Question

The dotted appearance of cortex of kidney is due to (a) ducts of Bellini (b) convoluted parts (c) loop of Henle (d) collecting tubes.

Short answer

The dotted appearance of the cortex of the kidney is due to the ducts of Bellini (option a).

Step-by-step solution

Understand the Structure of the Kidney

The human kidney is made up of roughly 1 million filtering units called nephrons. Each nephron consists of a renal corpuscle and a renal tubule, which includes the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and connecting tubules leading to the collecting ducts.

Identify the Structure Responsible for the Dotted Appearance

The dotted or granular appearance of the kidney cortex is attributed to the presence of numerous structures within it. Understanding the basic anatomy, we can utilize elimination to determine which structures could be responsible. Ducts of Bellini, also known as papillary ducts, are the terminal parts of the collecting ducts and discharge urine into the minor calyces of the renal pelvis.

Determine the Correct Option

Option (a), ducts of Bellini, is correct. These ducts are located in the medulla but project into the cortex where they join with the renal corpuscles, giving the cortex its dotted appearance when observed in cross-section.

Key concepts

Nephron Structure

The human kidney is an intricate organ performing vital functions, including waste removal and blood filtration. To understand how the kidney achieves these tasks, it is essential to comprehend the structure of a nephron, the kidney's fundamental functional unit. Each kidney contains about 1 million nephrons working in concert.

A nephron is composed of two main parts: the renal corpuscle and the renal tubule. The renal corpuscle is the initial filtering component that is responsible for filtrating blood. The renal tubule, a complex structure, then leads the filtrate through various segments such as the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule, before connecting to collecting tubules. It is in these tubules where the filtrate is converted into urine by reabsorbing water and nutrients, and secreting additional wastes.

In understanding the nephron structure, we appreciate the kidney's immense efficiency in filtering blood repeatedly each day, which is paramount to maintaining the body's homeostasis.

Renal Corpuscle

At the beginning of the nephron rests the renal corpuscle, integral in initiating urine formation. The renal corpuscle is comprised of two components: the glomerulus, a tangle of capillaries, and Bowman's capsule, a surrounding double-walled cup-shaped structure.

Within the glomerulus, blood is filtered under high pressure, and the filtrate, excluding large proteins and cells, enters the Bowman's capsule. From here, the filtrate is funneled into the renal tubule where various substances are reabsorbed or secreted.

Understanding the role of the renal corpuscle is key to grasping how the kidney regulates the composition of blood, balances electrolytes, and controls blood pressure. Moreover, disturbances in the function of the renal corpuscle can lead to several kidney disorders, underlining its significance in kidney health and function.

Loop of Henle

Part of the nephron's renal tubule, the Loop of Henle, is specifically designed for urine concentration. This U-shaped structure descends into the renal medulla and then ascends back into the cortex, creating a countercurrent multiplier system that greatly increases the kidney's ability to reabsorb water and salt.

The Loop of Henle can be split into three segments: the descending limb, the thin ascending limb, and the thick ascending limb. The descending limb is permeable to water but not to salts, which allows the filtrate to become more concentrated as it moves down. Conversely, the ascending limb is impermeable to water but actively pumps out salt, making the filtrate within this segment more dilute.

Understanding the specialized function of the Loop of Henle highlights its vital role in the concentration of urine and the regulation of body fluid balance. This information is essential for comprehending how the kidney adapts to varying hydration levels and how it conserves water, a function critical to survival in environments that challenge body water resources.