Epithelial tissue: sheets of tightly packed cells that covers the outside of the body and lines organs and cavities within the body
-closely joined, the cells are riveted together by tight junctions
-The cells at the base of an epithelial layer are attached to a basement membrane- a dense mat of extracellular matrix
-free surface of the epithelium is exposed to air or fluid
Functions:
1. barrier protecting against mechanical injury, invasive microorganisms, and fluid loss
2. glandular epithelia-absorb or secrete chemical solutions
-lines the lumen of the digestive and respiratory tracts
-form a mucous membrane that secretes mucus (slimy solution)-->lubricates the surface and keeps it moist
Classification:
-classified by the number of cell layers and the shape of the cells on the free surface
1. simple epithelium has a single layer of cells
2. stratified epithelium has multiple tiers of cells
3. “pseudostratified” epithelium is single-layered but appears stratified because the cells vary in length
-shapes of cells on the exposed surface may be:
1. cuboidal (like dice)
2. columnar (like bricks on end)
3. squamous (flat like floor tiles)
-have a sparse population of cells scattered through an extracellular matrix
-matrix consists of a web of fibers embedding in a uniform foundation that may be liquid, jellylike, or solid
Classifications:
-three kinds of connective tissue fibers, which are all proteins:
1. collagenous fibers:
-made of collagen-the most abundant protein
-nonelastic and do not tear easily when pulled lengthwise
2. elastic fibers:
-long threads of elastin
-provides a rubbery quality that complements the nonelastic strength of collagenous fibers
3. reticular fibers:
-very thin and branched
-composed of collagen and continuous with collagenous fibers
-->form a tightly woven fabric that joins connective tissue to adjacent tissues
-major types of connective tissues in vertebrates:
1. loose connective tissue:
-binds epithelia to underlying tissues and functions as packing material, holding organs in place
-has all three fiber types
-Fibroblasts secrete the protein ingredients of the extracellular fibers
-Macrophages are amoeboid cells that roam the maze of fibers, engulfing bacteria and the debris of dead cells by phagocytosis
2. adipose tissue:
-a specialized form of loose connective tissue that stores fat in adipose cells distributed throughout the matrix
-pads and insulates the body and stores fuel as fat molecules
-Each adipose cell contains a large fat droplet that swells when fat is stored and shrinks when the body uses fat as fuel
3. fibrous connective tissue:
-dense, due to its large number of collagenous fibers
-fibers are organized into parallel bundles, an arrangement that maximizes nonelastic strength
-forms tendons, attaching muscles to bones, and ligaments, joining bones to bones at joints
4. cartilage:
-an abundance of collagenous fibers embedded in a rubbery matrix made of a substance called chondroitin sulfate, a protein-carbohydrate complex
-Chondrocytes secrete collagen and chondroitin sulfate
-The composite of collagenous fibers and chondroitin sulfate makes cartilage a strong yet somewhat flexible support material
-as flexible supports in certain locations, such as the nose, ears, and intervertebral disks
5. bone:
-The skeleton supporting most vertebrates is made of bone, a mineralized connective tissue
-osteoblasts (bone-forming cells) deposit a matrix of collagen
microscopic structure of hard mammalian bones consists of repeating units called osteons
-Each osteon has concentric layers of mineralized matrix deposited around a central canal containing blood vessels and nerves that service the bone
-Calcium, magnesium, and phosphate ions combine and harden within the matrix into the mineral hydroxyapatite
-combination of hard mineral and flexible collagen makes bone harder than cartilage without being brittle
6. blood:
-functions differently from other connective tissues, but it does have an extensive extracellular matrix
-matrix is a liquid called plasma-water, salts, dissolved proteins
-liquid matrix enables rapid transport of blood cells, nutrients, and wastes
-in the plasma are erythrocytes (red blood cells), leukocytes (white blood cells), and cell fragments called platelets
1. Red cells carry oxygen
2. White cells function in defense against viruses, bacteria, and other invaders
3. Platelets aid in blood clotting.
Muscle: composed of long cells called muscle fibers that are capable of contracting when stimulated by nerve impulses
-Arranged in parallel within the cytoplasm of muscle fibers are large numbers of myofibrils made of the contractile proteins actin and myosin
-most abundant tissue in most animals, and muscle contraction accounts for most of the energy-consuming cellular work in active animals
Classification:
-three types of muscle tissue in the vertebrate body:
1. skeletal muscle:
-attached to bones by tendons
-responsible for voluntary movements
-consists of bundles of long cells called fibers: each fiber is a bundle of strands called myofibrils
-striated muscle because the arrangement of contractile units, or sarcomeres, gives the cells a striped (striated) appearance
2. cardiac muscle:
-forms the contractile wall of the heart
-striated like skeletal muscle, and its contractile properties are similar to those of skeletal muscle
-carries out the unconscious task of contraction of the heart (unlike skeletal muscle)
-branch and interconnect via intercalated disks, which relay signals from cell to cell during a heartbeat
3. smooth muscle:
-lacks striations
-found in the walls of the digestive tract, urinary bladder, arteries, and other internal organs
-cells are spindle-shaped
-contract more slowly than skeletal muscles but can remain contracted longer
-controlled by different kinds of nerves than those controlling skeletal muscles-->responsible for involuntary body activities including
1. churning of the stomach
2. constriction of arteries
Nervous:
-senses stimuli and transmits signals from one part of the animal to another
-neuron (nerve cell)-functional unit of nervous tissue, which is uniquely specialized to transmit nerve impulses
-consists of a cell body and two or more processes called dendrites and axons
1. Dendrites-transmit impulses from their tips toward the rest of the neuron
2. Axons-transmit impulses toward another neuron or toward an effector, such as a muscle cell that carries out a body response
-In many animals, nervous tissue is concentrated in the brain
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