The HPA Axis And Growth Hormone Flashcards
What is the HPA axis?
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 located?
The pituitary gland sits beneath the hypothalamus in a socket of bone called the sella turcica
Name some processes the hypothalamus and pituitary glans modulate
Body growth milk secretion - oxytocin reproduction - FSH and LH lactation - prolactin adrenal gland function thyroid gland function water homeostasis - ADH puberty
What are the 2 parts of the pituitary gland?
•Anterior pituitary gland
(Adenohypophysis) - arises from evagination of oral ectoderm (Rathke’s pouch - primitive gut tissue)
•Posterior pituitary gland
(Neurohypophysis) - originates from neuroectoderm (primitive brain tissue)
- The anterior and posterior pituitary glands have distinct embryological origins and distinct functions
- The posterior pituitary gland is physically connected to the hypothalamus, since the hypothalamus drops down through the infundibulum to form the posterior pituitary - Posterior pituitary is not a gland as it dos not make its own hormones - it stores hormones from the hypothalamus - travel via neurones
What is the neurocrine function of the posterior pituitary
•Oxytocin and antidiuretic hormone produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus - both nuclei generate oxytocin and ADH
•Transported down nerve cell axons to the capillary bed of the posterior pituitary.
•Stored and released from posterior pituitary into the general circulation to act on distant target tissues
NOTE: the posterior pituitary gland does not synthesise these hormones. It just releases them.
What is the function of the anterior pituitary?
• Hormones synthesised in hypothalamus are transported down axons and stored in median
eminence before release into
hypophyseal portal system.
(Terminate in primary capillary plexus - hypophyseal portal system
Portal system allows hormones to travel directly to anterior pituitary from capillary plexus though hypophyseal portal vein to capillary bed in anterior pituitary)
• These hormones stimulate (or inhibit)
target endocrine cells in the anterior pituitary gland (neurocrine
function).
• Endocrine cells of anterior pituitary
secrete a variety of hormones into the
bloodstream to act on distant target
cells (i.e. endocrine function).
• Anterior pituitary hormones also
effect neighbouring cells (autocrine
and paracrine function).
What are 2 pathways that the hormones produced by the hypothalamus act by
The hormones produced by nerve cells in the hypothalamus act via two distinct neurocrine pathways
• Direct effects on distant target tissues via oxytocin and
antidiuretic hormone from the posterior pituitary - produced in hypothalamus
• Hormones secreted exclusively into hypophyseal portal system affect endocrine cells within the anterior pituitary
What connects the posterior pituitary to hypothalamus
Infundibulum (pituitary stalk)
What are the 2 hormones RELEASEd from the posterior pituitary?
OT Oxytocin
(Milk let down and uterus contractions during birth) - Travels around systemic circulation - myoepithelial cells in mammary tissue surrounding alveoli where milk produced - contract myoepithelial cells - squeezes milk into collecting duct
Pressure on the cervix, OT released and binds to receptors on uterine wall - contractions
ADH Antidiuretic hormone (also called vasopressin)
(Regulation of body water volume) - ADH binds to receptors - receptors activated promote aquaporins into walls - higher reabsorption - more concentrated urine - absorbing more water from the blood
What are tropic hormones?
Hormones that have an affect on other hormones in the target tissue
What are the 6 tropic hormones of the hypothalamus?
• TRH Thyrotropin releasing hormone - stimulates release of TSH
- (PRH) Prolactin releasing hormone (not rly this) = TRH (minor +ve control on prolactin)
• PIH Prolactin release-inhibiting hormone (Dopamine) - dominant control of prolactin
• CRH Corticotropin releasing hormone - stimulates release of ACTH which acts on adrenal gland
• GnRH Gonadotropin releasing hormone
• GHRH Growth hormone releasing hormone
• GHIH Growth hormone-inhibiting hormone (Somatostatin)
(RH= releasing hormone, IH = inhibitory hormone)
What are hormones produced by the anterior pituitary?
- TSH Thyroid stimulating hormone - Secretion of thyroid hormone from thyroid gland
- ACTH Adrenocorticotropic hormone - Secretion of hormones from adrenal cortex
- LH Luteinising hormone - Ovulation and secretion of sex hormones
- FSH Follicle stimulating hormone - Development of eggs and sperm
- PRL Prolactin - Mammary gland development and milk secretion
- GH Growth hormone - Growth and energy metabolism. Stimulates IGFs
Summarise the hormones of the anterior pituitary
See slide for diagram
How are the hypothalamus and ant pituitary hormones release regulated?
The pathways by which hypothalamic and anterior pituitary hormones are produced are often regulated by NEGATIVE FEEDBACK
Name sone factors which influence growth
Genetics, environment, nutrition, hromones (growth hormones is the most important endocrine regulator of postnatal growth)
