Download Histological Organization 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
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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 vasa vasorum
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
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
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
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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
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
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
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Capillary Beds
 Capillaries do not function as individual units
 Capillaries form an interconnected network of capillaries (capillary beds)
 The capillary bed consists of vessels connecting arterioles with venules
 There are precapillary sphincters involved in regulating blood flow
through the capillaries
Histological Organization of Blood Vessels
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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 (collateral arteries) typically fuse forming an arterial
anastomosis
 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, blood flow through some
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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 arteriovenous anastomosis
Histological Organization of Blood Vessels
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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
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Venules
 Smallest of the veins
 Collect blood from the capillaries
 Lack or have thin tunica media
Histological Organization of Blood Vessels
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Medium-Sized Veins
 The adventitia (tunica externa) is the largest of the layers
 Contains elastic fibers
Histological Organization of Blood Vessels
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Large Veins
 All three layers are relatively thick
 Examples of large veins are:
 Superior vena cava
 Inferior vena cava
Histological Organization of Blood Vessels
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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 (venous valves)
 These valves compartmentalize the blood in the veins thus acting as
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one-way valves
 Valves prevent backflow of blood
Histological Organization of Blood Vessels
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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
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Functional patterns of the pulmonary and systemic circuits
 The distribution of arteries and veins is the same on the left side of the
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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 pulmonary
valve
 Enters the pulmonary trunk
 Enters the left and right pulmonary arteries
 Blood arrives at the lungs to drop off carbon dioxide and pick up oxygen
 Oxygenated blood returns to the heart via the pulmonary veins
 Blood enters the left atrium of the heart
Systemic Arteries
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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 aortic valve
 Enters the ascending aorta
 At the base of the ascending aorta are the branches of the coronary
vessels
 Enters the aortic arch
 From the aortic arch, blood branches into numerous vessels
Systemic Arteries
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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
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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
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Systemic Arteries
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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
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The Subclavian Arteries
 The subclavian arteries
 Continue to form the axillary arteries
 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
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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
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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
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External carotids
 Supply the neck and outside of the skull
 Branches to form:
 Lingual artery
 Facial artery
 Occipital artery
 Superficial temporal artery
Systemic Arteries
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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 lateral surfaces
of the brain)
Systemic Arteries
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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 cerebral arterial
circle (circle of Willis)
Systemic Arteries
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The Descending Aorta
 A continuation of the aortic arch
 Divided into thoracic aorta and abdominal aorta at the diaphragm area
Systemic Arteries
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The Thoracic Aorta
 Branches to form the following vessels:
 Bronchial arteries
 Pericardial arteries
 Mediastinal arteries
 Esophageal arteries
 Intercostal arteries
 Superior phrenic arteries
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Systemic Arteries
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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
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The Celiac Trunk
 Supplies the following organs:
 Liver
 Stomach
 Esophagus
 Gallbladder
 Duodenum
 Pancreas
 Spleen
Systemic Arteries
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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
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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
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 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
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Renal arteries
 Supply the right and left kidneys
Systemic Arteries
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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:
 Dorsalis pedis 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
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

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
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
 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
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
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
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Systemic Veins

Veins Draining the Abdomen
 The abdominal portion of the inferior vena cava collects blood from:
 Lumbar veins
 Gonadal veins
 Hepatic veins
 Renal veins
 Suprarenal veins
 Phrenic veins
Systemic Veins

Veins Draining the Lower Limb
 Blood returns to the heart from the feet in the
following sequence
 Plantar veins
 Drain into the anterior tibial, posterior tibial, and fibular veins
 Popliteal vein
 Femoral vein
 External iliac vein
 Common iliac vein
 Inferior vena cava
 Right atrium
Systemic Veins

Veins Draining the Lower Limb
 Blood also leaves the foot and returns to the heart via the following veins
 Dorsal venous arch
 Great saphenous vein
 Femoral vein
 External iliac vein
 Common iliac vein
 Inferior vena cava
 Right atrium
Systemic Veins

The Hepatic Portal System
 Blood from the small intestine, large intestine, stomach, and pancreas
flows into the hepatic portal system
 Inferior mesenteric vein drains a portion of the large intestine
 Splenic vein drains the spleen, lateral border of the stomach, and the
pancreas
 Superior mesenteric vein drains a portion of the stomach, small
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intestine, and a portion of the large intestine
Systemic Veins

The Hepatic Portal System
 From the hepatic portal veins, venous blood enters into:
 Liver sinusoids
 Hepatic veins
 Inferior vena cava
 Right atrium
Cardiovascular Changes at Birth

The fetal cardiovascular system differs from the adult cardiovascular system
 The fetal lungs are nonfunctional
 The fetal digestive system is nonfunctional
 All fetal nutritional and respiratory needs are provided by diffusion across
the placenta
 Blood in the fetal internal iliacs enters the umbilical arteries
 Enters the umbilical cord
 Enters the placenta
Cardiovascular Changes at Birth

All fetal nutritional and respiratory needs are provided by diffusion across the
placenta
 Blood leaves the placenta
 Enters the umbilical vein
 Enters the ductus venosus
 Enters the fetal liver
 Enters the inferior vena cava
 Enters the fetal right atrium
Cardiovascular Changes at Birth

Fetal heart circulation uses two “short circuits” to the lungs
 Blood in the right atrium can enter into the left atrium via the foramen
ovale
 Blood in the pulmonary trunk can enter into the aortic arch via the ductus
arteriosus
Cardiovascular Changes at Birth

Upon birth:
 Smooth muscles of the ductus arteriosus contract forming the
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
ligamentum arteriosum found in the adult heart
Pressure in the left atrium increases, thus closing the valvular flap of the
foramen ovale, forming the fossa ovalis found in the adult heart
Aging and the Cardiovascular System

Age-related changes in the cardiovascular system
 Blood changes
 Decreased hematocrit
 Thrombi and emboli form more easily
 Pooling of blood in veins of the leg
 Heart changes
 Reduced efficiency and elasticity
 Atherosclerosis of coronary vessels
 Scar tissue forms
 Blood vessel changes
 Loss of elasticity
 Calcium deposits damage vessel walls
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