14.1 Kidney Structure and Function

4 min read•august 28, 2024

The kidneys are amazing filtration machines in our bodies. They clean our blood, balance fluids, and make hormones. Without them, we'd be in big trouble. Let's dive into how these bean-shaped organs work their magic.

From their structure to their function, kidneys are complex yet efficient. We'll explore how they filter blood, make urine, and keep our bodies in balance. Understanding kidneys helps us grasp the whole urinary system's role in our health.

Kidney Anatomy and Spatial Relationships

Location and Gross Anatomy

Top images from around the web for Location and Gross Anatomy

  • File:Kidney Cross Section.png - Wikimedia Commons View original

    Is this image relevant?

  • Renal column - Wikipedia View original

    Is this image relevant?

  • File:Kidney Cross Section.png - Wikimedia Commons View original

    Is this image relevant?

1 of 3

Top images from around the web for Location and Gross Anatomy

  • File:Kidney Cross Section.png - Wikimedia Commons View original

    Is this image relevant?

  • Renal column - Wikipedia View original

    Is this image relevant?

  • File:Kidney Cross Section.png - Wikimedia Commons View original

    Is this image relevant?

1 of 3
  • The kidney is a bean-shaped organ located in the retroperitoneal space, typically with one on each side of the vertebral column at the level of T12 to L3
  • The renal hilum is a concave opening on the medial aspect of the kidney where the renal artery, renal vein, and ureter enter and exit the kidney
  • The renal capsule is a thin, fibrous layer that surrounds the outer surface of the kidney, providing protection and support

Internal Structures and Regions

  • The kidney is divided into two main regions: the outer renal cortex and the inner renal medulla. The renal medulla is further divided into multiple renal pyramids
  • The renal columns are extensions of the renal cortex that separate the renal pyramids
  • The renal pelvis is a funnel-shaped structure that collects urine from the renal pyramids and drains into the ureter
  • The renal papilla is the apex of each renal pyramid, where collecting ducts converge to form the minor and major calyces, which empty into the renal pelvis

Functional Units of the Kidney

Nephron Structure and Components

  • The nephron is the basic functional unit of the kidney, responsible for filtering blood and producing urine. Each kidney contains approximately 1 million nephrons
  • The nephron consists of the renal corpuscle and the renal tubule. The renal corpuscle is composed of the glomerulus and Bowman's capsule, while the renal tubule includes the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct
  • The glomerulus is a network of capillaries where blood is filtered, and the filtrate enters the Bowman's capsule. The filtration barrier consists of the fenestrated endothelium, basement membrane, and podocytes (specialized epithelial cells)

Tubular Functions in Urine Formation

  • The proximal convoluted tubule reabsorbs essential nutrients (glucose, amino acids), ions (sodium, chloride, bicarbonate), and water from the filtrate, while also secreting waste products and toxins (urea, creatinine, drugs)
  • The loop of Henle, particularly the ascending limb, is responsible for creating the medullary osmotic gradient necessary for concentrating urine. It also reabsorbs ions (sodium, chloride, potassium) and water
  • The distal convoluted tubule fine-tunes the composition of the filtrate by selectively reabsorbing or secreting ions (sodium, chloride, calcium, magnesium) and responds to hormonal signals (aldosterone, parathyroid hormone)
  • The collecting duct system is the final site of urine modification, where water reabsorption occurs under the influence of antidiuretic hormone (ADH), and urine is concentrated

Blood Supply and Innervation of the Kidney

Renal Vasculature

  • The renal artery, a branch of the abdominal aorta, supplies oxygenated blood to the kidney. It divides into segmental arteries, which further branch into interlobar, arcuate, and interlobular arteries
  • The afferent arterioles arise from the interlobular arteries and supply blood to the glomeruli. The efferent arterioles emerge from the glomeruli and form the peritubular capillaries, which surround the renal tubules
  • The renal vein drains deoxygenated blood from the kidney and empties into the inferior vena cava. The venous system follows a similar pattern to the arterial system, with interlobular, arcuate, and interlobar veins

Renal Innervation and Juxtaglomerular Apparatus

  • The kidney receives innervation from the renal plexus, which consists of both sympathetic and parasympathetic nerve fibers. Sympathetic innervation plays a role in regulating renal blood flow and renin secretion
  • The juxtaglomerular apparatus (JGA) is a specialized structure located at the junction of the afferent arteriole and distal convoluted tubule. It consists of the macula densa cells (specialized tubular cells) and juxtaglomerular cells (modified smooth muscle cells), which are involved in the regulation of renal blood flow and renin secretion

Endocrine Functions of the Kidney

Hormones Produced by the Kidney

  • Renin is an enzyme produced by the juxtaglomerular cells in response to decreased renal blood flow, decreased sodium delivery to the distal tubule, or sympathetic stimulation. Renin initiates the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and sodium balance
  • Erythropoietin (EPO) is a hormone produced by the peritubular cells in the kidney in response to hypoxia. EPO stimulates red blood cell production in the bone marrow, increasing the oxygen-carrying capacity of the blood
  • The kidney also produces prostaglandins, such as prostaglandin E2 and prostacyclin, which have vasodilatory effects and help maintain renal blood flow

Activation and Regulation of Hormones

  • The kidney is involved in the activation of vitamin D. The proximal tubule cells convert 25-hydroxyvitamin D to the active form, 1,25-dihydroxyvitamin D (calcitriol), which regulates calcium and phosphate homeostasis
  • Kallikrein is an enzyme produced by the distal tubule cells that participate in the kinin-kallikrein system, which has vasodilatory and natriuretic effects (increased sodium excretion), contributing to blood pressure regulation
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Back
Glossary
Glossary
Next guide