section 1, chapter 5
DESCRIPTION
tissuesTRANSCRIPT
Section 1, Chapter 5
Introduction to Tissues& Epithelial Tissues
Tissues
A Tissue is to a group of similar cells that carries out a specialized function.
Histology is the science of tissues.
examples of tissues
Muscular tissue – specialized to contract
Nervous tissue – conducts, senses, and stores information
Epithelial tissue – forms coverings (skin) & linings (blood vessels)
Connective tissues – support, transport, protect
There are four broad categories of tissues
Intercellular junctions
1. Tight Junction
A tight junction fuses the cell membranes of adjacent cells together so molecules cannot move between the cells. Instead, they must move through the cells.
Tight junctions prevent the passage of unwanted & harmful substances
Examples: Blood Brain Barrier & Digestive Tract
Interlocking membranes form tight junction between two cells
Cell 1
Cell 2
Cells may be separated by a matrix or connected together by cellular junctions.
2. Desmosomedesmosomes form “spot welds” between cellsProvides structural supportExamples of desmosomes are in the epidermis of the skin
Cellular Junctions
Cells connected by desmosomes
3. Gap JunctionGap Junctions connect cells by protein ion channels that allow for cell-to-cell diffusion of ions
Example of gap junctions are within the intercalated discs of cardiac muscle
Intercalated discs of cardiac muscle are one type of gap junction.
Cellular Junctions
Types of Tissues: Epithelial Tissue
Epithelial tissue lines cavities, such as the digestive & respiratory tracts
It also forms coverings, such as the skin
Functions include protection, secretion, absorption, excretion
Epithelial Tissue:
Epithelium: structureEpithelium is anchored to a layer of connective tissue, called the basement membrane.
Epithelium has a basal surface that faces the basement membrane
The free (apical) surface is exposed to the open space (lumen)
apical surfa
ce
basal surfa
ce
Basement membrane
Open space = lumen
Characteristics of Epithelial Tissue
Epithelium consists of tightly packed cells
They lack a blood supply, instead they receive nutrients by diffusion
Epithelium readily divide, so they are continually replaced = rapid healing
1. Simple = Single layer of epithelial cells
Classifications of Epithelial Tissues
2. Stratified = two or more layers of cells
Epithelium are classified by the layer of cells
And they’re classified by the shape of cells
1. squamous = scale-like
2. cuboidal = cube-like shape
3. Columnar = tall cells
Simple Squamous Epithelium
Single layer of flattened cells
Functions include diffusion, filtration, and secretion
Locations include:air sacs of lungs (alveoli)
lining of capillaries and the walls of blood vessels
glomerulus of kidneys.
surface view of simple squamous ep. alveoli of lung
squa
mou
s ce
lls
Simple Cuboidal Epithelium
Single layer of cube-shaped cells
Functions include secretion and absorption
Locations includethe lining and the ducts of some glands
tubules within kidneys
lumen
cross-section of tubules in kidneys
Simple Columnar Epithelium
Single layer of elongated cells and their nuclei appear as a single row
Functions include absorption, secretion, or transport
Often contain goblet cells Goblet cells secrete mucus onto apical surface
may be ciliated, or have microvilli, or have no modifications on apical surface.
goblet cell
columnar cells
microvilli “brush border”
Cilia beat constantly in a rhythmic motion to propel substances across the cell surface.
Cilia propels the egg through uterine tube
Simple Columnar Epithelium
Some simple columnar epithelium are covered with cilia on their free surface.
Microvilli are extensions of the cell membrane that increases the surface area of a cell.
Example of microvilli include the intestinal epithelium, where they increase the amount of contact each cell makes with food.
Microvilli greatly enhance absorption of nutrients.
Simple Columnar Epithelium
Some simple columnar epithelium are covered with microvili on their free surface.
Pseudostratified Columnar Epithelium (PSCE)
PSCE appear striated, but each cell touches the basement membrane.
Usually ciliated
Most PSCE contain goblet cells that secrete mucus
Locations of PSCE include the lining of the respiratory tract: nasal cavity, pharynx, trachea, bronchi
Functions: Mucus from goblet cells traps debris & cilia moves the mucus (and trapped debris) away from the lungs
Stratified Squamous Epithelium
Several layers of cells = thick tissue
Primary function is to protect underlying tissues from abrasion
Superficial cells are squamous but the deeper cells are cuboidal or columnar
May be keratinized or non-keratinized
Keratinized epithelium is found in the epidermis (outer layer) of skin
Keratin is an insoluble protein that hardens and forms a protective coating.
Cells accumulate keratin over time, so the older outermost cells of the epidermis are keratinized
Stratified squamous epithelium of epidermis
Keratinized Stratified Squamous Epithelium
Non-keratinized (moist) stratified squamous epithelium lines the esophagus, oral cavity, vagina, and anal canal.
Apical surface
Basal surfaceStratified squamous epithelium of vagina
Non-keratinized Stratified Squamous Epithelium
Transitional Epithelium
Transitional epithelium forms an expandable lining (Function: permit expansion)
Locations include the inner layer of the urinary bladder & ureters
The lining is several layers thick and the cells appear cuboidal when the urinary bladder is contracted, but only a few layers thick when the urinary bladder is distended and the cells appear squamous.
empty urinary bladder distended urinary bladder
Glandular Epithelium Glandular epithelium is specialized to produce & secrete substances
Glandular epithelium form glands
Exocrine GlandsExocrine glands secretes substances through ducts onto an open surface Examples includes goblet cells, sweat glands, and mammary glands
Duct of a sweat gland
Endocrine GlandsEndocrine glands secretes substances (hormones) directly into the blood stream.
Examples includes the thyroid gland, pituitary gland, adrenal glands, ect.
Follicles of thyroid gland are composed of simple cuboidal epithelium
Glandular Epithelium
End of Section 1, Chapter 5