Blood VesselsPART 1

Blood Vessels 3 major types of blood vessels:

Arteries – carries blood away from the heart

Capillaries – The functional vessels which actually delivers nutrients to cells

Veins – return blood to the heart

Structure of Blood Vessels Composed of three layers (tunics)

Tunica intima – composed of simple squamous epithelium

Tunica media – sheets of smooth muscle Contraction – vasoconstriction Relaxation – vasodilation

Tunica externa – composed of connective tissue

Lumen Central blood-filled space of a vessel

Generalized structure of arteries, veins, and capillaries.

Artery VeinTunica intima

Tunica media(smooth muscle andelastic fibers)

Tunica externa(collagen fibers)

Capillary

Lumen

Endothelial cells

Basement membrane

Lumen

Capillary network

Valve

Vasa vasorum

External elastic membrane

Internal elastic membraneSubendothelial layer

Endothelium

Structure of Arteries, Veins, and Capillaries

Figure 19.1a

Types of Arteries Elastic arteries – the largest arteries

Diameters range from 2.5 cm to 1 cm Includes the aorta and its major branches Sometimes called conducting arteries High elastin content dampens surge of blood

pressure

Figure 19.2a

Types of Arteries

Muscular (distributing) arteries 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 elastic laminae

Figure 19.2b

Figure 19.2c

Types of Arteries Arterioles

Smallest arteries Diameters range from 0.3 mm to 10 µm Larger arterioles possess all three tunics Diameter of arterioles controlled by

Local factors in the tissues Sympathetic nervous system

Capillaries Smallest blood vessels

Diameter from 8–10 µm Red blood cells pass through single file Types of Capillaries:

Continuous – most common – diffusion and intercellular clefts for larger molecules

Fenestrated – “windows” has holes – found in kidneys, intestines and endocrine glands

Sinusoids – wide, leaky capillaries. Follows a twisted path and has wide and narrow areas. Useful when exchange of large materials is necessary such as in the bone marrow and spleen

RBCs in a Capillary

Figure 19.3

Capillary Beds Network of capillaries running

through tissues Precapillary sphincters

Regulate the flow of blood to tissues Tendons and ligaments – poorly

vascularized Epithelia and cartilage – avascular

Receive nutrients from nearby CT

Capillary Beds

Figure 19.4a

Capillary Beds

Figure 19.4b

Capillary Permeabillity Endothelial cells – held together by tight

junctions and desmosomes 4 Routes of molecules:

1. Direct Diffusion through endothelial membrane 2. Intercellular clefts – unjoined areas of cell membrane

to allow passage of large molecules 3. Pinocytotic vesicles – vesicles invaginate from the

plasma membrane and migrate across the endothelial cell transporting dissolved gasses, nutrients and wast products

4. fenestrations – pores in the endothelial cells allow passage of many small molecules

Structure of Capillaries – Cross Section

Figure 19.5a

A vesicle within an endothelial cell to transport liquid from blood to tissues

Structure of Capillaries – Cross Section

Figure 19.5b

In kidneys

Routes of Capillary Permeability

Four routes into and out of capillaries Direct diffusion – across capillary wall

(endothelial cell membrane)

Through intercellular clefts – most Through cytoplasmic vesicles Through fenestrations - kidneys

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 Intercellular clefts are wide open

Occur in bone marrow and spleen Sinusoids have a large diameter and

twisted course

Sinusoids

Figure 19.5c

Veins Conduct blood from capillaries toward the heart Blood pressure is much lower than in arteries Smallest veins – called venules

Diameters from 8 – 100 µm Smallest venules – called postcapillary

venules Venules join to form veins

Tunica externa is the thickest tunic in veins

Figure 19.6

Mechanisms to Counteract Low Venous Pressure

Valves in some veins Particularly in

limbs Skeletal muscle

pump Muscles press

against thin-walled veins

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

Veins anastomose more frequently than arteries

Vasa Vasorum Tunica externa of large vessels have

Tiny arteries, capillaries, and veins Vasa vasorum vessels of vessels

Nourish outer region of large vessels such as the aorta, brachiocephalic a., common iliac a.

Inner half of large vessels receive nutrients from luminal blood

It’s how the cells of the large vessels receive nutrients

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 – largest artery in the body

Major Arteries

Figure 19.8a

The Aorta Ascending aorta – arises from the left

ventricle Branches – coronary arteries

Aortic arch – lies posterior to the manubrium Branches

Brachiocephalic trunk Left common carotid Left subclavian arteries

The Aorta

Figure 19.9

The Aorta Descending aorta – continues from

the aortic arch Thoracic aorta – in the region of T5–T12

Abdominal aorta – ends at L4

Divides into right and left common iliac arteries

Arteries of the Head and Neck

Figure 19.10a

Figure 19.10c

Major Arteries Serving the Brain Cerebral arterial circle – Circle of Willis

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 and Main Branches

Figure 19.13

Figure 19.14

Distribution of the Superior and Inferior Mesenteric Arteries

Arteries of the Pelvis and Lower Limbs

Internal iliac arteries External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery

Internal Iliac Artery

Figure 19.15b

Arteries of the Pelvis and Lower Limbs

Figure 19.16a

Arteries of the Pelvis and Lower Limbs

Figure 19.16b

Figure 19.17

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 Showing Vasculature

Figure 19.19

Major Veins of the Systemic Circulation

Figure 19.18

Figure 19.20b

Veins of the Head and Neck Dural Sinuses

Superior and inferior sagittal sinuses

Straight sinus Transverse

sinuses Sigmoid sinus

Figure 19.20a

Veins of the Head and Neck

Venous drainage Internal jugular veins External jugular veins Vertebral veins

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

Figure 19.21a

Antecubital Fossa Form

anastomese frequently

Median cubital vein is used to obtain blood or administer IV fluids

Figure 19.22

Figure 19.21b

Veins of the Thorax Azygos vein Hemiazygos vein Accessory

hemiazygos vein

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 and 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

Figure 19.26b

Figure 19.27

Disorders of the Blood Vessels Aneurysm – a ballooning out of a major artery such as the aorta Deep vein thrombosis of the lower limb – formation of clots in the veins of the leg or

thigh. The clot may detach and travel to the heart and pulmonary trunk, blocking a branch of the pulmonary artery which may be fatal

Venous disease – inadequate drainage of venous blood from the limb. Tissues become ischemic and vulnerable to damage and ulceration. Caused by the failure of valves so blood pools and causes swelling of legs.

Arteriovenous malformation – a congenital condition in which capillaries fail to develop in a certain location so that an artery continues directly into a vein. The high pressure entering a vein cause an aneurysm which can compress nearby tissues or burst and cause a stroke. Normally occurs in the brain

Atherosclerosis – arterial walls become thick and stiff from hypertension, chemicals or viral or bacterial infections. Irritation of the endothelium prompts inflammatory response. LDL is attracted, cholesterol follows.

Microangiopathy of diabetes – complication of diabetes. Elevated blood sugar lead to deposit of glycoproteins in the basement membrane of capillaries diminishing the efficiency of the capillary. Organs most vulnerable are: kidneys, retina, periheral nerves and feet.