Digestive System

Question 1

What are enzymes?

Answer 1

A protein catalyst that increases the rate at which a chemical reaction proceeds. They are highly specific (active site).

Question 2

What enzyme breaks down lipids?

Answer 2

Lipase

Question 3

What enzyme breaks down proteins?

Answer 3

Protease.

Question 4

What enzyme breaks down carbohydrates?

Answer 4

Amylase

Question 5

What are the salivary glands?

Answer 5

Glands that produce and secrete saliva into the oral cavity.

Question 6

What is the role of saliva?

Answer 6

Protects oral cavity, moistens, lubricates and digests food.

Question 7

What is lysozyme?

Answer 7

An antibacterial enzyme found in the mouth

Question 8

What is the process of swallowing?

Answer 8

1. Voluntary phase: tongue pushes bolus to the back of the oral cavity towards the pharynx.
2. Pharyngeal phase: soft palate closes off nasopharynx. Bolus touches receptors on oropharynx and swallowing reflex moves bolus down pharynx and into oesophagus. Epiglottis covers trachea.
3. Oesophageal phases: bolus moves down oesophagus by peristalsis.

Question 9

What is the role of the stomach?

Answer 9

Stomach churns bolus into chyme (thick liquid).

Produces mucus, hydrochloric acids and protein-digesting enzymes (pepsin).

Question 10

What is the structure of the stomach?

Answer 10

Contains a thick mucus layer that lubricates and protects epithelial cells on stomach wall from acid (pH: 2-3).
Opening: gastroesophageal (to oesophagus) and pyloric sphincter (to duodenum).

Question 11

What are the layers of the stomach?

Answer 11

Visceral peritoneum, muscularis (outer longitudinal, middle circular, inner oblique), submucosa, mucosa and rugae (folds in stomach wall that allow stomach to stretch after eating).

Question 12

What are the movements of the stomach?

Answer 12

3 muscles layers enable churning of food to make chyme.
Combination of mixing waves (80%) and peristaltic waves (20%).
Both esophageal and pyloric sphincters are closed.
Stomach empties ever 4 hours (6-8 after a fatty meal).

Question 13

What is the structure of the small intestine?

Answer 13

~6m in length, small diameter.
Large surface area for absorption.
Divisions: duodenum (first 25cm), jejunum (2.5m), ileum (3.5m).

Question 14

What is the role of the duodenum?

Answer 14

Chyme mixes with various digestive enzymes.
Bile enters from liver/gall bladder via the common bile duct, emulsifies fats.
Enzymes enter via pancreatic duct.
Lipase: breaks down lipids
Pancreatic amylase: breaks down carbohydrates.
Trypsin: breaks down proteins.

Question 15

What is the structure of the wall of the small intestine?

Answer 15

Folds increase surface area.

1. Plicae circulares - circular folds in the wall.
2. Villi - folds of mucosa that contain capillaries and lacteals.
3. Microvilli - small folds on the epithelial cell surface.

Question 16

Where do nutrients that are absorbed in the small intestine travel to?

Answer 16

Lipids travel to the lacteals and lymph nodes.

Carbohydrates and proteins travel to the capillaries and the blood.

Question 17

What is the role of the liver in the digestive system?

Answer 17

Produces bile (~100mL/day). Stores glucose (as glycogen) and lipids for energy. Involved in detoxification.

Question 18

What is the role of the gallbladder in digestion?

Answer 18

Stores concentrated bile.

Question 19

What is the role of the pancreas in digestion?

Answer 19

Produces digestive enzymes. Produces insulin and glucagon for blood sugar homeostasis.

Question 20

What is the role of the large intestine?

Answer 20

Absorption of water.
Bacteria/microbes synthesise vitamin B & K.
Defecation reflex.

Question 21

What does the large intestine do in digestion?

Answer 21

1500mL of chyme enters the cecum, 90% absorbed yielding 80-150mL of faeces.
Transit time: 18-24hrs (chyme to faeces).

Question 22

What is the structure of the large intestine?

Answer 22

Extends from ileocecal junction to anus.

Consists of cecum, colon (ascending, transverse and descending, sigmoid), rectum and anal canal.

Question 23

Summarise the digestive process.

Answer 23

1. Breakdown of food molecules by mechanical and chemical digestion in mouth and stomach.
2. Absorption of nutrients in small intestine, absorption of water in large intestine.

Question 24

What are nutrients?

Answer 24

Chemicals taken into the body to produce energy and provide building blocks to build other molecules.

Question 25

What are the six classes of nutrients?

Answer 25

Carbs, proteins, lipids, vitamins, minerals and water. | They are all organic molecules which means they all contain carbon.

Question 26

What are some examples of carbohydrates?

Answer 26

Mono/di/polysaccharides - plants/vegetables.

Question 27

What are some examples of lipids?

Answer 27

Triglycerides - oils. dairy, animal fat, eggs.

Question 28

What are some examples of proteins?

Answer 28

Chains of amino acids - meat, fish, poultry.

Question 29

What is the structure of carbohydrates?

Answer 29

Contain carbon, hydrogen and oxygen. 2 hydrogen for every carbon. Can be mono, di or polysaccharides.

Question 30

What is the process of carbohydrate absorption?

Answer 30

Polysaccharide chain digested by saliva in the mouth and pancreatic amylase in the duodenum. Disaccharide chain digested by sucrase in the intenstine Monosaccharide chain - glucose absorbed into blood via villi/microvilli in intestine, transported to liver via hepatic portal vein.

Question 31

What are some examples of mono, di and polysaccharide carbohydrates?

Answer 31

Monosaccharides: fructose, glucose, galactose. Disaccharides: sucrose, lactose, maltose. Polysaccharides: glycogen, starch and cellulose.

Question 32

What are the uses of carbohydrates in the body?

Answer 32

Glucose produces ATP. Excess glucose is turned into glycogen and stored in muscle and liver cells. Excess beyond storage becomes fat. Sugars also become part of DNA, RNA, ATP, glycoproteins and glycolipids.

Question 33

What is the structure of proteins?

Answer 33

Contains carbon, hydrogen, oxygen, nitrogen and sometimes sulfur. Building block: amino acids. Each amino acid has an amine group (NH2), a carboxyl group (COOH), a hydrogen group and a side group.

Question 34

What are the functions of proteins?

Answer 34

Globular proteins form haemoglobin. Form muscle proteins or connective tissue. Assist in cell membrane transport. Assist in enzyme formation, hormones and antibodies.

Question 35

What is the process of protein absorption?

Answer 35

Protein digested by pepsin in the stomach. Polypeptides digested by trypsin in the duodenum. Peptides and individual amino acids are absorbed into the blood.

Question 36

What is the structure of lipids?

Answer 36

Composed of carbon, hydrogen, oxygen and sometimes nitrogen and phosphorus.

Question 37

What is the function of lipids?

Answer 37

Lipids/fats are broken down to release energy.

Question 38

What is the structure of triglycerides?

Answer 38

Glycerol + 3 fatty acids. Triglycerides make up 95% of the body.

Question 39

What are the types of fatty acids?

Answer 39

Saturation: refers to how many H atoms on each chain. Saturated: animal fats. Unsaturated: contains one or more double bonds in the carbon chain, less H. Trans fats: unsaturated fats artificially altered to be more saturated.

Question 40

What is the process of lipid absorption?

Answer 40

Begins in duodenum, bile from gall bladder emulsifies lipids. Lipase from pancreas causes a further breakdown. Short chain fatty acids are absorbed into lympthatic system. Lipids are stored in adipose tissue and liver.

Question 41

What are the uses of lipids in the body?

Answer 41

Cholesterol: component of plasma membrane. Phospholipids: plasma membranes, myelin sheath, bile. Eicosanoids: inflammation, blood clotting, tissue repair, smooth muscle contraction.