Endocrine Physiology - Hormones and the Stress Response Flashcards
- PB_BK_87 Hormonal control of metabolism: regulation of plasma glucose, response to trauma - PB_BK_88 Physiological alterations in starvation, obesity [including normal and abnormal BMI ranges], exercise and the stress response - PB_BK_90 Hormones; types, receptors, heirarchy, extracellular signalling - PB_BK_91 Mechanisms of hormonal control; feedback mechanisms, effects on membrane and intracellular receptors (4 cards)
What is the stress response?
A multi-system, neuroendocrine and metabolic response to injury. Aims to produce a state of catabolism & maintain cardiovascular stability.
Release of ACTH and Cortisol
Lipolysis
Proteolysis
Hyperglycaemia
Growth-hormone
Tissue repair & protein anabolism
ADH
Vasoconstriction & fluid retention
Prolactin & endorphins
Sympathetic nervous stimulation triggers catecholamine release
Renin conversion & angiotensin II production increase aldosterone levels leading to fluid & salt retention.
Metabolism:
Increased lipolysis (and ketogenesis), amino acid production via proteolysis
Increased gluconeogenesis & glycolysis - hyperglycaemia (above 12mmol/L impairs wound healing)
Incrased metabolic rate, O2 consumption & CO2 production, body temperature
Increased cytokine production & inflammatory mediators
The surgical stress response can be reduced through opioids, balanced anaesthesia, and minimally invasive surgery.
What is a hormone?
IMAGE
Chemical messengers secreted into the blood by endocrine organs that act at distant tissues.
Steroids
Act via nuclear receptors
Slower onset but longer duration of action
Cortisol, Aldosterone, Sex steroids
Amino Acid derivatives
Tyrosine derivatives:
Catecholamines & thyroid hormones
Peptides
Rapid onset, via changes in protein activity
Insulin, Glucagon, ACTH, PTH
What factors influence hormone release?
Negtive feedback
Autonomic/CNS input
Ions/Molecule concentration (Na+/Glucose)
Other hormones (Paracrine/trophic hormones)
Direct/Physical (Eg Gut hormones)
For example cortisol
Diurnal variation, autonomic, chemical (5HT3) and CNS affect the hypothalamus, which produces CRH
This affects the anterior pituitary, which produces ACTH (inhibitory on CRH)
Adrenal cortex then produces cortisol (Inhibitory on CRH and ACTH)
What are the effects of anaesthesia on the stress response?
High dose opioids reduce hypothalamic and pituitary secretory responses
Etomidate reduces corticosteroid production by reversibly inibiting 11-β-hydroxylase.
Can lead to catastrophic adrenal failure (particularly after long infusions).
A single induction dose can prevent aldosterone/cortisol production for 8 hours
Regional anaesthesia causes reduction in glucose, ACTH, adrenaline and cortisol.
