Download Lab #5: Animal Digestion

Lab #5: Animal Digestion and Digestive Structures
OBJECTIVES:
•
Compare the basic layout and functions of digestive organs of the different animal forms
INTRODUCTION
In this Lab exercise, we will explore the digestive structures of animals. The main objective of this lab is to compare
the various digestive structures of the animal kingdom (relying on some of our previous work).
As you may recall from our study of animal diversity, the evolution of digestive structures and systems played a big
part in the changes we saw in various animal bodies. Briefly, we began our look at the animal kingdom by examining the
animals with body cavities that took on numerous roles for the organism. For instance, the spongocoel of a Poriferan and
the gastrovascular cavity of Cnidarians and Platyhelmintheans served the animals as digestive, circulatory, and excretory
structures. In the “simpler” animals, this one cavity must serve all these roles (among others). These cavities we
considered as “incomplete”. Later, in the more “complex” animals we see “complete” digestive tracts that function
almost entirely for digestive function (along with removal of solid waste). These complete digestive tracts are one-way,
two-opening tracts which are often “regionalized” and included specific segments that handled various digestive and
absorptive functions. For instance in the earthworm (Phylum Annelida), we will see in lab today that the digestive tract is
organized into a “mouth” a “pharynx”, an “esophagus”, a “crop”, a “gizzard”, an “intestine” and an “anus” that all have
specific functions for the overall process of the digestive system. Not all animals contain these regions, but the overall
processes are basically the same.
Part 1: A Tour through the Animal Kingdom, Gazing at the Digestive Systems and Structures
Background: As mentioned above, there is a wide array of digestive systems and structures we have already looked at as
we examined the “evolutionary trends” of the Animal Kingdom. This is an opportunity to bring all of these different
digestive structures into view at one time for comparison. As you examine the slides, consider the following questions…
• What are the digestive structures you can see and identify?
• Is this a complete or an incomplete digestive system? You may have to look and consider beyond the crosssectional slides.
• How are digestion and absorption processes handled by these structures?
• How are the products of digestion (basically organic and inorganic nutrients) distributed from these structures to
the other cells of the body?
Materials Needed
Preserved specimens for dissection: Rat (1 rat per 2 students)
Pigeon demonstration (if available)
Plastic earthworm model, hydra model
Various slides (see below)
Structures and cells to look for and identify:
Microscope Slides & models:
For each of the specimens below, note what phylum they belong to.
o
Grantia (c.s. and l.s.)—Identify the ostia (pores), spongocoel, choanaocytes
o
Hydra (c.s.)—Identify gastrodermis, epidermis, gastrovascular cavity
o
Planaria (c.s. and l.s.)—Identify the gastrovascular cavity intestine; pharynx, pharyngeal cavity
o
Earthworm (c.s.)—Identify the intestine, typhlosole (functions to increase surface area of the intestine), and
the coelom (look for mesodermal layers), epidermis
•
Earthworm model: Use this to draw and identify the regions of the digestive tract. Using your textbook and
other resources, label the mouth, pharynx, esophagus, crop, gizzard, and intestine.
Lab: Animal Digestion
Part 2: Animal Dissection
Use the Rat Dissection handout for instructions on proper analysis and dissection techniques.
In your notebook, make a drawing of the rat and clearly identify each of the structures listed below. You will also need to
know the functions of each structure, but you do not have to list function in your notebook.
Rat
External Anatomy: mouth, incisors, anus
Internal Anatomy: coelom, liver, esophagus, stomach, spleen (not-digestive), pancreas, small intestine (specific area of
duodenum as well as entire small intestine), mesentery, caecum, large intestine, rectum
Note: You will not be seeing structures of the upper portion of the digestive track this week (e.g. pharynx, salivary glands,
epiglottis). You will see them when the thoracic cavity is opened for circulation.
Part 3: Demo Pigeon
Examine the demonstration pigeon at the front of the room.
In your notebook, make a drawing of the pigeon and clearly identify each of the structures listed below. You will also
need to know the functions of each structure, but you do not have to list function in your notebook.
Pigeon
External anatomy: beak, vent
Internal Anatomy: esophagus, crop, stomach, gizzard, small intestine, large intestine, cecum, rectum
For your Notebook:
1. Labeled drawings of the slides and earthworm model – include specimen name, total magnification, labels of structures
to identify and any notes that will help you with identification for study and for the practicum!
2. Labeled drawings of rat and pigeon with clear labels for structures to identify.
3. Question for discussion/conclusion: Compare and contrast the digestive systems of the bird and the rat, two vertebrate
animals. Describe common structures and features, and how these features are modified for the particular organism’s
diet and lifestyle.
NOTE: Get checked off for your rat dissection before leaving lab!
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