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Biology Lesson # 6
Animal Organs & Systems
Tissues & Organs
 Recall that there are four animal tissues: epithelial,
connective, muscle, and nervous tissue. Most organs
are made up of all four tissues. There are too many
organs to discuss in one lesson, but we will focus on a
few important ones in the human body.
 Biologists categorize organ systems according to their
main functions, and there are 11 main organ systems in
the human body. We will only focus on five.
The Respiratory System
 The main function of this system is gas exchange – oxygen is
inhaled and carbon dioxide is released – the site of gas
exchange is in the alveoli.
 The main organ involved: the lungs
Respiratory
 Air Passage: mouth/nose pharynx  trachea  bronchi 
bronchioles  alveoli  capillaries
 Air enters the mouth or nose and travels into the pharynx (back of
mouth/throat)
 trachea (also called the windpipe) – flexible tube made of cartilage
rings (connective tissue)
 bronchi (tubes, there are 2 of them, one for each lung) into smaller
tubes called bronchioles
 finally into smaller sacs called alveoli (made of epithelial tissue)
 alveoli are surrounded by thin blood vessels called capillaries that
allow O2 to enter the capillaries into the blood to travel
throughout the body, and allow CO2 to travel from the capillaries
back to the alveoli and out the same way it came through the
mouth or nose.
Lungs
The Circulatory System
 The main function of this system is to transport
blood throughout the body.
 The main organ involved: the heart
 Arteries are thick-walled vessels that carry blood
away from the heart, with a strong pressure that
pushes the blood along
 Veins carry blood back to the heart, and are thinner
and lower in pressure. They also contain valves to
ensure blood does not flow backwards.
Capillaries & Diffusion
 Capillaries connect the veins and arteries, and are
the smallest blood vessels – about one cell thick.
 Oxygen and carbon dioxide flow in and out of capillaries by
diffusion (the movement of a substance from an area of
high concentration to low concentration).
 If the blood has more oxygen than the tissues, oxygen will
diffuse across the capillary walls and enter the tissues.
 Carbon dioxide and wastes are also removed from the
tissues across the capillary walls, to the blood, where it
travels to the lungs and is removed as you exhale.
The Digestive System
 The main function of this system is to absorb and
transport nutrients throughout the body (all the
way from the mouth to the anus).
 Absorption is the process by which food that has
already been broken down passes through the walls
of the intestine (mainly the small versus the large)
into the bloodstream.
Digestive Organs
 Food Passage: Mouth → Tongue → Esophagus →
Stomach → Small Intestines → Large Intestines →
Rectum → Anus
 Mouth
 Lined with epithelial tissue and covered in glands
that secrete mucus, saliva, and enzymes
 Tongue
 Made of epithelial tissues and glands, connective
tissues, and muscle tissue
Digestive Organs (continued)
 Esophagus
 A tube of smooth muscles where food travels
down from the mouth due to a rhythmic
constriction and relaxation called peristalsis
 Lined with a protective layer of epithelial tissue
 Stomach
 Made of epithelial, connective, nervous, and
muscle tissues
 The stomach churns food and mixes it with
digestive juices (strong acids) and enzymes
Digestive Organs (continued)
 Intestines
 Both digestive nutrients and undigested waste
products move into the small and large intestines,
which are areas of chemical digestion and removal
of wastes
 Solid wastes are then stored in the rectum and
exit the body through the anus
Digestive System
Videos
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Respiratory System
Respiratory Song to “Live While We’re Young”
Circulatory System
Circulatory Song to “Call Me Maybe”
Heart Song to “Ho Hey”
Digestive System
Digestion Song to “Lightening”