capillaries and arteries

What are the three layers of blood vessels

outer = tunica externa

• comprised of areolar CT, also contains vasa vasorum

middle = tunica media

• elastin and collagen, smooth muscle

inner = tunica intima

• simple squamous, CT, fenestrated layer

What are the histology differences between veins and arteries?

arteries tend to be more rounded and veins tend to be more irregularly shaped

• arteries have large tunica media

  • elastic arteries have largest diameters and strength (aorta)

• veins havelarge tunica adventitia

muscular arteries

medium and small arteries (distributing arteries) can regulate blood flow to various regions of the body

*IEM = internal elastic membrane

Different kinds of capillaries

*vary in size and permeability, internal lining of simple squamous epithelial cells is called endothelium

*substances that move through capillaries by diffusion through small openings = fenestrations

Fenestrated capillaries

areas of thin endothelial cells or small openings of pores that allow a great deal of fluid transport between blood and interstitial fluid

• nutrient absorption in small intenstine and hormon absorption endocrine glands

continuous capillaries

held together by tight junctions, blood brain barrier

sinusoidal capillaries

large openings or gaps in endothelial lining allowing large formed elements such as proteins to pass

• located in liver, spleen, bone marrow allowing large molecules and even cells to diffuse across membrane

distribution of blood in percentage of total blood in different parts of the circulatory system

Capillary blood flow

arterioles —> metarterioles —> capillary network

distal part of metarterioles are thoroughfare channel connecting with venus capillaries and eventually the venule draining the capillary bed

smooth muscle sphincters control blood flow through the true capillary since there is not enough blood to fill all the capillaries at any given time

types of blood flow

laminar: velocity of flow in the center of the vessel is far greater than that toward the outer edges (due to resistance)

turbulent: when rate of blood flow becomes too great, when it passes by an obstruction in a vessel, or when it makes a sharp turn, or when it passes over a rough surface flow becomes disorderly

perfusion

the volume of blood flowing through arteries, veins, and capillaries

elasticity is the tendency of the arteries and veins to stretch in response to rpessure has large effect on perfusion and blood pressure

• as we age the body makes less elastin which effects the elasticity of the walls of blood vessels

Blood pressure

the force of blood over the area in which it is distributed (walls of vessel)

what two factors determine blood flow?

1. pressure difference of the pressure of blood between the two ends of the vessel (pressure gradient)

2. vascular resistence which is the impediment to blood flow through the vessel

Peripheral vascular resistanc (systemic vascular resistance, SVR)

resistance in the circulatory system that is used to create blood pressure

• vasoconstriction —> increase SVR

• vasodilation —> decrease SVR

(if in pulmonary vasculature —> PVR)

Mechanisms of venous return

1. musculovenous pump: where muscular contractions become a compressive force propelling venous blood against gravity

2. valves: obstruct retrograde flow