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Cell division
Cell division is the formation of two daughter cells from a single parent cell.
The new cells necessary for growth and tissue repair are formed through mitosis,
and the sex cells necessary for reproduction are formed through meiosis.
Mitosis
DNA replicates during interphase, the time between cell division. Mitosis is
divided into four stages:Prophase- the chromatin condenses into chromosomes. Each chromosome
consists of two chromatids joined at the centromere. The nucleolus and the
nuclear envelope disappear.
Metaphase- Chromosomes align at the center of the cell.
Anaphase- Chromatids separate at the centromere and migrate to opposite poles.
Telophase- The two new nuclei assume their normal structure, and cell division
is completed, producing two new daughter cells.
Meiosis
Meiosis results in the formation of gametes (sperm cells or oocytes). Gametes
have half the number (haploid number) of chromosomes as other body cells.
There are two cell divisions in meiosis. Each division has four stages similar to
those in mitosis.
Interphase
Anaphase
Prophase
Telophase
Metaphase
Mitosis is complet
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Animal Tissues
Tissues are groups of cells with a common embryonic origin that work together
to perform a certain function or functions. Animal tissues are usually divided
into four main types: (1) epithelial tissue, (2) connective tissue, (3) muscular
tissue, and (4) nervous tissue.
Epithelial tissue
The principal function of epithelial tissues is to cover and protect surfaces. in
addition to covering the outside of the body like the outer layers of your skin,
other kinds of epithelial tissues line internal cavities and ducts, and form glands.
Various kinds of epithelia are characterized mainly by the shape and
arrangement of their cells.
1-Simple epithelial tissues
Simple epithelium consist of single layers of cells.
• Obtain a slide with simple sequamous epithelium from the peritonium. The
cells appear flat, adhere tightly to each other, and form a sheet with the thickness
of a single cell layer. The irregular cell boundaries are highly visible. The
nucleus exhibits a central location in the cytoplasm.
Simple sequamous epithelium (surface view)
2-Stratified epithelial tissues
Stratified epithelium is made up of several layers of cells stacked on top of each
other.
• Examine a slide of stratified epithelium from the esophagus. Observe a fine
basement membrane separates the epithelium from the underlying connective
tissue. The basal cells are low columnar or cuboidal. Cells in the intermediate
layers are polyhedral with round or oval nuclei. Above the polyhedral cells are
several rows of sequamous cells. Cells and nuclei become progressively flatter
as the cells migrate toward the free surface.
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Stratified sequamous epithelium (L. section)
3- Glandular epithelial tissues
The body contains a variety of glands. They are classified as either exocrine
glands or endocrine glands.
• Obtain a slide of human skin and observe the complex structure of the
multilayered integument, or outer covering, of the human body. Two kinds of
glands are present in the skin: sebaceous and sweat. Sebaceous gland is an
alveolar gland and secrets into the hair follicles. Sweat gland is a tubular gland
located in the dermis. It empties through canals out onto the skin surface.
Human skin
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Connective Tissue
All connective tissues exhibit relatively large amounts of nonliving, intercellular
substance produced by the living cells. This intercellular substance may be
liquid, semisolid, or solid. You will study three examples of connective tissue in
this exercise: loose connective tissue, bone and blood.
1- General connective tissue
Histologically, General connective tissue (connective tissue proper) is composed
of special cells, protein fibers and a ground substance that varies among the
several types.
• Obtain a slide of loose connective tissue from the outer ear. Loose connective
tissue consists of scattered cells surrounded by a clear ground substance and two
types of fibers: thin elastic (yellow) fibers and thick collagenous (white) fibers.
The collagenous fibers are thin, fine and single fibers. The elastic fibers are
thickest, largest, and numerous.
Loose connective tissue
2- Skeletal connective tissues
Skeletal connective tissues involve bones and cartilages.
• Examine a thin section of compact bone prepared from a long bone, such as
the femur of a human or other mammal, and identify the following structures. (I)
the central Haversian canal through which passes many small blood vessels and
nerves; (2) the concentric layers of bone (lamellae); (3) the lacunae, or spaces
that house the bone cells or osteocytes; and (4) the numerous fine canaliculi,
which serve to interconnect the lacunae and the Haversian canals.
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Compact bone (C. section)
3- Specialized connective tissues
These types of tissues include two divisions: blood and lymph.
• Obtain a prepared slide with a blood smear and study the types of human
blood.
1. Erythrocytes. Observe that human red blood cells are small, circular,
biconcave and lack nuclei. They contain large amounts of hemoglobin.
2. Leucocytes. There are five types of white blood cells: neutrophils, basophils,
eosinophils, lymphocytes and monocytes. Leucocytes are subdivided into
different types according to the shape pf their nuclei, the absence or presence of
cytoplasmic granules, and the staining affinities of their granules.
A- Granulated Leucocytes
The nucleus of neutrophil consists of several lobes. The cytoplasm contains fine
violet granules.
The nucleus of eosinophil is bilobed and the cytoplasm is filled with large,
bright pink granules.
The nucleus of basophil is not markedly lobulated. The granules are more
variable in size and stain dark blue or brown.
B- A granulated Leucocytes
The densely stained nucleus in small lymphocyte occupies most of the
cytoplasm, and the cytoplasm is seen as a thin rim around the spherical nucleus.
Monocytes are the largest leucocytes. The nucleus varies from oval to kidneyshaped.
3. Thrombocytes. Blood platelets are small. They are about one-third the size of
erythrocytes and are not usually preserved in prepared microscope slides.
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Leucocytes
Erythrocytes
Muscular Tissue
Three different types of muscular tissue are distinguished based on its location
and structure: smooth muscle, skeletal muscle, and cardiac muscle.
1-Smooth Muscle
Smooth muscle forms the simplest type of muscle tissue and is generally found
in parts of the body not under voluntary control such as in the walls of the
digestive tract, in the walls of blood vessels, and in the walls of the urinary
bladder and the uterus.
• Study a microscope slide of smooth muscle and observe the spindle-shaped
cells with a single, central nucleus This type of muscle is sometimes referred to
as nonstriated muscle because it lacks the cross striations.
Smooth muscle
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2- Skeletal Muscle
The large muscles attached to various parts of the skeleton are composed of
skeletal, or voluntary, muscle.
• This type of muscular tissue is made up of long cylindrical fibers containing
many nuclei. Note the conspicuous cross striations in these fibers and the outer
sarcolemma.
Skeletal Muscle
3- Cardiac Muscle
Cardiac involuntary muscle is found in the walls of the heart of vertebrate
animals.
• Cardiac muscle consists of striated muscle fibers, which branch and reunite
with other fibers to form a continuous network of muscle fibers. Cardiac muscle
is divided into cell-like units by many intercalated discs, which partially divide
the fibers.
Cardiac muscle
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Nervous Tissue
The nervous system of vertebrate animals consists of the brain, spinal cord, and
nerves. Nervous tissue consists of highly specialized cells that carry impulses
from one part of the body to another. A nerve cell (neuron) consists of a cell
body containing the nucleus and two or more elongated nerve processes. These
processes are axons and dendrites. All peripheral nerves are covered by a thin
neurolemma.
Anatomically, three major groups of neurons exits: unipolar, bipolar and
multipolar. Their anatomic classification is based on the number of processes
that originate from the cell body.
1- Unipolar neuron
• Obtain a prepared slide with unipolar neurons from embryo. These cells have
spherical nuclei which have dark-staining nucleolus. The cell contains only the
axon. Pseudounipolar neuron found in the nervous ganglia.
2- Bipolar neuron
• Study a microscope slide of bipolar neurons from the retina of eye. The oval
cell has two processes: axon and dendrite.
3- Multipolar neuron
• Examine a slide of the gray matter from the spinal cord. Observe the
large neurons (easily seen under low power). Select a typical cell and note the
cell body, nucleus, nucleolus, numerous dendrites, and the longer axon. Observe
the numerous fine fibrils (neurofibrils) within the cytoplasm of the cell body and
extending into the processes. Also the cytoplasm contains Nissl bodies.
e
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Phylum Protozoa
Several groups of small, unicellular, eukaryotic organisms formerly called
protozoa, have traditionally been thought to be related to animals and regularly
studied in zoology classes. These organisms include several forms that are
commonly found in ponds, lakes, and streams. Among them are many forms that
are important pathogens and parasites, and forms that play an important role in
natural ecosystems.
Amoeba proteus (Class: Rhizopoda)
It is found in ponds and streams. It is a minute organism measuring from 0.25
mm to 1.00 mm. the body is irregular appears like a colourless gelatinous mass
of protoplasm. An amoeba moves about by extending pseudopodia.
With the aid of Prepared microscope slide identify and study the following
structures found in the amoeba:1. Endoplasm- the inner granular region that forms the bulk of the cytoplasm.
2. Ectoplasm- the thin layer of clear cytoplasm that surrounds the endoplasm.
3. Cell membrane- the outer membrane surrounding the amoeba. Sometimes
also called the plasmalemma.
4. Nucleus- a transparent structure with no fixed position in the cell.
5. Contractile vacuole- a clear vacuole found in the endoplasm.
6. Food vacuoles- vacuoles containing bits of ingested food.
Amoeba proteus
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Euglena viridis (Class: Mastigophora)
It is a common green flagellate often found in the greenish surface scum of
standing or slowly moving water. It is oval, spindle-shaped measuring from 50
to 100 microns in length. The active swimming movements result from the
beating of the long flagellum.
Identify the following structures under high power on your compound
microscope:1. Pellicle- the thick outer covering of the body.
2. Chloroplasts- with green chlorophyll.
3. Nucleus- exhibiting a large central endosome in stained preparations;
4. Reservoir.
5. Contractile vacuole.
6. Red stigma or eye spot.
7. Long flagellum- arising from the base of the reservoir.
8. Paramylum grains- a type of starch that represents stored food materials.
Euglena viridis
Paramecium caudatum (Class: Ciliata)
It is a common protozoon often found in water containing bacteria and decaying
organic matter. The body is slipper-shaped measuring about o.3 mm in length.
The Cilia of Paramecium play an important role in locomotion.
Obtain a prepared slide of pa and observe the following main structures:I. Cilia- the numerous cylindrical protoplasmic extensions that cover the surface.
2. Pellicle- the thick outer covering of the body.
3. Macronucleus- the large nucleus located near the center of the cell.
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4. Micronucleus- a smaller nucleus located close to and lying partly within a
depression on the oral side of the macronucleus.
5. Cytostome (cell mouth)- a permanent opening near the posterior end of the
oral groove through which food is passed.
6. Cytopharynx- a short tube extending from the cytostome posteriorly and
downward into the cytoplasm where food vacuoles are formed.
7. Contractile vacuoles- two clear, slowly pulsating vesicles located near each
end of the body. Each contractile vacuole is surrounded by several radiating
canals.
8. Food vacuoles- numerous vacuoles located within the cytoplasm.
Paramecium caudatum
Phylum: Echinodermata
The phylum echinodermata is a unique group of spiny-skinned marine animals.
Echinoderms are widespread in the seas, occurring in shallow waters and in the
depths of the sea in all parts of the world.
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Asterias forbesi (Class: Asteroidea)
Asterias forbesi is a common sea star .Obtain a preserved specimen of sea star
and observe its radial symmetry. Note the central disc on the upper and the five
rays or arms. Also note the many spines scattered over the surface of the arms
and the central disc.
Observe the skeletal calcareous plates, or ossicles, on a dried sea star
specimen. Note on the oral side of the sea star: the mouth, guarded by
specialized oral spines and surrounded by a soft membrane, the peristome; the
five grooves, extending from the mouth and along the middle of each arm; and
the numerous tube feet in the grooves, extending from the water vascular
system. There is also a sensory tentacle at the tip of each ray.
Sea star, oral view
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Phylum: Chordata
The phylum chordata includes a remarkable range forms, varying from
relatively simple marine animals to highly specialized birds and mammals.
Despite the wide range of diversity in the phylum, however, all members exhibit
three fundamental chordate characteristics during some stage in their life
histories. These distinctive chordate features are (1) notochord; (2) nerve cord,
and (3) pharyngeal gill slits. The living members of this phylum are commonly
divided into three subphyla.
Subphylum: Urochordata (Tunicates)
Molgula
The larval stages of tunicates are of special importance because they clearly
exhibit the fundamental chordate characteristics: notochord, nerve cord, and
pharyngeal gill silts. The first two of these features are lost in the adult tunicate,
presumably because of the specialization of the adult due to its sessile mode of
life.
Adult tunicates may be solitary or colonial. The most familiar ones are the
sessile forms found attached to rocks, jetties, and pilings in shallow seas. Study
a specimen of Molgula and note the tough, fibrous outer covering called the
tunic. Projecting from the globular body are two siphons: the incurrent siphon
and excurrent siphon. Locate the numerous gill slits within the pharynx. Ventral
to the pharynx are the short esophagus, the bulbous stomach, and the beginning
of the intestine. The intestine continues dorsally and ends at the anus just below
the excurrent siphon.
Larval stage
Adult tunicate
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Subphylum: Cephalochordata (Lancelets)
Branchiostoma
The lancelet or Amphioxus has received considerable interest among zoologists
on account of the fact that this small animal displays all the features of the basic
plan of chordate organization in a clear diagrammatic form.
Amphioxus is fish-like, about 5 cm in length. It has the habit of burying itself
in the sand during the day, with its anterior part only protruding, but swims
actively during the night.
Study a preserved specimen and observe its general form and external
feature. The general body form, is elongated, pointed at both ends and flattened
from side to side. The anterior end projects forwards as the rostrum.
The fins arc generally low and continuous with each other: a dorsal, a ventral
and a caudal, and two lateral fins or metapleural folds.
The mouth lies ventral to the rostrum and is guarded by the oral hood, the
anterior edge of which carries long processes, the oral cirri.
The atriopore is median and ventral and lies at the junction of the two
metapleural folds and the ventral fin, at about one- third the length of the animal
from its posterior end. It is the opening of the atrium. The anus lies on the left
side, a short distance in front of the posterior end.
The myotomes are arranged on both sides of the body as metamerical blocks
of striated muscle fibers, separated by V shaped partitions of connective tissue,
the myosepta.
The gonads are about 26 pairs, metamerically arranged on both sides of the
pharynx. The two sexes are separate, but are not externally distinguishable.
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Subphylum: Vertebrata
Members of the subphylum vertebrata have, at some stage of life, a notochord, a
nerve cord, and pharyngeal pouches. Vertebrates have three characteristics that
distinguish them from other chordates. First, Vertebrates have vertebrae, bones
or cartilages that surround the nerve cord. Second, Vertebrates have a cranium
that protects the brain. Third, all Vertebrates have an endoskeleton composed of
bones or cartilages.
Rana ridibunda (Class: Amphibia)
It is important to remember that the amphibians are transitional animals that
typically live a portion of their lives in the water and another portion on land.
Generally the adults live in wet or moist environments.
A study of frog anatomy does serve to illustrate effectively the basic body
organization of a vertebrate animal. Some of the specialized features of the adult
frog include the following: (1) the absence of a tail, (2) the loss of certain skull
bones, (3) the anterior attachment of the tongue, (4) the absence of ribs, (5) the
lack of a distinct neck, and (6) the powerful and highly developed hind limbs.
Study a living frog and note the smooth, moist, and pliable skin. Observe the
pattern of coloration of the dorsal and ventral surfaces of the body. Note the
broad, flat head with the large mouth, the nostrils or external nares, and two
conspicuous eyes. The nictitating membrane helps keep the eye moist while the
frog is on land and also helps protect the eye under water from abrasion. The
circular tympanic membranes located behind the eyes.
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Internal Organs
Anesthetize or pith the animal according to directions of your laboratory
instructor. If you are dissecting the specimen, take care to minimize the cutting
of blood vessels to prevent the blood from obscuring your view of the internal
organs. Keep your specimen covered with cold water during dissection. Note the
position, size, shape, color, and texture of the principal internal organs.
- The heart is enclosed in a membranous sac, the pericardial cavity, the two
lungs, in a living or freshly frog the lungs will be semitransparent, pink,
and inflated.
- The large, three-lobed liver and the gallbladder.
- The curved, tubular stomach, small intestine, and large intestine (rectum).
- The testes in a male specimen. If your specimen is a mature female, much
of the visceral cavity will be filled with many black and white eggs
enclosed in the large, membranous ovaries.
- Note the two kidneys and the fat bodies.
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