S8) The HPA Axis & Growth Hormone Flashcards
Describe the relationship between the hypothalamus and the pituitary gland
The hypothalamus and pituitary gland form a complex functional unit that serves as the major link between the endocrine and nervous systems
Where is the pituitary gland found?
The hypothalamus and pituitary gland modulate a wide variety of processes.
Identify some
- Body growth
- Reproduction
- Lactation
- Thyroid & adrenal gland function
- Water homeostasis
The pituitary gland consists of two distinct parts.
What are they?
The anterior and posterior pituitary glands have distinct embryological origins.
Describe these
- Anterior pituitary gland (adenohypophysis) arises from evagination of oral ectoderm (primitive gut tissue)
- Posterior pituitary gland (neurohypophysis) originates from neuroectoderm (primitive brain tissue)
The hormones produced by nerve cells in the hypothalamus act via two distinct neurocrine pathways.
Describe these pathways
- Direct effects on distant target tissues via oxytocin and antidiuretic hormone from the posterior pituitary
- Hormones secreted exclusively into hypophyseal portal system affect endocrine cells within the anterior pituitary
In 3 steps, outline the neuroendocrine function of the posterior pituitary gland
⇒ Oxytocin and ADH are produced by neurosecretory cells in the supraoptic and paraventricular nuclei of hypothalamus
⇒ Transported down nerve cell axons to the posterior pituitary
⇒ Stored and released from posterior pituitary into the general circulation
In four steps, describe the synthesis, transport, release and action of the hormones acting on the anterior pituitary gland
⇒ Hormones synthesised in hypothalamus
⇒ Hormones transported down axons and stored in median eminence
⇒ Hormones released into hypophyseal portal system
⇒ Hormones stimulate/inhibit target endocrine cells in the anterior pituitary gland
Describe the action of the hormones produced by the anterior pituitary gland
⇒ Endocrine cells of anterior pituitary secrete a variety of hormones into the bloodstream to act on distant target cells (endocrine function)
⇒ Anterior pituitary hormones also effect neighbouring cells (autocrine and paracrine function)
Which hormones are released from the posterior pituitary gland and what do they do?
- Oxytocin – milk let down and uterine contractions during birth
- Antidiuretic hormone – regulation of body water volume
6 tropic hormones produced in the hypothalamus and have direct effects on the release of anterior pituitary hormones.
Identify them
- TRH – Thyrotropin releasing hormone / PRH
- PIH – Prolactin release-inhibiting hormone (dopamine)
- CRH – Corticotropin releasing hormone
- GnRH – Gonadotropin releasing hormone
- GHRH – Growth hormone releasing hormone
- GHIH – Growth hormone-inhibiting hormone (somatostatin)
Identify the 6 hormones produced in the anterior pituitary gland
- TSH – Thyroid stimulating hormone
- ACTH – Adrenocorticotropic hormone
- LH – Luteinising hormone
- FSH – Follicle stimulating hormone
- PRL – Prolactin
- GH – Growth hormone
Summarise the relationship between the tropic hormones of the hypothalamus and the hormones produced by the adenohypophysis as well as their respective effects
Outline the hypothalamic-pituitary-adrenal axis as an example of a negative feedback system
Growth is influenced by many factors.
Identify some of these
GH secretion is regulated by long loop and short loop negative feedback.
Describe the long loop negative feedback mechanism
Mediated by IGFs:
- Inhibit release of GHRH from hypothalamus
- Stimulate release of somatostatin from hypothalamus
- Inhibit release of GH from anterior pituitary
GH secretion is regulated by long loop and short loop negative feedback.
Describe the short loop negative feedback mechanism
Short loop negative feedback – mediated by GH itself via stimulation of somatostatin release
How does GH exert its effects on cells?
GH receptors activate Janus kinases (JAKs)
There are 2 IGFs in mammals.
Describe their respective actions
- IGF1 – major growth factor in adults
- IGF2 – mainly involved in fetal growth
