Excretory System

Question 1

Excretory system

Answer 1

filters blood and body fluids to remove waste
maintains osmotic balance of cells to prevent extreme volume change (osmoregulation)
active secretion and reabsorption of specific molecules
freshwater: need to excrete water, conserve solutes
terrestrial: need to conserve water and excrete solutes
vertebrates: kidneys

Question 2

Waste products

Answer 2

Carbohydrates and fats: CO2 and water

Proteins and nucleic acids: -NH2 groups (ammonotelic, ureotelic, uric acid)

Question 3

Nephron

Answer 3

functional unit of kidney
3 major parts:
renal corpuscle, renal tubule, collecting duct

Question 4

Renal corpuscle

Answer 4

made up of the glomerulus and bowman’s capsule, located in renal cortex
site of filtration

Question 5

Renal tubule

Answer 5

site of tubular secretion and absorption
surrounded by capillaries
loop through renal medulla
has specialized zones:
-Proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct

Question 6

Collecting duct

Answer 6

site of urine processing: concentrate or dilute

start at renal cortex, pass through medulla and empty into ureter

Question 7

Afferent arterioles

Answer 7

incoming (glomerulus)
dilate if systemic pressure decreases
if it becomes dialated, the glomerular filtration rate increases

Question 8

efferent arteriole

Answer 8

connects glomerulus to peritubular capillaries

Question 9

Glomeruli

Answer 9

part of the renal corpuscle
highly permeable capillary beds
blood pressure forces water and small molecules out and into Bowman’s capsule

Question 10

Bowman’s capsule

Answer 10

cells that surround the glomeruli

Question 11

Podocytes (CIV)

Answer 11

surface cells of the Bowman’s capsule

filter: large things stay in blood and small go out

Question 12

Proximal convoluted tubule

Answer 12

part of the renal tubule
transports NaCl out of tubular fluid and water follows
transports glucose and amino acids out of tubular fluid
-major site of reabsorption of NaCl, glucose and amino acids, water flows by osmosis
-pH regulation by secretion of H+ and reabsorption of HCO3- (blood pH ~7.35-7.45)
-site of secretion of NH3 and assorted poisons
-materials removed from tubules is returned to venous blood through uptake in peritubular capillaries
-cells have losts of microvilli on lumen face (large surface area for reabsorption)
-reabsorption requires active transport which is supported by many mitochondria

Question 13

Loop of Henle

Answer 13

part of renal tubule
permeable to water and small molecules
counter-current multiplier: creates concentration gradient in medulla by countercurrent exchange
has descending limb and ascending limb, and bottom of loop (permiable to NaCl)
osmolarity of lumen increases transiently in medulla
establishes an external concentration gradient in medulla

Question 14

Distal convoluted tubule

Answer 14

part of the renal tubule

transports NaCl out of the tubular fluid

Question 15

Collecting duct

Answer 15

part of the renal tubule
little active transport, urine concentration through osmosis
permeable to water but not ions
slightly permeable to urea at bottom
passes through increasing osmolarity of medulla (created by loop of Henle)
water leaves collecting duct by osmosis which causes urine to become more concentrated
the degree of concentration depends on magnitude of gradient

Question 16

Countercurrent exchange

Answer 16

anti-parallel flow of materials used to create steep gradient
creates steeper gradient than parallel flow because concentration gradients maintained throughout area of exchange

Question 17

Descending limb

Answer 17

Part of loop of Henle

relatively unspecialized and highly permeable to water but not ions

Question 18

Ascending limb

Answer 18

part of loop of Henle
actively secretes NaCl and has low water permeability
osmotic water movement is limited to permeable cells

Question 19

How much fluid?

Answer 19

Kidneys
recieve 1100-2000 liters of blood per day
filter ~180 L/day
urinate ~2-3 L/day
98-99% of water volume is reabsorbed in the proximal tubule, descending limb of loop of Henle and the collecting duct

Question 20

Massive water flux

Answer 20

occurs across the cell layers of the proximal tubule, descending limb of loop of Henle and the collecting duct
due to aquaporins

Question 21

Aquaporins

Answer 21

water channels
integral membrane proteins that form water-selective channels
expressed in tissues/membranes with high water permeabilities (proximal convoluted tubule, descending limb of loop of Henle, collecting duct)

Question 22

Diabetes insipidus

Answer 22

production of lots of dilute urine

can result from mutation in an aquaporin family member

Question 23

Filtration

Answer 23

requires adequate blood pressure
regulatory mechanisms maintain a constant high glomerular filtration rate
both local and systemic control mechanisms
if systemic pressure decreases, afferent (incoming) renal arterioles dilate to maintain flow through capillaries

Question 24

Renin-angiotensin-aldosterone system

Answer 24

response to decreased blood bolume and blood pressure
increases local and sustemic blood pressure by effects on vessels and fluid intake:
-efferent renal arteriole constricts
-peripheral blood vessels constrict
-aldosterone stimulates Na+ reabsorption
-stimulates thirst

Question 25

Anti-diuretic hormone (ADH) system

Answer 25

response to incresed osmolarity
Increases water reabsorption to concentrate urine
Increases water permeability of collecting duct via effects on aquaporin content

Question 26

Atrial natriuretic peptide (ANP)

Answer 26

systemic regulation of blood pressure
released in response to atrial stretch
decreases salt and water uptake in kidney
inhibits the synthesis and relaese of aldosterone
inhibits renin production and ADH release