Veterinary Histology UFF
Department of Morphology - Biomedic Institute
LaBEc - Laboratory of Cellular and Extracellular Biomorphology 		 
Veterinary Histology Atlas
    Versão em Português
Introduction
Circulatory System of Birds

• The heart pumps blood and transports it to the tissues and organs through blood vessels.
The fluid that escapes the blood returns to the venous system through the lymphatic vessels.
• The vessels of the cardiovascular system are lined by an endothelium that is typically a layer of squamous cells.
• The smallest of blood vessels, the capillaries, are tiny endothelial tubes. They are easily disregarded in histological sections, especially if they are compressed or collapsed.
• The walls of the arteries and veins are arranged in concentric layers: the inner tunica intima, the intermediate tunica media and the outer tunica adventitia. The composition and thickness of these walls vary according to the size and type of vessel. The tunica media is not always present.

Cardiovascular System

Heart


• The heart is a muscular organ whose wall is formed by an endocardium, a myocardium, and a epicardium.
• The thickness and composition of the wall varies, being thickest in the ventricles and thinnest in the atria.
• The middle layer of cardiac muscle is predominant, the myocardium.
• The valves of connective tissue covered by endothelium are extensions of the endocardium.

• The cardiac regions, including the base of the aorta and the pulmonary trunk, as well as the orifices and the interventricular septum, are supported by the cardiac skeleton. This cardiac skeleton can be in the form of a dense irregular connective tissue, fibrocartilage, hyaline cartilage or bone, and varies according to age and between individuals.
• A small amount of fluids occur in the pericardial cavity, between the epicardium(visceral pericardium) and the parietal pericardium.

Arteriole

• The small arteries can be freely defined as possessing eight to nine layers of smooth muscle cells in the tunica media. The smallest of these vessels is generally called an arteriole.
• Its wall is formed by an endothelium(tunica intima), one or two layers of smooth muscle cells circularly arranged(tunica media) and a little surrounding loose connective tissue(tunica adventitia).
• Some of the larger small arteries have an inner elastic membrane.
• The small arteries are accompanied by small veins.

Medium Arteries

• As the diameter of a vessel increases, the tunica becomes larger and more elaborate.
• For example, the tunica intima of a medium artery contains connective tissue intertwined between the endothelium and the inner elastic membrane.
• The thick tunica media, with various proportions of smooth muscle fibers and elastic fibers, comprise the volume of the wall.
• The connective tissue of the tunica adventitia contains collagen and elastic fibers, small blood vessels (vaso vasorum) and nerves. Conversely, a medium vein has less smooth muscle fibers and much less elastic fibers in its tunica media and a thicker tunica adventitia. The arteries normally seem round in cross-sections and present an obvious pruned inner elastic membrane.

Elastic Arteries

- Muscular arteries - distribution

Venules

• The smaller veins are called venules.
• These are similar to arterioles, but have relatively thin walls and do not have a tunica media of smooth muscle.
• In the small veins, there is also no inner elastic membrane.

 

Vein

• Conversely, the accompanying veins have a larger diameter with an irregular or collapsed lumen and thinner walls, except for a few larger ones, they do not have a inner elastic membrane.
• The lumen of the blood vessels in tissue sections frequently contains blood cells, plasma or both.
• Though it may be difficult to distinguish between veins and lymphatic vessels, the latter present thinner walls than veins of similar size and normally do not contain haematids.
• Valves can occur in veins as well as in lymphatic vessels.
• There are many variations from “typical” blood vessels: the tunica adventitia of large veins adjacent to the heart contains cardiac muscle instead of smooth muscle. Some arteries contain smooth muscle in their tunica intima, as well as the tunica media. The smooth muscle can have a longitudinal or circular orientation. The tunica adventitia of veins can be abundant or scarce.

Arteriovenous anastomosis

• The arteries from arteriovenous anastomosis do not have an inner elastic membrane, but have epithelioid (similar to an epithelium) smooth muscle cells arranged longitudinally.
• Special structures (the aortic and carotid bodies) associate themselves close to the tunica adventitia of their respective arteries.
• Many special vessels exclusive to certain organs (such as the hepatic sinusoids, the lymphonodal postcapillary venules and the helicine arteries of the penis) are present in other locations, along with their appropriate organ systems.

 

 


 
Credits
Tissues
Epithelial
Connective
Cartilaginous
Osseous
Nervous
Muscle
Systems
Circulatory
Blood
Imune
Digestive
Accessory Gls.
Respiratory
Integumentary
Urinary
Endocrine
Male Reprod.
Female Reprod.
Birds Histology
Quiz
Videos
Bibliography