11/17/2014 Microscopic Anatomy Introduction & Epithelium Thomas Poole Flashcards
What is histology (microscopic anatomy)?
The study of tissues and their components
What do tissues consist of?
Groups of cells with varying amounts of extracellular matrix that perform specific functions
What are organs?
Larger functional units of two or more tissues
How can organs be divided?
- parenchyma
- cells responsible for the main organ function
- stroma
- supporting elements or matrix of the organ
What are the four basic types of tissues?
- Epithelial Tissue
- Connective Tissue
- Muscular Tissue
- Nervous Tissue
Describe nervous tissue
- intertwining elongated processes
- no extracellular matrix
- transmits nervous impulses
Describe epithelial tissue
- aggregated polyhedral cells
- very small amount of extracellular matrix
- lines surface of body cavities and involved in glandular secretion
Describe muscle tissue
- elongated contractile cells
- moderate amount of extracellular matrix
- involved in movement
Describe connective tissue
- several types of fixed and wondering cells
- abundant amount of extracellular matrix
- involved in support and protection
What does the preparation of tissue for light microscopy involve?
- fixation
* preserves the structural organization
* formalin most common fixative –> cross-links proteins & nucleic acids
* osmium tetroxide (osmic acid) –> fixes lipids - sectioning
* cut 3 to 10 micron sections of specimens embedded in paraffin - staining
* localize and distinguish cell and tissue components
What does eosin (acidic stain) bind?
Basic structures and components
- Na+(dye)-
- acid radical has the dye
- cytoplasm, cytoplasmic filaments, collagen fibers, and basement membrane
- stained objects –> acidophilic or eosinophilic
What does hematoxylin (basic stain) bind?
Acidic structures and components
- (dye)+Cl-
- basic radical has the dye.
- heterochromatin, nucleolus, the rough endoplasmic reticulum, and sulfated GAGs
- stained objects –> basophilic
What does the stain mixture of hematoxylin and eosin (H & E) distinguish?
Nucleus from cytoplasm
What is epithelium?
- group of closely coherent cells that form cellular sheets
- cover and line the many surfaces and lumens of the body
- derived from all three germ layers of the embryo
Describe epithelial cells
- polyhedral in shape –> packing in layers or in three dimensions
- shapes: columnar, cuboidal, and squamous
- shape of the nucleus corresponds to shape of cell
- long axis of the nucleus parallel to long axis of the cell
- long axis of columnar cell perpendicular to basal lamina
- most epithelial cells rest on connective tissue
- in digestive, respiratory, and urinary systems called lamina propria
What are the small invaginations of the lamina propia that provide more area of contact called?
Papillae
What are basal laminae composed of?
type IV collagen
laminin
entactin
proteoglycans
Who attaches the basal laminae to the connective tissue?
Anchoring fibrils made of type VII collagen
Is the basal lamina visible with the light microscope?
No, only visible with the electron microscope where one can see a dense 20-100 nm thick layer of fine fibrils called the lamina densa
What type of fiber are associated with the basal lamina forming a reticular lamina in some tissues?
reticular fibers (type III collagen)
What is the basement membrane?
Thicker layer of basal lamina and reticular lamina visible in the light microscope
What structures contribute to cohesion of epithelial cells?
Cadherins and interdigitations of lateral membrane
What can be found in some epithelial cells such as those in the intestinal epithelium?
A junctional complex of zonula occludens (tight junction) and zonula adherens as well as desmosomes and gap junctions are found on the lateral surfaces
What is the role of the zonulae occludens?
Permeability
What do hemidesmosomes help do?
Bind some epithelial cells to the basal lamina
What are microvilli?
Fingerlike extensions found on the apical surface of epithelial cells that increase
surface area or move particles for example, in the small intestine
What do we call the microvilli and glycocalyx of the small intestine?
The striated border
What is the brush border?
A slightly longer complex of microvilli found on the proximal renal tubule
What are sterocilia?
Long, nonmotile extensions of the apical surface that are actually microvilli of the cells of the epididymis and ductus deferens of the male reproductive tract
Where else are cilia also found?
Respiratory system
What is each cilium associated with just below the apical plasma membrane?
A basal body
How many names can epithelia have?
2 or 3
What is the first name of epithelium?
number of cell layers
- simple
- stratified
- pseudostratified
What is the second name of epithelium?
shape of cells in the most superficial layer
- squamous
- cuboidal
- columnar
When is the third name of epithelium used?
If the free surface has cilia or keratin (ciliated or keratinized)
Define myoepithelial cells
Branched contractile cells found in secretory units of mammary, sweat, and salivary glands
____is another name for the simple squamous epithelium lining blood and lymphatic vessels
Endothelium
____is the term given the simple squamous epithelium lining body cavities such as the peritoneum
Mesothelium
When is the term epithelioid used?
For some tissues containing cells that are closely associated so that they resemble an epithelium
Describe the lifespan of intestinal epithelial cells
Renewed every 4 to 6 days by mitotic activity of stem cells located in the lower portion of intestinal glands (crypts of Lieberkuhn)
Describe the lifespan of skin cells
Replaced in most sites every 28 days and arise from stem cells in the basal layer of the epidermis
Describe the lifespan of other epithelial cells residing in complex glands
Can have a much longer lifespan
How do epithelial cells respond to stress?
By undergoing:
- atrophy
(death) - hypertrophy
(increase in size) - hyperplasia (increase in number)
- dysplasia (change in organization)
- metaplasia (transformation into another cell type)
An example of ___ can be seen in the ___ epithelium of the bronchi of heavy smokers that can be transformed into ___ epithelium
metaplasia; respiratory; stratified squamous
The skin is __
The heaviest single organ comprising 16% of total body weight
Describe functions of the skin
- mechanical and permeability barrier
- source of sensory and immunologic input
- regulator of homeostasis (body temperature and water loss)
- performs both endocrine and exocrine functions
- site of drug delivery for lipid-soluble substances
What is the skin composed of?
Epidermis
*extends epidermal pegs or ridges downwards
Dermis
*layer of connective tissue that includes dermal papillae
What is the hypodermis?
Not considered part of the skin, but rather binds skin to underlying tissues
What distinguishes thin skin from thick skin?
The thickness of the epidermal layer
Where is thick skin found?
palms and soles
*lacks epidermal appendages such as hair follicles and sebaceous glands found in thin skin that covers the rest of the body
What are the layers of the epidermis?
- Stratum basale – a single cell layer of stem cells
- Stratum spinosum – mitotically active prickle cell layer
- Stratum granulosum - non-proliferating cells with stained granules
- Stratum lucidum - clear layer seen only in thick skin
- Stratum corneum – keratinized cell “ghosts”
What are keratinocytes?
Keratinizing epidermal cells that are the predominant cell type
Where can you find keratin?
Assembled into keratin filaments (intermediate filaments or tonofilaments) in the stratum basale and stratum spinosum
Describe keratohyaline granules
- synthesized in the upper portion of the spinous layer
- dense, non-membrane bound masses of filaggrin and other proteins associated with keratin
- produce lamellar bodies that contain a lipid mixture that is discharged to form the epidermal water barrier
What are melanocytes derived from?
Neural crest cells
What are melanocytes located?
Stratum basale
Where is melanin synthesized and packaged?
Synthesized in the melanocyte and packaged in a melanosome
Melanin granules are phagocytosed by the ___ as they bud off of the tips of the ___
keratinocyte; melanocyte
Is the number of melanocytes the same in all races?
Yes
What are skin color differences due mainly?
Number and distribution of melanin granules in keratinocytes
What are Langerhans cells?
- antigen-presenting cells that are derived from the bone marrow that make up 2-8% of the epidermal cells
- component of SALT (skin associated lymphoid tissue)
- play a role in delayed-type hypersensitivity reactions.
Can Langerhans cells be distinguished in H & E sections?
No, but they can be selectively stained with gold chloride
Describe Merkel cells or epithelial tactile cells?
- mainly found in the stratum basale and are more numerous in thick skin
- can be associated with an expanded terminal bulb of an afferent nerve fiber
- along with neurite complex function as a sensitive mechanoreceptor in areas such as fingertips
