homeostasis and the kidney

Question 1

define homeostasis

Answer 1

the maintenance of constant or steady state conditions within the body

Question 2

features of homeostatic responses

Answer 2

• a control system with sensors (receptors) for monitoring of the factor being controlled
• if a receptor shoes a departure from the set point a corrective mechanism takes place
• corrective mechanism involves a negative feedback system

Question 3

define corrective mechanism

Answer 3

brings about a change which returns factor back to its normal level

Question 4

define negative feedback

Answer 4

occurs as the factor being controlled returns back to normal level causing corrective mechanisms to be switches off, preventing over correction.

Question 5

examples of corrective mechanisms

Answer 5

sweating, vasodilation

Question 6

homeostatic control of mammalian body systems are essential why?

Answer 6

-they provide optimum conditions for enzyme reaction in terms of pH and temperature
-avoid osmotic problems in cells and body fluid

Question 7

what factors are kept constant

Answer 7

water ion content temperature pH oxygen

Question 8

what do less complex animals do

Answer 8

living in an environment where the external environment is relatively constant

Question 9

eg of homeostatic control

Answer 9

correct solute potential of blood > person eats salty meal > solute potential of blood becomes more negative > brain releases adh > solute potential of blood becomes less negative > brain releases less adh to prevent blood becoming too dilute

Question 10

define excretion

Answer 10

removal of toxic waste products of metabolism eg urea nitrogenous waste creatine phosphate

Question 11

define osmoregulation

Answer 11

control of water potential of bodily fluids

Question 12

function of the kidney

Answer 12

function of kidney is to operate as a complex filter keeping useful products in the blood and eliminating excretory products and excess water

Question 14

order of urinary system

Answer 14

kidney, ureter, bladder, sphincter muscle, urethra

Question 15

what is the name of the capillary network formed by the efferent arteriole branches

Answer 15

vasa recta

Question 16

define ultrafiltration

Answer 16

the filtration of plasma and substances below a certain size into bowmans capsule (not selective)

Question 17

what is reabsorbtion

Answer 17

as ultrafiltration is purely based on molecular size, it is essential that filtered usefulness products are selectively reabsorbed back into the bloodstream from the nephron

Question 18

why does blood entering glomerulus have high hydrostatic pressure

Answer 18

-short distance from the heart, blood travels down the aorta into kidney before branching into kidney arterioles
-afferent arterioles are wider than efferent arterioles
-coiling of capillaries in glomerulus further restricts blood flow therefore increasing pressure

Question 20

adaptations of squamous endothelial cells

Answer 20

-single layer
-contain small pores
-lined with specialised cells known as podocytes which have extensions in two planes that allow filtered material to pass through easily

Question 21

what is the basement membrane

Answer 21

the effective filter which determines which components of the blood enter the bowmans capsule

Question 22

what is glomerular filtrate

Answer 22

small molecules, glucose, amino acids, ions/salts, urea, creatinine, water, very small proteins, hormones and vitamins

Question 23

how does filtration occur

Answer 23

water potential within glomerular capillaries must exceed water potential within the bowman’s capsule ie the glomular filtrate must have a more negative water potential
pressure potential of blood is much greater than the back pressure created by the filtrate in the nephron

Question 24

define loop of henle

Answer 24

the part of the nephron that enables mammals to produce a urine hypotonic to the blood and plays a significant role in water reabsorption of collecting ducts

Question 25

where does reabsorbtion occur

Answer 25

pct

Question 26

what substances are reabsorbed

Answer 26

gkucose amino acids and water

Question 27

how are glucose and amino acids reabsorbed

Answer 27

50% by facilitated diffusion along the concentration gradient then when concentration gradient changesthe other 50% is carried against the concentration gradient by active transport

Question 28

how is water reabsorbed and which part of the nephron reabsorbs the most water

Answer 28

in pct 70% of water is reabsorbed , the osmotic effect created causes over 70% of water in filtrate to reenter blood capillaries passively by osmosis

Question 29

how are cuboidal epithelial cells of pct adapted?

Answer 29

1. microvilli to increase surface area for reabsorption, increasing number of carrier proteins 2. cell surface membrane contains carrier proteins for selective reabsorption 3. infolding of membrane further increase surface area 4. mitochondria provide ATP for active transport

Question 30

what is urea

Answer 30

toxic metabolic waste

Question 31

what occurs on the DCT

Answer 31

further regulation of blood composition takes place. the pH and ionic composition of blood in the capillaries surrounding the tubules are adjusted and some toxic substances are secreted from blood into the filtrate for disposal eg. creatinine

Question 32

is urea reabsorbed?

Answer 32

yes. up to 50% can be reabsorbed not selectively but some urea passes from the nephron back to blood by diffusion (passive diffusion)

Question 33

***how does conc of urea change across length of pct

Answer 33

although some urea diffuses back into the blood by diffusion along the length of the pct, the conc of urea in the **filtrate** increases along its length due to the reabsorbtion of water. at the end of the pct the filtrate is isotonic with blood plasma

Question 34

what is the role of the collecting duct

Answer 34

where water regulation takes place, although most water is reabsorbed in pct, the process is passive and the exact volume of water reabsorbed back into the blood cannot be controlled (osmosis-travels down the solute potential gradient)

Question 35

how can reabsorbtion in collecting ducts be controlled

Answer 35

by varying the permeability of the collecting ducts- those is where fine control of water balance takes place the adh is crucial in this process as it can control the degree of permeability of the collecting ducts walls

Question 37

the roll of the antidiuretic hormone

Answer 37

ADH is produced in the hypothalamus and then secreted into the posterior love of the pituitary body where it is stored and then released into blood the solute potential of the blood is monitored by osmoreceptors in the hypothalamus

Question 38

what happens if blood becomes TOO CONC (more neg solute potential)

Answer 38

occurs due to sweating after exercise, not drinking enough water or eating a very salty meal osmoregulators detect more negative solute potential posterior lobe of the pituitary body releases more adh into the blood, this caused walls of the dct to become more permeable so more water is reabsorbed by osmosis passively down the osmotic gradient, solute potential returns to normal levels

Question 39

what happens if blood is too dilute

Answer 39

blood develops a less negative (higher) solute potential less adh released ducts become less permeable, large volumes of dilute urine are produced

Question 40

difference between ascending and descending loop of henle

Answer 40

ascending limb is thicker and HIGHLY impermeable to water descending limb is thin and permeable

Question 41

function of loop of henle

Answer 41

ascending limb secreted Na+ and Cl- ions into the medulla this process involves active transport the sodium chloride salt builds up in the interstitial fluid in medulla creating a very negative solute potential as a result of ions leaving ascending limb the filtrate becomes progressively more dilute and us hypotonic by the time it reaches the top

Question 42

what is the main function of the loop of henle

Answer 42

TO CREATE VERY CONC INTERSTITIAL FLUID IN THE MEDULLA A FEATURE WHICH FACILITATES THE OSMOSIS REMOVAL OF WATER FROM THE COLLECTING DUCTS

Question 43

how do cuboidal epithelial cells help in the ascending limb

Answer 43

they are rich in mitochondria which provides atp necessary to pump Na+ and Cl- into medulla

Question 44

why is the process described as counter current multiplier effect

Answer 44

the osmotic differences between the ascending and descending limbs at any one level are small but the cumulative effect over the length of limbs are significant this together with the filtrates in the limbs travelling in opposite directions is why the process is described as CCME

Question 45

why does water have very little effect on the solute potential of interstitial fluid

Answer 45

water that leaves descending limb by osmosis enters vasa recta and is removed from the medulla

Question 46

what is the correlation between length of loop of henle and water reabsorbed

Answer 46

there is a positive correlation between length of loop and ability to reabsorb water the longer the loop the more water can be reabsorbed (animals in the desert) longer loop allows medulla to have an even more negative water potential (more ions pumped out)