The vasa recta of the kidney, (vasa recta renis) are the straight arterioles, and the straight venules of the
kidney
In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...
, – a series of
blood vessel
Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...
s in the
blood supply of the kidney that enter the
medulla as the straight arterioles, and leave the medulla to ascend to the cortex as the straight venules. (
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
: ''vās'', "vessel"; ''rēctus'', "straight"). They lie parallel to the
loop of Henle.
These vessels branch off the
efferent arterioles of
juxtamedullary nephrons (those
nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structu ...
s closest to the medulla). They enter the medulla, and surround the loop of Henle. Whereas the
peritubular capillaries surround the cortical parts of the tubules, the vasa recta go into the medulla and are closer to the loop of Henle,
and leave to ascend to the cortex.
Terminations of the vasa recta form the straight venules, branches from the plexuses at the apices of the
medullary pyramids. They run outward in a straight course between the tubes of the medullary substance and join the
interlobular veins to form venous arcades. These in turn unite and form veins which pass along the sides of the renal pyramids. The descending vasa recta have a non-fenestrated endothelium that contains a facilitated transport for urea; the ascending vasa recta have, on the other hand, a fenestrated endothelium.
Structure
Microanatomy
On a histological slide, the straight arterioles can be distinguished from the tubules of the
loop of Henle by the presence of blood.
Function
Each straight arteriole has a hairpin turn in the medulla and carries blood at a very slow rate – two factors crucial in the maintenance of
countercurrent exchange
Countercurrent exchange is a mechanism between two flowing bodies flowing in opposite directions to each other, in which there is a transfer of some property, usually heat or some chemical. The flowing bodies can be liquids, gases, or even solid ...
that prevent washout of the concentration gradients established in the renal medulla.
The maintenance of this concentration gradient is one of the components responsible for the kidney's ability to produce concentrated
urine
Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...
.
On the descending portion of the vasa recta, sodium, chloride and urea are reabsorbed into the blood, while water is secreted. On the ascending portion, sodium chloride and urea are secreted into the interstitium, while water is reabsorbed.
Clinical significance
The slow blood flow in the straight arterioles makes them a likely location of
thrombosis
Thrombosis () is the formation of a Thrombus, blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thrombocytes) and fib ...
from
thrombophilia
Thrombophilia (sometimes called hypercoagulability or a prothrombotic state) is an abnormality of blood coagulation that increases the risk of thrombosis (blood clots in blood vessels). Such abnormalities can be identified in 50% of people who ...
, or tissue loss
due to
red blood cell sickling in
sickle cell disease.
Ischemia
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
that results may lead to
renal papillary necrosis.
Nomenclature
According to
Terminologia Anatomica, the term "vasa recta renis" is an alternate name for "arteriolae rectae renis", and a separate term, venulae rectae renis, is used to identify the venous portion.
However, other sources consider "vasa recta" to refer to both the arterial and venous portions.
The term ''vasa recta'' is also used for the intestines –
vasa recta (intestines) (in the
ileum
The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...
and
jejunum
The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been pr ...
)
References
External links
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Kidney anatomy