Regulation of digestion Flashcards
What is physical digestion?
the physical breakdown of food into small particles by grinding or chewing to increase surface area
What is Enzymatic Digestion?
The breakdown of complex food molecules by hydrolytic enzymes usually secreted into the gut lumen
- so that food molecules are broken down into monomers that can be absorbed and utilised by cells
Why is digestion necessary?
- major food nutrients are large macromolecules which cannot pass through the lining of the itestine
- therefore must be broken down to small molecules via chemical and physical digestion to pass through cell membranes
Incisors
required for cutting, chopping or gnawing
Canines
For stabbing, ripping and shredding
Molars and Premolars
for shearing, crushing and grinding
What is the hard material covering the tooth?
Enamel - Calcium Phosphate
What is involved in the enzymatic reaction in the mouth?
Enzyme - amylase
Substrate - Starch/glycogen
End product - Maltose (disaccharide)
What is the oesophagus
Muscular tube which transports food through the thorax and diaphragm to the stomach
What are the 3 types of secretory cells in the gastric pits of the stomach?
- chief cells - secrete pepsinogen
- parietal cells - produce hydrochloric acid
- epithelial cells - secrete mucus which protects the tissues from the acids and enzymes
Stomach
- thick muscular walls to churn food
- secretes protective mucus from secretory cells
- gastric glands secrete gastric juice including HCl and pepsin
Describe the enzymatic reaction that occurs in the stomach
Enzyme - pepsin
Substrate - proteins
End product - large peptides
What is the small intestine and its function?
- long muscular tube/large SA
- moves chyme forwards from the stomach
- continues enzymatic digestion with secretions from cells in its walls and from accessory digestive glands
- absorbs products of digestion through villi
What are the 3 different regions of the small intestine?
- duodenum
- jejunem
- ileum
Where is bile produced and secreted?
the liver
Why does the pancreas produce bicarbonate solution?
Bicarbonate is required to neutralise the pH of the chyme released from the stomach
Where does bile travel?
- bile flows through the hepatic duct to the duodenum
* through the cystic duct to the gallbladder where bile is stored
Briefly describe the digestion of fats?
- dietary fats are emulsified into tiny droplets called micelles - through the action of bile salts
- pancreatic lipase hydrolyses fats in micelles to produce fatty acids and monoglycerides
- fatty acids and monoglycerides enter the cell by diffusion - resynthesised into triglycerides in the ER
- Triglycerides are packaged with cholesterol and phospholipids
What happens in the large intestine?
- Absorption of water and inorganic ions
* formation and storage of faeces from undigestible material - periodically excreted through the rectum
How do bacteria contribute to digestion?
- they obtain nutrition from passing food
- prevent harmful microbes from establishing
- produce vitamins K and biotin
Where is pepsin found?
Stomach
Describe the absorption of carbohydrates in the small intestine
- absorbed as monosaccharides into capillaries of villi
- glucose is taken up by active transport
- blood vessels drain into hepatic portal vein which carries blood to liver
- the liver converts carbohydrates into glycogen which is stored in the liver
How are proteins absorbed in the small intestine?
- absorbed into capillaries as amino acids
- taken up directly by cells which are synthesising proteins
- excess de-aminated by liver which uses nitrogen to form urea for excretion
Absorption of water, salts and alcohol in the small intestine
- may be absorbed directly into underlying blood vessels irrespective of need
- excess excreted by kidneys
- alcohol is absorbed directly through the stomach - hence the rapidity of intoxication
How are fats absorbed in the small intestine?
- Fats absorbed as glycerol and neutralised fatty acids into lacteals and then via lymphatics back to major veins near the heart
- excess store in adipose tissue
What secretions occur in the stomach and what stimulates these secretions?
- food entering the stomach stimulates the release of the hormone gastrin from the stomach mucosa into the blood
- this causes the release of HCl and pepsin from the stomach mucosa
What hormones are secreted in the duodenum and what stimulates this secretion?
- acid in the duodenum causes the release of the hormone secretin from intestinal mucosa into the blood
- this causes the pancreas to release HCO3- and the gall bladder to release bile
How is the secretion of saliva control?
under nervous control
What is peristalsis?
The involuntary constriction and relaxation of the circular muscles in the oesophagus to push the food bolus to the stomach
(peristalsis can occur in intestine or other canal)
What is the phyloric sphincter?
- between the stomach and the duodenum of the small intestine
- acts as a valve to control the flow of partially digested food from the stomach to the small intestine
Where is amylase found?
salivary glands and pancreas
where is protease found?
Pancreas and stomach
where is lipase found?
pancreas
What is the caecum?
A large sac like structure that is the first part of the large intestine
What is the colon?
• The section in the large intestine after the caecum • has 3 other sections - ascending - transverse (Across the body) - descending
What is the rectum?
Last section of the large intestine
• terminates at the anus - a sphincter that control the exit of faeces from the digestive system
What are the 3 main sections of the large intestine?
- caecum
- colon (Ascending, transvers, descending)
- rectum
List the major components of the digestive system in order
- mouth
- oesophagul sphincter
- stomach
- phyloric sphincter
- pancreas
- hepato- pancreatic duct
- small intestine - dueodenum, ileum
- large intestine - caecum, colon , rectum
- anus
Pepsin formation
Pepsinogen is secreted by chief cells in the stomach
• when it comes into contact with stomach acid it is converted to the active form pepsin
