Test: Urine Formation & Functions of Tubules - NEET MCQ

Urine formation involves three main processes namely, glomerular filtration, reabsorption, and secretion, that take place in different parts of the nephron.

Descending limb is the first part of the loop of Henle. It helps to maintain the concentration of urine. It is highly permeable to water thus water is readily reabsorbed from the descending limb by osmosis. It is impermeable to sodium and chloride ions.

On average, our kidneys filter 1100-1200 ml of blood every minute. This blood that is filtered per minute constitutes for about 1/5^th of the total blood pumped out by each ventricle of the heart in a minute. Therefore, we can say that the whole blood of our body gets filtered in approximately 5 minutes.

The glomerular filtrate when passes through the convoluted tubules, the useful components present in the filtrate is reabsorbed by tubular reabsorption. It occurs via three mechanisms they are osmosis, diffusion, and active transport. Most of the volume of the filtrate is reabsorbed in the proximal convoluted tubule (PCT). This includes some water and most/all of the glucose (except in the case of diabetics).
So, the correct answer is option B.

The first step in urine formation in the nephron is glomerular filtration. This process involves the filtration of blood through the glomerulus, where blood constituents pass through three layers: the endothelium of glomerular blood vessels, the epithelium of Bowman's capsule, and a basement membrane. The podocytes within Bowman's capsule are arranged in a way that creates filtration slits, allowing for the fine filtration of blood components. This initial step is crucial for the subsequent processes of reabsorption and secretion to occur effectively.

Podocytes are the epithelial cells within Bowman's capsule that are intricately arranged to form filtration slits or slit pores. These specialized cells play a key role in the ultrafiltration process by allowing the passage of almost all constituents of plasma except proteins into the lumen of Bowman's capsule. The presence of these filtration slits is essential for the precise filtration of blood components during glomerular filtration.

The correct answer is Option B: Glomerular filtration rate (GFR). The glomerular filtration rate refers to the volume of fluid filtered by the glomeruli of the kidney per minute. It is a crucial indicator of kidney function, with a normal GFR being around 125 ml/minute. The GFR helps in estimating how well the kidneys are working and how efficiently they are filtering waste from the blood.

The correct answer is Option C: Juxtaglomerular apparatus (JGA). The JGA is a specialized region located where the distal convoluted tubule and the afferent arteriole come into contact. It plays a crucial role in regulating blood pressure and the filtration rate of the kidneys. When there is a decrease in glomerular filtration rate, the JG cells within the JGA can release renin, which initiates a series of events to help restore the GFR back to normal levels.

The primary function of the Proximal Convoluted Tubule (PCT) is the reabsorption of essential nutrients, electrolytes, and water. This segment is lined by simple cuboidal brush border epithelium, which significantly increases the surface area for reabsorption. Nearly all essential nutrients and a significant portion of electrolytes and water are reabsorbed in the PCT. This process is crucial for maintaining the body's overall balance of nutrients and fluids.

c) Reabsorption of HCO3-

The Distal Convoluted Tubule (DCT) plays a crucial role in:

• Reabsorption of ions like HCO3- (bicarbonate), sodium, and calcium.
• Regulation of pH by secreting hydrogen ions (H⁺) and reabsorbing bicarbonate (HCO3⁻).
• Water reabsorption under the influence of hormones like antidiuretic hormone (ADH) and aldosterone. However, the reabsorption of water is not the primary function in the DCT (compared to the collecting duct and loop of Henle).