Chapter 4 - Human Digestion and Absorption

Question 1

Types of Tissues in the body

Answer 1

• Epithelial: skin and linings of GI tract which absorb, secrete, cover and protect underlying tissues
  
  • Connective: supports, protects and holds the body
  • Muscle: contract and relax and permits movements
    
    • Nervous: transmit nerve impulses

Question 2

Roles of GI tract

Answer 2

• Digestion of food
  
  • Absorption of nutrients
  • Excretion of wastes
  • Aids with immunology
    
    • Houses bacteria

Question 3

GI Tract/Alimentary Canal flow

Answer 3

1. Mouth and salivary glands
   
   2. Esophagus
   3. Stomach
   4. Pancreas
   5. Liver
   6. Gall bladder
   7. Small Intestine
   8. Large intestine
   9. Rectum
      
      10. Anus

Question 4

Layers of GI Tract

Answer 4

• Mucosa: the innermost layer lined with epithelial cells and glands
  ○ Lined with lumen: tiny, fingerlike structures which increases the surface area of the mucosa
  
  • Submucosa: second deepest layer consisting of loose connective tissues, glands, blood vessels and nerves
    ○ Blood vessels carry nutrients and substances from GI tract
  • Muscle: a double layer with an inner layer of smooth circular muscles which encircle the tube and an outer layer of longitudinal muscle fibers
    ○ Both muscle layers help move food through the tube
    
    • Serosa: the outer layer which protects the tract, and secretes serous fluid to cushion and reduce friction as it moves

Question 5

Sphincters of GI Tract

Answer 5

• Lower esophageal sphincter: prevents backflow(reflux) of the stomach contents into the esophagus
  
  • Pyloric Sphincter: controls flow of stomach contents into the small intestine
  • Hepatopancreatic sphincter: controls flow of bile, pancreatic juices from common bile and pancreatic ducts into the small intestine
  • Ileocecal valve: prevents contents from large intestine reentering small intestine
    
    • Anal sphincters: prevents defecation until a person desires too

Question 6

Peristalsis

Answer 6

moves food down the GI tract in a coordinated wave of muscular contractions of the two muscle layers of the GI tract wall
○ Most frequent peristalsis contractions occur in the small intestine(every 3-4 secs)
○ Large intestine only has peristalsis contracts 2-3 times per day normally after meals which lead to mass movements of fecal matter

Question 7

Segmentation

Answer 7

occurs in the small intestine where contents are broken apart and mixed with digestive juices

Question 8

Digestive Enzymes

Answer 8

• Enzymes which break down macronutrients through hydrolysis reactions
  
  • Produced in the salivary gland, pancreases, stomach and small intestine
  • Pancreas adjusts its enzyme production to match the macronutrient content of the diet
    
    • Food not completely digested will be converted by bacteria in LI into gases and acids which can bloat the abdomen

Question 9

Secretions alongside Digestive Enzymes within the GI tract

Answer 9

• Saliva from salivary glands
  
  • Mucus produced along entire tract
  • HCI from stomach
  • Bicarbonate from pancreas
  • digestive enzymes from pancreas
  • Bile from liver
• Hormones

Question 10

Where Digestion Begins

Answer 10

as we cook
○ Dicing, pounding, marinating and heating
○ E.g. starch granules in food swell as they soak up water during cooking making it easier to digest

Question 11

Bolus

Answer 11

mass of food that is swallowed

Question 12

Stage of Digestion: Mouth

Answer 12

• Teeth grind and tear solid food
  
  • The tongue presses morsels of food against hard palate and helps mix the food with saliva
    • Food bolus drops onto epiglottis, preventing it from going down the trachea and instead the esophagus relaxes and opens

Question 13

Taste and Smell

Answer 13

• We have taste buds on the papillae of our tongue and soft palate which detect compounds in food
  
  • 80% of taste is due to smell
  • Due to 6 million olfactory cells in the nose which are stimulated when we chew

Question 14

5 basic tastes

Answer 14

5 basic tastes of the tongue:
- Sweet
- Salty
- Sour
- Bitter
- Umami: savory, brothy or meaty taste from amino acids
e.g. MSG, parmesan cheese

Question 15

Stages of Digestion: Stomach

Answer 15

• Entry of food is through the lower esophageal sphincter
  
  • 3 muscle layers mix the food in the stomach with the gastric juices
  • Mixing transforms food into chyme: a soupy acidic mixture
• GDIP and pyloric sphincter then slowly releases chyme into the SI

Question 16

Gastric Juices in Stomach

Answer 16

○ HCI
○ Gastric lipase
○ Pepsinogen
- Mucus(coats lining of the stomach which protects it from self-digestion)

Question 17

Stage in Digestion: Small Intestine

Answer 17

• enters into duodenum, then jejunum and finally ileum
• lined with microvilli and Vili which increase its surface area 600 times over which contributes to its efficiency in absorbing nutrients
  
  • The circular folds, which is the mucus membrane folding over and over again forces the chyme to flow slowly in a spiral motion, completely mixing the chyme with digestive juices and bringing it into contact with villi.

Question 18

What are Villi Lined with to increased absorption of Nutrients

Answer 18

○ Goblet cells: secrete mucus
○ Endocrine cells: produce hormones and hormone like substances
○ Cells which produce digestive enzymes
- Enterocytes: Cells which absorb nutrients

Question 19

Accessory Organs

Answer 19

• Involves the Liver, Gallblader and Pancreas
• they work to help SI digest but do not physically get involved
  
  • Secretions from these organs are delivered through the common bile duct and the pancreatic duct which come together at the hepatopancreatic sphincter and empty into the Duodenum

Question 20

Accessory Organs: Liver

Answer 20

• Liver produces bile which contains cholesterol and aids in fat digestion and absorption
  Bile breaks the large fat globules into micelles; tiny fat droplets suspended in watery chyme

Question 21

Accessory Organs: Gallbladder

Answer 21

• Bile is stored in the Gallbladder
  - Once released into the duodenum it is reabsorbed in the ileum and returned to the liver for recycling; Enterohepatic circulation
  - this process allows the release of cholesterol from the body as not all is released, and some is excreted

Question 22

Accessory Organs: pancreas

Answer 22

produces an alkalinic juice with a mix of sodium bicarbonate(NaHCO3) and enzymes
○ Neutralizes acidic chyme which protects the SI from damage
○ Digestive enzymes include:
§ Pancreatic amylase(starch)
§ Pancreatic lipase(fat)
§ Several proteases(protein)

Question 23

Hormones responsible for regulation of Digestive System: Ghrelin

Answer 23

Released by:
- Stomach before/during eating

Function:
- Increases appetite and food intake

Question 24

Hormones responsible for regulation of digestive system: Gastrin

Answer 24

released by:
- stomach and duodenum when food reaches stomach

Function:
- triggers the release of HCI and pepsinogen
- stimulates gastric and intestinal motility

Question 25

Hormones responsible for regulation of digestive system: CCK

Answer 25

released by: - SI in response to presence of fat function: - Stimulates release of pancreatic enzymes and bile

Question 26

Hormones responsible for regulation of digestive system: Secretin

Answer 26

Released by: - SI as digestion progresses or in response to acidic chyme Function: - Stimulates release of pancreatic bicarbonate

Question 27

Hormones responsible for regulation of digestive system: Somatostatin

Answer 27

Released by: - Stomach, SI and Pancreas Function: - Inhibits release of GI hormones - Slows Gastric emptying, GI motility and blood flow to the Intestine

Question 28

Method of Absorption for nutrients in the SI

Answer 28

○ Passive diffusion(fats, water and some minerals) ○ Facilitated diffusion(fructose) ○ Active absorption(amino acids, glucose) - Phagocytosis/pinocytosis(large protein particles like immune substances in breast milk)

Question 29

Stage in Digestion: transport of Nutrients: cardiovascular system

Answer 29

- Moves water soluble nutrients such as: ○ Proteins ○ Carbs ○ B-vitamins ○ Vitamin C ○ Short and medium fatty acids - are absorbed straight into the bloodstream in the capillary found in villi - This blood flows into the hepatic portal vein system: veins leaving the stomach, intestines, spleen and pancreas which flow into the liver - The liver metabolizes or stores a portion of the absorbed nutrients, and the ones not stored re-enter general circulation

Question 30

Stages in Digestion: Transport of Substances: Lymphatic System

Answer 30

- Provides an alternative route into the bloodstream for large and fat soluble molecules: ○ Most fats ○ Vitamin A, D, E, K ○ Some proteins - Lacteals: special lympahtic vessels in the villi transport nutrients to larger lymphatic vessels connected to the thoracid duct - This extends from the abdomen to the neck and connects to the bloodstream at the left subclavian vein - Here they are now transported around as normal

Question 31

Stages of Digestion: Large Intestine

Answer 31

- When chyme reaches the LI, only water, some minerals and undigested food fibers are remaining - Electrolytes such as sodium, potassium and teh rest of water are absorbed by the LI in the first half - housed gut microbiota metabolize complex carbs and synthesize vitamins

Question 32

Stages of Digestion: Elimination of Feces

Answer 32

- After 12-24 hours of food travelling to get to the end of the LI, the food is in a semi solid mass - Peristaltic waves, normally the greatest following meals, push it into the rectum - This stimulates muscular reflexes in the sigmoid colon and rectum as well as relaxation of internal and external anal sphincters ○ External anal sphincter is under voluntary control

Question 33

Sections of Large Intestine

Answer 33

○ Colon § Cecum § Ascending Colon § Transverse Colon § Descending Colon § Sigmoid Colon ○ Rectum Anus

Question 34

Dysbiosis

Answer 34

the disruption between levels of beneficial and pathogenic bacteria leading to GI infections such as vomiting, cramping, diarrhea and dehydration

Question 35

Probiotics

Answer 35

live microorganisms that colonize the LI and provide health benefits Found in fermented foods

Question 36

Prebiotics

Answer 36

nondigestible food ingredients that promote growth of beneficial bacteria - E.g. inulin, a carb known as fructan which is found in wheat, onions, garlic, asparagus and bananas - E.g. resistant starch, isnt affected by digestive enzymes, meaning the bacteria in the LI can ferment it