Excretory system

Question 1

What is Bilirubin?

Answer 1

The compound that gives feces its colour. It is produced in the liver when old Heme groups are broken down

Question 2

what is urea? What synthesizes it?

Answer 2

Urea is a chemical compound synthesized in the liver. Its job is to carry excess nitrogen in the blood to eventually be filtered by the kidneys. Ammonia is very toxic to the body and therefore it must turned into urea

Question 3

Is the skin an excretory organ?

Answer 3

yes: the sweat it produces has urea, ions, and H2O. However we do not sweat for the purpose of excretion and therefore the skin is a secondary excretion organ.

Question 4

What are the medullary pyramids, papillae, calyx renal pelvis, and ureter? (hint they are all connected

Answer 4

Blood enters the kidney through the renal artery, is processed by the glomerulus, and then leaves via the renal vein to the inferior vena cava.

filtrate then goes through the renal tubules to reach the collecting ducts.

1. the convergence of many collecting ducts creates the renal pyramids
2. at the tip of each pyramid is what is called the papilla
3. urine leaves the papilla into surrounding space called the calyx
4. the calyx space narrows into a region called the renal pelvis which empties filtrate into the ureter
5. the ureter takes the filtrate to the bladder

Question 5

what is the network of blood vessels surrounding the nephron called?

Answer 5

the peritubular capillaries which allow for reabsorption and secretion

Question 6

explain the general process of filtration starting with the afferent arteriole.

Answer 6

renal artery splits into afferent arterioles which pass through capillary networks called Glomeruli. Each glomerulus is surrounded by a structure called the Bowman’s capsule.

when the efferent arteriole constricts, blood pressure is increased which facilitates the movement of plasma from the blood into the lumen of the bowman’s capsule

note: the vasoconstriction of the afferent arteriole will lead to less blood flow and less filtration (similarly, the vasodilation of the afferent arteriole will also decrease GFR)

Question 7

where does most reabsorption occur within the nephron ?

Answer 7

Most solute reabsorption occurs in the proximal convoluted tubule (PCT). Here roughly 70% of solute is taken back

additionally! all solute movement in the PCT is accompanied with water movement and therefore most H2O resorption occurs here too.

Question 8

true or false, the PCT is highly regulated and selective

Answer 8

false, the proximal tubule is selective in what it transports, but it is not regulated by many things. Its job is to reabsorb as much as possible and has no external influences such as hormones

Question 9

explain diabetes insipidus vs diabetes mellitus

Answer 9

diabetes mellitus –> the bodies ability to produce or respond to insulin is impaired and therefore the individual has high glucose levels in the blood

diabetes insipidus –> production or response to ADH is impaired (ADH is responsible for water retention) which leads to major loss in water

Question 10

why is glucose excreted by individuals with diabetes mellitus?

Answer 10

since they have such a high glucose conc. the transporters responsible for glucose reabsorption become saturated and unable to bring back all glucose.

Question 11

where does most secretion take place?

Answer 11

in the distal convoluted tubule (DCT) and the collecting duct (unlike the PCT where most of reabsorption occurs)

Question 12

explain the action of ADH.

Answer 12

ADH aka vasopressin is a hormone released from the posterior pituitary and acts on the Distal nephron.

ADH ,when released, increases the permeability of water in the CD and the DCT (without ADH the collecting duct is impermeable to water). Due to the high osmolarity of the inner medulla, water leaves the pores formed and enters the peritubular capillaries.

This ADH secretion is caused by dehydration which is indicative of low blood volume or high blood solute.

Question 13

why does alcohol cause diuresis? (water in urine)

Answer 13

it blocks the action of ADH

Question 14

explain the action of aldosterone.

Answer 14

when blood pressure is low, aldosterone is released from the adrenal cortex which increases sodium reabsorption into the blood at the DCT. This increase in sodium (i.e. increase in plasma osmolarity)) increases water intake and ADH release which will increases blood pressure.

note: at the distal tubule, the movement of ions is not accompanied by water which is true for the PCT

Question 15

explain the permeability of the descending loop of Henle?

Answer 15

the Descending loop of Henle is permeable to water. As it descends into the increasing tissue osmolarity of the medulla, water is lost from the filtrate (making the filtrate quite conc.)

Question 16

explain the permeability of the ascending loop of Henle?

Answer 16

the ascending loop of Henle is split into two sections: thin and thick.
the ascending loop of henle is impermeable to water but permeable to ions

at the higher thick region, Ions such as sodium, potassium, and chloride are lost which decreases filtrate osmolarity and increases medulla osmolarity.

Question 17

explain how the loop of Henle’s structure takes advantage of osmolarity.

Answer 17

The transporters of ions can only work against a 200 osmolarity difference.

as you move from cortex to inner medullar, the tissue osmolarity increases dramatically.

the loop of henle actively cycles through the osmolarity difference to allow many transporters to work together to pump against a much larger osmolarity difference

Question 18

what is the osmolarity of blood

Answer 18

300 osmoles

Question 19

What is the countercurrent multiplier effect of the nephron

Answer 19

This refers to the loop of henle’s opposite direction of filtrate flow and difference in permeabilities. This maintains a high osmolarity in the medulla which is important for water retention when ADH acts on the collecting ducts to become permeable to water (water flows into the medulla then capillaries)

Question 20

what is The Vasa Recta

Answer 20

this is the main blood vessel that follows the nephron

Question 21

what is countercurrent exchange (not the same as countercurrent multiplier)

Answer 21

counter current exchange refers to the Vasa Recta running in opposite direction as the loop of Henle. The Vasa Recta is an efferent arteriole which means its blood has been filtered and therefore its eager to reabsorb water.

as the Vasa Recta descends its blood gets increasingly salty (on the side where ions are pumped out). However it then goes up the descending limb which pumps water out. The Vasa Recta picks this up and slowly equilibrates so that its blood osmolarity is back to 300 at the end.

Question 22

what is the juxtaglomerular apparatus?

Answer 22

The JGA is a specialized point of contact between the afferent arteriole and the distal tubule. It monitors blood pressure.

Question 23

what are macula densa cells?

Answer 23

these are a collection of juxtaglomerular cells which are chemoreceptors. They detect filtrate osmolarity and use it as an indication of blood pressure. Low filtrate osmolarity indicates low blood pressure.

Question 24

Explain the process of producing angiotensin 2 and aldosterone upon macula densa cell activity.

Answer 24

The macula Densa cells of the JGA recognize low blood pressure. These causes them to release a hormone called Renin

1) renin converts angiotensinogen (produced in the liver) into angiotensin 1
2) angiotensin 1 travels to the lungs where it is converted to angiotensin 2 by angiotensin converting enzyme (ACE)
3) angiotensin 2 is a vasoconstrictor which increases blood pressure
4) angiotensin 2 also acts on the kidney for the adrenal cortex to release aldosterone which increases sodium retention which leads to increased blood pressure.

Question 25

how can glomerular filtration rate be increased? (GFR)

Answer 25

macula densa cells cause dilation in afferent arterioles which increases blood flow the the glomerulus. Also vasoconstriction of efferent arterioles will increase pressure of filtration.

Question 26

t or f, both kidney auto-regulation via macula densa cells and SNS regulation of afferent arterioles regulates GFR

Answer 26

true

Question 27

what does hyperventilation do to plasma pH?

Answer 27

aside from the kidney, the lungs also control pH.

Upon hyperventilation (deep, rapid breathing), you are getting rid of lots of carbonic dioxide (acidic) therefore increasing the pH of plasma.

Question 28

what do C cells of the the thyroid gland secrete? what does this secreted molecule do?

Answer 28

C cells of the thyroid gland secrete Calcitonin which which responds to too high calcium conc. (lowers plasma calcium)

Question 29

how does calcitonin lower plasma Calcium?

Answer 29

1. encourages bone deposition
2. reduced absorption by the gut
3. excretion in urine (therefore acts on kidneys)

Question 30

what does the parathyroid gland secrete, what does it do, where does it act?

Answer 30

PTH is secreted which acts on bone to increase plasma calcium. It also acts on the gut to increase calcium absorption and acts on the kidneys to increase reabsorption.

Question 31

what is the only hormone produced by the kidneys? what it do?

Answer 31

Erythropoietin which induces red blood cell production in bone marrow. (released upon low oxygen content)