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What are the three layers of the heart wall?
- Endocardium (inner)
- Myocardium (middle)
- Epicardium (outermost)
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
What is the description of cardiac valves?
Endocardial folds that consist of a central layer of dense CT covered by endothelium
What is the composition of myocardium?
- Cardiac muscle cells
- SA and AV nodes (impulse generating)
- Purkinje fibers (impulse conducting)
- Cardiac skeleton
What are modified cardiac muscle cells with fewer myofibrils that make up the SA and AV nodes?
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
What are the different compositions for the fibrous triangle?
- Dense irregular CT - pigs and cats
- Fibrocartilage - dog
- Hyaline cartilage - horse
- Bone - large ruminants
What is the description of Epicardium?
Loose CT containing blood vessels, nerves and ganglia and adipose tissue
What lines the epicardium?
Simple squamous epithelium of the visceral pericardium
What does parietal pericardium consist of?
Mesothelial layer, followed by a layer of collagen and elastic fibers
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
What is the microvasculature?
What are the general layers of blood vessels?
- Tunica intima
- Internal elastic membrane
- Tunica media
- External elastic membrane
- Tunica externa
What is the composition of the tunica intima?
- Endothelium of simple squamous cells
- Subendothelial layer of collagen and elastic fibers and smooth muscle cells
What is the general make-up of the tunica media?
Smooth muscle cells, layered in a helical arrangement with elastic and collagen fibers
What is the general composition of the tunica externa (adventitia)?
- Mostly collagen and elastic fibers
- Maybe smooth muscle cells
- Vasa vasorum
- Nervi vasorum
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
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
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
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
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
Where are sinusoids present?
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.
What are the characteristics of post-capillary venules?
- Larger in diameter than capillaries
- Continuous or fenestrated endothelial cells
- Functional significance in lymphoid organs
In which type of vessel do pericytes form the continuous layer plus collagen fibers form a thin tunica externa?
Pericytic or collecting venules.
What are the characteristics of muscular venules?
- Pericyte layer is replaced by one or two smooth muscle layers
- Tunica externa is more prominent
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)
T/F: Lymph capillaries are usually smaller than blood capillaries.
False, they are larger than blood capillaries (basal lamina is either absent or discontinuous)
What is present in all types of lymph vessels except lymph capillaries?
What are arteriovenous anastomoses?
Direct connections between arterioles and venules without an intervening capillary bed
What are AV anastomoses present in?
- Nasal mucosa
- Male and female reproductive tract
What are the functions of AV anastomoses?
- Regulation of blood pressure
What are the components of blood?
What type of cells are in blood?
- Erythrocytes (RBCs)
- Thrombocytes (platelets)
- Leucocytes (WBCs)
What is the percentage of blood out of the total body weight in large animals and lab animals?
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)
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
What animal has the largest and smallest erythrocytes?
- Largest - dogs (7.0 microns)
- Smallest - goats (4.0 microns)
What is anisocytosis?
Variation in the size of erythrocytes
What is poikilocytosis?
Variation in the shape of the erythrocytes (condition is normal in goats)
What is anemia?
Decreased number of erythrocytes in the blood.
What are echinocytes?
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
What are immature erythrocytes?
What are tiny DNA fragments in RBCs?
What are Heinz bodies?
- Oxidized hemoglobin
- Feline is most susceptible (2-3% normal in felines)
- More in case of toxicity (onion, acetominophen)
What are the lifespan of erythrocytes?
- Dogs - 120 days
- Cats - 75 days
- Cow - 160 days
- Pigs - 85 days
- Horse and sheep - 150 days
What are the polymorphonuclear granulocytes?
- Neutrophils -
- Eosinophils -
- Heterophils (neutrophils in birds) - spindle-shaped granules
What are the mononuclear agranulocytes?
What makes up the majority of leucocyte counts?
Neutrophils and lymphocytes
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
What are immature neutrophils?
Band or nonsegmented cells (present during disease)
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
In horses, granules of which cells are extremely large and tightly packed, giving a mulberry-like appearance ?
What is the function of eosinophils?
Play a role in allergic and anaphylactic reaction and in parasitic infestation
What is the function of basophils?
Major role in mediating inflammatory reactions (release histamine and heparin)
What is the difference between mast cells and basophils?
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)
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)
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
What do monocytes differentiate into?
Macrophages, once they pass into tissue
What is cell signaling?
The intimate contact of lymphocytes and monocytes is necessary for maximal immunological response
What are the largest leucocytes and their nucleus may appear oval, kidney-shaped or bean shaped or horse-shoe shaped?
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
What is the function of platelets?
Where is the primary site of hematopoisis in adult animals?
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
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)
What is the sequence of maturiy for erythrocytes?
- Myeloid stem cells ->
- Erythrocyte CFC ->
- Metarubricyte ->
- Reticulocyte ->
What is the sequence of maturiy for platelets?
- Pluripotent cell ->
- Platelet CFC ->
- Megakaryocyte ->
What is the sequence of maturiy for macrophages?
- Pluripotent cells ->
- Myeloid cell ->
- Granulocyte and monocyte CFC ->
- Monoblast ->
- Monocyte ->
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
What is the sequence of maturiy for lymphocytes?
- Pluripotent stem cells ->
- Lymphoid stem cells ->
- T-cells, B-cells or NK-cells
What forms the parenchyma of the immune system?
- Lymphocytes (B cells, T cells, NK cells)
What forms the stroma of the immune system?
- Reticular cells
- Epithelial reticular cells
- Dendritic cells
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
What is the function of dendritic cells?
Capture and present antigens to lymphocytes
What are the primary lymphoid organs?
- Produce lymphocyte precursors
- Embryonic yolk sac
- GALT (Payer's patches)
- Cloacal bursa (birds)
- Bone marrow
What are the secondary lymphoid organs?
- House mature immunocytes and site of immune responsiveness)
- Lymph nodes
function and placement of lymph nodes
- situated along lymph vessels
- filter the lymph before returning it to the blood stream
Which lymphiod organ has both afferent and efferent vessels?
What animals do not have lymph nodes?
What are the sinuses of lymph nodes?
What lines the sinuses of lymph nodes?
Epithelium like reticular cells
What lies free within the stromal mesh and in the sinus lumen?
Lymphocytes and macrophages
Lymph nodes are separated into an outer _______ and an inner ______.
What does the outer cortex of lymph nodes consist of?
Primary and secondary lymphatic nodules
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.
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)
What part of the lymph nodes branch and anastomose throughout the medulla and contain the lymphatic tissue?
What cells are in the medullary cords of lymph nodes?
- Plasma cells
What animal has cortical and medullary tissues reversed?
What type of epithelium do post-capillary venules have?
Simple cuboidal epithelium