The human respiratory and circulatory systems work together to oxygenate the blood. The respiratory system brings air into the lungs through the nose, pharynx and trachea, where gas exchange occurs in the alveoli via diffusion. Oxygenated blood enters the pulmonary vein and is pumped by the heart through arteries to the body. Deoxygenated blood returns to the heart via veins and is pumped to the lungs to repeat the cycle. The circulatory system is a closed network of vessels that transports blood, nutrients and gases throughout the body using the heart as a pump.

2. The human body needs oxygen to
sustain itself. The human respiratory
system is a series of organs responsible
for taking in oxygen and expelling
carbon dioxide. The respiratory center in
the medulla oblongata and the pons of
the brainstem

3. Air passes through the
nostrils; organ of smell
and entrance to the
respiratory tract right to
the nasal cavity, the
pharynx, and the larynx
above the vocal cords.
Nasal cavity
Pharynx
Larynx

4. Air passes the epiglottis, that is a cartilaginous
structure that closes the opening to the trachea
when swallowing, to prevents food and drink
from entering the larynx and trachea.
The trachea, also called the windpipe, filters the air that
is inhaled. The trachea has a membrane lining that
produces a layer of mucus that helps filter waste that an
organism breathes in through the air. There is also a
small lining of tiny hairs in our lungs called cilia. These
tiny hairs act as a filter in our lungs and control the
amount of mucus that enters our lungs.
The reason why we cough, sneeze, and spit is because
the cilia push up the mucus, so not too much enters our
lungs, for either expectoration or swallowing to the
stomach where the acidic pH helps to neutralize foreign
material and micro-organisms.

5. When air passes the trachea, gets to the bronchi
located inside the lungs. The bronchi form the
bronchial tree and at the end of the bronchial tree
lie the alveolar ducts, the alveolar sacs, and the
alveoli.
A typical pair of human lungs contain about
700 million alveoli The alveoli contain
some collagen and elastic fibres. The elastic
fibers allow the alveoli to stretch as they are
filled with air during inhalation. They then
spring back during exhalation in order to expel
the carbon dioxide-rich air.
Pulmonary gas exchange takes place by
passive diffusion. During this exchange of
oxygen, energy is not required to be burned by
the cells. Gases move due to a concentration

6. Molecules of oxygen and carbon dioxide
are passively exchanged, by diffusion,
between the gaseous external
environment and the blood.
Blood passes through the capillaries. The
pulmonary artery carries blood containing
carbon dioxide to the air sacs, where the gas
moves from the blood to the air. Oxygenated
blood goes to the heart through the pulmonary
vein, and the heart pumps it throughout the body.

7. The diaphragm is a sheet of internal skeletal
muscle that extends across the bottom of
the thoracic cavity. The diaphragm separates
the thoracic cavity, containing
the heart and lungs, from the abdominal
cavity.
It performs an important function in respiration:
as the diaphragm contracts, the volume of the
thoracic cavity increases and air is drawn into
the lungs.
The diaphragm has openings through which
structures pass between the thorax and abdomen.
There are three large openings—the aortic hiatus,
the esophageal hiatus, and the caval opening—plus a
series of smaller ones.

9. The circulatory system, also known as the
cardiovascular system is a vast network of
organs and vessels that is responsible for
the flow of blood (simply a highway for
blood) nutrients, hormones, oxygen and
other gases to and from cells.

10. It is made up of three independent systems
that work together: the heart
(cardiovascular); lungs (pulmonary); and
arteries, veins, coronary and portal vessels

11. As we breathe, oxygen enters the lungs and is absorbed
into the blood stream. The body's oxygen transport
system takes oxygen to the working muscles, through
the circulatory and respiratory systems working
together. The main workers are
the heart, blood and lungs. The whole oxygen transport
system works in a cycle.

13. In the average
human, about 2,000
gallons (7,572 liters)
of blood travel daily
through about 60,000
miles (96,560
kilometers) of blood
vessels.

14. The essential components of
the human cardiovascular
system are the heart, blood and
blood vessels. The
cardiovascular systems of
humans are closed, meaning
that the blood never leaves the
network of blood vessels.

15. The blood moves at a speed of about 30cm / sec, where a
drop of blood takes about 20 seconds to travel the entire
human body and return to the point where it left (full

16. The heart pumps oxygenated blood
to the body and deoxygenated blood
to the lungs. In the human there are
four chambers in total: left
atrium, left ventricle, right
atrium and right ventricle. The right
atrium is the upper chamber, that
receives deoxygenated (poor in
oxygen) and passed into the right
ventricle to be pumped through the
pulmonary artery to the lungs for re-
oxygenation and removal of carbon
dioxide.

17. The left atrium receives newly
oxygenated blood from the lungs
which is passed into the strong left
ventricle to be pumped through the
aorta to the different organs of the
body.
The ventricles are separated from each other by
the interventricular septum. The heart has
four valves, the valves between the atria and
ventricles are called the atrioventricular
valves. Between the right atrium and the right
ventricle is the tricuspid valve. The mitral
valve lies between the left atrium and left
ventricle.

18. The heart wall is made up of three layers:
the inner endocardium,
middle myocardium and
outer epicardium. These are surrounded
by a double-membraned sac called the
pericardium.
Two additional semilunar valves sit at the
exit of each of the ventricles.
The pulmonary valve is located at the
base of the pulmonary artery. The
semilunar aortic valve is at the base of
the aorta.

20. The blood from the heart is carried through the body by
a complex network of blood vessels . Arteries take blood
away from the heart. The main artery is the aorta that
branches into other major arteries, which take blood to
different limbs and organs.
These major arteries include the carotid artery, which
takes blood to the brain; the brachial arteries, which take
blood to the arms; and the thoracic artery, which takes
blood to the thorax and then into the hepatic, renal, and
gastric arteries for the liver, kidneys, and stomach,
respectively. The iliac artery takes blood to the lower
limbs. The major arteries diverge into minor arteries, and
then into smaller vessels called arterioles, to reach more
deeply into the muscles and organs of the body.

21. Veins are blood vessels that carry blood toward the heart. The
largest veins in the human body are the venae cavae. These are
two large veins which enter the right atrium of the heart from
above and below. The superior vena cava carries blood from the
arms and head , while the inferior vena cava carries blood from
the legs and abdomen to the heart. The major arteries diverge into
minor arteries, and then into smaller vessels called arterioles, to
reach more deeply into the muscles and organs of the body.

22. Capillaries are the smallest of a body's blood vessels (and lymph
vessels) that make up the microcirculation. These microvessels,
connect arterioles and venules, and they help to enable the exchange
of water, oxygen, carbon dioxide, and many other nutrients and
waste substances between the blood and the tissues surrounding
them. Lymph capillaries connect with larger lymph vessels to
drain lymph collected in the microcirculation. Blood flows from the
heart through arteries, which branch and narrow into arterioles, and
then branch further into capillaries. The capillaries then join and
widen to become venules, which in turn widen and converge to
become veins.

23. As mentioned earlier the
cardiovascular system is
closed, the other component
of the circulatory system,
the lymphatic system is open,
and is a vital part of
the immune system,
comprising a network
of lymphatic vessels that
carry a clear fluid
called lymph.

24. The lymphatic system works in
close cooperation with other
body systems to
destroy pathogens and filter
waste. Often called the body’s
two "circulatory systems”, but
the
lymph flows to the heart, and
thanks to a valve system that
prevents recoil moves.

25. Organs of the lymphatic system include the tonsils,
thymus gland and spleen. The thymus gland produces
T cells or T-lymphocytes and the spleen and tonsils help
in fighting infections. The spleen’s main function is to
filter the blood, removing unwanted red blood cells, also
detects viruses and bacteria and triggers the release of
pathogen fighting cells.