Histology π¬ Flashcards
What are the parts of the cell?
1) Cell membrane
2) Cytoplasm - cytosol - cytoplasmic matrix
3) Cell organelles
4) Cell inclusion
What is cell membrane?
It is a membrane that surrounds cell and controls the passage of substances in and out of the cell.
How is the cell membrane seen under microscopes?
-It canβt be seen under light microscope but seen under electron microscope as tri laminar structure with two electron dense layers surrounding a electron lucent layer. (They are called unit membranes)
What is cell membrane composed of chemically?
Proteins-lipids-Carbs.
What is the role of lipids in the cell membrane?
-It forms a double layer of phospholipids which consist of hydrophilic polar head and hydrophobic non-polar tail which act as passage for lipid soluble substances
-Cholesterol which is found in the cytoplasmic side of the bilayer.
What is the role of proteins in cell membrane?
Integral protein: which play a role in the passage of water soluble substances.
Peripheral proteins
What is the role of carbohydrates in cell membrane?
It forms glycocalyx which is glycolipids and glycoproteins.
And it is well developed and thick in small intestine.
What is the func. Of cell membrane?
Keep the composition of the cell.
Bulk transport (Exocytosis) (Endocytosis)
(Pino=Liquid) (Phago=Solid).
Cell coat (Attachment to other cells - Cell recognition - Immunity- Receptors )
What is the mitochondria?
-It is the powerhouse of the cell as it produces ATP and it may reach 1000 in number like in liver cells
How is the mitochondria seen under Light microscope?
-It isnβt seen by LM except by using iron H which gives dark blue color or by using janus green B which gives green color or histochemically by using succinic dehydrogenase activity.
How is the mitochondria seen under EM?
- it can be seen by EM and it appears as double membrane vesicle in which the outer membrane is smooth and allows the passage of small molecules and ions where the inner membrane is folded into the matrix, these folds are called cristae or shelves.
The inner membrane contains electron transport and respiratory enzyme and by negative stain it shows elementary particles which are sites for phosphorylation enzymes.
What is the matrix?
-It is the substance enclosed by the inner membrane and it is more electron dense than the cytoplasm where it contains matrix granuales that are rich in Ca and Mg cations and are electron dense, these granuales contain citric acid cycle(krebs) enzymes and mitochondrial DNA and RNA
What is the func. Of mitochondria?
-Production of ATP for cell use.
-Has DNA and RNA to inc. in No. when needed.
-plays an imp. Role in B-Ox. Of short chain fatty acids.
What is the endoplasmic reticulum?
-It is a system of flattened membrane bounded, anastomosing and inter-communicating narrow tubules and cisternae.
What is the site of rEM?
In protein secreting cells like plasma cells and pancreas
How is rEM seen under LM and EM?
LM:basophilic due to ribosomes.
EM: parallel flattened membranous cisternae and the cytoplasmic surface is rough due to ribosomes.
How is sEM seen under EM and LM?
LM: canβt be seen
EM: smooth communicating narrow tubules with no ribosome
What is the site of sEM?
-It is found in lipid forming cells like liver cells.
What is the func of rEM?
It is responsible for glycosylation of proteins, segregation and packaging and transferring to golgi body as transfer vesicles.
What is the func of sEM?
-Synthesis of lipids.
-Play a role in muscle contraction.(store ca in skeletal muscles)
-Breaking of glycogen.
-Detoxification of certain drugs and hormones in the liver.
what is the Golgi apparatus?
It is a membranous organelle. Plays an important role in the secretory system of the cells.
how is Golgi apparatus seen under LM?
the area occupied by the Golgi apparatus appears unstained. It is called a Negative Golgi image. demonstrated by (silver) stain &appears as a brown network.
How is golgi body seen under EM?
4-10 saccules (flattened membranous cisternae) piled one above the other forming a stack. Each saccule is narrow at its central part and wide at its periphery. Each stack has a concave surface called mature face or trans face
convex surface called immature face, cis face, or forming face.
Micro-vesicles (transfer vesicles): They are tiny vesicles present at the immature
face. They originate by budding from the rER.
Macro-vesicles (secretory vesicles): large in size pinched out from the mature face
of Golgi stack, migrate to the cell membrane, fuse with it and discharge their
content by exocytosis or Remain in the cell as lysosomes
What is the function of the Golgi apparatus?
- Concentrates & modifies proteins by adding (carbohydrate or sulfates).
- It involves in storage, modification, and packaging of excretory products.
- It makes lysosomes.
- recycling re-usable membrane and maintaining the cell membrane and cell coat in a good condition
what are the lysosomes?
membranous organelles contain a large variety of acid hydrolases for intra-cytoplasmic digestion.
what are the types of lysosomes?
primary and secondary.
what are primary lysosomes?
They are spherical flattened membrane-bounded vesicles filled with hydrolytic enzymes, they have moderate electron-dense granular core and they are smaller, homogenous, and not yer engaged in intra-cytoplasmic digestion.
what are secondary lysosomes?
They are spherical flattened membrane-bounded vesicles with hydrolytic enzymes, they have heterogenous electron-dense core and they are larger and engaged in intra-cytoplasmic digestion.
what is the result of fusion of primary lysosome with phagosome?
heterolysosome
what is the result of the fusion of primary lysosome with dead organelles?
autophagic vacoule
what is the result of the fusion of the primary lysosome with pinocytotic vesicles?
multi-vesicular body
what happens after the turning of primary lysosome into secondary one?
it digests these bodies with enzymes then the remaining undigested part is called the residual body.
what is the fate of heterolysosome?
It will be expelled to the outside by exocytosis.
what is the fate of autophagic cells?
accumulate in the cells of: liver, heart and nerve cells as lipofuscin pigment (wear and tear pigment)
what is the fate of multi-vesicular vesicles?
Unknown
what happens after death concerning lysosomes?
After death, anoxia increases the lysosomal permeability. The hydrolytic enzymes leak to the cytoplasm and digest it (Post mortem degeneration and autolysis).
what are the functions of lysosomes?
- Digestion of nutrients within the cell
- Defensive
- Removal of old organelles
- Change of inactive hormones to active ones
- Help sperm to penetrate the ovum
what happens in case of congenital abnormal function or deficiency in one of the lysosomal enzymes?
Impair the function of the cell as a result of the accumulation of certain materials.
what are lysosomal storage diseases?
- Tay Sachβs syndrome.
- Gaucher disease.
- Gout.
what are peroxisomes and microbodies?
they are tiny spherical membrane-bounded vesicles.
what do peroxisomes contain?
Contains:
Hydroxy acid oxidase.
D-amino acid oxidase
Uricase (in rodents only)
catalase enzyme converts H2O2 β H2O + O2
how are peroxisomes seen under LM?
LM: H&E Cannot be identified.
Histochemical: for catalase enzyme.
How are peroxisomes seen under EM?
EM:
a-In human: membrane-bounded vesicles containing a homogenous electron-dense granular material.
b- In rodents: possess an electron-dense semicrystalline (nucloid) core rich in uricase
enzyme.
what is the function of peroxisomes?
1-Segregate the developing H2O2 and protect the cell from its damaging effect.
2. Important for the formation of bile acids.
3. B-oxidation of long-chain fatty acids.
4. Play role in the metabolism of alcohol.
what are ribosomes?
They are non-membranous organelles that are responsible for protein synthesis.
How are ribosomes seen under LM?
spherical small particles and they are basophilic as they contain phosphate groups in the RNA.
How are Ribosomes seen under EM?
electron-dense granules of a diameter of 20-30 nm which consists of two subunits, each one consists of protein associated with rRNA.
what is the function of ribosomes?
synthesis of protein.
what are the types of ribosomes?
free ribosomes: responsible for protein synthesis within the cell for its usage.
attached ribosomes; Responsible for protein synthesis that are segregated in rER and transported to the outside of the cell.
what are cytoplasmic fibres?
non-membranous organelles in the form of thread-like structures.
what are the types of cytoplasmic filaments?
thin
thick
intermediate
thin cytoplasmic filaments
Structure ο Actin
Diameter ο 6-7 nm
Contractility ο Contractile
Distribution & function ο Microvilli for their movement.
ο In cleavage furrow during cell division.
ο In muscles for contraction.
thick cytoplasmic filaments
Structure ο Myosin
Diameter ο Variable(12-16nm)
Contractility ο Contractile
Distribution & function ο In muscle associated with actin filaments
Intermediate cytoplasmic filaments
Structure ο 5 types
Diameter ο 10-12nm
Contractility ο Non-Contractile
Distribution&function
ο In muscles (desmin), nerve cells (neurofilaments), and epithelial cells (cytokeratin).
ο Support and maintain the shape of the cell.
ο Important for identification of tumors.
ο can be used as cell type specific markers for different types of tumors.
What are microtubules?
They are non-membranous organelles in a pipe-like structure.
what is the structure of microtubules?
tubulin protein
what is the distribution and function of microtubules?
All over the cytoplasm and it is used in many functions like
ο Components of the cytoskeleton which support, maintain, and stabilize the shape of the cell.
ο They act as guiding tracks for transporting vesicles and organelles.
ο Mitotic spindle formation.
ο The main structural component of cilia, flagella and
centriole
what is the length and diameter of microtubules?
25 nm in diameter but variable in length.
How do cytotoxic drugs work?
They prevent the formation of new microtubules so they lead to the stoppage of mitosis and consequently the growth of cancer cells.
what are centrioles?
They are non-membranous organelles that are responsible for cell division.
how are centrioles seen under LM?
-they are seen as dark blue stained granules by iron hematoxylin.
what is the site of centioles?
in non-dividing cells, it is present as a pair of centrioles in a juxtanuclear position associated with Golgi bodies.
how are centrioles seen under EM?
- Each centriole is a short cylinder. (Perp. To each other)
-The wall of the cylinder is composed of 27 microtubules longitudinally arranged in 9 (nine) bundles.
-Each bundle consists of three micro-tubules (triplets) which are surrounded by fibrillar electron dense material.
what are the functions of centrioles?
- Play an important role in cell division.
-In non-dividing cells, it serves as a center about which other cell organelles are polarized.
- Its location plays a key role in the three-dimensional organization of the cell as it regulates the location of the nucleus and different organelles.
- In ciliated cells, act as basal bodies of the cilia.
what is cilia?
-they are Hair like processes projecting from the free surface of certain epithelial cells.
what is the site of cilia?
-Respiratory system; trachea and bronchioles.
-Female genital system; uterus and fallopian tube.
How are cilia seen under LM?
- Could be seen vaguely on the surface of the cell facing the lumen or cavity.
what is the length and number of cilia?
10-15 micrometer - several hundred per cell
How are cilia seen under EM?
Consists of:
1) The shaft: formed of microtubules (2 central singlets + 9 peripheral doublets)
2) The basal body: made of modified centriole.
3) The rootlets.
what is the function of cilia?
Cilia are beating rhythmically in one direction to move a thin film of fluid or mucous which is present on the surface of the cell.
what are flagella?
cytoplasmic processes like in the tail of sperm.
What is the structure of flagella?
same as centrioles
how many flagella per cell?
1
how long is a flagellum?
Much longer than cilia 200 um
How does a flagellum move?
Have whip-like swimming Movement
Immotile cilia syndrome
β abnormality in proteins of the cilia and flagella.
β characterized by chronic respiratory infections caused by the lack of the cleansing action of cilia in the respiratory tract and male infertility due to immotile spermatozoa.
How is cell coat seen under EM?
-It is seen as moderate electron dense fuzzy coat over the surface of microvilli of the cells.
What is microvilli?
-Finger-like processes projecting from the surface of cells and contain actin filaments.
Polyribosome
Electron dense granules are attached together by thin electron dense filament of mRNA forming whorls figures on the outer surface of rER.
What kind of electron microscopes are used to examine cilia and microvilli?
SEM
Difference between cilia and microvilli
Cilia; of large size and projecting on the free border of some cells. Microvilli; smaller in size and projecting on the free border of other cell.
-The microvilli are smaller in diameter and have a core of electron dense microfilaments.
Light band
Actin
Dark band
Actin and myosin
H-zone
Myosin
What is cell inclusion?
-It is non-living material in the cytoplasm.
What does cell inclusion include?
-Stored food
-Pigments
-Crystals
How are carbohydrates stored as cell inclusion?
In the form of glycogen granules.
Where are carbohydrates stored?
In liver and muscles.
How are lipids stored as cell inclusion?
As small droplets in liver cells and large globules in connective tissue fat cells.
What are pigments?
They are colored substances that can be seen without staining
What is stored food as cell inclusion?
Carbohydrates and lipids.
What are types of pigments?
-Exogenous and Endogenous
What are examples of exogenous pigments?
1) Lipochrome pigments: e.g. carotene.
2) Dust: -Small dust particles are continuously inhaled and enter the respiratory system.
-They are phagocytosed by
macrophages in the lung and cause
black pigmentation.
3) Minerals.
4) Tattoo marks.
What are examples of endogenous pigments?
1) Hemoglobin.
2) Hemoglobin derivatives e.g. bilirubin.
3) Melanin.
4) Lipofuscin pigment: (golden brown):
- Present in cardiac muscle fibers, nerve cells and hepatocytes.
- Considered as wear and tear pigment or as residual bodies that are not hydrolyzed by lysosomal enzymes.
-They increase with age
What is the nucleus?
It is a rounded or elongated structure which is responsible for all the cellular activities and plays an important role in cell division and hereditary.
what is the site of the nucleus?
It is found in nearly all cells except RBCs and blood platelets.
what is the number of nuclei?
mono: In most of the body cells.
bi: in liver cells and the top cells of the transitional layer of epithelium
multi: in cells like osteoclast and skeletal muscle fibres
what is the size of the nucleus?
It may be small, medium-sized, or large. It may reach 25 um like in the ovum and some ganglion cells
what is the shape of the nucleus?
it differs according to the type of the cell as it may be rounded, elongated, rod-shaped, bent rod, bilobed, segmented, kidney shaped.
what is the position of the nucleus?
it occupies the widest area of the cell and it may be central, eccentric, peripheral, or basal.
how does the nucleus appear under LM?
-it appears as a basophilic structure due to its content of nucleic acids.
-appears in two shapes: vesicular (open face) or condensed
Describe the vesicular (open face) nucleus
-lightly stained
-its content can be seen
-in highly metabolic cells like liver and nerve cells
Describe the condensed nucleus
-Heavily stained
-Its details cant be identified
-in low metabolic cells like small lymphocytes
How does the nucleus appear under EM?
consists of 4 parts:-
nucleolus
chromatin
nuclear sap
nuclear membrane
what is the nuclear envelope?
It is a double membraned membrane that surrounds the nucleus and separates it from the cytoplasm.
how is the nuclear membrane seen under LM?
-It is seen as a monolayer membrane as it is basophilic due to the chromatin associated with it.
how is the nuclear membrane seen under EM?
-It is seen as a double membranes membrane that consists of inner and outer layers and is interrupted by nuclear pores.
what is the function of the nuclear envelope?
- it separates the nucleus from the cytoplasm
-it allows the passage of certain substances in and out of the nucleus.
what is chromatin?
it is a basophilic material from which chromosomes are formed.
what is the structure of chromatin?
it is formed of nucleoprotein
what are the types of chromatin?
-extended chromatin and condensed chromatin
extended chromatin
(structure-activity-function-LM-EM-distribution)
-Extended parts of chromosomal threads.
-Carries active genes.
-Directs protein synthesis.
-Appears as clear areas (too thin to be seen).
-Could be seen with high magnification and appears as shades of grey.
-Occupies the more central regions of the nucleus.
condensed chromatin
(structure-activity-function-LM-EM-distribution)
-Coiled parts of chromosomal threads
-Carries inactive genes
-Doesnβt direct protein synthesis
-Fine or coarse basophilic chromatin granules
-Appears as electron-dense granules
-Peripheral chromatin, Nucleolus associated chromatin. and Chromatin islands.
what is the nucleolus?
one or more rounded basophilic bodies present in the interphase nuclei.
How is the nucleolus seen under LM?
-its size may reach up to 1um and it is mostly present in protein synthesizing cells.
-not surrounded by a membrane.
-It is basophilic as it contains RNA and chromatin attached to it
what is the function of the nucleolus?
- Synthesis of ribosomal RNA (rRNA).
- rRNA is conjugated with protein and migrates through the nuclear pores to reach the cytoplasm as ribosome subunits.
what are the nuclear changes indicating the death of the cell?
- Pyknosis: the nucleus becomes homogenous, smaller in size, darker in staining, and eccentric in position.
- Karyorrhexis: the nucleus is broken into small fragments.
- Karyolysis: the nucleus dissolves and finally disappears.
what are the main types of tissues in our bodies?
-epithelial
-connective
-muscular
-nervous
what are the characteristics of epithelial tissue?
1- The cells are close to each other with minimal intercellular substance.
2- The cells rest on a basement membrane.
3- The cells are supported by underlying connective tissue.
4-High rate of degeneration and regeneration (can divide and form new cells).
5- Nerves can enter between the epithelial cells.
6- No blood vessels enter between the cells.
7-from 3 embryonic origins (mesodermal-ectodermal-endodermal).
how are epithelial tissues classified functionally?
-covering:- covers the body and lines the cavities.
-glandular:- secretion
-neuro:- perception of stimuli
what are the types of covering epithelium?
-simple
-stratified
what are the types of simple epithelium?
-squamous
-cuboidal
-columnar
-pseudostratified
squamous simple epithelium
-1 layer
-flat cells
-flat and bulging nuclei
-in the lung alveoli, the lining of the heart, lining of blood vessels(endothelium), and external layer of the bowmanβs capsule.
cuboidal simple epithelium
- 1 layer
-cuboidal cells
-central and rounded cells
-medium ducts of glands and kidney tubules.
columnar simple epithelium
-1 layer
-tall, elongated cells
-the nucleus is basal and oval
-non-modified in large ducts of glands
what are the sites of modified columnar epithelium?
-stomachβ-contain vacuolated cytoplasm
-intestineβ-where the cells have microvilli on their free side (brush border) for increasing the surface area and consequently absorption and it is associated with goblet cells for secretion of mucous
-uterus and fallopian tube (with cilia).
what is the shape of cells in pseudostratified epithelium?
tall and short
what is the shape of the nuclei in pseudostratified cells of epithelium?
they are arranged at different levels.
what is the site of pseudostratified epithelium?
ciliated with goblet cells: upper respiratory passages (nose-trachea-bronchi)
non-celiated: large ducts of glands
why are pseudostratified epithelium called by this name
-because cells are arranged at different levels even though they rest on the same basement membrane.
why are the nuclei arranged at different levels even though they rest in the same basement membrane?
-Due to the crowding during development.
How are stratified epithelium classified?
according to the shape of top layer cells
what are the types of stratified epithelium?
-Transitional
-columnar
-squamous
what is the structure of squamous stratified epithelium?
-has a thick wavy basement membrane.
-base layer is composed of columnar cells with basal, oval nuclei and is responsible for the regeneration of cells.
-middle layer is composed of polyhedral cells with central, rounded nuclei and is responsible for junctions between cells.
-top layer is from flat cells and flat nuclei
what is the number of layers in squamous stratified cells?
30
what are the types and sites of squamous stratified epithelium?
keratinized: is dry found in the epithelial layer of skin with horny covering scales
non-keratinized: wet and found in the mouth cavity, esophagus, anal canal, vagina, and terminal urethra.
what is the structure of transitional stratified epithelium?
-thin ill-defined basement membrane.
-base layer is composed of low columnar cells with basal, oval nuclei
-middle layer is composed of polyhedral cells with central, rounded nuclei and is separated by mucous-like substance that helps in the gliding of cells
-superficial layer consists of the top layer and the underlying layers.
top:composed of cuboidal layer which is dome-like and binucleated which is responsible for protecting underlying layers from the bad effect of urine.
underlying layers are flask-shaped
how many layers are there in transitional squamous epithelium?
6-8 layers
what are the sites of transitional stratified epithelium?
-ureter
-urinary bladder
-prostatic urethra
-pelvis of the kidney
what are the forms of transitional stratified epithelium and what does it depend on?
-it depends on the degree of distention of viscus
-in the case of full bladder it consists of two layers the upper is flat and the underlying is cuboidal
-in the case of an empty bladder it returns back to normal.
What is glandular epithelium?
It is a modified type of epithelium specialized for secretion.
How are glands classified?
-presence of ducts or not
-no. Of cells
-Branching and shape of ducts and secretory parts.
-mode of secretion
-Type of secretion
What are glands classified into according to the presence or absence of ducts?
Exocrine: salivary glands
Endocrine: suprarenal-pituitary-thyroid
Mixed: liver and pancreas
What are glands classified into according to no. of cells?
Mono like goblet cells and multi-like liver and salivary glands.
What are glands classified Into according to branching and shape of ducts and secretory parts?
Simple: no branching
Simple branched: branching in secretory part
Compound branched:Branching in both
What are types of simple glands?
Simple tubular: Have tubular secretory part
Simple alveolar: Have an alveolar (flask-shaped) secretory part.
Simple tubualveolar: Have both tubular and alveolar secretory part
What are the types of simple branched glands?
1- simple branched tubular
2- simple branched alveolar
3- simple branched tubualveolar
What are the types of compound branched glands?
1- compound branched tubular
2- compound branched alveolar
3- compound branched tubualveolar
What is the classification of glands according to the mode of secretion?
Merocrine glands:
- The cells of the glands are intact at the time of secretion
E.g. Salivary glands
Holocrine glands:
- The cells are shed at the time of secretion and then replaced by new cells
E.g. Sebaceous glands
Apocrine glands:
- The apical portions of the cells are pinched off at the time of secretion
E.g. Mammary glands
What is the Classification of glands according to Nature of secretion?
What is the structure of neuroepithelium?
1- sensory cells:
apical part: hairlets (microvilli)
basal part: surrounded by nerve fibrils
2- supporting cells
3- basal cells (can give the other two types)
What are the sites of neuroepithelium?
- Taste buds (tongue)
- Organ of corti (inner ear)
- Olfactory epithelium (nose)
What is the definition of intracellular junctions?
The lateral membranes of the epithelial cells show several specialized structures called intercellular junctions that contribute to adhesion and communication between the cells
What are the types of intracellular junctions?
Types
1- Tight junction
2- Adherens junction
3- Gap junction
What is the structure of occludens (tight) junctions?
The 2 adjacent cell membranes fuse completely at certain points (ICS=0) to form a seal between I.C & luminal fluids
What are the sites & types of occludens (tight) junctions?
- Epithelial cells of the intestine
- Proximal convoluted tubules of the kidney
- Capillary endothelial cells
What is the function of occludens (tight) Junctions?
Forming a complete seal that prevent passage of materials (water & other fluids) from the lumen to the I.C.S
What is the structure of adherens junctions?
The 2 adjacent cell membranes are separated by wide I.C.S filled with binding (adhesive) material
What are the sites of adherens junctions?
Firm adhesion between the cells that fix them strongly and preventing their separation
What is the structure of gap junctions?
The 2 adjacent cell membranes are separated by 2nm gap to allow cell communication
What are the sites & functions of gap junctions?
1- In the heart, rapid transmission of nerve impulse between the cells so heart contract as one unit (coordinated heart beat)
2- In smooth muscle: transmission of wave of contraction to act in coordination
3- Between the bone cells for rapid exchange of small molecules
What is the function of CT?
The CT supports, surrounds, binds, and separates various tissues and organs.
What are the types of CT?
True(proper)β->loose and dense
Supportiveββ>bone and cartilage
Liquidββ>blood
What are the characters of white collagenous fibers?
β Color: the bundles are white in color.
β Strong and resist stretch.
β It forms wavy bundles.
β Can be affected by
ο² converted into gelatin by boiling
ο² Destroyed by acids & alkalies.
What are the components of CT?
-cells, fibres and matrix
How is white collagenous fibres seen under LM?
The bundles can be stained:
ο² Acidophilic with Hx & E.
ο² Blue with Mallory trichrome stain.
ο² Red with Van Giesonβs stain.V
How is white collagenous fibres seen under EM?
β Each collagenous bundle is formed of a group of fibers which are composed of fibrils.
β Each fibril is formed of tropocollagen molecules: -.
ο Synthesized by Fibroblasts
ο Length is 280 nm
ο Each molecule is composed of 3 polypeptide chains twisted around each other to form a triple helix.
ο The arrangement of tropocollagen molecules gives the fibril a cross banding appearance Structure
What are the types and sites of collagen?
What are the characters of yellow elastic fibers?
ο Color: yellow.
ο Elastic in nature
ο The fibers branch & anastomose
How is yellow elastic fibre seen under LM?
ο Hx & E.: acidophilic.
ο Van Giesonβs stain: yellow.
ο Ver-Hoffβs stain: black.
How are yellow elastic fibres seen under EM?
Each fiber is formed of:
ο² Amorphous protein in the center called elastin
ο² Microfibrils in the periphery called oxytalan fibers.
What are the sites of yellow elastic fibres?
ο In the walls of arteries.
ο In the trachea, bronchi, and bronchioles.
ο Ligamentum flavum between vertebrae.
ο Ligamentum nuchae in the back of the neck
οSuspensory ligament of the penis
What is the structure of reticular fibers?
ο They are very thin fibers that branch and anastomose to form a network.
How are reticular fibres seen under LM?
ο Hx & E: not stained.
ο Silver: brown to black (Agyrophilic)
ο PAS: Magenta colored (polysaccharides).
What are the sites of reticular fibers?
ο The stroma of parenchymatous organs e.g. Liver, spleen, and lymph nodes.
ο Reticular lamina of the basement membranes.
What is the matrix composed of?
ο Composed of three components:
1) Amorphous component.
2) Fibrous component
3) Tissue fluid
What is the amorphous part composed if?
ο The amorphous part: formed of two main parts:
1) Glycosaminoglycans (gags)
2) Glycoproteins
GAGS in CT
Non-sulphated type (hyaluronic acid)
Soft jelly-like
Not linked to a core of protein
Can be hydrolyzed by hyaluronidase enzyme
Sulphated type (chondroitin sulphate)
hard
Linked to a core of protein forming proteoglycans.
Not affected.
ο Stain: Metachromatic stain e.g., Toluidine blueβreddish-purple in Color.
Glycoproteins in CT.
Act as adhesive material.
Examples:
ο² Chondronectin in cartilage.
ο² Osteonectin in bone.
ο Stain: PASβ magenta-colored.
What are fixed CT cells?
-undifferentiated mesenchymal cell
-fibroblasts
-adipocytes (fat cells or adipose cells)
-reticular cells
-macrophages (clasmatocyes or histiocytes)
What is the origin of the undifferentiated mesenchymal cell?
Mesodermal cells of the embryo
Can mesenchymal cells divide?
Yes
Are mesenchymal cells differentiated?
No
How is UMC seen under LM?
Cytoplasm: pale basophilic due to little ribosomes
Nucleus:clovesβ->central,vesicular,large,oval,single
Sites: pre-natalβ->in the embryonic CT
Post-natalβ->in decides teeth and in pericytes surrounding the blood capillaries
Shape: Branched with few cell processes which are thin and long
Number: common in embryonic CT (mucoid and mesenchymal)
Size: Tiny
How is UMC seen under LM?
Cytoplasm: pale basophilic due to little ribosomes
Nucleus:clovesβ->central,vesicular,large,oval,single
Sites: pre-natalβ->in the embryonic CT
Post-natalβ->in decides teeth and in pericytes surrounding the blood capillaries
Shape: Branched with few cell processes which are thin and long
Number: common in embryonic CT (mucoid and mesenchymal)
Size: Tiny
how is UMC seen under EM?
Mainly free polysomes (little rER and small Golgi)
What is the function of UMC?
It acts as a multipotent stem mother cell.
What are fibroblasts?
The most common type of C.T. cells that are responsible for the synthesis of C.T. matrix and fibers.
What is the origin of fibroblasts?
develop from pericytes (branched cells around blood capillaries) which develop from U.M.C.
Can fibroblasts divide?
No
Are fibroblasts differentiated?
Yes
How are fibroblasts seen under LM?
Cytoplasm: Deep basophilic with negative Golgi image
Nucleus: oval, vesicular (with fine chromatin and prominent nucleolus), and eccentric in position
Shape: branching spindle-shaped cells.
Sites: The most common type of C.T. cells, very numerous in the loose C.T.
How are fibroblasts seen under EM?
ο The cytoplasm is rich in ribosomes, rER, and prominent Golgi.
ο Some mitochondria
ο Microtubules and microfilaments preserve the shape of the cell.
What is the function of fibroblasts?
1- Synthesis of the components of the C.T. matrix.
2- Synthesis of nearly all types of C.T. fibers (fiber-forming cells).
3- Responsible for the growth of C.T. and healing of wounds.
What are fibrocytes?
Fibrocytes: are old fibroblasts characterized by:
ο² Shape: spindle-shaped but flatter and has fewer processes.
ο² Nucleus: darker.
ο² Cytoplasm: less basophilic (less rER).
ο² Function: preserve and renew the already formed components of the CT matrix and fibers.
What are the steps of the formation of white adipocytes?
UMCs β Lipoblast β Brown adipocyte β White adipocyte.
Can both brown and white adipocytes divide?
No
Are both brow and white adipocytes differentiated?
Yes
How are the brown adipocytes seen under LM?
Cytoplasm: Contains many fat droplets:
Paraffin sections (Hx&E) β Cytoplasm is acidophilic with many vacuoles due to dissolved fat droplets.
Nucleus: single central and rounded nucleus.
Shape: oval
Sites: In sites of Brown adipose CT
Number: The main cells in adipose CT
Size: 10-times smaller than white adipocytes
How are the white adipocytes seen under LM?
Cytoplasm: Contains a large fat globule:
1. Paraffin sections (Hx&E) β an empty space due to dissolved fat globule.
Nucleus: A single flat peripheral nucleus pushed to one side giving a Signet Ring appearance.
Shape: oval
Sites: Mainly in sites of white adipose CT, Also in loose CT.
Number: The main cells in adipose CT
Size: 10 times larger than brown adipocytes.
How are brown adipocytes seen under EM?
Multiple fat droplets.
ο sER and numerous mitochondria are scattered among
the fat droplets
How are white adipocytes seen under EM?
sER & some mitochondria are present in the remaining
cytoplasm beside the nucleus.
What is the origin of white reticular cells?
UMC
Can reticular cells divide?
No
are reticular cells differentiated?
Yes
How are reticular cells seen under EM?
Few organelles include rER, ribosomes, and mitochondria.
How are reticular cells seen under LM?
Cytoplasm: Hx & E β Pale basophilic.
Special stain β Silver stain
Nucleus: central,oval, and pale
Site: reticular stroma of parenchymatous organs.
Shape: branched with many processes
Size: small
Number: most common cell in reticular CT.
What is the function of reticular cells?
It acts as a multipotent stem (mother) cell for:
1. Supportive function: with reticular fibers, they both form a delicate network that supports parenchymal cells.
- Antigen Presenting Cells (APCs): present antigens to T-Helper lymphocytes to activate the immune system.
- Phagocytic function.
What is the origin of macrophages?
From migrating blood monocytes (that originally develop from UMCs in bone marrow).
Can macrophages divide?
No
Are macrophages differentiated?
Yes
How are macrophages seen under LM?
Cytoplasm: Hx & E: Pale basophilic and not clear.
ο Special stains:
ο² Vital stain e.g. trypan blue.
ο² Supravital stain e.g. neutral red.
Nucleus: Eccentric, small, kidney-shaped oval or irregular, single and pale.
Site: mainly in loose CT
Shape: rounded with pseudopodia
Number: the 2nd most common in loose CT
Size:large
How are macrophages seen under EM?
Many lysosomes, few rER and free polysomes, small Golgi, and few mitochondria.
ο Pseudopodia, phagosomes, and pinocytotic vesicles.
What are the types and functions of macrophages?
A) M1 βkillerβ macrophages:
- Phagocytic function: can phagocytize foreign bodies e.g. bacteria.
- Many phages may fuse together to form multinucleated foreign body giant cells to attack a large foreign body
- Antigen Presenting Cells (APCs): present antigens to T-Helper lymphocytes to activate immunity
- Secretory function: they secrete enzymes (e.g. collagenase and elastase) and cytokines.
B) M2 βrepairβ macrophages: function in constructive processes like wound healing and tissue repair, they secrete growth factors and other cytokines
What is the function of adipocytes?
Same as adipose connective tissue
What are free connective tissue cells?
ο Mast cells.
ο Plasma cells.
ο Melanophores = Chromatophores = Melanophages.
ο Migrated Blood leucocytes.
ο Wandering (Free) macrophages.
What is the origin of mast cells?
UMC
Can Mast cells divide?
No
Are mast cells differentiated?
Yes, Fully differentiated
How are Mast cells Seen under LM?
How are Mast cells Seen under LM?
What is the shape of Mast cells under EM?
ο The cell border is irregular with short process.
ο The cytoplasm contains: Much membrane-bounded electron dense granules, ribosomes, rER and mitochondria
What are the functions of Mast cells?
ο Secretion of Heparin: natural anticoagulant.
ο Synthesis, storage and secretion of Histamine: in cases of allergy and inflammation.
ο Secretion of Slow Reacting Substance of Anaphylaxis (SRS-A): has similar action as histamine but longer in duration.
ο Secretion of Eosinophil Chemotactic Factor (ECF): attract eosinophils
What is the origin of plasma cells?
Activation of B-lymphocytes (originating from UMCs) by specific antigen leads to formation of plasmablasts which mature into plasma cells.
Do plasma cells divide and are they differentiated?
- Cannot divide.
- Fully differentiated.
What is the Shape of plasma cells under LM?
What is the shape of plasma cells under EM?
ο Cell border is irregular.
ο The cytoplasm is rich in rER, ribosomes, prominent Golgi and mitochondria.
What are the functions of plasma cells?
Secretion of antibodies (responsible for humoral immunity).
What are melanophores? (Pigment cells)
Melanin-containing C.T. macrophage that engulfs melanin made by melanocytes.
What is the site of melanophores?
Found in the choroid of the eye and dermis of skin.
What is the shape and structure of Melanophores?
Branched with melanosomes in the cytoplasm.
what are migrated leukocytes?
Blood leucocytes leave the blood stream and accumulate in the C.T. in certain conditions, e.g.:
(i) Eosinophils: in allergy or parasitic infestation.
(ii) Neutrophils: in acute infections.
(iii) Monocytes & lymphocytes: in chronic infections.
What are the types of connective tissue proper?
1- Loose (areolar =ordinary) CT.
2- Adipose C.T.
3- Yellow elastic C.T
4- Reticular C.T
5- White fibrous C.T.
6- Mucoid C.T.
What are the characters of loose connective tissue?
ο It binds tissues and organs together.
ο It carries blood vessels, lymphatics and nerves.
ο Called areolar as the matrix shows false cavities called areolae.
ο Called ordinary as it is widely distributed all over the body; found around blood vessels, in the submucosa of the digestive organs and in the serous membranes e.g. peritoneum.
What is the structure of loose connective tissue?
- Fibers: collagenous and elastic fibers.
- All types of cells specially fibroblasts, macrophages and fat cells.
- The matrix is rich in hyaluronic acid.
What are the functions of loose connective tissue?
- Carries blood vessels, lymphatics & nerves.
- Binds tissues & organs together.
- Swells during inflammation (edema)
What is the color of white adipose connective tissue?
White due to natural color of fat.
What are the sites of white adipose connective tissue?
- The majority of adipose C.T. in adults e.g. buccal pad of fat, subcutaneous tissue and perinephric fat.
- In β more in the back of neck & upper shoulder.
- In β more in hip region & upper thigh and breast region.
What is the structure of white adipose connective tissue?
- Lobules of White adipocytes separated by loose C.T.
- with less capillary supply than the brown type.
What are the functions of white adipose connective tissue?
- Energy depot (Storage of fat).
- Heat insulation.
- Gives contour to the body.
- Support organs e.g. kidney.
- Cushions during seating.
What is the color of brown adipose connective tissue?
Brown due to:
- cytochromes in its much mitochondria
- Blood color in its rich capillary supply.
What are the sites of brown adipose connective tissue?
- In newborn infants.
- In adults, present in:
1. Mediastinum.
2. Between the 2 scapulae.
What is the structure of brown adipose connective tissue?
- Lobules of Brown adipocytes separated by loose C.T.
- with more capillary supply than the white type.
What are the functions of brown adipose connective tissue?
- Rapid heat production in newborn infants on exposure to cold.
- Energy production in hibernating animals.
What are the sites of yellow elastic connective tissue?
- arteries
- Tracheo-bronchial tree and between lung alveoli.
- Ligaments:
- Ligamentum flavum between vertebrae.
- Ligamentum nuchae in the back of the neck.
- Suspensory ligament of the penis.
What is the structure of yellow elastic Connective tissue?
- Regular elastic fibers.
- Fibroblasts or fibrocytes between the fibers.
What is the staining of yellow elastic connective tissue?
- Hx & E β Acidophilic
- Van Giesonβs stain β yellow
- Ver-Hoff Μs stainβ black
What are the sites of reticular connective tissue?
- Stroma of parenchymatous organs e.g. liver, spleen and lymph nodes.
- Reticular lamina of the basement membranes
What is the structure of reticular connective tissue?
Formed of reticular cells and fibers that form a network.
what is the staining of reticular connective tissue?
Silver stainβ brown to black
What are the sites of regular type of white fibrous connective tissue?
tendons and cornea of the eye.
What is the structure of the regular type of white fibrous connective tissue?
- Parallel collagenous bundles.
- Fibroblasts (tendon cells, corneal corpuscles): the cells have thin nuclei and the cytoplasm is not apparent.
what are the sites of the irregular type of white fibrous connective tissue?
sclera of the eye, capsule of organs and outer fibrous layer of the periosteum & perichondrium.
What is the structure of the irregular type of white fibrous connective tissue?
- Irregular collagenous bundles.
- Fibroblasts or fibrocytes between the bundles.
What are the stains used for white fibrous connective tissue?
βBoth regular and irregularβ
Hx & E β Acidophilic
Van Giesonβs stain β red
Mallory trichrome stainβ blue
What are the sites of mucoid connective tissue?
- Whartonβs jelly of the umbilical cord.
- Vitreous body of the eye.
- Pulp of the teeth.
What is the structure of mucoid connective tissue?
- The matrix is soft as it is rich in mucin and hyaluronic acid.
- UMCs or young fibroblasts (mucinous cells) with long processes which intercommunicate with those of the neighboring cells.
What are the functions of connective tissues?
What is the nervous system classified into?
The nervous system is classified into:
- Central nervous system (C.N.S): include brain and spinal cord.
- Peripheral nervous system (P.N.S):
Peripheral nerves: may be cranial or spinal nerves
Ganglia: may be spinal or autonomic ganglia.
What is the definition of neurons?
β Neurons are the structural& functional unit of the nervous system.
β It is a specialized cell that transmit impulses within the nervous system.
What is the structure of the neuron?
β The neuron or the nerve cell consists of:
Cell Body: It contains the nucleus and surrounding cytoplasm contain many organelles (Nissl granules, Golgi apparatus, Mitochondria)
Processes: axon and dendrites.
What is the shape of nissl granules under LM?
Basophilic granules scattered in the cytoplasm.
What is the distribution of Nissl granules?
All over the neuron except in:
ο² Around the nucleus.
ο² Axon
What is the stain of Nissl granules?
Stained basophilic by Hx
What is the function of Nissl granules?
Synthesis of protein
Compare between the processes of the nerve cell
What is the classification of New Orleans according to the number of processes (polarity)?
Unipolar nerve cells
Pseudounipolar nerve cells
Bipolar neurons
Multipolar neurons
Unipolar nerve cells
- Nerve cells are rounded with only one process.
- e.g. mesencephalic nucleus of trigeminal nerve.
Pseudounipolar nerve cells
- Nerve cells are rounded.
- single process which divides in inverted T-shaped manner into 2 branches, a dendrite and an axon.
- e.g. sensory ganglia or spinal ganglia
Bipolar neurons
- The cells are fusiform, with 2 processes, a dendrite and an axon.
- e.g. bipolar neurons of retina and olfactory epithelium
Multipolar neurons
- Have many dendrites and one axon.
- Have star-shaped body.
- e.g. neurons in sympathetic ganglia
What is the definition of nerve fibers?
It is the axon of the nerve cell with its surrounding membranes.
What is the structure of nerve fibers?
- The axon membrane named (axolemma) and its cytoplasm named βaxoplasmβ.
- Have no Nissl granules.
- It may be:
ο² Naked or ensheathed (with myelin sheath, neurolemma or both).
What is a histological appearance of myelin sheath?
- White tubular covering of the axon
- Interrupted at intervals called (nodes of Ranvier)
- Segment between two successive nodes is called (internodal segment)
- Appears in the form of concentric layers derived mainly from the cell membrane of Schwann cell
What is the function of myelin sheath?
Insulation of the nerve impulses.
What is the histological appearance of Neurolemmal Sheath (Schwann Cells)?
ο Chain of cells forming a tube around myelin sheath
ο Each cell has a flat oval nucleus
ο Corresponds to an internodal segment
What are the functions of Neurolemmal Sheath (Schwann Cells)?
ο Insulation in nonmyelinated nerve fibers.
ο Regeneration of peripheral nerve after injury.
ο Myelin formation
What are the types of nerve fibers according to its covering?
1) Naked Fibers:
ο² (Non-myelinated without neurolemma) e.g. gray matter.
2) Ensheathed fibers:
ο² Myelinated with neurolemma: e.g. peripheral nerves.
ο² Myelinated without neurolemma: e.g. nerve fibers in the white matter.
ο² Non-myelinated with neurolemma: e.g. sympathetic nerve fibers.
What is the structure of nerve trunk?
1) Nervous component:
ο² Groups of nerve fibers (myelinated axons with neurolemma) arranged in
bundles.
2) C. T. component:
ο² Epineurium: It is a dense C. T. surrounds the whole nerve trunk.
ο² Perineurium: It is a dense C. T. surrounds the bundles of nerve fibers.
ο² Endoneurium: It is a delicate loose C. T. lie between the individual nerve fibers.
What is neuroglia?
β It is the interstitial supporting tissue of the nervous system
β Non-neuronal cells present in the CNS& PNS.
What is the Neuroglia Of CNS?
ο Astrocytes
ο Oligodendroglia
ο Microglia
ο Ependymal cells
What is the neuroglia of PNS?
ο Satellite cells
ο Schwann cells
What is the shape and function of astrocytes?
Shape: It is star-shaped branching cells
Function: Nutrition by connecting neurons to blood vessels
What is the shape of Microglia?
It is small cells having spiny processes
What is the function of microglia?
- can transform into a macrophage that migrate to the site of infection or injury to phagocytose foreign bodies or bacteria.
- Hence, microglia are described as (police man of the brain).
What is the shape of oligodendroglia?
It is cells have few processes
What is the function of oligodendroglia?
Formation of myelin sheath of nerve fiber in the CNS.
What is the shape of ependymal cells?
It is cells Line the spinal cord and the ventricular system of the brain
What is the function of ependymal cells?
Secretion of cerebrospinal fluid (CSF).
What is the shape of satellite cells?
It is small cells that surround neurons in sensory, sympathetic, and parasympathetic ganglia
What is the function of satellite cells?
They are highly sensitive to injury and inflammation
What is the shape of Schwann cells?
It is Flat cells forming a tube around myelin sheath of nerve fiber
What is the function of Schwann cells?
Formation of myelin sheath of nerve fiber in the PNS.
Notes about neuroglia
β In CNS: Oligodendrocyte have processes that wrap around the axons. One oligodendrocyte forms myelin sheath for several neurons (3- 50 neurons).
β In PNS: only one Schwann cell provides myelination for one axon (only a segment of one axon).
What is the definition of nerve ganglia?
β Collection of nerve cells and nerve fibers, covered by a C. T. capsule, outside the C. N. S.
What are the types of nerve ganglia?
1) Spinal.
2) Autonomic: Sympathetic or Parasympathetic.
Compare between spinal (dorsal root) ganglion and sympathetic ganglion
Photo
What are the types of skin?
β Thick (non-hairy) skin: found in palms and soles.
β Thin (hairy) skin: covers the rest of the body.
What are the layers of skin?
β Epidermis: Stratified squamous keratinized epithelium.
β Dermis: Connective tissue.
N.B: The hypodermis is the subcutaneous adipose tissue (It is not a part of the skin).
What is the structure of thin skin?
formed of two layers
1) Epidermis: Contains 4 types of cells: (KMβL)
ο² keratinocytes (85% of cells).
ο² Langerhans cells.
ο² Melanocytes.
ο² Merkel cells.
2) Dermis: (PR)
ο² Papillary layer
ο² Reticular layer
How many layers are keratinocytes arranged in?
4
Malpighian layer (2 layers) - stratum basale and stratum spinosum
Granular layer (Skin Barrier layer) - stratum granulosom
Clear layer - stratum lucidum
Horny cell layer - stratum corneum
Characters of the basal cell layer in the skin
S: Single layer of columnar cells.
N: Nucleus: basal & oval.
C: Cytoplasm: deep basophilic& (due to ribosomes).
E: By EM: It contains prekeratin filaments.
F: Function: Responsible for regeneration of keratinocytes so it shows mitotic figures.
Characters of a prickle cell layer in the skin
L: L/M: Formed of 4-8 cell layers.
S: Shape: polyhedral.
N: Nuclei: Central and rounded.
C: Cytoplasm: pale basophilic.
E: EM: The cells are connected by cytoplasmic processes. (Desmosome)
Characters of the granular layer in the skin
S: Shape: 2- 4 layers of flattened, diamond-shaped cells.
N: nuclei: flat & central.
C: Cytoplasm: has basophilic Keratohyaline-granules.
E: EM: The cytoplasm contains βlamellar granulesβ, which
contain phospholipids
F: Function: The granules are released in the intercellular
space to act as skin barrier because they are:
ο² waterproofing skin.
ο² preventing foreign bodies from penetrating the skin.
What are the characteristics of the clear layer of the skin?
ο It appears as a (CHAT W) thin, wavy, clear, homogenous acidophilic line.
ο It is formed of dead non-nucleated flattened cells, βscalesβ which contain βeleidin granulesβ (derivative of kerato- hyaline granules).
What are the characteristics of the horny cell layer in the skin?
ο It consists of several layers of (AHS) acidophilic horny scales called βsquamesβ
ο The scales contain soft keratin (derived from eleidin).
ο The squames are continuously shed or sloughed from the surface and continuously replaced by new ones from the deeper cells.
What is the site of melanocytes?
between the cells of the basal layer of the epidermis.
What is the LM of melanocytes?
S: shape: branched cells with rounded cell bodies
N: Nucleus: rounded and central
C: Cytoplasm: contains melanin pigment (brown to black
pigment, responsible for pigmentation of the skin).
What is the function of melanocytes?
synthesis of melanin
What are the clinical applications of melanocytes?
Albinism
What is albinism and what is its cause?
- an inherited disease characterized by white hair and very light-colored skin.
- Cause: Albinism is caused by a mutation in genes responsible for melanin formation.
What is the site of langerhans cells ?
upper layers of Spinouts layer.
What is the origin of Langerhans cells?
blood monocytes.
What is the LM on Langerhans cells?
S: Shape: branched.
N: Nucleus: central.
C: Contain Birbeck granules.
Stained with silver& vital stains.
What is the function of Langerhans cells?
Phagocytic& antigen-presenting cells (APC).
What is the site of Merkels cells?
Basal cell layer of epidermis.
What is the function of Merkels cells?
Receptors for touch sensation.
Compare between the papillary layer and the reticular layer of the dermis
What are the histological differences between thin and thick skin?
What are skin related structures?
β They include:
ο² Sweat glands.
ο² Hair& hair follicle.
ο² Sebaceous glands.
ο² Arrector pili muscle.
What is the site of sweat glands?
deep in the dermis or the hypodermis.
What is the number of sweat glands?
more numerous in the thick skin than in the thin skin.
What are the types of sweat glands? And compare between them.
What is the structure of sweat glands?
1) The secretory parts (acini)
2) The Excretory parts (ducts)
- Duct collects sweat secretion from the acini
- In merocrine glands: duct ascends in a spiral course to the epidermis
- It opens on the surface of the skin.
What does the hair consist of (by naked eye)?
Shaft: projecting above skin surface.
Root: embedded or implanted in the skin.
Hair bulb:
β’ the expanded lower end of the hair.
β’ It consists of (hair matrix) which is a cellular mass.
β’ Proliferation of the matrix cells results in growth of the hair in length.
What does the shaft of the root of the hair consist of?
Medulla: It contains soft keratin.
Cortex: It contains hard keratin and melanin pigments which give the color of the hair.
Cuticle: It contains hard keratin.
What is the definition of hair follicles?
It is a hole formed by an epidermal down-growth in which the root of the hair is present.
What is the structure of hair follicles?
The wall of the hair follicle is called (root sheath) which is divided into 3 types:
Inner root sheath: ββββ
Outer root sheath: It is identical with the malpighian layer of the epidermis.
CT Sheath: It is a condensed part of C. T. of the dermis.
What is the site of sebaceous glands?
They open into the upper 1/3 of the hair follicle at the obtuse angle between the follicle and the surface of the skin
What is the mood of secretion of Sebaceous glands?
Holocrine
i.e. the central cells disintegrate completely to secrete (sebum).
What is the mood of secretion of Sebaceous glands?
Holocrine
i.e. the central cells disintegrate completely to secrete (sebum).
What is the structure of sebaceous glands?
- Secretory part: It is a sac-like structure i.e formed of one or more alveoli which open into a common duct.
- Excretory duct: Short, wide and opens into the upper 1/3 of the hair follicle, Lined with stratified squamous epithelium.
What is the definition of arrector pili muscles?
β It is a band of smooth muscle fibers touching the bottom of the sebaceous gland.
What is the function of the arrector pili muscles?
β Contraction of this muscle due to stress or emotion (as fear) leads to:
ο² Erection of the hair shaft.
ο² Appearance of goose-skin.
ο² Squeezing of sebaceous secretion into the duct
