AP chpt 5 histology

Four primary tissue types

• Epithelial tissue — covers surfaces, lines cavities, forms glands

• Connective tissue — supports, binds, protects, stores, transports

• Muscle tissue — produces movement by contraction

• Nervous tissue — communicates using electrical signals

Epithelial tissue — properties

• Cells are tightly packed with little extracellular space

• Has an apical surface and a basal surface

• Attached to a basement membrane

• Usually avascular (no blood vessels)

• Regenerates quickly

• Functions: protection, absorption, secretion, filtration, sensation

Simple vs. stratified epithelium

• Simple — 1 layer of cells

• Stratified — 2+ layers mainly provides protection

Three epithelial cell shapes

• Squamous — flat • Cuboidal — cube-shaped • Columnar — tall/rectangular@

Simple squamous epithelium

• 1 layer of flat cells • Function: diffusion, filtration, reduces friction • Locations: alveoli, blood vessels, serous membranes, kidneys • Thin structure allows substances to pass through easily@

Simple cuboidal epithelium

• 1 layer of cube-shaped cells • Function: secretion and absorption • Locations: kidney tubules, small gland ducts, thyroid follicles • Often has microvilli for absorption@

Simple columnar epithelium

• 1 layer of tall cells • Function: absorption and secretion • Locations: digestive tract and gallbladder • May contain goblet cells • May have microvilli or cilia@

Pseudostratified columnar epithelium

• Appears to have multiple layers but all cells touch the basement membrane • Usually contains cilia and goblet cells • Function: secretion and movement of mucus • Location: respiratory tract, especially trachea and bronchi@

Cilia and goblet cells

• Cilia — move mucus and trapped particles across the epithelial surface • Goblet cells — secrete mucus • Together, they help protect and clean the respiratory tract@

Stratified squamous epithelium

• Multiple layers with flat cells at the surface • Main function: protection from abrasion • Two types: keratinized and non-keratinized@

Keratinized vs. non-keratinized stratified squamous epithelium

• Keratinized — surface cells are dead and filled with keratin • Location: epidermis of skin • Non-keratinized — surface cells remain alive and moist • Locations: mouth, esophagus, vagina@

Exfoliation

The shedding or removal of dead cells from the surface of an epithelium@

Transitional epithelium

• Specialized stratified epithelium that stretches • Surface cells change shape as the tissue stretches • Allows organs to expand without tearing • Location: urinary bladder, ureters, and part of urethra@

Connective tissue — functions

• Supports and connects tissues • Protects organs • Stores energy as fat • Transports substances • Provides immune defense • Helps repair damaged tissue@

Three categories of connective tissue

• Fibrous connective tissue • Supportive connective tissue • Fluid connective tissue@

Connective tissue — general structure

• Cells are separated by extracellular matrix • Matrix = ground substance + protein fibers • Usually vascular, but some types have poor blood supply or are avascular@

Connective tissue fibers

• Collagen fibers — strong • Elastic fibers — stretch and recoil • Reticular fibers — form supportive networks@

Ground substance

The non-fibrous part of the extracellular matrix that surrounds connective tissue cells and fibers@

Loose connective tissue

• Includes areolar, adipose, and reticular tissue • Generally provides support, cushioning, insulation, and binds structures together@

Areolar connective tissue

• Loose arrangement of collagen and elastic fibers • Functions: wraps and cushions organs, binds tissues • Location: beneath epithelia and around organs, nerves, and blood vessels@

Adipose connective tissue

• Contains adipocytes that store fat • Functions: energy storage, insulation, cushioning • Locations: beneath skin and around organs@

Reticular connective tissue

• Contains reticular fibers forming a supportive network • Supports immune cells • Locations: lymph nodes, spleen, bone marrow@

Dense connective tissue

• Contains many collagen fibers • Strong and resistant to pulling • Types: dense regular, dense irregular, elastic@

Dense regular connective tissue

• Collagen fibers run parallel • Provides strong attachment in one direction • Locations: tendons and ligaments@

Dense irregular connective tissue

• Collagen fibers run in many directions • Resists stress from multiple directions • Locations: dermis of skin and organ capsules@

Elastic connective tissue

• Contains many elastic fibers • Allows stretch and recoil • Locations: walls of large arteries and some airways@

Supportive connective tissue

• Cartilage — flexible support • Bone — rigid support and protection@

Hyaline cartilage

• Most common cartilage • Smooth, flexible support • Locations: nose, trachea, larynx, costal cartilage, articular surfaces of joints@

Elastic cartilage

• Contains many elastic fibers • Provides flexible support • Locations: external ear and epiglottis@

Fibrocartilage

• Very strong and resists compression • Contains abundant collagen fibers • Locations: intervertebral discs, pubic symphysis, menisci@

Bone tissue

• Hard connective tissue containing calcium salts and collagen • Provides support, protection, movement, mineral storage, and blood cell production • Highly vascular@

Fluid connective tissue

• Blood and lymph • Has a fluid extracellular matrix • Functions in transport, immunity, and maintaining homeostasis@

Blood

• Fluid connective tissue • Matrix = plasma • Cells include red blood cells, white blood cells, and platelets • Functions: transport, defense, clotting, regulation@

Connective tissue cells

• Fibroblasts — produce fibers and ground substance • Adipocytes — store fat • Chondrocytes — maintain cartilage • Osteocytes — maintain bone • Blood cells — transport, defense, and clotting • Macrophages — engulf pathogens and debris • Mast cells — release chemicals involved in inflammation@

Vascular vs. avascular tissues

• Highly vascular: most connective tissues, muscle, bone • Poorly vascular: cartilage • Avascular: epithelial tissue • Poor blood supply usually means slower healing@

Slow-healing tissues

Tissues with little or no blood supply heal slowly because they receive less oxygen, nutrients, and repair cells@

Excitable tissue

Tissue that can respond to a stimulus by producing an electrical signal@

Neuron — major parts

• Cell body (soma) — contains nucleus and organelles • Dendrites — receive signals • Axon — carries signals away from cell body • Axon terminals — release neurotransmitters to communicate with other cells@

Muscle tissue — functions

• Produces movement • Maintains posture • Generates heat • Moves substances through the body • Pumps blood@

Skeletal vs. cardiac vs. smooth muscle

• Skeletal — striated, voluntary, long cylindrical cells with many nuclei • Cardiac — striated, involuntary, branched cells with usually one nucleus, has intercalated discs • Smooth — non-striated, involuntary, spindle-shaped cells with one nucleus@

Skeletal muscle location

Attached to bones@

Cardiac muscle location

Found in the wall of the heart@

Smooth muscle location

Found in walls of hollow organs such as the stomach, intestines, blood vessels, bladder, and uterus@

Endocrine vs. exocrine glands

• Endocrine — ductless • Exocrine — release secretions through ducts onto an epithelial surface or into a body cavity@

Organs with both endocrine and exocrine functions

• Pancreas — digestive enzymes + hormones such as insulin • Ovaries — eggs + hormones • Testes — sperm + hormones@

Typical exocrine gland

• Secretory portion produces the substance • Duct carries the secretion to the surface or body cavity • Can be simple or compound depending on duct structure@

Parenchyma

The functional cells of an organ that perform its primary functions@

Goblet cells — locations

Found mainly in the respiratory and digestive tracts@

Goblet cells — secretion

Mucus, which lubricates and protects epithelial surfaces@

Simple vs. compound glands

• Simple — one unbranched duct • Compound — branched duct system@

Types of exocrine glands by secretion

• Serous — watery, protein-rich secretion • Mucous — thick, mucus-rich secretion • Mixed — both serous and mucous secretions@

Holocrine secretion

The entire secretory cell breaks down and becomes part of the secretion@

Apocrine secretion

The apical portion of the secretory cell pinches off and becomes part of the secretion@

Merocrine secretion

The secretion leaves the cell by exocytosis without damaging the cell@

Body membranes

• Cutaneous — skin • Serous — lines closed body cavities and covers organs • Mucous — lines passages that open to the outside • Synovial — lines movable joint cavities@

Cutaneous membrane

The skin@

Serous membrane

Thin membrane lining closed body cavities and covering organs@

Mucous membrane

Lines body cavities and tubes that open to the outside@

Synovial membrane

Lines movable joint cavities and produces synovial fluid to reduce friction and nourish cartilage@

Marfan syndrome

Inherited connective tissue disorder involving abnormal fibrillin@

Ehlers-Danlos syndrome

Group of inherited connective tissue disorders involving abnormal collagen@

Osteogenesis imperfecta

Inherited disorder involving abnormal collagen that causes fragile bones and frequent fractures@

Scurvy

Vitamin C deficiency that impairs collagen production and causes poor wound healing, bleeding gums, and weakened connective tissues@

Differentiation vs. metaplasia

• Differentiation — cells become specialized for specific functions • Metaplasia — one mature cell type changes into another mature cell type, often as an adaptation to stress@

Three types of tissue growth

• Hyperplasia — increase in cell number • Hypertrophy — increase in cell size • Neoplasia — abnormal, uncontrolled cell growth@

Embryonic vs. adult stem cells

• Embryonic stem cells — can develop into many different cell types • Adult stem cells — more limited in the types of cells they can produce, help maintain and repair specific tissues@

Atrophy

Decrease in the size of a tissue or organ, usually because cells become smaller or cell number decreases@

Necrosis

Uncontrolled cell death caused by injury or disease@

Apoptosis

Programmed, controlled cell death that removes unwanted or damaged cells without usually causing inflammation@

Tissue repair — two methods

• Regeneration — damaged cells are replaced with the same type of cells • Fibrosis — damaged tissue is replaced with connective tissue scar tissue@

Tissue repair process

• Inflammation — removes damaged tissue and pathogens • Organization — repair cells and connective tissue enter the damaged area • Regeneration and/or fibrosis — tissue is restored or replaced with scar tissue • Remodeling — repaired tissue is reorganized and strengthened@

Regeneration vs. fibrosis

• Regeneration restores normal tissue structure and function • Fibrosis replaces damaged tissue with scar tissue, which may reduce normal function@

Bioreactor

A device used in tissue engineering to provide cells with controlled conditions that help them grow and develop into functional tissue@

Mutation

A permanent change in the DNA sequence@

Carcinogen

An environmental factor or substance that increases the risk of developing cancer@

Mutagen

An agent that causes or increases mutations in DNA@

Cancer

A disease involving uncontrolled abnormal cell growth and division@

Tumor

An abnormal mass of cells caused by uncontrolled cell growth@

Benign vs. malignant tumors

• Benign — noncancerous • Malignant — cancerous, can invade surrounding tissues and spread@

Metastasis

The spread of cancer cells from the original tumor to other parts of the body@

Causes of cancer

• Mutations in DNA • Inherited genetic changes • Carcinogens such as tobacco smoke and radiation • Certain infections • Environmental factors • Random DNA replication errors@

Body defenses against cancer

• DNA repair mechanisms • Apoptosis • Immune system recognition and destruction of abnormal cells • Tumor suppressor genes that stop abnormal cell division@

Oncogenes

Genes that promote cell division and growth@

Tumor suppressor genes

Genes that normally slow cell division, repair DNA, or trigger apoptosis@

Effects of cancer on the body

• Invades and damages normal tissues

• Uses nutrients and oxygen needed by healthy cells

• Can cause pain, bleeding, or organ dysfunction • Can spread through metastasis

• May interfere with normal body functions and eventually become life-threatening