Physiology Basics: the Digestive System, Animation

Physiology Basics: the Digestive System, Animation

The digestive system is composed of 2 main
components: the gastrointestinal tract, or GI tract, where digestion and absorption take
place; and accessory organs which secrete various fluids/enzymes to help with digestion. The GI tract is a continuous chain of organs
where food enters at one end and waste gets out from the other. These organs are lined with smooth muscles
whose rhythmic contractions generate waves of movement along their walls, known as peristalsis. Peristalsis is the force that propels food
down the tract. Digestion is the process of breaking down
food into smaller, simpler components, so they can be absorbed by the body. Basically, carbohydrates such as sugars and
starch are broken down into glucose, proteins into amino acids, and fat molecules into fatty
acids and glycerol. Digestion starts in the oral cavity where
the food is moistened with saliva and chewed, food bolus is formed to facilitate swallowing. Saliva is secreted by the salivary glands
and contains the enzyme amylase. Amylase breaks down starch into maltose and
dextrin which are processed further in the small intestine. The food bolus is propelled down the esophagus
into the stomach, the major organ of the GI tract. The stomach produces gastric juice containing
pepsin, a protease, and hydrochloric acid which act to digest proteins. At the same time, mechanical churning is performed
by muscular contraction of the stomach wall. The result is the formation of chyme, a semi-liquid
mass of partially digested food. Chyme is stored in the stomach and is slowly
released into the first part of the small intestine, the duodenum. The duodenum receives the following digestive
enzymes from accessory organs: – Bile, produced in the liver and stored in
the gallbladder; bile emulsifies fats and makes it easier for lipases to break them
down. – Pancreatic juice from the pancreas. This mixture contains proteases, lipases and
amylase, and plays major role in digestion of proteins and fats. The small intestine also produces its own
enzymes: peptidases, sucrase, lactase, and maltase. Intestinal enzymes contribute mainly to the
hydrolysis of polysaccharides. The small intestine is where most of digestion
and absorption take place. The walls of the small intestine absorb the
digested nutrients into the bloodstream, which in turn delivers them to the rest of the body. In the small intestine, the chyme moves more
slowly allowing time for thorough digestion and absorption. This is made possible by segmentation contractions
of the circular muscles in the intestinal walls. Segmentation contractions move chyme in both
directions. This allows a better mixing with digestive
juices and a longer contact time with the intestinal walls. The large intestine converts digested left-over
into feces. It absorbs water and any remaining nutrients. The bacteria of the colon, known as gut flora,
can break down substances in the chyme that are not digestible by the human digestive
system. Bacterial fermentation produces various vitamins
that are absorbed through the walls of the colon. The semi-solid fecal matter is then stored
in the r. until it can be pushed out from the body during a bowel movement.

21 thoughts on “Physiology Basics: the Digestive System, Animation

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