Related Subjects:
|Metabolic acidosis
|Lactic acidosis
|Acute Kidney Injury (AKI) / Acute Renal Failure
|Renal/Kidney Physiology
|Chronic Kidney Disease (CKD)
|Anaemia in Chronic Kidney Disease
|Analgesic Nephropathy
|Medullary Sponge kidney
|IgA Nephropathy (Berger's disease)
|HIV associated nephropathy (HIVAN)
Overview of Renal Anatomy
The kidneys are a pair of bean-shaped organs located in the retroperitoneal space on either side of the spine. They play a crucial role in filtering blood, removing waste products, regulating electrolyte balance, and maintaining fluid homeostasis. Each kidney is approximately 10-12 cm in length, 5-7 cm in width, and 3 cm in thickness.
Gross Anatomy of the Kidneys
- External Structure:
- Hilum:
- Located on the medial concave surface of the kidney.
- Entry and exit point for the renal artery, renal vein, ureter, lymphatics, and nerves.
- Capsule:
- A fibrous capsule surrounds each kidney, providing protection and structural support.
- Internal Structure:
- Cortex:
- Outer region of the kidney, containing the renal corpuscles and the proximal and distal convoluted tubules.
- Medulla:
- Inner region composed of 8-18 renal pyramids, which contain the loops of Henle and collecting ducts.
- The base of each pyramid faces the cortex, while the apex (renal papilla) points towards the renal pelvis.
- Renal Pelvis:
- Funnel-shaped structure that collects urine from the renal papillae and channels it into the ureter.
- Divided into major and minor calyces that drain urine from the renal pyramids.
Nephron: Functional Unit of the Kidney
- Each kidney contains approximately 1-1.5 million nephrons.
- Renal Corpuscle:
- Comprised of the glomerulus (a network of capillaries) and Bowman's capsule.
- Responsible for the initial filtration of blood plasma.
- Renal Tubule:
- Proximal Convoluted Tubule (PCT): Reabsorbs water, ions, and nutrients from the filtrate.
- Loop of Henle: Establishes a concentration gradient in the medulla, essential for water reabsorption.
- Descending Limb: Permeable to water but not to solutes.
- Ascending Limb: Impermeable to water, actively transports sodium and chloride ions.
- Distal Convoluted Tubule (DCT): Further regulates electrolyte balance and pH.
- Collecting Duct: Receives urine from multiple nephrons, final site for water and electrolyte reabsorption.
Vascular Supply of the Kidneys
- Renal Arteries:
- Each kidney is supplied by a renal artery, which arises from the abdominal aorta.
- Renal arteries branch into segmental arteries, interlobar arteries, arcuate arteries, and interlobular arteries.
- Afferent Arterioles:
- Branch from the interlobular arteries and supply blood to the glomerulus.
- Glomerulus:
- A network of capillaries where filtration of blood occurs.
- Efferent Arterioles:
- Carry blood away from the glomerulus.
- Further divide into peritubular capillaries and vasa recta that supply the renal tubules and medulla.
- Renal Veins:
- Blood from the peritubular capillaries and vasa recta drains into interlobular veins, arcuate veins, and interlobar veins, eventually merging into the renal vein.
- Renal veins exit the kidney and drain into the inferior vena cava.
Neural Supply of the Kidneys
- Sympathetic Innervation:
- Provided by the renal plexus, which originates from the celiac plexus and thoracic splanchnic nerves.
- Sympathetic nerves regulate renal blood flow, glomerular filtration rate, and release of renin by the juxtaglomerular apparatus.
- Parasympathetic Innervation:
- Supplied by the vagus nerve (cranial nerve X), though its role in renal function is less significant compared to sympathetic innervation.
- Renal Sensory Innervation:
- Sensory fibers travel with sympathetic nerves and relay information about renal function and pain to the central nervous system.
Summary
The kidneys are vital organs with a complex structure that enables them to filter blood, regulate electrolyte balance, and maintain fluid homeostasis. Their anatomy includes the cortex, medulla, and renal pelvis, with the nephron being the functional unit. The kidneys receive a rich blood supply from the renal arteries, and their function is modulated by sympathetic and parasympathetic innervation. Understanding renal anatomy and its vascular and neural supply is essential for comprehending the physiological processes and clinical conditions related to kidney function.