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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
14
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
16
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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17
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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.
19
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)
20
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
22
• 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.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
25
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
26
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
29
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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30
ENDOCYTOSIS
Cytoplasm
Vesicle
(a) (b) (c) (d)
Receptorprotein
Cellmembrane
Moleculesoutside cell
Cellmembraneindenting
Receptor-ligandcombination
Nucleus Nucleolus
Particle VesiclePhagocytizedparticle
Cellmembrane
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31
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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32
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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