Overview
This lecture covers the structural organization of the human body from cells to organ systems, the four basic tissue types, major organs, and how organ systems work and coordinate to keep organisms alive.
Levels of Body Organization
- The body has hierarchical organization: cells form tissues, tissues form organs, and organs form organ systems.
- Unicellular organisms consist of one cell, while multicellular organisms (like humans) have trillions of specialized cells.
- Extracellular fluid surrounds cells in multicellular organisms, providing nutrients and removing wastes.
Types of Tissues
- Four main tissue types: epithelial, connective, muscle, and nervous tissue.
- Epithelial tissue covers body surfaces and lines cavities, forming barriers and having polarized (apical/basal) sides.
- Connective tissue consists of cells in an extracellular matrix (solid, liquid, or jellylike); includes loose, dense, adipose, bone, cartilage, and blood.
- Muscle tissue enables movement and consists of skeletal (voluntary), cardiac (heart, involuntary), and smooth (internal organs, involuntary) types.
- Nervous tissue conducts signals and processes information using neurons (signal transmission) and glia (support cells).
Organs
- Organs are made of two or more tissue types and perform specific functions (e.g., heart pumps blood, stomach digests food).
- Most organs, like the intestine, combine epithelial, connective, muscle, and nervous tissues.
Organ Systems
- Organs group into organ systems that perform functions necessary for life (e.g., cardiovascular, respiratory, digestive).
- Major organ systems include cardiovascular, lymphatic, digestive, endocrine, integumentary, muscular, nervous, reproductive, respiratory, skeletal, urinary, and immune.
- Some organs belong to multiple systems or have overlapping functions.
Cooperation of Organs and Organ Systems
- Organs in an organ system must work together (e.g., digestive organs process food in sequence).
- Organ systems also interact (e.g., respiratory and circulatory systems cooperate to deliver oxygen and remove carbon dioxide).
- The nervous and endocrine systems coordinate body functions via neurotransmitters and hormones; nervous system acts quickly, endocrine system's effects are slower.
- The fight-or-flight response is a coordinated action between the nervous and endocrine systems, preparing the body for emergencies.
Key Terms & Definitions
- Tissue — A group of similar cells working together on a specific function.
- Organ — A structure made of two or more tissues performing a specific task.
- Organ system — A group of organs working together for a broader function.
- Extracellular fluid — Fluid surrounding body cells, providing nutrients and removing waste.
- Epithelial tissue — Sheets of cells covering surfaces and lining cavities.
- Connective tissue — Tissue with cells in an extracellular matrix, supporting or connecting other tissues.
- Muscle tissue — Tissue that contracts to produce movement.
- Nervous tissue — Tissue specialized for signal transmission and processing.
- Neuron — Nerve cell that transmits electrical impulses.
- Glia — Support cells in nervous tissue.
Action Items / Next Steps
- Review the functions and components of each major organ system.
- Study diagrams of tissue types, organs, and organ systems for better visualization.
- Prepare to explain the roles of different tissue types and how organ systems interact.