitary
What is another name for antidiuretic hormone?
Vasopressin
What do tropic hormones do?
Have direct effects on release of anterior pituitary hormones
Name the 6 tropic hormones produced in the hypothalamus
1) TRH (thyrotropin releasing hormone)
2) PIH (prolactin release-inhibiting hormone)
3) CRH (corticotropin releasing hormone)
4) GnRH (gonadotropin releasing hormone)
5) GHRH (growth hormone releasing hormone)
6) GHIH (growth hormone inhibiting hormone)
Which hormones are produced by the anterior pituitary and what are their functions?
1) TSH - secretion of thyroid hormone from thyroid gland
2) ACTH (adrenocorticotropic hormone) - secretion of hormones from adrenal cortex
3) LH - ovulation and secretion of sex hormones
4) FSH - development of eggs and sperm
5) PRL (prolactin) - mammary gland development and milk secretion
6) GH (growth hormone) - growth and energy metabolism
What does oxytocin do?
Milk let down and uterus contractions during birth
What does antidiuretic hormone do?
Regulation of body water volume
Which hormone/s cause the anterior pituitary gland to release:
1) TSH
2) ACTH
3) prolactin
4) growth hormone
5) LH and FSH
1) TRH (thyrotropin releasing hormone)
2) CRH (corticotropin releasing hormone)
3) TRH and negative effect of PIH (prolactin release-inhibiting hormone)
4) GHRH and negative effect of GHIH
5) GnRH
What regulates the pathways by which hypothalamic and anterior pituitary hormones are produced?
Negative feedback
What is the most important endocrine regulator of postnatal growth?
Growth hormone
Which factors influence growth?
Genetics
Nutrition
Environment
Hormones
What inhibits the production of growth hormone?
Somatostatin (GHIH)
How are growth-promoting effects mainly exerted?
Via insulin-like growth factors (somatomedins)
Which cells produce and secrete insulin-like growth factors (IGFs) in response to growth hormone (GH)?
Liver cells
Skeletal muscle cells
True or false: GH stimulates long bone growth
TRUE
What do insulin-like growth factors (IGFs) stimulate?
Bone and cartilage growth
What role do GH and IGFs have in adults?
Maintain muscle and bone mass and promote healing and tissue repair as well as modulating metabolism and body composition
Which factors increase GH secretion?
- stress (trauma, surgery)
- exercise
- decrease in glucose or fatty acids
- fasting
Which factors decrease GH secretion?
- R.E.M. Sleep
- increase in glucose or free fatty acids
- obesity
Describe the long loop negative feedback mechanism of GH secretion
Mediated by IGFs
- inhibit release of GHRH from hypothalamus
- stimulates release of somatostatin from hypothalamus
- inhibit release of GH from anterior pituitary
Describe the short loop negative feedback mechanism of GH secretion
Mediated by GH itself via stimulation of somatostatin release
What does complete or partial GH deficiency in childhood lead to?
Pituitary dwarfism
Which type of therapy is used to treat pituitary dwarfism?
GH therapy
True or false: there is delayed or no sexual development during teen years in someone with pituitary dwarfism
TRUE
What does an excess in GH lead to in childhood?
Gigantism (often caused by pituitary adenoma)
What does an excess of GH lead to in adulthood?
Acromegaly - large extremities (hands, feet etc)
How does GH exert its effects on cells?
1) GH binds to GH receptor
2) GH receptor activates Janus kinases (JAKs) by cross phosphorylation of JAK
3) phosphorylation of GH receptor
4) activation of signalling pathways
5) transcription factor activation and IGF production
Which receptor family are Janus kinases in?
Tyrosine kinase
Which mammalian IGF is mainly involved in foetal growth?
IGF2
Which mammalian IGF is the major growth factor in adults?
IGF1
What modulates the availability of IGFs?
Binding proteins
True or false: actions of IGFs can only be paracrine
FALSE - can be autocrine and endocrine as well
IGFs act through IGF receptors to modulate what?
1) hypertrophy
2) hyperplasia
3) increase in rate of protein synthesis
4) increase in rate of lipolysis in adipose tissue
How does insulin influence growth?
Enhances somatic growth; interacts with IGF receptors
How do thyroid hormones influence growth?
Promote CNS development and enhance GH secretion
How do androgens influence growth?
Accelerate pubertal growth spurt
Increase muscle mass
Promote closer of epiphyseal plates
How do estrogens influence growth?
Decrease somatic growth
Promote closure of epiphyseal plates
How do glucocorticoids influence growth?
Inhibit somatic growth
