Excretion in Humans

Question 1

define excretion and explain the importance of removing nitrogenous and other compounds from the body

Answer 1

excretion is the process by which metabolic waste products and toxic subs are removed from the body of an organism
- metabolic waste products cn be harmful or toxic if they accumulate in the body

Question 2

explain ultra-filtration

Answer 2

• ultrafiltration removes small molecules from the blood
• caused by high hydrosatic blood pressure/high blood pressure: the afferent arteriole that brings blood into the glomerulus is wider than the efferent arteriole that carry blood away, creating hbp in glomerulus, providing the main force required for the filtration process
• basement membrane: partially permeable membrane that wrape arnd the glomerular blood caps is like a fine filter, has very small pores allowing only water & vv small molecules(glucose, AA, MS & nirogenous waste products) to pass through
• water & these vv small moelcules forced out of glomerulus into Bowman’s capsule, forming the filtrate.

Question 3

explain selective reabsorption

Answer 3

• as filtrate passes throught the tubule, useful subs are taken back(reabsorbed) into bloodstream by SR
  1. @PCT, most of MS(Na+ ions) & in a healthy person, all of glucose & AAs are reabsorbed through walls of tubule into surr. blood caps, via diffusion & AT. (only subs required are reabsorbed readily) Most of water in filtrate reabsobed by osmosis here.
  2. @loop of henle, some water reabsorbed.
  3. @DCT, some water & MS reabsorbed
  4. @CD, some water reabsorbed. Excess water+salts & MWP(urea, uric acid, creatinine) pass out of CD into renal pelvis as urine.

Question 4

role of anti-diuretic hormone (ADH) in osmoregulation

Answer 4

• amount of water in blood plasma is controlled by ADH
• ADH: produced by hypothalamus, released by pituitary gland, increases water reabsorption @ nephrons
  1. When WP in blood plasma increases, hypothalamus is stimulated & pituitary gland releases less ADH into bloodstream, cells in walls of CDs: less permeable to water, less water reabsorbed, larger vol of urine produced, urine more diluted
  2. When WP in blood plasma decreases, hypothalamus is strimulated & pituitary gland releases more ADH into bloodstram, cells in walls of CDs: more permeable, more water reabsorbed, smaller vol of urine, urine more concentrated

Question 5

mechanism of dialysis in the case of kidney failure

how it works + features

Answer 5

1. Blood is drawn from vein in patient’s arm & is allowed to be pumped through tubing in dialysis machine
2. Tubing is bathed in a specially controlled dialysis fluid. The **walls **of tubing in dialysis machine are partially permeable
3. Small molecules(urea, other MWP) diffuse out of tubing into dialysis fluid. Blood cells, platelets & large molecules remain in tubing
4. Filtered blood then returned to a vein in patient’s arm

• dialysis fluid: same conc if essential subs as healthy blood - ensures essential subs(glucose, AAs & MS) do not diffuse out + lack of subs, diffuse in
• dialysis fluid: no MWP - sets up conc gradient, allows MWPs (urea, uric acid, creatinine, excess water & MS to diffuse out. this maintains the correct solute composition & WP of the blood
• tubing: narrow, long & coiled - increases SA:V, speed upp rate of exchange of subs
• opp direction - maintains conc gradient for removal of WPs