6. animal tissues

7/21/2019 6. Animal Tissues

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Tissues are groups of specialized cells that work together for a

particular function.

There are four types of tissue.

Epithelial(covering) Connective (support)

Muscle(movement)

Nervous(control)


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Epithelial tissues cover body surfaces.

Outer layer of skin and the lining of organs

Also found in glandular tissue

Play roles in absorption, filtration, secretion, and protection

against foreign substances


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Usually fit closely together in continuoussheets

Exception: glandular epithelium

Avascular(Have no blood supply of theirown)

How do they get nutrients?

If well nourished, epithelial cells

regeneratethemselves easily.


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Have one free (unattached) surface or

edge called the apical surface

Exposed to bodys exterior or to the

cavity of an internal organ

Lower surface of an epithelium rests

on a basement membrane

Structureless material secreted by

both the epithelial cells and the

connective tissue cells


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Each epithelium is given 2 names

First: indicates relative number of

CELL LAYERS

Simple(one layer of cells)

Stratified(more than one cell

layer)


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Second: describes the SHAPE OFCELLS

Squamous(cells flattened likescales)

Cuboidal(cube-shaped)

Columnar(shaped like columns)


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Simple squamous (SS) tissue is composed of flat, scale-like cellsthat usually forms membranes

It lines the walls of blood vessels, pulmonary alveoli (ss), and thelining of the heart, lung, and peritoneal cavities.


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This tissue is composed of a single layer of cube-like cells. It lines the walls of kidney tubules, covers the surface of ovaries,and is common in glands and their ducts.


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This tissue is composed of a single layer of tall cells. It often includes mucus-producing goblet cells.

It often lines the digestive tract.


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Although this tissue appears stratified,it is actually composed of a single layerof cells of different types.

Although their nuclei are found at

different levels, each cell adjoins thebasal membrane (BM).

This tissue lines the larger respiratorypassageways.

It is often ciliated (arrows).


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Main functions: absorption and secretion Ciliated variety lines respiratory tract

Mucus produced by goblet cellstrapsdust and other debris

Cilia propel mucus upward and away from the lungs


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The term stratifiedrefers to the layered arrangement of cells.

The outer layers of cells appear flat, but the inner cells vary in shapefrom cuboidal to columnar.

Stratified squamous epithelium serves as a barrier to the outsideenvironment in locations such as the skin, mouth, and esophagus.


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Stratified cuboidal epithelium (SC) is found in the ducts of sweatglands and surrounds Graafian follicles of ovaries(shown below).


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Shape of cells depends upon the amount of stretching It lines organs of the urinary system.


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Some epithelial membranes are

made up of cells with cilia, tiny

projections that beat in unison to

move mucus along the surface.

Ciliated epithelia in the trachea,

for example, sweep debris out of

the respiratory tract.


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A gland is defined as one or more cells responsible for secreting aparticular product

Two major gland types

Exocrine gland

Secretions empty through ducts to the epithelial surface

Include sweat and oil glands

Endocrine gland

Ductless since secretions diffuse into blood vessels

All secretions are hormones

Examples include pituitary, pancreas, ovaries, testes


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Connective tissue differs from other tissues in that it contains large

amounts of extracellular matrix.

Extracellular matrix is nonliving material that surrounds living cellsIt is found everywhere and includes the most abundant and widely

distributed tissue


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Connective tissues function to

bind other tissues together

provide support

provide nourishment

store wastes repair damaged tissues

These tissues are generally well vascularized

Exceptions: tendons, ligaments, cartilage The exceptions are avascular


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Two main elements:

Ground substance

Mostly water along with

glycoproteins and large

polysaccharide molecules

May be liquid, gel-like, or rock-hard

Fibers

Collagen fibers (high strength)

Elastic fibers (stretch and recoil) Reticular fibers (fine fibers, internal

skeleton)


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Bone

Various types of cartilage

Adipose tissue Dense and loose connective tissue

Blood


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Composed of

Bone cells in lacunae (cavities)

Hard matrix of calcium salts

Large numbers of collagen fibers

Used to protect and support the body


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Most common type of cartilage

Composed ofcollagen fibers hidden by a rubbery matrix with a

glassy blue-white appearance

Found in the larynx, attaches ribs to sternum, at the end of

many bones

Entire fetal skeleton before birth


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Elastic

Provides elasticity

Supports the external ear

Fibrocartilage

Highly compressible Forms cushion-like discs between

vertebrate


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Dense connective tissue contains a large number of fibers with

only a few cells. Fibers shown here are all running parallel to each other, and no

cells are present.

Tendons (muscle to bone) and ligaments (bone to bone) arecomposed of dense connective tissue.


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Loose connective tissue has few fibers, a number of cell types,

and a large amount of matrix. It functions to bind epithelia to underlying tissues.

Includes areolar, adipose, & reticular connective


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Most widely distributed connectivetissue

Soft, pliable cobwebby tissue thatcushions and protects the bodys

organs it wraps

Holds internal organs together and intheir proper positions

Under microscope: matrix appears asempty space, reservoir of water andsalts


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When a body region is inflamed, the areolar tissue in the area soaks

up the excess fluid like a sponge, and the area swells andbecomes puffy.


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Adipose cells are bundled together by connective tissue.

Each cell appears as a clear space, representing the site of thelarge drop of lipid (fat) before it dissolved during preparation ofthe microscope slide.

The nuclei appear as small disks on the periphery of cells.

Functions to insulate the body, protect organs, and fuel storage


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Consists of a delicate network of interwoven reticular fibers Forms the stroma(internal framework) which can support free blood

cells in lymphoid organs (lymph nodes, spleen, & bone marrow)


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Consists of blood cells surrounded by nonliving, fluid matrix

called blood plasma Fibersonly visible during blood clotting

Functions as a transport medium for materials


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Muscle is a contractile tissue.

There are three types of muscle:

Skeletal

Cardiac Smooth

Main function is to produce movement.


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Under voluntarycontrol

Contracts to pull on bones or skin Produces gross body movements or facial expressions

Characteristics of skeletal muscle cells

Striated (stripe-like pattern)

Multinucleate (more than one nucleus)

Long, cylindrical


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Under involuntarycontrol

Found only in the heart Function is to pump blood

Characteristics of cardiac muscle cells

Cells are attached to other cardiac muscle cells at

intercalateddisks

Striated

One nucleus/cell


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Under involuntarymuscle

Found in walls of hollow organs such as stomach, uterus, andblood vessels

Characteristics of smooth muscle cells

No visible striations

One nucleus/cell Spindle-shaped cells


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Nervous tissue, which occurs throughout the body, receives and

transmits stimuli. It converts a stimulus, whether chemical or physical in nature,

into an electrical impulse that is conducted by neurons.

Nervous tissue also consists of glia, which are the various types

of supporting cells in the nervous system.


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The surface of the cerebellum is

highly fissured. Outer layer is the molecular layer,

which contains some glial cells but

consists mostly of neuronal processes

(dendrites and axons).

Darkly stained area is the granularlayer and is composed mostly of

nerve cell bodies of tiny granule cells

(a neuron type) along with some

larger Golgi cells (another neuron

type). Between the molecular and granular

layers lies the Purkinje layer.


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Immunohistochemistry is used to reveal BrdU (brown), athymidine analog that is incorporated in cells undergoing S phase. Cellsstained brown were caught in the act of DNA synthesis. These cells arefound in the hippocampus, one of the only brain regions where newneurons are formed.

(One example)


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Immunofluorescence labeling shows new neurons in the hippocampus.

Green is BrdU (the marker that labels cells undergoing S phase), red is a

NeuN (a neuron-specific marker), and blue is GFAP (a glial marker). Cells

co-labeled green and red are new neurons.


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6. animal tissues

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