SN4
SHORT NOTE
5M
★ High-yield
Define end artery. Give its types with examples and the consequences of its occlusion.
Definition
An end artery is an artery that constitutes the sole arterial supply to a segment of tissue, with no effective anastomosis with neighbouring vessels.
- The concept was described by Cohnheim
Types
| Type | Definition | Examples |
|---|---|---|
| Anatomical (absolute) end artery | NO anastomosis whatever with adjacent arteries | Central artery of the retina; arteries to the brain, spleen, kidney; vasa recta of the intestine; labyrinthine artery |
| Functional end artery | Anastomoses exist but are inadequate to maintain the tissue if the main vessel is blocked | Coronary arteries; cerebral, renal, splenic and intestinal arteries |
Consequence of Occlusion — Infarction
| Tissue | Tolerance of ischaemia |
|---|---|
| Brain (neurones) | 3–5 minutes |
| Retina | A few minutes |
| Myocardium | 20–30 minutes before irreversible injury |
| Kidney | About 30 minutes |
| Skeletal muscle | 4–6 hours |
| Bone and cartilage | Hours to days |
Important Clinical Examples
| Vessel | Result of occlusion |
|---|---|
| Central artery of the retina | Sudden painless permanent blindness; cherry-red spot at the macula |
| Coronary artery | Myocardial infarction |
| Cerebral artery | Cerebral infarction (stroke) |
| Splenic artery branch | Splenic infarct — wedge-shaped |
| Vasa recta | Segmental intestinal necrosis |
| Labyrinthine artery | Sudden deafness and vertigo |
| Artery to the head of femur | Avascular necrosis after a subcapital fracture |
Contrast — Regions with Good Anastomosis
- Around the elbow, knee and scapula — the main vessel can be ligated safely
- Palmar arches — either the radial or ulnar artery can be sacrificed; the basis of the Allen test before radial cannulation
- Circle of Willis — gradual occlusion of one internal carotid may cause no infarct at all
- Marginal artery of Drummond — links the superior and inferior mesenteric territories
- Mesenteric arcades — abundant, though the terminal vasa recta are end arteries
Applied Aspects
- Sudden occlusion is far worse than gradual narrowing — slow stenosis allows collaterals to develop, which is why an embolus is more damaging than the same degree of atheroma
- Avascular necrosis of the femoral head, scaphoid, talus and lunate all follow the same principle — a single retrograde blood supply interrupted by fracture
- The retina cannot be salvaged after more than a few minutes, which is why central retinal artery occlusion is one of the true ophthalmic emergencies
- Watershed (border) zones between two arterial territories are particularly vulnerable to hypotension — the splenic flexure of the colon and the cerebral watershed areas
All questions in General Anatomy & Osteology
- Q1Classify bones with examples. Describe the parts of a long bone and its blood supply. Add a note on the types of epiphysis. ★
- Q2Classify joints with examples. Describe the structure of a synovial joint and add a note on Hilton's law. ★
- Q3Classify skeletal muscle according to shape and action. Describe its nerve supply and add a note on the functional groups of muscles. ★
- Q4Describe the types of blood vessels. Define anastomosis and end artery with examples, and add a note on portosystemic anastomoses. ★
- Q5Describe the structure of skin and fascia. Add a note on the lymphatic system and the thoracic duct. ★
- SN1Describe the epiphyseal plate with its zones. Add a note on the Salter–Harris classification. ★
- SN2Classify cartilage with its sites and features. Add a note on articular cartilage. ★
- SN3Describe the structure and types of a synovial joint. Add a note on synovial fluid. ★
- SN4Define end artery. Give its types with examples and the consequences of its occlusion. ★
- SN5Describe the types of ossification with examples. Add a note on the cells of bone. ★
- SN6Describe the deep fascia with its modifications and functions. Add a note on compartment syndrome. ★
- SN7Describe the anatomical position, the planes of the body and the terms of movement.