Cells & Tissues

Week 3

Plasma Membrane

• A selective barrier that separates the internal and external environment

• Regulates the flow of materials in and out of the cell

• Plays a role in communication between cells and between the cell and it’s external environment

• Fluidity of the membrane increases cell mobility and allows for membrane repair

Lipid Bilayer

• Phospholipid “heads” are hydrophilic (water loving)

• Fatty acid “tails” are hydrophobic (water fearing)

• On either side of the lipid bilayer is a watery fluid

• Cytosol inside, extracellular fluid (ECF) outside

Membrane Proteins

Proteins dispersed in the bilayer with various functions

Channels/Carriers

Allow for movement of ions in and out of the cell

Receptors

Cellular recognition sites (targeted)

Enzymes

Catalysts

Linkers

Connect cells together

Cell-identity Markers

Recognize like-cells, danger, foreign cells

Permeability

• Highly permeable to non-polar molecules like O2, CO2, and steroids - (permeable to water due to specialized channels)

• Impermeable to ions (require protein channels)

Concentration Gradient

A difference in concentration of a chemical from one location to another (extracellular/intracellular)

Electrical Gradient

Difference in electrical charges between two regions (extracellular/intracellular)

Passive Transport

Does not require cellular energy. Moves “down” the concentration/electrical gradient

Active Transport

Requires cellular energy. Moves against concentration/electrical gradient.

Diffusion

• Particles move from an area of high concentration to low concentration until it is evenly mixed

• Certain factors affect diffusion: steepness, temperature, mass of particles, surface area and distance

Simple Diffusion

Substances move freely through lipid bilayer (O2/CO2)

Facilitated Diffusion

Membrane proteins assist polar and charged solutes through channels/carriers (glucose transport in cells)

Osmosis

• Diffusion where a solvent moves across a selectively permeable membrane down the concentration gradient

• Occurs when a membrane is permeable to water but not permeable to certain solutes

Hydrostatic Pressure

The pressure of the fluid volume on the semipermeable membrane (blood flow in arteries)

Osmotic Pressure

The pressure that must be applied to a solution to stop fluid movement (stop osmosis) when a semipermeable membrane separates a solution from water

Tonicity

A measure of a solutions ability to change the volume of cells by altering their water content

Isotonic Solution

• A solution with an equal concentration of solutes to the cytosol

• Cells in isotonic solutions maintain their normal shape/size - no water movement - ie. NaCl 0.9% (IV fluid)

Hypotonic Solution

• A solution that has a lower concentration of solutes then in the cytosol (more water)

• Water flows into the cell via osmosis causing the cell to swell and burst

• Lysis is cell bursting, hemolysis is RBC rupture

Hypertonic Solution

• A solution that a higher concentration of solutes then inside the cell (less water)

• Water flows out of the cell via osmosis causing the cell to shrink

• Crenation, NaCl 3% (hypertonic saline)

Primary Active Transport 

• Energy from ATP pumps substances against a concentration gradient

Sodium-Potassium Pump

• Expels sodium ions (Na+) and brings potassium (K+) in

• Sodium and potassium slowly and continuously “leak” back therefore Na-K pump is working constantly

• Crucial for maintaining normal cell volumes and the generation of electrical impulses (action potentials)

Secondary Active Transport

• Energy stored in the Na+ or H+ concentration gradients is used to drive substances against their concentration gradient

• Sodium ions have stored potential energy

• As sodium leaks back in it produces kinetic energy allowing for the transport of other substances

Transport in Vesicles

• Vesicle: Small spherical sac

• Substances are transported in vesicles across membrane

• Requires ATP

Endocytosis

Materials move into cell

Exocytosis

Materials exit the cell

Cytoplasm

• Consists of all the cellular contents between the plasma membrane and the nucleus

• Main components include cytosol and organelles

Cytosol

• Intracellular fluid that surrounds organelles in a cell

• 75-90% water, dissolved components

• Site for chemical reactions for cell existence

Centrosomes

Involved in cell division

Cilia

Moves fluid/foreign objects along cells surface

Flagella

Moves an entire cell (sperm)

Ribosomes

• Site of protein synthesis in cytosol or plasma membrane

• High RNA content

Endoplasmic Reticulum

Synthesis of glycoproteins, phospholipids, fatty acids and steroids

Golgi Complex

• Modifies, sorts, packages and transports proteins received from ER

• Forms vesicles

Mitochondria

Generate ATP through aerobic cellular respiration (Krebs cycle)

Lysosomes

Digest foreign objects, autophagy (digestion of worn out organelles), autolysis (digestion of a cell)

Peroxisomes

Involved in metabolism

Proteasomes

Degradation of proteins

Nucleus

• Most cells have none, one or multiple

• Nuclear envelope, a double lipid bilayer membrane, separates the nucleus from the cytoplasm

• Controls cellular structure, directs cellular activities, produces ribosomes

• Contains one or more nucleoli (nucleolus) that function in production of ribosomes

• Contains genes arranged on 46 chromosomes (23/parent)

Chromosome

• Long molecule of DNA coiled together by proteins

• Chromatin is a complex of DNA, RNA and proteins

Nucleoplasm

Substance where organelles of nucleus are suspended

Tissues

• Group of cells that have a common origin and function

• Includes epithelial, connective, muscle and nervous 

Epithelial Tissue

• Cell arranged in sheets of single or multiple layers

• Responsible for protection, filtration, secretion, absorption and excretion

• High rate of cell division (heals itself)

• Two divisions: Covering and lining epithelium, glandular epithelium

Squamous Cells

Thin

Cuboidal Cells

Cube Shaped

Columnar Cells

Taller than wide

Transitional Cells

Change shape as needed

Simple Epithelium 

Single layer of cells, diffusion, osmosis, secretion, and absorption

Stratified Epithelium

Consist of two or more layers, protection

Pseudostratified Epithelium

Appears to have multiple layers

Covering and Lining Epithelium

• Outer covering of skin and some internal organs

• Inner lining of blood vessels, ducts and body cavities

• Interior of the respiratory, digestive, urinary and reproductive system

Glandular Epithelium

A gland is something that secretes substances into ducts, onto a surface or into the blood

Exocrine Glands

Secrete their products into ducts and onto the surface of covering and lining epithelium

Endocrine Glands

Secretes hormones into intestinal fluid and then diffuses into bloodstream (no ducts)

Connective Tissue

• Most abundant and widely distributed tissues in the body

• Does not usually occur on body surfaces

• Highly vascular

• Binds, supports, strengthens other body tissues

• Protects and insulates internal organs

• Compartmentalizes structures

• Immune response

• Stores energy 

Fibroblasts

Most numerous, present in all connective tissue

Macrophages

Involved in immunity

Plasma Cells

Found in GI and respiratory tract

Mast Cells

Inflammatory response

Adipocytes

Fat (adipose) cells

Leukocytes

Immunity (WBC)

Extracellular Matrix

Ground substance and fibres

Ground Substance

• Supports cells, binds them together, stores water

• May be fluid, semi fluid, gelatinous or calcified

Fibres

Collagen, elastic and reticular

Collagen

Strong and resists pulling/stretching (bone, cartilage, tendons)

Elastic

Strong but can stretch up to 150% (skin, vessels, lung tissue)

Reticular

Provide support and strength (adipose, nerve, smooth muscle)

Connective Tissue Membranes

• Flat sheets of pliable tissue that cover or line a part of the body

• Majority consists of and epithelial layer with underlying connective tissue layer

Mucus Membrane (mucosa)

Lines the body cavity that opens directly to the exterior (digestive, respiratory, urinary and reproductive tracts)

Serous Membrane (serosa)

Lines a body cavity that does not open to the exterior (pleura, pericardium, peritoneum)

Cutaneous Membrane (skin)

Covers the entire surface of the body (epidermis, dermis)

Synovial Membrane

Line the cavities of joints, no epithelial layer, synovial fluids lubricates joints

Muscular Tissue

• Consists of muscle fibres (aka myocytes) that use ATP to generate force

• Produces movement, generates heat, provides protection, maintains posture

• Skeletal (attached to bone), cardiac (pumping muscle of heart), smooth (arteries, GI tract, hollow organs)

Nervous Tissue

Found in brain, spinal cord and nerves

Neurons

• Convert stimuli into electrical impulses call action potentials

• Conduct action potential to other neurons, muscle tissue or glands

• Consist of cell body, axon, dendrites

Neuroglia

Homeostasis in nerve tissue

Aging

• Epithelial tissues get progressively thinner

• Connective tissues become more fragile

• Cell division can become less frequent

Evidence of Aging

• Increased susceptibility to bruising

• Slower healing

• Higher likelihood bone fractures

• Increased joint pain

• Reduced skeletal muscle mass/strength

• Decline in pumping efficiency of the heart

• Decreased smooth muscles activity (GI/urinary tracts)

Youth

• Tissues heal faster and leave fewer scars

• Younger bodies have more efficient metabolism, better blood supply and better nutritional health