Digestion & Absorption Flashcards
Digestive system key features/
- One long tube
- Mucosa
- Secretion & absorption
- Muscle
6 process of digestive system
- Ingestion
- Secretion
- Motility
- Digestion
- Absorption
- Defaecation
Digestive system organs
- Mouth
- Salivary glands
- Stomach
- Pancreas
- Gall bladder
- Liver
- Small intestine
- Large intestine
Oral cavity
- Mouth & pharynx
- Mastication (chewing)
- Voluntary & involuntary
- Teeth (mechanical digestion)
- Saliva (enzymes)
- Tongue (mix, swallow)
- Deglutition
Saliva
- 3 glands provide 95% (1L per day)
- is mainly water, electrolytes, proteins (immunoglobin A, lysozyme), enzymes (amylase, lipase), lubrication
Salivary gland secretion function
- Acinar (mucous cells) secretion isotonic with plasma - cells in the gland ducts actively reabsorb Na+ & Cl- & secrete some k+ & hco3- (alkaline = protection from acidic food) - duct is impermeable to water - Hypotonic salvia for lubricant
3 stages of swallowing
- Buccal phase (bolus to back of throat)
- Pharyngeal phase (bolus enters oesophagus, respiratory pathway closed)
- Oesophageal phase (bolus moves down the oesophagus by peristalsis)
Oesophagus structure & role
- mucosa, submucosa, 2 layers of muscle, circular then longitudinal
- move food from mouth to stomach 4-8s (by peristalsis = circular muscle contracts longitudinal relaxes in progressive reoccurring wave
Oesophageal sphincter (role)
- sphincter at the top of the stomach controlling what enters
- closes when stomach is mixing to prevent acid reflux
Stomach structure (4 Parts)
Cardia - connected to stomach at the top
Fundus - above to the left of cardia, main storage
Body - mixing
Pylorus - connects to duodenum controls flow to small intestine
- can hold 6L
3 functions of the stomach
- a reservoir
- create chyme (acidic paste like soup) w/ gastric juice ( 3 waves a min)
- regulating emptying of stomach
Absorption in stomach
- some water & alcohol absorbed here
- order of foods leading stomach: carbs, proteins, lipids
Secretion in stomach
Pepsinogen - chief cells Lipases - chief cells Intrinsic factor from parietal cells HCL from parietal cells ions mucus (mucous cells) (HCL activates pepsinogen)
mucus cells in stomach
they release mucus & bicarbonate ions (prevents damage from acidic environment)
3 phase of gastric secretion - Cephalic phase
Cephalic phase - 30% of response (happens before food arrives from taste & smell = gastrin = gastric juice secretion)
3 phase of gastric secretion - Gastric phase
Gastric phase - 60% response, ^ gastric juice, protein digestion
3 phase of gastric secretion - Intestinal phase
Intestinal phase - chyme entering duodenum, remove peptide fragements, decrease ph (duodenum distends = hormone release)
3 accessory organs -
- Pancreas, liver, gallballder
Pancreas role
- Endocrine cells produce hormones
- Exocrine cells release digestive juice(caused by CCK+) - neutralises acids and stops pepsin
- Enzymes - 50% CHO, 50% pro, 80-90% fat
Liver role
- Portal vein brings blood from digestive tract to pancreas/liver
- Bile production
- Metabolism (glucose/glycogen)
- Processes drugs & hormones (detoxification)
Pancreas role (bile)
- Stores & concentrates bile (release stimulated by secretin & CCK)
- 90% bile salts reabsorbed & recycled
- Organ can be removed = 40% less lipids absorbed
Small intestine role, structure
- 3 parts - site of digestion & absorption
- Mucosal lining
- 2 layers of muscle
Small intestine adaptations
- Large SA
- Villi, microvilli maximises absorption
- Replaced 2-5 days
Small intestine peristalsis
- circular & longitudinal muscle can move food over short distances
- Segmentation helps with mixing with pancreatic secretions
- pacemaker cells keep bolus moving
- intrinsic enteric NS (myogenic) detects stretch =
^ contractions
Large intestine role, structure
- Ileocecal sphincter (ileum to cecum)
- reabsorb water
- store faeces
- bacterial fermentation
- mass movement only 2-3 times a day
- chyme here for 3-10 hours
Timings of the whole system
Mouth -> stomach = 10 seconds
stomach = 2-4 hours
intestine = 3-10 hours
total = 24-72 hours
Carbohydrate enzymes
- Complex carbs digested (poly, tri, disaccharides must be hydrolysed to mono)
- enzymes = glycosidases or carbohydrase’s
Carb digestion
- starts in mouth but most done in SI w/ pancreatic alpha amylase
- mechanical & some chemical breakdown in mouth, none in stomach (acid)
- lots in duodenum w/ debranching enzymes
Carb absorption
- Glucose & galactose facilitated with sodium through SGLT1 (sodium pumped into lumen to maintain gradient)
- Fructose though glut 5 into intestinal wall
- all 3 through GLUT 2 into blood (travels to liver)
Protein digestion - stomach
- HCL (from parietal cells) helps break down structure
- Primary protease = Pepsin (active in stomach from inactive form - pepsinogen)
- produces tripeptides
protein digestion - SI
- Pancreas secretes proteases (trypsin - also an activator)
- enzymes also breakdown the gut lining for replacement
- produces dipeptides & peptides
Endo & exopeptidases
Endo - interior bonds
Exo - exterior bonds
Protein absorption
- Amino acids absorbed into capillary by sodium co transport or via diffusion
- further breakdown will occur in the epithelial cell if required
Fat digestion locations
mouth - lingual lipase (from serous gland)
stomach - 10-30% from gastric lipase
Duodenum - lipases, bile salts (CCK), bicarbonate
- Triglycerides broken into monoglycerides & fatty acids
Fat digestion - Bile salts
- Fats are hydrophobic
- bile salts emulsifies fats -increases SA
Enzymes - esterase’s, lipase, phospholipase, cholesterol esterase break down the triglycerides, phospholipids, sterols
Fat absorption - short chains
- short chain fatty acids (SCFA) diffuse into portal vein to bind with albumin
Fat absorption - longer chains
- Packaged into micelles which are absorbed into epithelial wall
- packaged back into triglycerides (w/ fatty acids) and then into chylomicrons (/w Golgi body proteins)
- Chylomicrons drain into the lacteal & are transported away
Alcohol
in stomach alcohol dehydrogenase produces acetaldehyde (less intoxicating)
- food longer in stomach (eg because of a fatty meals) = less intoxicating because less alcohol in blood
Vitamin absorption
- Fat soluble - A,D,E,K follow fats to lymph system
- Water soluble diffuse straight across or actively transport depending on concentration
Water absorption
8 litres absorbed a day 6 litres secreted into GI tract 90% in SI 10% in LI water follows osmotic gradient (hypotonic = ^ absorption) Failure to absorb = diarrhoea
