Topic 5 Digestive System: Digestion in Humans

Question 1

• Network of fat and connective tissue that serve as digestive system through structural support, fat storage, and by providing a framework through which blood supply, nerves, and the lymphatics can reach various locations

Answer 1

Mesenteries

Question 2

1. Starches -> glucose
2. Proteins -> amino acids
3. Fats -> fatty acids
4. Nucleic acids -> nucleotides

Answer 2

Groups of molecules encountered in digestive system

Question 3

• Salivary amylase breaks down starch into maltose by breaking starch’s a-glycosidic bonds
• Chewing creates a bolus which is swelled, and also increases the surface area of food, thus exposing it to more enzymes

Answer 3

Mouth

Question 4

• Area where food and air passages cross

- Epiglottis: flap of tissue that blocks trachea so only solid and liquid enter, located here

Answer 4

Pharynx (throat)

Question 5

• Tube leading to stomach, food travels by contractions (wave motion peristalsis via smooth muscle) and saliva lubricates this

Answer 5

Esophagus

Question 6

• Secreted gastric juice (digestive enzymes and HCl) and food enters stomach through lower esophageal/cardiac sphincter
• Contains exocrine glands (local secretion by way of duct) within gastric pits (indentation in stomach that denote entrance to gastric glands) which contain secreting chief cells, parietal cells, G cells, and mucous cells (secrete mucus to prevent backwash)

Answer 6

Stomach

Question 7

• Storage
• Mixing
• Physical Breakdown
• Chemical Breakdown
• Controlled release

Answer 7

Functions of Stomach

Question 8

• Stomach contains accordion-like folds that allow 2-4 liters of storage

Answer 8

Storage

Question 9

• Mixes food with H2O and gastric juice, forming chyme, a creamy medium

Answer 9

Mixing

Question 10

• Muscles are activated to break down food; HCl denatures proteins and kills bacteria

Answer 10

Physical Breakdown

Question 11

• Pepsin (secreted by chief cells) digests proteins
• Pepsinogen -> pepsin activated by HCl, which is secreted by parietal cells
  a. Peptic Ulcers: cause by failure of mucosal lining to protect stomach. Can also be cause by excess stomach acid or H. Pylori, which can be treated with antibiotics

Answer 11

Chemical Breakdown

Question 12

• Chyme enters the small intestine via the pyloric sphincter

Answer 12

Controlled Release

Question 13

• Mucous Cells
• Chief Cells
• Parietal Cells
• G Cells
• ECL Cells

Answer 13

Stomach Cells

Question 14

• secrete mucus that lubricates and protects stomach’s epithelial lining from acid environment. Mucus is mainly composed of sticky glycoproteins and electrolytes, and come cells also secrete a small amount of pepsinogen

Answer 14

Mucous Cells

Question 15

• secrete pepsinogen (zymogen precursor to pepsin). Pepsinogen is activated to pepsin by the low pH in stomach, and once active, it begins protein digestion

Answer 15

Chief Cells

Question 16

• secrete HCl; intrinsic factor that assists ileum’s B-12 absorption. Possess many mitochondria for energy to establish proton gradient

Answer 16

Parietal Cells

Question 17

• secrete gastrin, a large peptide hormone which is absorbed into blood and stimulates parietal cells to secrete HCl

Answer 17

G Cells

Question 18

• all cell types are affected by acetylcholine, which increases secretion of each cell. Gastrin and histamine also increase HCl secretion

Answer 18

Note

Question 19

• neuroendocrine cells in digestive tract; gastrin stimulates them to release histamine which in turn stimulates parietal cells to produce gastric acid

Answer 19

ECL Cells

Question 20

• Full stomach has a pH of 2, which is extremely acidic and beneficial for killing ingested bacteria and is the optimal pH for pepsin

Answer 20

Stomach pH

Question 21

• Stomach contains these folds/rippled areas to increase the surface area of the stomach lumen

Answer 21

Rugal Folds

Question 22

• Protein digestion begins in stomach, but no absorption whatsoever occurs in the stomach

Answer 22

Overall Note