Biology 211 Anatomy & Physiology I Histology: Tissues of the Human Body

Recall: SYSTEMS are composed of one or more organs, all serving a common function ORGANS are composed of one or more types of tissues, all serving a common function TISSUES are composed of one or more types of cells and their products, all serving a common function The study of structure at the level of tissues is called histology.

All tissues: - Cells - Extracellular Matrix Ground Substance Fibers

With only a few, rare exceptions, all organs of the human body are composed of four types of tissue: Epithelium lines internal and external surfaces, including hollow organs. Forms glands. Connective Tissue provides support and fills spaces Muscle Tissue produces force and movement Nervous Tissue carries and integrates electrical information Each of these can have one or more subtypes

Epithelium - Covers body surfaces (e.g. skin, cornea) - Lines body cavities (e.g. peritoneal & pericardial cavities - Lines insides of hollow organs (e.g. stomach, heart, lung, aorta, oviduct) - Forms glands (e.g. sweat glands, pancreas, salivary glands)

Characteristics of Epithelium - Highly cellular, with very little extracellular matrix - Cells form close contacts with each other - Avascular - High capacity for regeneration Functional characteristics of epithelia depend on the cells, rather than the extracellular matrix which is unspecialized

Epithelium always supported by connective tissue and separated from it by a basement membrane. Depends on connective tissue for vessels, nerves, etc. Epithelium Basement membrane Connective tissue Mucous Membrane or Serous Membrane

Flat = "squamous" Epithelium Different types for different functions. Classified according to: a) Number of layers of cells b) Shape of cells in the top layer Single layer = "simple" Two or more layers = "stratified" Actually one layer but looks like more = "pseudostratified" Flat = "squamous" Cube-shaped = "cuboidal" Taller than wide = "columnar" Change shape from squamous to cuboidal = "transitional"

Epithelium Number of layers Shape of surface cells Squamous Simple Cuboidal Stratified Columnar Pseudostratified Transitional

Simple Cuboidal Epithelium Simple Squamous Epithelium Pseudostratified Columnar Epithelium Simple Columnar Epithelium

Stratified Squamous Epithelium Stratified Cuboidal Epithelium Stratified Columnar Epithelium (Stratified) Transitional Epithelium

Epithelium also forms all glands in the body Glands classified by a) Whether or not they have ducts b) Their method of secretion Yes = Exocrine; Duct carries product to surface No = Endocrine; Product secreted into surrounding extracellular matrix, picked up by blood vessels Merocrine: Product released from undamaged cells Apocrine: Top part of cell lost during secretion Holocrine: Entire cell lost during secretion

Exocrine glands also classified by c) Shape, and whether or not either the duct and/or the secretory part branches

Connective Tissue - Lots of extracellular matrix; Relatively few cells - Cells usually do not communicate with each other - Highly vascular - Different types of CT all arise from embryonic mesenchyme Functional characteristics of connective tissues depend primarily on the extracellular matrix, which is often highly specialized, and not on the cells.

Connective Tissues Common cells Fibers Fibroblasts / Fibrocytes Collagen Adipocytes Elastic Mast cells Reticular Plasma cells Macrophages Lymphocytes (many others) How those cells and fibers are arranged determines the specific type of connective tissue

Connective Tissues Ordinary connective tissues Specialized connective tissues Loose (areolar) connective tissue Adipose connective tissue Reticular connective tissue Elastic connective tissue Dense regular connective tissue Dense irregular connective tissue Blood Bone Cartilage

Loose / Areolar Connective Tissue Adipose Connective Tissue Reticular Connective Tissue

Dense Regular Connective Tissue Dense Irregular Connective Tissue

Specialized Connective Tissues: Cartilage Hyaline Cartilage Elastic Cartilage More detail on cartilages and their cells when we discuss the skeletal system Fibrous Cartilage

Specialized Connective Tissues: Bone Blood More detail on these tissues and their cells when we discuss the skeletal and circulatory systems

Muscle Tissue: Skeletal Muscle Cardiac Muscle Smooth Muscle Voluntary Striated Involuntary Nonstriated

Muscle Muscle Muscle Myocytes Nuclei Striations Skeletal Cardiac Smooth Muscle Muscle Muscle Very long Unbranched Shorter Branched Short Spindle-shaped Hundreds per cell Peripheral One or two per cell Central One per cell Yes No Myocytes Nuclei Striations More detail on muscle tissues and their cells when we discuss the muscular, circulatory, and other systems

Nervous Tissue: (no subtypes) 1) Neurons (Excitable cells) Carry electrical signals from one place to another 2) Supporting Cells Nonexcitable Support & nourish neurons Glia in CNS Satellite cells Schwann cells More detail on nervous tissue and its cells when we discuss the nervous system