Chapter 5: Nutrition in Humans Flashcards
What processes does ‘Nutrition In Humans’ consist of?
- Ingestion
- Digestion
- Absorption
- Assimilation
- Egestion
What are the organs in our human digestive system and its accessory organs?
- Mouth
- Oesophagus
- Stomach
- Small intestine (duodenum & ileum)
- Large intestine (Colon, rectum and anus)
- Liver (bile duct)
- Gall bladder
- Pancreas
Where does the oesophagus pass through and what does it join together?
It passes through the thorax (chest), and joins the mouth to the stomach.
What are the names of the 2 layers of muscles?
- Longitudinal muscles
- Circular muscles
What is special about the walls of the oesophagus?
It contains two layers of muscles, and they are present along the whole alimentary canal from the oesophagus to the rectum.
What are the positions of the 2 muscles in the oesophagus?
- Longitudinal muscles are found on the outer side of the gut wall.
- Circular muscles are found on the inner side of the gut wall.
What is peristalsis?
It is the rhythmic, wave-like muscular contractions in the wall of the alimentary canal.
What does peristalsis enable food to do?
It enables the food to be mixed with digestive juices and also pushes the food along the gut.
What happens when the circular muscles contract?
The longitudinal muscle relaxes. As a result, the wall of the gut constricts and becomes narrower and longer, causing food to be pushed forward.
What happens when the longitudinal muscles contract?
The circular muscles relax. As a result, the gut dilates and becomes wider and shorter, widening the lumen for food to enter.
Describe the features of the stomach.
It is a distensible muscular bag, with thick and well-developed muscular walls
What is special about the inner surface of stomach wall?
They have numerous pits, the walls of which are lined with gastric glands. These gastric glands secrete gastric juice which plays an important part in digestion.
What is in gastric juice?
Protease and hydrochloric acid (pH 2)
Why are these 2 components needed in gastric juice for digestion?
- Protease allows for chemical digestion.
- Hydrochloric acid allows the protease to have a suitable environment to function as the optimum pH level for protease is pH 2, which is the pH level of hydrochloric acid.
What are the different parts of the small intestine?
- Duodenum
- Ileum
What parts is the duodenum connected to?
Stomach, pancreas and bile duct
What is the function of the pancreas being connected to the duodenum?
This allows the pancreas to release pancreatic juice.
What is special about the lining of the walls of the small intestine?
They contain glands that secrete digestive enzymes.
What are the different parts of the large intestine?
- Colon
- Rectum
- Anus
What happens in the rectum?
- Faeces are stored temporarily in the rectum.
- When the rectum contracts, the faeces are expelled through the anus.
What is the main function of the colon?
It absorbs about 90% of the remaining water and mineral salts from the undigested food material.
What are the accessory organs for the alimentary canal?
- Liver
- Gall bladder
- Pancreas
What do liver cells do?
They produce and secrete bile.
What is bile?
It is an alkaline yellowish-green liquid that contains bile salts.
How does bile help in digestion of food?
Though it does not contain any enzymes, it aids in the physical digestion of food.
What is the gall bladder’s function?
It stores bile temporarily in itself.
What happens when the gall bladder contracts?
Bile flows into the duodenum via the bile duct.
How is the pancreas connected to the duodenum?
The pancreatic duct connects the two organs together.
What is the function of the pancreas?
- Produces pancreatic juice, which has pancreatic amylase, protease and liapse in it, which aids in chemical digestion
- Secretes hormones such as insulin and glucagon, which are hormones that control the blood sugar level in the body.
What is digestion?
It is the process where large, insoluble food molecules are broken down into small, soluble molecules that can enter the body cells’ cell membrane be absorbed by it.
What is physical digestion?
It is the mechanical break-up of large food pieces into smaller pieces.
What does physical digestion do to help in the digestion process?
It increases the surface area-to-volume ratio of the ingested food so that enzymes can act on it more efficiently.
What is chemical digestion?
It is the breaking down of large insoluble food molecules into smaller, soluble food molecules that can enter the body cell’s cell membrane to be absorbed.
What are the processes that take place in the mouth? (Physical Digestion)
- Food in the mouth stimulates salivary glands to secrete saliva.
- Saliva is mixed with the food, softening it.
- Teeth chews the large food pieces into smaller pieces, increasing the surface area-to-volume ratio for the salivary amylase to work on.
- The tongue rolls the food into boli and moves it to the back of the throat during swallowing.
- Boli are swallowed and passed down into the oesophagus via pharynx.
- Peristalsis in the walls of the oesophagus pushes each bolus of food down into the stomach.
What are the processes that take place in the mouth (Chemical Digestion)
- Saliva contains salivary amylase, which digests starch to maltose.
- The optimum pH for salivary amylase is pH7, which is the mouth’s pH level.
What are the processes that take place in the stomach (Physical Digestion)
- The presence of food in the stomach stimulates the gastric glands to secrete gastric juice into the stomach cavity.
- Peristalsis in the stomach wall churns and breaks up the food, and mixes the food with gastric juice.
3.The mucus layer in the stomach protects the stomach wall against being digested by the enzymes it produces, and moistens the food to allow easy movement within the stomach. - Food nromally remains in the stomach for about 3-4 hours. The partly digested food becomes liquefied, forming chyme.
- Chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes and opens.
What are the processes that take place in the stomach (Chemical Digestion)
Gastric juice in the stomach contains hydrochloric acid (about pH2), mucus and pepsin, a protease. The protease digests proteins into polypeptides.
What is the role of hydrochloric acid in the stomach’s gastric juice?
- It stops the action of salivary amylase by denaturing it.
- It provides a lwo pH environment within the stomach, about pH2, which is the optimum pH level for pepsin to digest proteins.
- It kills certain potentially harmful microorganisms in food.
What are the processes that take place in the small intestine? (Physical Digestion)
When chyme enters the dudodenum, it stimulates the gall bladder to release bile. Bile passes through the bile duct into the duodenum. Bile salts speed up the digestion of fats.
What are the processes that take place in the small intestine? (Chemical Digestion)
When chyme enters the duodenum, it stimulates:
1. the pancreas to secrete pancreatic juice. It passes through the pancreatic duct into the duodenum.
2. the epithelial cells in the small intestine to produce intestinal juice, which contains maltase, protease and lipase.
What do pancreatic juice, bile and intestinal juice have in common?
They are all alkaline.
What is the function of pancreatic juice, bile and intestinal juice being alkaline?
- It neutralises the acidic chyme.
- It provides a suitable alkaline medium (pH8) for the action of the pancreatic and intestinal enzymes.
