Transcript Chemical digestion

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Sylvia S. Mader
Immagini e
concetti
della biologia
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
C7 - Digestive
system and
nutrition
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Digestion helps homeostasis
A digestive system involves various processes:
Ingestion
Mechanical digestion
Chemical digestion
Absorption
Elimination
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Digestion helps
homeostasis
Chemical digestion involves
specific enzymes in the
macromolecule breakdown.
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Digestive tract
An incomplete digestive tract as in planaria (a
flatworm) has a single opening through which nutrients
enter and exit.
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Digestive tract
A complete digestive tract, as in birds and worms, has
a mouth, an anus and specialized parts: crop (for
storage), gizzard (for first mechanical digestion) and
intestine (for chemical digestion).
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Digestive system in mammals
Carnivores have a short digestive tract, as they obtain
nutrients from meat more easily.
They also have a relatively small cecum.
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Digestive system in mammals
Herbivores have a long digestive tract, as it takes a
long time to digest cellulose from plants, and a large
cecum with specialized enzymes.
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Digestive system in mammals
Some herbivores called ruminants (cows, sheep) have
specialized stomaches divided into: rumen (1), reticulum
(2), omasum (3) and abomasum (4) hosting microbial flora.
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Human digestive
system
Our digestive system is
adapted to an omnivorous
diet.
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The mouth
Both first mechanical and
chemical digestion occur in the
mouth.
•32 teeth divided into 4 classes
chew food
•3 pairs of salivary glands contain
salivary amylase for digesting
starch
•The tongue (skeletal muscle)
forms a food bolus for swallowing
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The esophagus
The esophagus is a muscular tube that passes from the
pharynx to the stomach.
During swallowing, the air passage is blocked by soft palate
(1) and epiglottis (2), so the food bolus enters the
esophagus (3).
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The esophagus
After swallowing, peristaltic
movements push the food
bolus in the esophagus to the
stomach.
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The stomach
Food storage and second chemical digestion take
place in the stomach.
The food is mixed with
gastric acid juices
containing a protein digesting
enzyme called pepsin.
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The small intestine
Chemical digestion ends and absorption of nutrients
takes place in the 5 to 9 meters long small intestine.
Bile and pancreatic juices prepare carbohydrates, proteins
and fats for digestion by maltase, peptidase and lipase.
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The small intestine
Intestinal enzymes complete digestion to small nutrient
molecules which are absorbed by the villi on the
intestinal wall.
villi
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Pancreas and liver
Pancreas and liver are accessory digestive organs that
produce pancreatic juice and bile respectively.
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Stomach and duodenum
Stomach and duodenum (the upper part of the
intestine) are also endocrine glands and secrete
hormones.
Stomach produces gastrin to help
regulate food digestion.
Duodenum produces secretin and
cholecystokinin for stimulating the
digestion of fats and proteins.
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Liver diseases
Liver malfunctioning has effects on the whole
organism.
Liver disorders include:
•Jaundice - yellow pigmentation of the skin caused by
increased levels of bilirubin in the blood.
•Hepatitis - inflammation of the liver caused by viruses.
•Cirrhosis - damage of tissues leading to loss of liver
functions.
•Liver cancer.
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The large intestine
The large intestine absorb water, minerals and vitamins
and prepare waste for elimination. Is divided into cecum,
colon and rectum.
The cecum controls the flux of
material through the intestine
and the appendix protects from
infections.
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The large intestine
The colon is the last portion of the digestive tract and
extracts water and minerals from waste before final
elimination. Bacteria-aided fermentation occurs.
The rectum is the final part of the large intestine and
terminates in the anus. Here feces are formed and
expelled.
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Nutrition
Alimentation must provide all nutrients in
balance amount.
The most important nutrients are:
•Carbohydrates
•Lipids
•Proteins
•Minerals
•Vitamins
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Carbohydrates
Carbohydrates (sugars, starch and fibers) provide
immediate energy.
Whole-grain carbohydrates are more nutritious while
fibers are indigestible cellulose carbohydrates that
stimulate intestine functions.
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Lipids
Lipids supply long-term energy and are stored in fat cells.
Foods from animals (butter,
meat, cheese) is rich in
saturated fats and
cholesterol.
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Proteins
Proteins supply amino acids, the building
blocks for cells.
8 out of 20 amino acids are essential as
they can not be synthesized by our cells.
Protein-rich food include meat, fish, eggs,
nuts, soybean and cheese.
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Minerals
Minerals regulate biochemical reactions, maintain fluid
balance and are incorporated into structures and
compounds.
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Vitamins
Vitamins are organic compounds that regulate
metabolism and physiological development. Vitamins are
classified as lipo-soluble (as A and D) or hydro-soluble
(as C and B).
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Vitamins
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Nutrition disorders
Obesity is defined as weighing 30% more than ideal body
weight. Obesity is often associated with Type 2 Diabetes
and cardiovascular diseases.
Other common nutrition disorders are anorexia nervosa
(distorted body image that leads to hypo-nutrition) and
bulimia nervosa (binge-eating and purging).
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