Difference Between PCT and DCT

Main Difference – PCT vs DCT

Renal corpuscle and renal tubule are the two structural components of a nephron. Renal corpuscle is continuous with the renal tubule. Renal corpuscle comprises glomerulus and Bowman’s capsule. Renal tubule comprises proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting duct. Both PCT and DCT occur in the renal cortex. Reabsorption and secretion are the functions of both PCT and DCT. The main difference between PCT and DCT is that PCT is mainly involved in the reabsorption whereas DCT is mainly involved in secretion. 66% of water, glucose, amino acids, and the electrolytes such as sodium, chloride, potassium, and calcium are reabsorbed in the PCT while urea, uric acid, creatinine, sodium, potassium, and hydrogen ions are secreted into the filtrate in the DCT.

Key Areas Covered

1. What is PCT
      – Definition, Reabsorption, Secretion
2. What is DCT
      – Definition, Reabsorption, Secretion
3. What are the Similarities Between PCT and DCT
      – Outline of Common Features
4. What is the Difference Between PCT and DCT
      – Comparison of Key Differences

Key Terms: Distal Convoluted Tubule (DCT), Proximal Convoluted Tubule (PCT), Reabsorption, Renal Corpuscle, Renal Tubule, Secretion

What is PCT

Proximal convoluted tubule (PCT) refers to the convoluted portion of the nephron between Bowman’s capsule and the loop of Henle. PCT is the site in which most (65%) of the reabsorption of water and electrolytes occurs. The lumen of the PCT is made up of simple cuboidal epithelium. The microvilli present in the epithelium increases the surface area of the lumen, increasing the reabsorption. The components of a nephron are shown in figure 1.

Figure 1: Components of a Nephron

The reabsorption of most of the important molecules such as glucose, amino acids, lactate, citrate, and phosphate ions occurs in the early PCT. This occurs through the sodium co-transporters in the epithelial cells of the PCT. Since negative ions such as bicarbonates are reabsorbed in the early PCT, chloride ions are concentrated in the filtrate. The reabsorption of chloride ions occurs in the late PCT. The movement of chloride ions either occurs through the chloride/formate ion exchangers or the passive movement of ions through the epithelial surface.

Ultimately, 66% of water, 100% of glucose and amino acids, 65% of potassium ions, 50% of urea, and 85% of phosphate ions are reabsorbed in the PCT. Hydrogen, ammonia, urea, uric acid, creatinine, and some organic substances such as antibiotics, diuretics, and hormones are secreted into the filtrate at the PCT as well.

What is DCT

Distal convoluted tubule (DCT) refers to the convoluted portion of the nephron between the loop of Henle and the collecting duct. The epithelial cells of the DCT are smaller and more lightly stained. Though the lumen of the DCT is lined by the simple cuboidal epithelium, this epithelium lacks microvilli. Secretion is the main function of the DCT. However, some of the molecules are reabsorbed from the filtrate in the DCT as well. The reabsorption and secretion of molecules in each part of the nephron is shown in figure 2.

Figure 2: Reabsorption and Secretion in the Nephron

5% of the sodium ions are reabsorbed in the early DCT while the remaining 3% of the sodium ions are reabsorbed in the late DCT. The reabsorption of sodium in the DCT is regulated by the hormone aldosterone. Calcium and chloride reabsorption occurs through the sodium/potassium pump. The reabsorption of calcium ions is regulated by the parathyroid hormones. In both PCT and DCT, the secretion of hydrogen ions while reabsorbing the bicarbonate ions helps the regulation of pH in the body. Potassium ions and some urea can also be secreted to the filtrate at the DCT.

Similarities Between PCT and DCT

Both PCT and DCT are two components of the renal tubule of the kidney.
Both PCT and DCT occur in the renal cortex.
The lumen of both PCT and DCT are lined by the simple cuboidal epithelium.
Both PCT and DCT are involved in the reabsorption and secretion.
Secondary active transport is involved in reabsorption and secretion in both PCT and DCT.
Both PCT and DCT exchange hydrogen ions and bicarbonate ions, regulating the pH of blood.
The action of both PCT and DCT is responsible for the production of urine from the filtered blood plasma.

Definition

PCT: Proximal convoluted tubule (PCT) refers to the convoluted portion of the nephron between Bowman’s capsule and the loop of Henle.

DCT: Distal convoluted tubule (DCT) refers to the convoluted portion of the nephron between the loop of Henle and the collecting duct.

Start

PCT: PCT starts from the Bowman’s capsule.

DCT: DCT starts from the loop of Henle.

Continuance

PCT: PCT is continuous with the loop of Henle.

DCT: DCT is continuous with the collecting duct.

Epithelium

PCT: The lumen of the PCT is made up of simple cuboidal epithelium with microvilli.

DCT: The lumen of the DCT is made up of simple cuboidal epithelium without microvilli.

Acidity/Basicity

PCT: PCT is more acidophilic.

DCT: DCT is less acidophilic.

Microscopic Examination of the Lumen

PCT: The boundaries and the lumen of the PCT are clearly visible.

DCT: The boundaries and the lumen of the DCT are less visible.

Cytoplasm of the Epithelial Cells

PCT: The epithelial cells of the PCT consist of more cytoplasm.

DCT: The epithelial cells of the DCT consist of less cytoplasm.

Readily Discernible Nucleus

PCT: The epithelial cells of the PCT do not have a readily discernible nucleus.

DCT: The epithelial cells of the DCT have a readily discernible nucleus.

Length

PCT: PCT is long.

DCT: DCT is shorter than the PCT.

Convolution

PCT: PCT is more convoluted.

DCT: DCT is less convoluted than the PCT.

Similar Structures

PCT: PCT is similar to the descending limb of the loop of Henle.

DCT: DCT is similar to the ascending limb of the loop of Henle.

Main Function

PCT: The main function of the PCT is reabsorption.

DCT: The main function of the DCT is secretion.

Reabsorption

PCT: PCT reabsorbs 66% of water, glucose, amino acids, and electrolytes such as sodium, chloride, potassium, and calcium.

DCT: DCT reabsorbs water and electrolytes such as sodium, calcium, and chloride.

Secretion

PCT: Uric acid, creatinine, antibiotics, and diuretics are secreted into the PCT.

DCT: Ammonia, hydrogen, and potassium ions are secreted into the DCT.

Conclusion

PCT and DCT are the two convoluted parts of a nephron found in the renal cortex. PCT occurs after the Bowman’s capsule while DCT occurs after the loop of Henle. PCT is mainly involved in the reabsorption whereas secretion occurs in the DCT. The main difference between PCT and DCT is that PCT is the function of each part in the nephron.

Reference:

1.“Tubular reabsorption article.” Khan Academy, Available here.
2.“Reabsorption and Secretion Along the Proximal Tubule – Anatomy & Physiology.” WikiVet English, Available here.
3.“Reabsorption and Secretion Along the Distal Tubule and Collecting Duct – Anatomy & Physiology.” WikiVet English, Available here.

Image Courtesy:

1. “Anatomy and physiology of animals Kidney tubule or nephron” – original uploader was Sunshineconnelly at English Wikibooks – Transferred from en.wikibooks to Commons by Adrignola using CommonsHelper (CC BY 3.0) via Commons Wikimedia
2. “Renal Diuretics” By Haisook at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia