MEH: The Hypothalamic Pituitary Axis Flashcards
Describe the relationship between the hypothalamus and the anterior pituitary gland.
The two are physically connected.
Oxytocin and anti-diuretic hormone produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus and stored and then eventually released by the posterior pituitary.
Describe the relationship between the hypothalamus and the posterior pituitary.
Tropic hormones synthesised and released by the hypothalamus are transported down axons and stored in the medial eminence before being released into the hypophyseal portal system.
These hormones either stimulate or inhibit the release of endocrine hormones from the anterior pituitary.
Name the hormones produced by the hypothalamus for release from the posterior pituitary.
- Oxytocin
- ADH
Name the hormones produced by the anterior pituitary gland.
- TSH Thyroid stimulating hormone
- ACTH Adrenocorticotropic hormone
- LH Luteinising hormone
- FSH Follicle stimulating hormone
- PRL Prolactin
- GH Growth hormone
Describe the factors controlling GH secretion (long and short loop negative feedback).
Long Loop:
- Mediated by IGFs which inhibits the release of GHRH from hypothalamus
- Stimulates release of somatostatin (GHIH) from hypothalamus
- Inhibits the release of GH from anterior pituitary
Short Loop:
-Mediated by GH itself via stimulation of GHIH (somatostatin) release
Describe how GH exerts its effects on cells directly.
Activates Janus Kinase receptors (JAKs) through cross phosphorylation and subsequent phosphorylation of the GH receptor. This causes activation of signalling pathways and ultimately transcription factor activation and IGF production.
Describe how GH exerts its effects on cells indirectly through Insulin like growth factors.
In response to GH cells of the liver and skeletal muscle produce and secrete IGFs. (IGF1-Adults, IGF2-fetal growth).
These act through IGF receptors to modulate:
• Cell growth (Hypertrophy)
• Cell number (Hyperplasia)
• Increase in the rate of protein synthesis
• Increase in the rate of lipolysis in adipose tissue
Where is the pituitary gland situated?
Beneath the hypothalamus in a socket of bone called the sella turcica
Where does the anterior pituitary arise from embryologically?
Primitive gut tissue
Where does the posterior pituitary arise from embryologically?
Primitive brain tissue
Describe the biological role of Oxytocin.
Milk let down and uterus contractions.
Describe the biological role of Antidiuretic hormone.
Also called vasopressin, its role is to regulate the water volume in the body.
Name the 6 tropic hormones produced by the hypothalamus.
- TRH (Thyrotropin releasing hormone)
- PIH (Prolactin release-inhibiting hormone)
- CRH (Corticotropin releasing hormone)
- GnRH (Gonadotropin releasing hormone)
- GHRH (Growth hormone releasing hormone)
- GHIH (Growth hormone-inhibiting hormone)
Define tropic hormone.
Hormones which affect the release of other hormones.
Describe the biological role of TSH (thyroid stimulating hormone)
Secretion of thyroid hormone from thyroid gland
Describe the biological role of ACTH (Adrenocorticotropic hormone)
Secretion of hormones from adrenal cortex
Describe the biological role of LH (luteinising hormone)
Ovulation and secretion of sex hormones
Describe the biological role of FSH (Follicle stimulating hormone)
Development of eggs and sperm
Describe the biological role of PRL (Prolactin)
Mammary gland development and milk secretion
Describe the biological role of GH (growth hormone)
Growth and energy metabolism. Stimulates IGFs
Describe events that cause an increase in GH.
- Deep sleep
- Stress
- Exercise
- Decrease in glucose or fatty acids (i.e fasting)
Describe events that cause a decrease in GH.
- Rapid eye movement (REM)
- Obesity
Describe the clinical features of pituitary dwarfism.
- Proportionate type of dwarfism
- Height below 3rd percentile on standard growth charts
- Growth slower than expected for age
- Little or no sexual development during teen years
Describe the clinical features of acromegaly.
Large extremities
e.g. jaw, hands, feet
