principles of human anatomy and physiology, 11e1 chapter 21 the cardiovascular system: blood vessels...

Principles of Human Anatomy and Physiology, 11e 1

Chapter 21

The Cardiovascular System: Blood Vessels and Hemodynamics

Lecture Outline


INTRODUCTION

• One main focus of this chapter considers hemodynamics, the means by which blood flow is altered and distributed and by which blood pressure is regulated.

• The histology of blood vessels and anatomy of the primary routes of arterial and venous systems are surveyed.


Chapter 21The Cardiovascular System: Blood Vessels and

Hemodynamics

• Structure and function of blood vessels

• Hemodynamics– forces involved in

circulating blood• Major circulatory routes


STRUCTURE AND FUNCTION OF BLOOD VESSELS

• Angiogenesis: the growth of new blood vessels– It is an important process in the fetus and in postnatal

processes– Malignant tumors secrete proteins called tumor

angiogenesis factors (TAFs) that stimulate blood vessel growth to nature the tumor cells

• Scientists are looking for chemicals that inhibit angiogenesis to stop tumor growth and to prevent the blindness associated with diabetes.


Vessels

• Blood vessels form a closed system of tubes that carry blood away from the heart, transport it to the tissues of the body, and then return it to the heart.– Arteries carry blood from the heart to the tissues.– Arterioles are small arteries that connect to capillaries.– Capillaries are the site of substance exchange between

the blood and body tissues.– Venules connect capillaries to larger veins.– Veins convey blood from the tissues back to the heart.– Vaso vasorum are small blood vessels that supply blood

to the cells of the walls of the arteries and veins.


Arteries

• The wall of an artery consists of three major layers (Figure 21.1).

• Tunica interna (intima)– simple squamous epithelium

known as endothelium– basement membrane– internal elastic lamina

• Tunica media– circular smooth muscle &

elastic fibers• Tunica externa

– elastic & collagen fibers


Arteries

• Arteries carry blood away from the heart to the tissues.• The functional properties of arteries are elasticity and

contractility.– Elasticity, due to the elastic tissue in the tunica internal

and media, allows arteries to accept blood under great pressure from the contraction of the ventricles and to send it on through the system.

– Contractility, due to the smooth muscle in the tunica media, allows arteries to increase or decrease lumen size and to limit bleeding from wounds.


Sympathetic Innervation

• Vascular smooth muscle is innervated by sympathetic nervous system– increase in stimulation causes muscle contraction or

vasoconstriction• decreases diameter of vessel

– injury to artery or arteriole causes muscle contraction reducing blood loss (vasospasm)

– decrease in stimulation or presence of certain chemicals causes vasodilation

• increases diameter of vessel• nitric oxide, K+, H+ and lactic acid cause vasodilation


Elastic Arteries• Large arteries with more elastic fibers and less smooth

muscle are called elastic arteries and are able to receive blood under pressure and propel it onward (Figure 21.2).

• They are also called conducting arteries because they conduct blood from the heart to medium sized muscular arteries.

• They function as a pressure reservoir.


Muscular Arteries

• Medium-sized arteries with more muscle than elastic fibers in tunica media

• Capable of greater vasoconstriction and vasodilation to adjust rate of flow– walls are relatively thick– called distributing arteries because they direct blood flow


Arterioles

• Arterioles are very small, almost microscopic, arteries that deliver blood to capillaries (Figure 21.3).

• Through vasoconstriction (decrease in the size of the lumen of a blood vessel) and vasodilation (increase in the size of the lumen of a blood vessel), arterioles assume a key role in regulating blood flow from arteries into capillaries and in altering arterial blood pressure.


Arterioles

• Small arteries delivering blood to capillaries– tunica media containing few

layers of muscle• Metarterioles form branches into

capillary bed– to bypass capillary bed,

precapillary sphincters close & blood flows out of bed in thoroughfare channel

– vasomotion is intermittent contraction & relaxation of sphincters that allow filling of capillary bed 5-10 times/minute


Capillaries form Microcirculation

• Microscopic vessels that connect arterioles to venules• Found near every cell in the body but more extensive in highly active

tissue (muscles, liver, kidneys & brain)– entire capillary bed fills with blood when tissue is active– lacking in epithelia, cornea and lens of eye & cartilage

• Function is exchange of nutrients & wastes between blood and tissue fluid

• Capillary walls are composed of only a single layer of cells (endothelium) and a basement membrane (Figure 21.1).


Types of Capillaries

• Continuous capillaries– intercellular clefts are gaps between

neighboring cells– skeletal & smooth, connective tissue and

lungs• Fenestrated capillaries

– plasma membranes have many holes– kidneys, small intestine, choroid plexuses,

ciliary process & endocrine glands• Sinusoids

– very large fenestrations– incomplete basement membrane– liver, bone marrow, spleen, anterior pituitary,

& parathyroid gland


Venules

• Small veins collecting blood from capillaries• Tunica media contains only a few smooth muscle

cells & scattered fibroblasts– very porous endothelium allows for escape of

many phagocytic white blood cells• Venules that approach size of veins more closely

resemble structure of vein


Veins

• Veins consist of the same three tunics as arteries but have a thinner tunica interna and media and a thicker tunica externa– less elastic tissue and smooth muscle– thinner-walled than arteries– contain valves to prevent the backflow of blood (Figure

21.5).• Vascular (venous) sinuses are veins with very thin walls with

no smooth muscle to alter their diameters. Examples are the brain’s superior sagittal sinus and the coronary sinus of the heart (Figure 21.3c).


Veins• Proportionally thinner walls

than same diameter artery– tunica media less muscle– lack external & internal

elastic lamina• Still adaptable to variations

in volume & pressure• Valves are thin folds of

tunica interna designed to prevent backflow


Varicose Veins

• Twisted, dilated superficial veins– caused by leaky venous valves

• congenital or mechanically stressed from prolonged standing or pregnancy

– allow backflow and pooling of blood• extra pressure forces fluids into surrounding tissues• nearby tissue is inflamed and tender

• The most common sites for varicose veins are in the esophagus, superficial veins of the lower limbs, and veins in the anal canal (hemorrhoids). Deeper veins not susceptible because of support of surrounding muscles

• The treatments for varicose veins in the lower limbs include: sclerotherapy, radiofrequency endovenous occlusion, laser occlusion, and surgical stripping


Anastomoses• Union of 2 or more arteries supplying the same body region

– blockage of only one pathway has no effect• circle of willis underneath brain• coronary circulation of heart

• Alternate route of blood flow through an anastomosis is known as collateral circulation– can occur in veins and venules as well

• Arteries that do not anastomose are known as end arteries. Occlusion of an end artery interrupts the blood supply to a whole segment of an organ, producing necrosis (death) of that segment.

• Alternate routes to a region can also be supplied by nonanastomosing vessels

• Table 21.1 summarizes the distinguishing features of the various types of blood vessels.


Blood Distribution (Figure 21.6).

• 60% of blood volume at rest is in systemic veins and venules– function as blood reservoir

• veins of skin & abdominalorgans (liver and spleen)

– blood is diverted from it intimes of need

• increased muscular activityproduces venoconstriction

• hemorrhage causes

venoconstriction to help

maintain blood pressure• 15% of blood volume in arteries & arterioles


Capillary Exchange

• Movement of materials in & out of a capillary– diffusion (most important method)

• Substances such as O2, CO2, glucose, amino acids, hormones, and others diffuse down their concentration gradients.

• all plasma solutes except large proteins pass freely across– through lipid bilayer, fenestrations or intercellular clefts– blood brain barrier does not allow diffusion of water-soluble

materials (nonfenestrated epithelium with tight junctions)– transcytosis

• passage of material across endothelium in tiny vesicles by endocytosis and exocytosis

– large, lipid-insoluble molecules such as insulin or maternal antibodies passing through placental circulation to fetus

– bulk flow see next slide


Bulk Flow: Filtration & Reabsorption

• Movement of large amount of dissolved or suspended material in same direction– move in response to pressure

• from area of high pressure to area of low– faster rate of movement than diffusion or osmosis

• Most important for regulation of relative volumes of blood & interstitial fluid– filtration is movement of material into interstitial fluid

• promoted by blood hydrostatic pressure & interstitial fluid osmotic pressure

– reabsorption is movement from interstitial fluid into capillaries• promoted by blood colloid osmotic pressure

– balance of these pressures is net filtration pressure


Dynamics of Capillary

Exchange• Starling’s law of the

capillaries is that the volume of fluid & solutes reabsorbed is almost as large as the volume filtered (Figure 21.7).

910


Net Filtration Pressure

• Whether fluids leave or enter capillaries depends on net balance of pressures– net outward pressure of 10 mm Hg at arterial end

of a capillary bed– net inward pressure of 9 mm Hg at venous end of

a capillary bed• About 85% of the filtered fluid is returned to the

capillary– escaping fluid and plasma proteins are collected

by lymphatic capillaries (3 liters/day)


Edema

• An abnormal increase in interstitial fluid if filtration exceeds reabsorption – result of excess filtration

• increased blood pressure (hypertension)• increased permeability of capillaries allows

plasma proteins to escape– result of inadequate reabsorption

• decreased concentration of plasma proteins lowers blood colloid osmotic pressure

– inadequate synthesis or loss from liver disease, burns, malnutrition or kidney disease blockage of lymphatic vessels postoperatively or due to filarial worm infection

• Often not noticeable until 30% above normal


HEMODAYNAMICS: FACTORS AFFECTING BLOOD FLOW

• The distribution of cardiac output to various tissues depends on the interplay of the pressure difference that drives the blood flow and the resistance to blood flow.

• Blood pressure (BP) is the pressure exerted on the walls of a blood vessel; in clinical use, BP refers to pressure in arteries.

• Cardiac output (CO) equals mean aortic blood pressure (MABP) divided by total resistance (R).


Hemodynamics - Overview

• Factors that affect blood pressure include cardiac output, blood volume, viscosity, resistance, and elasticity of arteries.

• As blood leaves the aorta and flows through systemic circulation, its pressure progressively falls to 0 mm Hg by the time it reaches the right atrium (Figure 21.8).

• Resistance refers to the opposition to blood flow as a result of friction between blood and the walls of the blood vessels.

• Vascular resistance depends on the diameter of the blood vessel, blood viscosity, and total blood vessel length.

• Systemic vascular resistance (also known as total peripheral resistance) refers to all of the vascular resistances offered by systemic blood vessels; most resistance is in arterioles, capillaries, and venules due to their small diameters.


Hemodynamics

• Factors affecting circulation– pressure differences that drive the blood flow

• velocity of blood flow• volume of blood flow• blood pressure

– resistance to flow– venous return

• An interplay of forces result in blood flow


Volume of Blood Flow

• Cardiac output = stroke volume x heart rate• Other factors that influence cardiac output

– blood pressure– resistance due to friction between blood cells and

blood vessel walls• blood flows from areas of higher pressure to

areas of lower pressure


Blood Pressure• Pressure exerted by blood on walls of a

vessel – caused by contraction of the ventricles– highest in aorta

• 120 mm Hg during systole & 80during diastole

• If heart rate increases cardiacoutput, BP rises

• Pressure falls steadily insystemic circulation with distance from left ventricle– 35 mm Hg entering the capillaries– 0 mm Hg entering the right atrium

• If decrease in blood volume is over 10%, BP drops

• Water retention increases blood pressure


Velocity of Blood Flow

• The volume that flows through any tissue in a given period of time is blood flow.

• The velocity of blood flow is inversely related to the cross-sectional area of blood vessels; blood flows most slowly where cross-sectional area is greatest (Figure 21.11).

• Blood flow decreases from the aorta to arteries to capillaries and increases as it returns to the heart.


Velocity of Blood Flow

• Speed of blood flow in cm/sec is inversely related to cross-sectional area– blood flow is slower in the

arterial branches• flow in aorta is 40 cm/sec while

flow in capillaries is .1 cm/sec• slow rate in capillaries allows for

exchange• Blood flow becomes faster when vessels merge to form veins• Circulation time is time it takes a drop of blood to travel from

right atrium back to right atrium


Venous Return (Figure 21.9).

• Volume of blood flowing back to the heart from the systemic veins– depends on pressure difference from venules (16 mm

Hg) to right atrium (0 mm Hg)– tricuspid valve leaky and

buildup of blood on venousside of circulation

• Skeletal muscle pump– contraction of muscles &

presence of valves• Respiratory pump

– decreased thoracic pressure and increased abdominal pressure during inhalation, moves blood into thoracic veins and the right atrium


Clinical Application

• Syncope, or fainting, refers to a sudden, temporary loss of consciousness followed by spontaneous recovery. It is most commonly due to cerebral ischemia but it may occur for several other reasons


Factors that Increase Blood Pressure


Resistance

• Friction between blood and the walls of vessels

– average blood vessel radius

• smaller vessels offer more resistance to blood flow

• cause moment to moment fluctuations in pressure

– blood viscosity (thickness)

• ratio of red blood cells to plasma volume

• increases in viscosity increase resistance

– dehydration or polycythemia

– total blood vessel length

• the longer the vessel, the greater the resistance to flow

• 200 miles of blood vessels for every pound of fat

– obesity causes high blood pressure• Systemic vascular resistance is the total of above

– arterioles control BP by changing diameter


Control of Blood Pressure & Flow

• Role of cardiovascular center– help regulate heart rate & stroke volume– specific neurons regulate blood vessel diameter


Cardiovascular Center - Overview

• The cardiovascular center (CV) is a group of neurons in the medulla that regulates heart rate, contractility, and blood vessel diameter.– input from higher brain regions and sensory receptors

(baroreceptors and chemoreceptors) (Figure 21.12).– output from the CV flows along sympathetic and parasympathetic

fibers.– Sympathetic impulses along cardioaccelerator nerves increase heart

rate and contractility.– Parasympathetic impulses along vagus nerves decrease heart rate.

• The sympathetic division also continually sends impulses to smooth muscle in blood vessel walls via vasomotor nerves. The result is a moderate state of tonic contraction or vasoconstriction, called vasomotor tone.


Input to the Cardiovascular Center

• Higher brain centers such as cerebral cortex, limbic system & hypothalamus– anticipation of competition– increase in body temperature

• Proprioceptors– input during physical activity

• Baroreceptors– changes in pressure within blood vessels

• Chemoreceptors– monitor concentration of chemicals in the blood


Output from the Cardiovascular Center• Heart

– parasympathetic (vagus nerve)• decrease heart rate

– sympathetic (cardiac accelerator nerves)• cause increase or decrease in contractility & rate

• Blood vessels– sympathetic vasomotor nerves

• continual stimulation to arterioles in skin & abdominal viscera producing vasoconstriction (vasomotor tone)

• increased stimulation produces constriction & increased BP


Neural Regulation of Blood Pressure

• Baroreceptors are important pressure-sensitive sensory neurons that monitor stretching of the walls of blood vessels and the atria.– The cardiac sinus reflex is concerned with maintaining

normal blood pressure in the brain and is initiated by baroreceptors in the wall of the carotid sinus (Figure 21.13).

– The aortic reflex is concerned with general systemic blood pressure and is initiated by baroreceptors in the wall of the arch of the aorta or attached to the arch.

• If blood pressure falls, the baroreceptor reflexes accelerate heart rate, increase force of contraction, and promote vasoconstriction (Figure 21.14).


Neural Regulation of Blood Pressure

• Baroreceptor reflexes– carotid sinus reflex

• swellings in internal carotid artery wall• glossopharyngeal nerve to cardiovascular

center in medulla• maintains normal BP in the brain

– aortic reflex• receptors in wall of ascending aorta• vagus nerve to cardiovascular center• maintains general systemic BP

• If feedback is decreased, CV center reduces parasympathetic & increases sympathetic stimulation of the heart


Innervation of the Heart

• Speed up the heart with sympathetic stimulation• Slow it down with parasympathetic stimulation (X)• Sensory information from baroreceptors (IX)


Carotid Sinus Massage & Syncope

• Carotid sinus massage can slow heart rate in paroxysmal superventricular tachycardia

• Stimulation (careful neck massage) over the carotid sinus lowers heart rate– paroxysmal superventricular tachycardia

• tachycardia originating from the atria• Anything that puts pressure on carotid sinus

– tight collar or hyperextension of the neck – may slow heart rate & cause carotid sinus syncope or

fainting


Syncope

• Fainting or a sudden, temporary loss of consciousness not due to trauma– due to cerebral ischemia or lack of blood flow to the brain

• Causes– vasodepressor syncope = sudden emotional stress – situational syncope = pressure stress of coughing,

defecation, or urination– drug-induced syncope = antihypertensives, diuretics,

vasodilators and tranquilizers– orthostatic hypotension = decrease in BP upon standing


Chemoreceptor Reflexes

• Carotid bodies and aortic bodies– detect changes in blood levels of O2, CO2, and H+

(hypoxia, hypercapnia or acidosis )– causes stimulation of cardiovascular center– increases sympathetic stimulation to arterioles & veins– vasoconstriction and increase in blood pressure

• Also changes breathing rates as well


Hormonal Regulation of Blood Pressure• Renin-angiotensin-aldosterone system

– decrease in BP or decreased blood flow to kidney– release of renin / results in formation angiotensin II

• systemic vasoconstriction• causes release aldosterone (H2O & Na+ reabsorption)

• Epinephrine & norepinephrine– increases heart rate & force of contraction– causes vasoconstriction in skin & abdominal organs– vasodilation in cardiac & skeletal muscle

• ADH causes vasoconstriction• ANP (atrial natriuretic peptide) lowers BP

– causes vasodilation & loss of salt and water in the urine

• Table 21.1 summarizes the relationship between hormones and blood pressure regulation.


Local Regulation of Blood Pressure

• The ability of a tissue to automatically adjust its own blood flow to match its metabolic demand for supply of O2 and nutrients and removal of wastes is called autoregulation.

• Local factors cause changes in each capillary bed– important for tissues that have major increases in activity (brain,

cardiac & skeletal muscle)• Local changes in response to physical changes

– warming & decrease in vascular stretching promotes vasodilation• Vasoactive substances released from cells alter vessel diameter (K+,

H+, lactic acid, nitric oxide)– systemic vessels dilate in response to low levels of O2– pulmonary vessels constrict in response to low levels of O2


Evaluating Circulation

• Pulse is a pressure wave– alternate expansion & recoil of elastic artery after each systole of

the left ventricle– pulse rate is normally between 70-80 beats/min

• tachycardia is rate over 100 beats/min/bradycardia under 60• Measuring blood pressure with sphygmomanometer

– Korotkoff sounds are heard while taking pressure – systolic blood pressure is recorded during ventricular contraction– diastolic blood pressure is recorded during ventricular contraction

• provides information about systemic vascular resistance– pulse pressure is difference between systolic & diastolic– normal ratio is 3:2:1 -- systolic/diastolic/pulse pressure


Pulse Points


Evaluating Circulation


Blood Pressure

• The normal blood pressure of a young adult male is 120/80 mm Hg (8-10 mm Hg less in a young adult female). The range of average values varies with many factors.

• Pulse pressure is the difference between systolic and diastolic pressure. It normally is about 40 mm Hg and provides information about the condition of the arteries.


SHOCK AND HOMEOSTASIS

• Shock is an inadequate cardiac output that results in failure of the cardiovascular system to deliver adequate amounts of oxygen and nutrients to meet the metabolic needs of body cells. As a result, cellular membranes dysfunction, cellular metabolism is abnormal, and cellular death may eventually occur without proper treatment.– inadequate perfusion– cells forced to switch to anaerobic respiration– lactic acid builds up– cells and tissues become damaged & die


Types of Shock

• Hypovolemic shock is due to decreased blood volume.• Cardiogenic shock is due to poor heart function.• Vascular shock is due to inappropriate vasodilation.• Obstructive shock is due to obstruction of blood flow. • Homeostatic responses to shock include activation of the

renin-angiotensin-aldosterone system, secretion of ADH, activation of the sympathetic division of the ANS, and release of local vasodilators (Figure 21.16).

• Signs and symptoms of shock include clammy, cool, pale skin; tachycardia; weak, rapid pulse; sweating; hypotension (systemic pressure < 90 mm HG); altered mental status; decreased urinary output; thirst; and acidosis.


Types of Shock

• Hypovolemic shock due to loss of blood or body fluids (hemorrhage, sweating, diarrhea)– venous return to heart declines & output decreases

• Cardiogenic shock caused by damage to pumping action of the heart (MI, ischemia, valve problems or arrhythmias)

• Vascular shock causing drop inappropriate vasodilation -- anaphylatic shock, septic shock or neurogenic shock (head trauma)

• Obstructive shock caused by blockage of circulation (pulmonary embolism)


Homeostatic Responses to Shock

• Mechanisms of compensation in shock attempt to return cardiac output & BP to normal– activation of renin-angiotensin-aldosterone– secretion of antidiuretic hormone– activation of sympathetic nervous system– release of local vasodilators

• If blood volume drops by 10-20% or if BP does not rise sufficiently, perfusion may be inadequate -- cells start to die


Restoring BP during Hypovolemic Shock


Signs & Symptoms of Shock

• Rapid resting heart rate (sympathetic stimulation)• Weak, rapid pulse due to reduced cardiac output & fast

heart rate• Clammy, cool skin due to cutaneous vasoconstriction• Sweating -- sympathetic stimulation• Altered mental state due to cerebral ischemia• Reduced urine formation -- vasoconstriction to kidneys

& increased aldosterone & antidiuretic hormone• Thirst -- loss of extracellular fluid• Acidosis -- buildup of lactic acid• Nausea -- impaired circulation to GI tract


Introduction

• The blood vessels are organized into routes that deliver blood throughout the body. Figure 21.17 shows the circulatory routes for blood flow.

• The largest circulatory route is the systemic circulation.• Other routes include pulmonary circulation (Figure 21.29)

and fetal circulation (Figure 21.30).


Circulatory Routes

• Systemic circulation is left side heart to body & back to heart

• Hepatic Portal circulation is capillaries of GI tract to capillaries in liver

• Pulmonary circulation is right-side heart to lungs & back to heart

• Fetal circulation is from fetal heart through umbilical cord to placenta & back


Systemic Circulation

• The systemic circulation takes oxygenated blood from the left ventricle through the aorta to all parts of the body, including some lung tissue (but does not supply the air sacs of the lungs) and returns the deoxygenated blood to the right atrium.

• The aorta is divided into the ascending aorta, arch of the aorta, and the descending aorta.

• Each section gives off arteries that branch to supply the whole body.• Blood returns to the heart through the systemic veins. All the veins of

the systemic circulation flow into the superior or inferior venae caveae or the coronary sinus, which in turn empty into the right atrium.

• The principal arteries and veins of the systemic circulation are described and illustrated in Exhibits 21.1-21.12 and Figures 21.18-21.27.

• Blood vessels are organized in the exhibits according to regions of the body. Figure 21.18a shows the major arteries. Figure 21.23 shows the major veins.


Arterial Branches of Systemic Circulation

• All are branches from aorta supplying arms, head, lower limbs and all viscera with O2 from the lungs

• Aorta arises from left ventricle (thickest chamber)– 4 major divisions of aorta

• ascending aorta• arch of aorta• thoracic aorta• abdominal aorta


Aorta and Its Superior Branches

• Aorta is largest artery of the body– ascending aorta

• 2 coronary arteries supply myocardium– arch of aorta -- branches to the arms & head

• brachiocephalic trunk branches into right common carotid and right subclavian

• left subclavian & left carotid arise independently– thoracic aorta supplies branches to pericardium, esophagus, bronchi,

diaphragm, intercostal & chest muscles, mammary gland, skin, vertebrae and spinal cord


Coronary Circulation

• Right & left coronary arteries branch to supply heart muscle– anterior & posterior

interventricular aa.


Subclavian Branches • Subclavian aa. pass superior to

the 1st rib– gives rise to vertebral a. that

supplies blood to the Circle of Willis on the base of the brain

• Become the axillary artery in the armpit

• Become the brachial in the arm • Divide into radial and ulnar

branches in the forearm


Common Carotid Branches

• External carotid arteries– supplies structures external to skull as branches of maxillary and

superficial temporal branches• Internal carotid arteries (contribute to Circle of Willis)

– supply eyeballs and parts of brain

Circle of Willis


Abdominal Aorta and Its Branches

• Supplies abdominal & pelvic viscera & lower extremities– celiac aa. supplies liver, stomach, spleen & pancreas– superior & inferior mesenteric aa. supply intestines– renal aa supply kidneys– gonadal aa. supply ovaries

and testes• Splits into common iliac

aa at 4th lumbar vertebrae– external iliac aa supply

lower extremity– internal iliac aa supply

pelvic viscera


Visceral Branches off Abdominal Aorta

• Celiac artery is first branch inferior to diaphragm– left gastric artery, splenic artery, common hepatic artery

• Superior mesenteric artery lies in mesentery– pancreaticoduodenal, jejunal, ileocolic, ascending & middle colic aa.

• Inferior mesenteric artery

– descending colon, sigmoid colon & rectal aa


Arteries of the Lower Extremity

• External iliac artery become femoral artery when it passes under the inguinal ligament & into the thigh– femoral artery becomes popliteal artery behind the knee


Veins of the Systemic Circulation

• Drain blood from entire body & return it to right side of heart

• Deep veins parallel the arteries in the region

• Superficial veins are found just beneath the skin

• All venous blood drains to either superior or inferior vena cava or coronary sinus


Major Systemic Veins

• All empty into the right atrium of the heart– superior vena cava drains the head and upper extremities– inferior vena cava drains the abdomen, pelvis & lower limbs– coronary sinus is large vein draining the heart muscle back into the

heart


Veins of the Head and Neck

• External and Internal jugular veins drain the head and neck into the superior vena cava

• Dural venous sinuses empty into internal jugular vein


Venipuncture

• Venipuncture is normally performed at cubital fossa, dorsum of the hand or great saphenous vein in infants


Hepatic Portal Circulation

• A portal system carries blood between two capillary networks, in this case from capillaries of the gastrointestinal tract to sinusoids of the liver.

• The hepatic portal circulation collects blood from the veins of the pancreas, spleen, stomach, intestines, and gallbladder and directs it into the hepatic portal vein of the liver before it returns to the heart (Figure 21.28).– enables nutrient utilization and blood detoxification by the

liver.


Hepatic Portal System

• Subdivision of systemic circulation

• Detours venous blood from GI tract to liver on its way to the heart

– liver stores or modifies

nutrients

• Formed by union of splenic, superior mesenteric & hepatic veins


Arterial Supply and Venous Drainage of Liver


Pulmonary Circulation

• The pulmonary circulation takes deoxygenated blood from the right ventricle to the air sacs of the lungs and returns oxygenated blood from the lungs to the left atrium (Figure 21.29).

• The pulmonary and systemic circulations differ from each other in several more ways.– Blood in the pulmonary circulation is not pumped so far as in the

systemic circulation and the pulmonary arteries have a larger diameter, thinner walls, and less elastic tissue.

– resistance to blood flow is very low meaning that less pressure is needed to move blood through the lungs.

– normal pulmonary capillary hydrostatic pressure is lower than systemic capillary hydrostatic pressure which tends to prevent pulmonary edema.



• Carries deoxygenated blood from right ventricle to air sacs in the lungs and returns it to the left atria

• Vessels include pulmonary trunk, arteries and veins• Differences from systemic circulation

– pulmonary aa. are larger, thinner with less elastic tissue– resistance to is low & pulmonary blood pressure is

reduced


Fetal Circulation

• Oxygen from placenta reaches heart via fetal veins in umbilical cord.– bypasses liver

• Heart pumps oxygenated blood to capillaries in all fetal tissues including lungs.

• Umbilical aa. Branch off iliac aa. to return blood to placenta.


Ductus arteriosus is shortcut from pulmonary trunk to aorta bypassing the lungs.

Lung Bypasses in Fetal Circulation

Foramen ovale is shortcut from right atria to left atria bypassing the lungs.


DEVELOPMENT OF BLOOD VESSELS AND BLOOD

• Development of blood cells and blood vessels begins at 15 – 16 days. (Figure 21.31).

• It begins in the mesoderm of the yolk sac, chorion, and body stalk.

• A few days later vessels begin to form within the embryo• Blood vessels and blood cells develop from hemangioblasts.

– Blood vessels develop from angioblasts which are derived from the hemangioblasts

– Angioblasts aggregate to form blood islands– Spaces appear and become the lumen of the vessel– Blood cells develop from pluripotent stem cells which are

also derived from hemangioblasts.


Developmental Anatomy of Blood Vessels

• Begins at 15 days in yolk sac, chorion & body stalk

• Masses of mesenchyme called blood islands develop a “lumen”

• Mesenchymal cells give rise to endothelial lining and muscle

• Growth & fusion form vascular networks

• Plasma & cells develop from endothelium


Aging and the Cardiovascular System

• General changes associated with aging– decreased compliance of aorta– reduction in cardiac muscle fiber size– reduced cardiac output & maximum heart rate– increase in systolic pressure

• Total cholesterol & LDL increases, HDL decreases• Congestive heart failure, coronary artery disease and

atherosclerosis more likely


DISORDERS: HOMEOSTATIC IMBALANCES

• Hypertension, or persistently high blood pressure, is defined as systolic blood pressure of 140 mm Hg or greater and diastolic blood pressure of 90 mm Hg or greater.

• Primary hypertension (approximately 90-95% of all hypertension cases) is a persistently elevated blood pressure that cannot be attributed to any particular organic cause.

• Secondary hypertension (the remaining 5-10% of cases) has an identifiable underlying cause such as obstruction of renal blood flow or disorders that damage renal tissue, hypersecretion of aldosterone, or hypersecretion of epinephrine and norepinephrine by pheochromocytoma, a tumor of the adrenal gland.


DISORDERS: HOMEOSTATIC IMBALANCES

• High blood pressure can cause considerable damage to the blood vessels, heart, brain, and kidneys before it causes pain or other noticeable symptoms.

• Lifestyle changes that can reduce elevated blood pressure include losing weight, limiting alcohol intake, exercising, reducing sodium intake, maintaining recommended dietary intake of potassium, calcium, and magnesium, not smoking, and managing stress.

• Various drugs including diuretics, beta blockers, vasodilators, and calcium channel blockers have been used to successfully treat hypertension.

principles of human anatomy and physiology, 11e1 chapter 21 the cardiovascular system: blood vessels...

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