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The Circulatory System

YONG-MEI CHEN (陈咏梅)

Dept. of Anatomy, Histology & Embryology

Peking Union Medical College

Tel：69156461

E-mail address: pumc_he@yahoo.com.cn

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Blood vascular system + Lymphatic vascular system

heart capillary

artery

vein

Composition:

lymphatic vascular system

lymph

↔ tissue fluid ↔ cell

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General structure of blood vessels

Specific structure of blood vessels

including artery, vein & capillary

Structure of heart

Structure of lymphatic vessels

Content

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1. General structure of blood vessels--- 3 concentric layers

I. Blood vascular system

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(1) Tunica intima

1) Endothelium + basal lamina

2) Subendothelial layer: LCT

3) Internal elastic lamina –

a fenestrated sheet of elastin

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Weibel-Palade granules (W-P bodies): especially in the endothelial cells of elastic arteries, rod-shaped, having dense matrix housing parallel tubular elements, containing Von Willebrand’s factor (factor Ⅷ related antigen).

hemophilia

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Aorta Femoral artery

Myoendothelial junctions

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(2) Tunica media

1) Various numbers of

layers intermingled

with fibroelastic C.T.

2) External elastic lamina

smooth muscle cell

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Muscular A. Elastic A.

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(3) Tunica adventitia

vasa vasorumlymphatic vesselinnervation

fibroelastic C.T.

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1) Composition:

2. Specific structure of blood vessels(1) Capillaries

a. Pericytes:

Morphology: having long processes, basal lamina fusing with that of endothelial cell. Functions: contractility & participating in regeneration.

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b. Endothelial cells + basal lamina

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2) Ultrastructure and classification of the capillaries

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a. Continuous Capillaries:Morphology: continuous endothelium, tight junctions,

continuous basal lamina, pinocytotic vesicles.

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Distribution: muscle, lung, CNS, C.T., exocrine gland, etc.

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b. Fenestrated capillaries:

Morphology: fenestrates (pores) with or without diaphragm, continuous basal lamina.

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Distribution: stomach, intestine, endocrine gland, kidney, etc.

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c. Discontinuous sinusoidal capillaries (sinusoids):

Morphology: enlarged diameter, gaps, large fenestrates without diaphragm, discontinuous or absent basal lamina.

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Distribution: liver, spleen, bone marrow, etc.

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3) Functions:

b. Metabolic functions

a.

c. Antithrombogenic function

Permeability. exchange vessels

Activation angiotensin I ⎯⎯→ angiotensin II

Inactivation bradykinin, serotonin, etc.

Lipolysis lipoproteins

Production of vasoactive factors e.g, endothelins & NO

ACE

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4) Microcirculation: a. Composition:

b. Functions: blood pressure & blood flow regulation,and thermoregulation in particular areas.

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(2) Arteries

1) Arterioles (Peripheral resistance vessels)

Diameter < 0.5 mm (including all 3 layers)1-2 concentric smooth muscle layers in media, thin adventitia

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2) Muscular arteriesProminent internal elastic lamina, 3-40 concentric smooth muscle layers in media, external elastic lamina usually visible, adventitia equal in thickness to media.

a. Small arteries D < 1mm (Peripheral resistance vessels)

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b. medium - sized arteries (Distributing Vessels)

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3) Elastic Arteries (Conducting Vessels) yellowish color

Relatively thick intima, 40-70 elastic laminae in media, thin adventitia.

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4) Specialized arteries and age changes in arteries:

Newborn Adult

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Specific receptors:

a. Carotid bodies & aortic bodies: chemoreceptors,sensing O2, CO2 tension & pH

b. Carotid sinuses: baroreceptors, sensing BP

type I cell

type II cell

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(3) Veins (Capacitance vessels) Comparing with their corresponding arteries, veins have valves and squashed, larger lumen, thinner wall, and poorly demarcated layers.

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1) Venules diameter < 1mm

pericytes in postcapillary venules, discontinuous or no smooth muscle in media.

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venule

arteriole

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Permeabilitypostcapillary venule

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2) Small to Medium-Sized veins diameter: 1-9mm

2-4 1ayers of smooth muscle cells in media, intermixed with fibroelastic C.T., thicker adventitia with or without some longitudinal arranged smooth muscle cells.one- way valves in veins > 2mm diameter

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Venous valves: paired, semilunar folds of the intima.

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3) Large veinsrelatively thin media, thickest adventitia with many longitudinal bundles of smooth muscles.

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(4) Heart

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(4) Heart

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1) Tunics: a. Endocardium

Endothelial cells + basal lamina

Subendothelial layer

Subendocardial layer

Branches of Purkinje fibers in it

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c. Epicardium: CT + mesothelium

b. Myocardium

Subepicardial layer

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visceral pericardium

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2) Fibrous skeleton (cardiac skeleton) Including annuli fibrosi, the trigona fibrosa, and the septum membranaceum.

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3) ValvesTricuspid, mitral valves & semilunar valves A central core of dense C.T., lined on both sides by endothelial layers

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4) Impulse Conducting System

b. Atrioventricular (AV) node, in subendocardial layer

c. AV Bundle of His, in subendocardial layer

a. Sinoatrial (SA) node: pacemaker, in subepicardial layer

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Purkinje cell: specialized cardiac muscle cells, one or two nuclei, paler cytoplasm; clear (glycogen storage) area forms “halo” around nuclei, reduced number of myofibrils.

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II. Lymphatic Vascular System

Blind ended vessels, endothelial cells have no fenestrate, no tight junction, and little or no basal lamina.

1. Lymphatic capillaries

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2. Lymphatic vessels

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3. Main lymphatic trunks

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General structure of blood vessels--- 3 concentric layers

Summary

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Ultrastructure and classification of the capillaries

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Purkinje cell