Ch. 4Tissues

Objectives

• Define tissue

• Describe the four main tissue types

• Identify the various tissues that fall under the four main tissues types, their functions and composition

• Know how tissue growth and repair occur

Tissues

• Tissues– Group of cells that are similar in structure and

perform a common or related function

– The study of tissues and their arrangement into organs• Histology

– Four main types• Differ by type of cells and characteristics of matrix

Four Main Tissue Types

• Epithelial

• Connective

• Muscle

• Nervous

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Epithelial Tissue

• Sheet of cells that covers a body surface or lines a body cavity– Covering and lining epithelium

• Cells that compose glands of the body– Glandular epithelium

• Functions– Protection, absorption, filtration, secretion,

excretion, sensory reception

Characteristics of Epithelium• Cellularity

– Almost entirely composed of closely-packed cells• Minimal ECF

• Specialized connections– Continuous sheet of cells– Tight junctions and

desmosomes

• Polarity– Apical surface and basal

surface– Basal lamina

• Connective tissue support– All epithelium supported by

connective tissue– Reticular lamina– Basal lamina + reticular lamina

= basement membrane

• Avascular– No blood vessels within

epithelium– Is innervated

• Regeneration– high regenerative capacity

Classification of Epithelium• Based on number of cell layers and on cell shape

• Cell layers– Simple – refers to one layer of cells– Stratified – refers to two or more layers of cells

• Cell shape– Squamous – flat, scale-like cells– Cuboidal – cube shaped cells– Columnar – column shaped cells

• How is pseudostratified columnar classified?

Simple Squamous Epithelium

• Thin and permeable– Found where rapid filtration and diffusion is

desired• Kidneys, lungs

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Simple Cuboidal and Columnar

• Function in secretion and absorption

• Found in tubules of the kidneys and in ducts of glands

• Function in absorption and secretion

• Found in stomach, intestines, uterus, uterine tubes

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Pseudostratified Columnar Epithelium

• Function in secretion, absorption, and motility of mucus

• Cells vary in height, but all cells touch the basement membrane

• Found in the respiratory tract and male urethra

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Stratified Squamous• Most abundant stratified

epithelium

• Functions in protection against abrasion

• Found on outer layer of skin and extend a short way into every body opening that is continuous with the skin– Keratinized and non-keratinized

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Stratified Cuboidal and Columnar

• Functions in secretion and sperm production

• Found in sweat gland, ovaries, seminiferous tubules

• Function in protection and secretion

• Rare, found in ducts of large glands, male urethra

Transitional Epithelium

• Functions to allow distention of the urinary bladdery

• Found in the bladder

• Basal cells are typically cuboidal

• Apical cells vary in shapedspace.udel.edu

Glandular Epithelia• Glands are cells or organs that secretes a

substance for use or elimination– Originate from invagination of epithelial tissue

• Classified into two categories– Endocrine – Exocrine

• Unicellular glands– Composed of one cell that secretes its products into

its surroundings

Exocrine Glands

• Typically enclosed by fibrous capsule– Septa – capsular extension that divide gland into

lobes– Parenchyma – cells that synthesis and secrete

• Classified based on the duct– Simple – single unbranched duct– Compound – branching ducts

Exocrine Glands

Types of Secretions

• Serous glands– Thin watery fluids

• Mucus glands– Secrete mucin that is converted into mucus upon

absorption of water

• Cytogenic glands– Secrete whole cells

• Testes and ovaries

Epithelial Surface Features

• Three ways: Adhesion proteins, interdigitating folds, and specialized junctions

• Specialized junctions–Desmosomes–Tight junctions–Gap junctions

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Cell Adhesions

• Tight junctions • Gap junctions

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Epithelia Surface Features• Basal Features– Basement membrane

• Basal lamina

• Reticular fibers

• Apical Features– Microvilli

– Cilia

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Connective Tissue• Found everywhere in the body and most widely

distributed

• Functions– Connects, supports, protection, insulation, and

transportation

• Four main classes– Fibrous tissue and fat– Cartilage– Bone– Blood

Characteristics of Connective Tissue

• Common origin– All arise from mesenchyme

• Degree of vascularity– Some avascular, while others highly vascular

• Extracellular Matrix– Tissue made up mostly of matrix • Ground substance

Structural Elements of CT• Ground substance

– Interstitial fluid between the cells allows for diffusion between blood vessels and cells

– CAP, GAG, Proteoglycans

• Fibers– Provide support

• Collagen• Elastic• Reticular

• Cells– Fibroblasts, macrophages, leukocytes, plasma cells, mast cells,

adipocytes

Fibrous Connective Tissue• Loose connective tissue

– Areolar• Serves to support most epithelium• Very loose fibers run in various directions

– Reticular• Framework of “soft organs”

• Dense connective tissue– Dense regular

• Composed of closely packed parallel collagen fibers• Fibroblast only type of cell• Tendons and ligaments

– Dense Irregular• Thick collagen fibers running in various direction• Compose the dermis, and fibrous sheaths around various organs

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Fibrous Connective Tissue

• Adipose tissue– Composed of adipocytes

that store fat– Functions as insulation

and support– Most fat is white fat– Children also produce

brown fat• Heat production

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Cartilage• Supportive connective tissue with flexible

rubbery matrix

• Chondroblasts secrete matrix until they are trapped.– Chondrocytes

• Avascular– Dependent on diffusion– Slow metabolism, slow to heal

Cartilage• Three types

– Hyaline• Clear glassy matrix with collagen fiber• Found at the ends of bones, larynx, trachea, and chest• Composes fetal skeleton

– Elastic• Matrix composed of elastic fibers• Perichondrium sheath• Ear, epiglottis

– Fibrocartilage• Matrix composed of thick parallel collagen bundles• No perichondrium sheath• Pubic symphysis, intervertebral discs, menisci• Compression and shock absorption• Sometimes transition between dense connective tissue and hyaline

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biology.clc.uc.edu

Bone• Osseous Tissue– Spongy– Compact

• Hard calcified matrix containing collagen fibers– Deposited in concentric lamellae around central canal

• Blood vessels and nerves– Osteoblasts, osteocytes, osteoclasts

• Support, protection, movement, mineral and fat storage, blood production

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Blood

• Fluid connective tissue– Formed elements in a fluid matrix (plasma)

• Transport nutrients, wastes, gases ...

• Found within blood vessels

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Muscle Tissue

• Highly cellular, well vascularized tissues responsible for movement

• Capable of contraction and producing tension

• Three types– Skeletal– Smooth– Cardiac

Nervous Tissue

• Main component of nervous system– Regulates and controls various functions

• Capable of transmitting electrical impulses

• Two cell types– Neurons

• Conduct impulse– Supporting cells

• Nonconducting, insulate and protect neurons

• Read the section on inflammation and repair