Excretory Products and Their Elimination

In frogs, there are specialized venous connections that serve specific functions. One such connection links the liver and intestine, known as the hepatic portal system. Another connects the kidney to the lower parts of the body; this is referred to as the renal portal system. The renal portal system specifically involves the transfer of blood from the lower regions of the body to the kidneys.

During urine formation, the tubular cells secrete substances like $\mathrm{H}^{+}, \mathrm{K}^{+}$and ammonia into the filtrate. Tubular secretion is also an important step in urine formation as it helps in the maintenance of ionic and acid base balance of body fluids.

PCT $\rightarrow$ Selective secretion of $\mathrm{H}^{+}$, ammonia and $\mathrm{K}^{+}$into the filtrate.

DCT $\rightarrow$ Capable of reabsorption of $\mathrm{HCO}_3^{-}$and selective secretion of $\mathrm{H}^{+}, \mathrm{K}^{+}$and $\mathrm{NH}_3$.

The correct answer is Option C: Both Statement I and Statement II are correct.

Here's why:

Statement I: Concentrated urine is formed due to the countercurrent mechanism in the nephron.

This statement is correct. The countercurrent mechanism in the nephron is crucial for forming concentrated urine. Here's how it works:

• Loop of Henle: The loop of Henle, a part of the nephron, creates a concentration gradient in the medullary interstitium. The descending limb of the loop is permeable to water but not to solutes. As filtrate flows down this limb, water moves out due to the increasing solute concentration in the interstitium, making the filtrate more concentrated. The ascending limb is impermeable to water but permeable to solutes, actively pumping out solutes like sodium, potassium, and chloride ions. This contributes to the higher solute concentration in the interstitium.
• Vasa Recta: The vasa recta, the capillaries surrounding the loop of Henle, also participate in maintaining the concentration gradient. They have a countercurrent flow, meaning blood flows in the opposite direction of the filtrate in the loop of Henle. This helps preserve the osmotic gradient by preventing rapid removal of solutes from the interstitium.
• Collecting Duct: As filtrate flows through the collecting duct, it encounters the concentrated medullary interstitium. Water moves out of the collecting duct, becoming more concentrated, ultimately leading to the production of concentrated urine.

Statement II: Countercurrent mechanism helps to maintain the osmotic gradient in the medullary interstitium.

This statement is also correct. The countercurrent mechanism is the primary mechanism responsible for establishing and maintaining the high osmotic gradient in the medullary interstitium. This gradient is crucial for the reabsorption of water and for the excretion of concentrated urine.

In summary, the countercurrent mechanism in the nephron is essential for producing concentrated urine and maintaining the osmotic gradient in the medullary interstitium. Therefore, both statements are accurate.

Correct answer is option (B) because Statement I is false as the descending limb of loop of Henle is permeable to water and almost impermeable to electrolytes.

Statement II is false as proximal convoluted tubule is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption.

The juxta medullary nephrons are one of the two types of nephrons found in the kidneys, specifically in mammals, including humans. These nephrons have distinctive characteristics and play crucial roles in the process of urine concentration, which is essential for water conservation and the regulation of blood pressure.

Option A: Juxta medullary nephrons are located in the columns of Bertin.

This option is incorrect. The juxta medullary nephrons are not located in the columns of Bertin. The columns of Bertin, or renal columns, are extensions of the renal cortex located between the renal pyramids. They consist primarily of lines of blood vessels and cortical material. The juxta medullary nephrons, however, have their renal corpuscles located at the deep cortex, close to the medulla, not within the columns of Bertin.

Option B: Renal corpuscle of juxta medullary nephron lies in the outer portion of the renal medulla.

This option is incorrect. In juxta medullary nephrons, the renal corpuscles are not located in the outer portion of the renal medulla but are located deep in the renal cortex, close to the medulla. The renal corpuscles include the glomerulus and Bowman's capsule, which are essential for the filtration of blood.

Option C: Loop of Henle of juxta medullary nephron runs deep into the medulla.

This option is correct. The defining characteristic of juxta medullary nephrons is the long loops of Henle that extend deep into the renal medulla. This structural feature is critical for establishing the conditions needed for the concentration of urine, as it allows for a significant reabsorption of water and solutes under the influence of various gradients.

Option D: Juxta medullary nephrons outnumber the cortical nephrons.

This option is incorrect. Juxta medullary nephrons are much less numerous than cortical nephrons. Cortical nephrons make up the majority of nephrons in the kidneys and are primarily involved in the filtering of blood and initial urine formation under different conditions.

In summary, the correct statement about juxta medullary nephrons from the provided options is Option C: Loop of Henle of juxta medullary nephron runs deep into the medulla.

The Assertion (A) states: "Ascending limb of loop of Henle is impermeable to water and allows transport of electrolytes actively or passively." This is true. The ascending limb of the loop of Henle is indeed impermeable to water. This means that as the filtrate passes through this part of the loop, water cannot pass out of the tubule and back into the body, but electrolytes (like sodium and chloride ions) can be transported out, either actively (using energy) or passively (without using energy, following their concentration gradient).

The Reason (R) states: "Dilution of filtrate takes place due to efflux of electrolytes in the medullary fluid." This is also true. As the filtrate ascends the limb and electrolytes are transported out, the filtrate becomes more diluted. This is because the volume of the filtrate remains the same, but the number of electrolytes (which contribute to the filtrate's 'concentration') decreases.

Moreover, Reason (R) is explaining why the filtrate becomes dilute in the ascending limb, which is mentioned in Assertion (A). Therefore, (R) is indeed the correct explanation for (A).

So, the correct option is Option C: Both (A) and (R) are true and (R) is the correct explanation of (A).

The correct answer is :

Option C : Both Statement I and Statement II are true

Explanation :

Statement I is true as goblet cells are indeed unicellular glands. They secrete mucus and are found in the lining of the intestines and respiratory tracts, where the mucus acts as a protective layer.

Statement II is also true. Earwax, also known as cerumen, is a secretion from the ceruminous glands in the ear canal, which are a type of exocrine gland. Exocrine glands are glands that secrete their products onto body surfaces or into body cavities.

The correct answer is :

Option B : A is true but R is false.

Explanation :

Assertion A is correct. In the kidney, nephrons, the functional units responsible for filtration, reabsorption, and secretion processes, are indeed of two types: cortical and juxta-medullary. These types are classified based on their location within the kidney; cortical nephrons are primarily located in the cortex, while juxta-medullary nephrons are located near the junction between the cortex and medulla.

However, Reason R is incorrect. The assertion that juxta-medullary nephrons have short loops of Henle, while cortical nephrons have longer loops of Henle is false. In fact, it's the opposite. Juxta-medullary nephrons have longer loops of Henle which extend deep into the medulla. This allows them to concentrate urine more effectively than cortical nephrons, whose loops of Henle are shorter and do not extend as deep into the medulla.

The correct answer should be Option B : A-III, B-II, C-IV, D-I.

Explanation :

A) Taenia (a genus of tapeworm) has flame cells as its excretory organs.

B) Paramoecium, a unicellular protist, uses contractile vacuoles to excrete waste and excess water.

C) Periplaneta (the American cockroach) uses malpighian tubules for excretion, but "Urecose gland" is not a correct match. However, given the available options, it's the closest match.

D) Pheretima, a genus of earthworms, uses nephridia as excretory organs.

Option (A) is the correct answer because statements B, C and D are true statements. ADH facilitates water reabsorption from DCT of nephron to prevent diuresis, which causes increase in blood pressure. ANF which is secreted by the heart is a vasodilator.

Options (B), (C) and (D) are not correct because statements A and E are false. Excessive loss of body fluid from the body switches on the osmoreceptors.

Option (a) is the correct answer because statements (a), (b) and (c) are correct.

Angiotensin II activates the adrenal cortex of adrenal gland to release aldosterone. Aldosterone increases blood volume and thus blood pressure by increasing reabsorption of water and electrolytes from distal parts of nephron. ANF causes vasodilation and decreases blood pressure and thus GFR. Statements (d) and (e) are incorrect as ADH/vasopressin is a potent vasoconstrictor which is released from neurohypophysis.

Option (d) is the correct answer because birds (Pavo) excrete nitrogenous wastes as uric acid in the form of pellet or paste with minimum loss of water.

Option (c) and (b) are incorrect because many bony fishes (like Hippocampus) and aquatic amphibians (like Salamandra) are ammonotelic in nature.

Option (a) is incorrect because mammals (like Ornithorhynchus) mainly excrete urea and are called ureotelic animals.

Assertion is true, but reason is false. In most of the members of phylum–Arthropoda, excretion takes place through Malpighian tubules to maintain osmolarity, but they excrete their nitrogenous wastes as uric acid, which minimises the loss of water and are thus called uricotelics.