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 makes 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 Function

Plasma 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 Function

Nucleolus Dark spherical body in the nucleus

Storehouse/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