First, Understand the Basics The kidney needs a constant and good blood supply to work. It filters blood, removes waste, and cont
Renal Vascular Diseases --- First, Understand the Basics The kidney needs a constant and good blood supply to work. It filters blood, removes waste, and controls blood pressure. When the blood vessels supplying the kidney are damaged or narrowed, the kidney suffers — and when the kidney suffers, blood pressure goes up, and when blood pressure goes up, the vessels get damaged further. It becomes a vicious cycle. This topic is about what happens to the kidney when its blood vessels go wrong. --- 1. Nephrosclerosis What is it? Nephrosclerosis means hardening and scarring of the small arteries and arterioles inside the kidney. Think of it as the kidney's small pipes becoming stiff, thick, and narrow over time. What causes it? Hypertension — the most important cause. High pressure damages vessel walls over time Diabetes — accelerates the damage Old age — vessels naturally stiffen with age More common and more severe in people of African descent Important point: hypertension causes nephrosclerosis, but nephrosclerosis also worsens hypertension. Each makes the other worse. How does it develop? Two things happen to the vessel walls: Medial and intimal thickening — the middle and inner layers of the vessel wall thicken in response to high pressure, aging, or genetic damage. The vessel wall gets thicker but the channel inside gets narrower Hyaline arteriolosclerosis — plasma proteins leak through the damaged vessel wall and get deposited there, along with excess basement membrane material. The wall becomes glassy and homogeneous — this is hyalinization. The lumen narrows further The result: blood cannot flow properly through these narrowed vessels → the kidney tissue beyond them gets less blood → ischemia (shortage of blood supply) → glomeruli scar (glomerulosclerosis) → tubules atrophy → kidney shrinks and loses function What does the kidney look like? Smaller than normal — weight drops to about 110–130g Surface looks like grain leather — fine, even granularity This granular surface corresponds to tiny scars all over the cortex Under microscope: narrowed arterioles with hyaline walls, sclerotic glomeruli, atrophic tubules, interstitial fibrosis Larger vessels show fibroelastic hyperplasia — thickening of the intima with myofibroblastic tissue and duplication of the elastic lamina Who is at risk of progressing to renal failure? People of African descent Those with severely elevated blood pressure Those with a second disease, especially diabetes Malignant Hypertension — The Dangerous End About 5% of hypertensive patients develop malignant hypertension Defined as: systolic 200 mmHg AND diastolic 120 mmHg Features: severe hypertension + renal failure + retinal hemorrhages/exudates ± papilledema If untreated, death occurs within 1–2 years The kidney damage in this setting is called malignant nephrosclerosis About 30% develop microangiopathic hemolytic anemia Key mechanism: endothelial injury --- 2. Renal Artery Stenosis What is it? Stenosis means narrowing. Here, the main renal artery — the big pipe bringing blood to the kidney — becomes narrowed. The kidney on that side gets less blood and responds by raising blood pressure. This matters because it is one of the few curable causes of hypertension — fix the narrowing, fix the blood pressure. Responsible for 2–5% of all hypertension cases How does it raise blood pressure? The narrowed artery delivers less blood to the kidney. The kidney interprets this as low blood pressure in the whole body (even though it is just that one kidney getting less blood). So it activates the renin-angiotensin system: Juxtaglomerular apparatus detects low perfusion → releases renin Renin converts angiotensinogen → angiotensin I → angiotensin II Angiotensin II is a powerful vasoconstrictor → raises blood pressure Also causes sodium retention → raises blood pressure further This is why ACE inhibitors (which block angiotensin II) lower blood pressure in these patients. What causes the narrowing? 1. Atherosclerotic plaque (70% of cases) Plaque at the origin of the renal artery More common in men, older age, diabetics Plaque is concentric; thrombosis can occur on top of it 2. Fibromuscular dysplasia Fibrous thickening of the vessel wall — can involve intima, media, or adventitia More common in women, younger age groups (30s and 40s) No atherosclerosis involved What does the affected kidney look like? Smaller than normal Diffuse ischemic atrophy — crowded glomeruli, atrophic tubules, interstitial fibrosis Arterioles inside this kidney are actually protected — because the stenosis shields them from the high pressure. So they show only mild arteriolosclerosis The opposite kidney however — exposed to full high pressure — shows more severe arteriolosclerosis How is it diagnosed and treated? Bruit heard over the kidney on auscultation Elevated plasma renin levels Confirmed by arteriography Surgery cures 70–80% of well-selected cases --- 3. Thrombotic Microangiopathies (TMA) What is it? A group of conditi