Option D2 Digestion

Question 1

Exocrine glands produce and secrete…

Answer 1

substances via a duct onto an epithelial surface – either the surface of the body or the lumen of the digestive tract/ gut

Question 2

Examples of digestive glands

Answer 2

Gastric glands
Salivary glands
Pancreatic glands
Intestinal glands

Question 3

Gastric secretions - nervous mechanism

Answer 3

1. Immediate response to the sight or smell of food through secretion of gastric juices by the stomach pre-ingestion
2. Food entering the stomach causes distention, which is detected by stretch receptors in the stomach lining
3. Signals are sent to the brain, where sustained gastric simulation is triggered by the release of digestive hormones

Question 4

Gastric secretions - hormonal mechanism

Answer 4

1. Gastrin is secreted by the stomach and simulates the release of stomach acids
2. If stomach pH drops too low, secretion is inhibited by gut hormones
3. When digested food passes the small intestines, the duodenum also releases digestive hormones
   3a. Secretion and CCK simulate the pancreas and liver to release digestive juices
   3b. Pancreatic juices contain bicarbonate ions which neutralise stomach acids, while the liver produces bile to emulsify fats

Question 5

Normal pH of the stomach

Answer 5

Gastric glands that line the stomach wall secrete and acidic solution that creates a 1.5-2.0 pH which is optimum for hydrolysis reactions by stomach enzymes

Question 6

Function of acidic condition in the stomach

Answer 6

• assists in digestion of food
• activates stomach proteases (pepsin)
• prevents pathogenic infections

Question 7

Pancreas releases…

Answer 7

bicarbonate ions into the duodenum which neutralizes the stomach pH (intestinal pH~7.0-8.0)

Question 8

How is the low pH environment in the stomach maintained?

Answer 8

Proton pumps in the parietal cells of the gastric pits secrete H+ ions (active transport) which combine with Cl- ions to form hydrochloric acid

Question 9

Proton pump inhibitors (PPI)

Answer 9

drugs that irreversibly bind to proton pumps and prevents H+ production. This will raise the pH in the stomach however could cause increased susceptibility to gastric infections due to lower acidity

Question 10

The inner epithelial lining of the small intestine is…

Answer 10

highly folded finger-like projections called villi

Question 11

Features of Villi

Answer 11

M - Microvilli – Ruffling of epithelial membrane further increases surface area
R - Rich blood supply – Dense capillary network rapidly transports absorbed products

S - Single layer epithelium – Minimises diffusion distance between lumen and blood
L - Lacteals – Absorbs lipids from the intestine into the lymphatic system
I - Intestinal glands – Exocrine pits (crypts of Lieberkuhn) release digestive juices
M - Membrane proteins – Facilitates transport of digested materials into epithelial cells

Question 12

Structural features in the epithelial lining of villi

Answer 12

Tight Junctions: creating an impermeable membrane, they keep digestive fluids separate from tissues and maintain a one-way movement concentration gradient

Microvilli: it borders the villi and greatly increases the surface area allowing for more absorption

Mitochondria: epithelial cells of intestinal villi will possess large numbers of mitochondria to produce ATP for various transport mechanisms

Question 13

Summary of egested materials

Answer 13

B - Bile pigments
E - Epithelial cells
L - Lignin
C - Cellulose
H - Human flora (bacteria)

Question 14

Dietary fiber

Answer 14

indigestible portion of food derived principally from plants and fungi. Humans lack enzymes to break down certain plant matter

Question 15

Health benefits of a rich fiber diet

Answer 15

• reduction of constipation frequency
• lowers blood cholesterol and regulates blood sugar levels
• it aids in weight management

Question 16

Stomach ulcers

Answer 16

inflamed and damaged areas in the stomach wall, typically caused by exposure to gastric acids

Question 17

H. pylori

Answer 17

it can survive in acid conditions of the stomach by penetrating the mucus lining

Question 18

Stomach ulcer formation

Answer 18

1. H. pylori penetrates the mucus layer lining in the stomach
2. H. pylori damages the goblet cells responsible for mucus production
3. Loss of mucus exposes cell to stomach acids, causing ulcers

Question 19

Vibrio cholerae

Answer 19

bacterial pathogen that infects the intestines and causes acute diarrhea and dehydration

Question 20

Action of cholera toxin

Answer 20

the toxin creates cyclic AMP which activates specific ion channels within the cell membrane, causing an efflux of ions from the cell.

the build up of ions in the lumen draws water from cells and tissues via osmosis, causing acute diarrhea.

dehydration with then occur if left untreated