Chapter 47: The Digestive System 05/11/17

Many birds possess crops, although few mammals do. Suggest a reason for this difference between birds and mammals.

Birds feed their young with food they acquire from the environment. The adult bird consumes the food but stores it in her crop. When she returns to the nest, she regurgitates the food into the mouths of the fledglings. Mammals on the other hand, feed their young with milk that is produced in the mother's mammary glands. Their young feed by latching onto the mother's nipples and sucking the milk. Mammals have no need for a crop in their digestive system because they feed their young a liquid, which does not require the grinding provided by the crop in birds.

Suppose that you wanted to develop a new treatment for obesity based on the hormone leptin. What structures in the body produce leptin? What does it do? Should your treatment cause an increase in blood levels of leptin or a decrease? Could this treatment affect any other systems in the body?

Leptin is produced by the adipose cells and serves as a signal for feeding behavior. Since low blood leptin levels signal the brain to initiate feeding, a treatment for obesity would need to raise leptin levels, thereby decreasing appetite.

How could a drop in plasma proteins and a decrease in bile production be related to alcohol and drug abuse?

The liver plays many important roles in maintaining homeostasis. Two of those roles are detoxifying drugs and chemicals and producing plasma proteins. A drop in plasma protein levels is indicative of liver disease, which in turn could be caused by abuse of alcohol other drugs.

Unlike many cases of convergence (see section 47.5), ruminants and langur monkeys have modified the enzyme lysozyme in the same way to achieve the same end result. Why might this case be different?

The selective pressures that guide the adaptation of mutated alleles within a population were the same in these two groups of organisms Both ruminants and langur monkeys eat tough, fibrous plant materials, which are broken down by intestinal bacteria. The ruminants and langurs hen absorb the nutrients from the cellulose by the digesting those bacteria; this is accomplished through the use of these adapted lysozyme. Normal lysozyme, found in saliva and other secretions, work in a relatively neutral pH environment. These intestinal lysozyme, however, needed to adapt to an acidic environment, which explains the level of convergence.

Birds do not have teeth. Do you think they have adaptations to processing different types of food, comparable to the diversity in mammals? If so, what might these adaptive differences be?

Whereas mammalian dentition is adapted to processing different food types birds are able to process different types of food by breaking up food particles in the gizzard. Bird diets are comparably diverse to mammalian diets; some birds are carnivores, others are insectivores or frugivores, still others omnivores.

The _______ and ______ play important roles in the digestive process by producing chemicals that are required to digest proteins, lipids, and carbohydrates. a. liver; pancreas b. producing glucose c. synthesizing vitamin K d. both a and c are correct

a. liver; pancreas

How is the digestion of fats different from that of proteins and carbohydrates? a. Fat digestion occurs in the small intestine, and the digestion of proteins and carbohydrates occurs in the stomach. b. Fats are absorbed into cells as fatty acids and monoglycerides but are then modified for absorption; amino acids and glucose are not modified further. c. Fats enter the hepatic portal circulation, but digested proteins and carbohydrates enter the lymphatic system. d. Digested fats are absorbed in the large intestine, and digested proteins and carbohydrates are absorbed in the small intestine.

b. Fats are absorbed into cells as fatty acids and monoglycerides but are then modified for absorption; amino acids and glucose are not modified further.

Which of these pairings is incorrect? a. Fat transport/lymphatic system b. Glucose transport/lymphatic system c. Amino acid transport/circulatory system d. All of these pairings are correct

b. Glucose transport/lymphatic system

The primary function of the large intestine is to concentrate wastes into solid form (feces) for release form the body. How does it accomplish this? a. By adding additional cells from the mucosal layer b. by absorbing water c. by releasing salt d. All of these are methods used by the large intestine

b. by absorbing water

Which of the following represents the action of insulin? a. Increases blood glucose levels by the hydrolysis of glycogen b. Increases blood glucose levels by stimulating glucagon production c. Decreases blood glucose levels by forming glycogen d. Increases blood glucose levels by promoting cellular uptake of glucose

c. Decreases blood glucose levels by forming glycogen

Although the stomach is normally thought of as the major player in the digestive process, the bulk of chemical digestion actually occurs in the... a. mouth b. appendix c. duodenum d. large intestine

c. duodenum

Inactive forms of some molecules are secreted... a. bc they take less material and energy b. bc they must combine water to be activated c. so their activity can be regulated d. to prevent them from clogging the gland from which they are secreted

c. so their activity can be regulated

After being absorbed through the intestinal mucosa, glucose and amino acids are... a. absorbed directly into the systemic circulation. b. used to build glycogen and peptides before being released to the body cells. c. transported directly to the liver by the hepatic portal vein. d. further digested by bile before release into the circulation.

c. transported directly to the liver by the hepatic portal vein.

Obese humans probably have high levels of leptin bc... a. leptin stimulates eating b. something is wrong with the leptin receptors in their brain leading to increased leptin production to make up for the apparent shortage c. weight gain leads to the production of leptin d. leptin responds to mechanical stimulation in the adrenal cortex

c. weight gain leads to the production of leptin

Intestinal microorganisms aid digestion and absorption by a. digesting cellulose b. producing glucose c. synthesizing vitamin K d. Both a and c are correct

d. Both a and c are correct

The small intestine is specialized for absorption because it... a. is the last section of the digestive tract and retains food the longest. b. has saclike extensions along its length that collect food. c. has no outlet so food remains within it for longer periods of time. has an extremely large surface area that allows extended exposure to food.

d. has an extremely large surface area that allows extended exposure to food.