Download The Human Digestive System

Biology 2201
Chapter 11
11.1 & 11.2 (p. 354 – 373)
The Human Digestive System
Food - Getting / Nutrient Use
• All organisms, regardless of size or complexity, have
some method to obtain the essential nutrients they
need for survival.
• Heterotrophs are organisms that depend on organic
molecules manufactured by other living things.
• Autotrophs are organisms that nourish themselves
using inorganic material (examples: water and
carbon dioxide).
• 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.
• The digestive system breaks down food
masses into useful substances that can be
absorbed into the circulatory system where
nutrients are transported to individual cells
and are again absorbed.
• Digestion is the process of breaking
necessary substances into smaller
molecules so that they can be absorbed in
the body. This occurs in the alimentary
canal, a continuous tube beginning at the
mouth and ending at the anus.
Organisms Require Six Basic Nutrients:
The Essential Nutrients are the basic raw materials organisms
need to make their own structures, perform functions, and obtain
energy for survival.
There are Six Essential Nutrients:
1) carbohydrates
4) minerals
2) fats (lipids)
5) vitamins
3) proteins
6) water
* fibre
• Your body functions best when these essential nutrients are
present in correct proportions. A diet that satisfies this is called a
balanced diet. See Canada’s Food Guide handout.
Carbohydrates:
(60 – 75%
of daily calories)
• They consist of atoms of carbon, hydrogen, and oxygen
(CHO).
• Carbohydrates are broken down to simple sugars during
digestion such as glucose, fructose and galactose
• Their main function is to provide a source of energy. The
excess carbohydrates are converted to fat and stored.
• Some food sources would be glucose, rice, bread, pasta,
etc.
Fats (lipids):
(30% of daily calories)
• Their functions include providing a source of energy, insulating
the body from the cold, and protecting organs from injury.
• They can also be used as a building material for cell membranes
and hormones.
• They are broken down to fatty acids and glycerol by the
digestive system.
Fatty acids can be:
• polyunsaturated (oils)
• mono or unsaturated (spreadable margarine)
• saturated (solid animal fats, bacon)
• Cholesterol is a fat-like substance used to form cell
membranes, insulate nerves, produce Vitamin D,
and produce some hormones. Animal products are
rich in cholesterol, and it can also be produced in
the liver from saturated fats. Too much can cause
clogged arteries leading to heart attack or stroke.
Protein: (10%)
• They are made up of peptides which consist of strings of amino
acids (9 essential amino acids).
– A protein is complete if it contains all 9 essential amino acids (animal
source).
– A protein is incomplete if it is missing just 1 of the nine essential amino
acids (plant source).
• Their functions include, cell growth and repair, enzymes in your
body are all proteins (act in metabolism), and can supply energy.
– The predominant part of muscles, nerves, skin, and hair is protein.
– Things such as enzymes and antibodies are specialized proteins
• Some food sources would be meat, milk,
poultry, fish, eggs, cheese, etc.
Vitamins:
• Our bodies require very small amounts in
diet.
• They act as coenzymes, chemicals needed
to make enzymes function.
• Examples would be vitamins: A, B, C, D, E,
K. See table 11-1 page 358.
Minerals:
• They are the inorganic compounds that your body
needs in small amounts.
• Their functions include helping to build bones and
cartilage, enabling certain chemical reactions, and
helping to maintain acid-base balance within the body.
• They are readily absorbed into the bloodstream.
Water:
• It’s major role in the body is to act as a
solvent.
• Most chemical reactions (body metabolism)
that occur in the body require water.
• The main source would be food and liquids.
• Carbohydrates, lipids, and proteins require
digestion.
• Vitamins, water, and minerals do not.
• Regardless of an organisms food source, the
nutrients that an organism takes in or derives
from its food must be in a form that can
readily pass through the organism’s cell
membrane. Many organisms must reduce
their food to a form from which nutrients can
be absorbed.
• 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.
There are TWO basic types of digestion:
1. Mechanical Digestion:
• It is the initial stage of physically breaking down food into smaller pieces.
• It occurs mainly in the mouth where teeth chew food and tongue
manipulates the food.
2. Chemical Digestion:
• It is the separation of food into molecular components by chemical means.
• The process begins in the mouth with the secretion of saliva which contains
the digestive enzyme amylase.
• The chemically breaking down of food continues through the stomach and is
completed in the small intestine.
NOTE :
Mechanical and chemical digestion act together to speed up
the digestion process. Mechanical digestion aids chemical
digestion by exposing more food particles to digestive
enzymes.
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
animation
Chemical Digestion:
Six salivary glands release saliva that contains
salivary amylase (enzyme) and mucin.
(1)
(2)
Salivary amylase (enzyme) starts the
breakdown of starch (polysaccharide)
into maltose (disaccharide).
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) 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
Large Intestine
Structure:
• It is a tube 1.5m long with a larger diameter than the small
intestine. Consists of the caecum, colon, rectum, and anal
canal.
Function:
• To produce an alkaline mucus to neutralize acids and
lubricate fecal passage.
• Water, salts, and vitamins are absorbed, leaving the solid
feces waste (mostly cellulose, bacteria, bilirubin).
• Bacteria in the large intestine, such as E. coli, produce
vitamins (including vitamin K) that are absorbed.
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.
• 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
Digestion overview
Web Quest
Digestive Disorders
• Problems with the digestive system can range
from minor inconveniences (heartburn) to a
major impediment to a normal lifestyle (bleeding
ulcers)
• We will discuss the following 6 digestive
disorders.
–
–
–
–
–
–
1. Ulcers
2. Gallstones
3. Ileitis
4. Colitis
5. Anorexia Nervosa
6. Bulimia Nervosa
Ulcers
• Are slow healing sores in the linings of the
stomach and intestines.
• Causes:
– Acids – Cause breakdown of mucus layer of stomach and
intestines.
– Helicobacter pylori – Acid resistant bacteria that causes mucus
production to stop.
– Lifestyle – Stress, smoking, alcohol/beverage consumption
• Cures/Treatments range from medications to reduce acid
production to an overall change in lifestyle.
Gallstones
• Hard masses that form in the gall bladder. Cholesterol in
the bile “precipitates” out as a solid forming crystals.
• Causes:
– Obesity
– Alcohol
– Heredity
• Treatments:
– Ultrasound (breaks up the gall stone so it can pass)
– Diet Changes (lower fat content diet – reduce cholesterol)
– Surgery (Removal of gall bladder).
Ileitis
• Inflammation of the Ileum causing severe pain.
The inflammation causes the intestine to empty
often causing diarrhea.
• Causes:
– Relatively unknown
– Does run in families
• Treatments/Cures:
– There is no cure. Treatment includes drugs to reduce
swelling or surgical removal of affected area
Crohn’s & Colitis
• Inflammation and ulceration of the lining of the
Colon, Colitis affects the innermost lining of the
colon, where Crohn’s affects the entire thickness
of the colon. Both conditions can cause bleeding,
diarrhea and abdominal pain.
• Causes:
– Relatively unknown
– Does run in families
• Treatments/Cures:
– Again, no cure so treatment includes drugs to reduce
swelling and surgical removal of affected area
Other tests that may be done to help
diagnose this condition include:
Barium enema
Colonoscopy with biopsy is
generally used to diagnose
ulcerative colitis.
Anorexia Nervosa
• Eating disorder where a
person has a fear of
gaining weight so they
go on very restrictive
diets.
• The person often loses
excessive amounts of
weight and has a lack of
nutrients to the cells of
body.
Anorexia Nervosa
• Eating disorder where a
person has a fear of
gaining weight so they
go on very restrictive
diets.
• The person often loses
excessive amounts of
weight and has a lack of
nutrients to the cells of
body.
Bulimia Nervosa
• Eating disorder where a person has episodes
of binge eating followed by “purging” through
vomiting or taking laxatives.
• This is very dangerous because it affects
several organs. Damage to heart, kidneys,
esophagus and teeth are common.