Renal Physiology

Question 1

Functions of the renal system

Answer 1

-regulation
>water balance
>sodium balance
>hydrogen ions
-Filtration
>elimination of drugs
>metabolic waste products such as urea,Uris acid and creatine
-gluconeogenesis
>production of glucose from amino acids
-endocrine function
>renin
>erythropoietin and 1,25-dihydroxyvitamn d

Question 2

Main structures of the renal system

Answer 2

o Kidneys
o Back of abdominal wall behind the peritoneum
o Filters blood and the byproducts ultimately form urine
o Ureters o Bladder o Urethra
o Several sections based on tissue type; length dependent on gender

Question 3

Purpose of the kidneys

Answer 3

o Hilum
o Indented area on each kidney where blood supply enters via the renal artery and exits via the
renal vein
o Eachkidneyissurroundedbyarenalcapsule o Outerlayerofkidneyiscalledtherenalcortex o Innerlayerofkidneyiscalledtherenalmedulla
o Contains pyramid structures in which tubules transport urine o Each pyramid then empties into a calyx
o Whichemptiesintotherenalpelvis
oWhich empties into the ureter and exits the kidney via the hilum

Question 4

How many nephrons does each kidney contain

Answer 4

1 million nephrons

Question 5

Nephron

Answer 5

o This is where all the filtration of blood occurs o There are two distinct parts of the nephron
o The renal corpuscle
o The renal tubule
o The renal corpuscle is responsible for filtering the blood…
o After this, a “filtrate” is formed that doesn’t contain cells, polypeptides or proteins
o The renal tubule is responsible for adding or taking away substances from the filtrate which ultimately forms urine that is transported to the bladder for elimination

Question 6

Renal corpuscle

Answer 6

*The aim of this structure is to filter blood - it is effectively a sieve A renal corpuscle consists of
o A glomerulus
o Bowmans Capsule
A glomerulus represents a large number of interconnecting capillaries
o Provides a large surface area for filtration
o Bowmans Capsule is filled with fluid
o Blood enters the renal corpuscle via an afferent arteriole and empties via an efferent arteriole.

Question 7

List the 3 layers of cells that separate the glomerous from the bowman’s space

Answer 7

-endothelium of the capillaries
-a basal lamina membrane
-specialised epithelial cells called podocytes

Question 8

What are mesangial cells

Answer 8

Surround the capillaries of the glomerous
-it’s a later of smooth muscle cell that can influence the rate of filtration that takes place

Question 9

Renal tube

Answer 9

-FromBowman’sCapsule,thefiltrateenterstheRenalTubule
-This begins at the proximal tubule
o Proximal convoluted tubule
o Proximal straight tubule Loop of Henle
o Descendinglimb
o Ascending limb
o Distal convoluted tubule Collecting duct
o Cortical and medullary

Question 10

Proximal tubule

Answer 10

-response to metabolic acidosis
-response to angiotensin II
-response to captopril

Question 11

Henley’s Loop

Answer 11

-response to osmotic stress
-response to PTH,calcitonin,glucagon,vasopressin

Question 12

Distal convoluted tubule

Answer 12

-response to aldosterone
-response to vasopressin

Question 13

Collecting duct

Answer 13

-short term response to vasopressin
-long term response to vasopressin

Question 14

What happens to the filtrate(urine) coming form the collecting ducts

Answer 14

Enters the renal pelvis and then then the ureters

Question 15

% division between the different types of nephrons

Answer 15

15% juxtamedullary nephrons
85% cortical nephrons

Question 16

What are the long capillaries called that surround the juxtamedullary nephrons

Answer 16

Vasa recta

Question 17

Key features of the ascending limb that passes through the afferent and efferent artertiole of the nephron

Answer 17

-macula Densa (closely packed specialised cells, where distal tubule interfaces with glomerulus)
-afferent arteriole contains juxtaglomerular cells(synthesise store and secrete renin)

Question 18

Effect of renin

Answer 18

Renin increases the volume of extracellular fluid and causes arterial vasoconstriction.

Question 19

Juxtaglomerular apparatus

Answer 19

Regulates the function of each nephron

Question 20

Purpose of the renal corpuscle

Answer 20

-Filter blood by glomerular filtration
-filtrate then passes from the corpuscle into the renal tube where substances are either added or taken away

Question 21

Tubular reabsorption

Answer 21

When a substance is moved from the tubular lumen into the peritubuluar capillaries

Question 22

Tubular secretion

Answer 22

When a substance is moved from the peritubular capillaries into the tubular lumen

Question 23

Glomerular filtration

Answer 23

-determined by the startling equation = Underpinned by hydrostatic pressure difference and the protein concentration difference

o Blood pressure in the glomerular capillaries =60 mmHg
o Fluid pressure in Bowman’s Space = 15 mmHg
o Proteins in plasma but not in filtrate (difference =29 mmHg)
Difference = 60 - (29 + 15) = 16 mmHg

Question 24

Glomerular filtration rate

Answer 24

-Volume of fluid filtered per unit time
• Rate is directly proportional to the permeability of the capillaries and the surface area
• Surface area is significant, and the capillaries of the glomerulus are very permeable
• For 70kg person, GFR =180 L/day (125 mL/min)

Question 25

GFR changesbasedonneuralandhormonalinputto theefferentandafferentarterioles

Answer 25

o Constriction of afferent arterioles reduces blood flow in and, therefore, reduces GFR
o Constriction of efferent arterioles reduces blood flow out and, therefore increases GFR

Question 26

Tubular reabsorption

Answer 26

-substances are re absorbed within the renal system

o 180L of water is filtered per day and 99% of it is reabsorbed

o 180g of glucose is filtered per day, with 100% reabsorbed (in a healthy person)

o For some substances, such as water, the %reabsorption is under physiological control

Question 27

How is urea rebsorbed

Answer 27

Urea is reabsorbed via diffusion, allowing it to move freely across membranes, resulting in a
concentration in filtrate that is the same as plasma.

As filtrate moves through the proximal tubule, water is reabsorbed so the concentration of urea in the tubule increases…

As the concentration in tubule is now greater than that in the peritubular capillaries, urea is reabsorbed by diffusion

Thus, urea reabsorption is determined by water reabsorption

Question 28

Mediated transport

Answer 28

-involves the use of channels or transporters to move substances across membranes

-many substances are actively transported with sodium.Sodium moves across a membrane via a transporter from an area of high to
low concentration.At the same time, another molecule (i.e., amino acids, glucose) moves from an area of low to high concentration (against the concentration gradient) using the same transporter

Question 29

Tubular secretion

Answer 29

-similar to diffusion
-Combines Mediated transport and diffusion although direction is different… I.e. from peritubular capillaries into tubular lumen.
-managed substances include hydrogen ions and potassium ions as well as foreign chemicals

Question 30

Renal clearance

Answer 30

= mass of substance excreted per unit time / plasma concentration of substance
Forexample:Urine mass (urine concentration of substance *urine volume) / plasma concentration of substance

Question 31

Sodium balance

Answer 31

Sodium is the main ion found in extracellular fluid
o Normally between 135 and 145 mmol/L
o Sodium Balance is achieved when sodium intake is the same as sodium loss
o Sodium intake is in the form of food and drink (about 8.5g per day)
o Sodium loss is in the form of sweat, urine and loss via faeces (in total about 8.5g per day)

Question 32

Water balance

Answer 32

Watermakesupbetween55and75%ofbodymass
o Relatively small deviations can be problematic (i.e., Hypo or hyper-hydration)
o Water balance is achieved when water intake is the same as water loss
o Water intake=drinking,foodandmetabolicproduction(about3L perday)
o Water output=sweat,urine,breathing,skinloss,lossinfaeces(intotalabout3L perday)
o If water intake is increased, in normal situations water balance is ensured by an increase in urine production

Question 33

Nephron function(summary)

Answer 33

1)filtration by glomerous
2)obligatory absorption and secretion by proximal tubule
3)generation of osmotic gradient by loop of henle
4)regular red absorption and secretion by distal tubule
5)regulated by water uptake by collecting ducts

Question 34

Arginine Vasopressin (AVP)

Answer 34

-anti-diuretic hormone (ADH)

o Diuretic =substance that increases urine production
o Released from the anterior pituitary gland primarily as a result of an increase in plasma
osmolality…
…A reduction in plasma osmolality leads to reduced secretion of AVP
-Results in the insertion(reabsorption of water and the production of low volumes of concentrated urine )or removal of aquaporins from the collecting ducts

Question 35

Plasma and urine osmolality

Answer 35

o Filtrate in tubule follows a counter-current arrangement… i.e., Flows down the descending limb and up the ascending limb
o Sodium is actively transported out of the thick ascending limb
o The proximal tubule and the descending limb allow free movement of water and passive
movement of sodium
o The ascending limb, the distal tubule and the collecting ducts are relatively impermeable to sodium
o The ascending limb and the first section of the distal tubule are impermeable to water

Question 36

Counter Current Nephron Function(summary)

Answer 36

-Fluid filtered by the Glomerulus passes through the proximal tubule and enters the loop of Henle with an osmolarity of 300 mOsm/l
-Osmolarity changes as urine flows down the tubules
-formation of hypertonic urine is due to presence of ADH

Question 37

Renin-Angiotensin-Aldosterone System

Answer 37

Urinary loss of sodium is determined by the absorption or secretion of sodium within the nephron
o Remember, the proximal tubule and descending limb of loop of Henle allow passive movement of sodium - this happens anyway,regardless of sodium levels in blood
o The majority of regulation of sodium absorption or secretion into urine occurs in the distal tubule and the collecting ducts…
o Reabsorption is achieved through active transport that involves co-movement of potassium
o Recall from previous section that the ascending limb of loop of Henle passes between the afferent and
efferent arteriole supplying the glomerulus
Macula Densa + specialised cells in afferent arteriole = juxtaglomerular apparatus (JPA)
-When sodium of filtrate within distal tubule is low, juxtaglomerular cells secrete renin…

Question 38

What does renin convert

Answer 38

-Renin converts a protein called angiotensinogen to angiotensin1 which is then converted to angiotensin
2
-Occurs in the presence of angiotensin converting enzyme (ACE)

-Angiotensin 2 acts on the adrenal gland which leads to the release of aldosterone, subsequently this
leads to an increase in the number of sodium channels which are inserted into the collecting ducts…
More reabsorption of sodium (and water)…
Ultimately, when blood sodium increases, plasma volume increases (this also increases blood pressure!)
• Counteracted by Atrial Natriuretic Peptide

Question 39

Effect of low sodium in filtrate

Answer 39

-LOW SODIUM IN FILTRATE
- DETECTED BY JGA
-SECRETION OF RENIN INTO THE BLOOD
-ANGIOTENSINOGEN TO ANGIOTENSIN1
-ANGIOTENSIN 1 INTO ANGIOTENSIN 2
-ALDOSTERONE
-SODIUM REABSORPTION

Question 40

Atrial Natriuretic Peptide

Answer 40

-Hormone released from cells in the right atria (think close relationship with BP)…
o Key determinant of release is stretch of the right atria or ‘End Diastolic Pressure’..
-Release of it leads to
o Increased sodium secretion at collecting ducts o Reduced action of angiotensin 2
o Inhibition of renin secretion
o Increases glomerular filtration rate