Digestive System 2

• Caused by abnormal relaxation of esophageal sphincter
• Called gastroesophageal reflux disease (GERD) if it's chronic
• Can cause dramatic inflammation and ulcers in esophagus

• Muscular sac immediately inferior to diaphragm
• Stores food: volume can increase from 50 ml to 4 L
• Mechanically breaks up food, liquifies food
• Begins chemical digestion of protein and fat
• Produces chyme (soup of semi-digested food)

• Lesser curvature along superior surface
• Greater curvature along inferior surface
• Stomach lined with rugae
• Pyloric sphincter controls chyme entry into duodenum

• Bariatric Surgery
• Small stomach pouch

• Bariatric Surgery
• 85% of the stomach is removed

• Bariatric Surgery
• Small stomach pouch that is attached to jejunum

• Mucosa has many cells filled with mucin that becomes mucus
• Three layers of muscularis externa

• Depressions in gastric mucosa
• Lined with epithelial cells
• Opens up to glands in the bottom of each pit

Secrete mucus

Secrete HCl, intrinsic factor, and ghrenlin

Secrete gastric lipase and pepsinogen (converted to pepsin)

Secrete hormones and paracrine agents that regulate digestion

Secrete gastrin (stimulates secretion by parietal and chief cells and stimulate stomach contraction)

• Mixture of water, hydrochloric acid, digestive enzymes, mucous, hormones
• Produced by gastric glands
• Stomach produce 2-3 L/day
• pH as low as .8

• Activates lingual lipase
• Converts pepsinogen to pepsin
• Breaks up connective tissue and plant cell walls
• Converts Fe3+ to Fe2+ to be absorbed and used for hemoglobin synthesis
• Destroys most ingested pathogens

• Pepsinogen secreted by chief cells
• HCl removes some amino acids to form Pepsin
• Pepsin digests proteins to shorter peptide chains

• Produced by chief cells
• With lingual lipase, plays a minor role in digesting fats

• Secreted by parietal cells
• Essential for small intestine to absorb vitamin B12 (needed for hemoglobin synthesis)

• Secreted by enteroendocrine cells
• Affect gut motility and appetite regulation

• Swallowing center of medulla stimulates stomach to relax and accommodate food
• After food arrives, stomach contracts every 20 seconds to promote mechanical digestion and mixes food with gastric juice
• Contractions generated by pacemaker cells in muscularis externa
• With each contraction, 3 ml of chyme is secreted into duodenum
• Allows neutralization of acid and slow digestion
• Typical meal emptied from stomach in 4 hours

• Forceful ejection of chyme from the mouth
• Pyloric and esophageal sphincters open due to increases in abdominal pressure and muscle contractions
• Emetic center in medulla coordinates muscles
• Induced by overstretching stomach or duodenum, chemical irritant (like alcohol), visceral trauma, intense pain or psychological stimuli

• Salivary and gastric enzymes partially digest protein, and digest small amounts of starch and fat
• Most digestion occurs after chyme passes into small intestine
• Stomach only absorbs a few things (aspirin and alcohol)

• Mucous coat is very basic, so it protects against acid and enzymes
• Epithelial cells have tight junctions to keep gastric juice out
• Epithelial cells are replaced every 3-6 days
• Old cells become part of chyme

• Erosion in the stomach walls
• Most are caused by the bacteria Helicobacter pylori: Infection causes constant inflammation, and either reduces or increases amount of HCl secretion
• Some caused by excess NSAID use
• NSAID reduces ability to produce protective mucus

Increases gastric motility while eating and in anticipation of food (through myenteric plexus)

Suppresses gastric motility when the stomach empties

Stomach controlled by brain

Stomach controls itself

Stomach controlled by small intestine

• Stomach responds to sight, smell, taste or thought of food
• Hypothalamus relays signal to medulla
• Parasympathetic neurons from medulla stimulate enteric nervous system to activate gastric secretion

• Ingested food stimulates gastric secretion by activating short (myenteric) and long (vasovagus) reflexes
• Muscularis externa muscles conntract
• Acetylcholine and histamine and gastrin stimulates gastric secretion

Duodenum inhibits gastric secretion by inhibiting parasympathetic neurons in the medulla and stimulating sympathetic neurons

• Gland just inferior to the diaphragm
• Secretes bile to aid in digestion of lipids
• Plays many non-degestive roles: detoxification, nutrient and vitamin storage, RBC breakdown, and coagulant secretion

• Four lobes: right, left, quadrate, caudate
• Falciform ligament separates left and right
• Porta Hepatis: opening between quadrate and caudate lobes
• Hepatic portal vein, proper hepatic artery, and bile passages enter liver here

• About 1/3 from proper hepatic artery
• About 2/3 from hepatic portal vein
• From capillaries in esophagus, stomach, and intestines

• Central canal and sinusoids filled with blood
• Epithelial cells lining hepatocytes have many gaps (fenestrations) between them to allow blood plasma entry

• Absorb glucose, amino acids, iron, vitamins, and other nutrients after a meal
• Remove and degrade hormones, toxins, bile pigments and drugs
• Secrete albumin, lipoproteins, clotting factors, angiotensinogen
• Between meals (when glucagon present), they break down glycogen and release glucose
• Form and secrete bile

• Each lobule has 6 triads, which consists of two blood vessels (branches of proper hepatic artery and hepatic portal vein) and bile duct
• Proper hepatic artery and hepatic portal vein supply blood to sinusoids
• After filtering through sinusoids it's collected in the central canal
• Then flows to right and left hepatic vein and drains into inferior vena cava

• Bile is secreted into bile canaliculi to get to ductule in triad
• Bile flows into common hepatic duct on inferior side of liver
• Then flows into the bile ducts

• Bile duct joins with pancreatic duct in hepatopancreatic ampulla
• Hepatopancreatic sphincter regulates passage of bile and pancreatic juice into duodenum

• Small sac on inferior side of liver
• Stores and concentrates bile
• Absorbs water and electrolytes
• Neck leads into cystic duct

• Yellow-green fluid containing water, minerals, bilirubin, cholesterol, bile salts (lipids)
• Bacteria in large intestine metabolize biliruben to urorubin
• Responsible for brown color in feces

• Break up large lipid droplets (emulsification)
• This increases surface area so that more enzymes can contact lipids and metabolize them

• Liver fills bile duct with bile
• Stuck in duct until hepatopancreatic sphincter opens
• Sphincter only opens when fat in SI triggers cholecystokinin production

• Bile overflows into gallbladder until duct empties
• As it is stored, water is absorbed and bile becomes more concentrated
• Most bile reabsorbed by SI and returned to liver through hepatic portal vein