Lecture 2 - Digestion and the Alimentary Canal

Question 1

What are the main steps in the digestive process?

Answer 1

1. Indigestion - intake of food via the mouth
2. Digestion - mechanically or chemically breaking down food into their subunits
3. Movement - food must be moved along the GI tract in order to fulfil all functions
4. Absorption -

Question 2

What are the 4 main layers that make up the wall of the GI tract?

Answer 2

1. Mucosa - innermost layer that produces mucus that protects the lining and also produces digestive enzymes
2. Submucosa - 2nd layer of loose connective tissue that contains blood vessels, lymphatic vessels and nerves
3. Muscularis - 3rd layer made of 2 layers of smooth muscle that move food along the GI tract
4. Serosa - outer lining that is part of the peritoneum

Question 3

What is the pathway that food follows?

Answer 3

Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus

Question 4

The 1st part of the digestive tract includes?

Answer 4

1. Mouth
2. Pharynx
3. Esophagus

Question 5

Properties of the mouth?

Answer 5

1. 3 pairs of salivary glands secrete salivary amylase that begins carbohydrate digestion
2. Tonsils at the back of the mouth and other lymphatic tissues are important in fighting disease
3. Contains teeth that begin the mechanical breakdown of food
4. The tongue is covered in taste buds and also assists in the mechanical breakdown and movement of food
5. The tongue forms a bolus (mass of chewed food) and moves it toward the pharynx

Question 6

Anatomy of the mouth?

Answer 6

1. Hard palate
2. Soft palate
3. Uvula
4. Tonsil
5. Molars (3)
6. Premolars (2)
7. Canine (1)
8. Incisors (2)

Question 7

Properties of the pharynx and esophagus?

Answer 7

• Pharynx is a cavity between the mouth and esophagus that serves as a passageway for food (and air)
• Esophagus is a long, muscular tube that carries food to the stomach

Question 8

How do we swallow food?

Answer 8

• Voluntary phase:
  The beginning of food being swallowed from the mouth into the pharynx
• Involuntary phase:
  Once the food is in the pharynx swallowing becomes a reflex

The epiglottis covers the voice box to make sure food is routed into the esophagus

Food moves down the esophagus through peristalsis (rhythmic contraction)

Question 9

Describe properties of the stomach?

Answer 9

1. Functions to store food, start digestion of proteins and controls movement of chyme into the small intestine
2. J-shaped organ with a thick wall
3. There are 3 layers of muscle in the muscularis layer of the stomach wall helping in mechanical digestion and allowing it to stretch
4. The mucosa layer has deep folds called rugae and gastric pits that lead into gastric glands that secrete gastric juice
5. Gastric juice contains pepsin, an enzyme that breaks down proteins, and HCl and mucus
6. HCl gives the stomach of a pH of 2 which activates pepsin and helps kill bacteria found in food
7. A bacterium, Helicobacter pylori, lives in the mucus and can cause gastric ulcers
8. The stomach empties chyme into the small intestine after 2-6 hours.

Question 10

Properties of the small intestine?

Answer 10

1. Averages 6m (18ft) in length
2. Enzymes secreted by the pancreas into the small intestine digest carbohydrates, proteins and fats
3. Bile is secreted by the gallbladder into the small intestine to emulsify fats
4. Digested food is absorbed through large surface area created by numerous villi (finger-like projections) and microvilli
5. Amino acids and sugars enter the capillaries while fatty acids and glycerol enter the lacteals (small lymph vessels)

Question 11

Name the 3 accessory organs?

Answer 11

1. Pancreas
2. Liver
3. Gallbladder

Question 12

Name the 3 accessory organs?

Answer 12

1. Pancreas
2. Liver
3. Gallbladder

Question 13

What does the pancreas look like?

Answer 13

1. Fish-shaped spongy organ behind the stomach

Question 14

Functions of the pancreas?

Answer 14

1. Secretes enzymes into the small intestine
   - Trypsin digests proteins
   - Lipase digests fats
   - Pancreatic amylase digests carbohydrates
2. Secretes bicarbonate into the small intestine to neutralise stomach acids
3. Secretes insulin to the blood to keep blood sugar levels under control

Question 15

What does the pancreas look like?

Answer 15

1. Fish-shaped spongy organ behind the stomach

Question 16

Functions of the pancreas?

Answer 16

1. Secretes enzymes into the small intestine
   - Trypsin digests proteins
   - Lipase digests fats
   - Pancreatic amylase digests carbohydrates
2. Secretes bicarbonate into the small intestine to neutralise stomach acids
3. Secretes insulin to the blood to keep blood sugar levels under control

Question 17

Properties of the liver and gallbladder?

Answer 17

1. Large metabolic organ that lies under the diaphragm and is made of 100,000 lobules
2. Filters blood from the GI tract thus acting to remove poisons and detoxify the blood
3. Removes iron, vitamins A, D, E, K and B12 from the blood and stores them
4. Stores glucose as glycogen and breaks it down to help retain blood glucose levels
5. Makes plasma proteins and helps regulate cholesterol levels by making bile salts
6. Makes bile that is then stored in the gallbladder to be secreted into the small intestine to emulsify fats
7. Breaks down haemoglobin

Question 18

Hormones that control feeding?

Answer 18

1. Leptin
2. PYY
3. Insulin
4. Ghrelin

Question 19

Properties of the large intestine?

Answer 19

1. Includes the cecum, colon, rectum and anal canal
2. Larger in diameter but shorter than the small intestine
3. The cecum has a projection known as the appendix that may play a role in fighting infections
4. Functions to:
   a. absorb water to prevent dehydration
   b. absorbs vitamins (B complex and K) produced by intestinal flora
   c. Forms and rids the body of faeces through the anus

Question 20

Carbohydrates related to nutrition and weight control?

Answer 20

1. Sugars or polysaccharides that are digested into simple sugars that are an important energy source
2. Refined grains should be minimised in the diet because fibre and vitamins are removed (i.e. white bread, cake and biscuits)
3. Complex carbohydrates are recommended as a good source of vitamins and minerals (i.e. beans, whole-grain products, nuts and fruits)

Question 21

Protein related to nutrition and weight control?

Answer 21

1. Proteins are digested into 20 different amino acids which are used to produce cellular proteins
2. Essential amino acids are the 8 amino acids that must be attained through diet
3. Complete proteins that have all essential amino acids are usually derived from animals such as meat an diary
4. Non-animal sources of complete proteins are tofu, soymilk, and other processed food from soybeans
5. Incomplete proteins are ones that lack at least one essential amino acid (i.e. legumes, nuts, grains etc.) and need to be combined with another incomplete protein to allow all amino acids to be used in the body
6. Amino acids cannot be stored in the body, thus small amounts (2 meat servings) need to be ingested on a daily basis

Question 22

Lipids related to nutrition and weight control?

Answer 22

1. Includes fats, oils and cholesterol
2. Saturated fats (usually of animal origin) are usually solid at room temperature while unsaturated fats are usually liquid at room temperature
3. Essential fatty acids are ones that must be ingested include linoleic acid and linolenic acid (these can only be found in polyunsaturated oils such as corn and safflower)
4. Olive and canola oil contain more monounsaturated fats
5. Omega-3 fatty acids are thought to ward of heart disease and are found in some fish (salmon, sardines and trout) as well as some plants (flaxseed oil)

Question 23

Minerals related to nutrition and weight control?

Answer 23

1. The body contains >5g of each major mineral and <5g of each trace mineral
2. Major minerals make up components of cells, body fluids and tissues (i.e. calcium)
3. Minor minerals are components of larger molecules (i.e. iron in haemoglobin)
4. A varied and complete diet usually provides necessary minerals

Question 24

Vitamins related to nutrition and weight control?

Answer 24

1. Organic compounds (not including proteins, fats, or carbohydrates) used for metabolism but are not produced in high energy quantity by the body
2. Vitamins are often enzyme helpers (coenzymes)
3. There are a total of 13 vitamins in two groups: fats-soluble and water-soluble

Question 25

Antioxidants related to nutrition and weight control?

Answer 25

1. Are chemicals that decrease the rate of oxidation or transfer of electrons
2. Vitamin C, E and A are considered antioxidants because they are thought to defend the body against free radicals that can transfer electrons and damage cells and DNA
3. The vitamins are common in fruits and vegetables