SYSTEMIC VEIN ANATOMY & PHYSIOLOGY Nketi Forbang, MD, MPH T32 Mini Lecture, 07/13/18

LEARNING OBJECTIVES By the end of this lecture, you will be able to: Describe the basic structure and function of veins [& arteries] Identify the three layers that make up the walls of veins [& arteries] Understand the changes that take place as blood flows through veins [& arteries]

POST-QUIZ OUTLINE Pre-Quiz Introduction Structure & function of veins Wall layers (tunica) of veins Blood flow through veins POST-QUIZ

PRE-QUIZ #1) Which of the following best describes typical veins? A: Thick walled, small lumens, high pressure, lack valves, return blood to heart B: Thin walled, large lumens, low pressure, have valves, return blood to heart C: Thick walled, small lumens, high pressure, lack valves, return blood to heart D: Thick walled, large lumens, low pressure, have valves, return blood to heart

PRE-QUIZ #2) In general, compared to arteries, veins have: A: Thicker tunica intima, thicker tunica media, thinner tunica externa B: Thinner tunica intima, thinner tunica media, thicker tunica externa C: Thicker tunica intima, thicker tunica media, thinner tunica externa D: Thinner tunica intima, thinner tunica media, thicker tunica externa

PRE-QUIZ #3) Under normal physiologic conditions, the largest distribution of blood flow in humans can be found in the: A: Systemic veins B: Systemic arteries C: Pulmonary veins & arteries D: Heart

INTRODUCTION This slide is mostly here to mess with Cheryl who hates busy slides. But I think busy slides can be useful because they give you a view from 10,000 feet. The right side of the drawing present arteries without the veins, and the left side are the veins without the arteries. The important take away from this slide is: 1) each vein has a corresponding artery, or vice versa.

VEIN STRUCTURE & FUNCTION Veins and arteries are set up this way for one simple reason. Arteries take oxygenate blood from the left side of the heart to tissues for use, and veins take deoxygenated blood back to the left side of the heart & lungs to be replenished with oxygen.. Oxygenated blood leaves the left side of the heart via the aorta, is distributed to the extremities and organs via their corresponding arteries, and delivered to tissue via the capillary beds. The now deoxygenated blood is returned to the capillaries, distributed back to the extremities and organs via their corresponding veins, and returned to right side of the heart via the vena cava. The capillary beds connect the arterial system to the venous system and this where this exchange occurs.

VEIN LAYERS (TUNICA) Veins [& arteries] have the same three distinct tissue layers, called tunics (from the Latin term tunica or garments first worn by ancient Romans). The innermost layer is called the tunica intima. The muscular middle layer is called the tunica media, and the outermost layer is called the tunica externa or adventitia. Two important things: 1) the tunica intima is the only layer continuous throughout the circulatory system, because this is the only layer the capillaries; 2) only veins have valves which, primarily in their lower extremity which are differentiated endothelial cells.

VEIN LAYERS (TUNICA) Feature Typical artery Typical vein The outside images are drawings of the layers or tunics of a typical artery and vein. In middle image is a biopsy of a typical artery and its accompanying vein shown in cross-section under light microscopy. Compared to the typical artery, the typical vein has: 1) flatter larger lumen; 2) thinner tunica intima d/t absence of an internal elastin membrane; 3) thinner tunica media due to less smooth muscle cells; and 4) thicker tunica externa due to more connective tissue. Feature Typical artery Typical vein General appearance Rounder, smaller lumen Flatter, larger lumen Tunica intima Thicker, endothelium plus elastin Thinner, endothelium minus elastin Tunica media Thicker, more smooth muscle Thinner, less smooth muscle Tunica externa or adventitia Thinner, less connective tissue Thicker, more connective tissue

VEIN LAYERS (TUNICA) I used the term typical, because for both veins and arteries, the thickness of the different layers differ with the size of the vessel.

BLOOD FLOW Vessels size decrease, then increase Vessel area increases, then decreases Blood velocity decreases, then increases Blood pressure decreases As blood flows from arteries to veins, vessels become thinner before increasing in size. Capillaries are the smallest in size, but make up the largest total cross-section due to their share number. For this reason, they greatly influence both the velocity and pressure of blood flow which both decrease.

BLOOD FLOW This table shows the distribution of blood volume during normal resting state. As you can see most of the blood is found in the systemic veins, with a large reservoir in the liver, bone, and skin.

POST-QUIZ #1) Which of the following best describes typical veins? A: Thick walled, small lumens, high pressure, lack valves, return blood to heart B: Thin walled, large lumens, low pressure, have valves, return blood to heart C: Thick walled, small lumens, high pressure, lack valves, return blood to heart D: Thick walled, large lumens, low pressure, have valves, return blood to heart

POST-QUIZ #1) Which of the following best describes veins? A: Thick walled, small lumens, high pressure, lack valves, return blood to heart B: Thin walled, large lumens, low pressure, have valves, return blood to heart C: Thick walled, small lumens, high pressure, lack valves, return blood to heart D: Thick walled, large lumens, low pressure, have valves, return blood to heart

POST-QUIZ #2) In general compared to arteries, veins have: A: Thicker tunica intima, thicker tunica media, thinner tunica externa B: Thinner tunica intima, thinner tunica media, thicker tunica externa C: Thicker tunica intima, thicker tunica media, thinner tunica externa D: Thinner tunica intima, thinner tunica media, thicker tunica externa

POST-QUIZ #2) In general compared to arteries, veins have: A: Thicker tunica intima, thicker tunica media, thinner tunica externa B: Thinner tunica intima, thinner tunica media, thicker tunica externa C: Thicker tunica intima, thicker tunica media, thinner tunica externa D: Thinner tunica intima, thinner tunica media, thicker tunica externa

POST-QUIZ #3) Under normal physiologic conditions, the largest distribution of blood flow in humans can be found in the: A: Systemic veins B: Systemic arteries C: Pulmonary veins & arteries D: Heart

PRE-QUIZ #3) Under normal physiologic conditions, the largest distribution of blood flow in humans can be found in the: A: Systemic veins B: Systemic arteries C: Pulmonary veins & arteries D: Heart

THE END References https://courses.lumenlearning.com/suny-ap2/chapter/structure-and-function-of- blood-vessels/ Google images