Cells and Tissues
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Transcript of Cells and Tissues
Cells and TissuesUnit 2
Cells are primarily made of 4 elements:◦ Carbon, oxygen, hydrogen, and nitrogen◦ Water (H2O) is the most abundant substance
Also contain small amounts of other elements:◦ Calcium for blood clotting◦ Iron for hemoglobin, which carries oxygen in blood◦ Iodine used to make thyroid hormone that controls
metabolism◦ Metals (calcium, sodium, potassium, etc.) can carry
electrical charge electrolytes that are essential for nerve impulses
Overview of the Cellular Basis of Life
In multicellular organisms, cells can be specialized to perform specific tasks
However, all cells are able to perform the following functions:◦ Metabolism◦ Reproduction◦ Irritability◦ Mobility◦ Grow◦ Digestion◦ Excretion
Cell Functions
Cubelike Tilelike Disk-shaped Round spheres Branching Cylindrical
Different Cell Shapes
Surrounds all cells Contains salt and other materials similar
to sea water
Interstitial fluid
A cell’s structure greatly impacts its function◦ Neurons (nerve cells) have long processes for
receiving and transmitting messages and are covered with an extensive plasma membrane.
◦ Fat cells are large and spherical due to a large lipid droplet in their cytoplasm.
◦ Squamous epithelial cells are flat and fit together like tiles in order to protect the body.
◦ Skeletal muscle cells are elongated and filled with contractile filaments to help facilitate mobility.
Structure and function
Cell Structure Location FunctionPlasma membrane
External boundary of the cell
Confines cell contents; regulates entry and exit of minerals
Lysosomes Scattered in cytoplasm Digest ingested materials and worn-out organelles
Mitochondria Scattered throughout the cell
Control release of energy from foods; form ATP
Microvilli Projections of the plasma membrane
Increase the membrane surface area
Golgi apparatus Near the nucleus (in the cytoplasm)
Packages proteins to be incorporated into the plasma membrane or lysosomes or exported from the cell
Nucleus (Usually) center of the cell
Storehouse of genetic information; directs cellular activities, including division
Centrioles Two rod-shaped bodies near the nucleus
Direct formation of the mitotic spindle
Anatomy of a cell
Cell Structure Location FunctionNucleolus Dark spherical body in the
nucleusStorehouse/assembly site for ribosomes
Smooth ER In the cytoplasm Site of steroid synthesis and lipid metabolism
Rough ER In the cytoplasm Transports proteins (made on its ribosomes) to other sites in the cell; synthesizes membrane lipids
Ribosomes Attached to membrane systems or scattered in the cytoplasm
Synthesize proteins
Chromatin Dispersed in the nucleus Contains genetic material (DNA); coils during mitosis
Peroxisomes Scattered in cytoplasm Detoxify alcohol, hydrogen peroxide, etc.
Inclusions Dispersed in the cytoplasm Provide nutrients; represent cell waste, stored products, etc.
Anatomy of a cell
Anatomy of a cell
Cells come together to form tissues, joined at cell junctions
Types of junctions:◦ Tight junctions – impermeable, bind cells into leak-proof
sheets. Adjacent plasma membranes fuse together tightly like a zipper.
◦ Desmosomes – anchoring junctions that prevent cells from being pulled apart. Button-like thickenings of adjacent plasma membranes, which are connected by fine protein filaments.
◦ Gap junctions – allow communication, chemical molecules can pass from one cell to another, neighboring cells are connected by connexons, hollow cylinders composed of protein.
From cells to tissues
Epithelial – lining, covering, glandular Connective – connects body parts Muscle – able to contract (shorten) Nervous – conduct electrochemical impulses
from one part of the body to another irritability and conductivity
Types of tissues
Cells fit closely together to form continuous sheets Neighboring cells are bound together at cell junctions
Membranes always have one free (unattached) edge = apical surface exposed to exterior OR cavity of internal organ
Lower surface rests on basement membrane, a structureless material secreted by the cells
Don’t have a blood supply of their own rely on diffusion from capillaries
Epithelial tissue
Named for cells at the free surface, not those at basement membrane◦ Simple epithelium =
one layer of cells◦ Stratified epithelium =
more than one cell layer◦ Squamous cells =
flattened◦ Cuboidal = cube-shaped◦ Columnar = shaped like
columns
Epithelial tissue
Single layer of thin squamous cells resting on a basement membrane
Fit closely together, like floor tiles Usually found where filtration occurs or
where substances are exchanged through rapid diffusion
Example: Air sacs of lungs and walls of capillaries
Simple squamous epithelium
Single layer of cuboidal cells resting on a basement membrane
Common in glands and their ducts Forms walls of kidney tubules and covers
surface of ovaries
Simple cuboidal epithelium
Single layer of tall cells that fit closely together
Line the entire length of the digestive tract from stomach to anus
Simple columnar epithelium
All of the cells rest on a basement membrane, however, some appear shorter than others
False impression of stratification Lines the respiratory tract
Pseudostratified columnar epithelium
Consists of several layers of squamous cells Most common stratified epithelium in the
body Outer portion of skin, esophagus
Stratified squamous epithelium
Usually only two layers of cells that are cuboidal or columnar in shape
Fairly rare in the body, found mainly in the ducts of large glands
Stratified cuboidal and stratified columnar epithelia
Highly modified, stratified squamous epithelium that forms the lining of only a few organs
Urinary bladder, ureters, part of urethra all part of urinary system
Transitional epithelium
Glands make and secrete a particular product
Endocrine glands – “ductless” glands secrete directly into blood stream
Exocrine glands – secrete through ducts to the epithelial surface
Glandular epithelium
Connects body parts Most abundant and widely distributed of
tissues Most have a good blood supply, but there
are some exceptions, such as tendons, ligaments, and cartilages
Extracellular matrix – nonliving substance found outside of the cells
Connective tissue
Osseous tissue bone cells sitting in cavities called lacunae and surrounded by layers of a very hard matrix that contains calcium salts and collagen fibers
Very hard protects and supports body
Bone
Less hard and more flexible than bone Hyaline cartilage = abundant
collagen fibers hidden by a rubbery matrix; forms larynx, attaches ribs to sternum, and covers ends of bones where they form joints
Fibrocartilage = cushionlike discs between vertebrae of spinal column
Elastic cartilage = found where a structure with elasticity is desired, such as the external ear
Cartilage
Collagen fibers = main matrix element Fibroblasts = fiber-forming cells located
between collagen fibers Forms strong, ropelike structures such as
tendons (attach skeletal muscles to bones) and ligaments (connect bones to bones)
Dense connective tissue
Softer, more cells, fewer fibers Areolar tissue – cushions and
protects body organs, helps hold them together and in place, acts as a sponge and soaks up excess fluid
Adipose tissue – “fat,” forms subcutaneous tissue beneath the skin, insulates body and protects some organs, acts as fuel if needed
Reticular connective tissue – delicate network of interwoven fibers that helps support many free blood cells in lymphoid organs
Loose connective tissue
Blood is considered a connective tissue because it consists of blood cells surrounded by a nonliving, fluid matrix called plasma
The “fibers” are soluble protein molecules visible during clotting
Carries nutrients, wastes, respiratory gases, and many other substances
Blood
Specialized to contract, or shorten Three types:
◦ Skeletal◦ Cardiac◦ Smooth
Muscle tissue
Packaged by connective tissue sheets into organs called skeletal muscles
These muscles can be controlled voluntarily When they contract, they pull on bones or
skin Cells are long, cylindrical, and multinucleate Obvious striations (stripes)
Skeletal muscle
Found only in the heart Has striations like skeletal muscle, but the cells
only have one nucleus Branching cells fit tightly together like clasped
fingers at junctions called intercalated disks Contain gap junctions that allow ions to pass freely
from cell to cell, resulting in rapid conduction of the electrical impulses
Involuntary control
Cardiac muscle
No striations Cells have a single nucleus and are spindle
shaped Found in the walls of hollow organs, such as
the stomach, bladder, uterus, and blood vessels
Smooth muscle contractions help propel substances through an organ
Involuntary contractions
Smooth muscle
Neurons – cells that receive and send electrochemical signals from one part of the body to another
Cytoplasm is drawn out into long extensions, which allows a single neuron to conduct an impulse over long distances
Nervous tissue
Regeneration = replacement of destroyed tissue by the same kind of cells
Fibrosis = repair by dense (fibrous) connective tissue scar tissue
Depends on what type of tissue is damaged and the severity of the injury
Tissue Repair
3 things happen:◦ 1. Capillaries become permeable and “leak”
clotting factors.◦ 2. Granulation tissue forms, spreading new
capillaries that attach to nearby blood vessels. These new capillaries are weak and bleed easily (think about picking a scab).
◦ 3. The surface epithelium regenerates beneath the scab, which eventually falls off.
Tissue Repair
Neoplasm = “new growth,” cells divide rapidly without control tumors, cancer, etc.
Hyperplasia = temporary growth or enlargement
Atrophy = a decrease in size and strength due to lack of stimulation
Things that can happen to tissues and cells…