Visual Anatomy & PhysiologyFirst Edition

Martini & Ober

Chapter 3Cellular Level of

OrganizationLecture 5

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• Specialization and differentiation of cells

• General characteristics of cells

• The cell membrane

• Cellular organelles (summary table)

• Cell death; necrosis and apoptosis

• Stem cells and progenitor cells

• Cancer

• Movement of substances into and out of the cell

Lecture Overview

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Cells Are Specialized

• vary in size• vary in shape• vary in function• measured in micrometers

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A Composite Cell

• hypothetical cell• major parts

• nucleus• cytoplasm• cell membrane

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Cell Membrane

• outer limit of cell; isolates cell• controls what moves in and out of cell - selectively permeable

•phospholipid bilayer • water-soluble “heads” form outer surfaces• water-insoluble “tails” form interior• permeable to lipid-soluble substances only

• cholesterol stabilizes the membrane• proteins

• receptors• pores, channels, carriers• enzymes• CAMS• self-markers

• self-sealing

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Cell Membranes

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A Transmembrane Protein

Membrane Lipids

Hydrophilic channel

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Cellular Organelles

CELL COMPONENT DESCRIPTION/STRUCTURE

FUNCTION(S)

CELL MEMBRANE Bilayer of phospholipids with proteins dispersed throughout

cell boundary; selectively permeable (i.e. controls what enters and leaves the cell; membrane transport)

CYTOPLASM jelly-like fluid (70% water) suspends organelles in cell

NUCLEUS Central control center of cell; bound by lipid bilayer membrane; contains chromatin (loosely colied DNA and proteins)

controls all cellular activity by directing protein synthesis (i.e. instructing the cell what proteins/enzymes to make.

NUCLEOLUS dense spherical body(ies) within nucleus; RNA & protein

Ribosome synthesis

RIBOSOMES RNA & protein; dispersed throughout cytoplasm or studded on ER

protein synthesis

ROUGH ER Membranous network studded with ribosomes

protein synthesis

SMOOTH ER Membranous network lacking ribosomes

lipid & cholesterol synthesis

GOLGI “Stack of Pancakes”; cisternae modification, transport, and packaging of proteins

Table 1 of 2

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Cellular Organelles

CELL COMPONENT DESCRIPTION/STRUCTURE

FUNCTION(S)

LYSOSOMES Membranous sac of digestive enzymes destruction of worn cell parts (“autolysis) and foreign particles

PEROXISOMES Membranous sacs filled with oxidase enzymes (catalase)

detoxification of harmful substances (i.e. ethanol, drugs, etc.)

MITOCHONDRIA Kidney shaped organelles whose inner membrane is folded into “cristae”.

Site of Cellular Respiration; “Powerhouse of Cell”

FLAGELLA long, tail-like extension; human sperm locomotion

CILIA short, eyelash extensions;human trachea & fallopian tube

to allow for passage of substances through passageways

MICROVILLI microscopic ruffling of cell membrane increase surface area

CENTRIOLES paired cylinders of microtubules at right angles near nucleus

aid in chromosome movement during mitosis

Table 2 of 2

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Cell Death• Two mechanisms of cell death

– Necrosis– Programmed cell death (PCD or apoptosis)

• Necrosis– Tissue degeneration following cellular injury or

destruction– Cellular contents released into the environment

causing an inflammatory response

• Programmed Cell Death (Apoptosis)– Orderly, contained cell disintegration– Cellular contents are contained and cell is

immediately phagocytosed

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Necrosis vs. Apoptosis

Necrosis

ApoptosisFigure from: Alberts et al., Essential Cell Biology, Garland Press, 1998

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Cellular Pathways

of Apoptosis

Figure from: http://www.ambion.com/tools/pathway/pathway.php?pathway=Cellular%20Apoptosis%20Pathway

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Failure of Apoptosis - Syndactyly

Photo from: http://en.wikipedia.org/wiki/Apoptosis

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Stem and Progenitor Cells

Stem cell • can divide to form two new stem cells• can divide to form a stem cell and a progenitor cell• totipotent – can give rise to any cell type (Embryonic stem cells)• pluripotent – can give rise to a restricted number of cell types

Progenitor cell • committed cell• can divide to become any of a restricted number of cells • pluripotent

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Figure from: Hole’s Human A&P, 12th edition, 2010

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Cancer

Two types of tumors• benign – usually remains localized• malignant – invasive and can metastasize; cancerous

Genes that cause cancer• oncogenes – activate other genes that increase cell division• tumor suppressor genes – normally regulate mitosis; if inactivated they will not regulate mitosis

Oncology is the study of tumors

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Cancer is a Genetic Disorder

Figure from: Hole’s Human A&P, 12th edition, 2010

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Cancer

Cancers are due to:

Figure from: Hole’s Human A&P, 12th edition, 2010

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Cancer

Metastasis is the spread of a cancer from its site of origin to other areas of the body

Figure from: Hole’s Human A&P, 12th edition, 2010

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Movements Into and Out of the Cell

Passive (Physical) Processes• require no cellular energy• simple diffusion• facilitated diffusion• osmosis

Active (Physiological) Processes• require cellular energy• active transport• endocytosis• exocytosis• transcytosis

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Solutes will evenly disperse in a solvent with time by diffusion. This is the lowest energy state.

Simple Diffusion

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Simple Diffusion

• movement of substances from regions of higher concentration to regions of lower concentration (a physical process)

Figure from: Hole’s Human A&P, 12th edition, 2010

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Where Would You Rather Be?

“Spread out, would ya!?”

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Facilitated Diffusion

• diffusion across a membrane with the help of a channel or carrier molecule• e.g, transport of glucose across cell membrane

BUT…still from a region of higher concentration to a region of lower concentration

Figure from: Hole’s Human A&P, 12th edition, 2010

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Factors Influencing Diffusion Rates

• Distance (shorter is faster)

• Gradient size (bigger difference in concentration is faster)

• Molecule size (smaller is faster)

• Temperature (warmer is faster)

• Electrical forces (repulsion is better)

In the body, diffusion distances are typically limited to a maximum of about 125 µm

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Diffusion and the Cell Membrane

oxygen, carbon dioxide and other lipid-soluble substances diffuse freely through the membrane

Carrier/channel proteins required for all but fat-soluble molecules and small uncharged molecules

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Osmosis (Special case of passive diffusion)

• movement of water (solvent) through a selectively permeable membrane from regions of higher water concentration to regions of lower water concentration• *water moves toward a higher concentration of solutes

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Osmotic Pressure/Tonicity

Osmotic Pressure (Osmolarity) – ability of solute to generate enough pressure to move a volume of water by osmosis

*Osmotic pressure increases as the number of nonpermeable solutes particles increases

• isotonic – same osmotic pressure as a second solution

• hypertonic – higher osmotic pressure

• hypOtonic – lower osmotic pressure

0.9% NaCl5.0% Glucose

Crenation

The O in

hypotonic

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Filtration

• smaller molecules are forced through porous membranes• hydrostatic pressure important in the body• molecules leaving blood capillaries

Think ‘sprinkler hose’

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Active Transport

• carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration, i.e., against a concentration gradient

• sugars, amino acids, sodium ions, potassium ions, etc.

Active transport is a physiological process since it requires cellular energy

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Endocytosis and Exocytosis• 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

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• The cell is– The structural and functional unit of all living matter– Smallest body structure that can perform the functions of

‘life’

• Cells must specialize and differentiate, e.g., neurons (nerve cells) and muscle cells

• All eukaryotic cells have several major components in common– Nucleus– Cell membrane– Cytosol– Organelles– Inclusions

Lecture Review

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Lecture Review

TRANSPORTPROCESS

ISENERGYNEEDED?

CONCEN-TRATIONGRADIENT

GENERALDESCRIPTION

EXAMPLEIN HUMANS

SIGNIFICANCE

SIMPLEDIFFUSION

NO [HIGH]TO[LOW]

spreading out of molecules to equilibrium

O2 into cells; CO2

out of cells.

Cellular Respiration

FACILITATED DIFFUSION

NO [HIGH]TO[LOW]

Using a special cm carrier protein to move something through the cell membrane (cm)

Process by which glucose enters cells

OSMOSIS NO [HIGH]TO[LOW]

water moving through the cm to dilute a solute

maintenance of osmotic pressure of 0.9%.

Same

FILTRATION NO [HIGH]TO[LOW]

using pressure to push something through a cm (sprinkler hose)

manner in which the kidney filters things from blood

removal of metabolic wastes

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Lecture Review

TRANSPORTPROCESS

ISENERGYNEEDED?

CONCEN-TRATIONGRADIENT

GENERALDESCRIPTION

EXAMPLEIN HUMANS

SIGNIFICANCE

ACTIVE TRANSPORT

YES [LOW]TO[HIGH]

opposite of diffusion at the expense of energy

K+-Na+-ATPase pump

maintenance of the resting membrane potential

ENDOCYTOSIS YES [LOW]TO[HIGH]

bringing a substance into the cell that is too large to enter by any of the above ways;

Phagocytosi: cell eating;

Pinocytosis: cell drinking.

Phagocytosed (foreign) particles fuse with lysosomes to be destroyed

help fight infection

EXOCYTOSIS YES [LOW]TO[HIGH]

expelling a substance from the cell into ECF

Exporting proteins; dumping waste

Same