There Are Two Groups of Blood Vessels

Introduction

There are two groups of blood vessels

Pulmonary circuit

Blood goes to and from the lungs

Systemic circuit

Blood goes to the rest of the body and back to the heart

Blood goes to both circuits at the same time with each heartbeat

Histological Organization of Blood Vessels

The walls of the vessels consist of three layers

The layered walls give the vessels tremendous strength

The vessel walls are thick

The walls themselves are supplied with blood

These blood vessels are called vasavasorum

Histological Organization of Blood Vessels

Characteristics of the Three Layers

Intima (innermost layer)

Also called tunica intima

Makes up the endothelium of the vessel

Media (middle layer)

Also called tunica media

Consists of smooth muscle

Involved in vasoconstriction and vasodilation

Adventitia (outermost layer)

Also called tunica adventitia

Fibers of the adventitia anchor the blood vessels

Histological Organization of Blood Vessels

Distinguishing Arteries from Veins

Most arteries and veins run parallel to each other

Arteries carry blood away from the heart

Veins carry blood toward the heart

Walls of arteries are thicker than veins

Arteries maintain their circular shape and veins typically collapse when cut

Endothelial lining of arteries have pleated folds—endothelial lining of veins do not

Histological Organization of Blood Vessels

Arteries

As blood leaves the heart, it travels through:

Elastic arteries

Muscular arteries

Arterioles

Histological Organization of Blood Vessels

Elastic Arteries

Large vessels up to 2.5 cm in diameter

Very resilient

Examples are:

Aorta

Brachiocephalic

Pulmonary trunk

Common carotid

Subclavian

Common iliac

Histological Organization of Blood Vessels

Muscular Arteries

Medium-sized arteries up to 0.4 cm diameter

Examples are:

Radial and ulnar

External carotid

Brachial

Femoral

Mesenteric

Histological Organization of Blood Vessels

Arterioles

Small arteries around 30 microns in diameter

Poorly defined adventitia

Control blood flow between arteries and capillaries

Histological Organization of Blood Vessels

Capillaries

Smallest of all vessels

Most delicate of all vessels

Walls are thin enough to permit exchange of gases between the blood and the interstitial fluid

The diameter is about 8 microns

A red blood cell diameter is also about 8 microns

Histological Organization of Blood Vessels

Types of Capillaries

Continuous

Endothelial lining is complete

Fenestrated

Endothelial lining is not complete

These capillaries have pores in their lining

Histological Organization of Blood Vessels

Capillaries (continued)

There are four mechanisms regarding the passage of material across the walls of capillaries

Material can diffuse across the endothelial lining

Material can diffuse through gaps between adjacent cells of the lining

Material can diffuse through pores

Material can move via endocytosis

Histological Organization of Blood Vessels

Capillary Beds

Capillaries do not function as individual units

Capillaries form an interconnected network of capillaries (capillarybeds)

The capillary bed consists of vessels connecting arterioles with venules

There are precapillarysphincters involved in regulating blood flow through the capillaries

Histological Organization of Blood Vessels

Capillary Beds (continued)

In areas such as the brain, heart, and stomach, a continuous, rich flow of blood is required

In these areas, more than one artery supplies a specific area

These arteries (collateralarteries) typically fuse forming an arterialanastomosis

If one arteriole is blocked, the other one will supply blood to the capillary bed

Histological Organization of Blood Vessels

Capillary Beds (continued)

In areas such as the joints or visceral organs, bloodflow through some vessels may be hindered due to body movement

In order to accommodate this, there must be a direct connection between arterioles and venules

This direct connection is called an arteriovenousanastomosis

Histological Organization of Blood Vessels

Veins

Veins collect blood from tissues and return the blood to the heart

As blood leaves the tissue and travels to the heart, it travels through the following vessels:

Capillary beds

Capillaries

Venules

Medium-sized veins

Large veins

Histological Organization of Blood Vessels

Venules

Smallest of the veins

Collect blood from the capillaries

Lack or have thin tunica media

Histological Organization of Blood Vessels

Medium-Sized Veins

The adventitia (tunica externa) is the largest of the layers

Contains elastic fibers

Histological Organization of Blood Vessels

Large Veins

All three layers are relatively thick

Examples of large veins are:

Superior vena cava

Inferior vena cava

Histological Organization of Blood Vessels

Venous Valves

Blood in the veins returning to the heart from the lower extremities has to go against gravity

To assist in this process, many veins have valves (venousvalves)

These valves compartmentalize the blood in the veins thus acting as one-way valves

Valves prevent backflow of blood

Histological Organization of Blood Vessels

Blood in the veins from the lower extremities has to ascend to the heart

Blood in the veins returning to the heart from the lower extremities has to go against gravity

The skeletal muscles of the legs help to propel the blood back to the heart

Changes in thoracic pressure helps to move the blood through the venae cavae back to the heart

The Distribution of Blood

The total blood volume is distributed unevenly within the vessels of the body

Arteries and capillaries contain 30–35 percent of the volume

Veins contain 65–70 percent of the volume

Veins are more distensible than arteries

Based on blood pressure, a vein can expand about 8 times as much as a parallel artery

Blood Vessel Distribution

Blood vessels can be divided into two circuits

Pulmonary circuit

Composed of arteries and veins that transport blood between the heart and the lungs

Arteries and veins travel relatively short distances

Systemic circuit

Composed of arteries and veins that transport oxygenated blood between the heart and all other tissues

Arteries and veins travel longer distances

Blood Vessel Distribution

There are functional and structural differences between the vessels in the two circuits

Blood pressure in the pulmonary circuit is lower than in the systemic circuit

Walls of the pulmonary arteries are thinner than the walls of systemic arteries

Blood Vessel Distribution Vessel Distribution

Functional patterns of the pulmonary and systemic circuits

The distribution of arteries and veins is the same on the left side of the body as it is on the right side of the body except for the venae cavae and the aorta

A single vessel will have different names according to specific anatomical boundaries

Arteries and veins often anastomose

The Pulmonary Circuit

Blood on the right side of the heart is on its way through the pulmonary circuit

Deoxygenated blood leaves the heart by passing through the pulmonaryvalve

Enters the pulmonary trunk

Enters the left and right pulmonaryarteries

Blood arrives at the lungs to drop off carbon dioxide and pick up oxygen

Oxygenated blood returns to the heart via the pulmonaryveins

Blood enters the left atrium of the heart

Systemic Arteries

Blood on the left side of the heart is on its way through the system circulation

Oxygenated blood leaves the heart by passing through the aorticvalve

Enters the ascending aorta

At the base of the ascending aorta are the branches of the coronary vessels

Enters the aorticarch

From the aortic arch, blood branches into numerous vessels

Systemic Arteries

Blood in the aortic arch branches into the following vessels:

Brachiocephalic trunk

Then the right common carotid and right subclavian arteries

Left common carotid artery

Left subclavian artery

Descending aorta

Systemic Arteries

The Ascending Aorta

Begins at the aortic valve

Left and right coronary arteries branch off the base of the ascending aorta

Aortic arch

Forms an arch going toward the left and posterior side of the heart

Branching off the aortic arch are three elastic arteries

Systemic Arteries

Branches of the Aortic Arch

Brachiocephalic trunk

Gives rise to the right common carotid artery

And gives rise to the right subclavian artery, which supplies blood to the right side of the head and brain and to the right subclavian artery (supplies blood to the right arm)

Left common carotid artery

Supplies blood to the left side of the head and brain

Left subclavian artery

Supplies blood to the left arm

Systemic Arteries

The Subclavian Arteries

The subclavian arteries

Continue to form the axillaryarteries

Prior to forming the axillary arteries, the subclavians form three branches:

Thyrocervical trunk

Supplies muscles of the neck, head, and upper back

Internal thoracic artery

Supplies the pericardium and anterior wall of the chest

Vertebral artery

Supplies the brain and spinal cord

Systemic Arteries

The Flow of Blood from the Subclavians to the Arms

Axillary artery

Brachial artery

Radial and ulnar arteries

Arteries anastomose at the wrist forming the superficial palmar arch and deep palmar arch

Systemic Arteries

The Carotid Arteries and the Blood Supply to the Brain

The common carotids ascend the neck

Divide to form the internal carotids and external carotids

The carotid sinus is at the base of the internal carotid artery consisting of baroreceptors and chemoreceptors

Systemic Arteries

The Internal and External Carotid Arteries

External carotids

Supply the neck and outside of the skull

Branches to form:

Lingual artery

Facial artery

Occipital artery

Superficial temporal artery

Systemic Arteries

The Internal and External Carotid Arteries

Internal carotids

Enter the skull to deliver blood to the brain

Branches to form:

Ophthalmic artery (supplies the eyes)

Anterior cerebral artery (supplies frontal and parietal lobes of the brain)

Middle cerebral artery (supplies the midbrain and lateralsurfaces of the brain)

Systemic Arteries

Blood Supply to the Brain

Blood in the vertebral arteries reaches the brain via:

Left and right vertebral arteries fuse to form the basilar artery

Basilar artery branches many times in the area of the pons

Basilar artery eventually forms the vessels of the cerebralarterial circle (circle of Willis)

Systemic Arteries

The Descending Aorta

A continuation of the aortic arch

Divided into thoracic aorta and abdominal aorta at the diaphragm area

Systemic Arteries

The Thoracic Aorta

Branches to form the following vessels:

Bronchial arteries

Pericardial arteries

Mediastinal arteries

Esophageal arteries

Intercostal arteries

Superior phrenic arteries

Systemic Arteries

The Abdominal Aorta

Branches to form the following vessels:

Celiac trunk

Superior mesenteric artery

Inferior mesenteric artery

Inferior phrenic arteries

Suprarenal arteries

Renal arteries

Gonadal arteries

Lumbar arteries

Right and left common iliac arteries

Systemic Arteries

The Celiac Trunk

Supplies the following organs:

Liver

Stomach

Esophagus

Gallbladder

Duodenum

Pancreas

Spleen

Systemic Arteries

The Celiac Trunk

Branches to form the left gastric artery

Supplies the stomach

Branches to form the splenic artery

Supplies the spleen

Branches to form the left gastroepiploic artery to supply the stomach

Branches to form the pancreatic arteries to supply the pancreas

Systemic Arteries

The Celiac Trunk

Branches to form the common hepatic artery

Branches to form:

Hepatic artery proper

Supplies the liver

Right gastric artery

Supplies the stomach

Cystic artery

Supplies the gallbladder

Gastroduodenal artery

Supplies the duodenum

Systemic Arteries

Superior Mesenteric Artery

Branches to supply

Pancreas

Inferior pancreaticoduodenal artery

Duodenum

Inferior pancreaticoduodenal artery

Small intestine

Intestinal arteries

Large intestine

Right colic artery

Middle colic artery

Ileocolic arteries

Systemic Arteries

Inferior Mesenteric Artery

Branches to supply

Terminal portion of the large intestine

Left colic artery

Sigmoid arteries

Rectum

Rectal arteries

Systemic Arteries

Five paired arteries branch off the descending aorta

Inferior phrenic arteries

Suprarenal arteries

Renal arteries

Gonadal arteries

Lumbar arteries

Systemic Arteries

The five paired arteries supply:

Inferior phrenic arteries

Supply inferior portion of esophagus and diaphragm

Suprarenal arteries

Supply the suprarenal glands

Renal arteries

Supply the right and left kidneys

Systemic Arteries

The five paired arteries supply (continued)

Gonadal arteries

Supply testes, scrotum, ovaries, uterine tubes, uterus

Lumbar arteries

Supply vertebrae, spinal cord, abdominal wall

Systemic Arteries

Arteries of the Pelvis and Lower Limbs

The descending aorta branches to form:

The common iliac arteries branch to form:

The internal iliac artery (supplies the urinary bladder, walls of the pelvis, external genitalia, and the medial side of the thigh)

The external iliac artery (supplies blood to the legs)

Systemic Arteries

Arteries of the Thigh and Leg

External iliac arteries form the:

Deep femoral artery

Femoral artery

Continues to form the popliteal artery

The popliteal bifurcates to form anterior tibial and posterior tibial arteries

The posterior tibial artery gives rise the fibular artery

Systemic Arteries

Arteries of the Foot

The anterior tibial artery forms:

Dorsalispedis artery

The posterior tibial artery forms:

Medial and lateral plantar arteries

Systemic Veins

Systemic Veins

Veins collect blood from the body tissues and return it to the heart

Blood returns to the heart from the lower extremities

Via the inferior vena cava to the right atrium

Blood returns to the heart from the upper extremities

Via the superior vena cava to the right atrium

Blood returns to the heart from the lungs

Via the pulmonary veins to the left atrium

Systemic Veins

The Superior Vena Cava

All veins drain into the superior vena cava and the inferior vena cava except:

Cardiac veins

Superior vena cava receives blood from:

The head

The neck

The chest

The shoulders

The upper limbs

Systemic Veins

Venous Return from the Cranium

The superficial cerebral veins drain into:

Superior and inferior sagittal sinuses

Petrosal sinuses

Occipital sinus

Left and right transverse sinuses

Straight sinus

Venous blood from the cranium drains into the internal jugular veins, which drain into the brachiocephalic veins

Systemic Veins

Venous Return from the Cranium (continued)

Venous blood from the posterior skull and the cervical spinal cord drain into:

The vertebral veins

Drain into brachiocephalic veins

Systemic Veins

Superficial Veins of the Head and Neck

Veins from the head converge to form the:

Temporal vein

Drains into the external jugular vein then into the subclavian vein

Maxillary veins

Drain into the external jugular vein then into the subclavian veins

Facial vein

Drains into the internal jugular vein then into the subclavian veins

Systemic Veins

Venous Return from the Upper Limb

Blood returns to the heart from the hands in the following sequence

Digital veins

Superficial and deep palmar veins

The superficial palmar veins drain into the cephalic vein

Subclavian vein

Brachiocephalic vein

Superior vena cava

Right atrium

Systemic Veins

Venous Return from the Upper Limb

Blood can also return to the heart from the hands in the following sequence

The superficial palmar veins drain into the cephalic vein

Median cubital vein

Basilic vein

Axillary vein

Subclavian vein

Brachiocephalic vein

Superior vena cava

Right atrium

Systemic Veins

Venous Return from the Upper Limb

Blood can also return to the heart from the hands in the following sequence

The superficial palmar veins drain into the basilic vein

Axillary vein

Subclavian vein

Brachiocephalic vein

Superior vena cava

Right atrium

Systemic Veins

Venous Return from the Upper Limb

Blood can also return to the heart from the hands in the following sequence

The deep palmar veins drain into the radial and ulnar veins

Those veins will unite to form the brachial vein

Axillary vein

Subclavian vein

Brachiocephalic vein

Superior vena cava

Right atrium

Systemic Veins

The Formation of the Superior Vena Cava

The following veins drain into the superior vena cava, which then drains into the right atrium

Azygos veins

Brachiocephalic veins

Subclavian veins drain into the brachiocephalic veins

Internal thoracic veins drain into the brachiocephalic veins

Systemic Veins

The Inferior Vena Cava

The following veins drain into the inferior vena cava, which drains into the right atrium

Common iliac veins

Lumbar veins

Gonadal veins:

The right gonadal vein drains into the inferior vena cava, the left gonadal vein drains into the left renal vein and then into the inferior vena cava

Hepatic veins

Systemic Veins

Veins Draining the Pelvis

The following veins drain into the internal iliac and then into the common iliac and then into the IVC

Gluteal veins

Internal pudendal veins

Obturator veins

Lateral sacral veins

Median sacral veins drain into the left common iliac

Systemic Veins

Veins Draining the Abdomen

The abdominal portion of the inferior vena cava collects blood from: