Biology 25: Human Biology Chapter 4 Biology 25: Human Biology Prof. Gonsalves Los Angeles City College Loosely Based on Mader’s Human Biology,7th edition

I. Life is based on many structural levels Levels of animal structure: Atoms and molecules Cells Tissues Organs Organ systems Organism: May consist of a single cell or a complex multicellular organism.

Levels of Structural Organization in an Animal

TISSUES: Most animal cells are organized into tissues. Cooperative unit of very similar cells that perform a specific function. Tissue comes from Latin word meaning “weave”. Cells of tissues may be held together by: Fibers Glue-like substance Plasma membrane structures Tissue structure is related to its function.

TISSUES: There are four main types of animal tissue: 1. Epithelial 2. Connective 3. Muscle 4. Nervous

1. Epithelial Tissue Cells are tightly fitted together in continuous layers or sheets. Cover outside of body (skin), line organs and internal body cavities (Mucous membranes of digestive, respiratory, and reproductive systems). Tight packaging allows tissue to act as a barrier to protect against mechanical injury, infection, and fluid loss. Two surfaces: Free surface: Exposed to air or fluid. Bottom surface: Attached to underlying tissues by a basement membrane, a dense layer of protein and polysaccharides.

1. Epithelial Tissue Can be classified based on two criteria: A. Number of layers: Simple: One layer. Stratified: Several layers B. Shape of cells: Squamous: Flat cells. Cuboidal: Cube shaped cells Columnar: Column shaped cells Example: Simple squamous epithelium Stratified columnar epithelium

1. Epithelial Tissue Some epithelial tissues, such as mucous membranes, absorb and secrete chemical solutions. Mucous membranes: Digestive tract epithelium (mucous membranes) secretes mucus and digestive enzymes. Respiratory tract epithelium secretes mucous that helps trap dust particles before they reach the lungs.

Cell Surfaces B. Extracellular matrix: Sticky layer of glycoproteins found in animal cells. Important for attachment, support, protection, and response to environmental stimuli. Junctions Between Animal Cells: Tight Junctions: Bind cells tightly, forming a leakproof sheet. Example: Between epithelial cells in stomach lining. Adhesion Junctions: Rivet cells together, but still allow material to pass through spaces between cells. Gap Junctions: Allow water and other small molecules to flow between neighboring cells.

2. Connective Tissue Relatively few cells surrounded by large amounts of nonliving material (matrix). Cells secrete the matrix, which can be solid, liquid, or gelatinous. Diverse functions. Mainly bind, support, and connect other tissues. Six types of connective tissue in humans: 1. Loose Connective Tissue: Most widespread connective tissue in vertebrates. Loose matrix with fibers, packing material. Attaches skin to muscles, binds and holds tissues and organs in place. 2. Adipose (fat): Pads and insulates body. Energy storage.

Types of connective tissue in humans (Continued): C. Blood: Fluid matrix (plasma) has water, salts, and proteins. Red and white blood cells. D. Fibrous Connective Tissue: Matrix of densely packed collagen fibers. Strong and nonelastic. Found in: Tendons: Attach muscles to bones. Ligaments: Attach bone to bone. E. Cartilage: Rubbery matrix with collagen fibers. Found on end of bones, nose, ears, and between vertebra. F. Bone: Supports the body of most vertebrates. Solid matrix of collagen fibers and calcium, phosphate, and magnesium salts. Bone is harder than cartilage, but not brittle because of collagen.

Connective Tissue Binds and Provides Support A. Loose Connective Tissue D. Fibrous Connective Tissue B. Adipose Tissue E. Cartilage C. Blood F. Bone

3. Muscle Tissue Most abundant type of tissue in most animals. Accounts for two-thirds (2/3) of human weight. Specialized for contraction. Made up of long cells that contract when stimulated by nerve impulses. Muscle cells have many microfilaments made up of actin and myosin. Muscle contraction accounts for much of energy consuming work in animals. Adults have a fixed number of muscle cells. Weight lifting doesn’t increase number of muscle cells, only their size.

3. Muscle Tissue There are three types of muscle tissue: A. Skeletal (striated) muscle : Attached to bones by tendons. Responsible for voluntary movements. B. Cardiac muscle: Forms contractile tissue of heart. Not under voluntary control. C. Smooth muscle: Found in walls of digestive tract, bladder, arteries, uterus, and many internal organs. Responsible for peristalsis and labor contractions. Contract more slowly than skeletal muscle, but can remain contracted longer.

4. Nervous Tissue Senses stimuli and transmits signals from one part of the animal to another. Controls the activity of muscles and glands, and allows the animal to respond to its environment. Neuron: Nerve cell. Structural and functional unit of nervous tissue. Consists of: Cell body : Contains cell’s nucleus. Dendrite: Extension that conveys signals towards the cell body. Axon: Extension that transmits signals away from the cell body. Supporting cells: Nourish, protect, and insulate neurons.

ontractions.

Organs are Made of Several Different Tissues

Major Organ Systems in Mammals Digestive system Respiratory system Circulatory system Cardiovascular Lymphatic and Immune system Excretory system Endocrine system Reproductive system Nervous system Muscular system Skeletal system Integumentary

Major Organ Systems in Mammals Digestive system Respiratory system Circulatory system Cardiovascular Lymphatic and Immune system Excretory system Endocrine system Reproductive system Nervous system Muscular system Skeletal system Integumentary