36.1. Types
of Tissues
A. Levels of Organization
1. Levels of organization are cells, tissues, organs, and organ systems.
2. Structure and function of each
level depends on structure and function of organ, tissue, and cell type.
B. Four Major Types of Tissue
1. Epithelial tissue covers body surfaces and lines body
cavities.
2. Connective tissue
binds and supports body parts.
3. Muscular tissue
causes body parts to move.
4. Nervous tissue
responds to stimuli and transmits impulses.
C. Epithelial Tissue
1. Epithelial tissue forms a continuous layer over body surfaces
including inner cavities.
2. There are three types of
epithelial tissue. (Fig. 40.2)
a. Squamous
epithelium is composed of flat cells (e.g. air sac linings of lungs,
walls of capillaries).
b. Cuboidal
epithelium has cube-shaped cells.
c. Columnar
epithelium has elongated cells that resemble pillars or columns (e.g.
small intestine).
3. Epithelium varies in number of
cell layers.
a. Simple
epithelium has one cell layer; all cells contact basement membrane.
b. Pseudo
stratified epithelium appears layered; actually, all cells contact
basement membrane.
c. Stratified
epithelium is composed of more than one layer of cells.
4. Epithelial cells can have cilia.
a. Ciliated
epithelium cells are covered with cilia (e.g., lining of human
respiratory tract).
b. Cilia can
bend and move material over the surface of the epithelium.
5. Secretory epithelia can be
unicellular or have multicellular glands.
a. Glands
are a single cell or a group of cells that secrete products into the lumen of or
onto the lining of
a tube or cavity, into blood, or to outside of the body; they are classified in
two types:
1) Exocrine glands secrete their products into ducts or directly
into a tube or cavity.
2) Endocrine glands secrete their product directly into the
bloodstream.
6. Epithelium forms outer layer of
skin of animals; it may produce an outer, nonliving protective cuticle.
7. Epithelial tissue cells are
packed tightly; they join to one another in one of three ways:
a. Tight
junctions have plasma proteins extending between neighboring cells;
bind cells tightly.
b. Adhesion
junctions have cytoskeletal elements joining internal plaques in
neighboring cells.
c. Gap
junctions form when two identical plasma membrane channels of
neighboring cells join; ions
and small molecules pass between cells.
D. Connective Tissue
1. Connective tissue binds structures together, fills spaces,
stores fat, and forms blood cells.
2. Connective tissue provides source
cells for muscle and skeletal cells in animals that regenerate parts.
3. Connective tissue cells are
separated widely by a matrix, a noncellular material between cells.
4. Loose Fibrous and Dense Fibrous
Connective Tissue
a. Cells of
loose and fibrous connective tissues are fibroblasts.
b.
Fibroblasts space apart separated by jelly matrix of white collagen fibers and
yellow elastic fibers.
c. Collagen
fibers provide flexibility and strength; elastic fibers provide elasticity.
d. Loose
fibrous connective tissue supports epithelium and provides support,
flexibility, and protective
covering encasing internal organs.
e. Dense
fibrous connective tissue contains closely packed collagenous fibers;
found in tendons, which
attach muscles to bone, and ligaments, which bind bones to other bones at
joints.
5. Adipose Tissue and Reticular
Connective Tissue
a. Adipose
Tissue
1) This is loose connective tissue that insulates, provides protective padding,
and stores fat.
2) In mammals, it is beneath skin, around kidneys, and on surface of heart.
b. Reticular
Connective Tissue
1) It is present in lymph nodes, spleen, and bone marrow.
2) Reticular fibers associated with reticular cells resembling fibroblasts
supports free blood cells.
6. Cartilage and Bone
a. Cartilage
and bone are rigid connective tissues.
b.
Structural proteins (cartilage) or calcium salts (bone) are deposited in
intercellular matrix.
c. Cartilage
cells lie in small chambers or lacunae embedded in a
strong, flexible matrix. (Fig. 40.3c)
1) In some animals, such as sharks and rays, entire skeleton is cartilage.
2) Human fetal skeleton is entirely cartilage but is gradually replaced by
bone.
3) Various types of cartilage are classified by type of collagen and elastic
fiber found in matrix.
4) Cartilage is at end of long bones, human nose, framework of human ear, in
walls of respiratory
ducts, and within intervertebral discs.
d. In bone,
matrix of calcium salts is deposited around protein fibers.
1) Calcium salts give bone rigidity; protein fibers provide elasticity and
strength.
2) Compact bone cells (osteocytes) lie within
lacunae arranged in concentric circles within osteons
(Haversian systems) around tiny tubes called central canals.
3) Canals contain nerve fibers and blood vessels.
4) Nutrients brought by blood reach all of cells via minute canals (canaculi)
containing thin processes
of osteocytes that connect them with one another and with central canals.
5) Spongy bone at end of long bones is designed for strength, has
many long bony bars and plates.
E. Blood
1. Blood transports nutrients and oxygen to cells and removes CO2
and wastes; also has role in fluid, ion
and pH
balance.
2. Blood is connective tissue
with cells separated by liquid plasma.
3. In vertebrates, the blood
cells are mainly of two types.
a. Red
blood cells (erythrocytes) carry oxygen.
b. White
blood cells (leukocytes) aid in fighting infection.
4. Platelets present
in plasma are fragments of giant cells found in bone marrow; and
play a role in blood clotting.
5. Unlike other connective tissues,
intercellular matrix of blood (i.e., plasma) is not made by cells; instead,
plasma is a
mixture of molecules that enter blood at various locations.
F. Muscular Tissue
1. Muscular (contractile) tissue is composed of cells called muscle
fibers.
2. Muscle fibers
contain actin and myosin filaments; interactions
result in animal movement.
3. Three types of vertebrate
muscle tissue are: skeletal, cardiac, and smooth.
4. Skeletal muscle
attaches by tendons to bones of skeleton.
a. Skeletal
muscle moves body parts, is under voluntary control, and contracts faster than
other types.
b. Skeletal
muscle fibers are long, cylindrical, multinucleate cells arising from fusion of
several cells.
c. Skeletal
fibers are striated due to light and dark bands of overlapping
actin and myosin filaments.
5. Smooth (visceral) muscle
is not striated.
a.
Spindle-shaped fibers form layers with the thick middle portion of one fiber
opposite the thin ends
of adjacent fibers.
b. Nuclei
form an irregular pattern in the tissue.
c. Smooth
muscle is not under voluntary control; it is therefore involuntary.
d. Smooth
muscle is found in walls of viscera (e.g. intestine, stomach, etc.) and blood
vessels.
e. Smooth
muscles drive intestinal contractions and blood vessel constrictions.
6. Cardiac muscle is
found only in heart wall and powers the heartbeat that pumps blood.
a. Cardiac
muscle combines features of smooth and skeletal muscle. (Fig. 40.5c)
b. Unlike
skeletal muscles with many nuclei, cardiac muscles have one centrally placed
nucleus.
c. Although
it appears to be one mass of muscle fibers, cardiac muscle fibers are
individual cells.
d. Cardiac
muscle cells are bound end-to-end at intercalated disks where folded membranes
between
two fibers contain desmosomes and gap junctions.
e. Impulses
move from cell to cell so heartbeat is coordinated.
G. Nervous Tissue
1. Nervous tissue is composed of neurons in the
brain, spinal cord and nerves.
2. Neurons have three parts:
a. Dendrites
receive a stimulus and conduct signals to cell body.
b. Cell
body contains most cytoplasm and nucleus of the neuron.
c. Axon
conducts nerve impulses away from cell body.
3. Long axons and dendrites form
neuron fibers; bound together by connective tissue, they form nerves.
4. Neurons detect stimuli and
conduct signals to brain or spinal cord; nerves lead to muscles or glands.
H. Neuroglia
1. There are several types of neuroglial cells in the Central
Nervous System (CNS). (Fig. 40.6)
2. Neuroglial cells outnumber
neurons nine to one; once thought to only support or nourish neurons.
3. Oligodendrocytes
form myelin around an axon.
4. Microglial cells also phagocytize
bacterial and cellular debris.
5. Astrocytes provide nutrients and
produce a growth factor known as glial-derived growth factor
(GDGF)
that may be
used to cure diseases of neural degeneration.
6. They lack long processes but
communicate among themselves and with neurons.
36.2. Organs
and Organ Systems
A. Organs are combinations of two or more different tissues
performing common functions.
1. Organ systems are many different organs performing common
functions.
2. Skin is considered an integumentary
system since it cannot be placed in another system; it is a system
composed of skin
and accessory organs (i.e., nails, hair, glands, and sensory
receptors).
B. Skin as an Organ
1. Human skin protects underlying tissues from trauma, desiccation, radiation
damage, and microbial invasion.
2. Skin produces a precursor
molecule that is converted to vitamin D after exposure to UV light.
3. Skin helps regulate body
temperature.
4. Laden with sensory receptors,
skin collects information about external environment.
5. Skin has an outer epidermal layer
(epidermis) and a deeper layer (dermis).
C. Regions of Skin
1. Epidermis is the outer, thinner layer of skin.
a. Epidermis
is composed of stratified squamous epithelium.
b. Cells are
derived from a basal layer of stem cells that undergo continuous cell division.
c. Newly
formed cells push to the surface away from their blood supply; they flatten and
harden as they
accumulate keratin, a hard, waterproof protein.
d.
Eventually, keratinized cells die and are sloughed off.
e. Melanocytes
located in basal layer produce melanin pigment that absorbs UV
light, protecting cells
from radiation damage.
f. Nails
grow from special epidermal cells at base of the nail in a region called the
nail root.
1) Visible portion of a nail is the nail body.
2) Cells become keratinized as they grow out over the nail bed.
3) Vascular dermal tissue under nail provides pink color; white half-moon area
is thicker germinal area.
2. Dermis is the
deeper and thicker layer of skin.
a. Dermis
contains elastic fibers and collagen fibers; these run parallel with skin
surface.
b.Hair
follicle contains a nonliving hair shaft and living hair
root that produced it.
1) Hair shaft is formed of dead, keratinized epidermal cells that protect the
surface of skin.
2) Arrector pili muscle is smooth muscle attached to hair
follicle; contracting causes hair to erect.
3) Follicles have sebaceous glands producing sebum,
an oil secreted to lubricate hair and skin.
c. Sweat
(sudoriferous) glands are coiled tubules present in most regions of
skin that secrete a fluid
(sweat) onto the surface of skin.
d. Many
small receptors are present in dermis.
1) There are separate receptors for pressure, touch, temperature, and
pain.
2) Pressure receptors have onion-like sense organs buried deep in
dermis and around joints.
3) In cats, Pacinian corpuscles are concentrated in paws, leg joints, and
abdomen.
4) Closely related sensors in tongue of woodpeckers help them find insects in
tree bark.
5) Touch receptors are flat and oval shaped: concentrated in
fingertips, palms, lips, tongue, nipples,
penis, and clitoris.
6) Heat and cold sense organs are encapsulated inside sheaths of
connective tissue.
7) Nerve fibers branch out through skin; free nerve endings are pain
receptors.
e. Dermis
contains blood vessels that constrict (you turn pale) and dilate (you blush).
3. Subcutaneous layer
lies below dermis.
a. It is
composed of loose connective tissue, including adipose tissue.
b. Adipose
tissue helps insulate the body by minimizing both heat gain and heat
loss.
c. This
layer gives a rounded appearance to the body.
d. Excessive
development of adipose tissue occurs with obesity.
4. Skin Cancer
a. There has
been an increase in persons with skin cancer due to sunbathing and use of
tanning machines.
b. Excessive
exposure to UV radiation can convert cells in basal layer of epidermis to
cancer cells.
D. Organ Systems
1. Individual organs function as part of organ systems.
2. Organ systems carry out life
processes..
3. Body Cavities
a. Human
body has two main cavities: dorsal cavity with
brain and spinal cord, and larger ventral cavity.
b. Ventral
cavity located on front side of body develops from coelom and is
divided by muscular
diaphragm in humans and other mammals.
c. Thoracic
(chest) cavity is located in upper part of the ventral cavity, above a
muscular diaphragm,
and contains heart and lungs.
d. Abdominal
cavity is located in lower part of ventral cavity, below a muscular
diaphragm, and
contains major portions of digestive and excretory systems, and much of
reproductive system.
36.3.
Homeostasis
A. Cells of the body live in an internal environment, tissue fluid
that bathes the cells of an animal's body.
1. This concept was first proposed by Claude Bernard, a famous French
physiologist in 1859.
2. Quality of internal environment
(e.g., composition and temperature) must stay within normal range.
3. Relative internal stability
allows animals to tolerate considerable external variation.
4. American physiologist Walter
Cannon first used term: homeostasis.
B. Homeostasis is maintenance of internal conditions in a cell or
organism by means of self-regulating
mechanisms that curtail
fluctuations above and below a normal range.
1. Most organ systems of human body contribute to homeostasis.
a.
Respiratory system adds oxygen, removes carbon dioxide; amounts are increased
to meet needs.
b. Liver
removes and stores glucose as glycogen, then replaces blood glucose levels when
low.
c. Hormone
insulin is secreted by pancreas to regulate glucose levels.
d. Kidneys
are under hormonal control to excrete wastes and salts and to maintain blood
pH.
2. Although homeostasis is
controlled by hormones, it is ultimately controlled by nervous system.
3. Brain contains centers that
regulate temperature and blood pressure.
4. Regulation requires a receptor
that detects unacceptable levels and signals a regulator center that can
direct an
adaptive response; once normalcy is obtained, receptor is no longer stimulated.
5. Negative feedback mechanism
involves a response in which output is counter to and cancels input,
decreasing
likelihood of a response.
a. A house
thermostat is an analogy.
b. Negative
feedback causes heater or air conditioner to maintain temperature within narrow
limits.
6. Positive feedback mechanism
involves output that intensifies and increases the input, thereby increasing
likelihood
of a response.
a. Once
childbirth begins, each event makes the process continue until completion.
b. Sequences
in blood clotting likewise progress to form a blood clot.
C. Regulation of Body Temperature
1. Regulator center for body temperature is located in hypothalamus, a part of
the brain.
2. When body temperature of blood
falls below normal, a regulator center directs smooth muscles of the
blood
vessels in skin to constrict, which reduces blood flow to peripheral tissues,
and thereby reduces
loss of heat
to external environment.
3. In hairy animals, arrector pili
muscles pull hairs erect forming a thicker insulation.
4. If temperature falls even lower,
regulator center sends nerve impulses to skeletal muscles, initiating
shivering to
generate heat.
5. If body temperature is too warm,
regulator center directs skin blood vessels to dilate, which increases
blood flow
to peripheral tissues and increases heat loss.
6. Regulator center activates sweat
glands, increasing sweat production and increasing evaporative cooling.