Location: Retroperitoneal, posterior abdominal wall, level of T12-L3.
The right kidney is lower than the left kidney.
Shape: Bean-shaped.
3 coverings – perirenal fat, renal fascia and pararenal fat.
2 surfaces – anterior and posterior
2 poles – superior and inferior
2 borders – lateral (convex) and medial (concave)
Hilum: located in the centre of medial margin
renal veins
renal artery
ureter
Supplied by renal artery
Drained by renal vein
Normally, the kidneys are not palpable (not ballotable) on abdominal examination.
Internal Anatomy
Surrounded by dense irregular connective tissue capsule.
Consist of outer cortex and inner medulla.
Medulla contains cone-shaped renal pyramids. The base forms the cortico-medullary junction. The apex form renal papilla.
Renal papilla surrounded by minor calyx→major calyx→renal pelvis.
Renal column are extension of cortex.
Nephron
Nephron = renal corpuscle + renal tubules.
Types of nephrons:
Corticol nephrons (in the cortex).
Juxtamedullary nephrons (at the corticomedullary junction).
Renal corpuscle
The initial segment of each nephron. Function as the filtration unit of blood.
Consist of a tuft of capillaries (glomerulus).
Glomerulus
Endothelium is porous (fenestrated) and highly permeable (except blood cells and protein).
Surrounded by a double layer of epithelial cells (Bowman’s capsule).
Bowman’s capsule
The visceral layer – modified epithelial cells, forms finger-like projection (podocytes).
The parietal layer – simple squamous epithelium.
Consist of vascular pole (afferent enters) and urinary pole (filtrate exit).
Filtration unit
Podocytes
Podocyte - a highly differentiated epithelial cell located on the outside of the glomerular capillary loop.
Functions as structural support of the capillary loop, is a major component of the glomerular filtration barrier to proteins, and is involved in synthesis and repair of the glomerular basement membrane.
Foot processes
The extensions of the podocyte that terminate on the glomerular basement membrane.
Foot processes of a podocyte interdigitate with those from adjacent podocytes and are connected by a slit called the slit diaphragm.
Slit diaphragm
Slit diaphragm is one of the major impediments to protein permeability across the glomerular capillary wall.
Slit diaphragms are not simple passive filters; they consist of numerous proteins that contribute to complex signaling pathways and play an important role in podocyte function.
Important component proteins of the slit diaphragm include nephrin, podocin, CD2AP, and α-actinin 4.