Chapter 3 cells and tissues

CHAPTER 3CELLS AND TISSUES

Cells – Cell Theory In 1665, and English scientist named

Robert Hooke looked at empty cork cells and identified the first cells

he used the word cell to describe the empty spaces in the cork

Cells – Cell Theory Robert Brown was the first

person to discover the nucleus: the cell part that controls most of the cell’s activities

Two German biologists Mathias Schleiden and Theodor Schwann formed the theory that all plants and animals are made up of cells

Cells – Cell Theory All these ideas combined into the

modern Cell Theory: 1. All living things are made of one or

more cells 2. Cells are the basic units of structure

and function 3. All cells come from existing cells

Cells – The basics All cells are primarily made of four

elements: Carbon, Oxygen, Hydrogen, Nitrogen

Living cells are about 60% water

Cells – Interstitial Fluid In addition to large amounts of water,

the body cells are constantly covered in a dilute saltwater solution called interstitial fluid

This fluid is derived from blood

Two main types of cells

Prokaryotic Cells Eukaryotic Cells

“pro” means before More primitive Lack a nucleus DNA is free floating

“eu” means true More complex Have a nucleus that

contain DNA Have organelles (“tiny

organs”)

What type of cell is this?

What about this one?

Cells – The generalized cell No one cell type is exactly like another Most do have the same parts Let’s talk about a generalized cell: a

basic cell used to demonstrate most cell features

Cells – The generalized cell

Cells – The generalized cell

The cell – The nucleus Nucleus: controls all of the cell’s

activities Contains DNA The “boss” of the cell Determines how and when

proteins are made Controls cell reproduction The nucleus usually conforms to

the shape of the cell

The cell – the nucleus Is enclosed by a nuclear membrane (or

nuclear envelope) Nuclear membrane: structure that

surrounds the nucleus and separates it from the rest of the cell

Nuclear pores: openings in the nuclear membrane that allows molecules to pass

Nucleoplasm: the jelly-like fluid between the two layers of the nuclear membrane

The cell – the nucleus Nucleolus: the center of the nucleus Some cells contain multiple nucleoli Contains the DNA Helps makes ribosomes Contains chromatin

The cell – the nucleus

Chromatin: a loose network of DNA combined with protein scattered throughout the nucleus

When a cell is dividing, the Chromatin condenses and coils to form chromosomes

Chromosomes: threadlike structures with information that determines traits a living thing will have

The cell – the nucleus

The cell – the plasma membrane

The cell – the plasma membrane Plasma membrane: a fragile, transparent barrier

that contains the cell contents and separates them from the surrounding environment

It is semi-permeable or selectively permeable which means it allows some things to pass while blocking others

The cell – the plasma membrane The plasma

membrane is a phospholipid bilayer

This means it has two layers of fats that line up tail to tail

The cell – the plasma membrane The phospholipids each

have a hydrophilic and a hydrophobic end

This allows the membrane to reseal itself quickly when damage occurs

A substantial amount of cholesterol is also found in the plasma membrane

The cell – the plasma membrane The proteins scattered in the lipid bilayer

are responsible for most of the membrane’s specialized functions

Ex. enzymes, hormone receptors, binding sites, protein channels, etc

The cell – Specializations of the plasma membrane

Let’s talk about microvilli and membrane junctions

Microvilli: tiny fingerlike projections that greatly increase the cell’s surface area to increase the rate of absorption

The cell – specializations of the plasma membrane Membrane junctions: specialized

connections between plasma membranes

Three main types are: 1. Tight junctions 2. Desmosomes 3. Gap junctions

The cell – membrane junctions 1. Tight junctions: impermeable junctions

that bind cells together into leakproof sheets that prevent substances from passing through the extracellular space between cells

Plasma membranes fuse together like a zipper

Ex. in the small intestine, these junctions prevent digestive enzymes from seeping into the bloodstream

The cell – membrane junctions Tight Junction

The cell – membrane junctions 2. Desmosomes: anchoring junctions that

prevent cells subjected to mechanical stress from being pulled apart

Structurally these junctions are buttonlike thickenings of adjacent plasma membranes (plaques), connected by fine protein filaments

Thicker protein filaments extend from the plaques inside the cells to the plaques on the cells’ opposite side, forming an internal system of strong wires

Ex. skin cells

The cell – membrane junctions Desmosomes

The cell – membrane junctions 3. Gap junctions: common to heart cells and

embryonic cells, these junctions function mainly to allow communication

Chemical molecules (nutrients, ions, etc) pass directly from one cell to another through the gap

In gap junctions, the neighboring cells are connected by connexons: hollow cylinders composed of proteins that span the entire width of the adjoining membranes

The cell – membrane junctions Gap junctions

The cell – the cytoplasm Cytoplasm: the cellular material outside

the nucleus and inside the plasma membrane

It is where most chemical reactions occur inside the cell

Made of three major elements: 1. the cytosol 2. the organelles 3. inclusions

The cell – the cytoplasm The cytosol is the semitransparent fluid

that suspends the other elements The organelles or “tiny organs” are the

machinery of the cell Inclusions are chemical substances that

may or may not be present, depend on the cell typeInclude stored nutrient, lipids, glycogen,

mucus, various crystallized products, etc

The cell – the cytoplasm

Organelles - Mitochondria Mitochondria: energy-producing

organelle in animal cells Consists of two membranes The outer is smooth and featureless The inner contains shelflike protrusions

called cristae

Organelles – Mitochondria Break down food through the

process of cellular respiration to form ATP molecules

ATP molecules provide the energy for all cellular work

“Busy” cells such as liver and muscles cells have larger amounts of mitochondria

Organelles - Ribosomes Ribosomes: tiny, bilobed, dark bodies

made of proteins and RNA Site of protein synthesis in the cell Two types:

Free – free floating in the cellBound/Attached – attached to the

Endoplasmic Reticulum

Organelles - Ribosomes Ribosomes: tiny particles of RNA and

protein The sight of protein synthesis Two types:

1. Free – free-floating in the cytoplasm2. Bound/Attached – found on the rough

Endoplasmic Reticulum

Organelles – Endoplasmic Reticulum Endoplasmic Reticulum: a system of

fluid-filled sacs and membranes located near the nucleus that packages and exports protein, lipids and other small molecules.

Accounts for about half of a cell’s membrane

Organelles – Endoplasmic Reticulum Endoplasmic Reticulum: a system of

fluid-filled canals (cisterns) that coil and twist through the cytoplasm

Accounts for about half the cell’s membranes

Provides a network of channels for carrying substances

Organelles – Endoplasmic Reticulum Two forms of the ER: 1. Rough ER: studded with ribosomes

All of the building materials of cellular membranes are formed either in or on it:

Proteins are packaged and sent out in transport vesicles

Greater number in organs that require more proteins,○ Ex. pancreas

Organelles – Endoplasmic Reticulum 2. Smooth ER: plays no role in protein

synthesis Functions in lipid metabolism and

detoxification Therefore there are many smooth ER in

liver cells

Organelles – Endoplasmic Reticulum

Organelles – Golgi Apparatus Golgi Apparatus: flattened stack of

membranous sacs that modifies and packages proteins and lipids

Forms secretory vesicles including lysosomes

Organelles - Lysosomes Lysosomes: small, enzyme-filled

organelles Digest worn-out cell structures, foreign

substances, etc Many in phagocytes, cells that dispose

of bacteria and debris

Organelles - Peroxisomes Peroxisomes: mebranous sacs

containing powerful oxidase enzymes that use molecular oxygen to detoxify a number of harmful or poisonous substances

Most important function is to “disarm” free radicals

Organelles - Peroxisomes Free radicals: highly reactive chemicals

with unpaired electrons that can scramble the structure of proteins and nucleic acids

Free radicals are usually produced by cellular respiration but if they accumulate they have devastating effects on the cell

Organelles - Peroxisomes Peroxisomes convert free radicals to

hydrogen peroxide Are created by budding from the Golgi

apparatus

Organelles - Cytoskeleton Cytoskeleton: an elaborate network of

protein the cell’s “bones and muscles” Determine:

Cell shapeSupports the organellesProvides the machinery needed for

intracellular transport and various types of cellular movement

Organelles - Cytoskeleton 3 types of cytoskeleton: 1. Microfilaments

Involved in cell motility and changes in cell shape

2. MicrotubulesDetermine the overall shape of a cell and

the distribution of organelles 3. Intermediate Filaments

Help form desmosomes, resist pulling forces on the cell

Organelles - Cytoskeleton

Organelles - Cytoskeleton Centrioles: rod-shaped bodies that lie at

right angles to each other Made up of fine microtubules Best known for their role in cell division (direct the formation of the mitotic

spindle)

Organelles - Cytoskeleton Some cells have projections known as

cilia and flagella Cilia: whiplike cellular extensions that

move substances along the cell surfaceEx. ciliated respiratory cells moving mucus

Flagella: substantialy longer projections formed by the centriolesonly flagellated human cell is a sperm cell

Organelles - Cytoskeleton

Cell Diversity

Cell Diversity 1. Cells that connect body parts 2. Cell that covers and lines body organs 3. Cells that move organs and body parts 4. Cells that stores nutrients 5. Cells that fight disease 6. Cells that gather information and controls

body functions 7. Cells of reproduction

1. Cells that connect body parts Fibroblast: most common connective

cells in animals Elongated shape Secretes cable-like fibers Produce large amounts of collagen Abundant rough ER and large Golgi

Apparatus (make and secrete necessary proteins

Important in wound healing

1. Cells that connect body parts Erthrocyte: red blood cell Carries oxygen in the bloodstream Concave disk shape

Extra surface area So much oxygen-carrying pigment

(hemoglobin) is packed in that other organelles have been excluded to make room

2. Cells that cover and line body organs

Epithelial cell Hexagonal shape Allows cells to pack

together Many intermediate

filaments that resist tearing

3. Cells that move organs and body parts Skeletal muscle and smooth muscle

cells Elongated Filled with many contractile filaments

Can shorten with great force○ Moves bone○ Change size of internal organs

4. Cells that store nutrients Fat cell (adipose cell) Large and spherical Produced by large lipid droplets in the

cytoplasm

5. Cells that fight disease Macrophage (phagocytic cell) Long, extendable pseudopods (“false

feet”) Crawl through tissue to reach infection

sites Lysosomes within the cell digest the

infectious microorganisms

6. Cells that gather information and control body functions Nerve cell (neuron) Has long processes for receiving and

transmitting messages Processes are covered with an

extensive plasma membrane Large rough ER to synthesize

membrane components

7. Cells of reproduction Oocyte (female): egg cell Largest cell in the body Contains several copies of all organelles

7. Cells of reproduction Sperm (male) Long and streamlined (built for

swimming) Flagellum acts as a motile whip to

propel the sperm

CELL PHYSIOLOGY

Membrane Transport The fluid environment on both sides of

the plasma membrane is an example of a solution.

Solution: a homogeneous mixture of two or more components

Membrane Transport - solutions Every solution is made of two major

components – a solvent and solutes Solvent: the substance present in the

largest amount that does the dissolvingUsually a fluid (liquid or gas)

Solute(s): the substance(s) present in smaller amount that get dissolved

Membrane Transport

Intracellular Fluid: a solution containing small amounts of gases, nutrients, and salts dissolved in water

Interstitial Fluid: the fluid that continuously bathes the exterior of our cellsA rich, nutritious “soup”Contains amino acids, sugars, fatty acids, vitamins, etc

Membrane Transport Quick reminder! Plasma membranes are selectively or

semi-permeable This means they let some things pass

while blocking others

Membrane Transport Movement of substances through the

plasma membrane happens two ways1. Passive Transport2. Active Transport

Passive Transport Passive Transport: movement in which

substances are transported across the membrane without energy input from the cell

Passive Transport Diffusion: the

movement of particles from an area of high concentration to an area of low concentration

High to Low, Go with the Flow!

Passive Transport The particles are said to

move down their concentration gradient: the gradual change in the concentration of solutes in a solution

Speed of diffusion is affected by the size of the molecules (smaller = faster) and temperature (warmer = faster)

Passive Transport The hydrophobic core of the plasma

membrane makes it a physical barrier to diffusion

Particles will still diffuse if:1. they are small enough to pass through

the membrane pores2. they can dissolve in the fatty portion of

the membrane 3. they are assisted by a membrane carrier

Passive Transport Simple diffusion:

unassisted diffusion of solutes through the plasma membrane

Facilitated diffusion: provides passage for certain needed substances that are both lipid-insoluble and too large to pass through the pores

Passive Transport Although facilitated diffusion follows the

laws of diffusion, a protein membrane channel is used

This acts as a transport vehicle

Passive Transport Substances that

pass into and out of cells by diffusion save energy

Includes the movement of key molecules like water, glucose, oxygen and carbon dioxide

Passive Transport Osmosis: the diffusion of water

across a selectively permeable membrane

Remember water is highly polar and is repelled by the non-polar core of the membrane, so it must pass through aquaporins

aquaporins: special pores created by membrane proteins that allow osmosis to occur

Passive Transport Filtration: the process by which water

and solutes are forced through a membrane by fluid, or hydrostatic pressure

In the body, this is usually seen in blood

Passive Transport This is a passive process The gradient however, is the pressure

gradient that pushes solute-containing fluid (the filtrate) from high-pressure areas to low pressure areas

Important to kidneys

Active Transport Whenever a cell uses some of its ATP

supply to move substances across the membrane, the process is considered active

Active Transport: also called solute pumping, requires ATP –energized protein carriers to transport substances across the membrane

Active Transport The ATP-energized protein carriers used

in active transport are called solute pumps Amino acids, some sugars, and most ions

are transported across the membrane in this way

And in most cases, they travel against the concentration gradient

This is opposite to the direction in which substances would normally flow

Active Transport Movement against the concentration

gradient requires energy (ATP) Ex. Sodium-Potassium Pump Simultaneously carries Sodium (Na+)

ions out of the cell and Potassium (K+) ions into the cell

The Na-K Pump is essential for normal nerve cell transmissions

Active Transport

Vesicular Transport Vesicular transport: moves substances

in or out of cells without their actually crossing the plasma membrane

Requires ATP

Vesicular Transport Two main types:

1. Endocytosis2. Exocytosis

Vesicular Transport

Endocytosis Exocytosis

Endocytosis take up, or engulf, extracellular substances by enclosing them in a small membrane vesicle

Once the vesicle, or sac, is formed, it detaches from the plasma membrane and moves into the cytoplasm, where it fuses with a lysosome and its contents are digested

Exocytosis moves substances out of cells

Is how cells actively secrete hormones, mucus and other products

Products are packed in small vesicles or sac

The sac migrates to the plasma membrane and fuses

The contents are then spilled outwards

Vesicular Transport Three types of endocytosis: 1. phagocytosis: “cell eating”

Ingestion of solid substances 2. pinocytosis: “cell drinking”

Ingestion of liquid substances 3. Receptor-mediated endocytosis: main

cellular mechanism for taking up specific target moleculesBoth receptor and the target molecule are taken

into the vesicle

Vesicular Transport

CELL DIVISIONMITOSIS

Cell Division The cell life cycle is the series of

changes a cell goes through from the time it is formed until it divides

The cycle has two major periods: 1. Interphase, in which the cell grows

and carries on it usual metabolic activities

2. Cell Division, time when the cell reproduces itself

Cell Division – Cell Cycle

Cell Division - Interphase Interphase has three major stages 1. G1 – Growth 1

Cell increases in size 2. S – Synthesis

DNA and organelles are replicated 3. G2 – Growth 2

Continued cell growth before division

Cell Division - Interphase

Cell Division Mitosis: division of the nucleus Cytokinesis: division of the cytoplasm

Cell Division Mitosis is divided into

four major phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase And results in two

identical daughter cells

1. Prophase As cell division begins, the chromatin

threads condense to form barlike bodies called chromosomes (“colored bodies”)

1. Prophase The centrioles separate from each other

and begin to move to opposite sides (“poles”) of the cell

The direct the assembly of the mitotic spindle

The mitotic spindle provides the structure for attachment and movement of the chromosomes for the duration of mitosis

1. Prophase The nuclear envelope and nucleoli break

down and disappear Chromosome attach randomly to spindle

fibers at the centromere

2. Metaphase The chromosome cluster and align

along the metaphase plate (center of the spindle midway)

Creates a straight line of chromosomes

3. Anaphase The centromeres split The sister chromatids split (now called

chromosomes again) Chromatids move to opposite poles of the

cell When chromosome movement ends

4. Telophase Essentially prophase in reverse Chromosomes uncoil and become

chromatin again Spindle fibers break down and

disappear Nuclear envelopes reform and nucleoli

reappear around each group of chromatin

4. Telophase

Cytokinesis Cytokinesis usually begins during late

anaphase and finishes in telophase A contractile ring of microfilaments forms

a cleavage furrow over the midline of the spindle

This squeezes the original cytoplasmic mass into two parts

Each daughter cell is smaller, but genetically identical

Cytokinesis

Mitosis and Cytokinesis Mitosis and Cytokinesis usually go

together, but sometimes the cytoplasm does not divide

This creates binucleated or multinucleated cells

This is common in liver cells

PROTEIN SYNTHESISTranscription and Translation

Protein Synthesis DNA is the blueprint for protein

synthesis A gene is defined as the DNA segment

that carries the information for building one protein of a poly peptide chain

Protein Synthesis - RNA DNA requires a messenger and a

decoder to complete the building of proteins

These jobs are carried our by RNA There are three varieties of RNA

involved in protein synthesis:1. transfer RNA (tRNA)2. ribosomal RNA (rRNA)3. messenger RNA (mRNA)

Protein Synthesis Protein Synthesis occurs in two major

phases:1. Transcription – when complementary

mRNA is made at the DNA gene2. Translation – when the information carried

in the mRNA molecules is “decoded” and used to assemble proteins

Protein Synthesis - Transcription Transcription involves the

transfer of information from DNA’s base sequence into the complementary base sequence of mRNA

Occurs in the nucleus Only DNA and mRNA are

involved in transcription Each DNA triplet (three-base

sequence) complements a mRNA codon

Protein Synthesis - Transcription So if the DNA sequence is: ATG – TCT – GAA (triplets) The transcribed mRNA sequence is: UAC – AGA – CUU (codons)

Protein Synthesis - Translation In translation the language

of nucleic acids (the base sequence) is “translated” into the language of proteins (amino acids)

Occurs in the cytoplasm Involves three major

varieties of RNA

Protein Synthesis - Translation Once the mRNA attaches to the

ribosome, tRNA comes into the picture Each tRNA carries or “transfers” an

amino acid to the ribosome They match a three-base anticodon

with the codon of the mRNA as it reads through the ribsome

Protein Synthesis - Translation

Protein Synthesis - Translation Once the first tRNA has moved itself into the

correct position, the ribosome moves the mRNA strand along, bringing the next codon into position to be read by the tRNA

As each amino acid is brought in, they are joined together by enzymes

As the amino acids join, each tRNA is released

When the last codon, or “stop” codon is read, the protein is released

Protein Synthesis

BODY TISSUES

Body Tissues Tissues: groups of cells that are similar

in structure and function Four primary tissue types: 1. Epithelial (covering) 2. Connective (support) 3. Muscular (movement) 4. Nervous (control)

Epithelial Tissues Epithelial Tissue (epithelium): the lining,

covering and glandular tissue of the body

Helps form boundaries and separate Nearly all substances the body gives off

or receives must pass through the epithelium

Epithelial Tissues Functions of the epithelium: Protection Absorption Filtration Secretion

Epithelial Tissues - Characteristics 1. Fit closely together (except glandular cells)

Bound together by many desmosomes and tight junctions

2. One free edge or surfaceApical surface

3. Lower surface rests on a basement membrane

4. No blood supply of their ownAvascularDepend on diffusion from the capillaries

5. Regenerate themselves, if well nourished

Epithelial Tissues - Classification Each epithelium is given two names The first indicates the relative number of

cell layers

Epithelial Tissues - Classification The classifications by cell arrangement are: Simple epithelium – one layer Stratified epithelium – more than one layer

Epithelial Tissues - Classification The second indicates the shape of the

cell. There are: Squamous – flattened like scales Cuboidal – Cube-shaped Columnar – Column-shaped (stratified epithelia are named for the

cells at the free surface not those on the basement membrane)

Epithelial Tissues - Classification

Epithelial Function Simple Epithelia are concerned mainly

with absorption, secretion and filtration

Stratified epithelia function primarily to protect

Glandular Epithelium A gland consists of one or more cells

that make and secrete a particular product

This product is called a secretion Usually consists of protein molecules in

an aqueous solution fluid

Glandular Epithelium Two major types of glands develop from

epithelial sheets: 1. Endocrine glands 2. Exocrine glands

Endocrine Glands Endocrine glands: glands

that lose their connection to the surface or duct (also called ductless glands)

Secretions diffuse directly into the blood vessels that weave through the gland

Ex. thyroid, adrenals, pituitary

Exocrine Glands Exocrine glands:

gland that retain their ducts

Secretions empty through the ducts to the epithelial surface

Ex. sweat and oil glands, liver, pancreas

Glandular Epithelium The term secretion

also indicates an active process in which the glandular cells obtain needed materials from the blood and use them to make their secretion, which they then discharge

CONNECTIVE TISSUE

Connective Tissue Connective Tissue: connects body parts Found everywhere in the body Most abundant and widely distributed of

the tissue types

Connective Tissue The characteristics of connective tissue

include: 1. Variations in blood supply

Most connective tissue is well vascularizedExceptions – Ligaments, Tendons, Cartilages

○ As a result these heal very slowly 2. Extracellular Matrix

Varying amounts of a nonliving substance outside the cells

Connective Tissue The extracellular matrix distinguishes

connective tissue from other cell types Has two main elements – a structureless

ground substance and fibers

Connective Tissue The ground substance of the matrix is

composed largely of water plus some adhesion proteins and large, charged polysaccharides

The adhesion proteins are the “glue” that allows the connective tissues to attach themselves to matrix fibers embedded in the ground substance

The charged polysaccharides trap water as they intertwine

Connective Tissue Various types and amounts of fibers are

in the matrix and form parts of the matrix itself

Including collagen (white) fibers, elastic (yellow) fibers and reticular (fine collagen) fibers

Connective Tissues Because of the extracellular matrix,

connective tissue can form soft packing tissue around organs, bear weight, and withstand stretching and other abuses

Connective Tissue There is great variation in connective

tissue The major classes are: Bone Cartilage Dense Connective Loose Connective Blood

Connective Tissue - Bone Bone (osseous tissue) Composed on bone cells sitting in

cavities called lacunae (pits) and surrounded by layers of a very hard matrix that contains calcium salts and large numbers of collagen fibers

Important in protecting and supporting other body organs

Connective Tissue - Bone

Connective Tissue - Cartilage Less hard and more flexible than bone Found a few places in the body Most widespread is hyaline cartilage:

abundant collagen fibers hidden by a rubbery matrix with a glassy blue-white appearance

Connective Tissue - Cartilage Forms supporting structures in the

larynx, attaches ribs to the breastbone, covers ends of bones at joints

Connective Tissue There are other types of cartilage: Fibrocartilage: highly compressible that

forms the cushionlike disks between the vertebrae of the spinal column

Elastic cartilage: is found where a structure where elasticity is desired

Ex. external ear

Connective Tissue Dense Connective Tissue:

collagen fibers as its main matrix element

Crowded between the collagen fibers are rows of fibroblasts that manufacture the building blocks of the fibers

Forms tendons and ligaments

Connective Tissue Tendons: attach skeletal muscles to

bones Ligaments: connect bones to bones at

joints Ligaments are more stretchy and elastic

than tendons

Connective Tissue Loose Connective Tissue: softer, have

more cells and fewer fibers Areolar Tissue: most widely distributed

connective tissue variety in the body Cushions and protects body organs

Connective Tissue When a body region is inflamed, the

areolar tissue in the area soaks up the excess fluid like a sponge, and the area swells and becomes puffy

This is called an edema

Connective Tissue Adipose Tissue:

commonly called fat, areolar tissue in which fat cells predominate

Forms subcutaneous tissue

Connective Tissue Reticular connective tissue: a delicate

network of interwoven reticular fibers associated with reticular cells, which resemble fibroblasts

Forms stroma, the internal framework which can support many free blood cells and in lymphoid organs

Connective Tissue Blood: (vascular tissue) is

considered connective tissue because it consists of blood cells surrounded by nonliving, fluid matrix called blood plasma

The “fibers” of blood are soluble protein molecules that become visible only during blood clotting

Muscle Tissue Muscle tissue: highly specialized to

contract, or shorten, to produce movement

Muscle Tissue Three main types: 1. skeletal muscle 2. cardiac muscle 3. smooth muscle

Muscle Tissue Skeletal Muscle attached to the skeleton can be controlled voluntarily when contracted they pull on

bones or skin the cells of skeletal muscle

are long, cylindrical, multinucleate and have obvious striations

Muscle Tissue Cardiac Muscle Found only in the heart As it contracts, the heart acts as a pump and

propels blood through the blood vessels Has striations Uninucleate, relatively short, branching, and

fit tightly together through intercalated disks Under involuntary control

Muscle Tissue

Muscle Tissue Smooth Muscle (visceral muscle) No visible striations Single nucleus, spindle-shaped Found in the walls of hollow organs As it contracts, the cavity of an organ

contracts or enlarges Contracts more slowly than the other two

types Ex. peristalsis

Nervous Tissue Think neurons All neurons receive and conduct

electrochemical impulses from one part of the body to another

Irritability and conductivity are their two major functional characteristics

Nervous Tissue Drawn out cytoplasm, allow for long

signal transmission With supporting cells, neurons make up

the structures of the nervous system

TISSUE REPAIR

Tissue Repair Tissue repair occurs in two major ways: Regeneration – replacement of

destroyed tissue by the same kind of cells

Fibrosis – involves repair by dense connective tissue by the formation of scar tissueDepends on the type of tissue damaged and

the severity of the injury

Tissue Repair Tissue injury sets the following steps in

motion: 1. capillaries become permeable

Fluid rich in clotting proteins seep into the injured areas

2. granulation tissue formsDelicate pink tissue composed largely of new

capillaries 3. surface epithelium regenerates

Makes its way across the granulation tissue

Tissue Repair

Three other important terms: Neoplasm: an abnormal mass of

proliferating cells Benign or malignant

Hyperplasia: when certain body tissues may enlarge because there is some local irritant or condition that stimulates the cells

Atrophy: a decrease in size in an organ or body area that loses its normal stimulation