DIGESTIVE SYSTEM

I.   INTRODUCTION
–  Gastrointestinal (GI) tract: tube that extends from mouth to anus
*  mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus
*  functions:
*  digestion:  process of breaking down food into small fragments

* Mechanical digestion:

* Chemical Digestion:

*  absorption: water and food molecules pass through to lymphatics and blood vessels

* elimination of wastes

–   accessory digestive organs: not part of GI tube, but assist with digestion
*  tongue, teeth, salivary glands, liver, gallbladder, pancreas

--  digestive system controlled by autonomic nervous system
*  parasympathetic:  increases activity of GI tract

*  sympathetic:  decreases activity of GI tract

–  abdominopelvic cavity is lined by peritoneum
*  parietal peritoneum lines abdominal wall
*  visceral peritoneum covers abdominal organs

*  peritoneal cavity

II.  ORAL CAVITY (MOUTH)
–  continuous posteriorly with oropharynx
–  nonkeratinized stratified squamous epithelium

–  upper part of the oral cavity: palate
*  hard palate:  anterior 2/3 of palate, bony

*  soft palate:  posterior 1/3, formed from skeletal muscle

* uvula

- teeth:

–  tongue

*  functions:

*   stratified squamous epithelium

–  3 pairs of salivary glands:

*  secrete saliva

*  functions of saliva:

What do you think?  Research suggests that a “dry mouth” (inadequate production of saliva) is correlated with an increase in dental problems, such as cavities.  What are the possible reasons for this correlation?

III. PHARYNX
–  “throat”
–  muscular tube that connects nasal cavity and mouth, to larynx and esophagus
*  function:

–  only the oropharynx and laryngopharynx conduct both food and air!

*  epithelium of both is nonkeratinized stratified squamous epithelium

IV.  GENERAL HISTOLOGY OF GI TRACT (ESOPHAGUS TO LARGE INTESTINE)
–  the walls contain 4 layers, or tunics:

A.  Mucosa:  innermost tunic

1)  epithelium:

*  esophagus has nonkeratinized stratified squamous epithelium
*  stomach to anal canal has simple columnar epithelium

2)  areolar CT

3)  Muscularis Mucosae:  thin layer of smooth muscle

B.  Submucosa:
*  connective tissue
*  contains major blood vessels

C.  Muscularis:           
*  typically contains 2 layers of smooth muscle:
*  exception:  stomach

1)  inner circular layer
2)  outer longitudinal layer

*  responsible for peristalsis: alternate waves of contraction and relaxation

D.  Serosa or Adventitia:  outermost layer
*  serosa = visceral peritoneum + areolar CT

*  adventitia = areolar CT only

V.   ESOPHAGUS

A.  Gross Anatomy:
–  muscular tube that connects pharynx to stomach
–  function:

B.  Histology:

–  mucosa: nonkeratinized stratified squamous epithelium

--  muscularis:  2 layers of muscle
*  upper 1/3:  skeletal muscle
*  middle 1/3:  skeletal + smooth
*  lower 1/3: smooth muscle only

VI.  STOMACH

A.  Gross Anatomy:
–  connects to esophagus and duodenum

–  main function:

B.  Histology:

–  mucosa has simple columnar epithelium
–  mucosa contains gastric pits

–  branching off of gastric pits are gastric glands:

What do you think? What prevents the gastric juices from eating away at the stomach itself? 

–  muscularis:  has three (3) layers of smooth muscle, not two!
*  innermost oblique, inner circular, outer longitudinal

VII. SMALL INTESTINE

A.  Gross Anatomy:
–  functions:

1)

2)

–  3 specific segments:

1)  duodenum:
*  receives bile and pancreatic enzymes through duodenal papilla

2)  jejunum:  2nd part

3)  ileum:  3rd part
*  connects to cecum of large intestine

B.  Histology:

–  mucosa has simple columnar epithelium w/ goblet cells

–  circular folds (plicae circulares):
*  folds of mucosa AND submucosa!

* functions:

–  on circular folds are villi
*  folds of the MUCOSA only!
* function:

*  in center of each villus are blood vessels and a lacteal

VIII. LARGE INTESTINE

A.  Gross Anatomy:
-- functions:

– specific segments :

1)  cecum:  sac, connects to ileum
* lower right part of abdomen
*  vermiform appendix

2)  ascending colon:  right side of body

3)  transverse colon:  runs from the right to left side of body

4)  descending colon:  left side of body

5)  sigmoid colon:  in pelvic cavity, S-shaped

6)  rectum and anal canal: terminal portion of large intestine
*  feces leaves anal canal through anus (external opening)

 

NOW YOU SHOULD KNOW HOW FOOD TRAVELS THROUGH THE GI TRACT.
REVIEW THIS PROCESS WITH THE   FOOD FLOW LEARNING EXERCISE

B.  Histology:

–  mucosa: simple columnar epithelium w/ goblet cells

–  muscularis:  2 layers of smooth muscle
*  outer longitudinal layer consists of  teniae coli

**  haustra

REVIEW THE EPITHELIAL LININGS AND FUNCTIONS OF THE GI SEGMENTS WITH
THE  DIGESTIVE SYSTEM: EPITHELIUM/FUNCTION MEMORY MATRIX

NOW COMPARE AND CONTRAST THE "TUNICS" AMONG THE DIFFERENT PARTS
OF THE GI TRACT, WITH THE  GI TUNICS MEMORY MATRIX

IX.  LIVER, GALLBLADDER, PANCREAS

A.  Liver:
–  upper right part of abdomen
– functions:

1)

2)

B.  Gallbladder:

–  underneath liver
–  function:

C.  Pancreas:

–  behind stomach
–  acinar cells
*  secrete pancreatic juice

*  the pancreatic juice is carried out via a pancreatic duct

WE NOW HAVE COVERED ALL OF THE ACCESSORY DIGESTIVE ORGANS.  REVIEW
THEIR CHARACTERISTICS AND FUNCTIONS WITH THE
 ACCESSORY DIGESTIVE ORGANS MEMORY MATRIX

SEVERAL ACCESSORY GI ORGANS SECRETE MATERIALS TO AID WITH DIGESTION.
REVIEW THEM WITH THE  GI SECRETIONS MEMORY MATRIX

X.   BILIARY APPARATUS

– biliary apparatus: a network of “tubes” that transport bile and pancreatic juices TO the duodenum!
-- right and left hepatic ducts drain all bile from liver
-- Right and left hepatic ducts unite to form the common hepatic duct

--  Gallbladder has a cystic duct

-- Cystic duct and common hepatic duct unite, forming common bile duct
* it connects with pancreatic duct

–  common bile duct opens into duodenum at the duodenal papilla
*  here, bile and pancreatic juices are secreted!

XI.  BLOOD SUPPLY TO ABDOMINAL GI TRACT

A.  Arterial Supply:
–  from branches of:

1)  celiac trunk

2)  superior mesenteric artery
3)  inferior mesenteric artery

B.  Venous Supply:

--  hepatic portal system: veins that drain blood from GI tract directly TO liver

-- 4 main veins:

1.  Superior Mesenteric vein
2.  Splenic vein
3.  Inferior Mesenteric vein
4  Hepatic portal vein - receives blood from 1,2, and 3, and goes directly to the liver   

 

–  blood from hepatic portal vein is processed by the liver cells (hepatocytes)

–  once processed, the blood from the liver then goes into the inferior vena cava

REVIEW HOW VENOUS BLOOD TRAVELS FROM THE GI TRACT, TO THE LIVER,
AND THEN TO THE SYSTEMIC CIRCULATION BY COMPLETING THE
 HEPATIC PORTAL SYSTEM LEARNING EXERCISE

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