Digestive system Flashcards
what is the Digestive tract also called?
alimentary tract or canal
what are some of the parts of the Digestive tract and accessory organs?
◦ Tube from oral cavity to
anus
◦ GI tract: refers to
stomach and intestines
Accessory organs
◦ Primarily glands, secrete fluids into tract
what are the functions of the digestive tract? part 1
- Ingestion: introduction of food into stomach
- Mastication: chewing
◦ Increases surface area - Propulsion
◦ Deglutition: swallowing
◦ Peristalsis: moves material through digestive tract - Mixing – contractions to increases contact with enzymes
what are the functions of the digestive tract? part 2
- Secretion: lubricate, liquify, digest
◦ Mucus: secreted along entire digestive tract, lubricates food and lining, protects from mechanical digestion, acid and digestive enzymes
◦ Water: makes food easier to digest and absorb
◦ Bile: emulsifies fats
◦ Enzymes: chemical digestion - Digestion: Mechanical and chemical
- Absorption: Movement from tract into circulation or lymph
- Elimination: Waste products removed from body;
Defecation
what is the Histology of the digestive tract-Mucosa?
Mucosa. Innermost layer, consisting of:
- Mucous epithelium
- Lamina propria: loose C.T.
- Muscularis mucosae: smooth muscle.
• Mucosa extends into lamina propria in places to
form intestinal glands or crypts.
what is the Histology of the digestive tract-Submucosa?
Thick C.T. layer with nerves,
blood vessels, small glands. Parasympathetic submucosal plexus.
what is the Histology of the digestive tract-Muscularis?
2 or 3 layers of smooth muscle, including circular and longitudinal layers.
Muscularis contains the myenteric plexus between circular and longitudinal layers. Plexus controls movements along GI tract.
what is the Histology of the digestive tract-Serosa or adventitia?
Connective tissue.
regulation of the Digestive system-Nervous system?
• Local: enteric nervous system
◦ Coordinates peristalsis and
regulates local reflexes
• General: coordination with the CNS.
◦ May initiate reflexes because of sight, smell, or taste of food.
◦ Primarily parasympathetic
regulation of the Digestive system-Chemical system?
• Production of hormones
– Gastrin, secretin
• Production of paracrine
chemicals like histamine
Saliva and its function
• Compound alveolar salivary glands produce saliva
◦ Prevents bacterial infection
◦ Lubrication
◦ Contains salivary amylase that breaks down
◦ Helps to form bolus for swallowing
◦ Parasympathetic input causes salivary production
stomach and its openings
◦ Gastroesophageal: from oesophagus
◦ Pyloric: to duodenum
what is the first stage of the Cephalic phase?
The taste, smell, or thought of food or tactile sensations of food in the mouth stimulates oblongata
what is the second stage of the Cephalic phase?
Vagus nerves carry parasympathetic action potentials to the stomach, where enteric plexus neurons are activated.
what is the third stage of the Cephalic phase?
Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells
what is the fourth stage of the Cephalic phase?
Gastrin is carried through the circulation back to the stomach, where, along with histamine, it stimulates secretion
what is the first stage of the Gastric phase?
Distention of the stomach stimulates mechanoreceptors and activates a parasympathetic reflex. Action potentials generated by the mechanoreceptors are carried by the vagus nerves to the medulla oblongata
what is the second stage of the Gastric phase?
The medulla oblongata increases action potentials in the vagus nerves that stimulate secretions by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells
what is the third stage of the Gastric phase?
Distention of the stomach also activates local reflexes that increase stomach secretions
what is the fourth stage of the Gastric phase?
Gastrin is carried through the circulation back to the stomach, where, along with histamine, it stimulates secretion.
what is the first stage of the Intestinal phase?
Chyme in the duodenum with a pH less than 2 or containing fat digestion products 9 lipids) inhibits gastric secretion by three mechanisms (2-4)
what is the second stage of the Intestinal phase?
chemoreceptors in the duodenum are stimulated by H+ (low pH) or lipids. Action potentials generated by the chemoreceptors are carried by the vagus nerves to the medulla oblongata, where the inhibit parasympathetic action potentials, thereby decreasing gastric secretion
what is the third stage of the Intestinal phase?
local reflexes activated by H+ or lipids also inhibit gastric secretion
what is the fourth stage of the Intestinal phase?
secretin and cholecystokinin produced by the duodenum decrease gastric secretions in the stomach.
small intestine characteristics and divisions
• Site of greatest amount of
digestion and absorption
of nutrients and water
• Divisions:
◦ Duodenum- first 25 cm
◦ Jejunum- 2.5 m
◦ Ileum- 3.5 m
Small intestine-Duodenum
• Curves to the left; head
of pancreas in the curve
what are the modifications to increase surface area of the small intestine?
• Increase surface area 600 fold: ̶ Plicae circulares ̶ Villi ̶ Microvilli
small-intestine-Jejunum and Ileum
• Similar in structure to the duodenum
- Gradual decrease in:
- Diameter
- Thickness of intestinal walls
- Number of circular folds
- Number of villi
• Duodenum and Jejunum are the major site of nutrient
absorption
what is the first stage of the Liver, Gallbladder, Pancreas and Ducts?
The hepatic ducts, which carry bile from the liver lobes, combine to form the common hepatic duct.
what is the second stage of the Liver, Gallbladder, Pancreas and Ducts?
The common hepatic duct combines with the cystic duct from the gallbladder to form the common bile duct.
what is the third stage of the Liver, Gallbladder, Pancreas and Ducts?
The common bile duct and the pancreatic duct combine to form the hepatopancreatic ampulla
what is the fourth stage of the Liver, Gallbladder, Pancreas and Ducts?
The hepatopancreatic ampulla empties bile and pancreatic secretions into the duodenum at the major duodenal papilla
what is the fifth stage of the Liver, Gallbladder, Pancreas and Ducts?
The accessory pancreatic duct empties pancreatic secretions into the duodenum at the minor duodenal papilla
what are the functions of the liver? part 1
• Bile production: 600-1000 mL/day. Bile salts,
cholesterol, fats, fat-soluble hormones, lecithin
◦ Neutralizes and dilutes stomach acid
◦ Bile salts emulsify fats. Most are reabsorbed in the ileum.
◦ Secretin (from the duodenum) stimulates bile secretions, increasing water and bicarbonate ion content of the bile
• Storage
◦ Glycogen, fat, vitamins, copper and iron. Hepatic portal blood comes to liver from small intestine.
what are the functions of the liver? part 2
• Nutrient interconversion
• Detoxification
◦ Hepatocytes remove ammonia and convert to urea
• Phagocytosis
• Synthesis
◦ Albumins, fibrinogen, globulins, heparin, clotting factors
Pancreas-Endocrine and Exocrine
- Pancreas both endocrine and exocrine
- Endocrine: pancreatic islets. Produce insulin, glucose, and somatostatin
- Exocrine: grape-like clusters form lobules separated by septa.
Large intestine characteristics and what does it consist of?
• Consists of cecum, colon, rectum, anal canal
• Movements sluggish (18-24 hrs); chyme
converted to faeces.
• 90% of volume of chyme is reabsorbed in the
large intestine
Anatomy of the large intestine?
Cecum
◦ Blind sac, appendix attached.
Colon
◦ Ascending - transverse
◦ Descending - sigmoid
Rectum
◦ Straight muscular tube,
thick muscular tunic
Anal canal
◦ Internal anal sphincter (smooth muscle)
◦ External anal sphincter (skeletal muscle)
Digestion and absorption- Digestion function
• Digestion
◦ Breakdown of food molecules for absorption into circulation
• Mechanical: breaks large food particles to small
• Chemical: breaking of covalent bonds by digestive
enzymes
Digestion and absorption- absorption and transport function
• Absorption and transport
◦ Molecules are moved out of digestive tract and into
circulation for distribution throughout body
what is the movement of Carbohydrates through the digestive system?
Mouth: salivary amylase= polysaccharides
Stomach: same
Duodenum: Pancreatic amylase= Disaccharides
Epithelium of small intestine: Disaccharidses= monosaccharides
what is the movement of Lipids through the digestive system?
Mouth: Lingual lipase
Stomach: Gastric lipase
Duodenum: Bile salts+ Pancreatic lipase
Epithelium of small intestine: fatty acids, monoglycerides
what is the movement of Proteins through the digestive system?
Mouth: nothing
Stomach: Pepsin= polypeptides
Duodenum: Trypsin, chymotrypsin, carboxypeptidase= peptides
Epithelium of small intestine: peptidases=amino acids, dipeptides, tripeptides
Water and ions- water
• Water: can move in
either direction across wall of small intestine depending
on osmotic gradients
Water and ions-ions
• Ions: sodium, potassium, calcium, magnesium, phosphate are actively transported
movement of water in the digestive system?
mouth: Ingestion (2 L), salivation gland secretions (1 L)
stomach: gastric secretions (2 L)
Duodenum: Bile (0.7 L), Pancreatic secretions (1.2 L)
Epithelium of small intestine: small intestine secretions (2 L) 92% absorbed in the small intestine, 6%-7% absorbed in the large intestine
(water in feces=ingested+ secreted- absorbed)
