Histology and Layers

Tissue

An aggregation of cells and cell products of similar structure and embryonic origin that perform a common function

Histology

The Study of tissue, especially their structure and arrangement

Four Primary Types

Epithelium, Connective, Muscle, Nervous

Epithelium

Protects body from microbes and gives Hydration Ex: Skin

Connective

Protects, supports and binds other tissue together bones, cartilage, tendons, fat and blood

Muscle

Contracts to produce movement and exert force, Ex Bones, Cardiac Muscle

Nervous

Transmits electrical impulses for fast communication

Epithelial Tissues are found where?

Body Coverings

Body Linings

Glandular tissue

Charicteristics and Functions of epithelial tissue

Cells fit closely together(Sheet like cover)

Tissue layer always has one free surface(apical surface)

The lower surface is always bound by a basement membrane

Avascular(Meaning no blood supply)/ Can regenerate easily if well nourished

Functions are to protect (Through diffusion)

Absorbtion

Filtration

Secretion

Epithelium Characteristics

Epithelium lines pathways that are open to the external environment ( GI Tract, Respiratory tract, etc)

Endothelium

(Lines the inside) Epithelium that lines the blood vessels, heart and lymphatic vessels

Mesothelium

Lines the cavities. Epithelium that lines peritoneum (abdomen cavity, pleura, lung cavity) and paricardium(heart cavity)

Layers

Simple- one layer

Stratified- more than one

Shape of cells

Squamous- flattened ( squeezed nucleus)

Cuboidal- cube shaped ( normal nucleus)

Columnar- cloumn like ( oval shape towards basement membrane)

Epithelial types

Simple Squamous- inside blood vessels

Simple cuboidal- lines ducts ex. kidney, tubules and mucous glands

Simple columnar- lining - of small intestine

Pseudostratified- columnar- trachea- bronchi

Simple Squamous

Single flat layer of cells

Usually forms membranes

lines lungs and capilaries

Squamous definition

The epithelium is a single layer of flat, or squamous cells

The peripheral cytoplasm of each cell is so attenuated that it is usually not resolvable; the nucleus is usually the only cellular structure available

Nucleus usually has a flattened appearance due to the width of the cells

No speciallized structures at the top like cilia or microvilli

Simple Cuboidal

Single layer of cube- like cells common in glands and their ducts

Forms walls of kidney tubules

Covers the ovaries

Cuboidal

This epithelium consists of a single layer of cuboidal cells resting on an undetectable basement membrane

The height of each epithelial cell is nearly equal to the width of the cell

The cells are tightly packed, forming a continuous wall of cells

The Nucleus is spherical and sits at the center of the cell

The nuclei of adjacent cells are relatively close together, certaininly closwer than in a simple squamous epithelium, aligned in a single row

Simple Columnar

Single layer of tall cells

Often includes goblet cells, which produce mucus

Lines digestive tract

Columnar

The Epithelial containing a single layer of columnar cells ( the cell’s height are significantly greater than the width) and rests on a basement membrane, cells are tightly packed, forming a continuous sheet of cells that effectively form the protective lining of the stomach

The nucleus is generally ovoid and sits at the lower to mid portion of the cell

Pseudo stratified

Single layer, but some cells are shorter than others often looks like a double cell layer, sometimes ciliated, the respiratory tract may function in absorption or excretion

Cilia of the respiratory epithelium beat constantly towards the pharynx and nasal passages, creating a continuous flow of mucus in that direction

Presence of goblet cells secreting mucus over the surface of the epithelium

Stratified Squamous

Cells at the free edge are flattened found as a protective covering where friction is common (Skin, Mouth and Esophagus)

Transitional Epithelium

Shape of cells depends on the amount of stretching

Lines organs of the urinary system (ureter, bladder, part of the urethra)

Glandular Epithelium

Gland- one ore more cells that secretes a particular product

Two major gland types

Endocrine- ductless and secretions are hormones

Exocrine- Empties through ducts at the epithelial surface Includs oil and sweat glands.

Connective Tissue

Found everywhere in the body

Includes the most abundant and widely distributed tissues

Functions of Connective

Binds body Tissue

Supports the body

Provides protection

Where is connective located?

Commonly found under epithelium

Special characteristics

Variations in blood supply

Vascularized (rich with blood vessels)

Avascularized( no blood vessels)

affects the ability to repair itself

Extracellular matrix (non living material that surounds cells)

Matrix main elements(individual numbers, variables, expressions, or characters organized inside its grid of rows and columns)

Ground substance

inorganic mostly water along with adhesion protiens and mostly polysacharide molecules

Collagen Fibers

Thick, appear parallel and are strong, not stretchy (in skin) usually pink under microscope

Elastic Fibers

Cells spread apart, stretchy reticular fine fibers in soft organs such as spleen (support network thin fibers)

Collagen

Most abundant protein in our body

Type 1 Collagen

mostly abundant in bones, tendons, skin and ligaments

Type II

mostly abundant in cartilage (Especially hyaline and articular)

Type III

Abundant with reticular fibers in soft tissues

Reticular fiber - fine collagenous fibers that form a delicate internal support system

Fine delicate thin fibers that forms supporting network Found in soft organs like the spleen

Lining cells

Within a protective layer called the Lacuna

Cell that makes the fibers

Osseous Tissue

Composed of Bone cells in Lacunae (Cavities)

Hard Matrix of Calcium Salts( Make rigid)

Large numbers of collagen fibers

Used to protect and support the body

Matrix of Bone

Innorganic material salts provide bone’s hardness

Organic collagen fibers provide bone flexability

in demineralization

Denature colagen by heating and bones will be brittle

Bone is not completely solid since it had small spaces for vessels and red bone marrow

Spongy bone had many such spaces -compact bone has very few such spaces

Hyaline Cartilage

The most abundant type of cartilage, characterized by a glossy, semi-translucent matrix containing fine Type II collagen fibers and chondrocytes situated inside lacunae. It provides smooth, flexible support and reduces friction; found on the articular surfaces of long bones, the costal cartilages of the ribs, the nose, trachea, larynx, and embryonic skeleton.

Elastic Cartilage

A flexible variety of cartilage containing a dense network of elastic fibers within its extracellular matrix, allowing it to withstand repeated bending while maintaining its shape; found in the external ear (auricle) and the epiglottis.

Fibro Cartilage

he strongest and most durable type of cartilage, composed of dense parallel bundles of thick Type I collagen fibers and chondrocytes housed in lacunae. It provides exceptional tensile strength, cushioning, and shock absorption to withstand heavy compression; found in intervertebral discs, the pubic symphysis, and the menisci of the knee.

Dense Connective Tissue

class of connective tissue characterized by tightly packed collagen fibers with relatively few cells (mainly fibroblasts) and minimal ground substance, providing high tensile strength and resistance to pulling forces; categorized into regular (found in tendons and ligaments), irregular (found in the dermis of the skin and joint capsules), and elastic connective tissue (found in the walls of large arteries).

Adipose Tissue

Matrix is areolar

Tissue in which fat globules predominate

Many cells contain large lipid deposits

Insulates the body

Protects some organs

Serves as a site of fuel storage

Reticular Connective

Delicate Network of Interwoven fibers

Forms stroma (Internal supporting network) of lymphoid organs

Lymph roles Spleen and bone marrow

Blood

Bone cells surrounded by a fluid matrix

Fibers are visible during clotting

functions as the transport vehicle for materials

Epithelial membrane

An epithelial membrane is a thin layer of tissue composed of an epithelial tissue sheet bound to an underlying layer of connective tissue

Serous membrane

a thin, double-layered tissue that lines closed body cavities not open to the outside world and covers the organs inside them

Found as the paricardial sack which prevents friction when the heart beats, pleural membranes around the lungs, mesentaries attaching the intestines

Mucous membrane

a moist, soft-tissue layer that lines body cavities, tracts, and organs open to the external environment

Forms structure of GI tract and Respiratory passageway

Muscle Tissue

40% of your body weight

Fibers contract to produce tension

associated tissues or tendons

Cells have the ability to contract ( contractability)

Have the ability to respond to a stimulus (irratibility)

Muscle cells (myocytes) have the ability to contract

Function

Locomotion

Other body movements

Posture and Body support

Heat Production

Skeletal Muscle

Location= attached to bones via tendons

Voluntary movement (unique)

cells in bundles

long and cylindrical

Fibers are striated-Alternating light and dark bands

Each myofibril is multinucleated

Short and intense reaction

Smooth muscle

Walls of internal organs (except heart)

Involuntary movement

Non striated

Long, spindle shape

Single nucleus(uninucleated)

Two layers at 90 degrees

Constrict of dilate lumen

Propels substances along

Stracts like draw string bag

Smooth muscle can tense and relax but had greater elastic properties than striated muscle

Thi is important in organ systems like the urinary bladder where contractile tone must be preserved

Actin and myosin form continous chains with the smooth muscle cell which are achored at the dense bodies

Cardiac Muscle

Striations

Involuntary

One nucleus

Intercalated disks (unique) link cells together

Communication so all cells contract together in a rhythym

Deep center

Bundles branched

Heart muscle

Nervous Tissue

Neuron= Specialized cell of Nervous System

Cells with the ability to:

Respond to Stimuli (irritability)

Transmit impulses (conductivity)

Ability to transmit impulses through an electrochemical impulse

Parts of a Neuron:

Dendrite, Cell Body, Axon

Cell Body

Also known as the soma, this part of the neuron contains the nucleus, which controls the cell’s activities and contains the genetic material. The soma also contains organelles that support and maintain the neuron’s functioning

Axon

This part of the neuron looks like a long tail and sends messages from the cell. The axon terminal is the end part of the axon that makes a synaptic connection with another cell

Dendrites

These parts of the neuron look like branches of a tree and receive messages for the cell. Dendrites branch as they move towards theirtips and have leaf like structures on them called spires

Tissue Repair

Depends on Vascularization of Tissue Repair

Vascularization of tissues

The body's process of restoring architecture and function after an injury, occurring through two main mechanisms: regeneration (replacing lost tissue with the same cell type) or repair/scarring (replacing lost tissue with fibrous connective tissue)

Regeneration

Repaired by same type of cells, cells continue to function normally

On Epithelial tissue

Exhibits rapid mitosis with original function retained

Although avascular, vessels are nearby

Occurs in: Skin, Respiratory tracts, liver, glands, mucous membranes and blood vessels

Fibrosis

Fibrosis tissue knits damaged parts together (scar tissue)

Poor vascularization with slow repair and non functional tissue occurs in connective tissue layers not bone, adipose and areolar

Areolar Tissue

Areolar connective tissue is the most common type of loose connective tissue in vertebrates, acting as the body's universal packing material to bind, support, and cushion organs.

Wound Healing

Hemostasis, Inflammation, Granulation, Regeneration or Fibrosis

Hemostasis

• Timeline: Begins immediately after injury (lasts from minutes to a few hours).

• What happens: Blood vessels constrict (vasoconstriction) to reduce blood loss. Platelets stick together and form a plug, while clotting proteins like fibrin create a stable seal (blood clot) over the wound.

• Goal: Stop bleeding and create a temporary barrier against bacteria.

Inflammation

• Timeline: Lasts about 1 to 5 days (or up to a week).

• What happens: Blood vessels dilate (vasodilation) to let immune cells enter the site. White blood cells (neutrophils and macrophages) clear out bacteria, dead tissue, and foreign debris.

• Signs: Common symptoms include redness, warmth, swelling, and pain.

• Goal: Prevent infection and prepare the tissue for new growth.

Proliferation

• Timeline: Lasts from about 3 to 21 days (several weeks).

• What happens: The body rebuilds the damaged area. Fibroblasts build new collagen and an extracellular matrix, while new blood vessels grow (angiogenesis) to supply oxygen and nutrients. Granulation cells make new capillaries, fibroblasts Macrophages digest original clog (phagocytosis) and scar tissue comes where the clot was

• Goal: Close the wound and restore tissue structure.

Vasodilation increased( more blood vessels)

Regeneration or Fibrosis

Tissue repair after an injury results in either regeneration (restoring normal structure and function) or fibrosis (forming excessive scar tissue), depending on the severity of the damage, the type of tissue, and cellular signals.

Acute

a sudden break in the skin or soft tissue that progresses through normal healing stages and typically heals within 8 to 12 weeks (often much faster, within 1 to 4 weeks) with minimal scarring such as an abrasion or cut

Chronic

an injury that fails to progress through normal healing or does not show significant improvement within 4 weeks to 3 months, often becoming stuck in a prolonged inflammatory state (veneous and and aretorial ulcers)

Hypertrophic

Extra connective tissue forms within the original wound area

Keloid Scar

Extra connective tissue extends beyond the original wound

Body Membranes

Epithelial membrane

Cutaneous membrane

Serous membrane

Connective tissue membrane

Mucous membranes

moist, soft-tissue linings that cover internal cavities, organs, and tracts which are open or exposed to the external environment

• Respiratory tract: Nose, sinuses, throat, trachea, and lungs

• Digestive tract: Mouth, lips, esophagus, stomach, and intestines

• Reproductive and urinary tracts: Uterus, urethra, and rectum

• Sensory cavities: Conjunctiva of the eyes and the middle ear / Eustachian tube

Cutaneous membrane

Skin ,an epithelial tissue membrane that forms the body's outer protective boundary formed by keratinized stratified squamous epithelium

Connective Tissue Membrane

ules

surounding joints

in synovial joints

Integumentery System

The integumentary system is the body's largest organ system, forming a physical barrier between the internal body and the external environment.

Skin Functions

Protects deeper tissues from

Mechanical damage

Chemical damage

Bacterial damage

Thermal Damage

Ultraviolet radiation

Desiccation- prevents drying out or lysis because of keratin

Aids in heat regulation

Aids in excretion of urea and uric acid

Synthesizes vitamin d

Epidermis

The outermost, avascular (no blood vessels) cellular layer made of stratified squamous epithelium. It includes sub-layers like the stratum corneum and stratum basale.

Dermis

Deep connective tissue The thick inner connective tissue layer containing blood vessels, nerves, hair follicles, and sweat glands.

Hypodermis

A deeper layer of adipose and areolar tissue that anchors the skin to underlying muscle and bone while providing insulation. [1, 2, 3, 4]

Stratum Basale

• Location: Deepest layer, attached to the basement membrane.

• Cells: Contains stem cells (basal cells) that constantly divide to produce new keratinocytes, along with melanocytes (pigment producers) and Merkel (tactile) cells. [1, 2]

Stratum spinosum

• Location: Just above the stratum basale.

• Cells: Keratinocytes linked together by desmosomes (giving a spiny shape under a microscope); contains immune-defending Langerhans (dendritic) cells.

• Function: Provides strength and flexibility.

Stratum Granulosum

• Location: Above the stratum spinosum.

• Cells: Cells flatten out and fill with keratohyalin granules and lamellar bodies.

• Function: Marks the transition where cells die and release waterproofing lipids.

Stratum lucidum

• Location: Present only in thick skin (palms of hands and soles of feet) between the granulosum and corneum.

• Cells: Thin, translucent layer of dead, flattened keratinocytes

Stratum corneum

• Outermost surface of the skin.

• Cells: Composed of 20 to 30 layers of dead, fully keratinized, scale-like cells (corneocytes) that constantly shed.

• Function: Acts as the primary barrier against pathogens, UV rays, and water loss.

Dermis Papilarry layer

Pain receptors capilary loops

Reticular layer

Blood vessels Glands Nerve receptors

Blister

A bubble of fluid underneath the outer layer of skin, Friction causes the layers of skin to seperate and fill with fluidn

Frostbite vs Hypothermia

Hypothermia is a fancy way of saying you have an abnormallt low body temperature

core temperature of 95 or less

lead to cardiac and respiratory failure

Frostbite is frozen body rissue, causing injury by freezing, often affects your hands and feet

Burn

tissue damage caused by heat, chemicals, electricity, sunlight, or radiation

Associated dangers (Dehydration immeadiate)

Circulatory ahock (Life threatening after 24 hours

First Degree Burn

affects only the outer layer of your skin, called the epidermis. like sunburn

Second degree

damages both the outer layer of skin (epidermis) and part of the inner layer (dermis), causing deep redness, swelling, fluid-filled blisters, and a shiny, moist surface that is very painful to the touch. No pain sometimes due to damaged receptors

Third degree

a severe, full-thickness injury that destroys the top layer of skin (epidermis), the middle layer (dermis), and reaches down into the deep fatty layer (hypodermis).

Fourth degree

A fourth-degree burn is a critical, life-threatening injury that penetrates past all skin layers into fat, muscle, tendons, and bone.

Critical Burn

Burns are only considered critical if over 25% of the body has 2nd degree burns

If there are over 10% third degree

There are 3rd degree on hands and faces

Rule of 9s

Way to determine the extent of burns Body is divided into 11 areas, 10 = 9% pubic area is 1%

Skin Cancer

Cancer = abnormal cell mass Skin cancer most common

Benign

does not spread, distinct smooth regular borders

malignant

Moves to other parts of the body grows faster than a benign tumor