1. Blood, Skin & Lymphoid
Study Guide
Samantha Blum

2. Blood

3. Blood Smear: Erythrocytes
Rouleaux= stacks of RBCs

4. Rouleaux

5. Blood Smear: Platelets
Platelets appear as the small
blue “fragments”

6. Blood Smear: Eosinophils
Eosinophil

7. Eosinophil

8. Blood Smears: Basophils

9. Blood Smears: Lymphocytes &
Monocytes
Note the differences between the nuclei

11. Blood within vessels of heart
Contains blood cells other than
erythrocytes

12. Blood within vessels of kidney
Notice how abundant blood cells
and vessels are in this highly
vascular organ.

13. General organization and components
of bone marrow
• Bone marrow is actually an organ comprised of different tissue components. It can be divided
into a vascular compartment (40X) (arteries, veins, sinusoids) and a hemopoietic
compartment (50X) (stroma of reticular tissue and free cells).

14. Erythropoesis
During erythropoiesis, cell size
decreases, the nucleus becomes
condensed (and eventually
discarded), and the cytoplasm becomes
increasingly acidophilic.

15. Erythropoesis
Basophilic erythroblast- Note the rim of intensely basophilic cytoplasm
Polychromatophilic erythroblast- "checkerboard" nucleus and slate-colored cytoplasm
Normoblast- The cytoplasm of these cells is decidedly acidophilic, due to loss of RNA and increase in
hemoglobin. Look for normoblasts in the process of extruding pyknotic nuclei
Reticulocyte- Note that reticulocytes have the same appearance as mature erythrocytes in a
conventionally-stained slide. When RNA specifically stained, you can distinguish between reticulocytes
and mature erythrocytes.

16. Erythropoesis Intermediates

17. Granulocytopoesis
•The cells in these three lines of development can be readily identified by the presence
of pronounced cytoplasmic granules, and by the gradual lobation of the nucleus. The
stem cell is the same or similar to that for erythropoiesis.
•You will only be responsible for identifying those granulocyte precursors that have
specific granules.
•Note: Mature granulocytes have segmented nuclei.

18. Granulocytopoesis

19. Megakaryocytes & Platelet Formation
•Megakaryocytes have multi-lobed nuclei
•Located near sinuscytoplasmic extensions break off to form platelets

20. Monocytopoesis & Lymphocytopoesis
• Development of the agranular leukocytes is
difficult to follow at the light microscopic
level. You will not be held responsible for
identifying cell intermediates in these
pathways (monocytes and lymphocytes).

21. Distinguishing Hemopoietic Stages
• Erythropoiesis:
– Basophilic erythroblast has basophilic/blue
Basophilic and
cytoplasm, while polychromatophilic
erythroblast has “slate”-colored cytoplasm Poly.
and a “checkerboard” pattern of granules Erythroblast
– Normoblast has acidophilic/pink
cytoplasm and can be seen in process of
extruding nucleus
• Granulocytopoiesis: Normoblast
– In all stages
• Eosinophilic= pink granules
• Neutrophilic= neutral granules
• Basophilic= blue granules
– Myelocyte= round nucleus
– Metamyelocyte= approaching band/stab
cell curved nucleus
– Band/Stab= U-shaped nucleus
– Mature= segmented nucleus

22. Blood Clinical Correlation
• Iron deficiency anemia:
– Lack of adequate dietary iron results in abnormally
low levels of the blood pigment hemoglobin
(which binds to, and requires, iron to function).
Low hemoglobin content results in smaller
erythrocytes that have a thin rim of hemoglobin
around their periphery
• Sickle cell anemia:
– Sickle cell anemia is a condition caused by a
mutation in the gene that codes for hemoglobin.
The pathological hemoglobin causes red cells to
adopt a spiky, "sickle" shape
• Chronic myelogenous leukemia:
– In chronic myelogenous leukemia (CML), a
mutation occurs that prevents cells of a particular
line from maturing, but allows them to continue to
self-renew, leading to a massive increase in their
number. The immature myeloid cells (myeloblasts)
accumulate in the marrow, where they replace
normal elements. These abnormal cells often
circulate in the peripheral blood. In the
acute, "blast crisis" phase of this disease, large
numbers of myeloblast-like cells appear in the
peripheral blood.

23. Skin

24. Thick Skin
• Note the absence of hair follicles.
• Note that the epidermis is quite thick relative to the dermis.
• Identify the well-defined outermost epidermal layer, the stratum corneum.

25. Thin Skin
• Note that the epidermis is thin, relative to the dermis.
• Notice the variation in abundance and type of hair follicles and glands, and in the thickness of the dermis.

26. Epidermis: Stratum Basale
• This layer is also called stratum germinativum; why?
• Note that these cells are highly mitotic.

27. Epidermis: Stratum Basale

28. Epidermis: Stratum Spinosum
• this layer is formed as daughter cells from the stratum basale migrate toward the epidermal surface.
• Identify the numerous artifactual intercellular "bridges" that give these cells a spiny appearance. The
bridges are due to spot desmosomes

29. Epidermis: Stratum Granulosum
• Not consistently present in thin skin, this layer (2-5 cells thick) contains darkly-staining cells.
• Identify the keratohyalin granules (100X, 100X), which are responsible for the pronounced staining and
granular appearance of this layer. The granules are not pigment, and are unrelated to the naturally
pigmented melanin granules.
• Examine keratinocyte nuclei (100X, 100X), which are beginning to degenerate in this layer.

30. Epidermis: Stratum Granulosum

31. Epidermis: Stratum Lucidum
• This translucent layer of flattened cells is almost never seen in thin epidermis.
• Note that nuclei are absent, and that cell boundaries are indistinct

32. Epidermis: Stratum Corneum
•Identify the dead, scale-like cells (40X, 50X).
•Note that the number of cell layers varies tremendously

33. Epidermis: Stratum Corneum

34. Epidermis: Melanin Granules
• Note the widespread distribution of orange-brown granules in cells of the stratum basale, and, to some
extent, in cells of the stratum spinosum (50X, 100X).
• Note that melanin granules are present throughout the thickness of the epidermis, but are more difficult
to see in superficial layers.

35. Epidermis: Melanocytes
• These cells (schematic) occur with a low frequency (the melanocyte/ keratinocyte ratio is
1/36), and are difficult to see by these staining methods.
• Note that melanocyte cytoplasm is lighter than the cytoplasm of surrounding keratinocytes (blue
arrows, 100X). The melanocyte secretes pigment-containing melanosomes that are then taken up
by the epidermal keratinocytes and degraded to add pigment to their cytoplasm.

36. Dermis: Papillary Layer & Reticular
Layer
• Papillary Layer:
– The papillary and reticular layers are
most easily distinguished in a
trichrome-stained section.
– Examine this C.T. network of fine
collagenous, reticular and elastic fibers
and note that dermal papillae extend
upward into the epidermis . What is the
function of these structures
• Reticular Layer:
– In this layer (and often extending into
the subcutaneous region) are hair
follicles, sweat and sebaceous
glands, and smooth muscle (see
below).

37. Hypodermis
• Note that adipocytes predominate in this subcutaneous layer (4X, 10X, 40X), which is not a part of the
skin.
• Identify Pacinian corpuscles (5x, 10X, 40X) in hypodermis (and deep dermis). What is their function?
– Pacinian corpuscles= encapsulated mechanoreceptors especially adapted to detect pressure and
vibration
– Distinctive onion-like appearance due to tight Schwann cell wrapping around the bare sensory nerve
ending

38. Sweat (Eccrine) Glands
• These are found in both thick and thin skin. The type of secretion that occurs here is merocrine (eccrine).
They are the only cutaneous glands in thick skin. Identify these unbranched, coiled, tubular, serous glands
located in superficial hypodermis (4X, 20X, 20X, 50X).
• Identify myoepithelial cells (40X, 50X), which are associated with secretory portions (best seen in the C.P.-
Trichrome slide).
• Try to find an excretory duct (40X) passing straight through the dermis, and emptying at the epidermal
surface.
• Note that the walls of sweat gland ducts are stratified cuboidal epithelium, with two layers of cuboidal
cells (40X, 50X, 100X).

39. Sweat (Eccrine) Glands
Acini and ducts

40. Apocrine Glands (in Axilla)
• Note that both eccrine and apocrine glands (4X) are present here.
• Note that apocrine glands usually extend deeper into the hypodermis than do eccrine glands (4X).
• Note that the secretory portion of an apocrine gland is also coiled and tubular, but has a considerably
wider lumen than that of an eccrine gland (20X).

41. Apocrine Glands
Note the difference between apocrine glands (left) and eccrine glands (right)

42. Sebaceous Glands
• Sebaceous glands. Hair follicles are almost always associated with sebaceous glands (20X). The
secretory product, sebum, is produced by holocrine secretion. Note that the secretory portion is
comprised of stratified epithelial cells that crowd into, and occlude, the lumen (50X). Identify lipid-
filled vacuoles in these cells.
• Note that the excretory ducts are quite short and wide, with a stratified epithelium that is
continous with the epithelial hair sheath (40X).

43. Hair Follicles
• Components of Hair Follicle:
– Germinal matrix epithelial cells
Hair
– Vascular connective tissue papilla
bulb
– Hair bulbs
– Hair root
– Medulla, cortex and cuticle of hair.
– Internal and external root sheath

44. Arrector Pili Muscles
• Note the presence of bundles of smooth muscle cells (10X, 20X) in fortuitous sections. What is the
function of these structures?
– Makes hair stand erect
– Pulls skin in to form dimples
– Both functions “goosebumps”

45. Nails
• Components of a Developing (Monkey) Finger:
– Nail, or nail plate: body and root
– Nail bed: This is comprised of an epidermis without stratum granulosum or stratum lucidum, and the
underlying dermis.
– Nail matrix : epithelium
– Eponychium: cuticle
– Hyponychium: This structure secures the free edge of the nail plate at the fingertip.

46. Clinical Correlation
• Squamous cell carcinoma of skin:
– Squamous cell carcinoma is the most
common type of sun-associated
tumor, although it may also be caused by
chewing tobacco, carcinogenic
chemicals, or ionizing radiation. Such cells
may have an epithelioid (flattened)
shape, or they may be rounded (1X, 5X).
Squamous cell carcinomas are commonly
removed surgically before they
metastasize.
• Basal cell carcinoma of skin:
– Basal cell tumors arise when cells in the
basal layer of the epithelium of skin begin
growing and dividing abnormally. The
cells often grow in clumps (nodular
lesions) surrounded by fibroblasts and
lymphocytes (10X); the cells at the
periphery of these islands are often
arranged radially (40X). Basal cell
carcinomas grow slowly and usually do
not metastasize.

47. Clinical Correlation
• Melanoma:
– Malignant melanoma is a cancer that
results from uncontrolled growth of
melanocytes. It occurs most commonly
in skin that has been heavily exposed
to sunlight. Melanoma cells are
large, have large nuclei, and can be
found in any layer of the skin (5X, 40X).
These cells have a high incidence of
metastasis.
• Bullous pemphigoid:
– In this autoimmune
disorder, antibodies attack one of the
protein components ("bullous
pemphigoid antigen") of the
hemidesmosome (schematic; EM).
Since the hemidesmosome anchors
the epithelium to the underlying
connective tissue, its destruction
loosens that connection and results in
the formation of blisters.

48. Lymphoid

49. Thymus
The thymus, a central lymphoid organ, is the organ
in which T-cell precursors differentiate to become
immunocompetent T-lymphocytes capable of
responding to antigen in the context of "self". The
thymus is not a site where immune responses to
foreign antigen occur, and thus it differs from the
peripheral lymphoid tissues in structure and
organization; specifically, it contains neither
nodules nor germinal centers. It is a bi-lobed
organ whose size and appearance varies with age.

50. Thymus: Overall Structure
• Identify the connective tissue capsule and trabeculae that divide the thymus into lobules (4X).
• Note the variation in lobule size.
• Identify cortex and medulla of lobules (10X).
• Note that lobules are not completely separated by trabeculae. Each lobe of the thymus contains a
medullary core that extends into each lobule (4X).
• Note the absence of lymphoid nodules and sinuses; you should be careful not to confuse circular regions
of medulla with germinal centers.
• Note that trabeculae are cortical structures; they do not extend into the medulla.

51. Thymic Cortex
• Identify large, mitotic thymocytes (100X, thymic lymphocytes), and note that they decrease in size as the
medulla is approached.
• Identify reticular epithelial support cells (schematic, 100X); these have a stellate shape, and pale-staining
nuclei with distinct nucleoli.
• Note that, unlike other lymphoid organs, the thymus has an entirely cellular stroma; no reticular fibers are
present.
Green arrows= reticular epithelial support cells
NOTE: These cells appear to be “outlined”

52. Thymic Medulla
• Note that lymphocytes are less dense here (medulla is less stained than the cortex on previous slide…), so
that reticular epithelial cells are more readily identified.
• Identify reticular epithelial cells (100X), which have large, oblong nuclei.
• Locate a Hassall's corpuscle (50X), and identify the concentric reticular cells that are hyalinized (100X, EM)
and degenerated toward the center of the corpuscle.

53. Hassal’s Corpuscles

54. Thymus: Blood Vessels
• Note that only capillaries (50X) are present in the cortex. Epithelial reticular cells ensheath thymic cortical
capillaries, thereby contributing to a blood-thymic barrier (schematic) that keeps the cortex free of
circulating antigens.
Epithelial reticular cells cover thymic cortical capillaries blood-thymic barrier

55. Diffuse Lymphoid Tissue
• This tissue is often present as an infiltration of the lamina propria of mucous membranes, especially in
gastrointestinal and respiratory tracts. Lymphocytes, plasma cells, macrophages and some other blood
cells are scattered within the reticular connective tissue among the components of the lamina propria.
Scan these slides of various regions of the digestive tract and locate diffuse lymphoid tissue (10X, 40X).
Diffuse lymphoid tissue is particularly abundant in the lamina propria of colon. In all slides, identify:
• Lymphocytes (100X). These are the most abundant cell type.
• Macrophages (100X, lamina propria of small intestine). Both fixed and free macrophages are generally
present.
• Plasma cells (20X, 100X). You may also see these antibody-producing cells.

56. Lymphoid Nodules
• Lymphoid tissue arranged in a dense, spherical
aggregation is called a lymphoid nodule.
These can occur as solitary nodules, as
loosely-organized aggregations, or as part of
an encapsulated lymphoid organ.

57. Solitary Lymphoid Nodules
• Solitary One nodule on its own, at a distance from other nodules
• Note that nodules can vary considerably in size.
• Identify lymphocytes in the nodules.
• Identify lymphoid nodules (4X, 10X, 10X, 10X) and secondary nodules (4X, 10X). Note that secondary
nodules have lighter-stained germinal centers.
• Note that nodules may be surrounded by diffuse lymphoid tissue.

58. Aggregate Lymphoid Nodules
• Aggregate multiple nodules adjacent to one another
• Examine this section for loose aggregates of lymphoid nodules. In the ileum, these characteristic
aggregates may include 10-100 lymphoid nodules and are called Peyer's patches (4X, 20X). They aid in the
identification of this region of small intestine (to be studied later).
• Identify lymphoid nodules and note secondary nodules

59. Peripheral Lymphoid Organ
• A lymphoid organ is an aggregation of
lymphoid tissue that has a capsule of dense
connective tissue. Lymph nodes, spleen and
thymus are lymphoid organs that have
complete capsules; tonsils are partially
encapsulated lymphoid organs.

60. Lymph Nodes: General Structure
• Note the overall bean-like shape, with a hilus at the concavity.
• Identify the dense irregular connective tissue capsule with septa (20X, 40X) or trabeculae extending into
the organ.
• Identify both afferent (4X, 10X, 40X) and efferent lymphatic vessels. This feature is unique to lymph
nodes.
• Identify both cortical and medullary regions.

61. Lymph Nodes: Cortex
• Identify lymphoid nodules surrounded by diffuse lymphoid tissue.
• Lymphoid nodules in their inactive state are primary nodules; secondary nodules are easily identified by
their germinal centers.
• Note that cells within the germinal centers (40X) are larger, and have paler-staining, more euchromatic
nuclei (100X), than do the cells surrounding them.

62. Lymph Nodes: Medulla
• Note that the lymphoid tissue is arranged here as cords (20X).
• Identify medullary sinuses.

63. Lymph Nodes: Framework
• Note that the capsule (50X) and trabeculae (50X) are composed of dense C.T.
• Identify fibroblasts in the dense C.T. (50X, 50X)
• Study the delicate reticular tissue (50X) of the stroma. Note the reticular fibers stained specifically on
especially slide 0-45.
• Examine the reticular cells (50X), which are responsible for producing reticular fibers. The reticular cells
form a network of cell processes associated with the supporting reticular fiber network.
• Note that the reticular framework extends into sinuses, as well as into nodules and cords (50X, 50X).
• Identify fixed macrophages (100X).

64. Lymph Nodes: Sinuses
• Lymph enters the node via afferent vessels, passes through the node via sinuses, and exits at the hilus via
efferent vessels. The sinuses have discontinuous walls lined by reticular cells and fixed
macrophages, allowing lymphocytes to move into sinuses, and, eventually, into efferent lymphatics.
• Identify afferent lymphatics (4X, 10X, 40X) piercing the capsule at a number of sites.
• Identify subcapsular sinuses (20X).
• Identify cortical (trabecular) sinuses (20X).
• Identify medullary sinuses (50X).
• Identify efferent lymphatics at the hilus.
See Medulla slide for medullary sinus

65. Lymph Nodes: Blood Vessels and
Nerves
• Identify arteries at the lymph node hilus that provide branches to medulla, cortex, and trabeculae.
• Identify the dense network of capillaries (40X) in the medullary cords.
• Note that the cuboidal endothelium of post-capillary (high-endothelial) venules
(100X, 100X, 100X, animation) is the site where B- and T-lymphocytes leave the blood to enter the lymph
stream. They eventually leave the lymph node via efferent lymphatics.
• Locate nerves entering the lymph node at the hilus.

66. Tonsils
• Although considered lymphoid organs by virtue of their partial connective tissue
capsule, tonsils are not much more organized than Peyer's patches. Three groups
of tonsils form a ring of lymphoid tissue around the pharynx. All are aggregates of
nodules embedded in diffuse lymphoid tissue. They have an invaginated surface
epithelium and an underlying connective tissue capsule.

67. Palatine Tonsils
• Identify lymphoid nodules (4X).
• Note that the surface epithelium
extends into deep
invaginations, the tonsillar crypts
(10X).
• Identify lymphocytes invading the
epithelium (40X).
• What type of C.T. is present in the
hemi-capsule (40X) that separates
the tonsil from underlying muscle?
– Fibrous connective tissue

68. Lingual Tonsils
• These tonsils are actually aggregations of epithelial pits surrounded by lymphoid tissue.
• Identify crypts (4X).
• Identify surface epithelium (40X, 40X).
• Identify nodules and internodular spaces (4X, 40X).
• Examine the hemi-capsule (4X, 40X).

69. Pharyngeal Tonsils
• Located in the nasopharynx, rather than the oropharynx, these tonsils differ somewhat from palatine and
lingual tonsils.
• Examine the surface invaginations (4X). These are actually longitudinal folds, rather than crypts.
• Identify the surface epithelium (20X, 40X).
• Identify nodules (4X).
• These tonsils have a hemi-capsule, although the capsule is not visible in these particular slides because it
was not dissected along with the specimen.

70. Spleen: Overall Structure
• Identify the capsule and branching trabeculae (4X).
• Distinguish white pulp and red pulp. Identify splenic nodules (10X) within the white pulp.

71. Spleen: Capsule and Trabeculae
• Note the presence of blood vessels (10X) in the trabeculae.
• Within the connective tissue, identify elastic fibers (100X) and smooth muscle cells (20X, 100X).

72. Spleen: Reticular Framework
• Slide E-47, with reticular stain, demonstrates the presence of a delicate reticular tissue stroma, upon
which free cells are supported.

73. Reticular Cell/Fibers in Framework of
Spleen

74. Spleen: White Pulp
• Identify lymphocytes (100x).
• Locate a secondary lymphoid nodule in the white pulp. Identify the central artery/arteriole
(20X, 20X, 100X). The nodule is actually a local expansion of the lymphoid ensheathment of the artery.
• Note the eccentric placement of the central artery (20X, 40X) in those nodules that have a germinal center.
All secondary lymphoid nodules, which are activated for a humoral response, have germinal centers.
• Identify the Periarteriolar Lymphoid Sheath (PALS) of lymphocytes surrounding the central artery
(20X, 20X, 20X, 40X, 100X). T-lymphocytes principally surround the central artery, while B-lymphocytes are
primarily located in the secondary nodules with germinal centers (100X). A germinal center is a site of B-
lymphocyte proliferation.
• Why is white pulp called white pulp?
– White pulp contains lymphocytes (WHITE blood cells) and can be distinguished from red pulp, which contains
sinusoids filled with RED blood cells.
B-lymphocytes
T-lymphocytes

75. Spleen: Red Pulp
• Two components are present in red pulp:
venous sinuses and pulp cords.

76. Red Pulp: Pulp Cords
(aka Cords of Bilroth)
• These structures consist of a spongy network of cells arranged on the reticular stroma. Identify the
principal cell types (40X, 100X, 100X) present in the cords (20X): lymphocytes, macrophages
(40X, 100X), plasma cells (100X), and erythrocytes.
• Note that red pulp cords gradually merge into white pulp.
• Note that lymphocytes (of all sizes) are less numerous in red than white pulp (20X, 40X).
• Note that the pulp cords contain a large population of highly phagocytic cells (macrophages; 100X). What
do these cells do here?
– Macrophages destroy aged/damaged RBCs that move freely through the cords and venous sinuses.
• Why is red pulp called red pulp?
– Much less lymphocytes than white pulp; greater number of RBCs

77. Splenic Phagocytosis
• Slide O-18 demonstrates the presence of phagocytic cells in spleen (100X)
by uptake of India ink (only phagocytic cells can sequester the ink, which is
made up of tiny carbon particles).

78. Red Pulp: Venous Sinuses
• These lie between pulp cords (20X, 100X). Note that they are lined by endothelial cells that form a
discontinous sinus wall (100X, 100X, EM).
• Study the contents of the venous sinuses.

79. Spleen: Blood Circulation
• You should make sure that you can identify the following splenic structures in your
slides:
• Splenic artery.
• Trabecular arteries.
• Central arteries of white pulp.
• Penicillar arterioles of red pulp (with pulp arteriole, sheathed arteriole, and
terminal arterial capillary).
• Venous sinuses.
• Pulp veins.
• Trabecular veins.
• Splenic veins.

80. Clinical Correlation
1. Follicular lymphoma (HD047).
A follicular lymphoma is a tumor of
lymphoid cells (most often B-cells), in
which the cells cluster into nodules that
resemble normal lymphoid follicles. All
lymphoid tumors derive from a single
transformed cell, so they are
monoclonal, which means that all of
the tumor cells are identical. As it fills
with abnormal lymphocytes, the lymph
node's normal structure is destroyed
(1X).
2. Hodgkin lymphoma (HD045).
Hodgkin lymphoma is a lymphoid
cancer that begins as an enlargement
of a single node, then spreads to
neighboring nodes. Its most
characteristic feature is the
giant, neoplastic Reed-Sternberg (RS)
cell. This form of the disease (Nodular
Sclerosis) shows a modified form of the
RS cell, the lacunar cell (5X, 40X).
40x 5x