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Cells and Tissues. Unit 2. Overview of the Cellular Basis of Life. Cells are primarily made of 4 elements: Carbon, oxygen, hydrogen, and nitrogen Water (H 2 O is the most abundant substance Also contain small amounts of other elements: Calcium for blood clotting

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Cells and Tissues

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overview of the cellular basis of life
Overview of the Cellular Basis of Life
  • 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
cell functions
Cell Functions
  • 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
different cell shapes
Different Cell Shapes
  • Cubelike
  • Tilelike
  • Disk-shaped
  • Round spheres
  • Branching
  • Cylindrical
interstitial fluid
Interstitial fluid
  • Surrounds all cells
  • Contains salt and other materials  similar to sea water
structure and function
Structure and function
  • 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.
from cells to tissues
From cells to tissues
  • 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.
types of tissues
Types of 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
epithelial tissue
Epithelial tissue
  • 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 tissue1
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
simple squamous epithelium
Simple squamous epithelium
  • 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 cuboidal epithelium
Simple cuboidal 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 columnar epithelium
Simple columnar epithelium
  • Single layer of tall cells that fit closely together
  • Line the entire length of the digestive tract from stomach to anus
pseudostratified columnar epithelium
Pseudostratified 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
stratified squamous epithelium
Stratified squamous epithelium
  • Consists of several layers of squamous cells
  • Most common stratified epithelium in the body
  • Outer portion of skin, esophagus
stratified cuboidal and stratified columnar epithelia
Stratified cuboidal and stratified columnar epithelia
  • 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
transitional epithelium
Transitional epithelium
  • 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
glandular epithelium
Glandular 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
connective tissue
Connective tissue
  • 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
  • Osseous tissue  bone cells sitting in cavities called lacunaeand surrounded by layers of a very hard matrix that contains calcium salts and collagen fibers
  • Very hard  protects and supports body
  • 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
dense connective tissue
Dense connective tissue
  • 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)
loose connective tissue
Loose 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
  • 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
muscle tissue
Muscle tissue
  • Specialized to contract, or shorten
  • Three types:
    • Skeletal
    • Cardiac
    • Smooth
skeletal muscle
Skeletal muscle
  • 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)
cardiac muscle
Cardiac 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
smooth muscle
Smooth 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
nervous tissue
Nervous tissue
  • 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