Blood Vessels
Chapter 19
Introduction
• Blood vessels (BVs) - dynamic structures that
form a closed delivery system
- powered by a pump (the heart)
- pulsate, constrict, and relax
- proliferate to meet changing needs of the body
- stretch for 60,000 miles in adults
• Heart contraction forces blood into large arteries
that leave the ventricles
• Blood moves successively into smaller arterial
branches
- ultimately reach the arterioles that feed into the capillaries
• Venules – collect the blood leaving the capillaries
- merge to form the larger veins that empty into the heart
• Lumen – central blood-filled space of a BV
Structure of Blood Vessels
Except for the smallest are composed of 3 tunics:
• Tunica intima – in contact with the lumen blood
- composed of simple squamous epithelium (the
endothelium) that lines the lumen of all vessels
• Tunica media – sheets of smooth muscle
- contraction causes vasoconstriction
- relaxation causes vasodilation
• Tunica externa (adventitia) – composed of CT
- contains many collagen and elastic fibers
- cells and fibers run longitudinally
Structure of Arteries and Veins
Figure 19.1a
Types of Blood Vessels
• Arteries – carry blood away from the heart
- oxygenated blood in the systemic circuit
- oxygen-poor blood in the pulmonary circuit
• Capillaries – smallest blood vessels
- the site of exchange of molecules between blood and
tissue fluid
• Veins – carry blood toward the heart
- oxygenated blood in the pulmonary circuit
- oxygen-poor blood in the systemic circuit
Arteries
• Passage of blood through the arteries:
Elastic arteries Muscular arteries Arterioles
Elastic Arteries
The largest arteries:
• Diameters range from 2.5
cm to 1 cm
• Includes the aorta and its
major branches
• Aka conducting arteries
• High elastin content
- dampens surge of blood
pressure (BP)
Figure 19.2a
Muscular (Distributing) Arteries
‘Middle-sized’
• Lie distal to elastic arteries
• Diameters range from 1 cm
to 0.3 mm
• Includes most named
arteries
• Tunica media is thick
• Unique features
- internal and external thick
sheets of elastic laminae
Figure 19.2b
Arterioles
Smallest arteries
• Diameters range from
0.3 mm to 10 µm
• Larger arterioles
possess all three tunics
• Diameter of arterioles
controlled by
- local signaling factors in the
tissues
- sympathetic division of ANS
Figure 19.2c
Capillaries
• Smallest blood vessels - diameter from 8–10 µm
- a single layer of endothelial cells surrounded by a
basement membrane
- most important, renew and refresh interstitial fluid
- RBCs pass through in single file
• Site-specific functions of capillaries:
- Lungs: oxygen enters blood, carbon dioxide leaves
- Small intestines: receive digested nutrients
- Endocrine glands: pick up hormones
- Kidneys: removal of nitrogenous wastes
RBCs in a Capillary
Figure 19.3
Capillary Beds
• Network of capillaries running through most
tissues, especially loose CT
- tendons and ligaments are poorly vascularized
- epithelia and cartilage are avascular
• Terminal arterioles lead to metarterioles then
branch into true capillaries
• True capillaries merge into thoroughfare
channels to join venules
Capillary Beds
Fig 19.4a
Precapillary Sphincters
• Regulate flow of blood into tissues
• Composed of smooth muscle cells
• Wrap around the root of each true capillary
where it leaves the metarteriole
Precapillary Sphincters
• Sphincters relax - blood fills true capillaries
- tissues are functionally active
Fig 19.4b
• Sphincters contract – forcing blood to flow
- from metaarterioles to thoroughfare channels
- bypassing true capillaries (tissues have adequate O2)
Capillary Permeabillity
• Endothelial cells – held together by tight junctions
and desmosomes
- tight junctions block passage of small molecules
• Intercellular clefts – gaps of unjoined membrane
- passageway for small molecules to enter and exit
Two types of capillary
• Continuous: most common and lack pores
- found in most organs (skeletal muscle, skin, and the CNS)
• Fenestrated: pores span the endothelial cells
- occur where high exchange rates are needed
Continuous Capillary
Figure 19.5a
Fenestrated Capillary
Fig 19.5b
Routes of Capillary Permeability
Four routes into and out of capillaries
• Direct diffusion
• Through intercellular clefts
• Through cytoplasmic vesicles
• Through fenestrations
Low Permeability Capillaries
Blood-brain barrier
• Capillaries have complete tight junctions
• No intercellular clefts are present
• Vital molecules pass through highly selective
transport mechanisms
• Not a barrier against oxygen, carbon dioxide,
and some anesthetics
Sinusoids
Wide, leaky capillaries found in some organs
• Usually fenestrated with fewer cell junctions
• Intercellular clefts are wide open
• Have a large diameter and twisted course
• Occur where an extensive exchange of large
materials (proteins or cells) is required
- bone marrow and spleen
Sinusoids
Figure 19.5c
Veins
• Conduct blood from capillaries toward the heart
- systemic circuit carries O2 poor blood to the heart
- pulmonary circuit carries O2 rich blood to the heart
• Blood pressure is much lower than in arteries
- walls of veins are thinner
• Venules - smallest veins
– diameters from 8 – 100 µm
– smallest venules are called postcapillary venules
• Venules join to form veins
- the thickest tunic in veins is the tunica externa
Mechanisms to
Counteract Low
Venous Pressure
• Valves (in some veins)
- opened by blood flowing
toward the heart
– closed by backflow
• Skeletal muscle pump
- aids venous return
- muscles press against thin-
walled veins
- propel blood toward the heart
forcing proximal valves to open
- distal valves to close Figure 19.6
Vascular Anastomoses
Vessels interconnect to form vascular anastomoses
• Organs receive blood from more than one arterial
source
- neighboring arteries form arterial anastomoses
- provide collateral channels (alternative pathways)
- can be 90% occluded before a myocardial infarction occurs
• Veins anastomose more frequently than arteries
- abundant so occlusion of a vein raely blocks bloodflow
- example: dorsal surface of your hand
Vasa Vasorum
• Tunica externa of large vessels contain arteries,
capillaries, and veins
- arise from tiny branches from the same vessel or from
nearby vessels
• Vasa vasorum - vessels of vessels
- nourish outer region of large vessels
- inner half of large vessels receive nutrients by diffusion
from luminal blood
• Small vessels need no vasa vasorum
- entirely supplied by luminal blood
Pulmonary Circulation
• Pulmonary trunk leaves the right ventricle
- divides into right and left pulmonary arteries
• Superior and inferior pulmonary veins
- carry oxygenated blood into the left atrium
Pulmonary Circulation
Figure 19.7
Systemic Circulation
• Systemic Arteries - carry oxygenated blood
away from the heart
- aorta, the largest artery in the body
Major Arteries
Figure 19.8a
The Aorta
• Ascending aorta – arises from the left ventricles
- in the heart branches into the coronary arteries
• Aortic arch – lies posterior to the manubrium
• Branches include:
– Brachiocephalic trunk
– Left common carotid
– Left subclavian arteries
The Aorta
Figure 19.9
The Aorta
• Descending aorta – continues from the aortic
arch and includes the
– Thoracic aorta: region of T5–T12
– Abdominal aorta: ends at L4
• Divides into right and left common iliac arteries
Head and Neck Arteries
Fig 19.10a
Major Arteries Serving the Brain
Figure 19.10c
Arteries of the Upper
Limb and Thorax
Figure 19.11
Arteries of the Abdominal Aorta
• Inferior phrenic arteries
• Celiac trunk
• Superior mesenteric artery
• Suprarenal arteries
• Renal arteries
• Gonadal (testicular or ovarian) arteries
• Inferior mesenteric artery
• Common iliac arteries
Arteries of the Abdominal Aorta
Figure 19.12
The Celiac Trunk & Main Branches
Figure 19.13
Superior/Inferior Mesenteric Arteries
Figure 19.14
Arteries of the Pelvis/Lower Limbs
• Internal iliac arteries
• External iliac artery
• Femoral artery
• Popliteal artery
• Anterior tibial artery
• Posterior tibial artery
Internal Iliac Artery
Fig 19.15b
Arteries of the
Pelvis and Lower
Limbs
Figure 19.16a
Arteries of the
Lower Limbs
Figure 19.16b
Figure 19.17
Fenestrated Capillary
• Describe relevance of pulse points to
clinical anatomy
Figure 19.5b
Systemic Veins
• Three major veins enter the right atrium
• Superficial veins lie just beneath the skin
• Multivein bundles – venous plexuses
• Unusual patterns of venous drainage
– Dural sinuses
– Hepatic portal system
Venae Cavae and Tributaries
• Superior vena cava
– returns blood from body regions superior to the
diaphragm
• Inferior vena cava
– returns blood from body regions inferior to the
diaphragm
• Superior and inferior vena cava
– join the right atrium
Abdominal Cavity Vasculature
Figure 19.19
Major Veins of
the Systemic
Circulation
Figure 19.18
Veins of the Head and Neck
Dural Sinuses
• Superior and inferior
sagittal sinuses
• Straight sinus
• Transverse sinuses
• Sigmoid sinus
Figure 19.20b
Veins of the
Head and Neck
Venous drainage
• Internal jugular veins
• External jugular veins
• Vertebral veins
Figure 19.20a
Veins of the Upper Limbs
• Deep Veins
- follow the paths of companion arteries
- have the same names as the companion arteries
• Superficial veins - visible beneath the skin
- Cephalic vein
- Basilic vein
- Median cubital vein
- Median vein of the forearm
Veins of the
Right Limb
Figure 19.21a
Antecubital Fossa
• Form anastomese
frequently
• Median cubital vein
- used to obtain blood or
administer IV fluids
Figure 19.22
Veins of the Thorax
• Azygos vein
• Hemiazygos vein
• Accessory
hemiazygos vein
Figure 19.21b
Veins of the Abdomen
• Lumbar veins
• Gonadal (testicular or ovarian) veins
• Renal veins
• Suprarenal veins
• Hepatic veins
Tributaries of the Inferior Vena Cava
Figure 19.23
The Hepatic Portal System
• A specialized part of the vascular circuit
• Picks up digested nutrients
• Delivers nutrients to the liver for processing
The Basic Scheme of the Hepatic
Portal System
Figure 19.24
Veins of the Hepatic Portal System
Figure 19.25
Veins of the Pelvis & Lower Limbs
• Deep veins
– Share the name of the accompanying artery
• Superficial veins
– Great saphenous vein empties into the
femoral vein
– Small saphenous vein empties into the
popliteal vein
Veins of the Right
Lower Limb and Pelvis
Figure 19.26a
Veins of the Right Lower Limb
Figure 19.26b
Figure 19.27
Disorders of the Blood Vessels
• Aneurysm
• Deep vein thrombosis of the lower limb
• Venous disease
• Microangiopathy of diabetes
• Arteriovenous malformation
Blood Vessels Throughout Life
Fetal Circulation
• All major vessels in place by month three of
development
• Differences between fetal and postnatal
circulation include:
- fetus must supply blood to the placenta
- very little blood is sent through the pulmonary circuit
Vessels to and from the Placenta
• Umbilical vessels run in the umbilical cord
- paired umbilical arteries
- unpaired umbilical vein
• Fetal vessels and structures
- Ductus venosus
- Ligamentum teres
- Ligamentum venosum
- Medial umbilical ligaments
Fetal Circulation
• Shunts Away from the
Pulmonary Circuit
- Foramen ovale
- Ductus arteriosus
Figure 19.28a
Newborn
Circulation
• Ductus arteriosus
- Ligamentum arteriosum
• Foramen ovale
- Fossa ovalis
Figure 19.28b
Blood Vessels in Adulthood
• Atherosclerosis begins in youth
- consequences evident in middle to old age
• Males
- more atherosclerosis than females between ages
45 – 65
• Females
- experience heart disease and atherosclerosis later in life