Tubular Reabsorption

Question 1

All plasma constituents except the plasma proteins are indiscriminately filtered together through the

Answer 1

glomerular capillaries

Question 2

The filtered fluid contains

Answer 2

nutrients, electrolytes, and other substances that the body cannot afford to lose in the urine

Question 3

The essential materials that are filtered are

Answer 3

returned to the blood by tubular reabsorption

Question 4

Tubular reabsorption is

Answer 4

tremendous, highly selective, and variable.
This means that Only a small percentage, if any, of filtered plasma constituents that are useful to the body are present in the urine

Question 5

Of the 125 mL of fluid filtered per minute, typically 124 mL/min are reabsorbed

Answer 5

A large percentage of filtered waste products are present in the urine - These wastes are generally are not reabsorbed

Question 6

Characteristics of the tubule wall

Answer 6

The tubule wall is one cell thick and is close to a surrounding peritubular capillary

Question 7

Tubular reabsorption involves transepithelial transport

Answer 7

1. Leave the tubular fluid by crossing the luminal membrane of the tubular cell.
2. Pass through the cytosol from one side of the tubular cell to the other.
3. Cross the basolateral membrane of the tubular cell to enter the interstitial fluid.
4. Diffuse through the interstitial fluid.
5. Penetrate the capillary wall to enter the plasma.

Question 8

2 types of tubular reabsorption

Answer 8

• active
• passive

Question 9

The two types of tubular reabsorption depend on

Answer 9

whether local energy expenditure is needed for reabsorbing a particular substance

Question 10

In passive reabsorption

Answer 10

• the substance’s net movement occurs down electrochemical or osmotic gradients

Question 11

In active reabsorption

Answer 11

• net movement of the substance occurs against an electrochemical gradient

Question 12

______ of the total energy spent by the kidneys is used for Na+ transport

Answer 12

80%

Question 13

Na+ is reabsorbed throughout

Answer 13

most of the tubule

Question 14

99.5% of the Na+ that is filtered is

Answer 14

normally reabsorbed

Question 15

on average the reabsorption of Na+ is as follows:

Answer 15

67% is reabsorbed in the proximal tubule
25% in the loop of Henle
8% in the distal and collecting tubules.

Question 16

Question 17

Sodium is reabsorbed throughout the tubule with the exception of the

Answer 17

descending limb of Henle’s loop

Question 18

Na+ reabsorption involves the

Answer 18

energy-dependent Na+–K+ ATPase carrier located in the tubular cell’s basolateral membrane

Question 19

Na+ Reabsorption

Answer 19

Sodium reabsorption in the proximal tubule plays a pivotal role in reabsorbing glucose, amino acids, H2O, Cl-, and urea.

Sodium reabsorption in the ascending limb of the loop of Henle, along with Cl- reabsorption, plays a critical role in the kidneys’ ability to produce urine of varying concentrations and volumes.

Sodium reabsorption in the distal and collecting tubules is variable and subject to hormonal control.

Question 20

Aldosterone

Answer 20

stimulates Na+ reabsorption

Question 21

In the proximal tubule and loop of Henle

Answer 21

a constant percentage of the filtered Na+ is reabsorbed regardless of the Na+ load

Question 22

In the distal and collecting tubules,

Answer 22

the reabsorption of a small percentage of the filtered Na+ is subject to hormonal control

Question 23

Sodium and its accompanying anion Cl- account for more than 90% of the

Answer 23

ECF’s osmotic activity

Question 24

The Na+ load is subject to regulation;

Answer 24

Cl- passively follows along

Question 25

The most important hormonal system involved in regulating Na+ is

Answer 25

the renin–angiotensin– aldosterone system (RAAS).

Question 26

secrete renin

Answer 26

The granular cells

Question 27

The granular cells secrete renin into the blood in response to

Answer 27

a fall in NaCl, ECF volume, and arterial blood pressure.

Question 28

The following three inputs to the granular cells increase renin secretion:

Answer 28

The granular cells themselves function as intrarenal baroreceptors. When the granular cells detect a fall in blood pressure, they secrete more renin. The macula densa cells of the juxtaglomerular apparatus are sensitive to the NaCl moving past them. In response to a fall in NaCl, the macula densa cells trigger increased renin secretion. The granular cells are innervated by the sympathetic nervous system. When blood pressure falls below normal, the baroreceptor reflex increases sympathetic activity. Increased sympathetic activity stimulates the granular cells to secrete more renin.

Question 29

Question 30

Functions of the Renin–Angiotensin–Aldosterone System

Answer 30

Aldosterone increases Na+ reabsorption by the principal cells of the distal and collecting tubules. RAAS promotes salt retention and a resulting H2O retention and rise in arterial BP This system alleviates the factors that triggered the initial release of renin Angiotensin II is a potent constrictor of the systemic arterioles - directly increasing BP Stimulates thirst and stimulates vasopressin – results in plasma volume expansion and elevation of arterial pressure. By varying the amount of renin and aldosterone secreted in accordance with the salt determined fluid load in the body, the kidneys can finely adjust the amount of salt conserved or eliminated.

Question 31

inhibit Na+ reabsorption

Answer 31

The natriuretic peptides These peptides produce natriuresis, or excretion of large amounts of sodium in the urine

Question 32

A Na+ losing, blood pressure–lowering system that involves

Answer 32

the hormones atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP).

Question 33

The heart, in addition to its pump action, produces

Answer 33

ANP and BNP

Question 34

The main action of ANP and BNP is to

Answer 34

directly inhibit Na+ reabsorption in the distal parts of the nephron, thus increasing Na+ excretion and accompanying osmotic H2O excretion in the urine.

Question 35

Question 36

natriuretic peptides inhibit:

Answer 36

- renin secretion by the kidneys - act on the adrenal cortex to inhibit aldosterone secretion. - they inhibit the secretion and actions of vasopressin, the H2O-conserving hormone.

Question 37

ANP and BNP also promote

Answer 37

natriuresis and accompanying diuresis by increasing the GFR

Question 38

ANP and BNP directly

Answer 38

lower blood pressure by decreasing cardiac output and reducing total peripheral resistance

Question 39

Large quantities of nutritionally important organic molecules are completely reabsorbed into the blood.

Question 40

Glucose and amino acids are reabsorbed by

Answer 40

secondary active transport - the sodium and glucose cotransporter (SGLT)

Question 41

All actively reabsorbed substances bind with plasma membrane carriers that transfer them across the membrane against a concentration gradient

Question 42

An upper limit exists on how much of a particular substance can be actively transported from the tubular fluid in a given period

Answer 42

This maximum reabsorption rate is designated as the tubular maximum, or Tm

Question 43

The normal plasma concentration of glucose is

Answer 43

100 mg of glucose for every 100 mL of plasma

Question 44

With 125 mL of plasma normally being filtered each minute,125 mg of glucose pass into Bowman’s capsule with this filtrate every minute

Answer 44

Filtered load of a substance = plasma concentration X GFR of the substance Filtered load of glucose = 100 mg/100 mL X 125 mL/min = 125 mg/min The Tm for glucose averages 375 mg/min – the glucose carrier mechanism is capable of actively reabsorbing up to 375 mg of glucose per minute before it reaches its maximum transport capacity. Renal Threshold for Glucose = 300 mg/100 mL

Question 45

Phosphate is

Answer 45

actively reabsorbed and regulated

Question 46

The kidneys do directly contribute to the regulation of many electrolytes

Answer 46

e.g. phosphate and calcium

Question 47

Excess ingested phosphate is

Answer 47

quickly spilled into the urine, restoring the plasma concentration to normal

Question 48

The reabsorption of phosphate and calcium is also subject to

Answer 48

hormonal control

Question 49

The amount of Cl2 reabsorbed is determined by

Answer 49

the rate of active Na+ reabsorption instead of being directly controlled by the kidneys.

Question 50

How is water absorbed?

Answer 50

Water is passively reabsorbed throughout the length of the tubule as H2O osmotically follows actively reabsorbed Na+

Question 51

Where does water absorption occur?

Answer 51

80% is obligatorily reabsorbed in the early parts of the nephron. 20% is reabsorbed in the distal portions of the tubule

Question 52

H2O passes primarily through aquaporins (AQPs)

Answer 52

– In the proximal tubule AQP-1, are always open. - Whereas, the AQP-2 channels in the distal parts of the nephron are regulated by the hormone vasopressin.

Question 53

Return of filtered H2O to the plasma is enhanced by the fact that

Answer 53

the plasma-colloid osmotic pressure is greater in the peritubular capillaries than elsewhere

Question 54

Passive reabsorption of urea is indirectly linked to

Answer 54

active Na+ reabsorption

Question 55

A concentration gradient is created for urea to

Answer 55

passively diffuse from the tubular lumen into the peritubular capillary plasma

Question 56

Only about _____ of the filtered urea is passively reabsorbed

Answer 56

50%

Question 57

Urea molecules

Answer 57

- the smallest of the waste products - are the only wastes passively reabsorbed

Question 58

The other wastes cannot be passively reabsorbed because they

Answer 58

cannot permeate the tubular wall.

Question 59

What happens to other waste that cannot be passively reabsorbed?

Answer 59

These waste products generally remain in the tubules and are excreted in the urine in highly concentrated form