Blood vessels metacognition L4

What do blood vessels form?

A closed circulatory system powered by the pumping of the heart

List the direction of blood flow through blood vessels from the heart and going back to the heart

Heart → arteries → Arterioles → capillaries → venules veins →heart

1. The walls of most blood vessels are composed of three distinct layers: Tunica intima, tunica media, and tunica externa. Describe each layer 

• Tunica Intima: The inner mor tunis, which contain the endothelium (simple squamous epithelium) that lines the lumen of all vessels.

• Tunica Media: The middle tunica convicts of circularly arranged sheets of smooth muscle fibers that sandwich sheets of elastin and collagen fibrils.

• Tunica Externa: The outermost layer of vessel wall; composed of connective tissue (elastic and collagen fibers). Protects the vessel, further strengthens its wall, and anchors the vessel to surrounding structures. 

What type of blood do arteries normally carry?

Arteries are vessels that carry oxygenated blood away from the heart

Which arteries do NOT carry oxygen rich blood?

Pulmonary arteries

1. Describe elastic arteries. What are they able to withstand?

• Elastic (conducting) arteries 1 cm- 2.5cm : thick-walled arteries near the hart (aorta and its major branches)

• Lare lumen allow low-resistance conduction of blood; contains elastin in all three tunics

• Withstands and dampens large blood pressure fluctuations to allow blood flow to flow fairly continuously through the body.

1. Describe muscular arteries. What are they active in?

• (0.3mm- 1cm)Distal to elastic arteries and deliver blood to body organs; have thick tunica media with more smooth muscle and less elastic tissue; active in vasoconstriction. 

1. Describe arterioles. What do they lead to? How do they control flow?

• Smallest arteries;lead to capillary beds and control flow into capillary beds via vasodilation and constriction

• Their tunica media contains only one or two layers of smooth muscle cells.

What are pericytes?

• Spider-shaped cells who form a network around the periphery of the capillary and serve to strengthen and stabilize the capillary.

What is the function of capillaries?

1. The smallest blood vessels, with a diameter of 8-10 micrometers just large enough to enable RBC’s to pass through in a single file.

2. Renew and refresh interstitial fluid with oxygen nutrients cells need, and remove carbon dioxide and nitrogenous wastes that cells deposit into the fluid. 

What are continuous capillaries?

Most common; are abundant in the skin and muscles, and have endothelial cells that provide uninterrupted lining, adjacent cells that are held together with tight junction but have  intercellular clefts of unjoined membranes that allow the passage of fluids

What does the blood brain barrier lack?

Blood-brian barrier: the capillaries of the brain LACk the structural feature that account for capillary permeability

1. What are fenestrated capillaries characterized by? What does this allow? Where are these capillaries found?

• Characterized by: an endothelium riddled with fenestrations(pores) allowing greater permeability to solutes and fluids than other capillaries 

• FOund where there are high    rates of exchange of small molecules between the blood and the surrounding tissue fluid ( small intestine, endocrine glands, and kidneys)

What are sinusoidal capillaries? What does this allow? Where are these capillaries found?

• Characterized by a twisted, leaky, fenestrated capillaries with large lumens 

• Allow large molecules (proteins and blood cells) to pass between the blood and surrounding tissue 

• Found in the liver, bone marrow, lymphoid tissue and in some endocrine organs. 

What are the simplest veins? When do they form?

Venules are the simplest veins that are formed when capillary beds unite.

Why are the walls of veins thinner than arteries 

• Veins have much lower blood pressure and thinner walls than arteries.

How much of the blood supply is in veins?

Veins are formed when venules converge and are capacitance vessels (blood reservoirs) that contain 65% of blood supply; veins have much lower blood pressure and thinner walls than arteries.

In veins, compare the tunica externa and the tunica media?

In the veins, the tunica externa is thicker than the tunica media (opposite in arteries)

What mechanism counteracts the low blood pressure and helps move the blood along its course back to the heart?

• Large-diameter lumens, which offer little resistance to flow

• Valves (resembling semilunar heart valves), which prevent backflow of blood; abundant in the veins of the limbs

What are vascular anastomoses?

Merging blood vessels, more common in the veins than arteries