Human Body Notes #1
The Circulatory System
The circulatory system delivers materials, including nutrients and oxygen, to all
cells in the body and carries away wastes. This system is made up of blood, the
heart, and blood vessels.
Blood
Structure of blood:
 plasma
 red blood cells
 white blood cells
 platelets
Functions of the blood:
 carries oxygen and nutrients to the cells of the body
 removes carbon dioxide (wastes) from the cells of the body
 carries other waste products to the kidneys for removal
 helps to fight infections
 helps to form blood clots and seal small wounds
Characteristics of the Parts of Blood
Plasma
Red Blood Cells
White Blood Cells
Platelets
colorless
cell fragments
defend the body
against infection
some absorb dead
cells
creates blood
clots (scabs –
concave shaped
Structure
liquid portion
Function
carries all
substances
dissolved in
the blood
Other
have no nucleus
contain hemoglobin
(that carries O2)
carries oxygen
through body
made in long bones
and spleen
surface & bruise –
under skin)
made in bone
marrow
The Heart
The heart is a fist-sized, muscular pump that circulates blood. It is divided into
left and right halves and has four chambers. The two upper chambers are called
atria (atrium, singular) and the two lower chambers are called ventricles. Without
the strength of the muscles of the heart (known as cardiac tissue), there would
not be enough force to circulate the blood throughout the entire body. Blood
never flows backwards because there are valves that close and prevent backward
flow. This diagram illustrates the major structures of the human heart:
aorta
right atrium
left atrium
valves
valves
right ventricle
left ventricle
HEART 2nd PAGE: The function, or job, of the heart is circulation. When the heart
contracts, it pumps blood to other parts of the body. The blood moves due to the
increase in pressure within the heart. It pumps oxygen-poor blood to the lungs to
expel carbon dioxide, and it pumps oxygen-rich blood from the lungs throughout
the rest of the body. Oxygen-poor blood travels to the heart in blood vessels
called veins. Oxygen-rich blood travels away from the heart in blood vessels called
arteries. Capillaries connect arteries and veins. It is important for students to
remember that the process of circulation is continuous. The heart actually acts
like two separate pumps and oxygen-poor and oxygen-rich blood are being moved
simultaneously. The following flow chart traces blood circulation through a single
trip in the body:
oxygen-rich blood from the lungs enters the left atrium
↓
left atrium contracts and blood passes through valve
↓
in left ventricle
↓
left ventricle contracts, sending blood out the aorta and to the rest of the body
↓
oxygen-poor blood returns to the heart and enters the right atrium
↓
right atrium contracts and blood passes through valve
↓
in right ventricle
↓
right ventricle contracts, sending blood to the lungs to pick up more oxygen
If the heart is cut open to reveal the inside, the wall of the left ventricle is
obviously thicker than the wall of the right ventricle. The reason for this is the
distance from the heart to the lung is much smaller than from the heart to the
entire body. Blood coming out of the heart on the right side requires a greater
force to pump it because it must travel to the entire body. This is an excellent
example with which to illustrate how structure is directly related to function.
The Blood Vessels
Structure
Arteries
thick, elastic walls
Function
carry oxygen-rich blood
away from heart
Other
aorta is largest in body
Veins
thinner than
arteries
carry oxygen-poor
blood back to the
heart
Capillaries
only one cell layer
thick
allow nutrient and
waste exchange at
cellular level
connect arteries
and veins
The following are a few examples of how the circulatory system helps maintain
homeostasis:
 controlling blood pressure
 constriction and dilation of blood vessels to regulate blood flow and body
temperature
 “fight or flight” reaction/response – heart beats faster to increase oxygen
flow to muscles etc.
 regulation of blood flow to critical organs during exercise – less to digestive
system, kidneys, etc.
 CO2 – O2 exchange maintains equilibrium of blood composition
 formation of blood clots prevents infection and disease from entering at site
of a wound and maintains blood volume by preventing blood loss
The Respiratory System
The respiratory system provides the oxygen that humans need to survive. Oxygen
combines with glucose (sugar) to provide energy for the body in a process known as
respiration. The cells release carbon dioxide as waste, and it is removed from the
body. The following table lists some of the structures of the respiratory system
along with their functions:
Structure
nose and mouth
trachea (windpipe)
bronchi & bronchioles
lungs
alveoli
diaphragm
openings
tube in throat
tubes - 1 bronchi
branches into each lung
and 1000’s of bronchioles
split from each bronchi
2 – sponge like – contain
the bronchioles and
alveoli
tiny sacs branching off
bronchioles
dome-shaped muscle
below lungs
Function
air entry; warms & filters air
air pathway to lungs
carry oxygen to air sacs,
called alveoli
main organs in system – site
of (large-scale) CO2 – O2
exchange
surrounded by capillaries for
CO2 – O2 exchange
contracts and air is pulled
into lungs; expands and air is
pushed out of lungs
Structures of the
respiratory system:
The following flow chart traces the pathway of oxygen and carbon-dioxide through
the respiratory system:
air enters through the mouth and nose where it is warmed, filtered and moistened
↓
enters trachea
↓
enters bronchi and bronchioles of each lung
↓
enters alveoli (within lungs)
↓
capillaries surrounding alveoli
↓
in blood and to the heart to be pumped throughout the body
↓
oxygen – carbon dioxide exchanged at the cellular level
↓
carbon dioxide carried in blood to the heart to be pumped to the lungs
The following are a few examples of how the respiratory system helps maintain
homeostasis:
 interacts with the circulatory system, including the process of CO2 – O2
exchange to maintain equilibrium of blood composition
 contraction of the bronchioles, coughing, sneezing etc.. to expel pollen,
smoke or other airborne allergens and pollutants
 monitoring of the carbon-dioxide levels in the blood by the nervous system
may lead to an increase or decrease in breathing rates
The Digestive and Excretory Systems
The process of breaking down food into usable nutrients is called digestion.
Digestion is both a mechanical and a chemical process. Mechanical digestion breaks
down food into smaller pieces through processes such as chewing and swallowing.
Chemicals, such as saliva and acid in the stomach, are used to break down food into
nutrients the body can utilize. Some organs, such as the liver and pancreas, are
involved in digestion but food does not directly pass through them. These organs
aid digestion by producing important chemicals that are needed in the process.
This flow chart traces the pathway of food and wastes through digestion:
liver
Structures of the
digestive system:
mouth (including teeth, tongue and saliva)
↓
esophagus
↓
stomach
↓
small intestine
↓
large intestine
↓
rectum and anus
pancreas
Materials are moved through the digestive tract by muscular contractions, called
peristalsis. The rectum and anus are responsible for moving solid wastes out of
the body. As a result, these organs can be considered a part of the excretory
system. Liquid waste, in the form of urine, is formed in the kidneys. From the
kidneys it travels to the bladder where it is stored before being eliminated
through the urethra, a tube leading to the outside of the body. The following table
outlines the major structures of the digestive and excretory systems and lists
their functions:
Structure
mouth
teeth, tongue, saliva
esophagus
stomach
tube
muscular, baglike organ;
contains acid
long, muscular, tubelike
tract
small intestine
pancreas
small organ near stomach
and small intestine
liver
large, red-brown organ
above stomach on right
side of body
large intestine
muscular, tubelike tract
rectum
anus
kidney
bladder
urethra
pouch; last section of the
large intestine
opening
2 – bean shaped organs
muscular pouch
tube with opening
Function
teeth begin mechanical digestion;
tongue moves food; saliva begins
chemical digestion
carries food from mouth to stomach
muscles grind food while acids break
down food into liquid form
most chemical digestion occurs here,
nutrients absorbed into bloodstream
chemicals released into the small
intestine aid in digestion; insulin helps
regulate blood sugar levels
makes bile to aid small intestine in
breaking down fats; stores nutrients;
breaks down toxins in blood
stores, compacts and eliminates
materials that can not be digested;
water is absorbed out of wastes
stores solid wastes (feces)
exit of feces
clean/filter blood; creates urine
stores urine
exit of urine
The following are examples of how the digestive and excretory systems help to
maintain homeostasis:
 diarrhea and vomit remove toxins, parasites, food infected with bacteria,
etc.
 kidneys clean/filter blood and they control the amount of water left in
the blood
 insulin production by the pancreas controls blood sugar levels
 water is excreted in the form of sweat and evaporation of sweat leads to
cooling/temperature regulation
 excretion of water (and salts) through sweat and urine maintains
equilibrium of fluid levels
The Skeletal and Muscular Systems
The skeletal and muscular systems work together to assist the human body with
movement, support, protection and strength. Many of our body’s muscles are
connected to bones in our skeletal system, enabling movement. It would be
appropriate at this time to briefly revisit the unit on simple machines, helping
students to understand that a muscle pulling on a bone is acting as a lever.
Students should not be required to memorize all of the bones of the skeletal
system, but they need to understand the vast functions of the skeletal system.
Students should learn the three types of muscle and be able to explain the
difference between voluntary and involuntary muscles.
The Skeletal System
The human skeleton is made of bone and cartilage. Bone is made of living cells.
Bones contain primarily two minerals, calcium and phosphorus. The body gets these
two minerals from diet and they are responsible for making bone hard. Bones
contain blood vessels and nerves. They also can grow and repair themselves. There
are 206 bones in the human body. The bones of the human skeleton have the
following primary functions:
 to provide a place for muscles to attach so that movement can occur
 protection of body organs
 support the body and give it shape
 store minerals
 make blood cells – within the soft, inner marrow
The place where two bones come together is called a joint. Some joints move and
some do not. The joints found in the skull do not move. Joints are held together by
ligaments which are made of a tough connective tissue. Cartilage is found at the
ends of bones to help reduce friction from rubbing against each other. Other
places where cartilage can be found are the human ear and the end of the nose.
Cartilage is very different from bone. It is more flexible and does not contain
blood vessels or minerals.
The Muscular System
The human body has three types of muscles: skeletal, smooth and cardiac. Skeletal
muscles are voluntary because they move under our conscious control. These
muscles contract to move bones, attached with a tissue called a tendon. Skeletal
muscles are very strong, but they tire easily compared to other muscles. They also
work in pairs because muscles can pull but not push. They work opposite of each
other. In other words, if one contracts then the other will relax. Smooth and
cardiac muscles are involuntary, meaning they are not under conscious control.
Cardiac muscle is the muscle of the heart. The following table classifies each
muscle type:
Structure
Skeletal
striated (striped)
Function
bone movement
Location
Voluntary
vs.
Involuntary
attached to bones
Smooth
not striated
aids internal organs with their
jobs
digestive organs; blood vessels
voluntary
involuntary
Cardiac
striated
pumping of the
heart
heart only
involuntary
The following are examples of how the skeletal and muscular systems help to
maintain homeostasis:
 muscles shiver to produce heat
 “fight or flight” response or any need for greater O2 – CO2 exchange –
cardiac muscle works harder as heart beats faster and blood flow is
increased to skeletal muscles
 production of blood cells in bone marrow to replace those that worn out,
fight infection and clot blood as needed
The Nervous and Endocrine Systems
The nervous system and endocrine system work together to transmit information
throughout the body. The nervous system uses chemicals and electrical signals to
help the body respond to changes either internally or externally. The endocrine
system uses glands to send chemical messages to the body. Glands produce
hormones which go directly into the bloodstream and then the hormone is carried
to the area of the body that needs it. The hormone will tell the body to specifically
make a substance or perform a response. Some hormones are responsible for
telling the body to quit making a particular substance or perform the opposite
response. The central nervous system is made up of the brain and the spinal cord.
Nerves that branch out from the central nervous system send information to the
brain and from the brain to the body organs. The nervous system controls every
move, every thought, the senses and all body activities. Because the nervous
system coordinates the activities all other human body systems, it is involved in all
matters related to homeostasis.
The Integumentary System (optional info)
The integumentary system is made up of skin, hair, and nails. The function of this
system is to protect the body by being its first line of defense. It helps the body
to control the amount of water in the body. It provides the sense of touch.
Through the production of sweat, it helps the body regulate its temperature and
get rid of wastes. The skin’s structure is composed of three layers: the
epidermis, dermis, and an underlying fat layer. The epidermis is the thin outer
layer and dead skin cells are constantly being replaced. The dermis contains blood
vessels, nerves, hair follicles, sweat and oil glands.
The following are examples of how the integumentary system helps to maintain
homeostasis:
 sweat production for temperature regulation and waste removal
 melanin production to reduce sun damage
 hair for the prevention of heat loss
 works with platelets to clot blood on skin with scabs, preventing blood
volume loss and infection