In for nutrients through six activities: Ingestion,

In human’s body, one of the essential systems
is the digestive system, which breaks
down the foods what we eat into nutrients such as proteins, carbohydrates,
vitamins and fats. The bloodstream would be absorbed by them. Therefore, it
provides the body with energy, repair and growth. Also, the three types of processes that food able
to passes through the human body are digestion, absorption and elimination. The
digestive system prepares the body cells for nutrients through six activities:
Ingestion, Mechanical digestion, Propulsion, Chemical digestion, Absorption and



The digestive system is consists of the gastrointestinal (GI) tract also known as the digestive tract or alimentary
canal, with pancreas, liver and gallbladder. The GI tract is large muscles
with the long and twisting tube that connects from the mouth to the anus – it
consists of the oral cavity, pharynx, oesophagus, stomach, small intestine and
large intestine and anus. In addition, the teeth, gallbladder, pancreas, liver,
tongue and salivary glands are the accessory organs of the digestive system. Thus,
these organs secrete fluids into the digestive tract.

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The first digestion process of the human
body called ingestion, which is divided
into two parts: the mechanical digestion
and the chemical digestion.
Originally, the digestion processes begin in the mouth, when large pieces of
food enter the oral cavity and chewing or mastication by the teeth; the
muscular movements of the digestive tract physically break down food into
smaller particles from the oral cavity, called mechanical digestion. In this
case, the salivary glands secrete saliva and food particles mixed together,
which contain enzymes (a protein
that accelerates chemical reactions in vivo), called amylase. These smaller
particles can be used by a variety of enzymes and begin to break down
polysaccharide into disaccharides, food particles into nutrient molecules such
as starches and carbohydrates in the food, this is called chemical digestion.
Hence, saliva is helpful for moistening the food during chewing for easy passage
into the pharynx.


After a bolus of food is leaving from the oral
cavity must pass through the respiratory tract (trachea is before the
oesophagus) by a complex mechanism called deglutition and swallowing, this
makes sure the oral cavity is emptied and that food doesn’t enter the windpipe.
(CHB Leeds)


Also, the tongue, oesophagus and soft
palate involve the swallowing coordinated function. In this stage, swallowing
is a voluntary act, when the tongue forces the food into the pharynx. After
this the process is reflex. The tongue blocks the oral cavity, the nose closed
off by the soft palate and the larynx go up and make the trachea closed off by
the epiglottis. Therefore, food through assist of the gravity pushed into the
pharynx. (If we try to talking and swallowing food at the same time, the food
may enter the respiratory tract, cause a cough reflex and spit the bolus of
food out.)




Moreover, the oesophagus is a tubular
organ that serves as a passageway between the pharynx and stomach. The muscular
tubes of the oesophagus are able to carry liquids, food, and saliva from the
oral cavity to the stomach. The oesophagus must also accommodate a wide variety
of food and drink. (Many people try to eat too quickly, swallow something too
large and drink hot and cold liquids. They may feel uncomfortable).Once,
swallowing begins, all the digestive process begins automated and proceeds
under control of the oesophagus and brain.



In addition, the muscular layers of
the oesophagus are ordinarily clamped together at the upper and lower ends by
muscles, known as the sphincter. In
this case, the sphincter opens makes the oesophagus able to (peristalsis) propels food to the
stomach by coordinated contractions and relaxations of its muscular lining. After
swallowing, the sphincters relax involuntarily to allow drink or food to
through from the oral cavity into the stomach. When there is no swallowing
action, the muscles would close rapidly to prevent the swallowed food or liquid
from leaking out of the stomach back into the oesophagus or into the mouth. (,)

the alimentary canal (GI tract), walls are composed of the four basic tissue
layers, (also known as tunics). From the lumen of the GI tract, these layers
are the mucosa, submucosa, muscularis and serosa. Firstly mucosa is essentially
the mucous membrane which is the innermost layer of the GI tract. It has three
layers are epithelial, an underlying layer loose connective tissue which is
lamina propria and a thin smooth muscle layer called the muscularis mucosa. In
the oral cavity, pharynx, oesophagus and anal canal, the epithelium is stratified squamous epithelium. The stomach and
intestines have a simple columnar epithelial layer for secretion and
absorption. Under the epithelium is the lamina
propria of the mucosa which includes numerous blood and lymphatic vessels, it
transport nutrients absorbed into the GI tract to the liver. The lamina propria
also includes most of the immune cells that constitute the mucosa-associated
lymphatic tissue (MALT). External to the lamina propria is the muscularis mucosa layer which produces
local movements of the mucosa. Small changes in the many small folds in the
mucous membrane of the stomach and small intestine increase the surface area
available for digestion and absorption.


Secondly, the
Submucosa binds the muscularis external. It is a loose connective tissue layer
with blood, lymphatic vessels (which transports absorbed food molecules) and
nerves and the submucosal plexus (which is part of nervous system control)


Thirdly, in the
oral cavity, pharynx and middle and superior oesophagus, the muscularis (also
called muscularis externa layer), which involved skeletal muscle that we use to
swallowing autonomously. The sphincter and external was also made by skeletal
muscle, which allows us voluntary control of defecation. In addition, there are
normally two layers; the inner layer is circular,
and the outer layer is longitudinal.
These layers of smooth muscle are used for peristalsis to move food through the


Finally, the
serosa is the outermost layer of the intraperitoneal organs. In most case GI
tract, this serous membrane is made up of areolar connective tissue with
mesothelium, a single layer of squamous epithelial cells.
















The stomach
contains two sphincters at both ends to regulate food movement. (The cardiac
sphincter near the oesophageal, and pyloric sphincter near the small
intestine).It makes the bolus of food can smoothly enter and leave the stomach.
The stomach is J-shaped sac; divided into four regions are the funded, cardiac,
body, and pyloric. It also contains thick fold called gastric rugae at its
layer, as the stomach expands the rugae flatten out to allow the stomach’s
expansion. Furthermore, the main functions of the stomach are bulk storage of
food, digestion of proteins, kill bacteria with the strong acidity (low pH of
the gastric acid), mechanical- and chemical digestion.


Once the
food enters the stomach, caused lining releases enzymes that begin breaking
down proteins in the food.  Protein
digestion is conducted by an enzyme called pepsin in the stomach chamber. In
the highly acidic environment able to kills many microorganisms in the food
and, combined with the action of the enzyme pepsin, results in the catabolism
of protein in the food. Chemical digestion is promoted by the churning action
of the stomach caused by contraction and relaxation of smooth muscles.


Moreover, gastric acid contains hydrochloric acid, mucus and pepsinogen; important ingredients to
digestion. Secretions are controlled by nervous and endocrine signals. The
hydrochloric acid and pepsin secreted by the stomach. Hydrochloric acid (HCl)
lowers pH of the stomach, therefore, pepsin is activated. Pepsin is an enzyme
which controls the hydrolysis of proteins to peptides. Chemical digestion is promoted by
the churning action of the stomach caused contraction and relaxation of smooth
muscles. Chemical digestion is aided by mechanical
digestion in the stomach. Peristalsis of the stomach wall churns food for
several hours. It breaks down the food into smaller pieces mechanically. The
partially digested food mixes with digestive acid it produces and slowly
empties its contents, called chyme.

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