Anatomy Test #2

Histology

Histology

• Study of tissues and their arrangement in organs

Tissues formed of cells and extracellular matrix

Matrix

Protein fibers and ground substance

Tissues are classified according to:

1. Types and functions of cells

2. Composition of matrix

3. Relative space filled by cells vs matrix

Classified into 4 major tissue categories:

Epithelial, connective, nervous, muscular

Embryonic Tissues

Three major tissue layers in embryos: Ectoderm, Endoderm, Mesoderm

Ectoderm (outer):

epidermis and nervous system

Endoderm (inner):

inner lining of digestive tract

Mesoderm (middle):

 muscle, bones, blood and other connective tissue

Longitudinal section (I.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 diagonal to long axis

Smear

- Tissue rubbed or spread across a slide

- Ex: Blood

Spread

- Cobwebby tissue laid out on a slide

- Ex: Areolar Tissue

Epithelial Tissue

Categorized by cell layers and cell shape

Simple squamous epithelium

• Single layer of thin cells

• Permits rapid diffusion or transport of materials

- Lung tissue; inner lining of blood vessels, (endothelium); outer lining of internal organs in abdominal cavity (mesothelium)

Simple cuboidal epithelium

• Single layer square cells

• Key roles in secretion and absorption

- Mammary, salivary and sweat glands

- Kidney tubules

- Thyroid gland

Simple Columnar Epithelium

• Single layer tall, narrow cells

- Often with Brush Border

- Goblet cells common

• Big for absorption, still some secretion

- Inner lining of small intestine and stomach

Pseudostratified Epithelium

• Appears multilayered but all cells touch basement membrane

- Often ciliated

- Goblet cells common

      - Secretes and propels mucus

- Trachea, larynx (respiratory tract)

Stratified Squamous Epithelium (Keratinized)

• Many layers (30+)

- Basal cells cuboidal or columnar

- Apical cells are flat

- Surface layer cells dead

• Resists abrasion, water loss, penetration by pathogens

• Only place we will see this is Epidermis of the skin

Stratified Squamous Epithelium (Non-Keratinized)

• Many layers (20+)

- Lacks surface layer of dead keratinized cells

• Resists abrasion, pathogens

- Vaginal walls

- Oral mucosa

Urothelium (Transitional Epithelium)

• Surface cells charge from round to flat when stretched

• Allow urinary tract organs to expand when filled

- Kidney ureter, urinary bladder

Nervous Tissue

- Specialized for electrical/chemical signaling

• Two major types

- Brain, spinal cord (CNS tissue)

- Nerves (PNS tissue)

Neurons

detect stimuli and send signals

Neuroglia

Help neurons carry out functions

Muscular Tissue

• Cells contract when stimulated

- Exert physical force on other tissues and organs

• Basis of regional and whole-body movement:

- Breathing

- Blood circulation

- Digestion

- Excretion

• Help generate body heat

• Three types distinguished by:

- Dominant cell shape

- Extent to which each is voluntary or involuntary

• Presence/absence of striations

Skeletal Muscles

• Voluntary muscle tissue

- Most attached to bone

- Made of long, thin striated cells *muscle fibers(

- Contain multiple nucleus

Cardiac Muscle

• Involuntary muscles cells of heart (cardiocytes)

• Striated, but shorter than muscle fibers

Single nucleus surrounded by glycogen

Adjacent cells connected by intercalated discs

Smooth Muscle

• Short, unstriated, involuntary fusiform cells

- One central nucleus

•  Found in most organs: most important in digestive, respiratory, urinary tracts

Connective Tissue: Overview

• Most abundant and histology variable primary tissue

• Binds supports, and protects organs 

• Often highly vascular

• Cells fill less space in ECM

• Defined by cell compactness, major fiber type and orientation, and extent of matrix

Fiber

Collagen Fibers, Elastic Fiber, Reticular Fiber

Collagen fibers

made of collagen

Elastic fibers

• made of elastin

- thinner than collagen fibers

- allow tissues to stretch and recoil

Reticular Fiber

thin collagen fiber with glycoprotein

- Important in Spleen and lymph nodes

Ground substance

• Gelatinous/rubbery consistency

- Absorbs compressive forces

- Binds cells and extracellular molecules

- Slow down pathogenic organisms

Fibrous Connective Tissue

• Fiber often loosely organized, abundant blood vessels, and much empty space

• Found in almost every part of the body

Fibroblast

cells that produce fibers and ground substance

Types of fibrous tissue

Loose connective tissue

• Matrix mostly ground substance

• Lots of empty space between cells

• Areolar and Reticular

Dense Connective Tissue

• Matrix mostly closely-packed fibers

Areolar Tissue

• Found throughout body

• Loosely organized fibers, many blood vessels, substantial empty space

- Upper layers of Dermis

- Between muscles

Reticular Tissue

• Mesh of reticular fibers, fibroblasts, WBCs

• Framework for lymphatic organs

- Lymph nodes, spleen, bone marrow

Dense Regular Connective Tissue

• Collagen fibers tightly packed in parallel

- Stresses imposed in predictable directions

- Tendons and ligaments

• Fibroblasts abundant, but few other types

• Few blood vessels, slow to heal

Dense Irregular Connective Tissue

• Collagen fibers tightly packed randomly

- Resists stresses from unpredictable directions

• Many blood vessels

- Lower layer of dermis

Adipose Tissue

• Fat tissue: contains many adipocytes

- Primary energy reservoir (triglycerides)

- Source of thermal insulation

- Anchors and cushion organs

- Contributes to body shape

• Number of adipocytes stable in adults

- Individual cells shrink or swell

Yellow Adipose Tissue

• Yellow color when fresh

- Subcutaneous fat (hypodermis) , breasts, mesenteries of abdominal cavity

• Preserved cells mostly empty

- Triglycerides dissolve

- little cytoplasm

Brown Adipose Tissue

• Heat generating tissue found in shoulders, upper back and kidneys

- 6% in infants; less in adults

• Brown color from blood vessels, mitochondria

- Multiple globules of small triglyceride

Cartilage

• Stiff connective tissue with flexible, rubbery matrix

- Few blood vessels, slow to heal

• Chondroblasts

• Chondrocytes

Chondroblasts:

produce extracellular matrix

Chondrocytes:

• former chondroblast locked into space (lacuna) surrounded by matrix

Hyaline Cartilage

• Clear, glassy appearance

- Very fine collagen fibers

• Eases movement of joints

- Articular Cartilage

- Fetal Skeleton

Fibrocartilage

• Bundles of large, parallel collagenous fibers around chondrocytes

• Resists compression; absorb shock

- Pubic Symphysis

- Intervertebral discs

Elastic Cartilage

• Elastic fibers around chondrocytes

• Provides flexible, elastic support

- External Ear

- Epiglottis: Found at top of our larynx/voice box, folds down

Osseous Tissue (bone)

• Mineralized connective tissue that forms internal bony skeleton 

• Organ bones composed of two major tissue types

- Compact bone

- Spongy bone

Compact Bone

• Dense tissue forming outer layer of organ bone

• Arranged in cylinders around longitudinal central canals

- Blood vessels, nerve pass through canals

• Bone deposited by osteocytes in onion-like layers

• Osteocytes deposit bone within lacunae

- linked to neighboring cells through canaliculi and gap junctions

Spongy (Trabecular) Bone

• Spongy network of thin plates of bone

- Imparts strength with lightness to skeleton

- Surrounds bone marrow

      -    Covered by Compact Bone

Blood

• Fluid connective tissue

• - Transports cells, dissolved materials around body

• Plasma: liquid ground substance

• Forced elements:  blood cells and cell fragments

- Erythrocytes (RBCs), Leukocytes (WBCs), and Platelets (cell fragments)

Cell Junctions

• Anchor cells to each other or their matrix

• Resist physical Stress

• Support intercellular communication

Tight Junctions

• Cell-adhesion protein binds cell tightly, sealing off intercellular space

- Materials pass through cells, not around them

- Block pathogenic organisms

• Common in epithelia, especially in digestive tract

Desmosomes

• Intermediate filaments linked to cell-adhesion proteins

- Keeps cells from pulling apart; resist stress

- Hold cells more loosely than tight junctions

• Common in epidermis, cardiac muscle

Hemi-desmosomes

Anchor basal cells of epithelium to basement membrane

Gap Junctions

• Formed by connexons

- Six transmembrane proteins arranged like orange segments

- Pore allows materials to pass from one cell to the next

• Common in cardiac, smooth muscle

- Help ensure uniform contraction

Glands

• Organs or cells releasing products for use in other organs or elimination from body

- Mostly formed of epithelia, often surrounded by connective tissue

Exocrine Glands

• Delivered to skin surface or internal organ lumen by duct

- Sweat, mammary, pancreatic glands

Endocrine Glands

• Secrete products (hormones) directly into bloodstream

- Lack contact with surface and have no ducts

• Thyroid, adrenal, and pituitary glands

Merocrine (Eccrine) Glands

Releases secretions from vesicles by exocytosis at plasma membrane

• Example: tear glands, most sweat glands

Apocrine Glands

Release secretions in lipid enclosed droplets

• Mammary Glands

Holocrine Glands

• Cells produce product, then disintegrate

• Secretion is mixture of cell fragments and synthesized substance

- Ex: sebaceous glands

Cutaneous Membrane (skin)

Outer boyd membrane

• Keratinized stratified squamous epithelium (epidermis); connective tissue layer (dermis)

• Largest membrane; serves protective functions

Mucous Membrane (mucosa)

Line internal passages open to the external environment

• Inner epithelium; middle areolar tissue; and outer smooth muscle

• Absorptive, secretory, and productive functions

• Digestive, respiratory, urinary, reproductive tracts

Serous Membrane (Serosa)

Covers organs and lines walls of body cavities

• Produces serous fluid that reduces muscle friction

• Simple squamous epithelium and areolar tissue

• Ex: digestive tract; pericardium of the heart

Integumentary system

• Skin (integument): largest organ in the body

- about 10-15% body mass

• Accessory organs: hair, nails, skin glands

• Skin is the most vulnerable organ

- Exposed to radiation, trauma, infection, and chemicals*

- Receives more medical treatment than any other organ

Dermatology: Study and medical treatment of the integumentary system.

Functions of Integumentary System

• Protection

- Antimicrobial environment

- Protection from mechanical damage

- Blocks UV radiation and toxic chemicals

• Regulates body water

• Helps make Vitamin D

- Important in bone physiology 

• Sensation

- Touch, pain, heat, cold

• Thermoregulation

- Sweating

- Blood flow in the skin

• Nonverbal communication

- Facial muscles

- Condition of skin, hair, nails

Epidermis

• Keratinized stratified squamous epithelium

- Surface layer of dead cells

- Lacks blood vessels

- Few nerve endings

Dermis

• Connective tissue layer deep to the epidermis

- Rich in blood vessels, nerves, and glands

- Areolar and dense irregular connective tissue

- Support hair follicles, nail roots, facial muscles

- Upper papillary layer and deeper reticular layer

• Dermal papillae

- Upward extensions of dermis at boundary of epidermis

- Give rise to friction ridges (fingerprints)

Hypodermis

• Connective tissue beneath dermis (subcutaneous tissue)

- Not part of skin but physically linked to it

- Mostly adipose tissue

- Common site of drug injection, contains rich blood vessels

Keratinocytes

• Synthesize Keratin

• Comprise most epidermal cells

• Found in all layers of epidermis

• Produced by all cells

Epidermal Stem Cells

Give rise to Keratinocytes

Melanocytes

• Produce pigment melanin

- Keratinocytes store particles around nucleus

- Absorbs UV radiation, protecting DNA

- Induces skin color

• Found only in stratum basale

Tactile (Merkel Cells)

• Touch Receptor

- Underlying nerve fiber carries touch signals

• Found only in stratum basale

Dendritic (Langerhans) Cells

• Immune cell derived from monocytes (WBC)

- originate in bone marrow; migrate to epidermis

• Guard against invading pathogens and toxins

• Found in stratum spinosum and granulosum

Epidermal Layers

Stratum Basale, Stratum Spinosum, Stratum Granulosum, Stratum Lucidum, Stratum Corneum

Stratum Basale:

bottom single cell layer

- Mostly keratinocytes, but stem cells, melanocytes, tactile cells also present

Stratum Spinosum:

 multiple layers of keratinocytes

- Cells shrink during tissue preservation; linkage by desmosomes gives spiny appearance

Stratum granulosum:

• 3-5 layers of kratinocytes containing many dark-staining granules

- Secrete protein that bundles keratin

- Helps in formation of epidermal water barrier

Stratum Lucidum

• thin layer of dead keratinocytes

- seen only in thick skin

Stratum corneum

• Less than or equal to 30 layers of dead keratinocytes

- Resists abrasion, water loss, penetration by pathogenic organisms; surface cells exfoliate

Keratinocyte Life History

• Originate from stem cells in stratum basale

• New keratinocytes push older cells up

- Lack of nutrients inhibits cell division > 1-2 cell layers from dermis

- Produce keratin filaments and lipid-filled membrane-coating vesicles

• In stratum granulosum, epidermal water barrier forms

- Keratin tied into bundles and enclosed into sacs

- membrane-coating vesicles release waterproofing lipids onto cell surface

• Cells above stratum granulosum die from lack of nutrients

• Dead cells exfoliate from stratum corneum as dander cells migrate to skin surface in 30-40 days

• Sustained stress on skin results in thickening of stratum corneum

- Corns or callouses

Pigments: Melanin

• Most significant factor in human skin solar

- Melanin granules released by melanocytes accumulate around nuclei of keratinocytes

• Two main types:

- Eumelanin (brownish black pigment)

- Phaeomelanin (red-yellow pigment)

• Variation in human skin color primarily due to differences in:

- Amount of melanin produced

- Distribution of melanin within keratinocytes

- Differences in the decay rate of melanin

- Exposure to ultraviolet (UV) rays of sunlight

- induces skin tanning

UV Effects on Skin

• UV: high energy radiation in sunlight

- Stimulates Vitamin D produce

- Damages DNA and folate and folat (Vitamin B9)

• Melanin absorbs UV, protecting against its harmful

• UV most intense at equator, weekend towards poles

Human Population Variation

Legacy of variation among historical populations in the intensity of UV exposure

Pigments: Hemoglobin

• Red pigment of red blood cells

- Adds reddish hue to the skin (e.g., lips)  

Pigment: Carotene

• Yellow pigment acquired from vegetables        

• Not produced naturally by body

• Concentrates in stratum corneum

Hair

• Filament of mostly dead keratinized cells

• Found over most body surfaces but absent from:

- Palms and soles

- Ventral, lateral surfaces of digits

- Lips, nipples, parts of genitals

Structure of Hair

• Bulb: swelling where hair arises (usually in the dermis)

- Only region in hair with living cells

• Root: hair between the bulb and surface

Shaft: Portion above skin surface

Anatomy of the Hair Bulb:

• Dermal papilla

- Bud of connective tissue encased by bulb

- Provides nutrition for hair

• Hair matrix

- Mitotic cells above dermal papilla

- All cells above are dead

Anatomy of the Hair Root

• Medulla: inner core

- Loosely arranged cells and air spaces

• Cortex: middle layer

- Elongated cells

- Majority of hair mass

• Cuticle: Outer Layer

- Thin, scaly cells

- Grip, hair follicle; resist removal

Hair Texture

• Texture due to cross-sectional shape

- Straight hair is round

- Curly hair is flat

Hair color

• Brown/Black hair has mostly eumelanin

• Blond/Red hair has mostly phaeomelanin

• Gray/White hair lacks melanin and has medulla full of large air pockets

Function of Hair in Humans

• Different types of remaining hair probably have different functions

- Parasite detection (body hair)

- Retention of heat (scalp)

- Protection against sunburn (scalp)

- Protect against entry of foreign particles (nose, ear)

- Signal Reproductive status (beard, axilla, pubic hair)

- Enhance facial expression and nonverbal communication (eyebrows, eyelashes)

Cutaneous Glands

Skin has five major types of glands

Merocrine Sweat Glands/Major Functions

• Evaporative cooling of skin

• Waste removal

Generates antibacterial acid mantle of skin