Histology and Types of Human Tissues for Anatomy and Physiology

Tissue

A group of similar cells that usually have a similar embryological origin and are specialized for a particular function, sharing a common function.

Histology

One of the subspecialties of anatomy that deals with the study of tissues.

Pathologist

Physicians who specialize in laboratory study of cells and tissues that help or aid other doctors in making diagnoses. They look for tissue changes that may indicate disease and perform autopsies.

Four Basic Types of Tissue

Epithelial Tissue, Connective Tissue, Muscle Tissue, Nerve Tissue.

Epithelial Tissue

Covers surfaces (cells are in contact), lines hollow organs, cavities, and ducts, forms glands when cells sink under the surface. Found on our skin and hollow organs. Functions: protection from potential infectious agents, absorption of nutrients, and sensation. Characterized by closely packed cells forming continuous sheets.

Basement Membrane

The structure that holds epithelial cells to the connective tissue. It is made up of the basal lamina and the reticular lamina, and it divides the connective tissue from the epithelial tissue.

Covering and Lining Epithelium

A type of epithelium found in the epidermis of our skin, the lining of blood vessels and ducts, and the lining of the respiratory, reproductive, urinary, and gastrointestinal tracts.

Glandular Epithelium

The secreting portion of glands. Located in organs such as the thyroid gland, adrenal gland, and sweat glands.

Simple Epithelium

Classified by arrangement of cells into layers, it consists of only one layer of cells.

Stratified Epithelium

Classified by arrangement of cells into layers, it contains many cell layers (two or more). It is thicker than simple epithelium.

Pseudostratified Epithelium (or Pseudostratified Columnar Epithelium)

A single layer of cells where all cells do not reach the apical surface, giving the false appearance of having multiple layers because the nuclei are found at different levels. All cells attach to the basement membrane. Found in the respiratory system, male urethra, and epididymis.

Squamous Cells

Epithelial cells that are flat and thin.

Cuboidal Cells

Epithelial cells that are cube-like in shape.

Columnar Cells

Epithelial cells that are tall and column-shaped.

Transitional Cells/Transitional Epithelium

Epithelial cells that change shape (e.g., from squamous to cuboidal and back). It is multilayered. Found in the urinary bladder, where cells become cuboidal when filled with urine and revert to squamous after urination. It lines hollow organs that expand from within.

Simple Squamous Epithelium

Composed of a single layer of flat and thin cells. It lines blood vessels and body cavities. It is very thin, and its main function is to control diffusion, secretion, and filtration.

Simple Cuboidal Epithelium

A single layer of cube-shaped cells. The nuclei are round and centrally located. It is usually found lining the tubules of the kidney and functions for absorption or secretion.

Simple Columnar Epithelium

A single layer of rectangular cells.

goblet cells

unicellular glands responsible for mucus secretion.

mucus

serves as a lubricant in the gastrointestinal, respiratory, reproductive, and urinary systems.

microvilli

finger-like cytoplasmic projections that increase surface area for cells and function for absorption, particularly in the gastrointestinal tract.

Stratified Squamous Epithelium

Composed of two or more layers of cells, with the surface cells being flat. It is thicker than simple epithelium.

Keratinized

The surface cells are dead and filled with keratin. Found on the epidermis of the skin.

Keratin

A protein that provides stretching capability without tearing and is produced by keratinocytes.

Non-keratinized

There is no keratin in the moist, living cells at the surface. Found in the mouth and vagina, which have smoother surfaces.

Papanicolaou (Pap Smear)

A procedure used to collect a slough of cells from the uterus and vaginal walls to detect cellular changes, particularly precancerous cells. Recommended annually for women over 18 or if sexually active.

Connective Tissue

Material found in between cells. Its cells are in an extracellular matrix (fibers and ground substance secreted by cells). Its consistency varies from liquid to gel to solid.

Functions of Connective Tissue

Supports and binds structures together (e.g., binds organs together). Protects and supports the body and its organs. Stores energy as fat. Provides immunity to diseases or disease-causing agents.

Matrix (Connective Tissue)

The fibers and ground substance that are secreted by the cells within the connective tissue. Its consistency can vary from liquid to gel to solid.

Blast Type Cells (in Connective Tissue)

Connective tissue cells that retain the ability to divide and produce matrix.

Fibroblast

Secretes fibers.

Chondroblast

Cartilage-forming cells.

Osteoblast

Bone-forming cells.

Cyte Type Cells (in Connective Tissue)

Mature connective tissue cells that cannot divide or produce matrix. They are the mature form of blast cells.

Chondrocyte

A mature chondroblast.

Osteocyte

A mature osteoblast; derived from osteoblasts and surrounded by the products they secreted.

Connective Tissue Ground Substance

A component of the matrix that supports the cells and fibers and helps determine the consistency of the matrix. It can be fluid or gel.

Collagen Fiber

A type of connective tissue fiber that constitutes 25% of protein in our body. It is tough, resistant to pull, yet pliable, forming strong, flexible bundles of protein.

Elastic Fiber

A type of connective tissue fiber found in the lungs, blood vessels, and ear cartilage. It is stretchable, formed from the protein elastin surrounded by glycoprotein fibrillin.

Reticular Fiber

A type of connective tissue fiber found in the spleen and lymph nodes. It is an 18-branched fiber that forms the framework of the organ.

Mature Connective Tissue

Includes loose connective tissue, dense connective tissue, cartilage, bone, blood, and lymph.

Loose Connective Tissue

A type of mature connective tissue characterized by loosely woven fibers throughout the tissues. Types include areolar, adipose, and reticular tissue.

Areolar Connective Tissue

A type of loose connective tissue that is most widely distributed in the body. It contains several types of cells and three fibers. It provides strength, elasticity, and support.

Adipose Tissue

A type of loose connective tissue where peripheral nuclei are due to a large fat storage droplet. Found in the deeper layer of the skin, serving as organ padding, and also in the yellow marrow. Functions include reducing heat loss, energy storage, and protection. It acts as an energy reserve when stored glucose is depleted and provides support and protection as organ padding.

Reticular Connective Tissue

A type of loose connective tissue that forms a network of fibers and cells producing the framework of an organ and holding it together. Found in the liver, spleen, lymph nodes, and bone marrow. Functions include filtering blood and removing different microbes in the body.

Dense Connective Tissue

A type of mature connective tissue that has more fibers present but fewer cells compared to loose connective tissue, making it thicker. Types include dense regular and dense irregular.

Dense Regular Connective Tissue

A type of dense connective tissue where collagen fibers are in parallel bundles with fibroblasts between them. It is white, tough, and pliable when unstained. It forms the tendons and ligaments. Also known as white fibrous connective tissue.

Tendons

A type of dense regular connective tissue that connects muscle to bone.

Ligaments

A type of dense regular connective tissue that connects bone with another bone.

Dense Irregular Connective Tissue

A type of dense connective tissue where collagen fibers are irregularly arranged or interwoven. This tissue can resist tension from any direction and is very tough. Found in the white of the eyeball, the dermis of the skin, and the heart. Its function is to provide tensile strength in many directions.

Cartilage

A type of mature connective tissue consisting of a network of fibers in a rubbery ground substance. It is resilient and can endure more stress than loose or dense connective tissue. Referred to as 'soft bones,' it is found in the septum of the nose and ears. It is stretchable due to containing elastic fibers. It grows and repairs slowly because it is avascular (no blood vessels).

Hyaline Cartilage

A type of cartilage that is a bluish, shiny white, rubbery substance. Chondrocytes sit in spaces called lacunae. It has no blood vessels or nerves, so its repair is very slow. It reduces friction at joints as articular cartilage. Found on long bones, ribs, nose, larynx, trachea, and bronchial tubes of the respiratory system. Also seen in embryonic and fetal skeletons. Its function is to provide a smooth surface for the movement of joints.

Fibrocartilage

A type of cartilage characterized by many more collagen fibers that cause rigidity and stiffness. It is the strongest type of cartilage. Found on the intervertebral discs, where it supports and joins structures together (e.g., holding the spinal column together), avoids friction, and allows limited movement.

Elastic Cartilage

A type of cartilage where elastic fibers help maintain shape after deformations.

Interstitial Growth (of Cartilage)

A method of cartilage growth and repair where chondrocytes divide and form new matrix. This process primarily occurs in childhood and adolescence, leading to bones fusing together.

Appositional Growth (of Cartilage/Bone)

A method of cartilage/bone growth where chondroblasts (or substances like calcium and phosphate in bones) secrete matrix onto the surface, producing an increase in width. This growth in width can occur as long as the epiphyseal plate is present in bones.

Bone Tissue

A type of mature connective tissue whose functions include protection, providing for movement, storing minerals, and being the site of blood cell formation. It provides support and storage of mineral deposits.

Spongy Bone

A type of bone tissue that is sponge-like with spaces and trabeculae (strands of bone) surrounded by red bone marrow. It has no osteons (no cellular organization), and its spaces contribute to its 'soft' nature.

Compact Bone

A type of bone tissue that is solid and dense. Its basic unit of structure is the osteon (also known as the Haversian system). It is hard and rigid because calcium and phosphate are deposited in its spaces.

Osteon (Haversian System)

The basic unit of structure of compact bone. It consists of lamellae (rings of mineralized matrix where calcium and phosphate are deposited, providing rigidity) and interwoven collagen fibers that provide strength.

Lacunae (in Bone)

Spaces where osteocytes are found, located in between the lamellae of osteons.

Canaliculi

Small or tiny canals that connect one cell to another within bone tissue.

Blood

A type of connective tissue with a liquid matrix called plasma. Cell Types: Red blood cells (erythrocytes), white blood cells (leukocytes), and cell fragments called platelets. Location: Blood vessels and the heart. Functions: Provides clotting, immune functions, and carries oxygen and carbon dioxide.

Muscle Tissue

Composed of cells that shorten in length, producing movement. It provides motion, posture, and heat. It generates heat that warms the body and functions for contraction. Without muscle cells and bones, the body cannot move.

Skeletal Muscle

A type of muscle tissue characterized by long, cylindrical cells with many peripheral nuclei. It has visible light and dark banding (striations). It moves voluntarily (under conscious control). It is attached to bones by tendons. Its functions include motion, posture, heat production, and protection.

Cardiac Muscle Tissue

A type of muscle tissue that has striations and is branched. It moves involuntarily (cannot be controlled). It is found in the heart and its function is to pump blood.

Smooth Muscle

A type of muscle tissue that is non-striated. It moves involuntarily. It is found on the walls of hollow organs, particularly in blood vessels, the gastrointestinal tract, and the bladder.

Nerve Tissue

A type of tissue whose cells conduct electrical signals. It detects changes inside and outside the body and responds with nerve impulses. It functions for the body's response towards a certain stimulus (internal or external), activating muscular contraction and glandular secretion. It is located in the nervous system.