Intro to Functions of Alimentary Tract Flashcards
What is the gastrointestinal tract?
The main organs of the digestive system form the gastrointestinal (GI) tract to create an open tube that runs from the mouth to the anus
What passes through the GI tract?
Everything we eat is processed through the GI tract
What is the role of the digestive system?
The digestive system:
- prepares ingested nutrients for digestion & absorption
- protects against consumed micro organisms and toxins
What processes occur to ensure the functions of the digestive system are carried out?
- ingestion
- digestion
- absorption
- elimination
What do the processes of the GI tract depend upon?
The processes occurring in the GI tract depend upon the motility / movement of the GI tract and the digestive juices & enzymes secretions
What are the functions of the digestive tract?
Accommodation & Storage
Mechanical & enzymatic breakdown
Slow delivery of chyme to duodenum
What does the pancreas secrete?
a bicarbonate rich solution
How does the stomach accommodate storage during digestion?
Food stored during the first stage of digestion may remain in the stomach for ~1 hr unmixed - acts as a reservoir
Explain how the fundus is adapted to aid storage of food in the stomach?
The fundus and body of the stomach have thinner muscle tone which relax to allow a larger volume (~1.5 L) of food storage
What is the role of vagal reflex in storage of food?
Vagal reflex inhibits smooth muscle tone - mechanoceptors cause fundic relaxation via VIP/NO
What is the role of the antrum in storing food in the stomach?
The antral region mixes / grinds food with gastric secretions enabling digestion
What is the role of the colon / rectum?
Storage of indigestive residues and faecal matter
Where are gastric secretions stored?
The stomach stores 2-3 Litres of gastric juices every 24 hrs
What does gastric juice consist of?
mucus
pepsinogen
intrinsic factor
lipase
What is the role of gastric secretions?
Aid in digestion and food absorption
Where is mucus secreted from?
Goblet cells and mucus neck cells
What is the role of mucus?
Acts as a lubricant by acting as a barrier to protect the stomach and colon esp. from gastric acid
- prevents trauma
What is the role of lipase?
converts TG → FA + glycerol
Where is pepsin scereted from?
Secreted by chief cells / peptic cells as the precursor pespinogen
What is the role of pepsin?
protein digestion
Where is HCl secreted from?
Parietal cells
What is the role of HCl?
important in defence and converts pepsinogen →pepsin
Which cells secrete Intrinsic factor (IF)?
parietal cells
What is the role of Intrinsic Factor?
aids vitamin B12 absorption
Describe features of paracrine secretions
local hormones
secreted from cells in mucosa
Chemicals act locally on adjacent cells via interstitial fluid
Give an example of a paracrine secretion
somatostatin - inhibits gastrin release in stomach
What is the role of gastrin?
Controls parietal cell acid secretion
Where are exocrine secretions from?
Salivary glands
Gastric glands
Liver
Pancreas
What exocrine secretions are produced in the salivary glands?
Mucus; lubrication for mastication and speech
Lipase
What does the exocrine pancreas secrete?
Bicarbonate ions
Enzymes; amylase, lipase, carboxypeptidase
What exocrine secretions are produced by the gastric glands?
HCl, pepsin, mucus
What does the exocrine liver secrete?
bile salts and bile acids
What is the role of exocrine secretions?
Secretions from numerous glands with ducts enter lumen of the gut and are involved in digestion, lubrication and protection
What is carboxypeptidase?
Protease enzyme that hydrolyses a peptide bond at the carboxy-terminal (C-terminal) end of a peptide/protein
What is amylase?
hydrolyses starch -> sugars
What are endocrine secretions?
Hormones synthesised by ductless glands
How do endocrine secretions achieve their effect?
Enter bloodstream to travel to their target tissue(s) where they bind to specific receptors to elicit their effects
Name endocrine secretions and where they’re secreted
Gastrin - stomach (G cells in antrum)
Secretin - duodenal mucosa
pancreozymin-CCK - duodenal mucosa
Insulin - pancreatic beta Cell
How is food made of use to the body?
Nutrients resulting from digestion must be transported across the intestinal epithelium into the blood
e.g. glucose, amino acids
or, lymph via lacteals (fats/lipids)
Where does absorption of food occur?
absorption occurs mainly in small intestine
Where is fluid mostly absorbed?
Absorption of fluid occurs in the small intestine and colon
- colon absorbs 90% water
Where is digested food predominantly stored before excretion?
proximal stomach and descending colon
How does motility of food occur in the GI tract?
Movement of muscular wall (mostly smooth muscle except extreme ends of the upper oesophagus / rectum)
What is the significance of gut motility?
Allows:
- movement from one region to another; mass of
evacuation
- Mechanical degradation (gastric antrum)
- Mixing lumen contents e.g. small intestine
- Transport of nutrients, water and of urea and
electrolytes
- Digestion and absorption
How are drugs and metabolism excreted?
Drugs and some products of normal metabolism may leave the body in:
- saliva
- bile
- faeces
- vomit
Indigestible food residues (e.g. tomato skin) leave the body via the faeces
What is the significance of the gut epithelium in defence?
If there is a breach in the barrier ‘toxins’ will enter the blood
it’s largest lympho-epithelial organ and mucosal surface
Is exposed to the heaviest burden of environmental antigens
How is the gut protected from the external environment?
- Sight, smell and taste alerts us to harmful food
substances - vomit reflex
- HCl in stomach kills bacteria
- Mucus secretions
- Natural bacteria flora prevents harmful bacteria
colonisation - Lymphoid tissue aggregation; react to food borne
antigens - Peyer’s patches in lamina propria
Where are the metabolic functions of the gut carried out?
In the liver
- involved in carbohydrate, nitrogen and lipoprotein
metabolism
- produces bile and excretes bilirubin
Outline the functions and mechanisms of the GI tract
- Storage
- Paracrine secretions
- Exocrine secretions
- Endocrine secretions
- Absorption
- Motility / transport
- Excretion / transport
- Defence
- Metabolism
