11.3 - the kidney and osmoregulation

Question 1

what is osmolarity?

Answer 1

• the solute concentration of a solution

Question 2

what is osmoregulatory?

Answer 2

• Animals are known as osmoregulators as they maintain a constant internal solute concentration despite different osmolarities of the environment i.e. marine environments.

Question 3

what are osmoconformers?

Answer 3

• Osmoconformers are animals whose internal solute concentration tends to be the same as the concentration of solutes in their
  environment.
• Osmoconformers cannot adapt their internal solute concentration.
• Examples of osmoconformers include jellyfish and squid.

Question 4

where is hemolymph?

Answer 4

• Insects belong to the arthropoda phylum, where members have an open circulatory system that lacks blood vessels
• insects have circulating fluid called hemolymph

Question 5

what is the Malpighian tubule system in insects?

Answer 5

• Insects have tubes that branch off from their intestinal tract, which are known as Malpighian tubules
• Cells lining the tubules actively transport ions and uric acid from the hemolymph into the lumen of the tubules
• Most of the water and salts are reabsorbed by the hindgut, while the nitrogenous wastes are excreted with faeces
• The Malpighian tubules function similarly to kidneys in animals

Question 6

the kidney in insects?

Answer 6

• Osmoregulation is a form of homeostasis where the concentration of hemolymph or blood is kept within a certain range.
• Waste products from the breakdown of amino acids need to be excreted as nitrogenous wastes can be toxic.
• The waste product in mammals is urea whilst the waste product in insects is uric acid.
• In mammals, the kidney is used to remove these waste products

Question 7

drawing the human kidney.

Answer 7

• kidney should be roughly oval
  with a concave side.
• The renal artery and vein are attached to the concave side, where the renal artery has a smaller diameter than the renal vein.
• The labelled cortex should be the edge of the kidney with a thickness of about 1/5 of the entire width.
• The medulla should be shown inside the cortex with pyramids.
• The renal pelvis should be shown on the concave side of the kidney, and it should drain into the ureter.

Question 8

how does blood travel through the kidney?

Answer 8

• The kidney has a dual function as it is involved in osmoregulation as well as excretion where waste substances from the blood are removed.
• Blood enters the kidney through the renal artery and exits through the renal vein.
• Therefore, the composition of blood in the renal artery is different to that in the renal vein due to the function of the kidney.

Question 9

blood consumption in the renal artery and the renal vein.

Answer 9

• The renal artery has a higher concentration than the renal vein of toxins and other substances not fully metabolized by the body e.g. drugs.
• The renal artery also has a higher concentration of waste products such as urea than the renal vein.
• Due to osmoregulation, blood in the renal vein has a more constant concentration of water and salt than the renal artery.
• Unwanted substances pass out of the body in urine and so the renal artery has a higher concentration of these substances than the renal vein, which should not have these substances present.
• The blood in the renal vein is deoxygenated due to the metabolic activity of the kidney whereas the blood in the renal artery is oxygenated.

Question 10

how does the concentrations of plasma protiens and glucose in the kidney change?

Answer 10

• The concentration of glucose is slightly lower in the renal vein than the artery as the cells of the kidney uses some of the glucose for its metabolic activity.
• The concentration of plasma proteins remain constant in the renal artery and vein as these are not filtered by the kidney.

Question 11

drawing a nephron.

Answer 11

• Diagrams of the nephron should include the glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, the relationship between the nephron and collecting duct should also be included.

Question 12

how to draw a nephron?

Answer 12

• A nephron is the functional unit of the kidney.
• The nephron is a tube with a wall consisting of one layer of cells in which substances move across to leave the body.

Question 13

how to draw a Bowman’s capsule?

Answer 13

• Bowman’s capsule: a cup-shaped structure with a porous inner wall that collects fluid filtered from the blood.

Question 14

how to draw a Glomerulus?

Answer 14

• Glomerulus: a tight, knot—like capillary bed structure where blood filtration occurs.

Question 15

how to draw a Proximal convoluted tubule?

Answer 15

• Proximal convoluted tubule: a twisted section of the nephron where the cells in the wall have many mitochondria, microvilli projecting into the lumen for reabsorption of glucose, amino acids, sodium ions, chloride ions and water.

Question 16

how to draw a Loop of Henle?

Answer 16

Loop of Henle: a tube shaped like a hairpin with a descending limb that carries filtrate into the medulla of the kidney and an ascending limb that brings filtrate back to the cortex.

Question 17

how to draw a Distal convoluted tubule?

Answer 17

• Distal convoluted tubule: another twisted section with fewer microvilli and mitochondria.

Question 18

how to draw a Collecting duct?

Answer 18

Collecting duct: a wide tube that carries the filtrate through the cortex and medulla to the renal pelvis towards the ureter and bladder.

Question 19

how to draw a Afferent arteriole?

Answer 19

• Afferent arteriole: brings blood from renal artery into the glomerulus.

Question 20

how to draw Peritubular capillaries?

Answer 20

• Peritubular capillaries: low pressure capillary bed that surrounds the convoluted tubule to absorb fluid
  from the filtrate.

Question 21

how to draw Vasa recta?

Answer 21

• Vasa recta: unbranched capillaries that carries blood into the medulla or into the cortex.

Question 22

how to draw Venules?

Answer 22

Venules: carry blood to the renal vein.

Question 23

how to draw a Efferent arteriole?

Answer 23

• Efferent arteriole: narrow vessel that restricts blood flow to generate high pressure in the glomerulus. Takes blood to the renal vein.

Question 24

what is ultrafiltration in the glomerulus?

Answer 24

• glomerulus functions to produce filtrate from the blood through a process called ultrafiltration.
• The blood in the capillaries of the glomerulus of the kidney is particularly high and the permeability of the capillary wall is far greater than in other tissues.
• The increased pressure and permeability forces fluid out and this is called the glomerular filtrate.
• If particles pass the fenestrations, the basement membrane and the podocytes, they become part of the glomerular filtrate that is collected by Bowman’s capsule and flows into the proximal convoluted tubule

Question 25

why does ultrafiltration occor?

Answer 25

a) The blood pressure is very high as the vessel taking blood away from the glomerulus (efferent arteriole) is narrower than the vessel bring blood to the glomerulus (afferent arteriole). b) The blood capillaries in the glomerulus are fenestrated meaning they have pores between the cells in the capillary wall. These fenestrations are ~100nm in diameter so it allows fluid but not blood cells to escape. c) A basement membrane covers and supports the wall of the capillaries that prevents plasma proteins from being filtered out. d) Podocytes form the inner wall of the Bowman’s capsule that prevent small molecules from being filtered out of the blood in the glomerulus.

Question 26

how are solutes reabsorbed from the glomerular filtrate?

Answer 26

- large volume of glomerular filtrate flows into the proximal convoluted tubule and it contains large quantities of essential ions and molecules - Reabsorption allows for the recovery of important ions such as sodium and chloride, and nutrients including glucose, amino acids and vitamins - chemical composition of body fluids is precisely regulated by the control of solute reabsorption from the glomerular filtrate

Question 27

what does the proximal convoluted tubule do?

Answer 27

- Most of the selective reabsorption occurs in the proximal convoluted tubule - The wall of the nephron consists of a single layer of cells and in the proximal convoluted tubule the cells have microvilli projecting into the lumen, so the surface area is increased for reabsorption - By the end of the proximal convoluted tubule, all glucose and amino acids, and 80% of water, sodium and other mineral ions have been absorbed

Question 28

how do pumps in the membrane help reabsorb substances?

Answer 28

- they reabsorb useful substances by active transport, using ATP produced from the many mitochondria present in the cells - Sodium ions are moved by active transport. - Chloride ions are attracted out of the filtrate due to the charge gradient established by the sodium ion movement - Glucose and amino acids are co-transported out of the filtrate through separate co-transporter proteins

Question 29

how does active transport mover filtrate?

Answer 29

- Active transport of solutes makes the total solute concentration higher in the cells of the wall than in the filtrate in the tubule. - water moves from the filtrate to the cells and on to the adjacent blood capillary by osmosis. - Only 20% of the original volume of water remains in the tubule that flows to the loop of Henle.

Question 30

what does the ascending limb of the loop of Henle do?

Answer 30

- The ascending limb is permeable to sodium ions but not water. - The ascending limb pumps sodium ions from the filtrate into the medulla by active transport, and this facilitates in creating a high solute concentration in the medulla.

Question 31

what does the descending limb of the loop of Henle do

Answer 31

- The descending limb is permeable to water but not sodium ions. - Water leaves the nephron by osmosis due to the increasing solute concentrations of the medulla.

Question 32

what does the loop of Henle do

Answer 32

- The overall effect of the loop of Henle is to create a concentration gradient of solute concentrations in the medulla.

Question 33

how does the loop of Henle work?

Answer 33

- As the filtrate flows down the descending limb into the region of high solute concentration, some water is drawn out by osmosis. - This dilutes the interstitial fluid in the medulla slightly. - The vasa recta counters the dilution of the solute concentration in the medulla by removing the water with some sodium ions. - The filtrate that leaves the loop of Henle is more dilute than the fluid entering it.

Question 34

how does the length of the loop of henle affect it?

Answer 34

- The longer the loop of Henle, the more water volume can be reabsorbed from the filtrate. - Animals adapted to living in dry or desert habitats will often have long loops of Henle so they can retain as much water as possible. - This also results in a much higher concentration of metabolic wastes in the urine of these animals. - To accommodate the longer loop of Henle, the medulla is also relatively thicker

Question 35

how do desert animals maintain levels of water and salt?

Answer 35

- desert rodents produce very high concentrations of urine because they have very long loops of Henle and thicker medulla regions of the kidney, there are very high number of mitochondria to produce high quantities of ATP to establish concentration gradients, and there are more aquaporins to preserve water.

Question 36

how does the solute concentration affect blood?

Answer 36

- as the filtrate moves from the loop of Henle to the distal convoluted tubule, the solute concentration is hypotonic as more solutes were reabsorbed than water in the loop of Henle - If the solute concentration of the blood is too low, relatively little water is reabsorbed in the distal convoluted tubule and collecting ducts - The wall of these parts of the nephron have low permeability to water and more water is excreted in urine with low solute concentration, thus increasing the solute concentration of blood - If the solute concentration of blood is too high, the hypothalamus of the brain detects this and causes the pituitary gland to secrete the hormone – antidiuretic hormone or ADH (used in preference to vasopressin).

Question 37

What does ADH do?

Answer 37

- makes the cells of the distal convoluted tubule and collecting duct produce membrane channels (called aquaporins) to increase water permeability - As the filtrate passes down the collecting duct through the medulla, the high solute concentration of the medulla causes most of the water in the filtrate to be reabsorbed by osmosis. - so, a small volume of concentrated urine is produced as water reabsorption increase to reduce blood solute concentration

Question 38

what is osmoregulation?

Answer 38

- the water content of the blood is kept within narrow limits, an example of homeostasis

Question 39

how does alcohol affect ADH?

Answer 39

- alcohol inhibits ADH release and causes excess urinary water loss. - This leads to dehydration and the effects of a hangover

Question 40

what is dehydration?

Answer 40

- occurs when more water leaves the body than comes into the body. - Factors affecting dehydration include exercise, insufficient water intake, or diarrhoea. - This leads to darkened urine due to the increase solute concentrations. - Water is necessary to remove metabolic wastes and so dehydration can lead to tiredness and lethargy due to decreased muscle functions. - Blood pressure can fall due to low blood volume, which can lead to increased heart rate. - Body temperature regulation may be affected due to an inability to sweat

Question 41

what is hydration?

Answer 41

- occurs when too much water is consumed and this results in a dilution of blood solutes. - Overhydration may occur as a result of large amounts of water being consumed following intense exercise, without replacing the electrolytes lost. - This makes the body fluids hypotonic, and could result in the swelling of cells due to osmosis. - The most common symptoms of this are headache and nerve function disruption.

Question 42

what is kidney failure?

Answer 42

- most commonly a complication from diabetes or high blood pressure - Patients can undergo renal dialysis, where an artificial dialysis machine performs the roles of ultrafiltration and reabsorption instead of the kidney

Question 43

what is the process of renal dialysis?

Answer 43

- The patients blood passes over a semi-permeable membrane in the machine with the small waste products passing through the membrane but not the blood cells or proteins. - The purified blood is returned to the patient via a vein. - The procedure takes several hours, and dialysis carries the risk of infection and other complications

Question 44

what is a kidney transplant?

Answer 44

- Humans have two kidneys but can survive with one; thus the donor may be living or deceased. - A kidney transplant allows the patient more independence, freedom of movement but can lead to organ rejection

Question 45

what is Urinalysis?

Answer 45

- Urine is a product of osmoregulation, excretion and metabolism, all of which can be disrupted by illness or drug abuse. - Urinalysis in a clinical procedure that examine the urine for any deviation form normal compositions. - This can be performed using a urine test strip, which indicates the pH, protein level and glucose level in the urine

Question 46

what can your urine show?

Answer 46

- High levels of glucose in urine can be an indication of diabetes - High protein levels can indicate damage to the kidneys as these do not normally flow into the filtrate during ultrafiltration. - Urine can also be tested in this way for the presence of banned or controlled drugs. - Microscopic examination of urine is carried out to determine whether cells are present, as cells are not normally present in urine. - The presence of neutrophils, a type of white blood cell, can be a sign of a urinary tract infection (UTI). - The presence of red blood cells can be sign of a kidney stone or tumour in the urinary tract

Question 47

what is Nitrogenous wastes?

Answer 47

- form due to the breakdown of amino acids and nucleic acids

Question 48

what is Ammonia?

Answer 48

- produced from this breakdown, and it is alkaline and alters the pH balance. - Ammonia is also toxic as it is a highly reactive chemical

Question 49

what are Marine organisms?

Answer 49

- release waste directly as ammonia as it is easily diluted in the surrounding water

Question 50

how are different waste produced in animals?

Answer 50

- terrestrial organisms must expend energy to convert ammonia to less toxic forms: urea or uric acid - Most animals produce urea, which is water-soluble and requires water to be released, thus urea is removed with urine - Birds and insects convert ammonia to uric acid, but does not require water for removal as it is not water-soluble. - Therefore, these organisms can reduce the weight of nitrogenous wastes as water does not need to be carried for excretion. - Uric acid is also linked to adaptations for reproduction for organisms that develop within eggs. - Uric acid crystallises rather than building up to toxic levels inside the egg.