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What are the three layers of the heart wall?
- Endocardium (inner)
- Myocardium (middle)
- Epicardium (outermost)
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What are the three layers of the endocardium and what do they consist of?
- Endothelium - simple squamous epithelium
- Inner subendothelial layer - Dense irregular CT with collagen and elastic fibers and occasional smooth muscle cells
- Outer subendothelial layer - loosely arranged collagen and elastic fibers
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What is the description of cardiac valves?
Endocardial folds that consist of a central layer of dense CT covered by endothelium
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What is the composition of myocardium?
- Cardiac muscle cells
- SA and AV nodes (impulse generating)
- Purkinje fibers (impulse conducting)
- Cardiac skeleton
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What are modified cardiac muscle cells with fewer myofibrils that make up the SA and AV nodes?
Nodal cells
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What are the three parts of the cardiac skeleton?
- Fibrous rings (surround the AV, aortic and pulmonary trunk openings)
- Fibrous triangle (between the AV openings and base of the aorta)
- Fibrous part of the interventricular septum
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What are the different compositions for the fibrous triangle?
- Dense irregular CT - pigs and cats
- Fibrocartilage - dog
- Hyaline cartilage - horse
- Bone - large ruminants
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What is the description of Epicardium?
Loose CT containing blood vessels, nerves and ganglia and adipose tissue
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What lines the epicardium?
Simple squamous epithelium of the visceral pericardium
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What does parietal pericardium consist of?
Mesothelial layer, followed by a layer of collagen and elastic fibers
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What is the space between the parietal and visceral pericardium and what does it consist of?
- Pericardial cavity
- Serous fluid lubricating the surfaces for frictionless cardiac movement
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What is the microvasculature?
- Arterioles
- Capillaries
- Venules
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What are the general layers of blood vessels?
- Tunica intima
- Internal elastic membrane
- Tunica media
- External elastic membrane
- Tunica externa
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What is the composition of the tunica intima?
- Endothelium of simple squamous cells
- Subendothelial layer of collagen and elastic fibers and smooth muscle cells
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What is the general make-up of the tunica media?
Smooth muscle cells, layered in a helical arrangement with elastic and collagen fibers
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What is the general composition of the tunica externa (adventitia)?
- Mostly collagen and elastic fibers
- Maybe smooth muscle cells
- Vasa vasorum
- Nervi vasorum
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What are the special characteristics of elastic arteries?
- Tunica intima usually thicker (subendothelial layer has numerous fine elastic fibers)
- Tunica media is thickest layer and consists of concentrically arranged fenestrated elastic laminae with smooth muscle in between
- Tunica externa has bundles of collagen fibers with few elastic fibers plus vasa vasorum and nervi vasorum
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What are the special characteristics of muscular arteries?
- Tunica media is thick, mainly smooth muscle cells in circular or helical pattern
- External elastic membrane is not always clearly defined
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What are the special characteristics of arterioles?
- Internal elastic membrane is fenestrated, disappears in smaller arterioles
- Tunica media has 1-3 layers of smooth muscle, may contain collagen fibers
- External elastic membrane is absent
- Tunica externa has loose CT
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What are the two ways for arterioles to connect to capillaries?
- Directly into capillaries through pre-capillary sphincter of smooth muscles
- Metarterioles, which have isolated bundles of smooth muscles
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What are the different types of capillaries and where are they found?
- Continuous capillaries - muscles
- Fenestrated capillaries (visceral capillaries) - GIT
- Sinusoidal capillaries - fenestrated capillaries in endocrine glands
- Porous capillaries - Kidney glomerulus
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Where are sinusoids present?
Liver parenchyma
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T/F: Sinusoids are larger than capillaries and their shape changes with the surrounding parenchyma.
True, they also have large openings in the endothelial cells to provide maximum exchange.
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What are the characteristics of post-capillary venules?
- Larger in diameter than capillaries
- Continuous or fenestrated endothelial cells
- Functional significance in lymphoid organs
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In which type of vessel do pericytes form the continuous layer plus collagen fibers form a thin tunica externa?
Pericytic or collecting venules.
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What are the characteristics of muscular venules?
- Pericyte layer is replaced by one or two smooth muscle layers
- Tunica externa is more prominent
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How do veins differ from arteries?
- Tunica media relatively thinner
- Tunica externa relatively thicker
- Total wall thickness is relatively reduced
- Greater luminal diameter
- Paired semi-lunar valves (folds of tunica interna with core of collagen fibers)
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T/F: Lymph capillaries are usually smaller than blood capillaries.
False, they are larger than blood capillaries (basal lamina is either absent or discontinuous)
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What is present in all types of lymph vessels except lymph capillaries?
Valves
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What are arteriovenous anastomoses?
Direct connections between arterioles and venules without an intervening capillary bed
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What are AV anastomoses present in?
- Skin
- Lip
- Intestine
- Nasal mucosa
- Male and female reproductive tract
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What are the functions of AV anastomoses?
- Regulation of blood pressure
- Thermoregulation
- Erection
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What are the components of blood?
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What type of cells are in blood?
- Erythrocytes (RBCs)
- Thrombocytes (platelets)
- Leucocytes (WBCs)
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What is the percentage of blood out of the total body weight in large animals and lab animals?
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What are the components and percentages of centrifuged blood?
- 45% PCV or hematocrit (erythrocytes) in lowest layer
- 1% buffy coat (thrombocytes and leucocytes) in middle layer
- Uppermost layer is plasma (92% water, 7% proteins, 1% solutes)
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What are the characteristics of erythrocytes in most domestic animals and what are the exceptions?
- Non-nucleated biconcave discs in most animals
- Flattened discs in goats and pigs
- Elliptical shaped in camel and llama
- Nucleated, elliptical shaped in reptiles, amphibians, birds
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What animal has the largest and smallest erythrocytes?
- Largest - dogs (7.0 microns)
- Smallest - goats (4.0 microns)
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What is anisocytosis?
Variation in the size of erythrocytes
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What is poikilocytosis?
Variation in the shape of the erythrocytes (condition is normal in goats)
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What is anemia?
Decreased number of erythrocytes in the blood.
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What are echinocytes?
Crenated cells
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What is rouleaux formation?
- When erythrocytes adhere to each other and form long chains resembling stacks of coins
- Prominent in horses and cats, intermediate in dogs and pigs, rare in ruminants
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What are immature erythrocytes?
Reticulocytes
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What are tiny DNA fragments in RBCs?
Howel-jolly bodies
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What are Heinz bodies?
- Oxidized hemoglobin
- Feline is most susceptible (2-3% normal in felines)
- More in case of toxicity (onion, acetominophen)
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What are the lifespan of erythrocytes?
- Dogs - 120 days
- Cats - 75 days
- Cow - 160 days
- Pigs - 85 days
- Horse and sheep - 150 days
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What are the polymorphonuclear granulocytes?
- Neutrophils -
- Eosinophils -
- Basophils
- Heterophils (neutrophils in birds) - spindle-shaped granules
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What are the mononuclear agranulocytes?
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What makes up the majority of leucocyte counts?
Neutrophils and lymphocytes
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What are the types of granules in neutrophils and what is their function?
- Cytoplasmic granules (bactericidal compound)
- Azurophilic granules (hydrolytic enzymes)
- Defend the body against bacteria by phagocytosis
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What are immature neutrophils?
Band or nonsegmented cells (present during disease)
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What are the types of nuclei in neutrophils, eosinophils and basophils?
- Neutrophils - heterochromatic segmented nuclei with 3-5 lobes joined by thin strands
- Eosinophils - usually bilobed nucleus
- Basophils - segmented or irregularly shaped heterochromatic nuclei
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In horses, granules of which cells are extremely large and tightly packed, giving a mulberry-like appearance ?
Eosinophils
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What is the function of eosinophils?
Play a role in allergic and anaphylactic reaction and in parasitic infestation
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What is the function of basophils?
Major role in mediating inflammatory reactions (release histamine and heparin)
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What is the difference between mast cells and basophils?
Different origin
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What are the different types of lymphocytes and their characteristics?
- B-lymphocytes (10%)
- T-lymphocytes (75%)
- Natural killer cells (NK cell) (10-15%)
- Small round cells with compact spherical nucleus (can't tell the difference histologically)
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What are the origins of the different lymphocytes?
- B-lymphocytes (10%) - Bone marrow and cloacal bursa (birds)
- T-lymphocytes (75%) - thymus
- NK cells (10-15%) - bone marrow (do not require cloacal bursa/thymus for further development)
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What are the functions of the different lymphocytes?
- B-lymphocytes (10%) - Humoral immunity; produce antibodies (plasma cells)
- T-lymphocytes (75%) - Cell-mediated immunity
- NK cells (10-15%) - non-specific role in immunity, mainly protection against tumor cells
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What do monocytes differentiate into?
Macrophages, once they pass into tissue
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What is cell signaling?
The intimate contact of lymphocytes and monocytes is necessary for maximal immunological response
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What are the largest leucocytes and their nucleus may appear oval, kidney-shaped or bean shaped or horse-shoe shaped?
Monocytes
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What are the characteristics of monocytes?
- Cytoplasm is grayish-blue, often appearing foamy or vacuolated and has fine azurophilic granules
- Nucleus may appear oval, kidney-shaped or bean-shaped or horseshoe-shaped
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What is the function of platelets?
Blood coagulation
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Where is the primary site of hematopoisis in adult animals?
Bone marrow
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What is the sequence for locations of hematopoisis in embryonic stages?
- Wall of the yolk sac
- Fetal liver
- Bone marrow, spleen, lymph nodes and thymus
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What are the types of bone marrow and their function?
- Red marrow - actively involved in hematopoisis
- Yellow marrow - inactive and contains fat
- (Both forms are convertible depending on the demand of blood cells in the body)
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What is the sequence of maturiy for erythrocytes?
- Myeloid stem cells ->
- Erythrocyte CFC ->
- Metarubricyte ->
- Reticulocyte ->
- Erythrocyte
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What is the sequence of maturiy for platelets?
- Pluripotent cell ->
- Platelet CFC ->
- Megakaryocyte ->
- Platelets
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What is the sequence of maturiy for macrophages?
- Pluripotent cells ->
- Myeloid cell ->
- Granulocyte and monocyte CFC ->
- Monoblast ->
- Monocyte ->
- Macrophage
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What is the sequence of maturiy for neutrophils, basophils and eosinophils?
- Pluripotent cells ->
- Myeloid cells ->
- Granulocyte and monocyte CFC ->
- Myeloblast ->
- Band cell ->
- Basophil, Neutrophil (majority), or Eosinophil
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What is the sequence of maturiy for lymphocytes?
- Pluripotent stem cells ->
- Lymphoid stem cells ->
- T-cells, B-cells or NK-cells
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What forms the parenchyma of the immune system?
- Lymphocytes (B cells, T cells, NK cells)
- Neutrophils
- Macrophages
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What forms the stroma of the immune system?
- Reticular cells
- Epithelial reticular cells
- Dendritic cells
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What are the origin and location of the stromal cells of immune system?
- Reticular cells - Mesenchymal origin; form a reticulum in lymphatic organs except thymus and cloacal bursa
- Epithelial reticular cells - Epithelial origin (endoderm); thymus and cloacal bursa
- Dendritic cells - Bone marrow origin; nearly all tissues
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What is the function of dendritic cells?
Capture and present antigens to lymphocytes
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What are the primary lymphoid organs?
- Produce lymphocyte precursors
- Embryonic yolk sac
- Thymus
- GALT (Payer's patches)
- Cloacal bursa (birds)
- Bone marrow
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What are the secondary lymphoid organs?
- House mature immunocytes and site of immune responsiveness)
- Lymph nodes
- Spleen
- MALT
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function and placement of lymph nodes
- situated along lymph vessels
- filter the lymph before returning it to the blood stream
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Which lymphiod organ has both afferent and efferent vessels?
Lymph nodes
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What animals do not have lymph nodes?
Birds
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What are the sinuses of lymph nodes?
- Subcapsular
- Trabecular
- Medullary
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What lines the sinuses of lymph nodes?
Epithelium like reticular cells
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What lies free within the stromal mesh and in the sinus lumen?
Lymphocytes and macrophages
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Lymph nodes are separated into an outer _______ and an inner ______.
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What does the outer cortex of lymph nodes consist of?
Primary and secondary lymphatic nodules
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T/F: Primary lymphatic nodules contain germinal centers.
- False, primary lymphatic nodules consist of reticular connective tissue with small, tightly packed lymphocytes
- Secondary lymphatic nodules contain germinal centers.
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What do secondary lymphatic nodules contain?
- Germinal centers, which have:
- Dark zone (large lymphocytes with intense mitotic activity)
- Light zone (small lymphocytes with few mitotic cells)
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What part of the lymph nodes branch and anastomose throughout the medulla and contain the lymphatic tissue?
Medullary cords
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What cells are in the medullary cords of lymph nodes?
- Lymphocytes
- Plasma cells
- Macrophages
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What animal has cortical and medullary tissues reversed?
Pig
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What type of epithelium do post-capillary venules have?
Simple cuboidal epithelium
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