Biology 3B Laboratory Histology Objectives • To be able to identify the four major types of vertebrate tissues (epithelial, connective, nervous and muscle). • To understand how each type of tissue is organized and the distinguishing features of each type of tissue. • To associate tissue structure with its function for each tissue type. INTRODUCTION Tissues are formed when cells with similar structure and embryonic origin are aggregated together, performing a particular function. In this laboratory you will examine the four major groups of tissues based upon their structure and function: epithelial, connective, muscle and nervous tissues. The study of tissues, especially the structure and arrangement, is called histology. In Biology 3A, we examined organisms at the molecular and cellular levels of biological organization. Now, we will examine organisms from the tissue level of organization up. As you recall, tissues are grouped to form organs which work together as systems. Atomic Æ Molecular Æ Cellular Æ Tissue Æ Organs Æ Organ systems Æ Organism A. EPITHELIAL TISSUE Epithelial tissue form sheet like layer of cells with very close cell to cell contact. They function in protection, absorption and excretion of materials for an organism. Epithelial tissue is classified based upon 1) the number of layers and 2) the shape of the cells on the free surface: Simple epithelia are surface linings consisting of a single layer of cells. These are usually found at places where selective diffusion, absorption, or secretion occurs. Simple epithelia can range from squamous (flattened) to cubiodal to columnar in shape depending on their function. All epithelial cells secrete a non-living matrix called the basement membrane. This is essentially a dense layer of extracellular material that acts as a “glue” to hold cells together. Simple squamous epithelium: a single layer of thin flattened cells, usually containing a flattened nucleus. They line the lumens of the entire blood vascular system (specifically called endothelium here), the renal corpuscles, and the lumenal surfaces of the pleural and peritoneal membranes. In these areas, they function in diffusion of materials. They also line the thoracic, abdominal and cardiac cavity (mesothelium). • Observe dorsal view of the frog skin (may look hexagonal) • Observe the cross section of a blood vessel and find the endothelium that lines the lumen of the blood vessel. Biology 3B Lab Histology Page 1 of 8Simple cubiodal epithelium: a single layer of cube-shaped cells with a centrally located nucleus. This epithelial tissue can be found in exocrine glands (salivary and mucus), lining small ducts and tubules (kidney tubules). They function in secretion and some diffusion. Other areas found: ovaries and pancreatic duct • You may be looking at the kidney tubules, thus look for circular tubes of simple cuboidal cells. Simple columnar epithelium: the height of these cells are great than the width and the depth. All the cells touch the basement membrane and the nuclei are usually aligned in the center or towards the bottom of the cells. Some cells are ciliated. These cells are specialized in secretion and some absorption. Goblet cells are often associated with columnar cells and secrete mucus. Are any of these cells ciliated? Locations: nonciliated ciliated lines stomach & intestines uterine tubes some salivary glands fallopian tubes gall bladder upper respiratory tract Goblet cell Psuedostratified columnar epithelium: all cells begin at a common basement membrane but some cells do not reach the free surface. The nuclei in largest dimension of cytoplasm; therefore, appear in two rows, thus the appearance of stratification. Some may be ciliated. Typical locations include: eustachian tubes, upper respiratory tract, epididymis, vas deferens. They are typically found in areas of high abuse forming linings. Stratified squamous epithelium: composed of cells with many layers, cells flattened at free surface but typically cuboidal or columnar at basement layer. They function in protection and coverings, in areas with lots of abuse. Locations include: skin and lining wet surfaces: mouth, esophagus, and vagina. Biology 3B Lab Histology Page 2 of 8B. CONNECTIVE TISSUE There are two types of connective tissue: loose, the most wide spread connective tissue, and dense connective tissue. Connective tissue is composed of cells and extracellular fibers imbedded in a ground substance (matrix). The ground substance or matrix can be jelly-like, liquid or solid non-living cement of glue secreted by the cells. There are three types of fibers that are typically found in the various types of connective tissue. Elastic fibers are composed of elastin (protein) with a stretchy and flexible characteristic. These fibers form thin wavy lines that can be stained purple, red or brown in color. Collagen fibers are composed of collagen protein and found only in animals. These fibers are characteristically thick and resist stretching. When stained, they appear as thick wavy lines that are either pink or red. Reticular fibers are inelastic and branching forming a network. These fibers are difficult to see without specialized staining. Cells that are found in connective tissues are named according to their function. Cells called “blasts” are responsible for production a particular substance, “clasts” are responsible for reabsorbing substances, and “cytes” are resting or mature cells that are not producing or reabsorbing substances. For example, fibroblasts produce fibers. Fibrocytes are mature fiber cells and fibroclasts are responsible for reabsorbing (breaking down) fibers. Loose Connective Tissue: Areolar connective tissue: this is the least specialized connective tissue in the adult organism. This is essentially the “packing material” of the body. It is often found anchoring blood vessels, nerves and body organs. cells: fibroblasts/macrophages/mast cell/adipose cells/plasma cells fibers: elastic fibers = composed of protein elastin (stretch & rebound) collagenous fibers = composed of protein collagen - inelastic = high tensile strength - can flex but NOT stretch to any great degree location: subcutaneous layer of skin, supports blood vessels, nerves and epithelia