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Year 1 Animal Physiology > 8. Renal Physiology > Flashcards

8. Renal Physiology Flashcards

1
Q

Name the 4 main functions of the kidneys.

A

1) Excretion of metabolic waste products (ingestion/metabolism) and foreign chemicals
2) Regulation of water and electrolyte balance
3) Regulation of body fluid osmolality and electrolyte concentrations
4) Regulation of acid-base balance

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2
Q

Name the 4 indirect functions of the kidney.

A

1) Regulation of arterial pressure
2) Regulation of erythrocyte production
3) Secretion, metabolism and excretion of hormones
4) Gluconeogenesis

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3
Q

Describe the General Organisation of the Kidney

A

Two Kidneys, Hilum (Renal Artery, vein, lymphatics, Nerve, Ureter), tough fibrous capsule and inner medulla.

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4
Q

List the components of the inner medulla.

A

Renal Pyramids, Cortex-medulla border, Papilla and Renal Pelvis (contains major calyces. minor calyces - collect urine from the tubules of each papilla).

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5
Q

Describe the Renal Blood Supply.

A

Has a renal artery and vein, Afferent arterioles lead to glomerular capillaries. Then to efferent arterioles. The kidney tubules are also surrounded by peritubular capillaries. Two capillaries seperated by efferent arteriole. 22% of cardiac output.

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6
Q

Name the 5 parts of the nephron.

A

Renal Corpuscle, Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule and Collecting duct.

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7
Q

Do nephrons regenerate?

A

No - ageing involves loss of nephrons

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8
Q

What structure surrounds the glomerulus?

A

Bowman’s capsule

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9
Q

What are the differences between cortical nephrons and Juxtamedullary nephrons?

A

Cortical: Glomeruli in cortex, short loops of Henle, Short distance to medulla
Juxtamedullary: Long loops of Henle, Deep into medulla, long efferent arterioles and has specialised peritubular capillaries to form concentrated urine.

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10
Q

Name the 3 basic renal processes.

A

Glomerular Filtration, Tubular Reabsorption and tubular Secretion

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11
Q

What occurs during Glomerular Filtration?

A

Movement of fluid from the blood into lumen of nephron

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12
Q

What occurs during Tubular Reabsorption?

A

Movement of substances of value to the body in the filtrate from the lumen of the tubules back into the blood flowing through peritubular capillaries

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13
Q

What occurs during Tubular Secretion?

A

Selected transfer of sunstances from peritubular capillaires into the lumen. Second route for substances to enter renal tubules.

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14
Q

What is found in the glomerular filtrate?

A

Water, Electrolytes, Waste and Nutrients but NOT PLASMA PROTEINS

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15
Q

What happens if all the water and dissolved solutes move out of the glomeruli into the lumen of the nephron?

A

Formation of sludge of RBC which remains in glomeruli and doesn’t flow in the blood.

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16
Q

Name the 3 layers that make up the glomerular membrane.

A

Glomerular Capillary Wall, Basement membrane and Inner layer of Bowman’s capsule.

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17
Q

What is the role of the 3 layers that make up the glomerular membrane?

A

Acts as a fine molecular sieve that retains the blood cells and plasma proteins but permits water and solutes of small molecular dimensions to filter through.

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18
Q

What is the structure of the Glomerular Capillary wall?

A

Single layer of flattened endothelial cells, perforated with large pores and is 100x more permeable to water and solute than capillaries elsewhere in the body.

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19
Q

What is the structure of the Basement membrane?

A

Acellular, Collagen and glycoproteins discourage filtration of small plasma proteins. Glycoproteins are negatively charges and they repel plasma proteins also resulting in protein free urine.

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20
Q

What is the structure of Inner layer Bowman’s capsule?

A

Contains Podocytes and filtration flits. The fluid leaving the glomerular capillaires enter the lumen of the bowman’s capsule.

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21
Q

Name the two constituents of glomerular capillary blood pressure.

A

Blood pressure and Resistance

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22
Q

What creates the plasma-colloid osmotic pressure?

A

Plasma proteins in capillaries and water down concentration gradient.

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23
Q

What creates Bowman’s capsule hydrostatic pressure?

A

Pressure exerted by the fluid in this iniial part of the tubules out of the Bowman’s capsule.

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24
Q

What is Glomerular Filtration rate and what does it depend upon?

A

The actual rate of filtration and it depends not only on the net filtration pressure, but also on how much glomerular surface area is avaliable for penetration and how permeable the glomerular membrane is.

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25
Q

Is the glomerular filtration rate relatively constant?

A

yes - If arterial BP increases, so does the capillary BP and GFR also increases.

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26
Q

What causes the afferent arteriole to constrict?

A

GFR increases and BP increases. (want to reduce the BP)

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27
Q

Describe the process of Tubular Reabsorption.

A

Selective Process. Tubule wall is one cell thick and close to the surrounding peritubular capillary. It happens by transepithelial transport through 5 barriers via eityher passive or active reabsorption.

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28
Q

Name the 5 barriers between the tubular lumen and peritubular capillary.

A

Luminal Cell Membrane, Cytosol, Basolateral Cell Membrane, Interstitial Fluid and Capillary Wall.

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29
Q

What is the difference between passive and active reabsorption?

A

Passive: down electrochemical or osmotic gradients
Active: against an electrochemical gradient

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30
Q

Where is most of Na+ ions reabsorbed and why are they reabsorbed at this location?

A

67% at proximal Tubule - linked to reabsorption of glucose, amino acids, water, Cl- and urea.

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31
Q

What is the function of reabsorption of Na+ in the loop of Henle?

A

Linked to the production of concentrated urine.

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32
Q

What is the function of reabsorption of Na+ in the Distal and Collecting Tubule.

A

Linked to long term control of blood pressure and linked with K+ secretion

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33
Q

Where in the nephron can Na+ not be reabsorbed?

A

Descending part of the loop of Henle

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34
Q

How is intracellular Na+ concentration kept low?

A

Basolateral pump exchanges Na+ out of the tubular cells into the lateral space for a molecules of K+ (NA+-K+ ATPase pump) This maintains low concentration of Na+ in the cell.

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35
Q

Why does intracellular Na+ concentration need to be low?

A

Low concentration in the tubular cells allows passive movement of Na+ from the tubular lumen due to having a higher concentration. They move via Na+ symporters in the proximal tubule and Na+ leak channel in the collecting duct.

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36
Q

How does Na+ get into the peritubular capillaries?

A

High concentration in lateral space so Na+ diffuses down concentration gradient into interstitial fluid and into peritubular capillary blood

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37
Q

What is the role of Aldosterone?

A

Stimulates Na+ reabsorption in the distal and collecting tubules. Too little Na+ in the bloodstream resulting in more being reabsorbed and less excreted in urine. Release of aldosterone happens in response to circulating ANGII acting on the adrenal cortex.

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38
Q

Fill in the Words: In the ________ and ________, there is always a constant percentage of Na+ reabsorbed regardless of Na+ load.

A

Proximal Tubule and Loop of Henle

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39
Q

Name the 2 types of tubular cells found in the distal and collecting tubule.

A

Intercalated (involved in acid-base balance) and Principal (Releases Aldosterone and Vasopressin)

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40
Q

What is the role of Natriuretic Peptides?

A

They inhibit Na+ reabsorption. Indirectly lower BP. Reduce Na+ load and hence fluid load. Reduce Cardiac Output

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41
Q

What is the difference between RAAS-renal handling of Na+ and Natriuretic peptide hormones handling of Na+?

A

RAAS - Na+ retaining, blood pressure raising system

Natriuretic peptide hormones - Na+ losing, Blood pressure lowering system.

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42
Q

What triggers release of Natriuretic peptide from the heart?

A

Heart muscle being mechanically stretched. Stored in granules.

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43
Q

How do Natriuretic peptides carry out their role?

A

Inhibit Renin secretion by the kidney
Inhibit Aldosterone secretion from adrenal cortex
Inhibit secretion and actions of vasopressin.

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44
Q

How would you increase Glomerular Filtration Rate?

A

Vasodilate afferent arteriole and Vasoconstrict efferent arteriole. Relax glomerular mesengial cells to increase Kf

45
Q

Where does ANP and BNP come from?

A

ANP: Atrial Cardiac Muscle Cells
BNP: ventricular cardiac muscle cells

46
Q

Is ANP or BNP more effective?

A

ANP

47
Q

What is the role of the sodium and glucose cotransporters?

A

They allow passive Na+ across luminal membrane and that movement pulls glucose against its concentration gradient

48
Q

How does glucose move across the basolateral membrane in plasma?

A

Passive diffusion down concentration gradient via facilitative carrier glucose transporter (GLUT)

49
Q

How is water reabsorbed?

A

H2O passively pass through the length of tubule via aquarporins or water channels, osmotically following actively reabsorbed Na+

50
Q

What is the difference between AQP-1 and AQP-2?

A

AQP-1 - Proxomal tubules, always open

AQP-2: Distal tubules, under vasopressin control

51
Q

Where is most of the water reabsorbed?

A

Proximal Tubule

52
Q

How is Urea Reabsorbed in the Proximal Tubule?

A

Urea becomes more concentrated as more water leaves the proximal tubule. There is a concentration gradient between filtrate and plasma for urea so passive diffusion at the end of the proximal tubule. Tubule walls not fully permeable to urea so 50% reabsorbed - adeqquate removal.

53
Q

What makes up urea?

A

Uric Acid, Creatine and Phenols.

54
Q

Why is K+ ions not secreted in the proximal tubule but it is in the distal tubules?

A

In the proximal tubule, there is no K+ leaku channels between the principle cells and nephron lumen so K+ moves back into the interstitial fluid. Whereas in the distal tubule, these K+ leaky channels are present, hence secretion of K+ In the proximal tubule K+ is recycled to keep the Na+ reabsorption going through Na+-K+ ATPase.

55
Q

What is secreted by tubules?

A

Hydrogen and Potassium ions, and organic anions and cations.

56
Q

Why is H+ secreted by the tubules?

A

H+ is secreted in acid-base balance regulation - extent depends upon acidity of body fluids.

57
Q

What controls K+ secretion?

A

Aldosterone

58
Q

Where is K+ reabsorbed?

A

Proximal Tubule - active reabsorption without regulation

59
Q

Where does the K+ ions found in urine come from?

A

Controlled K+ secretion in distal parts of the nephron.

60
Q

When is K+ secretion reduced in the distal nephron?

A

When there is a K+ depletion in the plasma - conserves more of the K+ and less lost in urine.

61
Q

K+ ion secretion is coupled to the reabsorption of what?

A

Na+ ions

62
Q

How does K+ move through the nephron lumenal wall?

A

Via leaky Channels via passive diffusion when the K+ concentration is greater inside the cells than in the nephron lumen

63
Q

How does K+ enter the principle cells from the intersitial fluid?

A

K+ exchanged with Na+ in a Na+-K+ ATPase.

64
Q

Does Aldosterone increase or decrease K+ secretion by the principle tubular cells?

A

Increase

65
Q

How do you increase aldosterone release?

A

Rise in plasma K+, Na+ depletion, extracellular fluid volume reduction, or a fall in blood pressure

66
Q

Increase of K+ secretion decreases the secretion of what?

A

H+

67
Q

What is reabsorbed by the proximal tubule?

A

Na+, Glucose, Amino Acids, Electrolytes, H2O, Urea and K+

68
Q

What is secreted by the proximal tubule?

A

H+ and Organic Ions

69
Q

What is reabsorbed by the distal tubule?

A

Na+ and H2O

70
Q

What is secreted by the distal tubule?

A

H+ and K+

71
Q

What does excretion rate depend upon?

A

Filtration rate and whether the substance is reabsorbed, secreted or both.

72
Q

Define Plasma Clearance.

A

Volume of plasma completely cleared of that substance bu the kidneys per minute. Expresses the kidney’s effectiveness in removing various substances from the internal fluid environment

73
Q

How would you work out clearance rate of a substance?

A

urine concnetration of the substance x urine flow rate / Plasma concentration of the substance

74
Q

What would make the plasma clearance equal to the GFR?

A

If a substance is filtered but not reabsorbed or secreted.

75
Q

What molecules is freely filtered and not reabsorbed and secreted and can be used to work out the GFR?

A

Inulin - All glomerular filtrate formed is cleared of inulin, the volume of plasma cleared of inulin per minute equals the volume of pplasma filtered per minute - that is the GFR

76
Q

Other than inulin, what other molecule can be used to measure GFR?

A

Creatinine

77
Q

If a substance is filtered and reabsorbed but not secreted, its plasma clearance rate is always _____ than the GFR

A

Less

78
Q

If a substance is filtered and secreted but not reabsorbed, its plasma clearance is always ______ than the GFP

A

Greater

79
Q

Which limb of the loop of Henle is highly permeable to H2O due to having AQP-1 channels which are always open.

A

Descending Limb

80
Q

Which limb of the loop of Henle actively transports NaCl from lumen into interstitial fluid?

A

Ascending Limb

81
Q

Why does H2O leave the loop of Henle?

A

H2O flows osmotically out of the descending limb into more concentrated interstitial fluid - passive movement of H2O until osmolarities are equilibrated

82
Q

What is the point of concentrating the fluid and then diluting it?

A

Vertical gradient in the medullary interstitial fluid that colecting ducts utilise to concentrate tubular fluid further so that urine more concentrated than the body fluid is excreted.

83
Q

is fluid in the distal tubule hypotonic or hypertonic?

A

Hypotonic

84
Q

What is the role of Vasopressin?

A

It is a Antidiuretic Hormone (ADH) and its presence allows lumen wall to become permeable to H2O (normally is not permeable). Produced in the Hypothalamus and stored in posterior pituitary gland. Plasma Osmolarity triggers release. Aquaporins are stored in vesicles ready for insertion.

85
Q

How do osmoreceptors get activated?

A

They are stretch sensitive neurons that increase firing rate as osmolarity increases. Cells shirk, non-specific cationic channels linked to actin filaments open, depolarising cell.

86
Q

Where does water move to from the collecting duct?

A

Interstitial fluid into an area with lower water potential.

87
Q

Does the medulla alongside the collecting duct have the same water potential along the lenght of the collecting duct?

A

No, it is hyperosmotic and so the water potential decreases as you get further down the medulla.

88
Q

In excess of water, what happens in the collecting duct? ?

A

Hypotonic tubular fluid enters distal and collecting duct so there is no reabsorption and no vasopressin. This results in a large volume of dilute urine.

89
Q

How does the renal countercurrent multiplier in the loop of Henle work?

A

Descending limb permeable to water but not ions. Water moves by osmosis from the descending limb into progressively more concentrated interstitial fluid. In ascending limb, the tube is not permeable to water but allows active transport of Na+, K+ and CL- out of the tubule to interstitial fluid via NKCC symporters. Filtrate osmolarity descreases from medulla to cortex. Hyperosmotic interstitial fluid in medualla and hyposmotic filtrate leaving loop of Henle.

90
Q

Why doesn’t water leaving the descending limb of the loop dilute interstitial fluid of medulla?

A

Vasa Recta removes water. Blood flow back to cortex, taking water with it maintaining low osmolarity in medulla and higher in cortex.

91
Q

What happens to H+ and K+ during acidosis?

A

Excretes H+ and reabsorbs K+

92
Q

What happens to H+ and K+ during alkalosis?

A

Reabsorbs H+ and Excretes H+

93
Q

Name 5 H+ inputs.

A

Fatty Acids, Amino Acids, CO2, Lactic Acid and Ketoacids

94
Q

Name three buffers

A

HCO3-, Proteins, Ammonia and Phosphates

95
Q

Name two things that can be done to maintain pH homeostasis in the kidneys.

A

1) Excreting or Reabsorbs H+

2) Changing rate at which HCO3-buffer is reabsorbed and excreted.

96
Q

What traps H+ during acidosis?

A

Ammonia from amino acids and phosphate ions.

97
Q

What is the role of the Apical Na+-H+ exchanger?

A

Indirect active transport to bring Na+ into epithelial cells moving H+ against concentration into epithelial cell.

98
Q

What is the role of Basolateral Na+ HCO3_ symporter?

A

Moves Na+ HCO3- out of epithelial cells into interstitial fluid. Indirect active transporter couples energy of HCO3_ diffusion down its concentration gradient to the uphill movement of Na+ from the cell to the extracellular fluid.

99
Q

What is the role of H+ ATPase in Renal Handling of H+HCO3-?

A

Uses energy from ATP to acidify urine pushing H+ against its concentration gradient into the lumen of the distal nephron.

100
Q

What is the role of H+ K+ ATPase in Renal Handling of H+HCO3-?

A

Puts H+ into urine in exchange for reabsorption of K+. This contributes to K+ imbalance that sometimes accompanies acid-base disturbances.

101
Q

What is the role of Na+ NH4+ antiporter in Renal Handling of H+HCO3-?

A

Moves NH4+ from the cell to the lumen in exchange for Na+

102
Q

Does the Proximal Tubule Secrete H+ and reabsorb HCO3-?

A

Yes, reabsorbs HCO3- to maintain buffer capacity.

103
Q

Which cells are responsible for acid-base regulation in the distal tubule?

A

Intercalated Cells

104
Q

How does bicarbonate leave I cells?

A

Bicarbonate leaves cell by HCO3-Cl- antiporter exchanger.

105
Q

What do Type A I cells do?

A

Secrete H+ and reabsorb bicarbonate in response to acidosis.

106
Q

What happens to the blood during respiratory acidosis?

A

Hypoventilation, CO2 retention and elevated CO2 in blood plasma, elevated H+ and HCO3- and acidic pH

107
Q

What happens to the blood during metabolic acidosis?

A

Dietary and metabolic input H+ excees H+ excretion. Lactic Acidosis, Ketoacidosis (excessive breakdown of fats or certain AAs)

108
Q

What happens to the blood during respiratory alkalosis?

A

Hyperventilation, Plasma PCO2 decreases and both plasma H+ and HCO3-. Low plasma HCO3 indicates respiratory disorder. Renal: Excretes more HCO3- and reabsorbs H+

109
Q

What happens to the blood during metabolic alkalosis?

A

Excessive vomiting of acidic stomach content, excessive ingestion bicarbonate antacids and reduced H+, PCO2 and increase HCO3-

Year 1 Animal Physiology (9 decks)

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