ELECTRON MICROGRAPH KEY
These micrographs from the grey envelope are available with questions and answers on
the department intranet at: http://med.uc.edu/labmanuals/ma/emenv/
The number for each electron micrograph (e.g., E.M. 1) appears in lower right corner of the
micrograph. The numbers in the list for each micrograph (e..g., l. Bile canaliculus with
microvilli) refer to the numbers that are located on or near particular structures. Each of these
electron micrographs is included in the Virtual Laboratory Manual.
E.M 1
Liver Parenchymal Cell (Hepatocyte)
1. Bile canaliculus with microvilli
2. Liver sinusoid
3. Rough endoplasmic reticulum (RER)
4. Mitochondria
5. Peroxisomes
6. Region of the Golgi Apparatus
7. Glycogen particles
8. Heterochromatin
9. Nucleolus
10. Lysosomes
11. Euchromatin
Which of the numbered structures listed can be considered organelles? Inclusions? Why?
Why is the double membrane of the mitochondria difficult to detect in this micrograph?
Is the double membrane of the nuclear envelope evident?
E.M. 2.
Rough Endoplasmic Reticulum (RER)
1. Cisternal space (The number lies between the membranes of the RER.)
2. Ribosome (Could this ribosome be part of a polysome?)
3. Mitochondrial crista
4. Outer mitochondrial membrane
5. Inner mitochondrial membrane
What is the potential relationship between the cisternal space of the RER and the nuclear
envelope?
Are most ribosomes organized in short rows on the RER membrane as is apparent in this
micrograph?
In addition to the RER, where are ribosomes attached to a membrane?
E.M. 3.
Pancreatic Acinar Cell
1. Mature secretory granule
2. Nucleolus
3. Forming secretory granules
4. Mitochondrion
5. RER
6. Plasma membrane (Plasmalemma)
7. Basal lamina
How would one demonstrate the material at #5 (RER) for identification by light microscopy?
What is the origin of #7 (basal lamina)?
What is the sequential relationship of #1 (secretory granules) to other cell organelles?
Why are the two membranes of the RER visible, whereas the two plasma membranes of
adjacent cells appear as a single line?
2
E.M. 4.
Enterocyte (Intestinal Absorptive Cell)
1. RER
2. Smooth endoplasmic reticulum (SER) continuous with RER
3. Lysosome
4. Microfilaments
5. Plasma membrane (Plasmalemma)
6. Microtubules - longitudinal
7. Microtubules - cross section
What is the structural difference between microtubules and SER? Microfilaments?
Are the microtubules in this micrograph part of a cilium or a centriole?
What is the composition of the plasma membrane?
E.M. 5.
Liver Parenchymal Cell
1. RER
2. Region of Polysomes
3. Glycogen
4. Higher magnification of polysomes. In an appropriate
micrograph messenger RNA may be observed between the
ribosomes.
What is the functional significance of free ribosomes? Polysomes? RER?
recognition particle?
Signal
What does the appearance of the chromatin in the nucleus suggest about the cell's activity?
E.M. 6.
Mitochondrion in cytoplasm of a Pancreatic Acinar Cell
10. Matrix
11. Crista
12. Outer mitochondrial membrane
13. Calcium
In general, what enzymatic reactions occur in the matrix? In the inner membrane?
What chemical components other than proteins may be found in the matrix? Of what
significance are they?
E.M. 7.
Nucleus of a Liver Parenchymal Cell (Hepatocyte)
1. Heterochromatin
2. Euchromatin
3. Perinucleolar chromatin
4. Fibrillar portion of the nucleolus
5. Granular portion of the nucleolus
6. Outer leaflet of the nuclear envelope
What is the general composition of #3, #4 and #5?
Nuclear pores cannot be resolved on this micrograph, but where would you expect to find
them? See next micrograph for location.
3
E.M. 8.
Liver Parenchymal Cell (Hepatocyte)
1. Heterochromatin
2. Euchromatin
3. Perinucleolar chromatin
4. Granular portion of the nucleolus
5. Nuclear pore
6. Fibrillar portion of the nucleolus
Which structure(s) #1, #3 or #4 would show the presence of DNA in light microscopy?
Which structure #2, #3 or #6 would be digested by RNAse activity?
E.M. 9.
Intestinal Absorptive Cell (Enterocyte) and Goblet Cell
1. Intestinal lumen
2. Microvilli
3. Region of the Golgi apparatus
4. Capillary
5. Goblet cell
6. Junctional complex
7. Terminal web
What might be the significance of the localization of mitochondria in the two positions within the
absorptive cell?
Which regions of the cells in this micrograph would show a positive PAS reaction?
What differences and similarities exist for the function of the Golgi apparatus in the two cell
types shown?
Based on your knowledge of this organ, what type of capillary is indicated by #4? (Difficult to
determine in this micrograph).
E.M. 10.
Intestinal Absorptive Cell
1. Microvilli
2. Microfilaments
3. Lipid droplets within SER
4. Matrix lipid droplets
5. RER
6. Membrane of SER
Trace the pathway of lipids absorbed by the cell from the intestinal lumen to a lacteal, noting all
histologic and E.M. compartments through which it must pass.
4
E.M. 11.
Epididymal Cell - Golgi Apparatus
1. Transport vesicle
2. Flattened cisternae of the cis face
3. Dilated cisternae of the trans face
4. Secretory vesicle
5. Multivesicular body
What is the relationship between the Golgi apparatus and transfer and secretory vesicles?
What is the role of the Golgi apparatus in the formation of glycoproteins?
What is the role of RER in the formation of glycoproteins?
E.M. 12.
Leydig Cell (small region of cytoplasm without nucleus)
1. Plasmalemma
2. Mitochondrion
3. SER
Name several functions of structure #3.
E.M. 13.
Liver Parenchymal Cell
1. Glycogen (alpha particles)
2. Lysosomes
3. Peroxisome
4. Ribosomes
5. Glycogen (beta particles)
6. Mitochondria
7. SER
What is the difference between a primary and secondary lysosome? A phagosome?
Define the following terms: Heterophagy? Autophagy? Residual body? Endocytosis?
Exocytosis?
E.M. 14.
Liver Parenchymal Cell
1. Lysosome (How can you distinguish primary and secondary lysosomes?)
2. Peroxisome
3. RER
4. Glycogen
5. SER
What is the difference between a lysosome and peroxisome? (This micrograph shows a good
example of each.)
E.M. 15.
Connective Tissue
1. Elastic fiber (amorphous and fibrillar components)
2. Collagen fibrils – in longitudinal section
3. Collagen fibrils – in cross section
What causes the banding of collagen fibrils? Is all collagen banded?
What is the cellular origin of elastic fibers?
5
E.M. 16.
Enterocyte (Intestinal Absorptive Cell) - Junctional Complex
1. Zonula occludens
2. Zonula adherens
3. Macula adherens
Define the following terms: Gap junction? Hemidesmosome? Terminal bar?
E.M. 17.
Liver
1. Sinusoid
2. Endothelial cell of sinusoid
3. Space of Disse with microvilli
4. Bile canaliculus
5. Nucleus of hepatocyte
Name a cell type (not shown here) that can be found adjacent to hepatocytes and the space of
Disse.
What is a Kupffer cell?
Relate the organelles and inclusions of a hepatocyte to as many functions of the liver as you
can.
Find the lipid droplets (if any) in this micrograph.
What are the morphological and functional differences between the liver sinusoids and bile
canaliculi?
What are the “endocrine” and “exocrine” functions of the liver?
E.M. 18.
Lung (Fetal)
1. Capillary
2. R.B.C. in capillary (Is there another R.B.C. in a capillary)?
3. White blood cell in capillary
4. Glycogen
5. Lamellar bodies in alveolar space
6. Type II pneumocyte
7. Lamellar bodies in Type II pneumocyte
8. Macrophage (dust cell)
Note - Lysosomes and ingested lamellar bodies
What substance is contained in the lamellar bodies and what is its function?
What type of endothelium is found in the alveolar capillaries?
E.M. 19.
Lung (Adult)
1. Endothelium
2. Basal lamina
3. Alveolar epithelium - Type I pneumocyte
4. Elastic fiber
5. R.B.C. in capillary
6. Endothelial nucleus
7. Fibroblast in interalveolar space
Note the components of the blood - air "barrier".
6
E.M. 20.
Skin
1. Stratum corneum
2. Stratum granulosum
3. Nucleus of a cell in the stratum spinosum
4. Keratohyalin granules
5. Melanosomes
6. Desmosomes
7. Tonofibrils composed of tonofilaments (keratin filaments)
How many separate cells are seen in this electron micrograph?
What is the origin of the melanosomes?
E.M. 21.
Early Amnion
1. Simple squamous epithelium
2. Basal lamina
3. Collagen
4. Fibroblasts
Are the fibroblasts seen here relatively active or inactive?
From its appearance suggest the type of collagen that is evident at #3.
E.M. 22.
Gap junctions are bimembranous plaques that bond apposed cell membranes
together and are thought to serve a regulatory function. They range in size from 0.3 µm or so
to 5 or 6 µm in diameter. They are most frequently found in the plasma membrane of secretory
cells and may be rapidly modulated through the insertion of elements into the membrane;
aggregation of elements through lateral diffusion within the plane of the membrane, and by
removal from the membrane by an endocytotic process which results in the degradation of gap
junction membrane through fusion with lysosomes. Gap junctions can be visualized by several
ultrastructural methods that distinguish them from other junctional structures.
a.
Stained thin section of gap junction in liver cell. The gap junction is recognized
as a region where the intercellular space (ics) narrows to bring the membranes of adjacent cells
into close apposition. Profiles of gap junctions are often straight or slowly curving and
characterized by densely staining material on their cytoplasmic faces (1) and frequently by
periodic densities midway between the apposed membranes (2). X180,000.
b.
Unstained lanthanum infiltrated gap junction in a cultured hepatoma. Gap
junctions acquired their name by virtue of the ability of lanthanum to percolate into a 2-4 nm
wide intercellular space at the gap junction (3). This space, however, is often interrupted by
unstained cell-cell bridges with the same periodicity as the intercellular densities observed in
stained sections (small arrows). X190,000.
7
c.
Freeze fracture replica of gap junctions in ependymal cell of the rat brain (4).
This technique which splits membrane lipid bilayers at the level of the hydrophobic interface has
revealed that gap junctions consist of plaque-like or button-like aggregations of 8 nm particles
found in both apposed membranes. Every particle in one of the membranes matches with a
particle protruding from the apposed membrane within the intercellular space. In this example
imagine sitting within a cell looking at its lateral membrane. The fracture procedure has
removed the entire membrane of the cell you are sitting in and the outer leaflet of the
membrane of the adjacent cell in all regions except area (5). The leaflet of the membrane
indicated by (4) (nonjunctional) and by P (junctional) is the P leaflet or protoplasmic leaflet of
the adjacent cell. The region indicated by (5) and E represents a piece of the extra- cellular
leaflet of the cell you are sitting within. The fracturing process has removed the protoplasmic
leaflet only of this cell in this region. The freeze fracture process leaves particles on the
protoplasmic leaflet and complementary pits on the extracellular leaflet of vertebrate gap
junction regions. (6) is an area where the fracture has dipped into the cytoplasm of the
adjacent cell. X62,000.
d.
Enlargement of gap junction particles on the P leaflet (7) and pits on the E leaflet
(8). X211,000.
e.
3-dimensional representation of about 1/4 of a gap junction plaque. The
intercellular space (ics) narrows to a 2-4 nm gap where the intramembranous particles (imp)
characteristic of gap junctions ( 8 nm in diameter) provide membrane-to-membrane contact.
Gap junctional plaques are also characterized by slightly thickened membrane possibly
resulting from the adherence of cytoplasmic dense material (cdm).
f.
Freeze fracture replica of gap junction formation plaque in rabbit granulosa cell.
Gap junctions of granulosa cells during early folliculogenesis consist of numerous small clusters
of 8 nm particles on the P leaflet (9) thought to originate through the aggregation of 10-11 nm
particles (10) clearly more homogeneous in shape and size than typical nonjunctional particles
(11). Such structures may form within minutes when single cells are heavily plated in culture.
X120,000.
g.
Gap junction plaques of granulosa cells of mature ovarian follicles may occupy
areas as large as 30-40 µm2 (12). X24,000.
h.
Large gap junctional caps may invaginate from one cell into another (13) nuc =
nucleus. X15,000.
i.
After pinching off the invaginated membrane becomes a bimembranous gap
junctional vesicle separated from the cell surface (14). X90,000.
j.
Such cytoplasmic gap junctional vesicles can also be observed in freeze fracture
replicas and are characterized by typical P-leaflet particles (P) and E-leaflet pits. X44,000.
E.M. courtesy of Dr. Larsen.
8
E.M. 23.
Skeletal Muscle (Monkey Soleus)
1. Z Line
2. I Band
3. A Band
4. H Band
5. M Line
6. Dilated terminal cisternae of sarcoplasmic reticulum
7. A-I junction; location of triads
8. Glycogen
Define the limits of a sarcomere.
Compare the organization of the muscle in this micrograph with that of cardiac muscle.
What structures are included in a triad?
The Z lines do not form a straight line through this micrograph, they are staggered. Each
separate region of Z line represents the width of one _________?