Digestion Flashcards
Enzyme
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
Anatomy of Digestive system
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)
Functions of the digestive system
- 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
Histology of digestive tract
- 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
Pertioneum
Serous membrane in abdominopelvic cavity
> Visceral peritoneum - covers organs
> Parietal peritoneum - covers interior surface of body wall
Mesenteries
- peritoneum which connects organs together
> vessels and nerves pass from body walls to organs - surrounded by fatty tissue for protection
Greater omentum
connects stomach to transverse colon
Lesser omentum
liver to diaphragm
Oral cavity
Chewing, mastication
> masticate food into bolus
Teeth
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
Pharynx
connects oral cavity to oesophagus
> uvula (soft palate) prevents food/drink entering nasopharynx
Oesophagus
connects pharynx to stomach; 25cm, posterior to the trachea
> epiglottis stops food entering the trachea
Swallowing
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
Peristalsis
Process by which food moves through the gut; waves of smooth muscle relaxations and contractions
Stomach
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
Stomach - enzymes
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)
Wall of the stomach
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 2LMovements of the stomach
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
Small Intestine
~6m, small diametre
Large SA for efficient nutrient absorption
> duodenum - first 25m after pyloric sphincter
> jejunum - 2.5m
> ileum - 3.5m
Duodenum
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
Duodenum - structures that increase SA
- 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
Liver
Makes bile ~100mL/day; stores excess glucose as glycogen; detoxification
Gall Bladder
Stores concentrated bile
Pancreas
Produces digestive enzymes; sugar homeostasis
Large Intestine
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
Digestion
breakdown of molecules for absorption into circulation
- mechanical - large to small
- chemical - breaking covalent bonds by digestive enzymes
