Question

1. Discuss six fundamental activities of the digestive system, giving an example of each

2. Compare and contrast the neural and hormonal controls involved in digestion

Answer 1

1. The six findemental activities of the digestive system are as follows,

a) Ingestion of food, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that break down carbohydrates and lipids.

b) Propulsion of food, which  is the movement of food along the digestive tract., swallowing is an example of propulsion.

c) Peristalasis, which consists of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along.

d) Mechanical digestion of food : Mechanical digestion involves physical movement to make foods smaller,  It includes mastication, or chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva. The mechanical churning of food in the stomach serves to further break it apart

e) Chemical digestion of food : chemical digestion uses enzymes to break down food, chemical digewstion starts in the mouth and is completed in the small intestine, for eg, breaking of proteins into smaller amino acids.

f) Absorption : This involves movement of nutrients from the GI tract to blood or lymph, which takes place primarily within the small intestine. where most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream.

g) Defecation, which involves elimination of waste food or undigested food and mainly takes place in the large intestine

2.) The activities of the digestive system are regulated by both hormones and neural reflexes

Neural control, the walls of G.I tract contain various receptors like, mechanoreceptors, chemical receptors, osmoreceptors which are capable of detecting various stimuli, these receptors can sense when the presence of food has caused the stomach to expand, whether food particles have been sufficiently broken down, how much liquid is present, and the type of nutrients in the food.. Stimulation of these receptors causes an appropriate reflex that improves the process of digestion. The walls of the entire alimentary canal are embedded with nerve plexuses that interact with the central nervous system and other nerve plexuses, the myenteric plexus (plexus of Auerbach) lies in the muscularis layer of the alimentary canal and is responsible for motility, especially the rhythm and force of the contractions of the muscularis. The submucosal plexus (plexus of Meissner) lies in the submucosal layer and is responsible for regulating digestive secretions and reacting to the presence of food.

Hormonal control, Hormones play an important role regulating gastric motility. They also control the secretion of gastric and pancreatic juice plus other secretory activities.The main digestive hormone of the stomach is gastrin, which is secreted in response to the presence of food,  During a meal, gastrin stimulates the stomach to release gastric acid. This allows the stomach to break down proteins swallowed as food and absorb certain vitamins. other hormones involved include, secretin produced by the duodenum which is responsible for secretion of bicarbonates, cholecystokinin,which stimulates the secretion of pancreatic enzymes and bile from the liver and release of bile from the gallbladder.