Question

Chapter 23

• Identify the route and main structures along the GI tract including sphincters

• Describe the layers of the GI tract along the route

• Explain the various processes along the route including mastication, peristalsis, segmentation, deglutition, and elimination

• Differentiate between mechanical and chemical digestion along the GI tract route

• Understand the structure of the stomach and the chemical processes that occur here including the formation and role of chyme and gastric juice

• Know the various components and roles of each component in the gastric juice

• Identify the nerve plexuses involved in the process of digestion

• Describe the structure and function of the small intestine including the sections and microscopic structure (villi and microvilli)

• Explain the roles of the accessory organs in chemical digestion including the liver, gall bladder, and pancreas

• Identify which enzymes work on which types of molecules such as carbs, proteins, and lipids and where they are secreted from

• Explain the role of various hormones involved in the digestion process such as gastrin, secretin, CCK, and GIP

• Discuss the role of the hepatic portal system

Answer 1

1) Buccal cavity, tongue, pharyngs, oesophagus, cardiac spinchter, stomach (cardiac,fundic pyloric), pyloric spinchter,smallintestine, large intestine, rectum ,anus liver,pancreas,gall bladder,salivary glands

2)

Serosa :

It is outer most layer ol gut, serosa ( visceral peritoneum) is composed of areolar and simple squamous epithelium ( mesothelium). Some part of gut is lined with tunica adventitia which is made up of areolar connective tissue only.

Muscle layer:

is formed by circular inner layer and longitudinal outer layer of smooth muscles. Thickest layer is found in stomach maximum peristalsis) and thinnest layer in rectum minimum peristalsis) Stomach contains an additional oblique muscle layer just interior to circular muscle

Sub mucosa :

It is composed of areolar connective tissue layer with blood vessels, lymph vessels and nerves

Mucosa :

It is the innermost layer of gut which contains the secretory and absorptive cells Mucosa is differentiated into 3 layers.

• Outer layer (towards submucosa) is called mucosa muscularis.It is made up of smooth muscle.

• Middle layer is lamina propria it contains lym phatic tissues refers as MALT (-Mucosa Associated Lymphoid Tissue) which provides immunity

• Innermost layer (in contact of food) is epithelial mucosa

3)• Ingestion is the Process of entry of food into the alimentary canal through the mouth is termed as ingestion

• Peristalsis is involuntary movements of the longitudinal and circular muscles of alimentary wall in alternate waves of contraction and relaxation to push the food along .it also helps in mixing food with digestive juices.

• Segmentation occurs in the small intestine, here contractions of circular muscle of the muscularis layer of the alimentary canal takes place which isolate intestine into small sections , it move their contents , breaking up, and mix the contents. And facilitate absorption.

• The digested food and nutrients enters the bloodstream for work. This process is called absorption.

• Defecation or elimination is the final step of digestion, in which undigested food materials are removed from the body as feces.

• Deglutition is the transport of a bolus of food from the mouth to the stomach.

4 )Mechanical digestion is the process in which the food is broken down into digestible particles mainly by the teeth while Chemical digestion is the process by which complex compounds in the food are broken down into small simpler substances for absorption by the body.
Mechanical digestion takes place from the mouth to the stomach while chemical digestion takes place from the mouth to the intestine

Most foods in mechanical digested in the mouth while most part of chemical digestion takes place in the stomach

In mechanical digestion food is digested by teeth while chemical digestion operated by enzymes

Mechanical digestion Increases the surface area for the enzymatic reactions while chemical digestion Increases the absorption of the nutrients by breaking down them into simpler molecules

Mechanical process of digestion in intestine mainly occurs by the help of segmentation. It is a mixing of kind with digestive juice and bring food particle in to contact of mucosa.

It starts with contraction of circular muscle this action constrict the intestine in small segment and further each segment constrict from middle and divide each constricted segment again, finally first contracted fibre relax and each small segment unite with adjoining small segment, so large segment form again.