Description
- INTRODUCTION
- The gastrointestinal system is divided into the organs of the alimentary canal or gastrointestinal (GI) tract, and the accessory digestive organs. The alimentary canal includes the following organs: mouth, pharynx, esophagus, stomach, small intestine, and large intestine. It is a continuous tube that stretches from the mouth to the anus. The alimentary canal functions to breakdown food by mechanical and chemical processes
- Peristalsis, the wavelike contraction of longitudinal and circular smooth muscles of the muscularis externa, serves to move food along the alimentary canal. In the esophagus, peristaltic contractions quickly move the bolus (ball of food) from the mouth to the stomach. Gastric glands in the stomach secrete hydrochloric acid and pepsinogen, the precursor protein of the enzyme. Low pH, the hydrolytic activity of pepsin, and contractions of the longitudinal, circular, and oblique layers of the muscularis externa turn the food into a partially digested mass called chyme. Once the chyme passes into the duodenum of the small intestine, each peristaltic contraction of the small intestine will only move food forward about 1 cm. In contrast, segmentation, which is coordinated movements of the musclaris externa that causes mixing of food, takes over in the small intestine.
In the small intestine, digestive enzymes from the pancreas and bile, which were produced in the liver and stored in the gall bladder, are released into the duodenum by a valve called the hepatopancreatic sphincter. Most of the absorption of nutrients occurs in the small intestine, and it is accomplished efficiently because of the high surface area in small intestine. The mucosal tunic of the small intestine folds to create fingerlike projections into the lumen of the small intestine called villi. A layer of absorptive cells (simple columnar epithelium) line the villi, and the plasma membrane of each cell forms small projections, microvilli, into the lumen that may be mistaken for cilia. However, these cells are non-ciliated. The circular folds of the small intestine are formed by deep, permanent folds of the mucosal and submucosal layers. The villi, microvilli, and the circular folds function to vastly increase surface area of the small intestine, allowing absorption of nutrients into the network of capillaries and lymphatic vessels that underly the villi in the submucosa.
Simple sugars (monosaccharides) and amino acids are absorbed by absorptive cells and into the capillaries in the underlying submucosa. Lacteals, vessels of the lymphatic system, are also found in the submucosa. These vessels absorb tiny emulsified particles of fat called chylomicrons, which are transported through the lymphatic system as chyle and eventually into the systemic circuit. By the time the digested food reaches the ileocecal valve, between the ileum of the small intestine and the cecum of the large intestine, most nutrients have been absorbed by the small intestine.
The muscular layer of the muscularis externa of the large intestine is reduced to three longitudinal layers, called teniae coli. Large pouchlike sacs, haustra, fill with the remaining fecal matter. The remaining water is absorbed by the large intestine. Additionally, bacteria comprising the normal flora produce vitamins B and K, which are absorbed by the large intestine. Vitamin K is essential for proper blood clotting, and vitamin B has various functions. Undigested food is moved along the large intestine to the anus and rectum primarily by voiding, which normally occurs one or twice every 24 hours.
In the following laboratory exercises, you will explore the structure and function of the organs that comprise the gastrointestinal system.
TERMS TO DEFINE BEFORE LAB
Peristalsis
Segmentation
Chyme
Chyle
Lacteal
Villi
Microvilli
LABORATORY PROCEDURES
In Activity 1, you will identify the major organs of the gastrointestinal system on diagrams and models.
In Activity 2, you will observe prepared slides of various structures of the alimentary canal and accessory organs of the gastrointestinal system and create diagrams.
In Activity 3, you will observe and identify various structures of the gastrointestinal system by virtually dissecting a cat specimen
ACTIVITY 1 – IDENTIFY THE ORGANS OF THE GASTROINTESTINAL SYSTEM
Part 1A. Identify the Major Organs of the Gastrointestinal Systems on Diagrams
Instructions: Using your textbook, identify each of the following structures on diagrams. As you are identifying the organs, list its function in the table below.
Organs of the Gastrointestinal System
Anatomical Feature
Function
Oral Cavity & Pharynx
Oral cavity
Cheeks
Hard palate
Soft palate
Pharynx
Nasopharynx
Oropharynx
Laryngopharynx
Teeth (Accessory Organ)
Incisor
Canine (cuspid)
Premolar (bicuspid)
Molar (tricuspid)
Tongue
Salivary glands (3 pairs), (Accessory Organ)
Parotid glands
Submandibular glands
Sublingual glands
Gastrointestinal tract (alimentary canal)
Esophagus
Gastroesophageal sphincter (cardiac sphincter)
Stomach
- Lesser curvature
- Greater curvature
- Body
- Rugae
- Pyloric sphincter
- Small intestine
- Duodenum
Jejunum
Ileum
Villus (villi = plural)
- Ileocecal valve
- Large intestine
- Cecum
Appendix
Colon
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Taeniae coli
Haustra
Greater omentum
Rectum
Anal canal
Internal anal sphincter
Involuntary; prevents feces from escaping until voluntary sphincter opens.
External anal sphincter
Voluntary; allows anus to open and close voluntarily.
Liver (Accessory Organ)
Gall Bladder (Accessory Organ)
Cystic duct
Bile duct
Pancreas (Accessory Organ)
Main pancreatic duct
Hepatopancreatic ampulla and sphincter
Peritoneum
Visceral peritoneum
Parietal peritoneum
Blood Supply
Celiac trunk (artery)
- Superior mesenteric artery
Inferior mesenteric artery
Hepatic portal vein
Part 1B. Identifying the Select Muscles of the Gastrointestinal System on Models
Instructions: Watch the videos, which review structures of the gastrointestinal system using models.
Instructions: Identify the structures listed below on models. Click on the file below to access photos of models. Your laboratory atlas also has labeled photos of models.
- Click Here for Models of the Gastrointestinal SystemDownload Click Here for Models of the Gastrointestinal System
Select Organs of the Gastrointestinal System
Anatomical Feature
Pharynx & Oral Cavity
Pharynx
Nasopharynx
- Oropharynx
Laryngopharynx
Hard palate
Soft palate
Dentition
Incisor
- Canine
Premolar
Molar
Parotid glands
Submandibular glands
- Sublingual glands
Esophagus
Gastroesophageal sphincter (cardiac sphincter)
Stomach
Cardiac sphincter (gastroesophageal sphincter)
Lesser curvature
- Greater curvature
Body
Rugae
Pyloric sphincter
Small intestine
Duodenum
- Jejunum
Ileum
Villus (villi = plural)
Microvilli
Lacteal
Intestinal crypt
- Mucosa vs submucosa
Goblet cell
Large intestine
Cecum
Appendix
Ascending colon
Transverse colon
Descending colon
Haustra
- Taeniae coli
Sigmoid colon
Greater omentum
Rectum
Anal canal
- Accessory Digestive Organs
Liver
Right lobe
Left lobe
Falciform ligament
- Caudate lobe
Quadrate lobe
Liver tissue
Liver lobule
Portal triad
- Bile duct
Portal venule
Portal arteriole
Central vein
Hepatic artery (R/L)
Hepatic vein (R/L)
Hepatic portal vein
Heptaic duct (R/L)
Common hepatic duct
Gall bladder
Cystic duct
Common bile duct
Pancreas
- Main pancreatic duct
Hepatopancreatic ampulla
Visceral peritoneum
Parietal peritoneum
Celiac trunk (artery)
- Superior mesenteric artery
Inferior mesenteric artery
ACTIVITY 2 – MICROSCOPIC OBSERVATION OF TISSUES OF THE GASTROINTESTINAL SYSTEM
Instructions: Watch the video, which reviews various tissues of the gastrointestinal system., then create a quick sketch of each tissue and label the structures listed below. You may also use your lab atlas and textbook as resources.
Tissue
- Label the following in your drawing
Diagram
Parotid gland
· Serous acinar cell
· Mucous acinar cell
· Ducts
· Adipocytes
Magnification: _____X
What is the functional difference between serous acinar cells and mucous acinar cells?
- Tissue
Label the following in your drawing
Diagram
Stomach tissue
· Gastric pit
- · Rugae
· Mucous cells
· Lamina propria
Magnification: _____X
What are rugae, and how are they beneficial in the stomach?
- Which cells in the stomach secrete hydrochloric acid? Which cells secrete pepsin?
Tissue
Label the following in your drawing
Diagram
Duodenum
· Villi
- · Mucosa
· Submucosa
· Crypt
· Lumen
Magnification: _____X
Tissue
- Label the following in your drawing
Diagram
Jejunum
· Villi (longer)
· Mucosa
· Submucosa
- · Crypt
· Lumen
Magnification: _____X
Tissue
Label the following in your drawing
Diagram
- Ileum
· Villi (shorter)
· Mucosa
· Submucosa
· Crypt
· Lumen
- · Peyer’s patch
Magnification: _____X
What do all of the small intestine tissues have in common?
What are the differences between the tissues of the small intestine?
Tissue
- Label the following in your drawing
Diagram
Large intestine
· No villi
· Mucosa
· Submucosa
- · Crypt
· Lumen
Magnification: _____X
What is one major structural difference between the tissues of the small intestine and the tissue of the large intestine?
What are the major functional differences between the small intestine and large intestine?
Tissue
- Label the following in your drawing
Diagram
Normal liver
· Central vein
· Lobule
· Portal triad (if you can identify it)
- Magnification: _____X
Tissue
Label the following in your drawing
Diagram
Liver (Cirrhotic)
· Central vein
- · Nodule
· Fibrous tissue
Magnification: _____X
What is cirrhosis, and how is it contracted?
What are the major structural differences between normal and cirrhotic liver tissues?
Are hepatocytes regenerative? If so, why is cirrhosis a problem? Can’t the liver just regenerate itself?
- ACTIVITY 3 – ANALYZE ORGANS OF THE GASTROINTESTINAL SYSTEM ON A CAT SPECIMEN
Instructions: Watch the video, which shows a dissection of the cat gastrointestinal system.
Instructions: Using your lab atlas and the cat dissection photos provided below, identify the organs of the digestive system on a cat specimen.
Click Here for Cat Dissection Photos
Organs of the Gastrointestinal System
- Esophagus
Stomach
Cardiac sphincter
Rugae
Cardia
Fundus
- Body
Pyloric sphincter
Pancreas
Liver
Common bile duct
Common hepatic duct
- Cystic duct
Gall bladder
Greater omentum
Lesser omentum
Duodenum
Jejunum
- Ileum
Superior mesenteric artery and vein
Ileocecal valve
Cecum
Ascending colon
Transverse colon
Descending colon
- Rectum
