Question

Topic: Animal physiology and human physiology. Digestive System

1.) Identify the parts and organs of the human digestive system, and give the functions of each.

2.) How are the digestive organs modified for the efficient mechanical digestion in the following: a.) grazers (ruminants) b.) seed eaters without teeth (birds)

Answer 1

1.) The human digestive system starts with mouth & ends in rectum.

The hollow organs that make up the digestive tract are the mouth, esophagus, stomach, small intestine, large intestine, and rectum. The liver, pancreas, and gallbladder are the solid organs of the digestive system.

The mouth is the beginning of the digestive tract; and, in fact, digestion starts here when taking the first bite of food. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.

Esophagus receives food from your mouth when you swallow. By means of a series of muscular contractions called peristalsis, the esophagus delivers food to your stomach.

The stomach secretes acid and enzymes that digest food. Ridges of muscle tissue called rugae line the stomach. The stomach muscles contract periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

The small intestine has three distinct regions – the duodenum, jejunum, and ileum. Functions of the small intestine. The small intestine is the part of the intestines where 90% of the digestion and absorption of food occurs, the other 10% taking place in the stomach and large intestine. The main function of the small intestine is absorption of nutrients and minerals from food.

The major function of the large intestine is to absorb water from the remaining indigestible food matter and transmit the useless waste material from the body.

The rectum is the opening at the far end of the digestive tract through which stool leaves the body.

The liver has multiple functions, but its main function within the digestive system is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat.

Gall bladder aids in digestion by storing bile, a fluid made by the liver that helps in the digestion of fats.

Pancreas is part of the digestive system and produces insulin and other important enzymes and hormones that help break down foods.

2.) a. Grazers or ruminants (including cattle, deer, and their relatives) are unable to digest plant material directly, because they lack enzymes to break down cellulose in the cell walls. Digestion in ruminants occurs sequentially in a four-chambered stomach. Plant material is initially taken into the Rumen, where it is processed mechanically and exposed to bacteria than can break down cellulose (foregut fermentation). The Reticulum allows the animal to regurgitate & reprocess particulate matter ("chew its cud"). More finely-divided food is then passed to the Omasum, for further mechanical processing. The mass is finally passed to the true stomach, the Abomassum, where the digestive enzyme lysozyme breaks down the bacteria so as to release nutrients. Use of plant material is thus indirect, with primary processing by the bacterial flora maintained in the stomach.

b.) Birds have a duodenum and stomach similar to humans, but they also have an extra organ at this stage in digestion, the gizzard. The ventriculus, or gizzard, is a part of the digestive tract of birds, reptiles, earthworms, and fish. Often referred to as the mechanical stomach, the gizzard is made up of two sets of strong muscles that act as the bird's teeth and has a thick lining that protects those muscles .