23-1

Human Anatomy, Second Edition

McKinley & O'Loughlin

Chapter 23 Lecture Outline: Vessels and Circulation

23-2

Blood Vessels The heart and blood vessels form a

closed-loop system. Blood is continuously pumped to

and from the tissues. The vessels can pulsate and

change shape in accordance with the body’s needs.

23-3

Blood Vessels Often share names with either the body

region they traverse or the bone next to them.

Some are named for the structure they supply.

Arteries and veins that travel together sometimes share the same name.

The systemic circulation and pulmonary circulation work continuously and with each other.

23-4

Anatomy of Blood Vessels Arteries carry blood away from the

heart to the body tissues. They branch into progressively smaller vessels

until they feed into the capillaries, where gas and nutrient exchange occurs.

From the capillaries, venules and then veins return blood to the heart.

Veins become progressively larger as they merge and get closer to the heart.

23-5

The aorta (d=1 inch) branches and branches into

Several hundred million tiny arteries and arterioles that branch into

10 billion capillaries (25,000 miles) that merge to form

Venules which merge to form Veins Total: 100,000 km or 60,000 miles of

blood vessels!

Extensive Blood Supply

23-6

Anastomoses Site where two or more vessels merge to

supply or drain the same body region is called an anastomosis. arterial anastomoses provide collateral

circulation (most tissues supplied by more than one artery)

end arteries, if blocked, lead to necrosis of tissue beyond

functional end arteries have such small anastomoses that they function as end arteries (e.g., the heart)

veins tend to form many more anastomoses than do arteries

23-7

Blood Vessel Tunics Tunica Intima, or Tunica Interna

composed of an endothelium and a subendothelial layer Tunica Media

especially important in arteries composed of circularly arranged layers of smooth muscle

cells vasoconstriction and vasodilation

Tunica Externa, or Tunica Adventitia relatively thicker in veins, but distensible composed of an areolar connective tissue that contains

elastic and collagen fibers helps anchor the vessel to other tissues vasa vasorum are blood vessels to the thicker blood

vessels

8

9

23-10

Arteries Three basic types of arteries:

elastic (conducting) arteries (2.5 cm to 1 cm) recoil to maintain blood pressure

muscular (distributing) arteries (1 cm to 0.3 mm) control blood flow supply groups of organs, organs, and parts of organs

arterioles (0.3 mm to 10 microns - almost microscopic) artery like near artery and capillary like near capillary important in regulating blood flow into capillaries and

controlling blood pressure local factors sympathetic division controls diameter

as an artery’s diameter decreases corresponding decrease in the amount of elastic fibers relative increase in the amount of smooth muscle

11

23-12

Capillaries Only the tunica intima: a basement membrane and

endothelium only. There may be gaps or pores. About 8-10 microns in diameter Thin wall and slow flow allow gas and nutrient

exchange between the blood and the body tissues to occur rapidly.

Smallest blood vessels, connect arterioles to venules (microcirculation).

The functional units of the cardiovascular system. Near almost all cells Distribution varies with activity Direct or branching network A group of capillaries (10–100) functions together and forms

a capillary bed.

13

23-14

The Three Basic Kinds of Capillaries Continuous capillaries

the most common type Examples: skeletal and smooth muscle, connective tissues,

lungs, CNS Fenestrated capillaries

many pores Examples: kidneys, small intestinal villi, choroid plexuses,

ciliary processes, endocrine glands, synovial membranes Sinusoids, or discontinuous capillaries

wider, tortuous, spaces between endothelial cells basement membrane is incomplete or absent specialized lining cells for function of tissue blood moves slowly through there which is good for exchanges Examples: liver, spleen, anterior pituitary, parathyroid gland,

bone marrow

15

23-16

Routes of Capillary Permeability Direct diffusion Intercellular clefts Pinocytic vesicles and caveolae Fenestrations

23-17

Veins Walls are relatively thin and the vein

lumen is larger (often collapse). Systemic veins carry deoxygenated blood to the right

atrium of the heart, while pulmonary veins carry oxygenated blood to the left atrium of the heart.

Blood pressure is substantially reduced by the time blood reaches the veins.

Veins function as blood reservoirs. Hold about 60% of the body’s blood at rest. Major reservoirs in the abdominal organs (esp. liver

and spleen) and skin Blood can move quickly when increased muscular

activity or hemorrhage

23-18

Veins Most veins run with corresponding arteries But, some important differences in distribution

One systemic artery (aorta) leaves the left ventricle, but 3 veins enter the right atrium

All large and medium-sized arteries are deep for protection but many veins are superficial

Several parallel veins instead of one larger vein (may include anastomoses)

Two unusual drainage patterns Dural sinuses Hepatic portal system

23-19

From Venules to Veins Venules merge to form veins (greater than 100

micrometers). Blood pressure in veins is too low to overcome the

forces of gravity, but there is a slight pressure gradient.

To prevent blood from pooling in the limbs, most veins contain one-way numerous valves to prevent blood backflow.

Many deep veins pass between skeletal muscle groups, the skeletal muscle pump.

Also a respiratory pump, the changes in pressure in the thoracic region from breathing help move blood back to the heart from the lower part of the body.

23-20

Vascular Sinus A vein without smooth muscle

so no change in diameter Examples: dural venous sinuses of

brain and coronary sinus of heart

21

23-22

Blood Pressure Force per unit area that blood places on the

inside wall of a blood vessel Measured in millimeters of mercury (mm Hg)

with a sphygmomanometer Use brachial artery Systolic pressure/diastolic pressure (less than

120/80 mm Hg is considered normal now) Increased by blood volume and cardiac output,

vasoconstriction, drugs (can increase or decrease)

23

23-24

Hypertension: The “Silent Killer” Chronically elevated blood pressure, greater

than 140 mm Hg systolic and/or 90 mm Hg diastolic.

90-95% is essential hypertension. Cause: idiopathic (unknown).

5-10% secondary hypertension (usually renal disease or an adrenal gland tumor)

Serious effects: damages blood vessel walls leading to atherosclerosis, arteriosclerosis, renal failure, stroke, heart failure

Treatment: weight loss, diet, exercise, no smoking, drugs (diuretics, beta-blockers, ACE inhibitors that cause vasodilation)

23-25

Systemic Circulation

23-26

Branches off the Aorta All systemic arteries branch directly or indirectly

from the aorta First branching off the ascending aorta are the

right and left coronary arteries Branching off the aortic arch are in order:

brachiocephalic trunk, l. common carotid, and l. subclavian(A, B, C ‘s)

The brachiocephalic trunk branches into the right common carotid and right subclavian

The vertebral arteries branch off the subclavians and go through the transverse foramina

The descending aorta is the thoracic aorta and then the abdominal aorta

27

23-28

Circle of Willis (Cerebral Arterial Circle) An important anastomosis of

arteries around the sella turcica. Blood enters through two routes: the basilar

artery which is formed from the vertebral arteries that branch off the subclavians and the internal carotid arteries that branch off the common carotids

Equalizes blood pressure in the brain and can provide collateral channels should one vessel become blocked.

29

30

23-31

Veins of the Head and Neck Internal jugulars

From the sinuses Drain the face and neck, brain Join the subclavian, etc.

External jugulars Lateral to the internal jugulars Drain the salivary glands, facial muscles, scalp and other

superficial structures Join the subclavian, etc. May get distended during right sided heart failure or normally

with coughing or exercise Vertebral veins

Drain the deep neck structures Go through the transverse foramina into the subclavian

23-32

Veins of the Head and Neck From the subclavian veins, the

venous blood goes to the two brachiocephalic veins and then into the superior vena cava that drains venous blood from above the diaphragm

33

34

35

36

23-37

Arteries of the Thorax and Abdomen The descending aorta is the thoracic aorta above

the diaphragm and then the abdominal aorta below the diaphragm

Celiac trunk off the abdominal aorta Common hepatic artery Left gastric artery Splenic artery

Superior mesenteric Inferior mesenteric Common iliac arteries

Internal iliac artery External iliac artery becomes the femoral artery in

the thigh

38

39

23-40

Veins of the Thorax The inferior vena cava empties into

the right atrium Brachiocephalic veins empty

into the superior vena cava Azygos system of veins

23-41

The Azygos System The azygos veins collect blood

from the thorax, but also may be used for a bypass for the inferior vena cava or the hepatic portal vein if they are blocked

They empty into the superior vena cava and brachiocephalic

42

43

23-44

Veins of the Abdomen and Pelvis Inferior vena cava drains the

abdominal viscera and wall Returns blood from below the

diaphragm Widest vessel Edema and varicose veins during

pregnancy for some Many of the veins have the same

names as the arteries

23-45

Hepatic Portal System A venous network that drains the GI tract and shunts the blood

to the liver for processing and absorption of transported materials.

The hepatic portal vein brings deoxygenated, but nutrient rich blood to the liver.

Needed because the GI tract absorbs digested nutrients, and these nutrients must be processed and/or stored in the liver.

The hepatic artery brings oxygenated, but nutrient poor blood to the liver.

Branches of these two vessels merge and mix the two bloods in the hepatic sinusoids.

Blood exits the liver through hepatic veins that merge with the inferior vena cava.

A hepatic portal triad is a branch of the hepatic portal vein, a branch of the hepatic artery, and a bile duct.

46

47

23-48

Arteries of the Upper Extremities The subclavian artery becomes the Axillary artery that becomes the Brachial artery (blood pressure

taken here) that becomes the Radial and ulnar arteries that

become the arteries in the hand (including anastomoses) The radial artery is a major artery for

taking the pulse

49

50

51

23-52

Veins of the Upper Extremities Superficial and deep have

valves Superficial are larger and often

visible Lots of anastomoses Deep often accompany arteries

and have the same names Most deep veins are paired

23-53

Veins of the Upper Extremities Superficial

Cephalics Basilar Median antebrachials Median cubital veins are used often for blood samples

and injections Deep run with the arteries (note the same

names) Radials Ulnars Brachials Axillaries Subclavians

54

23-55

Arteries of the Lower Limb External iliac artery becomes the

femoral artery in the thigh then the Popliteal artery that becomes the Anterior tibial artery, posterior tibial

artery, and fibular artery, etc. Anterior tibial artery becomes the

doralis pedis artery (important for assessing circulation in the lower limbs)

56

23-57

Veins of the Lower Extremities Superficial

Great saphenous Longest vein - used often for bypasses (mammary arteries

used for short bypasses also) Anterior to the medial malleolus so it is useful for

prolonged IVs Subject to varicosities

Small saphenous Deep

Same names as arteries usually Examples: anterior and posterior tibial, politeal, femoral

Many anastomoses between the superficial and between the superficial and the deep

58

59

23-60

Palpating the Pulse Temporal artery Facial artery Common carotid artery Brachial artery Radial artery Femoral artery Popliteal artery Posterior tibial artery Dorsalis pedis artery Above are also pressure points to prevent

bleeding

23-61

Varicose Veins Incompetent valves Causes: heredity, mechanical factors, aging Especially common in surface veins of leg Treatment: rest, elevation, stockings, sclerosing

chemicals, surgery Hemorrhoids: varicose veins in anorectal region Mild form: spider veins Possible consequences

Edema Blood clots, phlebitis, gangrene

23-62

Deep Vein Thrombosis (DVT) Thrombus Common site: calf (sural) region, also

femoral region Occurs in heart disease, inactivity,

immobilization (“economy class syndrome”), pregnancy

Symptoms: fever, tenderness and redness, severe pain and swelling, rapid heartbeat

Severe complication: pulmonary embolism Treatment: anticoagulants

23-63

Progressive disease of the elastic and muscular arteries. Characterized by atheroma (or atheromatous plaque) leading to thickening of the tunica intima and narrowing of the lumen.

Not well understood, most accepted is response-to-injury hypothesis. Infection, trauma, hypertension.

Risk factors: hypercholesterolemia, being male, age, smoking, and hypertension.

Treatment options: angioplasty, coronary bypass surgery

Prevention: healthy diet, drugs for high cholesterol, not smoking, monitoring and treating hypertension.

Atherosclerosis

23-64

Pulmonary Circulation Responsible for carrying deoxygenated

blood from the right side of the heart to the lungs, and then returning the newly oxygenated blood to the left side of the heart.

65

66

67

23-68

Differences from the Systemic Circulation Only postnatal arteries carrying O2 poor blood

and veins carrying O2 rich blood Shorter distance Arteries are more like systemic veins:

Larger diameter, thinner, less elastic tissue Less resistance and, therefore, less pressure needed

Less hydrostatic pressure (B.P.) decreases risk of edema

Vessels constrict when O2 low so blood goes to where O2 can be picked up (in tissues vessels dilate when O2 is low to bring more oxygenated blood to the O2 poor tissues)

23-69

Fetal Circulation Oxygenated blood from the placenta enters through

the umbilical vein. Blood is shunted away from the liver and to the inferior vena

cava through the ductus venosus and oxygenated blood mixes with deoxygenated blood.

Blood empties into the right atrium. Most of the blood is shunted to the left atrium via the

foramen ovale. Blood flows into the left ventricle and out the aorta. A small amount of blood enters the right ventricle and

pulmonary trunk, but much of this blood is shunted to the aorta through ductus arteriosus.

Blood travels to the rest of the body, and the deoxygenated blood returns to the placenta through umbilical arteries.

70

23-71

If ductus arteriosus fails to close, then blood from the aorta can enter the pulmonary system

Over several years, results in pulmonary hypertension and failure of the right ventricle

Treat first with prostaglandin-inhibiting medication. If not successful, then surgery.

Patent Ductus Arteriosis

23-72

Aneurysm = a localized, abnormal dilation of a blood vessel

Aorta especially prone between the renal arteries and the bifurcation of the common iliac arteries

Often a consequence of atherosclerosis Enlarges and may rupture Severe medical emergency May replace with an artificial vascular

prosthesis or reinforce with a stent

Abdominal Aortic Aneurysm

23-73

Aging and the Cardiovascular System Heart and blood vessels become less resilient. Elastic arteries are less able to withstand the

forces from the pulsating blood. Systolic blood pressure may increase with age. Apt to develop an aneurysm, whereby part of

the arterial wall thins and balloons out. Wall is more prone to rupture, which can cause

massive bleeding and death. Incidence and severity of atherosclerosis

increases.