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Cells and Tissues

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Cells and Tissues

Concepts of the Cell Theory

A cell is the basic structural and functional unit of living organisms.

The activity of an organism depends on the collective activities of its cells.

According to the principle of complementarity, the biochemical activities of cells are dictated by the relative number of their specific subcellular structures.

Continuity of life has a cellular basis.

Chemical Components of Cells

Most cells are composed of the following four elements

Carbon

Hydrogen

Oxygen

Nitrogen

Cells and Tissues

Carry out all chemical activities needed to sustain life

Cells are the building blocks of all living things.

Tissues are groups of cells that are similar in structure and function.

Anatomy of the Cell

Cells are not all the same.

All cells share general structures.

All cells have three main regions

Nucleus

Cytoplasm

Plasma membrane

The Nucleus (p66)

Control center of the cell

Contains genetic material (DNA)

Three regions

Nuclear envelope (membrane)

Nucleolus – are sites where ribosomes are assembled.

Chromatin – when a cell is not dividing, it’s DNA is combined with protein and forms a loose network of bumpy threads called chromatin. (see below)

CHROMOSOMES – when a cell is dividing to form two daughter cells, the chromatin threads coil and condense to form dense, rodlike bodies called chromosomes.

The Nucleus

Nuclear envelope (membrane)

Barrier of the nucleus

Consists of a double membrane

Contains nuclear pores that allow for exchange of material with the rest of the cell

The Nucleus

Nucleoli

Nucleus contains one or more nucleoli

Sites of ribosome assembly

Ribosomes migrate into the cytoplasm through nuclear pores

The Nucleus

Chromatin - when a cell is not dividing, it’s DNA is combined with protein and forms a loose network of bumpy threads called chromatin.

Composed of DNA and protein

Present when the cell is not dividing

Scattered throughout the nucleus

Condenses to form chromosomes when the cell divides

DNA is much like a blueprint that contains all the instructions needed for building the whole body.

Plasma Membrane

Barrier for cell contents

Double phospholipid layer

Hydrophilic heads

Hydrophobic tails

Also contains proteins, cholesterol, and glycoproteins

Plasma Membrane Junctions

Membrane junctions

Tight junctions

Impermeable junctions

Bind cells together into leakproof sheets

Desmosomes

Anchoring junctions that prevent cells from being pulled apart

Gap junctions

Allow communication between cells

Cytoplasm

The material outside the nucleus and inside the plasma membrane

Site of most cellular activities

Cytoplasm

Contains three major elements

Cytosol

Fluid that suspends other elements

Organelles

Metabolic machinery of the cell

“Little organs” that perform functions for the cell

Inclusions

Chemical substances such as stored nutrients or cell products

Cytoplasmic Organelles

Mitochondria

“Powerhouses” of the cell

Change shape continuously

Carry out reactions where oxygen is used to break down food

Provides ATP for cellular energy

Ribosomes

Made of protein and 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 tubules for carrying substances

Two types of ER

Rough endoplasmic reticulum

Studded with ribosomes

Synthesizes proteins

Smooth endoplasmic reticulum

Functions in lipid metabolism and detoxification of drugs and pesticides

Golgi apparatus

Modifies and packages proteins

Produces different types of packages

Secretory vesicles

Cell membrane components

Lysosomes

Lysosomes

Contain enzymes produced by ribosomes

Packaged by the Golgi apparatus

Digest worn-out or nonusable materials within the cell

Peroxisomes

Membranous sacs of oxidase enzymes

Detoxify harmful substances such as alcohol and formaldehyde

Break down free radicals (highly reactive chemicals)

Replicate by pinching in half

Cytoskeleton

Network of protein structures that extend throughout the cytoplasm

Provides the cell with an internal framework

Three different types of elements

Microfilaments (largest)

Intermediate filaments

Microtubules (smallest)

Centrioles

Rod-shaped bodies made of microtubules

Direct the formation of mitotic spindle during cell division

Cellular Projections

Not found in all 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

Solutions and 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

Intracellular fluid—nucleoplasm and cytosol

Interstitial fluid—fluid on the exterior of the cell

Selective Permeability

The plasma membrane allows some materials to pass while excluding others.

This permeability influences movement both into and out of the cell.

Cell Physiology: Membrane Transport

Another function to to protect)
Passive doesn’t need energy
Active needs energy

TRANSPORT MECHANISMS: TYPES, CHARACTERISTICS

Membrane transport—movement of substances into and out of the cell

Cell membranes are selectively permeable (some substances can pass through but others cannot)

Two basic methods of transport

Passive processes

No energy is requi red

Active processes

Cell must provide metabolic energy (ATP)- no energy

Passive Processes – doesn’t need energy

Diffusion

Particles tend to distribute themselves evenly within a solution

Movement is from high concentration to low concentration, or down a concentration gradient

Types of diffusion

Simple diffusion

An unassisted process

Solutes are lipid-soluble materials or small enough to pass through membrane pores

Osmosis—simple diffusion of water

Highly polar water molecules easily cross the plasma membrane through aquaporins

Facilitated diffusion

Substances require a protein carrier for passive transport

Transports lipid-insoluble and large substances

DOES NOT REQUIRE ATP

Passive Processes

Filtration

TO do a filtration we need pressure different
Kidney is an example

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

A pressure gradient must exist – kidney (filtering blood)

Solute-containing fluid is pushed from a high-pressure area to a lower pressure area

Active Processes

Too large to pass (they may not be able to dissolve in the fat core of the membrane)

Substances are transported that are unable to pass by diffusion

Substances may be too large

TOO LARGE TO PASS - Substances may not be able to dissolve in the fat core of the membrane

Substances may have to move against a concentration gradient

ATP is used for transport

Active Processes

Two common forms of active transport

Active transport (solute pumping)

Vesicular transport

Exocytosis

Endocytosis

Phagocytosis

Pinocytosis

Active Processes

Active transport (solute pumping)

Amino acids, some sugars, and ions are transported by protein carriers called solute pumps

ATP energizes protein carriers

In most cases, substances are moved against concentration gradients

From low to high concentration

Active Processes

Vesicular transport

Exocytosis

Moves materials out of the cell

Material is carried in a membranous vesicle

Vesicle migrates to plasma membrane, vesicles protect these chemicals until they are ready to be transported out

Vesicle combines with plasma membrane

Material is emptied to the outside

Active Processes

Vesicular transport (continued)

Endocytosis

Extracellular substances are engulfed by being enclosed in a membranous vescicle

Types of endocytosis

Phagocytosis—“cell eating”

Pinocytosis—“cell drinking”

Cell Life Cycle

Cells have two major periods

Interphase

Cell grows

Cell carries on metabolic processes

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

DNA uncoils and each side serves as a template

Events of Cell Division

Mitosis—division of the nucleus

Results in the formation of two daughter nuclei

Produces body cells
Produces genetically identical cells (feature)

Cytokinesis—division of the cytoplasm

Begins when mitosis is near completion

Results in the formation of two daughter cells

Stages of Mitosis

Prophase

First part of cell division

Centrioles migrate to the poles to direct assembly of mitotic spindle fibers

DNA appears as double-stranded chromosomes

Nuclear envelope breaks down and disappears

Stages of Mitosis

Metaphase

Chromosomes are aligned in the center of the cell on the metaphase plate

Stages of Mitosis

Anaphase

Chromosomes are pulled apart and toward the opposite ends of the cell

Cell begins to elongate

Stages of Mitosis

Telophase

Chromosomes uncoil to become chromatin

Nuclear envelope reforms around chromatin

Spindles break down and disappear

Stages of Mitosis

Cytokinesis

Begins during late anaphase and completes during telophase

A cleavage furrow forms to pinch the cells into two parts

Protein Synthesis

Gene—DNA segment that carries a blueprint for building one protein

Proteins have many functions

Building materials for cells

Act as enzymes (biological catalysts)

RNA is essential for protein synthesis

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

Transcription and Translation

Transcription

Transfer of information from DNA’s base sequence to the complimentary base sequence of mRNA

Three-base sequences on mRNA are called codons

Transcription and Translation

Translation

Base sequence of nucleic acid is translated to an amino acid sequence

Amino acids are the building blocks of proteins

Body Tissues

Tissues

Groups of cells with similar structure and function

Four primary types

Epithelial tissue (epithelium)

Connective tissue

Muscle tissue

Nervous tissue

Epithelial Tissues

Locations

Body coverings

Body linings

Glandular tissue

Functions

Protection

Absorption

Filtration

Secretion

Epithelium Characteristics - important

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 quickly easily if well nourished

Classification of Epithelia can be based on layers, shape

Number of cell layers

Simple—one layer

Stratified—more than one layer

Classification of Epithelia

Shape of cells

Squamous

flattened

Cuboidal

cube-shaped

Columnar

column-like

Simple Epithelia

Simple squamous

Single layer of flat cells

Location - usually forms membranes

Lines body cavities

Lines lungs and capillaries

Functions in diffusion, filtration, or secretion in membranes

Simple Epithelia

Simple cuboidal

Single layer of cube-like cells

Locations

Common in glands and their ducts

Forms walls of kidney tubules

Covers the ovaries

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

Simple Epithelia

Simple columnar

Single layer of tall cells

Often includes mucus-producing goblet cells

Location - lines digestive tract

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

Simple Epithelia

Pseudostratified columnar

Single layer, but some cells are shorter than others

Looks like with many layers but it is not – “pseudo”

Often looks like a double layer of cells but all cells rest on the basement membrane

Location - respiratory tract, where it is ciliated

Functions in absorption or secretion

Stratified Epithelia

Stratified squamous - common

Cells at the apical surface are flattened

Functions as a protective covering where friction is common

Locations - lining of the:

Skin

Mouth

Esophagus

Stratified Epithelia

Stratified cuboidal (rare)—two layers of cuboidal cells; functions in protection

Stratified columnar (rare)—surface cells are columnar, cells underneath vary in size and shape; functions in protection

Stratified cuboidal and columnar

Rare in human body

Found mainly in ducts of large glands

Stratified Epithelia

Transitional epithelium

Composed of modified stratified squamous epithelium

Shape of cells depends upon the amount of stretching

Functions in stretching and the ability to return to normal shape

Location - lines organs of the urinary system

Resembles both stratifies squamous and cuboidal. S

Glandular Epithelium

Gland

One or more cells responsible for secreting a particular product

Secretions contain protein molecules in an aqueous (water-based) fluid

Glandular Epithelium

Two major gland types

Endocrine gland

Ductless since secretions diffuse into blood vessels

All secretions are hormones

Exocrine gland

Secretions empty through ducts to the epithelial surface

Include sweat and oil glands

Connective Tissue

Found everywhere in the body

Includes the most abundant and widely distributed tissues

Functions

Binds body tissues together

Supports the body

Provides protection

Connective Tissue Characteristics

Variations in blood supply

Some tissue types are well vascularized

Some have a poor blood supply or are avascular

Extracellular matrix

Non-living material that surrounds living cells

Extracellular Matrix

Two main elements

Ground substance—mostly water along with adhesion proteins and polysaccharide molecules

Fibers

Produced by the cells

Three types

Collagen (white) fibers - strength

Elastic (yellow) fibers - stretch

Reticular fibers – structural network, forms internal “sjeleton”

Connective Tissue Types

Bone (osseous tissue)

Composed of

Bone cells in lacunae (cavities)

Hard matrix of calcium salts

Large numbers of collagen fibers

Functions to protect and support the body

Connective Tissue Types

Hyaline cartilage

Most common type of cartilage

Composed of

Abundant collagen fibers

Rubbery matrix

Locations

Larynx

Entire fetal skeleton prior to birth

Functions as a more flexible skeletal element than bone

Connective Tissue Types – ear,

Elastic cartilage

Provides elasticity

Location

Supports the external ear

Fibrocartilage –forms cushion-like discs between ver…

Highly compressible

Location

Forms cushion-like discs between vertebrae

Connective Tissue Types

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

Dermis—lower layers of the skin

Connective Tissue Types

Loose connective tissue types

Areolar tissue

Most widely distributed connective tissue

Soft, pliable tissue like “cobwebs”

Functions as a packing tissue

Contains all fiber types

Can soak up excess fluid (causes edema)

Connective Tissue Types

Loose connective tissue types

Can absorb extra fluid

Adipose tissue – function is to store lipid droplets

Matrix is an areolar tissue in which fat globules predominate

Many cells contain large lipid deposits

Functions

Insulates the body

Protects some organs

Serves as a site of fuel storage

LOCATION: under skin, around kidneys, behind eyeballs, within abdomen and in breasts; Hypodermis.

Connective Tissue Types

Loose connective tissue types

Reticular connective tissue

Delicate network of interwoven fibers

Locations

Forms stroma (internal supporting network) of lymphoid organs

Lymph nodes

Spleen

Bone marrow

Connective Tissue Types

Blood (vascular tissue)

Blood cells surrounded by fluid matrix called blood plasma

Fibers are visible during clotting

Functions as the transport vehicle for materials

Muscle Tissue – 50%

Function is to produce movement

Three types

Skeletal muscle

Cardiac muscle

Smooth muscle

Muscle Tissue Types

Skeletal muscle – produce body movement

Under voluntary control

Contracts to pull on bones or skin

Produces gross body movements or facial expressions

Characteristics of skeletal muscle cells

Striated

Multinucleate (more than one nucleus)

Long, cylindrical cells

Muscle Tissue Types

Cardiac muscle – pump blood

Under involuntary control

Found only in the heart

Function is to pump blood

Characteristics of cardiac muscle cells

Striated

One nucleus per cell; intercalated discs – unique for this muscle

Cells are attached to other cardiac muscle cells at intercalated disks

Muscle Tissue Types

Smooth muscle

Under involuntary muscle

Found in walls of hollow organs such as stomach, uterus, and blood vessels. Surrounds hollow organs and passageways

Characteristics of smooth muscle cells

No visible striations

One nucleus per cell

Spindle-shaped cells

Nervous Tissue 2%

Composed of neurons and nerve support cells

Function is to send impulses to other areas of the body

Irritability

Conductivity

Support cells called neuroglia insulate, protect, and support neurons

Neurons – to send nerve inpuleses
Axons – long extensions
Dendrites – short extensions

Tissue Repair (Wound Healing)

Regeneration

Replacement of destroyed tissue by the same kind of cells

Fibrosis

Repair by dense (fibrous) connective tissue (scar tissue)

Whether regeneration or fibrosis occurs depends on:

Type of tissue damaged

Severity of the injury

Events in Tissue Repair

Inflammation

Capillaries become very permeable

Clotting proteins migrate into the area from the blood stream

A clot walls off the injured area

Granulation tissue forms

Growth of new capillaries

Rebuild collagen fibers

Regeneration of surface epithelium

Scab detaches

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

Developmental Aspects of Tissue

Epithelial tissue arises from all three primary germ layers

Muscle and connective tissue arise from the mesoderm

Nervous tissue arises from the ectoderm

With old age, there is a decrease in mass and viability in most tissues

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