Laboratory 2.2: Identification of Tissues

What is histology?

The study of tissues.

What is a tissue?

A group of cells with similar structures and functions that work together.

What is the most widely distributed tissue type in the human body?

Connective tissue.

What are the functions of connective tissue?

Supports organ structures, transports nutrients and wastes, stores fat for energy, repairs damaged tissues, and binds other tissues together.

What is the extracellular matrix (ECM)?

A non-living substance secreted by tissue cells that gives the tissue its function; composed of ground substance and fibers.

What are glycosaminoglycans (GAGs)?

Complexes of carbohydrates and proteins that make up the ground substance; hyaluronic acid is one example.

What makes ground substance resist compression?

Hyaluronic acid, which can bind 1000x its weight in water, giving the ground substance its water-retaining and compression-resisting properties.

What are the three fiber types found in connective tissue matrix?

Collagen (white), elastic, and reticular fibers.

What are the cells found in areolar tissue?

Fibroblasts, macrophages, mast cells, and adipocytes.

What type of ground substance does areolar tissue have?

Gel-like, highly hydrated ground substance rich in hyaluronic acid.

What fibers are present in areolar tissue?

All three types: collagen, reticular, and elastic fibers.

What are the functions of areolar tissue?

Wraps and cushions organs, allows immune cells to fight infection and cause inflammation, and holds and moves fluid.

Where is areolar tissue located?

Under epithelia (lamina propria), wrapping around organs and capillaries; connects skin to underlying muscle.

What are adipocytes?

The cells of adipose tissue that store triglycerides in a large vacuole, giving them a hollow, ring-like (gemstone ring) appearance.

Why do adipocytes look like gemstone rings microscopically?

A large lipid-filled vacuole takes up most of the cell, pushing the nucleus to the edge like a gem in a ring setting.

What are the functions of adipose tissue?

Energy storage, heat insulation, and support/protection of organs.

What is subcutaneous fat vs. visceral fat?

Subcutaneous fat is found under the skin; visceral fat surrounds internal organs such as kidneys and eyeballs.

What is dense regular connective tissue and where is it found?

Collagen fibers run parallel in one direction; found in tendons, ligaments, and aponeuroses where force is applied in one direction.

What is dense irregular connective tissue and where is it found?

Collagen fibers are randomly oriented to resist tension in multiple directions; found in the dermis, fibrous organ capsules, and joint capsules.

What cells and fibers are found in dense fibrous connective tissue?

Mainly fibroblasts; predominantly collagen fibers with minimal ground substance.

What distinguishes blood from other connective tissues?

Its matrix is fluid plasma, and it contains no collagen, elastic, or reticular fibers.

What are the cells of blood?

Erythrocytes (RBCs), leukocytes (WBCs), and platelets (cell fragments).

What is the function of blood?

Transports gases (O2, CO2), nutrients, wastes, and hormones throughout the body.

What are chondrocytes?

The mature cells of cartilage, trapped in spaces called lacunae.

Why is cartilage avascular?

It has no blood vessels; nutrients and wastes reach chondrocytes by diffusion through the semi-solid matrix.

What are the three types of cartilage?

Hyaline, elastic, and fibrocartilage.

What is hyaline cartilage and where is it found?

Has diffuse collagen fibers and a glassy/smooth appearance; covers ends of long bones, connects ribs to sternum, and forms the tracheal C-rings, nose tip, and larynx.

What is elastic cartilage and where is it found?

Predominantly elastic fibers; provides structure and flexibility; found in the external ear and epiglottis.

What is fibrocartilage and where is it found?

Thick parallel bundles of collagen fibers; resists compression; found in the intervertebral discs.

What is a Haversian system (osteon)?

The structural unit of bone: a central canal containing blood vessels and nerves surrounded by concentric rings (lamellae) of matrix and osteocytes.

What are osteocytes?

Mature bone cells trapped in lacunae within the calcified bone matrix.

What is the ground substance of bone?

Calcified (solid) matrix made of hydroxyapatite (inorganic calcium salts) and collagen fibers.

What is the periosteum?

A layer of dense irregular connective tissue that wraps around the outer surface of bones.

What are the functions of bone?

Resists compression and tension, supports the body, and protects vital organs.

What are the two unique properties of all muscle tissue?

Elasticity (can stretch and return to original length) and contractility (can shorten in length).

What are the three types of muscle tissue?

Skeletal, cardiac, and smooth muscle.

Describe skeletal muscle.

Striated, voluntary, multinucleated cells bundled into fibers; attached to bone for locomotion.

What causes the striations in skeletal and cardiac muscle?

Alternating bands of actin and myosin proteins that allow the fiber to contract.

Describe cardiac muscle.

Striated, involuntary, branching cardiomyocytes connected by intercalated discs (gap junctions) that coordinate contraction; found only in the heart.

What are intercalated discs?

Specialized gap junctions between cardiomyocytes that allow coordinated muscle contraction in the heart.

Describe smooth muscle.

Non-striated, involuntary, spindle-shaped, uninucleate cells arranged in sheets; found in hollow organs like the GI tract, bladder, uterus, and blood vessels.

What is peristalsis?

The wave-like contractions of smooth muscle that move fluids and substances through hollow organs.

What is the arrector pili muscle?

Smooth muscle attached to each hair follicle in the skin; its contraction causes goosebumps.

What are the functions of epithelial tissue?

Covers body surfaces and hollow passageways, secretes substances (via glands), and absorbs materials.

Why is epithelial tissue avascular?

It has no blood vessels; nutrients, wastes, and gases diffuse through interstitial fluid.

What are the three basic shapes of epithelial cells?

Squamous (flattened), cuboidal, and columnar.

What is the difference between simple, stratified, and pseudostratified epithelium?

Simple = one cell layer; stratified = multiple layers; pseudostratified = all cells touch the basement membrane but nuclei appear at different levels.

What are the three types of epithelial membranes?

Mucous membranes, serous membranes, and the cutaneous membrane.

What is a mucous membrane and where is it found?

Lines body cavities that open to the exterior (GI, respiratory, urogenital tracts); secretes mucus to trap and remove foreign particles.

What epithelium lines areas subject to abrasion (e.g., oral cavity, vagina)?

Stratified squamous epithelium.

What epithelium lines areas involved in absorption and secretion (e.g., GI tract)?

Simple columnar epithelium, often with mucus-secreting goblet cells.

What is a serous membrane and where is it found?

A thin double-walled membrane of simple squamous epithelium lining the ventral body cavities and organ surfaces; secretes a lubricating fluid to reduce friction.

What is the difference between parietal and visceral peritoneum?

Parietal peritoneum lines the wall of the abdominal cavity; visceral peritoneum covers the surfaces of individual organs.

What is the cutaneous membrane?

The skin; the external covering of the body made of stratified squamous epithelium.

What are retroperitoneal organs?

Organs located posterior to the peritoneal cavity, including the kidneys, pancreas, ureters, adrenal glands, aorta, esophagus, and rectum.

What membrane covers the heart?

The pericardium, which is a serous membrane.

What membrane covers the lungs?

The pleura, which is a serous membrane.