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					Lab 2.                                        PCB4023L- Tissues & Cells

 This is the reading material to understand the lab, also it important for quiz.

Introduction
         Histology is literally the study of tissues but is more broadly defined as the study of cells (cytology), tissues
(histology) and organs (organology) in relation to their function. Often the term microscopic anatomy or
microanatomy is employed.

          Tissues are collections of similar cells and the intercellular substances around them. There are four basic
types of tissue and vast majority of cell types can be classified as one of these four.

1)       Epithelia - continuous layers of cells with little intercellular space which line surfaces and form glands




1. I.     Simple Squamous
          Simple Squamous epithelium is very thin and flat. It forms the peritoneal lining (mesothelium) and the
inner lining (luminal surface; endothelium) of all vascular elements (arterial, venous, capillary, lymphatic). Other
examples of simple squamous epithelia include the alveoli of the lung and the Bowman’s capsule of the kidney’s
nephrons.
          Mesothelium (small intestine)
          Endothelium (artery, vein and nerve)
                  alternative: find vessels in adult lung
          Lung alveoli (lung)
          Bowman’s capsule (kidney)

1. II.   Simple Cubical
         This epithelium lines small tubules and follicles and the cells are about equal in height and width with a
central nucleus. It can be found most easily lining the collecting tubules of the kidney. Other examples include the
lens capsule and some of the ducts in some exocrine glands (e.g., salivary glands).
          renal tubules (kidney)

1. III.  Simple Columnar
         Simple columnar epithelium is found in organs adapted for absorption and secretion. The cells are taller
than they are wide and the height varies a great deal. They are found throughout the lining of the gut (stomach,
small intestine, colon). Note that in the duodenum the lumenal surface shows columnar cells covering the villi
(projections of the mucosa into the lumen). Many of them are striated (i.e., possess microvilli) on their free surface
and scattered throughout-are goblet cells, which are adapted for mucous secretion (see below). Other sites
containing this epithelium include the uterine tubes and cavity and occasionally in the larger ducts of exocrine
glands.
         small intestine
         colon

1. IV.    Pseudo stratified Columnar
          This epithelium contains columnar and basal cells and gives the appearance that it is layered. While all
cells attach to the basement membrane, not all extend to the lumen. The pseudostratified columnar epithelia lining
the upper respiratory tract (trachea and bronchi) are ciliated and contain scattered goblet cells (unicellular glands).
Other tissues containing this epithelium include the male reproductive tract (epididymis, ductus deferens and
portions of the urethra).
          Trachea
                   Alternative: use lung bronchi
          Epididymis (with testis)

1. V.     Stratified Squamous
          This rather thick epithelium is found where protection is needed, such as body surface and body entrances.
In the skin notice that the basal cells in the epithelium are rounded with a progressive flattening of the cells toward
the free surface. When the surface is moist, as in the tongue, the free surface cells are not visibly cornified. Non-
keratinized stratified squamous epithelia can also be found in the lining of the oral cavity (varies with species),
esophagus, anal canal and vagina.
          Skin (keratinized)
          Tongue (non-keratinized)

1. VI.   Stratified Cuboidal and Columnar
         These relatively rare types can be found lining large ducts (e.g., salivary, mammary), the pharynx, the
palpebral conjunctiva, and the urinary passages. In the urethra the surface cells are tall and thus are stratified
columnar. In salivary gland look for large, open ducts and notice that basal cells are low but the surface cells can be
either Cuboidal or columnar in shape.
         Urethra (prostate and urethra)
         Sublingual gland; look for larger ducts

1. VII. Transitional
          This unusual epithelium lines the urinary tract from the renal calyces through to a portion of the urethra,
and the urinary bladder is perhaps the best example of this type. It is found in organs which undergo distention and
therefore becomes thicker and thinner. Take note of the surface cells and compare them with the surface cells from
stratified squamous as seen in the esophagus.
          Urinary tract (transitional epithelium)

1. VIII. Epithelial Specializations

Goblet cells (gut and respiratory tract) are epithelial cells adapted for the secretion of mucous. The striated border
of the duodenum is made up of many small finger-like projections called microvilli and these increase the surface
area and are for absorption. Cilia (trachea) are whip-like structures that beat and move substances along the surfaces
of their cells. The sterocilia seen in the epididymis are actually giant microvilli.
          Goblet cells: duodenum
          Microvilli - duodenum
          Cilia - trachea, lung
         Sterocilia - epididymis

1. IX. Functions of Epithelial Cells
        Epithelial cells are specialized for different functions. Protection results from layering or stratification.
Pseudostratified ciliated cells function in transporting mucus and particulate matter along their surfaces. Epithelia
which secrete. absorb, resorb and filter are single-layered, and their height correlates with their function.

1. X. Glands
           The simplest glands are the unicellular (i.e., glands consisting of one cell) and a good example is the goblet
cell. Still simple, but multicellular, are the short tubular glands of the colon. An example of a compound acinar
gland is the exocrine cells of the pancreas. Finally, the suprarenal gland is an example of an endocrine cell.
           Unicellular goblet: small intestine; colon
           Simple tubular: colon
           Compound acinar: pancreas
           Endocrine cells: suprarenal

2)     Connective tissue - cells embedded in intercellular substances (extra-cellular matrix); the matrix is
typically abundant and the cells less so.




          General connective tissues are dispersed widely throughout the body. These tissues are produced mainly
by fibroblasts. The matrix (sparse in adipose tissue) is generally a network of protein fibers (collagen or elastic) in a
ground substance of polysaccharide gel. If the fibers are relatively sparse, they are considered loose connective
tissues (mesenchyme, adipose, alveolar). If the fibers are densely packed, they are considered fibrous (or dense) and
further subdivided as to regular (fibers exhibit a uniform orientation) or irregular (fibers exhibit an irregular
orientation).

         The remaining connective tissues are classified as special. Two (or three), cartilage and bone [and dentin],
form the skeleton and provide a rigid framework to which all other tissues/organs attach. Blood is considered a fluid
connective tissue. The blood stem cells, hematopoietic tissue in the bone marrow, are the fourth special connective
tissue.

         Cartilage is a firm but flexible skeletal tissue. The matrix consists of gel-like substances (proteoglycans)
and varying amounts and types of protein fibrils. Two types of protein fibrils are found in cartilage, collagen and
elastin. Collagen is much more common and its fibers are relatively flexible but with limited reversible
extensibility. Elastin fibers are less widely distributed but stretch easily with almost perfect recoil. These are found
in the ligaments of the vertebral column and in elastic cartilage. The proteoglycans are carbohydrate polymers
linked to core proteins and can bind water. These form hydrated gels, which allow for the rapid diffusion of water-
soluble molecules and cells. The latter is important because cartilage is an avascular tissue.

         Cartilage is produced by chondrocytes. Within the cartilage, the chondrocytes are housed in small cavities
called lacunae (L., dim. of lacus (lake, hollow)). Surrounding the cartilage (except along articular surfaces) is the
perichondrium, a fibrocellular layer containing the proliferative cartilage stem cells.

         The physical properties of cartilage are determined by the ground substance and by the type and abundance
of the protein fibers. Cartilage is both aneural and avascular, the nutrients and gases diffusing through the ECM to
provide the chondrocytes (and conversely, the wastes diffusing out). Cartilage can calcify (become embedded with
calcium salts) but its minerals are not as highly ordered as in bone.




           Three types of cartilage can be differentiated on the basis of their type and abundance of protein fibers:
hyaline, fibro- and, elastic cartilage. Hyaline (Gr. hyalos, glass) is the most common. It consists of sparse collagen
fibrils in a “glassy” matrix. It is firm with slight elasticity and can be found in the costal cartilages, bronchi, trachea
and articular cartilages. It also forms the cartilaginous precursor to endochondral bones.

         Fibrocartilage has abundant, densely interwoven collage fibrils with correspondingly less ground substance.
It is found in areas subject to compressive loading, e.g., all symphyses including intervertebral discs (between
vertebral bodies), articular menisci (discs), and sutures.

       Elastic cartilage contains numerous elastin fibers. It is often associated with vibrational functions (sound
wave production and collection) and thus can be observed in the pinna (external ear; sound collection) and the
smaller laryngeal cartilages (sound production). It is also the most flexible cartilage and thus is also found in the
nasal septum and epiglottis, skeletal structures capable of a good amount of wiggle. [Demonstrate this on yourself
to your lab mate.]

3) muscles - There are three types of muscle cells or fibers present in vertebrates: smooth, cardiac, and skeletal.
All are specialized for contraction and all work on the same principle: ATP-powered sliding filaments. Like
neurons, all possess electrically excitable membranes, and almost all can generate action potentials (tonic skeletal
muscle fibers cannot).
4) nervous tissue The two types of nervous tissue
are: (A) cells specialized for conducting and
transmitting electrochemically mediated information
(i.e., neurons); and (B) the cells which support those
engaging in this activity (e.g., neuroglia or glia).

          The nervous system is the organ system
concerned with processing information from the
environment and using that information to control
the physiology and behavior of the organism. The
nervous system has three basic components: (1)
Sensory input by sensors which tranduce stimuli into              Smooth muscle is found in the viscera of the
electrical signals; (2) integration components which     digestive, respiratory, excretory and reproductive
decide what to do with this information; and (3)         systems, blood vessels, hair follicles, etc. It occurs in
motor components which direct the response to            both sheets (e.g., muscular walls of blood vessels and
effector organs (e.g., muscles, glands, etc.).           organs) and as isolated cells (e.g., myoepithelial cells).
                                                         Smooth muscle is under involuntary control of the
          Anatomically (but not functionally), the       autonomic nervous system and keeps air, food, waste and
vertebrate nervous system can be divided into two        blood moving. Histologically, smoother muscle fibers
subdivisions: (1) the central nervous system (CNS)       are elongated, spindle-shaped cells with a single,
consisting of the brain and spinal cord and derived      centrally located nucleus. Since the contractile proteins
from the neural tube; and (2) the peripheral nervous     are not systematically arrayed, they lack striations.
system (PNS) consisting of (a) all the nerves that       Physiologically, smooth muscle fibers produce slow and
emanate from the CNS (spinal and cranial) and (b)        sustained levels of tension and are resistant to fatigue.
the peripheral ganglia and the nerves originating        The fibers are electrically coupled (gap junctions) to one
from them. In contrast to the CNS, neurons within        another resulting in the spread of action potential across
the PNS are derived from the neural crest and neural     adjacent fibers. Thus, in contrast to skeletal muscle, each
placodes. In the CNS collections of axons bound          smooth muscle fiber is not individually innervated.
together with connective tissue are called tracts        Contraction (= tension generation) can either be
whereas such structure in the PNS are termed nerves      myogenic (self-initiated, often in response to stretch) or
(thus the phrase “peripheral nerve” is redundant, and,   neurogenic.
paradoxically, there are no nerves in the central
nervous system). Similarly, a group of neuron cells               Cardiac muscle fibers are is found in the heart
bodies in the CNS is called a nucleus whereas in the and in the proximal regions of the great arteries (aortae,
PNS such a structure is called a ganglion.              pulmonary trunk, etc.). These are single, branching cells
                                                        (cardiocytes) arranged in a meshwork, which can resist
          Macroscopically, the CNS can be observed high pressure without tearing.              Their sarcoplasm
to consist of gray and white matter. Gray matter is (cytoplasm) appears striated due to the orderly
dominated by neuron cell bodies and white matter arrangement of contractile proteins into units known as
consists chiefly of tracts (the white appearance is due sarcomeres. Cardiac muscle fibers are joined to one
to the lipids of the myelinated axons). In the spinal another via intercalated discs.          These specialized
cord, the gray matter [which in fact is lighter than intercellular junctions provide strong mechanical
white matter] is internal to the white matter and in adhesion and are the site of electrical coupling (gap
transverse sections takes the shape of a butterfly with junctions). Thus, as in smooth muscle, it is not necessary
dorsal and ventral horns. The dorsal horns contain that every cardiac muscle fiber be individually
neurons receiving information from sensory neurons innervated.          Physiologically, cardiac muscle fibers
whose cell bodies are found in ganglia (e.g., spinal) produce rapid and forceful levels of tension, and,
and whose axons form the dorsal root to enter the thankfully, are resistant to fatigue. The rate of the
spinal cord. Conversely, the ventral horns contain heartbeat is under control of autonomic nervous system
the motoneurons whose axons from the ventral roots but the heartbeat itself is intrinsic (myogenic), being
and convey information to the effector organs in the initiated by pacemaker cells in sinoatrial node.
periphery (glands and muscles). Also in the gray
matter are interneurons, which, as their name                     Skeletal muscles fibers are not true cells but
suggests, connect to other neurons. Peripherally, the syncitiums containing multiple nuclei and developing
ventral and dorsal roots converge to form spinal from the fusion of many cells. This fusion permits the
nerves.                                                 fibers to grow very large and they are easily visible to the
                                                        naked eye. Skeletal muscle fibers, like cardiac fibers and
                                                        for the same reason, are striated in appearance. In
                                                        contrast to cardiac and smooth fibers, skeletal fibers are
                                                        not electrically coupled (at least when mature) but are
                                                        individually innervated and contraction (tension
                                                        generation) is neurogenic. These muscles are under
         The macroscopic structure of the brain is a good deal more variable than the spinal cord and cannot be so
simply summarized. In general, the gray and white matter is more intermixed although in the cortex of the cerebrum
and cerebellum the gray matter is external and the white matter internal. [The good news is that the gray matter in
the brain is grayer and the white matter is whiter.]

          Surrounding, supporting and protecting the CNS are three concentric connective tissue layers called the
meninges (Gr, membrane). From superficial to deep these are (1) the dura mater (L, tough mother), (2) the
arachnoid mater (G., spider-like mother), and (3) the pia mater (L, tender mother). As their names suggest, the dura
is the thickest and toughest layer, the arachnoid mater is wispy, resembling the silk threads of a spider’s web, and
the pia mater is adherent to the underlying nervous tissue. Cerebrospinal fluid (CSF) and circulatory vessels run in
the space (subarachnoid) between the arachnoid and pia maters.

         Nervous tissue is comprised to two classes of cells, both of ectodermal origin: (1) neurons, cells with
excitable membranes and (2) neuroglia or glia (L., glue), support cells. Neurons form the functional units of the
nervous system and are electrically excitable cells whose membranes can undergo changes in charge. Reversal of
this charge across the membrane, the nerve impulse or action potential, is the language by which neurons
communicate.

         The majority of neurons possess 4 anatomically distinct
regions: (1) Dendrites (Gr, tree) are the processes which receive signals
from other cells; (2) the soma (or perikaryon or body) integrates
information coming from the dendrites, generates the action potential (in
most neurons) and is also the biosynthetic center; (3) the axon is the
process that conducts impulses away from the soma, and are of variable
length (motoneuron axons can reach meters in length); and (4) the axon
terminal. Axon terminals are usually multiple, the axon typically
dividing into several branches next to its target cell(s). The tips of the
axon terminals contain the synapses, electrical or chemical junctions
between the neuron and its target cell.

         The various types of neurons differ in their elaboration of these
regions and reflect their diverse functions. For example, neurons important
in receiving and integrating information (e.g., Purkinje cells of the
cerebellum) typically have elaborate dendrites.

         Neuroglia or glia support, nourish, and insulate the neurons. Unlike
neurons, their cell membranes are not electrically excitable. In the central
nervous system (CNS) glia cells typically outnumber neurons 10:1. In
addition to their support role in mature tissue, glia play an important role in
development of the nervous system by acting to guide axons to their proper
targets.

          In the CNS there are four types of glial cells: (1) Astrocytes pass
nutrients between capillaries and neurons and form the well-known blood-
brain barrier; (2) microglia are phagic cells which engulf foreign material
and bacteria; (3) oligodendrocytes provide the myelin sheathing for the
axons; and (4) ependymal cells are epithelial like neurons lining the central
canal of the spinal cord and brain (ventricles).
          In the peripheral nervous system (PNS) there are two types of
glial cells: (1) Satellite cells provide nutritional support and (2) Schwann
cells provide myelination for the axons of nerves.


          [N.B. There are, however, a few cell types that do not fit neatly
into these classifications. For example, ependymal cells are nervous tissue
forming epithelial-like sheets with epithelial adhesions. Myoepithelial
cells are epithelial cells containing contractile proteins.]


Lab Assignment

         In today’s lab, you and your partner need to pick a slide for each
one of the four types of tissues (cells). Draw a picture of what you see,
write down the classification the tissue belongs to, and describe the
structure’s properties.

         N.B. Due to [unprogrammed] slide death, your slide box may not contain the required slide. If this is the
case, notify an instructor and they will provide a replacement or suggest an alternative. If you end up borrowing a
slide from one of your colleagues’, please don’t forget to return it to them.

				
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