Anatomy and Physiology 2 Chapter 21 - Vessel Anatomy

blood vessels

delivery system of dynamic structures that begins and ends at the heart

what is the general vessel wall structure for arteries and veins and their differences

• vaso vasorum (vessels of vessels): found in tunica externa and contains small arteries and veins in the large vessels

• tunica externa: collagen and elastic fibers

  • artery

  • vein: and includes smooth muscle

• tunica media: dominated by smooth muscle and elastic fibers

  • artery: thick and external elastic membrane present

  • vein: thin and no external elastic membrane present

• tunica intima: includes endothelium

  • artery: endothelium ripped due to vessel constriction and internal elastic membrane present

  • vein: endothelium is often smooth and no internal elastic membrane present

• lumen: central blood-containing space

vessel wall structure of capillaries

sparse basal lamina (basement membrane) with endothelium

arteries

carries blood away from the heart and appears round with relatively thick wall; it is oxygenated except for pulmonary circulation and umbilical vessels of fetus

3 types of arteries

1. elastic arteries: large thick-walled arteries with elastin in all 3 tunics, large lumen offers low resistance, and inactive in vasoconstriction; acts as pressure reservoir due to expansion and recoiling from blood ejection

2. muscular arteries: distal from elastic arteries and deliver blood to body organs, thick tunica media with more smooth muscle, active in vasoconstriction to push blood to necessary organs

3. arterioles: smallest arteries, lead to capillary beds, and control flow into capillary beds via vasodilation and vasoconstriction

aneurysms

a weakening in the arterial wall causing an outpouching or enlargement of the artery

capillaries

contact tissue cells and directly serve cellular needs such as gas exchange, nutrients, waste, hormones, etc. between blood and interstitial fluid; diameter allows for a single RBC to pass at a time

precapillary sphincter

is at the entrance of each capillary and alters blood flow to capillary beds

3 types of capillaries

1. continuous capillaries: connected to arterioles, used for controlling what goes in and out, and have tight junctions to permit some diffusion; supply most regions of the body and the endothelium is a complete lining

2. fenestrated capillaries: connected to venules and contain pores that penetrate endothelial lining to allow loss of fluids to filter something

3. sinusoids: resemble fenestrated capillaries in flatness and irregular shape, have a discontinuous epithelium, commonly have gaps between adjacent endothelial cells, basement membrane is thinner/absent to allow free exchange of water/solutes (more leaky than fenestrated)

capillary beds

interconnected network of capillaries

anastomoses

interconnections of blood vessels and bypass blockages in vessels

• arterial: provide alternate pathways to given body region

• venous: are common for veins

angiogenesis

formation of new blood vessels from pre-existing ones and occurs under the direction of vascular endothelial growth factor (VEGF)

veins

carry blood toward the heart and appears flattened or collapsed with relatively thin wall and larger lumen; deoxygenated except for pulmonary circulation, blood pressure is lower, and have valves to push blood to heart

2 types of veins

1. venules: formed when capillary beds unite and are the smallest postcapillary; consist of an endothelium and few pericytes and are very porous to allow fluids/WBCs into tissue

2. medium-sized and large veins: medium-sized has a thin tunica media, thick tunica externa, and contains few smooth muscle cells; large has all 3 layers present, slender tunica media, and thick tunica externa

venous valves

prevent backflow of blood and most abundant in limbs

blood flow

volume of blood flowing through vessel, organ, or entire circulation in a given period; measured as mL/min, equivalent to cardiac output, relatively constant at rest, and varies widely through each organ

tissue perfusion is involved in what 4 things for blood flow

1. delivery of O2 and nutrients to, and removal of wastes from tissue cells

2. gas exchange (lungs)

3. absorption of nutrients (GI tract)

4. urine formation (kidneys)

blood pressure

force per unit area exerted on wall of blood vessel by blood; expressed in mmHg, measured as systemic arterial BP in large arteries near heart

peripheral resistance (resistance)

measure of amount of friction blood encounters with vessel walls, generally in systemic circuit; caused by blood pressure

3 factors affecting blood pressure

1. blood viscosity: the “stickiness” of blood due to formed elements and plasma proteins; increased viscosity = increased resistance

2. blood vessel diameter: greatest influence and what are nervous system controls; vasoconstriction = greater resistance

3. total length of blood vessel: longer vessel = greater resistance due to contact with more surface

systemic blood pressure

highest in aorta, declines throughout pathway, and steepest drop occurs at arterioles

what is the relationship between cross sectional area and blood flow velocity

the greater the cross sectional area = slower the velocity of blood flow; inversely related

cross sectional area: having more vessels increases this drastically

systolic pressure

pressure exerted in aorta during ventricular contraction; averages 120 mmHg

diastolic pressure

lowest level of aortic pressure; averages 80 mmHg

pulse pressure

difference between systolic and diastolic pressure (throbbing of arteries = pulse)

mean arterial pressure

diastolic + 1/3 pulse pressure

exchange of materials at capillaries (2 main parts with subparts)

1. vasomotion: slow, intermittent flow; reflects on/off opening and closing of precapillary sphincters

2. diffusion: fluid leaves capillaries at arterial end, and most returns to blood at venous end which depends on..

   1. filtration: arterial end of capillary

      1. hydrostatic pressure: around 35 mmHg, forcing fluid out of capillary

      2. osmotic pressure: stays constant at 25 mmHg

   2. reabsorption: venous end of capillary

      1. hydrostatic pressure: around 18 mmHg, moving fluid back into capillary

      2. osmotic pressure: stays constant at 25 mmHg

3 venous return mechanisms

1. muscular pump: contraction of skeletal muscles “milks” blood toward heart; valves prevent backflow

2. respiratory pump: pressure changes during breathing move toward heart by squeezing abdominal veins as thoracic veins expand

3. vasoconstriction: under sympathetic control, pushes blood toward heart

2 ways blood pressure is regulated

1. neutral short-term regulation

2. renal long-term regulation

neutral short-term regulation

controlled by the nervous system and occurs immediately or almost immediately; operate via reflex arcs that involve baroreceptors to counteract fluctuations in BP by altering peripheral resistance and cardiac output via vasoconstriction

renal long-term regulation

controlled by kidneys/hormones and occurs in hours to days; counteracts fluctuations in BP by altering blood volume via direct and indirect renal mechanism (RAAS)

8 things that cause variations in blood pressure

1. posture

2. physical exertion

3. emotional upset/mood

4. fever

5. age

6. weight

7. sex

8. race

*first 4 refer to transient variation

hypertension

high blood pressure (usually 130/80 or higher); prehypertension if values elevated but not yet in hypertension range