Lecture 33

Question 1

Oral phase

Answer 1

• under autonomic control (mostly parasympathetic)
• solubilization of material for taste
• lubrication and moistening of food

In mouth:
Mechanical digestion of everything begins in mouth through chewing

Carbohydrates in the mouth:
Chemical digestion of carbohydrates begins in mouth because of salivary amylase
Mechanical digestion because chewing up food

Lipids in mouth:
Chemical digestion of lipids also begins in mouth but it’s a small component because lingual lipase (minor contributor to chemical fat digestion)

Antibacterial actions:
- lysozyme will break down anything that shouldn’t be there
- Immunoglobulins are antibodies

Question 2

The swallowing reflux

Answer 2

1. It is triggered when tongue pushes bolus against soft palate and back of the mouth because there are stretch receptors which sense this
2. The epiglottis will then fold down over the trachea to help keep swallowed material out of airways. The upper esophageal sphincter relaxes when swallowing to allow food to enter esophagus
3. Food moves down esophagus through peristalsis contractions and lower esophageal sphincter relaxes

Question 3

The gastric phase

Answer 3

• mechanical digestion through peristaltic contractions slamming food in stomach wall and breaking it up into bits and pieces
• chemical digestion are secretions
• once bolus enters the stomach it is referred to as chyme
• stomach is an acidic environment (pH=2) that destroys pathogens and destroys epithelial lining of stomach so mucous cells will secrete mucous to cover innermost layer of stomach and bicarbonate to neutralize acidic contents that come in contact with wall
• storage: release of chyme into SI is regulated by ENS

Question 4

The mucous-bicarbonate Barrier

Answer 4

Is a physical and chemical barrier that protects against acid and damage

Question 5

Protein digestion in stomach

Answer 5

• mechanical digestion by peristaltic mixing/churning
• main food that is being chemically digesting in stomach is protein
• pepsinogen is an inactive protease that is secreted by chief cells of gastric glands and is activated at low pH to pepsin
• protein is denatured by acid, but pepsin begins protein digestion by cleaving specific peptide bonds of polypeptides
• protein product entering SI are short/long polypeptides and some free amino acids

Question 6

Lipid digestion in the stomach

Answer 6

• minor chemical digestion happening here through gastric lipase hydrolyzing triglycerides into monoglycerides and some free fatty acids
• majority of fat digestion happening in the stomach is mechanical digestion through course emulsification due to stomach contractions. It forms an emulsion of lipids and gastric lipase to get big droplets because large fat droplets are suspended in chyme

Question 7

Carbohydrate digestion in stomach

Answer 7

• on hold because salivary amylase is denatured because of low pH in stomach
• mechanical digestion due to peristaltic contractions (mixing and churning)

Question 8

Secretions into the lumen of the stomach: mucous and bicarbonate

Answer 8

Cell type: mucous cells
Function 1: provide a physical barrier between lumen and epithelium
Function 2: neutralize gastric acid that comes in contacts with stomach wall to prevent damage

Question 9

Secretions into the lumen of the stomach: gastric acid

Answer 9

Cell type: parietal cell
Function: activate pepsin, denture protein, destroy pathogens

Question 10

Secretions into the lumen of the stomach: pepsin(ogen) and gastric lipase

Answer 10

Cell type: chief cells
Function 1: major contributor to chemical protein digestion in stomach
Function 2: minor contributor to chemical fat digestion in stomach

Question 11

The small intestine

Answer 11

1. Regulation of gastric emptying
   - chyme in the small intestine triggers feedback to regulate further release from the stomach
2. Secretions into the duodenum of the small intestine
   - Epithelial cells: mucous (all the way along your GI tract to keep things lubricated, digestive (brush boarder) enzymes (break things down into absorbable bits)
   - Pancreas: HCO3- (neutralize chyme as it enters SI and to allow pancreatic enzymes to work), digestive enzymes (course, continues chemical digestion in SI)
   - Liver and gallbladder: bile (break things down into almost absorbable bits
3. Digestion of fats, carbohydrates and lipids
   - mechanical digestion is mostly done
   - chemical digestion through all these enzymes that are being dumped into SI and segmental contractions that are mixing contents of the SI with enzymes that are being dumped in
4. Absorption
   - free amino acids, sugars, free fatty acids, nutrients, vitamins

Question 12

Enterocytes

Answer 12

• microvilli increase surface area and have brush border that have a bunch of transporters for absorption
• digestive enzymes on the brush border

Question 13

Crypt epithelial cell

Answer 13

Secrete water, ions and hormones

Question 14

Goblet cell

Answer 14

Secrete mucous for protection and lubrication

Question 15

Capillaries

Answer 15

Transport absorbed nutrients

Question 16

Lacteals

Answer 16

Transport absorbed fats via lymphatic system

Question 17

The exocrine pancreas

Answer 17

• secretions that are destined to leave the body
• there are two type of cells here acinar cells and duct cell
• acinar cells make enzymes to chemically digest protein, carbohydrates and lipids (proteases, amylases and lipases)
• duct cells make bicarbonate to neutralize chyme that comes from stomach and continue chemical digestion of whatever is in there

Question 18

Biliary secretions

Answer 18

• bile is amphipathic which helps suspend lipids in a solution
• bile is produced in the liver
• stored and concentrated in the gallbladder

Question 19

How are carbohydrates absorbed

Answer 19

• as monosaccharides
• glucose, fructose, galactose

Question 20

Carbohydrate digestion in small intestine

Answer 20

• most digestion occurs here for carbohydrates
• continued mechanical digestion through segmental contractions by mixing and mashing
• chemical digestion through pancreatic amylase secreted into the lumen of the duodenum breaking down carbs to tri/disaccharides
• brush border enzymes on the apical surface of epithelial cells of the duodenum further break carbs down into single sugars

Question 21

Example of brush border enzymes

Answer 21

Maltase, sucrase and lactase

Question 22

Course enzymes

Answer 22

• pancreatic amylase

Question 23

Fine enzyme

Answer 23

• maltase
• sucrase
• lactase

Question 24

Protein digestion in small intestine

Answer 24

• mechanical digestion through segmental contraction that’s mix and mash back and forth
• chemical digestion through cleavage by endo- and exopeptidase
• trypsin, chymotrypsin, carboxypeptidase
• Product : di and tri peptides and free amino acids

Question 25

Endopeptidases

Answer 25

Cleave internal peptide bonds

Question 26

Exopeptidases

Answer 26

Cleave terminal (at C or N) peptide bonds

Question 27

Brush border enzyme for protein

Answer 27

Aminopeptidase

Question 28

What are the functions of fats

Answer 28

- provide high density source of energy and reserve - form hormones - are a part of cell membranes - provide insulation and shock absorption - transport fat soluble vitamins and other compounds

Question 29

Majority of fats are stored as

Answer 29

Triglycerides

Question 30

Lipid digestion in small intestine

Answer 30

- major chemical digestion through pancreatic lipase because fat droplets are small enough for pancreatic lipase to come in and do its job - mechanical digestion by bile salts through the process of fine emulsification which increases SA and eventually forms a micellar solution. Which are composed of teeny tiny fat droplets due to mixing of bile salts, pancreatic amylase and chyme through segmental contractions with teeny tiny droplets now we can get the break down of triglycerides into free fatty acids that can be absorbed by pancreatic lipase and colipase

Question 31

What is needed when micelles are brought near enterocytes

Answer 31

Nothing they are hydrophobic so they will pass without the help of need of transporters

Question 32

Fat absorption

Answer 32

- bile salts help with fine emulsification and coat fat droplets - pancreatic lipase and co lipase break down fats into monoglycerides and fatty acids stored in micelles - monoglycerides and fatty acids move out of micelles and are absorbed across the apical membrane of enterocytes - cholesterol is transported into cell and combine with absorbed fats and proteins to form chylomicrons - chylomicron will enter lacteal and be removed by lymphatic system

Question 33

The large intestinal phase

Answer 33

- 1.4L/day of unabsorbed liquid enters the large intestine

Question 34

Functions of small intestine

Answer 34

- fine tuning of water and salts, so further absorption of water and electrolytes - supports and environment that facilitates colonization by healthy bacteria - bacteria digests fibers (cellulose) and then we absorb them - storage of waste in rectum till it can be eliminated

Question 35

Colonic microflora

Answer 35

- digest fiber - produce vitamin k (50% of total need) - limit growth or invasion of pathogens

Question 36

Defecation composed of

Answer 36

- undigestible material, dead bacteria and epithelial cells, biliary metabolites and H2O

Question 37

What is it called when you have presence of fats in fecal matter

Answer 37

Steatorrhea

Question 38

Where along the way could there be a problem if there is a presence of nutrient along the way

Answer 38

- could be a problem with liver and bile synthesis - could be a problem with gallbladder of bile concentration or release - could be lack of brush boarder enzymes - lack of transporters