Question

1. trace the path of ingested food from the oral cavity to the anus

2. describe the digestion ( mechanical and chemical) processes and locations in the alimentary canal

3. discuss the anatomical adapations that increase the main function of the small intestine.

Answer 1

1). Path of ingested food from oral cavity to anal canal :

• Buccal cavity : this consists of teeth and tongue which causes breakdown of food products .
• Pharynx : it is a common passage of food and air , epiglottis prevents entry of food into glottis .
• Esophagus: the food processed which enters esophagus is called bolus . The food passes down by peristalsis.
• Stomach: from esophagus it enters stomach , where enzymes of stomach acts upon food and passes out as chyme .
• Small intestine: food from stomach enters small intestine, it consists of 3 parts first duodenum, next jejunum and next ileum .
• Then large intestine: it enters caecum, ascending colon , transverse colon , descending colon , sigmoid colon , rectum and finally through anal canal .

2). Mechanical digestion occurs in buccal cavity where food is broken down by mastication with the help of teeth and tongue

Chemical digestion:

• It starts from buccal cavity , where salivary glands are present these glands produce saliva which consists of ptyalin in it . This breaks down starch to dissacharide .
• In stomach , hcl from oxyntic cells , mucus and bicarbonate from goblet cells and proenzymes pepsinogen from zymogen cells which is converted to pepsin by action of hcl are present. This pepsin converts protein to peptones . Mucus and bicarbonate protects gastric mucosa from erosin .
• In small intestine, bile from liver and pancraetic juice from pancreas are secreted into the duodenum which is guarded by sphincter of odiii . Intestinal juice os also secreted . Bile causes emulsification of fat , and activates lipase to digest lipids . Pancreatic juice has trypsinogen and chymotrypsinogen which in its active form breaks down proteins , pancreatic amylase which breaks glycogen ,pancreatic lipase which breaks lipids , nuclease which breaks nucleic acids to nucleosides and nucleotides .
• Intestinal juice that is succus entericus consists of maltase , lactase , sucrase , dipeptidase , lipase , nucleosidase .

3). Small intestine is mainly associated with absorption of nutrients. It is mainly due to mucosal projections called villi , which has microvilli within it , which increases surface area of absorption. Inside the villi , the blood vessels and lacteals make up within it so nutrients is taken up by blood by diffusion or active , passive and facilitated transport . Glucose , amino acids and electrolytes are taken up by simple diffusion or by active transport against concentration gradient. Fructose is carried by facilitated transport . Insoluble substances like fatty acids , glycerol, fat soluble vitamins forms micelles taken up by lacteals in intestinal villi into lymphatic dicts and from there they reach liver to other regions where absorbed substances is utilized by tissues in the body by assimilation.