***************************************************** Lab 1-11-99 *************************************************************
From inside the jejunum to outside the layers are:
Mucosa is in contact with the lumen. Fingerlike projections from the mucosa into the lumen are called villi. The core of the
villus is called the lamina propria ( made of CT)
Submucosa extends into the plicae
Plicae contain mucosa and submucosa
The next layer is the muscularis: 2 regions
The outermost layer is the serosa
Stains
Hematoxolyn – purple nuclei
Eosin – pink cytoplasm, muscle fibers, and collagen; pale pink nerve fibers
Connective tissue stains: Azan ( esp for pancreas and pituitary )
Masson’s trichrome
Mallory’s triple stain:
blue CT
Red muscle
Orange-red RBCs
Periodic acid Schiff (PAS) reaction: id’s carbos, rose or purplish red
Weigert’s elastic blood stain – dark blue elastic fibers
Wright’s stain - blood
**************************************************** Lecture 1-13-99 **************************************************
There are 4 basic tissues, all of which are composed of functionally related cells:
1. Epithelial tissue
2. Connective tissue
3. Nervous tissue
4. Muscle tissue
Epithelial – means upon. There are 3 types of epithelial tissues
1. Surface epithelium – is arranged in sheets, covers all body surfaces and body cavities, and and organs with free
surface. EXCEPTION: there is no surface epithelium in the synovial joints
2. Glandular epithelium – is made of cells that have specific secretory function. It is found in the ducts that carry the
secretion
3. Special epithelium – germinal epithelium in the male testes
Epithelial origins
1. Endoderm – GI tract lining
2. Mesoderm – muscle tissues, blood vessels
3. Ectoderm – skin
General characteristics of epithelial tissues
1. Avascular – nutrients come in from underlying connective tissues by diffusion
2. Contiguous – all cells are attached, all touch
3. Polarized – externally – apical, basal, and lateral
Internally – nuclear region
4. Regeneration – constant renewal of cells
5. Metaplasia – if irritated, epithelium can change from one type of epithelium to another.
EXAMPLE: in the respiratory tract of a smoker, the epithelium has changed into stratified squamous
epithelium ( premalignant condition?)
6. Basement membrane – or basal lamina – all cells rest on one the attaches it to the underlying connective tissue.
Functions of epithelial tissues
1. Semipermeable membrane or selective barrier – things have to go through epithelial cells. This can be complete or
incomplete. EXAMPLE of complete: brain-blood barrier.
2. Protection – skin
3. Absorption – GI tract
Marie Paas
Page 1
533579581
03/08/16
4. Secretion – glands – ( useful products )
5. Excretion – ( waste products )
6. Transportation – internal mechanism – nutrients ( active function )
External mechanism – respiratory tract moves debris out
7. Conduit – epithelial cells act like a hose ( passive function )
8. Lubrication – mesothelial cells secrete watery fluid for easy sliding
9. Extension – bladder – transitional
10. Sensation – incoming sensations to taste buds, olefactory
11. ( Contractility – myoepithelial cells )
Usually there is one primary function, but there can be more than one.
Classification of epithelial tissues
Epithelial cells are arranged in sheets that can be classified by 3 factors:
1. By number of layers
a. simple – one layer
b. stratified – more than one layer
c. pseudostratified
2. According to the shape of the superficial layer of cells. The nucleus often corresponds roughly with cell shape
a. squamous – flat, wide, but not tall, fried egg appearance in surface view.
Nucleus: flat
b. cuboidal – square
Nucleus: round
c. columnar – rectangular
Nucleus: elongated
d. transitional
We will be asked to identify a vertical section most likely, except for simple squamous.
3. By types
Simple squamous epithelium
1. regular
2. endothelial
3. mesothelial
Location – Bowman’s capsule, parietal layer, nothing gets through. Loop of Henle. Lungs: alveolar lining
Function - selective barrier
Location endothelia – entire vascular system: heart, blood vessels, lymphatic vessels
Function – selective barrier
Location Mesothelia – lining of major body cavities: pleural, pericardial, and peritoneal cavities. Lines the free surface of
organs within those cavities. These are membranes that are continually moist.
Simple cuboidal tissue
Square cells with round, central nuclei
Location
thyroid follicles
salivary gland ducts
kidney tubules: proximal, distal, and collecting
ovarian surface: outer lining
= germinal epithelium ( misnomer )
ducts of exocrine glands
Function
secretion
conduit, absorption, secretion
absorption and secretion
burial and protection
conduit
Simple columnar epithelium
Basally located, elongated nucleus.
Location
GI tract: stomach through rectum
Gall bladder ( best developed SCE in body!)
Kidney- papillary ducts
( final pathway of urine in the kidneys)
Fallopian tubes
Lining of the uterus
Marie Paas
Function
absorption, some secretion
absorption
conduit
conduit, secretion
secretion
Page 2
533579581
03/08/16
Pseudostratified
Considered a simple epithelium, all cells rest on the basement membrane, but not all cells stretch to the top. It only looks
stratified. Contains goblet cells. Usually this tissue is ciliated, but not always.
Location
Function
PCCE: in most of the respiratory tree. Ciliated
conduit, secretion, transport
Epidydimus – sterocilia – these are not cilia, but long, branching forms of villi
absorption
Male urogenital tract – vas deferens
Stratified squamous epithelium (always identify tissue in lab as keratinized or non-keratinized )
Polygonal – look at the outer cells
Keratinized – dead cells are outermost – like in skin – waterproof, upper cells are filled with the protein keratin.
Non-keratinized – oral cavity, esophagus, vagina, anal canal, true vocal cords. These are part of a mucus membrane that
is continually moist.
Stratified cuboidal epithelium
Is not very common. Usually 2 layers of cuboidal cells. Lines the ducts of sweat glands, functions in absorption and
secretion. In the large salivary ducts it also functions as conduit.
Stratified columnar epithelium
Usually 2 layers, a basal layer that consists of cuboidal cells and a superficial layer made up of columnar cells.
Located in large exocrine glands, palpebral conjunctiva, male and female reproductive tract, tansitional epithelium.
Transitional epithelium
This is a variety of stratified epithelium with large, dome shaped cells in outermost layer. Some of them are bi-nucleate
( only ones in the body ). This type of tissue can alter its shape. Cells in the bladder are often times 6-8 layers thick, but
can thin out to only 3 layers when stretched. Found only in the urinary tract, major and minor calyces, renal pelvis, and the
ureters.
Surfaces and Surface Specializations of Epithelial Cells
Structural specializations reflect specific activities at the various cell surfaces and are an important part of cell polarity.
1. Apical surface -faces lumen (below)
2. Basal surface - attaches to basal lamina
3. Lateral surfaces - intercellular junctions
4. Apical surface specializations ( 1-3 below )
5. Basal surface specializations
6. Lateral surface specializations ( below )
Apical surface specialization
Cilia – are membrane bound. Their function is to beat rhythmically to move substances across surfaces. There are about
250 cilia on each cell, arranged in parallel rows. Cilia are arranged in what is called 9+2 arrangement: (page 44)
1. Cilia
a. motile
b. most found on pseudostratified variety
c. inner structure:
1. microtubules, composed of tubulin
2. 9 pairs of microtubules - 9 cilia doublets (a) microtubule A-with dynein arms (b) microtubule B
3. central pair of microtubules
4. 9+2 arrangement or axoneme
d. attached to a basal body
e. basal bodies have 9 microtubule triplets
f. cilia move to and fro in order to move substances across their surface
2. Microvilli are extensions of plasmalemma on most cells. There are many or few, depending on the absorptive
properties of the particular tissue. Each microvillus is part of the cell itself and is covered with plasmalemma. Due to the
resulting increase in surface area this also increases absorptive capacity of the cell. Microvilli are shorter than cilia, and
they lack the inner structure of cilia. The core of an microvillus consists of actin microfilaments. The basal ends of these
microfilaments mix with the microfilaments of the terminal web just underneath the microvilli, so these actin filaments are
extensions of the terminal web. The terminal web consists of several types of filaments and is thought to provide the
Marie Paas
Page 3
533579581
03/08/16
apex of the cell with rigidity. Microvilli can be found in the GI tract as (striated border) or in the PCT of the kidney ( brush
border ) – these are light microscopy terms because these structures give a double red line. Microvilli have mostly
absorptive function.
The glycocalyx is a filamentous coat covering the microvillus. It contains glycoproteins ( PAS +). The complex of
microvilli and glycocalyx is easily seen with the light microscope and is called brush border ( or striated border ) More
on apical surface than anywhere else. Carbohydrates attach to lipids or proteins of the membrane. The function of this
glycocalyx is cellular recognition, it determines what “self” is. EXAMPLE: blood type. Another function is cellular
adhesion.
3. Stereocilia
These are long, branched microvilli that are found in the epididymis and sensory hair cells of the ear
Basal surface specializations
1. basement membrane - basal lamina and reticular lamina, made of type IV and type VII reticular fibers
2. basal lamina
a. attachment site of epithelial cells to connective tissue
b. lamina densa – always 1
c. lamina rare or lamina lucida – sometimes more than 1
d. components of the basal lamina
(1) type of IV collagen
(2) heparin sulfate – glycoseaminoglycans/proteoglycans –negatively charged, impedes particles
(3) chondroitin sulfate - glycoseaminoglycans –negatively charged, impedes particles
(4) laminin – basal protein, acts as glue, adhesive molecules
(5) fibronectin – basal protein, acts as glue, adhesive molecules
(6) entactin – basal protein, acts as glue, adhesive molecules
(7) anchoring filaments – type VII collagen connects the basal lamina to reticular lamina
All these components are produced by the epithelial cells.
3. reticular lamina
a. not always present
b. type III collagen
4. stains for basement membrane
a. PAS - stains carbohydrates in proteoglycans
b. silver stain - stains type III collagen ( reticular fibers ) and is therefore called argyrophilic
Hematoxolyn and Eosin do not show the basement membrane
5. hemidesmosomes – a site of adhesion between 2 epithelial cells
6. basal infoldings can be found in the kidney and in the striated ducts of the salivary ducts. They have elongated
mitochondria. Therefore these infoldings indicate the active transport of ions.
Lateral surface specializations
These are also called intercellular junctions, which serve as sites of adhesion as well as sealing the cell, but they also
allow for intercellular communication. The various junctions are usually present in a distinctive order from the apex to the
base of the cell.
Terminal bar is another light microscope term. The terminal bar can be seen at the apical portion as a dark dot. It
represents the junctional complex consisting of the following items (Junctional complex is an electron microscope term)
(1) zonula occludens
(2) zonula adherens
(3) Desomosome or macula adherens
1. Zonula occludens
a. most apical point of the cell and also most apical component of the junctional complex
b. forms a complete ring around cell
c. a pentalaminar structure
e. functions as a barrier preventing anything from entering the space between cells, but is not very resistant to
stress
f. The number of fusion sites has a high correlation with the leakiness of the epithelium. (book page 64)
g. gaps are ca. 2nm
2. Zonula adherens
a. just below zonula occludens
b. forms a complete ring – belt desmosome
c. binding proteins in the intercellular space that attaches cells together
d. intracellular and extracellular components
Marie Paas
Page 4
533579581
03/08/16
e. intracellular area contains dense plaques of the following proteins: myosin, tropomyosin, actinin, vinculin
f. actin microfilaments from the terminal web enter these plaques
g. calcium dependent junction that deteriorates in the absence of Calcium
h. provides a firm attachment site for adjacent cells
i. gaps are ca. 15-20nm
3. Desmosomes or Macula adherens
a. a "spot weld" – spot desmosome
b. exceptionally strong attachment site
c. lower most and most numerous of the intercellular connections, scattered all over the surface of the cell
d. intercellular space contains a dense material - intermediate line
(1) desmocollins - linker proteins
e. intracellular region contains attachment plaques
f. intermediate filaments enter the plaque, these consist of condensation from glycocalyces
(1) may from hairpin loops and re-enter the cytoplasm, forming very, very tight connections
g. calcium dependent
h. gaps are ca. 30nm
i. desmosomes are the only type of junction found in the StSE of the skin
Gap junctions
a. aka nexus
b. not part of the junctional complex
c. connexons – made of 6 integral membrane proteins in dumbbell structure
d. connexons of adjacent cells are in register
e. allows communication between cells of molecules less than 1500 Molecular Weight due to pearcing of
membranes through hydrophilic channels
f. cells are about 2 nm apart
Summary of junctions
Adhering junctions
a. zonula adherens
b. desmosomes = macula adherens
c. hemidesmosomes
Impermeable junctions
a. zonula occludens
Communicating junctions
a. gap junctions
GLANDULAR EPITHELIUM
Glandular epithelial cells are specialized to perform a secretory function
Classification of glandular epithelia
1. Exocrine glands usually release their secretions to a surface usually through a duct system. These external
secretions act locally, close to where they were produced.
2. Endocrine glands pass their secretions directly into the blood or lymph. These internal secretions are usually
hormones whose targets can be quite a way away. The effects are far-reaching or systemic.
Glandular epithelia can be unicellular or multicellular:
1. Unicellular exocrine gland - goblet cell, in the GIT, respiratory tract (PCCE). The mucin they produce protects the
linings or traps debris.
2. Unicellular endocrine gland – entero-endocrine cells of the GI tract
3. Mlticellular exocrine gland - salivary glands, pancreas
4. Multicellular endocrine gland – endocrine organs: pituitary, thyroid…
Multicellular exocrine gland classification
Classification is based on
A. Presence or absence of branching in the ducts
1. Simple multicellular exocrine gland - unbranched
2. Compound multicellular exocrine gland - branched
B. Based on cellular arrangement of the secretory unit
1. alveolar or acinar - round
Marie Paas
Page 5
533579581
03/08/16
2. tubular- tube shaped, long and slender
3. tubuloalveolar - mixed
Examples:
1. simple tubular - crypts of Lieberkuhn in the colon
2. simple coiled tubular - sweat glands
3. simple branched tubular - fundic glands of the stomach – branching is in the secretory unit and not in duct!
4. simple alveolar - none in humans, poisonous amphibians
5. simple branched alveolar - sebaceous glands in hair follicles in the skin
6. compound tubular - cardiac glands of the stomach
7. compound alveolar - exocrine pancreas
8. tubuloalveolar - salivary glands
Types of secretions
A. serous – thin secretion, glands secreting this have round nuclei, small lumens
B. mucous – thick secretion, glands secreting it have flat nuclei and a larger lumen
C. seromucous
Methods of secretion
( Compound acinar )
A. holocrine - results in cell death, whole cell is secreted, duct can get clogged causes acne
1. sebaceous and tarsal glands
B. apocrine - results in loss of some cytoplasm, point – only top of cell pinches off and secretes
1. mammary gland (lipid)
C. merocrine - exocytosis - most glands, no part of the cell is lost
Classification:
1. Exocrine
2. Endocrine
3. Unicellular – One cell makes up the substance
a. unicellular endocrine – goblet cells – reverse tear drop shaped  mucin
b. unicellular exocrine – enteroendocrine or cardiac cells of GI tract
4. Multicellular exocrine glands – salivary glands, pancreas
a. unbranched ducts – simple
b. branched ducts – compound
c. rounded or grapelike secretory units – acinar or alveolar
d. tube shaped - tubular
e. mixed – tubuloalveolar or tubuloacinar
EXAMPLES
simple tubular – Crypts of Lieberkühn in the colon
simple coiled tubular – sweat glands
simple branched tubular – fundic glands of stomach - branching not in duct, but secretory unit
simple alveolar – none in humans
simple branched alveolar – sebaceous glands
compound tubular – cardiac glands of the stomach
compound alveolar – exocrine pancreas
tubuloalveolar – salivary glands
5. Multicellular endocrine glands – thyroid and pituitary
Connective tissue
Mesenchyme – the mother of all connective tissues, an early embryonic tissue that migrates into developing organs
Marie Paas
Page 6
533579581
03/08/16
Questions:
Zona occludens functions as a barrier preventing anything from entering the space between cells, but is not very
resistant to stress
PER BOOK: The number of fusion sites has a high correlation with the leakiness of the epithelium. (p 64)
From the notes I thought the terminal bar is made up of the junctional complex which in turn is made up of both zonulas
and the macula. In the book (p 64) it comes across that the terminal bar is made up of only the zonula occludens and the
zonula adherens
Marie Paas
Page 7
533579581
03/08/16
Mononuclear phagocyte system( MPS ),a widely distributed collection of both free and fixed macrophages derived from
bone marrow precursor cells by way of monocytes; their substantial phagocytic activity is mediated by immunoglobulin
and the serum complement system. In both connective and lymphoid tissue, they may occur as free and fixed
macrophages; in the sinusoids of the liver, as Kupffer cells; in the lung, as alveolar macrophages; and in the nervous
system, as microglia.
Marie Paas
Page 8
533579581
03/08/16