chapter 11 excretion in humans

Question 1

what is excretion

Answer 1

excretion is the process by metabolic, nitrogenous waste products and toxic substances are removed from the body through excretory organs

Question 2

why is excretion important

Answer 2

1. Prevents accumulation of waste products in body = may be toxic to cells
2. Water potential in blood stream cannot be regulated at normal level = may be concentrated with waste products

Question 3

what is excreted out of our body through urine (4)

Answer 3

Excess mineral salts
Urea (deamination of excess protein)
Uric acid (breakdown of nucleic acid)
Creatinine (breakdown of muscle proteins)

Question 4

how does blood flow in the nephron

Answer 4

1. Blood enters kidney by renal artery = branches out into arterioles = branch into mass of blood capillaries (glomerulus) in Bowman’s capsule
2. after small soluble substances have been filtered out, Blood leaves glomerulus, enters blood capillaries surrounding nephron
3. Blood capillaries unite to form venules = join a branch of renal vein

Renal vein carries blood from kidney right after ultrafiltration and SR

Question 5

what is ultrafiltration caused by

Answer 5

→ caused by:
1. hydrostatic blood pressure: blood that flows in from wider afferent arteriole flows into smaller efferent arteriole that carries blood away = large amount of blood forced into smaller diameter = high blood pressure
2. glomerular blood capillaries surrounded by partially permeable membrane (basement membrane): allows only water molecules and very small and soluble molecules to pass through

Question 6

what substances pass through the partially permeable basement membrane?

Answer 6

water, glucose, Amino acids, mineral salts and waste products are forced out of glomerulus into Bowman’s capsule = forms filtrate = passes into proximal convoluted tubule

Question 7

what substances do not pass through the partially permeable membrane?

Answer 7

large molecules such as protein and fats, and RBCs are retained in the glomerular capillaries = carried away by bloodstream (do not pass through basement membrane)

Question 8

what happens in the proximal convoluted tube? (thicker S shape)

Answer 8

1. most mineral salts (Na+ ions), all glucose and amino acids are reabsorbed through tubule walls into blood capillaries = via diffusion
2. Glucose can be taken in by active transport also: when there is more glucose in bloodstream than tubule (against concentration gradient, from tubule to bloodstream) as all glucose still needs to be reabsorbed
3. wSome water in filtrate reabsorbed by osmosis

Question 9

what happens in the loop of Henle

Answer 9

most water is reabsorbed

Question 10

what happens in the distal convoluted tube (thinner S shape)

Answer 10

some water and mineral salts reabsorbed

Question 11

what happens in the collecting duct

Answer 11

1. some water reabsorbed
2. Excess water, salts and metabolic waste substances (eg urea, uric acid, creatinine) pass out of CD = form urine = go into renal pelvis

Question 12

how is nephron adapted for selective reabsorption

Answer 12

1. Long and/or convoluted at certain regions (at PCT and DCT): increase SAVR = efficient reabsorption of the substances like glucose, amino acids, mineral salts and water into blood capillary
2. Cells that form the wall of the nephron (especially in PCT and DCT) contain many mitochondria: = release energy for active transport of substances against its concentration gradient from glomerular filtrate to blood
3. Walls of nephron are made of a single layer of cells = shorter distance for movement of substances = increases rate of diffusion, osmosis and active transport
4. Cells that form the wall of the nephron at the PCT, loop of Henle and DCT have numerous microvilli: to increase SAVR for efficient reabsorption;

Question 13

what is in urine and what is not in urine?

Answer 13

urine is mostly made up of water, some mineral salts and urea

→ no protein/fats in urine = still retained in the glomerular capillaries

→ no glucose/amino acids in urine: have been completely reabsorbed from filtrate in PCT by diffusion/AT

Question 14

what happens when you have a large intake of water

Answer 14

1. water potential is above normal level in blood plasma
2. stimulates hypothalamus in the brain to trigger pituitary gland to secrete less ADH into bloodstream
3. low concentration of ADH in blood plasma stimulates cells in the walls of the collecting ducts to become less permeable to water
4. reduced water reabsorption from the collecting duct into the blood capillaries
5. more water is excreted in urine = volume of urine produced increases and urine is diluted

Question 15

what happens when you are dehydrated

Answer 15

1. decrease water potential below normal level in blood plasma
2. stimulates hypothalamus in the brain to trigger pituitary gland to secrete more ADH into bloodstream;
3. high concentration of ADH stimulates cells in the walls of the collecting ducts become more permeable to water
4. more water reabsorption from the collecting duct into the blood capillaries;
5. less water is excreted in urine = volume of urine produced decreases and urine is concentrated

Question 16

what is the process of dialysis

Answer 16

1. Blood is drawn from the vein in the patient’s arm and pumped through the tubing in dialysis machine: bathed in dialysis fluid + partially permeable tubing walls
2. Small molecules such as urea and other metabolic waste products diffuse through the tubing from the blood into the dialysis fluid = blood cells, platelets and large molecules remain in the tubing
3. Dialysis fluid: the same concentration of essential substances as healthy blood to ensure that essential substances (glucose, amino acids and mineral salts) do not diffuse out of the blood into the dialysis fluid -> there is no concentration gradient created
4. Dialysis fluid does not contain metabolic waste products = sets up a steep concentration gradient (blood higher concentration than fluid) = increases rate of diffusion of waste products (urea, uric acid, creatinine and excess mineral salts) out of the tubing into the dialysis fluid
5. a steep water potential gradient is created (blood has higher water potential than fluid) = increase rate of osmosis of excess water molecules into the fluid (excess water from blood enters fluid by osmosis)

Question 17

what happens when kidneys fail

Answer 17

person cannot excrete their metabolic waste products, cannot regulate water and solute concentration in body = they can go through a kidney transplant or dialysis

Question 18

adaptations of dialysis

Answer 18

1. Tubing is narrow, long and coiled = increases SAVR = speed up the rate of diffusion of waste substances into the dialysis fluid
2. Direction of the blood flow is opposite to the flow of the dialysis fluid = maintain a steep concentration gradient = increase rate of diffusion of waste materials into the fluid;