24. Digestive System Flashcards
Are 2 anatomical subdivisions of the digestive system
Gastrointestinal Tract (GIT) includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine
Accessory Digestive Organs
includes the teeth, tongue, salivary glands, liver, gall bladder, pancreas
digestive system Involves 6 essential functions:
Ingestion Secretion Mixing and propulsion Digestion – mechanical/chemical Absorption Defecation
Histology of 4 layers
- Mucosa (lines the lumen)
• epithelium + areolar CT + thin layer of smooth muscle - Submucosa
• areolar CT
• containing blood vessels, lymph vessels, nerves and glands - Muscularis
• two layers of smooth muscle – inner circular fibers and outer longitudinal fibers - Serosa (outermost)
• visceral peritoneum – areolar CT + simple squamous cells
Define • Parietal peritoneum: • Visceral peritoneum: • mesentary: • greater omentum: • lesser omentum: • falciform ligament: • mesocolon:
- Parietal peritoneum: lines the abdominopelvic cavity
- Visceral peritoneum: covers some organs
- mesentary: suspends small intestine from posterior body wall
- greater omentum: extends from greater curvature of stomach and drapes over intestines
- lesser omentum: extends from lesser curvature of stomach to the liver
- falciform ligament: attaches liver to anterior body wall and diaphragm
- mesocolon: suspends large intestine from posterior body wall
Mouth
- formed by
- epithilium type
- Formed by the lips, cheeks, hard and soft palates and tongue
- nonkeratinized stratified squamous epithelium
Salivary glands
• produce and secrete saliva into mouth – parotid, sublingual and submandibular glands
• SALIVA - dissolves some ingested material for taste identification
> contains mucus to lubricate and form bolus
> contains salivary amylase that starts breakdown of starch → sugar
> contains lysozyme (antibacterial)
Fancy word for swallowing & what happens during it
deglutition
1) Tongue pushes food against hard palate
2) Bolus is forced into oropharynx
3) Receptors are stimulated that initiate swallowing reflex in medulla and pons
4) Soft palate and uvula rise and close off nasopharynx
5) Larynx elevates and epiglottis covers glottis and food/liquid passes through upper esophageal sphincter
6) Peristaltic contractions propel bolus down
7) Lower esophageal sphincter opens
Esophagus
-how does food pass?
• Muscular tube lined with nonkeratinized stratified squamous epithelium (25-30 cm long)
• Alternating waves of contraction and relaxation of the muscularis propel bolus to stomach (peristalsis)
> Above bolus: circular muscle fibers contract constrict
> Below bolus: longitudinal fibers contract to shoten/expand
4 regions of stomach
cardia, fundus, body and pylorus
Stomach overview
• food holding area
> empty: volume is 50ml
> capacity: 1.5-2.5 L
> very distended: 4L
• Mucosa: simple columnar epithelium, when emply forms folds (rugae)
• Muscularis has 3 layers (added inner oblique) allows the stomach to compress, knead and twist
Cell Types in Stomach
1) mucus neck cell – produce mucus
2) parietal cells – produce HCl & intrinsic factor for vitamin B12 absorption
3) chief cells – produce pepsinogen
4) enteroendocrine cells – G cells secrete gastrin
Stomach Function
- Serves as a storage and mixing chamber (mechanical digestion)
- PROTEIN DIGESTION BEGINS IN THE STOMACH (pepsin activated by HCL)
- Absorb some water, ions, alcohol, drugs (aspirin)
- Periodically about 3 ml of chyme is forced through pyloric sphincter into duodenum with a mixing wave
Small intestine:
- epithilim
- 3 things to increase absorption
- a simple columnar epithelium
- villi in mucosa
- microvilli, extensions of epithelial cells – form a “brush border”
- plicae circulares, permanent folds of the mucosa and submucosa
Small intestine Mucosa cell types - 5
1) Absorptive Cells – absorb and digest nutrients
2) Goblet Cells – produce mucus
3) Secretory Cells – secrete alkaline intestinal juice (water & mucus; NO enzymes)
4) Paneth Cells – secrete lysozyme
5) Enteroendocrine Cells – S cells secrete the hormone secretin; CCK cells secrete the hormone cholecystokinin
Functions of the Small Intestine
- FAT DIGESTION BEGINS HERE!!
- mechanical digestion occurs
- segmentation mixes chyme with intestinal juice, pancreatic juice and bile
- completes carbohydrate, protein and lipid digestion
Pancrease endocrine gland sectetion pathway
secrete pancreatic juice into small ducts → pancreatic duct → hepatopancreatic ampulla → duodenum
What’s pancreatic Juice composed of?
mostly water
some salts
sodium bicarbonate
digestive enzymes
Regulation of pancreatic secretion:
• PNS stimulates pancreatic secretion when stomach is active
• amino acids/fatty acids entering duodenum stimulate small intestine enteroendocrine cells to produce hormones CCK and secretin
> cholecystokinin secreted in response to fatty-protein chyme
> secretin secreted in response to acidic chyme
BOTH CCK & secretin: ↓ gastric gland activity ↓ stomach motility ↓ stomach emptying Want TIME to process food in small intestine before the stomach empties further!
Liver Function
• what does it store
• what does it synthesis
• produce
- Stores: glycogen + triglyceride + vitamins A, B12, D, E, K + iron & copper
- Synthesis: protein + lipoprotein (LDL, HDL) + glucose + urea
- detoxification of drugs and other toxins
- produces bile
Bile
- what does it comtain
- how does it leave the liver?
Contains • NO enzymes • mostly water + several ions • bile pigments (main pigment is bilirubin) • cholesterol • bile salts (emulsify lipids)
Bile is continuously produced, draining into bile ducts, leaving the liver in the common hepatic duct
emulsification:
breakdown of large lipids into a suspension of small lipid globules
Gall Bladder
-pathway of release
Function: stores and concentrates bile
releases bile when needed into cystic duct → common bile duct → hepato-pancreatic ampulla → duodenum
Regulation of bile secretion:
- PNS stimulates liver to increase bile production after a meal
- CCK stimulates gallbladder to contract and bile enters duodenum
- secretin stimulates liver to produce bile rich in bicarbonate ions
Large Intestine Overview
- Mucosa: simple columnar epithelium + form long, straight intestinal glands (crypts)
- taenia coli = thickened bands in muscularis
- haustra = pouches in intestinal wall
