Lecture: Physiology of the Pituitary and Adrenal Glands Flashcards
Where does the glandular tissue of the anterior pituitary arise from?
invagination of pharangeal epithelial tissue
Where does the posterior pituitary arise from?
Out growth/extension of the hypothalamus
Where are the hormones that are released from the posterior pituitary synthesised?
Magnocellular neurons from the Supraoptic Nucleus and Paraventricular Nucleus.
What hormones are released from the PP?
ADH (SON)
Oxytocin (PVN)
What stimulates glandular tissue in AP to release hormones?
Neurohormones from hypothalamus carried by capillaries - hypophysal portal vein to stimulate glandular tissue
What cell types is the PP primarily comprised of?
The posterior pituitary is comprised primarily of glial-like
cells called pituicytes – these cells do not secrete hormones. Hormones of the posterior pituitary are secreted by magnocellular neurons - cell bodies in the PVN and SON of the hypothalamus. The hormones are synthesized in the cell bodies and transported down the nerve axons into the posterior pituitary
What stimulates oxytocin release?
Positive feedback loop. Suckling, sensory stimulation areola,
Function of oxytoxin?
- Milk ejection – contracts myoepithelial cells that surround
the mammary alveoli - Hastens delivery, promotes delivery of the placenta, reduces
bleeding – contracts uterine smooth muscle
(NOT THE PHYSIOLOGICAL TRIGGER FOR PARTURITION)
MOA of oxytocin?
via G-Protein coupled receptor; 2nd
messengers: IP3, DAG
IP3 is the chemical mediator that causes the release of calcium.
MOA of ADH?
- Reabsorption of water in connecting/collecting tubules via V2 rec. -> cAMP -> insertion of aquaporin-2 into the luminal membrane.
- Vasoconstriction via V1 rec. -> IP3, DAG -> ↑[Ca2+]i
- Increases thirst (via actions on the CNS)
- ↑ACTH from anterior pituitary - ↑aldosterone - ↑
conservation of Na+ and H2O (Note: plasma K+ and angiotensin II are the main regulators of aldosterone secretion)
What stimulates hormone secretion from the anterior pituitary?
Hypothalamic releasing/inhibitory hormones enter a portal system and are conducted to the anterior pituitary
Proportion of AP cells made up of thyrotropes?
Thyrotropes (3-5%)
Thyroid-stimulating hormone (TSH) (aka thyrotropin)
Target: thyroid
stimulates T3 & T4 secretion
Proportion of AP cells made up of corticotropes?
Corticotropes (15-20%)
Adrenocorticotropic hormone (ACTH) (aka corticotropin)
Target: adrenal cortex
stimulates cortisol secretion
Proportion of AP cells made up of somatotropes?
Somatotropes (40-50%)
Growth hormone (GH) (aka somatotropin)
Target: bone, tissues, liver
Growth; influences metabolism
Proportion of AP cells made up of gonadotropes?
Gonadotropes (10-15%)
Follicle-stimulating hormone (FSH) & Luteinizing hormone (LH)
Target: ovaries & testes sex hormone secretion;
gamete production