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Levels of Organization
• cell differentiation
• stem cell
• tissue
• organ
• organ system
Multicellular Organisms (cont.)
• All cells in a multicellular organism come
from one cell: a fertilized egg.
• The process by which cells become
different types of cells
is called cell
differentiation.
Multicellular Organisms (cont.)
Stem cells are unspecialized animal
cells that are able to develop into many
different cell types.
Multicellular Organisms (cont.)
• Plants have unspecialized cells similar
to animal stem cells.
• These cells
are grouped
in areas of a
plant called
meristems.
Multicellular Organisms (cont.)
Tissues are groups of similar types of
cells in multicellular organisms that work
together to carry out specific tasks.
Multicellular Organisms (cont.)
• Humans, like most other animals,
have four main types of tissue:
muscle, connective, nervous, and
epithelial.
• The three main types of plant tissue
are dermal, vascular, and ground
tissue.
Multicellular Organisms (cont.)
• Organs are groups of different tissues
working together to perform a particular
job.
• Organ systems are groups of different
organs that work together to complete
a series of tasks.
Multicellular Organisms (cont.)
Multicellular organisms usually have many
organ systems that work together to carry
out all the jobs needed for the survival of
the organism.
Transport and Defense
• organ system
• lymphocyte
• homeostasis
• immunity
• nutrient
• Calorie
The Body’s Organization
• Groups of organs
that work together
and perform a
specific task are
organ systems.
• Organ systems
provide movement,
transport
substances, and
perform many other
functions.
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Digestion and Excretion
• The human body breaks down food
through the process of digestion.
• Substances that are not used by the
body are removed through the digestive
system and by the excretory system.
Digestion (cont.)
The esophagus
connects the
mouth to the
stomach—a
flexible baglike
organ that contains
enzymes that
break down food
into smaller parts
to be used by the
body.
Hutchings Photography/Digital Light Source
Digestion (cont.)
• The small
intestine has
two functions—
digestion and
absorption.
• Nutrients are
absorbed by the
body through the
small intestine.
Hutchings Photography/Digital Light Source
Digestion (cont.)
The liver makes
bile and the
pancreas makes
enzymes, both of
which break down
food in the small
intestine.
Hutchings Photography/Digital Light Source
Digestion (cont.)
• The large intestine receives solid waste
from the small intestine.
• The large intestine absorbs excess water
from the waste material.
• The rectum of the large intestine stores
the solid waste until the waste is
expelled from the body.
Digestion (cont.)
Some foods, like
insoluble fiber, that
are not digested
leave the body
through the rectum.
Hutchings Photography/Digital Light Source
Digestion (cont.)
• Nutrients are the parts of food used by
the body to grow and survive.
• Proteins, fats, carbohydrates, vitamins,
and minerals are all nutrients.
• Calories are a measure of the amount
of energy in food.
Excretion
The excretory system removes liquid and
gas wastes from the body. This system
includes—
• lungs
• ureter
• skin
• bladder
• liver
• urethra
• kidneys
Excretion (cont.)
• When the liver breaks down proteins,
urea forms. Urea is toxic if it stays in the
body.
• The kidneys remove urea from the body
by making urine.
Excretion (cont.)
• Urine leaves
each kidney
through the
ureter and is
stored in a
flexible sac,
called the
bladder.
• Urine is removed from the body through
the urethra.
Respiration
The respiratory
system
exchanges
gases between
the body and
the environment.
Respiration (cont.)
• When you inhale,
air enters the nostrils
and passes through the
pharynx to the trachea.
• Inhaling and
exhaling require
the movement of
a muscle under
the lungs called the
diaphragm.
Respiration (cont.)
The trachea, or
windpipe, connects
the pharynx to the
bronchi.
Respiration (cont.)
There are two
bronchi; one enters
the left lung and
one enters the
right lung.
Respiration (cont.)
The bronchi divide
into smaller tubes
that end in tiny
groups of cells
called alveoli.
Respiration (cont.)
The alveoli are
surrounded by
blood vessels
called capillaries.
Respiration (cont.)
Gas Exchange
Circulation
• Oxygen in the alveoli enters the
capillaries.
• The blood inside capillaries transports
oxygen to the rest of the body.
Circulation (cont.)
The heart, blood, and
blood vessels make
up the circulatory
system which
transports nutrients,
gases, wastes, and
other substances
through the body.
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Circulation (cont.)
• Blood vessels transport blood to all
organs of the body.
• Contractions of the heart’s muscles
pump blood to the rest of the body.
• Blood travels through the body in tiny
tubes called vessels.
Circulation (cont.)
• Arteries carry blood away from your
heart.
• Veins carry blood back to your heart.
Circulation (cont.)
Capillaries are tiny
vessels that allow
gases and nutrients
to move between
the blood and the
entire body.
Circulation (cont.)
• The liquid part of blood is called plasma
and contains nutrients, water, and CO2.
• Blood also contains red blood cells,
which carry oxygen, and platelets, which
help the body heal when a vessel is cut.
• White blood cells help the body defend
itself from toxins and diseases.
Different people have different proteins on
the surfaces of their red blood cells which
scientists classify into groups called blood
types.
Lymphatic System
Tonsils, the spleen, the
thymus, bone marrow, and
lymph nodes are parts of
the lymphatic system.
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Lymphatic System (cont.)
• The lymphatic system’s three main
functions are removing excess fluids
around organs, producing white blood
cells, and absorbing and transporting
fats.
• The lymphatic system helps your body
maintain fluid homeostasis.
Lymphatic System (cont.)
• Fluid that travels through the lymph
vessels flows into organs called lymph
nodes, which protect the body by
removing toxins, wastes, and other
harmful substances.
• The lymphatic system makes white blood
cells to help the body defend against
infection.
Immunity
• Protection from infection or toxins is
called immunity.
• The skeletal system produces immune
cells, which include lymphocytes and
other white blood cells, and the
circulatory system transports them
throughout the body.
• The immune cells attack and destroy
viruses, bacteria, and other foreign
substances.
Immunity (cont.)
• Humans make billions of different types
of antibodies.
• Infectious diseases are caused by
pathogens, such as bacteria and viruses,
and are usually contagious.
• A noninfectious disease is caused by the
environment or a genetic disorder.
Immunity (cont.)
Immunity (cont.)
• The body’s first line of defense against
viruses, bacteria, and harmful
substances is the skin and mucus which
prevent toxins and other substances from
entering the body.
• The second line of defense is the
immune response in which white blood
cells attack and destroy harmful
substances.
Immunity (cont.)
The third line of defense is immune cells
which make antibodies that destroy
harmful substances.
Structure, Movement,
and Control
• compact bone
• reflex
• spongy bone
• hormone
• neuron
Structure and Movement
• The skeletal system protects internal
organs, provides support, helps the body
move, and stores minerals, such as
calcium.
• An adult’s skeleton has 206 bones.
• The skeleton also contains ligaments,
tendons, and cartilage.
Structure and Movement (cont.)
• Compact bone is
the hard outer layer
of bone.
• Spongy bone is the
interior region of
bone that contains
many tiny holes.
CMCD/Getty Images
Structure and Movement (cont.)
• The muscular
system is made of
three different types
of muscle tissue.
• Skeletal muscle
works with the
skeletal system and
helps you move.
Structure and Movement (cont.)
• Cardiac muscle is
only in the heart.
• It continually
contracts and
relaxes and moves
blood throughout
your body.
Structure and Movement (cont.)
• Smooth muscle
tissue is in organs
such as the
stomach and the
bladder.
• Blood vessels also
have smooth
muscle tissue.
Control and Coordination
• The brain and the spinal
cord form the central
nervous system.
Doug Pensinger/Getty Images
• All other nerves are part
of the peripheral nervous
system that extends
throughout the entire
body.
Control and Coordination (cont.)
The nervous system is a group
of organs and specialized cells
that detect, process, and
respond to information.
Nerve cells, or neurons, are the basic unit
of the nervous system.
Doug Pensinger/Getty Images
Control and Coordination (cont.)
• Information enters the nervous system
through neurons in the peripheral
nervous system.
• Most of the information then is sent to
the central nervous system for
processing.
• After the central nervous system
processes information, it signals the
peripheral nervous system to respond.
Control and Coordination (cont.)
• The body carries out both voluntary and
involuntary functions that depend on the
nervous system.
• Automatic movements in response to a
signal are called reflexes.
Control and Coordination (cont.)
Humans detect their external environment
with five senses—vision, hearing, smell,
touch, and taste.
Control and Coordination (cont.)
• Each of the five senses has specific
neurons that receive signals from the
environment.
• Information detected by the senses is
sent to the spinal cord and then to the
brain for processing and a response.
Endocrine System
The endocrine
system, like the
nervous system,
sends signals to
the body.
Mark Andersen/Getty Images
Endocrine System (cont.)
• Chemical signals released by the organs
of the endocrine system are called
hormones.
• Hormones travel in blood through blood
vessels and cause organ systems to
carry out specific functions.
• Some hormones work with other organ
systems to maintain homeostasis and
other hormones work with many organ
systems to help you grow.
Reproduction and Development
• reproduction
• fertilization
• gamete
• zygote
• sperm
• ovum
Reproduction and Hormones
• Some of the organs of the endocrine
system produce hormones that help
humans reproduce.
• Reproduction is the process by which
new organisms are produced.
Reproduction and Hormones (cont.)
• Human reproductive cells, called
gametes, are made by the male and
female reproductive systems.
• Male gametes are called sperm.
• Female gametes are called ova, or eggs.
• A sperm joins with an egg in a
reproductive process called fertilization.
Reproduction and Hormones (cont.)
The cell that forms when an egg and a
sperm join together is called a zygote.
Reproduction and Hormones (cont.)
• The endocrine system controls egg
maturation and release and thickening of
the lining of the uterus in a process
called the menstrual cycle.
• The menstrual cycle takes about 28 days
and has three parts.
Human Development
• During human development, the zygote
develops into an embryo, which is a ballshaped structure that attaches inside the
uterus.
• The embryo develops into a fetus, the
last stage of birth.
• During the developmental period, called
pregnancy, the organ systems of the
fetus will develop and the fetus will get
larger.