KIDNEYS AND HOMEOSTASIS
LECTURE SUMMARY
Saskia Cornet
BIOMEDICAL SCIENCES, YEAR 2 LUMC
,Kidney anatomy
General kidney knowledge
The general exocrine functions of the kidney are the conservation of fluid and electrolytes and the
removal of metabolic waste. It regulates the water- and electrolyte balance, tissue osmolarity, blood
pressure and acid balance of the body.
Furthermore, the kidney also has important endocrine functions including the synthesis and
secretion of erythropoietin, which stimulates erythrocyte production in the bone marrow, Renin,
which regulates blood pressure, and it activates Vitamin D, which is of importance in the calcium
metabolism.
The kidneys are located retroperitoneally high in the abdomen in a very posterior position, where
they are protected by the thoracic cage. The kidneys are surrounded by layers of fat known as the
Para- and Perinephric fat. The perinephric fat is located directly on the kidney, consisting of
structural fat meant to keep the kidney in place, while the paranephric fat is general fat located
retroperitoneally near the kidney. The two layers are divided by a connective tissue layer called the
Renal fascia.
The kidneys are supplied of blood by the left- and right renal arteries. The deoxygenated blood is
taken away from the kidneys via the left- and right renal vein. Important to note is that the left renal
vein is longer than the right one since it is further removed from the vena cava, and that the left
suprarenal vein and gonadal veins end in it. It is also located between the aorta and the superior
mesenteric artery, making it prone to blockage if either of those experience and aneurism (renal
entrapment syndrome).
Macroscopic anatomy
The kidney is a multi-lobular, bean shaped organ which is concaved medially, where
the renal hilum is also located. The renal hilum is the entrance to the kidney, where
the blood vessels and the renal pelvis can enter and exit the organ. The renal pelvis
, is located posteriorly. The adrenal gland is located on top of the kidney, separated by the perinephric
fat.
The kidney tissue is surrounded by a fibrous capsule made up of a fibroblast and myofibroblast layer,
which aids in resisting volume and pressure variations.
Cortex and medulla
The kidney tissue can be divided into the cortex (outer part) and the medulla (inner part). In between
the medullary pyramids as the madulla is also called, prodjections of cortex are located, called the
renal column (considdered medulla in ross, but is cortex).
Located in the cortex are the renal corpuscles. These can also be
found in the renal columns, but not in medulla.
Medullary pyramids have a base and an apex, which is called the
renal papilla and ends in a renal calyx which combines with other
calyxes to form the renal pelvis which connects to the ureter.
Small stripes of medulla known as medullary ray's project into the
cortex. The cortical tissue surrounding these rays forms the cortical
labyrinth. The combination of a ray and labyrinth is known as a
lobule.
Renal sinus
The renal sinus is a space within the kidney outside the medulla and cortex. It contains the renal
calyces, renal pelvis and the blood vessels, lymphatic vessels and innervation, as well as inwardly
protruding perinephric fat.
Blood supply and drainage
Blood enters via the renal artery, which then splits into 5 segmental arteries. Each of these feeds
their own segment, splitting into interlobar arteries, which, in the cortex, give rise to arcuate
arteries located at the base of the medullary pyramids. From these, small interlobular arteries
extend into the cortex. In the end 95% of the renal blood supply is in the cortex and only 5% is in the
medulla.
In a pyramidal fashion, the veins of the kidney start in the cortex with the interlobular veins, then the
arcuate veins, the interlobar veins and the segmental veins, ending in the renal vein, which finally
empties in the vena cava inferior.
Vasa recta supply the loops of Henle of the juxtamedullary nephrons with
blood and can therefore be found in medullary pyramids. They have special
properties in that their endothelial cells are fenestrated so water and ions can
pass according to the osmotic gradient, which it also helps maintain it.
Segmentation
The presence of segments should be remembered. However, the names of
each segment are not of importance.
