Page 1019 - Fundamentals of anatomy physiology

1006 Unit 5 Environmental Exchange

Table 26–1 The Organization of the Nephron and Collecting System

Region Histological Characteristics Length Diameter Primary Function

Nephron
Glomerulus (capillary knot), mesangial 150–250 m 150–250 m Filtration of blood plasma
Renal corpuscle cells, and dense layer, enclosed by the (spherical)
glomerular capsule; visceral epithelium
Capsular (podocytes) and capsular epithelium
space separated by capsular space

Capsular
epithelium

Capillaries
of glomerulus

Visceral
epithelium

Renal tubule
Proximal convoluted Cuboidal cells with microvilli 14 mm 60 m Reabsorption of ions, organic
tubule (PCT) molecules, vitamins, water;
secretion of drugs, toxins, acids

Microvilli

Nephron loop Squamous or low cuboidal cells 30 mm
15 m Descending limb: reabsorption
30 m of water from tubular fluid
Ascending limb: reabsorption
30–50 m of ions; assists in creation of a
Distal convoluted tubule (DCT) Cuboidal cells with few if any microvilli 5 mm concentration gradient in the
medulla

Reabsorption of sodium ions and
calcium ions; secretion of acids,
ammonia, drugs, toxins

Collecting System
Collecting duct Cuboidal cells 15 mm 50–100 m Reabsorption of water, sodium
Intercalated ions; secretion or reabsorption of
Columnar cells 5 mm bicarbonate ions or hydrogen ions
cell

26 Principal 100–200 m Conduction of tubular fluid
cell to minor calyx; contributes to
concentration gradient of the
Papillary duct medulla

&T i p s T r i c k s Each nephron empties into the collecting system, a ser­
In the nephron, the terms proximal tubule and distal tubule ies of tubes that carry tubular fluid away from the nephron.
refer to how far along the renal tubule these structures are C­ ollecting ducts receive this fluid from many nephrons. Each col-
situated from the renal corpuscle. Think of proximal (nearer lecting duct begins in the cortex and descends into the medulla,
the renal corpuscle) as being first, and distal (farther from the carrying fluid to a papillary duct that drains into a minor calyx.
renal corpuscle) as being last.
Nephrons from different locations within a kidney differ
slightly in structure. Approximately 85 percent of all nephrons