Pulmonary circuit and systemic arteries

⭐ **BIOM2020 – Vascular System (Transcript 6)

High‑Yield, Exam‑Ready Notes**

🩸 1. Circulatory Loops

Systemic Circulation

  • Supplies all body systems: MSK, GU, GI, reproductive, etc.

  • Pathway: Left heart → body → right heart.

Pulmonary Circulation

  • Only goes to/from lungs.

  • Function: oxygenate blood.

  • Pathway: Right heart → lungs → left heart.

Accessory Systems

  • Portal system:

    • Portal vein = splenic vein + inferior mesenteric vein + superior mesenteric vein.

    • Carries nutrient‑rich, low‑oxygen blood to liver.

  • Azygous system:

    • Drains thoracic cage + posterior abdominal wall.

🔗 2. Anastomoses & Collateral Circulation

Types of Anastomoses

  • Arterio‑arterial → e.g., Circle of Willis.

  • Veno‑venous → e.g., median cubital vein.

  • Arteriovenous → e.g., fingertips (important for pulse reading).

Collateral Circulation

  • Provides alternate pathways when a vessel is blocked or kinked.

  • Example:

    • If superficial femoral artery is kinked → deep femoral artery maintains supply.

🚨 3. Shunts

Foetal Shunts

  • Ductus arteriosus → pulmonary trunk → aorta.

  • Ductus venosus → bypasses liver → IVC.

  • Foramen ovale → RA → LA.

Adult Remnants

  • Ductus arteriosus → ligamentum arteriosum.

  • Ductus venosus → ligamentum venosum.

  • Foramen ovale → fossa ovalis.

Dermal Shunts

  • Thermoregulation:

    • Cold → vasoconstrict → conserve heat.

    • Heat/exercise → vasodilate → dissipate heat.

Intestinal Shunts

  • Divert blood away from gut during exercise (fight/flight).

🫁 4. Pulmonary Vasculature

Pulmonary Trunk

  • Origin: Right ventricle.

  • Guarded by pulmonary valve (prevents backflow).

  • Divides into:

    • Right pulmonary artery

    • Left pulmonary artery

Pulmonary Veins

  • ONLY veins in the body carrying oxygenated blood.

  • Drain into left atrium.

Bronchial Arteries

  • Supply non‑respiratory tissues of lungs (bronchi, connective tissue).

  • Branches of thoracic aorta.

Organs least likely to infarct

  1. Liver (best collateral supply)

  2. Lungs

  3. Small intestine

🩻 5. Arterial System Overview

Conducting Arteries

  • Example: Aorta.

  • Function: Move blood from heart to major regions.

  • Highly elastic to withstand high pressure.

Distributing Arteries

  • Examples: brachial, femoral.

  • Function: Deliver blood to organs/tissues.

  • Run on flexor surfaces (protected from compression).

Arterioles

  • Thick smooth muscle walls.

  • Under neurohormonal control → regulate blood flow distribution.

Capillaries

  • Exchange vessels.

  • Types:

    • Continuous

    • Fenestrated

    • Sinusoids → rapid exchange (liver, spleen, bone marrow).

End Arteries

  • No collateral supply → blockage = tissue death.

  • Found in:

    • Heart

    • Kidney

    • Brain

    • Eye

🫀 6. Aorta – Structure & Branches

Three Parts

  1. Ascending aorta

    • Branches: Right & Left coronary arteries

  2. Arch of aorta

    • Branches (in order):

      1. Brachiocephalic trunk

      2. Left common carotid artery

      3. Left subclavian artery

  3. Descending aorta

    • Thoracic aorta → intercostal, bronchial, oesophageal branches

    • Passes diaphragm at T12

    • Becomes abdominal aorta

Abdominal Aorta Branches

  • Celiac trunk → foregut

  • Superior mesenteric artery → midgut

  • Renal arteries

  • Inferior mesenteric artery → hindgut

  • Bifurcates at L5 into:

    • Right common iliac

    • Left common iliac

🧠 7. Circle of Willis (High Yield)

Formed by:

  • Internal carotid arteries (2)

  • Vertebral arteries (2) → join to form basilar artery

Key branches:

  • Anterior cerebral artery (ACA)

  • Middle cerebral artery (MCA)

  • Posterior cerebral artery (PCA)

  • Basilar artery

Mnemonic from transcript:

  • Eyes = ICA

  • Eyelashes = MCA

  • Forehead = ACA

  • Scarf = PCA

  • Torso = basilar

  • Legs = vertebral arteries

💪 8. Upper Limb Arteries

Pathway:

  1. Subclavian artery

  2. → passes under clavicle → Axillary artery

  3. → past pectoralis minor → Brachial artery

  4. → at elbow → Radial + Ulnar arteries

🦵 9. Lower Limb Arteries

  • Common iliac →

    • External iliac → passes under inguinal ligament → Femoral artery

    • Internal iliac → pelvic organs (bladder, uterus, rectum)