Overview of Human Anatomy and Organ Systems
The picture above is a very simplified representation of the major organs that make up the human body.
If you were to cut open your chest and abdominal cavity and look inside, it would look a lot messier than
then this diagram. Still, most of your organs would be in pretty much the same place. As you read the
descriptions below, try to locate each of the organs on this diagram so you understand exactly where
they are.
Major Organ Systems
Respiratory System: Through our respiratory system, we are able to absorb oxygen, and release carbon
dioxide back into the air around us. The major organs of the respiratory system are the mouth & nose,
the trachea (windpipe), and the lungs. The trachea is the wind pipe through which air enters and exits
the lungs. It is made of hard, ribbed cartilage. You can feel it at the front of your neck. The trachea leads
to the bronchiole, which are smaller tubes that spread out inside the lungs. Humans have two lungs, one
on each side of the chest. Lungs are made of very soft tissue that expands and shrinks as we breathe in
and out.
Circulatory System: The respiratory system is closely intertwined with the circulatory system.
Sometimes they’re grouped together into one big system (the cardiovascular system). The role of the
circulatory system is to bring oxygen to every cell in your body, and to remove CO2 from those cells (so
they can do cellular respiration). The major organs in the circulatory system are the heart, the blood
vessels (veins, arteries, and capillaries) and the blood. The aorta is the main artery leaving the heart. The
heart is the central pump for your body. When your heart beats, it is actually contracting (squeezing)
and releasing. This squeezing action causes blood to move through all of the interconnected blood
vessels that spread out to every cell in your body. Blood that has been freshly oxygenated from the
lungs gets pumped out to the rest of the body. Blood that has been de-oxygenated and is carrying CO2
gets pumped back towards the lungs. Blood also transports many other important materials to cells
including water, hormones, and nutrients from food. The heart is located on the left side of your chest,
just under the lungs, which makes sense since that’s where all the fresh oxygen is coming from! Most
people can feel their heart beat if they put their hand on the left side of their chest. You can also feel
your pulse (blood pumping) at numerous places on your body.
Digestive System: The job of our digestive system is to absorb water and nutrients into our bodies so
our cells and tissues can stay alive. Organisms that don’t do photosynthesis need to eat sugars in order
for their cells to carry out cellular respiration. We also eat other types of food to build the molecules and
new cells that make up our bodies. The digestive system includes the mouth, esophagus, stomach, liver,
gall bladder, small intestine, large intestine (colon), and anus. Food that we eat generally follows a
pathway through each of the organs listed above with the exception of the liver and gall bladder. The
gall bladder sits just below the liver, near the start of the intestines. When we fatty foods enter the
small intestine, the liver and gall bladder release bile (a watery brown liquid) into the intestines to mix
with the fat particles and make it easier for the body to absorb them. Most of the nutrients in our food
gets absorbed when it’s in the stomach or small intestine. Enzymes in this organs break down food
particles into smaller bits that can be absorbed across the wall of the organ and into the blood stream.
The liver also plays another important role within our digestive system besides producing bile – blood
that has just absorbed nutrients from the small intestine gets filtered by the liver, which is responsible
for removing any toxins from the blood before it enters the rest of our body.
Urinary/Excretory System: The urinary system is responsible for removing waste from the body. It is
closely intertwined with the digestive system. The urinary system consists of two kidneys, the bladder,
and the urethra. Blood from the body gets absorbed by the kidneys which filter out waste (mainly urea).
Those materials are sent to the bladder through tubes called ureters. Kidneys also absorb water from
the blood stream. It is an important job of the kidneys to also filter out excess water from the body so
we don’t get over-hydrated. The bladder is like an empty balloon. Once if fills up with liquid, it triggers
nerves that tell us we have to pee. Urine (water and urea) exits the body through the urethra.
Nervous system: One major organ system not represented in this diagram is the nervous system. This
includes your brain, your spinal cord, and trillions of nerves throughout your body. It also includes your
skin, eyes, ears, nose, and tongue, which are responsible for sensing the world around you. Nerves
throughout your body sense the world around them through touch, taste, smell, sight, or sound. They
send an impulse back to the brain, which processes this information, and then sends back instructions to
the rest of the body, telling it how to respond to this sensation. The role of the spinal cord is to send
protected nerve impulses to parts of your body that are far from your skull, where the brain is. People
who injure their spinal cord above their legs lose nerve function in their legs because those messages
can no longer get there. People who injure their spinal cord above their arms lose nerve function in both
their arms and legs.
Skeletal and Muscular Systems: Our skeletal system has two important roles in our bodies – structure
and protection. The bones in our body give our body structure and shape – could you imagine what your
body would look like if you didn’t have any bones? They also protect important, soft organs. The rig cage
protects our lungs and heart. The cranium protects our precious brains. Our muscular system also
provides structure to our bodies. Again imagine what your legs and arms would look like if you didn’t
have any muscles. Muscles also allow the body to move and carry out activities. Muscles get signals from
the brain to respond to various stimulus. They contract and release as we carry out everyday functions.
A lot of the time we are using our muscles without even thinking about it. Technically, your heart is the
most important muscle in our bodies.
Reproductive system: Also not included in the diagram, the reproductive system is different for male
and females. Males have testes (testicals), a prostate, and a penis. The testes produce and hold the sex
cells (sperm). During sex, these cells travel from the testes through the penis where they are expelled in
hopes of finding and fertilizing and egg. Females have ovaries, fallopian tubes, a uterus, and a vagina.
The ovaries produce and release sex cells (eggs) once a month. The egg travels down the fallopian tube
and into the uterus. If the egg is fertilized, it will implant itself in the uterus and eventually grow into a
baby. If it is not fertilized, it will leave the body as menstruation.