M2.2.5 - Digestion

Question 1

Absorption

Answer 1

The movement of small nutrients into the body across a membrane
e.g. from the small intestine into blood capillaries

Occurs through
- Diffusion
- Facilitated diffusion
- Active transport

Question 2

Assimilitation

Answer 2

The use of absorbed nutrients to form parts of an organism e.g. amino acids from food is used to build new proteins

Question 3

Digestion osmosis

Answer 3

Passive transport
- e.g. if the chyme (semi-digested food) is dilute, water is absorbed from it into the villi capillaries of the intestinal mucosa. Conversely, water can also flow from plasma into the chyme, until it is isosmotic.

Question 4

Facilitated diffusion example

Answer 4

e.g. Glucose uses a glucose transporter protein, amino acids also use transport systems

Question 5

Active transport

Substances transported actively in the digestive system

Answer 5

Ion uptake, e.g. sodium, calcium, magnesium and iron, and transport of disaccharides

Sodium-potassium pump

Disaccharides (complex sugar), dipeptides and tripeptides (complex amino acids) are also actively transported.

Question 6

Endocytosis example

Answer 6

Humans: Immunoglobulins is absorbed via receptor mediated endocytosis.
Vascular plants: endocytosis transports SUCROSE from the phloem into the cells of the sink

Question 7

Different systems of absorption

What substances go into the bloodstream/lymphatic system. What substances remain unchanged through absorption

Answer 7

• Bloodstream: Amino acids, carbohydrates and minerals
• Lymphatic system: fatty acids, glycerol

Only a small amount of fluid is absorbed

Immunoglobulins, breast milk and oral vaccines remain unchanged through absorption

Question 8

Stomach absorption

Answer 8

The stomach is a poor absorptive area. Only highly lipid soluble substances (alcohol, aspirin) can be readily absorbed
* No villi: low surface area
* Tight junctions: does not allow much movement of material between cells

Question 9

Small intestine absorption

Features + functions

Answer 9

Where most food particles are absorption.

• Villi and microvilli: high surface area, very efficient
• Smooth muscle in the wall causes peristalsis- involuntary contraction and relaxation, moving food through the tract
• Duodenum (first section) pancreatic juices released into the area. Bicarbonate ions neutralise acidic chyme from the stomach. Most of absorption occurs here.
• Jejunum (middle section): plicae (fold/ridge) within villi, increase surface area. Some water absorption.
• Ileum (last section): villi becomes smaller → less absorption of digested products.
• Peyer’s patches: small clusters of lymphatic tissue that inhibit spread of microflora from the large intestine

Question 10

Elimination

Answer 10

Passing undigested material out of the alimentary canal

Question 11

Large intestine structure

Answer 11

• Consists of the caecum, appendix, colon and rectum. In humans, the caecum and appendix are bypassed, with food entering the ascending colon.
• No villi, as only absorption of water occurs.
• Movement of material controlled by a sphincter muscle and valve, preventing backflow. Movement by peristalsis.
• The material entering the colon are undigested substances, compacting into faeces. Colon terminates in the rectum.

Question 12

Large intestine microflora

Answer 12

• Some microflora can produce absorbable vitamins, but if spread to other parts of the body can become pathogenic

E.g. vitamin K, a lipid-soluble vitamin which helps blood clot

Question 13

Large intestine absorption

Answer 13

• Water, mineral ions and some vitamins are absorbed across the cell membrane into the bloodstream
• Faeces moves by mass movement caused by peristalsis

Question 14

Mechanical digestion

Answer 14

• The process of applying force to break down food
• Begins in the mouth with chewing - teeth shapes changed as the diet evolved. (Incisors vs molars)
• Churning motion of the stomach further breaks down food
• Mechanical digestion increases surface area of food so that chemical digestion enzymes can act on it faster

Question 15

Chemical digestion

Answer 15

• Large complex molecules are broken down chemically by digestive enzymes
• Begins in the mouth with salivary amylase breaking carbohydrate starch into simpler sugars
• Stomach: gastric juices - HCl breaks down food; acid kills bacteria; digestive enzymes split up proteins. Mixed with the bolus, it becomes chyme
• There are different enzymes in the small intestine
• The molecules are broken down into substances that can be used for cell reactions and synthesising other substances.

Question 16

Chemical digestion enzymes

Amylase, protease, lipase

Answer 16

• Carbohydrates with amylase → glucose
• Proteins with protease → amino acids
• Lipids with lipase → glycerol + fatty acids

Question 17

Carbohydrate breakdown

Answer 17

• Amylase breaks down carbohydrates → glucose

Question 18

Disaccharides breakdown

Answer 18

• Disaccharides broken down into monosaccharides in the duodenum by maltase, sucrase, and lactase enzymes
• Resulting monosaccharides are absorbed into the bloodstream and transported to cells to be used in energy-harnessing metabolic pathways

Question 19

Protein breakddown

Answer 19

• In the stomach, the protease pepsin break protein down into single amino acids
• Amino acids get absorbed into the bloodstream through the small intestine

Question 20

Lipid digestion

Answer 20

• Occurs in small intestine
• Bile salts emulsify (break down) lipids, allowing lipase to divide lipids into fatty acids + monoglycerides
• Monoglycerides and fatty acids leave the small intestine and recombine into chylomicrons, which enter the bloodstream

Question 21

Vitamins absorption

Answer 21

• Fat-soluble: absorbed in the same way as lipids
• Water-soluble: directly absorbed into the bloodstream through the intestines

Question 22

Liver function

Answer 22

• Digested food that has been absorbed into the bloodstream travels to the liver
• Liver keeps sugars, glycogen, and protein levels in balance in the body. Also detoxifies blood
• Is the centre of food metabolism