Arteries, Veins and Blood Vessel Tunics

Arteries and Veins

• Arteries carry blood away from the heart and are known as efferents.
• Arteries typically carry oxygenated blood, with the exception of the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs.
• Veins carry blood towards the heart and are known as afferents.
• Veins typically carry deoxygenated blood, with the exception of the pulmonary veins, which carry oxygenated blood from the lungs to the heart.
• Umbilical vessels are also an exception to the typical blood type carried in arteries and veins.

Blood Vessel Tunics

• Blood vessels have three main tunics: tunica intima, tunica media, and tunica adventitia.
• Tunica intima (interna) is the innermost layer.
  • It is the only layer present in capillaries.
  • It is made of a smooth layer of simple squamous epithelium-lined lumen, which reduces friction.
  • It also lines heart chambers.
• Tunica media is a thick middle layer.
  • It consists of smooth muscle and elastin.
  • It constricts and dilates as needed for blood pressure regulation.
• Tunica adventitia (externa) is the outermost layer.
  • It is made of tough connective tissue that provides protection and support.

Arteries & Arterioles

• Arteries and arterioles have thicker walls (tunica/tunics).
• Arteries and arterioles have higher pressure.
• The diameter of arteries and arterioles decreases distally to maintain pressure over distance.
• Arteries an arterioles have a round lumen.

Veins & Venules

• Veins and venules have thinner walls (tunics).
• Veins and venules have low pressure.
• The diameter of veins and venules gets larger toward the heart.
• Veins have one-way valves and use skeletal muscle "pump".
• The rate/depth of breathing also affects veins and venules through thoracic pressure.
• Veins and venules have an irregular/"floppy" lumen
• Sedentary behavior and excessive standing may lead to:
  • blood pooling
  • varicose veins
  • thrombus (clot)

Capillaries

• Walls are thin and consist of a single cell layer.
• Composed of only one tunic which is the tunica intima (interna).
• Facilitate O2 - CO2 gas exchange
• Allow exchange between plasma and tissues.
  • This includes nutrients like O2, CO2, water, glucose.
  • Antibodies
  • Leukocytes
  • Acids

Vessels

• Internal carotid arteries, external carotid arteries, common carotid arteries, and subclavian arteries branch off the aorta.
• Blood vessel and organ relations reviewed for fetal pig dissections include:
  • Heart, Lungs, Thymus, Thyroid, Liver, Stomach, Spleen, Small Intestine, Large Intestine, Kidneys, Pancreas, Ovaries and Testes
  • Arteries: Aorta, Subclavians, Common carotid, Celiac trunk, Superior mesenteric, Renal, Gonadal (Genital), Inferior mesenteric, Common Iliac -Veins: Superior Vena Cava, Inferior Vena Cava, Brachiocephalic, Renal, Gonadal (Genital), Common Iliac, Hepatic portal (injected yellow)

Vessel Details

• Right subclavian artery comes off the Brachiocephalic Trunk.
• Left subclavian artery is the 3rd branch that comes directly off the Aortic Arch.
• The carotid body is located at the bifurcation and acts as a chemoreceptor for O2, pH & CO₂ levels.
• The carotid sinus is found in the proximal internal carotid artery; a baroreceptor sensitive to blood pressure.
• The Great Saphenous Vein is the longest vessel in the body.
  • It is more superficial and medial than the Femoral vein.
• The Left Gonadal vein drains into the Left Renal vein, not directly into the IVC like the Right side.
• Gastrointestinal drainage goes into the Liver to:
  • Filters toxins
  • Metabolizes nutrients
  • Breaks down old RBCs