The document discusses the levels of organization in the human body from simplest to most complex. It begins with the cellular level as the basic unit of structure and function, followed by tissues, organs, organ systems, and finally the organism level as the most complex level comprising all the lower levels working together. Key terms defined include tissues as groups of similar cells performing a specific function, organs as structures made of multiple tissue types performing a distinct function, and organ systems as groups of organs working together to perform a body function. Connective tissues are also summarized, including their main cell and fiber types, functions of connecting and supporting other tissues, and classifications.

1. Anatomy
the study of structure/structural relationships
Physiology
the study of structural FUNCTIONS; what does the structure do; the functions dictates the design of the
structure
Homeostasis
maintenance of a relatively constant internal environment; every sickness/imbalance in the body is a result of
homeostatic disruption; deviation from the set point
Negative Feedback Mechanisms
(A GOOD THING)
mechanisms (methods) the body uses to maintain homeostasis; the body's attempt to resist change away from
the set point
example: high temps producing sweat to cool during evaporation
Positive Feedback Mechanisms
(ALMOST ALWAYS BAD)
makes a deviation greater- "snowball effect"
example: decrease in blood pressure going down until it is no longer able to sustain life
Anatomic Position
Reference point: standing erect (up and straight) with palms facing forward
Supine
Laying on the back
Prone
Laying on the belly
Sagittal Plane
(head to toe long axis) divides body into right and left halves to create a side view
Coronal Plane
(head to toe long axis) divides body into front and back sections
Transverse/Horizontal Plane
(perpendicular to long axis) divides body into upper and lower halves

2. Right and Left
from anatomical position- will be opposite of normal because of the way we face a patient
Inferior
below
Superior
above
Anterior
ventral-toward the front
Posterior
dorsal-toward the back
Proximal
closer to the point of attachment
Distal
further from the point of attachment
Medial
closer to the midline of the body
Lateral
further from the midline of the body
Finger and toe numbering
thumb and big toe are always #1
pinky and pinky toe are always #5
(remember anatomical position)
Superficial
closer to the surface (skin)
Deep

3. further (deeper) from the surface
Cards
Sensory Input
Definition
The information gathered by the nervous system's
sensory receptors.
Integration
Definition
Processing and interpreting sensory input and deciding
what should be done at each moment.
Motor Output
Definition
A response that is caused by activating effector organs.
Central Nervous System
Definition
Consists of the brain and spinal cord, which occupy the
dorsal body cavity.
Peripheral Nervous System
Definition
The part of the nervous system outside of the CNS,
consists mainly of the nerves that extend from the
brain and spinal cord.
Definition

4. Afferent Division Consists of nerve fibers that convey impulses to the
central nervous system from sensory receptors located
throughout the body.
Efferent Division
Definition
Transmits impulses from the CNS to effector organs,
which are the muscles and glands.
Somatic Nervous System
Definition
Composed of somatic motor nerve fibers that conduct
impulses from the CNS to skeletal muscles.
Autonomic Nervous System
Definition
Consists of visceral motor nerve fibers that regulate the
activity of smooth muscles, cardiac muscles, and glands.
Neuroglia
Definition
The small cells that neurons associate with.
Processes
Definition
Promineces or projections.
Dendrites
Definition
Branching neuron process that serves as a receptive, or
input, region; transmits an electrical signal toward the
cell body.

5. Axon
Definition
Neuron process that carries impulses away from the
nerve cell body; efferent process; the conducting
portion of a nerve cell.
Myelin Sheath
Definition
Fatty insulating sheath that surrounds all but the
smallest nerve fibers.
Nodes of Ranvier
Definition
The gaps in the sheath between Schwann Cells.
White Matter
Definition
Regions of the brain and spinal cord containing dense
collections of myelinated fibers.
Gray Matter
Definition
Contains mostly nerve cell bodies and unmyelinated
fibers.
Multipolar Neurons
Definition
Have three or more processes. The most common
neuron type in humans, and the major neuron type in
the CNS.
Definition

6. Bipolar Neurons Have two process, and axon and a dendrite, that extend
from opposite sides of the cell body. They are rare
neurons that are found in some of the special sense
organs.
Unipolar Neurons
Definition
Have a single short process that emerges from the cell
body and divides the T-like into proximal and distal
branches.
Association Neurons
Definition
Lie between motor and sensory neurons in neural
pathways and shuttle signals through CNS pathways
where integration occurs.
Resting Membrane Potential
Definition
The voltage that exists across the plasma membrane
during the resting state of an excitable cell; rabges from
-90 to -20 millivolts depending on cell type.
Depolarization
Definition
A reduction in membrane potential: The inside of the
membrane becomes less negative than the resting
potential.
Hyperpolarization
Definition
Occurs when the membrane potential increases,
becoming more negative than the resting potential.

7. Graded Potential
Definition
Short-lived, localized changes in membrane potential
that can be either depolarizations or
hyperpolarizations.
Action Potential
Definition
A brief reversal of membrane potential with a total
amplitude of about 100mV.
Repolarization
Definition
Movement of the membrane potential to the initial
resting state.
Synapse
Definition
A junction that mediates information transfer from one
neuron to the next or from a neuron to an effector cell.
Presynaptic Neuron
Definition
The neuron conducting impulses toward the synapse.
Postsynaptic Neuron
Definition
The neuron transmitting the electical signal away from
the synapse.
Definition

8. Electrical Synapses Specialized to allow the flow of ions between neurons.
Chemical Synapses
Definition
Specialized for release and reception of chemical
neurotransmitters.
Neurotransmitters
Definition
Chemical messenger released by neurons that may,
upon binding to receptors of neurons or effector cells,
stimulate or inhibit those neurons or effector cells.
Diverging Circuts
Definition
One incoming fiber triggers responses in ever-increasing
numbers of neurons farther and farther along the
circut.
Converging Circuts
Definition
The pool receives inputs from several presynaptic
neurons, and the circut has a funneling effect.
Oscillating Circuts
Definition
The incoming signal travels through a chain of neurons,
each of which makes collateral synapses with neurons
in a previous part of the pathway.
Definition

9. Parallel After-Discharge Circuts The incoming fiber stimulates several neurons arranged
in parallel arrays that eventually stimulate a common
output cell.
The highest level of organization for living things is the biosphere; it encompasses all other levels. The biological levels of organization of living
things arranged from the simplest to most complex are: organelle, cells, tissues, organs, organ systems, organisms, populations, communities,
ecosystem, and biosphere.
The largest structural level is the organism level. All the parts which make up the body and function with each other form the total organism (one
living individual). Thesix levels of structural organization are: chemical, cellular, tissue, organ, system and organism.
Multicellular organisms are made of many parts that are needed for survival. These parts are divided into levels of organization. There are
five levels: cells, tissue, organs, organ systems, and organisms. All living things are made up of cells.
Multicellular organisms are made of many parts that are needed for survival. These parts are divided into levels of organization. There are
five levels: cells, tissue, organs, organ systems, and organisms. All living things are made up of cells.

13. The organism level is the highest level of organization. An organism is a living being that has a cellular structure
and that can independently perform all physiologic functions necessary for life. In multicellular organisms,
including humans, all cells, tissues, organs, and organ systems of the body work together to maintain the life and
health of the organism.
cell
smallest independently functioning unit of all organisms; in animals, a cell contains cytoplasm, composed of
fluid and organelles
organ
functionally distinct structure composed of two or more types of tissues
organ system
group of organs that work together to carry out a particular function
organism
living being that has a cellular structure and that can independently perform all physiologic functions
necessary for life
tissue
group of similar or closely related cells that act together to perform a specific function
As may be obvious from its name, one of the major functions of connective tissue is to connect tissues and organs. Unlike epithelial tissue, which is
composed of cells closely packed with little or no extracellular space in between, connective tissue cells are dispersed in a matrix. The matrix
usually includes a large amount of extracellular material produced by the connective tissue cells that are embedded within it. The matrix plays a
major role in the functioning of this tissue. Two major components of the matrix are ground substance and protein fibers. This ground substance is
usually a fluid (water), but it can also be mineralized and solid, as in bones. Connective tissues come in a vast variety of forms, yet they typically
have in common three characteristic components: cells, large amounts of ground substance, and protein fibers. The amount and structure of

14. each component correlates with the function of the tissue, from the rigid ground substance in bones supporting the body to the inclusion of
specialized cells; for example, a phagocytic cell that engulfs pathogens and also rids tissue of cellular debris.
The most common cell found within connective tissue is the fibroblast. Polysaccharides and proteins secreted by fibroblasts combine with
extra-cellular fluids to produce a viscous ground substance that, with embedded fibrous proteins, forms the extra-cellular matrix.
Three main types of fibers are secreted by fibroblasts: collagen fibers, elastic fibers, and reticular fibers. Collagen fiber is made from fibrous protein
subunits linked together to form a long and straight fiber. Collagen fibers, while flexible, have great tensile strength, resist stretching, and give
ligaments and tendons their characteristic resilience and strength. These fibers hold connective tissues together, even during the movement of the
body.
Elastic fiber contains the protein elastin along with lesser amounts of other proteins and glycoproteins. The main property of elastin is that after
being stretched or compressed, it will return to its original shape. Elastic fibers are prominent in elastic tissues found in skin and the elastic ligaments
of the vertebral column.
Reticular fiber is also formed from the same protein subunits as collagen fibers; however, these fibers remain narrow and are arrayed in a branching
network. They are found throughout the body, but are most abundant in the reticular tissue of soft organs, such as liver and spleen, where they anchor
and provide structural support to the parenchyma (the functional cells, blood vessels, and nerves of the organ).
All of these fiber types are embedded in ground substance. Secreted by fibroblasts, ground substance is made of water, polysaccharides, specifically
hyaluronic acid, and proteins. These combine to form a proteoglycan with a protein core and polysaccharide branches. The proteoglycan attracts and
traps available moisture forming the clear, viscous, colorless matrix you now know as ground substance.
Functions of Connective Tissues
Connective tissues perform many functions in the body, but most importantly, they support and connect other tissues; from the
connective tissue sheath that surrounds muscle cells, to the tendons that attach muscles to bones, and to the skeleton that supports the positions of the
body. Protection is another major function of connective tissue, in the form of fibrous capsules and bones that protect delicate organs and, of course,
the skeletal system. Specialized cells in connective tissue defend the body from microorganisms that enter the body. Transport of fluid, nutrients,
waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph. Adipose cells store surplus energy in the
form of fat and contribute to the thermal insulation of the body.

15. Classification of Connective Tissues
Categories of connective tissue include the following:
Loose Connective Tissue – large amounts of ground substance and fewer fibers
 Aerolar
 Adipose
 Reticular
Dense Connective Tissue – large amounts of fibers and less ground substance
 Dense Regular
 Dense Irregular
 Elastic CT
Cartilage – specialized cells called chondrocytes are within the matrix (cartilage cells)
 Hyaline Cartilage
 Elastic Cartilage
 Fibrocartilage
Bone – strongest connective tissue with little ground substance, hard matrix of calcium and phosphorous and specialized bone cells called osteocytes
Blood – fluid connective tissue, no fibers – only ground substance (plasma) and cells (red, white, and platelets)
Loose Connective Tissue
Loose connective tissue is found between many organs where it acts both to absorb shock and bind tissues together. It allows water,
salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues.
Adipose tissue consists mostly of fat storage cells called adipocytes that store lipids as droplets that fill most of the cytoplasm
(figure 4.6). A large number of capillaries allow rapid storage and mobilization of lipid molecules. Fat contributes mostly to lipid storage, can serve
as insulation from cold temperatures and mechanical injuries, and can be found protecting internal organs such as the kidneys and eye.

16. Figure 4.6. Adipose Tissue
Areolar tissue shows little specialization. It contains all the cell types and fibers previously described and is distributed in a random, web-
like fashion. It fills the spaces between muscle fibers, surrounds blood and lymph vessels, and supports organs in the abdominal
cavity. Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes, which are
described further in a later section.

17. Figure 4.7. Areolar Tissue. This is a loose connective tissue widely spread throughout the body. It contains all three types of fibers (collagen,
elastin, and reticular) with much ground substance and fibroblasts.
Reticular tissue is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver (Figure 4.8).
Reticular cells produce the reticular fibers that form the network onto which other cells attach. It derives its name from the Latin reticulus,
which means “little net.”
Figure 4.8. Reticular Tissue
This is a loose connective tissue made up of a network of reticular fibers that provides a supportive framework for soft organs. LM ×
1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Dense Connective Tissue
Dense connective tissue contains more collagen fibers than does loose connective tissue. As a consequence, it displays greater resistance to
stretching. There are three major categories of dense connective tissue: regular, irregular, and elastic. Dense regular connective tissue fibers are
parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fiber orientations. Ligaments and tendons are
made of dense regular connective tissue.
In dense irregular connective tissue, the direction of fibers is random. This arrangement gives the tissue greater strength in all directions and less
strength in one particular direction. In some tissues, fibers crisscross and form a mesh. In other tissues, stretching in several directions is achieved by
alternating layers where fibers run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. The dermis of the
skin is an example of dense irregular connective tissue rich in collagen fibers. Dense irregular elastic tissues give arterial walls the strength and the
ability to regain original shape after stretching (Figure 4.9).

18. Figure 4.9. Dense Connective Tissue
(a) Dense regular connective tissue consists of collagenous fibers packed into parallel bundles. (b) Dense irregular connective tissue
consists of collagenous fibers interwoven into a mesh-like network. From top, LM × 1000, LM × 200. (Micrographs provided by the
Regents of University of Michigan Medical School © 2012)
Elastic connective tissue is a modified dense connective tissue that contains numerous elastic fibers in addition to collagen fibers, which allows the
tissue to return to its original length after stretching Figure 4.10). The lungs and arteries have a layer of elastic connective tissue that allows the
stretch and recoil of these organs.

19. Figure 4.10. Elastic Connective Tissue
Elastic connective tissue consists of collagenous fibers with interwoven elastic fibers.
Cartilage
The distinctive appearance of cartilage is due to the presence of polysaccharides called chondroitin sulfates, which bind with ground substance
proteins to form proteoglycans. Embedded within the cartilage matrix are chondrocytes, or cartilage cells, and the space they occupy are
called lacunae (singular = lacuna). A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage. Cartilaginous tissue is
avascular, thus all nutrients need to diffuse through the matrix to reach the chondrocytes. This is a factor contributing to the very slow healing of
cartilaginous tissues.
The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage (Figure 4.11). Hyaline cartilage, the most common
type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans. Under the microscope,
tissue samples appear clear. The surface of hyaline cartilage is smooth. Both strong and flexible, it is found in the rib cage and nose and covers bones
where they meet to form moveable joints. It makes up a template of the embryonic skeleton before bone formation. A plate of hyaline cartilage at the
ends of bone allows continued growth until adulthood. Fibrocartilage is tough because it has thick bundles of collagen fibers dispersed through its
matrix. The knee and jaw joints and the the intervertebral discs are examples of fibrocartilage. Elastic cartilage contains elastic fibers as well as
collagen and proteoglycans. This tissue gives rigid support as well as elasticity. Tug gently at your ear lobes, and notice that the lobes return to their
initial shape. The external ear contains elastic cartilage.

20. Figure 4.11. Types of Cartilage
Cartilage is a connective tissue consisting of collagenous fibers embedded in a firm matrix of chondroitin sulfates. (a) Hyaline cartilage
provides support with some flexibility. The example is from dog tissue. (b) Fibrocartilage provides some compressibility and can absorb
pressure. (c) Elastic cartilage provides firm but elastic support. From top, LM × 300, LM × 1200, LM × 1016. (Micrographs provided by
the Regents of University of Michigan Medical School © 2012)

21. Bone
Bone is the hardest connective tissue. It provides protection to internal organs and supports the body. Bone’s rigid extracellular matrix contains
mostly collagen fibers embedded in a mineralized ground substance containing hydroxyapatite, a form of calcium phosphate. Both components of the
matrix, organic and inorganic, contribute to the unusual properties of bone. Without collagen, bones would be brittle and shatter easily. Without
mineral crystals, bones would flex and provide little support. Osteocytes, bone cells, are located within lacunae. The histology of transverse tissue
from long bone shows a typical arrangement of osteocytes in concentric circles around a central canal (Figure 4.12). Bone is a highly vascularized
tissue. Unlike cartilage, bone tissue can recover from injuries in a relatively short time.
Cancellous bone looks like a sponge under the microscope and contains empty spaces between trabeculae, or arches of bone proper. It is lighter than
compact bone and found in the interior of some bones and at the end of long bones. Compact bone is solid and has greater structural strength.
Figure 4.12. Bone Connective Tissue
There are two types of bone tissue: compact and spongy. Picture shown is of compact bone tissue. This is most common and has the
appearance of the matrix forming concentric rings around cavities for blood vessels. The osteocytes (bone cells) position themselves
within the concentric rings.
Blood
Blood is a fluid connective tissues. Blood has two components: cells and fluid matrix (Figure 4.13). Erythrocytes, red blood cells, transport oxygen
and some carbon dioxide. Leukocytes, white blood cells, are responsible for defending against potentially harmful microorganisms or molecules.
Platelets are cell fragments involved in blood clotting. Some white blood cells have the ability to cross the endothelial layer that lines blood vessels
and enter adjacent tissues. Nutrients, salts, and wastes are dissolved in the liquid matrix called plasma and transported through the body.

22. Lymph contains a liquid matrix and white blood cells. Lymphatic capillaries are extremely permeable, allowing larger molecules and excess fluid
from interstitial spaces to enter the lymphatic vessels. Lymph drains into blood vessels, delivering molecules to the blood that could not otherwise
directly enter the bloodstream. In this way, specialized lymphatic capillaries transport absorbed fats away from the intestine and deliver these
molecules to the blood.
Figure 4.13. Blood: A Fluid Connective Tissue
Blood is a fluid connective tissue containing erythrocytes and various types of leukocytes that circulate in a liquid extracellular matrix.
LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
INTERACTIVE LINK
View the University of Michigan Webscope at http://virtualslides.med.umich.edu/Histology/Cardiovascular%20System/081-
3_HISTO_40X.svs/view.apml to explore the tissue sample in greater detail.
INTERACTIVE LINK
Visit this link to test your connective tissue knowledge with this 10-question quiz. Can you name the 10 tissue types shown in the histology slides?
LICENSES AND ATTRIBUTIONS
PreviousNext

23. Adipose Tissue - Anatomy & physiology revision about the structure and functions of human tissue types. Adipose tissue is a loose
fibrous connective tissue packed with many fat cells called adipocytes.
n humans, adipose tissue is located beneath the skin (subcutaneous fat), around internal organs (visceral fat), in bone marrow (yellow bone
marrow), intermuscular (Muscular system) and in the breast tissue. Adipose tissue is found in specific locations, which are referred to as adipose
depots
Adipose Tissue is a loose fibrous connective tissue packed with many cells (called "adipocytes") that are specialized for storage of triglycerides
more commonly referred to as "fats". Each adipocyte cell is filled with a single large droplet of triglyceride (fat).
Adipose tissue, or fat, is an anatomical term for loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat,
although it alsocushions and insulates the body
Bones in our body are living tissue. They have their own blood vessels and are made of living cells, which help them to grow and to repair
themselves. As well, proteins, minerals and vitamins make up the bone. We are born with about 300 softbones.
Connective tissue is the most abundant tissue in the human body and forms all tendons and ligaments, but is also found throughout the body
in fibrous membrane coverings. These coverings encase and surround things like bone, cartilage, nerve fibers, and muscle fibers
Dense regular connective tissue provides connection between different tissues in the human body. The collagen fibers in dense regular
connective tissue are bundled in a parallel fashion.
This one will cover the more densely arranged types of connective tissue proper called: dense irregular, dense regular, and
dense elastic. Dense regular connective tissue is composed of fibroblasts that excrete high amounts of collagen fibers. The collagen fibers are
stacked on one another in a neat parallel array.
Adipose tissue, or fatty tissue, connective tissue consisting mainly of fat cells (adipose cells, or adipocytes),
specialized to synthesize and contain large globules of fat, within a structural network of fibres. It is found mainly under
the skin but also in deposits between the muscles, in the intestines and in their membrane folds, around the heart, and
elsewhere. It is also found in the bone marrow, where it imparts a yellow colour; yellow marrow is most abundant in
adults. The fat stored in adipose tissue comes from dietary fats or is produced in the body.

24. When hormones signal the need for energy, fatty acids and glycerol are released from triglycerides stored in fat cells (adipocytes) and are delivered to organs and
tissues in the body.Encyclopædia Britannica, Inc.
Mammals have two different types of adipose: white adipose tissue and brown adipose tissue. White adipose, the most
common type, provides insulation, serves as an energy store for times of starvation or great exertion, and forms pads
between organs. When muscles and other tissues need energy, certain hormones bind to adipose cells and trigger the
hydrolysis of triacylglycerol, resulting in the release of energy-rich fatty acids and glycerol—a process known as lipolysis.
The enzyme responsible for hydrolysis is lipase, which occurs in the blood, certain gastrointestinal juices, and adipose
tissue. Lipase is activated by the hormones epinephrine, norepinephrine, glucagon, andadrenocorticotropin, which bind
to adipocytes.

25. White adipose tissue also is a source of a number of different hormones, which serve various roles inmetabolism and
endocrine function. The adipose-produced hormones adiponectin, leptin, and resistin are involved in energy metabolism,
for example, whereas plasminogen activator inhibitor-1 prevents the dissolution of blood clots.
Brown adipose, found mainly in newborn animals, generates heat and actually consumes energy. In humans, the
percentage of brown adipose found in the body decreases with age. In other animals, however, particularly those that
hibernate (e.g., grizzly bears and black bears), it is found in adults and plays an important role in survival. Species that
hibernate experience a drop in body temperature and a slowing of metabolism during winter dormancy, which allows
them to conserve energy. Brown adipose, by consuming energy, releases heat, which is vital for awakening and
emergence from dormancy. Brown adipose tissue typically is tan to red in colour. Its colour and heat-generating
properties are imparted by the abundance of organelles known as mitochondria found in brown fat cells. (Mitochondria
are the energy-producing components of cells.)
In humans, the distribution of adipose tissue in the body can vary depending on sex. In general, men accumulate fat
around the waist, and women tend to accumulate more fat around the hips than the waist. Geneticists have located
distinct regions in the human genome that are associated with fat distribution, and several genes in particular appear to
have a greater influence on waist-to-hip ratio in women than in men. Because these genes are involved in regulating the
activities of fat cells, knowledge of their precise functions could provide insights into the biological mechanisms
underlying obesity, diabetes mellitus, and cardiovascular disease.
Elastic fibers (or yellow fibers) are bundles of proteins (elastin) found in extracellular matrix of connective tissue and produced by fibroblasts and
smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed.
Blood, a fluid connective tissue, provides a transport system within our body for oxygen and other important substances. Cartilage provides strong
support and connection for our skeletal framework. And the function of bones is to support and protect soft tissues and organs in our body.Dec 3,
2014

26. Elastin: A protein that coil and recoils like a spring within the elastic fibers of connective tissue and accounts for the elasticity of structures such the
skin, blood vessels, heart, lungs, intestines, tendons, and ligaments. Elastin functions in connective tissue together with collagen.
The cells that make the reticular fibers are fibroblasts called reticular cells. Reticular connective tissueforms a scaffolding for
other cells in several organs, such as lymph nodes and bone marrow. ... Then, when you switch to a higher power, the reticularfibers
will be easier to see.
Function. The fibers form a soft skeleton (stroma) to support the lymphoid organs (lymph node stromal cells, red bone marrow, and spleen).
Adipose tissue is held together by reticular fibers.
Fibroblastic reticular cells (FRCs) are stromal cells of mesodermal origin which arefound in secondary lymphoid organs (SLO). The most studied
are the FRCslocated in the lymph nodes