Order 1218450: A & P Chap 1-4

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05 Histology

Expected Learning Outcomes • Define the term histology.

• List the four major tissue types.

• Contrast the general features of the four major tissue types.

• Classify the different types of epithelial tissues based on distinguishing structural characteristics.

• Describe locations in the body where each type of epithelial tissue can be found.

• Describe the functions of each type of epithelial tissue in the human body and correlate function with structure for each tissue type.

• Classify the different types of connective tissues based on distinguishing structural characteristics

• Describe locations in the body where each type of connective tissue can be found.

• Describe functions of each type of connective tissue in the human body and correlate function with structure for each tissue type.

• Compare and contrast the roles of individual cell types and fiber types within connective tissue.

• Classify the different types of muscle tissues based on distinguishing structural characteristics and location in the body.

• Describe functions of each type of muscle tissue in the human body and correlate function with structure for each tissue type.

• Describe locations in the body where nervous tissue can be found.

• Describe the structure and function of neurons and neuroglial cells in nervous tissue

• Describe the structure and function of mucous, serous, and cutaneous membranes.

• Describe locations in the body where each type of membrane can be found.

• Distinguish between exocrine and endocrine glands, structurally and functionally.

• Identify example locations in the body of exocrine and endocrine glands.

• Classify the different kinds of exocrine glands based on structure and function.

Introduction

• There are 50 trillion cells of 200 different cell types

• Four broad categories of tissues • Epithelial tissue

• Connective tissue

• Nervous tissue

• Muscular tissue

• Histology (microscopic anatomy) - the study of tissues and how they are arranged into organs

• Organ - structure with discrete boundaries that is composed of two or more tissue types

The Study of Tissues

The Primary Tissue Classes

• Tissue - a group of similar cells and cell products working together to perform a specific role in an organ

• The four primary tissues (epithelial, connective, nervous, and muscular) differ from each other in: • Types and functions of their cells

• Characteristics of the matrix (extracellular material)

• Relative amount of space occupied by cells versus matrix

• Matrix (extracellular material) is composed of: • Fibrous proteins

• Clear gel called ground substance • Also known as tissue fluid, extracellular fluid (ECF), interstitial fluid

Interpreting Tissue Sections

• Histologists preserve (fix), slice into thin sections one or two cells thick, and artificially colored with histological stains tissues

• Some stains bind to different cellular components

• Leads to ‘artifacts’ • Cell may be larger or smaller • Nucleus may be missing • Ducts might not look continuous

Interpreting Tissue Sections

• Longitudinal section (l.s.) • Tissue cut on its long axis

• Cross section (c.s. or x.s.) or transverse section (t.s.) • Tissue cut perpendicular to long axis of

organ

• Oblique section • Tissue cut at angle between cross and

longitudinal sections

Epithelial Tissue

• Epithelia are sheets of closely adhering cells, one or more cells thick • Covers body surfaces, lines body cavities, makes most glands • Functions vary

• Protect deeper tissues from injury and infection • Produce and release chemical secretions • Excrete wastes • Absorb chemicals including nutrients • Selectively filter substances • Sense stimuli

• Avascular (does not have blood vessels) • Usually nourished by underlying connective tissue

• Between an epithelium and underlying connective tissue is Basement Membrane • Collagen, reticular proteins, glycoproteins, other protein-carbohydrate complexes that

anchors to connective tissue below

• Apical surface - surface of epithelial cell that faces away from the basement membrane

• Basal surface - surface of epithelial cell facing the basement membrane • Cells closest to connective tissue usually have a high rate of mitosis

Cell Shapes in Epithelial Tissue • Simple epithelia contain one layer of cells

• Named by shape of cells

• All cells touch basement membrane

• Stratified epithelia contain more than one layer • Named by shape of apical cells

• Some cells rest on top of others and do not touch basement membrane

Simple Squamous Epithelium • Single row of thin cells

• Locations: air sacs of lungs, some kidney tubules, lining of heart and blood vessels (endothelium), and serosa

• Functions: Permits rapid diffusion or transport of substances, secretes serous fluid

a: © McGraw-Hill Education/Dennis Strete, photographer

Simple Cuboidal Epithelium

• Single layer of square or round cells

• Locations: Liver, thyroid, some glands, bronchioles, and most kidney tubules

• Functions: Absorption and secretion of substances, mucus production

Simple Columnar Epithelium • Single row of tall, narrow cells with oval nuclei in basal half of cell

• Often have microvilli (brush border)

• Ciliated in some organs

• May possess goblet cells

• Locations: Lining of GI tract, uterus, kidney, and uterine tubes

• Functions: Absorption and secretion of substances, mucus production

Pseudostratified Epithelium

• Looks multilayered, but all cells touch basement membrane

• Nuclei at several layers

• Often has cilia and goblet cells

• Locations: Respiratory tract and portions of male urethra

• Functions: Secretes and propels mucus

Keratinized Stratified Squamous Epithelium

• Multiple cell layers; cells become flat and scaly toward surface

• Locations: epidermis; palms and soles very heavily keratinized

• Functions: Resists abrasion; retards water loss through skin; resists penetration by pathogenic organisms

Non-keratinized Stratified Squamous Epithelium

• Same as keratinized epithelium without surface layer of dead cells

• Locations: Tongue, oral mucosa, esophagus, and vagina

• Functions: Resists abrasion and penetration of pathogens

Stratified Cuboidal Epithelium

• Two or more cell layers; surface cells square or round

• Locations: Sweat gland ducts, ovarian follicles, and seminiferous tubules

• Functions: Secretes sweat, produces sperm, produces ovarian hormones

Transitional Epithelium

• Multilayered epithelium with surface cells that change from round to flat when stretched

• Locations: ureter and bladder

• Functions: Allows for filling of urinary tract

Connective Tissue

Connective Tissue: Overview

• Diverse, abundant type of tissue in which cells occupy less space than matrix

• Supports, connects, and protects organs

• Highly variable vascularity • Loose connective tissues have many blood vessels • Cartilage has few or no blood vessels

• Functions of connective tissues vary • Connecting organs - tendons and ligaments • Support - bones and cartilage • Physical protection - bone • Immune protection - white blood cells attack foreign invaders • Movement - bones provide lever system • Storage - fat, calcium, phosphorus • Heat production - brown fat in infants • Transport – blood

• Four categories: Fibrous, adipose, supportive, and fluid

1 - Fibrous Connective Tissue

• Compos of Cells, Fibers, and Ground substance

1. Cells • Fibroblasts produce fibers and ground substance of matrix • Macrophages (from monocytes) phagocytize foreign

material and activate immune system when they sense foreign matter (antigens)

• Leukocytes (WBCs) • Neutrophils attack bacteria

• Lymphocytes react against bacteria, toxins, and other foreign agents

• Plasma cells (from lymphocytes) synthesize antibodies • Mast cells often found alongside blood vessels

• Secrete heparin to inhibit clotting

• Secrete histamine to dilate blood vessels

• Adipocytes store triglycerides

1 - Fibrous Connective Tissue 2. Fibers

• Collagenous fibers • Tough, flexible, and stretch-resisant • Tendons, ligaments, and deep layer of the skin are mostly collagen • Less visible in matrix of cartilage and bone

• Reticular fibers • Thin collagen fibers coated with glycoprotein that form framework of spleen and lymph nodes as well

as basement membrane

• Elastic fibers • Thin, branching • Made of protein called elastin • Allows stretch and recoil

3. Ground Substance • Glycosaminoglycans (GAGs)

• Long polysaccharides composed of amino sugars and uronic acid (disaccharides) • Regulate water and electrolyte balance of tissues • Chondroitin sulfate—most abundant GAG

• Responsible for stiffness of cartilage

• Other examples: heparin and hyaluronic acid

• Proteoglycans • Gigantic molecules (core protein plus GAGs) shaped like bottle brushes • Form gravy-like colloids that hold tissues together

• Adhesive glycoproteins • Protein-carbohydrate complexes • Bind components of a tissue together

Types of Fibrous Connective Tissue

• Loose connective tissue • Much gel-like ground substance between cells • Types

• Areolar

• Reticular

• Dense connective tissue • Fibers fill spaces between cells • Types vary in fiber orientation

• Dense regular connective tissue

• Dense irregular connective tissue

Loose Connective Tissue: Areolar • Lots of seemingly empty space is ground substance

• Possess all six cell types (Fibroblasts, Macrophages, Neutrophils, Lymphocytes, Plasma cells, Mast cells, and Adipocytes)

• Fibers run in random directions • Mostly collagenous, but elastic and reticular also present

• Found in tissue sections from almost every part of the body, surrounds blood vessels and nerves

• Nearly every epithelium rests on a layer of areolar tissue • Blood vessels provide nutrition to epithelium and waste removal • Ready supply of infection-fighting leukocytes that move about freely in areolar tissue

Loose Connective Tissue: Reticular Tissue

• Mesh of reticular fibers and fibroblasts

• Found in lymph nodes, spleen, thymus, and bone marrow

• Forms supportive stroma (framework) for lymphatic organs

Dense Regular Connective Tissue • Densely packed, parallel collagen fibers

• Only cell type is fibroblast with compressed nuclei

• Found in tendons (attach muscles to bones) and ligaments (attach bones to bones)

• Some ligaments have extra elastic fibers (elastic tissue)

Dense Irregular Connective Tissue

• Densely packed, randomly arranged, collagen fibers and few visible cells

• Withstands unpredictable stresses

• Locations: deeper layer of skin; capsules around organs

2 - Adipose Tissue • Adipocytes are dominant cell type

• Space between adipocytes is occupied by areolar tissue, reticular tissue, and blood capillaries

• Adipose tissue is the body’s primary energy reservoir

• Empty-looking cells due to large central globule of triglycerides

• Nucleus pressed against cell membrane

• Functions: Energy storage, insulation, cushioning • Brown fat of infants, children, and juveniles produces heat

3 - Supportive Connective Tissue: Cartilage

• Stiff connective tissue with flexible matrix

• Matrix rich in glycosaminoglycans and collagen fibers

• Cells • Chondroblasts - cartilage cells that produce the matrix that will trap them

• Chondrocytes - cartilage cells that are trapped in lacunae (cavities)

• No blood vessels • Diffusion brings nutrients and removes wastes (thus heals slowly)

• Wrapped with sheath of dense irregular connective tissue (perichondrium) with reserved chondroblasts • Except articular cartilage and fibrocartilage

• Three types of cartilage • Hyaline cartilage, fibrocartilage, and elastic cartilage

Hyaline Cartilage

• Clear, glassy appearance because of fineness of collagen fibers

• Eases joint movement, holds airway open, moves vocal cords, growth of juvenile long bones

• Locations: Articular cartilage, costal cartilage, trachea, larynx, fetal skeleton

Elastic Cartilage

• Cartilage containing abundance of elastic fibers

• Provides flexible, elastic support

• Locations: external ear and epiglottis

Fibrocartilage

• Cartilage containing large, coarse bundles of collagen fibers

• Resists compression and absorbs shock

• Lacks perichondrium

• Locations: pubic symphysis, menisci, and intervertebral discs

3 - Supportive Connective Tissue: Bone • Bone (osseous) tissue is a calcified connective tissue

• Bones of the skeleton are organs (made of bone tissue, cartilage tissue, marrow, and other tissue types)

• Wrapped with periosteum (dense irregular connective tissue)

• Osteocytes - mature bone cells within lacunae

• Two forms of osseous tissue • Spongy bone: porous appearance

• Delicate struts of bone (trabeculae) covered by compact bone • Found in heads of long bones and in middle of flat bones such as the sternum

• Compact bone: denser, with no visible spaces • Arranged in cylinders that surround central (haversian) canals that run longitudinally through shafts of long bones

• Blood vessels and nerves travel through central canal

• Bone matrix deposited in concentric lamellae around each central canal • Osteon - central canal and its surrounding lamellae • Delicate canals (canaliculi) allow osteocytes in lacunae to contact each other

4 – Fluid Connective Tissue: Blood • Transports cells and dissolved matter from place to place

• Plasma - blood’s ground substance

• Formed elements - cells and cell fragments • Erythrocytes - red blood cells (RBCs): transport O2 and CO2 • Leukocytes - white blood cells (WBCs): defend against infection and disease

• Neutrophils, eosinophils, basophils, lymphocytes, monocytes

• Platelets - cell fragments involved in clotting

Nervous and Muscular Tissues - Excitable Tissues

Nervous and Muscular Tissues—Excitable Tissues

• Excitability - ability to respond to stimuli by changing membrane potential

• Membrane potential - electrical charge difference (voltage) that occurs across the cell membrane

• Developed to highest degree in nervous and muscular tissues

• In nerve cells: changes in voltage result in rapid transmission of signals to other cells

• In muscle cells: changes in voltage result in contraction, shortening of the cell

Nervous Tissue

• Consists of neurons (nerve cells) • Detect stimuli

• Respond quickly

• Transmit coded information rapidly to other cells

• Neuroglia (glial) • More numerous than neurons

• Neuron parts • Neurosoma (cell body)

• Houses nucleus and other organelles

• Dendrites • Multiple short, branched processes

• Receive signals from other cells

• Transmit messages to neurosoma

• Axon (nerve fiber) • Sends outgoing signals to other cells

• Can be more than a meter long

Muscular Tissue

• Muscular tissue—elongated cells that are specialized to contract in response to stimulation

• Primary job is to exert physical force on other tissues and organs

• Creates movements involved in body and limb movement, digestion, waste elimination, breathing, speech, and blood circulation

• Important source of body heat

• Three types of muscle: skeletal, cardiac, and smooth

1 - Skeletal Muscle Tissue

• Made of muscle fibers long thin cells

• Most skeletal muscles attach to bone

• Contains multiple nuclei adjacent to plasma membrane

• Striations - alternating dark and light bands

• Voluntary - conscious control over skeletal muscles

Cardiac Muscle Tissue

• Found only in wall of heart

• Cardiomyocytes are branched, shorter than skeletal muscle fibers

• Contain one centrally located nucleus

• Intercalated discs join cardiomyocytes end to end • Provide electrical and mechanical connection

• Striated and involuntary (not under conscious control)

Smooth Muscle Tissue

• Made of fusiform myocytes lacking striations • Cells are relatively short and have one central nucleus

• Involuntary function

• Most is visceral muscle - making up parts of walls of hollow organs

Cell Junctions, Glands, and Membranes

Cell Junctions • Most cells are

anchored to each other or their matrix

• Connections between cells - Cell Junctions

• Four main types of cell junctions

1. Tight junctions

2. Desmosome 3. Hemidesmosome 4. Gap junction

Tight Junctions

• Tight junction—linkage between two adjacent cells by transmembrane cell-adhesion proteins

• In epithelia, they form a zone that completely encircles each cell near its apical pole

• Seals off intercellular space, making it difficult for substance to pass between cells

Desmosomes and Hemidesmosomes

• Hook-like, J-shaped proteins arise from cytoskeleton • Anchor cytoskeleton to membrane plaque

• Transmembrane proteins from each cell joined by cell adhesion proteins

• Keeps cells from pulling apart—resist mechanical stress

• Hemidesmosomes - half desmosomes that anchor basal cells of an epithelium to underlying basement membrane • Epithelium cannot easily peel away from underlying tissues

Gap Junctions

• Gap (communicating) junction formed by connexon proteins

• Connexon form ring in membrane surrounding water filled pore

• Located in cardiac and smooth muscle to allow ions to pass • Not found in skeletal muscle

• Located in lens and cornea to allow nutrients to pass

Glands • Gland - cell or organ that secretes

substances for use elsewhere in the body or releases them for elimination from the body

• Usually composed of epithelial tissue in a connective tissue framework and capsule

• Classified as

• Exocrine glands - maintain their contact with surface of epithelium by way of a duct • Surfaces can be external (examples:

sweat, tear glands) or internal (examples: pancreas, salivary glands)

• Endocrine glands - have no ducts; secrete hormones directly into blood • Hormones: chemical messengers that

stimulate cells elsewhere in the body • Examples: thyroid, adrenal, and pituitary

glands

• Some organs have both endocrine and exocrine functions • Examples: liver, gonads, pancreas

• Unicellular glands – Secretory cell found in an epithelium that is predominantly nonsecretory • Can be exocrine or endocrine • Examples: mucus-secreting goblet cells in

trachea or endocrine cells of stomach

Exocrine Gland Structure

• Capsule - connective tissue covering of exocrine gland • Septa or trabeculae: extensions of capsule that divide interior of gland into

compartments (lobes and lobules)

• Stroma—connective tissue framework of the gland • Supports and organizes glandular tissue

• Parenchyma—cells that perform the tasks of synthesis and secretion • Typically cuboidal or simple columnar epithelium

Classification of Exocrine Glands by Structure

• Duct shape: simple (unbranched) vs. compound (branched)

• Gland shape • Tubular: narrow secretory portion

• Acinar: secretory cells form dilated sac (acinus or alveolus)

• Tubuloacinar: both tubular and acinar portions

Classification of Exocrine Glands by Types of Secretions

• Serous glands • Produce thin, watery secretions

• Perspiration, milk, tears, digestive juices

• Mucous glands • Produce glycoprotein, mucin, which absorbs water to form mucus

• Goblet cells: unicellular mucous glands

• Mixed glands • Contain both serous and mucous cell types and produce a mixture of the two

types of secretions

• Salivary glands produce this watery saliva for food digestion or thick saliva for protection

Classification of Exocrine Glands by Modes of Secretion

• Merocrine secretion (used by eccrine glands) uses vesicles that release their secretion by exocytosis • Examples: tear glands, pancreas, gastric glands, and others

• Apocrine secretion - lipid droplet covered by membrane and cytoplasm buds from cell surface • Mode of milk fat secretion by mammary gland cells

• Note Apocrine sweat glands (in axillary region) are misnamed: use merocrine secretion

• Holocrine secretion - cells accumulate a product until they disintegrate • Secrete a mixture of cell fragments and synthesized substances • Examples: oil glands of skin

Membranes

• Membranes may be only epithelial, only connective, or a mix of epithelial, connective, and muscular tissues • Examples of membranes of only connective tissue: dura

mater, synovial membranes, periosteum • Examples of membranes of only epithelium: anterior

surfaces of cornea and lens of eye

• Cutaneous membrane (the skin)—largest membrane in the body • Stratified squamous epithelium (epidermis) resting on a

layer of connective tissue (dermis) • Relatively dry layer serves protective function

Mucous and Serous Membranes • Mucous membrane (mucosa)

lines passages that open to the external environment • Sublayers: epithelium, lamina

propria (areolar tissue), muscularis mucosa (smooth muscle)

• Absorptive, secretory, and protective functions

• Often have mucus producing goblet cells

• Serous membrane (serosa)— internal membrane • Simple squamous epithelium

resting on a layer of areolar tissue • Produces serous fluid that arises

from blood • Covers organs and lines walls of

body cavities • Endothelium lines blood vessels and

heart • Mesothelium lines body cavities

(pericardium, peritoneum, and pleura)