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(B) Histology of kidney: The vertical section of a kidney (Fig.19.2) shows that it consists of two regions, the outer dark region called the cortex, and the inner, lighter colored zona medulla. It also shows a large number of tiny tubules (nephrons), many capillaries and connective tissue. There is a collecting space called the pelvis where the ureter leaves the kidney; 6 to 15 cones or pyramids of kidney tissue project into this space.

The renal artery divides into capillaries, which carry blood to the glomerulus of the uriniferous tubules. The renal vein carries blood away from the uriniferous tubules through its capillary network.

Figure 19.2 Sagittal Section of a Kidney

i) Structure of a uriniferous tubule (Nephron)

The nephron (Fig. 19.3) is the basic excretory unit of the kidney; there are over a million in each kidney. Each nephron consists of a glomerulus, Bowmanís capsule and associated renal tubules.

The glomerulus is a small knot of blood vessels formed by a capillary network from the renal artery (afferent vessel). The smaller efferent vessels take the blood away from the glomerulus and enter the capillary network around the tubule of the nephron. The capillaries unite to form the venules to form the renal vein which joins the inferior vena cava.

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Table of Contents

19.0 - Introduction
19.1 - Ammonotelism, Ureotelism and Uricotelism
19.2 - Excretory System of Man
19.3 - Skin and Lungs as Accessory Excretory Organs

Chapter 20


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