STRUCTURES OF THE GI TRACT

1. Layers     2. Mouth     3. Pharynx     4. Esophagus     5. Stomach     6. Peritoneum     
7. Pancreas     8. Liver     9. Gallbladder     10. Small Intestine     11. Large Intestine

1. Layers of the GI Tract

4 layers from esophagus to anus:
Mucosa- inner mucous membrane composed of epithelium, connective tissue, smooth muscle.
Submucosa – contains blood, lymphatic vessels and neurons. Connects mucosa to muscularis.
Muscularisskeletal muscle in mouth, pharynx, part of esophagus (swallowing) and anal sphincter (defecation).                                                      smooth muscle in rest of the tract, produces involuntary contractions to move food along and break it down.
Serosa – superficial layer of serous membrane. Also called visceral peritoneum as it is part of the peritoneum.

2. Mouth

Teeth – break down food by mastication (chewing and mixing with saliva)
Tongue – a muscle, aids in chewing, swallowing, speech. Has taste buds and glands that produce saliva.
Salivary glands – 3 main pairs controlled by ANS:
               parotid – largest, below and to front of ears.
               Submandibular – inside lower jaw.
              Sublingual – under tongue. Secrete either serous fluid or mucous.

3. Pharynx

passage of food bolus from mouth to esophagus and air passage to trachea.
3 main divisions
              oropharynx – back of throat below soft palate
              nasopharynx – upper part of the throat above soft palate
              laryngopharynx – lower part of the throat

4. Esophagus

About 25cm long, 1.5 -2 cm wide. 
Behind the trachea and heart; passes through the diaphragm.  
Passageway for food from pharynx to the stomach.  
Upper esophageal sphincter relaxes -> food moves from laryngopharynx to esophagus -> peristalsis moves along -> lower esophageal sphincter relaxes -> food flows into stomach.

5. Stomach

Between the esophagus and the duodenum in the left upper quadrant of the abdomen right below the diaphragm.  
Dilates and holds over 1 litre of food or liquid.  
The mucous membrane (inner lining) has a pH of 7 and is always covered by thick mucus which protects and lubricates. 

See more information on the stomach here.

6. Peritoneum

Largest serous membrane in the body made of epithelium and connective tissue.
Divided into: parietal peritoneum – lines walls of abdominopelvic cavity.
                         visceral peritoneum – covers organs in the intraperitoneal space.
Peritoneal cavity – space between parietal and visceral peritoneum with small amount of serous fluid.
Ascites – accumulation of fluid in the peritoneal cavity
Retroperitoneum “behind” the peritoneum. Organs at the posterior abdominal wall are only covered by peritoneum at their anterior surface so they are technically not in the peritoneum (kidneys, parts of large intestine ,duodenum, pancreas).  

7. Pancreas

An abdominal organ that is really a “retroperitoneal gland” as it produces both hormones and enzymes.
J-shaped, elongated and narrow about 12 -15 cm long and 2.5 cm thick.
Lies across the upper left abdomen behind the stomach and the spleen.

See more information about the pancreas here.

8. Liver

Both an organ and a gland because it secretes substances.
Weighs about 1200-1600 g in adults, measuring 20-22 cm horizontally, 15-18 cm vertically and  10-13 cm in thickness.
Below the diaphragm in the upper right portion of the abdominal cavity under the ribcage.
Divided into right (larger) and left (smaller) lobes.
The liver receives about 1.4 litres of blood every minute via the hepatic artery and the hepatic portal vein.

See more information about the liver here.

9. Gallbladder

Pear shaped, about 7-10 cm long, posterior to liver.
Stores and concentrates bile (holds up to 50 mls) from the liver.

See more information about the gallbladder here.

10. Small Intestine

Begins at the pyloric sphincter of the stomach, coils through the abdominal cavity and ends at the large intestine.
About 2.5 cm (3-4cm?) in diameter and 3m long (670-760cm?).
Mixes and transports contents, produces enzymes and other substances needed in digestion, absorbs nutrients.
Divided into: duodenum – first part
                         jejunum – middle part
                         ileum – final part

See more information about the small intestine here.

11. Large Intestine

About 1.5 m long and 6.5 cm wide from ileum to anus.
A reservoir for liquids from small intestine.
4 regions: cecum
                   colon (ascending, transverse, descending & sigmoid)
                   rectum
                   anal canal

See more information about the large intestine here.

 

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