Textbook Physiology part 1 Flashcards
what does the GI consist of?
oesophagus
stomach
small intestine
large intestine
what does digestion mean and where does this primarily take place?
digestion is the chemical and mechanical breakdown of food which takes place primarily in the lumen of the gut (GI from stomach to anus)
what are the accessory glandular organs?
salivary glands liver gallbladder pancreas - they aid digestion
what is chyme?
soupy mixture of food and secretions.
what happens to the products of digestion?
they are absorbed across the intestinal epithelium and pass into the interstitial fluid. this them moves into the blood or lymph to be distributed throughout the body.
how is the GI different to other systems?
it is the only system that is open to the outside world - the tract and its lumen are open to the outside world..
Where are most bacteria found in the GI? what are they called?
most bacteria are found in the lumen especially the large intestine and they are called commensals
what is the digestive system in simple terms?
a tube
The first stage of digestion starts with chewing and secretion of saliva. what are the three salivary glands that produce saliva and where are they found?
sublingual glands- under the tongue
submandibular gland- under jawbone
parotid gland- near the hinge of the jaw
how is the sectional view of the stomach different from the small intestine? (4)
The intestine contains villi.
The intestine contains Peyer’s patch (circle) in the mucosa.
Invaginations in the intestine are called crypts whereas invaginations in the stomach are called gastric glands.
The stomach has oblique muscles whereas the small intestines has submucosal plexus in that space.
what are the three sections of the stomach?
the upper fundus (usually gas)
the central body (where digestion occurs)
the lower antrum
what does the stomach do?
continues digestion that began at the mouth by mixing food with acid and enzymes to make chyme.
what is the pylorus?
the opening between the stomach and the small intestine that is guarded by the pyloric valve.
what does the pyloric valve do?
its a thickened band of smooth muscle that only relaxes to allow small amounts of chyme into the small intestine.
where does most digestion take place?
in the small intestine which as three sections
what regulates the rate that the chyme enters the small intestine?
integrated signals and feedback loops between the stomach and small intestine
what are the three sections of the small intestine?
duodenum(25cm)
jenunum
ilium
the latter have a combined length of 260cm.
what is the smallest section of the small intestine?
duodenum
where does digestion finish?
in the small intestine
what are the two accessory glandular organs that aid the small intestine?
pancreas and liver
where are most of the digested nutrients and secreted fluids absorbed?
in the small intestine
what does the Sphincter of Oddi do?
it keeps pancreatic fluid and bile from entering the small intestine except during a meal.
where does the watery chyme become semisolid faeces?
in the proximal section of the large intestine (colon)
what is the terminal section of the large intestine known?
rectum
how does the faeces leave the GI tract?
through the anus, with its external anal sphincter, which is under voluntary control.
what are the 4 layers of the GI tract wall?
The mucosa
Submucosa
Muscularis Externa
Serosa
what features of the GI tract allow it to have a larger surface area?
the gut wall is crumpled into folds
there are tubual invaginations of the surface that extend to connective tissue
the intestinal mucosa also has villi
what is rugae?
gut folds in the stomach
what is plicae?
gut folds in the small intestine
what are gastric glands?
tubular invaginations of the surface that extend to connective tissue present in the stomach
what are crypts?
tubular invaginations of the surface that extend to connective tissue present in the small intestine.
what can some of the deeper tubular invaginations form?
submucosal glands that open into the lumen through ducts
what is the mucosa of the GI tract?
the inner lining of the GI tract.
what are the three layers of the Mucosa?
Mucosal epithelium
Lamina propria
Muscularis mucosae
what is the most variable feature of the GI tract and why?
the mucosal epithelium as it changes from section to section depending on the needs
what do the cells of the mucosa include and where are they found?
Transporting mucosal cells (enterocytes in the small intestine)
Endocrine and exocrine secretory cells
Stem cells
what is the average life span of an epithelial GI cell? why can this be a problem?
a few days - can be a problem as rapid turnover and cell division rate make them more susceptible to developing cancers.
what is the lamina propria? what does it do?
its a subepithelial connective tissue that contains nerve fibres and small blood and lymph vessels
what does the lamina propria contain?
wandering immune cells such as macrophages and lymphocytes.
what is different about the lamina propria in the small intestine compared to the stomach?
Peyers Patches are present in the small intestine - these are collections of lymphoid tissue adjoining the epithelium to form small nodules.
what is the muscularis mucosae?
Final layer of the mucosa
Thin layer of smooth muscle which contracts and in doing so moves the villi back and forth
what is the submucosa made of and where is it found?
its the middle layer of the gut wall and is composed of connective tissue with large blood and lymph vessels going through
which one of the two major nerve networks of the enteric nervous system is found in the submucosa? how does it function?
the submucosal plexus innervates cells in the epithelial layer as well as smooth muscle of the muscularis mucosae.
what is the muscularis externa and what is it made of?
its the outer wall of the gastrointestinal tract which consists of primarily two layers of smooth muscle - an inner circular layer, an outer longitudinal layer
what does the contraction of the circular layer of the muscularis externa do?
contraction decreases the diameter of the lumen
what does the contraction of the longitudinal layer of the muscularis externa do?
contraction shortens the the tube
which one of the two major nerve networks of the enteric nervous system is found in the muscularis externa? how does it function?
the myenteric plexus lies between the two muscles and controls and coordinates the motor activity of the muscularis externa.
where is the myenteric plexus found and what does it do?
the myenteric plexus lies between the two muscles of the muscularis externa.
It controls and coordinates the motor activity of the muscularis externa.
what is the serosa? what is it made of?
what does it do?
the outer covering of the entire digestive tract.
its a connective tissue membrane that is a continuation of the peritoneal membrane.
the peritoneum also forms sheets of mesentery which holds the intestines in place so they do not become tangled as they move.
what is the serosa a continuation of?
it’s a connective tissue membrane that is a continuation of the peritoneal membrane.
what is digestion in the GI tract?
is the chemical and mechanical breakdown
what is absorption in the GI tract?
the movement of substances from the lumen of the GI tract to the extracellular fluid.
what is secretion in the GI tract?
it can mean 2 things:
- the movement of water and ions from the extracellular fluid to the digestive tract lumen
- release of substances synthesised by GI epithelial cells into the lumen or extracellular fluid.
what is motility in the GI tract?
movement of material in the GI Tract as a result of muscle contraction
what are the 3 challanges the digestive system faces?
Avoiding autodigestion
Mass balance
Defence
what is auto digestion and how can it go wrong?
powerful enzymes need to be released in order to digest the food into micromolecules so they can be absorbed by the body.
Problems can arise as too much of the GI itself could become digested and if protective mechanisms fail then raw patches known as peptic ulcers can develop on the walls of the GI tract
what is mass balance and how can it go wrong?
matching fluid output with fluid input.
we secrete more fluid that we take in so there would be a problem with dehydration if we could not reabsorb the fluid that we excreted.
For example if we vomit or have diarrhoea then this can deplete the extracellular fluid volume and the circulatory system may not be able to maintain adequate blood pressure.
what is defence of the GI tract and how can it go wrong?
protecting the body from foreign invaders.
The GI is fighting between reabsorbing nutrients and water and also defending the body from bacteria, viruses and other pathogens.
Do we secrete or ingest more fluid?
we secrete more fluid - typically we pass 9 litres however only 2 litres of that enters the GI through the mouth
what is mucous primarily composed of?
Glycoproteins
where is mucous made?
In the specialised exocrine cell called “mucous cells” in the stomach and salivary glands as well as “goblet cells” in the intestine.
what is the difference between digestion and metabolism?
Digestion is the conversion of the food macromolecules to micromolecules to be absorbed by the body.
Metabolism is the breakdown of the micromolecules down through chemical processes to break down the macromolecules into energy.
