Transcript digestive system - Zanichelli online per la scuola

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Digestion and
water balance
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The digestive
system
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Functions of the digestive system
The functions of the digestive system are:
• breaking down foods into their molecular particles
(mechanical and chemical digestion)
• transferring these molecular particles to the blood and
lymphatic stream (absorption).
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Structure of the digestive system
The digestive system consists of the gastrointestinal tract
and accessory organs.
The gastrointestinal tract has
two endings (mouth and anus)
and is formed by specialized
organs.
The accessory glands
(salivary glands, pancreas,
liver and gallbladder) produce
substances that aid digestion
and absorption.
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Phases of the digestive process
/mouth
The digestive process includes four phases:
• ingestion of food (mouth)
• mechanical and chemical digestion (mouth, stomach,
accessory organs, small intestine)
• absorption (small and large intestine)
• elimination of waste products (rectum).
The first phase occurs in the mouth: the tongue and teeth
begin mechanical digestion, salivary glands produce saliva
and the amylase enzyme starts chemical digestion.
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Phases of the digestive process
/digestion
The functions of the stomach are to:
• break down and mix food particles;
• produce gastric juices which continue chemical digestion
and kill bacteria;
• begin the digestion of proteins.
Chemical digestion continues in the small intestine, helped
by the secretion of bile juice from the liver, pancreatic juice
from the pancreas and intestinal enzymes.
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Phases of the digestive process
/absorption
During absorption, nutrients pass from the gastrointestinal
tract to the blood and lymphatic streams which transport
nutrients to cells.
Absorption takes place mainly in the small intestine.
Its epithelium has plicae circulares, villi and microvilli that
increase its surface size, thereby facilitating absorption.
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Phases of the digestive process /
large intestine
The large intestine is the last part of the gastrointestinal tract,
and it is composed of three parts: cecum, colon, rectum.
Its functions are to:
• absorb water, salts and vitamins;
• collect waste materials and eliminate them as feces.
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Nutrients
Nutrition supplies necessary nutrients to the organism,
including:
• carbohydrates;
• lipids;
• proteins;
• vitamins;
• minerals;
• water.
Vitamins and minerals do not provide energy, but take part
in all metabolic functions. Only small amounts of vitamins
and minerals are necessary.
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The food pyramid
meat,
sweets
poultry,
fish, eggs,
legumes
milk and
dairy
products
fruits,
vegetables
olive
oil
rice, bread,
other cereals
A balanced diet provides all the
nutrients necessary for the
organism.
The food pyramid indicates the
types and amounts of foods that
should be included in a balanced
diet.
Foods at the bottom should be
eaten more often and in larger
quantities than foods at the top.
water
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The urinary
system
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Osmoregulation and the urinary
system
Osmoregulation is the process that maintains a stable fluid
balance and stable concentration of solutes in the organism
thereby regulating osmotic equilibrium.
kidney
ureter
The urinary system (kidneys,
ureters, bladder, urethra) is
responsible for the filtration of
blood and for the elimination of
metabolic waste as urine.
bladder
urethra
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Kidneys
Kidneys are the most important organs in the urinary system.
Their functions are to:
• eliminate metabolic waste;
• regulate the concentration of salts;
• maintain fluid balance;
• produce erythropoietin (which stimulates red blood cell
production);
• regulate blood volume and pressure.
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The nephron
The nephron is the basic functional unit of kidneys.
It is formed by the renal tubule and the glomerulus.
In the glomerulus, blood is
filtered.
Water and salts are reabsorbed
in the renal tubule.
The remaining waste molecules
are eliminated as urine which
contains water, salts and uric
acid.
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