Introductions to the functions and control of the alimentary tract Flashcards
What are the 3 digestive functions of the stomach?
- Accommodation & storage
- Mechanical and enzymatic breakdown
- Slow delivery of chyme to duodenum
What is the purpose of bile salts?
The salts in bile emulsify fat (break fat into small droplets, like a detergent) so that digestive enzymes (e.g. pancreatic lipase) can act on fat more effectively.
What is the purpose of the stomach and how long can food remain in the stomach?
Stomach: Food stored here during the first stage of digestion; may remain there for ~1hr unmixed (acts as a reservoir)
What is the purpose of the antral region of the stomach Antral region
It mixes/grinds food with gastric secretions → Digestion
What is the purpose of the colon/ rectum?
Storage of indigestive residues and faecal matter
The stomach stores 2-3 litres of gastric juice/24hr (mucus, pepsinogen, intrinsic factor, lipase) which help in digestion and absorption of food.
What is the purpose of mucus in the stomach?
Mucus (secreted by goblet cells and mucus neck cells) – acts as a lubricant by acting as a barrier that protects the stomach and colon especially from gastric acid (prevents trauma)
What does lipase do in the stomach?
Lipase – converts triglycerides to fatty acids and glycerol
What does pepsin do in the stomach?
Pepsin (secreted by chief cells or peptic cells as pepsinogen): protein digestion
What cells are HCl secreted from?
What does HCl do in the stomach?
HCl (secreted by parietal cells) – important in defence
What is the purpose of intrinsic factors in the stomach?
Intrinsic (secreted by parietal cells) – for vitamin B12 absorption
What are paracrine secretions?
Where are they secreted from?
How are they different from local hormones?
Give an example
- Often called “local hormones”
- Secreted from cells in the mucosa, but unlike hormones, the chemical acts locally on adjacent cells via the interstitial fluid
Somatostatin inhibits gastrin release in the stomach
What do salivary glands secrete? (2)
mucus (lubrication for mastication and speech); lipase
What do gastric glands secrete? (3)
Hydrochloric acid, pepsin, mucus
What does the pancreas secrete?
bicarbonate ions, enzymes (e.g. amylase, lipase, carboxypeptidase)
What does the liver secrete?
Liver: bile salts, bile acids
Secretions from numerous glands with ducts enter the lumen of the gut and are involved in digestion, lubrication and protection
What do carboxypeptidase is a protease enzyme do?
hydrolyses (cleaves) a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide
What does Amylase hydrolase?
Amylase hydrolyses starch into sugars
Salivary glands, gastric, pancreas, liver and carboxypeptidase and amylase are all a type of ______ secretion?
Exocrine
Where are gastrin cells located?
stomach (G-cells in antrum)
Where is Secretin located?
duodenal mucosa
Where are pancreozymin-cholecystokinin located?
duodenal mucosa
Where is B-cells located?
pancreas (beta-cells)
What the difference between exocrine and endocrine secretions?
Endocrine glands release chemical substances directly into the bloodstream or tissues of the body. The chemical substances released by the endocrine glands are known as hormones. Exocrine glands release chemical substances through ducts to outside the body or onto another surface within the body.9
In order for the body to use the food where must nutrients be transported to and from?
• For food to be of use to the body, the 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 the absorption of solids and fluids occur?
Absorption occurs mainly in the small intestine
Absorption of fluid occurs in the small intestine and colon
How much water does the colon absorb?
Colon absorbs 90% of water, reducing the volume to 200ml of semi-solid faecal matter
Where does motility occur?
Storage, e.g. proximal stomach, descending colon
What does the movements of the muscular wall (mostly smooth muscle except extreme ends of the upper oesophagus/rectum) allow:
- Movement from one region to another (law of gut); mass evacuation
- Mechanical degradation, e.g. gastric antrum
- Mixing lumen contents, e.g. small intestine
- Transport of nutrients, water and of urea and electrolytes
- Digestion and absorption
Give some examples of bodily excretion
• 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 in the faeces
The gut is unsterile as it is open to external environment
Give some examples of how the gut helps to protect itself
- Sight, smell and taste alerts us to harmful food substances
- Vomit reflex
- Acid in stomach (HCl) kills most harmful bacteria
- Mucus secretions
- Natural bacterial flora prevents colonisation of harmful bacteria
- Aggregation of lymphoid tissue (e.g. Peyer’s patches) able to mount a response to food-borne antigens - analyse and respond to pathogenic microbes
- Peyer’s patches: located in the lamina propria layer of the mucosa and extending into the submucosa of the ileum
Describe the metabolic functions of the liver
- The liver is a major metabolic organ in the abdominal cavity and weighs about 1.3 Kg in an adult.
- It is involved in carbohydrate, nitrogen and lipoprotein metabolism as well as the production of bile and excretion of bilirubin
Give the list of functions and mechanisms of the gut?
- Storage
- Paracrine secretions
- Exocrine secretions
- Endocrine secretion
- Absorption
- Motility/transport
- Excretion/transport
- Defence
- Metabolism
What factors and mechanisms are involved with storage and digestion?
Mastification, swallowing, enzymatic digestion absorption
What factors and mechanisms are involved with motility?
Peristalsis, mass movement, Ach, motilin, NO and VIP
What factors and mechanisms are involved with defence?
Smell, sight, taste, gastric acid, vomit reflex, mucus, immune system, IgA
What factors and mechanisms are involved with exocrine secretion?
Saliva secretion, mucus secretion, HCl, pepsin, HCO3, amylase, lipase, bile salts,
What factors and mechanisms are involved with endocrine secretion? (3)
Insulin, gastrin and secretin
What factors and mechanisms are involved with paracrine secretion?
Somatostatin
What factors and mechanisms are involved with excretion
defecation
Describe the integrated response to a meal
On image
