Overview of Kidney function

Question 1

what is water and electrolyte homeostasis?

Answer 1

when intake and loss are in balance over a significant period. it does not happen by accident.

Question 2

what are some complications that can arise with water and electrolyte imblanance?

Answer 2

-haemorrage
-unusual eating or drinking
-severe dehydration, rapid fluid loss from gut or after burns
-unintended consequences of drug actions

Question 3

what is the typical water input and output a day?

Answer 3

input - 2.5L
output -2.5

Question 4

how do we output water/fluids?

Answer 4

-urine (1500ml)
-sweat (100ml)
-faeces (200ml)
-invisible loss (700ml)

Question 5

what happens when sweat loss increases?

Answer 5

urine output can be reduced in these conditions

Question 6

at rest how much kidney tissue does cardiac output supply?

Answer 6

25% Of CO about 200g so about 625ml/100g/min

Question 7

why do kidneys receive such a high blood flow?

Answer 7

much higher flow than is required to support flow, tissue metabolism and make sure its filtered.

Question 8

what is blood pressure like in golemerular capillaries?

Answer 8

high, around 50-60mmHg

Question 9

what is the structure of a renal artery like?

Answer 9

-short
-relatively large radius
-unusual sequence of blood vessels

Question 10

what is the blood flow like in renal artery?

Answer 10

afferent arterioles -> glomerular capillaries -> efferent arterioles -> tubular capillaries -> venule

Question 11

what is the functional unit for the kidney?

Answer 11

nephron

Question 12

what are the 2 types of nephrons?

Answer 12

superficial (shorter) and juxtamedullary (longer)

Question 13

where is water reabsorption more effective?

Answer 13

jaxta-medullary as they have longer loops

Question 14

what does each nephron look like?

Answer 14

-a tube
-the nephron wall is a continuous layer of epithelium
-cell shapes in the walls are very different
-shape reflects activity; surface area ; ion pumping etc

Question 15

what are the 4 sections of nephrons?

Answer 15

-proximal convoluted tubules
-loop
-distal convoluted tubule
-collecting duct

Question 16

what is ultrafiltration?

Answer 16

driven by blood pressure in glomerular capillaries
-high renal blood flow (25%)
-high filtration rate

Question 17

what is reabsorption?

Answer 17

active pumping from filtrate in tubules
-for substances to be retained eg water, glucose, amino acids electrolytes

Question 18

what is secretion?

Answer 18

active pumping into tubules
-for substances to be eliminated faster than filtration alone
-allows H+ ammonia, uric acid and some drugs

Question 19

Which hormone controls pumping rates?

Answer 19

aldosterone can adjust the rates of Na+ and K+ pumping

Question 20

where does the filtration of small molecules occur?

Answer 20

through slits between podocytes
-limited by the space between the podocyte processes

Question 20

how much salt is recommended?

Answer 20

adults should eat no more than 6g of salt a day

Question 21

where does ultrafiltration occur?

Answer 21

glomerular capsule

Question 22

what is the cut off size for molecules?

Answer 22

67KD

Question 23

how is the limit of molecule filtration controlled?

Answer 23

-the space between the podocyte process (primary filtration mechanism)
-charge of the molecule (secondary filtration mechanism)

Question 24

in what cases would the filtration mechanisms go wrong?

Answer 24

-high blood pressure -inflammatory disease -can cause the podocyte processes to move further apart

Question 25

what is the normal glomerular filtration rate

Answer 25

90-140ml/min

Question 26

what is the brush border?

Answer 26

a layer of densely packed microvilli projecting from the inside surface of a tubular passage.

Question 27

what is the proximal convoluted tubule?

Answer 27

site of reabsorption -has active reabsorption of glucose, amino acids, Na+ and K+ ions -co-transporters, aqueous channels, membrane pumps -substantial water reabsorption

Question 28

what should have occurred by the end of the Principle convoluted tubule?

Answer 28

-complete reabsorption of glucose, amino acids -substantial reabsorption of Na+ and water -volume of filtrate reduced by 2/3rds

Question 29

where is the loop of henle wall thinner?

Answer 29

descent into the medulla

Question 30

when is the loop of henle wall thicker?

Answer 30

ascent from medulla

Question 31

how does the loop of henle work?

Answer 31

-thicker wall on ascent, active pumping out of tubule -solute diffuses into descending tubule; counter-current mechanism 'recycles' solutes -ion pumping develops high osmotic pressure at the tip of the loop -no net reabsorption here

Question 32

what makes the high osmotic pressure?

Answer 32

most ions can diffuse back into the descending tubule, recirculation of solute generates a region of high osmotic pressure.

Question 33

what happens in the distal convoluted tubule?

Answer 33

more solute reabsorption and secretion -less intense electrolytes and water reabsorption -DCT ion pumping can be controlled by hormones like aldosterone to fine tune Na+ and K+ exchange.

Question 34

what happens in the collecting duct?

Answer 34

-CDs pass close to tips of loop of henle -if CDs are permeable to water, then moves out of the duct to concentrate filtrate -duct permeability is set by ADH/AVP

Question 35

what is the normal plasma osmolarity?

Answer 35

300 mOsm

Question 36

how is the control of blood osmolarity regulated in a case of restricted water intake?

Answer 36

1. when water intake is restricted, plasma osmolarity increases 2. more ADH/AVP is secreted by hypothalamus 3. ADH increases the water permeability of collecting ducts 4. more water is reabsorbed 5. concentrated urine is produced

Question 37

what happens when ADH/AVP is present?

Answer 37

aquaporins are inserted into the luminal membrane to allow water movement. this rapid insertion/removal allows quick responses

Question 37

what happens when water intake is restricted?

Answer 37

plasma osmolarity increases

Question 37

what happens when there is an excess water intake?

Answer 37

osmolarity falls -hypothalamus secretes less ADH/AVP -collecting duct walls lose permeability to water -dilute urine produced

Question 37

what is the half life of ADH/AVP in circulation?

Answer 37

15 mins

Question 38

what are the juxtaglomerular apparatus?

Answer 38

a mass of cells that detects sodium levels in DCT.

Question 38

what does hypo-filtration initiate?

Answer 38

-secretion of renin by the juxtaglomerular apparatus

Question 38

what is the function of renin?

Answer 38

-splts angiotensinogen to make angiotensin I which is converted to angiotensin II

Question 38

what is low sodium interoperated as?

Answer 38

hypofiltration and so low blood pressure

Question 39

what is angiotensin II?

Answer 39

a powerful vasoconstrictor

Question 40

what does the renin/ angiotensin/ aldosterone system do?

Answer 40

regulates renal blood flow and glomerular filtration rate (low BP, low renal flow, hypo filtration ect.

Question 41

what effect does the sympathetic nerve have on the renin/ angiotensin/ aldosterone system?

Answer 41

enhances this action

Question 42

what does aldosterone do?

Answer 42

increases reabsorption of Na+ and Cl- ions from loop of henle, DCT AND CD cells. also increases K+ secretion. -also has effects on outside of kidney, increases absorption of sodium from the gut and reduces excretion of sodium in sweat and tears.

Question 43

how is aldosterone secretion increased?

Answer 43

when electrolyte concentrations fall (secreted by glomerulosa cells of the adrenal cortex)

Question 44

what happens when electrolyte absorption increases?

Answer 44

water reabsorption also increases

Question 45

what are the 3 components that make up the filtration barrier?

Answer 45

-endothelial cells of glomerular capillaries -golmerular basement membrane -epithelial cells of Bowmans capsule (podocytes)

Question 46

what is ultrafiltration?

Answer 46

filtration that occurs under high pressure

Question 47

how does charge affect filtration

Answer 47

negatively charged ions filter less easily positively charged ions filter easily

Question 48

what is the function of glycocalyx in the glomerulus?

Answer 48

restrict negatively charged molecules from being filtered.