Download Nutrition and Digestion

Digestion and Nutrition
Nutrition
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Living organisms need food
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All food contains nutrients
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Nutrients are substances that provide the energy
and materials needed for growth, repair and
maintenance of cells and regulation
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Nutrition is the process by which organisms get
food and break it down so it can be used
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Nutrients include:
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Proteins
CHO (carbohydrates)
Fats
Vitamins
Minerals
Water
Water and minerals are inorganic nutrients which must
be obtained from the environment
Minerals are chemical elements that organisms need for
normal functioning
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Plants absorb minerals from soil
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Animals obtain minerals by eating plants or
by eating other animals that have eaten
plants
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Organic nutrients include essential organic
compounds (contain C and occur naturally
only in living organisms or in their products)
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Organisms get needed organic nutrients in 2
basic ways:
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1. Synthesizing or making their own nutrients
from simple inorganic substances
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2. Ingest or take in food containing organic
nutrients form other plants or animals
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Green plants and algae are examples of
autotrophs (organisms that synthesize their
own nutrients)
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Most autotrophs are photosynthetic or use
energy from sunlight and CO2 and H2O from
the environment to make their own food
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They are called phototrophs
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Chemotrophs are organisms that synthesize
their nutrients through chemical reactions
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Heterotrophs are the organisms that cannot
make their own organic nutrients
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Heterotrophs include all animals and certain
types of microorganisms
Energy Content of Food
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Energy is provided by the chemical
breakdown of CHO, fats and proteins
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The calorie is the unit used to measure energy
content of food
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Calorie is defined as the amount of heat
needed to raise the temperature of 1 gram of
water 1oC
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Humans need the 6 basic nutrients
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These nutrients are obtained by eating a healthy diet
from the 4 major food groups:
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Grains and grain products (G & GP)
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Dairy and dairy products (D & DP)
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Fruits and vegetables (F & V)
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Meats and alternates (M & A)
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Along with the 6 nutrients, humans need fibre
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Fibre is made of cellulose and other
indigestible materials found in the cell walls of
fruits, vegetables and grains
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Fibre stimulates the muscles of the digestive
system to keep foods moving through it
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Digestion and Absorption
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Digestion is the chemical process by which
food molecules are broken down into simpler
compounds
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Digestions allows for nutrients to be
absorbed or pass through the cell membrane
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In many organisms, pieces of food are first
cut, crushed or broken down w/o being
changed chemically
The Mouth and the Pharynx
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Food enters the body through the mouth
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Mechanical and chemical digestions occurs
here
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Mechanical digestion involves biting food with
teeth and ground into small pieces that can
be swallowed
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The tongue moves and shapes the food
around the mouth
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Chemical digestion involves the incorporation
of saliva from the salivary glands
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2 types of saliva
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Thin, watery secretion; wets the food
Thicker, mucous secretion that acts as a lubricant
and causes the food particles to stick together to
form a bolus (food mass)
Saliva contains a digestive enzyme called
salivary amylase which breaks down starch
(polysaccharide) into a disaccharide
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Once food is chewed, it is pushed by the
tongue to the back of the throat or pharynx
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An automatic swallowing reflex occurs which
forces food into the esophagus (a tube
leading to the stomach)
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The epiglottis is flap of tissue that closes off
the larynx and trachea to the lungs
The Esophagus
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Food passes from the pharynx to the
stomach via a tube called the esophagus
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The movement of food down the digestive
tube is aided by alternate waves of relaxation
and contraction of the muscular walls
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This is called peristalsis
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The muscles in the front of the food mass
relax, while those behind the food mass
contract, pushing food forward
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Food passes down the esophagus and into
the stomach
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Where the esophagus and stomach meet is a
ring of muscle called the cardiac sphincter
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This muscle ring acts as a valve that controls
the passage of food into the stomach
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Peristalsis moves down the esophagus,
reaches the cardiac sphincter and causes it
to relax and open to allow food in
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The Stomach
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The stomach is a thick-walled, muscular sac
where food is stored temporarily
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The mechanical breakdown of food and
partial digestion of proteins occur here
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Food is broken down mechanically by
contractions of the muscular stomach walls
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Food is churned and mixed with acidic gastric
juice secreted by glands in the stomach wall
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The lining of the stomach contains 2 types of
glands:
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Pyloric glands- secrete mucus which covers the
stomach lining and protects it from being digested
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Gastric glands- secrete gastric juice which has a
pH of 1.5 – 2.5 (due to its high [HCl])
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HCl kills most of the bacteria swallowed in food
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Gastric juice also contains pepsin, a digestive enzyme,
that breaks down proteins into short chains of amino
acids call polypeptides
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The salivary amylase, released in the mouth,
continues to digest starches in the stomach
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Eventually, the low pH of the acid in the
stomach inactivates the enzyme and starch
breakdown stops
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When the stomach is empty, there is little
gastric juice present
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When food is eaten, the flow of gastric juice
increases
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The stimulation of the gastric juice involves 3
mechanisms:
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1) Thought, sight, smell, or taste of food
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2) Food touching the lining of the stomach
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3) Food enters the stomach and stretches the
stomach wall
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The stretching stimulates the lining of the stomach to
secrete a hormone called gastrin which stimulates the
gastric glands in the stomach
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Liquids pass through the stomach in 20
minutes or less
Solids must be turned into chyme, a thin,
soupy liquid
The chyme passes in small amounts at a
time through the pyloric sphincter, the ring of
muscle that connects the stomach to the
small intestine
The stomach will empty 2-6 hours after a
meal
Hunger is felt when an empty stomach is
churning
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Stomach ulcers develop when the thick
mucous layer that protects the stomach wall
breaks down
This exposed area will be digested
Pain will occur when the hydrochloric acid
comes into contact with the exposed stomach
wall
Ulcers may be caused by the over secretion
of gastric juices, brought on by stress or
nervousness
Ulcers can be treated through diet,
medication or surgery
The Small Intestine (S.I.)
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About 6.5 metres long; 2.5 cm in diameter
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Food leaves the stomach through the pyloric
sphincter
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S.I. consists of 3 parts:
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Duodenum (shortest of the 3 sections- 25 cm)
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Jejunum
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Ilium
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Most chemical digestions takes place in the
S.I.
Following digestion, simple sugars, amino
acids, vitamins, minerals and other
substances are absorbed
Absorption takes place through the wall of the
small intestine into the blood vessels of the
circulatory system
Fatty acids and glycerol are absorbed into the
lacteals, vessels of the lymphatic system
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(collects excess fluid from intercellular spaces in the body and
returns them to the blood)
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Many factors allow the S.I. to be well suited
for absorption
Very long
Lining has many folds
Lining is covered with millions of finger-like
projections called villi
Epithelial cells that make up the intestinal
lining have brush borders
Brush borders are the cells face into the
intestinal opening which have miro-villi
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Within the centre of each villus is the lacteal,
surrounded by blood vessels
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Epithelial cells with microvilli cover each villus
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During absorption, nutrients pass through the
epithelial cells and enter the capillaries or the
lacteal
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Absorption involves both diffusion and active
transport
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2.
3.
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The S.I. is in constant motion when food is
present
These peristaltic movements have four main
effects:
They squeeze chyme through the intestine
They mix the chyme with the digestive
enzymes present in the small intestine
They break down food particles
mechanically
They speed up absorption of digestive end
products by bringing the intestinal contents
into contact with them intestinal wall
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Fluids in the S.I. are mostly alkaline
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Chyme is mixed with:
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pancreatic juice (pancreas)
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bile (liver)
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intestinal juice (from the glands in the wall of the
intestine)
These 3 secretions contain the enzymes and
other substances necessary to complete
digestion
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Pancreatic Juice
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The hormones secretin and cholecystokinin are
secreted when acid chyme enters the S.I.
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The hormones stimulate the pancreas to secrete
pancreatic juice and pancreatic enzymes
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Pancreatic juice will pass through the pancreatic
duct to the upper part of the S.I.
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Sodium bicarbonate is found in the pancreatic
juice and it neutralizes the acidic chyme and
makes the pH of the S.I. alkaline
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Bile
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Cells of the liver produce bile and is stored in the
gallbladder
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Bile is released when stimulated by the hormone
cholecystikinin
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Bile passes through the bile duct into the upper
part of the small intestine
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Bile is alkaline and aids in neutralizing acidic
chyme
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Intestinal Juice (I.J.)
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I.J. is secreted from the millions of intestinal
glands located in the wall of the S.I.
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I.J. contains enzymes peptidase and maltase
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These complete the digestion of CHO, fats and
proteins
Page 166, Figure 8-17- Secretions of the HDS
Large intestine
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The Large Intestine (L.I.)
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Undigested and unabsorbed materials pass
from the S.I. through a sphincter into the L.I.
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The L.I. is about 1.5 metres long and 6 cm in
diameter
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Digestion does not occur here, but most of
the water reabsorption from food mass does
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Water is mixed with food as it moves through
the digestive system
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Normally, ¾ of the water is reabsorbed
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Reabsorption in the L.I. allows the body to
conserve water
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Too little water absorbed = diarrhea
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Too much water absorbed = constipation
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L.I. also absorbs vitamins produced by
intestinal bacteria living in the L.I.
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Intestinal bacteria live on undigested food
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The vitamins are absorbed with the water
from the food mass
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Antibiotics can kill the intestinal bacteria
which can lead in vitamin deficiencies
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The L.I. is important in the removal or
undigested and indigestible material from the
digestive tract
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Ex. Cellulose, large quantities of bacteria,
bile, mucus, worn-out cells from the digestive
tract
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This material becomes feces or stool
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“Poo” is stored in the last part of the L.I.,
rectum and passed through the anus