Histology and Tissue Types Flashcards

Histology: The Study of Tissues

• Histology is the microscopic study of tissues, focusing on how cells organize to perform specific functions.

Four Tissue Classes

• Epithelium: Covers body surfaces and lines internal organs/passageways.
• Connective Tissues: Support, connect, and protect body parts.
• Muscular Tissue: Facilitates movement.
• Nervous Tissue: Transmits signals for communication and coordination.
• Organs consist of two or more tissue types functioning together (e.g., the eye).

The Human Eye as an Example

• Epithelium: Thin, fragile skin surrounding the eye.
• Connective Tissue: Structures of the eyeball itself, covered by the tough corneum.
• Nervous Tissue: Optic nerve for nervous system input and output.
• Muscular Tissue: Allows eye movement and regulates pupil diameter.

Detailed Tissue Class Overview

Epithelium

• Covers body surfaces, lines internal organs, and forms glands.
• Composed of closely packed cells forming a barrier.
• Functions: Protection, secretion (hormones, enzymes), and absorption.
• Examples: Epidermis (skin), lining of the digestive tract, liver, and glands.
• Two types of glands: Exocrine and endocrine.

Connective Tissue

• Variable tissue type with more matrix than cells.
• Matrix: Space between cells containing proteins and ground substance.
• Functions: Support (cartilage, bone), binding (tendons, ligaments), protection, and transport (blood).

Nervous Tissue

• Excitable cells that respond to stimuli and carry signals.
• Central Nervous System (CNS): Brain and spinal cord.
• Peripheral Nervous System (PNS): Nerves extending from the CNS.

Muscular Tissue

• Excitable cells that enable movement.
• Three types: Skeletal, cardiac, and smooth.
  • Skeletal: Voluntary movement.
  • Cardiac: Involuntary, found in the heart.
  • Smooth: Involuntary, lines internal organs.

Tissue Composition and Origin

• Tissues consist of cells and their products.
• Mature tissues originate from embryonic tissue layers.

Key Differences Between Tissues

• Cell types and functions.
• Characteristics of the matrix (extracellular space).
• Matrix consists of fibrous proteins and ground substance (the "goo" in which proteins are embedded).
• Some tissues are highly cellular with little matrix, while others have abundant matrix.

Embryonic Tissue Layers

• Ectoderm: Outermost layer, forms epidermis and nervous system.
• Endoderm: Inner lining, forms mucous membranes of the gastrointestinal and respiratory tracts, and digestive glands.
• Mesoderm: Middle layer, forms mesenchyme, muscle, bone, and blood.

Epithelium Details

• Covers outer surfaces and lines internal passages.
• Apical surface: Exposed to the outside or lining an internal passageway/organ.
• Avascular: No blood vessels present; relies on diffusion.
• Adheres to a basement membrane composed of collagen and adhesive proteins.

Epithelium Thickness

• Simple epithelium: Single layer of cells.
• Stratified epithelium: Multiple layers of cells (up to 20-30 layers).

Cell Shapes

• Squamous: Flattened cells.
• Cuboidal: Square-shaped cells.
• Columnar: Rectangular-shaped cells.

Naming Conventions for Stratified Epithelium

• Named based on the shape of the cells at the outermost (apical) layer.

Example

• Stratified Squamous: Multiple cell layers with squamous cells at the apical surface.

Simple Epithelium Types

Simple Squamous Epithelium

• Single layer of flattened cells allowing for easy diffusion.
• Found in alveoli of lungs (gas exchange) and filters of kidneys.

Simple Cuboidal Epithelium

• Single layer of cube-shaped cells.
• Forms a relatively thin barrier.
• Found in glands and kidney tubules; involved in absorption and secretion.

Simple Columnar Epithelium

• Single layer of cells taller than they are wide
• Contains goblet cells (mucus makers) and microvilli.
• Found in the lining of the stomach and intestines; involved in absorption and mucus secretion.

Pseudostratified Columnar Epithelium

• Appears stratified but is actually a single layer of cells.
• Also known as respiratory epithelium.
• Contains goblet cells and cilia.
• Found in the respiratory system (nasal cavity to bronchi); traps particles via mucus.

Stratified Epithelium

• Consists of more than one cell layer (2-20 layers).
• Named for the shape of the surface cells.
• Exception: Transitional epithelium.

Stratified Squamous Epithelium

• Numerous cell layers with squamous cells at the surface.
• Abrasion-resistant.

Keratinized

• Contains a dead layer of cells at the surface (e.g., epidermis).

Nonkeratinized

• Live cells all the way to the apical surface (e.g., lining of the mouth, esophagus, vagina).

Stratified Cuboidal

• Found in glands (e.g. sweat glands).

Transitional Epithelium

• Named for its function: ability to stretch and recoil.
• Found in the lining of the bladder and parts of the umbilical cord.

Connective Tissues

• Most variable tissue type.
• Functions: Connects organs, supports and protects, stores energy, produces heat, and transports substances.
• Examples: Bone, cartilage, fat.

Connective Tissue Cells

• Fibroblasts: Produce collagen.
• Adipocytes: Store triglycerides.

Connective Tissue Fibers

• Collagen: Provides strength and resilience.
• Reticular: Provides support for blood-filled organs.
• Elastic: Allows stretch and recoil.

Tensile Properties

• Collagen is stronger then steel

Loose Connective Tissue

• More ground substance and cells than fibers.
• Types: Areolar, reticular, and adipose.

Areolar

• Contains all three fiber types and various cell types.
• Found everywhere; acts as packaging material.

Reticular

• Heavy with reticular fibers.
• Acts as a scaffold for blood-filled organs (e.g., spleen, lymph nodes).

Adipose

• Fat tissue; storage site for energy (triglycerides).
• Cushions and insulates.

Dense Connective Tissue

• Tons of fibers; very little space between them.

Types

• Dense Regular: Fibers align (e.g., tendons and ligaments).
• Dense Irregular: Fibers don't align (e.g., underlying layers of the skin).

Cartilage

• Connective tissue with a rubbery matrix.
• Cell type: Chondrocytes.
• Avascular: Relies on diffusion.
• Three types: Hyaline, fibrocartilage, and elastic.

Types Of Cartilage

Hyaline

• Basic form; forms embryonic skeleton and covers joint surfaces.

Elastic

• Contains elastic fibers; highly flexible.
• Found in the external ear and epiglottis.

Fibrocartilage

• Contains an abundance of collagen fibers; strong
• Found in the pubic symphysis, intervertebral discs, and meniscus in the knee joint.

Bone

• Connective tissue with a hard matrix (collagen).
• Structural unit: Osteon.
• Central canal: Contains blood vessels and nerves.
• Functions: Forms the skeleton, protects organs, acts as levers for movement, and stores calcium and phosphorus.

Blood

• Connective tissue with a fluid matrix.
• Cell types: Erythrocytes (red blood cells), leukocytes (white blood cells), and platelets.
• Functions: Transports gases and nutrients, provides defense mechanisms, and balances clotting factors.

Nervous Tissue

• Excitable tissue that perceives and responds to stimuli.
• Cell type: Neuron.
• Found in the brain, spinal cord, and nerves.

Muscle Tissue

• Excitable tissue that contracts to create movement and produce heat.
• Three types: Skeletal, cardiac, and smooth.

Muscle Varieties:

Skeletal muscle:

• Striated.
• Voluntary control.
• Multiple nuclei.

Cardiac muscle:

• Striated.
• Involuntary control.
• One nucleus per cell.
• Intercalated discs.
• Located in the Heart.

Smooth muscle:

• Nonstriated.
• Involuntary control.
• One nucleus per cell.
• Walls of internal viscera.

Intracellular Junctions

• Ways cells join to one another.
• Types: Tight junctions, desmosomes, and gap junctions.
• Based on protein interactions in plasma membranes.
• Not found in red and white blood cells.

Forms of intracellular junctions:

Tight Junction

• Zipper-like; prevents passage between cells.
• Located towards the apical surface.
• Important in GI and urinary tracts.

Desmosomes

• Snap-like; holds cells physically together.
• Located at the basal cell surface (bottom).
• Prevents cells from tearing apart.

Gap Junctions

• Form pores that allow transport of signaling molecules and ions between cells.*Important in embryonic development and in the cardiac and smooth muscle

Glands

• Secrete substances, mostly composed of epithelium (cuboidal).
• Two types: Exocrine and endocrine.

Exocrine

• Connects to the surface with a duct (e.g., sweat, oil, mammary, digestive glands).

Endocrine

• Does not connect to the surface; secretes products directly into the bloodstream (hormones).

Composite Organs:

• Some organs do both (liver, gonads, pancreas).

Tissue Growth

Health Tissue Growth Forms:

Hyperplasia

• Growth due to an increase in cell number (childhood development).

Hypertrophy

• Enlargement of preexisting cells (muscle growth).

Unhealthy Tissue Growth:

Neoplasia

• Abnormal growth; formation of tumors.

Tissue Shrinkage and Death

Atrophy

• Loss of cell size or number due to disease (disuse atrophy).

Necrosis

• Pathological death and loss of cells due to toxins, trauma, or infection (gangrene).

Apoptosis

• Programmed cell death; healthy form of cell turnover without inflammation.