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196 Cards in this Set

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Functions of the epithelia
1. Protect
2. Barrier
3. Transport (absorb/secrete)
4. Synthesize
There are 4
Characteristics of epithelia
1. Continuous sheet of cells
2. No extracellular material between cells
3. Polarized (apex, base, lateral sides)
4. Avascular
There are 4
Shapes of epithelial cells
1. squamous
2. cuboidal
3. columnar
There are 3
Criteria for classifying epithelia
1. Shape of cells in apical layer
2. Number of layers
3. Modifications in apical plasmalemma (cilia, microvilli, stereocilia)
4. Presence of goblet cells
There are 4 criteria
Names for epithelial cell layers
1. Simple
2. Stratified
3. Pseudostratified
There are 3
Definition: Endothelium
Simple squamous epithelia that lines the heart, blood, and lymphatic vessels. Must ALWAYS be classified as enothelium instead of simple squamous epithelia.
Restricted to fluid pumping areas
Definition: Mesothelium
Simple squamous epithelia that line the pleural, pericardial, and peritoneal cavities. CAN be classified only as simple squamous epithelia
Name locations of this tissue
Definition: Goblet cells
Unicellular excocrine glands that secrete mucus. ONLY in simple and pseudostratified epithelia. Found in digestive and respiratory tracts, where lubrication is essential. Differential stain due to abundance of sugars in cytoplasm.
The difference between cilia vs. microvilli and stereocilia
-Sterocilia and microvilli are made of actin filaments
-Cilia are made of microtubules and attached to a basal body. They are the only visible structures under the light microscope
Composed of...
Difference: Keratinizing vs. Mucosal stratified squamous epithelium
-Keratinizing= apical layer dead; used in tissue that undergoes mechanical stress
-Mucosal= apical layer alive; used in tissues that need to be moist
Give definitions of both
Definition: pseudostratified epithelia
One layer of cells, all of which touch the base lamina but do not reach the free surface. Nuclei appear to be at different levels. Respiratory epithelia is an example.
Give example
How to delineate pseudostratified epithelia vs. stratified epithelia
Goblet cells are PRESENT in pseudostratified (and simple) epithelia, but are ABSENT in stratified epithelia
Presence/absence of something
Definition: metaplasia. Give example
Stress on epithelium causes it to be replaced by a more durable type of epithelium. Ex. Smoker's lungs. Healthy=pseudostratified columnar epithelium. Smoker=stratified squamous epithelium. Metaplasia is reversible
A condition cause by stress
Functions of the basement membrane
1. separate and attach epithelium to connective tissue
2. selective barrier
3. establish epithelia polarity
4. guide repair
There are 4
Layers of the basement membrane and where they come from
1. Lamina rara (secreted by epithlia)- containing laminin
2. Lamina densa (secreted by epithelia)- containing collagen type IV
3. Lamina reticularis (secreted by connective tissue)- containing collagen type III
*** #1&2 ONLY are referred to as basal lamina
There are 3
Sequence of connections between epithelium and basement membrane
Basal plasmalemmal laminin receptors (of epithelium)- Laminin (of lamina rara)- heparan sulfate proteoglycan (HSPG of the lamina densa)- type IV collagen (of the lamina densa)- HSPG (of the lamina densa)- type III collagen (of lamina reticularis)- connective tissue
Sequence contains two layers of HSPG
Definition: Alport Syndrome
Inherited disorder of the basement membrane. Affects kidney, eye, cochlea of ear. Defect on X chromosome
Do not need specific cause
Definition: external lamina
Basal lamina-like formations when any two tissue types are in contact with e/o. Surrounding cells are NOT polarized
Steps of wound repair
1. Epithelials lose polarity, collapse onto basement membrane and repair basement membrane
2. Epithelials become polarized along horizontal axis.
3. Collapsed epithelials divde.
4. Epithelials migrate across wound.
5. When cells on both sides meet, they reestablish original polarity and restore normal epithelium
There are 5 steps.
Definition: Urothelium
Transitional epithelium that change their shape depending on their function. Ex. in bladder, cells change shape from cuboidal/columnar to squamous
Give example
Definition: Cystinurea
The inability to transport the amino acid cystine from urine or intestine into the blood. Cystine stones form in the kidney.
Give both cause and clinical manifestation
Function of tight junctions
To selectively dictate what can pass between epithelial cells (in the paracellular pathway) and force certain molecules to go through cells. Tight junctions are a type of occluding junction and are found ONLY in epithelia. Made from the weaving of integral membrane proteins around the apex of the cell.
Interaction between two cells
Functional groups of cell junctions in the epithelium
1. Occluding junctions- seal cells together. Form barrier and control passage of molecules within the paracellular space.
2. Anchoring junctions- hold epithelia together
3. Communicating junctions- passage for communication signals
There are 3
Definition: adhesion belts
Hold epithelial cells together. Formed by a plaque in the cell wall attached to cadherins on the outside and actin filaments on the inside. Lies just basal of the tight junctions.
Definition: terminal web
Actin filaments and myosin that extend from the adhesion belt's plaque in a web that is below the apical surface of the cell. Provides the anchor for cilia, microvilli, and stereocilia.
Involved with adhesion belt
Definition: spot desmosomes
Hold adjacent epithelial cells together. Absorbs and dissapates the effects of mechanical stress. Occurs below the adhesion belt. Composed of plaques (desmoplakin, plakoglobin), keratin filaments (attached on cytoplasm side), and cadherins that bind the desmosomes to each other. Occur on lateral and basal sides (basally are called hemidesmosomes).
Types of cytoskeletal components
1. Actin filaments
2. Intermediate filaments
3. Microtubules
There are 3
Definition: Pemphigus
Person makes antibodies against one of desmosomal cadherin proteins. Antibodies break up desmosomes, causing blistering and leakage of body fluids. Only occurs in desmosomes of the skin.
Skin disorder
Definition: Junctional complex
1 tight junction, 2 anchoring junctions, adhesion belt, spot desmosome.
At apex of epithelia.
It has 4 components
What is the terminal bar?
What the junctional complex looks like under the light microscope. It looks like a dot at the apical extreme of the lateral surface of the epithelial cell.
Appearance of something under the light microscope
What are gap junctions?
Communication junctions between the lateral surfaces of epithelial cells. They permit chemical/electrical signals to pass between cells.
SHUT= high calcium ions, low PH
OPEN= low calcium ions, high PH
-Gap junctions are permeable, while tight junctions are only selectively permeable
These do NOT hold cells together
What is a gap junction composed of?
Gap junctions are made of 6 connexins that form 1 pore called a connexon. Gap is 2-4nm.
There are 6 of these integral membrane proteins
Definition: Kartagener's Syndrome
Congenital disorder where cilia are defective. Causes infertility and inability to clear upper respiratory tract of mucus.
Cilia involved
What is a hemidesmosome?
Anchoring junctions that attach the basal surface of an epithelial cell to the lamina rara of the basement membrane. Chemically distinct from spot desmosomes. Attached to the spot desmosomes via keratin filaments (intermediate filaments) Integrins function as the transmembrane linker protein between the basement membrane and plasma membrane.
At the bottom of an epithelial cell
Definition: Basal infoldings
Internal projections of the basal plasmalemma into the cytoplasm, used to increase surface area on the basal side of the cell (example: in saliva glands and in kidney, where they alter ionic concentrations)
Function like lateral interdigitations
What determines polarity of an epithelial cell?
The basement membrane
Think down
How do glands form during development?
Invagination of the epithelial cells
How do endocrine glands secrete their products?
Via the basal surface of the epithelia cell into the connective tissue below the basement membrane
Directly to the bloodstream
What is the parts of a multicellular exocrine gland?
1. Duct
2. Adenomere
2 parts
What classifies a compound gland?
If a duct branches. If there is a single duct, then it is classified as simple
It has to do with the duct
What are the different shapes of an adenomere (the body of a gland) called?
Tubular and alveolar/acinar (grape shaped). A gland can have one, the other, or either shape. If there are multiple adenomeres supplying a gland, it is considered branched.
2 types
What determines the complexity of a gland's morphology?
1. How much product is needed
2. Where it is needed
There are two reasons
Name the general categories of secretions that glands make
Serous, mucus, and mixed (of the aforementioned two); Consistency of the secretion is dependent on how much sugar is liked to the glycoprotein that is being secreted
There are 3
How can you tell, histologically, what type of secretion a gland makes?
By the stain- serous stains with eosin (mucus does not); Periodic Acid Schiff (PAS) only will stain mucus
By the position of the nucleus- serous secreting cells have rounded nuclei while mucus secreting cells have nuclei that are flattened and pushed to the wall of the cell membrane
There are two major ways
Name the methods of secretion
1. Merocrine glands- product released by exocytosis, very little cytoplasm lost (most exocrine glands are this type)
2. Apocrine glands- apex of cell is pinched off and a large portion of the cytoplasm and plasmalemma is lost (ex. mammary and sweat glands)
3. Holocrine gland- entire cell is secreted and dies, sebaceous glands are the ONLY ones of this type
There are 3
All connective tissues have these two major components...
Extracellular matrix and non-polarized cells; combinations of which determine the tissue's properties
What are the properties of the extracellular matrix and which materials give it those?
1. Elasticity from elastic fibers
2. Tensile strength from collagens
3. Resiliance from proteoglycans
The three important components of the ECM are ground substance, fibrous proteins, and water. 1 and 2 above properties are due to the fibrous elements. The third is a property of ground substance.
There are three major properties
The ground substance of the extracellular matrix is an amorphous gel composed of...
Proteoglycans and glycoproteins
2 things
Describe the structure of a proteoglycan molecule and its important features
A proteoglycan is composed of core proteins and glycosaminoglycans (GAGs), which are long, unbranched chains of repeating disaccharides with alternating amino and acidic sugars. The negative charge of the glycoproteins allows them to attract water and other ions and allows for their movement throughout the tissue when they are compressed.
"Bottle brush" configuration
What particular GAG associated with all proteoglycans of connective tissues and how does it differ structurally from other GAGs?
Hyaluronan (aka hyaluronic acid). In contrast to other GAGs (which are bound to core proteins), the ends of core proteins bind to the hyaluronan core via linker proteins. These giant aggregates of proteoglycans in the ground substance can bind to fibers of the ECM like collagen.
They form larger aggregates. Why?
As opposed to proteoglycans in their role to maintain structure in connective tissue, what is the use of glycoprotein in ground substance?
Glue- the binding domains on the glycoproteins can adhere to surface proteins of cells and other connective tissue components. The amount of protein is greater than the amount of sugar in these molecules.
Glycoprotein is also important in cell recognition and migration
What holds things together?
Name two types of adhesive glycoproteins in connective tissue
Laminin and fibronectin
One is found in the basement membrane of an epithelial cell, while the other is secreted by fibroblasts
What is the name of the glycoprotein found in cartilage?
What is the name of the glycoprotein found in bone?
Name the two types of fibrous elements in the ECM
Collagen and elastin
Describe the four major types of collagen and some of their various attributes
Types I, II, III, and IV all have a high degree of tensile strength. Type I and Type III collagen both are fibrils (of different diameters) that join together to become fibers. Type II only exists as a fibril. Type IV collagen forms a mesh-like network that can interact with the other types of collagen to increase connective tissue stability
Fibers, fibrils, meshes...
Describe the steps in the formation of collagen
transcription/translation--> alpha chains of polypeptide (in RER)--> 3 alpha chains=procollagen (RER)-->procollagen goes to Golgi and is exocytosed-->terminal peptides cleaved, tropocollagen formed--> tropocollagen can form a meshwork if it is collagen IV or it can form fibers if it is collagen I, III, or III
procollagen and tropocollagen involved
_____ makes up the lamina reticularis, which is secreted by fibroblasts. _____ is part of the lamina dense, which is secreted by the epithelia cells along with the lamina rara
1. Type III Collagen (which forms reticular fibers)
2. Type IV Collagen
Both are types of collagen
______ and ______ comprise elastic fibers.
1. Fibrillin- forms the template via microfibrils
2. Elastin- fills the template in. They are crosslinked, but appear more ordered when stretched.
The amount of elastic fibers in a given tissue determine its flexibility!
Fib... and ela...
Name two major sources of elastic fibers and why they produce them.
1. Fibroblasts to lend elasticity to connective tissue.
2. Smooth muscle that produce it in blood vessels, where the fibers form fenestrated sheets that can expand or contact so the tissue does not rupture
Elastic fibers are needed in ligaments and blood vessels. What produces tissues in those areas?
What causes scurvy?
The enzyme that hydrolyzes collagen residues (allowing for them to form stable triple helices from 3 alpha helices) cannot function due to a lack of dietary vitamin C. This leads to abnormal bone growth, poor fracture healing, and a tendency to bleed.
It has to do with collagen formation...
What is Ehlers-Danlos Syndrome?
An inherited disease that disrupts the synthesis of collagen. Patients with EDS have hyper-extensible, fragile skin
Global connective tissue disorder
What is Marfan's Syndrome?
An inherited disease where the patient has a defective fibrillin gene. Symptoms are long limbs, dilation of the ascending aorta and partial dislocation of the lens.
A person with a defective gene that codes for a component of elastic fibers.
What cell types normally populate connective tissues?
Fibroblasts (aka chondroblasts or osteoblasts, depending on their location), mast cells, macrophages, and adipocytes. They function in defense, support, metabolism, and tissue repair.
There are 4
Where do fibroblasts originate?
Fibroblasts, the cells of connective tissue that are responsible for producing the components of the extracellular matrix, originate from mesenchymal cells with an embryonic supporting tissue known as mesenchyme. They remain fairly genetically adaptable throughout their lifespan.
Mesoderm becomes what type of tissue?
What two receptors do macrophages have in order to recognize antigens?
Fc and C3. Fc recognizes the fragment c portion of antibodies, while C3 recognizes complement. Antibodies and complement opsonize an antigen, coating it so that a macrophage can recognize and engulf it.
A macrophage must recognize antibodies and complement. How?
What tissue do mast cells and macrophages originate from?
Bone marrow. Pre-macrophages are call monocytes.
B cells also originate here.
Name some of the materials that mast cells release during an inflammatory response.
Histamine, slow-reacting substance of anaphylaxis, eosinophil chemotactic factor of anaphylaxis, and heparin. The Fc region of antibodies become attached to receptors on mast cells. Antigens attach to these and crosslink the antibodies, causing the mast cells to degranulate and trigger the inflammatory response.
There are 4 main ones
Name the three categories of nonspecialized connective tissue and how they differ.
1. Loose connective tissue- always irregular, elastic and collagen fibers are small, lots of ground substance and lots of cells
2. Dense regular CT- collagen fibers are larger, there are fewer cells and less ground substance; found in area where the directionality of mechanical stress is inconsistent
3. Dense regular CT- fibers oriented in parallel, least amount of ground substance and fewest cells (material that comprises tendons and ligaments)
There are three types and differ due to their function.
What types of adipocytes are there?
White adipocytes and brown adipocytes. White predominate in adults, where they function in energy storage and production, thermal insulation, organ positioning, and shock absoption. They have a single, large lipid droplet in their cytoplasm, which displaces the nucleus to the cell wall. Reticular collagen III fibers bind these cells together.
Brown adipocytes predominate in infants and have the additional function of producing heat. They have multiple lipid droplets in their cytoplasm as well as many mitochondria and a more centally located nucleus. They have sympathetic nerves running through them to trigger a heating response.
They are named by color
From what cell type do adipocytes arise?
Mesenchymal cells
Similar to fibroblasts
How does cartilage differ from other connective tissue?
Lack of blood vessels, nerves, and lymphatics. It relies heavily on diffusion.
It is the lack of several features
Functions of cartilage
1. Support soft tissues
2. Shock absoption
3. Provide structural framework
4. All skeleton to move smoothly against each other
5. Give basic skeletal model
There are 5, most of which have to do with bone
Definition: perichondrium
A capsule-like sheath surrounding the cartilage that connects cartilage to the tissue it supports and provides cells for its regeneration. (Dense irregular CT usually surrounds growing cartilage)
"peri-" here is similar to how the prefix is used in muscle tissue
How does cartilage form?
1. Appositional growth- fibroblasts embedded in the connective tissue of the perichondrium differentiate into chondroblasts. Chondroblasts produce the cartilage matrix which surrounds them (the space they occupy is called a lacuna) and comprises the new surface. Once the chondroblast is surrounded with matrix, it is called a chondrocyte.
2. Interstitial growth- a cluster of chondrocytes (an isogenous group) forms when chondrocytes divide. Each cell surrounds itself with a matrix and the isogenous group separates.
There are two types of growth
What molecules comprise the cartilageous matrix?
Hyaluronan, collagen type II, chondroitin sulfate, keratan sulfate
There are 4 things
Definition: chondronectin
Chondronectin is the glycoprotein that makes chrondrocytes adhere to the cartilage matrix. (analogous to fibronectin in connective tissue)
Similar to fibronectin
Name the three types of cartilage
1. Hyaline
2. Elastic
3. Fibrocartilage
There are 3 types
Describe hyaline cartilage. How does it differ from elastic cartilage?
Hyaline cartilage has a homogenous appearance due to the amorphous matrix. The type II collagen that is part of the matrix does not form fibers (hence the amorphous appearance). Hyaline is the model for bone formation, however it persists on joint surfaces, the ventral connections of the ribs to the sternum, and the trachea and larynx.
Elastic cartilage only differs by the presence of elastic fibers. It exists in the pinna of the ear, the walls of the external auditory meatus, the nose, and the epiglottis.
The presence of one additional type of molecule is the only difference
Definition: chondroclasts
Cells that are responsible for destroying the cartilage that was previously used as the model for bone formation. They are derived from monocytes and are huge multinucleated cells
"-clast" implies destroy
What happens during osteoarthritis?
Chondrocytes lose their ability to proliferate as well as their ability to produce proteoglycans in the matrix of the hyaline cartilage on the articular surfaces of joints.
Hyaline cartilage breaks down. Why?
What comprises fibrocartilage?
Fibrocartilage merges with dense regular CT. Chondrocytes are either alone or in isogenous groups embedded in type I collagen fibers. The collagen I fibers are highly organized by running parallel to each other, in a woven arrangement, or in a herringbone pattern. There is NO perichondrium and there is little extracellular material.
This tissue is usually found in intervertebral disks and replaces hyaline cartilage when it is damaged. The key to spotting this type of cartilage is that the chondrocytes are round.
In what ways does fibrocartilage differ from hyaline cartilage?
What do proteoglycans do in cartilage?
Allow for nutrient and water diffusion into the avascular tissue. Depending on the arrangement of proteoglycans, the water is organized differently. The proteoglycans resist compression due to their highly negative charge.
Collagen provides structure and support, but how is cartilage "fed" if it is avascular?
Definition: superficial fascia
A subcutaneous tissue that contains varying amounts of fats and collagen fibers that attach to the dermis and blend with the deeper investing fascia.
Definition: investing fascia
The outermost tissue surrounding skeletal muscle.
What are Cooper's ligaments?
They are ligaments found in the mammary glands which are exaggerated retinacula cutis with adipocytes in between. They attach to the skin and can produce a "dimple" on the breast if the ligaments are occluded by a cancerous tumor.
In the breast
What are the functions of the skin? (5)
1. barrier
2. sensory
3. to regulate body temp.
4. produce vitamin D
5. eliminates waste
Name 5
What are the two major types of skin and where are they found?
Thick (on the palms and soles of feet) and thin (everywhere else)
Classified by thickness
From where is the dermis of the skin derived?
The dermatome, which is derived from embryonic somites.
The two major layers of the skin are the _____ and the _____.
Dermis and epidermis
The dermis contains the vasculature and innervation of the skin, which get smaller as they approach the epidermal boundary. The dermis may also contain hair follicles and glands in thin skin.
The epidermis is keratinized stratified squamous epithelium that protects the outermost surface of the body.
The two layers of the dermis are the _____ and the _____.
papillary and reticular
Describe the papillary layer. What type of collagen is found here?
It consists of a layer of loose connective tissue (collagen type I). The dermal papillae interdigitate into epidermis in areas known as epidermal ridges. The more abrasions the skin undergoes, the more dermal papillae there are.
Projections of the dermis into the epidermis.
Describe the reticular layer of the dermis. What type of collagen is found here and how does it differ from the papillary layer?
The reticular layer is made of dense irregular connective tissue (unlike the papillary layer where it is loose) with larger collagen type I fibers in an ordered arrangement. The collagen bundle arrangements are known as Langer's lines.
More density...
The reticular layer of the dermis is attached to a lower layer called the _____.
Hypodermis, a layer of loose connective tissue that contains varying amounts of adipocytes.
"Hypo-" means beneath
From where is the epidermis derived?
From the surface ectoderm.
Name the five layers of the epidermis.
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum
5. Stratum corneum
Definition: keratinocytes
They are the predominant cells of the epidermis that go through a predictable pattern of development until they are sloughed off the surface of the epidermis. The purpose of these cells is to have a constant supply of tough cells that resist wear and are watertight for epithelial turnover.
Keratinizing cells are born to die
What happens in the stratum basale? What are the layer's characteristics?
Stratum basale is a single layer of cuboidal or columnar cells that contact the basement membrane (top of the dermis). The undifferentiated keratinocyte stem cells are found here, held in place by hemidesmosomes. Keratinocytes begin their differentiation here. All mitosis is initiated here and usually ends here as well.
What shape are the cells and what is their function?
What are the characteristics of the stratum spinosum?
It has a spiny appearance due to the great number of spot desmosomes holding the cells together. The cells also start to have a "flat" apearance that is a classic keratinocyte feature. They also start to accumulate a few granules in their cytoplasm. This layer is 2-10 cell layers thick, depending on the thickness of the skin.
Spinosum=spiny. What make them spiny?
Describe the stratum granulosum.
The keratinocytes in this layer continue to flatten and are still held together by spot desomsomes and internal keratin filaments. These cells develop abundant granules filled with various substances.
What types of granules are in the stratum granulosum of the epidermis?
1. Lamellar granules are membrane bound and contain glycolipids that form the extracellular water barrier.
2. Homogenous deposit granules are not membrane-bound and contain a chemical that is used to coat the inner surface of the plasmalemma with a protein layer called involucrin. This layer forms the intracellular water barrier.
3. Keratohyalin granules are also intracellular and surround extensive bundles of keratin filaments. This keratinazation further strengthens the keratinocyte against mechanical stress.
There are 3, one membrane bound, two that are not
Where do cells in the epidermis die and why?
Along their way in the stratum granulosum because the products they produce essentially suffocate the cell. The keratinocytes are on a suicide mission to the surface of the epidermis in order to protect the tissues within. Organelles, including the nucleus, break down until the keratinocytes become nothing but flattened sacs.
The cells commit suicide
Describe the stratum lucidum.
This layer is present ONLY in thick skin. Cells are dead and appear glassy and flat, because they are essentially flattened sacs of involucrin and keratin held together by spot desmosomes. This layer is 4-6 cell layers thick.
This layer is dead
What are the characteristics of the stratum corneum?
This is the most superficial layer of the epithelium that varies widely in thickness. It is composed of dead, keratin-filled squamous cells that form a barrier to mechanical stress and microorganisms.
What characteristics are good for an exterior layer?
Definitions: desqaumation
Dead keratinocytes are sloughed off of the surface. The last step in the life of a keratinocyte.
Dead cells must be kicked out somehow!
What are Merkel cells?
The "touch receptors" in the epidermis. They attach to keratinocytes with desmosomes, contain neurosecretory granules and contact sensory neurons in the basement membrane. Located in BASAL layers of the epidermis
They are how the epidermal layer can sense touch.
What are Langerhans cells?
Antigen presenting cells that migrate from the bone marrow into the stratum spinosum. They have numerous processes, but do NOT form junctions with keratinocytes. They migrate out of the epidermis in order to present antigens to T cells. Can be destroyed by UV rays.
They are a component of the immune system
What are melanocytes and from where are they derived?
Melanocytes are derived from neural crest cells that migrate into the epidermis. Located in the stratum basale, they are responsible for pigment formation from the melanosomes (melanin-containing granules) in the cytoplasm. Melanosomes are released from the melanocyte and go into the surrounding keratinocytes. They are attached via hemidesmosomes to the basal lamina, but not attached to keratinocytes.
Melanin lends a skin its pigmentation
What causes the differences in skin pigmentation?
Different types of melanin are produced by different races and the lifespan of the melanin varies depending on race.
It is not due to the number of melanocytes!
Define the two types of skin cells carcinoma and how they differ
1. Basal cell carcinoma- stem cells from the stratum basale grow out of control and invade the dermis. This type rarely metastasizes.
2. Melanoma- melanocytes grow out of control and penetrates the dermis. This type is very invasive.
Which cells have the greatest carcinogenic potential?
How does a hair follicle form?
The interaction between the epidermis and the dermis causes the epidermis to invaginate into the dermis. A tuft of loose connective tissue and vasculature called dermal papilla stimulates the keratinocytes and melanocytes to produce hair. Cells that become keratinized, pigmented and die. Hair color depends on the type of melanin produced.
What happens during the development of baldness?
Long hair follicles are converted to short hair follicles that eventually die and no longer produce hair.
What happens to the individual hair follicles to make this happen?
What the structures are associated with hair follicles and what do they do?
1. Arrector pili muscles- small, smooth muscles that attach to the base of the hair follicle and the basement membrane of the epidermis. Sympathetic nervous system stimulates these muscles to produce goosebumps.
2. Sebaceous glands- an outgrowth of the hair follicle, which serves as its duct. The cells of this gland produce sebum, which fills the cells and the entire cells is secreted. (holocrine gland). Sebum is broken down after secretion into fatty acids that irritate the skin.
3. Sweat glands- responsible for thermoregulation and excretion of waste products.
Goosebumps and zits
Name the two types of sweat glands and how they differ.
1. Eccrine sweat glands- the most common. They are exocrine glands that have the secretory portion (adenomere) that is pseudostratified epithelium deep in the dermis or hypodermis. These cells produce watery sweat (glycoproteins, water, ions) that myoepithelial cells cel force to the surface. The ducts are lined with stratified cuboidal epithelium.
2. Apocrine sweat glands- secrete into hair follicles (whereas eccrine go directly to the epidermis) of the armpit, nipples and genitalia. They are innervated by a different subset of sympathetic neurons that trigger when we are nervous. Their secretion is more viscous.
They differ in location and function
What are the types of innervation in the skin?
1. Motor from the sympathetic nervous system. The arrector pili muscles and smooth muscles of the blood cells are used in thermoregulation.
2. Sensory innervation, with several types of receptors
Somatomotor neurons stop before this layer, but the other two types continue to the surface
What are the two categories of sensory receptors in the skin? Describe them
1. Unencapsulated receptors- which are free nerve endings, which sense pain and temperature and are covered in Schwann cells that end in the stratum granulosum, and Merkel endings, which sense touch and end in the basal layers of the epidermis
2. Encapsulated receptors- includes Meissner's corpuscles (highly sensitive to light touch) that have dendrite spirals among Schwann cells and Pacinian corpuscles (sense vibrations) that have a myelinated axon surrounded by flattened layers of cells in the dermis or hypodermis
They are classified depending on how the fibers are covered (not the axons, which are always myelinated)
The mammary gland consists of 4 parts. Name them
1. glands
2. subcutaneous connective tissue
3. adipose tissue
4. nipple
Describe the development of the mammary glands.
Lactiferous sinuses that open to the nipple continue into lactiferous ducts as they go deeper into the tissue. The sinuses are lined with stratified squamous epithelium, which changes to stratified cuboidal and then stratified columnar epithelium as you go further into the ducts. Myoepithelial cells are at the base of the epithelium and contract to produce secretion. Estrogens produced during puberty cause the lactiferous ducts to branch and form interlobular ducts, that further branch to form intralobular ducts. These ducts are lined with simple cuboidal epithelium. Adipose tissue and connective tissue accumulate as well.
Puberty triggers the development of the the glandular system. How so?
Which cells produce milk during pregnancy?
The aveoli, interlobular ducts and intralobular ducts all produce milk, which is pumped out via myoepithelia cells. The order goes aveoli->intralobular duct->interlobular duct
They are the structures at the end of the lactiferous ducts.
Definition: colostrum
A watery, protein- and antibody-rich fluid that is a merocrine secretion. Oxytocin forces the myoepithelial cells to contract and push colostrum from the aveoli through the ducts and out the nipple in a process called letdown. Prolactin release is necessary for this process to occur and is inhibited by progestrone and estrogen.
Where to oxytocin and prolactin come from? (as well as growth hormone)
The hypothalamus (prolactin) and pituitary (oxytocin)
In the brain
Which organs produce progesterone and estrogen?
The ovary and the placenta
NOT in the brain
How does lactation work?
Prolactin-inhibiting hormones, estrogen, and progesterone levels all drop enough for prolactin to be produced by the anterior pituitary. This stimulates milk production in the aveoli while oxytocin stimulates muscle contractions that eject the milk. Protein (produced in the RER) and lactose (produced in the Golgi) are secreted together via merocrine secretion. Lipids are made in the SER and release via apocrine secretion.
What hormones are involved and how is milk made?
Definition: anastomoses
End to end continuity of two vessels
Lymph and blood vessels do this
Why are lymphatic vessels more permeable than blood capillaries?
The gap between adjacent endothelial cells open when interstitial pressure increases. Particles up to 24 uM can enter the lymphatic capillary.
Think junctions between cells
A condition that results from the blockage of the lymph system. Plasma proteins that escape from the capillaries cannot be returned to the blood supply and instead remain in the tissues.
Lymphatic filariasis causes this.
Since the lymphatic system has no pump, how does lymph move?
Valves (which makes sure movement is unidirectional), movement of adjacent structures, and negative intrathoracic pressure all propel lymph to where it is supposed to go.
There are 3 major ways
Describe the pathway of lymph
Fluid that has escaped from the capillaries is moved along into lymphatic vessels. They dump into larger collecting ducts. These converge until they reach a series of lymph nodes, where antigens are removed and lymphocytes are produced. The remaining fluid is channeled into veins, where it is returned to the bloodstream.
What are the two major collecting ducts for the lymph system called?
The right lymphatic duct and the thoracic duct. The regions of the body that are drained by these are NOT symmetrical! The thoracic duct drains considerably more of the body's lymph. Both deliver their lymph to the junctions between the jugular and subclavian veins at the base of the neck. (The thoracic on the left)
One is the opposite of left and the other begins with a th____.
Where does superficial lymph drain from the skin and subcutaneous tissue when it is from below the head and neck?
All lymph from the skin/subcutaneous drains into the axillary nodes if it is above the belly buttom (umbilicus). Anything below the umbilicus drains into the inguinal nodes.
Armpit and groin
Give one example of cutaneous lymph drainage and explain how it works.
The mammary gland. Most lymphatic channels pass laterally to a series of axillary lymph nodes. However others can go one of several other routes: medially to parasternal nodes, superiorly to supraclavicular nodes, and inferiorly to the abdominal wall and other lymphatic channels.
It looks like a giant net of lymphatic ducts over the breast.
Explain the drainage pattern of deep lymph. What qualifies as deep?
Deep lymph is from the abdominal and pelvic organs. These drain to iliac and intestinal nodes or to nodes associated with individual visceral organs. These eventually go into the thoracic duct.
What happens to lymph from the stomach, pancreas, spleen, and liver?
What is the importance of supraclavicular nodes? What pathological meaning is there when they are enlarged?
Supraclavicular nodes are the final set of lymph nodes before the lymph gets returned to the bloodstream. They are on either side of the body. Right side enlargement may indicate problems in the thorax. Left side enlargement indicates problems in the thorax, abdomen, or pelvis.
They are also known as sentinal nodes. Why?
Describe perfusion fixation vs. immersion fixation
In perfusion fixation, the vasculature is pumped through with saline to remove the blood, then the fixative is pumped though. In immersion fixation, the cells are directly put into the fixative.
One involves the pumping of fluid
What is the importance of the plane of section artifacts and how do you choose to name tissue accordingly?
Wherever you take the cross section may go through different dimensions of an organ or tissue, hence the "artifacts" left behind after cutting vary to a certain degree. The thinest layer of cells is where you should look to define a tissue, since this is probably the optimal place to take a cross section for that particular tissue or organ.
How does the cross section you take when making a slide make a difference.
PAS stain looks for...
Sugars, hence why goblet cells are so easy to spot.
It turns pink.
Toluidine blue stains ____ a dark blue.
Nucleic acid. Specifically, chromatin show up intensely. Nuclei of cells stained with this procedure show up clearly.
The brain of the cell
A hematoxylin and eosin stain will dye serous secretions ____ly and will dye mucous secretions ____ly.
Darkly and lightly. In order to stain mucous secretions, you must use a PAS stain for sugars.
Adenomeres of serous secreting glands will have nuclei that are ____ and toward the ____ of the cell. However, mucous secreting adenomere will have ____ nuclei that are shifted to the _____ of the cell.
1. rounded, bottom
2. flat, periphery
These differences are fairly easy to distinguish in a stain.
Their locations are similar, but the morphology of their nuclei are drastically different.
How does the epithelial cell morphology change as you go down ducts of increasing diameter?
Simple squamous--> simple cuboidal--> simple columnar or pseudostratified columnar (many times with goblet cells)
How do you think that the supporting cells for a larger duct must be versus that for a smaller duct? (especially if the layer is only a simple one)
How do you distinguish between myoepithelial cells and the cells of the aveolus in the mammary gland?
Myoepithelial cells have elongated nuclei that are parallel to the basement membrane of the epithelium.
Key is to look at the nuclei!!
Describe the process of myofiber formation after the migration of the somites.
The myotome cells (somites) form all skeletal muscle. After migration, the cells are called myoblasts. These cells divide and start to fuse with each other to form a myotube. The myotube is a giant, multinucleated cell where the centrally located nuclei can no longer divide. The myotubes synthesize the contractile proteins (myosin and actin) and they organize to form sarcomeres. The sarcomeres link together to form myofibrils that fill the myotube and displace the nuclei to the periphery. This increase in diameter is called hypertrophy. This is final form is classified as a myofiber.
Myoblast-> myotube-> sarcomere formation-> myofibrils-> myofiber
What is the difference between myofibrils and myofibers?
Myofibrils are subcellular organelles that are not membrane bound and run from one end of the myofiber to the other.
Myofibers are the multinucleated cells that synthesize myosin and actin.
One is a part of the other.
What are satellite cells on myofibers? What is their function?
The satellite cells are myoblasts that do not fuse the the myofiber during development. They act as reserve cells that wait for muscle tissue to be damaged before they kick into action and repair the tissue. They are a type of adult stem cell. They remain between the myofiber sarcolemma and the external lamina. Skeletal muscle can regenerate completely because of these cells.
Stem cells
Definition: endomysium
The layer of loose connective tissue that surrounds each myofiber. It is a blending of the reticular lamina of the myofibers. At least one capillary runs parallel to each myofiber within the endomysium.
Nearest to the myofiber
Definition: perimysium
Myofibrils are grouped together into bunches of 10-50 that are bundled into coarser wrappings of loose connective tissue that is the perimysium. These bundles are called fasicles.
The fasicles can contract and relax independently of each other and provide paths for larger vessels.
Groups myofibers together
Defintion: Epimysium
The epimysium bundles fasicles together into the named muscles groups that we know. It is made of dense irregular connective tissue.
Outermost layer of muscle
What is the myotendinous junction?
It is where tendons and muscles meet. The tendons are made up of dense, regular connective tissue that transmits contractile force of the muscle.
What tendons generally do
Describe the nuclei of mature myofibers.
They are always found at the perimeter, underneath the sarcolemma. They have intermediate chromatin density and are shaped like long, slender rectangles with rounded corners. The nuclei always run in parallel with myofiber.
Shape, position, density of nucleic acid
Each myofiber has a single axon that terminates on it at a single _____ _____, where the nervous signal that stimulates contraction meets the muscle fiber.
Neuromuscular junction
They usually are located in the middle of myofibers and send branches out through the connective tissue so that each individual myofiber is reached.
What is the synaptic cleft?
A concavity of the sarcolemma where the axon meets the myofiber. The external lamina of the axon extends throughout the cleft area.
What are junctional folds?
The foldings of the sarcolemma that increase its surface area.
Name the neurotransmitter that stimulates muscle contractions.
Define a motor unit
One motor neuron and all myofibers it innervates. All myofibers of a motor unit are identical (i.e. type of myosin, profile of metabolic enzymes). The type and number of motor units recruited for a particular task depend on the amount of force (strength) or finesse (fine motor control) needed.
What are the characteristics of red fibers of muscle tissue?
Red fibers have slow contraction times, are resistant to fatigue, depend on oxidative phosphorylation to generate ATP, have many mitochondria, and lots of myoglobin.
Endurance muscles
What are the characteristics of white fibers of muscle tissue?
White fibers have fast contraction times, fatigue easily, depend on anaerobic glycolysis for ATP, have few mitochondria, and little myoglobin. They have LARGE stores of glycogen
Quick muscles
What are the characteristics of intermediate fibers of muscle tissue?
They have a mixture of the endurance characteristics of red fiber and the quick characteristics of white fiber.
Red + white
How can muscle fibers types be distinguished?
An enzymatic reaction for myosin ATPase that changes the color of the myofibers. Red fibers stain the LEAST dark, while white fibers appear the darkest.
Myosin ATPase
Describe the organization of muscle from the largest unit to the smallest
Muscle--> fascicles (bundles of myofibers)--> myofiber (multinucleated cell)--> myofibrils-->sarcomeres (smallest contractile units of the myofibril)
Delineate the bands of the sarcomere. What does each contain?
1. I band- contains thin filaments (actin), appears light
2. A band-contains thick filaments (myosin), appears dark
3. Z disc/line-where thin filaments crosslink, appears as a line in the I band
4. M line- where thick filaments are crosslinked, appears as dark line in the middle of the H band.
5. H band- part of A band free of thin filaments when muscle is relaxed, appears as light band in A band
Bands and lines of the sarcomere
Where are the organelles of the myofiber located?
At the poles of the nuclei. There are few or no sarcomeres here.
Where are there no sarcomeres?
In striated muscle, where is the myosin located?
The A band. This is where myosin overlaps with actin and it stains darkly.
Describe the composition of myosin and how it assembles in the sarcomere.
It has 6 subunits- 4 light chains and two heavy chains. The paddle-shaped heads are actin binding sites and they contain an ATPase enzyme. The hinge regions are where the head bends during a contraction. Myosin self-assembles into thick filaments that interdigitate their tails, so that for any two myosin, their heads are point in opposite directions. The middle third of the thick filament is bare, but the two ends appear rough due to the head pieces sticking out from the surface.
How are the heads and rest of filament arranged? What enzyme does the head contain?
How do different myosin isoforms play a role in the muscle scheme?
The isoforms belong to a multigene family and each has a distinct ATPase activity. Each has a different associated velocity and therefore makes up the differnt fiber types (i.e. fast, slow, etc.) Many types can make up a single myofiber.
Different types of muscle fibers (fast, slow, etc.)
What is the M band and what happens there?
The M band is the darkest region in the middle of the A band. This is the place where thick filaments are held in their arrangement by the middle of their myosin bare region.
In the middle of the A band
What materials compose the I band?
Actin, tropomyosin, troponin
Actin is only one of the three
What types of actin are there in the I band and how do they differ?
1. G-actin, which is globular
2. F-actin, which is filamentous. It is made of two alpha-helices twisted around each other
There are two types, differentiated by protein structure
Describe the I band and the relationship of the Z band within it.
The I band is where there are only thin filaments. Actin filaments extend perpendicularly from both surfaces of the dark Z band that is in the middle of the I band. Tropomyosin and troponin complex with the actin to complete the thin filament.
Arrangement of actin is perpendicular to the Z band
Describe tropomyosin. What is its function?
It is a slender, rod-like protein that fits into the grooves of the actin filament. It prevents the myosin from binding to actin.
No myosin/actin interaction.
What is the function of troponin and how does it work?
Troponin is a calcium sensitive regulatory protein that binds to thin filaments at regular intervals. When bound to calcium, the troponin's conformation changes and it moves tropomyosin out of the grooves of the actin filament. This exposes the myosin binding site and the muscle contraction can occur.
Allows for a contraction when bound to a particular molecule
simple columnar epithelium with microvilli and goblet cells
Name the tissue in this picture and be complete
Locate the structures of the epithelium here. Be specific. Name the tissue as well.
See the circled structures
Where is the H band and what happens to it during a contraction?
The H band is the light band in the middle of the A band when the sarcomere is relaxed. This is where only myosin is found (NO actin). The H band disappears during a contraction because the myosin pulls the actin toward the M band (as the heads moves in the + direction of actin).
In middle of A band, but it is not the M band
What are T-tubules?
T tubules are narrow tubular invaginations of the sarcolemma at the junction of the A band and the I band (in skeletal muscle). They penetrate the sarcoplasm perpendicular to the myofibers. They look like bracelets and they wrap around EACH myofibril's A/I junction.
Bracelets around sarcomere
What makes up the triad seen in a sarcomere?
The triad is made up of a single T-tubule at the A/I junction that is flanked on either side by sarcoplasmic reticulum cisterns called lateral expansions. This is the diagnostic feature of skeletal muscle at the electon microscope level.
T-tubule and cisterns
How do the T-tubules function in a muscular contraction?
The T-tubules carry the action potential that generates a contraction along to the deepest sarcomeres of the myofiber from where the potential originated- the neuromuscular junction. This assures that the potential is carried in a single, synchronous wave that causes the contraction of successive sarcomeres that travels down the myofiber.
Waves of sarcomeres contracting...
What is the sarcoplasmic reticulum in skeletal myofibers and what is its function?
The sarcoplasmic reticulum is a discontinuous sleeve that encloses each myofibril and runs from T-tubule to T-tubule. This structure, which is akin to the smooth endoplasmic reticulum, regulates calcium concentrations. Upon stimulation from an action potential, the SR releases calcium into the sarcoplasm and generates a contraction.
Stores calcium
Describe the process of striated muscle contraction at the cellular level from action potential to completion.
An action potential travels from the motor neuron to the neuromuscular junction at the myofiber. Acetylcholine is released into the junctional folds of the NMJ, where it binds to a receptor in the sarcolemma. Sodium enters into the sarcoplasm via transmembrane ion channels and the membrane depolarizes. The T-tubules carry this sodium action potential to the interior sarcomeres. This action potential causes the sarcoplasmic reticulum to release calcium into the sarcoplasm where it binds to troponin. The troponin changes its conformation and removes with it the tropomyosin from the actin binding site. The myosin head, an ATPase, can then bind actin. The hydrolysis of ATP causes the myosin to straighten out, while the release of the inorganic phosphate allows it to bind to actin again, and the release of ADP causes the power stroke. The binding of a new ATP causes the myosin head to once again release the actin filament and the process repeats. This continues until calcium is removed from the sarcoplasm and the troponin moves the tropomyosin back into place.
NMJ-> T-tubule-> sarcoplasmic reticulum-> sarcoplasm-> motion in the sarcomere
What is a muscle spindle and what does it do?
A muscle spindle is a sensory receptor that monitors both the length of the muscle and the rate of the contraction.
It is a type of sensory receptor
What is the structure of a muscle spindle?
Each spindle is surrounded by the perineurium layer. Inside this sheath are intrafusal fibers. There are two types of intrafusal fibers- nuclear bag (all nuclei located in one, midfiber enlargement) and nuclear chain fibers (nuclei lined up single file down center of fiber).
Intrafusal fibers
Where is smooth muscle predominantly found?
Walls of vascular system, digestive, reproductive, respiratory, and urinary systems.
What are the physical features of smooth muscle cells?
They form long, slender spindles whose only organelle is the cigar-shaped nucleus with a smooth border in the middle of the cell. There is very little extracellular space or connective tissue. When contracted, the sarcolemma and nucelar membrane are corrugated like an acordion. They can be found as single cells or slender groups of a few cells. They are linear. In walls of vasculature, they exist grouped together as long, overlapping helical bands that wind around tubes. Smooth muscle depends on connective tissue for nutrition and for transmission of the force they generate.
How does it differ from striated muscle?
What are the three layers of connective tissue that surround smooth muscle and what do they consist of?
1. Endomysium- type III collagen fibrils secreted by smooth muscle
2. Perimysium- myocytes organized into helical bands that are separated from each other by this layer, which contains nerves and vessels
3. Epimysium- entire smooth muscle structure encased in dense CT that allows for slippage planes between muscle bundles
Same as striated muscle
What are the differences in vasculature of the smooth muscle versus that in striated muscle?
Smooth muscle has much less vasculature, since it has less metabolic requirement for nutrients.
Smooth muscle uses less energy
What are the two classes of smooth muscle?
Unitary (viceral) smooth muscle and multiunit (vascular) smooth muscle
One part and many parts...
Describe unitary smooth muscle and where it is found.
It is found in the urinary, reproductive and digestive tracts.
A single nerve ending innervates many myocytes, though they are only partially dependent on innervation. Myocytes can contract spontaneously in response to stimuli such as stretching. Groups of myocytes, known as pacemaker regions, initiate action potentials. Adjacent monocytes are connected via gap junctions (nexuses) and organized into fasicles. There is electrical continuity within the entire fascile. A pacemaker region exists in a fasicle at the cranial end.
One nerve innervates many myocytes
Describe multiunit smooth muscle and where it is found.
It is found in ciliary muscle, the pupil, the eyelid, and the blood vessels.
Here, one neuron innervates a few myocytes with simple neuromuscular junctions. Myocytes cannot function without innervation and there are no gap junctions between cells that carry the action potential. The myocytes are organized into motor units- one neuron and all of the cells in innervates. There are no pacemaker regions and the cells rely exclusively on the motor nerve for impulse.
One nerve innervates few myocytes
Describe the fine structure of smooth muscle.
The sarcoplasm is dominated by thin actin filaments that attach at one end to the dense bodies found throughout the sarcoplasm. Most organelles are found at the poles of the cells except mitochondria, which are found throughout. There are thick filaments of myosin that link the actin filaments to each other. The dense bodies, made up of alpha actinin, act as the "Z bands" of smooth muscle structure. Desmin filaments, a type of intermediate filament, provide structural support and anchor into these dense bodies at both ends of the filament. The outer layer of each myocyte has a complete external lamina over the plasmalemma, but very little vasculature is found in the endomysial tissue.
Thin filaments, desmin filaments, thick filaments...
What is the difference between contractions of smooth muscle versus striated muscle?
Smooth muscles contract much more slowly. Unitary muscle is particularly slow but with a much greater force/weight ratio than striated muscle. These contractions can even last for days!
Speed of contraction, force of contraction, length of contraction
What happens during the contraction of smooth muscle?
The myocyte is depolarized and extracellular calcium enters the sarcoplasm. Calcium bind with calmodulin (a protein) and then this complex activates the myosin light chain kinase that phosphorylates myosin. Myosin then binds actin, which activates the actin-myosin ATPase. The energy from ATP changes the conformation of myosin and allows the myosin and actin filaments to slide past each other. Myosin becomes dephosphorylated upon removal of calcium, which detaches myosin from actin. NOTE: Calcium acts on myosin in smooth muscle and on actin (troponin) in striated muscle.
Calcium causes phosphorylation of myosin directly
Are smooth muscle cells capable of regeneration?
Yes, upon injury or even in the cycle of their lifespan (i.e. the uterus), they can enter the mitotic cycle again.
How does smooth muscle cause hypertension?
From prolonged contraction of the vascular smooth muscle.
Long contraction
What is an aneurysm?
A ballooning of the vessel due to weakening of the smooth muscle in the wall of the vessel.
Ballooning of vessel
What is Hirschsprung's disease?
A congenital defect where the terminal portion of the intestine is not innervated by smooth muscle.
Congenital smooth muscle defect
The only two types of cells that make up the nervous system are ____ and ____.
Nerve cells (cells that transmit electrophysiological properties) and the cells that support them (cells that maintain the chemical environment and produce insulating material)
Those that carry electric impulses that those that do not
What nerves make up the peripheral nervous system?
1. Spinal nerves (innervate body wall of trunk and limbs)
2. Cranial nerves (innervate head; embryonic nerves that migrated to head, neck, shoulder, thorax, and abdomen)
3. Splanchnic nerves (innervate smooth muscle, cardiac muscle, and glands of internal organs)
4. Ganglia- sensory and motor nerve cell body collections
There are 4 major types