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.