Thinking Process

Nitrogenous waste such as ammonia, urea and uric acid are produced during protein metabolism according to the species. Their excretory form product from the animals body depends on the availability of water.

Answer

(b) Uric acid is the least toxictions. Insects, land tortoises, lizards and birds change most of their nitrogenous waste into uric acid. It is the least toxic because it is insoluble in water as there are in solid form, thus, contains the least water. In birds, uric acid mixes with undigested food to form the bird dropping.

Urea moves to blood get filtered and eliminated with water in urine via kidneys.

Ammonia is very toxic and needs water for diffusion.

Carbon dioxide excretion takes place through the lungs.

Answer

(d) Filtration of blood takes place at Malpighian body.

Malpighian body or corpuscle comprises of glomerulus and Bowman’s capsule. Filtration of blood takes place in glomerulus through glomerular filtration.

In which blood enters in the glomerules through an afferent arteriole and leaves it through efferent arteriole.

Proximal Convoluted Tubule (PCT), is lined by cuboidal epithelium cells bearing brush border and allows the reabsorption of salts by active transport.

Distal Convulated Tubule (DCT), allows conditional reabsorption of $\mathrm{Na}^{+}$and water and selective secretion of $\mathrm{H}, \mathrm{K}^{+}, \mathrm{NH}_{3}$ to maintain $\mathrm{pH}$ and $\mathrm{Na}-\mathrm{K}$ balance in blood.

Collecting Duct extends from cortex of kidney to the inner part of medulla. Large amount of water is reabsorbed from this region to produce the concentrated urine.

Answer

(a) ADH (Antidiuretic Hormone) or vasopressin is secreted by posterior pituitary. It is involved in facilitating water reabsorption from later parts of the tubule, hence preventing diuresis.

It regulates water excretion by increasing permeability of collecting duct for water and salt and by accelerating water and ion transfer determined by osmotic gradient.

Thinking Process

$\mathrm{CO}_{2}$ and water both are metabolic wastes produced during oxidation of food in the cells.

Answer

(c) Our lungs remove large amounts of $\mathrm{CO}_{2}$ (18L/day) and also significant amount of water everyday.

While respiration, $CO_{2}$ alone can not be eliminated from the body and the same holds true for $H_{2} \mathrm{O}$. Ammonia is highly toxic, out is not found in free $\mathrm{NH}_{3}^{+}$form, thus it is immediately converted to non-toxic form.

Thinking Process

The urine is a light yellow coloured watery fluid, which is slightly acidic and has a characteristic odour.

Answer

(a) The pH of human urine is approximately 6.0. Other options are not the $\mathrm{pH}$ of urine.

Thinking Process

Animal kingdom possess a variety of excretory structures for excretion.

Answer

(a)

1 Prawn possesses green glands or antennal glands as their excretory structures.

2 Cockroach possesses Malpighian tubules as their excretory structures.

3 Earthworm possesses nephridia as their excretory structures.

4 Flatworm possesses protonephridia as their excretory structures.

Thinking Process

Animals secreting urea as their excretory product are called ureotelic animals. Animals secreting uric acid and ammonia are called uricotelic and ammonotelic respectively.

Answer

(d) Birds and reptiles are uricotelic (not ureotelic) as they excrete nitrogenous waste uric acid in the form of pellet or paste with a minimum loss of water.

Answer

(b) Insects excrete nitrogenous wastes as uric acid hence are uricotelic. Ureotelic animals involve mammals, adult amphibians and elasmobranchs. Whereas, birds are uricotelic (correct option) and tadpoles excretion ammonia. Elephant being a mammal is ureotelic.

Thinking Process

Inside the kidney, there are two zones, an outer cortex and an inner medulla.

Answer

(b) Inside the kidney the cortical region extends in between the medullary pyramids as renal columns are called column of Bertini, not as renal pelvis. Rest other statements are true.

Answer

(c) Uremia is accumulation of urea in blood. It occurs due to malfunctioning of kidney.

Renal calculi refers to the formation of stones or insoluble mass of crystallised salts (oxalates, etc) with in the kidney.

Glomerulonephritis is the inflammation of glomeruli of kidney.

Ketonuria is a medical condition in which ketone bodies are present in the urine. It is seen during starvation or more commonly in type 1 diabetes mellitus.

Answer

(b) Vasopressin is also known as Antidiuretic Hormone (ADH). It is secreted from the neurohypophysis of pituitary and facilitates water reabsorption from latter parts of the tubule, thereby preventing diuresis.

Oxytocin is a mammalian neurohypophysial hormone produced by the hypothalamus and is stored and secreted by the posterior pituitary gland. Oxytocin stimulus contractions of uterus at the end of pregnancy and also contractions of mammary glands the help in flow of milk.

Adrenaline is relesed by adrenal medulla at the time of emergency, hence has a role in ‘fight or flight’ reaction.

Calcitonin is produced in humans primarily by the parafollicular cells of the thyroid. It acts to reduce blood calcium $\left(\mathrm{Ca}^{2+}\right)$, level opposing the effect of parathyroid hormone.

Answer

(b) Proximal convoluted tubule is involved in reabsorption of $70-80 %$ of electrolytes.

Distal convoluted tubule is involved in secretion of hydrogen, potassium ions and $\mathrm{NH}_{3}$ in order to maintain $\mathrm{pH}$ and sodium-potassium balance in blood (ionic balance).

Henle’s loop (the descending limb) is permeable to water, but almost impermeable to electrolytes. This concentrates the urine (filtrate) as it moves down.

Counter current mechanisms helps to maintaining a concentration gradient in the medullary interstitium of kidney.

Renal corpuscle involves filtration of blood via glomerulus and Bowman’s capsule.

Answer

(c) Glycosurea/glucosuria is the presence of glucose in the urine.

Renal calculi is the formation of mass of crystallised salts within the kidney.

Glomerular nephritis is the inflammation of glomeruli of kidney.

Gout is the accumulation of uric acid crystals in joints causing inflammation.

Answer

(d) Counter current mechanism in Henle’s loop and vasa recta helps to maintain concentration gradient in the medullary interstitum. Presence of such interstitial gradient helps an easy passage of water from the collecting tubule thereby concentrating the urine.

PCT helps in maintaining pH and ionic balance of the body fluid by the secretion of $\mathrm{H}^{+}$, ammonia and potassium ions and reabsorbing $70-80 %$ of electrolytes and water.

Collecting duct helps in reabsorption of water to produce concentrated urine and in maintaining osmolarity. It also plays a vital role in maintaining $\mathrm{pH}$ and ionic balance in blood by secreting $\mathrm{H}^{+}$and $\mathrm{K}^{+}$ion.

DCT reabsorb $\mathrm{Na}^{+}$and water along with $\mathrm{HCO}_{3}^{-}$, maintaining $\mathrm{pH}$ and sodium-potassium/ionic balance in blood by the selectively secreting hydrogen and potassium ions.

Thinking Process

Dialysis is a process for removing waste and excess water from the blood and is used primarily as an artificial replacement for lost kidney function in people with renal failure.

Answer

(c) The dialysing unit (fluid) has the same composition as that of plasma except the nitrogenous waste ( urea). Other options are wrong, as dialysing unit will not have high glucose, high urea or high uric acid.

Answer

The selective reabsorption of glomerular filtrate takes place in Proximal Convoluted Tubules (PCT) and Distal Convoluted Tubules (DCT).

In PCT all essential elements nutrients, $70-80 %$ of electrolytes and water is absorbed whereas, Distal Convoluted Tubule (DCT) is involved in conditional reabsorption of $\mathrm{Na}^{+}$and water.

Thinking Process

Animals accumulate ammonia, urea, uric acid, carbon dioxide, water and ions like $\mathrm{Na}^{+}$, $\mathrm{K}^{+}, \mathrm{Cl}^{-}$phosphate sulphate, etc., either by metabolic activities or by other means like excess ingestion. The waste products are removed in the form of nitrogenous water.

Answer

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

Thinking Process

Perspiration (sweating, transpiration) is the production of sweat and secretion by the sweat glands in the skin of mammals.

Answer

Sweat produced by sweat glands is a watery fluid containing $\mathrm{NaCl}$, small amounts of urea, lactic acid, etc. Its primary function is to facilitate a cooling effect on the body surface and also to helps in removal of waste.

Answer

In prawns, the excretory organs are known as antennary glands or green glands. These glands are opaque-white pea sized structures, enclosed in the coxa of each 2nd antenna. They mainly excrete ammonia.

Thinking Process

Amoeba is a protozoan which forms the simplest of all organism in the animal kingdom. Inspite of being unicellular, it is physiologically balanced and performs all the essential processes of an animal.

Answer

Contractile vacuole is the excretory organ in Amoeba. It is also involved in osmoregulation.

Answer

(a) ANF Atrial Natriuretic Factor

(b) ADH Antidiuretic Hormone

(c) GFR Glomerular Filteration Rate

(d) DCT Distal Convoluted Tubule

Answer

Difference between glycosuria and ketonuria is as follows

Answer

Sebaceous glands are involved in the elimination of certain substances like cholesterol, squalene, triglycerides wax and esetrs through sebum. This secretion provides oily covering to the skin.

Answer

The substances that are actively transported in the glomerular filtrate are glucose and amino acids.

Answer

Metabolic disorders that can be diagnosed by analysis of urine are

(i) Hematuria It is the presence of blood or blood cells in the urine, which could be a sign of kidney stone or a tumor in urinary tract.

(ii) Albuminuria It is the presence of albumin in urine and occurs in nephritis i.e., inflammation of glomeruli. In this condition the size of filtering slits becomes enlarged.

Answer

Urine formation includes glomerular filteration (ultra filteration), selective reabsorption and tubular secretion that takes place in different parts of the nephron.

Glomerular filteration involves the filteration of blood, which is carried out by glomerulus.

Selective reabsorption is the absorption of filtrate through renal tubules either actively or passively.

Tubular secretion involves secretion through tubular cells in urine in order to maintain ionic and acid-base balance of body fluids.

Thinking Process

The tubular epithelial cells in different segments of nephron perform reabsorption either by active or passive mechanism.

Answer

Actively transported substances during reabsorption of GFR- Glucose, amino acids, $\mathrm{Na}^{+}$.

Passively transported substances during reabsorption of GFR-Nitrogenous wastes, water.

Answer

(a) Urinary excretion =tubular reabsorption + tubular secretion -filtration

(b) Dialysis fluid = plasma - nitrogenous wastes.

Answer

The concentration gradient in medullary interstitium is established primarily by renal tubules of loop of Henle and the blood vessels surrounding them (vasa recta) in a process called countercurrent exchange.

The substances that exit from tubules for maintenance of such gradient are mainly sodium chloride $(\mathrm{NaCl})$, water and urea (contaning $\mathrm{H}^{+}, \mathrm{K}^{+}$and $\mathrm{NH}_{3}^{+}$).

Answer

$\begin{array}{ll} \text { Organ } & \text { Excretory wastes } \\ \text { (a) Kidneys } & \text { Urine } \\ \text { (b) Lungs } & \mathrm{CO}_2 \\ \text { (c) Liver } & \text { Urea } \\ \text { (d) Skin } & \text { Sweat } \end{array}$

Answer

Representing the structure of a renal corpuscle

Thinking Process

The functioning of kidney is efficiently monitered and regulated by hormonal feedback mechanisms involving the hypothalamus, JGA and to certain extent, the heart.

Answer

Renin is released from the Juxta-Glomerular Apparatus (JGA) on activation by fall in the glomerular blood pressure/flow. Renin converts angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II, being a powerful vasoconstrictor, increases the glomerular blood pressure and thereby Glomerular Filteration Rate (GFR).

Angiotensin II also activates the adrenal cortex to release aldosterone. Aldosterone causes reabsorption of $\mathrm{Na}^{+}$and water from the distal parts of the tubule. This also, leads to an increase in blood pressure and GFR. This complex mechanism is generally known as Renin Angiotensin Aldosterone System or RAAS.

Answer

The process of excreting ammonia is called ammonotelism. many bony fishes, aquatic amphibians and aquatic insects are ammonotelic in nature. Ammonia, as its readily soluble, in water is excreted by diffusion across body surface or through gill surfaces (in fishes) as ammonium ions.

It is highly soluble in water and requires large amounts of water to be lost from the body. Such a mode of excretion is thus suitable for aquatic organisms which have a constant access to water.

Terrestrial adaptation requires the production of lesser toxic nitrogenous wastes like urea, as urea is less toxic and less soluble in water. This is important adaptation for water conservation in animals body. Mammals, many terrestrial amphibians and marine fishes mainly excrete urea and are called ureotelic animals.

In most insects land snails, reptiles etc., uric acid is excreted, hence they are called uricotelic animals. Conversion of ammonia to uric acid and its elimination requires less water, thus it is very essential for terrestrial forms that do not have constant water supply.

Answer

The composition of glomerular filtrate and urine is not the same as the glomerular filtrate contains a large amount of water and other dissolved substances such as urea, uric acid, creatinine, amino-acid, glucose, sodium, potassium vitamins, etc.

Urine on the other hand is a transparent, light yellow fluid, which is formed after rigrous reabsorption and secretion from the filterate. It constitute about $95 %$ water and $5 %$ of other organic and inorganic substances.

Organic substances in urine includes nitrogen, urea, creatine, ammonia uric acid, oxalic acid, vitamins, hormones and enzymes.

Whereas inorganic substance in urine include chloride, phosphate, sulphate, potassium, sodium, calcium, magnesium, iodine, arsenic and lead. Glucose is not found in urine normally. Hence, composition of glomerular filtrate and urine is different.

Thinking Process

Malfunctioning of kidneys can lead to the accumulation of urea in blood (uremia), which is highly harmful and may lead to kidney failure.

Answer

Kidney transplantation is the ultimate method for the correction of acute/extreme renal failure (kidney failure). A functional kidney is used as a transplant from a donor, preferably a close relative, to minimise its chances of rejection by the immune system of the host. Modern clinical procedures have increased the success rate of such a complicated technique.

Answer

Terrestrial adaptation necessitated the production of lesser toxic nitrogenous wastes like urea and uric acid for the conservation of water. Mammals and many terrestrial amphibians mainly excrete urea and are called uriotelic animals.

Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood, which is filtered and excreted out by the kidneys.

Some urea is retained in kidney in order to maintain osmolarity, reptilelos birds, land snails and insects excrete nitrogeneous waste, as uric acid in the form of pellet or paste with a minimum loss of water and are called uricotelic animals. Conversion of ammomia to uric acid and its subsequent elimination requires lesser amount of water.

Hence, due to less availability of water on land, and in order to minimise water loss, terrestrial organism adapted themselves accordingly.

Answer

The labelling part of the given figure are as listed

Answer

Haemodialysis This method is a boon for thousands of uremic (accumulation of urea in blood) patients all over the world.

Haemodialysing unit act an on artificial kidney by removing urea from patients blood due to kidney failure. In this process blood is drained from artery an pumped into a dialysing unit after the addition of an anticoagulant like heparin.

The unit contains a coiled cellophane tube surrounded by a dialysing fluid having the same composition as that of plasma except nitrogenous waste. The porous cellophane membrane of the tube allows the passage of molecules based on concentration gradient.

Due to the absence of nitrogenous wastes in dialysing fluid these substances freely move out, thereby clearing the blood.

In the end the cleared blood is pumped back to the body through a vein after the addition of anti-heparin to it thereby completing the process.

Answer

The functioning of the kidneys is efficiently monitored and regulated by Antidiuretic Hormone (ADH), Juxtaglomerular Apparatus (JGA) and Atrial Natriuretic Factor (ANF).

(a) Antidiuretic Hormone(ADH) or vasopressin from the neurohypophysis, facilitates water reabsorption from latter parts of tubule, i.e., distal convoluted tubule and collecting duct by increasing the permeability to water and salt and by accelerating water and ion transfer in a direction determined by the osmotic gradient.

(b) Juxta Glomerular Apparatus (JGA) operates a multihormonal. Renin Angiotensin Aldosterone System (RAAS). JG cells secrete an enzyme, renin, which, changes plasma protein called angiotensinogen to a peptide called angiotensin I and further to angiotensin II, which works as a hormone.

Angiotensin II, being a powerful vasoconstrictor increases the glomerular blood pressure and thereby GFR. It also stimulate’s soduim absorption by proximal tubules.

(c) Angiotensin II also activates the adrenal cortex to release aldosterone. Aldosterone induces the distal convoluted tubule to absorb more $\mathrm{Na}^{+}$and water.

(d) Atrial Natriuretic Factor (ANF) is produced by the atria of heart. It regulates blood flow by causing vasodilation and increasing sodium excretion. It is also involved in checking of renin-angiotensin mechanism.

Thinking Process

Urine is transparent, light yellow liquid with a slightly acidic $\mathrm{pH}$ (6.0). The colour of urine is caused by the pigment urochrome, which is a breakdown product of haemoglobin from wornout RBCs.

Answer

Mammals have the ability to produce concentrated urine. The loop of Henle and vasa recta play a significant role in it, which can be discussed as follows

(i) The proximity between the Henle’s loop and vasa recta, as well as the counter current (formed due to the flow of filtrate in two limb’s of Henle’s loop in opposite direction) help in maintaining an increasing osmolarity towards the inner medullary interstitium,

i.e., from $300 \mathrm{mOsmoL}^{-1}$ in the cortex to about $1200 \mathrm{mOsmoL}^{-1}$ in the inner medulla.

Diagrammatic representation of a nephron and vasa recta showing counter current mechanism (ii) This gradient is caused mainly due to $\mathrm{NaCl}$ and urea. $\mathrm{NaCl}$ is transported by the ascending limb of Henle’s loop, which is exchanged with the descending limb of vasa recta.

(iii) $\mathrm{NaCl}$ is returned to the interstitium by the ascending portion of vasa recta.

(iv) Similarly, a small amount of urea enters the thin segment of the ascending limb of Henle’s loop, which is transported back to the interstitium by the collecting tubule.

(v) This special arrangement of Henle’s loop, and vasa recta, is called the counter current mechanism.

(vi) The counter current exchange reduces the rate of dissipation. This, inturn reduces the rate at which the current must pump $\mathrm{Na}^{+}$to maintain any given gradient.

(vii) Presence of such interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine).

(viii) Human kidneys can produce urine nearly four times concentrated than the initial filtrate formed.

Answer

A diagram showing reabsorption and secretion of major substances at different parts of the nephron are as follows

Proximal Convoluted Tubule Distal Convoluted Tubule

Answer

The process of release of urine is called micturition and the neural mechanism. causing it is called the micturition reflex.

The urinary bladder and the internal sphincter are supplied by sympathetic and parasympathetic nervous systems of autonomic nervous system. In response, the stretch receptors on the walls of the bladder send signals to the Central Nervous System (CNS).

The CNS passes on motor messages to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.

Disorders of excretory system includes

(i) Uremia It is the malfunctioning of kidneys, which leads to accumulation of urea in blood in turn the kidney faliure. In such patients urea can be removed by haemodialysis.

(ii) Renal Failure (RF) It is caused by a decrease in glomerular filteration. In Acute Renal Failure (ARF) both kidneys abruptly stop working due to damaged renal tubules, kidney stones, antibiotics, etc. Haemodialysis and renal transplant are the only ways to auruve overcome renal failure.

(iii) Renal Calculi It is the formation of stones or insoluble mass of crystallised salts in the kidney.

(iv) Glomerulonephritis It is the inflammation of glomeruli of kidney.

Thinking Process

Tubular secretion is an important step in urine formation as it helps in the maintenance of ionic and acid base balance of body fluid.

Answer

In addition to the role of Proximal Convoluted Tublues (PCT) in selective reabsorption of materials from the glomerular filtrate back into the blood of peritubular capillaries via the renal interstitium, they also alter the composition of filtrate by the process of secretion.

In its distal part, epithelial cells extract certain excretory substances from the blood of peritubular capillaries and secrete these into the filtrate.

Creatinine, hippuric acid, pigments, drugs including penicillin are actively secreted into the filtrate in the proximal convolued tubule from the interstitial fluid. Hydrogen ions and ammonia are also secreted into the proximal convoluted tubules.

Urea enters the filtrate via diffusion in the thin segment of ascending limb of Henle’s loop.

Maximum hydrogen secretion occurs in the proximal convoluted tubules. Removal of hydrogen ion and $\mathrm{NH}_{3}$ from the blood in the PCT and Distal Convoluted Tubule (DCT) helps in maintaining $\mathrm{pH}$ of the blood, i.e., between 6 to 8 .

Tubular secretion although possess a minor role in functioning of the human kidney, but plays an essential role in animals like marine fishes and desert amphibians, because these animal do not possess well developed glomeruli hence their urine is mainly formed by the tubular secretion of urea, creatinine and mineral ions.

Answer

The glomerular filtrate in the loop of Henle gets concentrated in the descending loop and then gets diluted in the ascending limb. The thin wall of descending limb of Henle’s loop is permeable to water, but not to the solutes. The isotonic tubular fluid flows down the limb.

It gradually looses its water the by exosmosis due to increasing osmolarity of medullary interstitium through which the limb extends.

Thus, the filtrate becomes hypertonic to blood plasma. The ascending limb of loop of Henle is impermeable to water, but permeable to ions like $\mathrm{K}^{+}, \mathrm{Cl}^{-}, \mathrm{Na}^{+}$and it is partially permeable to urea.

Thus, in the thick ascending limb of the loop of Henle, $\mathrm{Na}, \mathrm{K}, \mathrm{Ca}, \mathrm{Mg}$ and $\mathrm{Cl}$ are reabsorbed, making the filtrate hypotonic to blood plasma and diluted as compared to descending limb.

Thinking Process

In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a urethra.

Answer

Human kidney are reddish-brown, bean-shaped structures situated between the last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity. Each kidney of an adult human measures $10-12 \mathrm{~cm}$ in length, $5-7 \mathrm{~cm}$ in width, $2-3 \mathrm{~cm}$ in thickness with an average weight of 120-170 gm.

The kidney is covered by a fibrous connective tissue, the renal capsula, which protect the kidney. Internally, it consists of outer dark cortex and an inner light medulla, both containing nephron (structural and functional units of kidney).

The median conconcave border of a kidney contains a notch called hilum. Through which ureter blood vessels and urinitus.

The renal cortex is granular in apperance and contains convoluted tubules and Malpighian corpuscles. The renal medulla contains loop of Henle, collecting ducts and tubules and ducts of Bellini.

Medulla is divided into conical masses, the medullary pyramids which further form papillae.The papillae form calyces, which join to renal pelvis leading to ureter. Between the medullary pyramids, cortex extends into medulla and forms renal columns which are called as column of Bertini.