HISTO AI Flashcards
What are the four basic tissue types in the human body?
Epithelial, connective, muscular, and nervous tissues
What is the primary function of epithelial tissues?
Covering, lining, and protecting surfaces; absorption; secretion
What is the extracellular matrix (ECM)?
A network of proteins and molecules that provides structural and biochemical support to surrounding cells
What distinguishes connective tissue from other tissue types?
It has abundant extracellular matrix produced by its cells
What are the two main components of an organ’s structure?
Parenchyma and stroma
What is the role of parenchyma in an organ?
It is composed of cells responsible for the organ’s specialized functions
What is the role of stroma in an organ?
It consists of supportive cells, usually connective tissue, except in the brain and spinal cord
What are the characteristic features of epithelial cells?
Closely aggregated polyhedral cells adhering strongly to one another and to ECM
What is the basement membrane?
A thin extracellular layer that supports epithelial tissues and acts as a filter
What are the two parts of the basement membrane identified by electron microscopy?
Basal lamina and reticular lamina
What components are characteristic of the basal lamina?
- Type IV collagen
- Laminin
- Nidogen
- Perlecan
What is the function of tight junctions in epithelial cells?
They form a seal between adjacent cells, preventing passive flow of materials
What are adherens junctions?
Sites of strong cell adhesion in epithelial tissues
What is the function of gap junctions?
Channels for communication between adjacent cells
What is the difference between apical and basal poles of epithelial cells?
The basal pole contacts the ECM, while the apical pole faces a space
Fill in the blank: Epithelial cell nuclei may be ______, spherical, or flattened.
[elliptic (oval)]
True or False: Most epithelia contain blood vessels.
False
What are papillae in relation to epithelial tissues?
Small evaginations from connective tissue into the epithelium that increase contact area
What is the role of the basement membrane in epithelial repair?
It serves as a scaffold allowing rapid epithelial repair and regeneration
What are myoepithelial cells?
Contractile cells found within certain epithelia
What is the significance of tight junctions in maintaining cell polarity?
They restrict movement of membrane proteins and lipids, maintaining distinct apical and basolateral domains
List the main functions of the basement membrane.
- Provides structural support
- Attaches epithelia to connective tissue
- Acts as a filter
- Regulates macromolecular exchange
What proteins are involved in tight junctions?
- Claudin
- Occludin
What happens when tight junction proteins are disrupted by pathogens?
It can lead to loss of tissue fluid and other pathological conditions
What is the role of proteins of tight junctions in medical applications?
They provide targets for certain common bacteria of medical importance.
For example, the enterotoxin from Clostridium perfringens binds claudin molecules and disrupts tight junctions.
What effect does Helicobacter pylori have on tight junctions?
It binds the extracellular domains of tight-junction proteins and disrupts signaling from the junction.
This is linked to the etiology of gastric ulcers.
What is the function of the adherens junction?
It provides points linking the cytoskeletons of adjacent cells and strengthens nearby tight junctions.
This junction encircles the epithelial cell immediately below the tight junction.
What are the major transmembrane link proteins of tight junctions?
Occludins, claudins, ZO proteins.
These proteins are crucial for the integrity of tight junctions.
What is the main function of desmosomes?
They provide points of strong intermediate filament coupling between adjacent cells, strengthening the tissue.
Desmosomes resemble spot welds rather than forming a belt around cells.
What are the major components of gap junctions?
Connexins that form hexameric complexes called connexons.
These structures allow for intercellular communication.
What is the primary function of hemidesmosomes?
They anchor the cytoskeleton to the basal lamina.
Hemidesmosomes link to laminin molecules.
What are microvilli and their function?
Cytoplasmic projections that increase the apical surface area for better absorption.
They are particularly prominent in absorptive cells lining the small intestine.
Fill in the blank: Microvilli are usually _____ long and _____ wide.
1 μm long and 0.1 μm wide.
They can increase the total surface area by 20-30 fold.
What medical condition is characterized by loss of the microvilli brush border?
Celiac disease.
This condition results from an immune reaction against gluten.
What is the difference between stereocilia and microvilli?
Stereocilia are longer, less motile, and may branch distally.
They are found in the male reproductive system and inner ear sensory cells.
What are cilia and their primary function?
Long, highly motile apical structures containing microtubules; they facilitate movement of substances along the epithelial surface.
Primary cilia are non-motile and involved in signal transduction.
True or False: Desmosomes are responsible for cell-to-cell adhesion.
True.
They provide strong adhesion through intermediate filaments.
What intracellular structures are linked to the adherens junctions?
Actin filaments.
These filaments form part of the terminal web in epithelial cells.
What is the function of focal adhesions?
They link integrins to actin filaments and are involved in cell signaling, adhesion, and mobility.
Focal adhesions are important during epithelial repair and in migrating cells.
What are the major functions of tight junctions?
Seals adjacent cells, controlling passage of molecules between them; separates apical and basolateral membrane domains.
Defects in tight junctions can lead to various medical conditions.
What is a primary cilium?
A short projection on most cell types, enriched with receptors and signal transduction complexes for detection of light, odors, motion, and liquid flow.
What are motile cilia?
Cilia abundant on cuboidal or columnar cells that are typically 5-10 μm long and 0.2 μm in diameter.
What is the structural composition of a typical cilium?
A core structure with nine peripheral microtubule doublets and two central microtubules, known as the axoneme.
What proteins are involved in the movement of cilia?
Kinesin and cytoplasmic dynein motors.
What is the function of cilia?
To move a current of fluid and suspended matter in one direction along the epithelium.
How does ciliary motion occur?
Through changes in the conformation of the axoneme facilitated by dynein-powered sliding of adjacent doublets.
What is Kartagener syndrome?
A condition caused by mutations in cilia and flagella proteins, leading to chronic respiratory infections and immotile spermatozoa.
What are the two main groups of epithelia?
Covering (or lining) epithelia and secretory (glandular) epithelia.
Define simple epithelia.
Epithelia composed of one cell layer.
Define stratified epithelia.
Epithelia composed of two or more layers of cells.
What are the three types of simple epithelial cell shapes?
- Squamous
- Cuboidal
- Columnar
What is the primary function of stratified squamous keratinized epithelium?
Protection against dehydration.
Where is stratified squamous nonkeratinized epithelium found?
In moist internal cavities such as the mouth, esophagus, and vagina.
What is unique about transitional epithelium?
It can distend and is characterized by dome-like superficial cells.
What is the role of pseudostratified columnar epithelium?
Protection, secretion, and cilia-mediated transport of particles.
What are the characteristics of simple cuboidal epithelium?
Cells are roughly as tall as they are wide, allowing for high levels of active transport.
Fill in the blank: Stratified cuboidal epithelium is found in _______.
[the excretory ducts of salivary and sweat glands]
What is the function of the basal body in cilia?
To anchor the axoneme to the apical cytoplasm.
True or False: Stratified columnar epithelium is commonly found.
False
What is transcytosis?
The process by which substances are transported across a cell.
What are the protective functions of stratified squamous epithelia?
Protection against invasion by microorganisms and water loss
Particularly important in the epidermis
What happens to differentiating cells in the epidermis of stratified squamous epithelium?
They become keratinized, lose their nuclei and organelles, and form flattened squames
This process helps impede water loss
Where can nonkeratinized stratified squamous epithelia be found?
Esophageal lining and outer covering of the cornea
These cells retain their nuclei and provide protection against microorganisms
What are the functions of stratified cuboidal or columnar epithelia?
Occur in excretory ducts of certain glands, such as sweat glands
They allow additional functions due to their double layer of cells
True or False: Chronic bronchitis leads to decreased numbers of goblet cells in the airways.
False
It leads to an increase in goblet cells and excessive mucus production
What is the primary function of secretory epithelia?
To produce and secrete various macromolecules
This can include proteins, lipids, or carbohydrate-protein complexes
What are unicellular glands?
Scattered secretory cells in simple cuboidal, simple columnar, and pseudostratified epithelia
An example is the goblet cell in the small intestine
What do goblet cells secrete?
Lubricating mucus
This aids the function of the small intestine and respiratory tract
What is the difference between exocrine and endocrine glands?
Exocrine glands have ducts and secrete substances to specific organs, while endocrine glands lack ducts and release hormones into the bloodstream
Endocrine glands are rich in capillaries
What are the three basic mechanisms of secretion?
- Merocrine secretion
- Holocrine secretion
- Apocrine secretion
Each mechanism involves different processes of product release
What is merocrine secretion?
The most common method of secretion involving exocytosis from membrane-bound vesicles
Seen in protein or glycoprotein secretion
Describe holocrine secretion.
Cells accumulate product, undergo terminal differentiation, and release product and cell debris into the gland’s lumen
Best seen in sebaceous glands
What occurs during apocrine secretion?
Product accumulates at the apical end of cells, which then pinch off to release the product
This process is seen in mammary glands for lipid droplets
What are serous cells?
Cells that synthesize proteins, mostly not glycosylated, and stain intensely with basophilic or acidophilic stains
Found in acini of the pancreas and parotid salivary glands
What distinguishes mucous cells from serous cells?
Mucous cells contain heavily glycosylated proteins called mucins that form mucus when hydrated
Goblet cells are an example of mucous cells
What type of cells assist in the propulsion of secretory products in exocrine glands?
Myoepithelial cells
These cells help contract and propel secretory products from acini into the duct system
How do endocrine glands release their products?
By exocytosis for proteins and by diffusion for lipophilic steroids
Hormones are transported in blood to target cells
What is transcellular transport?
The transfer of ions and water across the epithelium via ion pumps and aquaporins
Apical tight junctions prevent paracellular diffusion
Where are key sites for ion and water transport in the body?
Epithelia of kidney tubules
These cells are specialized for maintaining the body’s overall balance of salts and water
What are the key sites for ion and water transport in the kidney?
Helia of kidney tubules
They maintain the body’s overall balance of salts and water.
What structural specialization do proximal renal tubule cells have for transcellular transport?
The apical surface is freely permeable to Na+ and basolateral membranes have sodium pumps
This allows for the active extrusion of Na+ into the interstitial fluid.
What maintains osmotic and electrical balance in proximal renal tubule cells?
Passive transfer of chloride ions (Cl−) and water into the cell.
How is the basal membrane of proximal renal tubule cells structured?
Elaborately folded with mitochondria located between the folds.
What process allows all cells to internalize extracellular molecules and fluid?
Endocytosis and formation of cytoplasmic, membrane-bound vesicles.
What is transcytosis?
The process of moving substances across a cell via vesicles, occurring in simple cuboidal and columnar epithelia.
How often is the intestinal epithelium replaced?
Every week.
Where do stem cells and mitosis occur in stratified epithelial tissues?
Only within the basal layer in contact with the basal lamina.
What are malignant tumors of epithelial origin called?
Carcinomas.
What are adenocarcinomas?
Malignant tumors derived from glandular epithelial tissue.
What happens to epithelial tissues after major damage?
Cells of undamaged regions quickly begin active proliferation to regenerate tissue.
What is dysplasia in epithelial cells?
Abnormal growth that can progress to neoplasia.
What is metaplasia?
Transformation of one type of epithelial tissue into another type under abnormal conditions.
What is the defining feature of simple glands?
Ducts do not branch.
What type of secretion is characteristic of merocrine glands?
Release of products via exocytosis.
How do holocrine glands release their secretions?
By disintegration of the secretory cells themselves.
What distinguishes apocrine secretion?
Loss of membrane-enclosed apical cytoplasm containing lipid droplets.
What are the three major types of intercellular junctions in epithelia?
Tight junctions, adherent junctions, and gap junctions.
What do tight junctions prevent?
Paracellular passage of substances.
What are adherent junctions formed by?
Interacting proteins of the cadherin family.
What is the function of gap junctions?
Allow passage of small molecules from one cell to another.
What is the basal lamina composed of?
Type IV collagen and laminin.
What is the role of hemidesmosomes?
Attach cells to proteins of the basal lamina.
What structures increase the apical surface area for absorption in epithelial cells?
Microvilli.
What are stereocilia?
Long microvilli with specialized mechanosensory function.
What is the axoneme in cilia?
A 9 + 2 arrangement of microtubules.
What characterizes simple epithelia?
One cell layer.
What type of epithelium is protective against urine?
Transitional epithelium or urothelium.
What are exocrine glands characterized by?
Epithelial ducts carrying secretions to specific sites.
What distinguishes endocrine glands?
Lack ducts and secrete hormones into the bloodstream.
What types of glands produce mucus?
Mucous glands.
What types of glands produce enzymes?
Serous glands.
