Chapter 5: Nutrition in Humans Flashcards
What is physical digestion?
-Mechanical break-up of food into smaller pieces
-No enzymes involved
-Increases surface area to volume ratio of food particles for higher rate of digestion
What is chemical digestion?
-Break-down of large molecules in food into small soluble molecules that can be absorbed into body cells
-Hydrolytic reactions catalysed by enzymes
Describe digestion in the mouth.
(Physical & Chemical)
Physical:
-Teeth break down large pieces of food into smaller pieces
Chemical:
-Salivary glands secrete saliva (containing salivary amylase & mucin) into the mouth.
-Salivary amylase catalyses digestion of starch to maltose
-Mucin softens food
Describe peristalsis.
-The rhythmic, wave-like muscular contraction in the wall along the alimentary canal.
-Wall of alimentary canal constricts to push food forward (circ musc contract, long musc relax)
-Wall of alimentary canal dilates to allow food to enter (circ musc relax, long musc contract)
Describe digestion in the stomach.
(Physical & Chemical + OTHER)
Physical:
-Peristalsis in stomach walls mixes food w/ gastric juice. (churning)
Chemical:
-Pepsin catalyses breakdown of proteins into polypeptides
OTHER:
-Hydrochloric acid denatures salivary amylase, converts inactive pepsinogen into pepsin, kills harmful organisms in food
-Mucus protects stomach wall from being digested by pepsin, lubricates food for easy movement in stomach
What are the 3 parts of the small intestine?
Duodenum
Jejunum
Ileum
Describe digestion in the small intestine.
(Physical & Chemical + OTHER)
Physical:
-Bile (produced in liver, stored in gallbladder) helps speed up fat digestion by emulsifying large fat globules into smaller fat droplets.
-Peristalsis
Chemical:
1. Carbohydrate digestion:
Starch (pancreatic amylase) -> maltose (intestinal maltase) -> glucose
2. Protein digestion:
Protein (pancreatic trypsin)-> polypeptide (intestinal peptidase)-> amino acid
3. Fat digestion (pancreatic & intestinal lipase)-> fatty acids+glycerol
4. Sucrose (intestinal sucrase)-> glucose+fructose
5. Lactose (intestinal lactase)-> glucose+galactose
OTHER:
-Pancreatic juice, intestinal juice & bile->alkaline, neutralise acidic chyme
Large intestine consists of?
Colon
Rectum
What is the main function of the colon?
Absorb water and mineral salts from undigested food material.
What is the main function of the rectum?
Temporarily stores faeces before it expels through the anus.
What are the factors that increase the rate of absorption?
- Large surface area
- Thin separating material
- Steep concentration gradient
How is the small intestine adapted for its function?
1. Large surface area
-Inner surface of ileum is folded extensively, has numerous villi to increase surface area to volume ratio for increased rate of absorption of nutrients
-Epithelial cells of villi have many microvilli, further increase ~~~
-Long length of small intestine, more time for absorption to take place
2. Thin separating material
-Wall of the epithelium is only one-cell thick, to provide shorter diffusion distance.
3. Steep concentration gradient
-Dense network of blood capillaries, to help carry absorbed glucose and amino acids away quickly to maintain steep conc gradient
-Lacteal in each villus to transport fats away from intestine
How are glucose and amino acids absorbed into the bloodstream?
-Diffuse into the blood capillaries of the villi
-By active transport (when lower conc in lumen than villi)
How are fats absorbed into the bloodstream?
-Fatty acids & glycerol diffuse into epithelium, then combine to form minute fat globules which enter the lacteals
How are glucose and amino acids transported and assimilated?
Transported from small intestine to liver by hepatic portal vein
