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AKA cricopharyngeal sphincter. It is the cricopharyngeal muscle which keeps air from going into the stomach.

AKA Cardiac. lower 1-2 cm of esophagus (which is ~25 cm long)

Cholinergic vagal stimulation increases tone, non-cholinergic, non-adrenergic stimulation relaxes. Gastrin

4 layers of GI wall
Mucosa: mucous epithelium, Lamina propria, Muscularis mucosae

Submucosa: ducts

Muscularis: circular muscle layer; Longitudinal muscle layer

Serosa: Connective tissue layer, peritoneum
Plexes of GI
Enteric plexus
  • Myenteric plexus: between circular and longitudinal layers
  • Submucosal plexus: just under circular muscle.




3 glands: Submandibular, lingual and parotid.

1 L/day

sympathetic and parasympathetic innervation.

Water with mucus, sodium, bicarbonate, chloride, potassium, salivary α-amylase, pytalin and IgA
Divisions of stomach

Layers of muscle

limitations of absorption
Fundus: where LES enters

Body: main section

Antrum: where pylorus and pyloric sphincter exist.

3 layers of smooth muscle
: outer longitudinal, middle circular, and inner oblique Innervation: sympathetic and parasympathetic.

It can absorb alcohol and aspirin, not H2O

Gastrin: With presence of partially digested proteins it stimulates gastric glands to secrete HCl and pepsinogen.

Cholecystokinin: With presence of chyme in duodenum it stimulates the gallbladder to eject bile and pancreas to secrete alkaline fluid. It decreases gastric motility, constricts the pyloric sphincter and inhibits gastrin.
Gastric Pits


cells and what they secrete
in the fundus and body:

Mucous neck cells: secrete mucous
Parietal cells: secrete HCl and intrinsic factor
Chief cells: secrete pepsinogen (which is readily made to pepsin @ pH2)
Pyloric gland mucosa secretions
G cells: gastrin

Enterochromaffin-like cells: secrete histamine

D cells: secrete somatostatin.
Small intestine

segments, where they start

blood supply
Duodenum, jejunum and ilium.

Jejunum starts at the Treitz ligament

no anatomical marker for start of ilium though jujunum has a slightly larger lumen. Blood supply
  • Gastroduodenal artery
  • Superior mesenteric artery branches
    Superior mesenteric and splenic veins
In the small intestine. It's how fats get into the systemic circulation and are delivered to liver.
Carbohydrate digestion and absorption
After salivary amylase gets a hold of it, the pancreatic amylase and brush-border enzymes (lactase, maltase and sucrase) of the SI make it into forms absorbed by capillaries in the villa and transported to liver by portal veins.
Protein digestion and absorption
After pepsin of stomach does its thing, the pancreatic enzymes (trypsin, chymotrypsin and carboxypeptidase and brush-border enzymes (amnopeptidases and dipeptidases) of the SI turn them into a.a.s that are hepatic portal bound.
Fat digestion
Emulsifying agents (bile acids, fatty acids monoglycerides, lecithin, cholesterol and protein) and Pancreatic lipases of SI digest them into monoglycerides and fatty acids and glycerol and fatty acids.

Monoglycerides and fatty acids are absorbed by lacteals in the villi and transported to liver in systemic circulation.

Clycerol and fatty acids are absorbed by capillaries in the villi and transported to liver by the portal vein.
Large intestine
Cecum, colon (ascending, transverse, descending and sigmoid), rectum and anus
Where things are absorbed
Stomach: alcohol & aspirin

SI: Duodenum: Iron, Calcium, Fats, Sugars, Water, Proteins, Vitamins, Magnesium, Sodium
Jejumun: sugars & proteins
Ileum: Bile salts, Vitamin B12, Chloride

Colon: water & electrolytes

Location, lobes
Falciform ligament separates the lobes and attaches the liver to the anterior abdominal wall.

Coronary ligament attaches it to the diaphragm

Glisson capsule contains blood and lymphatics and can be involved with effusion and ascites.

The right lobe is HUGE and contains the gall bladder, caudate and quadrate lobes. Left lobe is significantly smaller




Bile canaliculi

Common bile duct

major duodenal papilla

Kupffer cells

Stellate cells

Pit cells

Disse space
Hepatocytes: functional cells of liver

Lipocytes: Star-shaped cells that store lipids (incl. vit A)

Sinusoids: small capillaries located between plates of helatocytes which receive a mixture of arterial and venous blood. It then drains to a central vein in the middle of each lobule to hepatic vein to inf. V.C.

Bile canaliculi: channels adjacent to hepatocytes that conduct bile (produced by hepatocytes)

Common bile duct: where all the bile canaliculi lead to.

Major duodenal papilla (Sphincter of Oddi): how bile gets to duodenum

Kupffer cells: phagocytic cells; the largest population of tissue macrophages.

Stellate cells: contain retinoids (vit. A) and are contactile.

Pit cells: NK cells found in sinusoidal lumen important in tumor defense

Disse space: drains interstitial fluid into hepat lymphatics and sits between endothelial lining of the sinusoid and hepatocyte.
Contents of bile

bile salts
bile salts, cholesterol, bilirubin, electrolytes, and water

Bile salts are important in the digestion of fat. Recycles through the enterohepatic circulation.
Critical Liver functions (5)
  • Lipid, carbohydrate and protein processing and metabolism
  • Removal of waste products (ammonia to urea for disposal by kidney)
  • vitamin storage (fat soluble K, A, D, E and B12)
  • Mineral storage: converts iron to ferritin and stores
  • drug inactivation
  • Phagocytosis and antigen presentation: Kupffer cells
  • Synthesis of plasma proteins: albumins, clotting proteins
  • Removal of circulating hormones: epinephrine, norepinephrine, insulin, steroid hormones like ADH, aldosterone, estrogen
  • Conversion of Vitamin D to 25 hydroxy vit D which is used by the kidney in the formation of calcitrol (vit D3)
  • Synthesis and secretion of bile needed for emulsification of fats
Stores and concentrates about 90ml of bile between meals.

Empties through cystic duct and when it meets with common hepatic duct it forms the common bile duct
Exocrine pancreas

cells, what they produce, duct system with names of where they empty.

ANS innervation
Acini are cells that secrete alkaline fluids and enzymes important to digestive functions.

They are drained by ducts that lead to the pancreatic duct (Wirsung duct) which empties into the common bile duct at the ampulla of Vater. Some individuals have an accessory pancreatic duct that empties contents into the minor duodenal papilla.

Preganglionic parasympathetic stimulation from vagus nerve. Sympathetic fibers of the celiac and superior mesenteric plexes innervate blood vessels and cause vasoconstriction.
What the pancreas secretes:
Isotonic aqueous secretions: K+, Na+, HCO3-, MG, Ca2+ and Cl-

  • Trypsinogen, chymotrypsinogen, and procarboxypeptidase
  • Trypsin inhibitor
  • Pancreatic α-amylase
  • Pancreatic lipase



Acid activation and inhibition





Enterokinase: secreted by the duodenal mucosa that activates proenzymes secreted by pancreas.

Secretin: produced by the S cells of the duodenum. Hormone that stimulates acinar and duct cells to secrete pancreatic aqueous and enzymatic components.

Pepsin: ACh, gastrin and secretin stimulate chief cells to release. Gastrin does so indirectly.

secretion by parietal cells stimulated by ACh, gastrin, histamine and inhibited by somatostatin

Somatostatin: with acid it inhibits more and pepsinogen and gastrin

Histamine: with gastrin it stimulates acid secretion

ACh: with vagal and local nerve stimulation it stimulates release of pepsinogen and acid secretion

Gastrin-releasing peptide (bombesin): same as ACh

Motilin: with presence of acid and fat in duodenum it increases gastrointestinal motility
Aging and digestion
No teeth, senses or saliva.

Decreased motility, absorption and liver enzymes/perfusion which makes drug and alcohol metabolism shaky.
Heme is separated into Iron and Biliverdin. Biliverdin is enzymatically converted to bilirubin in the macrophage of the mononuclear phagocytic system (in the spleen) and released into plasma where it binds to albumin and becomes unconjugated bilirubin (free bilirubin, lipid soluble).

Once in the liver, it gets to the hepatocytes via sinusoids and becomes conjugated bilirubin (water soluble).

It is then excreted in the bile and excreted in urine and feces (in yet another form).


Amylase breaks down starches into sugars

tripsin (from pancrease as tripsinogen) breaks down proteins to a.a.s

Pytalin comes from saliva and helps break down carbohydrates
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