Excretory Products and their Elimination


Give a brief account of the counter current mechanism.


The kidneys have a special mechanism for concentrating the urine, it is called counter current mechanism. The mechanism is said to be a counter current mechanism because the out flow (in the ascending limb) of Henle’s loop runs parallel to and in the opposite direction of the inflow (in the descending limb) and vasa recta. As the mechanism begins to function, the ascending limb of loop of Henle actively transports chloride and sodium ions out into the vasa recta from where it is secreted into the interstitial fluid. As a result the interstitial fluid around the loop of Henle contains large quantities of NaCl. The filtrate passes from the ascending limb of loop of Henle and enters a collecting duct. The collecting duct passes adjacent to the loop of Henle where the interstitial fluid contains large amounts of NaCl. The high osmotic pressure created by NaCl causes water to diffuse out of the collecting duct in the interstitial fluid and eventually to the blood of vasa recta. The filtrate becomes greatly concentrated and is now called urine. A similar counter current mechanism, operates between the interstitial fluid and blood passing through the vasa recta. As the blood capillary runs along the ascending limb of loop of Henle, NaCl diffuses out of the blood. The direction is reversed as the blood capillary passes along the descending limb of Henle. The blood flows in the vasa recta around the loop of Henle from ascending to the descending side while the fluid passing through the loop of Henle goes in the opposite direction. The arrangement helps to maintain the concentration gradient of NaCl.
The ‘overall function of counter current mechanism is to concentrate sodium chloride in the interstitial fluid and thereby cause water to diffuse out of the collecting ducts and concentrate the urine.


Excretory Products and their Elimination

Q 1.

What is the composition of sweat produced by sweat glands?

Q 2.

Fill in the blanks appropriately.
Organ Excretory wastes
(a) Kidneys ______________
(b) Lungs ______________
(c) Liver ______________
(d) Skin ______________

Q 3.

Label the parts in the following diagram.

Q 4.

Explain briefly, micturition and disorders of the excretory system.

Q 5.

Match the items of column I with those of column II.
Column I                                     Column II
(a) Ammonotelism                   (i)Birds
(b) Bowman’s capsule             (ii)Water reabsorption
(c) Micturition                          (iii)Bony fish
(d) Uricotelism                         (iv)Urinary bladder
(e) ADH                                       (v)Renal tubule

Q 6.

What are the main processes of urine formation?

Q 7.

Fill in the gaps.
(a) Ascending limb of Henle’s loop is________to water whereas the descending limb is________to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone________
(c) Dialysis fluid contains all the constituents as in plasma except________
(d) A healthy adult human excretes (on an average)________gm of urea/day.

Q 8.

Mention the substances that exit from the tubules in order to maintain a concentration gradient in the medullary interstitium.

Q 9.

Identify the glands that perform the excretory function in prawns.

Q 10.

Mention any two metabolic disorders, which can be diagnosed by analysis of urine.

Q 11.

Differentiate glycosuria from ketonuria.

Q 12.

Give a brief account of the counter current mechanism.

Q 13.

What is the significance of juxta glomerular apparatus (JGA) in kidney function?

Q 14.

What is the role played by renin-angiotensin in the regulation of kidney function?

Q 15.

What is the excretory product from kidneys of reptiles?

Q 16.

Indicate whether the following statements are true or false.
(a) Micturition is carried out by a reflex.
(b) ADH helps in water elimination, making the urine hypotonic.
(c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule.
(d) Henle’s loop plays an important role in concentrating the urine.
(e) Glucose is actively reabsorbed in the proximal convoluted tubule.

Q 17.

Explain the autoregulatory mechanism of GFR.

Q 18.

Sort the following into actively or passively transported substances during reabsorption of GFR. glucose, aminoacids, nitrogenous wastes, Na+, water

Q 19.

The composition of glomerular filtrate and urine is not same. Comment.

Q 20.

Explain, why a haemodialysing unit called artificial kidney?

Q 21.

Comment upon the hormonal regulation of selective reabsorption.

Q 22.

What is the role of sebaceous glands?

Q 23.

The glomerular filtrate in the loop of Henle gets concentrated in the descending limb and then gets diluted in the ascending limb. Explain.

Q 24.

Explain the mechanism of formation of concentrated urine in mammals.

Q 25.

Terrestrial animal saregenerally either ureotelic or uricotelic, not ammonotelic, why?

Q 26.

Define Glomerular Filtration Rate (GFR).

Q 27.

The following abbreviations are used in the context of excretory functions, what do they stand for?
(a) ANF (b) ADH
(c) GFR (d) DCT

Q 28.

How does tubular secretion help in maintaining ionic and acid-base balance in body fluids?

Q 29.

How have the terrestrial organisms adapted themselves for conservation of water?

Q 30.

What is the excretory structure in Amoeba?

Q 31.

Explain micturition.

Q 32.

Name the following.
(a) A chordate animal having flame cells as excretory structures.
(b) Cortical portions projecting between the medullary pyramids in the human kidney.
(c) A loop of capillary running parallel to the Henle’s loop.

Q 33.

Name two actively transported substances in glomerular filtrate.

Q 34.

Describe the role of liver, lungs and skin in excretion.

Q 35.

Where does the selective reabsorption of Glomerular filtrate take place?

Q 36.

What is meant by the term osmoregulation?

Q 37.

Describe the structure of a human kidney with the help of a labelled diagram.

Q 38.

Complete the following:
(a) Urinary excretion = Tubular reabsorption +Tubular secretion ________
(b) Dialysis fluid = Plasma ________

Q 39.

What is the procedure advised for the correction of extreme renal failure? Give a brief account of it.

Q 40.

Show the structure of a renal corpuscle with the help of a diagram.

Q 41.

Aquatic animals generally are ammonotelic in nature whereas terrestrial forms are not. Comment.

Q 42.

Draw a labelled diagram showing reabsorption and secretion of major substances at different partsof the nephron.