Passage
Excretion is the process of eliminating (1) metabolic wastes from the body. Animals that excrete ammonia directly are called (2), while those that convert ammonia to urea via the (3) cycle are called (4). Animals excreting uric acid as a semi-solid paste are called (5) — examples include (6) and (7).
The structural and functional unit of the kidney is the (8), of which there are approximately (9) per kidney. Glomerular filtration occurs at a rate of (10) mL/min, producing about (11) litres of filtrate per day. However, (12)% is reabsorbed, yielding only (13) litres of urine per day.
The PCT reabsorbs approximately (14)% of the filtrate, including (15) and (16) by active transport, and water by (17) osmosis. The descending limb of the loop of Henle is permeable to (18) but impermeable to (19). The ascending limb pumps (20) out but remains impermeable to (21).
The counter-current mechanism maintains a medullary osmotic gradient from (22) mOsm/L at the cortex to (23) mOsm/L at the inner medulla. Under the influence of (24), the collecting duct reabsorbs water and produces concentrated urine.
Aldosterone from the (25) stimulates Na+ reabsorption and K+ secretion in the (26). The RAAS cascade begins when (27) cells release (28) in response to low blood pressure. Renin converts (29) to (30), which is converted by (31) (ACE) to (32), which then stimulates (33) secretion.
Answer Key
- nitrogenous
- ammonotelic
- ornithine (urea)
- ureotelic
- uricotelic
- birds
- reptiles / land snails / insects (any two)
- nephron
- one million (10^6)
- 125
- 180
- 99
- 1.5
- 65–70
- glucose
- amino acids
- obligatory
- water
- solutes
- NaCl (sodium chloride)
- water
- 300
- 1200
- ADH (antidiuretic hormone)
- adrenal cortex (zona glomerulosa)
- DCT (distal convoluted tubule)
- juxtaglomerular (JG)
- renin
- angiotensinogen
- angiotensin I
- angiotensin converting enzyme
- angiotensin II
- aldosterone