Exam 4 Review:  Chapter 25:  The Nephron I - Renal Corpuscle

 

PCT = Proximal Convoluted Tubule, the exit point for plasma filtrate leaving the capsular space;  the "urinary pole" indicates the end of the renal corpuscle from which the plasma filtrate will exit

BC = (Bowman's) Capsule, the parietal layer of simple squamous cells lining the renal corpuscle

Glomerulus = the tuft of fenestrated capillaries from which the plasma filtrate will be extracted

BS = (Bowman's) capsular Space which receives the plasma filtrate from the glomerulus

Pd = Podocytes, the visceral layer of specialized epithelial cells, which line the glomerular capillary tuft

MD = Macula Densa cells, a part of the JuxtaGlomerular Apparatus

JGC = JuxtaGlomerular Cells, a part of the JuxtaGlomerular Apparatus

Aff Art = Afferent Arteriole, the blood vessel delivering arterial blood under high pressure into the glomerular capillaries so that filtration will occur to produce the plasma filtrate which will be modified and processed by the renal tubular cells to form the urine

renal corpuscle - The first portion of the nephron of the kidney which consists of a tuft of arterial (high pressure) fenestrated capillaries covered by a layer of specialized epithelial cells (the visceral layer), the podocytes, and contained within a small capsular space defined by a glomerular capsule lined by squamous epithelial cells (the parietal layer); it is here that blood is filtered to create a plasma filtrate to be modified and processed by the renal tubule cells.

glomerular capsule - The double-walled endothelial cup which surrounds the glomerulus in the renal corpuscle of the nephron of the kidney; it consists of epithelial cells, the outer or parietal layer which forms the wall of the capsule is composed of a simple squamous lining, while the inner or visceral layer is composed of a simple layer of highly specialized cells, the podocytes, which have cytoplasmic processes which adhere to the capillary wall of the glomerulus to assist in filtration of the blood passing through the glomerulus; the two layers are separated by a small capsular space which receives the plasma filtrate which is drawn from the blood.

capsular space - The small space, located between the visceral and parietal layers of the glomerular capsule, which receives the plasma filtrate which is drawn from the blood in the glomerulus within the renal corpuscle of the nephron of the kidney; the filtrate will leave this space to enter the lumen of the proximal convoluted tubule.

endothelial capsular membrane = filtration membrane - The series of layers which collectively determine the pore size through which water and small dissolved solutes exit the blood plasma to become the plasma filtrate in the renal corpuscle of the nephron of the kidney; it consists of four layers:  (1)  the inner layer of fenestrated capillary endothelial cells which forms the walls of the glomerulus, (2) the external protein meshwork of the capillary basement membrane, (3) the external protein meshwork of the podocyte's (the visceral layer of the glomerular capsule) basement membrane, and (4) the outer layer of podocyte's (the visceral layer of the glomerular capsule) which is interrupted by filtration slits between the cytoplasmic processes (pedicels) of the podocytes.

fenestrations - The large series of small openings in the walls of fenestrated capillary endothelial  cells through which water and small dissolved solutes pass to enter the endothelial capsular membrane of glomerulus, and, ultimately into the capsular space, in the renal corpuscle of the nephron of the kidney; these openings are sometimes covered by a compressed layer of capillary cell membrane; these openings are large enough to let water, electrolytes, small organic molecules, and the smallest proteins, e.g., albumin (MW ~65,000 Daltons) pass, but prevent the passage of larger proteins and the formed elements of the blood.

podocytes - The highly specialized cells of the visceral layer of the glomerular capsule of the renal corpuscle of the nephron of the kidney; they have cytoplasmic processes which surround the fenestrated capillary endothelial cells of the glomerulus; the bulk of each cell is not in direct contact with the fenestrated capillary endothelial cells, but small cytoplasmic extensions, pedicels, which interdigitate with similar processes on adjacent podocytes, make contact with the fenestrated capillary endothelial cells; between these small cytoplasmic extensions, the pedicels, are the filtration slits through which water and small dissolved solutes pass to enter the capsular space within the renal corpuscle.

Scanning Electron Micrograph of a Podocyte wrapping around a glomerular capillary

pedicels - The small cytoplasmic extensions of the podocytes (the highly specialized cells of the visceral layer of the glomerular capsule of the renal corpuscle of the nephron of the kidney), which interdigitate with similar processes on adjacent podocytes, and make the actual contact points with the fenestrated capillary endothelial cells; between these small cytoplasmic extensions are the filtration slits through which water and small dissolved solutes pass to enter the capsular space within the renal corpuscle.

filtration slits - The tiny spaces (~25 nm wide) between the pedicels (the small cytoplasmic extensions of the podocytes, the highly specialized cells of the visceral layer of the glomerular capsule of the renal corpuscle of the nephron of the kidney) through which water and small dissolved solutes pass to enter the capsular space and form the plasma filtrate; the dimensions of the slits and the presence of a molecular covering, the slit membrane, assist in resisting the passage of larger proteins and formed elements from the blood into the plasma filtrate within the renal corpuscle.

slit membrane - A special type of complex protein sheet-like covering for the filtration slits formed by the pedicels of adjacent podocytes (the highly specialized cells of the visceral layer of the glomerular capsule of the renal corpuscle of the nephron of the kidney) which acts as a shallow intercellular junction between the pedicels of the adjacent podocytes and assists in resisting the passage of larger proteins and formed elements from the blood into the plasma filtrate within the renal corpuscle.  aka - slit diaphragm (see below).

Sketch and label:

3. a simple sketch of the endothelial-capsular (i.e., filtration) membrane and label its structure. In particular, identify the features of the filtration membrane that retain some substances in the blood while allowing other substances to be filtered. Identify the substances that are retained in the blood versus those that enter the tubule.

Label:  fenestrated capillary endothelial cell, fenestration, basement membrane, foot process of podocyte, slit diaphragm,  filtration slit.
Identify the features of the filtration membrane that retain some substances in the blood while allowing other substances to be filtered:  fenestration, basement membrane, slit diaphragm.
Identify the substances that are retained in the blood:  the formed elements and most of the plasma proteins.
Identify the substances that enter the tubule:  water, electrolytes, all small to medium organic molecules (nutrients, regulatory substances, nitrogenous wastes, vitamins, etc.), and the smaller proteins, e.g., albumin at ~60,000 Daltons is size will be filtered.