Anatomy of the GI tract Flashcards
what are the accessory organs and why?
Liver, gall bladder and pancreas because they produce secretions which are vital for the body
what is hunger and satiety regulated by?
- plasma glucose levels
- hormones
-stretch receptors in the GI tract (activated after a meal) - Stress, body temperature, food palatability
What hormones regulate hunger and satiety and where are they produced
Leptin (produced in adipose tissue), ghrelin (produced in the stomach), insulin (produced in the pancreas) and glucagon (produced in pancreas)
what happens to glucose and insulin secretion in the well fed/absorptive?
insulin secretion enhances glucose uptake and metabolism in cells thereby reducing blood glucose
An increase in glucose increases storage and fuels and protein synthesis
what happens to glucose post-absorptive state?
Glucose decreases which causing an in glucagon causing glycogen breakdown
Gluconeogenesis occurs -production of new glucose from amino acids
Glucose sparing (fat utilisation-lipolysis) - ketones produced as a source of energy during prolonged fasting
During hunger what will decrease and what hormone is released?
Decrease in glucose, fat, protein
Increase in ghrelin (regulated by lateral hypothalamus - appetite centre)
What happens during satiety signals?
Increased glucose, fat, protein and leptin (regulated by the medial hypothalamus - satiety centre)
Stretch receptors are activated (mechanical)
How does different meal components empty at different rates?
More food = longer digestive phase
Larger amounts of food empty slowly to begin with, then more quickly
Nutritional density (calories) controls/slows gastric emptying
What is the effect of fat content?
- Important delaying factor in gastric emptying
- fat in duodenum causes fundus to relax, lowering the intragastric pressure
- high fat meals increase feeling of fullness for longer than low fat of the same energy content
- influenced intake of next meal
- prolongs elevation of pH in the stomach
Can food affect drug absorption?
Yes, there is a significant difference in the concentration of drugs between fast and non-fasted patients
What muscle is predominantly through the GI tract?
Smooth muscle
What nerve is responsible for sending signals to the muscle to contract to control motility?
Myenteric plexus
What is found in the submucosa?
glands and secretions produced which is close to the contents of the lumen
What increases surface area in the small intestine for absorption?
Villi
What is the myenteric plexus also know as? What does it do?
Auerbachs plexus
- influences muscle activity
what is the submucosal plexus also known as? What does it do?
Meissners plexus
Largely sensory, receiving signals from epithelium and stretch receptors influencing secretory activity
What does the myenteric + submucosa plexus equal
The enteric nervous system
what is the CNS?
Composed of brain and spinal cord
what is the peripheral ns?
Connects CNS to limbs and organs
What is the autonomic ns?
Division of the PNS influencing function or organs
What is the enteric NS
the intrinsic ns of gastrointestinal tract
What are the CNS and ENS connected by?
The vagus nerve, the 10th cranial nerve that runs from your brain stem down to your abdomen
Where are serotonin levels high in the body? How may this be a problem in antidepressants not being effective in treating depression?
They are highest in the intestines, sometimes proper dietary changes can help boost mood instead of certain anti depressants
What are afferent neurons?
also known as sensory receptor neurons which carry nerve impulses away from receptors or sense organs towards the CNS
What are efferent neurons?
otherwise known as motor or effector neurons, carry nerve impulses away from the CNS to effectors such as muscles or glands
what is parasympathetic input?
rest and digest - stimulates gut motility and secretory activity
what is sympathetic nerves?
fight or flight - causes presynaptic inhibition of parasympathetic-induced contraction (important for heart rate/activity)
what is segmentation?
facilitated mixing of food
what is peristalsis?
concerned mainly with propulsion of food along tract
what is peristalsis?
concerned mainly with propulsion of food along tract
What is ideal gut transit time?
Anywhere between 12 and 48hrs
- if transit is too fast (diarrhoea), absorption of nutrients from food is affected
- if transit is too slow (constipation) this can result in poor gut health
how can drugs affect transit time?
some drugs have side effect due to their non-specific targeting which may impact upon gut transit time
What is the target and action of loperamide?
Target: opiod receptors (agonist)
Action: motility suppressant that work through action on the myeteric plexus - decreased peristalsis, increase tone of anal sphincter (Ca2+ channel blocker)
how can antibiotics have negative effects on the gut microbiome?
can result in antibiotic resistant organisms, which lead to antibiotic associated diarrhoea. increased use of antibiotics suggests GI related problems may become more prevalent in the future
