Cardiorespiratory System- Blood Vessels

Question 1

What is the anatomy of blood vessels?

Answer 1

Systemic circulation extends to all body regions, while pulmonary circulation consists of vessels to and from the lungs

• Arteries carry blood away from the heart and become smaller as they branch and lead to capillaries
• Veins return blood to the heart and become progressively larger as they merge and approach the heart
• An anastomosis is the convergence of 2 or more vessels (veins do this more than arteries and end arteries don’t at all)
• Companion vessels are arteries and veins that lie next to each other

Question 2

What are blood vessel tunics?

Answer 2

• Artery and vein wall have 3 layers:
  1. Tunica intima: composed of endothelial and subendothelial layer areolar connective tissue
  2. Tunica media: Composed of circularly arranged smooth muscle (sympathetic makes smooth muscle contract resulting in vasoconstriction)
  3. Tunica externa: outer connective tissue that helps anchor blood vessels to their surroundings
• Capillary walls contain only tunica intima

Question 3

What are arteries?

Answer 3

• Transport blood away from the heart

- 3 types: elastic, muscular and arterioles

Question 4

What are elastic arteries?

Answer 4

• Largest arteries
• Walls contain many elastic fibers (mostly in tunica media)
• Most are near the heart because they allow stretching to occur when the heart pumps blood to them (aorta, pulmonary and brachiocephalic arteries)
• These arteries branch into muscular arteries

Question 5

What are muscular arteries?

Answer 5

• Medium-sized arteries
• Possess elastic fibers in 2 concentric rings: internal elastic lamina separates the tunica intima and media, whereas the external elastic lamina separates the tunica media and externa
• Have thicker tunica media with multiple layers of smooth muscle cells
• Most named arteries are muscular
• Muscular arteries branch into arterioles

Question 6

What are arterioles?

Answer 6

• The smallest arteries
• Number of tunics and the thickness of walls vary between larger and smaller arterioles
• Generally all have 6 layers of smooth muscle cells in the tunica media
• Sympathetic innervation to muscle fibers of tunica media cause vasoconstriction which elevates blood pressure upstream

Question 7

What are capillaries?

Answer 7

• The smallest blood vessels
• For most, their walls consist of tunica intima
• Allow for metabolic exchange between blood and tissues

Question 8

What are capillary beds?

Answer 8

• A group of capillaries
• Each bed is fed by a metarteriole
• Several true capillaries branch from the metarteriole to form the bulk of the capillary bed
• The metarteriole continues distally to the thoroughfare channel which then connect to the postcapillary venule
  1. Continuous: endothelial cells form a complete lining aided by tight junctions (most common in muscle and brain)
  2. Fenestrated: endothelial cells contain pores that allow fluid exchange between blood and interstitial fluid (in small intestine and kidneys)
  3. Sinusoids: have large gaps between endothelial cells and a discontinuous basement membrane which allows for the transport of large molecules and cells to and from blood (in bone marrow and liver)

Question 9

What are veins?

Answer 9

• Drain capillaries and return blood to the heart
• Pressure is lower in veins than in arteries
• At rest, they hold about 60% of the body’s blood
• Function as blood reservoirs
• Venules are small veins
• Companion vessels with arterioles
• Smallest are the postcapillary venules
• Diapedesis (leukocytes migrating from bloodstream to interstitial fluid) occurs through walls of postcapillary venules
• Venules merge to form veins
• Smaller and medium sized veins travel with muscular arteries
• Large veins travel with elastic arteries
• Contain valves formed by tunica intima that prevent blood pooling in veins
• Muscles bulge as they contract and push on veins, helping to move blood towards the heart (skeletal muscle pump)
• Venous return is also assisted by the respiratory pump which changes intrathoracic and intra-abdominal pressure

Question 10

What is blood pressure?

Answer 10

• The force per unit area that blood places on the inside of a blood vessel
• Measured by a sphygmomanometer
• Systolic BP: pressure during ventricular contraction
• Diastolic BP: pressure during ventricular relaxation
• Pressure is pulsatile until it reaches capillaries
• Pressure decreases from aorta to venae cavae

Question 11

What is the arterial flow out of the heart?

Answer 11

• Oxygenated blood is pumped out of left ventricle into ascending aorta from which the left coronary artery and right coronary artery branch off of
• 3 arterial branches emerge from the aortic arch: brachiocephalic trunk, left common carotid artery, left subclavian artery
• Descending thoracic aorta follows aortic arch and several arteries emerge to thoracic wall
• Changes name to descending abdominal aorta after it passes through diaphragm
• At fourth lumbar vertebra, the aorta bifurcates into left and right common iliac arteries
• Common iliac arteries further divide into internal and
  external iliac arteries

Question 12

What is the venous return to the heart?

Answer 12

• Superior vena cava is formed from a fusion of the right and left brachiocephalic veins and drains into the right atrium
• Inferior vena cava returns blood to the right atrium from
  lower limbs, pelvis and perineum, and abdominal structures

Question 13

What is the blood flow through the head and neck?

Answer 13

• Left and right common carotid arteries supply most of the blood to the head and neck
• At the superior border of the thyroid cartilage, they divide into external and internal carotid arteries
• External carotid artery provides blood to several branches:
  – Superior thyroid artery
  – Ascending pharyngeal artery
  – Lingual artery
  – Facial artery
  – Occipital artery
  – Posterior auricular artery
• External carotid artery then divides into maxillary artery and superficial temporal artery
• Venous blood return is through the internal jugular vein or the external jugular vein
• These two veins drain into the subclavian vein and then into the brachiocephalic vein

Question 14

What is blood flow through the cranium?

Answer 14

• Internal carotid arteries enter cranium through carotid canal
• They divide into anterior and middle cerebral arteries, which supply brain, and ophthalmic arteries, which supply the eyes
• Vertebral arteries branch from subclavian arteries and enter cranium through the foramen magnum where they merge to form the basilar artery
• The basilar artery and internal carotid arteries provide blood to vessels that create an anastomosis called the cerebral arterial circle
• Vessels in the circle include: anterior cerebral arteries, anterior communicating artery, posterior cerebral arteries, posterior communicating artery
• Most cranial venous blood drains through dural venous sinuses
• These large veins are formed between the two layers of dura mater
• There are no valves in the dural venous sinus system so blood can flow in more than one direction
  • The dural sinus system includes:
  – Superior sagittal sinus
  – Inferior sagittal sinus
  – Straight sinus
  – Left and right transverse sinuses
  – Left and right sigmoid sinuses

Question 15

What is blood flow through thoracic and abdominal walls?

Answer 15

• The internal thoracic artery arises from the subclavian artery
• It gives rise to upper anterior intercostal arteries (1–6) and then continues on to become the superior epigastric artery, which supplies blood to the superior abdominal wall
• The inferior epigastric artery is a branch of the external iliac artery and supplies blood to the inferior abdominal wall and forms an anastomosis with the superior epigastric artery
• Internal thoracic vein is formed by merger of intercostal,
superior epigastric and musculophrenic veins
• Inferior epigastric vein merges with external iliac vein
• Supreme intercostal vein that drains into brachiocephalic vein
• Lumbar and posterior intercostal veins enter azygous system
– Left side drains into the hemiazygos and accessory hemiazygos veins
– Right side veins and the hemiazygos vessels drain into the azygos vein
• Blood from the azygos vein drains into the superior vena cava just before it enters the right atrium

Question 16

What is blood flow through thoracic organs?

Answer 16

• The lungs are supplied by several bronchial arteries that
branch from the descending thoracic aorta
• The esophagus is mostly supplied by esophageal arteries that branch from the descending aorta
• The diaphragm is supplied from three sources:
– Superior phrenic arteries
– Musculophrenic arteries
– Inferior phrenic arteries

Question 17

What is blood flow through the gastrointestinal tract?

Answer 17

• Three unpaired arteries emerge from anterior wall of
descending abdominal aorta and supply blood to
gastrointestinal tract:
– Celiac trunk
– Superior mesenteric artery
– Inferior mesenteric artery

Question 18

What is the arterial supply to the abdomen?

Answer 18

• The celiac trunk gives off three branches:
1. Left gastric artery: Supplies lesser curvature of stomach and lower esophagus
2. Splenic artery: Supplies the spleen and part of the stomach
3. Common hepatic artery: Supplies the liver, gallbladder, and a portion of the stomach
• The superior mesenteric artery provides blood to the
following branches:
1. Inferior pancreaticoduodenal arteries: Supplies portions of the pancreas and duodenum
2. Intestinal arteries: Supply the jejunum and ileum
3. Ileocolic artery: Supplies the ileum, cecum, and appendix
4. Right colic artery: Supplies the ascending colon
5. Middle colic artery: Supplies most of the transverse colon
• The inferior mesenteric artery provides blood to the following branches:
1. Left colic artery: Supplies distal part of transverse colon and proximal part of descending colon
2. Sigmoid arteries: Supplies distal descending colon and sigmoid colon
3. Superior rectal artery: Supplies the rectum and upper half of the anal canal

Question 19

What is the hepatic portal system?

Answer 19

• The hepatic portal system is a network of veins that brings nutrient-rich blood from digestive organs to the liver
• The hepatic portal vein is formed by the fusion of three
abdominal veins
1. Inferior mesenteric vein: Drains the distal part of the colon
2. Splenic vein: Drains the spleen, pancreas, and stomach
3. Superior mesenteric vein: Drains blood from the small intestines, proximal part of colon, pancreas, and stomach
• Hepatic veins collect blood from liver and return it to the
inferior vena cava

Question 20

What is blood flow through the posterior abdominal organs, pelvis and perineum?

Answer 20

• Three paired arteries issued from the descending abdominal aorta include:
1. Middle suprarenal arteries: Supply the adrenal gland
2. Renal arteries: Supply the kidneys
2. Gonadal arteries: Either the testicular or ovarian arteries supplying the gonads
• Branches of the internal iliac artery include:
1. Superior and inferior gluteal arteries: Supply the gluteal region
2. Obturator artery: Supplies the medial thigh
3. Internal pudendal artery: Supplies the anal canal and the perineum
4. Middle rectal artery: Supplies the rectum
5. Uterine and vaginal arteries: Supply the uterus and vagina
• Venous drainage provided by internal iliac vein
– It merges with common iliac vein which then drains to inferior vena cava

Question 21

What is blood flow through the upper limb?

Answer 21

• Right and left subclavian arteries supply blood to upper limbs
• As the subclavian artery passes over lateral border of first rib, its name changes to the axillary artery
• The axillary artery supplies the shoulder and thoracic region
• As the axillary artery passes the inferior border of the teres major muscle, its name changes to the brachial artery
• In the cubital fossa, the brachial artery bifurcates into the ulnar and radial arteries
• These arteries of the forearm anastomosis and form the
superficial and deep palmar arches in the palm of the hand
• Digital arteries emerge from the arches to supply the fingers

Question 22

What is superficial venous drainage of the upper limb?

Answer 22

• On the dorsum of the hand, a dorsal venous network drains into the basilic and cephalic veins
• In the cubital fossa, these two veins are connected by the median cubital vein - a common site for venipuncture

Question 23

What is deep venous drainage of the upper limb?

Answer 23

• The digital veins and superficial and deep palmar venous arches drain into pairs of radial and ulnar veins in the forearm
• At the cubital fossa, the radial and ulnar veins merge to form a pair of brachial veins
• The brachial veins merge with the basilic vein to form the axillary vein
• The axillary vein changes its name to the subclavian vein as it crosses superior to the lateral border of the first rib

Question 24

What is blood flow through the lower limb?

Answer 24

• The right and left external iliac arteries supply blood to the lower limb
• As external iliac passes inferior to inguinal ligament, its name changes to femoral artery, which provides a branch called the deep femoral artery
• The deep femoral artery supplies the hip joint via medial and lateral circumflex arteries
• The femoral artery enters the posterior popliteal fossa, where its name changes to the popliteal artery
– Popliteal artery supplies the knee joint and muscles in that region
• The popliteal artery divides into the anterior and posterior tibial arteries, which supply the anterior and posterior compartments of the leg, respectively
• The posterior tibial artery provides a branch called the fibular artery, which supplies the lateral compartment of the leg
• The posterior tibial artery divides into the medial and lateral plantar arteries in the foot
• The anterior tibial artery becomes the dorsalis pedis artery at the anterior surface of the ankle
– This artery and a branch of the lateral plantar artery unite to form the plantar arch
• Digital arteries extend from the arch to supply the toes

Question 25

What is superficial venous drainage of the lower limb?

Answer 25

• On top of foot, a dorsal venous arch drains into the great saphenous vein medially and the small saphenous vein laterally
• The great saphenous vein drains into the femoral vein and the small saphenous vein drains into the popliteal vein

Question 26

What is the deep venous drainage of the lower limb?

Answer 26

• Digital veins and deep veins of the foot drain into pairs of medial and lateral plantar veins
• These veins drain into a pair of posterior tibial veins
• On the dorsum of the foot and ankle, deep veins drain into a pair of anterior tibial veins
• The anterior and posterior tibial veins merge to form the
popliteal vein in the popliteal fossa
• The popliteal vein curves onto the anterior thigh
compartment and becomes the femoral vein
• Once the femoral vein passes superior to the inguinal
ligament, it becomes the external iliac vein
• When the external iliac vein fuses with the internal iliac vein, the new vein is called the common iliac vein
• The left and right common iliac veins merge to form the
inferior vena cava

Question 27

What is pulmonary circulation?

Answer 27

• Pulmonary circulation carries deoxygenated blood from right side of heart to lungs and returns newly oxygenated blood to left side of heart
• In this circulation, arteries carry deoxygenated blood and veins carry oxygenated blood
– This is opposite the systemic circulation
• Deoxygenated blood exits the right ventricle into the
pulmonary trunk, which bifurcates into right and left
pulmonary arteries that go to the lungs
• These arteries branch into arterioles and then capillaries and finally return to the left atrium as pulmonary veins

Question 28

What is the aging of vessels?

Answer 28

• Vessels lose resilience with age
– Blood pressure may increase
– Older individuals more susceptible to aneurysms (ballooning out of artery wall that can rupture)
– Atherosclerosis risk also increases with age