Digestion

Question 1

What are exocrine glands?

Answer 1

• They produce and secrete substances via a duct into an epithelial surface either onto the surface of the body OR in the lumen of the digestive tract

Question 2

What are digestive glands and give four examples.

Answer 2

• They are exocrine glands that secrete substances into the lumen of the digestive tract
  1. Salivary glands - secrete saliva (with amylase)
  2. Gastric glands - secretes gastric juices which includes HCl and protease (enzyme for proteins)
  3. Pancreatic glands - secrete pancreatic juices (contains lipase, protease and amylase)
  4. Intestinal glands - secrete intestinal juices in the intestinal wall

Question 3

Describe the structure of an exocrine gland cells.

Answer 3

• They are a cluster of secretory cells which collectively form acini
• The acini are surrounded by a basement membrane and are held together by tight junctions between secretory cells
• Exocrine products are released by secretory vesicles into a duct which connect to an epithelial surface

Question 4

What 3 mechanisms control the secretion of digestive juices? What exactly do they control?

Answer 4

• Mechanical, nervous and hormonal mechanisms
• They control the volume and specific content of secretion

Question 5

How does the nervous mechanism control the secretion of digestive juices?

Answer 5

• Sight and smell of food may trigger an immediate response
• Gastric juice is secreted in the stomach and saliva in the mouth
• Body prepares for the future intake of food
• When food enters the stomach it causes swelling, detected by stretch receptors in stomach lining
• Signals are sent to the brain, triggers release of digestive hormones for gastric stimulation

Question 6

What 3 hormones are involved in the chemical control of digestion?

Answer 6

• Gastrin, Secretin, Cholecystokinin (CCK)

Question 7

How does Gastrin control the secretion of digestive juices?

Answer 7

• Gastrin is produced by G cells in the stomach, duodenum and pancreas
• Response to physical stimulation (smell) and chemical stimulation by protein
• When Gastrin is secreted into the bloodstream, it stimulates release of gastric juices

Question 8

What does gastric juice contain and what does it do?

Answer 8

• Contains H2O, HCl, inorganic ions, enzymes, mucus, polypeptides and instrinsic factor
• Instrinsic factor needed for absorbing vitamin B12
• Gastric juices change pH of food content 6.7 to 2, acidic conditions enhance digestion
• When enough gastric juice is present, production of gastrin stops

Question 9

How does Secretin control the secretion of digestive juices?

Answer 9

• Produced in response to presence of acid fluid
• Presence of gastric acid converts prosecretin into secretin
• Stimulate the pancreas and liver to release digestive juices to neutralize intestinal components
• When pH is 8, production of pancreatic juice is stopped

Question 10

How does CCK control the secretion of digestive juices?

Answer 10

• Produced in small intestine when food is present in this organ
• Controls release of pancreatic juice from pancreas and bile from the gall bladder
• Acts as hunger suppressor

Question 11

How does negative feedback control the secretion of digestive juices?

Answer 11

• This mechanism causes the presence of acid in the lumen of the stomach to stimulate somatostatin secretion, slows acid secretion

Question 12

How is stomach acid produced?

Answer 12

• Produced by H+ and Cl- ions. These ions are produced by parietal cells of the stomach lining.
• The H+ ions are released by protein carriers as K+ are taken in from the lumen of the stomach
• This requires ATP
  Check book

Question 13

What does stomach acid do?

Answer 13

• Assists in the digestion of food
• Activates stomach protease
• Prevents pathogenic infections (destorys microorganisms in ingested food)
• Normal pH 1.5-2.0, optimum pH for enzymes

Question 14

What are pepsin and pepsinogen, how is pepsinogen converted?

Answer 14

• Pepsinogen is an inactive form of pepsin
• Pepsin is an emzyme that breaks polypeptides into smaller monomers
• Pepsinogen is secreted by exocrine glands called gastric glands
• When pepsinogen reacts with HCl, it becomes ‘active’ as 44 amino acids are removed and is now pepsin
• Optimum pH is 2
• This is a hydrolysis reaction (into smaller pieces)

Question 15

How is the stomach wall protected from the acid?

Answer 15

• The wall is lined by a layer of mucus, protects it from being damaged
• The pancreas releases bicarbonate ions which neutralises the stomach to 7-8 pH

Question 16

What are stomach ulcers? What causes them?

Answer 16

• When excess gastric acid is produced in the stomach, this can damage the mucus layer which can lead to a gastric ulcer
• The lining of the stomach is disrupted
• Symptoms: stomach pain, heartburn, nausea)
• Can also be caused by a bacterium H. pylori that produces toxins that cause gastric inflammation

Question 17

How are stomach ulcers from H. pylori treated?

Answer 17

• Amoxicillin: antibiotic, inhibits synthesis of bacterial cell wall
• Clarithromycin: antibiotic prevents bacteria from growing (no protein synthesis)
• Proton Pump Inhibitor (PPI): inhibits acidification of stomach

Question 18

How do proton pump inhibitor drugs treat stomach ulcers?

Answer 18

• It blocks the proton pump responsible for the secretion of H+ ions in the stomach
• Less H+ in the lumen reduces amount of HCl produced, stomach is less acidic
• This prevents gastric discomfort caused by high acidity

Question 19

What are the 6 adaptations of villi? Check chapter 6.1

Answer 19

1. Increase surface area, microvilli
2. Many mitochondria, energy for active transport
3. Capillaries present, absorption of food into blood
4. Lacteal for absorption into lymphatic system
5. Pinocytotic vesicles, help uptake of fluids
6. Tight junctions, ensure molecules don’t escape, maintain concentration gradient

Question 20

What does the large intestine absorb?

Answer 20

• Absorbs water, minerals and vitamin K

Question 21

What is dietary fibre?

Answer 21

• The non-digestible carbohydrates, especially cellulose, that increase faecal mass, stimulates peristaltic movements

Question 22

What happens to the substances that are not absorbed?

Answer 22

• They are egested as faeces such as cellulose, lignin, bile pigments
• Peristalsis of the walls of the large intestine push the faecal matter toward the rectum and eventually eliminate through the anus

Question 23

What happens with an inadequate fibre intake?

Answer 23

• May lead to constipation (unsatisfactory defecation, infrequent bowel movement, difficult stool passage)

Question 24

What are the benefits of fibre intake?

Answer 24

• Reduces frequency of constipation, lowers risk of colon cancer
• Lowers blood cholesterol and regulates blood sugar levels
• Aids in weight management (volume eating)

Question 25

What is cholera?

Answer 25

• Disease caused by ingestion of food or water contaminated with bacterium V. cholerae
• When the cholera toxin infects the intestine, triggers endocytosis of the toxin in the epithelial cells
• Toxin is an active enzyme which activates ions and water to leave, diarrhea

Question 26

What are symptoms of cholera? What is a treatment?

Answer 26

• Vomiting, muscle cramps, diarrhea, cause dehydration, low blood pressure, death, increased thirst, swelling of brain, decreased urine output
• Treatment: antibiotics to kill bacteria, oral or intravenous rehydration