Question

Starting with the actions in the mouth describe the digestion, absorption, and elimination of a meal containing carbohydrates, lipids, and proteins (include mechanical and chemical digestion in each of the structures of the GI tract, the enzymes, movement of the material through the digestive tract, the roles of the accessory structures in digestion, and changes in pH).

Answer 1

Digestion:

· The digestion of food starts in the mouth or buccal cavity.

· The first process is mechanical digestion.

· This involves mastication of food particles by teeth.

· Food chewed and mixed with saliva forms a mass of ball like structure called the bolus, which help it to pass through the esophagus.

· Chemical digestion initiates in mouth with salivary digestion of starch.

· Saliva contains amylase enzyme, or Ptyalin.

· Salivary Amylase act on raw form of carbohydrates

· Pancreatic amylase is released by the pancreas into the duodenum.

· Pancreatic amylase work on complex form of carbohydrates and carbohydrates entering the intestine after partial digestion that remains undigested by salivary amylase.

· Thus, two amylases ensure that all carbohydrate forms are converted to simpler form or glucose.

· The 3 stages of swallowing is described as:

1.Oral phase- chewing of food, mixing with saliva. Bolus formation.

2.Pharyngeal phase- prevention of food from entering the respiratory tract.

3.Esophageal phase- Peristalsis of food to stomach through esophagus.

· The food then reaches the stomach.

· The stomach is divided into 3 regions: Cardiac-esophagus joins to this portion, Body- the middle and largest portion, Fundus- lower portion opening to intestine.

· Crunching mechanism by stomach muscle further aid in mechanical digestion of the food and converts it intoa semiliquid for.

· Protein digestion in stomach is conducted by pepsin.

· Pepsin is activated from pepsinogen in acidic pH. This is mediated by Oxyntic or Parietal cells, that produce. HCl.

· Antacids Eg. Milk of magnesia results in neutralization of stomach acid.

· Thus, excess of antacids causes change in stomach pH from acidic to neutral and prevent pepsin function.

· The effect of pH may be detected by measuring the activity of pepsin enzyme in acidic, neutral and basic pH.

· The acidic food pulp called chyme then enters the small intestine.

· The small intestion has three parts: Duodenum, Jejunum and ileum.

· Protein digestion is further completed in the small intestine. The enzymes include: trypsin, chymotrypsin, Carboxypeptidases (A and B), elastases.

· Protein digestion involves breaking of peptide bonds with help of peptidases enzymes.

· Peptide bonds are broken to produce simple di-peptides and tri-peptides and some amino acids.

· Carbohydrate digestion occurs further by Pancreatic amylases. Simple sugars are produced. The undigested part of fibres pass to large intestione.

· Liver produce bile juice.

· Bile helps in emulsification of fat.

· The bile is produced by liver is carried by the common hepatic duct to the gall bladder.

· Gall bladder is a hollow organ that is located beneath the liver.

· It stores bile and releases it to the duodenum via the common bile duct.

· If gall bladder is removed (cholecystectomy), the liver continues to supply bile directly and continuously.

· The reservoir for bile or gall bladder removal will pose difficulty when large amount of fat is endured or when there is saturated or hydrogenated fat.

Absorption:

· The absorption of food occurs through the lining of the small intestine.

· The intestinal walls have folds designated as Picae circulars and rugae, which help in absorption by distention and movements.

· The inner surface of small intestine is lined with columnar epithelium that has projection called villi or microvilli. These increase the absorptive surface.

· The digested and simplified substances may diffuse through the lining.

· Also, Sodium and potassium ions (thorough facilitated diffusion or pumps) help in movement of the simplified food through intestinal cells and get absorbed in blood.