Digestion

Question 1

Enzyme

Answer 1

protein catalyst that increases the rate at which a chemical reaction occurs without permanently changing the enzyme
> active site on enzyme can only bind to a specific reactant

Question 2

Anatomy of Digestive system

Answer 2

Comprised of digestive tract and accessory organs (salivary glands, pancreas etc.; secrete enzymes)

• Oral cavity - salivary glands
• Pharynx
• Oesophagus
• Stomach - churned into chyme
• Small intestine (duodenum, ileum, jejunum)
  
  • Liver, gall bladder, pancreas are accessory organs
• Large intestine (cecum, colon, rectum, anal canal)

Question 3

Functions of the digestive system

Answer 3

• Ingestion
• Mastication - mechanically increasing surface area to facilitate chemical digestion
• Secretion - enzymes; lubricate, liquefy, digest
• Absorption - movement of nutrients from small intestine to blood supply
• Elimination - removal of waste

Question 4

Histology of digestive tract

Answer 4

• Mucosa - innermost layer, secretes mucous; epithelial layer
• Submucosa - connective tissue, contains blood vessels and nerves
• Muscularis - 2/3 smooth muscle layers; movement (peristalsis), secretion
• Serosa/Adventitia - connective tissue, stability; attached to body wall/other organs

Question 5

Pertioneum

Answer 5

Serous membrane in abdominopelvic cavity
> Visceral peritoneum - covers organs
> Parietal peritoneum - covers interior surface of body wall

Question 6

Mesenteries

Answer 6

• peritoneum which connects organs together

> vessels and nerves pass from body walls to organs - surrounded by fatty tissue for protection

Question 7

Greater omentum

Answer 7

connects stomach to transverse colon

Question 8

Lesser omentum

Answer 8

liver to diaphragm

Question 9

Oral cavity

Answer 9

Chewing, mastication

> masticate food into bolus

Question 10

Teeth

Answer 10

Molars (12) - grinding
Premolars (8) - “
Canines (4) - tearing
Incisors (8) - cutting
> salivary glands - produce and secrete saliva; protect, moisten, lubricate, digests
amylase - breaks down carbs into smaller sugars
lysosomes - antibacterial

Question 11

Pharynx

Answer 11

connects oral cavity to oesophagus

> uvula (soft palate) prevents food/drink entering nasopharynx

Question 12

Oesophagus

Answer 12

connects pharynx to stomach; 25cm, posterior to the trachea

> epiglottis stops food entering the trachea

Question 13

Swallowing

Answer 13

Voluntary phase:
Tongue pushes bolus toward the back of the oral cavity to pharynx

Pharyngeal phase:
Uvula closes off nasopharynx.
Bolus touches receptors on oropharynx and swallowing reflexes moves bolus down pharynx into oesophagus.
Epiglottis covers trachea

Oesophageal phase:
Bolus is moved down oesophagus towards stomach by peristalsis

Question 14

Peristalsis

Answer 14

Process by which food moves through the gut; waves of smooth muscle relaxations and contractions

Question 15

Stomach

Answer 15

Holding point for food - enters through gastroesophageal opening
Food comes from oesophagus and its churned into chyme
- enters through gastroesophageal opening - cardiac - fundus - body - pyloric; antrum and canal

Question 16

Stomach - enzymes

Answer 16

Produces mucous, hydrochloric acid, pepsin
Contains a thick mucous layer that lubricates and protects epithelial cells on stomach wall from acid (pH level of 2-3 due to HCl)

Question 17

Wall of the stomach

Answer 17

visceral peritoneum/serosa
 muscularis
    - Outer longitudinal
    - Middle circular
    - Inner oblique
submucosa
mucosa
Ruggae - folds in the stomach wall; allows stomach to stretch, increased surface area - holds up to 2L

Question 18

Movements of the stomach

Answer 18

3 layers enable churning of food into chyme
combination of mixing waves (80%) and peristaltic waves (20%) - moving towards small intestine
both oesophageal and pyloric sphincters are closed
empties every 4hrs (6-8 fatty meal) into duodenum

Question 19

Small Intestine

Answer 19

~6m, small diametre
Large SA for efficient nutrient absorption
> duodenum - first 25m after pyloric sphincter
> jejunum - 2.5m
> ileum - 3.5m

Question 20

Duodenum

Answer 20

Chyme mixes various digestive enzymes
Liver/gall bladder - bile enters via common bile duct, emulsifies fats
Pancreas - enzymes enter via pancreatic duct
- Lipase - breakdown lipids (emulsification)
- Pancreatic amylase - breakdown carbs
- Trypsin - breakdown proteins

Question 21

Duodenum - structures that increase SA

Answer 21

• Plicae circulares - circular folds in the wall of the small intestine
• Villi - folds of the mucosa containing capillaries and lacteals
  (lipids absorbed by lacteals, into lymph)
  (carbs and proteins absorbed by capillaries, into blood)
• Microvilli - small folds on epithelial cell surface

Question 22

Liver

Answer 22

Makes bile ~100mL/day; stores excess glucose as glycogen; detoxification

Question 23

Gall Bladder

Answer 23

Stores concentrated bile

Question 24

Pancreas

Answer 24

Produces digestive enzymes; sugar homeostasis

Question 25

Large Intestine

Answer 25

Absorption of water
Extends from ileocecal junction to anus
> Cecum, colon (ascending, decending, transverse), sigmoid colon, anal canal
Bacteria and microbes synthesis (vitamin b and k)
- 18-24hrs chyme - facaes
- 1500ml chyme enter, 90% water absorbed ~ 80-150mL faeces

Question 26

Digestion

Answer 26

breakdown of molecules for absorption into circulation

• mechanical - large to small
• chemical - breaking covalent bonds by digestive enzymes