Excretion Notes from Old Notes

Question 1

Excretion

Answer 1

Getting rid of stuff in your tissues

Examples:
Exhalation of CO2 is excretion
Loss of material in sweat
Urine contents from kidney

Question 2

Nephrons are composed of

Answer 2

Bowmen’s capsule
Convoluted tubule
Loop of Henle

Question 3

What enters the bowmen’s capsule?

Answer 3

The blood plasma minus the big proteins: this substance is called filtrate

Question 4

Direction of blood flow in Kidney’s

Answer 4

Afferent arterioles -> glomerulus (capillary ball) -> efferent arterioles -> peritubular capillaries -> venuoles

Question 5

Vasa recta

Answer 5

A group of peritubular capillaries that surround the loop of Henle

Question 6

The outer region of the kidney

Answer 6

Renal Cortex

Question 7

The inner region of the kidney

Answer 7

Renal Medulla

Question 8

The bowmen’s capsule, glomerulus, convoluted tubules all are part of which region?

Answer 8

Cortex

Question 9

The Loop of Henle is in which region of the kidney?

Answer 9

Extends out of the cortex and into the medulla

Question 10

The entry point through the capsule

Answer 10

Hilum

Question 11

The Glomerular Filtration Rate (GFR)

Answer 11

115-125 ml filtrate/min is formed in bowman’s capsule by all nephrons (total)
The bulk of filtrate will be reabsorbed

Question 12

How can we regulate the filtration rate?

Answer 12

1. We adjust it by adjusting the blood pressure in the capillaries of the glomerulus:
   a. more pressure in capillary = more fluid forced out
   b. less pressure in capillary = less fluid forced out

Question 13

How do we adjust blood pressure in the capillaries of the glomerulus?

Answer 13

Dilation of arteriole; blood pressure in capillary is higher and more fluid is lost
Constriction of arteriole; blood pressure in capillary is lower and less fluid is lost

Question 14

After filtrate leaves the bowman’s capsule, it goes to…

Answer 14

The Proximal Tubule

Question 15

How much filtrate formed in the glomerulus gets reabsorbed in the proximal tubule?

Answer 15

Approximately 65% of the filtrate that’s formed in the glomerulus is reabsorbed in the proximal tubules

Question 16

T/F: Sodium is the major solute in blood. It is actively transported into blood and chloride follows by charge attraction

Answer 16

T

Question 17

T/F: Other solutes include glucose and amino acids which are transported into capillaries via special transporters

Answer 17

T

Question 18

When the filtrate leaves the proximal convoluted tubule does it contain glucose or amino acids?

Answer 18

When the filtrate leaves the proximal convoluted tubules it has no glucose nor amino acids in it because it has nearly been all reabsorbed. The reasons diabetics have glucose in their urine is because their blood glucose are so high that the filtrate also has high glucose concentration. Limited number of transporter protein that can move glucose in filtrate back into blood.

Question 19

What comes after the proximal tubule?

Answer 19

Loop of Henle

Question 20

What is the function of the loop of henle?

Answer 20

To create a concentration gradient within the medulla tissue
It’s function is not to alter the content of the filtrate very much, its real job is just to create a concentration gradient in the medullary tissue through which the loop of henle transverse

Question 21

Is the filtrate more concentrated when it enters or exits the loop of henle?

Answer 21

The filtrate is less concentrated when it leaves the loop of henle than when it enters it

Question 22

What comes after the loop of henle?

Answer 22

Collecting Duct

Question 23

What does ADH stand for?

Answer 23

Antidiuretic Hormone

Question 24

Explain antidiuretic hormone

Answer 24

Comes from the posterior pituitary (a neurosecretion)
Also known as a vasopressin because it constricts blood vessels
Increases the water permeability in the collecting duct

Question 25

What does antidiuretic mean?

Answer 25

Prevents loss of water

Question 26

Explain what happens when ADH acts on collecting duct

Answer 26

The filtrate comes in collecting duct and is not very concentrated, but as it moves down the collecting tube it encounters more concentrated filtrate. Water will leave the collecting duct, concentrating the urine. The urine will be low in volume and highly concentrated

Question 27

What happens when we are hydrated?

Answer 27

If we have too much water in our system, then we do not collect ADH and hence the walls of our collecting duct will not be permeable to water and therefore low concentrated filtrate comes in and large volume of low concentrated urine comes out

Question 28

What part of our brain senses water concentration?

Answer 28

The Hypothalamus

Question 29

Do our neurons fire or stop firing when there is too much water?

Answer 29

If there is too much water then neurons stop firing and there is no ADH secretion If one is dehydrated, neurons will increase firing rate and more ADH is secreted and collecting ducts become even more permeable to water and more water is retained

Question 30

Name 2 other chemicals that cause dehydration

Answer 30

Caffeine and alcohol both act on the hypothalamus and inhibit ADH secretion. Therefore it causes us to produce more dilute urine than you should. Dehydrating effect.

Question 31

How does the loop of Henle create a concentration gradient?

Answer 31

The thick ascending limb is impermeable to water and solutes. Even though it is impermeable there is active transport of sodium out of filtrate. The pumping of salt out of filtrate which adds salt to the extracellular fluid in the medulla causes the increase osmotic concentration outside. It is also responsible for the low concentration of the filtrate leaving the loop of henle. The thin ascending limb of loop of henle is permeable to solutes and water.

Question 32

Aldosterone

Answer 32

Comes from the adrenal cortex With aldosterone up to 100% Na+ reabsorbed K+ is secreted into filtrate Activates Na+/K+ pump further (Na+ leaves filtrate & K+ enters) Used to control the secretion of two ions: Retain Na+ Excrete K+

Question 33

How do we control for aldosterone secretion?

Answer 33

Secretion occurs when body is: low in Na+ or too much K+; | low K+ would inhibit secretion

Question 34

Juxtaglomerular apparatus

Answer 34

It is half distal tubule and half afferent arteriole Within the afferent arterioles are granular cells Within the distal tubule are macula densa cells

Question 35

Renin

Answer 35

An enzyme secreted by the granular cells

Question 36

Granular cells secrete

Answer 36

Renin into the blood that is flowing through the afferent arteriole. Does this when the blood flow in the arteriole is lowered. The cells act like stretch receptors. High flow (high volume) the arterioles are stretch so there is no secretion. Low flow (low volume) the arterioles are not stretched as much so there is secretion of renin.

Question 37

Angiotensinogen

Answer 37

A plasma protein produced by the liver that is always present in the blood

Question 38

T/F: Renin makes angiotensinogen into angiotensin I

Answer 38

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Question 39

Angiotensin II

Answer 39

The active hormone whose target organ is the adrenal cortex which triggers the secretion of aldosterone Is also a very strong vasoconstrictor which will constrict the arterioles and increase total peripheral resistance which will also increase blood pressure as a result. In particular within the afferent arterioles leading to the glomerulus that causes the glomerulus filtration rate to fall so less fluid is lost

Question 40

What is the active hormone that acts on the adrenal cortex in order to trigger the secretion of aldosterone?

Answer 40

Angiotensin II

Question 41

What happens with renin when your blood volume is too low (such as during severe dehydration)?

Answer 41

There is a low flow and little stretching so, Renin will be secreted, which will act on angiotensinogen to make angiotensin I which will go to the lungs and be converted into angiotensin II which will now act on the adrenal cortex to make aldosterone. Angiotensin II will reduce the Glomerulus filtration rate so we preserve fluid. Aldosterone increases pumping out of salt in the distal tubule which means more water will flow out of kidneys with the salt and into the blood, hence less water is lost in urine

Question 42

Macula densa cells

Answer 42

Act to inhibit renin secretion | They are part of the distal tubule so they respond to high sodium concentration in the filtrate in the distal tubules.

Question 43

What is there is too high of a sodium concentration in the blood either via high salt intake or loss of water?

Answer 43

You will have too high of an osmotic concentration. The hypothalamus is very sensitive to the osmotic concentration of the blood. Posterior pituitary produces antidiuretic hormone which doesn't allow water to leave and reclaim it from the collecting dust so less water is loss in urine. Attempt to restore osmotic concentration in blood. If excess sodium was the "trigger" for the restoration of osmotic concentration in blood then adding the reabsorbed H2O creates a too large blood volume. This will cause too much stretching in the arterioles so renin production will be inhibited therefore aldosterone production will stop which will reduce salt pumping in the distal tubules and enhance fluid loss in urine. This will also stop angiotensin II production hence less vasoconstriction so the glomerulus filtration rate increases and excess fluid ends up in nephron.

Question 44

Atrial Natriuetic Factor

Answer 44

Hormone produced when the atria is stretched too much (such as in the case of increased blood volume) ANH wil act to eliminate fluid via: 1. Inhibit ADH from posterior pituitary 2. Inhibits renin secretion (to prevent angiotensin system where water flow into blood via osmosis) 3. Inhibits aldosterone secretion 4. Increases permeability of glomerular capillaries which therefore glomerular filtration rate increases 5. Relaxes smooth muscles in the arterioles especially the afferent arterioles which therefore increases glomerular filtration rate

Question 45

How do Kidney cells in the nephron control the pH of the body fluid?

Answer 45

Secrete hydrogen ions into the urine

Question 46

Ways to estimate glomerulus filtration rate

Answer 46

Use inulin which is not normally found in the body The amount of inulin in the urine is a reflection of the amount filtered at glomerulus; related to GFR If you inject someone with inulin you can figure out its concentration in the blood and then collect the urine and see how much of it comes out in the urine per minute thus giving you GFR

Question 47

Paraaminohippuric acid

Answer 47

PAH All molecules of PAH in the blood are eliminated in one pass through the kidney It is filtered in the glomerulus PAH that did not get filtered is then secreted into filtrate from paratubular capillaries The clearance rate of PAH is equal to the blood flow to the kidneys