From Cells to
Systems
Lungs
Heart
Digestive System
Reproductive System
Cells to Systems
• In multicellular organisms, cells work together in
small groups called tissue
o Eg: muscle tissue, nerve tissue, skin tissue
• An organ is made up of different tissues working
together to perform a particular function
o Eg: the stomach is an organ that is made up of
tissues, which are made up of cells
• A system is made up of a group of organs that
work together to perform a particular function
o Eg: digestive system, circulatory system
THE LUNGS
The Lungs
• Major part of the respiratory system
• Main function is to transport oxygen from
the atmosphere into the bloodstream and
to release CO2 from the bloodstream into the
atmosphere
• They are a large organ because they need a
large surface area to exchange gasses
o This occurs in specialised cells that form
millions of tiny, highly specialised thin walled
air sacs called alveoli
Exchanging Gasses
• Air travels down the
trachea (windpipe) and
divides into 2 main
branches (bronchi)
• Air then continues to
subdivide into the
bronchioles until it
reaches the
alveoli where gas
exchange occurs
The Respiratory System
• Respiration: series of chemical
changes taking place in cells to
release energy
o In animals, this means we take in air
and extract oxygen from it
o Oxygen passes into the bloodstream to
be distributed throughout the body
o The walls of the alveoli and blood
capillaries are only 1 cell thick
HEART DISSECTION
THE HEART
The Circulatory System
The body’s own transport system that carries
substances around the body.
Which organs are involved in this system?
heart
blood vessels
blood
The Circulatory System
The circulatory system carries two types of blood:
oxygen-rich
blood
oxygen-poor
blood
 blood travelling
to the body cells
 blood travelling
away from the body cells
 high oxygen content
 low oxygen content
 low carbon dioxide
content
 high carbon dioxide
content
The Heart
The organ at the centre of the circulatory system. It pumps blood
around the body.
The Heart
The inside of the heart is divided into two sections so that the two
types of blood (oxygen-rich and oxygen-poor)
are kept apart.
right side
of the heart
oxygen-poor
blood
left side
of the heart
oxygen-rich
blood
The Heart and Lungs
lungs
body’s
cells
• Blood is pumped around the
body by the heart.
• It takes about 30 seconds for
blood to go once around the
body.
• The left side of the heart pumps
oxygen-rich blood to the rest
of the body.
• Blood picks up carbon dioxide
from the body’s cells.
• This oxygen-poor blood then
travels back to the right side of
the heart.
• Next, the right side of the heart
pumps oxygen-poor blood to
the lungs.
• In the lungs the blood gets rid
of the waste carbon dioxide and
collects more oxygen.
• The oxygen-rich blood then
returns to the left side of the
heart.
The Chambers of the Heart
Each section of the heart is called a chamber. There are 4.
An upper chamber is called an atrium (plural atria).
A lower chamber is called a ventricle.
right
atrium
left
atrium
right
ventricle
left
ventricle
The Chambers of the Heart
The chambers of the heart have different functions.
Pulmonary
artery - blood
to the lungs
Aorta - blood to
the body
Superior Vena
Cava - blood
from the body
The atria collect blood that enters the heart.
The ventricles pump blood out of the heart.
Pulmonary vein
- blood from the
lungs
Heart valves
Blood always flows in the same direction as it moves through the heart
during each circulation of the body.
The chambers of the heart are separated by valves which prevent blood
from flowing in the wrong direction.
Pulmonary Valve valve leading out of
right ventricle
Tricuspid Valve valve between
right atrium and right
ventricle
Aortic Valve - valve
leading out of
left ventricle
Mitral Valve - valve
between
left atrium and left
ventricle
Multiple-choice
quiz
THE DIGESTIVE SYSTEM
The Digestive System
• The digestive system
is used for breaking
down food into
nutrients
• These pass into the
circulatory system
and are taken to
where they are
needed in the body
The Digestive System
• The only visible parts of the digestive
system are the entry and exit points
(mouth and anus)
• Stretched out the digestive system is a
9m tube
– It is extremely folded and passes through
many organs
Physical vs Chemical Digestion
• Physical Digestion: changing the shape
of the food
• Chemical: breaking down the food to
release nutrients
Stages to Food Processing
1. Ingestion: taking in
food
2. Digestion: breaking
down food into
nutrients
3. Absorption: taking in
nutrients by cells
4. Egestion: removing
any leftover wastes
Mouth
• Begins when food
enters the mouth
• It is physically broken
down by the teeth
• It is begun to be
chemically broken
down by amylase, an
enzyme in saliva that
breaks down
carbohydrates
Mouth to Pharynx
• The tongue moves the
food around until it
forms a ball called a
bolus
• The bolus is passed to
the pharynx (throat)
and the epiglottis
makes sure the bolus
passes into the
esophagus and not
down the windpipe
Peristalsis
• The bolus
passes down
the esophagus
by peristalsis
– A wave of
muscular
contractions
that push the
bolus down
towards the
stomach
Into the Stomach
• To enter the
stomach, the
bolus must pass
through the
lower
esophageal
sphincter
– A tight muscle
that keeps
stomach acid
out of the
esophagus
The Stomach
• Contains folds called rugae
• A big muscular pouch which churns the
bolus (physical digestion) and mixes it
with gastric juice, a mixture of:
– Stomach acid: kills off any invading bacteria
or viruses
– Mucus: protects the lining of the stomach
from being eaten away by the acid.
– Enzymes: break down proteins and lipids
(chemical digestion)
Absorption in the Stomach
 Some medicines (eg.
aspirin), water and
alcohol are all
absorbed through the
stomach
 The digested bolus is
now called chyme and
it leaves the stomach
by passing through
the pyloric sphincter
Into the Small Intestine
• The majority of
absorption occurs
here
• The liver and
pancreas help the
small intestine to
maximize
absorption
• The small
intestine is
broken down into
three parts
Duodenum
• Receives chyme
from the stomach
• Bile breaks down
fats (stored in the
gall bladder)
• Pancreatic juice
reduces the acidity
of the chyme.
Jejunum
•
•
Where majority of
absorption takes
place
Lined with tiny
fingerlike projections
called villi (increase
surface area for
absorbing nutrients)
–
Each villi has
microvilli (further
increase surface area
for absorption)
Ileum
•
•
Last and longest
portion of small
intestine
Has fewer villi
and basically
compacts the
leftovers to pass
through the
caecum into the
large intestine
Into the Large Intestine
• Also known as the
colon
• Used to absorb
water from the
waste material
leftover
• Produces vitamin
K and some B
vitamins using the
helpful bacteria
that live here
The Large Intestine
• All leftover waste is
compacted and
stored at the end
of the large
intestine called the
rectum
• When full, the anal
sphincter loosens
and the waste
(feces) passes out
of the body
through the anus