Nakamura human Anatomy Ch 20 Flashcards
(18 cards)
Tunica intima
Composed of simple squamous epithelium
Tunica media
Sheets of smooth muscle
Middle layer
-in artery thicker bcuz more smooth muscle and contracts more
-in vein thinner because less smooth muscle and blood returns to heart
Contraction: vasoconstriction
Relaxation: vasodilation
Tunica externa
Composed of connective tissue
Types of blood vessels
Arteries: carry blood away from the heart
•Capillaries: smallest blood vessels, The site of exchange of molecules between blood and tissue fluid
•Veins: carry blood toward the heart
Types of arteries
- elastic arteries
- muscular (distributing) arteries
- arterioles
Elastic arteries
– the largest arteries
–Diameters range from 2.5 cm to 1 cm
–Includes the aorta and its major branches
–Sometimes called conducting arteries (strong contraction)
–High elastin content dampens surge of blood pressure
Muscular (distributing) arteries
-Lie distal to elastic arteries
–Diameters range from 1 cm to 0.3 mm (middle size)
–Includes most of the named arteries
–Tunica media is thick
–Unique features
•Internal and external elastic laminae
Arterioles
-Smallest arteries
–Diameters range from 0.3 mm to 10 µm
–Larger arterioles possess all three tunics
–Diameter of arterioles controlled by:
•Local factors in the tissues
•Sympathetic nervous systemCapillaries
- smallest blood vessels
- diameter from 8-10 um
- red blood cells as through single file
Functions of capillaries
-In the lungs: oxygen enters blood, carbon dioxide leaves
•In the small intestines: receive digested nutrients
•In endocrine glands: pick up hormones
•In the kidneys: removal of nitrogenous wastes
Structure of blood vessels
Composed of three layers (tunics) 1. Tunica intima 2. Tunica media 3. Tunica externa Lumen: central blood-filled space of a vessel
Capillary beds
Network of capillaries running through tissues
•Precapillary sphincters: Regulate the flow of blood to tissues
•Tendons and ligaments: poorly vascularized
•Epithelia and cartilage: avascular
–Receive nutrients from nearby connective tissues
Two types of capillaries
Two types of capillary
–Continuous capillary: most common
–Fenestrated capillary: have pores in their walls
Capillary permeability
-Endothelial cells: held together by tight junctions and desmosomes (Desmosome: a site of adhesion between two epithelial cells)
-Intercellular clefts: gaps of unjoined membrane
–Small molecules can enter and exit (allows permeability)
Veins
Conduct blood from capillaries toward the heart
•Blood pressure is much lower than in arteries
•Smallest veins: called venules
-tunica externa is the thickest tunic in veins
Venules
Diameters from 8–100 µm
–Smallest venules: called postcapillary venules
•Venules join to form veins
Mechanisms to counteract low venous pressure
- valves in some veins (particularly in limbs)
- skeletal muscle pump: muscles press against thin-walled veins
Pulmonary circulation
Study gas exchange
