Afferent arterioles
Encyclopedia
The afferent arterioles are a group of blood vessel
s that supply the nephron
s in many excretory systems
. They play an important role in the regulation of blood pressure
as a part of the Tubuloglomerular feedback mechanism.
The afferent arterioles branch from the renal artery
, which supplies blood to the kidney
s.
The afferent arterioles later diverge into the capillaries
of the glomerulus.
) or there is a decrease in sodium and chloride ion concentration, the macula densa
of the distal tubule releases prostaglandins, which cause the juxtaglomerular cells lining the afferent arterioles to release renin
, activating the renin-angiotensin-aldosterone system, to increase blood pressure and increase retention of sodium ions via aldosterone
.
The macula densa cell can also increase the local blood pressure of the afferent arterioles by increasing the synthesis of nitrous oxide
or decreasing the synthesis of adenosine or ATP
.
If the afferent arterioles are constricted then the blood pressure in the capillaries of the kidneys will drop.
They consist of blood plasma.
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s that supply the nephron
Nephron
The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron....
s in many excretory systems
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...
. They play an important role in the regulation of blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
as a part of the Tubuloglomerular feedback mechanism.
The afferent arterioles branch from the renal artery
Renal artery
The renal arteries normally arise off the side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle with the aorta....
, which supplies blood to the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
s.
The afferent arterioles later diverge into the capillaries
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
of the glomerulus.
Regulation
When renal blood flow is reduced (indicating hypotensionHypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
) or there is a decrease in sodium and chloride ion concentration, the macula densa
Macula densa
In the kidney, the macula densa is an area of closely packed specialized cells lining the wall of the distal tubule at the point of return of the nephron to the vascular pole of its parent glomerulus, ....
of the distal tubule releases prostaglandins, which cause the juxtaglomerular cells lining the afferent arterioles to release renin
Renin
Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...
, activating the renin-angiotensin-aldosterone system, to increase blood pressure and increase retention of sodium ions via aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
.
The macula densa cell can also increase the local blood pressure of the afferent arterioles by increasing the synthesis of nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
or decreasing the synthesis of adenosine or ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
.
If the afferent arterioles are constricted then the blood pressure in the capillaries of the kidneys will drop.
They consist of blood plasma.