The practical note
Dr. Omar Amer
Biology
[biol 106]
1
PART
1
TOUR OF THE CELL
2
TOUR OF THE CELL
Section A: How We Study Cells
1.Microscopes provide windows to the world of
the cell
2.Cell biologists can isolate ‫ يعزل‬organelles to study
their function
3
Microscopes provide windows to
the world of the cell
• The discovery and early study of cells
progressed with the invention and
improvement of microscopes in the
17th century.
• In a light microscope (LMs) visible
light passes through the specimen and
then through glass lenses.
– The lenses refract light
– the image is magnified
– into the eye or a video screen.
4
•Transmission electron microscopes
(TEM)
for studying internal structures
– A TEM aims an electron beam through a thin section of the
specimen.
– The image is focused and magnified by electromagnets.
5
•Scanning electron microscopes
(SEM)
for studying surface structures
– The sample surface is covered with a thin film of gold.
– The beam excites electrons on the surface.
– These secondary electrons are collected and focused on a
screen.
• The SEM has an
image that seems
three-dimensional.
6
Figure 1. The cell is seen to contain a
number of organelles that are
surrounded by membranes. These
organelles include Mitochondria (M),
the rough Endoplasmic Reticulum
(RER), the smooth Endoplasmic
Reticulum (SER), the Golgi Apparatus
(G), Secretory Granules (S), the
Centeriole (C) lysosomes (L), the
Nucleolus (Nu), the Nucleus (N) and
Plasma membrane (P).
This figure is a relatively low
magnification electron micrograph
of a cell from the pancreas of the
squirrel monkey.
Figure 2. Electron micrograph of section of
the monkey pancreas cell. 12,000 X.
M, mitochondrion; Nu, Nucleolus; RER,
rough Endoplasmic Reticulum; S, secretory
vesicle pouring its contents outside the
cell.
Arrow indicates double layer of Plasma
membrane, running parallel to one
another. 129,000 X
Figure 3. The cell nucleus.
Nu, Nucleolus
Ne, Nuclear envelop.
Figure 4.
Ribosomes
Bound and Free
Figure 5.
Rough & Smooth
Endoplasmic
Reticulum
FIGURE 6.
Electron micrograph
Mitochondrion.
of
Figure 7.
Golgi apparatus
Figure 8.
Lysosomes
cilia
Figure 9.
Cilia and Flagellum
1000 X.
flagellum
PART
II
Histology
Types of tissues
16
* Four main groups of tissues are known in
the body, these are:
A- Epithelial tissue
B- Connective tissue
C- Muscular tissue
D- Nervous tissue
A- Epithelial tissue
• These tissues arise from any of the three primary
germ layers; the ectoderm, endoderm or mesoderm.
• These tissues are characterized by:
- They are almost found covering a surface, external or
internal.
- They having a very little intercellular substance or matrix
in between their cells.
- They resting in the majority of cases on a basement
membrane (formed of the underlying connective tissue).
• The epithelial tissues are classified according to
form and structure into several types:
A- Epithelial tissues
I-Simple:
- The cells arranged principally in one layer and include the
following :
a- Squamous ( ‫)حرشفية‬
b- Cuboidal ( ‫)مكعبة‬
c- Columnar ( ‫) عمودية‬
d- Ciliated columnar (
e- Pseudostratified ( ‫)طبقية كاذبة‬
f- Pseudostratified ciliated ( ‫)مهدبة طبقية كاذبة‬
‫) عمودية مهدبة‬
a- Squamous ( ‫)حرشفية‬
(Endothelium wall of Bowman's capsule)
b- Cuboidal ( ‫)مكعبة‬
(Wall of sweat gland)
c- Columnar
( ‫) عمودية‬
(Mucous membrane of alimentary canal
of the toad, from oesophagusto rectum)
d- Ciliated columnar (
‫) عمودية مهدبة‬
(Mucous membrane lining the anterior region
of the oviduct of the toad).
e- Pseudostratified (
‫)طبقية كاذبة‬
(Inner wall lining ducts of some large glands)
f- Pseudostratified ciliated (
(Inner lining of trachea)
‫)مهدبة طبقية كاذبة‬
II) Stratified or compound:
Cells arranged in several layers and include the following:
a- Squamous ( ‫)حرشفية‬
b- Columnar ( ‫) عمودية‬
c- Ciliated columnar ( ‫) عمودية مهدبة‬
d- Transitional ( ‫)انتقالية‬
a- Squamous ( ‫)حرشفية‬
(Epidermis of vertebrate skin)
b- Columnar ( ‫) عمودية‬
(Conjunctiva of eye)
c- Ciliated columnar ( ‫) عمودية مهدبة‬
(Epithelium lining buccopharyngeal cavity of the toad)
d- Transitional ( ‫)انتقالية‬
(Inner lining of urinary passage)
B- Connective or Sustentacular tissues
(‫)االنسجة الضامة أو المدعمة‬
• These tissues arise from the mesoderm only and
characterized by:
- They have a large amount of intercellular substance
or matrix among their cells.
- They are never to be found on a surface.
- They do not rest on a basement membrane.
- Their main function is to connect other tissues or
organs together or support them.
• Their ground substance is either solid or fluid and
accordingly they are classified into three main
groups:
1- The connective tissues proper. (‫)االنسجة الضامة االصيلة‬
2- The skeletal tissues.
(‫)االنسجة الهيكلية‬
3- The vascular tissues.
(‫)االنسجة الوعائية‬
1- The connective tissues proper:
(‫)االنسجة الضامة االصيلة‬
- Six varities of these tissues are known:
a- Areolar connective tissue (‫)نسيج ضام فجوى‬
b- Fibrous connective tissue (‫)نسيج ضام ليفى‬
c- Elastic connective tissue (‫)نسيج ضام مرن‬
d- Adipose connective tissue (‫)نسيج ضام دهنى‬
e- Reticular connective tissue (‫)نسيج ضام شبكى‬
f- Mucous connective tissue (‫)نسيج ضام مخاطى‬
2- The skeletal tissues.
(‫)االنسجة الهيكلية‬
- These tissues compose the skeleton. They are either
cartilage or bone.
a- Cartilage
1- Hyaline cartilage (from trachea)
2- Fibro-cartilage
3- Elastic cartilage
b- Bone
Dense bone
3- The vascular tissues.
(‫)االنسجة الوعائية‬
- These comprise the blood and lymph only.
a- Blood film of man
White blood cells
b- Blood film of vertebrates ( Toad)
C- Muscular tissues
• These tissues form the muscles.
• They are made up of contractile muscle cells,
commonly reffered to as muscle fibers.
• There are three types of muscle fibers in the animal
body.
1- Unstriated muscle fibers (or smootrh muscle).
2- Striated muscle fibers (skeletal muscles).
3- Cardiac muscle fibers.
1- Unstriated muscle fibers ( Smooth muscles).
* Each muscle fiber (muscle cell) characterized by:
- Long
- Spindle- shaped with pointed ends and
thickened central part housing the nucleus.
- Contain a number of fine thread-like myofibrils
extend lengthwise in the cytoplasm.
*The unstriated muscles are usually found in the
walls of the viscera.
* They are called visceral or involuntry muscles
‫عضالت حشوية أو غير ارادية‬.
2- Striated muscle fibers ( Skeletal muscles).
* Each muscle fiber (muscle cell) characterized by:
- Large elongated cylindrical cell.
- Showing large number of fine alternating dark
and light cross striations called dark and light
bands.
- Surrounded by a thin structureless membrane
called sarcolemma.
- Contains a large number of peripherally situated
nuclei ( syncytium).
- Contains numerous myofibrils run
longitudinally in the sarcoplasm.
* The muscle fibers are not branch
anastomose and form bundles.
* The striated muscles are usually found
connected to the skeleton.
* They are called skeletal or voluntry
muscles.
Skeletal muscle (high power)
3 - Cardiac muscle fibers ( Skeletal muscles).
* Each muscle fiber (muscle cell) characterized by:
- Cylindrical but not much elongated .
- Has one ovoid central nucleus.
- Neighbouring fibers unite to form syncytium.
- Every two connected fibers have a darkly stained
transverse band called intercalated disc.
- Contains numerous myofibrils run longitudinally
in the sarcoplasm.
- Showing large number of fine alternating dark
and light cross striations called dark and light
bands.
- Surrounded by a thin structureless membrane
called sarcolemma.
* The cardiac fibers branch and unite with
each other.
* The cardiac muscles are found only in the wall
of heart and contract rhythmically.
D- Nervous tissues
* The nervous system consists of:
1- Central nervous system
( brain and spinal cord).
2- Peripheral nervous system ( nerves).
Sciatic nerve
Neuron
PART
III
Histology
organs
61
‫‪A- Blood vessels‬‬
‫االوعية الدموية‬
* The blood vessels formed from arteries and veins.
* Arteries and veins are built up on the same plan.
* The wall of each formed from three coats or layers:
- An inner epithelial and fibrous coat.
- A middle muscular coat.
- An outer connective tissue coat.
* You can distinguish between the artery and vein by
the differences in structure and relative thickness
of these layers or coats.
1- Artery
* The wall of artery
consists of:
i- Tunica intima
‫الطبقة الداخلية‬
ii- Tunica media
‫الطبقة المتوسطة‬
iii- Tunica adventitia
‫الطبقة الخارجية‬
i- Tunica intima:
or inner layer consists of an endothelium of
squamous cells followed by a wavy lamina of
elastic connective tissue
ii- Tunica media:
or middle layer consists of circular unstriated
muscle fibers held together by elastic and
collagenous connective tissue fibers. This is the
thickest layer in the wall of artery.
iii- Tunica adventitia:
or outer layer consists of areolar connective tissue
rich in elastic fibers.
2- Vein
* The wall of vein
consists of:
i- Tunica intima
‫الطبقة الداخلية‬
ii- Tunica media
‫الطبقة المتوسطة‬
iii- Tunica adventitia
‫الطبقة الخارجية‬
i- Tunica intima:
consists of an endothelium of squamous cells, but the
elastic connective tissue layer is poorly developed or may
be totally absent.
ii- Tunica media:
consists of circular unstriated muscle fibers, but this layer
is relatively much thinner than that of artery and contains
more collagenous than elastic connective tissue fibers.
iii- Tunica adventitia:
is the thickest layer in the wall of vein. It consists of
areolar connective tissue rich in collagenous fibers.
Low power view of medium artery
art = artefacts, tear (above) and fold
(below)
TA = tunica adventitia
TM = tunica media
Medium vein with valve
ad = adipose tissue
A = artery
TA = tunica adventitia
TM = tunica media
v = valve
High power view of small artery
ad = adipose (fat) cell
ef = elastic fibre
end = endothelial cell nuclei
ext = external ennnnlastic membrane
int = internal elastic membrane
n = smooth muscle nuclei
TA = tunica adventitia
TM = tunica media
High power view of medium vein
ad = adipose tissue
ner = nerve
SM = longitudinal smooth muscle bundle in
adventitia
TA = tunica adventitia
TM = tunica media
asterisk = tunica media broken up with
collagen fibres
B- Skin
‫الجلد‬
* Mammalian skin is composed of two primary layers:
1- The epidermis: This layer consists of a stratified squamous
epithelium. The cells of malpighian layer contain pigment
granules and the horny layer is thicker.
* Keratinocytes are the major cells, constituting 95% of the
epidermis, while Merkel cells, melanocytes and Langerhans
cells are also present.
* The epidermis can be further subdivided into the following
strata or layers (beginning with the outermost layer):
• Stratum corneum
• Stratum lucidum (only in palms and soles)
• Stratum granulosum
• Stratum spinosum
• Stratum germinativum (also called the stratum basale)
2- The dermis: This layer consists of a dense
areolar connective tissue rich in white fibers,
blood vessels and nerves. The outer part of
dermis projects into the epidermis forming
microscopic dermal papillae in which nerve
fibers are found.
* The mammalian skin is characterized by the
presence of hairs and glands, which all arise
principally from the epidermis, but lie
embedded by their basal parts in the dermis.
Skin
C- Alimentary canal
‫القناة الهضمية‬
* The
wall of alimentary canal consists of
four basic layers: starting at the
innermost (closes to the food) there's the
mucosa, then submucosa, then
muscularis, then serosa.
* The muscularis layer is made up of two
distinct, concentric muscular layers, the
inner circular and the outer longitudinal
(named for the general direction of their
muscle fibers).
1- Oesophagus
( T.S. of the Oesophagus of rabbit)
Oesophagus
Oesophagus
2- Stomach
( T.S. Stomach of rabbit)
* The
stomach wall consists of four layers:
1- serosa
2- Muscularis
3- Submucosa 4- Mucosa
* The mucosa layer is the thickest layer.
* It contains a simple columnar epithelium
( devoid of goblet cells) and characteristic gastric glands which open on to
the epithelium.
* They are usually of the simple or simple branched tubular type.
* Their cells consist of two varities:
- The first variety comprises cells which abound at the base of the gland, these
are polygonal, granular and take the blue colour with the common stains.
- The second variety comprises cells which abound towards the luminal part of
the gland, these are circular or oval, non-granulated and stain red.
- The cells of the first variety are peptic or central cells, secrete digestive
enzymes.
- The cells of the second variety are acidic or oxyntic or parietal cells, secrete
Hcl.
Stomach
3- Ileum
(T.S. of ileum of rabbit)
* The mucosa is thrown up into numerous finger-like folds
called villi all covered by a simple columnar epithelium
with scattered goblet cells.
Small intestine
D- Accessory digestive
glands
1- The liver
‫الكبد‬
Liver of mammals
(s. of the liver of pig)
* The liver of pig is a reticular gland, the cells of
which are arranged in strands crossing each other
forming a network.
* These strands are arranged in groups, each group
forming a hepatic lobule.
* The bile canaliculi lie among the cells and collect in
groups, each group forming a bile ductule which
lies, beside two blood vessels ( artery and vein), in a
certain space called the portal space.
Liver
2- The pancreas
‫البنكرياس‬
The pancreas
(S. of the pancreas of rat)
* The pancreas is a digestive gland of the compound tubulo-alveolar
type.
* It is a mixed gland for, besides being an exocrine gland with a duct,
it is also a ductless gland of internal secretion.
* The pancreatic acini or alveoli are the secretory parts of the gland.
* The wall of each acinus is formed of columnar or pyramidal cells.
* Each cell is differentiated into two zones, a basal zone contains the
nucleus, has a basophilic coarse granules and luminal zone is
strikingly acidophilic and contains fine and numerous granules.
* The islets of langerhans are scattered groups of cells which stain
paler in routine sections.
E- The spleen
‫الطحال‬
* Spleen Structure:
• The white pulp is circular in structure and is made
up mainly of lymphocytes.
• The red pulp surrounds the white pulp and contains
mainly red blood cells and macrophages. The main
function of the red pulp is to phagocytize old red
blood cells
* The spleen is an organ found in all vertebrate
animals with regenerative capabilities and has
important roles in regard to red blood cells and the
immune system.
* In humans, it is located in the left upper quadrant of
the abdomen.
* It removes old red blood cells and holds a reserve of
blood in case of hemorrhagic shock while also
recycling iron.
* As a part of the mononuclear phagocyte system, it
metabolizes hemoglobin removed from senescent
erythrocytes.
* The globin portion of hemoglobin is degraded to its
constitutive amino acids, and the heme portion is
metabolized to bilirubin, which is subsequently
shuttled to the liver for removal.
* It synthesizes antibodies in its white pulp and
removes antibody-coated bacteria along with
antibody-coated blood cells by way of blood and
lymph node circulation.
* The spleen is brownish.
* Recently, it has been found to contain in its reserve
half of the body's monocytes within the red pulp.
* These monocytes, upon moving to injured tissue ,
turn into dendritic cells and macrophages while
promoting tissue healing.
* It is one of the centers of activity of the
reticuloendothelial system and can be considered
analogous to a large lymph node, as its absence leads
to a predisposition toward certain infections.
Spleen
F- The lymph node
‫العقد اللمفية‬
* A lymph node is a small ball or an oval-shaped
organ of the immune system, distributed widely
throughout the body including the armpit and
stomach/gut and linked by lymphatic vessels.
* Lymph nodes are garrisons (‫ )ثكنات‬of B, T, and
other immune cells.
* Lymph nodes are found all through the body, and
act as filters or traps for foreign particles.
* They are important in the proper functioning of
the immune system.
* They are packed tightly with the white blood cells
called lymphocytes and macrophages.
* Lymph nodes also have clinical significance, they
become inflamed or enlarged in various
conditions, which may range from trivial, such as
a throat infection, to life-threatening such as
cancers.
* In the latter, the condition of lymph nodes is so
significant that it is used for cancer staging, which
decides the treatment to be employed, and for
determining the prognosis.
Schematic of lymph node showing lymph sinuses
* The lymph node is surrounded by a fibrous capsule, and inside
the lymph node the fibrous capsule extends to form trabeculae.
* The substance of the lymph node is divided into the outer cortex
and the inner medulla surrounded by the cortex all around
except for at the hilum, where the medulla comes in direct
contact with the surface.
* Thin reticular fibers, elastin form a supporting meshwork called
reticular network (RN) inside the node, within which the white
blood cells (WBCs), the most prominent ones being lymphocytes,
are tightly packed as follicles in the cortex.
* The RN provides not just the structural support, but also will
provide surface for adhesion of the dendritic cells, macrophages
and lymphocytes.
* It allows for exchange of material with blood through the high
endothelial venules and provides the growth and regulatory
factors necessary for activation and maturation of immune cells.
* The number and composition of follicles can change especially
when challenged by an antigen, when they develop a germinal
center.
*Lymph node structure:
* Cortex:
In the cortex, the subcapsular sinus drains to trabecular
sinuses, and then the lymph flows into the medullary
sinuses.
* The outer cortex consists mainly of the B cells arranged as
follicles, which may develop a germinal center when
challenged with an antigen, and the deeper cortex mainly
consisting of the T cells.
* There is a zone known as the subcortical zone where T-cells
(or cells that are mainly red) mainly interact with dendritic
cells, and where the reticular network is dense.
* The predominant site within the lymph nodes which
contain T cells & accessory cells is also known as
paracortex (reticular network).
* Medulla:
* There are two named structures in the medulla:
* The medullary cords are cords of lymphatic tissue,
and include plasma cells, macrophages, and B cells.
* The medullary sinuses (or sinusoids) are vessel-like
spaces separating the medullary cords.
* The Lymph flows into the medullary sinuses from
cortical sinuses, and into efferent lymphatic vessels.
* Medullary sinuses contain histiocytes (immobile
macrophages) and reticular cells.
* The Medulla contains large blood vessels, sinuses and
medullary cords that contain plasma cells secreting
antibody.
Lymph node, showing (1) capsule, (2) subcapsular sinus,
(3) germinal centers, (4) lymphoid nodule, (5) trabeculae.
Lymph node
G- The thymus gland
* The thymus is a specialized organ of the immune system.
* The thymus "educates" T-lymphocytes (T cells), which are
critical cells of the adaptive immune system.
* Each T cell attacks a foreign substance which it identifies with
its receptor.
* T cells have receptors which are generated by randomly
shuffling gene segments.
* Each T cell attacks a different antigen.
* T cells that attack the body's own proteins are eliminated in the
thymus.
* Thymic epithelial cells express major proteins from elsewhere in
the body, and T cells that respond to those proteins are
eliminated through programmed cell death (apoptosis).
* The thymus is composed of two identical lobes and is located
anatomically in the anterior superior mediastinum, in front of
the heart and behind the sternum.
* Histologically, the thymus can be divided into a central medulla
and a peripheral cortex which is surrounded by an outer
capsule.
* The cortex and medulla play different roles in the development
of T-cells.
* Cells in the thymus can be divided into thymic stromal cells and
cells of hematopoietic origin (derived from bone marrow
resident hematopoietic stem cells).
* Developing T-cells are referred to as thymocytes and are of
hematopoietic origin.
* Stromal cells include thymic cortical epithelial cells, thymic
medullary epithelial cells, and dendritic cells.
* The thymus provides an inductive environment for development
of T-lymphocytes from hematopoietic progenitor cells.
* In addition, thymic stromal cells allow for the selection of a
functional and self-tolerant T-cell repertoire.
* Therefore, one of the most important roles of the thymus is the
induction of central tolerance.
* The thymus is largest and most active during the neonatal and
pre-adolescent periods.
* By the early teens, the thymus begins to atrophy and thymic
stroma is replaced by adipose (fat) tissue. Nevertheless, residual
T lymphopoiesis continues throughout adult life.
* Structure:
* Each lateral lobe is composed of numerous lobules held together by
delicate areolar tissue; the entire organ being enclosed in an investing
capsule of a similar but denser structure.
* The primary lobules vary in size from that of a pin's head to that of a
small pea, and are made up of a number of small nodules or follicles.
* The follicles are irregular in shape and are more or less fused together,
especially toward the interior of the organ.
* Each follicle is from 1 to 2 mm in diameter and consists of a medullary
and a cortical portion, and these differ in many essential particulars
from each other.
* Cortex:
* The cortical portion is mainly composed of lymphoid cells, supported by
a network of finely-branched epithelial reticular cells, which is
continuous with a similar network in the medullary portion.
* This network forms an adventitia to the blood vessels.
* The cortex is the location of the earliest events in thymocyte
development, where T cell receptor gene rearrangement and positive
selection takes place.
* Medulla:
* In the medullary portion, the reticulum is coarser than in
the cortex, the lymphoid cells are relatively fewer in
number, and there are found peculiar nest-like bodies, the
concentric corpuscles of Hassall.
* These concentric corpuscles are composed of a central
mass, consisting of one or more granular cells, and of a
capsule formed of epithelioid cells.
* They are the remains of the epithelial tubes, which grow
out from the third branchial pouches of the embryo to
form the thymus.
* Each follicle is surrounded by a vascular plexus, from
which vessels pass into the interior, and radiate from the
periphery toward the center, forming a second zone just
within the margin of the medullary portion.
* In the center of the medullary portion there are very few
vessels, and they are of minute size.
* The medulla is the location of the latter events in
thymocyte development.
* Thymocytes that reach the medulla have already
successfully undergone T cell receptor gene
rearrangement and positive selection, and have been
exposed to a limited degree of negative selection.
* The medulla is specialised to allow thymocytes to
undergo additional rounds of negative selection to
remove auto-reactive T-cells from the mature
repertoire.
* The gene AIRE is expressed by the thymic medullary
epithelium, and drives the transcription of organspecific genes such as insulin to allow maturing
thymocytes to be exposed to a more complex set of
self-antigens than is present in the cortex.
Thymus
Micrograph showing
a thymic corpuscle
(Hassall corpuscle),
a characteristic histologic
feature of the human
thymus.
h- Thyroid gland
Thyroid gland
i- Respiratory organs
1- Lung
T.S of lung
Fetal lung histology
2- Trachea
* The trachea of rabbit consists of the following layers:
1- Mucosa:
It consists of a pseudostratified ciliated columnar epithelium
which rests on a distinct basement membrane. Among the
cells of this layer are unicellular glands or goblet cells.
2- Submucosa:
- It consists of areolar or loose connective tissue.
- It contains multicellular mucous glands, whose ducts open
onto the surface of the mucosa and blood vessels of various
sizes.
- This layer also contains a c- shaped incomplete ring of
hyaline cartilage.
3- The outer coat ( Adventitia):
- It consists of dense fibrous connective tissue which contains
some fat cells and blood vessels.
Trachea
j- Urinary organs
The kidney of rabbit
* The nephric unit (= nephron) consists of two parts:
- A small knob-like malpighian corpuscle .
- Very long uriniferous or convoluted tubule .
* The convoluted tubule differentiated into 3 main
sections:
1- Proximal convoluted tubule:
Relatively wide, thick-walled and pursues a tortuous
course in the cortex.
2- Loop of Henle:
a- Proximal descending limb b- Distal ascending limb.
3- Distal convoluted tubule.
* In the T.S. of kidney, we can observe the following:
* Capsule: fibrous connective tissue.
* Malpighian corpuscle:
* Bowmann’s capsule: double wall of simple
squamous epithelium.
* Glomerulus: capillary network.
* Proximal convoluted tubule: has a relatively narrow
lumen and thick walls of cuboidal or pyramidal
granular cells with distinct brush border.
* Distal convoluted tubule: has a larger lumen and
thinner walls of smaller cuboidal cells without brush
border.
* Medulla: contains the loops of Henle and the
collecting tubules.
* descending limb of loop of Henle: has very thin
walls of squmous epithelium.
* Ascending limb of loop of Henle: has thicker
walls of cuboidal epithelium.
* collecting tubule: are the largest in diameter.
Each has a wide lumen and thick walls of
cuboidal cells.
k- Genital glands
1- Testis
Semineferous tubule (Testis)
2- Ovary
Ovary