Lecture 25

Question 1

What are the secretions of exocrine glands?

Answer 1

Mucus
Electrolyte solution
Digestive enzymes

Question 2

Function of mucus?

Answer 2

} Protection and lubrication

} Aids mechanical digestion

Question 3

Function of electrolyte solution

Answer 3

} Dilutes food & provides optimal pH

} Essential for chemical digestion of food

Question 4

Function of digestive enzymes

Answer 4

} Essential for chemical digestion of food } Aids absorption

Question 5

composition of saliva?

Answer 5

Mucus
Dilution solution NaHCO3NaCl
Digestive enzymes (lingual lipase and a-amylase)

Question 6

Functions of salivary secretions?

Answer 6

Not essential.
Aids talking, chewing and swallowing.
Hygiene.
Digestion.

Question 7

How are salivary secretions regulated?

Answer 7

Nervous (stimulated by food)

Autonomic Nervous system: parasympathetic (copious quantities) Sympathetic (small volumes)

Question 8

Gastric secretions between meals?

Answer 8

Surface cells secreting mucous at a slow rate.

Question 9

Gastric secretions when eating?

Answer 9

Superimposed on basal rate.
Mucous cells - mucus
Parietal cells - HCL and intrinsic factor
Chief cells -0 pepsinogen

Question 10

What is the function of intrinsic factor?

Answer 10

Absorption of vitamin B12 in the SI

Question 11

Function of pepsinogen?

Answer 11

Converted to active form pepsin.by acid then starts digestion of proteins1`

Question 12

Functions of gastric acid?

Answer 12

Dilutes food 
Denatures protein 
Activates pepsinogen 
Creates optimum pH for pepsin action 
Protection

Question 13

Source of acid (H+)

Answer 13

} Formation of H2CO3 by carbonic anhydrase
} CO2 + H2OóH2CO3
} Dissociation of H2CO3 to give H+ and HCO3-
} H CO óHCO - + H+ 233

Question 14

Secretion of acid (H+)

Answer 14

H+-K+ ATPase
} Apical membrane of parietal cells
} Pumps H+ ions into lumen in exchange of potassium ions (K+)
} K+ return to lumen through membrane channel

Question 15

`Source of chloride (CL-) ?

Answer 15

} Anion counter transporter

} Serosal membrane of parietal cells } Ejects HCO3- into interstitial fluid } Imports Cl- ions into cell

Question 16

Secretion of chloride

Answer 16

} Cl- diffuse across cell

} Enters lumen via Cl- channel in apical membrane

Question 17

How is gastric secretion regulated?

Answer 17

Cephalic phase - head controls secretion
Gastric phase - stomach controls secretion
Intestinal phase - intestine controls secretion.

Question 18

Function of the cephalic phase?

Answer 18

Preparing for the arrival of food

Question 19

What stimulates the Cephalic phase?

Answer 19

Higher senses

Chewing action and taste.

Question 20

What regulates the Cephalic phase?

Answer 20

Parasympathetic Nervous System:
} Via enteric nervous system
} Stimulates parietal cells, chief cells and goblet
cells
} Stimulate secretion of hormone gastrin
¨ Released into blood
¨ Stimulates parietal cells and chief cells

Question 21

Function of the Gastric phase?

Answer 21

Ensures sufficient secretion to handle ingested food.

Question 22

What stimulates the Gastric phase?

Answer 22

Stimuli in the stomach:
} Stretch/distension stomach wall
} Products of digestion stomach lumen
} Elevated pH

Question 23

How is the gastric phase regulated?

Answer 23

nervous and Hormonal regulation:
} Local nervous reflex
- Enteric nervous system
} External nervous reflex
- Parasympathetic nervous system
} Stimulate
- Secretion- Motility
- Gastrin secretion
¨ Further stimulation of secretion and motility

Question 24

What is the function of the Intestinal phase?

Answer 24

Control delivery to Small intestine.

Question 25

What stimulates the intestinal phase?

Answer 25

} Distension of duodenum } Arrival in duodenum of } Acid chyme } Lipids and carbohydrates

Question 26

What regulates the intestinal phase?

Answer 26

``` Nervous and hormonal regulation } Hormones - GIP, CCK, Secretin } Nerves - Enterogastric reflex } Both inhibit secretion and motility ```

Question 27

Pancreatic secretion?

Answer 27

Endocrine and exocrine organ

Question 28

What are the components of pancreatic secretion?

Answer 28

``` Enzymes ¨ Acinar cells ¨ Chemical digestion of food Alkaline fluid ¨ Duct cells ¨ Neutralise acid ¨ Optimum pH for enzymes ```

Question 29

Why are pancreatic enzymes important?

Answer 29

Most important source of digestive enzymes - work on all classes of food

Question 30

Pancreatic enzymes?

Answer 30

} Lipolytic – lipase, phospholipase } Amylytic – pancreatic amylase } Proteolytic – Trypsin, chymotrypsin, carboxypeptidase } Nucleolytic – ribonuclease, deoxyribonuclease

Question 31

What cells secrete pancreatic enzymes?

Answer 31

Acinar cells

Question 32

What stimulates the release of pancreatic enzymes by acinar cells?

Answer 32

cholecystokinin (CCK)

Question 33

What stimulates CCKL secretion)?

Answer 33

Arrival of lipids and carbohydrates in duodenum?\

Question 34

What is the function of pancreatic enzymes?

Answer 34

Luminal chemical digestion of food

Question 35

What are proteolytic enzymes?

Answer 35

Enzymes that are secreted as inactive | precursors & activated in duodenum

Question 36

proteolytic enzymes?

Answer 36

} Trypsin – trypsinogen } Chymotrypsin – chymotrypsinogen } Carboxypeptidase – procarboxypeptidase

Question 37

What does activation of proteolytic enzymes involve?

Answer 37

``` } In small intestine activation involves } Enterokinase (=enteropeptidase) } Bound to duodenal membrane } Converts trypsinogen to trypsin } Trypsin converts other enzymes to active form ```

Question 38

Describe the secretion of Alkaline (HCO3 rich) fluid?

Answer 38

Produced by duct cells in the pancreas, stimulated by hormone secretin which is stimulated by the arrival of acid chyme in the duodenum./

Question 39

Function of alkaline fluid?

Answer 39

``` } Neutralises acid chyme delivered from stomach } Creates optimum pH (6.7-9.0)for pancreatic and intestinal digestive enzyme ```

Question 40

Volume of Biliary secretion?

Answer 40

0.5L per day consisting of products associated with digestion such as bile salts and HCO3 rich fluid As well has excretory products such as waste products, bile pigments and cholesterol.

Question 41

Functions of Biliary secretions?

Answer 41

Bile Salts for fat digestion. HCO3 rich fluid to neutralise fluid. Bile Pigments for excretion.

Question 42

How are biliary secretions regulated?

Answer 42

} Initial delivery of bile under hormonal control } Hormone CCK (cholecystokinin) } Produced in response to products of digestion in duodenum } Contraction of gallbladder } Relaxation of hepatopancreatic ampulla } Hormone secretin } Mild stimulation of bile by liver

Question 43

Where is Bile secreted?

Answer 43

Secreted constantly by liver but stored and concentrated in gallbladder. The delivered to duodenum with the arrival of food.

Question 44

What stimulates bile secretions?

Answer 44

Bile stimulates it's own secretion - } Enterohepatic circulation

Question 45

What is } Enterohepatic circulation?

Answer 45

``` Bile metabolically expensive to produce 95% reabsorbed in ileum Transported back to liver in enterohepatic circulation Reabsorbed and secreted Stimulation of bile secretion ```

Question 46

What is secreted by the small intestine?

Answer 46

``` 1.5L per day: Mucus Isosmotic fluid (Alkaline - mixture of NaCl and NaHCO3) Digestive enzymes ```

Question 47

zFunction of Isosmotic fluid secretions in the small intestine?

Answer 47

Neutralise food and dilute food to aid digestion.

Question 48

Function of digestive enzymes in the small intestine.

Answer 48

Shed cells.