Blood Vessels

Allied Guru

Introduction

Blood vessels body ke cells tak nutrients, oxygen aur hormones pahunchate hain aur blood ke through metabolic waste products aur CO₂ wapas nikal dete hain.
Inka exchange mainly capillary level par hota hai.

Types of Blood Vessels

Histology ke basis par, 5 main types ke blood vessels hote hain:

  1. Arteries

    • Large artery (elastic artery)

    • Medium-sized artery (muscular artery)

  2. Arterioles

  3. Capillaries

    • Continuous capillary

    • Fenestrated capillary

    • Sinusoidal capillary

  4. Venules

  5. Veins

    • Medium-sized vein

    • Large vein

Structure (General)

Sabhi blood vessels ki basic structure same hoti hai. Har ek mein 3 layers (coats ya tunics) hoti hain:

  1. Tunica intima – Endothelium (simple squamous epithelium) aur subendothelial connective tissue se bani hoti hai.

  2. Tunica media – Smooth muscle aur connective tissue se bani hoti hai.

  3. Tunica adventitia – Fibroelastic connective tissue se bani hoti hai.

 

Arteries

Features:

  • Arteries thick-walled hoti hain aur heart se blood ko capillaries tak le jaati hain.

  • Ye repeatedly divide hoti hain jaise tree ki branches, aur dheere-dheere size chhota hota jata hai.

  • Lekin inka luminal surface (andar ka area) bahut zyada badh jata hai, jiski wajah se blood ka flow slow ho jata hai. Ye hi capillaries mein exchange ko aasaan banata hai.

Types of Arteries (structure aur size ke basis par):

Large / Elastic / Conducting artery (jaise aorta)

    • Heart se blood conduct karti hai.

    • Wall ki thickness approx 1/10th hoti hai luminal diameter ki.

    • Elastic fibres ki wajah se systole mein expand aur diastole mein recoil hoti hai → isse blood pressure maintain hota hai aur flow smooth rehta hai.

    • Layers:

      • Tunica intima – Endothelium + subendothelial tissue.

      • Tunica media – 40–70 elastic laminae + smooth muscle cells.

      • Tunica adventitia – Fibroelastic tissue + vasa vasorum + sympathetic nerve fibres.

Medium-sized / Muscular / Distributing artery (jaise radial, ulnar artery)

    • Blood ko body ke alag-alag parts mein distribute karti hai.

    • Wall thickness approx 1/4th luminal diameter hoti hai.

    • Smooth muscle presence se vasoconstriction aur vasodilation possible hota hai.

    • Layers:

      • Tunica intima – Endothelium + internal elastic lamina.

      • Tunica media – Mainly smooth muscle (40 layers tak).

      • Tunica adventitia – Elastic + collagen fibres, vasa vasorum, sympathetic nerve fibres.

 

Capillaries

Feature:

  • Arterioles break hoke capillaries banti hain.

  • Capillaries ko “exchange vessels” kaha jata hai kyunki yahi pe gases, nutrients aur waste ka exchange hota hai.

  • High metabolic tissues (jaise kidney, liver, heart muscle) mein zyada capillaries hoti hain.

Structure:

  • Lumen 7–9 μm wide hota hai (RBC ke size jaisa).

  • Sirf endothelial cells se line hota hai (tunica intima only).

  • Endothelial cells tight aur gap junctions se connected hote hain.

  • Pericytes kabhi-kabhi milte hain jo contractile property rakhte hain.

  • Collagen fibre ka thin layer hota hai (tunica adventitia).

Types of Capillaries:

  1. Continuous capillary – Most common (muscle, brain, lung, connective tissue). Endothelium continuous hota hai.

  2. Fenestrated capillary – Pores present hote hain; permeability zyada hoti hai. (Kidney, intestine, endocrine glands).

  3. Sinusoidal capillary – Large lumen (30–40 μm), discontinuous endothelium, gaps hote hain (liver, bone marrow, spleen).

 

Veins

Feature:

  • Veins thin-walled hoti hain aur capillaries se blood leke heart tak le jaati hain.

  • Small veins milke large veins banati hain (jaise river ke tributaries).

  • Zyada tar veins mein valves hote hain jo blood ka backflow prevent karte hain.

Types of Veins:

  1. Medium-sized vein

    • Artery se differ karti hai: lumen collapsed hota hai, thin wall hoti hai, smooth muscle kam hota hai, elastic fibres kam hote hain, aur valves present hote hain.

    • Layers:

      • Tunica intima – Endothelium + thin subendothelium (no elastic lamina).

      • Tunica media – Few smooth muscle + collagen fibres.

      • Tunica adventitia – Loose fibroelastic tissue + vasa vasorum + nerves.

  2. Large vein

    • Layers:

      • Tunica intima – Well-developed (endothelium + connective tissue).

      • Tunica media – Thin ya absent.

      • Tunica adventitia – Thickest coat, smooth muscle bundles + connective tissue.