Interaction
Why must hormone signaling be inactivated
Hormone signaling must be deactivated to maintain homeostasis, prevent overstimulation of target cells, and ensure that physiological responses are appropriate to current, rather than past conditions
Maintain homeostasis, preventing overstimulation, reestablishing sensitivity, preventing pathological conditions, ensuring specificity and directionality
What is antagonism in regards to interaction of hormones at target cells? an example?
Hormones can diminish the effect of each other in various ways
What are the neuroendocrine hormones of the hypothalamus
Releasing hormones (+ stimulation) - GnRH, GHRH, CRH, PRH, TRH
Inhibitory hormones (- stimulation) = Somatostatin, dopamine
What do the nuclei of the hypothalamus do?
Different nuclei respond to different physiological signals (temperature, osmolarity, stress, reproduction) and release specific neurohormones accordingly
Supraoptic and paraventricular nuclei contain magnocellular neurons that synthesize ADH and OXY
What are the small neurohormones (9 amino acids)
Antidiuretic hormone (ADH or VP)
Oxytocin's
ADH and OXY are nonapeptides synthesized as preprohormones in the SON and PVN
Packaged with neurophysins in secretory vesicles and transported to the posterior pituitary for storage and release
What are two ways hormones signaling is deactivated
Ligand degraded by extracellular enzymes
Inactivation of signal transduction pathway
What is competitive antagonist?
Hormone binds to the receptor but does not activate it - ER antagonist tamoxifen -> used to treat cancers stimulated by estrogen
What are the neuroendocrine hormones of the pituitary
Anterior lobe - PRL, GH, FSH, and LH, ACTH, TSH
Intermediate lobe - POMC (specifically alpha-MSH, beta-endorphin, species dependent)
Posterior lobe - Oxytocin and vasopressin (ADH) - released only
What are the two mechanisms of hypothalamic control
Neural: direct autonomic outputs regulate heart rate, digestion, thermoregulation
Endocrine: neurohormones released either
- directly into systemic circulation via the posterior pituitary
- into the hypophyseal portal system to regulate anterior pituitary hormone secretion
What do the PP hormones ADH and Vasopressin do
ADH conserves water by increasing aquaporin-2 insertion in the kidney collecting duct
High plasma osmolarity -> increased ADH -> water reabsorption -> concentrated urine
Low plasma osmolarity -> decrease ADH -> dilute urine
Lack of ADH action causes diabetes insipidus
Lack of ADH secretion -> diabetes insipidus
How does interaction of hormones at target cells happen? What 3 ways does this happen
A tissue/organ if often affected by multiple hormone types - multiple receptor types present these hormones interact to produce a specific result within the tissue/organ
Additivity and synergism
Permissiveness
Antagonism
What is functional (or physiological) antagonist?
Have opposing physiological actions
Hormones act on two different types of receptors and antagonize the action of each other - glucagon and GH increase glucose in blood -> insulin decreases it, Histamine acts as H1 receptors vs epi acts on beta-2 receptors, act through different receptors/pathways
What are the neuroendocrine hormones of the pineal
melatonin
What are magnocellular neurons
Somas (cell bodies) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN)
Long axons extend into the posterior pituitary
Release antidiuretic hormone (ADH) and oxytocin into circulation
What does the PP hormone Oxytocin do
Oxytocin triggers milk let down via contraction of myoepithelial cells
During parturition, cervical stretch stimulates oxytocin release, which enhances uterine contractions
Oxytocin receptor expression increases markedly near term, enhancing uterine responsiveness
Primary stimulus for release: suckling -> neural signals -> PVN -> posterior pituitary
What is synergism? an example?
Combined effect of hormones that is greater than the sum of their individual effects
Glucagon, cortisol and epinephrine all raise blood glucose levels
Cellular mechanisms are not always clear - overlapping effects on 2nd messenger system
What is neuroendocrine control
The hypothalamus-pituitary unit integrates neural information and converts it into hormonal signals that regulate nearly all endocrine systems
What are the neuroendocrine hormones of the sympathoadrenal medulla
Catecholamines
What are parvocellular neurons
Somas (cell bodies) in the various nuclei
Axons only reach the median eminence
Secrete multiple releasing hormones into the portal system
What are the characteristics of releasing hormones? (Hint 6)
Secretion in pulses
Act on specific membrane receptors
Transduce signals via second messengers
stimulate synthesis of pituitary hormones
Stimulate release of stored pituitary hormones
Stimulates hyperplasia and hypertrophy of target cells in the pituitary gland
What is permissive in regards to interaction of hormones at target cells? an example?
One hormone affects the capacity of cells to respond to the other hormone
maturation of reproductive system is mainly controlled by reproductive hormones - but with thyroid hormones, reproductive maturation is delayed, and thyroid hormones cannot stimulate maturation on their own
How is the pituitary an organ of dual origin
The anterior pituitary: derived from oral ectoderm; epithelial tissue
Posterior Pituitary: derived from neural ectoderm; an extension of the hypothalamus
Development requires coordinated growth of Rathke's pouch and the neural infundibulum to form a functional HP axis
What is the hypothalamus
Portion of the brain that contains 12 small nuclei with a variety of functions that regulate autonomic, endocrine, and behavioural processes
- control of body temperature
- Control of blood circulation/pressure
- Regulation of food and water intake
= Maintain homeostasis
What are the hypothalamic hormones
GnRH, CRH, TRH, PRH, Dopamine, GHRH, Somatostatin
What are the two types of releasing hormones
Stimulatory - CRH, GHRH, GnRH, TRH
Inhibitory - PRL inhibitory (dopamine), GH inhibitory (somatostatin)