Digestion Flashcards
What is digestion?
- Digestion is the breakdown of large molecules into smaller, soluble molecules that can be absorbed into the body.
What is chemical digestion?
- Digestion of food using enzymes to speed it up
What is mechanical digestion?
- The physical breakdown of food.
How does chewing and cutting pieces of food in the mouth aid digestion?
- It cuts the food into smaller pieces and this increases their surface area.
- This measn that enzymes can act on the food more quickly.
What two layers of muscles can be found in the walls of the intestine?
- Circular muscle layer, which has fibres running in rings around the gut
- Longitudinal muscle layers, which has fibres running down the length of the gut
How do these two muscles push the food along?
- When the circular muscles contract and the longitudinal muscles realx, the gut is made narrower. Whent he opposite happens, the gut becomme wider.
- Waves of muscle contraction like this pass along the gut, pushing the food along
How does saliva enter the mouth?
- The presence of food in the mouth triggers a nervous reflex that causes the salivary glands to deliver saliva through ducts to the mouth.
What does the chemical mucin, found in saliva, help in the mouth?
- It protects the lining of the mouth from abrasion and lubricates food for easier swallowing.
What does the enzyme lysozome do?
- Kills many of the bacteria that enter the mouth with food.
What happens we swallow in the oesophagus?
- The top of the windpipe moves up so that its opening is blocked by a flap of tissue, the epiglottis.
How does the oesophagus conduct food from the pharynx down to the stomach?
- By perisaltis
How does peristaltsis work?
- Muscles in the wall of the oesophagus contract behind the bolus and relax in front, so that the bolus is squeezed along.
- The act of swallowing begins voluntarily, but then the involuntary waves of contraction by smooth muscles in the rest of the oesophagus take over.
Where does food boli enter the stomach from?
- From the oesophagus via the cardiac sphincter muscle
What digestive fluid does the stomach secrete?
- Gastric juice
How does the stomach mix this secretion with the food?
- By the churning action of the muscles in the stomach wall.
What does gastric juice contain?
- High concentration of hydrochloric acid
What is the pH of gastric juice?
- 2
What does the hydrochloric acid in the gastric juice do?
- The acid kills most bacteria that are swallowed with food.
Why is the lining of the stomach covered in mucus?
- To prevent the acid causing damage to the stomach lining itself
What does pepsin break down and where is it found in the stomach?
- Proteins
- Found also in the gastric juice
How does pepsin break down proteins?
- Pepsin breaks the bonds adjacent to specific amino acids, cleaving proteins into smaller polypeptides.
How does the low pH of the gastric juice help in the digestion of proteins in the stomach?
- It denatures (unfolds) the proteins in food, increasing exposure of their bonds to pepsin.
After mixing and enzyme action what is the food in the stomach turned into?
- Chyme
Why is the stomach closed at both ends most of the time?
- To prevent the backflow of acid chyme from the stomach into the lower end of the oesophagus, which can cause heartburn
What is at the opening from the stomach to the small intestine and how does it help?
- The pyloric sphincter, which helps regulate the passage of chyme into the intestine, one squirt at a time.
What occurs in the small intestine?
- Most of the enzymatic hydrolysis of food macromolecules and most of the absorption of nutrients into the blood occur in the small intestine.
What is bile and where is it stored and how does it get from where it is stored to the food?
- Green liquid
- Stored in the gall blader in the liver
- Passes down the bile duct on to the food
How does bile help in the breakdown of food?
- Bile act as emulsifier that break large lipid droplets up into smaller ones like a detergent and increase their surface area for the action of lipase.
What else does bile contain that neutralsies the stomacha acid in the food?
- Bicarbonate ions which are alkaline
What happens in the ileum?
- Here the small nutrient molecules released by mechanical and chemical digestion are absorbed into the bloodstream.
How do nutrients in the lumen enter the body?
- They have to cross the lining of the digestive tract
How is the ileum highly adapted to absorb the digested food?
- Lining of ileum hs a very large surface area, which means it can quickly and efficiently absorb the soluble products of digestion into the blood.
What helps to give the ileum a large surface area?
- The length of the intestine
- Folds in its lining
- Villi
How do villi help in the absorption of food in the ileum?
- There a millions of villi so the total area of the lining is thought to be 300m2.
- This provides a mssive area in cntact with the digested tract.
- Also, villi have microvilli which increae the surface area for absorption even more.
How does the digested food enter the villi?
- Through a newtork of blood capillaries
How does gylcerol and fatty acids enter the villi?
- Enter a tube in the middle of villus, called lacteal.
What do the lacteal form part of?
- The lymphatic system
Where do the blood vessels from the ileum join up to?
- Hepatic portal vein
Where does the hepatic portal vein lead to and why is this.
- To the liver
- This ensures that the liver has first access to amino acids and sugars absorbed after a meal is digested.
Where does the blood go from the liver?
- From the liver, blood travels to the heart, which pumps the blood and the nutrients it contains to all parts of the body.
What is assimilation?
- The process by which the digested fod molceules are distributed around the body by the blood system.
What is the function of the colon?
- To absorb the mremaining water from the contents, and leaving faeces.
Where is faeces stored and expelled from the body?
- Stored in the rectum
- Expelled through the anus
What enzyme are carbohydrates broken down by?
- Carbohydrase
What does amaylse break down and where is the source of it?
- Starch into maltose
- From salivary glands
What does maltase break down and where is the source of it?
- Maltose into glucose
- Source is wall of small intestine
What enzme are proeins digested by?
- Proteases
What does pepsin break down and where is the source of it?
- Proteins into peptides (short chains of amino acids)
- Stomach wall
What does trypsin break down and where is the source of it?
- Proteins to peptides
- Source in pancreas
What does peptidases break down and where is the source of it?
- Peptides to amino acids
- Source in wall of small intestine
What enzyme breaks down lipids?
- Lipase
What does lipase break down and where is the source of it?
- Lipids to glycerol and fatty acids
- Source in pancreas
