Blood Vessels Ch 19

Blood Vessels Blood is carried in a closed system of vessels that begins and ends at the heart The three major types of vessels are arteries, capillaries, and veins Arteries carry blood away from the heart, veins carry blood toward the heart Capillaries contact tissue cells and directly serve cellular needs

Tunics Tunica interna (tunica intima) Tunica media Endothelial layer that lines the lumen of all vessels In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present Tunica media Smooth muscle and elastic fiber layer, regulated by sympathetic nervous system Controls vasoconstriction/vasodilation of vessels

Tunica externa (tunica adventitia) Tunics Tunica externa (tunica adventitia) Collagen fibers that protect and reinforce vessels Larger vessels contain vasa vasorum

Blood Vessel Structure simple squamous epithelium smooth muscle tissue Blood Vessel Structure connective tissue

• Subendothelial layer Internal elastic lamina Tunica intima • Endothelium Valve • Subendothelial layer Internal elastic lamina Tunica media (smooth muscle and elastic fibers) External elastic lamina Tunica externa (collagen fibers) Lumen Vein Lumen Artery Capillary network Basement membrane Endothelial cells (b) Capillary Figure 19.1b

Artery vein

Arteries 1. Carry blood away from the heart. 2. Thick-walled to withstand hydrostatic pressure of the blood during ventricular systole. 3. Blood pressure pushes blood through the vessel

Elastic (Conducting) Arteries Thick-walled arteries near the heart; the aorta and its major branches Large lumen allow low-resistance conduction of blood Contain elastin in all three tunics Withstand and smooth out large blood pressure fluctuations Allow blood to flow fairly continuously through the body

Muscular (Distributing) Arteries and Arterioles Muscular arteries – distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle and less elastic tissue Active in vasoconstriction Arterioles – smallest arteries; lead to capillary beds Control flow into capillary beds via vasodilation and constriction

Pressure reservoir function of elastic arteries Fig.21.02 Pressure reservoir function of elastic arteries

Veins Carry blood to the heart. Thinner-walled than arteries. Possess one-way valves that prevent backwards flow of blood. Blood flow due to body movements, not from blood pressure.

One-Way Valves in Veins open valve closed valve

Capillaries One cell thick, endothilium Function: Diffusion Filtration Transcytosis

Diffusion CO2 O2

Filtration

Transcytosis Caveolae Pinocytotic vesicles Endothelial fenestration Lumen Caveolae Pinocytotic vesicles Endothelial fenestration (pore) Intercellular cleft Transport via vesicles or caveolae (large substances) 4 Movement through fenestrations (water-soluble substances) 3 Basement membrane Movement through intercellular clefts (water-soluble substances) 2 Diffusion through membrane (lipid-soluble substances) 1

Capillaries Capillaries are the smallest blood vessels Walls consisting of a thin tunica interna, one cell thick Allow only a single RBC to pass at a time Pericytes on the outer surface stabilize their walls There are three structural types of capillaries: continuous, fenestrated, and sinusoids

Continuous Capillaries Continuous capillaries are abundant in the skin and muscles, and have: Endothelial cells that provide an uninterrupted lining Adjacent cells that are held together with tight junctions Intercellular clefts of unjoined membranes that allow the passage of fluids

Continuous Capillaries Continuous capillaries of the brain: Have tight junctions completely around the endothelium Constitute the blood-brain barrier

Continuous Capillaries Figure 19.3a

Fenestrated Capillaries Found wherever active capillary absorption or filtrate formation occurs (e.g., small intestines, endocrine glands, and kidneys) Characterized by: An endothelium riddled with pores (fenestrations) Greater permeability to solutes and fluids than other capillaries

Fenestrated Capillaries Figure 19.3b

Sinusoids Highly modified, leaky, fenestrated capillaries with large lumens Found in the liver, bone marrow, lymphoid tissue, and in some endocrine organs Allow large molecules (proteins and blood cells) to pass between the blood and surrounding tissues Blood flows sluggishly, allowing for modification in various ways

Sinusoids Figure 19.3c

Capillary Beds A microcirculation of interwoven networks of capillaries, consisting of: Vascular shunts – metarteriole–thoroughfare channel connecting an arteriole directly with a postcapillary venule True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed

Capillaries capillary vessel

arteriole capillaries venule

(a) Sphincters open—blood flows through true capillaries. Vascular shunt Precapillary sphincters Metarteriole Thoroughfare channel True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open—blood flows through true capillaries. Terminal arteriole Postcapillary venule (b) Sphincters closed—blood flows through metarteriole thoroughfare channel and bypasses true capillaries. Figure 19.4

Blood pressure (BP) Force per unit area exerted on the wall of a blood vessel by the blood Expressed in mm Hg Measured as systemic arterial BP in large arteries near the heart The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

Resistance (peripheral resistance) Opposition to flow Measure of the amount of friction blood encounters Generally encountered in the peripheral systemic circulation Three important sources of resistance Blood viscosity Total blood vessel length Blood vessel diameter

Systemic Blood Pressure The pumping action of the heart generates blood flow Pressure results when flow is opposed by resistance Systemic pressure Is highest in the aorta Declines throughout the pathway Is 0 mm Hg in the right atrium The steepest drop occurs in arterioles

Systolic pressure Mean pressure Diastolic pressure Figure 19.6

Resistance Factors that remain relatively constant: Blood viscosity The “stickiness” of the blood due to formed elements and plasma proteins Blood vessel length The longer the vessel, the greater the resistance encountered

Resistance Frequent changes alter peripheral resistance Varies inversely with the fourth power of vessel radius E.g., if the radius is doubled, the resistance is 1/16 as much

Resistance Small-diameter arterioles are the major determinants of peripheral resistance Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance Disrupt laminar flow and cause turbulence

120- 80- Mm Hg Artery Arteriole Capillary Venule Vein

Baroreceptors . Baroreceptors a. Detect changes in arterial blood pressure i. Pressure sensitive mechanoreceptors ii. When BP rises, receptors are stretched b. Located in carotid sinuses, aortic arch and walls of all large vessels c. Stretching increases signaling to vasomotor center i. Inhibits vasomotor center ii. Causes dilation of arteries and veins d. Arteriole dilation reduces peripheral resistance e. Venodilation shifts blood to venous reservoirs i. Venous return decreases ii. Cardiac output declines f. Baroreceptors also send efferent signals to cardiac centers in the medulla i. Inhibit sympathetic NS ii. Stimulate parasympathetic NS iii. HR and contractile force decrease g. Respond to acute changes in blood pressure i. Carotid sinus reflex protects blood supply to brain ii. Aortic reflex maintains supply to systemic circuit

Short-Term Hormonal Control Vasoconstrictors: Norepinephrine and epinephrine Angiotensin II ADH Vasodilators: ANP

Sphygmomanometer Used to estimate pressure

Measuring Blood Pressure

Blood Pressure 120/80 is good

Superficial Pulse Points- arteries, not veins temporal 60 beats/minute facial carotid Temporal artery Facial artery Common carotid artery Brachial artery Radial artery Femoral artery Popliteal artery Posterior tibial artery Dorsal pedis artery brachial radial femoral popliteal Posterior tibial Dorsal pedis

Homeostatic Imbalances Tachycardia: abnormally fast heart rate (>100 bpm) If persistent, may lead to fibrillation Bradycardia: heart rate slower than 60 bpm May result in grossly inadequate blood circulation May be desirable result of endurance training

Circulatory Shock Any condition in which Blood vessels are inadequately filled Blood cannot circulate normally Results in inadequate blood flow to meet tissue needs

Circulatory Shock Hypovolemic shock: results from large-scale blood loss Vascular shock: results from extreme vasodilation and decreased peripheral resistance Cardiogenic shock: results when an inefficient heart cannot sustain adequate circulation

Three Types of Circulation Pulmonary Systemic Coronary

Pulmonary Circulation Figure 19.17b

Pulmonary Circulation Figure 19.17a

Systemic Circulation

Systemic Circulation Figure 19.18

Coronary Circulation Aorta Pulmonary Superior trunk vena cava Left atrium Anastomosis (junction of vessels) Left coronary artery Right atrium Circumflex artery Right coronary artery Left ventricle Right ventricle Anterior interventricular artery Right marginal artery Posterior interventricular artery (a) The major coronary arteries

Coronary Circulation Superior vena cava Great Anterior cardiac cardiac vein Anterior cardiac veins Coronary sinus Small cardiac vein Middle cardiac vein (b) The major cardiac veins Figure 18.7b

Major Arteries

Fig.21.18b

Fig.21.20

Fig.21.20

Fig.21.22a

Fig.21.23

Major Veins

Fig.21.25

Fig.21.26

Fig.21.27

Fig.21.28

Hepatic Portal Circulation Inferior Vena cava Hepatic Vein Left Gastric Vein Hepatic Portal Splenic Vein Inferior Mesentaric Vein Renal Vein Inferior Mesentaric Vein Right Gastropiplore Vein Superior Mesentaric Vein

Superior mesenteric vein Abdominal aorta Inferior vena cava Proper hepatic artery Tributaries from portions of stomach. pancreas & lg intestine Hepatic veins Splenic vein Tributaries from sm intestine & portions of stomach, lg intestine & pancreas liver Hepatic portal vein Superior mesenteric vein

Fetal circulation and changes at birth

INQUIRY Sedentary people with elevated triglyceride levels who continue to eat fatty foods are likely to have a high level of _____. Which vessels have valves? Which vessel is the thickest walled? What type of blood vessels carry blood away from the heart? What happens when blood is pumped into the thin- walled vessels of the lungs? Which blood vessel delivers blood to the brain? Which blood vessel delivers blood to the liver? The distinctive Korotkoff sounds heard when taking blood pressure are produced by ____.