Tissues, Organs and Organ Systems

Organisms are built on a pattern of increasing complexity. From smallest to largest:

• Atoms: Smallest unit of matter (e.g., Carbon, Hydrogen, Oxygen).
• Molecules: Atoms combine to form molecules (e.g., Water, Protein, DNA).
• Organelles: Molecules combine to form subcellular structures (e.g., Mitochondria for respiration, Ribosomes for protein synthesis).
• Cells: Smallest unit of life. Organelles assemble to form cells.
• Tissues: Group of similar cells performing a specific function.
  • Animals: Epithelial (covers surfaces), Muscle (movement).
  • Plants: Epidermal (protection), Vascular (transport - Xylem/Phloem).
• Organs: Structure made of related tissues working together (e.g., Heart, Stomach, Leaf, Root).
• Organ System: Multiple organs working together (e.g., Digestive System, Circulatory System, Root System).
• Organism: A living entity functioning independently (e.g., Human, Tree).

Definition: New functions that arise at higher levels of organization due to interactions between components of lower levels.

• Organelles to Cells: Individual organelles interact to create a living cell capable of metabolism.
• Cells to Tissues: Muscle cells combine to generate force/movement.
• Tissues to Organs: Muscle, nervous, and connective tissues work together to make the Heart pump blood.
• Organ Systems to Organisms: Consciousness and adaptability arise from system interactions.

• Roots: Anchor plant, absorb water/minerals.
• Stem: Supports leaves/flowers, transports materials via vascular tissue.
• Leaves: Primary site of photosynthesis and transpiration. Contains:
  • Epidermis: Outer layer with cuticle and Stomata (gas exchange).
  • Mesophyll: Palisade (photosynthesis) and Spongy (gas diffusion).
  • Vascular Tissue: Xylem (water) and Phloem (food) in midrib/veins.
• Flower: Reproductive part for sexual reproduction.

• Heart: Pumps blood.
• Lungs: Facilitate gas exchange (breathing).
• Brain: Control center for thought, emotion, and movement.
• Liver: Filters blood, produces bile, stores glucose.
• Kidneys: Filter waste, produce urine.
• Stomach: Muscular organ for digestion. Contains:
  • Epithelial Tissue: Secretes mucus, pepsinogen, and HCl.
  • Connective Tissue: Supports, contains blood vessels/nerves.
  • Muscle Tissue: Smooth muscles (Outer longitudinal, Middle circular, Inner oblique) churn food.
• Intestines: Absorb nutrients.
• Pancreas: Produces enzymes and hormones (Insulin/Glucagon).

• Skeletal: Bones/cartilage. Supports body, allows movement, produces blood cells.
• Muscular: Skeletal muscles. Produces movement and heat.
• Digestive: Breakdown and absorption of nutrients.
• Respiratory: Exchange of gases ($O_2$ and $CO_2$).
• Circulatory: Transports oxygen, nutrients, wastes via blood.
• Nervous: Brain/Spinal Cord. Coordinates body functions.
• Urinary: Eliminates waste, regulates water/salt balance.
• Integumentary: Skin. Barrier function, temperature regulation.

Definition: Maintenance of a stable internal environment despite external changes (e.g., Temperature, pH, Blood Glucose).

Examples:

• Sweating/Shivering: Regulates body temperature.
• Insulin: Lowers blood glucose after eating.
• Exercise: Heart rate and respiration increase to supply oxygen to muscles.