L2 - Intro to HPA axis Flashcards
What is the area directly above the pituitary gland
- Hypothalamus
What is the pituitary gland connected to the brain via
- Infundibulum
What is the pituitary gland divided into
- Anterior and posterior pituitary glands
- They effectively function independently
What is the posterior pituitary gland sometimes called
- Is a ‘down growth’ from the brain
- It is sometimes called the neurohypophysis
What are the hormones secreted by the posterior pituitary gland
- Antidiuretic hormone(ADH also called vasopressin)
- Oxytocin
What type of hormones are ADH and oxytocin
- Peptide hormones
- Nine amino acids each, of which seven are identical
Where are ADH and oxytocin produced
- Hormones are not synthesised within the gland, but are synthesised by the neurones of the hypothalamus
- Supraoptic nuclei and paraventricular nucleus
- These hormones are synthesised as inactive precursors and converted to active hormone within the posterior pituitary
What are the inactive precursors of ADH and oxytocin transported via
- Transported from the supraoptic and paraventricular nuclei along the hypothalamico-neurohypophyseal tract
- They are then stored within the posterior pituitary
What is secretion of ADH influenced by
- Plasma osmolarity
What does stimulation of V2 receptors cause
- Stimulation of V2 receptors causes translocation of aquaporins to the membrane of the kidney tubule, thus allowing water reabsorption
What does stimulation of v1 receptors cause
- Vasoconstriction
- This does not occur at physiological concentration
What do disorders of ADH secretion lead to
- Disorders of fluid balance
Effect of oxytocin
- Oxytocin acts via IP3 to cause contraction of the smooth muscle of the genital tract (uterus) and breast
- During parturition, oxytocin causes contraction of the smooth muscle of the uterus to aid expulsion of the infant
- Continued stimulation of the cervix causes continued secretion
What is secretion of oxytocin stimulated by
- Stimulation of the genitals and nipples
When is oxytocin most important
- At parturition and during lactation
When does oxytocin synthesis increase
- During pregnancy, but there is a parallel increase in oxytocinase activity
Is oxytocin necessary for initiation of normal labour
- Oxytocin is not necessary for the initiation of a normal labour
- But oxytocin may be administered to induce labour
What is anterior pituitary gland also called
- An ‘up growth’ from the palate
Hormones secreted by the anterior pituitary gland
- Growth hormone
- Prolactin
- Thyroid stimulating hormone
- Adrenocorticotrophic hormone
- Follicle stimulating hormone
- Luteinising hormone
Which cells synthesise thyroid stimulating hormone
- Thyrotrophe cells
Which cells synthesise adrenocrticotrophic hormone
- Corticotrophe cells
Which cells produce follicle stimulating hormone
- Gonadotrophe cells
Where are the releasing hormones secreted by the hypothalamus secreted into
- Hypothalamico-adenohypopyseal portal vessel which carries them to the anterior pituitary
- The releasing hormones do not enter the systemic circulation
Biochemical tests that are part of clinical investigations
Start with Signs and Symptoms
Followed by
Biochemical Tests
(Basal Levels)
* TSH(not water soluble) & FT4(is free and therefore soluble) * Cortisol * LH & FSH * Prl * Testosterone / “Periods”
What is the test carried out after biochemical tests
- Imaging(eg MRI)
Tests carried out after imaging
- Visual field tests
eg bilateral hemianopsia due to compression of optic chiasm
Why is the timing of tests important
- Diurnal rhythms
Why do you have to measure FT4 levels
- TSH is not biologically active
Where is prolactin synthesised
- Is 199 amino acid peptide, synthesised in the lactotrophe cells of the anterior pituitary
What is prolactin secretion controlled by
- The secretion of prolactin is under hypothalamic control by means of Prolactin Release Inhibiting Factor, which is DOPAMINE.
- TRH stimulates prolactin synthesis.
What is prolactin secretion stimulated by
- Mild stress
- Nipple stimulation
- Coitus
Primary role of prolactin
- To promote lactation, and development of breast tissue
- It is most important in females after puberty and during and after pregnancy
- Prolactin is secreted in both males and females
Where is growth hormone synthesised
• Growth hormone is synthesised in the somatotrophe cells of the anterior pituitary gland
What is secretion of growth hormone secretion controlled by
• Secretion is controlled by the hypothalamus via
- Growth Hormone Releasing Hormone (GHRH) and Growth Hormone Release Inhibiting Hormone (GHRIH, somatostatin).
· Growth Hormone Releasing Hormone (GHRH) is more important in control than
Growth Hormone Release Inhibiting Hormone (GHRIH, somatostatin).
What can secretion of growth hormone be stimulated by
· Secretion of growth hormone is stimulated by decreased carbohydrates and fatty acids and increased amino acids.
What can GH act via in some tissues
· In some tissues, GH acts via second messengers which are produced in the liver
· Insulin-like growth factor 1
· Insulin-like growth factor 2
What is the primary effect of GH
The primary effect of GH is to promote the linear growth of adolescence by increasing protein synthesis and collagen deposition
This is mediated via the nucleus
GH is also involved in tissue turnover and repair
Effect of GH on foetal growth
Foetal growth is relatively independent of gH
