Digestive system functions
Ingestion, Digestion (mechanical and chemical), Absorption, Defecation
Groups of organs in digestive system
Alimentary canal (GI tract - continuous hollow tube, organs ingest digest absorb and defecate) Mouth, esophagus, stomach, small intestine, large intestine, rectum.
Accessory organs - teeth, tongue, pancreas, liver, gallbladder.
Mouth physiology
Mastication (chewing) of food
Mixing masticated food with saliva
Initiation of swallowing by the tongue
Allows for the sense of taste
Pharynx physiology
Serves as a passageway for air and food•Food is propelled to the esophagus by two muscle layers•Longitudinal inner layer•Circular outer layer•Food movement is by alternating contractions of the muscle layers (peristalsis)
Stomach physiology
•Temporary storage tank for food•Site of food breakdown•Chemical breakdown of protein begins•Delivers chyme (processed food) to the small intestine
Stomach mucosa structure
Mucosa is simple columnar epithelium•Mucous neck cells—produce a sticky alkaline mucus•Gastric glands—situated in gastric pits and secrete gastric juice•Chief cells—produce protein-digesting enzymes (pepsinogens)•Parietal cells—produce hydrochloric acid•Enteroendocrine cells—produce gastrin
Small Intestine
The body’s major digestive organ•Site of nutrient absorption into the blood•Muscular tube extending from the pyloric sphincter to the ileocecal valve•Suspended from the posterior abdominal wall by the mesentery
Gastric gland cells (what they produce)
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Chemical digestion in small intestine
Chemical digestion begins in the small intestine•Enzymes are produced by•Intestinal cells•Pancreas
Pancreatic ducts carry enzymes to the small intestine
Bile, formed by the liver, enters via the bile duct
Three structures that increase surface area in sm. intestine
Microvilli—tiny projections of the plasma membrane (create a brush border appearance)•Villi—fingerlike structures formed by the mucosa •Circular folds (plicae circulares)—deep folds of mucosa and submucosa
Large Intestine Anatomy
No villi present•Goblet cells produce alkaline mucus which lubricates the passage of feces•Muscularis externa layer is reduced to three bands of muscle called teniae coli•These bands cause the wall to pucker into haustra (pocketlike sacs)
Saliva
Mixture of mucus (moistens and binds food to form bolus) and serous fluids•Contains salivary amylase to begin starch digestion•Dissolves chemicals so they can be tasted
Pancreas
Exocrine &endocrine gland. only one that produces a wide spectrum of digestive enzymes that break down all categories of food.Enzymes are secreted into the duodenum•Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach•Hormones produced by the pancreas•Insulin (lower BG level)•Glucagon.
Bile
Produced by cells in the liver•Bile leaves the liver through the common hepatic duct. Bile salts, Bile pigments (mostly bilirubin from the breakdown of hemoglobin)Cholesterol,Phospholipids, Electrolytes. Function to emulsify fats by physically breaking large fat globules into smaller ones
Gallbladder
Sac found in hollow fossa of liver•storage area for bile. When digestion of fatty food is occurring, bile is introduced into the duodenum from the gallbladder•Gallstones are crystallized cholesterol which can cause blockages
Fxn of digestive system
Propulsion—moving foods from one region of the digestive system to another
Peristalsis—alternating waves of contraction and relaxation that squeezes food along the GI tract, one way smooth muscle, weak
Segmentation—moving materials back and forth to aid with mixing in the small intestine.
Function of digestive system with processes (mechanical vs chemical)
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Carbohydrate digestion and absorption
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Protein digestion and absorption
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Fats digestion and absorption
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Control of digestive system
Mostly controlled by reflexes via the parasympathetic division•Chemical and mechanical receptors are located in organ walls that trigger reflexes (activation of granular activity by smooth muscle) Stimuli- stretch, pH, and presence of breakdown prod.
Degultition (swallowing)
Buccal phase- Voluntary•Occurs in the mouth, bolts formed,forced into the pharynx by the tongue.
Pharyngeal-esophageal phase- Involuntary transport of bolus, peristalsis moves bolus toward stomach. by saliva and mucus
Important cells and what they produce in stomach
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Food breakdown in stomach: Gastrin
regulated by neural and hormonal factors•Presence of food or rising pH causes the release of the hormone gastrin•
Gastrin causes stomach glands to produce•Protein-digesting enzymes•Mucus•Hydrochloric acid
Food breakdown in stomach: Hydrochloric acid
Hydrochloric acid makes the stomach contents very acidic •Acidic pH•Activates pepsinogen to pepsin for protein digestion•Provides a hostile environment for microorganisms
Chief cell
Releases pepsinogen (inactive) to pepsin (active) in the presence of HCL
pepsin: active protein digestive enzyme
random stomach
Hormone Gastrin produces pepsin and renin (enzymes), HCL, and mucus.
Alcohol and ASA are only substances absorbed in stomach
Stomach turns bolus into chyme into sm. intestine 3mL at a time
food mixed & rippling peristalsis occurs in lower stomach (propulsion) through pyloric sphincter
Digestion in small intestine
Pancreatic enzymes a muscle digestive fxn!
trypsin,chymotrypsin, carboxypeptidase
Regulation of Pancreatic Juice
Release of pancreatic juice into the duodenum is stimulated by•Vagus nerve•Local hormones•Secretin•Cholecystokinin (CCK)
—Bile is necessary for fat absorption and absorption of fat-soluble vitamins (K, D, A)
Absorption in small intestine
Water is absorbed along the length of the small intestine•End products of digestion•Most substances are absorbed by active transport through cell membranes•Lipids are absorbed by diffusion•Substances are transported to the liver by the hepatic portal vein or lymph
Regulation of Pancreatic Juice and bile Secretion
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Peristaltic waves in stomach
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Food Breakdown and Absorption in the Large Intestine
No digestive enzymes are produced•Resident bacteria digest remaining nutrients (Produce some vitamin K and B•Release gases)•Water and vitamins K and B are absorbed•Remaining materials are eliminated via feces
Propulsion in large Intestine
Sluggish peristalsis•Mass movements•Slow, powerful movements•Occur three to four times per day•Presence of feces in the rectum causes a defecation reflex•Internal anal sphincter is relaxed•Defecation occurs with relaxation of the voluntary (external) anal sphincter
Terms of digestion (mechanical and chemical)
Ingestion,
Masification,
Deglutition,
Perstalisis,
Churning,
Segmentation,
Defecation
Hepatic portal vein
From intestine goes to liver, decides what to keep, goes to heart and circulated through system. (glucose, fructose,galactose, amino acids, glycerol)
Fatty acids and monoglycerides don’t go to vein.
