Download Bio 2201 digestive system ppt

The Human Digestive System
Food - Getting / Nutrient Use
• All organisms need food, and all foods
contain nutrients. Nutrients are the
substances that provide the energy and the
materials needed for growth, repair,
regulation, and maintenance of the cells.
• Therefore, food is what the organism
consumes, and nutrients are substances within
food that are needed by the cells to sustain
life.
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Organisms Require Six Basic Nutrients:
1. Carbohydrates
Source - plants
Function - major source of energy in the body
2. Lipids (fats)
Source - ingestion of animal and plant fats;
conversion of carbohydrates into fats
Function - storage of energy; component of cell
membranes; cushion for delicate organs; carriers
for certain vitamins; raw materials for important
chemicals
• 3. Proteins
• Source - meat, fish, poultry
• Function - broken down into amino acids which
are used in the construction of human proteins.
Proteins are essential for the building, repair, and
maintenance of cell structure.
• The predominant part of muscles, nerves, skin,
and hair is protein.
• Things such as enzymes and antibodies are
specialized proteins.
• 4. Water
• Source - ingestion
• Function - a variety of functions including its role as a
solvent
• 5. Vitamins
• Source - the various vitamins are each ingested from a
variety of foods
• Function - various metabolic functions including
enzymatic activity
• 6. Minerals
• Source - the various minerals are each ingested from a
variety of foods
• Function - a large variety of bodily functions
• Carbohydrates, lipids, and
proteins require digestion.
• Vitamins, water, and minerals do
not.
Research Assignment
• Construct a chart displaying the specific sources
and functions of each of the following vitamins
and minerals:
• Vitamins - A, B1, B2, Niacin, B12, C, D, E, and K
• Minerals - calcium, phosphorous, sodium,
chlorine, potassium, magnesium, iodine, iron
• Foods taken into the body consist of large
complex organic compounds. Digestion must
occur in order to release the nutrients contained
within the food.
• Digestion will reduce the large complex organic
compounds into smaller, simpler units that can
be absorbed and used by the cells of the
organism.
• This is accomplished through a digestive
system. In such a system digestion occurs in
two ways:
• (A) Mechanical - food is broken down into
smaller pieces by the teeth. This prepares
the food for faster chemical digestion by
exposing more food surface to the action of
the digestive enzymes. Mechanical
digestion also includes the physical
movement of food.
• (B) Chemical - food is broken down into
smaller, simpler organic units through the
activity of the digestive enzymes.
• *The human digestive system consists of a
tract of organs and associated glands.
Digestive Tract / Alimentary Canal
Organs
Glands
Mouth
Salivary
Pharynx
Esophagus
Stomach
Gastric
Small Intestine
Liver
Large Intestine
Intestinal
Pancreatic
Rectum
Anus
Mouth
• Structure:
• Teeth - 20 infant, followed by 32 adult
• Tongue - location of taste buds, four types
being salty, sweet, sour and bitter
• Mechanical Digestion:
• (1) teeth tear and grind food into smaller pieces
• (2) tongue keeps the food between your teeth
and pushes it into the pharynx
• Chemical Digestion:
• Six salivary glands release saliva that
contains salivary amylase (enzyme) and
mucin.
• (1) Salivary amylase (enzyme) starts the
breakdown of starch (polysaccharide) into
maltose (disaccharide).
• (2) Mucin makes the food slippery and easy
to swallow. The food particles stick
together forming a food mass called a bolus
which the tongue pushes into the pharynx.
Pharynx
• Structure: Made up of muscular walls
containing two openings:
• trachea - leads to the lungs and is covered
by the epiglottis.
• esophagus - leads to the stomach
• Mechanical Digestion - none
• Chemical Digestion - none
Esophagus
• Structure: It is a tube about 30cm long
through which food passes from the
pharynx to the stomach.
• Mechanical Digestion: There are a series of
muscle contractions called peristalsis that
push food down the esophagus and into the
stomach.
• Chemical Digestion - none
Stomach
• Structure: It is a J-shaped tube that lies below the
diaphragm towards the left side of the abdomen.
• It is fitted with two sphincter muscles: cardiac
(entrance) and pyloric (exit)
• These sphincters act as valves and control the
passage of food into and out of the stomach.
• Mechanical Digestion: Peristalsis occurs that
churns and mixes the food and the digestive juices.
• The food stays in the stomach from 2 to 6 hours. It
can expand to hold more than 2 liters of food or
liquid.
• Chemical Digestion:
• Gastric glands found in the wall of the
stomach release gastric juices. A hormone
called gastrin controls the release of gastric
juice. This hormone’s release is triggered
by three mechanisms:
• (1) thought, sight, smell, or taste of food
• (2) food touching the lining of the stomach
• (3) stretching of the stomach wall
• Gastric juice contains:
• (1) Hydrochloric Acid (HCl)
• HCl drops the pH of the stomach to 2. This
lower pH stops the digestion of starch and is
necessary for the digestion of protein
• (2) Pepsinogen (inactive enzyme)
• Pepsinogen enters the stomach and comes
into contact with HCl. It converts to pepsin
which is an active enzyme. Pepsin breaks
protein into polypeptides.
Protection of Stomach
• The stomach protects itself from its own
digestive juices by way of pyloric glands.
• These glands secrete mucus which covers
the stomach lining and prevents it from
being digested.
• When this mucus lining breaks, an ulcer
forms.
• When the food is ready to leave the stomach
it is an acidic mass called chyme.
Small Intestine
• Structure:
• It is a tube 2.5cm in diameter and 7m long.
It is coiled inside the abdomen and consists
of three sections:
• (1) duodenum - 25cm long
• (2) jejunum - 2m long
• (3) ileum - 5m long
• * Digestion is completed here and nutrients
are absorbed.
Mechanical Digestion:
• (1) Peristalsis
• (2) Fats are emulsified. The liver produces
bile which is stored in the gall bladder.
• The bile enters the intestine at the duodenum
through a tube called the common bile duct.
• The bile emulsifies fats. This means fats, oils,
and waxes are broken down into very small
droplets increasing the surface area for
enzyme activity.
• Bile is not an enzyme.
Chemical Digestion:
• There are two important glands involved in
digestion in the small intestine:
• (A) Pancreas
• (B) Intestinal
(A) Pancreas
• It is located outside the small intestine and is
attached to the wall of the abdomen.
• It produces pancreatic juices which enter the
small intestine at the duodenum through the
pancreatic duct and into the common bile duct.
• The pancreatic juices contain:
• (1) Pancreatic amylase - an enzyme that
converts remaining starch to maltose.
• (2) Lipase - an enzyme that converts fats to fatty
acids and glycerol.
• (3) Proteases / Trypsin - enzymes that
convert the polypeptides produced in the
stomach into simpler polypeptides.
• (4) Erepsins - enzymes that convert simpler
polypeptides into amino acids. This is the
final stage in protein digestion.
• (5) Sodium bicarbonate - raises the pH to 8
(base) so the above enzymes can function.
It does this by neutralizing the acidic chyme
released from the stomach. Bile also aids in
the process.
(B) Intestinal Glands
• They are found in the wall of the small intestine.
They produce and release intestinal juices which
contain:
• (1) Peptidases - enzymes that convert simpler
polypeptides into amino acids.
• (2) Lipase - enzyme that converts fats to fatty
acids and glycerol
• (3) A group of enzymes that convert
disaccharides into glucose:
• A. maltase - converts maltose to glucose
• B. sucrase - converts sucrose to glucose
• C. lactase - converts lactose to glucose
Absorption
• The small intestine contains many fingerlike projections called villi. They increase
the surface area of the small intestine by a
factor of 10. To get the same surface area
without the villi, your small intestine would
have to be 70m long.
• The large surface area is ideal for nutrient
absorption.
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There are two major parts to each villus:
(A) Lacteal - part of the lymph system,
located in the center of the villus and absorbs
fatty acids and glycerol.
(B) Capillaries - part of the circulatory
system, located around the lacteal and
absorbs the following:
(i) glucose (simple sugar)
(ii) amino acids
(iii) vitamins
(iv) minerals
(v) water
• The capillaries of all villi join together to
form the hepatic portal vein that travels to
the liver.
• Once in the liver, glucose is converted into
glycogen and stored.
• The rest of the nutrients travel in the blood
around the body to every individual cell.
• The various nutrients enter the villus by the
various forms of transport discussed earlier:
Passive
diffusion
facilitated diffusion
osmosis
Active
carrier proteins
vesicles
exocytosis
endocytosis
pinocytosis
phagocytosis