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Anatomy and Physiology > Chapter 23 > Flashcards

Chapter 23 Flashcards

1
Q

Functions of the Kidneys

A
  1. They filter the blood plasma and excrete the toxic metabolic wastes
  2. They regulate blood volume, pressure, and osmolarity by regulating water output.
  3. They regulate the electrolyte and acid-base balance of the body fluids
  4. They secrete the hormone erythropoietin, which stimulates the production of red blood cells and thus supports the oxygen-carrying capacity of the blood.
  5. They help to regulate calcium homeostasis and bone metabolism by participating in the synthesis of calcitriol
  6. They clear hormones and drugs from the blood and thereby limit their action
  7. They detoxify free radicals
  8. In conditions of extreme starvation, they help to support the blood glucose level by synthesizing glucose from amino acids.
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2
Q

Metabolic Waste

A

A waste substance produced by the body.

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3
Q

Nitrogenous Waste

A

Small nitrogen-containing compounds.

About 50% is urea.

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4
Q

Excretion

A

The process of separating wastes from the body fluids and eliminating them from the body.

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5
Q

Excretion is carried out by 4 organ systems

A
  1. The respiratory system (CO2, gases, water)
  2. The integumentary system (water, inorganic salts, lactic acid, and urea)
  3. The digestive system (Eliminates food residue, excretes water, salts, CO2, lipids, bile pigments, cholesterol, and others)
  4. The urinary system (wastes, toxins, drugs, hormones, salts, hydrogen ions, and water)
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6
Q

Renal corpuscle

A

Filters the filtrate to urine

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7
Q

Renal Tubule

A

Converts the filtrate to urine

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8
Q

The flow of fluid

A
  1. Glomerular Capsule
  2. Proximal Convoluted Tubule
  3. Nephron Loop
  4. Distal Convoluted Tubule
  5. Collecting Duct
  6. Papillary Duct
  7. Minor Calyx
  8. Major Calyx
  9. Renal Pelvis
  10. Ureter
  11. Urinary Bladder
  12. Urethra
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9
Q

Basic Stages of Urine Formation

A
  1. Glomerular Filtration - Creates a plasmalike filtrate of the blood
  2. Tubular Reabsorption - removes useful solutes from the filtrate, returns them to the blood
  3. Tubular Secretion - Removes additional wastes from the blood, adds them to the filtrate
  4. Water Conservation - Removes water from the urine and returns it to blood; concentrates wastes.
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10
Q

Glomerular Filtration

A

A process in which water and some solutes in the blood plasma pass from capillaries of the glomerulus into the capsular space of the nephron.

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11
Q

The 3 barriers that constitute a filtration membrane are

A
  1. The fenestrated endothelium of the capillary
  2. The basement membrane
  3. Filtration slits
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12
Q
  1. The fenestrated endothelium of the capillary
A

Endothelial cells of the glomerular capillaries are honey-combed with large filtration pores and these are highly permeable.

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13
Q
  1. The basement membrane
A

Consists of a proteoglycan gel.

Few particles may penetrate small spaces but most would be held back.

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14
Q
  1. Filtration slits
A

A podocyte of the capsule is shaped like an octopus. Each arm got little extensions called foot processes. And that foot has negatively charged filtration slits.

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15
Q

Blood Hydrostatic Pressure (BHP) [out]

A

about 60 mm Hg.

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16
Q

Capsular Hydrostatic Pressure

A

about 18 mm Hg. Results from the high rate of filtration and continual accumulation of fluid in the capsule

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17
Q

Colloid Osmotic Pressure (COP) [in]

A

about 32 mm Hg.

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18
Q

Capsular Osmotic Pressure [in]

A

Almost protein-free and essentially is 0 mm Hg. But this may change if there is kidney disease.

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19
Q

Net filtration Pressure (NFP)

A

BHP - (COP + CP)

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20
Q

Glomerular Filtration Rate (GFR)

A

The amount of filtrate formed per minute by the 2 kidneys combined.

Males: 125 mL/min (180 L/day)

Females: 105 mL/min (151 L/day)

GFR = NFP * Kf

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21
Q

Filtration Coefficient (Kf)

A

Depends on the permeability and surface area of the filtration barrier.

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22
Q

Molecules that passes through the glomerular filtration membrane are:

A

Water, electrolytes, glucose, amino acids, fatty acids, vitamins, urea, uric acid, creatinine.

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23
Q

If GFR is too high…

A

Fluid flows through the renal tubules too rapidly for them to reabsorb the usual amount of water and solutes.

So urine output rises and creates dehydration and electrolyte depletion

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24
Q

If GFR is too low…

A

Fluid flows sluggishly through the tubules, they reabsorb wastes that should be eliminated in the urine, and azotemia may occur.

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25
Q

The only way to adjust GFR is to…

A

Change glomerular blood pressure

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26
Q

Change of Glomerular BP is achieved by 3 homeostatic mechanisms:

A
  1. Renal Autoregulation
  2. Sympathetic Control
  3. Hormonal Control
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27
Q

Renal Autoregulation

A

The ability of the nephrons to adjust their own blood flow and GFR without external (nervous/hormonal) control.

Helps to ensure stable fluid and electrolyte balance in spite of many circumstances.

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28
Q

There are 2 mechanisms of renal autoregulation

A
  1. Myogenic mechanism

2. Tubuloglomerular feedback

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29
Q

Myogenic Mechanism

A

Based on the tendency of smooth muscles to contract when stretched.

Afferent arteriole stretches when arterial BP rises and vice versa.

30
Q

Tubuloglomerular Feedback

A

By which the glomerulus receives feedback on the status of the downstream tubular fluid and adjusts filtration to regulate its composition, stabilize nephron performance, and compensate for fluctuations in BP.

Involves juxtaglomerular apparatus

Begins with Macula Densa, closely spaced sensory cells. When GFR is high, NaCl level is high too. So Macula Densa absorbs Na, K, Cl, then swell and then secret ATP from its surface.

Then, ATP is metabolized to adenosine by Mesangial Cells.

The adenosine actsas a messenger that stimulates juxtaglomerular cells.

Juxtaglomerular cells constricts the afferent arteriole which reduces the blood flow into the glomerulus, reducing GFR and completing the negative feedback loop.

31
Q

Granular cells

A

Contain granules of renin which is secreted in response to a drop in blood pressure. This initiates a renin-angiotensin-aldosterone mechanis,.

32
Q

2 important points about renal autoregulation

A
  1. It does not completely prevent changes in GFR. It maintains a dynamic equilibrium.
  2. It cannot compensate for extreme BP variations.
33
Q

Sympathetic Control

A

Sympathetic stimulation and adrenal epinephrine constrict the afferent arterioles which reduces GFR and urine output.

Strenuous exercise or circulatory shock indirectly triggers renin-angiotensin mechanism.

SNS directly stimulates JG cells to release renin

34
Q

Renin-Angiotensin-Aldosterone Mechanism

A

Restores BP and supports Blood volume

The drop in BP is detected by the baroreceptors.

35
Q

Angiotensin-Converting Enzyme (ACE)

A

Removes 2 more amino acids, converting itself to angiotensin II which restored fluid volume and BP in several ways.

36
Q

Several ways for Angiotensin II to restore fluid volume and BP

A
  1. Vasoconstrictor
  2. Constricts Efferent and Afferent arterioles. This raises glomerular BP and GFR, ensuring continued filtration of wastes from the blood even when BP has fallen.
  3. Constriction of efferent arteriole lowers the BP in the peritubular capillaries. This enhances the reabsorption of NaCl and water.
  4. Directly stimulates sodium and water reabsorption in the proximal convoluted tubule.
  5. Stimulates posterior pituitary gland to secrete antidiuretic hormone which promotes water reabsorption by the collecting duct.
  6. Stimulates the sense of thirst and encourages water intake.
37
Q

Proximal Convoluted Tubule

A

Reabsorbs about 65% of the glomerular filtrate while it removes substances from the blood and disposes in the urine.

38
Q

Tubular Reabsorption

A

Process of reclaiming water and solutes from the tubular fluid and returning them to the blood.

39
Q

The 2 routes of reabsorption:

A
  1. Transcellular

2. Paracellular

40
Q

Transcellular Route

A

Substances pass through the cytoplasm and out of the base of the epithelial cells

41
Q

Paracellular Route

A

Substances pass through gaps between the cells.

42
Q

Sodium Chloride Reabsorption

A
  • The key to almost everything because it creates an osmotic and electrical gradient that drives the reabsorption of water and other solutes.
  • Most abundant cation in the glomerular filtrate
43
Q

2 types of transport proteins are responsible for sodium uptake:

A
  1. Symports that simultaneously bind Na and another solute

2. Antiport that pulls Na into the cell while pumping H out of the cell into the tubular fluid.

44
Q

Chloride ions

A
  • Follow Na because they are electrically attracted to it.
  • Antiports that absorbs Cl in exchange for other anions that they eject into the tubular fluid
  • Cl and K are driven our through the basal cell surface by a K-Cl symport
45
Q

Glucose Reabsorption

A
  • Cotransported with Na by Sodium-Glucose Transporters
  • Then, removed from surface of the cell by facilitated diffusion.
  • Glucose in tubular fluid are usually reabsorbed but none in the urine.
46
Q

Other Electrolytes

A

Potassium, Magnesium, and Phosphate ions diffuse with water

47
Q

Nitrogenous Wastes

A

Urea passes through the epithelium with water.

48
Q

The mechanisms of capillary absorption are

A

Osmosis and Solvent Drag

49
Q

3 factors that promote osmosis into capillaries

A
  1. Reabsorbed fluid on the basal side creates high tissue fluid pressure that physically drives water into the capillaries
  2. The narrowness of the efferent arteriole lowers the BHP which makes it less resistance to reabsorb
  3. High COP and low BHP favors reabsorption
50
Q

Transport Maximum

A
  • Limited amount of solute that can be reabsorbed because of limited number of transport proteins in plasma membrane
  • The maximum rate of reabsorption is reached when the transporters are saturated
51
Q

Tubular Secretion

A

A process in which the renal tubule extracts chemicals from the capillary blood and secretes them into the tubular fluid.

52
Q

3 purposes of tubular secretion

A
  1. Acid-base balance by secreting proportions of hydrogen to bicarbonate ions
  2. Extract wastes from the blood: Urea, uric acid, bile acids, ammonia, catecholamines, creatinine.
  3. Clears drugs and contaminants from the blood: Penicillin, pollutants, morphine, and aspirin
53
Q

Purpose of nephron loop (loop of Henle)

A

To generate an osmotic gradient that enables the collecting duct to concentrate urine and conserve water.

54
Q

The effect of angiotensin II on Tubular Reabsoprtion

A
  1. Angiotensin II secreted
  2. Constricts afferent and efferent arterioles
  3. Maintains or increases GBP and Glomerular filtration and reduces BP in peritubular capillary
  4. Reduces resistance to tubular reabsorption
  5. Tubular reabsorption increases
  6. Urine volume is less but concentration is high
55
Q

Thin segment of loop of henle

A

Water can leave tubule

56
Q

Thick segment of loop of henle

A

Impermeable to water so, water cannot follow the reabsorbed electrolytes.

57
Q

Fluid in DCT contains about

A

20% of water and 10% of the salt from the glomerular filtrate.

(If this all passed as urine, we would be peeing about 36 Liters per day)

58
Q

Hormones that regulates reabsorption of water and salts by DCT and collecting duct

A
  1. Aldosterone
  2. Natriuretic Peptides
  3. Antidiuretic Hormone
  4. Parathyroid Hormone
59
Q

2 kinds of cells in the DCT and Collecting duct

A
  1. Principal Cells

2. Intercalated Cells

60
Q

Principal cells

A
  • More abundant
  • Have receptors for the foregoing hormones
  • Involved in salt and water balance
61
Q

Intercalated Cells

A
  • Fewer in numbers
  • Reabsorb K and secrete H into the tubule
  • Involved mainly in Acid-base balance
62
Q

Aldosterone

A
  • The “Salt-retaining hormone
  • Secreted by the adrenal cortex when the Blood Na concentration falls or K concentration rises
  • Indirectly, stimulates the kidney to secrete renin which leads to production of angiotesin II
  • It stimulates segments of the nephron to reabsorb Na and secrete K
  • It reduces urine volume
  • Water retention helps to maintain blood volume and pressure
63
Q

Natriuretic Peptides

A
  • Secreted by the heart in response to high BP
64
Q

4 actions of Natriuretic Peptides

A
  1. Dilate the afferent arteriole and constrict the efferent which increases GFR
  2. Inhibits renin and aldosterone secretion which antagonizes RAA mechanism
  3. Inhibit secretion of antidiuretic hormone and its action on the kidney
  4. Inhibit NaCl reabsorption by the collecting duct
65
Q

Antidiuretic Hormone (ADH)

A
  • Secreted by the posterior pituitary gland
  • In response to dehydration, loss of BV, and rising blood osmolarity
  • Makes the collecting duct more permeable to water so the water can re-enter the tissue fluid instead of being lost in the urine
66
Q

Parathyroid Hormone (PTH)

A
  • Secreted by Parathyroid gland
  • Stimulated by hypocalcemia (Calcium Deficiency)
  • Inhibits phosphate reabsorption on the PCT
  • Increases calcium reabsoprtion on the DCT and thick segment
  • Therefore, increases the phosphate content and lowers the calcium content of the urine
67
Q

The Collecting Duct

A

Reabsorbs water and concentrates the urine

68
Q

Steps of Countercurrent Multiplier of the Nephron Loop

A
  1. More salt is continually added by the PCT
  2. The higher the osmolarity of the ECT, the more water leaves the descending limb by osmosis
  3. The more water that leaves the descending limb, the saltier the fluid is that remains in the tubule
  4. The saltier the fluid in the ascending limb, the more salt the tubule pumps into the ECF
  5. The more salt that is pumped out of the ascending limb, the saltier the ECF is in the renal medulla.
69
Q

The Countercurrent Multiplier

A
  • Continually recaptures salt and returns it to the deep medullary tissue
  • It multiplies the osmolarity
  • Based on fluid flowing in opposite directions in 2 adjacent tubules
  • As more water gets drawn out, the filtrate becomes more concentrated since sodium is still in the fluid
  • In ascending limb, salts are removed from the tubular fluid.
  • More salts in the fluid means more can be removed
  • Now as the fluid moves up, there are fewer salts available for transport out of the tubule.
70
Q

The Countercurrent Exchange System

A
  • Basically a functional relationship of the nephron loop, vasa recta, and collecting duct
  • The structures maintain a gradient of osmolarity in the renal medulla
  • As blood flows downward into the medulla, the vessels exchange water for salt (diffuse)
  • After, the blood flows back up, as the vasa recta gives up salt and absorbs water
  • Vasa recta are arranged which enables them to remove water from the medulla without substracting from its osmotic gradient

Anatomy and Physiology (13 decks)

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