15- Tissue & Organ System Physiology

Tissue

A group of cells with similar structures that work together to perform a specific function

Tissue changes are the result of

Development, growth, aging, trauma, and disease

Four primary tissue types

-Epithelial

-Connective

-Muscle

-Nervous

Epithelium

-Covers internal and external surfaces

-Forms most glands

-Consists almost entirely of cells with little extracellular matrix between them

Epithelium characteristics

-Free surface = Layer of cells with one surface not in contact with other cells

-Basement membrane = Attaches cells to underlying tissues (Protein/carbohydrate secretion made by epithelial and underlying cells)

-Blood vessels do not extend from the underlying tissues into the epithelium

Major functions of epithelial tissue include

Protecting underlying structures

-Minimizes abrasion risk to underlying structures

Acting as barriers

-Prevents entry of many substances and organisms into the body

Selective permeability

-Allows movement of certain substances through the epithelium

Secreting/absorbing substances

-Release of sweat, mucus, or enzymes into outer environment

-Contain carrier molecules that regulate the absorption of materials

Epithelial classification is based on

Number of cell layers –

-Simple = A single layer of cells

-Stratified = More than one layer of cells stacked on top of each other

Shape of the cells –

-Squamous = Flat cells

-Cuboidal = Cubelike cells

-Columnar = Column-like (tall and thin)

What type of name is given to epithelia?

Compound name

-(e.g., simple squamous, simple columnar, etc.)

-When stratified: Name according to the cell shape at the free surface (e.g., stratified squamous)

Simple Squamous epithelium

-Location: Blood vessel lining, heart, serous membranes, alveoli

-Structure: Single layer of thin, flat cells

-Function: Diffusion, filtration, and friction protection

Simple Cuboidal Epithelium

-Location: Kidney tubules, glands, bronchioles, choroid plexus (brain)

-Structure: Single layer of cube-shaped cells; some have cilia

-Function: Secretion & absorption (Via active transport & facilitated diffusion); mucus movement (via cilia/microvilli)

Simple columnar epithelium

-Location: Lining of stomach, intestines, glands, ducts, auditory tubes

-Structure: Single layer of tall narrow cells; some have microvilli/cilia

-Function: Secretion; mucus movement (via cilia/microvilli)

Pseudo-stratified columnar epithelium

-Location: Lining of the nose, sinuses, pharynx, trachea, bronchi

-Structure: Single layer of irregularly-sized cells (some reach the free surface; others do not); ciliated and associated with goblet cells

-Function: Secretion (mucus); mucus movement (via cilia)

Stratified squamous epithelium

-Location: Skin, cornea, lining of mouth, throat, esophagus

-Structure: Many layers of cells; basal layer is cuboidal/columnar; cells become flattened at the free surface

-Function: Abrasion protection; infection barrier; prevents H2O loss

Transitional epithelium

-Location: Lining of urinary bladder, ureters/urethra

-Structure: Stratified cuboidal when at rest (not stretched); squamous when stretched

-Function: Accommodates fluid volume fluctuations in an organ or tube; protects against caustic effects of urine

How are epithelial cells connected to one another?

Through tight junctions, desmosomes/hemidesmosomes, and/or gap junctions

Tight junctions

-Bind adjacent cells together; form permeability barriers

-Prevent the passage of materials between epithelial cells

Desmosomes/hemidesmosomes

-Mechanical links that bind cells together (desmosomes)

-Modified desmosomes that anchor cells to the basement membrane (hemidesmosomes)

Gap junctions

-Small channels allowing the exchange of small molecules, ions, and electric potentials to pass from one cell to an adjacent cell

-Acts as communication signals to coordinate cell activity

Gland

a multicellular structure that secrets substances onto a surface, into a cavity, or into the blood

What are glands mostly comprised of?

epithelium

Types of glands

Exocrine and Endocrine

Exocrine glands

glands with ducts

-Simple = No branches

-Compound = Branches

-Tubular = Tube-shaped

-Acinus – Sac-like structure (grapelike)

-Alveolus – Small cavity

Endocrine glands

glands without ducts

-Hormones = carried by blood to other parts of the body

Connective tissue

-Extracellular materials that separate cells from one another

-Extracellular matrix = Consists of protein fibers, ground substance, and fluid

What are the protein fiber types found in connective tissue?

Collagen, Reticular, and Elastic

Collagen

Protein fibers grouped into bundles; flexible but resist stretching

Reticular

Very fine, short collagen fibers that branch to form a supportive network

Elastic

Stretchable coil-like fibers that are grouped into anastomosing bundles

How is connective tissue named?

Named according to their functions.

-Blast cells = Produce the extracellular matrix

-Cyte cells = Maintain the extracellular matrix

-Clast cells = Break down the extracellular matrix or remodel it

What tissue are immune system cells associated with?

connective tissue

Macrophages

ingest microorganisms found in the connective tissue

Mast cells

release histamine following stimulation with pro-inflammatory cytokines

Major functions of connective tissue include

Enclosing, separating, and storing

-Forms layers that separate tissues and organs; adipose tissue stores energy; bones store minerals

Connecting tissues together

-Tendons (attach muscle to bone), ligaments (attach bone to bone)

Supporting, moving, and transporting

-Bones and cartilage provide support for the body and joints for movement; blood transports substances throughout the body

Protecting, cushioning, and insulating

-Protects underlying tissues from injury; immune cells in blood protect against pathogens

§Adipose tissue cushions and protects tissues from trauma; also insulates the body to retain heat

Connective tissue classification

fibrous, special, cartilage, bone, and blood

Organ systems

A collection of anatomical structures (organs) that cooperate to carry out a specific task

What are the eleven organ body systems?

-Respiratory

-Lymphatic

-Cardiovascular

-Nervous

-Integumentary

-Reproductive

-Digestive

-Urinary

-Muscular

-Skeletal

-Endocrine

What does it mean that organ systems are interdependent?

They rely on each other to maintain overall body function and homeostasis

-A failure of one organ system can disrupt the function of others

--Can lead to severe health problems or death

Respiratory and Circulatory

-Work together to provide oxygen to the body cells and remove carbon dioxide waste

-Respiratory = Brings in oxygen; removes carbon dioxide

-Circulatory = Transports oxygen to tissues/cells; transports carbon dioxide away from tissues/cells

Digestive and Circulatory

-Work together to break down and deliver nutrients to the body cells

-Digestive = Breaks down ingested food to usable material (nutrients) for tissues/cells

-Circulatory = Transports nutrients to tissues/cells