Chapter 2: Cells and Tissues
I. Cells
A. Size and shape
1. Human cells vary considerably in size
2. All are microscopic
3. Cells differ notably in shape
B. Composition
1. Cytoplasm containing specialized organelles surrounded by a plasma membrane
2. Organization of cytoplasmic substances important for life
C. Structural Parts
1. Plasma Membrane
a. Forms outer boundary of cell
b. Thin, two-layered membrane of phospholipids containing proteins.
c. Is semi-permeable
2. Cytoplasm
a. Organelles
i. Ribosomes
1. May attach to rough ER or lie free in cytoplasm.
2. Manufacture proteins
3. Often called protein factories
ii. Endoplasmic Reticulum (ER)
1. Network of connecting sacs and canals
2. Carry substances through cytoplasm
3. Types are rough and smooth
4. Rough ER collects and transports proteins made by ribosomes
5. Smooth ER synthesizes chemicals and makes new membrane
iii. Golgi Apparatus
1. Group of flattened sacs near nucleus
2. Collects chemicals that move from the smooth ER in vesicles
3. Called the chemical processing and packaging center.
iv. Mitochondria
1. Composed of inner and outer membranes
2. Involved with energy-releasing chemical reactions
3. Often called power plants of the cell.
v. Lysosomes
1. Membranous-walled organelles
2. Contain digestive enzymes
3. Have protective function (eat microbes)
vi. Centrioles
1. Paired organelles
2. Lie at right angles to each other near nucleus
3. Function in cell reproduction
vii. Cilia
1. Fine, hairlike extensions found on free or exposed surfaces of some cells
2. Capable of moving un unison in a wavelike fashion
viii. Flagella
1. Single projections extending from cell surfaces
2. Much larger than cilia
3. Tails of sperm only example in humans.
3. Nucleus
a. Controls cell because it contains the genetic code instructions for making proteins, which in turn determine cell structure and function.
b. Component structures include nuclear envelope, nucleoplasm, nucleolus, and chromatin granules.
c. Chromosomes contain DNA.
D. Relationship of cell structure and function
1. Regulation of life processes
2. Survival of species through reproduction of the individual
3. Relationship of structure to function apparent in number and type of organelles seen in different cells.
a. Heart muscle cells contain many mitochondria required to produce adequate energy needed for continued contractions.
b. Flagellum of sperm cell gives motility, allowing movement of sperm through female reproductive tract, thus increasing chances for fertilization.
II. Movement of Substances Through Cell Membranes
A. Passive Transport processes do no require added energy and result in movement down a concentration gradient.
1. Diffusion
a. Substances scatter themselves evenly through an available space.
b. It is unnecessary to add energy to the system
c. Movement is from high to low concentration
d. Osmosis and Dialysis are specialized examples of diffusion across a selectively permeable membrane.
e. Osmosis is diffusion of water.
f. Dialysis is diffusion of solutes.
2. Filtration
a. Movement of water and solutes caused by hydrostatic pressure on one side of membrane.
b. Responsible for urine formation
B. Active transport processes occur only in living cells; movement is Up the concentration gradient; requires energy from ATP.
1. Ion Pumps
a. An ion pump is a protein complex in the cell membrane.
b. Ion pumps use energy from ATP to move substances across the cell membrane against the concentration gradient.
c. Examples: sodium-potassium pump, calcium pump
d. Some ion pumps work with other carriers so that glucose or amino acids are transported along with ions.
2. Phagocytosis and pinocytosis
a. Both are active transport mechanisms because they require energy.
b. Phagocytosis is a protective mechanism often used to destroy bacteria.
c. Pinocytosis is used to incorporate fluids or dissolved substances into cells.
C. Several severe diseases result from damage to cell transport processes.
1. Cystic Fibrosis, characterized by abnormally thick secretions in the airways and digestive ducts, results from improper Cl2 transport.
2. Cholera is a bacterial infection that causes Cl- and water to leak from cells lining the intestines, resulting in severe diarrhea and water loss.
III. Cell Reproduction
A. DNA Structure large molecule shaped like a spiral staircase; sugar (deoxyribose), and phosphate units compose sides of the molecule; base pairs (adenine-thymine or guanine-cytosine) compose steps; base pairs always the same, but the sequence of base pairs differs in different DNA molecules; a gene is a specific sequence of base pairs within a DNA molecule; genese dictate formation of enzymes and other proteins by ribosomes, thereby directly determining a cells structure and function; in short, genes are heredity determinants.
B. Genetic Code
1. Genetic information stored in base-pair sequences on genes expressed through protein synthesis.
2. RNA molecules and protein synthesis
a. DNA contained in cell nucleus.
b. Protein Synthesis occurs in cytoplasm, thus genetic information must pass from the nucleus to the cytoplasm.
c. Process of transferring genetic information from nucleus to cytoplasm where proteins are produced requires completion of transcription and translation.
3. Transcription
a. Double-Stranded DNA separates to form messenger RNA (mRNA)
b. Each strand of mRNA duplicates a particular gene (base-pair) sequence from a segment of DNA.
c. mRNA molecules pass from the nucleus to the cytoplasm, where they direct protein synthesis in ribosomes and ER.
4. Translation
a. Involves synthesis of proteins in cytoplasm by ribosomes.
b. Requires use of information contained in mRNA.
C. Abnormal DNA that is inherited, or that results from damage from viruses or other factors, is often the basis of disease.
D. Cell division reproduction of cell involving division of the nucleus (mitosis) and the cytoplasm; the period where the cell is not actively dividing is called the interphase.
E. DNA Replication process by which each half of a DNA molecule becomes a whole molecule identical to the original DNA molecule; precedes mitosis.
F. Mitosis process in cell division that distributes identical chromosomes (DNA molecules) to each new cell form when the original cell divides; enables cells to reproduce their own kind; makes heredity possible.
G. Stages of Mitosis
1. Prophase first stage
a. Chromatin granules become organized
b. Chromosomes (pairs of linked chromatids) appear
c. Centrioles move away from the nucleus
d. Nuclear envelope disappears, freeing genetic material.
e. Spindle Fibers appear
2. Metaphase second stage
a. Chromosomes align across center of cell
b. Spindle fibers attach themselves to each chromatid
3. Anaphase third stage
a. Centromeres break apart
b. Separated chromatids now called chromosomes
c. Chromosomes are pulled to opposite ends of the cell
d. Cleavage furrow develops at end of anaphase
4. Telophase fourth stage
a. Cell division is completed
b. Nuclei appear in daughter cells
c. Nuclear envelope and nucleoli appear
d. Cytoplasm is divided (cytokinesis)
e. Daughter cells become fully functional
H. Changes in cell growth and reproduction
1. Changes in growth of individual cells
a. Hypertrophy increase in size of individual cells, increasing size of tissue.
b. Atrophy decrease in size of individual cells, decreasing size of tissue.
2. Changes in cell reproduction
a. Hyperplasia increase in cell reproduction, increasing size of tissue
b. Anaplasia production of abnormal, undifferentiated cells.
c. Uncontrolled cell reproduction results in formation of a benign or malignant neoplasm (tumor)
IV. Tissues
A. Epithelial Tissue
1. Covers the body and lines body cavities
2. Cells packed closely together with little matrix
3. Classified by shape of cells
a. Squamous
b. Cuboidal
c. Columnar
d. Transitional
4. Classified by arrangement of cells
a. Simple
b. Stratified
5. Simple Squamous Epithelium
a. Single layer of scale-like cells
b. Transport (e.g. absorbtion) is function
6. Stratified Squamous Epithelium
a. Several layers of tightly packed cells
b. Protection is primary function
7. Simple Columnar Epithelium
a. Columnar cells arranged in a single layer
b. Line stomach and intestines
c. Contains mucus-producing goblet cells
d. Specialized for absorption
8. Stratified Transitional Epithelium
a. Found in body areas, such as urinary bladder, that stretch.
b. Up to 10 layers of roughly cuboidal-shaped cells that distort to squamous shape when stretched.
9. Pseudostratified Epithelium
a. Each cell touches basement membrane
b. Lines the trachea
10. Simple cuboidal epithelium
a. Often specialized for secretory activity
b. Cuboidal cells may be grouped into glands
c. May secrete into ducts, directly into blood, and on body surface
d. Examples of secretions include saliva, digestive juice, and hormones
B. Connective Tissue
1. Most abundant tissue in the body
2. Most widely distributed tissue in body
3. Multiple types, appearances, and functions
4. Relatively few cells in the intracellular matrix
5. Types
a. Areolar glue that holds organs together
b. Adipose lipid storage is primary function
c. Fibrous strong fibers; an example is tendons
d. Bone matrix is calcified; function is support and protection
e. Cartilage chondrocyte is cell type
f. Blood matrix is fluid; function is transportation
C. Muscle Tissue
1. Types
a. Skeletal attaches to bones; also called striated or voluntary; control is voluntary; striations appear when viewed under a microscope
b. Cardiac also called striated involuntary muscle; composes heart wall; ordinarily cannot control contractions.
c. Smooth also called nonstriated, visceral, or involuntary; no cross striations; found in blood vessels and other tube-shaped organs.
D. Nervous Tissue
1. Cell Types
a. Neurons conducting cells
b. Glia (Neuroglia) supporting and connecting cells
2. Neurons
a. Cell components
i. Cell Body
ii. Axon (one) carries nerve impulse away from cell body (transmitter)
iii. Dendrites (one or more) carries impulse towards cell body (receiver)
b. Function rapid communication between body structures and control of body functions.
E. Tissue Repair usually accomplished by means of regeneration of tissue.
1. Epithelial and connective tissues regenerate easily
2. Muscles and nervous tissues have very limited abilities to repair themselves.