The Human Digestive System
Intro To The Human Digestive System
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e-Human-Digestive-System/
All animals, fungi and humans are heterotrophs. A heterotroph is
an organism that obtains their nutrition by breaking down
organic molecules in foods. The digestive system varies
depending on the type of organisms; Fungi have the simplest
system and humans having the most elaborate. Like the digestive
systems in all organisms, the digestive system of the human is
vital for survival.
Most of the organs in the human body play a roll in the
digestion of nutrients. A nutrient basically is any element or
compound essential to maintain life and health. Nutrients can be
split up into 2 parts; Essential nutrients and Non-essential
nutrients. Essential nutrients include vitamins, minerals, amino
acids, fatty acids and some carbohydrates as a source of energy.
Non-essential nutrients are nutrients which the body has the
ability to synthesis from other compounds, as well as, from food
sources. Macro nutrients are nutrients that the body needs to
acquire daily in large amounts to sustain good health, and micro
nutrients are nutrients the body needs very little of and are
often stored in the body; both are vital. These nutrients are
found in the food we eat, this is where the body must break down
and digest the food and "extract" the nutrients from it.
Believe it or not, gravity helps the body digest food. Think of
the digestive system as an organic assembly line that starts at
the mouths and ends at the anus and urethra. There is anywhere
from 10 main parts to 100's of parts of the digestive system,
depending on how detailed it needs to be explained. The
digestive system is truly a marvelous attribute we have and
should not be taken for granted, or be neglected. This is why a
good general knowledge of the digestive system is important, not
only for self/health awareness, healthy living and BIO class but
because it is indeed, truly fascinating.
The Human Digestive System Part 1
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igestive-System-Part-1/
It all starts in the brain. The brain sends signals to the
organs involved in digesting, to the muscles, mouth, glands and
every thing that is living in the body. It produces hormones
that make us hungry and do an assortment of other tasks that aid
the digestive system. The hypothalamus (part of the brain) has
two centers that control hunger. One is the appetite center, the
other the satiety center. The body produces 3 main hormones that
control digestion. The hormones that control digestion are
gastrin, secretin, and cholecystokinin (CCK).
Gastrin causes increased stomach acid secretion and mobility of
the digestive tract to move food. It is also necessary for the
normal growth of the lining of the stomach, small intestine, and
colon.
Secretin causes the pancreas to send out a digestive juice that
is rich in bicarbonate. It stimulates the stomach to produce
pepsin, an enzyme that digests protein, and it also stimulates
the liver to produce bile.
CCK causes the pancreas to grow and to produce the enzymes of
pancreatic juice, and it causes the gallbladder to empty.
Two others that control appetite are; Ghrelin which is produced
in the stomach and upper intestine in the absence of food in the
digestive system and stimulates appetite and Peptide YY which is
produced in the GI tract in response to a meal in the system and
inhibits appetite. They both help the brain regulate the intake
of food for energy.
The Mouth:
The moment you take a bite of that apple or pull that tasty
piece of chicken off of your fork with your teeth, into your
mouth, the digestive system kicks in. As the mouth chews the
body starts signaling the rest of the digestive system,
preparing it for the work ahead. The salivary glands secrete
Salivary Amylase and Ptyalin enzymes begin the chemical
breakdown of starch into glucose. IgA antibodies are also found
in saliva, also found present is lysozyme; an anti bacterial
enzyme. Bicarbonate ions in saliva neutralize the acids in
foods. Mucus moistens the food and lubricates the esophagus and
then we swallow.
Esophagus:
Not much happens in the Esophagus. Its major role in digestion
is directing the food into our stomachs and not our lungs, and
keeping stomach content from spilling upwards into it ("heart
burn" -> "esophagus burn"). The Esophagus has a sphincter that
closes the stomach off from itself. Without it standing on our
heads would be a messy and painful maneuver. It also has a small
flap that directs water and food down into our stomach and air
into our lungs. Carbohydrate digestion, begun by salivary
amylase in the mouth, continues in the bolus (word for chewed up
food) as it passes thru the esophagus into the stomach. The food
reaches the stomach and that's where the body really starts to
work.
The Human Digestive System Part 2
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igestive-System-Part-2/
First, the stomach must store the swallowed food and liquid.
This requires the muscle of the upper part of the stomach to
relax and accept large volumes of swallowed material. The
stomach has a capacity of 1 liter, from an empty capacity of
50-100 milliliters, but the stomach can distend to hold 2 liters
or more. With most people, the stomach mucosa (lining) is able
to resist the juices in the stomach, although food and other
tissues of the body cannot. The stomach starts to churn the food
by muscular layers to form chyme. Epithelial cells line inner
surface of the stomach, and secrete about 2 liters of gastric
juices per day. Gastric juice contains hydrochloric acid,
pepsinogen, and mucus. Hydrochloric acid (HCl) lowers pH of the
stomach so that pepsin can is activated and also gives the
stomach the right acidity to inhibit further carbohydrate
breakdown. The enzyme pepsin splits off fragments of peptides
from protein molecules, and begin the break down of protein.
Chyme, the mix of acid and food in the stomach, then leaves the
stomach and enters the small intestine.
Liver: Duodenum: Gallbladder: Pancreas:
These 4 organs do various tasks involved with digestion, the
main one being the production and secretion of enzymes needed to
break down Chyme. Bile, a watery greenish fluid that is produced
by the liver and secreted via the hepatic duct and cystic duct
to the gall bladder for storage. At mealtime, it is squeezed out
of the gallbladder into the Duodenum via the bile duct. The
Duodenum(upper third of small intestine) releases Bile,
controlled by pyloric sphincter, into the small intestine as
food enters it.
Bile contains cholesterol, phospholipids, bilirubin, bile
pigments, and a mix of salts. Bile lowers pH of the chyme, Bile
salts and phospholipids emulsify fats, facilitating their
breakdown into progressively smaller fat globules until they can
be acted upon by lipases (enzyme secreted by the small
intestine). After the fat is dissolved, it is digested by
enzymes from the pancreas and the lining of the intestine.
The pancreas secretes digestive enzymes and stomach
acid-neutralizing bicarbonate. Proteases (enzymes secreted from
the pancreas) continue the breakdown of protein into small
peptide fragments and some amino acids.
Small Intestines:
As the food is digested in the small intestine and dissolved
into the juices from the pancreas, liver, and intestine, the
contents of the intestine are mixed and pushed forward.
Digestion of carbohydrates, proteins, and fats continues in the
small intestine. Starch and glycogen are broken down into
maltose. Maltose, sucrose, and lactose are the main
carbohydrates present in the small intestine; they are absorbed
by the microvilli.
Jejunum(8 feet)(second third of the small intestine) Final
digestion of proteins and carbohydrates must occur, and fats
have not yet been digested. Starch is broken down into
two-glucose units(maltose).
Ileum(13 feet)(lower third) - Fats are completely digested,
digested fats are not very soluble. Bile salts surround fats to
form micelles that can pass into the epithelial cells. The bile
salts return to the lumen to repeat the process. Fat digestion
is usually completed by the time the food reaches the ileum of
the small intestine. Bile salts are in turn absorbed in the
ileum and are recycled by the liver and gall bladder. Fats pass
from the epithelial cells to the small lymph vessel that also
runs through the villus. The small intestine drains fat and
other nutrient rich lymph into it via the hepatic portal system.
Villi (intestinal folds) have cells that produce intestinal
enzymes which complete the digestion of peptides and sugars and
push the remaining contents into the Caecum.
The Human Digestive System Part 3
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igestive-System-Part-3/
Large intestines:
Caecum Ascending Colon Transverse Colon Descending Colon
Sighnoid Colon
The first part of the large intestine is the caecum. It is a
repository for bacteria and other organisms able to digest
cellulose. Enzyme lactase produced by the intestinal walls helps
to break down lactose. Secretions in the large intestine are an
alkaline mucus that protects epithelial tissues and neutralizes
acids produced by bacterial metabolism. Water, salts, and
vitamins are absorbed, the remaining contents in the lumen form
feces (mostly cellulose, bacteria, bilirubin). Bacteria in the
large intestine, such as E. coli, produce vitamins (including
vitamin K) that are absorbed. where they remain, usually for a
day or two, until the feces are expelled by a bowel movement.
Anus has voluntary and involuntary sphincter and ability to
distinguish whether contents are gas or solid.
Urinary system:
The urinary system is a whole other system in itself, but is a
part of the digestion process. Liquids are absorbed in the
intestines and sent thru the blood stream and empty off into the
beginning of the urinary system. But that's a whole other
journey.
Conclusion:
In conclusion, even though this is only a brief explanation of
the basics of the digestive system, you can see how incredibly
complex it is. The true miracle is how every part works in
perfect harmony with one each other, "a well oiled machine" if
you will. The total time it takes for a meal to take the entire
journey depends on what was eaten. The time it takes to fully
digest a meal is anywhere from 2 hours to over 24 hours. High
fat diets make this time longer. It's important to take care of
your digestive system. Neglect can lead to digestive system
diseases, mal-nutrition and poor a quality of life.