Histology of circulatory system

1. In the name of God
HISTOLOGY OF THE CIRCULATORY
HISTOLOGY OF THE CIRCULATORY
SYSTEM
Dr. Zahiri

2. Dr. Maria Zahiri
The cardiovascular system is subdivided into
two functional parts
Bl d l t
1. Blood vascular system
1. Lymph vascular system

3. Dr. Maria Zahiri
Blood vascular system
• Distributes nutrients, gases, hormones to all parts of the
d
• Body
• collects wastes produced during cellular metabolism
• Consists of blood vessels (arteries, arterioles, capillaries,
venules, veins) and a muscular pump (heart)

4. Dr. Maria Zahiri
Lymph vascular system
• Collects tissue fluid from tissues and returns it to the
Collects tissue fluid from tissues and returns it to the
blood vascular system.
• Consists of blind-ended capillaries (lymphatic capillaries)
p ( y p p )
connected to venous vessel (lymphatic vessels) and
various lymphoid organs (e.g., lymph nodes).

5. Dr. Maria Zahiri
Structure of vessel walls
• Except for the smallest vessels, blood and lymphatic vessel
walls can also be viewed as three-layered structures.
y
• a. Inner layer = tunica intima
• b Middle layer = tunica media
• b. Middle layer = tunica media
• c. Outer layer = tunica adventitia

6. Dr. Maria Zahiri
Tunica intima
• Thin
• (1) Endothelium
• (1) Endothelium
• (2) A subendothelial layer (L.C.T. + muscular cell )
• Internal elastic lamina
• (in arterries- have fenestrae)

7. Dr. Maria Zahiri
Endothelium
• Angiotensin I AngiotensinII (effect on B.P)
• Lipolysis of Lipoprotein
• Lipolysis of Lipoprotein
• Produce Vasoactive factores(endothelin, NO)
• Produce VEGF (Vascular Endothelium Growth Factor)
• Prevent the adhesion of the blood cells to the wall of the
vessel and prevent the thrombosis and further
vessel and prevent the thrombosis and further
complications of thrombosis.

8. Dr. Maria Zahiri
Tunica media
• thick
(1) Ci l th l ( 0 l )
• (1) Circular smooth muscle( 5 - 40 layers)
• (2) Small amount of CT with collagen fibers , elastic and
reticular fibers, Gp, PG
(3) Thickness decreases as diameter of vessel decreases
• (3) Thickness decreases as diameter of vessel decreases
• External elastic lamina (May be indistinct in smaller muscular
arteries)
arteries)

9. Dr. Maria Zahiri
Tunica adventita
• - thick
• collagen I, Elastic fiber

10. Dr. Maria Zahiri
Atherosclerosis
• Problem in ECM(
Collagen I, III, GAG,
Elastin)
Elastin)
• an artery wall thickens
as a result of :
• the accumulation of
calcium and fatty
calcium and fatty
materials such as
cholesterol and
triglyceride
triglyceride.

11. Dr. Maria Zahiri
vasa vasorum
• a network of small
blood vessels
blood vessels
• provide blood supply
and nourishment for
t i d titi d
tunica adventitia and
outer parts of tunica
media of large vessels

12. Dr. Maria Zahiri
elastic arteries
large
large vein
vein elastic arteries
muscular arteries
large
large vein
vein
medium
medium-
-sized
sized vein
vein
arterioles
venules
venules
capillaries

13. A Comparison of a Typical Artery and a Typical Vein
Dr. Maria Zahiri
A Comparison of a Typical Artery and a Typical Vein

14. Largest conducting arteries lead directly
Dr. Maria Zahiri
Largest, conducting arteries – lead directly
from heart, subject to high pressures
Pulmonary trunk & aorta
and their major branches
Superior & inferior
vena cava and their and their major branches
vena cava and their
tributaries

15. Dr. Maria Zahiri
aneurysm
• Greek: "dilation“
is a locali ed blood filled balloon like b lge in the all of a blood
• is a localized, blood-filled balloon-like bulge in the wall of a blood
vessel
• can occur in any blood vessel
A l ithi th h t it lf
• Aneurysms can also occur within the heart itself.
A ruptured aneurysm can lead to bleeding and subsequent hypovolemic shock, leading
to death.
• Aneurysms are a result of a weakened blood vessel wall, and can be
a result of a hereditary condition or an acquired disease.

16. Dr. Maria Zahiri
Glomus body (glomus apparatus)
• Is a component of the dermis
layer of the skin
• Involved in body temperature
Involved in body temperature
regulation.
• consists of an arterio-venous
shunt(anastomosis)
d d b l f
• surrounded by a capsule of
connective tissue.
• most numerous in the fingers and
toes
toes
• (-) IEL, ↑TML, ↓Lumen
l
• Role :
• Regulation of blood temperature

17. Dr. Maria Zahiri
Regulation of blood flow with their T.M
↑subendothelial
I.E.L is prominence
↑ T M L
↑ T.M.L
External and internal
id b hi l & f l
External and internal jugular,
b hi l & f l i carotids, brachial & femoral
arteries
brachial & femoral veins
 2 - 9 mm
 ~ 4 mm

18. Dr. Maria Zahiri
↓subendothelial
(-) I.E.L
↓subendothelial
pericyte
↓ T.M.L
pericyte
↓ T.M.L
 ~ 10-50 µm  ~ 30 µm

19. Dr. Maria Zahiri
Capillaries
p
• smallest of a body's blood vessels(microcirculation)
• endothelial linings are only one cell layer thick(5-10 μm)
connect arterioles and venules
• enable the exchange of water, oxygen, carbon dioxide,
and many other nutrients and waste chemical substances
between blood and the tissues
between blood and the tissues

20. Dr. Maria Zahiri
Types
• There are three main types of capillaries:
• Continuous
• Continuous
• Fenestrated
• Sinusoidal

21. Dr. Maria Zahiri
Continuous (Somatic)
• Endothelial cells provide an
• Endothelial cells provide an
uninterrupted lining, and they only
allow small molecules, like water and
ions to diffuse through tight junctions
• Tight junctions can be further divided into
two subtypes:
• with numerous transport vesicles
p
(skeletal muscles, connective tissue,
gonads, Exocrine glands)
with few vesicles (central nervous
• with few vesicles (central nervous
system)
• These capillaries are a constituent of the
p
blood-brain-barrier.

22. Fenestrated (Visceral)
Dr. Maria Zahiri
Fenestrated (Visceral)
• "fenestra," Latin for "window"
• have pores in the endothelial cells (60-
80 nm in diameter)
• Have a diaphragm
• In the renal glomerulus there are cells
with no diaphragms called podocyte foot
with no diaphragms called podocyte foot
processes or "pedicels,“
d i l d i t ti
• endocrine glands, intestines, pancreas,
and glomeruli of kidney

23. Dr. Maria Zahiri
• Both of these types of blood vessels have continuous basal
lamina

24. Dr. Maria Zahiri
Sinusoidal capillaries
• are a special type of fenestrated capillaries
are a special type of fenestrated capillaries
• have larger openings in the endothelium
• allow red and white blood cells (7 5μm - 25μm diameter)
• allow red and white blood cells (7.5μm - 25μm diameter)
and various serum proteins to pass using a process that
is aided by a discontinuous basal lamina
• These capillaries lack pinocytotic vesicles
• Sinusoid blood vessels are primarily located in the bone
• Sinusoid blood vessels are primarily located in the bone
marrow, lymph nodes, and adrenal gland.

25. Dr. Maria Zahiri
Metarteriole
a short vessel that links arterioles and venules
• a short vessel that links arterioles and venules
• Instead of a continuous tunica media, they have
individual smooth muscle cells placed a short distance
apart, each forming a precapillary sphincter that
encircles the entrance to that capillary bed.
• Constriction of these sphincters reduces or shuts off
• Constriction of these sphincters reduces or shuts off
blood flow through their respective capillary beds.
• This allows the blood to be diverted to elsewhere in the
body

26. Microanatomy of Lymphatic Vessels
• A. Lymph capillaries
• 1 Structure - blind-ended tubules; consist only of endothelium (which
1. Structure blind ended tubules; consist only of endothelium (which
lacks cell junctions); similar to post capillary venules of blood vascular
system
• 2 Function to collect excess tissue fluid
• 2. Function - to collect excess tissue fluid
• B. Small to medium lymphatic vessels
• 1. Structure
• (similar to venous blood vessels of the next smaller size)
a Smaller lymphatic vessels consist of endothelium surrounded
• a. Smaller lymphatic vessels consist of endothelium surrounded
by collagen and elastic fibers and a few smooth muscle cells

27. Medium-sized lymphatic vessels
• b.
• (1) Tunica intima - thin; endothelium surrounded by few
ll d l ti fib b f ld d t f l
collagen and elastic fibers; may be folded to form valves
• (2) Tunica media - thin; helically arranged smooth
muscle, elastic fibers
• (3) Tunica adventita - thicker; collagen and elastic fibers,
few smooth muscle cells
• 2. Function - to collect lymph from lymph capillaries

28. Large lymphatic vessels
Large lymphatic vessels
• C. include the thoracic duct and right lymphatic duct.
• 1 Structure
• 1. Structure
• a. Tunica intima - thin
• (1) Endothelium
• (2) Subendothelial layer of collagen and elastic fibers, some
l d l h l
y g
longitudinal smooth muscle
• b. Tunica media - thickest; longitudinal and circular smooth
muscle bundles, loose FECT (similar to a medium blood vein)
• c. Tunica adventita - not well developed; coarse collagen fibers,
few longitudinal smooth muscle
2 F ti t ll t l h f di i d l h ti l
• 2. Function - to collect lymph from medium sized lymphatic vessels
and return it to largeveins
• D. Lymphatic vessels of any size may appear empty, may contain
y p y y pp p y, y
faint pink material (proteins),or may contain lymphocytes.

29. • 1. The heart wall can be viewed as a three-layered
structure.
• a. Inner layer = endocardium
• b. Middle Layer = myocardium
• c Outer layer = epicardium (also called the
• c. Outer layer = epicardium (also called the
pericardium)

30. 1. endocardium - in a sense, simply a continuation of tunica intima
, p y
a. consists of 3 parts
* endothelium resting on a basal lamina and associated thin layer
of collangenous fibers
* Beneath the endothelium is the sub-endothelial layer of
connective tissue containing elastic fibers and a few smooth
muscle cells (some texts call this loose C.T. and others dense C.T.)
muscle cells (some texts call this loose C.T. and others dense C.T.)
* Beneath that lies the subendocardial layer of loose connective
Beneath that lies the subendocardial layer of loose connective
tissue that contains small blood vessels and nerves. In the
ventricle, the Purkinje fibers are associated with the
subendocardial zone.

31. 2. Myocardium - consists of 2 components
a. fascicles of cardiac muscle cells that connect to the fibrous
connective tissue skeleton of the heart
b. Noncontactile, modified muscle cells that form the impulse (action potential) generating
and conducting system of the heart
c. cardiac muscle

32. 3. Epicardium - epithelium and connective tissue covering of heart. Also called
the visceral pericardium
the visceral pericardium.
a. squamous to cuboidal epithelial external lining - a continuation of the
mesothelium that lines the pericardial cavity.
b. below this is a layer of connective tissue with high concentration of
elastic fibers - elastic layer
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_15.html

33. Artery
White blood cells
Artery
White blood cells
Platelets
Red blood cells

34. • Deliver O2
• Remove metabolic wastes
• Maintain temperature pH and fluid volume
• Maintain temperature, pH, and fluid volume
• Protection from blood loss- platelets
• Prevent infection- antibodies and WBC
• Transport hormones
• Transport hormones

35. Plasma-55%
Buffy coat-<1%
Formed
Formed
elements-45%

36. 90% Water
8% Solutes:
8% Solutes:
• Proteins
Albumin (60 %)
Albumin (60 %)
Alpha and Beta Globulins
Gamma Globulins
Gamma Globulins
fibrinogens
• Gas
Gas
• Electrolytes

37. • Leukocytes
• Platelets
Platelets

38. • Erythrocytes (red blood cells)
• Leukocytes (white blood cells)
• Platelets (thrombocytes)
Platelets (thrombocytes)

39. E th t
Erythrocytes

40. Erythrocyte7.5m in dia
y y 7 5
 Anucleate- so can't reproduce
 Hematopoiesis- production of RBC
F i i
 Function- transport respiratory gases
 Hemoglobin- 2  chains and 2  chains
 Lack mitochondria Why?
 Lack mitochondria. Why?

 Men- 5 million cells/mm3
5 /
 Women- 4.5 million cells/mm3
 Life span 100-120 days and then destroyed in
spleen (RBC graveyard)

41. Hematopoiesis
p
• Hematopoiesis (hemopoiesis): blood cell
formation
formation
▫ Occurs in red bone marrow of axial skeleton, girdles
and proximal epiphyses of humerus and femur

42. Hematopoiesis
p
• Hemocytoblasts (hematopoietic stem cells)
▫ Give rise to all formed elements
▫ Give rise to all formed elements
▫ Hormones and growth factors push the cell toward
a specific pathway of blood cell development
p p y p
• New blood cells enter blood sinusoids

43. Erythropoiesis
Erythropoiesis
• Erythropoiesis: red blood cell
production
▫ A hemocytoblast is transformed into a
proerythroblast
▫ Proerythroblasts develop into early
y p y
erythroblasts

44. Stem cell
Phase 1
Ribosome
Phase 2
Hemoglobin
Phase 3
Ejection of
Committed
cell
Developmental pathway
Ribosome
synthesis
Hemoglobin
accumulation
Ejection of
nucleus
Hemocytoblast
Proerythro-
blast
Early
erythroblast
Late
erythroblast Normoblast
Reticulo-
cyte
Erythro-
cyte
Figure 17.5

45. R l ti f E th i i
Regulation of Erythropoiesis
• Too few RBCs leads to tissue hypoxia
• Too many RBCs increases blood viscosity
• Too many RBCs increases blood viscosity
• Balance between RBC production and
destruction depends on
▫ Hormonal controls
▫ Adequate supplies of iron, amino acids, and B
vitamins
vitamins

46. Hormonal Control of Erythropoiesis
•Erythropoietin (EPO)
y p ( )
▫ Direct stimulus for erythropoiesis
▫ Released by the kidneys in
▫ Released by the kidneys in
response to hypoxia

47. Hormonal Control of Erythropoiesis
y p
• Causes of hypoxia
▫ Hemorrhage or increased RBC destruction
▫ Hemorrhage or increased RBC destruction
reduces RBC numbers
▫ Insufficient hemoglobin (e.g., iron deficiency)
g ( g , y)
▫ Reduced availability of O2 (e.g., high altitudes)

48. Hormonal Control of Erythropoiesis
y p
• Effects of EPO
▫ More rapid maturation of committed bone marrow
▫ More rapid maturation of committed bone marrow
cells
▫ Increased circulating reticulocyte count in 1–
g y
2 days
• Testosterone also enhances EPO production,
resulting in higher RBC counts in males

49. Blood Cell Production

50. RBC Diseases
RBC Diseases
Anemia- when blood has low O2 carrying
capacity; insufficient RBC or iron deficiency.
Factors that can cause anemia- exercise, B12
deficiency
deficiency

51. Si kl ll i
RBC Diseases
RBC Diseases
Sickle-cell anemia-
•HbS results from a change in just one of the 287
amino acids in the  chain in the globin molecule.
•Found in 1 out of 400 African Americans.
ou d out o 400 ca e ca s.

52. RBC Diseases
RBC Diseases
Polycythemia- excess of erythrocytes,  viscosity of blood;
8-11 million cells/mm3
Usually caused by cancer; however, naturally occurs at high elevations

53. 2. White Blood Cells (Leukocytes)
. ( y )
M bil i f b d ’ d f
• Mobile units of body’s defense system:
• “Seek and Destroy” Functions:
y
1. Destroy invading microorganisms
2. Destroy abnormal cells (ie: cancer )
• Clean up cellular debris
(phagocytosis)
A i t i i j i
3. Assist in injury repair

54. 5 - Types of WBC’s
Granulocytes
Agranulocytes y
Agranulocytes
Each WBC has a specific function
Each WBC has a specific function

55. Blood Cell Origin and Production
Bone Marrow
Circulation
Figure 11-8

56. Types of WBC’s
l h l l
Polymorphonuclear Granulocytes
hil
1.Neutrophils
2 Eosinophils
2.Eosinophils
3.Basophils
3 p

57. 1. NEUTROPHILS
* 50-70% of all leukocytes
5 7 y
(most abundant of WBC’s)
* Important in inflammatory
responses
* Phagocytes that engulf
responses
g y g
bacteria and Debris

58. 2. EOSINOPHILS
* 1-4% of the WBC's
* Attack parasitic worms
* Important in allergic reactions

59. 3. BASOPHILS
3
* 0.5% of the WBC's
* Release histamine
0.5% of the WBC s
* Release histamine
and heparin
* Important in Allergic
R ti
Reactions

60. Types of WBC’s
Mononuclear Agranulocytes
4. Monocytes
5. Lymphocytes
(B d T ll )
(B and T cells)

61. 4. MONOCYTES
4. MONOCYTES
* 2-6 % of the WBC's
* Exit blood (diapedesis)
to become macrophages
* Phagocytic = defend against
i d b t i
viruses and bacteria

62. 5. LYMPHOCYTES
5. LYMPHOCYTES
* 25 33 % of the WBC's
* B lymphocytes:
* 25-33 % of the WBC s
* B-lymphocytes:
Produce Antibodies
* T-lymphocytes:
Di tl d t i
Directly destroy virus-
invaded cells and cancer
ll
cells

63. Blood vessel White blood cell
Red blood cell
White blood cell
Platelets
Plasma

64. 3. Platelets (Thrombocytes)
* Cell fragments bound to megakaryocytes
* “Bud Off” and are released into the blood

65. Never let monkeys eat bananas
4,000-11,000 cells/mm 3
Granulocytes
Neutrophils 40 70%
y
Neutrophils- 40-70%
Eosinophils- 1-4%
Basophils <1%
Basophils- <1%
Agranulocytes
Monocytes 4 8%
Monocytes- 4-8%
Lymphocytes- 20-45%

66. Basophil Eosinophil Lymphocyte
platelet
Neutrophil
Monocyte

67. • Leukopenia
• Abnormally low WBC count—drug induced
• Leukemias
• Cancerous conditions involving WBCs
• Named according to the abnormal WBC clone involved

68. Platelets
• Small fragments of megakaryocytes
• Formation is regulated by thrombopoietin
• Formation is regulated by thrombopoietin
• Blue-staining outer region, purple granules
• Granules contain serotonin, Ca2+, enzymes,
y
ADP, and platelet-derived growth factor (PDGF)

69. Stem cell Developmental pathway
Hemocyto-
blast Megakaryoblast
Promegakaryocyte
Megakaryocyte Platelets
Figure 17.12

70. Hemostasis- stoppage of bleeding
Platelets: 250,000-500,000 cells/mm3
Tissue Damage
Platelet Pl g
Platelet Plug
Clotting Factors

71. Hemostasis:
1. Vessel injury
V l
2. Vascular spasm
3. Platelet plug formation
4 Coagulation
4. Coagulation

72. Hemostasis
(+ feedback)
Clotting Factors
Clotting Factors
thromboplastin
Prothrombin Thrombin
Fibrinogen Fibrin
Traps RBC & platelets
p p
Platelets release thromboplasti

73. Blood Clot
Blood Clot
RBC
Fibrin thread
Platelet
Fibrin thread

74. Disorders of Hemostasis
• Thromboembolytic disorders: undesirable clot
formation
formation
• Bleeding disorders: abnormalities that prevent
normal clot formation
normal clot formation

75. Thromboembolytic Conditions
y
• Thrombus: clot that develops and persists in an
unbroken blood vessel
unbroken blood vessel
▫ May block circulation, leading to tissue death
• Embolus: a thrombus freely floating in the blood
Embolus: a thrombus freely floating in the blood
stream
▫ Pulmonary emboli impair the ability of the body to
obtain oxygen
▫ Cerebral emboli can cause strokes

76. Thromboembolytic Conditions
y
• Prevented by
A i i
▫ Aspirin
 Antiprostaglandin that inhibits thromboxane
A2
A2
▫ Heparin
 Anticoagulant used clinically for pre- and
g y p
postoperative cardiac care
▫ Warfarin
 Used for those prone to atrial fibrillation

77. Dr. Maria Zahiri
•
•
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