Intro Endocrinology and the Hypothalamus-Pituitary Axis Flashcards
5 functions of the endocrine system
- maintain internal homeostasis
- regulate growth and morphological changes
- coordinate development
- coordinate reproduction
- facilitate social and behavioural interactions.
Amino acid derivative hormones
Catecholamines
Thyroid hormones
Catecholamines synthesis
Synthesised from tyrosine, NE and EPI are formed in the cytoplasm of adrenal medulla cells where they are then stored in vesicles until release.
Thyroid hormone synthesis
Also synthesised from tyrosine, then incorporated into thyroglobulin and stored in large follicles in the thyroid gland. Combine with thyroxine-binding globulin in the plasma (carrier protein).
Peptide and protein hormones
Encoded in the genome, preprohormones -> prohormones -> stored in secretory vesicles after final product is completed by prohormone convertases.
May be released as prohormone and active hormone.
Steroid hormones
All derived from cholesterol, which cells store as cholesterol esters in cytoplasmic vesicles. Tissue specific enzymes in the mitochondria and ER determine the product.
Not stored, instead produced on demand in response to a stimulus.
Fatty acid derived hormones (eicosanoids)
Synthesised from arachidonic acid, and secreted by nearly every cell.
Function in inflammation, blood pressure, and blood clotting.
Arachidonic acid
20-carbon fatty acid
Characteristics of receptors
Affinity
Specificity
Capacity
Control of endocrine activity via control over the concentration of hormones is determined by:
Rate of:
- production
- delivery
- degradation/elimination.
Metabolic clearance rate
MCR = (mg/min removed)/(mg/ml of plasma) = ml cleared/min.
Mainly performed by the kidneys.
Hormones removed at the tissues:
- protein/amines - internalised and degraded.
- steroid/thyroid - degraded after complex binds DNA.
Ultraradian rhythm
Peak several times throughout the day - growth hormone, LH, FSH, etc.
Diurnal rhythms
Peak once throughout the day - cortisol.
Infradian rhythms
Peak over the span of a month - ovarian hormones (oestrogen, progesterone).
The SCN and PG
When the suprachiasmic nucleus sense light, it inhibits the pineal glandfrom releasing melatonin.
Magnicellular neurons
Have large cell bodies that extend to the posterior pituitary gland and secrete hormones directly to the blood stream. A.V.P. And oxytocin
Parvicellular (hypophyseotropic) neurons
Extend to the hypothalamus and induce the release of releasing factors that then stimulate the release of other hormones from the anterior pituitary.
Hypothalamic (projection) neurons
Neurons that extend from the hypothalami and synapse onto neuronal targets such as the sympathetic preganglionic neurons in the spinal card. Involves POMI processing.
Neurohypophysis
The posterior pituitary reached by the supraoptic and parma ventricular neuron axon projections.
Posterior hypothalamic neurons
ADH (AVP)
Oxytocin
Released to the
Oxytocin in parturition
Cervical stretch stimulates release, which then stimulates contractions during expulsive phase that then increase the pressure on the cervix, further increasing oxytocin release.
Pitocin
An oxytocin analogue used to induce labour.
Oxytocin and milk letdown
Milk secreted into mammary gland alveoli surrounded by myoepithelial cells. Hearing a baby cry/suckling causes oxytocin release, causing myoepithelial cell contraction.
