Question

1. In all mammals except for humans physical and chemical digestion begins where? Why are humans the exception?

2. Write these in the order of innermost (touching digesting food) to outermost (touching the inside of your body) and provide a brief description of each: connective tissue, epithelium, layer of muscle (thin), layer of muscle (thick) submucosa, subserosa, serosa

3. What are segmentation, peristalsis and reverse peristalsis and what is each used for in the body

Answer 1

1. Humans are special in many ways, one of them is the way humans digest their food.

The physical and chemical digestion of food in humans begins in the mouth itself. There are four sets of specialised teeth which helps in grinding, cutting and tearing of food. Teeth helps in making the large food particle to break down into small ones. This is physical digestion of food. Now the smaller food particles gets mixed with saliva with the help of tongue. Saliva contains enzymes like amylase, lipase etc. Amylase helps in the digestion of starch. It breaks down starch into simple sugars and helps in its easy digestion. Around 30% of starch is digested in mouth. This is called chemical digestion.

Humans are exception to this maybe because of having wide variety of food habit and small alimentary canal as compared to other large mammals. Because of this humans have to start digestion at an early stage.

2. Innermost to outermost :

• Epithelium
• Connective tissue
• Submucosa
• Layer of muscle (thin)
• Layer of muscle (thick)
• Serosa
• Subserosa

Epithelium is the lining of the lumen of alimentary canal.

Connective tissue who has the function of support and contains blood vessels, nerves, lymphatics.

Submucosa is thick, highly vascular. It has glands and nerve plexus.

Thin and thick layer of muscle helps in the peristaltic movement. This type of movement pushes the food bolus ahead.

Serosa consists of secretory epithelial cells. It provides partition between internal organs and abdominal cavity.

3. Segmentation is a type of intestinal motility. It occurs in large intestine and small intestine. It moves food chyme in both direction which helps it to mix well with the intestinal secretions. Segmentation occurs due to contraction of circular muscles.

Peristalsis is a series of wave like contraction and relaxation of circular and longitudinal muscle. It is an involuntary process. It helps in the movement of food bolus starting from the the oesophagus itself. The food bolus is pushed ahead by this movement.

Reverse peristalsis is the the reverse smooth muscle contraction of peristalsis. It is also involuntary in nature. It occurs during vomiting which carries food chyme from duodenum and stomach to mouth.