Question

DIGESTIVE SYSTEM: STRUCTURES THAT HELP PROMOTE FUNCTION

1) Provide two vertebrate innovations that helped promote ingestion of food. Include evidence to suggest the evolutionary origins of one of these innovations.

2) How does the esophagus promote both ingestion and digestion of food. For ingestion, be sure to describe how the food is moved through the esophagus.

3) Briefly describe how features of the stomach helps promotes the digestion of food. Include the major macromolecule that begins to get broken down in the stomach as well as the features that help break down that macromolecule.

4) What type of macromolecule is broken down by bile salts?

B) Explain the molecular feature of bile salts that help break down the macromolecule you described above.

5) Provide key features that promote absorption in the small intestine. Include both the organization of the small intestine at the tissue level as well as at the cellular level.

6) What animals have a crop and what is hypothesized to be the evolutionary advantage of having a crop in that organism?

7) What animals have a gizzard and why is that organ important for those animals (aka what item provides the analogous function in humans and thus why a gizzard isn't necessary)?

8) What type of organisms have rumens and why is a rumen important in these animals?

9) Provide the types of animals that have a large cecum and explain why.

B) Do humans have a cecum and if so, where is it found?

10) What is the function of the appendix in humans and what is it thought to have been derived from?

Answer 1

I am answering 5 subparts of the question (10 questions) given in here.

1) What animals have a crop and what is hypothesized to be the evolutionary advantage of having a crop in that organism?

Crop, also known as craw, is a muscular, thin-walled extension to the alimentary canal found in animals such as earthworms, slugs, leeches, snails and certain birds and insects. This organ functions to store food before being digested. Birds are known to carry food to their young ones in this crop. From the evolutionary point of view, it also helps the organisms to quickly take in excess of food, reserve some for times when there is scarcity. They may also benefit by quickly moving to a sheltered location, away from the eyes of the predators and then slowly digest the food. Certain birds such as flamingos produce partially digested food and store it in the crop. When they reach their nest, they feed their chicks with this partially digested food also known as ‘crop milk’.

2) What animals have a gizzard and why is that organ important for those animals (aka what item provides the analogous function in humans and thus why a gizzard isn't necessary)?

Gizzard, also known as gastric mill is an organ found in the digestive tract of animals such as dinosaurs, earthworms, alligators, crocodiles, some gastropods, some crustaceans and fish. It is usually located between crop and intestine.It helps in digestion of food that is difficult to digest. Teeth provide for the analogous functions in humans and therefore gizzard is not necessary. Mostly, humans cook food to make it soft and teeth help in grinding the food.

3) What type of organisms have rumens and why is a rumen important in these animals?

Animals such as deer, buffalo, camels, sheep, cattle, goat and elk. They have four compartments/chambers to the stomach. The four chambers are reticulum (having a unique honeycomb pattern), rumen (having several papillae that increase the surface area), omasum (having several folded tissues) and abomasum. The plant matter chewed and swallowed by the ruminants is separated into solid and liquid in the rumen. The rumen is a hub for fermentation as many microorganisms are provided shelter here. The microbes ferment food and produce large amount of volatile fatty acids which the organism uses as energy. Gases such as methane and carbon dioxide are removed by belching. Solids are regurgitated to the mouth to be broken down. The liquid drains into the reticulum. From the reticulum the liquids go to the omasum where fatty acids, sugars and nutrients are absorbed in the blood stream. From the omasum, food is then transported to the abomasum, the final stomach compartment that also secretes rennet.

4) Provide the types of animals that have a large cecum and explain why.

Cecum is necessary for animals who have a plant based diet, ideally the herbivores to break down cellulose. Cecum functions to absorb fluids and salts that are made after intestinal digestion and absorption and to mix its contents with mucus. In rodents such as rats, the cecum helps to ferment grains and seeds by breaking cellulose into nutrients.

B) Do humans have a cecum and if so, where is it found?

Humans do have cecum and it is present as a muscular pouch within the peritoneum at the beginning of the large intestine. It has a thick mucous membrane which secretes mucus through which salts and water are absorbed.

10) What is the function of the appendix in humans and what is it thought to have been derived from?

In humans, the appendix does not have a known function. It acts as a storeroom for good bacteria. It is known as a vestigial organs.