W7 L1 Cells to Systems

Levels of Organization in the Human Body

Chemical Level

  • All matter is composed of atoms.
    • Examples: Oxygen, Carbon, Hydrogen, Nitrogen.
  • Atoms combine to form molecules.
    • Examples: Proteins, Carbohydrates, Fats, Nucleic acids.

Cellular Level

  • Specific arrangements of molecules form cells.
  • Cells are the fundamental structural and functional units of a living organism.
  • Cells can exist alone or as part of a multicellular organism.
  • Cells require nutrients and oxygen for energy.
  • Cells synthesize proteins and other components for structure, growth, and function.
  • Cells eliminate waste products.
  • Cells have specialized functions in multicellular organisms.

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic:
    • Before nucleus (pro- = before; karyon = nucleus).
    • Contains nucleoid, flagellum, plasma membrane, cytosol, cell wall, and ribosome.
  • Eukaryotic:
    • True nucleus (eu- = true; karyon = nucleus).
    • Contains cytoskeleton, mitochondrion, endoplasmic reticulum, nucleus, Golgi apparatus.

Cell Diversity

  • Cells vary in:
    • Morphology (shape, size, structure, and biochemistry).
    • Specialization.

Cell Diversity in the Retina

  • The retina contains diverse cell types, including:
    • Pigment epithelium.
    • Rods.
    • Cones.
    • Müller cells.
    • Horizontal cells.
    • Bipolar cells.
    • Amacrine cells.
    • Ganglion cells.
    • Nerve fiber layer.
    • Inner limiting membrane.

Cell to Cell Adhesions

  • Plasma membranes facilitate cell-to-cell adhesion.
  • Three types of adhesions:
    1. Cell adhesion molecules.
    2. Extracellular matrix.
    3. Specialized cell junctions.

1. Cell Adhesion Molecules

  • Proteins protruding from the outer membrane surface forming loops and hooks.
  • Bind to other cells or the extracellular matrix.

2. Extracellular Matrix (ECM)

  • Molecules secreted by cells.
  • A meshwork of proteins embedded in interstitial fluid.
  • Provides structural and biochemical support.

3. Specialized Cell Junctions

  • Desmosomes (adhering junctions).
  • Tight junctions (impermeable junctions).
  • Gap junctions (communicating junctions).
Desmosomes
  • Attach two non-touching cells.
  • Represent the strongest attachment.
  • Plaque located on the inner surface with filaments linking adjacent cells.
Tight Junctions
  • Adjacent cells bind at points of direct contact.
  • Seal off the passageway between cells.
  • Prevent movement of materials between cells.
Tight Junctions in the Eye
  • Form blood retinal barrier and blood aqueous barrier.
  • Locations include:
    • Iridial capillary in the iris.
    • Nonpigmented ciliary epithelial cells in the ciliary body.
    • Retinal capillary endothelial cells in the retina.
    • Retinal pigment epithelial (RPE) cells in the retina.
Gap Junctions
  • Adjacent cells connected by small connecting tunnels (connexons).
  • Connexons are hollow tube-like structures that extend through the plasma membrane.
  • Communicating junctions allow molecules, ions, and electrical impulses to directly pass through a regulated gate between cells.
Why Gap Junctions?
  • Enable teamwork between cells.
  • Examples:
    • Cardiac muscles.
    • Smooth muscles.
    • Rod photoreceptors (modulate response variability).

Tissue Level

  • Cells combine to form tissues.
  • Various tissue types:
    • Muscle.
    • Nervous.
    • Epithelial.
    • Connective.

Muscle Tissue

  • Specialized for contracting to generate tension and facilitate movement.
    • Skeletal: attached to the skeleton.
    • Smooth: found in tubes and organs.
    • Cardiac: found in the heart.

Nervous Tissue

  • Specialized for initiating and transmitting electrical impulses.
  • Found in the brain, spinal cord, nerves, and special sense organs.

Fun Fact: The retina is part of the brain.

Epithelial Tissue

  • Specialized for exchanging materials between cells and the environment.
    • Epithelial sheets.
    • Secretory glands.

Connective Tissue

  • Specialized for connecting, supporting, and anchoring various body parts.
    • Examples: Tendons, ligaments, cartilage.

Organ Level

  • Two or more types of primary tissue organized to perform a particular function.
    • Example: the human eye.

Body System Level

  • Groups of organs organized into body systems.
  • The human body comprises 11 organ systems:
    1. Circulatory.
    2. Digestive.
    3. Respiratory.
    4. Urinary.
    5. Skeletal.
    6. Muscular.
    7. Integumentary.
    8. Immune.
    9. Nervous.
    10. Endocrine.
    11. Reproductive.

Levels of Organization Summary

  • Atom → Molecule → Macromolecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

Homeostasis

  • Maintenance of a relatively stable internal environment.
  • Establishes optimal conditions for a balanced and steady state.
  • Functions performed by each body system contribute to homeostasis.
  • Involves detecting deviations from the normal internal environment, integrating information, and making adjustments.

Control Systems

  • Intrinsically controlled: Built into or inherent in an organ.
  • Extrinsically controlled: Initiated outside an organ to alter organ activity.

Types of Feedback Control

  1. Negative feedback control.
  2. Positive feedback control.
  3. Feedforward control.
1. Negative Feedback Control
  • A change stimulates a response that seeks to restore to normal by moving the factor in the opposite direction of its initial change.
  • Reduces the impact of the initial change.
2. Positive Feedback Control
  • A response that seeks to amplify the change by moving it in the same direction as the initial change.
  • Allows for a rapid response to a stimulus.
  • Responses are limited; the maximum response may be regulated or trigger control systems that remove the original stimulus.
3. Feedforward Control
  • A response that seeks to restore the change by responding to anticipated change before it affects the system.