ZOOLOGY LAB [MODULE 1-3].pdf

ZOOLOGY LABORATORY: e. Arm - curved metallic part arising from the Module 1-A: The Microscope & Animal Cell pillar used for holding the microscope Structure...

ZOOLOGY LABORATORY: e. Arm - curved metallic part arising from the Module 1-A: The Microscope & Animal Cell pillar used for holding the microscope Structure f. Stage Clips Microscope - an instrument that enables the - Used to hold the specimen in place student to observe enlarged images of tiny objects g. Base - the part that supports the entire PARTS: microscope 1. Mechanical Parts - those parts concerned with the support and adjustment of the 2. The Magnifying Parts - those parts optical parts concerned with image enlargement of the specimen a. Revolving Nosepiece - Holds the 4 objective lenses a. Objective Lens - Will feel a distinctive “click” as each - Gives the initial magnification objective is in proper position for viewing - In general, the lower the magnification, - circular structure where the objectives the shorter is the objective lens and the are attached that permits the shifting farther is it positioned from the specimen objectives when focused i. Scanning Objective (4x) (red) - has b. Stage the broadest field of view; used for - Flat surface with the round opening or initial focusing of objects aperture in the center ii. Low-Power Objective (10x) (yellow) - specimen to be viewed is positioned on iii. High-Power Objective (40x) (blue) the stage over the aperture iv. Oil-Immersion Objective (100x) - This so-called mechanical stage allows (white) the slide to be manipulated by means of the two knobs located underneath the b. Eyepiece stage - Or ocular - The lens through which the object or c. Illuminator Control Knob specimen is viewed - Located on the side of base just below - This lens magnifies the image passing the mechanical stage adjustments knobs through it by 10 times - Controls the light output of the - It also has a pointer which may be used illuminator to indicate the part of an object being viewed d. Adjustment Knobs - Located on both sides of the 3. Illuminating Parts - those parts concerned microscope, just above the base with light provision and regulation to the - 2 TYPES: specimen i. Coarse Adjustment Knob - bigger; used to focus scanner and low a. Substage Condenser power objective (LPO) - A lens located under the stage aperture ii. Fine Adjustment Knob - smaller; - Its distance from the stage is controlled used to focus high power objective by a knob (HPO) and oil-immersion objective - Function: to condense or concentrate (OIO) the light and focus it on the specimen  b. Iris Diaphragm Measuring Specimen Using Ocular - Beneath the condenser Micrometer - Functions and control the amount of light ○ Ocular Micrometer: passing through the specimen More precise measurements can be made - Can be moved from side to side to affect using an ocular micrometer. a change in light intensity a thin circle of glass or plastic etched with a non-unit scale usually ranging from 0 to Magnification 100. ○ The compound microscope combines the ○ Stage Micrometer: magnifying power of the eyepiece with that A stage micrometer is a glass slide etched of the objective lens. with a scale of known units, usually ○ The magnifying power is marked on the divided into 0.01 mm graduations housing of each lens. ○ The ocular micrometer is calibrated using ○ Eyepiece (10) x Objective = Total the stage micrometer by aligning the images Magnification at the left of the scales. ○ When calibrating, remember the following: 1. Place the stage micrometer slide on the stage. Adjust the field so that the zero line of the ocular disc scale is exactly superimposed upon the zero line of the stage micrometer scale. Resolving Power 2. NOTE: a 1 mm microscopic ruler and with ○ This is a measure of lens quality. 100 divisions, each line is 10 microns or ○ Quality lenses have high resolving power, um the ability to deliver a clear image in fine detail. ○ If the magnification of the lens is high, but the resolution is low, it is of little value. ○ Resolution is also affected by the cleanliness of the lens. ○ It is a good practice to clean the lenses with lens paper before and after every use. Field of View ○ This is the size of the area that the lens views. ○ The higher the magnifying power of an ○ Formula: objective lens, the smaller the area viewed. ○ When one switches to a lens with higher magnification, the central portion of what was visible under low power is seen. Using the Microscope ○ parfocal capability - when a specimen is in focus under lpo, one can switch to hpo and have the specimen remain in fairly good focus [just little to no adjustments]  ○ Calibration Constant: Dissecting Microscope - Useful when magnifications between 5x Objective: # of Stage # of Ocular Calibration Micrometer Micrometer Constant: and 50x are desired - Useful for viewing entire specimens of Scanner 100 40 25 µm small animals or body parts of larger animals LPO 100 100 10 µm - Advantage of giving a three-dimensional HPO 25 100 2.5 µm (3D) view of the object - Some have built-in light sources, others do not Scanner: ○ Note: The dissecting microscope is binocular and has a single focusing knob and lens system LPO: Allows the change in magnification by rotating a dial or revolving nosepiece The stage of the microscope is usually equipped with a plate that can be reversed to provide either a white or black background. Living and preserved specimens are best HPO: viewed while completely immersed in water. This prevents formation of distorted image due to the refraction of light off moist surfaces. Module 1-B: Animal Cell Structure All living organisms are made up of cells that form the basic unit of structure and function Cytology - study of cells ○ Width of Paramecium: Cells ○ 2 Types of Cell: Prokaryotic Cell - in which the genetic material is not membrane bound Eukaryotic Cell - the genetic material is membrane bound ○ Differ in size and shape, which relate to their structure and function, location in the body and relationship with the other cells ○ Under the light microscope, 3 parts can be seen in the animal cell: Cell Membrane - the structure that surrounds the cell and regulates the flow of substances between the cell and its surroundings  Nucleus - usually spherical or ovoid Shapes of Animal Cells structure that contains the genetic material ○ Fusiform: Or spindle-shaped Cytoplasm - the substance outside the Located in the stomach nucleus where the other structures such Focus on the muscular layer of the organ as organelles are located These are smooth muscle cells Human Cheek Cell ○ Notes: normal saline solution: 0.9% NaCl solution Get a piece of absorbent paper; wrap it around one edge of the cover slip when staining Using a dropper, add 1 or 2 drops of diluted methylene blue stain on the ○ Spherical-Shaped: opposite edge In a frog’s ovary Egg cells An isolated spherical cell with a distinct nucleus Spherical in shape to accommodate yolk and facilitate fertilization ○ Oval: In a frog’s blood smear Red blood cells Has a distinct nucleus This shape maximizes surface area for oxygen exchange Staining cheek cells enhances visibility under a microscope, helping in the identification of cell structure and organelles. ○ Amorphous: Module 2-A: Cell Division - Mitosis Also in a frog’s blood smear Have no definite shape Cell Division White blood cells - an important process in living organisms Smaller than the RBCs - it is involved in the multiplication of cells Less numerous and nucleated for growth and development of an organism - plays a key role in repairing injured body parts of animals - processes such as regeneration and wound healing are affected by cell division - can be viewed as a cycle, categorized into two stages namely interphase and mitosis ○ Interphase: - Stage wherein the cell undergoes growth and prepares for cell division ○ Threadlike: - 90% of the cycle In a frog’s testis - All the necessary materials needed for Sperm Cells or Spermatozoa cell division are synthesized at this Has a whip-like flagellum that gives it stage (which include microtubule the threadlike appearance proteins among others) Has the tail that is used for motility, to - To ensure that each daughter cell would swim to the egg cells have a complete set of genetic material, actual replication of genetic material of DNA occurs in this phase ○ Mitosis: - 10% of the cycle - cell biologists consider several phases in mitosis based on the different events occurring in the nucleus and cytoplasm of the cell Specimen used: whitefish blastula (x.s)  Interphase: M-Phase: ○ Cell with a distinct nucleus, with an intact - Phase where the cell divides nuclear membrane - Divided into 4 stages: ○ The genetic materials inside the nuclear appear as thin, thread-like structures ○ Prophase appropriately called chromatin A cell in which the nuclear membrane ○ Within the nucleus is 1 to 2 nucleoli starts to disappear Nucleoli - dense, darkly stained bodies The chromatin fibers start to appear as formed by several chromosomal materials coiled, thickened, condensed structure that code for certain RNAs forming chromosomes that are visible ○ Near the nucleus is the centrosome which under the light microscope contains centrioles (may not readily be Centrioles are seen in the opposite poles seen using the light microscope) Locate ray-like microtubule bodies called asters radiating around each centrioles and mitotic spindles forming between centrioles The nucleoli disappear at this stage ○ Metaphase ○ Telophase Cell at this stage can readily be identified A cell where a cleavage furrow starts to from the rest of the phases of mitosis appear (start of early telophase) The chromosomes are aligned at the Cleavage Furrow - a constriction of equatorial region of the nucleus the plasma membrane at the region of The replicated chromosomes, which are the equatorial plate much shorter and more condensed, are The nuclear membrane and the nucleolus readily recognized start to reappear The chromosomes are made up of The chromosomes begin to uncoil and chromatids joined together at their central assume a threadlike appearance region called centromere The asters and mitotic spindles disappear A protein coat called kinetochore is found At late telophase, the cleavage furrow in each of the sister chromatid becomes more constricted leading to the The spindle fibers are attached at the formation of 2 daughter cells. centromere of each chromosome Cytokinesis - the division of the cytoplasm usually, occurs along with telophase. ○ Anaphase Completely separated daughter cells are A cell where the chromatids are pulled formed soon after mitosis. apart toward the opposite poles This stage is differentiated into early and late stages depending on the distance travelled by the chromatids Once the chromatids separate, these are considered as chromosomes reaching the opposite poles Module 2-B: Animal Development Cleavage: ○ is the process of transforming the single 2 types of development of organisms: celled zygote into a multicellular entity ○ Phylogeny ○ this process involves a series of mitotic Phylogenetic development refers to the division, which transforms the zygote to evolutionary history of the species. several cleavage cells or blastomeres ○ Ontogeny ○ the number of blastomeres determines Ontogenetic development refers to the whether it is in the early or late stage of entire life history of an organism. cleavage first mitotic division results into two Animal Embryology - deals with the study of blastomeres (2-cell stage) specific stages on the ontogenetic second mitotic division yields a 4-cell development of an animal, the embryo. stage The term embryo refers to the developing third mitotic division yields an 8-cell stage young from a fertilized egg to a form that is ○ subsequent cell divisions lead to a structurally similar to, but does not yet geometric increase in the number of precisely resemble, the adult. blastomeres The process of change occurring in a ○ mitotic divisions at the latter stages of developing embryo is a dynamic and cleavage occur asynchronously continuous one ○ the ball of cells that is formed as a result of The major stages of development are this series of cell division is called morula identified as: ○ Zygote (fertilized oocyte) Blastulation: ○ Cleavage ○ the process that involves an internal ○ Blastulation secretion of fluid by the blastomeres of the ○ Gastrulation morula ○ Organogenesis ○ results in the formation of a fluid-filled cavity, ○ Neurulation the blastocoel or segmentation cavity Observed in diverse groups of ○ the embryo at this stage is referred to as multicellular, sexually reproducing blastula animals. ○ there is also an emergence of distinctly two populations of cells Fertilization: ○ the layer of cells immediately surrounding ○ involves the union of the sperm and egg the blastocoel forms the endoderm nuclei ○ the outer layer of cells forms the ectoderm ○ estores the chromosome number or diploid ○ at this stage, the embryo is characterized as number of the organism didermic (di=two, dermis=layer/coat/skin) ○ the embryo as a result of fertilization is appropriately called a zygote ○ Fertilization in frogs occurs externally, that is, it occurs outside the female body, usually in moist, damp places.  Gastrulation: Neurulation: ○ is the stage that involves major cell ○ One of the organ systems that take shape movements and rearrangements to form the the earliest is the central nervous system body plan characteristic of a species (CNS) ○ these phenomena are collectively referred CNS of vertebrates develops from a to as “morphogenetic movements” dorsally situated ectodermal thickening ○ (gaster=stomach) called neural plate. ○ There is the laying out of the primitive gut, This structure invaginates to form a also known as gastrocoel or archenteron neural fold and a depression called Gastrocoel - This is the future digestive neural groove, which eventually tract of the embryo develops into a hollow neural tube. ○ An opening leading to the gastrocoel called The process involving the development of blastopore is formed in the earlier part of the CNS is called neurulation and the the gastrula stage. embryo at such a stage is referred to as Blastopore neurula. the future anal or cloacal opening in It should be noted that other organ deuterostomes (echinoderms and systems form during the neurulation stage. vertebrates) Becomes the mouth in protostomes ○ As development proceeds, the embryo gets (nematodes, mollusks and arthropods) its nourishment from the stored yolk or food material from the egg’s cytoplasm. ○ Another important event of gastrulation is ○ The frog’s egg is of mesolecithal type the establishment of the 3 germ layers: which means it contains moderate amount Ectoderm of yolk Mesoderm the stored food is depleted as Endoderm development continues serve as the foundation for the organ systems of the animal to take shape ○ The developing young emerge as a swimming larva called tadpole ○ The table below provides examples of organ ○ Further organogenesis and histogenesis systems and their corresponding germ layer proceed during the tadpole stage origin ○ The tadpole gets its nourishment by feeding on plankton and other microscopic organisms Germ Layer Organ Systems/Structures Derived from the Specified ○ The transformation of the tadpole to an adult Germ Layer frog occurs within 2.5 to 3 months through the process of metamorphosis. Ectoderm CNS, sense organs, epidermis Mesoderm Heart, muscles, urogenital system, vertebral column, dermis of the skin Endoderm Lining of the intestinal tract, lungs Organogenesis: ○ Process in which the different organs start to form [Methodology] ○ Late Cleavage - Find typical embryo at the late cleavage. Segmented or Unfertilized Egg 1. The blastomeres that are smaller are - Slide: frog’s ovary sometimes called micromeres and are - Find the spherical cells with well-defined situated at the animal pole. nucleus 2. The blastomeres that are larger are - The cytoplasm has granular appearance, called macromeres and are situated at usually darkly stained the vegetal pole (where the yolky - The cytoplasm of the egg is filled with material is concentrated). yolky material, which serves as - The rate of cell division is hampered by nourishment for the developing embryo. the presence of yolk. Hence, the - It is not evenly distributed. It is blastomeres at the vegetal pole are larger concentrated in one area of the egg. because of slower rate of cell divisions - The area where the yolky material is especially during the latter stages of concentrated is the vegetal pole. cleavage. - The area opposite the vegetal pole is called the animal pole. - Such type of egg based on yolk distribution is referred to as telolecithal type. Cleavage ○ Early Cleavage - Locate the cleavage cells or blastomeres making up the embryo - The outlines or boundaries of the blastomeres can be seen with the furrow or space in between them. Blastula - You can identify here the micromeres, macromeres, vegetal and animal pole - Has the blastocoel or segmentation cavity (fluid filled cavity found within the embryo) ○ Early Blastula  ○ Late Blastula Neurula ○ Neural Plates Stage - Neural Plate - an ectodermal thickening at the dorsal aspect of the specimen - This is the early stage in the development of the neural tube ○ Neural Fold Stage - Or neural groove stage - Find dorsally the neural folds formed by the ectodermal cells. - A depression or neural groove is seen bounded by the neural fold. ○ Neural Tube Stage Gastrula - At this stage, the neural folds meet at the - Locate the prominent cavity, the primitive center and move inward to form a neural gut or archenteron. tube. - Find the opening leading to this cavity called the blastopore. - Neural Tube - At this stage, notice that the blastopore - serves as the precursor of the brain and is filled with yolk plug. spinal cord. - The blastopore is bounded dorsally by the dorsal lip of the blastopore and - Notochord ventrally by the ventral lip of the - a round structure immediately below the blastopore. neural tube - 3 germ layers: - serves as the main axial support of - Ectoderm - the outer layer of the vertebrate embryos embryo - Endoderm - the inner layer immediately - Archenteron surrounding the archenteron - a cavity immediately below the - Mesoderm - the middle layer between notochord the ectoderm and the endoderm - or the primitive gut - the lining of the gut is the endoderm - Mesoderm - lateral to the notochord - Made up of mass of cells - is divided into segments or somites a. Epimere - Most dorsal somite - Situated at the level of the notochord b. Mesomere - A string of cells formed by the middle portion of the mesoderm - Origin of the urogenital system - Note: he mesoderm extends ventrally towards the guts.  c. Hypomere Histology: - Or lateral plate mesoderm - Ventral most portion of the A. Epithelial Tissue mesoderm - Composed of tightly packed cells with very - Subdivided into inner splanchnic little intercellular substance layer and an outer somatic layer - Covers the outer surface and inner lining of - a cavity is formed between these the body two layers which is the future - The principal tissue of the glands coelom or body cavity of the animal. - Characterized by: - Different shapes of cells: squamous, ○ Neural Crest Stage cuboidal, columnar, transitional - Number of Layers: a single layer (simple, pseudostratified) or in 2 or more layers (stratified) - Presence of a Basement Membrane and Apical Surface - Presence of specializations on its apical surface such as cilia and microvilli - Extremely Coherent Intercellular Adhesions - Types: a. Simple Epithelium Tissue - single layer of Module 3: Animal Histology and Organology cells lying upon a basement membrane 1. Simple Squamous Tissues: - Slide: x.s. of simple squamous ○ aggregations of cells with similar shape, - Cells are very thin and rectangular in functional association and intercellular profile component - Cells are arranged closely together to ○ Based on these characteristics, tissues are form a sheet classified into four basic types: - is seen in mesentery (mesothelium) 1. epithelial tissue and inner lining of the blood vessels 2. connective tissue (endothelium) 3. muscle tissue 4. nervous tissue ○ These basic types may combine to form larger functional unit called organs with their own unique histologic pattern and properties 2. Simple Cuboidal b. Stratified Epithelium Tissue - two or more - Slide: x.s. of thyroid follicle layers of cells - cells lining each circular thyroid follicle 1. Stratified Squamous - cells appear as box-like or cube-like - Slide: x.s. of frog’s skin cells with more or less equal height and - outer layer of the skin width - numerous layers of epithelial cells with shapes ranging from flattened superficial cells to cuboidal and columnar cells of the deeper layers - The cells of the deepest/basal most layer lying upon the basal membrane are thrown into folds showing considerable irregularity 3. Simple Columnar - Slide: x.s. of frog’s intestine - Finger-like projections on the surface of the intestine, these are called villi - Among tall columnar cells are pitcher-like mucus glands called goblet cells 2. Transitional Epithelium - Slide: x.s. of human urinary bladder - called transitional because the shape of the surface cells may vary depending on the degree of distention or stretching of the bladder - an empty bladder is characterized by a layer of round superficial cells while deeper layers have cuboidal to columnar shaped cells. - A filled bladder has an epithelium characterized by large squamous superficial cells overlying several layers of cuboidal cells.  3. Ciliated Pseudostratified Columnar - 3 TYPES OF PROTEIN FIBERS: - Slide: x.s. of human trachea ➔ Collagen Fibers - cells of this type are all in contact with ◆ White the basement membrane but not all of ◆ Thick them reach the surface ◆ Wavy - the cells vary in shape - nuclei are found on wider part of both ➔ Elastic Fibers cell shapes, giving the tissue a false ◆ Yellow impression of stratification ◆ Thin - Note: there is cilia on its apical surface ◆ Taut ➔ Reticular ◆ Extremely thin ◆ Tends to form branching networks ◆ Least in proportion ◆ May require special staining to be seen 2. Dense Connective Tissue - Slide: x.s. of tendon - The predominant fibers are collagen which are arranged parallel to each other B. Connective Tissue - This tissue contains a limited variety of - Comprises a diverse group of tissues that cell types, with fibroblasts being the serve to maintain and support the body most abundant - Main components is its extracellular matrix; - Fibroblasts are seen in between composed of protein fibers, an amorphous collagen fibers ground substance, and tissue fluid a. Connective Tissue Proper 1. Areolar Tissue - Or Loose Connective Tissue - Composed of a great deal of ground substance - Almost all types of cells (plasma, mast, macrophages) are found in this tissue - but the most numerous and easy to find cells are the spindle-shaped fibroblasts (with their large ovoid nuclei) b. Connective Tissue with Special ➔ Leucocytes Properties ◆ White Blood Cells 1. Adipose Tissue ◆ Cells have nucleus - Cells are called adipocytes ◆ There are types of leukocytes - These cells have a thing ting of depending whether they have cytoplasm surrounding a very large granulated cytoplasm or vacuole/space left by the dissolved lipid non-granulated cytoplasm. droplets - Nuclei are flattened and often seen at A. Granulocytes (granulated the sides or periphery of the cell cytoplasm) a. Neutrophils - nucleus consists of 3 or more lobes/segments; most abundant b. Eosinophils - bilobed nucleus; 1-3% of the blood leucocytes c. Basophils - U or J shaped nucleus; least numerous, only about 0.5% B. Agranulocytes (non-granulated cytoplasm) a. Lymphocytes - small round cells with an indented nucleus and a 2. Blood thin rim of clear blue cytoplasm; - Slide: x.s. of human blood smear 20-25% of the blood leucocytes - This specialized tissue is composed of b. Monocytes - larger than formed elements and a fluid matrix, the lymphocytes with round and plasma eccentric nuclei, more cytoplasm than lymphocytes; 3-8% of the blood leucocytes - The formed element consists of: ➔ Erythrocytes ◆ Red Blood Cells ◆ Observe that the cells in mammals have no nucleus but nucleated in other vertebrates ➔ Thrombocytes ◆ Cells are biconcave and tend to form ◆ Platelets aggregates ◆ Fragments of a large bone marrow cell called megakaryocyte c. Supporting Tissue ➔ Elastic Cartilage 1. Cartilage ◆ Slide: x.s. of elastic cartilage - chondrocytes or cartilage cells - are ◆ similar to hyaline, except for the embedded in a firm, gel-like extracellular numerous fine elastic fibers in its matrix matrix. - One or more cells can occupy a single ◆ Lacunae with chondrocytes appear cavity/lacuna which is filled with tissue more closely packed than that of fluid in life. hyaline cartilage. - This type of tissue does not have nerves ◆ This is the type of cartilage found in or blood vessels; relies only on simple the external ear, epiglottis, larynx, diffusion for nourishment. and in the walls of the auditory tube - 3 FORMS: classified on the bases of the amount of extracellular matrix and predominant fibers ➔ Hyaline Cartilage ◆ Slide: trachea ◆ Matrix is bluish-white and translucent with predominance of collagen fibers. ◆ The lacunae with chondrocytes may appear singly or in groups. ◆ the supporting cartilage at the middle is the hyaline cartilage surrounded by a dense connective tissue capsule, the perichondrium. ◆ This is the type of cartilage found in the nose, larynx, trachea, and in the bronchi. ➔ Fibrocartilage 2. Bone ◆ Slide: x.s. of fibrocartilage - The hard calcified matrix deposited with ◆ This has irregular, dense bundles of inorganic salts makes it a supporting collagen fibers. connective tissue ◆ Lacunae with chondrocytes appear - Each bone cell or osteocyte occupies a in rows due to parallel arrangement cavity called lacuna with several of collagen bundles. canaliculi radiating from it ◆ Matrix is less abundant. - In life, these lacunae are filled with ◆ A perichondrium is not identifiable tissue fluid - Unlike cartilage, the bone is rich in blood vessels and nerves - All bones are lined on its internal and external surface by layers of bone-forming/osteogenic cells - Haversian System: ➔ Haversian Canal - central canal of an osteon ➔ Interstitial Lamellae - concentrically arranged collagen bundles around the Haversian canal ➔ Lacunae - cavities found along the border of each lamellae; bone cells are no longer visible due to histologic preparations ➔ Canaliculi - seen as fine lines or canals that radiate from the lacunae C. Muscle Tissue c. Smooth Muscle a. Skeletal Muscle - Slide: teased smooth muscle - Slide: longitudinal section of skeletal - The cells of this tissue are muscle spindle-shaped or fusiform with a - Striated Muscle central nucleus - Note the long, cylindrical fibers - Each muscle fiber contains 2 or more nuclei located near the plasma membrane also called sarcolemma - The fiber also shows alternating light and dark bands. - The striations are due to the arrangement of the myofilaments. D. Nervous Tissue - main function: conductivity - main components: the neurons or nerve cells, the supporting cells called neuroglia - Neuroglia includes: b. Cardiac Muscle 1. Astrocytes - Slide: longitudinal section of cardiac 2. Oligodendrocytes muscle 3. Microglia - Cross striations are also observed on long 4. Schwann cells and branching fibers 5. ependymal cells - The fiber may have 1 or 2 centrally located nucleus - intercalated disks - appear as darkly stained transverse lines that cross the cardiac fibers at irregular intervals a. The Neurons ORGANOLOGY - Slide: cow’s nerve smear Organs - aggregates of tissues performing a - PARTS: specific function. 1. Cell Body Organology - the study of organs - spherical or ovoid nucleus is large with a conspicuous nucleolus Frog’s Skin - Nissl bodies - clumps of bluish ○ 2 Distinct Layers: material that are scattered in the cell 1. Epidermis body and dendrites - outer - consists of stratified epithelium 2. Dendrites a. stratum corneum - Short and numerous branching - the outermost part of the epidermis is processes radiating from the cell composed of layers of dead, flattened body cells - The animal usually sheds off this layer 3. Axon - single, thin, long process from the b. stratum germinativum cell body - Beneath the stratum corneum are - may be wrapped/ensheathed by several layers of cuboidal to columnar myelin (of Schwann cells) cells. - Myelinated axons have areas - The cells in this layer are actively "naked" with myelin, such areas dividing to replace the cells in the are called "nodes of Ranvier" stratum corneum located at regular intervals. - These axons terminate at 2. Dermis branching and twig-like "endings" - Inner, thicker layer called telondendria with small - Beneath epidermis swellings at each terminal twig; - 2 Layers: swellings are called "terminal a. stratum spongiosum buttons". - or stratum laxum - outer - composed of loosely arranged connective tissue fibers and abundant blood vessels - Melanophores or black pigment cells are seen in the junction of this layer with the stratum germinativum. - The abundant mucous glands open to the surface by means of a neck extending through the epidermis b. stratum compactum Frog’s Stomach and Small Intestine - outer ○ Rugae - folds in the inner wall of the - consists of white fibrous connective stomach which projects into the cavity/ tissue running parallel to the surface lumen of the organ of the skin. ○ Villi - thinner folds exhibited by the intestine - subcutaneous tissue ○ Layers of tissue starting from the lumen - Underneath the dermis is a connecting outward: layer made up of loose connective Tunica Mucosa tissue and adipose that anchors the - this layer is thrown into folds onto the skin to the tissue beneath lumen - or hypodermis - Layer consists of: - is not considered a part of the skin Simple Columnar Epithelium - in the small intestine, goblet cells may be seen among the columnar cells. (Goblet cells are absent in the stomach) Lamina Propria - a connective tissue layer containing glands and blood vessels Muscularis Mucosa - a thin layer of smooth muscle Submucosa - layer beneath the mucosa - made of connective tissues containing glands, blood vessels, and nerves Tunica Muscularis - a thick layer of circular and longitudinal smooth muscles Serosa - outermost layer of loose connective tissue covered by a layer of mesothelium  Blood Vessels ○ Layers of tissue from the central cavity/ Spinal Cord lumen to the outside: ○ Slide: x.s. of frog’s spinal cord Tunica Intima ○ central canal - small cavity at the center - internal layer which include the lining (can be viewed through scanner) epithelium of the vessel and a layer of elastic tissue in wavy appearance ○ ependymal cells - the columnar cells surrounding the canal (viewed through LPO) Tunica Media - is the intermediate layer made of smooth ○ gray matter - (can be viewed through muscle, collagenous and elastic fibers, scanner) outer to the central canal is a and connective tissue cells portion that resembles letter “H”; consists of nerve cells, neuroglia, naked fibers, and Tunica Externa blood vessels - Tunica adventitia - external layer in which the elements ○ white matter - Outer to the gray matter is a include external elastic membrane, lightly stained portion; composed of nerve collagenous and elastic fibers, blood fibers vessels, and loose connective tissue. ○ ○ pia mater - a thin sheath of connective tissue is seen adhering to the cord ○ dura mater - outer to the pia mater is another membrane which is in contact with the braincase; may not be seen in the section.