The GI System Flashcards
How is the stomach involved in food storage in the first stages of digestion?
Fundus and body of stomach (thinner muscle tone)
relax. This allows food to be stored at low pa whilst breakdown occurs. Food remains unmixed in the stomach for 1hr.
Stretch receptors in the stomach detect food. They relax the smooth muscle allowing space for more food. This is accommodation.
Vagal reflex inhibits smooth muscle contraction, VIP and NO are released to relax the smooth muscle.
How is food broken up into small pieces so it can pass through?
The antrum grinds food w gastric secretions to make them small enough to pass. If food>2mm they do not pass through
Pyloric sphincter is often relaxed but closes upon arrival of peristaltic wave. The pyloric sphincter also sends back particles to the antrum which are too large
Sometimes there is a cleansing motion which pushes undigestible food through
How is the stomach involved in food storage in the later stages of digestion?
The stomach shrinks when empty, but the vagovagal reflex allows accommodation when food is eaten. The body and oesophageal sphincter contract to prevent food reflux.
Stomach is then emptied at a pace the duodenum can handle. The antral area contracts and allows food down the pyloric sphincter. The fundus contracts to squirt chyme into the duodenum.
During emptying, secretin is secreted which allows bicarbonate from the pancreas to neutralize the acid
Colon/rectum stores digestive residues and faeces.
What is gastric juice and what does it contain?
Stomach stores 2-3L of gastric juice which help in digestion and absorption of food
Mucus acts as a lubricant barrier to protect the stomach and colon esp from gastric acid.
Lipase converts TG to fatty acids + glycerol
Pepsin (active component of pepsinogen) digests proteins. Secreted by chief/peptic cells as pepsinogen.
HCl (secreted by parietal cells) is important in defence. Also converts pepsinogen to pepsin.
Intrinsic factor is a glycoprotein secreted by parietal cells. It absorbs vitamin B12
Describe the function of absorption
Nutrients from digestion must be transported into the blood (e.g. glucose, aa.s) or lymph via lacteals (for lipids)
Enterocytes line the gut, facilitating nutrient absorption. Salts, water, nutrients are absorbed from the gut lumen.
Colon absorbs 90% of water, reducing vol for excretion
Fluid secretion/absorption issues can cause diarrhoea/constipation- If gut transit is too fast, no sera time for water reabsorption leading to liquid faeces.
What is motility and the function of motility?
Motility: movements of the smooth muscle in the muscularis layer of the gut wall (except extreme ends of the upper oesophagus/rectum). It allows:
Movement to follow the law of gut
Mechanical degradation, e.g. in gastric antrum
Mixing lumen contents, e.g. in small intestine
Transport of urea and electrolytes
Digestion and absorption. Storage
The time spent in each region of the gut varies – eg stomach stores food longer than the duodenum
What is excretion and what problems can arise w it?
Drugs and some metabolic waste may leave the body in:
•saliva, bile, faeces, and vomit- defies law of the gut
•Indigestible food residues leave via faeces
Decreased gut transit time leads to diarrhoea (the discharge of liquid faeces >3 times a day)
Increased gut transit time leads to constipation (difficulty opening the bowel, hard stools)
Explain the defence mechanisms of the gut
The gut is unsterile as it’s open to external environment.
Sight, smell, taste alerts us to harmful food. Vomit reflex.
Stomach HCl kills most harmful bacteria
Mucus secretions
Natural flora prevents harmful bacteria colonisation
Aggregation of lymphoid tissue (e.g. Peyer’s patches) respond to food-borne antigens.
The gut maintains mucosal repair via growth factors and prostaglandins
Where are Preyers patches located?
Peyer’s patches are located in the lamina propria layer of the mucosa, extend into the submucosa of the ileum
lamina propria layer = lies beneath the epithelium
What are the metabolic functions of the liver?
The liveris involved in carbohydrate, nitrogen and lipoprotein metabolism.
It produces bile and excretes bilirubin.
Describe innervation of the gut
The gut is under sympathetic and parasymp control
Parasymp: stimulates digestive and gallbladder activity. Gall bladder helps digest fat. Also reflexes rectum to excrete indigestible matter
Symp: inhibits digestive activity, stimulates glucose release (glycogenolysis) by liver
Draw a diagram to explain the autonomic innervations of the gut
All splanchnic nerves carry sympathetic fibres except for the pelvic splanchnic nerves which carry parasympathetic fibres.
Label and explain the diagram of the stomach
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Describe the stomach
Fundus= thin muscle layer, relaxes to accommodate
Gastrin acts on the fundus to release HCl
A pacemaker area in the fundus produces rhythmic contractions to allow food to move into the duodenum
Antrum- thick muscle layer, grinds food to pass through the pylorus, secretes gastrin to allows pylorus contraction
Pylorus contraction also promotes squirting of food through the pylorus and into the duodenum
What is this? label it
It shows the layers of the GI tract inc the myenteric plexus
