Tissues
-Whole body contains only 200 different cells types that
are organized into tissues
•Four primary tissue classes
–epithelial tissue
–connective tissue
–muscular tissue
–nervous tissue
•The extracellular fluid surrounding the cells within tissue
is called interstitial fluid
•Histology (microscopic anatomy)
–study of tissues and how they form organs
Epithelial Tissue
-Covers the entire surface of the body
–includes skin, lining of the lung, lining of the
digestive tract, lining of the urinary tract, lining of the
reproductive tract
-barrier between what is IN the body and what is OUT
of the body
-controls what substances enter/exit the body and
what substances stay in/out of the body
•Primary tissue type found in glands
–exocrine glands
•secrete substances outside of the body (sweat,
salivary, digestive)
–endocrine glands
•secrete substances (hormones) into the blood
(thyroid, adrenal, pituitary, pancreas
Epithelial Tissue: Basic Structure
• Made of epithelial cells that are connected to adjacent cells by
proteins called tight junctions
– make the tissue leakproof
– create “sheets” of epithelial cells
– similar in structure to a six-pack of cans
• Epithelial cell surfaces face 2 different environments
– apical surface of the cell faces toward the OUTSIDE of the body
– basal surface of the cell faces toward the INSIDE of the body
• Anchored to the body by a structure called the basement membrane
Classification of Epithelial Tissues
Epithelial tissue is classified based on 2 criteria:
• Cell shape
– squamous (flattened cells)
• cell width is larger than cell height
– cuboidal (cube-like cells)
• cell width is equal to cell height
– columnar (column-like cells)
• cell height is larger than cell width
Classification of Epithelial Tissues
• Number of layers of epithelial cells
– Simple
• one cell layer thick
• transports substances into or out of the body
– Stratified
• more than one cell layer thick
• protects body from mechanical damage (abrasion,
puncture…)
– Pseudostratified
• one cell layer thick made of different cell types
Epithelia: Simple
Squamous
• single layer of squamous
epithelial cells with flat
nuclei
Small intestine and cheek
Epithelia: Simple
Cuboidal
• single layer of cuboidal
epithelial cells with
spherical nuclei
Kidney
Epithelia: Simple
Columnar
• single layer of columnar
cells with oval nuclei
Interior of small intestine
Epithelia:
Pseudostratified
Columnar
• single layer of cells with
different heights; some
do not reach the surface
of the body
• the shape of the nuclei
is similar to the shape of
the cell
Trachea
Epithelia: Stratified
Squamous
• thick epithelium
composed of several
layers of squamous cells
with flat nuclei
Vagina
Epithelia: Stratified
Cuboidal and
Columnar
Rare in the body
• Stratified cuboidal
– 2-3 layers of cuboidal cells
with spherical nuclei
Sweat gland
Epithelia: Transitional
• The shape of the cells
change based on the amount
of stress (stretch) on the
tissue
• can appear as cuboidal or
columnar when not
stretched or squamous when
stretched
Umbilical cord and Urinary
bladder
Connective Tissue
-Most abundant and variable tissue type
•Consists of widely spaced cells separated by fibers and
ground substance
-4 primary types
–Connective tissue proper
•characterized by histological appearance
–loose
–dense
–Cartilage
–Bone
–Blood
•Functions
–connects organs to each other
–gives support & protection (physical & immune)
–storage of energy & heat production
–transport of materials
Structural Elements of Connective Tissue
3 structural elements (components) of connective tissue
•Ground substance
•unstructured (gel-like) material that fills the space
between cells (interstitial space)
•Fibers
•very large proteins outside of the cell which make a
web-like structure to hold the tissue together
-Ground substance + fibers = Extracellular Matrix
•Cells
•create the extracellular matrix by exocytosis
Structural elements of connective tissue
Fibers
3 primary types of extracellular protein fibers
•Collagen
–very thick and strong, do not stretch
–provides tough structure to tissue
•Elastic
–thin and strong, allow for stretch and then recoil
(return to original length) when released
–made from the protein elastin
•Reticular
–thin collagen fibers
–provide delicate structure to tissue
Cells
There are 4 different cell types which are responsible for
making the 4 different types of connective tissue
•blast = “to build”
•Fibroblasts
–connective tissue proper
•Chondroblasts
–cartilage
•Osteoblasts
–bone
•Hemocytoblast
–blood
Loose Connective Tissue
Proper: Areolar
Walls of abdomen
Loose Connective Tissue
Proper: Adipose
• stores lipids for use as fuel,
insulates and protects
Under skin
Loose Connective Tissue
Proper: Reticular
Kidney
Dense Connective Tissue
Proper: Regular
• many parallel collagen fibers
with a few elastic fibers
• attaches muscles to bone
(tendons) and bone to bone
(ligaments)
Tendons and ligaments
Dense Connective Tissue
Proper: Irregular
• many non-parallel
collagen fibers with
a few elastic fibers
Skin - Dermis
Connective Tissue:
Cartilage
• 3 types
– Hyaline
– Fibrocartilage
– Elastic
• made of chondrocytes
found in a lacuna (“pit”)
within the firm but
flexible extracellular
matrix comprised of a
network of collagen
fibers
Ossification is the gradual replacement of cartilage with bone
Occurs slowly so that by adulthood cartilage remains in a
limited number of places
- such as the ears, trachea, nose and between the
bones