2nd Lab

Tunics of the Blood Vessel Walls

  • Tunica Intima: The innermost layer, consisting of a simple squamous epithelium known as the endothelium, a subendothelial layer of loose connective tissue, and an internal elastic lamina in larger arteries. In lab, the endothelium often appears irregular or rippled, similar to "cottage cheese."

  • Tunica Media: The middle layer, primarily composed of smooth muscle cells and elastic fibers. This layer is significantly thicker in arteries than in veins to accommodate higher blood pressure and is responsible for vasoconstriction and vasodilation.

  • Tunica Externa (Adventitia): The outermost layer made of collagen and elastic fibers that anchor the vessel to surrounding tissues. Large vessels contain their own blood supply within this layer, known as the vasa vasorum.

Vascular Anatomy of the Head and Neck

  • Arterial Supply:

    • Common Carotid Arteries: The left common carotid branches directly from the aortic arch, while the right common carotid arises from the brachiocephalic trunk.

    • Internal Carotid Artery: Enters the cranium via the carotid canal to supply the brain and contribute to the Circle of Willis (the cerebral arterial circle).

    • External Carotid Artery: Supplies superficial structures including the face, scalp, and neck.

  • Venous Drainage:

    • Internal Jugular Vein: The primary drainage vessel for the brain, receiving blood from the dural venous sinuses like the Superior Sagittal Sinus.

    • External Jugular Vein: Drains more superficial structures of the face and scalp.

    • Anatomical Note: The internal jugular is significantly wider than the external jugular and is positioned more medially.

Upper Limb Circulation

  • Arterial Pathway: Subclavian Artery $\rightarrow$ Axillary Artery (transitioning at the $1^{st}$ rib) $\rightarrow$ Brachial Artery (transitioning at the teres major muscle).

  • Distal Arteries: The Brachial Artery bifurcates at the cubital fossa into the Radial Artery (lateral/thumb side) and the Ulnar Artery (medial/pinky side), which then form the Palmar Arches in the hand.

  • Venous Clinical Importance:

    • Superficial Veins: The Cephalic Vein (lateral) and Basilic Vein (medial) are connected by the Median Cubital Vein in the anterior elbow, which is the standard site for venipuncture.

    • Deep Veins: The Brachial Vein parallels the artery and drains into the axillary vein.

Abdominal and Visceral Circulation

  • Abdominal Aorta Branches:

    • Celiac Trunk: Provides oxygenated blood to the foregut via three branches:

    1. Left Gastric Artery: Supplies the stomach and esophagus.

    2. Splenic Artery: Supplies the spleen and pancreas.

    3. Common Hepatic Artery: Supplies the liver, gallbladder, and duodenum.

    • Superior Mesenteric Artery: Supplies the small intestine and the proximal half of the large intestine.

    • Inferior Mesenteric Artery: Supplies the distal half of the large intestine and rectum.

    • Renal Vessels: The Renal Arteries branch from the aorta at approximately the $L_{2}$ vertebral level, while Renal Veins return blood directly to the Inferior Vena Cava (IVC).

Hepatic Portal System

  • Function: Collects nutrient-rich, potentially toxin-containing blood from the digestive tract and directs it to the liver for processing before it enters systemic circulation.

  • Formation: The Hepatic Portal Vein is formed by the union of the Superior Mesenteric Vein and the Splenic Vein. The Inferior Mesenteric Vein typically drains into the splenic vein first.

  • Drainage: After hepatic processing, blood exits the liver via the Hepatic Veins into the IVC.

Lower Limb Circulation

  • Arterial Pathway: The Abdominal Aorta bifurcates at $L_{4}$ into the Common Iliac Arteries, which split into Internal (pelvic) and External Iliac Arteries.

  • Femoral and Below: The External Iliac becomes the Femoral Artery after passing the inguinal ligament. It continues as the Popliteal Artery behind the knee, branching into the Anterior Tibial (leading to the Dorsalis Pedis) and Posterior Tibial (leading to the Fibular) arteries.

  • Great Saphenous Vein: The longest vein in the human body, running medially from the foot to the thigh where it drains into the femoral vein. It lacks a corresponding artery and is frequently used in bypass surgeries.

Cerebral Circulation and Sinuses

  • Superior Sagittal Sinus: A dural venous sinus located in the superior border of the falx cerebri; it collects deoxygenated blood and cerebrospinal fluid (CSF) via arachnoid granulations.

  • Circle of Willis: An anastomosis involving the internal carotid and vertebral arteries that provides redundant blood supply to the brain, protecting against localized vascular blockages.