Urinary System

I. RENAL (URINIFEROUS) TUBULES (Figure 19-1) are the structural and functional units of the kidney and consist of a nephron and a collecting duct.

II. NEPHRONS consist of the following:

A. The renal glomerulus is a capillary network that receives blood from an afferent arteriole (major site of autoregulation of blood flow) and is drained by an efferent arteriole.

1. It contains a mesangium (extracellular matrix between capillaries) and mesangial cells, which have a phagocytic function, as well as receptors for angiotensin II and atrial natriuretic peptide.

2. It contains juxtaglomerular (JG) cells.

B. The renal capsule (Bowman's capsule) consists of simple squamous epithelium (parietal layer) that lines the outer wall and podocytes (visceral layer) that cover the capillary network. It contains the urinary space, which is between the parietal and visceral layers and is continuous with the lumen of the proximal convoluted tubule.

C. Proximal convoluted tubule consists of simple cuboidal epithelium with a brush border (microvilli), apical endocytic vesicles, lateral interdigitations, and basal infold-ings [with numerous mitochondria and Na + -K+-adenosine triphosphatase (AT-Pase)].

D. Loop of Henle

1. The proximal straight tubule (PST) is similar in morphology to the proximal convoluted tubule.

2. The descending thin limb (DTL) consists of simple squamous epithelium.

3. The ascending thin limb (ATL) consists of simple squamous epithelium.

4. The distal straight tubule (DST) is similar in morphology to the distal convoluted tubule. In the region of the afferent and efferent arterioles, the DST contains specialized macula densa cells.

E. The distal convoluted tubule consists of simple cuboidal epithelium with basal in-foldings (with numerous mitochondria and Na+-K+-ATPase). Principal cells and intercalated cells have been specifically described within the epithelium.

F. The connecting tubule consists of principal cells and intercalated cells.

Pulmones Cordero Dibujos

Figure 19-1. Diagram of an uriniferous tubule. The uriniferous tubule is rhe stmcrural and functional unit of the kidney. It consists of a nephron and collecting duct. The nephron (shaded area) consists of the renal glomerulus formed by the afferent arteriole (aa) and efferent arteriole (ea), renal (Bowman's) capsule (B), proximal convoluted tubule (PCT), proximal straight tubule (PST), descending thin limb (DTL), ascending thin limb (ATL), distal straight tubule (D.ST), distal convoluted tubule (DCT), and connecting tubule (CT). Note that a distinguishing feature of the kidney cortex is the presence of renal glomeruli, proximal convoluted tubule, and distal convoluted tubule. (Modified and reprinted with permission from Henrikson RC, Kaye Gl, Mazurkiewicz JE: NMS Histology. Baltimore, Williams and Wilkins, 1997, p 327.)

Figure 19-1. Diagram of an uriniferous tubule. The uriniferous tubule is rhe stmcrural and functional unit of the kidney. It consists of a nephron and collecting duct. The nephron (shaded area) consists of the renal glomerulus formed by the afferent arteriole (aa) and efferent arteriole (ea), renal (Bowman's) capsule (B), proximal convoluted tubule (PCT), proximal straight tubule (PST), descending thin limb (DTL), ascending thin limb (ATL), distal straight tubule (D.ST), distal convoluted tubule (DCT), and connecting tubule (CT). Note that a distinguishing feature of the kidney cortex is the presence of renal glomeruli, proximal convoluted tubule, and distal convoluted tubule. (Modified and reprinted with permission from Henrikson RC, Kaye Gl, Mazurkiewicz JE: NMS Histology. Baltimore, Williams and Wilkins, 1997, p 327.)

III. THE COLLECTING DUCT consists of principal cells and intercalated cells.

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