Cell Biology: Cell Theory and Zygote

Cell Theory

• Cell is the fundamental unit of all living organisms and the smallest structure capable of life functions.
• All organisms are made up of one or more cells, which arise from pre-existing cells.
• Historical figures and milestones in cell theory:
  • Hans and Zacharias Janssen: Invented the first optical microscope.
  • Anton Van Leeuwenhoek: Discovered bacteria, referring to them as "animalcules."
  • Robert Hooke: Coined the term "cell" after observing cork under a microscope.
  • Matthias Schleiden: Proposed that all plants consist of cells.
  • Theodore Schwann: Established that all animals are composed of cells.
  • Rudolf Virchow: Confirmed that all cells arise from other cells, summarizing with "Omnis cellula e cellula."
  • Francesco Redi: Proposed the "Theory of Spontaneous Generation," stating living organisms come from non-living matter.
  • Lazzaro Spallanzani: Demonstrated that microorganisms spoil food through air exposure.
  • Louis Pasteur: Advanced the principles of vaccination and pasteurization.

Zygote

• Defined as a fertilized egg resulting from the union of an egg cell and a sperm cell.

Levels of Organization

• Hierarchical structure: Cells > Tissues > Organs > Organ Systems > Organisms.

Cell Types

• Organisms are classified based on nuclei presence:
  • Prokaryotes: Lack a defined nucleus.
  • Eukaryotes: Contain a nucleus.
• Cell structures visible only under high magnification electron microscopes, organized into organelles.

Human Tissue Types

• Connective Tissue: Supports and connects organs; includes bone and blood.
• Epithelial Tissue: Covers body surfaces and lines cavities; functions in protection and secretion.
• Nervous Tissue: Transmits signals throughout the body.
• Muscle Tissue: Facilitates movement through contraction.

Epithelial Tissue Characteristics

• Composed of tightly packed cells forming continuous sheets, lacking blood vessels.
• Types based on cell layers:
  • Simple: One cell layer.
  • Stratified: Multiple layers.
• Cell shapes include:
  • Squamous: Flat cells; simple helps oxygen transport in lungs.
  • Cuboidal: Cube-shaped; filters blood in kidneys.
  • Columnar: Rectangular; lines digestive system and absorbs nutrients.

Connective Tissue Types

• General function: Connects and supports body parts.
• Specialized types include:
  • Bone: Framework and support holding organs.
  • Blood: Fluid connective tissue; composed of red blood cells, white blood cells, and platelets.
  • Dense Connective Tissue: Includes ligaments (connects bones) and tendons (connects muscles to bones).
  • Adipose Tissue: Provides insulation and energy storage.

Muscular Tissue

• Facilitates movement via contraction; involves actin and myosin proteins.
• Types:
  • Skeletal Muscle: Voluntary, attached to bones.
  • Smooth Muscle: Involuntary, involved in various bodily functions.
  • Cardiac Muscle: Involuntary, keeps the heart pumping.

Nervous Tissue

• Composed of neurons that transmit electrical impulses.
• Key structures:
  • Nerve Fibers: Long fibrous extensions of neurons.
  • Axon: Sends signals away from the nerve cell body.
  • Dendrite: Receives signals towards the nerve cell body.

Human Organ Systems

• Integumentary System: Protects against external threats; maintains body temperature; consists of skin, hair, and nails.

  • Epidermis: Outermost layer comprising stratified squamous epithelium.
  • Dermis: Middle layer containing connective tissue.
  • Hypodermis: Inner layer with adipose tissue.

• Muscular System: Enables body movement; characterized by extensibility, elasticity, excitability, and contractility.

• Skeletal System: Provides framework and support to protect organs; divided into axial (protecting internal organs) and appendicular skeletons (support and flexibility).

• Respiratory System: Facilitates gas exchange (oxygen in, carbon dioxide out); comprises external, internal, and cellular respiration.

• Digestive System: Processes food for energy and nutrients; involves ingestion, secretion of digestive fluids, mixing, digestion, absorption, and waste excretion.

• Excretory/Urinary System: Maintains osmotic balance and removes metabolic waste.

• Nervous System: Comprises the brain, spinal cord, and nerves; responsible for body control and communication; divided into CNS (central nervous system) and PNS (peripheral nervous system).

• Endocrine System: Regulates hormones influencing mood, growth, metabolism, and reproduction.

• Lymphatic System: Transports lymph containing immune cells, aiding in body detoxification.

• Circulatory System: Comprised of the pulmonary system (gas exchange) and systemic system (blood supply to tissues); functions to transport nutrients and oxygen throughout the body.