Human Anatomy,

First Edition McKinley & O'Loughlin Chapter 2 : The Cell: Basic Unit of Structure and Function 1

The Cell

  Cells:  structural and functional units of all living organisms.  building blocks of the human body.  adult human body contains ~ 75 trillion cells.

Each cell type performs specific functions .

 ~200 cell types in humans  subcategories of most 2-2

Common Characteristics of Cells

 Perform the general functions necessary to sustain life:     Obtain nutrients and other materials from its surrounding fluids.

 Fuel molecules, O 2, building blocks, minerals,etc Dispose of wastes products  Urea (from nitrogen), CO 2 , metabolic waste Maintain shape and integrity  Size and shape are related to function Cell division:   Mitosis: growth and repair Meiosis: gamete formation 2-3

Study of Cells

   Cytology: study of cells Microscopic anatomy  Individual cells observable by light microscopy  Subcellular structures observable by electron microscopy.   TEM SEM Unit of measure: micrometer (um)  RBC: 7-8um 2-4

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Cells

 Parts of a cell   Cell Membrane (or plasma membrane) Cytoplasm    Cytosol Organelles   Membranous Organelles Non-membranous Organelles Inclusions  Nucleus 2-6

Plasma (Cell) Membrane

  the outer, limiting barrier separates the internal contents of the cell from external materials. 2-7

Cytoplasm

 general term for all cellular contents located between the plasma membrane and the nucleus. 2-8

Nucleus

  “control center” of the cell controls protein synthesis  directs the functional and structural characteristics of the cell . 2-9

Plasma membrane: composition

 Lipids  Phospholipids  Head: hydrophilic   Tail: hydrophobic Form lipid bilayer   Cholesterol Glycolipids   Carbohydrate component Part of glycocalyx 2-10

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Plasma membrane: composition

 Protein     Integral membrane proteins Peripheral membrane proteins Some serve as enzymes, ion channels or receptors Glycoproteins 2-12

Plasma membrane: functions

    Selectively permeable barrier   Nutrient in Waste out Communication Intercellular connections Physical barrier 2-13

Transport Mechanisms

    Passive Transport Active Transport Bulk Transport Solution= solvent (H 2 O)+ solute 2-14

Passive Transport

   Movement of substances along a concentration gradient  [Hi] to [Low] ATP is not required Types:  Simple Diffusion: solutes    Facilitated Diffusion: solutes Bulk Filtration: solution Osmosis: solvent 2-15

Facilitated Diffusion

  Requires the participation of specific transport proteins that help specific substances or molecules move across the plasma membrane. “Carrier-mediated” 2-16

Bulk Filtration

  Involves the diffusion of both solvents and solutes together across the selectively permeable membrane.

Pressure gradients 2-17

Osmosis

  Involves the diffusion of a solvent (H2O), across a selectively permeable membrane.

Can cause a volume change 2-18

Active Transport

  Movement of a substance across a plasma membrane against a concentration gradient.

Materials must be moved from an area of low concentration to an area of high concentration.  requires cellular energy in the form of ATP (adenosine triphosphate)   uses transport proteins (carrier-mediated) ATP is continually synthesized by mitochondria 2-19

Ion Pumps

 Active transport processes that move ions across the membrane are called ion pumps .  ion pumps allow a cell to maintain its internal concentrations of small molecules or ions 2-20

Bulk Transport - Exocytosis

   Used by cells that secrete Usually movement of large molecules Movement out of the cell. 2-21

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Bulk Transport - Endocytosis

 process by which the cell acquires materials from the extracellular fluid: (3 Forms)    Phagocytosis:    Cell forms pseudopodia engulfs a particle internalize it into a vacuole Pinocytosis:   incorporation of droplets of extracellular fluid (solution) Taken into the cell in small vesicles Receptor-mediated endocytosis:    receptors in the cell membrane Bind with specific molecules Invagination forms around them to create a cytoplasmic vesicle 2-23

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Cytoplasm: cytosol

   Matrix; intracellular material Different in different cell Mostly water 2-26

Cytoplasm: Organelles

    Complex, organized structures Have unique, characteristic shapes.

Each type performs a different function for the cell.

Are essential for normal cellular structure and activities .

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Membranous Organelles

 Include:  Endoplasmic Reticulum  Rough Endoplasmic Reticulum (RER)    Ribosomes Make protein for export Peroxisomes made here  Smooth Endoplamic Reticulum (SER)   Lipids and carbohydrates Detoxification 2-28

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Membranous Organelles

 Peroxisomes     Vesicles formed from RER Use oxygen to detoxify Mediated by specific enzymes Most abundant in liver 2-31

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Membranous Organelles

  Golgi Apparatus   Modifies, stores and sorts material from RER Receiving region (cis-face)  Shipping region (trans-face) Produces Lysosomes   Autophagy: removal of old organelles Autolysis: destruction of the cell 2-33

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Mitochondria

   Mitochondria are organelles with a double membrane. Produce large amounts of ATP. Are called the “powerhouses” of the cell. 2-37

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Non-Membranous Organelles

   Not made of a membrane.

Usually made of protein Include:  Ribosomes: free and fixed   Cytoskeleton    Microfilaments Intermediate fibers microtubules Centrosome  centrioles 2-39

Ribosomes

   Small, dense granules  Protein  RNA Site of protein synthesis. Each ribosome has a small and a large subunit.  small subunit is about one-half the size of the large subunit. 2-40

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The Cytoskeleton

    Made of filamentous proteins Helps give the cell its shape Coordinates cellular movements. Three categories:    microfilaments intermediate filaments microtubules 2-42

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Non-membranous Organelles

 Centrioles and the centrosome  Centrosome  Area close to the nucleus   Organization site for microtubules Centrioles (exist as a pair)   In the centrosome Perpendicular to each other   9 sets of microtubule triplets Important in cell division (spindle) 2-44

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Microvilli, Cilia and Flagella

 Appendages extending from the surface of some cells.    Microvilli:   short, cytoplasmic extensions For absorption Cilia:   usually occur in large numbers work together to move materials or fluids along the surface of a cell. Flagella:   longer than cilia, and usually occur as single appendages.

Move the cell 2-46

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The Nucleus

   Control center of cellular activities. Usually, it is the largest structure within the cell Appears as a single spherical or oval structure. 2-48

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The Nucleus

  Enclosed by a double membrane called the nuclear envelope.

The nuclear envelope:  controls the entry and exit of materials between the nucleus and the cytoplasm. 2-50

Nucleolus

  The cell nucleus may contain one or more nucleoli. Nucleoli:  are responsible for making the small and the large subunits of ribosomes. 2-51

Chromatin and DNA

 DNA is the genetic material housed within the nucleus.   DNA is a polymer of nucleotides (sugar, phosphate, nitrogen base) Is a double helix.  Chromatin:  Strands of DNA and histone proteins   Euchromatin: uncoiled; active Heterochromatin: coiled. inactive 2-52

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Insert Figure 2.18

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Chromosome

   The chromosome is the most organized level of genetic material. Each chromosome contains a single, long molecule of DNA and associated proteins. Chromosomes become visible only when the cell is dividing. 2-55

The Cell Cycle

  The life cycle of the cell is called the cell cycle. New cells must be made continuously in order for an organism to grow and replace its damaged cells. 2-56

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Mitosis and Meiosis

   There are two types of cell division. Mitosis: is the cell division process that takes place in somatic cells. Meiosis: gametes.

is the cell division process that takes place in gonads to produce 2-58

Mitosis

      Interphase Prophase Metaphase Anaphase Telophase Cytokinesis 2-59

The Stages of Mitosis

 Prophase – the first and longest stage of mitosis  Early prophase – chromatin threads condense into chromosomes  Chromosomes are made up of two threads called

chromatids

   Chromatids are held together by the centromere Centriole pairs separate from one another The mitotic spindle forms 2-60

The Stages of Mitosis

 Prophase (continued)  Late prophase – centrioles continue moving away from each other  Nuclear membrane fragments 2-61

Early Prophase and Late Prophase

Figure 2.21

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The Stages of Mitosis

  Metaphase – the second stage of mitosis  Chromosomes cluster at the middle of the cell  Centromeres are aligned along the equator Anaphase – the third and shortest stage of mitosis  Centromeres of chromosomes split 2-63

Metaphase and Anaphase

Figure 2.21

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The Stages of Mitosis

  Telophase – begins as chromosomal movement stops    Chromosomes at opposite poles of the cell uncoil Resume their thread-like extended-chromatin form A new nuclear membrane forms Cytokinesis – completes the division of the cell into two daughter cells 2-65

Telephase and Cytokinesis

Figure 2.21

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Tumor

  Normal tissue development exhibits a balance between cell division and cell death. If this balance is upset and cells multiply faster than they die, abnormal growth results in a new cell mass that is called a neoplasm, or tumor.

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Cancer

   Benign neoplasms usually grow slowly and are confined within a connective tissue capsule. Cells within these tumors dedifferentiate—that is, they revert to a less specialized state, and cause an increase in their own vascular supply to support their growth.

These tumors airways. are usually not lethal , but they have the potential to become life-threatening if they compress brain tissue, nerves, blood vessels, or 2-68

Cancer

 Cancer is the general term used to describe a group of diseases characterized by various types of malignant neoplasms .

 unencapsulated     contain cells that dedifferentiate increase their vascular supply grow rapidly spread easily to other organs by way of the blood or lymph (metastasis) 2-69

Cancer

 Cancer cells lose control of their cell cycle .   they divide too frequently and grow out of control cancer cells lose contact inhibition  they overgrow one another to stop growing and dividing when they crowd other cells and lack the ability 2-70

Cancer Cells

    Exhibit dedifferentiation and revert to an earlier, less specialized developmental state. Produce chemicals that cause local blood vessel formation resulting in increased blood vessels in the developing tumor ( angiogenesis ). Have the ability to squeeze into any space ( invasiveness) permitting them to leave their place of origin and travel elsewhere in the body. Acquire the ability to metastasize —that is, spread to other organs in the body.

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