An In-Depth Report: The Human Digestive System, Function, and Diseases

This report provides a comprehensive overview of the human digestive system, starting with the mouth and progressing through the pharynx, esophagus, stomach, small and large intestines, rectum, anus, and associated organs like the pancreas, liver, and gallbladder. It details the mechanical and chemical processes involved in digestion, including the roles of enzymes such as salivary amylase, proteases, and lipases. The report further explores chemical tests for micronutrients, including starch, proteins, lipids, reducing sugars, non-reducing sugars, and vitamins, providing insights into their detection. It also covers the sources and deficiencies of carbohydrates, proteins, water, vitamins, and minerals. Finally, the report addresses a common digestive disease, celiac disease, describing its symptoms and management. The report is well-referenced with sources cited at the end.

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THE DIGESTIVE SYSTEM
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THE DIGESTIVE SYSTEM
The digestive system is a collection of organs which work in unison in converting food
through physical or chemical means into energy and nutrients.
Mouth
The mouth is the beginning of the alimentary canal located superior to the chin and
inferior to the nose. The oral cavity is surrounded by the alveolar bone, the back is covered by
the isthmus of the faucets and hard palate at the front of the roof. The cavity is occupied by the
tongue. The mucous membranous line covers the sides and the below surface of the tongue. The
mouth contains submandibular and sublingual glands which secrets the saliva (Shield et al.
2017). The area between the teeth, lips, and cheeks is known as the vestibule. The mouth orifice
is the line between the upper and the lower lips.
Pharynx
This is a muscular tubule projecting from the lower end of the skull to the base border of
the cricoid cartilage. It is divided into Nasopharynx is the upper part connecting to the skull, it
comprises of the adenoids which are the lymphoid structures on its posterior wall. The
oropharynx is located behind the oral cavity. It has epiglottis which closes the glottis, The
laryngopharynx as the caudal portion of pharynx connects the throat and esophagus.
Esophagus

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A muscular tube behind the trachea connecting the throat to the stomach. The walls are
made up of the mucosa, layers of muscle fibers and submucosa. It has two sphincters at the top
and bottom.
Stomach
It found on the left side of the upper abdomen, the muscular tissue connects to the
esophagus. It is surrounded by sympathetic and parasympathetic plexuses. It is flexible and has a
pyloric sphincter valve that controls food entry to small intestines. The stomach walls have
several glands for secretion of the digestive juices.
Small intestines
These are tubules connecting the stomach and the large intestines. The duodenum is the
shortest part of the small intestine and is connected to the bile duct from the liver. The jejunum is
the connection of the duodenum and ilium hence mid sectioned It has plicae and villi (Ingber
2016). Ilium is the last section connecting the small intestine to the colon, it contains the villi.
They also have secretory glands secreting digestive juice.
Large intestines
They are located from the beginning of the iliac region of the pelvis, joining the ilium to
the caecum through the ileocecal valve. It is divided into ascending colon, descending colon,
sigmoid colon and transverse colon. The parts can be intraperitoneal or retroperitoneum.
Rectum

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This is the last part of the colon which connects it to the anus is of the shape of the
sacrum and ends with an expansion of rectal ampulla.
Anus
It is the end of the digestive system located behind the perineum, a muscular opening
equipped by involuntary internal anal sphincter and voluntary external anal sphincter.
Pancreas
It is an organ located in the abdomen. It contains pancreas gland which secretes
pancreatic juice. The pancreatic duct connects to the bile duct.
Liver
It is found in the upper right quadrant of the abdomen below the diaphragm. It secretes
bile which aids in digestion, the bile duct connects to the duodenum.
Gall bladder
It is an organ cavity for storing the bile juice normally found beneath the liver
The function of the digestive system
Mechanical digestion occurs in the mouth whereby physical break down of larger food
particles to smaller particle. Salivary amylase digests starch through chemical digestion which
involves the breakdown of food into finer particles by the action of enzymes (Dawes et al 2015).

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Protein substances are broken down to amino acids by the action of the enzyme proteases a
catalyst. Water molecules are used in breakage of the bonds of the lipids in the process known as
hydrolysis, the process is facilitated by the enzyme lipase which catalyzes the reaction. The
digested food particles are then absorbed to the body cells through assimilation. The food is
absorbed by epithelial cells of the intestinal villi and microvilli. Absorption may be by active
transport through the plasma membrane of the cell walls or diffused across the plasma membrane
of the cell walls.
Chemical test for micronutrients
Starch is tested by adding the iodine-KI reagent to the food, if the color changes to blue-
black, starch is present.
Proteins are tested by adding drops of Biuret solution to the food, color change to purple
shows presence of protein.
Lipids are mixed ethanol; they dissolve to produce white emulsion hence the lipids are
present.
Reducing sugars are tested by adding few drops of Benedict's solution to the food and
heating in a water bath, if the solution changes to brick-red or orange then glucose is present
Non-reducing sugars are tested by mixing the food solution with dilute HCl and heating
before adding sodium hydrogen carbonate as it cools. Color change to brick red or yellow is a
confirmation of the presence of reducing sugars (Sauberlich 2018).

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Vitamin C by adding drops of the DCPIP to the food solution and shaking. Presence of
ascorbic acid decolorizes the DCIP.
Carbohydrates are derived from fruits, grains, vegetables, and milk products. They are the
main energy source for the body, they include lipids in the body (Berdanier and Berdanier 2015).
Deficiency can be noticed by lack of energy, hypoglycemia, and ketosis with fibers which are
obtained from vegetables, and fruits, they play an important role in peristalsis hence lack of fiber
leads to constipation.
Proteins are derived from seeds, meat, and milk products, they are bodybuilders and
inadequate proteins are characterized by weight loss.
Water is gotten from food or direct intake; it is essential in hydrolysis. Inadequate water
may lead to constipation.
Vitamins A, B, and C are derived from green vegetables with vitamin D gotten from sun
rays they play major roles bone and blood formation and boosting immunity (Kafeshani 2016).
Deficiency leads to night blindness, beriberi, anemia, and rickets respectively.
Minerals; iron, magnesium, and iodine are found in all food substances. Iron is vital in
blood formation, thyroid glands and in processing ATP (Schwalfenberg and Genuis 2015).
Deficiency leads to anemia, goiter, and hypomagnesemia respectively.
Digestive disease
Coeliac disease

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It is a disorder causing swelling and injury to small intestines. It is characterized by
diarrhea, bloating, fatigue, gas release, weight loss, anemia, and constipation (Green, Lebwohl
and Greywoode 2015). It is a prolonged condition without a cure, however, it is managed by
consumption of a gluten-free diet.

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References
Berdanier, C.D. and Berdanier, L.A., 2015. Advanced nutrition: macronutrients, micronutrients,
and metabolism. CRC Press.
Dawes, C., Pedersen, A.M.L., Villa, A., Ekström, J., Proctor, G.B., Vissink, A., Aframian, D.,
McGowan, R., Aliko, A., Narayana, N. and Sia, Y.W., 2015. The functions of human saliva: A
review sponsored by the World Workshop on Oral Medicine VI. Archives of oral biology, 60(6),
pp.863-874.
Green, P.H., Lebwohl, B. and Greywoode, R., 2015. Celiac disease. Journal of Allergy and
Clinical Immunology, 135(5), pp.1099-1106.
Ingber, D.E., 2016. Reverse engineering human pathophysiology with organs-on-
chips. Cell, 164(6), pp.1105-1109.
Kafeshani, M., 2016. Diet and immune system. Immunopathologia Persa, 1(1).
Sauberlich, H.E., 2018. Laboratory tests for the assessment of nutritional status. Routledge.
Schwalfenberg, G.K. and Genuis, S.J., 2015. Vitamin D, essential minerals, and toxic elements:
exploring interactions between nutrients and toxicants in clinical medicine. The Scientific World
Journal, 2015.
Shield, K.D., Ferlay, J., Jemal, A., Sankaranarayanan, R., Chaturvedi, A.K., Bray, F. and
Soerjomataram, I., 2017. The global incidence of lip, oral cavity, and pharyngeal cancers by
subsite in 2012. CA: a cancer journal for clinicians, 67(1), pp.51-64.