When you are hungry your whole body needs food, but the only system in the body that food actually enters is called the:
excretory system
digestive system
neurological system
there are challenges that every animal faces when needing food:
the need to obtain the food
the need to convert the food into useful molecules
both of the above
neither of the above
this system converts food into small molecules that can be used by the cells of the body
food is processed in the digestive system in four phases:
ingestion, digestion, absorption, elimination
digestion, absorption, production, elimination
ingestion is the first step and involves putting food into your mouth, the opening to the digestive tract
as food passes through the digestive system it is broken down in two ways by mechanical and chemical digestion
this type of digestion physically breaks down larger pieces of food into smaller pieces so that the smaller pieces can be swallowed and accessed by digestive enzymes
mechanical digestion
chemical digestion
In this type of digestion, enzymes break down food into small molecules that the body can use
once food has been broken into small molecules it can be absorbed by cells in the small intestines and this process is called
ingestion
digestion
absorption
elimination
From the small intestine the molecules enter the circulatory system which transports them throughout the body
the digestive system cannot digest and absorb all the substances in food that enter the body and some materials travel though the large intestine and are eliminated from the body
a one way tube that passes through the body that is vital to the human digestive system is called the
aluminium canal
aluminory canal
alimentary canal
During digestion, food travels through the mouth, espophagus, stomach and small intestine
mechanical and chemical digestion are the two processes by which food is reduced to molecules that can be absorbed
both mechanical and chemical digestion start in the
mouth
espohagus
the work of the digestive system begins in the
esophagus
the process of mechanical digestion begins with
chewing
swallowing
chemical digestion begins as digestive enzymes in saliva start the breakdown of complex carbohydrates into smaller molecules
the teeth are anchored in the bones of the jaw and their surfaces are protected by a coating of mineralized enamel
the teeth do much of the mechanical work of digestion as
the incisors, cuspids and bicuspids cut into and tear at food
the molars grind and cursh food into a fine paste that can be swallowed
this moves food around so that it comes into contact with your teeth
your lips
your teeth
as the teeth cut and grind the food, these glands secrete saliva which helps to moisten the food and make it easier to chew
salivary glands
thyroid glands
The release of saliva is under the control of the nervous system and can be triggered by the scent of food
saliva not only eases the passage of food through the digestive system but also begins the process of chemical digestion
saliva contains an enzyme called amylase that begins to break the chemical bonds in starches, forming sugars.
saliva also contains an enzyme that fights infection by digesting the cell walls of many bacteria that may enter the mouth with food- this enzyme is called
amylase
lysozyme
once food is chewed the combined actions of the tongue and throat muscles push the clump of food down the throat
the clump of food that forms once food is chewed is called
bolus
globule
when you first swallow the the bolus enters the area at the back of the throat called the
pharynx
a flap of tissue closes the opening of the trachea preventing food from moving into the air passageways to the lungs as it passes through the pharynx and into the esophagus and this flap of tissue is called
glottis
epiglottis
from the throat the bolus passes through a tube into the stomach, and this tube is called the
contractions of smooth muscles known as peristalsis provide the force that moves food through the espophagus toward the stomach
after food passes into the stomach a thick ring of muscle closes the esophagus. this ring is called the
cardiac sphincter
the cardiac sphincter prevents the contents of the stomach from flowing back
overeating or drinking excess caffeine can cause a backflow of stomach acid into the esophagus called heartburn
the stomach is a large muscular sac that contains the chemical and mechanical digestion of food
the lining of the stomach contains millions of microscopic gastric glands that release many substances into the stomach, some of the gland produce hydrochloric acid and others release an enzyme called pepsin
pepsin is an enzyme that
is activated in and function best in acidic conditions
breaks down proteins into smaller polypeptide fragments
another stomach gland produces mucus which is a fluid that lubricates and protects the stomach wall
if the protective layer fails acids may erode the stomach lining causing a sore called a peptic ulcer
most peptic ulcers are the result of infection with the bacterium Helibacter Pylori rather than from too much acid, and it can now be cured with antibiotics
alternating contractions of the stomach's three smooth muscle layers thoroughly churn and mix the swallowed food
the churning in the stomach causes
further breakdown of the chunks of swallowed food
allow enzymes greater access to the food
a mixture with an oatmeal like consistency is produced in the stomach called chyme
after an hour or two the pyloric valve located between the stomach and the small intestine opens and chime begins to spurt into the small intestine
as chyme is pushed through the pyloric valve it enters the duodenum
the duodenum is
the first part of the small intestine
where almost all of the digestive enzymes enter the intestine
most of the chemical digestion and absorption of the food you eat occurs in the small intestine
as chyme enters the duodenum from the stomach it mixes with the enzymes and digestive fluids from the pancreas, liver, and even the lining of the duodenum itself
the following is true about the pancreas
it is located just behind the stomach
produces hormones that regulate blood sugar levels
it produces enzymes that break down carbohydrates, proteins, lipids and nucleic acids
produces sodium bicarbonate, a base that quickly neutralizes stomach acid as chyme enters the duodenum
all of the above
the following is true about the liver
it assists the pancreas in fat digestion
it produces bile, a fluid loaded with lipids and salts
bile is stored in a small, pouchlike organ called the gallbladder
the following is true about fat
when fat is presented in the duodenum the gallbladder releases bile through a duct into the small intestine
fats tend to glob together which makes fat digestion by enzymes such as lipase difficult
bile breaks up the globs of fat into smaller droplets that disperse in the watery environment of the small intestine making it possible for enzymes to reach the smaller fat droplets and break them down
most nutrients from food are absorbed through the walls of the small intestine
the large intestine absorbs water and several vitamins and prepares waste for elimination from the body
after leaving the duodenum chyme moves along the rest of the small intestine and by now most of the chemical digestion has been completed and the chyme is now a rich mixture of small and medium sized nutrient molecules that are ready to be absorbed
the small intestine is especially adapted for absorption of nutrients in the following ways
its folded surface and fingerlike projections provide an enormous surface for absorption of nutrient molecules
the fingerlike projections called villi are covered with tiny projections known as microvilli
as slow, wavelike contractions move the chyme along the surface, microvilli absorb nutrients
nutrient molecules are rapidly absorbed into the cells lining the small intestine
most of the products of carbohydrate and protein digestion are absorbed into the capillaries in the villi
most fats and fatty acids are absorbed by lymph vessels
by the time chyme is ready to leave the small intestine it is basically nutrient free as complex organic molecules have been digested and absorbed, leaving only water, cellulose, and other undigestable substances behind
as material leaves the small intestine and enters the large intestine, it passes by a small saclike organ called the appendix
when chyme leaves the small intestine it enters the large intestine or colon
the following is true about the large intestine
the large intestine is actually much shorter than the small intestine
the large intestine gets its name due to its diameter which is much greater than the diameter of the small intestine
the primary function of the large intestine is to remove water from the undigested material that is left
water is absorbed quickly across the wall of the large intestine leaving behind the undigested material
rich colonies of bacteria present in the large intestine produce compounds that the body is able to absorb and use including Vitamin K
the concentrated waste material- the feces- that remains after most of the water has been removed passes into the rectum and is eliminated from the body through the anus
if not enough waster is absorbed a condition known as diarrhea occurs and if too much water is absorbed from the undigested materials a condition known as constipation occurs
