Excretory Products And Their Elimination – Animals produce different types of nitrogenous wastes as a result of various cellular reactions taking place in their body. These waste material, if allowed to accumulate in the body, may become toxic. Therefore, they must be removed outside from the body.
The proximal convoluted tubule is involved in active reabsorption of sodium. The majority (about 70%) of sodium is resorbed here, into the cytosol of the epithelial cells of the nephron (NEET-II 2016).
Arginosuccinase is a lyase as it breaks argininosuccinic acid into fumaric acid and arginic acid (EAMCET 2015, Chhattisgarh 2015).
Increase in blood flow to heart stimulates secretion of the atrial natriuretic factor. It acts when blood volume and pressure is high. It causes vasodilation of walls (MH CET 2015).
Ascending limb of Henle’s loop is impermeable to water and it does not allow transport of electrolytes. It makes the hypertonic urine in descending limb to be tubule (Kerala CEE 2015).
Flame cells are the structures in Platyhelminthes and In prawns, excretion occurs by the general body surface(Kerala CEE 2015).
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Diabetes insipidus is a condition characterized by excessive thirst and excretion of dilute urine with the reduction of fluid intake. ADH maintains the amount of electrolytes (Kerala CEE 2015).
Ammonia is the highly toxic excretory product (UK PMT 2015).
The longer the loop of Henle, the grater is the ability of an animal to form hypertonic urine (UK PMT 2015).
Renal calculi is the condition in which stones are formed in the kidney by the precipitation of uric acid or oxalate. This cause a severe back pain (Gujarat CET 2014).
Descending limb of Henle’s loop is permeable to water, i.e. water gets reabsorbed here due to increasing osmolarity of interstitial fluid, but it is impermeable to salts, i.e. sodium and electrolytes. Proximal Convoluted Tubule (PCT) reabsorbs nearly all essential nutrients, electrolytes, and water. Ascending limb of the loop of Henle is impermeable to water but permeable toK+, Cl-, Na+ and partially permeable to urea. Distal Convoluted Tubule (DCT) is responsible for reabsorption of water, sodium, and secretion of hydrogen and potassium (Gujrat CET 2015).
Podocytes – Excretory Products And Their Elimination
Podocytes or visceral epithelial cells are the cells in Bowman’s capsule of the kidney that wrap around the capillaries of the glomerulus. They create minute pores (site pores) for the filtration of blood into the Bowman’s capsule (CBSE AIPMT 2011).
When someone drinks a lot of water which is not required by the body, the osmolarity of the blood decrease. This decrease in osmolarity and inhibits the release of ADH (CBSE AIPMT 2011).
The ascending limb of Henle’s loop continues as another highly coiled tubular region called Distal Convoluted Tubule (DCT). The juxtamedullary nephrons have long Henle’s loop; Vasa recta is absent or highly reduced in cortical nephrons. Bowman’s capsule encloses the glomerulus (Kerala CEE 2011).
From the DCT, the filtrate enters the collecting tubule, where further reabsorption of water takes place. Now the filtrate becomes more concentrated which makes the urine hypertonic. When the collecting duct becomes less permeable to water it produces more dilute urine (MH CET 2011).
Urea cycle takes place in liver cells with the hydrolytic enzyme arginase, Arginase splits arginine into urea and ornithine with the elimination of a water molecule (UP CPMT 2011).
Proximal convoluted tubule of the nephron is a pivotal site for reabsorption f glucose, amino acid, Na+, K+ by active transport. Here, 80% of water is reabsorbed by passive transport (WB JEE 2011).
The blood pressure in glomerular capillaries becomes very high so that there is the continuous process of ultrafiltration. Glomerular Filtrate (GF) contains a large amount of H2O and other dissolved substances such as urea, uric acid, creatinine, amino acids, glucose, sodium, potassium, vitamins, etc. About 120 ml GF is produced per minute, i.e. approximately 170 L filtrate is produced in 24 hours (WBJEE 2011).
Glomerular filtrate – Excretory Products And Their Elimination
The plasma fluid that filters out from glomerular capillaries into Bowman’s of the nephron is called glomerular filtrate. A comparison of the volume of the filtrate formed per day (180 L/day) with that of the urine released(1.5 L), suggest that nearly 99% of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption (CBSE AIPMT 2010).
The lumen of the urinary bladder is lined by transition epithelium, which has great power of stretching. If stretch receptors of urinary bladder wall are totally removed the urine will continue to collect normally in the bladder (CBSE AIPMT 2009).
Urine is a transparent, light yellow liquid with slightly acidic pH. The pungent smell of urine is due to urinode while the color of urine is due to the pigment urochrome (Kerala CEE 2007).