Test: Human Excretory System - 3 - NEET MCQ

The nephrons are the functional unit of excretory organs, i.e., kidneys. Each nephron has two parts the glomerulus and the renal tubule. The renal tubule begins with a double walled cup-like structure, called as Bowman's capsule, which encloses the glomerulus. 
Glomerulus along with Bowman's capsule is called as the Malpighian body or renal corpuscle. The tubule continues further to form a highly coiled network proximal convoluted tubule (PCT). 
A hairpin-shaped Henle's loop is the next part of the tubule, which has a descending and an ascending limb. The ascending limb continues as another highly coiled tubular region, called as distal convoluted tubule (DCT). 
The DCTs of many nephrons open into a straight tube called as collecting duct, many of which converge and open into the renal pelvis through medullary pyramids in the calyces.

Ureotelic animals nculude, Ascaris earthworm, cartilaginous fishes, semiaquatic amphibians aquatic or semiaquatic reptilles like turles and alligators.

ADH is an antidiuretic hormone. A low level of ADH will cause the kidneys to excrete too much water. Urine volume increases lead to dehydration and blood pressure falls. A low level of ADH indicates damage to the hypothalamus or pituitary gland.

Hypertonic is the solution which contains more solute as compared to the solvent. Humans can survive with limited fluid intake because the kidneys can produce highly concentrated urine more than 4 times as concentrated as blood. The osmolarity of human blood is about 300 milliosmols per liter (mOsm /L). The kidneys can produce urine with an osmolarity of about 1200 mOsm / L. As the initial filtrate passes through various regions of the renal tubule, salt (NaCl) is reabsorbed into the interstitial fluid, and a salt concentration gradient is established. The gradient is used to produce a concentrated urine and makes it more hypertonic. Thus, the correct answer is option B.

The main function of the glomerulus is to filter plasma to produce glomerular filtrate, which passes down the length of the nephron tubule to form urine.

The nephrons along with collecting ducts are called as uriniferous tubule. The nephron is the structural and functional unit of the kidney. The body of the nephron is divided into  Renal corpuscle, PCT, a loop of Henle and DCT. Hence Loop of Henle is part of 'Uriniferous tubule'.
So, the correct answer is 'Uriniferous tubule'.

Reptiles, birds, land snails and insects excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water and are called as uricotelic animals.

The ascending limb of Henle’s loop continues as another highly coiled tubular region called distal convoluted tubule (DCT). The DCTs of many nephrons open into a straight tube called collecting duct, many of which converge and open into the renal pelvis through medullary pyramids in the calyces.

The loop of Henle is not situated in the cortical regions of the kidney as it is that part of renal tubule which dips into the medulla. The Malpighian corpuscle, PCT, and DCT are some parts of the nephron which are situated in the cortical regions of the kidney.

The nephron is the structural and functional unit of the kidney. The body of the nephron is divided into Bowman's capsule, proximal convoluted tubule (PCT), Henle's loop and Distal convoluted tubule( DCT). Hence Henle's loop is found in the Kidney.
So, the correct answer is 'Nephron' of the kidney.

The water reabsorption in the distal part of the nephron is in accordance with the body's state of hydration, under the influence of ADH and is termed as 'facultative reabsorption of water'. ADH is secreted in the hypothalamus of brain and released into blood stream from the pituitary gland. The collecting ducts become more permeable to water due to the effect of ADH, so more water is reabsorbed by osmosis and no expenditure of ATP energy is required. The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in osmolarity of the blood above a set point of 300mosmL−1. In this situation the osmoreceptors cells also promotes thirst. Drinking reduces the osmolarity of the blood, which inhibits the secretion of ADH.

Homeostasis is the tendency to resist change in order to maintain a stable, and constant internal environment. The internal environment should be contains the optimum concentration of gases, nutrients, ions, and water, has an optimal temperature, and has an optimal pressure for the health of the cells. For example, the concentration of various ions in the blood must be kept steady, along with pH and the concentration of glucose. Maintenance of homeostasis usually involves negative feedback loops. These loops act to oppose the stimulus. Its works on first, high temperature will be detected by sensors—primarily nerve cells with endings in the skin and brain—and relayed to a temperature-regulatory control center in brain. The control center will process the information and activate effectors—such as the sweat glands—whose job is to oppose the stimulus by bringing body temperature down.

In some of the nephrons in the kidney, the loop of Henle is very long and runs deep into the medulla. These nephrons dipping into the medullary region are known as juxtamedullary nephrons.

Metabolic wastes are substances left over from the excretory processes and cannot be used by the organism. While the metabolic wastes from the body include nitrogen compounds, water, sulfates, carbon dioxide and phosphates. While most of this is excreted as water solutes carbon dioxide which is excreted by the lungs is the most abundant and harmful waste product.
So, the correct answer is option A.

The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. The glomerular capillary blood pressure causes filtration of blood through 3 layers, i.e., the endothelium of glomerular blood vessels, the epithelium of Bowman's capsule and a basement membrane between these two layers. The epithelial cells of Bowman's capsule called podocytes are arranged in an intricate manner so as to leave some minute spaces called filtration slits or slit pores. Blood is filtered so finely through these membranes, that almost all the constituents of the plasma except the proteins and blood cells pass onto the lumen of the Bowmans capsule. Therefore, it is considered as a process of ultrafiltration.
So, the correct answer is option A.

In the fourth or in the final step of urea cycle, arginine is cleaved by arginase to form urea and ornithine. The ornithine is then transported back to the mitochondria to begin the urea cycle again.

So, the correct option is 'Breakdown of arginine'.

One of these forces is called hydrostatic pressure. In our case, this is the pressure exerted by fluid on the capillary walls of the glomerulus or the walls of the Bowman's capsule. The hydrostatic pressure in the glomerular capillaries is essentially the blood pressure in the glomerulus.

So, the correct option is 'Glomerulus of urinary tubule'.

ADH acts in the kidney to regulate the volume and osmolarity of the urine. Specifically, it acts in the distal convoluted tubule (DCT) and collecting ducts (CT) cells. 

In Bowman’s capsule filtration of blood to form urine takes place that is the reason no absorption of potassium and sodium ions takes place.

The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called as glomerular filtration. On an average,1100-1200 ml of blood is filtered by the kidneys per minute which constitute roughly 1/5th of the blood pumped out by each ventricle of the heart in a minute. The glomerular capillary blood pressure causes filtration of blood through 3 layers, i.e., the endothelium of glomerular blood vessels, the epithelium of Bowmans capsule and a basement membrane between these two layers. The epithelial cells of Bowmans capsule called as podocytes are arranged in an intricate manner so as to leave some minute spaces called filtration slits or slit pores. Blood is filtered so finely through these membranes, that almost all the constituents of the plasma except the proteins pass onto the lumen of the Bowmans capsule. Therefore, it is considered as a process of ultrafiltration.

Contractile vacuoles are responsible for maintaining homeostasis by osmoregulation. It is a membrane enveloped cellular organelle, found in many microorganisms, that periodically
expands, filling with water, and then contracts, expelling its contents to the cell exterior.
It's function is analogous to human kidneys.
Thus, the correct answer is option (B).

Erythropoietin is a peptide hormone that is released in response to low oxygen levels in kidney tissues. EPO stimulates the bone marrow to produce red blood cells.

Diuresis is when the body has too many of certain substances in the fluid that the kidneys filter. Eventually this fluid becomes urine and increases the amount of water expelled by the body, leading to increased or excessive urination.

The kidneys secrete 3 different types of hormones; erythropoietin, renin, and calcitriol (1,25- dihydroxycholecalciferol). Erythropoietin and renin are peptide hormones secreted by the juxtaglomerular cells of the kidney. Calcitriol is a steroid hormone synthesized by the cells of the proximal tubules of the nephrons. The renin secreted has enzymatic activity and is an important part of the renin-angiotensin-aldosterone system (RAAS). The RAAS plays an important role in regulating the cardiac output and arterial pressure. Thus the correct answer is option D.

Renin is produced by juxtaglomerular cells. These cells are similar to epithelium and are located in the tunica media of the afferent arterioles as they enter the glomeruli. The juxtaglomerular cells secrete renin in response to decrease in renal perfusion pressure (detected directly by the granular cells)

Urine formation involves three steps filtration, reabsorption and secretion. Reabsorption in Henle's loop segment is minimum. However, this region plays a significant role in the maintenance of high osmolarity of medullary interstitial fluid. The descending limb of loop of Henle is permeable to water but almost impermeable to electrolytes. Thus water is absorbed in the descending limb of loop of Henle. This concentrates the filtrate as it moves down. The ascending limb is impermeable to water but allows transport of electrolytes actively or passively. Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid.

The nitrogen compounds through which excess nitrogen is eliminated from organisms are called nitrogenous wastes or nitrogen wastes. They are ammonia, urea, uric acid, and creatinine. All of these substances are produced from protein metabolism.