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Chapter 4. Histology: The Study of Tissues. Tissue Level of Organization. The classification of tissue types is based on the structure of cells; the composition of noncellular substance surrounding cells (extracellular matrix) and the functions of the cells. Tissues and Histology.
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Chapter 4 Histology: The Study of Tissues
Tissue Level of Organization • The classification of tissue types is based on the structure of cells; the composition of noncellular substance surrounding cells (extracellular matrix) and the functions of the cells.
Tissues and Histology • Tissue Level of Organization • Epithelial • Connective • Muscle • Nervous • Histology: Microscopic Study of Tissues
Epithelium Characteristics • Consists almost entirely of cells • Covers body surfaces and forms glands • Has free and basal surface • Specialized cell contacts • Avascular • Undergoes mitosis
Functions of Epithelia • Protecting underlying structures • Acting as barriers • Permitting the passage of substances • Secreting substances • Absorbing substances
Types of Epithelium • Types of epithelium is based on the shape of the epithelial cells: • Squamous: cells are flat or scale-like • Cuboidal: cells are cube-shaped; about as wide as they are tall • Columnar: cells are taller tan they are wide.
Classification of Epithelium • Simple • Squamous, cuboidal, columnar • Consists of a single layer of cells with each extending from the basement membrane to the free surface • Stratified • Squamous, cuboidal, columnar • Consists of more than one layer of cells, only one of which is attached to the basement membrane.
Classification of Epithelium • Pseudostratified • Columnar • Special type of simple epithelium • It appears to be stratified but it is not (false – psuedo) • Consists of one layer of cells, with all the cells attached to the basement membrane.
Classification of Epithelium • Transitional • Cuboidal to columnar when not stretched and squamouslike when stretched
Simple Squamous Epithelium • Consists of a single layer of cells, with each cell extending from the basement membrane to the free surface. • The nuclei appear as bumps when viewed as a cross section because the cells are so flat
Simple Squamous Epithelium • Function: diffusion, filtration, some protection against friction, secretion and absorption • Location:lining of blood and lymphatic vessels (endothelium) and small ducts, alveoli of the lungs, loop of Henle in kidney tubules, lining of serous membranes (mesothelium) and inner surface of the eardrum.
Simple Cuboidal Epithelium • Cuboidal: cells are cube-shape; about as wide as they are tall. • Single layer of cube-shaped cells, some cells have microvilli or cilia.
Simple Cuboidal Epithelium • Function: active transport and facilitated diffusion result in secretion and absorption by cells of the kidney tubules, secretion by cells of glands and choroid plexus, movement of particles embedded in mucus out of the terminal bronchioles by ciliated cells.
Simple Cuboidal Epithelium • Location: kidney tubules, glands and their ducts, choroid plexus of the brain, lining of terminal bronchioles of the lungs, and surface of the ovaries
Simple Columnar Epithelium • Single layer of tall, narrow cells. Some cells have cilia (in bronchioles of lungs, auditory tubes, uterine tubes and uterus) or microvilli (intestines).
Simple Columnar Epithelium • Function: movement of particles out of the bronchioles of the lungs by ciliated cells. It is partially responsible for the movement of the oocyte through the uterine tubes by ciliated cells. Secretion by cells of the gland, the stomach and the intestine. Absorption by cells of the intestine.
Simple Columnar Epithelium • Location: Glands and some ducts, bronchioles of lungs, auditory tubes, uterus, uterine tubes, stomach intestines, gallbladder, bile ducts and ventricles of the brain.
Stratified Squamous Epithelium • Consists of more than one layer of cells, only one of which is attached to the basement membrane • Cells are cubodial in shape in the basal layer and progressively flatten toward the surface.
Stratified Squamous Epithelium • The epithelium can be moist or keratinized • In most the surface cells retain a nucleus and cytoplasm. • In keratinized stratified epithelium, the cytoplasm of cells at the surface is replaced by keratin, and the cells are dead
Stratified Squamous Epithelium • Function: protection against abrasion and infection. • Location: moist-mouth, throat, larynx, esophagus, anus, vagina, inferior urethra, and cornea. • Keratinized - skin
Stratified Cuboidal Epithelium • Multiple layers of somewhat cube-shaped cells. • Function: secretion, absorption and protection against infection. • Location: sweat gland ducts, ovarian follicular cells, and salivary gland ducts.
Stratified Columnar Epithelium • Multiple layers of cells, with tall, thin cells resting on layers of more cubodial cells. The cells are ciliated in the larynx • Function: protection and secretion • Location: mammary gland duct, larynx and a portion of the male urethra.
Pseudostratified Columnar Epithelium • Single layer of cells; some cells are tall and thin and reach the free surface and other do not. The nuclei of these cells are at different levels and appear stratified. The cells are almost always ciliated and are associated with goblet cells that secrete mucus onto the free surface.
Pseudostratified Columnar Epithelium • Function: synthesize and secrete mucus onto the free surface and move mucus (or fluid) that contains foreign particles over the surface of the free surface and from passages. • Location: lining of nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea and bronchi of the lungs.
Transitional Epithelium • Stratified cells that appear cubodial when the organ or tube is not stretched an squamous when the organ or tube is stretched by fluid.
Transitional Epithelium • Function: accommodates fluctuations in the volume of fluid in an organ or tube. Protection against the caustic effects of urine. • Location: lining of the urinary bladder, ureter, and superior urethra.
Cell Connections • Functions • Bind cells together • Form permeability layer • Intercellular communication • Types • Desmosomes • Tight • Gap
Exocrine Glands • Unicellular • Goblet cells
Exocrine Glands and Secretion Types • Merocrine • Sweat glands • Apocrine • Mammary glands • Holocrine • Sebaceous glands
Connective Tissue • Abundant • Consists of cell separated by extracellular matrix • Diverse • Performs variety of important functions
Connective Tissue Cells • Specialized cells produce the extracellular matrix • Suffixes • -blasts: create the matrix • -cytes: maintain the matrix • -clasts: break the matrix down for remodeling
Connective Tissue Cells • Adipose or fat cells • Mast cells that contain heparin and histamine • White blood cells that respond to injury or infection • Macrophages that phagocytize or provide protection • Stem cells
Extracellular Matrix • Components • Protein fibers • Collagen which is most common protein in body • Reticular fill spaces between tissues and organs • Elastic returns to its original shape after distension or compression • Ground substance • Shapeless background • Fluid
Connective Tissue Categories Adult • Loose • Dense • Connective tissue with special properties • Cartilage • Bone • Blood
Functions of Connective Tissue • Difficult to describe general properties of CT in the same way as epithelial tissue. • CT is so much more diverse. • Some of the characteristics may not fit all of the CT types perfectly-- but they will fit most of them.
Functions of Connective Tissue • Connective tissues are typically well-vascularized • They can usually reproduce well (to recover from injury) • Exception: They need a good number of cells to help with this, and dense connective tissue has only sparse numbers of cells.they have a lot of noncellular material, called extracellular matrix material (or just matrix).
Extracellular Matrix • The space between cells can be called the extracellular space/material or the intercellular space/material. • "Extra-" means outside of, while "inter-" means between. We will use the term extracellular space to prevent other confusion • That's because intercellular is easily confused with another term we will be using: intracellular. "Intra-" means within, and we will use intracellular to discuss what is inside the cell
Extracellular Matrix • To the right, the extracellular space is all in pink. • The space is filled with material. If the material is only liquid, the tissue as a whole will be loose. An example of that is in blood. • If the material in the extracellular space has some tough strands (called fibers) of protein in it, that gives the entire tissue a stronger consistency (because the cells are now sitting in a mesh of fibers).
Ground Substance: • This is the liquid portion of the extracellular matrix. • It is never entirely watery, but more gel-like. • A thin ground substance is seen in blood. The ground substance is not just water, but it is also filled with many dissolved solute particles.
Extracellular Matrix Fibers: • The number, properties, and alignment of fibers in the extracellular matrix will help determine the properties of the connective tissue. There are three main types of connective tissue fibers. Two are made out of a protein called collagen, while the third is made out of a protein called elastin.
Extracellular Matrix Fibers: • Collagen is a protein that forms a long strand. If many of these strands are put together the large resultant bundle can be quite strong. If only a few of these strands are intertwined, the small resultant bundle is only somewhat strong. Collagen is has greater properties of strength than of elasticity. • Elastin, on the other hand, is not so strong, but has elastic properties.
