Question

What does the tubular secretion add to the glomerular filtrate?
a. Urea
b. Uric acid
c. Ammonia
d. All the above

Answer 1

Hint: The both kidneys of the humans contain, the basic and structural unit called nephron, where it has glomerulus and tubular part, almost 5 liters of the blood are filtered per minute in the kidneys, and each kidney contain approximately 1.5 millions of nephrons.

Complete answer:
In the nephron three processes occur, they are glomerular filtration, reabsorption, tubular secretion.
Glomerulus is present as the beginning structure of the nephron, where it contains a network of capillaries called tuft, and this capillary network is supported by mesangial cells, which are nothing but gaps present between the capillary structures. At the start of a glomerulus, there is an afferent arteriole, which is larger and it allows the blood to the filtrate, where capillaries in the glomerulus exit as efferent arterioles and venules. Where they are small in size and create resistance, because of this ultrafiltration happens.

At the same time, the endothelium of the capillaries contain the sieve cells, so the molecules which are of that size enter the sieves and enter the bowman's capsule, where they again filtered in the tubular part of nephrons.

Tubular secretion is the process which extract the blood plasma, present in the peritubular capillaries, and secrete them into the tubular fluid in the renal tubule, the substances which secreted to glomerular filtrate are urea, ammonia and uric acid.

Hence, the correct answer is option (D).

Note: The factors, that govern the glomerular filtration rate is arterial pressure, afferent and efferent arterial resistance, colloidal osmotic pressure of the glomerulus, and the hydrostatic pressure of the bowman's capsule and sympathetic stimulation.