Hormones Flashcards
What are the different stimuli to hormone release? + Example of each
Humoral stimulus -
Change to extracellular fluid concentration.
E.G glucose = insulin release.
Neural stimulus - preganglionic sympathetic fibres stimulate the adrenal medulla to release NA/A.
Hormonal stimulus -
Hypothalamus releases GNrH which stimulates anterior pituitary to produce FSH, which acts on Gonads(ovaries) to release Oestrogen.
What is the structure of the Adrenal glands?
Sit atop the kidneys
Triangular shape - with outer cortex, and inner medulla.
Inner produces Adrenaline and NA.
Adrenal cortex has 3 zones:
But produces steroids…
Outer most = Glomerulata = Aldosterone (Mineralocorticoids)
Fasciculata = Cortisol (Glucocorticoid) and DHEA (Androgens)
Reticularis - DHEA
Medulla accounts for 20% of volume = Adrenaline, N.
How are steroids produced in the adrenal glands?
The adrenal cortex uses cholesterol as common precursor, with successive enzymatic modifications.
It has no intracellular storage - the rate of secretion depends on synthesis rate.
Passively diffuses through PM for release.
= Endocrine cells!!!
When is aldosterone produced?
Targets?
Effects?
Aldosterone produced by Endocrine cells of Zona Glomerulata.
In response to reduced plasma volume and Na+, or elevated plasma K+.
Aldosterone acts on renal tubule and collecting duct.
= To increase K+ excretion, Na+ reabsorption and therefore reabsorbe more water.
= Increase volemia and maintain hydric balance.
How is Cortisol produced?
Targets?
Effects?
ACTH released by Anterior Pituitary, stimulates Zona fasciculata to produce Cortisol.
Cortisol acts on nuclear receptors.
Metabolic = Raise liver gluconeogenesis, reduce glucose entry in cells except CNS, raise proteolysis and lipolysis.
= Raise glycemia!
Anti-inflammatory and immunosuppressive effects - limit amplitude and duration of responses.
Permissive effect - raise response to catecholamines.
How does cortisol signalling work?
Glucocorticoid receptor is intracellular receptor.
GR is cytoplasmic.
When absent, GR is inactive and bound to HSP + IP.
When present, GR-cortisol dissociates from HSP + IP, and translocates to nucleus.
Cortisol-GR activates gene transcription.
Catecholamine production and release?
All derived from Tyrosine.
Noradrenaline is precursor to Adrenaline, but adrenaline is released and produced in greater amounts.
Hydrophilic hormones, stored in Chromaffin granules (Storage vessicles).
Released by exocytosis.
What type of GPCR are a1, a2, b1, b2?
a1 = Gq = raise intracellular Ca2+.
a2 = Gi = inhibit AC, reduce cAMP.
b1, b2 = Gs = activate AC, riase cAMP.
What were the animal responses to stress in Selyes experiments?
His definition of stress?
Turgor of adrenal glands.
Involution of the Thymus and lymph nuclei (Immune system).
Stomach bleeding and adrenaline secretion.
The non-specific response of the body to any demand for change.
Modern definition of stress?
Response of organism to stressing environmental stimuli.
The environmental demand exceeds the natural regulatory capacity of the organism.
Env. modification = where regulatory mechanisms are insufficient so stress mechanisms activated .
What is allostasis?
Adaptive reaction of the organism that maintains a stable internal state despite presence of stressing elements.
What are the response trees to stress?
Stressing stimulus -> brain stress perception -> Sympathetic NS and HPA axis -> Biological effects.
Consideration of stress -> Rapid alarm stage -> Resistance stage -> Recovery or Exhaustion
How is stress perceived by the brain?
Sensory organs relay info. to Cortex (Sensory associative areas), The wider cortex attenuates emotions.
The limbic system:
Amygdala - quantifies emotional connotation of info. to determine importance.
Hippocampus - memorises info. modulated by amygdala.
= Limbic provides subjective interpretation of the stimulus, if threat to homeostasis = alarm signal.
What occurs during the alarm stage?
Neuroendocrine phase.
Limbic system activates the reticular formation.
This triggers pre-ganglionic sympathetic fibres to act on the adrenal medulla to release Adrenaline.
Adrenaline causes vasodilation, increased HR, fasting breathing etc.
+ Raises vigilance, cardiorespiratory mobilisation.
Declarative memorisation process - New scene is analysed with regard to past experiences.
What occurs during Resistance stage?
When stressor persists = Endocrine phase.
Limbic system acts via hypothalamus on the HPA axis.
Hypothalamus secretes CRH, Anterior pituitary secretes ACTH, adrenal cortex zona fasciculata produces cortisol.
Cortisols metabolic effects:
Raise gluconeogenesis in liver, raise lipolysis, proteolysis, reduce glucose entry.
= Raise glycaemia.
Permissive effects - raise response to catecholamines.
Suppressive effects: Suppress immune+inflammatory system.
= Keeps responses in physiological range.
What happens in Recovery/ exhaustion stage?
If the stressor is stopped, then in recovery, responses should have remained in physiological range.
In Exhaustion, there is pathological evolution.
= Stressor was too intense/long lasting.
= Inoperative stress reactions.
= Overwhelmed physiological responses.
What parts of brain are near the hypothalamus?
Where is the hypothalamus?
Pineal gland - produces melatonin.
Pituitary gland is below.
Next to the thalamus.
Ventral face of brain.
= part of the Ventral NS.
Composed of independent clusters of neurones (Hypothalamic nuclei)
Where is the pituitary gland?
Below the Hypothalamus
= Hypophysis.
Ventrally connected to hypothalamus.
Anterior = Adenohypophysis
Posterior = Neurohypophysis.
Hypothalamus is connected to the pituitary by the infundibulum/pituitary stalk.
What is the role of hypothalamus?
Independent clusters of neurones called Hypothalamic nuclei.
Integrate several stimuli.
Part of ventral NS.
Contains some neuroendocrine cells - producing peptidic hormones which interplay with pituitary gland.
Parvocellular vs Magnocellular systems
What are the Parvocellular and Magnocellular systems?
Endocrine neurones in the hypothalamus can interact with the pituitary gland with 2 systems.
Parvocellular system contains small, disseminated neuroendocrine cells interplay with anterior pitutary/adenohypophysis.
Magnocellular system has large, big cells of specific hypothalamic nuclei interplaying with posterior pituitary/neurohypophysis.
What are the names for the anterior and posterior pituitary hormones?
Anterior = Adrenohypophyseal hormones.
Posterior = Neurohypophyseal hormones.
What are the different origins and functions of the Posterior/Anterior Pituitary?
Anterior pituitary = Embryonic origin of epithelial cells.
Synthesis and release of adenohypophyseal hormones.
= Endocrine gland.
= Parvocellular system.
Posterior pituitary = neuroectoderm origin.
Posterior pituitary contains axonal extensions from hypothalamic neurones, which are responsible for synthesising neurohypophyseal hormones, which are released in the posterior pituitary.
Magnocellular system
- large hypothalamic nuclei axonal extensions into posterior pituitary.
Explain the parvocellular system?
Small, disseminated neuroendocrine cells in Hypothalamus produce hormones regulating the anterior pituitary gland.
These hormones are released into the 1st capillary meshwork.
Short-distance blood transport via the portal system.
This brings to capillary bed of the anterior pituitary.
Regulate secretion of adenohypophyseal hormones in the 2nd capillary meshwork (in the anterior pituitary) for release into general bloodstream.
How do histology of anterior and posterior pituitary compare?
Anterior = capillary meshwork surrounding endocrine cells filled with secretory vesicles.
Posterior = Axonal endings of hypothalamic neurones, containing secretory vesicles.
Near to fenestrated capillaries (endothelial)
