Histology

Histology • Study of microscopic anatomy • Only 200 different cell types • Four primary tissue classes – – – –

_Epithelial_ tissue _Connective_ tissue _Muscular_ tissue _Nervous_ tissue

Epithelial Tissue • One or more layers of closely adhering cells – extracellular material so thin it is not visible – no room for blood vessels - Avascular • depends on underlying connective tissue for oxygen.

– sits on _Basement membrane_ (basal surface of cells) • anchors epithelium to underlying connective tissue

Epithelial Tissue • Where Found? – – – – –

Covers body surfaces Lines body cavities Forms internal & external linings of many organs Bulk of most glands (Usually lie on a layer of connective tissue, on which they depend for blood supply and waste removal)

Functions of Epithelial Tissue • • • • • • • • •

Protection - skin Sensory Perception– skin Filtration– kidneys Lubrication– GI tract Secretions – nasal membranes Digestion – GI tract Absorption– GI tract Excretion– urinary tract Reproductive – fallopian tubes

Characteristics of Epithelial Tissue • • • • • • •

Cellularity – closely packed cells Specialized contacts – tight junctions Polarity – upper (apical) & lower (basal) surfaces Connective tissue support – rest upon CT Avascular - lacking blood vessels Innervated – nerve fibers Regeneration – replacement of lost or damaged cells

Simple Versus Stratified Epithelia • Two Types with 3 Shapes • _Simple_ epithelium – contains one layer of cells – every cell touches basement membrane – named by shape of cells

• _Stratified_ epithelium – contains more than 1 layer (2-20) – named by shape of apical cells

Simple Squamous Epithelia

• • • •

Single row of flat cells (thin & scaly) Allows rapid diffusion of substances Secretes serous fluid Found in alveoli, glomeruli, endothelium, & serosa

Simple Cuboidal Epithelia

• Single row of Cube Shaped cells, often with microvilli • Absorption & secretion; produces mucus • Liver, thyroid, mammary, salivary and other glands, bronchioles, and most kidney tubules

Simple Columnar Epithelia Goblet Cell

Microvilli (for absorption

• Single row of tall, narrow cells – vertically oriented, oval nuclei in basal half of cell

• Absorption & secretion; secretion of mucus • Inner lining of GI tract, uterus, kidney & uterine tubes

Pseudostratified Epithelia Cilia thin, hair-like structures; move the environment across the cell layer

Goblet cell Basal cell

produce mucous coatings

• Single row of cells not all of which reach the free surface – nuclei of basal cells give layer a stratified look

• Secretes and propels respiratory mucus • Found in respiratory system

CPS Questions: Which of the following is NOT one of the 4 main tissue types. A. Nervous B. Muscle C. Epithelial D. Bone E. Connective

Stratified Epithelia • Composed of more than one layer of cells & named for shape of surface cells • exception is transitional epithelium

• Deepest cells sit on basement membrane • Variations – Keratinized epithelium has dead cells. – nonkeratinized epithelium lacks the layer of dead cells

Stratified Squamous Epithelia • Most abundant type of epithelial cells • Deepest cells may be cuboidal or columnar, then become more flat as they reach the surface • Skin, cheek, cervix, etc. – Exfoliation – dead cells flaking away.

Keratinized Stratified Squamous

• Multilayered epithelium covered with layer of compact, dead squamous cells packed with a tough fibrous protein called protein Keratin • Retards water loss & prevents penetration of organisms • Forms the epidermal layer of our skin

Nonkeratinized Stratified Squamous Epithelial layer

• Moist, slippery, multilayered epithelium that lacks surface layer of dead cells • Abrasion-resistant – resists stress from chewing, swallowing, intercourse & childbirth • Found on tongue, oral mucosa, esophagus & vagina

Stratified Cuboidal Epithelia

• Two or more layers of cells; surface cells square or round • Secretes sweat; ovarian hormones & produces sperm • Found in sweat gland ducts, ovarian follicles & seminiferous tubules

Stratified Columnar Epithelia • Rare • Can be found in regions of the pharynx (throat) and larynx (voicebox) • Not found anywhere else in the body.

Transitional Epithelia

• Not really own type, just different shape near membrane vs surface • Multilayered epithelium with rounded surface cells that flatten when the tissue is stretched • Functions to allow stretching – ie. for filling of urinary tract • Found in urinary tract -- kidney, ureter, bladder

Endocrine & Exocrine Glands • Glands secrete substances for elimination or for use elsewhere in the body – composed predominantly of epithelial tissue

• Exocrine glands maintain connection to surface with a Duct (epithelial tube) • Endocrine glands have no ducts – secrete their products (hormones) directly into bloodstream

• Mixed organs – Liver secretes bile into ducts + albumin into blood – Gonads release gametes + secrete hormones into blood – Pancreas secretes digestive enzymes + hormones

Exocrine Gland Structure • Stroma = capsule & extensions of the capsule called septa divide gland into lobes & lobules • Parenchyma = cells that synthesize the secretions of the gland (functioning cell) – acinus is cluster of simple cuboidal cells surrounding the duct draining those cells

2 Classes of Exocrine Glands • Unicellular – A one-celled gland

– Goblet Cell • Found in intestinal & respiratory tracts

• Secretes Mucin -> forms mucus

• Multicellular – More complex – Have an epithelium-derived duct – Secretory unit – consists of secretory cells (acini)

Types of Multicellular Exocrine Glands

• Simple glands have an unbranched duct • Compound glands have a branched duct • Shape of gland – Acinar or alveolar if secretory cells form dilated sac – Tubular if duct & secretory cells are of uniform diameter

Types & Methods of Secretion • Serous Glands glands – produce thin, watery secretions • sweat, milk, tears & digestive juices

• Mucous glands – produce a glycoprotein, mucin that absorbs water to form a sticky secretion called

• Mixed glands contain both serous & mucous cells • Cytogenic glands release whole cells – sperm and egg cells

• Variations in methods of cellular secretion

Holocrine Gland • Secretory cells disintegrate in order to deliver their accumulated product & some cell fragments – _suicide_ mission

• Sebaceous Glands – Oil-producing glands of the scalp are an example

Merocrine & Apocrine Secretion • _Merocrine_ glands release their product by exocytosis – tears, salivary, gastric glands, pancreas, _most sweat glands_, etc.

• _Apocrine_ glands are really merocrine glands but confusing appearance (apical cytoplasm not lost as used to be believed) – mammary & armpit sweat glands

CPS Question: the basement membrane is located between which of the follow tissue types.

A. Nervous and connective B. Muscle and nervous C. Connective and muscle D. Epithelial and muscle E. Epithelial and connective

Connective Tissue • •

•

Most abundant and variable tissue type! Cells not in direct contact since volume of extracellular matrix is greater than the volume occupied by cells (More matrix than cells!) Functions 1. 2. 3. 4.

_connects_ organs to each other gives _support and protection_ (physical & immune) storage of energy &heat production _movement & transport_ of materials

Cells of Connective Tissue • _Fibroblasts_ produce fibers & ground substance • _Adiposcytes_ store fat • _White blood cells_ (WBCs) function in immunity and tissue repair

Fibers of Connective Tissue • _Collagen_ fibers called white fibers – tough, resist stretch yet flexible – _tendons, ligaments_ & deep layer of the skin (dermis)

• _Reticular_ fibers – thin collagen fibers coated with glycoprotein – form framework for spleen & lymph nodes

• _Elastic_ fibers - yellow fibers – thin branching fibers made of _elastin_ – _Strech & recoil_ like rubberband (elasticity) – give skin, lungs & arteries ability to stretch & recoil

Ground Substance of Connective Tissue • Gelatinous or rubbery material found in between fibers and cells. – glycosaminoglycans (GAGs) • unusual disaccharides that attract sodium & hold water • important role in regulating water & electrolyte balance

– proteoglycan is gigantic molecule shaped-like bottlebrush made of protein & GAGs • embedded in plasma membranes bonding to other cells or extracellular macromolecules

– glycoproteins • protein-carbohydrate complexes that bind plasma membrane to collagen or proteoglycans outside the cells • mark pathways for cell migration

Fibrous Connective Tissue • Loose – Areolar tissue – Adipose tissue – Reticular tissue

• Dense – Dense Regular – Dense Irregular

_Areolar_ Tissue

• Loose arrangement of collagenous and elastic fibers, scattered cell types (mainly fibroblasts) & abundant ground substance • _Underlying all epithelia_ forming passageway for nerves & blood vessels; fascia between muscles

_Reticular_ Tissue

• Loose network of reticular fibers and cells • Forms _forms supportive stroma (framework)_ for lymphatic organs • Found in lymph nodes, spleen, thymus & bone marrow

_Adipose_ Tissue (Fat)

• Large, empty-looking cells (adipose) with thin margins; nucleus pressed against cell membrane • Energy storage, insulation, space filled as cushioning. • Subcutaneous fat beneath skin & surrounding organs – brown fat found in hibernating animals produces heat only no ATP

Dense Regular Connective Tissue

• Densely, packed, parallel collagen fibers; compressed fibroblast nuclei & scanty open space • Tendons & ligaments attach muscles to bones & hold bones together • Non-vascular – slow to heal (no blood vessels)

_Dense Irregular_ Connective Tissue

• Densely packed collagen fibers running in random directions; scanty open space; few visible cells • Withstands stresses applied in different directions • Deeper portion of skin; capsules around organs

Supportive & Fluid Connective Tissues • • • • •

Cartilage Osseous tissue Dental tissue Blood Lymph

Cartilage • _Supportive_ connective tissue with rubbery , flexible matrix • Chondroblasts produce matrix, once surrounded are called _chondrocytes_ • No blood vessels so diffusion must bring in nutrients & remove wastes – injured cartilage heals slowly (no blood supply)

• Major types of cartilage depend upon fiber types – hyaline, fibrocartilage and elastic cartilage

Hyaline Cartilage

• Clear, glassy matrix; fine dispersed collagen fibers; chondrocytes in clusters enclosed in lacunae “little lake” • Supports airway, eases joint movements • Over end of bones at movable joints; sternal ends of ribs; supportive material in larynx, trachea, bronchi and fetal skeleton

Elastic Cartilage

• Hyaline cartilage with weblike mesh of elastic fibers amongst the lacunae • always has perichondrium (layer of fibrous connective tissue covering surface) • Provides flexible, elastic support • External ear, auditory canal and epiglottis

Fibrocartilage

• Cartilage containing extensive parallel collagen fibers; never has perichondrium • Resists compression and absorbs shock in some joints • Pubic symphysis, knee joints & intervertebral discs

Bone • Osseous Tissue; Cells are called osteocytes • Ground substance is hard calcium phosphate • _Spongy_ bone looks spongy in appearance – delicate struts of bone – fills heads of long bones – always covered by compact bone

• _Compact_ bone looks solid in appearance – more complex arrangement – cells and matrix surrounding vertically oriented blood vessels in long bones

Bone Tissue (compact bone)

• Calcified matrix in concentric lamellae • Physical support; leverage for muscles; mineral storage • Found in skeleton

Blood

• Variety of cells and cell fragments – Non-nucleated pale pink cells - red blood cells (RBCs) – Non-nucleated cell fragments – platelets (clotting) – Nucleated white blood cells - (WBCs or leukocytes)

• Ground substance is fluid • Found in heart and blood vessels

Membranes • synovial membrane lines joints (only connective tissue comprises this layer) – secretes synovial fluid rich in hyaluronic acid

• Cutaneous membrane (skin) – stratified squamous epithelium resting on layer of dermis – relatively dry layer serves protective function

• Serous membrane (serosa) – simple squamous epithelium on areolar tissue covers organs and body walls & produces serous fluid

• Mucous membrane (mucosae) – line passageways that open to the exterior: digestive, respiratory, urinary & reproductive – often covered with mucus secreted by goblet cells

Mucous Membrane Histology

• Consists of 2 to 3 layers • Absoptive, secretory, and protective function • Mucous coating & movement of cilia trap & remove foreign particles & bacteria from body

CPS Question: Which of the following connective tissues are avascular? A. Bone B. Epithelial C. Adipose D. Cartilage E. Areolar

Connective Tissue Diseases • Deficiencies in collagen & elastin cause serious problems • _Marfan syndrome_ = hereditary defect in elastin fibers – tall stature, long limbs, spinal curvature & weakening of heart valves & arterial walls (rupture of aorta)

• _Ehlers-Danlos syndrome_ = hereditary defect in collagen synthesis – stretchy skin, loose joints, abnormal blood vessels, intestines and bladder

• _Osteogenesis imperfecta (brittle-bone disease)_ = insufficient collagen in bones making them brittle • _Scurvy_ is lack of vitamin C needed for synthesis of 2 amino acids used to synthesize collagen. – poor wound healing & subcutaneous hemorrhages

Excitable Tissue • Excitability – the ability of a cell to respond to a stimulus (responsiveness) – Nervous – Muscle

Nerve Tissue

• Large neuron with long cell processes surrounded by much smaller glial cells lacking dendrites and axons • For internal communication between cells. • Found in brain, spinal cord, nerves & ganglia

Muscular Tissue Functions • Movement – whole body – body parts – substances through the body

• • • •

Posture – (prevent you from moving) Speech Respiration Heat production

Types of Muscle Tissue • _Skeletal_ – under voluntary control • _Cardiac_ – heart; involuntary • _Smooth_ – involuntary – Digestive track, lines blood vessels.

Skeletal Muscle

• Long, cylindrical, unbranched cells with _Striations_ and _Multiple peripheral nuclei_ peripheral nuclei • Attached to bone • Under Voluntary Control • Movement, facial expression, posture, breathing, speech, swallowing and excretion

Cardiac Muscle

• Short branched cells with _striations_ and _intercalated discs_; one central nuclei per cell • involuntary • Found in the _heart_ - pump blood • Individual cells are called _Cardiocytes_ or myocytes

Smooth Muscle

• Short fusiform cells; nonstriated with only one central nucleus • Involuntary • Swallowing, GI tract functions, labor contractions, control of airflow, erection of hairs & control of pupil • Sheets of muscle in viscera; iris; hair follicles & sphincters

CPS Question: Muscles for respiration, intercoastals and diaphram, are what type of muscle tissue

A. Cardiac B. Skeletal C. Smooth D. Both B & C

Changes in Tissue Types • Tissues are capable of changing from one type to another • Differentaition (immature to specialized mature) – unspecialized tissues of embryo to specialized mature types • mesenchyme to muscle

• Metaplasia (specialized mature tissue to another type of specialized mature tissue) – changing from one type of mature tissue to another – simple cuboidal tissue before puberty changes to stratified squamous after puberty in the female vagina

Tissue Growth • _Hyperplasia_ is tissue growth through cell multiplication • _Hypertrophy_is enlargement of preexisting cells – muscle grow through exercise

• _Neoplasia_ is growth of a tumor (benign or malignant) through growth of abnormal tissue

Stem Cells • Undifferentiated cells with developmental plasticity – diversity of mature cell types to which they can give rise

• Embryonic stem cells – _Totipotent_ - any cell type possible • source = cells of very early embryo

– _pluripotent_- tissue types only possible • source = cells of inner cell mass of embryo

• Adult stem cells - undifferentiated cells in tissues of adults – Multipotent – can give rise to two or more cell types • bone marrow producing several blood cell types

– unipotent - only one type of cell produced • epidermal cells; olfactory cells

Tissue Shrinkage and Death • Atrophy is shrinkage from loss of cell size/number – senile atrophy is due to aging – disuse atrophy from lack of use (leg in a cast)

• Necrosis is pathological death of tissue – Gangrene is due to insufficient blood supply • gas gangrene is due to anaerobic bacterial infection

– Infarction is sudden death of tissue from lack of blood – decubitus ulcer is bed sore or pressure sore

• Apoptosis is programmed cell death (through development) – cells shrink & are phagocytized (no inflammation) • webbing between fingers, uterus after delivery, earlobes

CPS Question: In smokers, pseudostratified ciliated columnar epithelium of bronchi may become stratified squamous epithelium, which of the following would NOT be a consequence?

A. Lack the ability to produce mucus B. Lack cilia C. Cannot move debris out of the lungs D. Cannot trap debris E. Cannot effectively exchange gases.

Tissue Repair • Damaged tissues are repaired in 2 ways: • Regeneration – replacement of dead or damaged cells with original cells – restores normal function – Skin, bone, liver can regenerate very well.

• Fibrosis – replacement of damaged cells with scar tissue (collagen) – helps hold organ together -- function is not restored – healing muscle injuries, scarring of lung tissue or healing of severe cuts & burns of the skin

Wound Healing of a Laceration • INFLAMMATION • Damaged vessels leak blood • Damaged cells & mast cells leak histamine – dilates blood vessels – increases blood flow – increases capillary permeability

• Plasma seeps into wound carrying antibodies, clotting factors & WBCs

Wound Healing of a Laceration • Clot Formation • Scab forms on surface • Macrophages start to clean up debris

Scab formation & macrophage activity.

Wound Healing of a Laceration • ORGANIZATION • Clot is replaced by

granulation tissue • New capillaries grow into wound • Fibroblasts deposit new collagen to replace old material

Wound Healing of a Laceration • REGENERATION & FIBROSIS • Surface epithelial cells multiply & spread beneath scab • Scab falls off • Epithelium grows thicker (regenerates) • Connective tissue forms only scar tissue (fibrosis) • Remodeling phase may last 2 years

Epithelial regeneration & connective tissue fibrosis

Tissue Engineering • Production of tissues and organs in the lab – Framework of collagen or biodegradable polyester fibers. – Seeded with human cells – Grown in “bioreactor” – inside of a mouse • Supplies nutrients and oxygen to growing tissue

– Skin grafts already available • Research in progress on heart valves, coronary arteries, bone, liver, tendons.