digestion (week 15)

Question 1

what is digestion?

Answer 1

the breakdown of large food molecules into smaller components that can be used by the body
molecules need to be small enough to be transported across the plasma membrane and into the bloodstream

Question 2

name the four stages of digestion

Answer 2

• ingestion: the consumption of, or taking in of nutrients
• digestion: the chemical breakdown of large organic molecules into smaller components by enzymes
• absorption: the transport or delivery of digested nutrients to body tissue
• egestion: the elimination of waste materials from the body

Question 3

the digestive tract

Answer 3

• aka the alimentary canal
• between 6.5 and 9 metres long
• is one continuous tube

Question 4

how does mechanically breaking down food help digestion?

Answer 4

• increases surface area
• allows for easier chemical digestion

Question 5

what happens in the mouth?

Answer 5

• saliva is released from the salivary glands
• contains amylase which breaks down starches into simple sugars
• lubricates the food and forms bolus

Question 6

what is the ball of food that is swallowed called?

Answer 6

bolus

Question 7

what is the epiglottis?

Answer 7

• flexible cartilage that guards the entrance to the larynx
• prevents food from entering the trachea

Question 8

what is the esophagus?

Answer 8

• 25cm tube, connects the mouth to the stomach
• food take 4-8 seconds to reach the stomach

Question 9

what is peristalsis?

Answer 9

involuntary muscle contractions that propel food through the digestive tract

Question 10

what happens in the stomach?

Answer 10

• food spends approx. 4 hours
• site of protein digestion
• movement in and out is controlled by circular muscles called sphincters

Question 11

what are the two types of sphincters and what do they do?

Answer 11

• lower oesophageal sphincter: allows food in, stops food from going back up into the oesophagus
• pyloric sphincter: slowly releases partially digested food (chyme) into small intestine

Question 12

what is chyme?

Answer 12

what the bolus is called when it leaves the stomach

Question 13

what are gastric fluids?

Answer 13

• fluids secreted by cells that line the stomach
• consists of mucus, hydrochloric acid, pepsinogen, etc.

Question 14

what does mucus do?

Answer 14

coats and protects the lining of the stomach

Question 15

what does hydrochloric acid do?

Answer 15

kills any harmful substances that have been digested, converts pepsinogen to pepsin

Question 16

what is pepsin?

Answer 16

a protein digesting enzyme: breaks large protein molecule chains into smaller ones

Question 17

what is a normal pH for the stomach? why?

Answer 17

2.0-3.0
- this acidity allows pepsin to work and makes the HCl effective at killing pathogens
- because of its acidtiy, the lining of the stomach is constantly being replaced
- it is completely replaced approx. every 6 days

Question 18

what is the small intestine?

Answer 18

• up to 7m long, 2.5cm wide
• the length is directly related to the diet:
• meat is easier to digest, therefore carnivores have shorter digestive tracts than omnivores and herbivores
• chyme remains in the small intestine for 4-8 hours

Question 19

what are the three sections of the small intestine?

Answer 19

• duodenum
• jejunum
• ileum

Question 20

what is the duodenum?

Answer 20

• where the majority of chemical digestion occurs
• approx. 30cm long
• contains opening from bile duct and pancreatic duct
• how bile and pancreatic enzymes enter the small intestine

Question 21

what is the jejunum?

Answer 21

• approx. 3m long
• additional chemical digestion, due to secretion of juices from the lining

Question 22

what is the ileum?

Answer 22

• approx. 4m long
• final and longest section
• responsible for the re-apsorption of nutrients

Question 23

what does the pancreas do?

Answer 23

• releases digestive chemicals and enzymes
• neutralises the chyme
• changes the pH from 2.0 - 9.0, inactivating the pepsin

Question 24

what does amylase released from the pancreas do?

Answer 24

breaks down large carbohydrate chains into disaccharides
disaccharide enzymes are then released, breaking the disaccharides into individual sugar molecules

Question 25

what are lipases?

Answer 25

- released by the pancreas - breaks fat down into fatty acids and glycerol - includes pancreatic lipase and phospholipase

Question 26

what does the liver do?

Answer 26

- emulsifies lipids so they can be broken down - constantly producing bile

Question 27

where is bile stored?

Answer 27

in the gall bladder, until it is needed in the small intestine

Question 28

what are villi?

Answer 28

- finger like projections on the folded inner walls of the small intestine - each villus has thinner projections called microvilli - these increase surface area to absorb nutrients - each villus contains a capillary network, along with a lacteal (a vessel of the lymphatic system)

Question 29

what happens to the end products?

Answer 29

- carbohydrates (monosaccharides)and protein (amino acids) enter the capillary network - fats (glycerol and fatty acid chains) are absorbed into the lacteal

Question 30

how is chyme moved along the small intestine?

Answer 30

through peristalsis

Question 31

what is the large intestine?

Answer 31

- aka the colon - approx. 1.5m long, 7.6cm wide - stores waste products for 8-10 hours - long enough so that water can be reabsorbed from the wastes - some inorganic salts, minerals and vitamins are also absorbed

Question 32

what fibre is most commonly found in humans?

Answer 32

- indigestible cellulose, found in plant cell walls