Digestive System Gastrointestinal Tract 1. Mouth 2. Pharynx 3. Esophagus 4. Stomach 5. Small...
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Transcript of Digestive System Gastrointestinal Tract 1. Mouth 2. Pharynx 3. Esophagus 4. Stomach 5. Small...
DigestiveSystem
Gastrointestinal Tract 1. Mouth 2. Pharynx
3. Esophagus 4. Stomach 5. Small Intestine 6. Large Intestine
Accessory Structures 1. Teeth 2. Tongue 3. Salivary Glands 4. Liver 5. Gallbladder
6. Pancreas
The Processes of Digestion1. Ingestion
taking food into the mouth 2. Secretion
GI tract and accessory cells secrete water, acid, buffers, and enzymes into lumen 3. Mixing and Propulsion
alternating contraction and relaxation of smooth muscles in the walls of the GI tract 4. Digestion
Breaking down of larger food particles into smaller molecules Mechanical Digestion
Chemical Digestion 5. Absorption
small molecules pass from the lumen into the blood and lymph 6. Defecation
elimination of indigestible substances and bacteria from the GI tract
Mouth (Oral Cavity)
Mechanical Digestion
mastication (chewing) tongue manipulates food teeth grind food saliva mixes so that food isreduced to a soft flexiblemass called a bolusthat is easily swallowed
Salivary Glands
Chemical Digestion
salivary amylase initiates the breakdown ofstarch ingested disaccharides and starches must be broken down into monosaccharides
lingual lipase initiates digestion of triglycerides into fatty acids and monoglycerides
Stomachconnects the esophagus to the duodenum (first part of the small intestine)
Functions:
1. serves as a mixing area for saliva, food and gastric juice
2. serves as a reservoir for holding food before release into the SI
3. secretes gastric juice (HCL, pepsin, intrinsic factor, gastric lipase) HCL kills bacteria, denatures protein pepsin begins digestion of proteins intrinsic factor aids absorption of vitamin B12 gastric lipase aids digestion of triglycerides
4. secretes gastrin (digestive hormone) into the blood
Physiology of Digestion and Absorption in the Stomach
Mechanical Digestion after food enters the stomach, gentlemixing waves pass over the stomach every 15-25 seconds it macerates the food and mixes it with gastric juice, forming chyme the chyme moves back and forthand keeps mixing until it is sentthrough the pyloric sphincter intothe duodenum
Chemical Digestion lingual lipase and salivary amylase continue to break down fats and carbohydrates respectively pepsin and HCL break down proteinsgastric lipase splits triglycerides into fatty acids and monoglycerides
Peristalsis
Regulation of Gastric Secretion and Motility• Cephalic Phase:
– Sight, smell, taste, and thought initiate reflex• Cortex and hypothalamus send impulses to medulla• Parasympathetic (Vagus nerve) impulses from medulla promote:
– Peristalsis in stomach– Gastric glands to secrete:
» Pepsinogen» HCL» Mucus» gastrin
• Gastric Phase:– Stretch receptors detect distention of stomach– Chemoreceptors detect increased pH of gastric juice
• Stimulates stomach churning and secreting– ACH from parasympathetic activity stimulates gastrin secretion
• Stimulates gastric juice secretion• Stimulates stomach motility
• Intestinal Phase– Stretch receptors detect distention of duodenum– Chemoreceptors detect fatty acids and glucose in duodenum
• Impulses from small intestine inhibit stomach secretions and motility• Stimulates release of:
– Gastric inhibitory peptide (GIP)» Inhibits gastric secretions and gastric motility in stomach
– Secretin» Decreases gastric secretions
– Cholecystokinin (CCK)» Inhibits stomach emptying» Inhibits gastric secretions and gastric motility in stomach
Small Intestines
Functions: 1. mixes chyme with digestive
juices and brings food in contact with surface mucosa for absorption
2. completes digestion of carbohydrates, proteins, & lipidsbegins & completes digestion of nucleic acids
3. is responsible for the absorption of about 90% of all nutrients
source of the major events of digestion and absorption its long length (over 10 feet) is to increase the surface area it has many circular folds, villi and microvilli
Small IntestinesPhysiology
Digestionchyme remains in SI for 3-4 hours Mechanical Digestion
mixes chyme with digestive enzymesundergoes peristalsis
Chemical Digestion pancreatic juice assists in digestion
Absorptionfood products pass through mucosa absorptive cellspassage of these molecules from the GI tract to the blood or lymph is called absorption
Brush Border Enzymes
• Carbohydrate digesting:– Alpha-dextrinase– Maltase– Sucrase– Lactase
• Protein digesting:– Aminopeptidase– Dipeptidase
• Nucleic Acid digesting– Nucleosidase– Phosphatase
GlucoseAbsorption
Carbohydrates arebroken down into monosaccharides likeglucose
Glucose passes throughSI Absorptive cells viafacilitative diffusion,actually with the help of a Na+ co-transporter
Glucose then passively diffuses into the blood
ProteinAbsorption
Proteins are broken down intoamino acids
Amino acids and the slightlylarger di-peptides passively diffuse across the membranesof the SI Absorptive cells
Amino acids then passivelydiffuse into the blood
Pancreatic Juice Enzymes• Carbohydrate digesting:
– Pancreatic amylase
• Protein digesting:– Trypsin– Chymotrypsin– Carboxypeptidase– Elastace
• Lipid digesting– Pancreatic lipase
• Nucleic Acid digesting– Ribonuclease– Deoxyribonuclease
FatAbsorption
Large fat droplets are emulsifiedinto monoglycerides and fatty acids by bile salts from the liver and are packaged into micelles
Micelles merge with SI Absorptivecells and via a type of endocytosisdeposit the fat fragments in the cells
The fat fragments are then reassembled into triglycerides in thecell and packaged in chylomicrons
Chylomicrons then exit the cell andenter the lymph on their way to the liver for final digestion and storage
Large Intestine (Colon)
Functions: 1. completion of absorption 2. manufactures vitamins
(some B’s & K)3. formation of the feces 4. expulsion of the feces
Structures: cecumascending colon transverse colon descending colon sigmoid colon rectum anal canal anus anal sphincters