LEC 4; Human Tissues and Cell Junctions: Histology and Function

What is a tissue in human anatomy?

A group of cells that usually have a common embryonic origin and function together to carry out specialized activities.

What are the four basic types of tissues in the human body?

Epithelial, Connective, Muscular, Nervous.

What is the function of tight junctions?

To inhibit the flow of substances between cells by fusing cell membranes together.

Where are tight junctions commonly found?

In epithelial tissues where fluid leakage is undesirable.

What role do adherens junctions play in tissues?

They anchor cells together and interact with microfilaments to resist separation during contractions.

What are desmosomes and their function?

Spot-weld type junctions that hold cells together during tension or contraction, attaching to intermediate filaments.

What is the function of hemidesmosomes?

To anchor cells to the protein laminin found in the basement membrane.

What is the purpose of gap junctions?

To allow small molecules and ions to pass between cells for communication and nutrient sharing.

What are the general features of epithelial tissue?

Cells are arranged in sheets, densely packed, mitosis occurs frequently, avascular, and exhibit polarity.

What is the composition of the basement membrane in epithelial tissue?

It is composed of a basal lamina and reticular lamina.

What is the basal lamina made of?

Proteins such as laminins and collagen secreted by basal cells.

What is the reticular lamina composed of?

Proteins produced by fibroblasts in the connective tissue.

What distinguishes the apical surface of epithelial cells?

It is the 'free' surface facing the body's surface, a lumen, or body cavity.

What is the significance of cellular polarity in epithelial tissues?

It refers to the distinct apical and basal sides of epithelial cells, which is crucial for their function.

How does epithelial tissue regenerate?

Epithelial tissue has rapid regeneration due to frequent mitosis.

What is the primary difference between epithelial and connective tissues?

Epithelial tissues are densely packed with cells and have no blood supply, while connective tissues have a varied structure and function.

What is the role of goblet cells in epithelial tissue?

Goblet cells secrete mucus to lubricate and protect the epithelial surface.

What are the characteristics of connective tissue?

a diverse composition of fibers and cells, providing support and structure.

What types of muscle tissue exist in the human body?

Skeletal, smooth, and cardiac muscle tissue.

What is the function of membranes in the body?

To cover surfaces, line cavities, and separate organs.

What is the significance of identifying tissue types from histology slides?

It helps in understanding the structure and function of different tissues in the body.

What are the three main shapes of epithelial cells?

Squamous, cuboidal, and columnar.

How are epithelial tissues classified based on layers?

They can be classified as simple, stratified, or pseudostratified.

What is the function of simple squamous epithelium?

It is present at sites of filtration (kidneys), diffusion (lungs, capillaries), and secretion in serous membranes.

Where can simple cuboidal epithelium typically be found?

where secretion and absorption can be seen

What is the primary function of simple columnar epithelium?

Secretion and absorption, with microvilli to increase surface area for absorption.

What distinguishes pseudostratified columnar epithelium?

It is characterized by absorption and secretion, often with cilia.

What is the role of stratified squamous epithelium?

It provides protection against abrasion, water loss, UV radiation, and foreign invasion.

What are the two types of stratified squamous epithelium?

Keratinized and non-keratinized.

What is the function of stratified cuboidal epithelium?

It provides protection and some secretion and absorption.

What is the primary function of stratified columnar epithelium?

Protection and secretion.

What is the function of transitional epithelium?

It allows urinary organs to stretch and maintain protective linings while holding variable amounts of fluid.

What defines glandular epithelium?

A gland is a single cell or mass of epithelial cells adapted for secretion.

How do endocrine glands release their secretions?

Their secretions enter the interstitial fluid and diffuse into the bloodstream.

How do exocrine glands release their secretions?

Their secretions enter ducts that empty onto the surface of covering or lining epithelium.

What is the structural classification of glandular epithelium?

It can be classified as unicellular (e.g., goblet cells) or multicellular (e.g., sweat glands, oil glands, salivary glands).

What is the significance of microvilli in simple columnar epithelium?

Microvilli increase the surface area for absorption.

What type of epithelium is found in the alveoli of the lungs?

Simple squamous epithelium.

What is the function of ciliated pseudostratified columnar epithelium?

It aids in the absorption and secretion processes.

What is the primary role of keratinized stratified squamous epithelium?

To provide a tough protective layer against environmental damage.

What is the main function of non-keratinized stratified squamous epithelium?

To protect underlying tissues in areas subject to abrasion.

What are the two basic elements of connective tissue?

Cells and extracellular matrix.

What type of glands are sebaceous glands and how do they function?

holocrine glands that secrete oils, are destroyed after releasing their contents, and are replaced by new glandular cells.

What is the most abundant cell type in connective tissue proper?

Fibroblast.

What role do fibrocytes play in connective tissue?

Fibrocytes are a less active form of fibroblast and the second most common cell type in connective tissue proper.

What are adipocytes and what do they store?

cells that store lipids as droplets that fill most of the cytoplasm.

What are the two types of adipocytes?

White and brown adipocytes.

What is the function of mesenchymal cells in connective tissue?

multipotent adult stem cells that can differentiate into any type of connective tissue cells needed for repair and healing.

What is the extracellular matrix composed of?

Fibers and ground substance.

What are the three types of fibers found in the extracellular matrix?

Collagen fibers, elastic fibers, and reticular fibers.

What is the primary function of collagen fibers in connective tissue?

provide strength and resist pulling forces (tension) while being flexible.

How do elastic fibers differ from collagen fibers?

Elastic fibers are smaller, strong, can be stretched up to 150% of their relaxed state, and branch to form a fibrous network.

What is the embryonic origin of all connective tissues?

All connective tissues derive from the mesodermal layer of the embryo.

What is mesenchyme?

first connective tissue to develop in the embryo and is the stem cell line from which all connective tissues are derived.

What is mucous connective tissue and when is it present?

forms in the umbilical cord and is not present after birth.

What characterizes areolar connective tissue?

highly cellular tissue with a sparse, random arrangement of collagen and some elastic fibers.

What is the primary function of adipose tissue?

stores fat for energy and provides insulation.

What is the structure and function of reticular connective tissue?

made up of a network of reticular fibers that provides a supportive framework for soft organs.

What distinguishes dense regular connective tissue?

collagen fibers oriented in the same direction, making it strong and suitable for tendons and ligaments.

What is the composition of dense irregular connective tissue?

Collagen fibers woven in multiple directions, providing strength in all directions.

What are the characteristics of hyaline cartilage?

It is the most common type of cartilage, with short and dispersed collagen fibers, large amounts of proteoglycans, a clear/glassy appearance, and is both strong and flexible.

Where is hyaline cartilage found in the body?

In the rib cage, nose, and covering bones at moveable joints.

What defines fibrocartilage?

It is tough and contains thick bundles of collagen fibers, found in structures like the menisci in the knee joint and intervertebral discs.

What are the key features of elastic cartilage?

It contains elastic fibers along with collagen and proteoglycans, providing rigid support and elasticity.

What is the hardest type of connective tissue?

Compact bone.

What is the composition of bone's extracellular matrix?

It consists mostly of collagen fibers embedded in a mineralized ground substance containing hydroxyapatite, a form of calcium phosphate.

What are the main components of blood?

Erythrocytes (red blood cells) for oxygen transport, leukocytes (white blood cells) for defense, and platelets for blood clotting.

What are the general characteristics of muscular tissue?

consists of fibers that provide motion, maintain posture, produce heat, are excitable, and contractile, and can be voluntary or involuntary.

What are the three types of muscle tissue?

Skeletal muscle, cardiac muscle, and smooth muscle.

What is the function of skeletal muscle tissue?

It allows voluntary movement, produces heat, and protects organs.

Where is skeletal muscle tissue located?

Attached to bones and around entry points to the body, such as the mouth and anus.

What is the primary function of cardiac muscle tissue?

It is involuntary and pumps blood to the body.

What are the characteristics of smooth muscle tissue?

It is involuntary, moves food through peristalsis, controls respiration, moves secretions, and regulates blood flow in arteries.

What are the two kinds of nervous cells?

Neurons and neuroglia.

What is the function of neurons?

They carry sensory or motor information and perform integrative functions.

What role do neuroglia play in the nervous system?

They protect and support neurons.

What are excitable cells?

Cells like neurons and muscle fibers that exhibit electrical excitability and respond to stimuli.

What are the two types of membranes?

Epithelial membranes (which include mucous, serous, cutaneous, and synovial membranes) and connective tissue membranes.

What distinguishes exocrine glands from endocrine glands?

Exocrine glands secrete substances through ducts to the outside of the body or into body cavities, while endocrine glands secrete hormones directly into the bloodstream.

What are the common characteristics of epithelial, connective, muscular, and nervous tissues?

Each type has distinct structures and functions that contribute to the overall functioning of the body.

How can you identify different tissue types from histology slides?

By observing their unique cellular structures, arrangements, and specific characteristics under a microscope.