Chapter 4: Histology

Histology - Study of Tissues

Biopsy - removal of tissues for diagnostic purposes

Autopsy - Examination of organs of a dead body to determine cause of death

Tissues

Classification based on structure of cells, composition of extracellular matrix and cell function

Types

• Epithelial

• Nervous - Neurons

• Muscular - Smooth, Skeletal, Cardiac

• Connective

Gastrulation - The cells between the epiblast and hypoblast layers become the primary Germ layer known as mesoderm; Other migrating cells displace the hypoblast cells an become endoderm; cells remaining in the epiblast become ectoderm

• Derived from epiblast

Ectoderm Differentiation

On the external surface of embryo

Develop into:

• Epidermis of Skin

• Hair and Nails

• Nervous system

Mesoderm Differentiation

5 regions

• Notochord - Tightly Packed Midline cells

• Paraxial Mesoderm - Beside notochord; develops into units (somites) that form axial Skeleton, muscle, dermis Skin, Connective Tissue

• Intermediate Mesoderm - lateral to Paraxial; urinary and reproductive systems

• Lateral Plate Mesoderm - lateral to intermediate: cardiovascular system, body Cavil, lining, connective tissue lining

• Head Mesenchyme - Forms connective tissue and musculature of the face

Endoderm Differentiation

Develop into:

• lining of digestive, respiratory, and urinary systems

• liver

• Gallbladder

• Pancreas

• Thyroid gland

• Parathyroid gland

• Thymus

Epithelial Tissue

Epithelial Tissue - covers body surfaces and forms glands

• Outside surface of body

• Lining of digestive, respiratory and urogenital systems

• Lining of heart and blood vessels

• Linings of mam, body cavities

Functions of Epithelial Cells

• Protect underlying Structures

• Barrier

• Permit passage of substances

• Secrete substances

• Absorb substances

  • Increase surface area

Epithelial Surfaces

Basement Membrane - Base barrier: Protection

Free surface - smooth, reduce friction

Microvilli - increase surface area for absorption/ secretion

Cilla - Mire materials across surface

Lateral Surfaces

Simple Squamous Epithelium

Function

• Filtration, Diffusion, secretion, absorption

• Secretes lubricating fluids

Location

• Lungs - alveoli

• Kidneys - Tubules and glomerular Capsule

• Endothelium - lining of BVs (Blood Vessels)

• Mesothelium - Serious membrane of ventral body cavity

Simple Cuboidal Epithelium

Function

• Secretion

• Absorption

• Mucous production

Location

• Kidney Tubules - storage

• Lungs - bronchioles

• Glands

Simple Columnar Epithelium

Function

• Absorption

• Secretion of mucous

Location

• Digestive - stomach lining

• Reproductive Systems

Modification

• Cilia - Material Movement

• Microvilli - increase surface area for absorption; small intestine

• Goblet cells - Secrete mucous for lubrication

Pseudostratified Columnar Epithelium

Modified Simple Epithelium

Rest on basement membrane

Nuclei at different levels

Location

• Respiratory and male reproduction systems

Function

• Secretion mucous

Modifications

• Cilla - Respiratory system

• Goblet cells - respiratory system

Stratified Squamous Epithelium

Function

• Protection from abrasion, Pathogens

• Reduces water loss - Keratinized

Location

• Keratinized - water proof

• Non Keratinized - Mules membrane

Stratified Cuboidal Epithelium

Location

• Ducts of sweat glands

• Follicles of ovary

• Seminiferous tubules of testis

Function

• Sweat and Hormone Secretion

Stratified Columnar Epithelial

Location

• Male urethra

• Mammary Gland duet

Function

• Mucus and fluid secretion

Transitional Epithelium

Stretched - uppermost are squamous

relaxed - uppermost are cuboidal

Location

• Kidney

• Ureter

• Bladder

• Urethra

Function

• Stretches for storage

• Cell Growth - bottom new, Top old

  • 

Glands

Infoldings of Epithelium

2 Types

• Endocrine - no open contact with exterior: no ducts: produce hormones

• Exocrine - open contact with Exterior; ducts

Structure

• Unicellular → Goblet Cells → Produce → Mucus

• Multicellular

Connective Tissue

Loose (areolar) - collagenous fibers are loosely aranged

Dense - Fibers form thick bundles that nearly fill all extracellular space

Supporting Connective Tissue

• Cartilage

• Bone

Fluid connective Tissue

• blood

Features of Connective Tissue

• Well-innervated - A lot of nerves

• Highly vascular; NOT cartilage

• Few cells embedded in large amount extracellular Matrix

each type has own cell type and matrix

Functions

• Enclosed organs

• Connect tissues

• Support and Movement

• Storage

• Cushion and Insulate

• Transport

• Protect

Extracellular Matrix

Protein fibers

Collagen - most common protein in body; strong, flexible, inelastic

Reticular - framework, fills spaces between tissues and organs. Fine collagenous, form branching network

Elastin - Returns to its original shape after distension or compression. Elastin resembles coiled springs

Cells of Connective Tissue

Specialized cells produce Extracellular matrix

Word Stems:

• Blast - Create matrix

• Cyte - Matin Matrix

• Clast - Break down matrix to remodel

Types of Connective Tissue

Loose Connective Tissue: Areolar

• Loose packing, support, nourishment

• Attaches skin to underlying tissues

• Contains: Collagen, reticular elasic fibers

• Cell Types - fibroblast, mast cells, lymphocytes adipose cans, macrophages

Adipose

• Padding, insulation, energy storage

• Cells are adipocytes, little ECM

• Yellow (white) - most abundant type has a wide distribution. White at birth, yellows with age

• Brown - found only in specific areas of body: axillae new, near Kidneys

Reticular

• Forms superstructure of lymphatic and hemopoietic tissues

• Found in: lymph modes, spleen, liver, Kidney

• Network of fine reticular fibers and cells

• Spaces between cans contain whit cans and dendrite cells

Dense Connective Tissue: Irregular Collagenous

Innermost layer of the dermis of the skin, scars, capsules of organs

Protein fibers randomly oriented network

Irregular Elastic

Walls of elastic arteries

Bundles and Sheets of collagenous fibers in multiple directions

Regular Elastic

Ligaments in vocal folds; nuchal ligament

collagen fibers give strength [EX. Shouting): Elastic fibers are more prevalent

Regular collagenous

Abundant Collagen fibers that resist stretching

Tendons = connect muscles to bones: non parallel Fibers

Ligaments - connect bones to bones: less compact collagen: flattened: sheets and bands

Supporting Connective Tissue: Cartilage

Types

Hyaline

• large amount of collagen fibers evenly distributed in proteoglycan matrix

• in Areas that support flexibility: ribcage, trachea, bronchi

Fibrocartilage

• found where a lot of pressure is applied to joints: knee, Jaw, vertebra

• Thick collogen fibers distributed in proteoglycan matrix; slightly compressible, very tough

Elastic

• External Ears and epiglottis: ridges w/ elastic properties

• proteoglycans and hyalvaronic acid complexed together

• Trap large amounts of water

• Avascular and no nerve supply: slow Healer

• Perichondrium - Dense irregular connective Tissue that surrounds cartilage

Bone

Spongy Bone - Light weight

Compact Bone - structure

Hard Connective Tissue composed of living cells, (osteocytes) one mineralized Matrix

Fluid Connective Tissue: Blood

Matrix: Plasma

formed by other tissues

• Moves through vessels, fluid and cells can travel in and out of vessels

• Consists of: Red cells, white calls, platelets

• Made by Hemopoietic tissue

  • Hemopoietic Tissue - Produces new blood cells

Osteons - mature bone

Perforating / Central canals - nutrient travel

Hemopoietic Tissue

Bone Marrow - Produces new blood cells stores lipids

Red Bone Marrow - Hemopoietic tissue surrounded by reticular fibers: produces red and white cells

Yellow Bone Marrow - yellow adipose tissue

Muscle Tissue

Contracts with force

Skeletal - striated and voluntary

Cardiac - striated and Involuntary: Heart only

Smooth - non striated and Involuntary

Nervous Tissue

Neurons / nerve cans have ability to produce action

Potentials: Multipolar, bipolar, unipolar

Neuroglia

Support cells of the brain, spinal cord, nerves

Nourish, Protect, Insulate Neurons

• Schwan cells

Tissue Regeneration

Tissue regeneration is the process by which damaged tissues are repaired or replaced

• Quick regeneration: epithelial tissues such as skin, connective tissue have the greatest regenerative capabilities. Keep in mind that some connective tissue like cartilage don’t have much regenerative capabilities due to poor blood supply. As far as muscle tissue goes, skeletal and smooth muscle have good tissue regeneration with smooth muscle having more regenerative capability than skeletal muscle. Cardiac and nervous tissue have the worst regenerative capability.

Tissue damage --> inflammation phase --> proliferation phase --> either fibrotic scar formation (tissue repair) or complete restoration of that tissue (tissue regeneration)

In the inflammation phase, is the first stage of tissue repair and is characterized by pain, swelling, redness, and heat. The inflammatory phase prepares the groundwork for the remaining two phases of the repair of injured tissue.