Tissues Introduction
Epithelial Tissue Classification
Glands
Cell Specialization Multicellularity requires a division
of labor Cells look and function differently
(specialize) in different parts of the body (ex. bone cell vs. nerve cell)
Cells specialize into types of tissues, then form organs.
Histology
Study of tissues (groups of cells that are similar in structure and function)
4 Tissue Types
1. Connective Tissue Support Connect layers of tissue to each
other Bone, ligaments, fat(we will study these in great detail in class later…)
2. Nervous Tissue Control Brain, nerves,
spinal cord Highly
specialized cells that generate and conduct nerve impulses
3. Muscular Tissue Movement Highly vascular Contracts with cytoskeletal
microfilament (actin) that works with motor protein called myosin
2 categories: Striated muscle tissue (voluntary or
indirect voluntary control) Smooth muscle tissue (involuntary)
3. Muscular Tissue Striated Muscle
Ex. Skeletal Attached to skeletal bones Long, cylindrical multi-nucleited cells (as
in background) Visible striations Voluntary control
Ex. Cardiac Also striated, but uni-nucleated Branching cells fit tightly with special
junctions called intercalated discs
3. Muscular Tissue Smooth muscle No striations Spindle shaped One central nucleus Involuntary muscle
Ex. digestive system
4. Epithelial TissueInterface tissue that forms boundaries
between environments and lines surfaces
“epithe-” means “laid on”
Coverings and Protection (ex. skin, serous membranes)
Excretion & Secretion (ex. glands) Filtration (ex. kidneys) Absorption (ex. digestive system)
Identifying Characteristics of Epithelial Tisues
1. Tight fitting sheets
Regardless of cell shape or number of layers
Identifying Characteristics2. Apical-Basal Polarity Apical Surface = top
surface that borders an “open” space called LUMEN
Basal Surface = bottom surface that borders underlying supportive connective tissue
LUMEN
Connective Tissue
Identifying CharacteristicsApical Surface Often w/ microvilli
(brush border) Increases SA in
areas that need to absorb or secrete
Some with cilia (longer) to move substances along lumen
LUMEN
Connective Tissue
Identifying CharacteristicsBasal Surface Has adhesive sheet of
glyco-proteins secreted by epithelial cells called the basal lamina
Connective Tissue beneath secretes collagen, creating the Reticular Lamina.
Basal Lamina + Reticular Lamina = Basement Membrane (defines the epithelial boundary)
LUMEN
Connective Tissue
LUMEN
Identifying Characteristics3. Avascular (a =
without) Lacks blood vessels Nourished by
connective tissueBut Innervated
w/ nerve fibers
4. Regeneration and repair quickly
Classification of Epithelial Tissue:
Cell ShapeCross-section
Squamous – flat, like a fried egg, or scale-like
Cuboidal – cubes, large spherical central nuclei
Columnar – columns, long oval nuclei, usually near basal surface
Classification of Epithelial Tissue Cell Layers
Simple (one layer) Thin: limited, no
protection Sparse cytoplasm Found where rapid
diffusion is a priority (ex. kidneys, lungs)
Stratified (many layers)
Thick Protective role,
subject to wear and tear
Regenerate from basal surface to replace apical surface cells that rub off or die
Cells differ in shape at apical and basal surface. (named for apical surface)
Pseudo-stratified
Shapes vary in height Nuclei at different levels – appear
stratified, but aren’t. All cells reach basement membrane;
only a few reach the surface
false
Simple Squamous Epithelium
Function and Location Areas of high diffusion rates:
gasses (ex lungs)nutrients and waste exchange (blood
vessels and surrounding cells)filtrates (kidneys)
Makes lubricating fluid in lining of body cavities (ex. serous membranes)
One layer Flat
Simple Squamous Epithelium(Top View) – cells fit like tiled
floor
Figure 4.2
LUMEN
Simple Squamous Epithelium(side view/cross section) – cells look like fried egg
LUMEN
Nucleus of squamous cell
Kidney
Simple Cuboidal Epithelium
Function and Location Secretion and Absorption Covers walls of SMALL ducts, glands,
kidney tubules, ovaries
One layer Cubed
LUMEN
Spherical, large nuclei
Basement membrane
Cuboidal Cell
Apical surface
LUMENSpherical, large nuclei Apical surface
Basal surface
Simple Columnar Epithelium
Function and Location Absorption & Secretion (ex. digestive tract) When in open to body cavities – called
mucous membranes Special Features
Often w/ microvilli on apical surface (brush border)
Goblet cells, single cell glands, produce protective mucus.
One layer columns
LUMEN
Apical surface
Basal surface
Pseudostratified Epithelium
Function Absorption Secretion of mucus by goblet cells Cilia (larger than microvilli) sweep
mucus Location
Respiratory Linings & Reproductive tract
LUMEN
CiliaBasement Membrane
Multilevel nuclei
LUMEN
Stratified Squamous Epithelium
Structure Cells often cuboidal or columnar below
apical squamous layer Function and Location
Protection Keratin (protein) is accumulated in older
cells near the surface – waterproofs and toughens skin
Location Skin (keratinized), mouth & throat
Multi-layer (thick!)
Flat (only cells on apical surface)
keratin
Dense-Irregular Connective Tissue
Basement Membrane
Squamous
Cuboidal
Columnar
Transitional Epithelium
Structure Multi-layer Basal surface cells are cuboidal or
columnar Apical surface cells vary: changes shape
to accommodate for change in volume due to stretching
Function Allows stretching
Location Urinary bladder, ureters & urethra
Figure 4.10
Glands Cells that secrete or export a product. Secretion = protein, lipids, hormones,
steroids, acids Endocrine glands (internally secreting)
No duct, release secretion into blood vessels Often hormones Thyroid, adrenal and pituitary glands
Exocrine glands (externally secreting) Contain ducts, empty onto epithelial surface Sweat, Oil glands, Salivary glands, Mammary
glands.
Shapes of Exocrine glandsBranching of ducts Simple – single, unbranched duct Compound – branched duct.
Shape of glands: Tubular – tube - like Alveolar – flasks or sacs Tubuloalveolar – has both tubes and sacs in gland
Modes of Secretion
Merocrine Released by exocytosis Gland is not altered (Ex: Sweat glands and salivary
glands)
Holocrine Gland ruptures and releases secretion
and dead cells as well. Sebaceous (ex. oil glands on the face)
Merocrine
Holocrine