Gastro-intestinal physiology: structure/function Flashcards
What is the GI tract made up of?
The mouth, pharynx, oesophagus, stomach, small intestine, liver, gall bladder, pancreas and large intestine.
What is the function of the oesophagus?
Transport of food.
What are the subdivisions of the stomach that are involved in the GI tract?
The fundus, body and antrum.
What is the body of the stomach?
The middle portion of the stomach that secretes mucus, pepsinogen, and HCl that is involved in storage and secretion.
What is the fundus of the stomach?
The upper portion of the stomach that secretes mucus, pepsinogen and HCl that is involved in storage of food.
What is the antrum of the stomach?
The lower portion of the stomach that is invlved in mixing, digestion and emulsification.
before it enters the small inestine
What subdivisions of the small intestine are involved in the GI tract?
The duodenum, jejunum and ileum.
What is the duodenum?
The first portion of the small intestine that is involved in regulation, coordination and digestion.
What is the jejunum?
The middle segment of the small intestine that is involved in dietary product absorption and rendering them to form suitable products to be taken up by the body.
What is the ileum?
The final, longest segment of the small intestine that is involved in water re-absorption.
What are the subdivisions of the large intestine?
The ascending colon, the transverse colon, the descending colon, the sigmoid colon and the rectum/anus.
What is the function of the pharynx?
Swallowing - voluntary control.
What are the liver, gall bladder and pancreas involved in?
Secretion.
What are the ascending, transverse and descending colon involved in?
Water re-absorption.
What is the sigmoid colon involved in?
Storage.
What is the rectum/anus involved in?
Storage and elimination - voluntary control.
How may diarrhea occur?
If parts of the large intestine are not functioning correctly, water will not have enough time to reabsorbed if the faeces is being secreted too quickly.
Where is faeces stored?
In the descending colon/sigmoid colon.
What is peristalsis?
Moving packets of partially digested products along the length of the intestine due to smooth muscle contraction and relaxation.
What is another word for peristalsis?
Segmentation.
What is the purpose of saliva?
Provides lubrication and protection - it contains lysozymes that are antibacterial and can break down the cell walls of bacteria. It also begins the process of digestion by containing alpha amylase that attacks complex carbohydrates, as well as lipase that attacks the fats present in food.
What glands are the main contributors to producing saliva?
The sublingual gland and the submandibular gland - these are underneath the tongue and produce around 75% of the total saliva.
thick and viscous
What glands produce thin and watery saliva?
The parotid duct and the parotid gland.
What are the main roles of the stomach?
Mixing, protein digestion (using HCl and pepsin) and fat emulsification.
What is chyne?
Partially digested food.
What are rugae?
Folds they increase the surface area for exchange.
allow for expansion when stomach fills by flattening
What do the three layers of muscle in the stomach allow for?
They help the walls of the stomach to contract, change shape and extend to move the food.
What is the spinchter and what is its purpose?
It ensures that food is retained until it is appropriate for it to be release into the duodenum and continue its journey.
What are parietal cells?
Cells lining the walls of the gland in stomach that secrete acid (hcl) and intrinsic factor.
What are chief cells?
They secrete pepsinogen.
How is secretion maximised by the parietal cells?
Canaliculi maximise the surface area.
What roles does ACh have in the stomach?
It regulates the production of acid.
What cells secrete gastrin?
G cells.
What is the role of mucus in the stomach?
It protects the stomach. The harsh conditions would kill the epithelial cells without the mucus lining.
Where is the small intestine located?
It leads from the stomach to the large intestine.
What is the small intestines role?
Breaking down intact or partially digested molecules using hydrolytic enzymes.
And absorption
What is the “second brain”?
The enteric nervous system in the gut.
What covers the surface of the GI tract to increase surface area, absorption and motility?
Villi.
What is the surface of each villus covered with?
Microvilli.
What is the brush border?
The collection of microvilli.
What do goblet cells do?
Secrete mucus that lubricates the wall of the small intestine.
What are crypts of Lieberkuhn?
Glands found in the intestine.
What is the significance of the crypts of Lieberkuhn?
They produce cells that migrate upwards to replaced the villus loss. They must be replaced exactly or the entire gut would die.
What do goblet cells contain?
Mucin droplets that form the mucin layer.
What are the three types of epithelial cells in the small intestine and what percentage do each make up of the total epithelial cells?
Goblet (9%), absorptive (90%) and enteroendocrine (0.5-1%).
What are enteroendocrine cells?
Chemical mediators that control the activity of the gut. They release hormones that pass into the bloodstream and keep CNS aware of whats going on.
What does it mean that epithelial cells are polarized?
They have a strong sense of up and down.
What do epithelial cells of the small intestines absorb?
Sugars, amino acids, fats and salts.
What are stimuli for the brush border enzymes?
Mechanical stimulation, food contents and pH.
What are the main roles of the large intestine?
Water and ion conservation by absorption, bulk movement of faeces, storage, lubrication and defaecation.
What is the lining in the large intestine composed of?
Smooth surface rather infolded.
What are the phases of digestion?
The cephalic phase, the gastric phase and the intestinal phase.
What are the main features of the cephalic phase?
This is the short, anticipatory period in which the sight and smell of food prepares the body for ingestion of food. There contraction and secretion within the intestinal tract that preceeds the act of ingestion of food.
What are the main features of the gastric phase?
This is the intermediate stag which is triggered by the presence of food in the stomach. There are neural and hormonal elements involved to cause the gut to move and breakdown the food.
What are the main features of the intestinal phase?
This is the long phase of digestion that is triggered by the presence of food in the small intestine. There are neural, hormonal, mechanical and pH responses along with contraction, secretion and absorption.
How is the brain involved in the control of feeding?
It sends chemical messengers to tell the body to eat more when you’re hungry.
What does the satiety centre do?
The centre that prevents overeating. It is subservient to signals from the sensory cortex. Feeding centres are influenced by blood levels of amino acids, glucose and lipids.
what enzyme does saliva contains and what is its function
lysozyme
acts as protection
antibacterial
What enzymes initiation digestion in saliva
a-amylase and lipase
Overview of processes in digestion
raw materials pass via oesophagus to stomach, where they undergo mechanical and chemical digestion
Then moves through small intestine by peristalsis in ping pong mechanism, undergoes absorption and digestion
Products pass to colon and bacteria attack products
3 layers of smooth muscle in the stomach
longitudinal-outer
circular-middle
oblique-inner
orientated differently in each layer
what is gastric juice made up of
hcl, mucus and pepsin, lipase
mechanical digestion in the stomach
muscular contractions churn contents to break down bolus and mix it with stomach secretions to form chyme
three layers of the stomach
mucosa, submucosa and muscularis externa (has the 3 layers of muscle)
gastric pits
epithelium of the mucosa of the fundus and body of the stomach forms these invaginations
lamnia propia
underlying connective tissue that contains gastric glands
What aids digestion in the small intestine
bile from liver and digestive enzymes from pancreas
myenteric plexus
coordinates activity of 2 muscle layers
submucosal plexus
regulation of secretion/ absorption across the gut
what forms the enteric nervous system and what does it do
myenetric and submucosal plexus
regulates function of GI system
villi function
increase SA for absorption and motility
paneth cells
at base of crypts
defensins
maintain stem cells needed for producing epithelial cells
