Tubular Secretion

Question 1

Tubular Secretion involves

Answer 1

transepithelial transport

Question 2

Provides a second route of entry into the tubules for selected substances

Answer 2

Tubular Secretion

Question 3

The most important substances secreted by the tubules:

Answer 3

Hydrogen ion
Potassium ion
Organic anions and cations

Question 4

Renal H+ secretion is extremely important in regulating

Answer 4

acid–base balance in the body.

Question 5

H+ secreted into the tubular fluid is eliminated from the body in

Answer 5

the urine.

Question 6

H+ can be secreted by the

Answer 6

proximal, distal, and collecting tubules

Question 7

H+ secretion _________ as required

Answer 7

increases/decreases

Question 8

K+ is selectively moved

Answer 8

in opposite directions in different parts of the tubule

Question 9

Filtered K+ is almost completely reabsorbed in the

Answer 9

proximal tubule

Question 10

most K+ in the urine is derived from

Answer 10

controlled K+ secretion in the distal parts of the nephron rather than from filtration

Question 11

During K+ depletion,

Answer 11

K+ secretion in the distal parts of the nephron is reduced to a minimum

Question 12

When plasma K+ levels are elevated,

Answer 12

K+ secretion is adjusted to reduce the plasma K+ concentration to normal

Question 13

K+ secretion is varied in a controlled fashion to

Answer 13

maintain the desired plasma K+ concentration

Question 14

Mechanism Of K+ Secretion

Answer 14

K+ secretion in the distal and collecting tubules is coupled to Na+ reabsorption

Question 15

Question 16

Control of K+ Secretion

Answer 16

Aldosterone stimulates K+ secretion by the principal tubular cells late in the nephron while simultaneously enhancing these cells’ reabsorption of Na+

Effect of H+ Secretion on K+ Secretion

Question 17

Question 18

The organic ion secretory systems serve three important functions:

Answer 18

Organic secretory pathways facilitate excretion of organic ions – e.g. certain blood-borne chemical messengers having served their purpose, must be rapidly removed from the blood so that their biological activity is not unduly prolonged

To be transported in blood, organic ions are extensively but not irreversibly bound to plasma proteins and therefore cannot be filtered through the glomeruli. Tubular secretion facilitates elimination of these nonfilterable organic ions in urine.

Most important, the systems play a key role in eliminating many foreign compounds from the body. Speeds up the removal of many foreign organic chemicals, including food additives, environmental pollutants, drugs, and other non-nutritive organic substances that have entered the body

Question 19

Summary of Reabsorptive and Secretory

Answer 19

Question 20

The final quantity of urine formed averages 1 mL/min

Answer 20

• of the 180 liters filtered per day, 1.5 liters of urine are excreted.

Question 21

Urine contains high concentrations of

Answer 21

various waste products plus variable amounts of the substances regulated by the kidneys

Question 22

A relatively small change in the quantity of filtrate reabsorbed can bring about a large change in the

Answer 22

volume of urine formed

Question 23

The plasma clearance of any substance is defined as

Answer 23

the volume of plasma completely cleared of that substance by the kidneys per minute

Question 24

a more useful measure than urine excretion

Answer 24

Plasma clearance

Question 25

The plasma clearance rate varies for different substances, depending on

Answer 25

how the kidneys handle each substance.

Question 26

Plasma clearance

Question 27

At normal fluid balance and solute concentration, the body fluids are

Answer 27

isotonic at an osmolarity of 300 milliosmols per liter (mOsm/L)

Question 28

Hypotonic vs Hypertonic

Answer 28

This gradient enables the kidneys to produce urine that ranges in concentration from 100 to 1200 mOsm/L, depending on the body’s state of hydration

Question 29

Long-looped nephron establishes a vertical osmotic gradient in the

Answer 29

renal medulla

Question 30

Long-looped nephron establishes a vertical osmotic gradient in the renal medulla. How?

Answer 30

via countercurrent multiplication

Question 31

Uncontrolled osmotic reabsorption of filtered H2O occurs in the

Answer 31

proximal tubule secondary to active Na+ reabsorption

Question 32

By the end of the proximal tubule, about _____ of the filtrate has been reabsorbed, but the remaining % in the tubular lumen still has the _________

Answer 32

65%
same osmolarity as the body fluids

Question 33

An additional 15% of the filtered H2O is obligatorily reabsorbed from the

Answer 33

loop of Henle

Question 34

Properties of the Descending Limb of a Long Henle’s Loop

Answer 34

1. Is highly permeable to H2O (via abundant, always-open AQP-1 water channels)
2. Does not actively extrude Na+

Question 35

Properties of the Ascending Limb of a Long Henle’s Loop

Answer 35

1. Actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid
2. Is always impermeable to H2O, so salt leaves the tubular fluid without H2O osmotically following along.

Question 36

Mechanism of Countercurrent Multiplication

Answer 36

Question 37

https://www.youtube.com/watch?v=hjQd9nWAxQk

Question 38

https://www.youtube.com/watch?v=cYyJF_aSC6o

Question 39

Benefits of Countercurrent Multiplication

Answer 39

1. It establishes a vertical osmotic gradient in the medullary interstitial fluid. This gradient, in turn, is used by the collecting ducts to concentrate the tubular fluid so that a urine more concentrated than normal body fluids can be excreted.
2. Because the fluid is hypotonic as it enters the distal parts of the tubule, the kidneys can excrete a urine more dilute than normal body fluids

Question 40

Vasopressin controls variable H2O reabsorption

Answer 40

After obligatory H2O reabsorption from the proximal tubule and loop of Henle, 20% of the filtered H2O remains in the lumen to enter the distal and collecting tubules for variable reabsorption under hormonal control.
20% X GFR (180 L/day) = 36 L/day to be reabsorbed to varying extents, depending on the body’s state of hydration
The fluid leaving the loop of Henle enters the distal tubule at 100 mOsm/L, so it is hypotonic to the surrounding isotonic interstitial fluid of the renal cortex
The distal tubule then empties into the collecting duct, which is bathed by progressively increasing concentrations (300 to 1200 mOsm/L) of the surrounding interstitial fluid as it descends through the medulla.

Question 41

For H2O absorption to occur across a segment of the tubule, two criteria must be met:

Answer 41

1. An osmotic gradient must exist across the tubule
2. The tubular segment must be permeable to H2O

Question 42

The distal and collecting tubules are impermeable to H2O except in the presence of

Answer 42

vasopressin (antidiuretic hormone)

Question 43

Question 44

Water Reabsorption

Answer 44

In the tubular segments permeable to H2O, solute reabsorption is always accompanied by comparable H2O reabsorption because of osmotic considerations.
Solute excretion is always accompanied by comparable H2O excretion because of osmotic considerations.
Osmotic Diuresis and Water Diuresis
A loss or gain of pure H2O that is not accompanied by comparable solute deficit or excess in the body (that is, “free” H2O) leads to changes in ECF osmolarity

Question 45

Question 46

Renal failure has a variety of causes, among the causes are the following:

Answer 46

1. Infectious organisms, either blood-borne or gaining entrance to the urinary tract through the urethra
2. Toxic agents
3. Inappropriate immune responses
4. Obstruction of urine flow by kidney stones, tumors, or an enlarged prostate gland
5. An insufficient renal blood supply that leads to inadequate filtration pressure, which can occur secondary to circulatory disorders

Question 47

Acute vs Chronic renal failure

Question 48

Question 49

Once urine has been formed by the kidneys, it is transmitted through the

Answer 49

ureters to the urinary bladder.

Question 50

Urine does not flow through the ureters by gravitational pull alone.

Answer 50

Peristaltic (forward-pushing) contractions of the smooth muscle within the ureteral wall propel the urine forward from the kidneys to the bladder.

Question 51

The ureters penetrate the wall of the bladder obliquely, coursing through the wall several centimetres before they open into the bladder cavity.

Answer 51

As the bladder fills, the ureteral ends within its wall are compressed closed

Question 52

Role of the Bladder

Answer 52

The bladder can accommodate large fluctuations in urine volume.

Question 53

as the bladder alternately fills and empties.

Answer 53

The epithelial lining can increase and decrease in surface area by the orderly process of membrane recycling

Question 54

Bladder muscle can

Answer 54

stretch tremendously without building up bladder wall tension

Question 55

In addition, the highly folded bladder wall

Answer 55

flattens out during filling to increase bladder storage capacity.

Question 56

empties urine from the bladder

Answer 56

Contraction

Question 57

The exit from the bladder is guarded by two sphincters:

Answer 57

Internal urethral sphincter
External urethral sphincter

Question 58

internal urethral sphincter

Answer 58

is smooth muscle and, accordingly, under involuntary control.
When the bladder is relaxed, the anatomic arrangement of the internal urethral sphincter region closes the bladder outlet.

Question 59

Farther down the passageway, the urethra is encircled by a layer of skeletal muscle, the external urethral sphincter.

Answer 59

This sphincter is reinforced by the entire pelvic diaphragm, a skeletal muscle sheet that forms the floor of the pelvis and helps support the pelvic organs

Question 60

The motor neurons that supply the external sphincter and pelvic diaphragm fire continuously at a moderate rate unless they are inhibited
Normally, when the bladder is relaxed and filling, both the internal and the external urethral sphincters are closed to keep urine from dribbling out.
Furthermore, because the external sphincter and pelvic diaphragm are skeletal muscle and thus under voluntary control, the person can deliberately tighten them to prevent urination from occurring even when the bladder is contracting and the internal sphincter is open.

Question 61

Micturition

Answer 61

urination

Question 62

Micturition (urination) the process of bladder emptying, is governed by two mechanisms:

Answer 62

The micturition reflex
Voluntary control

Question 63

Voluntary Control of Micturition

Answer 63

Bladder filling gives rise to the conscious urge to urinate
The perception of bladder fullness appears before the external sphincter reflexly relaxes, warning that micturition is imminent
If the time when the micturition reflex is initiated is inopportune for urination, you can voluntarily prevent bladder emptying by deliberately tightening your external sphincter and pelvic diaphragm
Urination cannot be delayed indefinitely
Micturition can also be deliberately initiated, even though the bladder is not distended, by voluntarily relaxing the external sphincter and pelvic diaphragm