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24 Cards in this Set

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number of nephrones

Healthy kidneys contain approximately 1 million indi­
vidual nephrons.

Nephrone parts

Each nephron consists of a glomerulus,
, a proxi­
mal renal tubule, a loop of Henle, a distal renal tubule
and a collecting duct,

Func of nephrone

which is responsible for ultrafiltration of blood

func of tub str

which together are responsible for
selective reabsorption of water and electrolytes that
have been filtered at the glomerulus (see Fig. 16.2,
p. 430).

fate of most of glum filtrate

Under normal circumstances, more than 99% of
the 170 litres of glomerular filtrate that is produced each
day is reabsorbed in the tubules.

amt of glum filt/day

Remainder fluid fate

The remainder passes through the collecting ducts of multiple nephrons and
drains into the renal pelvis and ureters

Glomerulus?

The glomerulus comprises a tightly packed loop of capil­
laries supplied by an afferent arteriole and drained by
an efferent arteriole. .

Bowman's cap?


Hist?

It is surrounded by a cup­shaped
extension of the proximal tubule termed Bowman’s
capsule, which is comprised of epithelial cells

Func of glom?


wht is GBM?

Blood
that enters the glomerulus undergoes ultrafiltration
across the glomerular basement membrane (GBM),
(Fig.
17.1C and D)

which is formed by fusion of the basement membranes
of tubular epithelial and vascular endothelial cells

How circ molec pass to GBM

The glomerular capillary endothelial
cells contain pores (fenestrae), through which circulat­ing molecules can pass to reach the underlying GBM.
(Fig. 17.1E).

Fenestrae

Glom epith cell also called?

Glomerular epithelial cells (podocytes) have multiple
long foot processes which interdigitate with those of the
adjacent epithelial cells

digitation

Func of podocytes?

As well as maintain­
ing a selective barrier to filtration, podocytes are involved
in regulating turnover of the GBM

Loc of mesangial cells

. Mesangial cells lie in
the central region of the glomerulus. They have contrac­tile properties similar to those of vascular smooth muscle
cells but also have macrophage­like properties.

property

Protein size permeable

Under normal circumstances, the glomerulus is
impermeable to proteins the size of albumin (67 kDa) or
larger, while proteins of 20 kDa or smaller are filtered
freely. .

b/w 20 -67kDA


dep upon?

The ability of molecules between 20 and 67 kDa
to pass through the GBM is variable and depends on the
size (smaller molecules are filtered more easily) and
charge (positively charged molecules are filtered more
easily)

Lipid filteration

Very little lipid is filtered by the glomerulus

Autoregulation of BP in Glom?

Filtration pressure at the glomerulus is normally
maintained at a constant level, in the face of wide vari­ations in systemic blood pressure and cardiac output, by
alterations in muscle tone within the afferent and effer­
ent arterioles. This is known as autoregulation. .

When is Renin Secreted?


wht it cleaves?


to release?


cleaved by?


to prd?

When there is a reduction in renal perfusion pressure, renin is released by specialised smooth muscle cells in the juxta­glomerular apparatus. Renin cleaves angiotensinogen
to release angiotensin I, which is further cleaved by
angiotensin­converting enzyme (ACE) to produce angi­otensin II
(Fig. 17.1D)

Short term rest of glom perf pressure

This restores glomerular perfusion pressure in the short term by causing vasoconstriction
of the efferent arterioles within the kidney and by induc­
ing systemic vasoconstriction to increase blood pressure
and thus renal perfusion pressure.

long term

In the longer term,
angiotensin II increases plasma volume by stimulating
aldosterone release, which enhances sodium reabsorp­
tion by the renal tubules

Histology of a normal glomerulus

 Histology of a normal glomerulus

Histology of a normal glomerulus

Schematic cross-section of a glomerulus, showing five
capillary loops, to illustrate structure and show cell types

Electron micrograph of the filtration barrier. (GBM =glomerular basement membrane