Metabolic activities or excess ingestion causes animals to accumulate uric acid, urea, water, carbon dioxide and ions such as K+, Na+, sulphate, etc which needs to be eliminated from the body either partially or completely. Through this unit, we learn about the various mechanisms through which these substances can be treated for removal, specifically nitrogenous wastes. Ammonotelism, the process of excreting ammonia, which is the most toxic substance and requires large amounts of water to be eliminated. Nitrogenous wastes such as uric acid in the form of a paste are excreted by insects, reptiles, etc with a little amount of water loss. These animals are known as uricotelic animals. Read on to know more.
Very Short Answer Type Questions
Q.1. Name the site where the selective reabsorption of filtrate from Glomerular occurs.
A.1. PCT – Proximal Convoluted Tubules and DCT – Distal Convoluted Tubules.
Q.2. Name the excretory product of reptiles from the kidneys.
A.2. They are uricotelic animals that excrete nitrogenous wastes in the form of uric acid as a paste with a minimum discharge of water.
Q.3. Write the composition of the sweat secreted by the sweat gland.
A.3. It is a watery fluid having NaCl, with a little quantity of urea, lactic acid, etc
Q.4. Which gland in the prawns performs excretory functions?
A.4. Their excretory organs are called as green glands or antennary glands. They secrete ammonia and are opaque-white pea-sized structures, confined in the coxa of each second antenna.
Q.5. Which is the excretory structure in amoeba?
A.5. Contractile vacuole
Q.6. Expand the following excretory functions:
a) ANF – Atrial Natriuretic Factor
b) ADH – Antidiuretic Hormone
c) GFR – Glomerular Filtration Rate
d) DCT – Distal Convoluted Tubule
Q.7. Write the significance of the sebaceous gland.
A.7. They are involved in the removal of substances, such as squalene, cholesterol, triglycerides, wax, and esters via sebum that provides a greasy covering to the skin.
Short Answer Type Questions
Q.1. Describe the role of Renin-Angiotensin in the management of Kidney function.
A.1. The Juxta-Glomerular Apparatus (JGA) releases renin on activation by fall in the blood flow in the glomerular. In blood, renin transforms angiotensinogen into angiotensin I and hence into angiotensin II which is a vasoconstrictor that raises the blood pressure in the glomerular and hence the Glomerular Filtration Rate(GFR). Also, the angiotensin II stimulates the adrenal cortex to secrete aldosterone, which in turn causes the reabsorption of water and Na+ from the distal parts of the tubule which results in an increase in the GFR and blood pressure, this is termed as RAAS (Renin Angiotensin Aldosterone System).
Q.2 Give reason why aquatic animals ate mostly ammonotelic in nature whereas terrestrial forms are not.
A.2. Ammonia needs a large amount of water for its removal as its the most toxic. To conserve water, terrestrials adapted to produce less toxic nitrogenous wastes like uric acid and urea. In ureotelic animals, ammonia released as a result of metabolic activities is converted into urea in their liver and released into the blood that is filtered and excreted by the kidneys.
Q.3. Explain why the composition of glomerular filtrate is not the same as urine.
A.3. When the volume of the filtrate is compared with that of the urine that is formed per day, which is 180 litres and 1.5. Litres respectively, it can be extrapolated that 99% of the filtrate needs to be reabsorbed by the renal tubules, the phenomenon is referred to as reabsorption. Substances such as amino acids, Na+, glucose are actively reabsorbed in the filtrate hence are not found in urine.
Q.4. What is the remedial measure advised for the correction of acute renal failure? Explain briefly.
A.4. The ultimate method for the correction of acute renal failure is Kidney transplantation. The kidney is transplanted from a donor having a functional kidney, a close relative preferably, so that chances of rejection by the host immune system are minimized.
Q.5. Why is the hemodialysis unit called an artificial kidney? Explain.
A.5. It acts as an artificial kidney by eliminating urea from the blood of the patients caused due to failure of the kidney. Blood is drained from the artery and pumped into the dialyzing unit after addition of heparin. The unit has a looped cellophane tube that is girdled by a dialyzing fluid which has a similar composition as plasma minus the nitrogenous waste. The cellophane membrane of the tube is permeable through which molecules pass based upon the concentration gradient. Blood is removed as nitrogenous wastes are absent in the dialyzing fluid hence they can move freely. The cleaned blood is pumped back to the body via a vein after supplementing with anti-heparin.
Long Answer Type Questions
Q.1. Explain the micturition and disorders of the excretory system.
A.1. In micturition, urine is formed by the nephrons that are transferred by the urinary bladder which stores in until a signal is generated by the CNS. The signal is triggered by the stretching of the urinary bladder due to the filling of urine, which is responded in the form of signals to the CNS by the stretch receptors present on the bladder walls. To trigger smooth contractions of the bladder muscles, the CNS transfers motor messages and parallelly relaxes the urethral sphincter thereby resulting in the release of urine. This phenomenon of releasing urine is called as micturition The following are the disorders:
- Kidney malfunction can cause urea accumulation in the blood, the condition is referred to as uremia that may lead to kidney failure. Urea in such patients is eliminated through hemodialysis and kidney transplantation ultimately.
- Renal Calculi is when insoluble or stones of crystallized salts are formed within the kidney.
- Inflammation of the glomeruli of the kidney – Glomerulonephritis
Q.2. What is the role of tubular secretion in maintaining acid-base and ionic balance in the body fluids?
A.2. The tubular cells produce ammonia, H+, and K+ into the filtrate during the formation of urine. Tubular secretion assists in maintaining ionic and acid-base balance in the body fluids and is a necessary step in urine formation. The PCT helps in doing so through selective secretion of ammonia, hydrogen ions, and potassium ions into the filtrate. The DCT is also able enough to selectively secrete ions of potassium and hydrogen and ammonia for the maintenance of the sodium-potassium balance pH in the blood. Another structure that plays a role in maintaining the pH and ionic balance of the blood by selectively secreting H+ and K+ ions is the collecting duct.
Q.3. Explain why in the loop of Henle, the glomerular filtrate gets concentrated in the descending limbs and diluted in the ascending limbs.
A.3. The thin wall of the Henle’s loop is permeable to water and not solutes. While the isotonic tubular fluid passes down the limb, it slowly loses its water through the exosmosis caused by increased osmolarity of the medullary interstitium from which the limbs stretch. Hence the filtrate tends to become hypertonic to the blood plasma. The ascending limb of the loop of Henle is permeable to ions of K+, Na+, Cl-, partially permeable to urea, and are impermeable to water. So, in the thick ascending limb of the loop of Henle, Ca, Mg, Cl, K, Na is reabsorbed, thereby causing the filtrate to become hypotonic to blood plasma and diluted in comparison to descending limb. Discover more about Excretion in mammals and related biological concepts by registering at BYJU’S.