Tissue is supplied by what?
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Tissue is supplied primarily by blood (via the vascular system). Here is a structured breakdown from authoritative medical textbooks:
What Supplies Tissue?
1. Blood Supply (Primary Route)
Blood is the main vehicle for tissue supply. It delivers:
- Oxygen - the essential molecule for generating cellular energy (ATP via oxidative phosphorylation)
- Nutrients - glucose, amino acids, fatty acids, vitamins, minerals
- Bicarbonate - to maintain tissue acid-base balance
- Hormones and regulatory molecules
And it removes:
- Carbon dioxide (CO2)
- Metabolic waste products (lactate, urea, etc.)
- H+ ions (to maintain pH)
"Blood flow delivers oxygen, nutrients, and bicarbonate and removes H+ and CO2, thereby maintaining normal tissue acid-base balance."
- Sleisenger and Fordtran's Gastrointestinal and Liver Disease
2. The Microcirculation - How It Actually Reaches Tissue
At the tissue level, supply is handled by the microcirculation:
| Vessel | Role |
|---|---|
| Arterioles | Regulate and distribute blood flow to specific tissue beds |
| Capillaries | Site of actual exchange - O2/nutrients diffuse out, CO2/waste diffuse in |
| Venules | Drain deoxygenated blood and waste away from tissue |
The arterioles of each tissue act as local sensors - they dilate or constrict based on local tissue needs (O2 levels, CO2 accumulation, metabolite buildup). This is called local blood flow autoregulation.
"The microvessels of each tissue, especially the arterioles, continuously monitor tissue needs, such as the availability of oxygen and other nutrients and the accumulation of carbon dioxide and other tissue waste products."
- Guyton and Hall Textbook of Medical Physiology
3. Special Cases - Avascular Tissues
Some tissues have no direct blood supply and rely instead on diffusion:
| Tissue | How it is supplied |
|---|---|
| Cartilage | Diffusion from capillaries in the surrounding perichondrium |
| Cornea | Diffusion from aqueous humor and tear film |
| Lens of the eye | Diffusion from aqueous humor |
| Intervertebral discs | Diffusion from adjacent vertebral end-plates |
"All types of cartilage lack vascular supplies with chondrocytes receiving nutrients and oxygen by diffusion from capillaries in surrounding connective tissue (the perichondrium)."
- Junqueira's Basic Histology, 17e
4. When Supply Fails
Disruption of tissue supply causes:
- Hypoxia - oxygen deficiency
- Ischemia - reduced blood supply (also cuts off nutrients)
- Both are among the most common causes of cell injury and death
"Hypoxia refers to oxygen deficiency, and ischemia means reduced blood supply. These are among the most common causes of cell injury."
- Robbins & Kumar Basic Pathology
In summary: Tissue is supplied by blood, delivered through arteries → arterioles → capillaries. The capillary bed is where exchange occurs. Avascular tissues rely on diffusion from nearby fluids or connective tissue capillaries.
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