TBL 3 Flashcards
what trilaminar germ layer are hemangioblasts from?
mesoderm
what two cells does the hemangioblast differentiate into? When?
endothelial cells and hematopoietic stem cells. at the onset of the embryonic period.
where do the hematopoietic stem cells initially form blood islands?
extraembryonic mesoderm
where do the hematopoietic stem cells migrate after forming blood islands in extraembryonic mesoderm? Name two steps
they migrate to liver which becomes temporary site of hematopoiesis, then they colonize the bone marrow as the hematopoietic organ
in what month is the bone marrow colonized as the hematopoietic organ?
the 7th month
what are two names for what pluripotential hematopoietic stem cells differentiate into in bone marrow?
progenitor cells and colony forming units (CFU) are synonymous
what 5 precursor cells do CFU’s differentiate into?
erythrocytic granulocytic monocytic lymphocytic thrombocytic Every Good Mother Lies Terrifically
what is the differentiation of CFU-E into RBCs called?
erythropoiesis
what three cells are produced from granulopoiesis?
CFU-GM -> neutrophils
eosinophils
basophils
what is differentiation of CFU-GM -> monocytes called?
monocytopoiesis
what is CFU-L -> lymphocyte differentiation called?
lymphocytopoiesis
megakaryocytes into platelets is called?
thrombocytopoiesis
CFU-GM can undergo what two differentiations?
granulopoiesis and monocytopoiesis
what dye stains hemoglobin orange-red to pink?
eosin
nuclei are stained dark blue by acidic or basic dyes?
basic dyes
what are the direct precursor descendants of CFU-E?
proerythroblasts
what characterize the lineage of erythroblastic precursor cells?
changes in cytoplasmic color
does extrusion of the nuclei occur in the earlier or later stage of erythropoiesis
later stages
how do you distinguish anucleate reticulocytes from mature erythrocytes?
they lack central pallor
describe basophilic erythroblast
basophilic erythroblast a nucleated precursor in the erythrocytic series, preceding the polychromatophilic erythroblast and following the proerythroblast; the cytoplasm is basophilic, the nucleus is large with clumped chromatin, and the nucleoli have disappeared.
describe polychromatophilic erythroblasts
A nucleated, immature erythrocyte in which the nucleus occupies a relatively smaller part of the cell than in its precursor, the basophilic normoblast. The cytoplasm is beginning to acquire hemoglobin and thus is no longer a purely blue color, but takes on an acidophilic tint, which becomes progressively more marked as the cell matures. The chromatin of the nucleus is arranged in coarse, deeply staining clumps.
describe orthochromatophilic erythroblasts aka normoblast
A cell derived from a polychromatophilic erythroblast in bone marrow. It has a dense nucleus and its cytoplasm is approaching the color of a mature erythrocyte (very pale peach). It differentiates into a reticulocyte when it extrudes its nucleus.
describe reticulocyte
Like mature red blood cells, in mammals, reticulocytes do not have a cell nucleus. They are called reticulocytes because of a reticular (mesh-like) network of ribosomal RNA that becomes visible under a microscope with certain stains such as new methylene blue and Romanowsky stain.
why does the cytoplasm progressively change from blue to reddish pink during erythropoiesis?
deep blue cytoplasm due to abundant ribosomal RNA which has affinity for basic dyes. Many free cytoplasmi ribosomes begin to synthesize hemoglobin. ribosomes decrease and hemoglobin builds up so the cell becomes more eosinophilic.
name stages of erythropoiesis in order
CFU-E -> large round proerythroblast. divides into two smaller -> basophilic erythroblasts -> polychromatophilic erythroblast -> orthochromatophilic erythroblast/late normoblast -> reticulocytes ->erythrocyte
how long to erythrocytes remain in bone marrow until maturity?
2-3 days
what is the principle stimulus for erythropoietin secretion?
erythrpoiesis is regulated by glycoprotein hormone erythropoietin, which is secreted by peritubular cells of kidney, mostly in response to hypoxia.
how long does erythropoiesis take?
from proerythroblast to mature erythrocyte, 7-8 days
what do myeloblasts differentiate into?
promyelocytes
how long does granulopoiesis take?
14-18 days
what completes the granulopoiesis process?
lobulation of horseshoe-shaped nuclei of band cells
describe promyelocytes
large round nuclei and reddish blue cytoplasmic granules
describe myelocytes
eccentrically positioned nuclei flattened on one side
describe metamyelocytes
indentations of the flattened sides of the nuclei
describe band cells
horseshoe-shaped nuclei
name order of CFU-GM to band cell
CFU-GM -> myeloblast -> promyelocyte -> myelocyte -> metamyelocyte -> band cell
rank from most common to least relative frequencies of types of leukocytes in blood smear
neutrophils, lymphocytes, monocytes, eosinophils, basophils
eosin stains large granules of eosinophils ___
orange red to pink
basic dyes stain large granules of basophils ___
deep blue
neutral dyes stain the fine granules of neutrophils ___
faint pink
the combination of dyes stain lysosomes of monocytes and lymphocytes ___
grayish blue
describe how to identify erythrocytes
biconcave disk, anucleate. pink cytoplasm due to acidophilia of hemoglobin. halo in center
describe how to identify neutrophils. what is their function?
segmented 3-5 lobe, densely stained nucleus. pale, finely granular cytoplasm. phagocytoses of bacteria
describe how to identify eosinophils. what is their function
bilobed, clumped, chromatin stained nucleus. cytoplasm with large homogeneous red granules that are coarse and highly reflective. phagocytoses of antigen-antibody complexes and parasites
describe how to identify basophils, what is their function?
bilobed or segmented nucleus. cytoplasm with large blue specific granules that stain with basic dyes and often obscure nucleus. involved in anticoagulation, increases vascular permeability
describe how to identify lymphocytes and their function
small round or slightly indented, dark stained nucleus. cytoplasm which is agranular, faintly basophilic, blue to gray. acts in humoral (b cells) and cellular (T cell) immunity
describe maturation of B and T cells
lymphocytopoiesis generates B and T lymphocytes. mature B cells are formed in bone marrow. but T cells must circulate to the thymus to mature
where does bilobed thymus reside?
beneath the sternum
what surrounds both lobes of the thymus?
dense connective tissue capsule
how does T cell maturation relate to age?
a substantial population of mature T cells develop in thymus before puberty and T cell maturation decreases during adulthood. by mid-twenties T cell progenies are established and fatty tissue begins to occupy adult thymus
describe organization of thymus
extensions from capsule subdivide lobes into lobules with outer dark stained cortex and central paler stained medulla
why is cortex darkly stained?
immature T cells from BM traverse capillary endothelium into medulla and migrate into the cortex to mature and proliferate, thus T cell population in cortex accounts for its dark staining intensity. Another way of saying it is because contains lymphoid nodules
what cells in cortical capillaries are essential for T cell maturation?
epithelial reticular cells (ERCs)
ERC’s, tight junctions of cortical capillary endothelium, thick basement membranes, and macrophages form the __
blood-thymus barrier
name two functions of blood-thymus barrier
- blocks devloping T cells from premature antigenic exposure
- circumvention of the barrier by nonself and or self-antigens drives reactive T cells into apoptosis thus preventing immune reactions in the thymus
is there a blood-thymus barrier in the medulla? why or why not?
No. allows mature T cells to traverse medullary capillary endothelium into circulation.
why does the thymus medulla have a weak staining intensity?
the transitory presence of immature and immunocompetent T cells in medulla account for this
what is another name for the thymic corpuscles. are they in cortex or medulla?
Hassall corpuscles. Because David Hassallhoff flexes his corpuscles on Baywatch. medulla
what does Hassall corpuscle consist of? how does it work
circumferentially arranged ERCs, many of which are degenerating. visible ERCs produce cytokines that induce formation of regulatory T cells.
what is function of regulatory T cells?
subclass that contributes to termination of immune responses outside the thymus
why do recurrent opportunist infections characterize Di George syndrome aka thymic aplasia ?
because thymus does not fully develop. due to defect on chromosome 22 because of recombination error. so faulty development of third and fourth pharyngeal pouches in early embryo. selective T cell deficiency leads to immunodeficiency with recurrent opportunistic infections. malformation of heart, esophagus, great vessels, and parathyroid glands also occur. maternal EtOH consumption in first trimester also may be responsible
what forms lymph?
unabsorbed capillary filtrates which is absorbed by porous lymphatic capillaries to prevent edema formation
lymphatic capillaries drain into __
lymphatic vessels
what kind of valves do lymphatic vessels posses?
bicuspid valves, to ensure unidirectional flow
in organ systems that contain a lumen, the endothelium and underlying loose connective tissue is generically designated __
mucosa
what forms lymphoid nodules in mucosa associated lymphoid tissue (MALT)?
progenies of antigen-activated B cells aggregate. T cells are dispersed among the nodules.
what are lymphangitis and lymphadenitis, why are they dangerous?
lymphangitis- inflammation of lymphatic vessels
lymphadenitis- inflammation of lymph nodes
dangerous because can lead to septicemia
what is lymphedema?
localized edema, occurs when lymph does not drain from an area of the body. solid cell growths may permeate lymphatic vessels and form minute cellular emboli (plugs) which may break free and pass to regional lymph nodes. so lymphangitis spreads.
about how many immunocompetent lymphocytes reside in how many lymph nodes in body?
billions of lymphocytes in 500-600 lymph nodes dispersed throughout body.
what two capillaries does arterial blood enter in thymus? where to they drain?
cortical and medullary capillaries. drain into high endothelial venules (HEV) which reside at boundary between cortex and medulla
what tissue type lines high endothelial venules? what molecules does it express/
simple cuboidal endothelium. expresses cell adhesion molecules that facilitate selective migration of T cells and B cells into lymph nodes
lymph in afferent lymphatic vessels enters the ___
subcapsular sinus, that is continuous with the cortical sinus
why is endothelium lining sinuses discontinuous?
so adjacent macrophages and lymphocytes can filter antigens from incoming lymph
how are lymphoid nodules formed?
B cells are selectively activated by incoming antigens, they replicate in cortex and form lymphoid nodules
what comprises the paler germinal centers within lymphoid nodules?
progeny B cells
how does lymph drain from lymph nodes?
drains from cortical sinuses into medullary sinuses that interweave amongst medullary cords
what are medullary cords?
linear aggregates of antigen-activated lymphocytes and plasma cells that migrate into medulla from cortex
function of medullary sinuses?
they coalesce into a single efferent lymphatic vessel that returns filtered lymph, fortified with activated lymphocytes and plasma cells from medullary cords, to lymphatic circulation
how do lymphocytes and plasma cells, which were activated in local lymph nodes by incoming lymph from MALT, exit lymph nodes and relocate to MALT?
lymphocytes leave lymph node by entering efferent lymphatics to travel in lymph and reenter systemic circulation
what kind of collagen comprises dense connective tissue of splenic pulp
type III collagen (reticular fibers)
what occupies most of splenic pulp?
extravasated RBCs, and designate red pulp
what is white pulp?
lymphoid nodules dispersed through red pulp of spleen
what accounts for extravasated RBCs in spleen
terminal branches of splenic artery empty into open-ended capillaries in red pulp
where is venus sinusoids of spleen?
slit like spaces between endothelial cells interweaved throughout red pulp
do aged RBCs squeeze through slit like spaces into sinusoids?
no, young extravasated blood cells do, but aged RBCs lose their pliability and are phagocytized by resident macrophages
what happens to blood born antigens in spleen?
either phagocytized by macrophages or selectively bound to extrvasated lymphocytes
what forms the lymphoid nodules of white pulp in spleen?
antigen activated B cells
how does immunologically filtered blood from spleen return to circulation?
small tributaries of splenic vein drain the venous sinusoids and return the filtered blood to circ
how do the clinical consequences of splenectomy in kids differ from those in adults
in adults usually has no clinical consequences but in kids leads to increased occurrence and severity of infections
why would an adult have a splenectomy?
due to splenomegaly from portal hypertension resulting from cirrhosis of the liver
