6.1 Digestion and Absorption

Question 1

How does the body convert into nutrients?

Answer 1

Through the digestive system that consists of digestion and absorption.

Question 2

What happens during digestion?

Answer 2

• “break down” of food into monomers of nutrient, ie. glucose, amino acid, fatty acid, nucleic acid. - Digestion or break down is by mechanical digestion (chewing) or by various enzymes

Question 3

What is absorption in the body?

Answer 3

• “suck in” nutrients. - This happens in the intestine.

Question 4

Draw and annotate a diagram of the digestive system (name & functions)

Answer 4

○ Mouth ○ Esophagus ○ Stomach ○ Small intestine ○ Large intestine ○ Pancreas ○ Liver ○ Gall bladder

Question 5

What is the function of the mouth?

Answer 5

Mouth: physical digestion takes place as the teeth cut and grind food into small pieces. The tongue helps to mix the food with saliva which is released by salivary glands. Saliva contains salivary amylase, an enzyme which begins the process of chemical digestion. Salivary amylase breaks down starch into maltose

Question 6

What is the function of the esophagus?

Answer 6

Esophagus: muscular tube which carries foods and liquids from the throat to the stomach. Food is pushed along the esophagus by a wave of muscular contractions. This type of muscle movement is called peristalsis.

Question 7

What is the function of the stomach?

Answer 7

Churning and mixing with secreted water and acid which kills foreign bacteria and other pathogens in food, plus initial stages of protein digestion

Question 8

What is function of small intestine?

Answer 8

final stages of digestion of lipids, carbohydrates, proteins, and nucleic acids, neutralizing stomach acid, plus absorption of nutrients

Question 9

What is the function of the liver?

Answer 9

produces a liquid called bile. Bile contains emulsifying agent which helps to dissolve fats/ lipids in water.

Liver is also a place to store glycogen (see more in starch digestion)

Question 10

What is the function of the gallbladder?

Answer 10

Stores bile until it is needed

Question 11

What is is the function of a pancreas?

Answer 11

Produces pancreatic juice (bunch of enzymes) which contains pancreatic amylase, lipase and protease. Pancreatic juice is squirted into lumen of the small intestine as soon as food leaves the stomach

Question 12

What is the function of the large intestine?

Answer 12

Re-absorption of water, further digestion especially of carbohydrates by symbiotic bacteria, plus formation and storage of feces.(Minerals & Vitamins absorbed)

Question 13

How does the main tract in digestion work?

Answer 13

The main tract consist of mouth, esophagus, stomach, small and large intestine. The liver makes bile, bile is stored in gall bladder, gall bladder then connect to deliver bile to the small intestine. The pancreas is also connected to the small intestine. (Draw diagram if necessary)

Question 14

What is peristalsis?

Answer 14

The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut (type of movement)

Question 15

Describe the structure of the small intestine.

Answer 15

The wall of the small intestine is made of layers of living tissues:

• Serosa: an outer coat
• Muscle layers: longitudinal muscle
• sub-mucosa: a tissue layer containing blood and lymph vessels
• mucosa: the lining of the small intestine, with the epithelium that absorbs nutrients on its inner surface (Draw Diagram)

Question 16

How does peristalsis work?

Answer 16

The circular/longitudinal muscle is a smooth muscle and consists of short cells (not elongated fibres). -exerts continues moderate force interspersed with short periods of more vigorous contraction (one direction) -contraction of circular muscles behind the food constricts the gut prevent it from being pushed back -contraction of longitudinal muscle where food is located moves it along the gut.

Question 17

How is peristalsis controlled?

Answer 17

-controlled unconsciously not by brain but by enteric nervous system (extensive and complex)

Question 18

What muscle is used during vomiting?

Answer 18

abdominal muscles

Question 19

What does pancreatic juice do?

Answer 19

There are two types of gland tissue where one group of cells secretes hormones (insulin&glucagon). The rest synthesizes digestive enzymes

Question 20

Where are digestive enzymes synthesized in a cell?

Answer 20

They are proteins and thus synthesized on ribosomes in the RER

Question 21

With the enzymes in the pancreatic juice, what can it breakdown?

Answer 21

-Amylase to digest starch -Lipases to digest lipids (triglyceride/phospholipids) -Proteases to digest proteins/peptides

Question 22

Which reactions does the small intestine carry out?

Answer 22

Hydrolysis reactions: - starch is digested to maltose by amylase - tryglycerides are digested to fatty acids and glycerol by lipase - phospholipds are digested to fatty acids and glycerol/phosphate by phospholipase - proteins and polypeptides are digested to shorter peptides by protease This does NOT allow small enough molecules to be absorbed.

Question 23

What enzymes are present in the plasma membrane of the epithelium cells (lining the small intestine)?

Answer 23

• Nucleases - Maltase - Lactase - Sucrase - Exopeptidases - Dipeptidases

Question 24

What does exopeptidases breakdown?

Answer 24

These are protesases that digest peptides by removing single amino acids either from the carboxy or amino terminal of the chain until only a dipeptide is left

Question 25

What feature do villi have for digestion?

Answer 25

Villi increase the surface area of epithelium over which absorption is carried out.

Question 26

How are monomers absorbed in the small intestine?

Answer 26

Villi absrob monomers formed by digestion as well as minerl ions and vitamins. Villus can absorb:

• glucose, fructose, galactose and other monosaccharides
• fatty acids, monoglycerides and glycerol
• bases from digestion of nucleotides
• mineral ions (Ca, K, Na)
• vitamins (Vitamin C)

Question 27

What is the epithelium?

Answer 27

The epithelium that covers the villi must form a barrier to harmful substances while at the same time being permeable enough to allow useful nutrients to pass through.

Question 28

What are the differente methods of absorption

Answer 28

Fat:

• Triglycerides are broken down to fatty acids and monoglyceride –> simple diffusion
• Fatty acids are also absorbed using fatty acid transporter –> facilitated diffusion
• Once inside the intestine cell, fat are re-assembled into triglycerides –> form lipoprotein –> carried away in blood or lymph to the body

Glucose:

• Glucose is polar (hydrophilic) and cannot pass through membrane –> need facilitated diffusion and active transport
• Transport glucose from the lumen (meaning inside) of small intestine to the blood requires the functions of
  
  • Sodium-glucose co-transporter protein
  • Sodium-potassium pump
  • Glucose channel

Question 29

Explain how the ileum absorbs and transports sugar and lipids. [6]

Answer 29

• digested foods absorbed through the villi;
• pass through plasma membrane of epithelium cells; microvilli increase surface area for absorption;
• lipids/fatty acids and glycerol enter the cells by (simple) diffusion;
• fructose enters by facilitated diffusion;
• glucose enters by active transport; sugars transported via the bloodstream;
• lipids enter the lacteal; lipids travel via the lymph system; pinocytosis-forming vesicles, absorption from vesicles;

Question 30

Material that cannot be absorbed

Answer 30

• Bile pigments
• Epithelial cells of the intestinal lining
• Lignin
• Cellulose
• Human flora / bacteria

Question 31

How is starch broke down in the small intestine?

Answer 31

• There are two types of starch called Amylose and Amylopectin
• the pancreas released many enzymes including amylase to completely break down starch to glucose.
• The product glucose is transport (via blood stream) to the liver.
• The liver re-assembles glucose into branched glycogen molecules, this is a major sugar storage in human body.
• When blood glucose is low (hungry), liver break down glycogen back into glucose and release glucose into the blood stream.

Question 32

What processes occur during assimilation of lipids?

Answer 32

Lipids are incoperated into new membranes