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Levels of Organization and Organ Systems
The human body is structured into systems. Recall that cells are the smallest units of life. Cells
that are similar in shape and function work together as tissue. The human body has four
primary kinds of tissue:
Epithelial tissue – covers and protects the body, organs and body cavities
Connective tissue – provides support and holds the body together
Examples: cartilage, bone, fat and blood
Muscle tissue – contains sheets or bundles of muscle cells to produce movement
Nervous tissue – provides communication between all body structures
Different types of tissues work together to form organs, which carry out particular functions.
Examples include, heart, liver, pancreas and stomach.
Organs cannot do all of the necessary work to sustain the body on their own. They must work
together with other organs with related functions (physiology) or structures (anatomy). This is
referred to as an organ system.
The following is a list of the body’s major organ systems and their functions:
Organ System Major Organs Major Function Digestive Esophagus, stomach,
intestines, liver, pancreas
Physical and chemical breakdown of food
Circulatory Heart, blood vessels Transportation of nutrients, gases and
waste; defence against infection
Respiratory Lungs, trachea, blood vessels Gas exchange
Reproductive Testes, vas deferens,
ovaries, uterus, fallopian
tubes
Sexual reproduction
Excretory Kidney, bladder, ureter,
urethra
Removal of waste
Locomotion Bones, muscles
Movement of body and body parts
Endocrine Pancreas, pituitary gland,
adrenal glands
Coordination and chemical regulation of
body activities
Nervous Brain, spinal cord, eyes, ears,
nose, tongue, nerves
Response to environment; control of
body activities
What is Nutrition?
Nutritional science is the study of nutrients and other substances found in foods that affect
human health and well-being. A thorough understanding about nutrition enables people to make
healthy lifestyle choices. A nutrient is an edible chemical that is broken down by the body.
Good nutrition is important because it:
a) Provides the energy we need to carry out all of our metabolic activities.
b) Provides us with the essential raw materials that we need as building blocks for cells,
muscles etc…
There are three main categories of nutrients:
1. MACRONUTRIENTS (Macromolecules)
Macromolecules are required by the body in large amounts. These molecules form the
structure and carry out the activities of all cells. They are organic molecules that may contain
anywhere from dozens to millions of carbon atoms. Because of their size and the intricate
shapes that macromolecules can assume, these large molecules are capable of performing a wide
variety of complex tasks with great precision and efficiency.
Macromolecules are polymers of smaller units (monomers) linked together.
There are four classes of macromolecules in cells:
i. CARBOHYDRATES (polymers of sugars)
ii. LIPIDS (polymers of fatty acids)
iii. PROTEINS (polymers of amino acids)
iv. NUCLEIC ACIDS (polymers of nucleotides)
Monomers are linked together by covalent bonds. Enzymes are responsible for the building and
breaking of macromolecules.
2. MICRONUTRIENTS
Micronutrients are needed by the body small amounts. There are two main classes:
i. Mineral - an inorganic substance (such as copper, iron, calcium or phosphorous) that is
needed in all body structures in trace amounts for various functions, such as
the transmission of nerve impulses and muscle contractions; cannot be made
by the body, therefore must be supplied by foods or supplements
ii. Vitamin – an organic molecule that acts as a catalyst for essential chemical reactions in
the body, such as converting fats and carbohydrates into energy; can be fat
soluble or water soluble; cannot be made by the body, therefore must be
supplied by foods or supplements
3. Special Nutrient
Water is the considered a special nutrient and is required by all living things. Water is the
most abundant molecule in any cell (constitutes 70-80% of the human body). It functions to
act as a carrier for dissolved molecules inside (intracellular) and outside (extracellular) of the
cell, and as a medium for chemical reactions (metabolism). It also functions as a lubricant
between organs, tissues and individual cells.
The following properties of water make life possible, as we know it:
a) Remains liquid over wide range of temp (1C - 99C)
b) Dissolves most substances involved in living processes such as oxygen, carbon dioxide,
glucose, amino acids and salts
c) Changes temperature gradually (high specific heat capacity) when heated or cooled so it
protects cells from rapid temperature changes and therefore a stable environment
A balanced diet should provide all essential vitamins and minerals. Supplements maybe required
for those who are ill, planning to have children, recovering from injury, suffering from digestive
problems or choose not to eat an optimal diet.
Canada’s Food guide recommends the following daily servings for a balanced diet:
Food Group
Grain Vegetables
and Fruit
Milk Products
or Substitutes
Meat and
Alternatives
Daily Servings 5-12 5-10 2-4 2-3
Nutritional information about the food you are eating is found on most packaging:
a) Specific amount of food
All the information in the Nutrition Facts table is based on a specific amount of food. The specific
amount may be indicated by a phrase such as: a slice, one egg, two cookies, followed by the
metric measure (grams, cups, millilitre etc…)
b) % Daily Value
The % Daily Value provides a quick overview of the nutrient profile of the food, allowing product
comparisons based on more than one nutrient. It puts nutrients on the same scale (0% - 100%
Daily Value). You can quickly identify the strengths and weaknesses of a food product.
c) Calories
Calories are an expression about the amount of energy a food provides. One calorie is measured
by the amount of energy it takes to raise 1 mL of water by 1 degree celsius. Foods that provide
energy and no other nutrients are called empty calories.
d) Nutrient claims
The Government has rules in
place that must be met before a
nutrition claim can be made on a
label. Examples of nutritional
claims include:
Functional foods - those that
provide more for your body than
just essential nutrients. These
benefits include strengthening
the immune system, slowing the
ageing process, aid digestion (probiotic yoghurt)
Whole foods - contain a natural level of a functional component (antioxidants)
Fortified foods - contain added ingredients (Orange juice - calcium enriched)
Enhanced foods - contain a functional component that has been introduced into the organism
from which the food comes – through breeding, feeding or genetic engineering (eggs – omega-
3)
e) List of ingredients
The list of ingredients is mandatory and has been on the food product package for many years.
All of the ingredients for a food are listed in descending order by weight. The ingredients
present in the greatest amount in a product are listed first. The list is also a source of
information for people who want to avoid certain ingredients or verify the presence of an
ingredient in a food.
Macromolecules
Carbohydrates A green plants ability to get energy from the Sun and turn CO2 from the air into sugars
(carbohydrates) is called photosynthesis and is represented by the chemical equation below:
6 CO2 + 12 H2O + Energy (Light) C6H12O6 (glucose) + 6 O2 + 6 H2O
Therefore, all carbohydrates come from green plants. Carbohydrates are nutrients based on
molecules of sugar; because of this they are called “saccharides” which means “sweet”. All
carbohydrates have the general formula C-H2O, in other words they are “carbon-hydrates”.
The function of carbohydrates are to act as the primary energy source in cells as they pass
through the process of cellular respiration, which is represented by the chemical equation
below:
C6H12O6 + 6 02 6 CO2 + 6 H2O + energy (ATP)
In photosynthesis light energy is used to produce food molecules (glucose). In cellular
respiration the food molecule (glucose) is broken down and releases energy (in the form of ATP)
for the cell to use.
Two important organelles are specialized for energy conversion.
1. Mitochondria (sites for cellular respiration)
2. Chloroplasts (sites for photosynthesis)
After plants produce glucose they can convert it
into a variety of other sugar molecules by
altering their shape or by bonding them together.
The two main varieties of carbohydrates that we consume
are simple sugars such as monosaccharides (glucose and
fructose) or disaccharides (sucrose and lactose), and
polysaccharides or complex carbohydrates (starch –
storage of sugar in plants).
Simple sugars tend to provided short term energy supplies
whereas complex carbs a more sustained source of energy.
Fibre is a carbohydrate (cellulose) found in
the cell walls of plants, that cannot be
digested by humans. It helps to hold water
and provide bulk in the large intestine, thus it
helps to eliminate our waste.
Current North American guidelines recommend that carbohydrates, especially complex
carbohydrates provide 55% to 60% of your daily energy requirements, which should be
approximately 130 g/day.
Healthy carbohydrates such as those provided
from whole grains, fruits and
vegetables are excellent dietary sources
of carbohydrates. When your diet is rich in
these carbohydrates, your body extracts
energy from them, saving protein for muscle
building and body repair.
Whole grains are those that include all portions
of the grain. Processed grains have had the bran and the germ portion removed. These areas
provide a number of essential vitamins and minerals along with some healthy fats and protein.
Carbohydrates are processed to alter their taste and to extend shelf-life.
Unhealthy sources of carbohydrates include white bread and
pasta, candy, pasteries, soda and any other highly processed
or refined foods. These carbs may contribute to weight gain,
interfere with weight loss and promote diabetes and heart
disease.
Glycogen is a carbohydrate that acts as a storehouse for
extra glucose in humans and animals. It is produced in the
liver. Excess consumption of carbohydrates can get
converted into fat (a long-term energy storage molecule) and
may lead to an increase in insulin production.
Celiac disease in an autoimmune response to gluten, a
collection of proteins found in grain products.
Lipids
Fats serve as a long-term storage of energy along with providing insulation, acting as hormones
and the main component of cell membranes. Current guidelines recommend that dietary fats
should supply no more than 30% of your daily energy requirements. There are two main types
of fat we consume, triglycerides and cholesterol.
Triglycerides are composed of a glycerol molecule attached to three fatty acid chains. The
fatty acid chains determines the type of triglyceride. The length and bonding can vary from one
fatty acid to another.
A) Saturated Fatty Acids
There are only single bonds between each carbon atom. This organization allows for a linear
arrangement of the fatty acid tails, allowing them to pack close together, which explains why
saturated fatty acids are solids at room temperature.
These are found in foods such as butter, lard, cheese and
meat. In the past, saturated fats have been closely
associated with heart disease. More recent evidence
suggests that there are other factors to consider when
looking at the impact of saturated fats. As a guide,
saturated fats should NOT be considered a healthy fat, but
if less than 10% of your daily calorie requirements is in the
form of saturated fat it will have little impact on risk of
cardiovascular disease.
B) Unsaturated Fatty Acids
There is one (monounsaturated) or more (polyunsaturated) double bonds in the carbon chain.
This means that not every carbon is bonded to its maximum number of hydrogen atoms. Double
bonds produce kinks in the fatty acid chain, consequently, the more double bonds the chain
possess, the greater the difficulty for these chains to pack together. This explains why
unsaturated fats form liquids at room temperature (oils). These are found in foods such as oils –
olive, corn, sunflower etc… avocados or nuts.
Most naturally occurring unsaturated fatty acids are found in what is called the cis-
configuration. These types of fats appear to lower total cholesterol levels.
Unsaturated fats can have their double bonds
chemically reduced with hydrogen atoms (a process
termed hydrogenation). During this process Trans fats
are produced. The resulting molecule creates
straighter chains, which are capable of being solids at
room temperature, such as margarine. Trans-fats
elevate LDL (bad) cholesterol levels and lowers HDL
(good) cholesterol levels.
Omega-3 and omega-6 fatty acids are essential fats
found mainly in fatty fish. Omega fats are required to
build myelin, the protective covering around neurons of
our brain cells.
There are two types of cholesterol; about 80% of cholesterol is made by our liver, while the
other 20% comes from food:
1. Dietary Cholesterol
Found in foods containing animal fat -
liver, egg yolks, meat, dairy products,
shrimp
Doesn’t normally cause blood cholesterol
to increase in most people
2. Blood Cholesterol
Most of this cholesterol is produced by the liver from the triglycerides consumed
Two types - HDL and LDL
HDL (good) - High-Density Lipoprotein
Helps remove cholesterol from body
To boost HDL - exercise, be smoke-free and maintain healthy body weight
LDL (bad) - Low-Density Lipoprotein
Clogs arteries because these are deposited on artery walls (plaque), blocks circulation,
increases risk of heart attack or stroke
To lower LDL - cut down on saturated and trans fats, eat more foods containing soluble
fibre
Proteins
Accounts for 50% of the dry weight of cells
Wide variety of functions in organisms –
enzymes, hormones, receptors etc…
Huge variety of structure – muscles, hair, finger
nails etc…
Each protein has a unique three-dimensional
shape
Always assembled from a common cellular pool of 20 amino acids
8 of the 20 amino acids are considered essential amino acids as they cannot be produced
by the body, but must be obtained through diet
Proteins should make-up 10-35% of daily energy requirements (more if doing weight
training)
Animals sources such as beef, poultry, fish and eggs are sources of complete proteins
(provide all 8 of the essential amino acids)
Grains, nuts, seeds and vegetables are incomplete proteins, because they do not provide
all the essential amino acids
Vegetarians attempt to avoid all meat products, although may consume dairy and egg
products. Vegans will restrict their diet to foods derived from plants
Vegetarians and vegans must carefully balance their food intake in order to obtain all
eight essential amino acids
An amino acid is composed of a carbon atom (called the alpha carbon) covalently bonded to four
different groups:
Amine group (NH2)
Carboxyl group
Hydrogen atom
Side chain shown as “R-group”
(different for all 20 amino acids)
Types of Digestion All organisms must have some way of obtaining essential nutrients needed to make their own
structures and to perform life functions. Organisms that depend on organic molecules
manufactured by other living things are called heterotrophs.
Digestion can occur externally or internally. External digestion is thought to be the first type
of system to evolve and organisms such as fungi and spiders still rely on it today. In this
process, enzymes are secreted into the environment surrounding the organism, where they
break down organic material and then some of the products diffuse (move from an area of high
concentration to low concentration) back to the organism.
Internal digestion evolved later, where animals make use of a tube system to digests organic
material inside of their body. This method is more efficient as it allows organisms to capture
and store their food and control and separate the environments more effectively for the
digestive process.
Digestion can also be considered as intracellular or extracellular. Intracellular digestion is the
type of digestion in which food particles are taken within cells and subjected to the action of
enzymes there. Extracellular digestion is the digestion of food occurring outside of the cells
(as in the tube arrangement common in animals).
Types of Digestive Systems There are three main types of digestive systems:
1. Vacuole System (intracellular)
2. Closed-Tube System (extracellular)
3. Open-Tube System (extracellular)
All of these systems follow the same four steps:
Ingestion – the taking in of nutrients
Physical and Chemical – the breakdown of complex organic molecules (polymers) Breakdown
into smaller components (monomers)
Absorption – the transport of digested nutrients to the tissues of the body
Egestion – the removal of waste food materials from the body
1. Vacuole System
Food is digested inside a vacuole formed within the cell.
Examples: paramecium and amoeba
2. Closed Tube System
This type of digestive system consists of a “baglike”
structure with only one opening. Both ingestion and
excretion occur through the same opening.
In the digestive cavity, food is partially broken down by
enzyme action and absorbed into cells lining the inside of
the "bag". These cells complete the digestion process.
Example: hydra and a planaria
3. Open Tube System
This type of digestive system consists of a tube with two
openings. One opening is used to ingest food particles and
the other is used to excrete waste. Examples: earthworms
and humans. Open tube systems usually require:
1. Specialized mouthparts for biting and tearing food
2. Digestive organs that supply digestive chemicals, aid in the physical breakdown of food, and
maximize the surface area for absorption
Ingestion
Ingestion
Digestion is a complex process, which results in food being broken down into its
component molecules (monomers). It involves:
1) Mechanical (Physical) Digestion
Physically breaking the food into small pieces (increase surface area) and
mixing it with liquids. No energy is released.
2) Chemical Digestion
Digestive enzymes split specific chemical bonds holding the food molecules
together.
Molecules must be small enough to be absorbed into the bloodstream and, in
turn, enter the cells of the body. This process happened by diffusion.
In humans, the digestion process takes about 24-33 hours and requires passage through an extremely long tube system (alimentary canal), separated into distinct regions that perform specific functions.
Section Length
Mouth 15 cm
Pharynx 15 cm
Esophagus 35 cm
Stomach 30 cm
Duodenum 25 cm
Jejunum 2.5 m
Ileum 3 m
Colon/Large intestine 1.5 m
Rectum 15 cm
Total Length = 8.35 m
The Mouth and Pharynx
Both physical breakdown and chemical digestion occur in the mouth. The teeth
and tongue are important for physical digestion and the salivary glands for
chemical digestion.
Inside of your mouth, covering the surface of your tongue are tiny projections
called papillae, and every one holds hundreds of taste buds.
Taste is closely linked to olfaction (smell); much of what we call the taste of food
is actually the aroma. Taste is a combination of sensations – sweet, sour, salty
and bitter.
One theory is that taste buds for the different sensations are clustered in
specific regions on the surface of the tongue. Can you figure out where these
clusters are located?
Sweet Sour Salty Bitter
Human teeth
Each tooth has two divisions, the root and
an enamel crown. Enamel, which is formed
of calcium compounds, is the hardest
substance in the body.
Type of Tooth Number Function
Incisor 8 Cutting
Canine 4 Tearing
Premolars 8 Grinding
Molars 8 Crushing
Wisdom 4 Crushing
How Chewing Helps Digestion?
Sugar Appearance Before Shaking Appearance After Shaking
Loose
Cube
A) How did the surface area of the two types of sugar compare?
B) How does surface area affect the rate of dissolving?
Chemical digestion begins as food is chewed, and it begins to mix with saliva
produced by the three salivary glands – parotid, sublingual and submandibular.
Some functions of saliva include:
It wets and lubricates so food can be swallowed easier and begins the
dissolving process (required for taste and absorption)
It causes the food particles to stick together to form a food mass, or bolus
It contains a digestive enzyme called ptyalin (or salivary amylase), which
breaks down starch into simple
carbohydrates
The tongue pushes the food bolus to the back of
the throat and against the soft palate, which
initiates the automatic swallowing reflex.
The epiglottis prevents food and liquids from
entering the lungs during swallowing, while the
uvula stops food from entering the nasal cavity.
The Esophagus
No digestion, neither physical nor chemical occurs in the esophagus. It secretes
mucin, a lubricant which aids the bolus of food in its journey to the stomach.
The movement of food down the digestive tube is aided by peristalsis.
Peristalsis consists of alternate waves of
relaxation and contraction in the muscular
walls of the alimentary canal.
Where the esophagus opens into the
stomach, there is a ring of muscle called a
sphincter.
The cardiac sphincter acts as a valve and
controls the passage of food from the
esophagus into the stomach.
Heartburn or acid indigestion occurs when
stomach acid backs up into the esophagus,
burning its lining. Pain is felt in the region
of the heart where the esophagus is
located, but the condition has nothing to do
with the heart.
The movement of food out of the stomach, up the esophagus and out the mouth is
called regurgitation.
The Stomach and Intestines
Through the digestive process, macromolecules are broken down into molecules small enough to be
absorbed from the intestine and transported to body cells:
Carbohydrates Monosaccharide (glucose)
Proteins Amino Acids
Lipids (triglycerides) Fatty Acids and Glycerol
Hydrolysis is the main process in which food is chemically broken down. During hydrolysis, a water
molecule is added at the point where a link occurs between monomers. Hydrolysis occurs at a very slow
rate, but is immediately sped-up by enzymes (biological catalysts made of protein).
Enzymes are formed by secretory cells, which can exist singly, in simple sacs or in glands. A gland is a
structure made up of a complex system of tubules connected to other areas by ducts. Enzymes are very
specific and will only catalyze specific linkages. Many enzymes require the presence of minerals or
vitamins in order to function properly.
The Stomach
The stomach is the site for temporarily storage of
food and initial protein digestion. Both physical
breakdown and chemical digestion occurs here.
Physically the stomach has a J-shaped appearance and
can hold up to 1.5 L of food.
The stomach has folds or rugae that allow it to expand
and contract. When your stomach is empty, your small
intestine produces a hormone called ghrelin that
travels to your brain to tell you that you are hungry.
When your stomach is full (stretched) the hormone
leptin is produced by adipose (fat) tissue to signal your
brain that you are full.
Food in the stomach is broken down mechanically into
smaller particles by the contractions of the muscular stomach walls (oblique muscles). This is referred
to as churning.
The food mass is broken down chemically as it is churned and mixed with gastric juice secreted by two
types of glands:
1. Pyloric glands
Secrete mucus, which covers the stomach lining and protects it.
2. Gastric glands
Secrete very acidic gastric juice, which has a pH of 1.5 to 2.5. Gastric juice contains
hydrochloric acid (HCl) and the digestive enzyme pepsinogen. When pepsinogen is
converted to its active form of pepsin, the breakdown of proteins into their individual
amino acids begins. HCl helps the breakdown of all macromolecules.
There are three mechanisms involved in stimulating the flow of gastric juice:
1. The thought, sight, smell, or taste of food stimulates the brain to send messages via nerve impulses
to the gastric glands.
2. Food touching the lining of the stomach.
3. Secretion of the hormone Gastrin caused by stretching of the stomach lining. Gastrin stimulates
production of large amounts of gastric juice.
In a typical day 9 litres of fluid pass through the lumen of an adult’s gastrointestinal tract. Only about 2
litres of that volume enters through the mouth. The remaining 7 litres come from body water secreted
along with enzymes and mucous.
A common disorder associated with the stomach occurs following the destruction of the cells lining in
the stomach. This leads to a peptic ulcer. Until recently, diet and stress were always thought to be the
leading cause of ulcer formation. Scientists have now discovered a remarkable organism, Helicobacter pylori, which thrive in the stomach’s formidable environment and are believed to cause most cases of
ulcers.
The Small Intestine
Most chemical digestion and almost all absorption of nutrients occur here. After food leaves the
stomach, regulated by the pyloric sphincter, it enters the first part of the small intestine called the
duodenum. At this stage, the partially digested food is called chyme. The presence of chyme in the
small intestine, stimulates secretion of the hormone secretin and cholecystokinin (CCK). When these
hormones reach the pancreas and liver they stimulate the production of pancreatic enzymes and bile.
The small intestine itself produces a number of enzymes that continue the chemical digestion process,
such as:
Secretes maltase which completes the breakdown of carbohydrates (maltose)
Secretes peptidases which complete the breakdown of proteins
Secretes lactase which breaks down lactose
The Pancreas
Produces sodium bicarbonate which neutralizes stomach acid
Secretes the digestive enzymes lipase (lipids), amylase (carbohydrates) and trypsin (protein)
Produces insulin and glucagon in response to blood-sugar levels
Insulin makes cell membranes more permeable to glucose and increases metabolism to lower blood
sugar levels
Glucagon raises blood sugar levels by stimulating the breakdown of glycogen in the liver
Insufficient insulin production can lead to diabetes
The Liver Produces bile – an emulsifying agent needed for the physical digestion of fats
Bile is stored in the gallbladder
Storage of carbohydrates (glycogen)
Production and storage of vitamins (A, D, E and K)
Process fats – triglycerides, cholesterol
Detoxifies many harmful substances (alcohol)
Excessive damage to liver tissue can lead to the development of scar tissue; a condition called
cirrhosis
Absorption
Peristaltic contraction continue throughout the intestines which has 3 main effects:
1. They squeeze chyme through the intestine moving the bolus along
2. They mix the chyme with digestive enzymes and break down food particles mechanically
3. Bring the intestinal contents into contact with the intestinal wall speeding absorption
During absorption, digested nutrients pass through epithelial cells and enter capillaries or lacteals in
structures called villi.
The capillaries act to absorb
simple sugars, vitamins, minerals
etc… into the circulatory system.
Lacteals are part of the
lymphatic system and absorb
fatty acids and glycerol into tiny
vessels.
The small intestine has a number
of structural features that
increase its surface area for
maximum absorption of nutrients:
1. The small intestine is very long
2. Its lining has many folds
3. The lining is covered with millions of finger-like projections called villi, which increase the
surface area by as much as 10 times
4. The epithelial cells of the villi that face into the intestinal opening have tiny projections called
microvilli that further increase the surface area
Celiac disease is an autoimmune disorder of the small intestine that occurs because of a reaction to
gluten which is found in wheat products. Exposure to gluten causes the villi of the small intestine to
atrophy. This interferes with the absorption of nutrients and water causing diarrhea and fatigue.
Crohn’s disease is a chronic inflammatory disease of the intestines, primarily caused by ulcers in the
small and large intestines, but can affect the digestive system anywhere between the mouth and the
anus.
The Large Intestine
Undigested and unabsorbed materials pass from the small intestine into the large intestine. No
digestion occurs in this portion of the digestive system.
Functions of the large intestine include:
1. Reabsorption of water from the food mass
2. Absorption of vitamins B and K produced by live bacteria in the large intestine
3. Elimination of undigested and indigestible material from the digestive tract (feces) Examples:
cellulose from plant cell walls, large quantities of bacteria, bile, mucus and worn-out cells from the
digestive tract
Fecal matter is stored in the last part of the large intestine, the rectum, and periodically eliminated, or
defecated, through the anus.