Topic 11.3 - Kidneys and osmoregulation

Question 1

Osmoregulators

Answer 1

Maintain a constant internal solute concentration despite external solute levels. Examples include all terrestrial animals, freshwater animals, and some marine animals like bony fish.

Solute concentration is typically a third of seawater and ten times that of freshwater.

Question 2

Osmoconformers

Answer 2

Contain a similar solute concentration to that of the surroundings. Examples include most marine invertebrates, some insects, and marine animals like sharks.

Question 3

Malpighian tubule system

Answer 3

Found in insects, tubes that branch from the intestinal tract. The cells lining this system actively transport ions and uric acid into the lumen of the tubules. This also draws water in by osmosis. The tubules dump the waste in the gut for excretion.

Carries out osmoregulation and nitrogenous waste removal. The equivalent of blood and tissue fluid in insects is called hemolymph. Osmoregulation causes the hemolymph concentration to be maintained.

Question 4

Removal of nitrogenous waste

Answer 4

Catabolism of amino acids causes the production of nitrogenous waste which is toxic and needs to be excreted.

Excretion -> removal of waste products produced by cell reactions/ metabolic pathways.

Question 5

Kidney

Answer 5

Draw kidney (cortex should be 1/5 thickness of kidney)

Blood enters the kidney through the renal artery
Cortex contains glomerulus
Medulla contains the loop of Henlé
Pelvis and ureter transport urine away from kidneys
The renal vein transports blood back to the heart to be oxygenated again.

Question 6

Renal vein vs renal artery

Answer 6

Renal artery blood contains more toxins and harmful waste than renal vein blood because they are mostly removed from the blood as it passes through the kidneys.

Less water and salts too because they are also removed if in excess.

Less O₂ and glucose and more CO₂ concentrations in renal vein. Energy and oxygen needed for kidney metabolism so concentration changes reflect this.

About 1/5 of blood plasma is filtered out of the body as it passes through the kidneys.

Question 7

Detection of potential kidney issues

Answer 7

Plasma proteins should not be filtered normally. If they are found in the urine, there is abnormal function - an issue with the kidneys.

Question 8

Glomerulus

Answer 8

High pressure in blood capillaries pushes plasma out of the wall, creating tissue fluid.

Higher capillary pressure and the capillary is more permeable so more fluid is pushed out (ungefähr 100x).

Released fluid is called glomerular filtrate.

Ions, water, glucose, urea, and other small molecules are filtered out of the blood plasma into the glomerular filtrate. Almost all proteins are kept in the blood plasma.

Question 9

Ultrafiltration

Answer 9

Separation of molecules differing in size by a few nanometers.

Three main parts:

1) Fenestrations - between cells in capillary wall, about 100nm in diameter, allow fluid to escape - not blood.
2) Basement membrane - covers and supports the capillary wall. Made of negatively charged glycoproteins, forming a mesh, blocking proteins due to size and charge
3) Podocytes - Specialised epithelial cells that cover the outer glomerular capillaries. Form inner wall of bowman’s capsule and have extensions that allow them to wrap around the capillaries and side branches (food processes). These side branches have small gaps which prevent small molecules from being filtered out.

Question 10

Proximal convoluted tubule

Answer 10

Selectively reabsorb useful substances by active transport. The volume of glomerular filtrate is extremely large 180 dm⁻³ (180l). This is several times the body fluid volume. About 1.5kg salt is contained and 5.5kg of glucose. The volume of urine produced per day is around 1.5 dm⁻³ containing no glucose and less than 1.5kg salt.

Proximal convoluted tubule reabsorbs these substances. By the end of the tubule around 80% are reabsorbed.

Question 11

Sodium ions (Na⁺)

Answer 11

Move by active transport from the filtrate to the space outside of the tubules. They then pass to the peritubular capillaries. Pump proteins for sodium are located on the outer membrane of tubule cells.

Question 12

Chloride ions (Cl⁻)

Answer 12

Move with sodium ions due to attraction to the charge gradient created by sodium ions.

Question 13

Glucose

Answer 13

Moved out of filtrate through co-transporter proteins. The movement of sodium ions gives the energy needed for glucose to also be transported out of the filtrate.

The same process is used for amino acid transportation.

Question 14

Water

Answer 14

Solute concentration gradient caused by solute movement causes water movement.

Question 15

Nephron

Answer 15

The functional unit of the kidney. A healthy adult should contain 1-1.5 million nephrons.

Starts with blood entering the nephron through the afferent arteriole. This blood moves into the glomerulus where the blood is filtered. The glomerular filtrate is then transported away by the bowman’s capsule. The blood then leaves the glomerulus through the efferent arteriole.

Blood can move either

1) through the peritubular capillaries where blood is filtered more with interaction with the convoluted tubules and then moved into the venules.
2) through the vasa recta where the blood moves deep into the medulla and interacts with the loop of Henlé then back up into the cortex and into the venules.

The venules then transfer the blood to the renal vein.

Question 16

Vasa recta

Answer 16

Unbranched capillaries that are similar in shape to the loop of Henlé. They move blood down the descending limb deep into the medulla and then up the ascending limb back to the cortex.

Question 17

Venules

Answer 17

Carry blood to the renal vein.

Question 18

Bowman’s capsule

Answer 18

Cup structure, a highly porous inner wall, takes in filtered fluid from the blood.

Question 19

Distal convoluted tubule

Answer 19

Like the proximal convoluted tubule but with fewer, shorter microvilli, fewer mitochondria. Perfectly round lumen.

Question 20

Collecting duct

Answer 20

Wider tube that carries the filtrate back through the cortex and medulla to the renal pelvis.

Question 21

Afferent arteriole

Answer 21

Brings blood from the renal artery.

Question 22

Efferent arteriole

Answer 22

Narrow vessel for blood leaving the glomerulus, restricted blood flow, helps maintain high pressure in the glomerulus.

Question 23

Peritubular capillaries

Answer 23

Low-pressure capillary bed that runs around the convoluted tubules, absorbing fluid.

Question 24

Loop of Henlé - how it works

Answer 24

Maintains hypertonic conditions in the medulla. Loop of Henlé creates a solute concentration gradient. Energy for this gradient is expended in ascending limb cell walls.

Proximal convoluted tubule -> descending limb -> ascending limb -> distal convoluted tubule.

Sodium ions are pumped out of filtrate into fluid between cells in medulla (interstitial fluid). Wall of ascending limb is impermeable to water so interstitial fluid becomes hypertonic.

Normal body fluid -> 300 mOsm
Sodium ions create -> +200 mOsm
interstitial fluid -> can reach 500 mOsm

Descending limb wall permeable to water, not to Na⁺. As filtrate goes down the descending limb, the water is drawn to the solute through osmosis so the milliosmolarity becomes the same in the interstitial fluid and filtrate.

Sodium pumps are able to generate higher mOsm as the descending limbs goes further down. This eventually reaches the human body’s maximum of 1200 mOsm.

Question 25

Loop of Henlé - what the system is an example of

Answer 25

Example of countercurrent multiplier system.

Countercurrent -> flows in opposite directions
ie:
70 60 50 40 30 20 10
65 55 45 35 25 15 05

instead of co-current:
50 45 40 35 30 30 30 30
05 10 15 20 25 30 30 30

Multiplier -> causes a steeper solute concentration gradient than would be possible using concurrent.

Also a countercurrent multiplier system in vasa recta - blood prevented from diluting medulla solute conc while still allowing it to send away water and Na⁺ ions from the descending limb.

Question 26

Loop of Henlé - in other animals

Answer 26

The length of the loop is positively correlated with the need for water.

Animals in desert loops have a longer loop. Medulla also become thicker as loops are in the Medulla.

Question 27

Function of ADH

Answer 27

anti-diuretic hormone controls reabsorption of water in the collecting duct. When filtrate enters the distal convoluted tubule, it is hypotonic. Loop of Henlé releases more solute than water typically.

Low solute conc - the wall of these parts of nephron have very low permeability to water, Large volume of urine, low solute conc, increasing blood solute concentration.

High solute conc - Hypothalamus detects this, stimulates pituitary gland to release ADH, makes wall more permeable to water, blood solute concentration reduced.

Blood solute conc always at a constant - osmoregulation.

Question 28

Dehydration

Answer 28

Occurs -> when more water is released out of the body than in.
Caused by -> exercise, diarrhoea, insufficient water intake.
Leads to -> disrupted metabolic processes.
Symptoms -> darker urine, tiredness, lethargy (lack of energy and enthusiasm), blood pressure falls because of lower blood volume, increased heart rate, bad body heat regulation because of inability to sweat.

Question 29

Kidney failure treatment

Answer 29

Kidney failure is often caused by diabetes / chronic high blood pressure (caused by bad pancreas (diabetes))

Kidney transplant is one

Hemodialysis / renal dialysis -> blood leaves body from arm, moves into machine with a countercurrent system with waste product being moved into the machine. Purified blood returned to the arm. Hemodialysis takes several hours.

Question 30

Urinalysis

Answer 30

Examines urine.

Detects blood cell / glucose / protein levels or drugs in the urine.

Glucose / proteins in urine is bad as glucose should be reabsorbed and proteins should not enter the urine (should be too big).

Question 31

Nitrogenous waste produced by animals

Answer 31

Marine / freshwater -> release ammonia directly - it will be diluted by the environment.

Terrestrial animals / marine mammals -> convert ammonia to the less toxic urea and then released.

Amphibians -> ammonia as larva, urea after metamorphosis.

Birds / insects -> uric acid because not soluble - doesn’t require water (birds can fly with least water needed).

Developing eggs -> uric acid better as it crystalises and is not soluble so it doesn’t build to toxic levels.

Question 32

Overhydration

Answer 32

Occurs -> Less common, overconsumption of water.
Caused by -> water consumed, electrolytes not replaced.
Leads to -> body fluids hypotonic, cells swell (osmosis).
Symptoms -> headache, nerve cell disruption.