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Lecture Presentation by

Patty Bostwick-Taylor

Florence-Darlington Technical College

Chapter 3

Cells and Tissues

© 2015 Pearson Education, Inc.

Cells

Cells are the structural units of all living things

The human body has 50 to 100 trillion cells


Four Concepts of the Cell Theory

1. A cell is the basic structural and functional unit of

living organisms.

2. The activity of an organism depends on the

collective activities of its cells.

3. According to the principle of complementarity, the

biochemical activities of cells are dictated by the

relative number of their specific subcellular

structures.

4. Continuity of life has a cellular basis.


Chemical Components of Cells

Most cells are composed of four elements:

1. Carbon

2. Hydrogen

3. Oxygen

4. Nitrogen

Cells are about 60% water


Anatomy of a Generalized Cell

In general, a cell has three main regions or parts:

1. Nucleus

2. Cytoplasm

3. Plasma membrane



Figure 3.1a Anatomy of the generalized animal cell nucleus.

Nucleus

Cytoplasm

Plasmamembrane

(a)

The Nucleus

Control center of the cell

Contains genetic material known as deoxyribonucleic

acid, or DNA

DNA is needed for building proteins

DNA is necessary for cell reproduction

Three regions:

1. Nuclear envelope (membrane)

2. Nucleolus

3. Chromatin



Figure 3.1b Anatomy of the generalized animal cell nucleus.

Nucleus

Rough ER

Nuclear envelope

Chromatin

Nucleolus

Nuclearpores

(b)

The Nucleus

Nuclear envelope (membrane)

Consists of a double membrane that bounds the

nucleus

Contains nuclear pores that allow for exchange of

material with the rest of the cell

Encloses the jellylike fluid called the nucleoplasm


The Nucleus

Nucleoli

Nucleus contains one or more nucleoli

Sites of ribosome assembly

Ribosomes migrate into the cytoplasm through

nuclear pores to serve as the site of protein

synthesis


The Nucleus

Chromatin

Composed of DNA and protein

Present when the cell is not dividing

Scattered throughout the nucleus

Condenses to form dense, rod-like bodies called

chromosomes when the cell divides


Plasma Membrane

Transparent barrier for cell contents

Contains cell contents

Separates cell contents from surrounding

environment


Plasma Membrane

Fluid mosaic model is constructed of:

Phospholipids

Cholesterol

Proteins

Sugars



Figure 3.2 Structure of the plasma membrane.

Glycoprotein Glycolipid

Cholesterol

Channel

Cytoplasm

(watery environment)

Filaments of

cytoskeleton

Proteins

Extracellular fluid

(watery environment)

Sugar

group

Polar heads

of phospholipid

molecules

Bimolecular

lipid layer

containing

proteins

Nonpolar tails

of phospholipid

molecules

Concept Link



Plasma Membrane

Fluid mosaic model

Phospholipid arrangement

Hydrophilic (“water-loving”) polar “heads” are oriented

on the inner and outer surfaces of the membrane

Hydrophobic (“water-hating”) nonpolar “tails” form the

center (interior) of the membrane


Plasma Membrane

Fluid mosaic model

Phospholipid arrangement

The hydrophobic interior makes the plasma

membrane impermeable to most water-soluble

molecules


Plasma Membrane

Fluid mosaic model

Proteins

Responsible for specialized functions

Roles of proteins

Enzymes

Receptors

Transport as channels or carriers


Plasma Membrane

Fluid mosaic model

Sugars

Glycoproteins are branched sugars attached to

proteins that abut the extracellular space

Glycocalyx is the fuzzy, sticky, sugar-rich area on the

cell’s surface


Cytoplasm

The material outside the nucleus and inside the

plasma membrane

Site of most cellular activities


Cytoplasm

Contains three major elements

1. Cytosol

Fluid that suspends other elements

2. Organelles

Metabolic machinery of the cell

“Little organs” that perform functions for the cell

3. Inclusions

Chemical substances, such as stored nutrients or cell

products


Figure 3.4 Structure of the generalized cell.

Chromatin

NucleolusNuclear envelope

Nucleus

Plasma

membrane

Roughendoplasmicreticulum

Ribosomes

Golgi

apparatus

Secretion beingreleased from cellby exocytosisPeroxisome

Intermediate

filaments

Microtubule

Centrioles

Mitochondrion

Lysosome

Cytosol

Smooth

endoplasmic

reticulum


Cytoplasmic Organelles

Organelles

Specialized cellular compartments

Many are membrane-bound

Compartmentalization is critical for organelle’s ability

to perform specialized functions



Mitochondria

“Powerhouses” of the cell

Change shape continuously

Mitochondrial wall consists of a double membrane

with cristae on the inner membrane

Carry out reactions where oxygen is used to break

down food

Provides ATP for cellular energy



Ribosomes

Bilobed dark bodies

Made of protein and ribosomal RNA

Sites of protein synthesis

Found at two locations:

Free in the cytoplasm

As part of the rough endoplasmic reticulum



Endoplasmic reticulum (ER)

Fluid-filled cisterns (tubules or canals) for carrying

substances within the cell

Two types:

Rough ER

Smooth ER




Rough endoplasmic reticulum

Studded with ribosomes

Synthesizes proteins

Transport vesicles move proteins within cell

Abundant in cells that make and export proteins


Figure 3.5 Synthesis and export of a protein by the rough ER.

Ribosome

1

2

34

23

4

1

mRNA

Rough ER

Protein

Transport

vesicle buds off

Protein inside

transport vesicle

As the protein is synthesized on the

ribosome, it migrates into the rough ER

cistern.

In the cistern, the protein folds into its

functional shape. Short sugar chains may be

attached to the protein (forming a

glycoprotein).

The protein is packaged in a tiny

membranous sac called a transport vesicle.

The transport vesicle buds from the

rough ER and travels to the Golgi apparatus

for further processing.

Slide 1



Ribosome

1

1

mRNA

Rough ER

Protein



cistern.

Slide 2



Ribosome

1

2

21

mRNA

Rough ER

Protein



cistern.




glycoprotein).

Slide 3





Ribosome

1

2

3

231

mRNA

Rough ER

Protein

Transport

vesicle buds off



cistern.




glycoprotein).

Slide 4


The transport vesicle buds from the

rough ER and travels to the Golgi apparatus

for further processing.




Ribosome

1

2

34

23

4

1

mRNA

Rough ER

Protein

Transport

vesicle buds off

Protein inside

transport vesicle



cistern.




glycoprotein).

Slide 5




Smooth endoplasmic reticulum

Functions in lipid metabolism

Detoxification of drugs and pesticides



Golgi apparatus

Appears as a stack of flattened membranes

associated with tiny vesicles

Modifies and packages proteins arriving from the

rough ER via transport vesicles

Produces different types of packages

Secretory vesicles (pathway 1)

In-house proteins and lipids (pathway 2)

Lysosomes (pathway 3)


Figure 3.6 Role of the Golgi apparatus in packaging the products of the rough ER.

Rough ER Cisterns Proteins in cisterns

Membrane

Transport

vesicle

Lysosome fuses

with ingested

substances.

Golgi vesicle containing

digestive enzymes

becomes a lysosome.

Golgi

apparatus

Pathway 1Secretory vesicles

Proteins

Secretion by

exocytosis


proteins to be secreted

becomes a secretory

vesicle.


membrane components

fuses with the plasma

membrane and is

incorporated into it.

Plasma membrane

Extracellular fluid

Pathway 2

Pathway 3



Lysosomes

Membranous “bags” packaged by the Golgi

apparatus

Contain enzymes produced by ribosomes

Enzymes can digest worn-out or nonusable cell

structures

House phagocytes that dispose of bacteria and cell

debris



Peroxisomes

Membranous sacs of oxidase enzymes

Detoxify harmful substances such as alcohol and

formaldehyde

Break down free radicals (highly reactive chemicals)

Free radicals are converted to hydrogen peroxide and

then to water

Replicate by pinching in half or budding from the ER



Cytoskeleton

Network of protein structures that extend throughout

the cytoplasm

Provides the cell with an internal framework

Three different types of elements:

1. Microfilaments (largest)

2. Intermediate filaments

3. Microtubules (smallest)


Figure 3.7 Cytoskeletal elements support the cell and help to generate movement.

Actin subunit

7 nm

Fibrous subunits

Tubulin subunits

10 nm 25 nm

Microfilaments form the blue

batlike network.

(a) Microfilaments (b) Intermediate filaments (c) Microtubules

Intermediate filaments form

the purple network

surrounding the pink nucleus.

Microtubules appear as gold

networks surrounding the

cells’ pink nuclei.



Centrioles

Rod-shaped bodies made of microtubules

Generate microtubules

Direct the formation of mitotic spindle during cell

division


Table 3.1 Parts of the Cell: Structure and Function (1 of 5).


Cell Extensions

Surface extensions found in some cells

Cilia move materials across the cell surface

Located in the respiratory system to move mucus

Flagella propel the cell

The only flagellated cell in the human body is sperm

Microvilli are tiny, fingerlike extensions of the plasma

membrane

Increase surface area for absorption


Figure 3.8g Cell diversity.

Nucleus Flagellum

Sperm

(g) Cell of reproduction


Cell Diversity

The human body houses over 200 different cell

types

Cells vary in length from 1/12,000 of an inch to over

1 yard (nerve cells)

Cell shape reflects its specialized function


Cell Diversity

Cells that connect body parts

Fibroblast

Secretes cable-like fibers

Erythrocyte (red blood cell)

Carries oxygen in the bloodstream


Figure 3.8a Cell diversity.

Rough ER and Golgi

apparatus No organelles

Nucleus

Fibroblasts

Erythrocytes

(a) Cells that connect body parts


Cell Diversity

Cells that cover and line body organs

Epithelial cell

Packs together in sheets

Intermediate fibers resist tearing during rubbing or

pulling


Figure 3.8b Cell diversity.

Nucleus

Intermediate

filaments

Epithelial

cells

(b) Cells that cover and line body organs


Cell Diversity

Cells that move organs and body parts

Skeletal muscle and smooth muscle cells

Contractile filaments allow cells to shorten forcefully


Figure 3.8c Cell diversity.

Nuclei

Contractile

filaments

Skeletal

muscle cell

Smooth

muscle cells

(c) Cells that move organs and body parts


Cell Diversity

Cell that stores nutrients

Fat cells

Lipid droplets stored in cytoplasm


Figure 3.8d Cell diversity.

Lipid droplet

Nucleus

Fat cell

(d) Cell that stores

nutrients


Cell Diversity

Cell that fights disease

Macrophage (a phagocytic cell)

Digests infectious microorganisms


Figure 3.8e Cell diversity.

Lysosomes

Macrophage

(e) Cell that fights

disease

Pseudo-

pods


Cell Diversity

Cell that gathers information and controls body

functions

Nerve cell (neuron)

Receives and transmits messages to other body

structures


Figure 3.8f Cell diversity.

Processes

Rough ER

Nucleus

(f) Cell that gathers information and

controls body functions

Nerve cell


Cell Diversity

Cells of reproduction

Oocyte (female)

Largest cell in the body

Divides to become an embryo upon fertilization

Sperm (male)

Built for swimming to the egg for fertilization

Flagellum acts as a motile whip


Figure 3.8g Cell diversity.

Nucleus Flagellum

Sperm

(g) Cell of reproduction


Cell Physiology

Cells have the ability to:

Metabolize

Digest food

Dispose of wastes

Reproduce

Grow

Move

Respond to a stimulus


Membrane Transport

Solution—homogeneous mixture of two or more

components

Solvent—dissolving medium; typically water in the

body

Solutes—components in smaller quantities within a

solution


Membrane Transport

Intracellular fluid

Nucleoplasm and cytosol

Solution containing gases, nutrients, and salts

dissolved in water

Interstitial fluid

Fluid on the exterior of the cell

Contains thousands of ingredients, such as nutrients,

hormones, neurotransmitters, salts, waste products


Membrane Transport

The plasma membrane is a selectively permeable

barrier

Some materials can pass through while others are

excluded

For example:

Nutrients can enter the cell

Undesirable substances are kept out


Membrane Transport

Two basic methods of transport

Passive processes

No energy (ATP) is required

Active processes

Cell must provide metabolic energy (ATP)

A&P FlixTM: Membrane Transport



Passive Processes

Diffusion

Particles tend to distribute themselves evenly within

a solution

Driving force is the kinetic energy (energy of motion)

that causes the molecules to move about randomly


Passive Processes

Diffusion

Molecule movement is from high concentration to

low concentration, or down a concentration gradient

Size of molecule and temperature affects the speed

of diffusion

The smaller the molecule, the faster the rate of

diffusion

The warmer the molecule, the faster the rate of

diffusion


Passive Processes

Example of diffusion:

Pour a cup of coffee and drop in a cube of sugar

Do not stir the sugar into the coffee; leave the cup of

coffee sitting all day, and it will taste sweet at the end

of the day.

Molecules move by diffusion and sweeten the entire

cup


Figure 3.9 Diffusion.


Passive Processes

Molecules will move by diffusion if any of the

following applies:

The molecules are small enough to pass through the

membrane’s pores (channels formed by membrane

proteins)

The molecules are lipid-soluble

The molecules are assisted by a membrane carrier


Passive Processes

Types of diffusion

Simple diffusion

An unassisted process

Solutes are lipid-soluble or small enough to pass

through membrane pores


Figure 3.10a Diffusion through the plasma membrane.

Lipid-

soluble

solutes

Extracellular

fluid

(a) Simplediffusion

of fat-solublemoleculesdirectlythrough thephospholipidbilayer

Cytoplasm


Passive Processes

Types of diffusion (continued)

Osmosis—simple diffusion of water

Highly polar water molecules easily cross the plasma

membrane through aquaporins

Water moves down its concentration gradient


Figure 3.10d Diffusion through the plasma membrane.

Water

molecules

Lipid

bilayer

(d) Osmosis, diffusionof water through aspecific channelprotein (aquaporin)or through the lipid bilayer


Passive Processes

Osmosis—A Closer Look

Isotonic solutions have the same solute and water

concentrations as cells and cause no visible changes

in the cell

Hypertonic solutions contain more solutes than the

cells do; the cells will begin to shrink

Hypotonic solutions contain fewer solutes (more

water) than the cells do; cells will plump


A Closer Look 3.1 IV Therapy and Cellular “Tonics.”

(a) RBC in isotonic

solution

(b) RBC in hypertonic

solution

(c) RBC in hypotonic

solution


Passive Processes

Types of diffusion (continued)

Facilitated diffusion

Transports lipid-insoluble and large substances

Glucose is transported via facilitated diffusion

Protein membrane channels or protein molecules that

act as carriers are used


Figure 3.10b-c Diffusion through the plasma membrane.

Lipid-

insoluble

solutes

Small lipid-

insoluble

solutes

(b) Carrier-mediatedfacilitated diffusion viaprotein carrier specific forone chemical; binding ofsubstrate causes shapechange in transport protein

(c) Channel-mediatedfacilitateddiffusion

through achannel protein;mostly ions,selected onbasis ofsize and charge


Passive Processes

Filtration

Water and solutes are forced through a membrane

by fluid, or hydrostatic pressure

A pressure gradient must exist

Solute-containing fluid (filtrate) is pushed from a high-

pressure area to a lower-pressure area

Filtration is critical for the kidneys to work properly


Active Processes

Sometimes called solute pumping

Requires protein carriers to transport substances

that:

May be too large to travel through membrane

channels

May not be lipid-soluble

May have to move against a concentration gradient

ATP is used for transport


Active Processes

Active transport

Amino acids, some sugars, and ions are transported

by protein carriers known as solute pumps

ATP energizes solute pumps

In most cases, substances are moved against

concentration (or electrical) gradients


Active Processes

Example of active transport is the sodium-

potassium pump

Sodium is transported out of the cell

Potassium is transported into the cell


Figure 3.11 Operation of the sodium-potassium pump, a solute pump.

Na+-K+ pump

2 31

321

Na+

Extracellular fluid

K+Na+

Na+

Na+

Na+

Na+

K+

K+

K+

P

P

ATP

ADP

Binding of cytoplasmic Na+

to the pump protein stimulatesphosphorylation by ATP, which causes the pump protein tochange its shape.

The shape change expelsNa+ to the outside. ExtracellularK+ binds, causing release of thephosphate group.

Loss of phosphaterestores the originalconformation of the pumpprotein. K+ is released to thecytoplasm, and Na+ sites areready to bind Na+ again; the cycle repeats.

Cytoplasm

Slide 1





Na+-K+ pump

1

1

Extracellular fluid

Na+

Na+

Na+

P

ATP

ADP

Cytoplasm

Slide 2






Na+-K+ pump

21

21

Na+

Extracellular fluid

K+Na+

Na+

Na+

Na+

Na+

K+

P

P

ATP

ADP

Cytoplasm

Slide 3





Loss of phosphaterestores the originalconformation of the pumpprotein. K+ is released to thecytoplasm, and Na+ sites areready to bind Na+ again; the cycle repeats.


Na+-K+ pump

2 31

321

Na+

Extracellular fluid

K+Na+

Na+

Na+

Na+

Na+

K+

K+

K+

P

P

ATP

ADP

Cytoplasm

Slide 4


Active Processes

Vesicular transport: substances are moved without

actually crossing the plasma membrane

Exocytosis

Endocytosis

Phagocytosis

Pinocytosis


Active Processes

Vesicular transport (continued)

Exocytosis

Moves materials out of the cell

Material is carried in a membranous sac called a

vesicle

Vesicle migrates to plasma membrane

Vesicle combines with plasma membrane

Material is emptied to the outside

Refer to Pathway 1 in Figure 3.6


Figure 3.6 Role of the Golgi apparatus in packaging the products of the rough ER.

Rough ER Cisterns Proteins in cisterns

Membrane

Transport

vesicle

Lysosome fuses

with ingested

substances.


digestive enzymes

becomes a lysosome.

Golgi

apparatus

Pathway 1Secretory vesicles

Proteins

Secretion by

exocytosis


proteins to be secreted

becomes a secretory

vesicle.


membrane components

fuses with the plasma

membrane and is

incorporated into it.

Plasma membrane

Extracellular fluid

Pathway 2

Pathway 3


Active Processes


Exocytosis docking process

Transmembrane proteins on the vesicles are called

v-SNAREs (v for vesicle)

Plasma membrane proteins are called t-SNAREs

(t for target)

v-SNAREs recognize and bind t-SNAREs

Membranes corkscrew and fuse together


Figure 3.12a Exocytosis.

Extracellular

fluid

2

3

1

Plasma

membrane

SNARE

(t-SNARE)

Vesicle

SNARE

(v-SNARE)

Molecule

to be

secretedSecretory

vesicle

Fusion pore formed

Fused

SNAREs

The membrane-

bound vesicle

migrates to the

plasma membrane.

There, v-SNAREs

bind with t-SNAREs,

the vesicle and

plasma membrane

fuse, and a pore

opens up.

Vesicle contents

are released to the

cell exterior.

Cytoplasm

(a) The process of exocytosis


Figure 3.12b Exocytosis.

(b) Electron micrograph of a

secretory vesicle in

exocytosis (190,000×)


Active Processes


Endocytosis

Extracellular substances are engulfed by being

enclosed in a membranous vescicle

Vesicle typically fuses with a lysosome

Contents are digested by lysosomal enzymes

In some cases, the vesicle is released by exocytosis

on the opposite side of the cell


Figure 3.13a Events and types of endocytosis.

Plasma

membrane

Lysosome

Pit

Ingested

substance

Detached vesicle

Vesicle

Extracellular

fluid Cytosol

Release of

contents to

cytosol

Vesicle fusing

with lysosome

for digestion

Transport to plasma

membrane and exocytosis

of vesicle contents

Membranes and receptors

(if present) recycled to plasma

membrane

1

(a)

2

3

Slide 1



Plasma

membrane

Extracellular

fluid

Vesicle fusing

with lysosome

for digestion

1

(a)

Slide 2



Plasma

membrane

Lysosome

Detached vesicle

Vesicle

Extracellular

fluid Cytosol

Release of

contents to

cytosol

Vesicle fusing

with lysosome

for digestion

Transport to plasma


of vesicle contents

1

(a)

2

Slide 3



Plasma

membrane

Lysosome

Pit

Ingested

substance

Detached vesicle

Vesicle

Extracellular

fluid Cytosol

Release of

contents to

cytosol

Vesicle fusing

with lysosome

for digestion

Transport to plasma


of vesicle contents



membrane

1

(a)

2

3

Slide 4


Active Processes


Types of endocytosis

1. Phagocytosis—“cell eating”

Cell engulfs large particles such as bacteria or dead

body cells

Pseudopods are cytoplasmic extensions that separate

substances (such as bacteria or dead body cells) from

external environment

Phagocytosis is a protective mechanism, not a means

of getting nutrients


Figure 3.13b Events and types of endocytosis.

Pseudopod

Bacterium

or other

particle

Extracellular

fluid

Cytoplasm

(b)


Active Processes



2. Pinocytosis—“cell drinking”

Cell “gulps” droplets of extracellular fluid containing

dissolved proteins or fats

Plasma membrane forms a pit, and edges fuse around

droplet of fluid

Routine activity for most cells, such as those involved

in absorption (small intestine)



Plasma

membrane

Lysosome

Pit

Ingested

substance

Detached vesicle

Vesicle

Extracellular

fluid Cytosol

Release of

contents to

cytosol

Vesicle fusing

with lysosome

for digestion

Transport to plasma


of vesicle contents



membrane

1

(a)

2

3


Active Processes



3. Receptor-mediated endocytosis

Method for taking up specific target molecules

Receptor proteins on the membrane surface bind only

certain substances

Highly selective process of taking in substances such

as enzymes, some hormones, cholesterol, and iron


Active Processes



3. Receptor-mediated endocytosis

Both the receptors and target molecules are in a

vesicle

Contents of the vesicles are dealt with in one of the

ways shown in the next figure



Plasma

membrane

Lysosome

Pit

Ingested

substance

Detached vesicle

Vesicle

Extracellular

fluid Cytosol

Release of

contents to

cytosol

Vesicle fusing

with lysosome

for digestion

Transport to plasma


of vesicle contents



membrane

1

(a)

2

3


Figure 3.13c Events and types of endocytosis.

Membrane

receptor

(c)


Cell Life Cycle

Cell life cycle is a series of changes the cell

experiences from the time it is formed until it divides


Cell Life Cycle

Cycle has two major periods

1. Interphase

Cell grows

Cell carries on metabolic processes

Longer phase of the cell cycle

2. Cell division

Cell replicates itself

Function is to produce more cells for growth and

repair processes


DNA Replication

Genetic material is duplicated and readies a cell for

division into two cells

Occurs toward the end of interphase

Concept Link



DNA Replication

DNA uncoils into two nucleotide chains, and each

side serves as a template

Nucleotides are complementary

Adenine (A) always bonds with thymine (T)

Guanine (G) always bonds with cytosine (C)

For example, TACTGC bonds with new nucleotides

in the order ATGACG


Figure 3.14 Replication of the DNA molecule during interphase.

KEY:

Adenine

Thymine

Cytosine

Guanine

Old(template)strand

Newlysynthesizedstrand

Newstrandforming

Old (template)strand

DNA of one chromatid


Events of Cell Division

Mitosis—division of the nucleus

Results in the formation of two daughter nuclei

Cytokinesis—division of the cytoplasm

Begins when mitosis is near completion

Results in the formation of two daughter cells

A&P Flix™: Mitosis



Stages of Mitosis

Prophase

First part of cell division

Chromatin coils into chromosomes

Chromosomes are held together by a centromere

A chromosome has two strands

Each strand is called a chromatid


Stages of Mitosis

Prophase (continued)

Centrioles migrate to the poles to direct assembly of

mitotic spindle fibers

Mitotic spindles are made of microtubules

Spindle provides scaffolding for the attachment and

movement of the chromosomes during the later

mitotic stages

Nuclear envelope breaks down and disappears


Stages of Mitosis

Metaphase

Chromosomes are aligned in the center of the cell on

the metaphase plate

Metaphase plate is the center of the spindle midway

between the centrioles

Straight line of chromosomes is now seen


Stages of Mitosis

Anaphase

Centromere splits

Chromatids move slowly apart and toward the

opposite ends of the cell

Anaphase is over when the chromosomes stop

moving


Stages of Mitosis

Telophase

Reverse of prophase

Chromosomes uncoil to become chromatin

Spindles break down and disappear

Nuclear envelope reforms around chromatin

Nucleoli appear in each of the daughter nuclei


Stages of Mitosis

Cytokinesis

Division of the cytoplasm

Begins during late anaphase and completes during

telophase

A cleavage furrow forms to pinch the cells into two

parts

Cleavage furrow is a contractile ring made of

microfilaments


Stages of Mitosis

Two daughter cells exist at the end of cell division

In most cases, mitosis and cytokinesis occur

together

In some cases, the cytoplasm is not divided

Binucleate or multinucleate cells result

Common in the liver

Mitosis gone wild is the basis for tumors and

cancers


Spindle

microtubules

Chromosome,

consisting of two

sister chromatids

Fragments of

nuclear envelope

Daughter

chromosomes

Figure 3.15 Stages of mitosis.

Centrioles Chromatin Centrioles

Forming

mitotic

spindleCentromere

Centromere

Plasma

membrane

Nuclear

envelopeNucleolus

Spindle

pole

Metaphase

plate

Nucleolus

forming

Cleavage

furrow

Spindle Sister

chromatids

Nuclear

envelope

forming

Interphase Early prophase Late prophase

Metaphase Anaphase Telophase and cytokinesis

Slide 1


Figure 3.15 Stages of mitosis (1 of 6).

Centrioles Chromatin

Plasma

membrane

Nuclear

envelopeNucleolus

Interphase

Slide 2



Chromosome,

consisting of two

sister chromatids

Centrioles

Forming

mitotic

spindleCentromere

Early prophase

Slide 3



Spindle

microtubules

Fragments of

nuclear envelope

Centromere

Spindle

pole

Late prophase

Slide 4



Metaphase

plate

Spindle Sister

chromatids

Metaphase

Slide 5



Daughter

chromosomes

Anaphase

Slide 6



Nucleolus

forming

Cleavage

furrow

Nuclear

envelope

forming

Telophase and cytokinesis

Slide 7


Protein Synthesis

DNA serves as a blueprint for making proteins

Gene: DNA segment that carries a blueprint for

building one protein or polypeptide chain

Proteins have many functions

Fibrous (structural) proteins are the building

materials for cells

Globular (functional) proteins act as enzymes

(biological catalysts)


Protein Synthesis

DNA information is coded into triplets

Triplets

Contain three bases

Call for a particular amino acid

For example, a DNA sequence of AAA specifies the

amino acid phenylalanine


Protein Synthesis

Most ribosomes, the manufacturing sites of

proteins, are located in the cytoplasm

DNA never leaves the nucleus in interphase cells

DNA requires a decoder and a messenger to build

proteins, both are functions carried out by RNA

(ribonucleic acid)


Protein Synthesis

How does RNA differ from DNA? RNA:

Is single-stranded

Contains ribose sugar instead of deoxyribose

Contains uracil (U) base instead of thymine (T)


Role of RNA

Transfer RNA (tRNA)

Transfers appropriate amino acids to the ribosome

for building the protein

Ribosomal RNA (rRNA)

Helps form the ribosomes where proteins are built

Messenger RNA (mRNA)

Carries the instructions for building a protein from the

nucleus to the ribosome


Role of RNA

Protein synthesis involves two major phases:

Transcription

Translation

We will detail these two phases next


Protein Synthesis

Transcription

Transfer of information from DNA’s base sequence to

the complementary base sequence of mRNA

Only DNA and mRNA are involved

Triplets are the three-base sequence specifying a

particular amino acid on the DNA gene

Codons are the corresponding three-base

sequences on mRNA


Protein Synthesis

Example of transcription:

DNA triplets AAT-CGT-TCG

mRNA codons UUA-GCA-AGC


As the ribosomemoves along the mRNA,a new amino acid isadded to the growingprotein chain.

Released tRNAreenters thecytoplasmic pool,ready to be rechargedwith a new aminoacid.

mRNA specifying one

polypeptide is made on

DNA template.

mRNA leaves

nucleus and attaches

to ribosome, and

translation begins.

Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via its anticodonto the codon.

mRNA

Figure 3.16 Protein synthesis.

Nuclear membrane

2

1

3

4

5

Nuclear pore

Nucleus

(site of transcription)DNA

Amino

acids

Cytoplasm

(site of translation)

Synthetase

enzyme

Correct aminoacid attached toeach species oftRNA by anenzyme

Growing

polypeptide

chain

Peptide bond

tRNA “head”

bearing anticodon

Large ribosomal subunit

Codon

Portion of

mRNA already

translated

Small ribosomal subunit

Direction ofribosome advance;ribosome moves themRNA strand alongsequentially as each

codon is read.

Met

Gly

Ser

Phe

Ala

Slide 1


mRNA specifying one


DNA template.

Figure 3.16 Protein synthesis (1 of 2).

mRNA

Nuclear membrane

1

Nuclear pore

Nucleus


Amino

acids

Cytoplasm


Synthetase

enzyme

Correct amino

acid attached to

each species of

tRNA by an

enzyme

Slide 2


Protein Synthesis

Translation

Base sequence of nucleic acid is translated to an

amino acid sequence

Amino acids are the building blocks of proteins


Protein Synthesis

Translation (continued)

Steps correspond to Figure 3.16 (step 1 covers

transcription)

2. mRNA leaves nucleus and attaches to ribosome,

and translation begins

3. Incoming tRNA recognizes a complementary mRNA

codon calling for its amino acid by binding via its

anticodon to the codon.


mRNA leaves

nucleus and attaches

to ribosome, and

translation begins.

mRNA specifying one


DNA template.


mRNA

Nuclear membrane

1

Nuclear pore

Nucleus


Amino

acids

Cytoplasm


Synthetase

enzyme

Correct amino

acid attached to

each species of

tRNA by an

enzyme

2

Slide 3




tRNA “head”

bearing anticodon


Codon

Portion of

mRNA already

translated



codon is read.

3

Slide 4


Protein Synthesis

Translation (continued)

Steps correspond to Figure 3.16

4. As the ribosome moves along the mRNA, a new

amino acid is added to the growing protein chain.

5. Released tRNA reenters the cytoplasmic pool,

ready to be recharged with a new amino acid.





Growing

polypeptide

chain

Peptide bond

tRNA “head”

bearing anticodon


Codon

Portion of

mRNA already

translated



codon is read.

3

4

Met

Gly

Ser

Phe

Ala

Slide 5


Released tRNAreenters thecytoplasmic pool,ready to be rechargedwith a new aminoacid.




Growing

polypeptide

chain

Peptide bond

tRNA “head”

bearing anticodon


Codon

Portion of

mRNA already

translated



codon is read.

3

4

5

Met

Gly

Ser

Phe

Ala

Slide 6

Concept Link



Body Tissues

Tissues

Groups of cells with similar structure and function

Four primary types:

1. Epithelial tissue (epithelium)

2. Connective tissue

3. Muscle tissue

4. Nervous tissue


Epithelial Tissues

Locations:

Body coverings

Body linings

Glandular tissue

Functions:

Protection

Absorption

Filtration

Secretion


Epithelium Characteristics

Cells fit closely together and often form sheets

The apical surface is the free surface of the tissue

The lower surface of the epithelium rests on a

basement membrane

Avascular (no blood supply)

Regenerate easily if well nourished


Figure 3.17a Classification and functions of epithelia.

Basal

surface

Apical surface

Basal

surface

Apical surface

Simple

Stratified

(a) Classification based on number of cell layers


Classification of Epithelia

Number of cell layers

Simple—one layer

Stratified—more than one layer


Figure 3.17a Classification and functions of epithelia.

Basal

surface

Apical surface

Basal

surface

Apical surface

Simple

Stratified

(a) Classification based on number of cell layers


Classification of Epithelia

Shape of cells

Squamous

Flattened, like fish scales

Cuboidal

Cube-shaped, like dice

Columnar

Column-like


Figure 3.17b Classification and functions of epithelia.

Squamous

Cuboidal

Columnar

(b) Classification based on cell shape


Figure 3.17c Classification and functions of epithelia.

Diffusion and filtration

Secretion in serous membranesProtection

Secretion and absorption; ciliated

types propel mucus or

reproductive cells

Secretion and absorption; ciliated

types propel mucus or

reproductive cells

Protection; these tissue types are rare

in humans

Protection; stretching to accommodate

distension of urinary structures

(c) Function of epithelial tissue related to tissue type

Number of layers

Cell shapeOne layer: simple epithelial

tissuesMore than one layer: stratified

epithelial tissues

Squamous

Cuboidal

Columnar

Transitional


Simple Epithelia

Simple squamous

Single layer of flat cells

Location—usually forms membranes

Lines air sacs of the lungs

Forms walls of capillaries

Forms serous membranes (serosae) that line and

cover organs in ventral cavity

Fxns in diffusion, filtration, or secretion in

membranes


Figure 3.18a Types of epithelia and their common locations in the body.

Nucleus of

squamous

epithelial cell

Basement

membrane

Air sacs of

lungs

Nuclei of

squamous

epithelial

cells

(a) Diagram: Simple squamous

Photomicrograph: Simple

squamous epithelium forming part

of the alveolar (air sac) walls (275×).


Simple Epithelia

Simple cuboidal

Single layer of cube-like cells

Locations:

Common in glands and their ducts

Forms walls of kidney tubules

Covers the surface of ovaries

Fxns in secretion and absorption; ciliated types

propel mucus or reproductive cells


Figure 3.18b Types of epithelia and their common locations in the body.

Nucleus of

simple

cuboidal

epithelial

cell

Basement

membrane

Simple

cuboidal

epithelial

cells

Basement

membrane

Connective

tissue

(b) Diagram: Simple cuboidalPhotomicrograph: Simple cuboidal

epithelium in kidney tubules (250×).

Simple Epithelia

Simple columnar

Single layer of tall cells

Goblet cells secrete mucus

Location:

Lines digestive tract from stomach to anus

Mucous membranes (mucosae) line body cavities opening to the exterior

Fxns in secretion and absorption; ciliated types propel mucus or reproductive cells



Figure 3.18c Types of epithelia and their common locations in the body.

Basement

membrane

Basement

membrane

Mucus of a

goblet cellNucleus of

simple columnar

epithelial cellSimple

columnar

epithelial cells

(c) Diagram: Simple columnar

Photomicrograph: Simple columnar

epithelium of the small intestine (575×).

Simple Epithelia

Pseudostratified columnar

All cells rest on a basement

membrane

Single layer, but some cells

are shorter than others

giving a false (pseudo)

impression of stratification

Location:

Respiratory tract, where it

is ciliated and known as

pseudostratified ciliated

columnar epithelium

Fxns in absorption or

secretion



Figure 3.18d Types of epithelia and their common locations in the body.

(d) Diagram: Pseudostratified

(ciliated) columnar

Photomicrograph: Pseudostratified

ciliated columnar epithelium lining the

human trachea (560×).

Basement

membrane

Basement

membrane

Pseudo-

stratified

epithelial

layer

Pseudo-

stratified

epithelial layer

Cilia

Connective

tissue


Stratified Epithelia

Stratified squamous

Named for cells present at

the free (apical) surface,

which are flattened

Fxns as a protective

covering where friction is

common

Locations—lining of the:

Skin (outer portion)

Mouth

Esophagus


Figure 3.18e Types of epithelia and their common locations in the body.

Basement

membraneBasement

membraneConnective

tissue

Stratified

squamous

epitheliumStratified

squamous

epithelium

(e) Diagram: Stratified squamous

Photomicrograph:

Stratified squamous

epithelium lining of the esophagus (140×).

Nuclei


Stratified Epithelia

Stratified cuboidal—two

layers of cuboidal cells; fxns

in protection

Stratified columnar—surface

cells are columnar, and cells

underneath vary in size and

shape; fxns in protection

Stratified cuboidal and

columnar

Rare in human body

Found mainly in ducts of

large glands

Stratified Cuboidal ET



Stratified Epithelia Transitional epithelium

Composed of modified

stratified squamous ET

Shape of cells depends

upon the amnt of

stretching

Fxns in stretching with the

ability to return to normal

shape

Locations: urinary system

organs


Figure 3.18f Types of epithelia and their common locations in the body.

Basement

membrane

Basement

membrane

Connective

tissue

Transi-

tional

epitheliumTransitional

epithelium

(f) Diagram: Transitional

Photomicrograph: Transitional epithelium lining of

the bladder, relaxed state (270×); surface rounded cells

flatten and elongate when the bladder fills with urine.


Glandular Epithelium

Gland

One or more cells responsible for secreting a

particular product

Secretions contain protein molecules in an aqueous

(water-based) fluid

Secretion is an active process



Two major gland types

Endocrine gland

Ductless; secretions diffuse into blood vessels

All secretions are hormones

Examples include thyroid, adrenals, and pituitary



Two major gland types

Exocrine gland

Secretions empty through ducts to the epithelial

surface

Include sweat and oil glands, liver, and pancreas

Includes both internal and external glands


Plasma Membrane Junctions

Membrane junctions

Cells are bound together in three ways:

1. Glycoproteins in the glycocalyx act as an adhesive

or cellular glue

2. Wavy contours of the membranes of adjacent cells

fit together in a tongue-and-groove fashion

3. Special membrane jxns are formed, which vary

structurally depending on their roles



Membrane jxns

Tight jxns

Impermeable jxns

Bind cells together into leak-proof sheets

Prevent substances from passing through

extracellular space between cells

Found at apical region of most ET


Membrane jxns

Adhesion/adhering jxns

Anchor/cement adjacent cells together so they fxn as

a unit

Skin and areas subjected to friction



Membrane jxns

Desmosomes

Bind cells together - prevent cells from being pulled as

a result of mechanical stress –Created by button-like

thickenings of adjacent plasma membranes

Intermediate filaments go across the cytoplasm and

anchor desmosomes together at opposite sides of cell

Common in cardiac muscle and ET


Membrane jxns

Hemidesmosomes

Anchor intermediate filaments in a cell to the basal

lamina of the basal membrane



Membrane jxns

Gap jxns

Allow communication between cells

Smooth muscle, , and other tissues in which

activities of adjacent cells must be coordinated.

Small water soluble molecules and ions can travel

directly from one cell to the next through these

channels


Figure 3.3 Cell junctions.

Microvilli

Connexon

Underlyingbasementmembrane

Extracellularspace betweencells

Gap(communicating) junction

Plasmamembranes ofadjacent cells

Desmosome

(anchoring

junction)

Tight(impermeable)junction


Connective Tissue

Found everywhere in the body

Most abundant and widely distributed tissues in

body

1° Fxn: Binds body parts together

2° Fxns:

Framework for internal organs

Packages and protects organs from injury

Supports body organs

Fat and E storage


Connective Tissue Characteristics

Variations in blood supply

Some tissue types are well vascularized

Some have a poor blood supply or are avascular

Extracellular matrix

Nonliving matl that accumulates and surrounds living

cells and fibers


Extracellular Matrix

Two main elements

1. Ground substance — mostly water along with

adhesion proteins and polysaccharide molecules

2. Fibers

Produced by the cells

3 types:

1. Collagen (white) fibers

2. Elastic (yellow) fibers

3. Reticular fibers (a type of collagen)


Connective Tissue Types

From most rigid to softest, or most fluid:

Bone

Cartilage

Dense CT

Loose CT

Blood



Bone (osseous tissue)

1° Fxns: to protect and support the body

Bone tissue stores mineral salts, produces blood

cells, and provides spaces for its own living

osteocytes.

Composed of:

Osteocytes (bone cells) sitting in lacunae (cavities)

Hard matrix of calcium salts

Large numbers of collagen fibers


Figure 3.19a Connective tissues and their common body locations.

Bone cells

in lacunaeCentral

canal

Lacunae

Lamella

(a) Diagram: Bone Photomicrograph: Cross-sectional

view of ground bone (165×)



Cartilage – a modified/specialized form of CT

Contains a dense array of fibers in a jelly-like ground

substance

Less hard and more flexible than bone

Found in only a few places in the body

Chondrocyte (cartilage cell) is the major cell type

1° Fxn

Cushion and maintain the shape of body parts

(Resists compression and is resilient)



Hyaline cartilage

Hyaline cartilage is the most widespread type of

cartilage

White or “glassy” appearance

Composed of abundant collagen fibers and a rubbery

matrix

Locations:

Larynx, covers bones in joints, provides structure for

nose, connects ribs to sternum, forms ring-like trachea

and bronchi of Respiratory tract

Entire fetal skeleton prior to birth

Epiphyseal plates

Fxns as a more flexible skeletal element than bone


Figure 3.19b Connective tissues and their common body locations.

Chondrocyte

(cartilage cell)

Chondrocyte

in lacuna

Matrix

Lacunae

Photomicrograph: Hyaline cartilage

from the trachea (400×)

(b) Diagram: Hyaline

cartilage


Connective Tissue TypesElastic cartilage

Provides elasticity – contains many elastic fibers

Location:

Supports the external ear

epiglottis

Fibrocartilage (Fibrous Cartilage)

Highly compressible – less rigid than hyaline

Heavy bundles of collagen

Location:

Forms cushion-like discs between vertebrae of the

spinal column (intervertebral discs)

Reinforces hyaline cartilage of knee and hip


Figure 3.19c Connective tissues and their common body locations.

Chondro-cytes inlacunae

Collagen

fibers

Chondrocytesin lacunae

Collagen fiber

Photomicrograph: Fibrocartilage of an

intervertebral disc (150×)

(c) Diagram:

Fibrocartilage



Dense connective tissue (dense fibrous tissue)

Main matrix element is collagen fiber

Fibroblasts are cells that make fibers

Locations:

Tendons—attach skeletal muscle to bone

Ligaments—attach bone to bone at joints and are

more elastic than tendons

Dermis—lower layers of the skin


Figure 3.19d Connective tissues and their common body locations.

Ligament

(d) Diagram: Dense

fibrous

Photomicrograph: Dense fibrous

connective tissue from a tendon (475×)

Collagen

fibers

Nuclei of

fibroblasts

Nuclei of

fibroblasts

Collagen

fibers

Tendon



Loose connective tissue types

Areolar tissue

Most widely distributed CT

Soft, pliable tissue like “cobwebs”

Fxns as a universal packing tissue and “glue” to hold

organs in place

Layer of areolar tissue called lamina propria underlies

all membranes

All fiber types form a loose network

Can soak up XS fluid (causes edema)


Figure 3.19e Connective tissues and their common body locations.

Mucosaepithelium

Laminapropria

Fibers of

matrix

Nuclei of

fibroblasts

Elastic

fibers

Collagen

fibers

Fibroblast

nuclei

(e) Diagram: Areolar Photomicrograph: Areolar connective tissue,

a soft packaging tissue of the body (270×)




Adipose tissue

Matrix is an areolar tissue in which fat globules

predominate

Many cells contain large lipid deposits with nucleus to

one side (signet ring cells)

Fxns

Insulates the body

Protects some organs

Serves as a site of fuel storage


Figure 3.19f Connective tissues and their common body locations.

Nuclei of

fat cells

Vacuole

containing

fat droplet

Vacuole

containing

fat droplet

Nuclei of

fat cells

(f) Diagram: Adipose Photomicrograph: Adipose tissue from the

subcutaneous layer beneath the skin (570×)




Reticular connective tissue

Delicate network of interwoven fibers with reticular

cells (like fibroblasts)

Locations:

Forms stroma (internal framework) of organs, such as

these lymphoid organs:

Lymph nodes

Spleen

Bone marrow


Figure 3.19g Connective tissues and their common body locations.

Spleen

(g) Diagram: Reticular Photomicrograph: Dark-staining network

of reticular connective tissue (400×)

Reticularcell

Bloodcell

Reticularfibers

White blood cell

(lymphocyte)

Reticular fibers



Blood (vascular tissue)

Blood cells surrounded by fluid matrix known as

blood plasma

Soluble fibers are visible only during clotting

Fxns as the transport vehicle for the cardiovascular

system, carrying:

Nutrients

Wastes

Respiratory gases


Figure 3.19h Connective tissues and their common body locations.

Photomicrograph: Smear of human

blood (1290×)

(h) Diagram: Blood

Blood cells

in capillary

White

blood cell

Red

blood cells

Neutrophil

(white blood

cell)

Red blood

cells

Monocyte

(white blood

cell)


Muscle Tissue

Fxn is to contract, or shorten, to produce mvmt in

response to stimulation - then passively lengthen

Three types:

1. Skeletal muscle

2. Cardiac muscle

3. Smooth muscle


Muscle Tissue Types

Skeletal muscle

Voluntarily (consciously) controlled

Attached to the skeleton and pull on bones or skin

Produces gross body movements or facial

expressions

Characteristics of skeletal muscle cells

Striations (stripes)

Multinucleate (more than one nucleus)

Long, cylindrical shape


Figure 3.20a Type of muscle tissue and their common locations in the body.

Nuclei

Part of muscle

fiber

Photomicrograph: Skeletal muscle (195×)(a) Diagram: Skeletal muscle


Muscle Tissue Types

Cardiac muscle

Involuntarily controlled

Found only in the heart

Pumps blood through blood vessels

Characteristics of cardiac muscle cells

Striations

Uninucleate, short, branching cells

Intercalated discs contain gap junctions to connect

cells together


Figure 3.20b Type of muscle tissue and their common locations in the body.

Intercalated

discs

Nucleus

Photomicrograph: Cardiac muscle (475×)(b) Diagram: Cardiac muscle


Muscle Tissue Types

Smooth (visceral) muscle

Involuntarily controlled

Found in walls of hollow organs such as stomach,

uterus, and blood vessels

Peristalsis, a wavelike activity, is a typical activity

Characteristics of smooth muscle cells

No visible striations

Uninucleate

Spindle-shaped cells


Figure 3.20c Type of muscle tissue and their common locations in the body.

Smooth

muscle cell

Nuclei

Photomicrograph: Sheet of smooth muscle (285×)(c) Diagram: Smooth muscle

Muscle Tissue

Skeletal Muscle Tissue

1. Skeletal muscle tissue attaches to

__________________ for voluntary movement;

it contains __________________,

_____________________, long cells.

2. Each unit, called a ___________________,

is contractile; muscle makes up ________ % of

the weight of average humans.

Cardiac Muscle Tissue1. ___________________ (heart) muscle is

composed of _______________,

______________________ branching cells that

can function in units.

2. Contraction signals pass quickly at gap junctions, and

the tissue is packed with

_________________________ to supply ATP for the

continual beating; no oxygen equals heart attack.

Smooth Muscle Tissue

1. Smooth muscle tissue contains ______________-

shaped cells.

2. Location__________________________________

_________________________________________

3. Its operation is ____________________________:

like cardiac.

4. This tissue is ____________________________,

hence the name, and its contractions are slower than

skeletal but can be prolonged.

Nervous Tissue

Nervous tissue exerts the greatest

control over the body's responsiveness to

changing conditions.

1. _______________________ are

excitable cells, organized as lines of

________________________________

throughout the body.

2. ________________________ are

diverse cells that protect and

metabolically support the neurons.

Various neurons detect stimuli; others

coordinate the body’s responses; still

others relay signals to muscles and

glands for response.


Nervous Tissue

Composed of neurons and nerve support cells

Function is to receive and conduct electrochemical

impulses to and from body parts

Irritability

Conductivity

Support cells called neuroglia insulate, protect, and

support neurons


Figure 3.21 Nervous tissue.

Brain

Spinal

cord

Nuclei ofsupportingcells

Cell body

of neuron

Neuron

processes

Nuclei of

supporting

cells

Neuronprocesses

Cell bodyof neuron

Diagram: Nervous

tissue

Photomicrograph: Neurons (320×)


Summary of Tissues

Figure 3.22 summarizes the tissue types and

functions in the body


Figure 3.22 Summary of the major functions and body locations of the four tissue types: epithelial, connective, muscle, and nervous tissues.

Nervous tissue: Internal communication• Brain, spinal cord, and nerves

Muscle tissue: Contracts to cause movement

Epithelial tissue: Forms boundaries betweendifferent environments, protects, secretes, absorbs,filters

Connective tissue: Supports, protects, bindsother tissues together

• Muscles attached to bones (skeletal)• Muscles of heart (cardiac)• Muscles of walls of hollow organs (smooth)

• Lining of GI tract organs and other hollow organs• Skin surface (epidermis)

• Bones• Tendons• Fat and other soft padding tissue


Tissue Repair (Wound Healing)

Tissue repair (wound healing) occurs in two ways:

1. Regeneration

Replacement of destroyed tissue by the same kind of

cells

2. Fibrosis

Repair by dense (fibrous) connective tissue (scar

tissue)


Tissue Repair (Wound Healing)

Whether regeneration or fibrosis occurs depends

on:

1. Type of tissue damaged

2. Severity of the injury

Clean cuts (incisions) heal more successfully than

ragged tears of the tissue


Events in Tissue Repair

Inflammation – occurs when tissues are damaged

Capillaries become permeable (↑ in diameter: dilate)

Redness, heat, ↑d blood flow, swelling (edema), pain

Clotting proteins migrate into injured area from the

bloodstream stops blood loss

Clot quarantines the injured area

Scab protects against infection

Macrophages and fibroblasts move in and remove

debris



Granulation tissue forms – delicate pink tissue

Growth of new capillaries from undamaged BVs

Phagocytes dispose of (remove) blood clot and old

fibroblasts

Rebuild collagen fibers & CT (fibroblasts scar

tissue)



Regeneration of surface epithelium begins beneath

the scab

Scab detaches

Whether scar is visible or invisible depends on

severity of wound


Regeneration of Tissues

Tissues that regenerate easily

Epithelial tissue (skin and mucous membranes)

Fibrous connective tissues and bone

Tissues that regenerate poorly

Skeletal muscle

Tissues that are replaced largely with scar tissue

Cardiac muscle

Nervous tissue within the brain and spinal cord


Scar Tissue

Strong

Lacks flexibility

Unable to perform normal fxn of tissue it replaces

Scar tissue may severely hamper the fxning of

affected organ (ex: wall of bladder, heart, other

muscular organ)

Contracture scar

Permanent tightening

of skin that affects the

underlying

tendons/muscles when

inelastic fibrous CT

replaces the normal

elastic CT



Development Aspects of Cells and Tissues

Growth through cell division continues through

puberty

Cell populations exposed to friction (such as

epithelium) replace lost cells throughout life

Connective tissue remains mitotic and forms repair

(scar) tissue

With some exceptions, muscle tissue becomes

amitotic by the end of puberty

Nervous tissue becomes amitotic shortly after birth.


Developmental Aspects of Cells and Tissues

Injury can severely handicap amitotic tissues

The cause of aging is unknown, but chemical and

physical insults, as well as genetic programming,

have been proposed as possible causes


Developmental Aspects of Cells and Tissues

Neoplasms, both benign and cancerous

(malignant), represent abnormal cell masses in

which normal controls on cell division are not

working

Hyperplasia (↑ in size) of a tissue or organ may

occur when tissue is strongly stimulated or irritated

Atrophy (↓ in size) of a tissue or organ occurs when

the organ is no longer stimulated normally

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