Digestive System

Esophagus

1

Cardiac region

2

Fundus

3

Body

4

Pyloris

5

Lesser curvature

6

Greater curvature 

1

Duodenum

2

Jejunum

3

Ileum

1

Cecum

2

Appendix

3

Ascending colon

4

Transverse colon

5

Descending colon

6

Sigmoid colon

1

Right Lobe

2

Left lobe

3

Quadrate lobe 

4

Caudate lobe

5

Hepatic artery

6

Hepatic portal vein

Porta hepatis 

Falciform ligament

1

Right hepatic duct

2

Left hepatic duct

3

Common hepatic duct

4

Gall bladder

5

Cystic Duct

6

Common bile duct

Pancreas

Submucosa

Areolar tissue surrounding the muscularis mucosa

Contents: blood vessels, lymphatics, exocrine glands, and submucosal plexus

Muscularis Externa

Made up of Circumferentially oriented and Longitudinally oriented fibers

Circumferentially oriented

Smooth muscle fibers (inner layer)

Churning the contents in the digestive tract

Longitudinally oriented

Smooth muscle fibers (outer layer)

Runs down the tract

Peristalsis

Movement of Digestive Materials

• Muscle cells are arranged in sheets or layers, and are
  electrically connected to adjacent muscles by gap junctions.

• Contractions spread in a wave through the tissue in response
  to motor neuron activation, chemicals, hormones, stretching,
  and pacesetter cells.

• Pacesetter cells trigger muscle contraction patterns
  (peristalsis and segmentation) that facilitate the propulsion
  and mixing of contents along the digestive tract.

Peristalsis

Process whereby wavelike contractions of the muscularis externa propel a bolus along the digestive tract. It requires the coordinated actions of the circular and longitudinal muscles.

Segmentation

Process in which contractions of the circular layer of the muscularis externa churn and mix the contents of the digestive tract. No net movement

Peritoneal Cavity Organization

• Parietal peritoneum: lines the inner surface of the body wall

• Visceral peritoneum/serosa: outer lining of digestive tract

• Mesenteries: fused, double sheets of peritoneal membrane

Mesenteries examples

• Lesser omentum: between stomach and liver

• Greater omentum: “fatty apron” that hangs anteriorly and inferiorly from the stomach

• Mesentery proper: suspends and wraps most of the small intestine

• Mesocolon: the mesentery that suspends and wraps part of the large intetsine

Mesenteries

• Provide an access route for blood vessels, nerves, and lymph to & from tract

• Stabilize the relative positions of the organs within the peritoneal cavity

Intraperitoneal organs

Organs are covered by visceral peritoneum and suspended by mesentery from the body wall. Ex: stomach - out in the cavity

Retroperitoneal organs

Mesentery has fused with the posterior abdominal wall. The organs lie posterior to (retro) the peritoneal cavity. Ex: pancreas - anchored to the wall

Oral Cavity accessory organs

• Tongue

• Teeth

• Salivary glands

Buccal Phase of swallowing

Compression of bolus against hard palate; elevation of soft palate, retraction of tongue

Pharyngeal Phase of swallowing

Bolus contacts posterior pharyngeal wall; elevation of larynx; folding of epiglottis backward

Esophageal Phase of swallowing

Opening of upper esophageal sphincter, peristalsis; opening of lower esophageal sphincter

Esophagus

Flat muscular tube that transports foods and liquids to the stomach

Rugae

Longitudinal folds in the mucosa of the stomach wall that permit the expansion of the gastric lumen

Small Intestine

20ft tube that functions in the enzymatic digestion and absorption of water, organic substrates, vitamins, and ions 

Duodenum

(the “mixing bowl”) receives chyme from stomach and digestive enzymes from pancreas and liver. Contains the pylorric sphincter

Jejunum

Bulk of chemicals and nutrients, absorption takes place here

Ileum

Controls flow of material into the large intestine via the ileocecal valve

The mixing bowl

The duodenum receives chyme from the stomach and mixes it with digestive enzymes from the following organs

• Liver: bile from the liver empties into the duodenum via the common bile duct  

• Pancreas: digestive enzymes from the pancreas (pancreatic juice) enter the duodenum through the main pancreatic duct

Absorptive Structures of the Small Intestines

Plica circulares 

Villi 

Microvilli: These structures function to increase the surface area of the inner intestinal wall

Movement of material through the large intestine

• Slow passage of material via peristaltic activity and Haustral Churning

• Periodic mass movements of fecal matter via powerful peristaltic contractions 

• Distension of recal wall stimulate conscious urge to defecate

Internal anal sphincter

Involuntary smooth muscle that relaxes in response to rectal wall distension  

External anal sphincter

Voluntary skeletal muscle whose relaxation allows for defecations 

The Liver

Largest visceral organ

Perform 200+ functions related to:

• Metabolic regulation: extraction and storage of nutrients from the blood; detoxification of harmful materials; storage of fat-soluble vitamins  

• Hematological regulation: blood reservoir and filter; removal of damaged blood cell/debris; synthesis of plasma proteins 

• Bile production 

Bile Production and Pathway

• Bile is produced in the liver and drained by right and left hepatic ducts into the common hepatic duct 

• Bile flows from the common hepatic duct through the cystic duct into the gallbladder for storage and concentration 

• When a fatty meal is eaten, bile is expelled from the gallbladder through the cystic duct into the common bile duct 

• The common bile duct empties bile into the duodenum to facilitate the breakdown of lipids into fatty acids suitable for absorption

Hepatic Portal System

• Normal blood flow: Aorta artery - capillary bed - vena cava veins - heart

• Portal system blood flow: Aorta artery - capillary bed in small and large intestines - Hepatic Portal vein - capillary bed in Liver - Inferior vena cava vein - heart 

• Most of the blood from the digestive tract is drained by the hepatic portal system.  Blood flowing in veins from the digestive organs drains into hepatic portal vein. 

• The hepatic portal vein drains blood into the liver, where it is filtered by specialized capillary beds (sinusoids). The modified/filtered blood then flows through the hepatic vein and into the inferior vena cava to the heart.

Blood Supply to the Digestive System

3 unpaired branches of the abdominal aorta provide blood supply to the digestive system: Celiac Trunk, Superior Mesenteric artery, and Inferior mesenteric artery

Celiac Trunk

Stomach, liver, gallbladder, pancreas, spleen, and a part of the duodenum  

Superior Mesenteric artery

Most of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, and first ½ of transverse colon

Inferior Mesenteric artery

Second ½ of transverse colon, descending colon, sigmoid colon, and a part of the rectum