The Tissue Level Of Organization Chapter 4 Introduction

The Tissue Level Of Organization Chapter 4

Introduction • Tissues are collection of specialized cells and cell products that are organized to perform a relatively limited number of functions. • The four tissue types are: – Epithelial tissue, connective tissues, muscle tissue and neural tissue Histology is the study of tissues

Epithelial Tissue • A epithelium is an avascular layer of cells that form a barrier that covers internal or external surfaces. • Glands are secretory structures derived from epithelia

Functions of Epithelia • Epithelia provide physical protection, control permeability, provide sensations, and produce specialized secretions.

– Gland cells are epithelial cells that produce secretions. • Exocrine secretions are released onto body surfaces • Endocrine secretions, known as hormones, are released by gland cells into the surrounding tissues.

Intercellular Connections • The individual cels that make up tissues attach to one another or to extracellular protein fibers in three major ways: – Tight junctions, gap junctions and desmosomes

• At a tight junction, the outer surfaces of the two cell membranes are bound tightly together. • These are the strongest intercellular connections.

• At a gap junction, two cells are held together by interlocked membrane proteins, forming a narrow passageway

• A desmosome has a very thin layer of intercellular cement between the cell membranes, reinforced by a network of protein fibers.

The Epithelial Surface • Many epithelial cells have microvilli, and some have stereocilia. The coordinated beating of the cilia on a ciliated epithelium moves materials across the epithelial surface.

The Basement Membrane • The inner surface of each epithelium is connected to a noncellular basement membrane.

Epithelial Renewal and Repair • Divisions by stem cells, or germinative cells, continually replace the short-lived epithelial cells.

Classifying Epithelia • Epithelia are classified on the basis of the number of cell layers and the shape of the exposed cells.

Simple epithelium • Simple epithelium has a single layer of cells covering the basement membrane

Stratified epithelium • Stratified epithelium has several layers

Squamous epithelium • In squamous epithelium the cells are thin and flat

Cuboidal epithelium • The cells resemble little hexagonal boxes

Columnar epithelium • The cells are taller and more slender.

Glandular Epithelia • A glandular epithelial cell may release its secretions through – Merocrine – Apocrine – holocrine

• Merocrine secretions: – The most common method of secretion, – The product is released through exocytosis

• Apocrine secretion – Involves the loss of both secretory product and cytoplasm

– Holocrine secretion • Unlike the first two methods, this destroys the cell, which becomes packed with secretions and finally bursts.

• Exocrine secretions may be serous(watery, usually containing enzymes) • Mucous-thick and slippery • Mixed-containing enzymes and lubricants.

Epithelium Quiz

What is this type of epithelium?

• What about this?

Answers • Simple cuboidal • Stratified columnar • Simple columnar.

Connective tissues • All connective tissues have specialized cells and a matrix, composed of extracellular protein fibers and a ground substance.

• Connective tissues are internal tissues with many important functions – Establishing a structural framework – Transporting fluids and dissolved materials – Protecting delicate organs – Supporting, surrounding, and interconnecting tissues – Storing energy reserves – Defending the body from microorganisms.

Classifying connective tissues • Connective tissue proper refers to connective tissues that contain varied cell populations and fiber types surrounded by a syrupy ground substance.

• Fluid connective tissues have a distinctive population of cells suspended in a watery ground substance containing dissolved proteins • The two types are blood and lymph

• Supporting connective tissues have a less diverse cell population than connective tissue proper and a dense matrix that contains closely packed fibers. • The two types of supporting connective tissues are cartilage and bone.

Connective tissue Proper • Connective tissue proper contains fibers, a viscous ground substance, and a varied cell population. • Resident and migrating cells may include fibroblasts, macrophages, rat cells, mast cells and various white blood cells.

• There are three types of fiber in connective tissue – Collagen fibers – Reticular fibers – Elastic fibers.

• Connective tissue proper is classified as loose or dense connective tissues. • Loose connective tissues include loose connective tissue, or areolar tissue and adipose tissue.

• Most of the volume in dense connective tissues consists of fibers. • Dense connective tissues form tendons and ligaments.

Fluid Connective tissues • Blood and lymph are connective tissues that contain distinctive collections of cells in a fluid matrix

• Blood contains red blood cells, white blood cells, and platelets • The watery ground substance is called plasma. • Arteries carry blood from the heart and toward capillaries, where water and small solutes move into the interstitial fluid of surrounding tissues. • Veins return blood to the heart.

• Lymph forms as interstitial fluid enters the lymphatic vessels, which return lymph to the cardiovascular system.

Supporting Connective Tissues • Cartilage and bone are called supporting connective tissues because they support the rest of the body. • The matrix of cartilage consists of a firm gel and cells called chondrocytes.

• A fibrous perichondrium separates cartilage from surrounding tissues. • The three types of cartilage are hyaline cartilage, elastic cartilage and fibrocartilage.

• Chondrocytes rely on diffusion through the avascular matrix to obtain nutrients.

• Bone or osseous tissue, has a matrix primarily consisting of collagen fibers and calcium salts which give it unique properties. • Osteocytes depend on diffusion through canaliculi for nutrient intake. • Each bone is surrounded by a periosteum.

Membranes • Membranes form a barrier or an interface. Epithelia and connective tissues combine to form membrane that cover and protect other structures and tissues. • There are four types of membranes – Mucous, serous, cutaneous, and synovial.

Mucous membranes • Mucous membrane line cavities that communicate with the exterior. Their surfaces are normally moistened by mucous secretions.

Serous membranes • Serous membranes line internal cavities and are delicate, moist, and very permeable.

Cutaneous membranes • The cutaneous membrane covers the body surface. Unlike serous and mucous membranes, it is relatively thick, waterproof, and usually dry.

Synovial Membranes • Synovial membranes, located at joints, or articulations, produce synovial fluid in joint cavities. Synovial fluid helps lubricate the joint and promotes smooth movement.

Identify the following connective tissues

And the answers are…. • Elastic cartilage • Blood • Hyaline cartilage • Bone • Adipose • Areolar

Muscle Tissue • Muscle tissue is specialized for contraction. • The three types of muscles tissue are: – Skeletal muscle – Cardiac muscle – Smooth muscle.

Skeletal Muscle Tissue • Skeletal muscle tissue contains large cells, or muscle fibers, tied together by collagen and elastic fibers. • Skeletal muscle fibers are multinucleated and have a striped appearance because of the organization of contractile proteins.

• Because we can control the contraction of skeletal muscle fibers through the nervous system, skeletal muscle can be considered striated voluntary muscle.

Cardiac Muscle Tissue • Cardiac muscle tissue is found only in the heart. • The nervous system does not provide voluntary control over cardiac muscle cells. • Cardiac muscle is striated involuntary muscle.

Smooth Muscle Tissue • Smooth muscle tissue is found in the walls of blood vessels, around hollow organs, and in layers around various tract. • It is classified as nonstriated involuntary muscle.

Identify the following muscle types

• What char. Help you identify the type of muscle? – Striations? – Nuclei? – Branching? – Intercalated disks?

• Characteristics – Striations? – Branching? – Nuclei? – Intercalated disks?

• Characteristics? – Striations? – Nuclei? – Branching? – Intercalated disks?

And the Answers are… • Cardiac tissue – Branching, striated, intercalated disks • Smooth muscle Tissue – No branching, not striated, single nucleus • Skeletal Muscle Tissue – Striated, multiple nuclei

Neural Tissue • Neural tissue is specialized to conduct electrical impulses that convey information from one area of the body to another.

• Cells in neural tissue are either neurons or neuroglia. • Neurons transmit information as electrical impulses in their cell membranes. • Several kinds of neuroglia serve both supporting and defense functions.

• A typical neuron has a cell body, dendrites, and an axon, which ends at synaptic terminals.

Tissue Injuries and Repairs • Any injury affects several tissues types simultaneously, and they respond in a coordinated manner. • Homeostasis is restored in two processes – Inflammation and regeneration

• Inflammation or the inflammatory response, isolates the injured area while damaged cells, tissue components, and any dangerous microorganisms are cleaned up. • Regeneration is the repair process that resores normal functions.

Tissues and Aging • Tissues change with age. Repair and maintenance grow less efficient and the structure and chemical composition of many tissues are altered. • Cancer incidence increases with age, with roughly three-quarters of all cases caused by exposure to chemicals or environmental factors.