BLOOD VESSELS - EIU



6.0 BLOOD VESSELS

a) Define and use properly the following words: Tunica intima, Tunica media, Tunica adventitia, Arteries, Elastic artery, Elastin, Muscular artery, Arteriole, Capillaries, Endothelial cell, Pinocytotic vesicles, Fenestrae, Diaphragms, Pericytes, Continuous capillaries, Fenestrated capillaries, Sinusoids, Blood sinuses, Venules, Postcapillary venules, Muscular venules , Small veins, Medium veins, Large veins, Circular sphincter muscle , Arteriovenous anastomoses, Lymphatic vessels.

b) Describe and associate basic structure/function for all structures listed above and identify specific locations for blood vessles, sinuses, sinusoids and lymphatics.

c) Identify by microscopy the cells, organelles, tissues, and organs listed above.

I. ORGANIZATION OF BLOOD VESSELS

Because of the pressure gradients created within the vessel due to the pumping action of the heart and the contraction of skeletal muscles, the structure of each vessel will differ according to the corresponding pressure.

A. TUNICA INTIMA

1. contains endothelium + basal lamina + loose CT ± internal elastic lamina (membrane)

B. TUNICA MEDIA

1. contains smooth muscle ± elastic fibers ± outer elastic lamina, collagen fibers, and ground substance

C. TUNICA ADVENTITIA

1. the outer layer

2. contains Connective Tissue, elastin and collagen, many cells: fibroblasts, mast cells, plasma cells, fat, sometimes smooth muscle, nerve (nervi vasorum) & small blood vessels (vasa vasorum), and lymphatic vessels

II. ARTERIES Elastic, Muscular, Arterioles

A. ELASTIC ARTERIES (Large)

1. Largest diameter, Aorta & branches

2. conduction tubes, aid the movement of blood

3. walls expand greatly during systole, and recoil during diastole due to the elastic fibers.

4. T. intima:

a. thin, consist essentially of the endothelium

5. T. media:

a. thickest layer with concentric layers of elastic laminae

b. elastic recoil for continuous flow of blood

c. smooth muscle, collagen fibers

6. T. adventitia:

7. no distinct external elastic lamina, blends with surrounding CT

B. MUSCULAR ARTERIES (Medium)

1. There is NO sharp dividing line between large elastic and medium muscular arteries

2. They are often intermediate; the elastic material decreases and the smooth muscle increases

3. But, there is always a prominent internal elastic and external elastic lamina

4. T. intima:

a. thin, Basal lamina may contact internal elastic lamina

5. T. media:

a. may be the thickest layer

b. mainly smooth muscle cells (circular or spiral)

c. some collagen & elastic fibers

d. NO fibroblasts.

6. T. adventitia

a. thick, collagen fibers primarily

b. vasa & nervi vasorum, lymphatics

c. External elastic lamina

C. ARTERIOLES

1. The small arteries and arterioles are distinguished by the number of smooth muscle cells in the tunica media

2. Arteriole = 1-2 layers; small artery = up to 8 layers

3. small arteries have an internal elastic lamina, but may be absent in arterioles.

III. CAPILLARIES

A. Capillaries are very small thin walled tubules arranged in a network to allow the exchange of substances between blood and tissues. They are about 8 µm diameter, contain a single layer of endothelium and basal lamina, and are joined by tight junctions.

B. The Endothelial cell-- contains few organelles, but the plasmalemma has pinocytotic vesicles and sometimes fenestrae (60-80 nm) with diaphragms or thin protein membranes (except in kidney)

C. Pericytes are sometimes found associated with endothelium. The pericyte is an undifferentiated perivascular cell that may differentiate into smooth muscle and fibroblasts and may be contractile.

D. CONTINUOUS CAPILLARIES

1. contains pinocytotic vesicles

2. serve for trans-epithelial transport

E. FENESTRATED CAPILLARIES

1. contain pores with or without diaphragm (thinner than plasmalemma)

2. without diaphragm found in kidney

F. SINUSOIDS

1. more permeable than capillaries

2. larger than capillaries, lack uniformity,

3. they are shaped to fill surrounding spaces

4. slows the blood flow

5. absence of or very little Basal lamina

6. Liver sinusoids are fenestrated

7. Can have unusual long parallel endothelial cells with discontinuous basal lamina; if present called Blood sinuses; found in spleen

IV. VEINS

A. The terms "small" "medium" and "large" have only relative meaning in any one animal. Large veins of cat may be smaller than the medium veins of cow.

B. Venules (small)

1. "POSTCAPILLARY VENULES"

a. receive blood from capillary

b. have endothelium, Basal lamina and pericytes

c. Sensitive to vasoactive agents such as histamine and serotonin, which cause movement of fluid and white cells into CT during inflammation and allergic reactions. Also, these agents cause the vessels to constrict (i.e.., narrow their lumens)

d. Important in lymph nodes

2. MUSCULAR VENULES

a. 1-2 layers smooth muscle

C. SMALL VEINS

1. 2-4 layers smooth muscle, circular, some CT

D. MEDIUM VEINS

1. typical 3 layers

2. T. intima (some elastic lamina)

3. T. media (much thinner than in arteries)

4. T. adventitia - CT elastic fibers

E. LARGE VEINS

1. T. intima (somewhat of an internal elastic lamina)

2. T. media (thin)

3. T. adventitia (thick, bundles of longitudinal smooth muscle in the vena cava and jugular vein)

V. SPECIAL VESSELS

A. Organ specific for specialized functions.

B. Very thick

1. arteries found in the teat and coronary heart arteries

2. thick veins in the glans penis

C. Very thin arteries

1. are found in the brain.

2. Brain capillaries have little or no spaces thus preventing infectious agents from passing from blood into brain

D. Circular sphincter muscle bundles are found in T. intima of special veins and arteries of penis, ovary, & uterus

E. Arteriovenous anastomoses

1. blood does not always pass from arteries to capillaries and then to veins.

2. direct routes from arterioles to venules,

3. they have thick smooth muscle in T. media

4. Physiological function: to shunt blood where needed

5. feet, lips, nose, ears (for maximum cooling, heating)

6. Also play a role in bronchioles, where deoxygenated blood is mixed with oxygenated blood. This decreases the amount of O2 reaching the tissue.

F. Lymphatic vessels

1. Drain the excess fluid from the connective tissue back into the circulatory system.

2. Thin wall; only any endothelium

3. large lumen; typically collapses or misshapened

4. Filled with plasma; no RBC; few WBC.

COMPARISON OF BLOOD VESSELS

|Elastic Arteries |Large Veins |Small Arterioles |Small veins |

|T. media > T. adventitia |T. adventitia > T. media |Small lumen |Larger lumen |

|Elastic fibers +++ |Elastic fibers + |Compact smooth muscle |Loose smooth muscle |

|Large lumen |Large lumen |Roundish |Irregular shape |

| |valves |no IEL/EEL |no IEL/EEL |

| | | |valves |

|Large Arterioles |Arteries |Veins |

|~3-6 layers |smooth muscle ~6-10 layers |2-6 layers |

|folded endothelium |folded endothelium |smooth endothelium |

|T.media >T.adventitia |Elastic fibers |no IEL |

|± ILE |IEL |no EEL |

|no EEL |EEL |thicker blood |

|Capillary |Sinusoid |Post-Capillary Venule |Collecting |Muscular |Lymphatics |

| | | |Venule |Venule | |

| |> lumen |> lumen |>> lumen |>> lumen |> to >> lumen |

|no muscle |no muscle |no muscle |no muscle |smooth muscle (1-2) |no muscle |

|Pericytes |no pericyte |Pericytes |Pericytes ++ |no Pericytes |no Pericytes |

| | | | | |valves |

| | | | | |no RBCs |

| *IEL = Internal Elastic Lamina; EEL = External Elastic Lamina | | |

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