BIO 2030 - Arteries, Veins, & Lymphatics

3 types of blood vessels

• Arteries

• Capillaries

• Veins

Arteries

Convey blood from the heart to capillaries

Have thicker tunica media and a narrower lumen, have more elastic and collagen fibers that help them retain their shape, making them more resilient and resistant to changes in blood pressure

Capillaries

Microscopic porous blood vessels that exchange substances between blood and tissues, connecting arterioles to venules

Have only tunica intima with no subendothelial layer, only composed of endothelium and a basement membrane, which lets them to have a thin wall that allows for rapid gas and nutrient exchange

3 types: Continuous, fenestrated, and sinusoid

Veins

Transport blood from capillaries to the heart, generally less in quantity than arteries

Have thicker tunica externa and larger lumen, have less elastic and collagen fibers, making them more susceptible to their walls collapsing if there’s no blood in the vessel

General structure of vessels

• Lumen

• 3 tunics:

  • Tunica intima

  • Tunica media

  • Tunica externa

Lumen

The inside space, hollow cavity, or channel within a vessel

Tunica intima

The innermost layer of the vessel wall, composed of simple squamous epithelium and a subendothelial layer of areolar connective tissue

AKA “endothelium”

Tunica media

The middle layer of the vessel wall, composed of circularly-arranged layers of smooth muscle cells with elastic fibers

Contractions of this vessel wall causes vasoconstriction and narrows the lumen, while relaxation of this vessel well causes vasodilation and widens the lumen

Tunica externa

The outermost layer of the vessel wall, composed of areolar connective tissue with elastic and collagen fibers, which helps anchor the vessel to other structures

May also contain vasa vasorum

Vasa vasorum

Small arteries that supply very large vessels’ walls of both arteries and veins

Different vessel types

• Companion vessels

• Arteries

• Veins

• Capillaries

Varicose veins

Caused by a sedentary lifestyle, which weakens venous valves and causes blood to pool

Artery branching

Vessels branch into smaller vessels extending from the heart, ultimately decreasing lumen diameter and elastic fibers, while increasing in relative amount of smooth muscle

Types of arteries

• Elastic

• Muscular

• Arterioles

Elastic arteries

Contains tunica intima, tunica media, and tunica externa, with elastic fibers distributed within the tunica media

Muscular arteries

Contains tunica intima, tunica media, and tunica externa, with elastic fibers in 2 layers surrounding the tunica media (internal elastic lamina and external elastic lamina)

Arterioles

Composed of almost entirely of smooth muscle layers and tunica media

Continuous capillaries

Capillaries with endothelial cells forming a continuous lining, with intercellular clefts, allowing smaller molecules to pass through the wall through pinocytosis

Commonly found in muscle, skin, lungs, and the CNS

Intercellular clefts

Tight junctions/gaps between endothelial cells of a continuous capillary wall

Pinocytosis

A type of active endocytosis where a cell engulfs extracellular fluid and dissolved solutes into tiny, membrane-bound vesicles; Done by continuous and fenestrated capillaries

AKA “cellular drinking”

Fenestrated capillaries

Capillaries with endothelial cells forming a continuous lining but the cells have fenestrations (pores)

Commonly found in areas where much fluid transport happens

Sinusoid capillaries

Capillaries with endothelial cells forming an incomplete lining with large gaps, with an incomplete or absent basement membrane, allowing transport of large substances (ex. formed elements, large proteins)

Commonly found in bone marrow, spleen, and some endocrine glands

Capillary beds

Groups of capillaries functioning together, which are fed by metarteriole

Metarteriole

A vessel branch of an arteriole that feeds capillary beds, consisting of a proximal part encircled by scattered smooth muscle cells, a distal part thoroughfare channel that has no smooth muscle cells, and connects to a postcapillary venule that drains the capillary bed

Thoroughfare channel

A specialized, intermediate blood vessel in a capillary bed that connects a metarteriole directly to a postcapillary venule

True capillaries

Vessels branching from the metarteriole, making up most of the capillary bed

Precapillary sphincter

Smooth muscle ring at the true capillary origin, with its relaxation allowing blood flow into the true capillaries and its contraction causing blood to bypass the capillary bed, ultimately permitting vasomotion

Vasomotion

Cycle of contraction and relaxation of precapillary sphincters

Perfusion

Amount of blood entering the capillaries per unit time per gram of tissue (mL/min/g)

Companion vessels

Pairs of arteries and veins that travel together through the same body regions, and share the same or similar names

Ex. Brachial artery and brachial vein

Venules

The smallest veins with diameters of 8-100 micrometers, being the companion vessels of arterioles, and ultimately merge to form veins

Smallest ones are the postcapillary venules and the largest ones have all 3 tunics

Small and medium-sized veins

Companion vessels with muscular arteries

Largest veins

Companion vessels with elastic arteries

Valves of the veins

Structures that prevent blood from pooling in the limbs and causing backflow of blood, which ensures flow toward the heart

Composed of tunica intima, and elastic and collagen fibers

What percentage of blood is in systemic circulation? (Systemic veins, systemic arteries, and systemic capillaries)

70%

55%, 10%, 5%

What percentage of blood is in pulmonary circulation?

18%

What percentage of blood is in the heart?

12%

Bloodflow in veins

Vasoconstriction moves blood into circulation, while vasodilation moves blood back into reservoirs

Pulmonary circulation

Blood draining into the right atrium of the heart, entering into the lung, and ultimately draining into the left atrium

Vessels of this circulation have less elastic connective tissue, wider lumen, are relatively short (since lungs are close to the heart), and have lower bp

Systemic circulation

Blood draining into the left atrium of the heart and leaving the heart through the aorta to be distributed throughout the body

Left and right coronary arteries

Arteries that emerge from the ascending aorta to supply the heart wall

3 main arterial branches from the aortic arch

• Brachiocephalic trunk

• Left common carotid artery

• Left subclavian artery

Brachiocephalic trunk

1 of the 3 main arterial branches from the aortic arch that bifurcates/divides into the right common carotid artery and the right subclavian artery

Right common carotid artery

Artery that supplies the right side of the head and neck

Right subclavian artery

Artery that branches off the brachicephalic trunk and supplies that right upper limb and some thoracic structures

Left common carotid artery

1 of the 3 main arterial branches from the aortic arch that supplies the left side of the head and neck

Left subclavian artery

1 of the 3 main arterial branches from the aortic arch that supplies the left upper limb and some thoracic structures

Once the aortic arch curves inferiorly, it becomes the

Descending thoracic aorta

Descending thoracic aorta

Part of the aorta that has several branches supplying the thoracic wall and viscera

As the descending thoracic aorta passes the diaphragm, its name becomes the

Descending abdominal aorta

Descending abdominal aorta

Part of the aorta that supplies the abdominal wall and organs

Once the descending abdominal aorta passes the 4th lumbar vertebra, it splits and becomes the

Left and right common iliac arteries

Left and right common iliac arteries

Arteries that each split into an internal and external iliac arteries

Internal iliac artery

Artery that supplies pelvic structures

External iliac artery

Artery that supplies the lower limb

3 general vessels for venous return to the heart

• Superior vena cava

• Inferior vena cava

• Coronary sinus

Superior vena cava

Formed from the merge of left and right brachiocephalic veins, draining blood from the head, neck, upper limbs, thoracic and abdominal walls to the right atrium

Inferior vena cava

Formed from the merge of veins below the diaphragm, draining blood from the lower limbs, pelvis, perineum, and abdominal structures to the right atrium

Coronary sinus

Vessel that drains blood from the heart myocardium to the right atrium

Common carotid arteries

Supply most of the blood to the body, dividing into the external and internal carotid arteries

External carotid artery

Branching off of the common carotid artery, supplying structures external to the skull

Internal carotid artery

Branching off of the common carotid artery, supplying internal skull structures

Subclavian arteries

Divides into the vertebral artery, thyrocervical and costocervical trunks

Vertebral artery

Branching off the subclavian artery, supplying the brain

Thyrocervical trunk

Branching off the subclavian artery, supplying the thyroid gland, and parts of the neck and shoulder

Costocervical trunk

Branching off the subclavian artery, supplying the deep neck and the upper intercostals

Cerebral arterial circle (circle of Willis)

An important arterial anastomosis around the sella turcica, formed from the posterior cerebral, posterior communicating, internal carotid arteries, anterior cerebral, and anterior communicating arteries

Functions in equalizing blood pressure in the brain and provides collateral channels if one vessel becomes blocked

Vertebral vein

Vein that empties into the subclavian vein

External jugular vein

Vein that drains the superficial head and neck, and empties into the subclavian vein

Internal jugular vein

Vein that drains the cranial cavity, merging with the subclavian vein to form the brachiocephalic vein

Dural venous sinuses

Large modified veins between 2 layers of dura mater, which drain primarily into the internal jugular veins and also receive excess CSF

Internal thoracic artery

Artery that supplies the anterior thoracic wall and mammary gland, emerging from the subclavian artery and branches into 6 anterior intercostal arteries, the musculophrenic artery, and becomes the superior epigastric artery

Interior epigastric artery

Artery that branches off the external iliac artery and supplies that inferior abdominal wall, and anastomoses with the superior epigastric artery

Supreme intercostal artery

Artery that branches off the costocervical trunk, then branches into posterior intercostal arteries 1-2

Posterior intercostal arteries 3-11

Arteries that branch off the thoracic aorta

Lumbar arteries

5 pairs of arteries that branch off the abdominal aorta and supply the posterolateral abdominal wall

Median sacral artery

An unpaired artery that extended from the bifurcation of the aorta in the pelvis, supplying the sacrum and coccyx

Internal thoracic vein

Vein that receives blood from the anterior intercostal, musculophrenic, and superior epigastric veins; Drains into the brachiocephalic vein

Inferior epigastric vein

Vein that merges with the external iliac vein

1st and 2nd posterior intercostal veins

Veins that merge with the supreme intercostal vein and drains into the brachiocephalic vein

Azygos system

Vein that receive blood from the lumbar and posterior intercostal veins

Hemiazygos and accessory hemiazygos veins on the left side, azygos vein on the right side; Drain into the superior vena cava

Vessels of the lungs

• Bronchial arteries → Branches off the descending thoracic aorta to supply bronchi and bronchioles

• Bronchial veins → Drains into azygos and pulmonary veins

Vessels of the esophagus

• Esophageal arteries → Several small branches off the descending thoracic aorta

• Esophageal branches also emerge off the left gastric artery

• Esophageal veins → Drain into azygos or left gastric vein

Vessels of the diaphragm

• Superior phrenic arteries → Pair emerging from the descending thoracic aorta

• Inferior phrenic arteries → Pair emerging from the descending abdominal aorta

• Musculophrenic and pericardiacophrenic arteries → Branches off the internal thoracic artery

• Superior and inferior phrenic veins → Drains into the inferior vena cava

• Musculophrenic vein → Drains into the internal thoracic veins

Gastrointestinal tract

Arterial supply comes from the abdominal aorta, with 3 branches being the celiac trunk, superior mesenteric artery, and inferior mesenteric artery

Celiac trunk

Artery that branches from the abdominal aorta, having 3 branches: left gastric artery, splenic artery, and common hepatic artery

Located just inferior to the diaphragm

Common hepatic artery

Artery that branches from the celiac trunk, and branches off into the hepatic artery proper and the gastroduodenal artery

Left gastric artery

Artery that supplies part of the stomach and esophagus

Splenic artery

Artery that supplies the spleen, and part of the stomach and pancreas

Hepatic artery proper

Artery that branches off the common hepatic artery and supplies the liver, gallbladder, and part of the stomach

Gastroduodenal artery

Artery that branches off the common hepatic artery and supplies the duodenum, pancreas, and part of the stomach

Superior mesenteric artey

Artery that branches off the abdominal aorta and contains 4 arterial branches: intestinal, middle colic, right colic, and ileocolic arteries

Located just inferior to the celiac trunk

Intestinal arteries

Arteries that branch off the superior mesenteric artery and supplies the jejunum and ileum

Middle colic artery

Artery that branch off the superior mesenteric artery and supplies most of the transverse colon

Right colic artery

Artery that branch off the superior mesenteric artery and supplies the ascending colon

Ileocolic artery

Artery that branch off the superior mesenteric artery and supplies the ileum, cecum, and appendix

Inferior mesenteric artery

Artery that branches off the abdominal aorta and has 3 branches: left colic, sigmoid, and superior rectal arteries

Located just above the bifurcation of the aorta

Left colic artery

Artery that branch off the inferior mesenteric artery and supplies the distal transverse colon and the descending colon

Sigmoid arteries

Arteries that branch off the inferior mesenteric artery and supplies part of the descending colon and sigmoid colon

Superior rectal artery

Artery that branch off the inferior mesenteric artery and supplies the rectum