26. Excretion of waste

Question 1

define osmoregulation and give an example of what it includes

Answer 1

a homeostatic process by which animals control solute concentrations and balance water gain and loss - must be kept within narrow limits.

includes sodium and calcium which must be maintained

Question 2

what are the four parts of the urinary system and give an example of what they do

Answer 2

kidneys - make urine and other functions

ureters - carry urine frm kidney to bladder

bladder - collects, stores and releases urine

urethra - expels urine from the bladder

Question 3

give at least three functions of the kidney

Answer 3

filters blood to produce a filtrate (reabsorbs and secretes)

removal of nitrogenous wastes (urea and uric acid)

regulation of water balance (blood pressure)

reguation of pH (acid base balance)

reguation of osmotic pressure

regulation of electrolyte leveles

regulation of concentration of many substances in plasma

hormone production - erythropietin, renin, vitamin D, prostaglandins

Question 4

describe the structure of the filteration system in a mammal

Answer 4

Question 5

what is a nephrons function?

Answer 5

they are the funcitonal unit of a kidney - a single long blind ended tubule and a glomerulus (ball of capillaries)

Question 6

name the six components of a nephron

Answer 6

glomerulus - ball of capillaries where filteration occurs

bowmans capusle - cup shaped blind end of tubule - surrounds glomerulus, collects fitrate

proximal convoluted tubule (PCT)

loop of henle - hairpin turn with descending limb and ascending limb

distal convoluted tubule (DCT)

collecting duct - adjusts volume nad concentration of urine (empties into renal pelvis which is drained by ureter)

study image

Question 7

how does filteration of blood occur?

Answer 7

blood pressure forces fluid from blood into glomerulus into lumen of bowmans capsule.

the capillaries and specialised cells of capsule are permeable to water and small solutes - not blood cells

Question 8

how does reabsorbtion occur?

Answer 8

the nephrons and connecting duct are lined by transport epithelium which reabsorbs solute and water.

Question 9

how does the proximal tubule contribute to reabsortbtion of nutrients? (5 steps)

Answer 9

1. NaCl diffuses into cells of transport epithelium - then Na+ is acitvley transported into interstittial fluid. Cl- passivley follows
2. water follows salt via osmosis
3. salt, H2O, glucose, amino acids, and K+ diffuse from filtrate and interstitial fluid into peritubular capillaires
4. secretion of H+ and NH3 (ammonia) and reabsorption bicarbonate for acid base balance (pH)
5. filtrate volume DECREASE, more CONCENTRATED

Question 10

how does the loop of henle - decending limb, contribute to reabsobtion in the kidneys?

Answer 10

1. reabsobtion of water occurs
2. aquat porin proteins form water channels - transport epithelium is freely permeable
3. interstitial fluid bathing tubule is hyperosmotic - increasing from cortex to medulla
4. water moves out of tubule by osmosis

Question 11

how does the loop of henle - ascending limb, contribute to reabsorbtion?

Answer 11

1. its impermeable to water - transport epithelium has ion channels but not water channels
2. there are thin and thick segments -

thin is where NaCl diffuses out of tubule via passive transport into interstitial fluid to maintain osmolarity in medula

thick segments - diffusion of NaCl continues by active transport

filtrate becomes more dilute

Question 12

how does the distal tubule help with reabsorbtion?

Answer 12

1. regulates potassium and NaCl concentation of body fluids -

K+ secreted INTO flitrate

NaCl REABSORBED

this contributes to pH regulation: H+ secreted and bicarbonate reabsorbed

Question 13

how does the collecting duct contribute to secretion?

Answer 13

1. carries filtrate through the medulla to the renal pelvis
2. water is lost with salt and urea - filtrate is more concentrated

Question 14

how does hormone control affect secretion in the collecting duct?

Answer 14

ADH levels high mean water conservation. Aquaporin channels in the collecting duct allow water to leave filtrate - epithelium is impremeabel to salt. filtrate becomes more concentrated. HIGH OSMOLARITY OF INTERSTITAL FLUID. this makes urine hyperosmotic to body fluids

ADH levels low means loosing water - dilute urine. active reabsorbtion of salt - no aqua porins

Question 15

how does urine prevet reflux when excreted?

Answer 15

the angle of insertion of the ureter prevents reflux

Question 16

how does excretion occur?

Answer 16

ureter delivers urine to the bladder and the bladder stores the urine until excreted

Question 17

how does the bladder store urine?

Answer 17

there are stretch receptors in the bladder that allow the smooth muscle to stretch

Question 18

what is the funciton of renin-angiotesnsin-aldosterone (RAAS)?

Answer 18

it increases salt and water reabsorbtion by responsding to a decreased blood volume by increasing the blood volume and blood pressure

• raises blood pressure
• decreases blood flow to kidneys

Question 19

what is the function of ADH?

Answer 19

increases water reabsorbtion in the distal tubules and collecting ducts of the kdiney

conserves water with aquaporins