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Chapter 4

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Tissues
Groups of cells similar in structure that perform common or related function
Histology
Study of tissues
Four basic tissue types
epithelial, connective, muscle, and nervous tissue
Epithelial tissue (epithelium)
-a sheet of cells that covers body surfaces or cavities
-Two main forms:
Covering and lining epithelia
-on external and internal surfaces (example: skin)
Glandular epithelia
-Secretory tissue in glands (example: salivary glands)
Main functions: protection, absorption, filtration, excretion, secretion, and sensory reception
Epithelial tissue has five distinguishing characteristics
Polarity
Specialized contacts
Supported by connective tissues
Avascular, but innervated
Regeneration
Polarity
Cells have polarity (top and bottom)
Apical surface
-Upper free side, is exposed to surface or cavity
-Most apical surfaces are smooth, but some have specialized fingerlike projections called microvilli
Basal surface
-Lower attached side, faces inwards toward body
-Attaches to basal lamina, an adhesive sheet that holds basal surface of epithelial cells to underlying cells
Specialized contacts
-Epithelial tissues need to fit closely together
-Many form continuous sheets
-Specialized contact points bind adjacent epithelial cells together
Lateral contacts include:
Tight junctions
Desmosomes
Connective tissue support
Reticular lamina
----Deep to basal lamina
----Consists of network of collagen fibers
Basement membrane
-----Made up of basal and reticular lamina
-----Reinforces epithelial sheet
-----Resists stretching and tearing
-----Defines epithelial boundary
Avascular, but innervated
-No blood vessels are found in epithelial tissue
-Must be nourished by diffusion from underlying connective tissues
-Epithelia are supplied by nerve fibers, however
Regeneration
-Epithelial cells have high regenerative capacities
-Highly mitotic
Classification of Epithelia
All epithelial tissues have two names
----First name indicates number of cell layers
Simple or Stratified
-----Second name indicates shape of cells
Squamous, Cuboidal or Columnar
In stratified epithelia, shape can vary in each layer, so cell is named according to the shape in apical layer
Simple squamous
Description: Single layer of
flattened cells with disc-shaped
central nuclei and sparse
cytoplasm; the simplest of the
epithelia.

Function: Allows materials to
pass by diffusion and filtration
in sites where protection is not
important; secretes lubricating
substances in serosae.

Location: Kidney glomeruli;
air sacs of lungs; lining of heart,
blood vessels, and lymphatic
vessels; lining of ventral body
cavity (serosae).
Simple cuboidal
Description: Single layer
of cubelike cells with large,
spherical central nuclei.

Function: Secretion and
absorption.

Location: Kidney tubules;
ducts and secretory portions
of small glands; ovary surface.
Simple columnar
Description: Single layer of tall
cells with round to oval nuclei; many
cells bear microvilli, some bear cilia;
layer may contain mucus-secreting
unicellular glands (goblet cells).

Function: Absorption; secretion
of mucus, enzymes, and other
substances; ciliated type propels
mucus (or reproductive cells) by
ciliary action.

Location: Nonciliated type lines
most of the digestive tract (stomach
to rectum), gallbladder, and excretory
ducts of some glands; ciliated variety
lines small bronchi, uterine tubes,
and some regions of the uterus.
Stratified squamous
Description: Thick membrane
composed of several cell layers;
basal cells are cuboidal or columnar
and metabolically active; surface
cells are flattened (squamous); in the
keratinized type, the surface cells are
full of keratin and dead; basal cells
are active in mitosis and produce the
cells of the more superficial layers.

Function: Protects underlying
tissues in areas subjected to
abrasion.

Location: Nonkeratinized type forms
the moist linings of the esophagus,
mouth, and vagina; keratinized variety
forms the epidermis of the skin, a dry
membrane.
SKIN
Stratified cuboidal
Quite rare
Found in some sweat and mammary glands
Typically only two cell layers thick
Stratified columnar
Also very limited distribution in body
Small amounts found in pharynx, in male urethra, and lining some glandular ducts
Usually occurs at transition areas between two other types of epithelia
Only apical layer is columnar
Simple epithelia
Involved in absorption, secretion, or filtration processes
Types:
Simple squamous epithelium
Simple cuboidal epithelium
Simple columnar epithelium
Pseudostratified columnar epithelium
Pseudostratified columnar
Description: Single layer of cells
of differing heights, some not
reaching the free surface; nuclei
seen at different levels; may
contain mucus-secreting cells and
bear cilia.

Function: Secrete substances,
particularly mucus; propulsion
of mucus by ciliary action.

Location: Nonciliated type in
males' sperm-carrying ducts and
ducts of large glands; ciliated
variety lines the trachea, most of
the upper respiratory tract

ONLY PSEUDOSTRATIFIED COLUMNAR HAS CILIA; NOT SIMPLE COLUMNAR
Stratified epithelial tissues
Involve two or more layers of cells
New cells regenerate from below
Basal cells divide and migrate toward surface
More durable than simple epithelia because protection is the major role
Types:
Stratified squamous epithelium
Stratified cuboidal epithelium
Stratified columnar epithelium
Transitional epithelium
Transitional epithelium
Description: Resembles both
stratified squamous and
stratified cuboidal; basal cells
cuboidal or columnar; surface
cells dome shaped or
squamouslike, depending on
degree of organ stretch.

Function: Stretches readily,
permits stored urine to distend
urinary organ.

Location: Lines the ureters,
bladder, and part of the urethra.

EMPTY BLADDER=Cuboidal
FULL BLADDER= Squamous
Gland
One or more cells that makes and secretes an aqueous fluid called a secretion
Relative number of cells forming the gland
Unicellular (example: goblet cells) or multicellular (example: salivary)
Endocrine
-Internally secreting (example: hormones)
-Ductless glands
-Secretions are not released into a duct; are released into surrounding interstitial fluid, which is picked up by circulatory system
-Secrete (by exocytosis) hormones, messenger chemicals that travel through lymph or blood to their specific target organs
-Target organs respond in some characteristic way
Exocrine
-Externally secreting (example: sweat)
-Secretions are released onto body surfaces, such as skin, or into body cavities
-More numerous than endocrine glands
-Secrete products into ducts
-Examples include mucous, sweat, oil, and salivary glands
Can be:
Unicellular
Multicellular
Unicellular exocrine glands
-The only important unicellular glands are mucous cells and goblet cells
-Found in epithelial linings of intestinal and respiratory tracts
-All produce mucin, a sugar-protein that can dissolve in water to form mucus, a slimy protective, lubricating coating
Multicellular exocrine glands
-Multicellular exocrine glands are composed of a duct and a secretory unit
Classified by:
Structure
Mode of secretion
Multicellular exocrine glands structure
-Simple exocrine glands have unbranched ducts, but compound glands have branched ducts
-In a tubular gland, secretory cells form a duct, whereas in alveolar glands, secretory cells form sacs
-Tubuloalveolar glands have both types
Multicellular exocrine glands mode of secretion
Merocrine, Holocrine, Apocrine
Merocrine
most secrete products by exocytosis as secretions are produced (sweat, pancreas)
Holocrine
accumulate products within, then rupture (sebaceous oil glands) (HOLE cell ruptures)
Aprocrine
accumulate products within, but ONLY apex ruptures; whether this type exists in humans is controversial (maybe mammary cells?)
Connective tissue
-The most abundant and widely distributed of primary tissues
-Major functions: binding and support, protecting, insulating, storing reserve fuel, and transporting substances (blood)
-Four main classes:
Connective tissue proper
Cartilage
Bone
Blood
Common Characteristics of Connective Tissue
-Three characteristics make connective tissues different from other primary tissues:
-All have common embryonic origin: all arise from mesenchyme tissue as their tissue of origin
-Have varying degrees of vascularity (cartilage is avascular, bone is highly vascularized)
-Cells are suspended/embedded in extracellular matrix (ECM) (protein-sugar mesh)
-Matrix supports cells so they can bear weight, withstand tension, endure abuse
3 main elements of connective tissue
-Ground substance
-Fibers
-Cells
***The first two elements (ground substance and fibers) together make up the extracellular matrix
-Composition and arrangement of these three elements vary considerably in different types of connective tissues
Ground substance
-Unstructured gel-like material that fills space between cells
-Medium through which solutes diffuse between blood capillaries and cells
Connective tissue fibers
Three types of fibers provide support
Collagen
Elastic fibers
Reticular
Collagen
-Strongest and most abundant type
-Tough; provides high tensile strength
Elastic fibers
Networks of long, thin, elastin fibers that allow for stretch and recoil
Reticular
-Short, fine, highly branched collagenous fibers (different chemistry and form from collagen fibers)
-Branching forms networks that offer more "give"
Connective Tissue Cells
"Blast" cells
-Immature form of cell that actively secretes ground substance and ECM fibers
-Fibroblasts found in connective tissue proper
-Chondroblasts found in cartilage
-Osteoblasts found in bone
-Hematopoietic stem cells in bone marrow
"Cyte" cells
-Mature, less active form of "blast" cell that now becomes part of and helps maintain health of matrix
Other cell types in connective tissues
-Fat cells
Store nutrients
-White blood cells
Neutrophils, eosinophils, lymphocytes
Tissue response to injury
-Mast cells
Initiate local inflammatory response against foreign microorganisms they detect
-Macrophages
Phagocytic cells that "eat" dead cells, microorganisms; function in immune system
Areolar tissue
Description: Gel-like matrix with
all three fiber types; cells:
fibroblasts, macrophages, mast
cells, and some white blood cells.

Function: Wraps and cushions
organs; its macrophages
phagocytize bacteria; plays
important role in inflammation;
holds and conveys tissue fluid

Location: Widely distributed
under epithelia of body, e.g.,
forms lamina propria of mucous
membranes; packages organs;
surrounds capillaries.

LOOSE CONNECTIVE TISSUE PROPER
Adipose Tissue
Description: Matrix as in
areolar, but very sparse; closely
packed adipocytes, or fat cells,
have nucleus pushed to the
side by large fat droplet.

Function: Provides reserve
food fuel; insulates against
heat loss; supports and
protects organs.

Location: Under skin in
subcutaneous tissue; around
kidneys and eyeballs; within
abdomen; in breasts.

LOOSE CONNECTIVE TISSUE PROPER
Reticular Tissue
Description: Loose network
of reticular fibers in a gel-like
ground substance; reticular
cells lie on the network.

Function: Fibers form a soft
internal skeleton (stroma) that
supports other cell types
including white blood cells,
mast cells, and macrophages.

Location: Lymphoid organs
(lymph nodes, bone marrow,
and spleen).

LOOSE CONNECTIVE TISSUE PROPER
Dense Regular Tissue
Description: Primarily parallel
collagen fibers; a few elastic
fibers; major cell type is the
fibroblast.

Function: Attaches muscles to
bones or to muscles; attaches
bones to bones; withstands
great tensile stress when
pulling force is applied in one
direction.

Location: Tendons, most
ligaments, aponeuroses.

DENSE CONNECTIVE TISSUE PROPER
Dense Irregular Tissue
Description: Primarily
irregularly arranged collagen
fibers; some elastic fibers;
fibroblast is the major cell type

Function: Withstands tension
exerted in many directions;
provides structural strength.

Location: Fibrous capsules of
organs and of joints; dermis of
the skin; submucosa of
digestive tract.

DENSE CONNECTIVE TISSUE PROPER
Elastic Tissue
Description: Dense regular
connective tissue containing a
high proportion of elastic fibers

Function: Allows tissue to
recoil after stretching; maintains
pulsatile flow of blood through
arteries; aids passive recoil of
lungs following inspiration.

Location: Walls of large
arteries; within certain ligaments
associated with the vertebral
column; within the walls of the
bronchial tubes.

DENSE CONNECTIVE TISSUE PROPER
Cartilage
-Matrix secreted from chondroblasts (during growth) and chondrocytes (adults)
-Chondrocytes found in cavities called lacunae
-80% water, with packed collagen fibers and sugar proteins (chondroitin and hyaluronic acid)
-Tough yet flexible material that lacks nerve fibers
Avascular
-Receives nutrients from membrane surrounding it (perichondrium)
-Periochondrium gives rise to chondroblasts and chondrocytes
Three types of cartilage
Hyaline cartilage
Elastic cartilage
Fibrocartilage
Hyaline Cartilage
Description: Amorphous but
firm matrix; collagen fibers form
an imperceptible network;
chondroblasts produce the
matrix and when mature
(chondrocytes) lie in lacunae

Function: Supports and
reinforces; serves as resilient
cushion; resists compressive
stress.

Location: Forms most of the
embryonic skeleton; covers the
ends of long bones in joint
cavities; forms costal cartilages
of the ribs; cartilages of the
nose, trachea, and larynx.
Elastic Cartilage
Description: Similar to hyaline
cartilage, but more elastic
fibers in matrix.

Function: Maintains the shape
of a structure while allowing
great flexibility.

Location: Supports the
external ear (pinna); epiglottis
Fibrocartilage
Description: Matrix similar to
but less firm than that in hyaline
cartilage; thick collagen fibers
predominate.

Function: Tensile strength
allows it to absorb compressive
shock.

Location: Intervertebral discs;
pubic symphysis; discs of knee
joint.
Bone (osseous tissue)
-Supports and protects body structures
-Stores fat and synthesizes blood cells in cavities
-Has more collagen compared to cartilage
-Has inorganic calcium salts
-Osteoblasts produce matrix
-Osteocytes maintain the matrix
-Reside in cavities in matrix called lacunae
-Osteons: individual structural units
****Richly vascularized
Osseous Tissue
Description: Hard, calcified
matrix containing many
collagen fibers; osteocytes
lie in lacunae. Very well
vascularized.

Function: Supports and
protects (by enclosing);
provides levers for the muscles
to act on; stores calcium and
other minerals and fat; marrow
inside bones is the site for
blood cell formation
(hematopoiesis).

Location: bones
Blood
-Most atypical connective tissue because it is fluid
-Consists of cells surrounded by matrix (plasma)
-Red blood cells are most common cell type
-Also contains white blood cells and platelets
-Fibers are soluble proteins that precipitate during blood clotting
-Functions in transport and in carrying nutrients, wastes, gases, and other substances
Blood Tissue
Description: Red and white
blood cells in a fluid matrix
(plasma).

Function: Transport
respiratory gases, nutrients,
wastes, and other substances

Location: Contained within
blood vessels.
Muscle Tissue
-Highly vascularized
-Responsible for most types of movement
-Muscle cells possess myofilaments made up of actin and myosin proteins that bring about contraction
-Three types of muscle tissues:
Skeletal muscle
Cardiac muscle
Smooth muscle
Skeletal Muscle Tissue
Description: Long, cylindrical,
multinucleate cells; obvious
striations.

Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression;
voluntary control.

Location: In skeletal muscles
attached to bones or
occasionally to skin.
Cardiac Muscle Tissue
Description: Branching,
striated, generally uninucleate
cells that interdigitate at
specialized junctions
(intercalated discs).

Function: As it contracts,
it propels blood into the
circulation; involuntary control.

Location: The walls of the
heart.
Smooth Muscle Tissue
Description: Spindle-shaped
(elongated) cells with central
nuclei; no striations; cells
arranged closely to form sheets.

Function: Propels substances
or objects (foodstuffs, urine,
a baby) along internal
passageways; involuntary
control.

Location: Mostly in the walls
of hollow organs.
Nervous Tissue
-Main component of nervous system (brain, spinal cord, nerves)
-Regulates and controls body functions
-Made up of two specialized cells:
****Neurons: specialized nerve cells that generate and conduct nerve impulses
****Supporting cells (neuroglial cells or glial cells) that support, insulate, and protect neurons
Nervous Tissue Diagram
Description: Neurons are
branching cells; cell processes
that may be quite long extend
from the nucleus-containing
cell body; also contributing to
nervous tissue are nonexcitable
supporting cells.

Function: Neurons transmit
electrical signals from sensory
receptors and to effectors
(muscles and glands); supporting
cells support and protect neurons.

Location: Brain, spinal
cord, and nerves.
Covering and Lining Membranes
-Composed of at least two primary tissue types: an epithelium bound to underlying connective tissue proper layer
-Three types:
Cutaneous membranes
Mucous membranes
Serous membranes
Cutaneous Membranes
-Another name for skin
-Keratinized stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis)
-Unlike other membranes, skin is a dry membrane
Mucous Membranes
-Mucosa indicates location, not cell composition
*Also called mucosae
-Line body cavities that are open to the exterior (example: digestive, respiratory, urogenital tracts)
-Moist membranes bathed by secretions (or urine)
-Epithelial sheet lies over layer of loose connective tissue called lamina propria
-May secrete mucus
Mucous Membrane picture
Mucous membranes line body
cavities that are open to the
exterior.
Serous Membranes
-Also called serosae
-Found in closed ventral body cavities
-Constructed from simple squamous epithelium (called mesothelium) resting on thin areolar connective tissue
-Parietal serosae line internal body cavity walls
-Visceral serosae cover internal organs
-Cavity between layers is filled with slippery serous fluid, so these are moist membranes
-Special names given to show location: pleurae (lungs), pericardium (heart), peritoneum (abdomen)
Serous membrane picture
Serous membranes line body cavities
that are closed to the exterior.
Tissue Repair
-When the body's barriers are compromised, the inflammatory and immune responses are activated
-Repair starts very quickly
-Repair is the function of the inflammatory process
-Repair can occur in two major ways:
***Regeneration: same kind of tissue replaces destroyed tissue, so original function is restored
***Fibrosis: connective tissue replaces destroyed tissue, and original function lost
Inflammation sets the stage (for repair)
Review powerpoint slide (slide 69 lol) for diagram because I couldn't make it look good on here
Tissues that regenerate extremely well include
Epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, blood-forming tissue
Tissue with moderate regenerating capacity
Smooth muscle and dense regular connective tissue
Tissues with virtually no functional regenerative capacity
-Cardiac muscle and nervous tissue of brain and spinal cord
-New research shows cell division does occur, and efforts are underway to coax them to regenerate better
Primary germ layers
-Superficial to deep: ectoderm, mesoderm, and endoderm
-Formed early in embryonic development
-Specialize to form the four primary tissues
***Nerve tissue arises from ectoderm
***Muscle and connective tissues arise from mesoderm
***Epithelial tissues arise from all three germ layers
Mesoderm, Ectoderm, Endoderm

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