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MEDICAL PHYSIOLOGY RHOADES TANNER - PART 6

Tham khảo tài liệu 'medical physiology rhoades tanner - part 6', y tế - sức khoẻ, y học thường thức phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 23 Kidney Function 381 .Histological appearance of the juxtaglomerular apparatus. A cross section through a thick ascending limb is on top and part of a glomerulus is below. The juxtaglomerular apparatus consists of the macula densa extraglomerular mesangial cells and granular cells. From Taugner R Hackenthal E. The Juxtaglomerular Apparatus Structure and Function. Berlin Springer 1989. FIGURE 23.4 prised of the macula densa extraglomerular mesangial cells and granular cells Fig. 23.4 . The macula densa dense spot consists of densely crowded tubular epithelial cells on the side of the thick ascending limb that faces the glomerular tuft these cells monitor the composition of the fluid in the tubule lumen at this point. The extraglomerular mesangial cells are continuous with mesangial cells of the glomerulus they may transmit information from macula densa cells to the granular cells. The granular cells are modified vascular smooth muscle cells with an epithelioid appearance located mainly in the afferent arterioles close to the glomerulus. These cells synthesize and release renin a proteolytic enzyme that results in angiotensin formation see Chapter 24 . AN OVERVIEW OF KIDNEY FUNCTION Three processes are involved in forming urine glomerular filtration tubular reabsorption and tubular secretion Fig. 23.5 . Glomerular filtration involves the ultrafiltration of plasma in the glomerulus. The filtrate collects in the urinary Kidney tubule I Filtration Reabsorption I Glomerulus FIGURE 23.5 I Secretion i I Excretion Peritubular capillary Processes involved in urine formation. This highly simplified drawing shows a nephron and its associated blood vessels. space of Bowman s capsule and then flows downstream through the tubule lumen where its composition and volume are altered by tubular activity. Tubular reabsorption involves the transport of substances out of tubular urine these substances are then returned to the capillary blood which surrounds the kidney tubules.