Download doc Lab 11

LAB 11
THE MAMMALS
Answers to the lab manual questions:
Digestive System
 How may a plant diet influence the structure and functions of an herbivore’s digestive
system?
(This question relates to the 4th question below) The length of the digestive tract of a
vertebrate is related to its diet. Herbivores require longer tracts because plant material
is harder to digest (requiring more time) than meat (muscle tissue). The longer the tract,
the more time it takes for the food to pass through it, and the more time available for
digestion and absorption. So, if a rat’s diet were largely plant material, they may evolve
longer tracts with a large caecum. This is true for rabbits and other herbivorous
vertebrates. In Lab 10, you learned about tooth structure adaptations in herbivores.
 Why would protein-digesting enzymes in the stomach normally be inactive?
To prevent digestion of the lining of the stomach.
 What is the role of the sodium bicarbonate released by the pancreas into the small intestine?
To neutralize the acidic secretions of the stomach which are entering the small intestine.
The release of sodium bicarbonate is triggered by receptors in the small intestine that
sense the low pH.
 What function would a caecum have in herbivorous mammals?
The caecum (cecum) is a sac located between the small and large intestine. In
herbivorous animals it is the home for mutualistic (+/+ symbiotic relationship) bacteria
that produce cellulase, an enzyme that breaks down the cellulose in the cell walls of
plants and some algae. The caecum of a koala is 2m long! A koala’s diet consists only of
eucalyptus leaves which have little nutritional value to the koala until the leaves are
fermented by the bacteria.
A word of caution to small pet owners: some rodents (e.g., guinea pigs, hamsters) and
rabbits (lagomorphs, not rodents) practice the behavior of “coprophagy” (copro = feces;
phage = to eat); they eat their own feces. Why? Think about the location of the caecum.
It is located AFTER the small intestine, the main structure of nutrient absorption. The
bacteria’s enzymes thus have little benefit. By eating their feces (and thus the beneficial
bacteria), the bacterial enzymes can be used in the stomach to digest plant material.
Now you will think twice before letting your guinea pig share your salad.
Urogenital System
 What are the functions of the adrenal glands?
The adrenal glands release hormones such as adrenaline.
 How do the number of openings in a female and male rat compare to that in female and male
perch?
Rat
Female: 3 (anus, urethra, vagina)
Male: 2 (anus, urethra)
Perch
Female: 2 (anus, urogenital pore)
Male: 3 (anus, urinary pore, genital pore)
Circulatory System
 Why would the ventricles need thicker, more muscular walls than the atria?
Thicker, more muscular walls allow the blood from the ventricles to be pumped with
greater force and under higher pressure. This is important because the blood is leaving
the heart (in arteries). The blood from the right ventricle is pumped to the lungs and
the blood from the left ventricle goes to the rest of the body.
 What is the function of the coronary arteries and coronary veins?
The coronary arteries and veins supply O2 and nutrients to and remove CO2 and wastes
from the muscle tissues of the heart.
 Explain why the pulmonary artery may be filled with blue latex, while the systemic arteries
are filled with red latex.
Red latex is injected in the systemic arteries and blue latex is injected in the systemic
veins to make their identification easier. Commonly the blue latex is injected into one of
the thoracic veins (e.g., jugular) returning to the heart. The blue latex would travel
through the heart (RA  RV) and then out the pulmonary arteries to the lungs. The
latex is too thick to travel through the capillaries in the lungs and thus stops there.
 Compare your rat’s heart to your perch’s heart dissected in Lab 9.
A fish heart only has two chambers and a mammal heart has four. Additionally, blood
flows in a single circuit in fish and in a double circuit in mammals. (see your lecture
notes for more details)