Excretory Products and their Elimination Test - 3

Potassium, sodium, glucose, amino adds, hormones, vitamins etc. are reabsorbed in proximal convoluted tubule (PCT). Potassium is reabsorbed by active transport.

Water reabsorption in descending limb of loop of Henle and collecting duct occurs under different conditions. In descending limb, water is reabsorbed due to increasing osmolarity of interstitial fluid. Collecting duct is entirely permeable to water. Water is reabsorbed here, under the influence of anti-diuretic hormone (ADH), which is released into the blood from the posterior lobe of pituitary gland.

A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released (1.5 litres), suggests that nearly 99% of the filtrate is reabsorbed by the renal tubules into the blood.

99 % of glomerular filtrate is reabsorbed by the renal tubules. Descending loop of Henle is permeable to water.
DCT can absorb Na⁺ ions. Ascending loop of Henle is permeable to electrolytes.

Most reabsorption of the major substances from the glomerular filtrate takes place in proximal convoluted tubule. Na⁺ ions, Cl^- ions and water are reabsorbed in distal convoluted tubules. Afferent arteriole carries the blood towards the glomerulus.

Malpighian corpuscle (A) is the site of ultrafitration. A considerable amount of water is reabsorbed in the collecting duct (E) under the influence of ADH. Proximal convoluted tubule (C) is the main site for the reabsorption of glucose and amino acids. In distal convoluted tubule (D), both hydrogen ions and ammonium ions are secreted, thus it maintains blood pH.

The diameter of afferent arteriole is larger than the efferent arteriole. This increases the volume of blood in glomerulus and increases the filtration rate. This causes the effective filtration pressure which is the total pressure that promotes filtration.

About 65% of the glomerular filtrate is reabsorbed in the proximal convoluted tubule (PCT). Glucose, amino acids, vitamins, hormones, sodium, potassium, chlorides, phosphates, bicarbonates, much of water and some urea are reabsorbed form the filtrate.

A fall in GFR can stimulate the JG cells to release renin which can stimulate the glomerular blood flow and thereby the GFR comes back to normal.

Juxtaglomerular cells are the smooth muscle cells of both the afferent and efferent arterioles that are swollen and contain dark granules. These cells secrete renin. Macula densa are the epithelial cells of the distal convoluted tubule that come in contact with the afferent and efferent arterioles. These cells are more dense than the other tubular cells. They act as chemoreceptors. Lacis cells are located in the interval between the macula densa and the afferent and efferent arterioles. The function of lacis cells is unknown. All these cells make up juxtaglomerular apparatus.

DCT maintains the pH and ionic balance in the blood by reabsorption of Na⁺, water, HCO₃^- and selective secretion of H⁺, K⁺ and NH₃. Collecting duct plays a role in the maintenance of pH and ionic balance of blood by reabsorption of water, and selective secretion of H⁺ and K⁺ ions.

Collecting duct also allows passage of small amounts of urea into the medulla to keep up the osmolarity.

Descending limb of loop of Henle is impermeable to salts.

Juxtaglomerular nephrons form about 15% of total nephrons. Their glomeruli are found in the inner margin of the cortex. They control plasma volume when water supply is short.

Juxtaglomerular nephrons form about 15% of total nephrons. Their glomeruli are found in the inner margin of the cortex. They control plasma volume when water supply is short.

Net pressure gradient = Glomerular hydrostatic pressure - (Blood colloidal osmotic pressure + Capsular hydrostatic pressure)
= 60 mm Hg - (30 mm Hg + 20 mm Hg)
= 60 - 50 = 10 mm Hg

In descending limb of loop of Henle, water is reabsorbed due to increasing osmolarity of interstitial fluid.

The maximum absorption of glucose, amino acids, and inorganic ions like Na⁺, K⁺, and Cl⁻ take place in the proximal convoluted tubule or PCT, and the maximum absorption of urea takes place in the ascending loop of Henle.
Thus, the correct answer is '(i) PCT (ii) PCT (iii) PCT (iv) Ascending limb of the loop of Henle.'

In the kidney, urine formation occurs in three steps, Glomerular filtration, Reabsorption, and tubular secretion. Glomerular filtration is the process by which nitrogenous waste likes Hippuric acid, creatinine and ketone bodies from glomerular blood are filtered through minute pores called filtration slits present in the wall of Bowman's capsule, tubular secretion is the transfer of nitrogenous waste materials like Hippuric acid, creatinine, and ketone materials from the peritubular capillaries to the renal tubular lumen. Hence Hippuric acid, creatinine, and ketones are added to urine through Glomerular filtration and Tubular secretion.

Three proceesses involved in urine formation are glomerular filtration, reabsorption and secretion. Filtration of blood by the glomerulus is called glomerular filtration, absorption of selected materials from the filtrate into the blood of the peritubular capillaries or vasa recta is called reabsorption and exxretion of additional wastes from the blood stream into the filtrate is called secretion.