The circulatory system is the body’s transport network, carrying oxygen, nutrients, hormones, and waste products to and from tissues. It consists of the heart, blood, and blood vessels (arteries, veins, and capillaries). This complex network ensures survival by maintaining homeostasis, regulating temperature, and supporting immunity.
This article explores the arterial and venous system in detail, explaining the major blood vessels, their pathways, and clinical significance.
Introduction to the Circulatory System
The circulatory system has two main divisions:
1. Systemic Circulation – Delivers oxygen-rich blood from the heart to the body and returns deoxygenated blood back.Blood vessels are categorized as:
- Arteries: Carry blood away from the heart (usually oxygenated).
- Veins: Carry blood towards the heart (usually deoxygenated).
- Capillaries: Microscopic vessels where exchange of gases and nutrients occurs.
Major Arteries of the Human Body
Arteries are thick-walled, muscular vessels that withstand high pressure from the pumping heart.
1. Arteries of the Head and Neck
Common Carotid Arteries (Right & Left) → Branch into internal and external carotid arteries.
- Internal Carotid Artery: Supplies brain, eyes.
- External Carotid Artery: Supplies face, scalp, oral cavity.
2. Arteries of the Thorax
Aortic Arch branches:
- Brachiocephalic Trunk → Right subclavian & right common carotid.
- Left Subclavian Artery: Supplies left arm.
- Left Common Carotid Artery: Supplies left head and neck.
3. Arteries of the Abdomen
Abdominal Aorta branches:
- Celiac Trunk (stomach, liver, spleen).
- Superior Mesenteric Artery (small intestine, colon).
- Renal Arteries (kidneys).
- Inferior Mesenteric Artery (large intestine).
- Gonadal Arteries (ovaries/testes).
4. Arteries of the Upper Limb
- Subclavian → Axillary → Brachial → Radial & Ulnar Arteries.
- Palmar Arches: Supply hand.
5. Arteries of the Lower Limb
- Common Iliac Artery → External Iliac → Femoral Artery.
- Popliteal Artery (behind knee).
- Anterior & Posterior Tibial Arteries (leg).
- Dorsalis Pedis & Plantar Arches (foot).
Major Veins of the Human Body
Veins have thinner walls, contain valves to prevent backflow, and carry blood at lower pressure.
1. Veins of the Head and Neck
- Internal Jugular Vein: Drains brain and face.
- External Jugular Vein: Drains superficial face and scalp.
- Venous Sinuses of Brain: Superior sagittal, transverse, cavernous sinuses.
2. Veins of the Thorax
- Superior Vena Cava: Collects blood from upper body.
- Inferior Vena Cava: Collects blood from lower body.
- Azygos & Hemiazygos Veins: Drain thoracic wall.
- Intercostal Veins: Drain chest wall.
3. Veins of the Abdomen
- Hepatic Veins: Drain liver.
- Renal Veins: Drain kidneys.
- Gonadal Veins: Drain testes/ovaries.
- Portal Vein: Carries nutrient-rich blood from intestines to liver.
4. Veins of the Upper Limb
- Cephalic Vein (lateral arm).
- Basilic Vein (medial arm).
- Median Cubital Vein (elbow, common site for IV access).
- Radial & Ulnar Veins (forearm).
5. Veins of the Lower Limb
- Femoral Vein.
- Great Saphenous Vein (longest vein in body, superficial).
- Small Saphenous Vein (posterior leg).
- Popliteal Vein (behind knee).
- Anterior & Posterior Tibial Veins.
Differences Between Arteries and Veins
| Feature | Arteries | Veins |
|---|---|---|
| Direction of Flow | Away from heart | Towards heart |
| Oxygen Level | Oxygen-rich (except pulmonary artery) | Oxygen-poor (except pulmonary vein) |
| Pressure | High | Low |
| Wall Thickness | Thick, muscular | Thin, less muscular |
| Valves | Absent | Present (prevent backflow) |
| Color (in diagrams) | Red | Blue |
Clinical Significance of Circulatory System
- Atherosclerosis – Plaque buildup in arteries restricting blood flow.
- Aneurysm – Weakening of arterial wall, risk of rupture.
- Varicose Veins – Swollen, twisted veins due to valve failure.
- Deep Vein Thrombosis (DVT) – Blood clot in deep veins, risk of pulmonary embolism.
- Stroke – Blockage/rupture of cerebral arteries.
- Hypertension – Chronic high blood pressure damaging arteries.
Importance of the Circulatory System
- Supplies oxygen and nutrients to tissues.
- Removes carbon dioxide and waste products.
- Distributes hormones and immune cells.
- Regulates temperature and pH balance.
- Maintains fluid homeostasis.
FAQs on Circulatory System
Q1. What are the main arteries in the human body?
The aorta, carotid arteries, subclavian, femoral, and coronary arteries.
Q2. What are the main veins in the human body?
Superior vena cava, inferior vena cava, jugular veins, femoral vein, and great saphenous vein.
Q3. Which is the largest artery?
The aorta.
Q4. Which is the largest vein?
The inferior vena cava.
Q5. What is the Circle of Willis?
An arterial ring at the base of the brain ensuring cerebral circulation.
Q6. Why do veins have valves?
To prevent backflow of blood, especially in legs against gravity.
Q7. Which vessel carries oxygen-poor blood away from the heart?
The pulmonary artery.
- Anatomy & Physiology: An Overview
- Cardiovascular System: Functions & Blood Cycle
- Endocrine System: Glands & Hormones
- Gastrointestinal System: Structure & Function
- Immune System: Components & Mechanisms
- Integumentary System: Skin, Hair, Nails
- Muscular System: Types & Functions
- Neurological System: Brain & Nerves
- Reproductive System: Male & Female
- Respiratory System: Lungs & Airways
- Skeletal System: Bones & Joints
- Urinary System: Kidneys & Bladder
