A&P

What are the four types of human tissues classified by structure and function?

Epithelial tissue: Forms boundaries; Muscle tissue: Enables contraction; Nervous tissue: Facilitates communication and control; Connective tissue: Provides connection and support.

What is epithelial tissue/epithelium?

a sheet of cells that covers a body surface or lines a body cavity.

How is epithelium classified by number of cell layers?

1 layer = simple; >1 layer = stratified.

What are the three major epithelial cell shapes?

Squamous: scalelike; Cuboidal: cubelike; Columnar: column-shaped.

What general principle connects epithelial structure and function?

Structure supports function.

What is the first common function of epithelial tissue?

Form barriers that separate the body from the external environment or divide bodily compartments with distinct physical or chemical properties.

What does the skin do as an epithelial barrier?

separates the internal from external environment.

What does the endothelium of blood vessels do as an epithelial barrier?

Acts as a barrier between the blood and the surrounding tissues of the body.

What does the blood-brain barrier separate?

the circulating blood from the brain’s extracellular fluid.

What are four common functions of epithelial tissue?

Form barriers, secretion, absorption, sensation.

What is an example of secretion by epithelial tissue?

sweat gland, sebaceous gland.

What is an example of absorption by epithelial tissue?

sweat gland duct.

What is an example of sensation by epithelial tissue?

Merkel cells.

What do external boundaries do?

separate the body from external environment.

What do internal boundaries do?

Separate one part of the body from another.

What is an example of an internal boundary?

Blood-Testis Barrier.

What are exocrine glands?

secretory epithelium surrounds a duct, which empties their secretion out of the body.

What are examples of exocrine gland secretions?

mucus, saliva, sweat, earwax, oils, and milk.

What are endocrine glands?

are ductless, they release their secretion (hormones) into the blood - circulatory system.

What are examples of endocrine glands?

pituitary gland, adrenal gland, and thyroid gland.

What are glandular cells?

specialized epithelial cells with secretory machinery.

What are the characteristics of epithelial tissues?

Polarity: apical vs basal; Specialized contacts: bound together by specialized junctions; Supported by connective tissue: basement membrane; Avascular but innervated; Regeneration.

What does polarity mean in epithelial tissues?

apical vs basal.

What are specialized contacts in epithelial tissue?

bound together by specialized junctions.

How are epithelial tissues supported by connective tissue?

basement membrane.

What is the basement membrane?

an acellular material secreted partly by the epithelial cells and connective tissue cells.

What does avascular but innervated mean for epithelial tissue?

depend on diffusion of nutrients from underlying connective tissue.

What is the regenerative characteristic of epithelial tissue?

epithelial cells can easily divide to regenerate the tissue.

What is Common Structural Feature #1 of epithelial tissue?

Various Cell Junctions Tighten the Packing of Epithelial Cells.

What is the main function of tight junctions?

Seal space between cells to prevent paracellular leakage.

What are the key proteins of tight junctions?

Claudins, occludins.

Where are tight junctions typically distributed in epithelium?

Apical region of absorptive epithelia (e.g., intestinal lining, kidney tubules) to maintain polarity.

What is the main function of adherens junctions?

Mechanical link between actin cytoskeletons of adjacent cells.

What are the key proteins of adherens junctions?

Cadherins (E-cadherin), catenins.

Where are adherens junctions typically distributed in epithelium?

Just below tight junctions in most simple epithelia (e.g., intestinal epithelium) to maintain tissue integrity.

What is the main function of desmosomes?

Strong spot-like adhesion, resist mechanical stress.

What are the key proteins of desmosomes?

Desmoglein, desmocollin (cadherins).

Where are desmosomes abundant?

stratified squamous epithelium (skin epidermis, esophagus).

What is the main function of hemidesmosomes?

Anchor basal surface of epithelial cells to basement membrane.

What are the key proteins of hemidesmosomes?

Integrins, BP180, BP230.

Where are hemidesmosomes typically found?

Basal surface of epidermis and other epithelia under mechanical stress.

What is the main function of gap junctions?

Direct communication via ion and small molecule exchange.

What are the key proteins of gap junctions?

Connexins.

Where are gap junctions found in epithelia?

Found in epithelia that coordinate activity, e.g., ciliated epithelium of respiratory tract, secretory epithelium of glands.

What is Common Structural Feature #2 of epithelial tissue?

Epithelial cells are polarized.

What does the basal surface of an epithelial cell do?

adheres to basement membrane (layers of extracellular matrix).

What does the apical surface of an epithelial cell face?

the lumen or external space.

What is epithelial polarity?

A structural and functional asymmetry exists within the cell.

What specialized feature allows epithelial cells in the small intestine to absorb nutrients?

Cells are equipped with specialized protein transporter that recognize and absorb various nutrients.

What does apical-basal polarity accomplish in the small intestine?

Protein machinery is localized to different surfaces, ensuring the proper execution of specific functions.

How much do villi and microvilli increase intestinal surface area?

Villi+Microvilli increase the surface area by ~600x compared to a smooth tube.

What specialized feature allows epithelial cells in gastric glands to generate acid?

Cells are equipped with specialized protein tools for generating acids and secretion.

What does active metabolism in parietal cells generate?

lots of CO2.

What enzyme catalyzes the formation of carbonic acid?

carbonic anhydrase.

What does carbonic anhydrase catalyze?

the formation of carbonic acid (H2CO3).

What does carbonic acid immediately dissociate into?

the bicarbonate ion (HCO3−) and a proton (H+).

What happens to the protons generated in parietal cells?

The protons are actively (using ATP) pumped into the stomach lumen.

What happens to HCO3− in parietal cells?

HCO3− is transported to blood in exchange for Cl− from the blood.

What is the exchange of HCO3− for Cl− called?

Chloride Shift.

What happens to Cl− after entering a parietal cell?

Cl− is then transported into the lumen via a Cl− channel.

What is endothelium?

Simple squamous epithelium lining the inner surface of blood vessel walls.

What forms the entire vessel wall in capillaries?

endothelium.

How does endothelium regulate vascular tone?

by releasing signaling molecules.

What is angiogenesis?

formation of new blood vessels.

What are major functions of endothelium?

Regulates vascular tone by releasing signaling molecules; involved in angiogenesis; facilitates immune cell trafficking; regulate blood clotting.

What does endothelium do in capillaries?

acts as a selective barrier between blood and tissues, allowing efficient exchange of gases, nutrients, and waste.

What are continuous capillaries?

Have tight junctions, forming a barrier as in the blood-brain barrier (BBB).

Where are continuous capillaries found?

brain, lungs.

What are fenestrated capillaries?

Have small pores within endothelial cells to allow greater permeability.

Where are fenestrated capillaries found?

kidneys, intestines.

What are sinusoidal capillaries?

Have large gaps between cells to allow the passage of larger molecules like proteins and cells.

Where are sinusoidal capillaries found?

liver, spleen.

What are the structural characteristics of epithelial tissue in the epidermis?

Avascular (lacking blood vessels or blood supply); Aneural (lacking nerves or nerve supply).

What is the main function of epithelial tissue in the epidermis?

Form barriers that separate the body from the external environment.

What are the layers of the epidermis from superficial to deep?

Stratum corneum; Stratum lucidum; Stratum granulosum; Stratum spinosum; Stratum basale.

What characterizes the stratum corneum?

20-30 layers of dead keratinocytes, shedding.

Where is the stratum lucidum found?

thick skin only.

What happens to keratinocytes in the stratum lucidum in response to mechanical stress?

keratinocytes are genetically programmed to pass through an extra transitional stage.

What is the stratum lucidum packed with?

eleidin, a clear, lipid-rich form of keratin derived from keratohyalin granules.

How many distinct keratins does human skin express?

20 distinct keratins (37 genes), e.g., hair, nail, wound etc.

What happens in the stratum granulosum?

Accumulate lamellar granules & keratohyalin granules; Apoptosis occurs, cells become flat and die.

What happens in the stratum spinosum?

Start to produce keratin and release glycolipids.

What connects cells tightly in the stratum spinosum?

Desmosomes ("spines").

What protection does the stratum spinosum provide?

Provide protection against penetration by irritants and pathogens and loss of water.

What occurs in the stratum basale?

Mitotic division, stem cells.

What are the key features of connective tissue?

Consists of cells loosely scattered within a liquid, jellylike, or solid matrix.

What determines a connective tissue's physical property?

The nature of the matrix determines the tissue’s physical property.

What do fibers provide to connective tissue?

strength to the tissue.

What does ground substance do in connective tissue?

traps water and fills space between cells and fibers.

Who usually secretes the connective tissue matrix?

The matrix is usually secreted by the connective tissue cells themselves.

What are the major components of connective tissue?

Cells, fibers, ground substance.

What proteins make up collagen fibers?

collagen proteins.

What proteins make up elastic fibers?

elastin + fibrillin proteins.

What proteins make up reticular fibers?

collagen proteins.

What are major components of connective tissue ground substance?

Polysaccharides; Proteoglycans.

What are the three groups of connective tissues?

Connective Tissue Proper; Supportive Connective Tissue; Fluid Connective Tissue.

What are the two major forms of connective tissue proper?

Loose connective tissue and Dense connective tissue.

What are the three forms of loose connective tissue?

Areolar, adipose, reticular.

Where is areolar connective tissue found?

Skin, GI tract.

Where is adipose connective tissue found?

Fat, bone marrow.