Human A&P 4: Cells

Study of Cells

Cytology

4 Things Cells Have in Common

1. Building blocks for all plants/animals

2. Come from division of pre-existing cells

3. Smallest units that perform all the vital physiological functions

4. Each cell maintains homeostasis on cellular level

3 Things Cells need to be able to do

1. Produce energy from nutrients and release wastes

2. Reproduce when necessary

3. Have all information necessary to carry out functions

3 Main Parts of the Cell

1. Plasma Membrane

2. Cytoplasm

3. Nucleus

2 Types of Cells

1. Sex Cells

2. Somatic Cells

5 Types of Somatic Cells

1. Nerve Cell

2. Muscle Cell

3. Bone Cell

4. Blood Cell

5. Gland Cell

Variations in Human Cells

1. Red blood cells have no nucleus

2. Striated muscle cells are multinucleated

3. Columnar Epithelial cell: simple shape

4. Neurons are highly branched

3 Extracellular Fluids

• Interstitial fluid: cell submersed

• Blood plasma: blood fluid

• Cerebrospinal fluid: surrounds nervous organs

Extracellular Materials

• Extracellular Fluids

• Cellular Secretions: saliva, mucus etc

• Extracellular Matrix: “glue”

4 Main Functions of Plasma Membrane

1. Physical Isolation: Barrier

2. Regulation of Exchange with the Environment: ions, nutrients, wastes, secretions

3. Sensitivity to Environment: 1st part of the cell affected by change in environment

4. Structural Support: Specialized connections, tissue stability

Phospholipid Bilayer

• Main component of cell membrane

• Phosphate heads are hydrophilic

• Lipid tails are hydrophobic

Membrane Proteins

• Integral Proteins: span width of membrane at least once

• Peripheral Proteins: bound to either side of membrane surface

3 Transport Mechanisms Through Plasma Membrane

• Diffusion

• Carrier Mediated Transport

• Vesicular Transport

Active/Passive Processes

P: Substance moves down concentration gradient

A: Uses cellular energy, usually ATP, against concentration gradient

Diffusion (Overview)

• Movement of ions, molecules down gradient

• Important in body fluids

  • CO2 moves freely through PM[CO2] → cell > ECF > circulating blood

• 3 Types:

  1. Simple

  2. Channel-Mediated

  3. Osmosis

Simple Diffusion

• Substances that can diffuse through bilayer

  • Alcohol

  • Fatty acids

  • Steroids

  • O2, CO2

  • Lipid soluble drugs

Channel Mediated (Facilitated) Diffusion

• Small channels (0.8 nm in diameter) exist in the membrane. Small ions and molecules may diffuse through via these channels.

• Facilitated by Protein Channels: The protein channels facilitate the transport of polar or charged substances, which cannot easily pass through the hydrophobic lipid bilayer of the cell membrane

• Certain factors influence diffusion rate:

  • size & charge of ion

  • size of hydration sphere

  • interactions between the ion and channel wall

    
    

Osmosis

• Movement of water molecules across selectively permeable membrane from low to higher solute concentration

• Total solute concentration is osmotic pressure

Carrier Mediated Transport (Active Transport)

• Movement of substances against gradient

• Requires ATP

• Primary AT

• Secondary AT

Vesicular Transport

• Materials move in/out of cells in vesicles

• Endocytosis

• Pinocytosis

• Phagocytosis/Exocytosis

Receptor-Mediated Endocytosis (7 Steps)

• Extracellular materials packaged in vesicles at cell surface and brought into cell

Pinocytosis

• A cellular process where a cell engulfs liquid and small particles from its surroundings.

• Plays a crucial role in nutrient uptake and cellular homeostasis.

Phagocytosis (7 Steps)

Cytoplasm

• All material inside cell

• Cytosol

  • Organelles

Cytosol

• Intracellular fluid

• Dissolved nutrients, ions, proteins, wastes

2 Classifications of Organelles

Nonmembranous

• Not completely enclosed by membranes

• Some contact with cytosol

Membranous

• Isolated from cytosol by membranes

6 Nonmembranous Organelles

1. Cytoskeleton

2. Microvilli

3. Centrioles

4. Cilia

5. Ribosomes

6. Proteasomes

6 Membranous Organelles

1. Endoplasmic Reticulum

2. Golgi Apparatus

3. Lysosomes

4. Peroxisomes

5. Mitochondria

6. Nucleus

Cytoskeleton

• Nonmembranous organelle

• Provides internal framework

• Microfilaments

• Intermediate Filaments

• Thick Filaments

• Microtubules

Microfilaments (Actin Filaments)

• Thinnest part of cytoskeleton

• Made of actin

Functions:

• Anchors cytoskeleton to integral proteins

• Determines consistency of cytoplasm

• Actin & myosin produce active movement

Intermediate Filaments

• Composition varies

• 7-11 nm

Functions:

• Strengthens cell/maintains shape

• Stabilizes organelles

• Stabilize wall position

Thick Filament

• Made of Myosin

• 15 nm

• Muscle cells only

• Interact with actin for muscle contractions

Microtubules

• Tubulin

• 25 nm

• Extend from centrosome

Functions:

• Cell rigidity

• Change cell shape through disassembly

• Monorail: can move vesicles & organelles

• Mitosis: form spindles

• Form centrioles and cilia

Microvilli

• Increases surface area of cell exposed to extracellular environment

• Small, finger-shaped projections

• Actively absorbing - GI tract

• Connects cytoskeleton to microfilaments

Centrioles

• Organizes cytoskeletal microtubules

• All animal cells capable of division have them

• Cylindrical, short microtubules

• Associated with centrosome

Cilia

• Long, slender extensions of cell membrane

• Found in the respiratory tract, reproductive tract

• Anchored to basal body found just beneath the cell’s
  surface

• “Beat” rhythmically – move fluids, secretions across
  the cell’s surface

  • stiff during the power stroke, and flexible during
    return stroke

• Smoking: damages cilia
  - can’t clear irritants away

Ribosomes

• Fixed ribosomes: attached to RER, produces plasma membrane/ secretory proteins

• Free ribosomes: Scattered throughout cytoplasm

• Protein synthesis

• Small & large subunit

• Contain special proteins & rRNA

• Uses mRNA to produce protein

Proteasomes

• Responsible for removing/recycling damaged or denatured proteins, and breaking down abnormal proteins

• Attach Ubiquitin tag to proteins that need to be recycled

• Tagged proteins broken down in proteasome and released

Endoplasmic Reticulum

• Network of intra-cellular membranes connected to nuclear envelope

• Hollow tubes, flattened sheets, cisternae

Functions:

• Synthesizes proteins, carbs, lipids

• Stores synthesized molecules

• Allows for transport of materials

• Detoxification: toxins neutralized by enzymes within

Golgi Apparatus

• Transport vesicle with new proteins goes to golgi from ER

• Membranous organelle

Functions:

• Modifies and packages secretions

• Renews or modifies plasma membranes

• Packages special enzymes for cytosol

Lysosome

Functions:

• Primary lysosomes: inactive enzymes that activate when fused with damaged organelles

• Secondary lysosomes: break down contents

• Destroy bacteria & dead/damaged cells

• Cleanup and recycling functions inside cell

Peroxisomes

Functions:

• Absorb & break down fatty acids & organic compounds, results in H2O2 production

• Enzymes break down H2O2, produces water & O2

• Cell is protected from potentially damaging effects of the free radicals produced during catabolism

Mitochondrion

• Cellular respiration

• Double membraned (cristae)

• Reactions release energy in mitochondria

• Activities that require energy occur in cytoplasm

• Semi-autonomous organelle, divides via fission

Nucleus

• Control center of cell

• Stores “blueprints” for synthesizing more than 100,000 different proteins

• Cells with nucleus have longer life span

Contains:

• Nuclear Envelope: Separates from cytosol, double layered

• Nucleolus: Synthesize rRNA

• Nucleoplasm: Fluid contents of nucleus

• Nuclear Pore: Channels between nucleus and cytosol, allows for exchange of ions & small molecules