Sistema Circulatório

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

Introduction

Circulatory System
Comprises the cardiovascular and lymphatic vascular system
Cardiovascular System Heart
	• It’s the pump of the cardiovascular system
• Formed by four chambers: -Atria(2) – receive blood -Ventricles(2) – send blood • Possesses three layers:
	I - Endocardium • Internal lining of the heart • Presents endothelial cells(simple squamous epithelium) and loose connective tissue • Beneath the endocardium, we find the Purkinje fibers
II - Myocardium • Middle layer • The fibers bisect and anastomose themselves forming Ys • Present transverse striations • Present one or two central nuclei III - Epicardium • Has a greater amount of adipose tissue in some points. • Mesothelial cells line this tissue
General Structure of Vessels
	Tunica Intima • Layer of endothelial cells that line the lumen of the vessel • Layer of loose connective tissue • Internal elastic lamina (separates the tunica intima from the media)
Tunica Media • Concentric cell layers composed of: -Smooth muscle cells, -Elastic fibers, -Collagen type III and -Proteoglycans • External elastic lamina(separates the tunica media from the adventitia) Tunica Adventitia • Lines the vessels externally • Becomes continuous with the underlying connective tissue • Composed of fibroblasts, collagen type I and elastic fibers
Arteries • Transport blood from the heart to the capillary beds • Normally possess a tunica media thicker than the adventitia • Classification:
	- Elastic arteries – conducting
	- Muscular arteries – distributing
	- Arterioles – supply blood to the capillary networks
- Metarterioles - form the capillaries
Capillaries • Formed by a single layer of endothelial cells • Their cells lye on a basal lamina • We find the pericytes: They are contractile and influence the local blood flow • Classification:
	- Continuous Capillaries: Do not have interruptions in their walls
	- Sinusoidal Capillaries: Irregular, adapt themselves to the shape of the structure in which they are located
- Fenestrated Capillaries: Present pores or fenestrae in their walls
Veins • Transport blood from the capillary beds to the heart • Possess a larger caliber • Tunica adventitia is more developed than the tunica media • Classification:
	- Large Veins
	- Small Veins
	- Venulles
• Along the capillaries and veins we find pericytes(contractile function) • Vaso vasorum -Are the arterioles, capillaries and venules -Responsible for the nutrition of the tunica media and adventitia of large vessels(thick walls)
Lymphatic Vascular System • Vessels that remove the excess tissular fluids in the interstitial spaces • All of its contents returns to the cardiovascular system • It’s an open system

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