CHAPTER 2

Cell and Tissues

Cells are the smallest living subunits of a multicellular organism such as a human being

Cells are the building blocks and functional units

of all living things. Carry out all chemical activities needed to sustain

life. Tissues are groups of cells that are similar in

structure and function.

WHAT ARE THE MAIN FUNCTIONS OF THE CELL? Metabolize Digest foods Get rid of wastes Reproduce Grow Move Respond to a stimulus (irritability)

Cells are not all the same but has a general structures and is formed of three main regions:Nucleus (RBCs are exception)CytoplasmPlasma membrane

I-The Nucleus Control center of the

cell, contains genetic material (DNA), RNA, & protein.

46 chromosomes Three regions:

a-Nuclear Membrane Consists of a double

phospholipid membrane

Contain nuclear pores that allow for exchange of materials with the rest of the cell.

Figure 3.1b

b- Nucleoli Nucleus contains one or more nucleoli. Sites of ribosome production

Ribosomes then migrate to the cytoplasm through nuclear pores Ribosomes are the site for protein systhesis

c-Chromatin Composed of DNA and protein Scattered throughout the nucleus Chromatin condenses to form chromosomes when the

cell divides.

II-Plasma Membrane :phospholipids, cholesterol (decreases the fluidity of the membrane), and proteins (channels, transporters, receptors).

Barrier for cell contents Double phospholipid layer (permit lipid-soluble materials to

easily enter or leave the cell by diffusion through the cell membrane

III-Cytoplasm watery solution of

minerals, gases, organic molecules, and cell organelles that is found between the cell membrane and the nucleus.

-Cytosol ,fluid that suspends other elements.

-Organelles ,metabolic machinery of the cell.

-Inclusions ,non-functioning units.

Cytoplasmic Organelles: the main organelles are:

1-Ribosomes:sites of protein synthesis2-Endoplasmic reticulum (ER):fluid-filled tubules for

carrying substances. It has two types: rough & smooth

3-Golgi apparatus: modifies and packages proteins & carbohydrates.

4-Lysosomes:contain enzymes that digest non-usable materials within the cell.

5-Mitochondria:“powerhouses” of the cell. mitochondria are he site of ATP (and hence energy) production

6-Centrioles:rod-shaped bodies made of microtubules. Direct the formation of mitotic spindle during cell division. Their function is to organize the spindle fibers during cell division

Cellular Physiology: Membrane Transport Membrane Transport is movement of substance into

and out of the cell The plasma membrane allows some materials to pass

while excluding others Transport is by two basic methods

Passive transport :No energy is required Active transport: Energy is needed and must be provided by the

cell

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MOVEMENTS INTO AND OUT OF THE CELL

Passive (Physical) Processes• Require no cellular energy

and include:• Simple diffusion• Facilitated diffusion• Osmosis• Filtration

Active (Physiological) Processes• Require cellular energy and

include:• Active transport• Endocytosis• Exocytosis• Transcytosis

Passive Transport Processes1-Diffusion

Particles tend to distribute themselves evenly within a solution

Movement is from high concentration to low one.Ex: Gas exchange

Types of diffusion-Simple diffusion :solutes are lipid-soluble materials or small enough to pass through

membrane pores.

-Osmosis :simple diffusion of water-Facilitated diffusion: Substances require a protein carrier for passive transport.

Figure 3.9

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SIMPLE DIFFUSION

• Movement of substances from regions of higher concentration to regions of lower concentration• Oxygen, carbon dioxide and lipid-soluble substances

Time

Solute molule

ater moule

A B A B

(2) (3)

A B

(1)

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FACILITATED DIFFUSION

• Diffusion across a membrane with the help of a channel or carrier molecule• Glucose and amino acids (needs carrier enzymes)

Region of higherconcentration

Transportedsubstance

Region of lowerconcentration

Protein carriermolecule

Cellmembrane

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Figure 3.10

Diffusion through the Plasma Membrane

2-Filtration

Water and solutes are forced from a high pressure area to a lower pressure area ,a pressure gradient must exist.

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OSMOSIS• Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration• Water will naturally tend to move to an areawhere there is more dissolved material, such as salt orsugar.

The process of osmosis also takes place in thekidneys, which reabsorb large amounts of water (manygallons each day) to prevent its loss in urines

Time

A BA B

(1) (2)

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OSMOSIS AND OSMOTIC PRESSURE

• Osmotic Pressure – ability of osmosis to generateenough pressure to move a volume of water

• Osmotic pressure increases as the concentrationof nonpermeable solutes increases

• Isotonic – same osmotic pressure• Hypertonic – higher osmotic pressure (water loss) ???• Hypotonic – lower osmotic pressure (water gain) ???

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© David M. Phillips/Visuals Unlimited

(b)

(a)

(c)

Active Transport ProcessesTransport substances that are unable to pass by diffusion.-They may be too large-They may not be able to dissolve in the fat core of the

plasma membrane-They may have to move against a concentration gradient requires the energy of ATP to move molecules from an area of lesser concentration to

an area of greater concentration.

ACTIVE TRANSPORT

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• Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration• Sugars, amino acids, sodium ions, potassium ions, etc.

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Carrier protein Binding site

(a)

(b)

Cel

l mem

bra

ne

Carrier proteinwith altered shape

Phospholipidmolecules Transported

particle

Cellularenergy

Region of higherconcentration

Region of lowerconcentration

TWO COMMON FORMS OF ACTIVE TRANSPORT:

1-Solute pumpingAmino acids, some sugars and ions are

transported by solute pumps.ATP energizes protein carriers, and in most

cases, moves substances against concentration gradients

The best example is Sodium-Potassium pump

EXAMPLES Nerve and muscle cells constantly produce

ATP to keep their sodium pumps (and similar potassium pumps) working and prevent

spontaneous impulses. Another example of active transport is the

absorption. The cells use ATP to absorb these nutrients

from digested food, even when their intracellular concentration becomes greater than their extracellular concentration. n of glucose

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ACTIVE TRANSPORT:SODIUM-POTASSIUM PUMP• Active transport mechanism• Creates balance by “pumping” three (3) sodium (Na+) OUT and two (2) potassium (K+) INTO the cell• 3:2 ratio

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FILTRATIONMovement of water and dissolved substances from an area of higher pressure to an area of lower pressure (blood pressure).• Smaller molecules are forced through porous membranes• Hydrostatic pressure important in the body• Molecules leaving blood capillaries

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Capillary wall

Larger molecules

Smaller molecules

Bloodpressure Blood

flow

Tissue fluid

The blood pressure in capillaries is higher than the pressure of the surrounding

tissue fluid. In capillaries throughout the body, blood pressure forces plasma (water) and dissolved materials through the capillary membranes into the surrounding tissue spaces

2-BULK TRANSPORT

Exocytosis Material inside the cell migrates to plasma membrane

where a vesicle is formed. It is emptied to the outside.

Endocytosis Extracellular substances are engulfed by being

enclosed in a membranous vesicle.

Types of endocytosis Phagocytosis – cell eating Pinocytosis – cell drinking

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ENDOCYTOSIS• Cell engulfs a substance by forming a vesicle around the substance• Three types:

• Pinocytosis – substance is mostly water• Phagocytosis – substance is a solid• Receptor-mediated endocytosis – requires the substance to

bind to a membrane-bound receptor

Nucleus Nucleolus

VesicleCellmembrane

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ENDOCYTOSIS

Cytoplasm

Vesicle

(a) (b) (c) (d)

Receptorprotein

Cellmembrane

Moleculesoutside cell

Cellmembraneindenting

Receptor-ligandcombination

Nucleus Nucleolus

Particle VesiclePhagocytizedparticle

Cellmembrane

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EXOCYTOSIS• Reverse of endocytosis• Substances in a vesicle fuse with cell membrane• Contents released outside the cell• Release of neurotransmitters from nerve cells

Nucleus

Endoplasmicreticulum

Golgiapparatus

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TRANSCYTOSIS

• Endocytosis followed by exocytosis• Transports a substance rapidly through a cell• HIV crossing a cell layer

Viruses budHIV

Exocytosis

Receptor-mediated endocytosis

HIV-infectedwhite blood cells Anal or

vaginal canal

Lining of anusor vagina(epithelial cells)

Virus infectswhite blood cells onother side of lining

Receptor-mediatedendocytosis

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Cellmembrane

DIFFUSIONOsmosis

Facilitated Diffusion

Active transport

Filtration

Phagocytosis

Pinocytosis

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THE CELL CYCLE

• Series of changes a cell undergoes from the time it forms until the time it divide• Stages:

• Interphase• Mitosis• Cytokinesis

Apoptosis

G2 phase

Prophase

Metaphase

AnaphaseTelophase

Cytokinesis

Restrictioncheckpoint

Remainspecialized

Proceedto division

S phase:geneticmaterialreplicates

G1 phasecell growth

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Cell Life Cycle Cells have two major periods

Interphase Cell grows but no cell division. 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

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.

Figure 3.14

CELL DIVISION

Cell division is the process by which a cell reproduces itself.

There are two types of cell division, mitosis and meiosis.

Although both types involve cell reproduction, their purposes are very different.

Events of Cell Division Mitosis

In mitosis, one cell with the diploid number of chromosomes (46 for people) divides into two identical cells, each with the diploid number of chromosome

The stages of mitosis are prophase, metaphase,

anaphase, and telophase.Division of the nucleusResults in the formation of two daughter nuclei

CytokinesisDivision of the cytoplasmBegins when mitosis is near completionResults in the formation of two daughter cells

Figure 3.15

Meiosis is a more complex process of cell division that results in the formation of gametes.

In meiosis, one cell with the diploid number of chromo cells, divides twice to form four cells each with the haploid number (half the usual number) of chromosomes.

Body Tissues Tissues are groups of cells with similar structure and

function.Four primary tissue types

-Epithelium - Connective tissue-Nervous tissue - Muscle Tissue

Epithelial Tissues,found in different areas:Body coverings Body linings Glands

Functions: Protection Absorption Filtration Secretion

EPITHELIAL CELLS are found on surfaces as either

coverings (outer surfaces) or linings (inner

surfaces).

Epithelium Characteristics Cells fit closely together Tissue layer always has one free

surface The lower surface is bound by a

basement membrane Avascular (have no blood supply) Regenerate easily if well nourished

Classification of Epithelium According to Number of cell layers

Simple – one layerStratified – more than one layer

(Oral cavity)

Figure 3.17a

According to the Shape of cells Squamous – flattened (alveoli) Cuboidal – cube-shaped (thyroid

gland) Columnar – column-like (stomach

lining); ciliated (trachea) Pseudostratified

Figure 3.17b

Glandular Epithelium Gland – one or more cells that secretes a particular

product. Three major gland types:

Endocrine gland = Ductless Secretions are called hormones

Exocrine gland Empty through ducts to the epithelial surface Include sweat and oil glands, saliva*Mixed glands: both endo and exocrine glands as

pancreas , ovaries and testes.

Connective Tissue Found everywhere in the body The most abundant and widely distributed tissues Functions

Binds body tissues togetherSupports the bodyProvides protectionAbility to absorb large amount of water (Water reservoir).

Connective Tissue shows variations in blood supplyMost conn. tissues are well vascularized.Tendons and Ligaments have a poor supply.Cartillages are avascular

Connective Tissues are made of : -Different types of cells.

-Non-living substance that surrounds living cells.-Different types of fibers(collagen,elastin,reticular).

Types of connective tissue Conn. T. differ in their fibers present in the

matrix From most rigid to softest,C.T. major classes are: -bone - cartilage - dense c.t. as tendon,ligament & dermis of

skin. - loose c.t.as areolar,adipose and reticular. -blood

Fibroblasts

Cartilage

Bone

Muscle TissueMuscle is very important, specialized for contraction.

It provides: movement maintains posture supports soft tissue guards orifices maintains body temperature

3 Kinds of Muscle CELLs

Skeletal muscle

Smooth muscle

Cardiac muscle

NERVE TISSUE consists of nerve cells called

neurons and some specialized cells found only in

the nervous system The nervous system has two divisions:

thecentral nervous system (CNS) and

the peripheral nervous system (PNS).

Neurons are capable of generating and transmitting electrochemical impulses.

Neural Tissue Sends messages throughout the body by

conducting electrical impulses The brain and spinal cord are control centers The neuron is the basic unit

Tissue Repair (wound healing) Healing may be by:1--regeneration(injured tissues are replaced by the

same type of cells2- -Fibrosis (the wound is repaired by scar tissue ) 3- or both Epith.& c.t. regenerate well. Mature cardiac muscle & nervous tissue are

repaired by fibrosis.

Developmental aspects Growth through cell division continues through

puberty. Cells exposed to friction replace lost cells

throughout life(skin , GI tract &bone marrow). Conn. T. remains mitotic& forms repair (scar)

tissue Muscle t. becomes amitotic by the end of

puberty. Nervous t.become amitotic shortly after birth