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GI and Renal Exam 1 > 3 - Renal Physiology I > Flashcards

3 - Renal Physiology I Flashcards

1
Q

What are the functions of the kidney?

A

Every thirty minutes, the kidneys filter the entire blood supply in your body (blood flow about 20% of cardiac output)

  • Excretion of metabolic waste products and foreign substances
  • Regulation of body fluids and electrolytes balance, acid-base balance and arterial blood pressure
  • Elaboration of endocrine hormones
  • Gluconeogenesis
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2
Q

Describe the excretion of metabolic waste products and foreign substances

A

Urea (protein metabolism), Uric acid (nucleic acid), creatinine (muscle creatine), chemicals and pesticides, etc.

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3
Q

Describe the elaboration of endocrine hormones

A

Secretion, metabolism and excretion of hormones [erythropoietin, 1,25-dihydroxy vitamin D3 (vitamin D activation), renin]

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4
Q

Describe the function of gluconeogenesis

A

Most gluconeogenesis take place in the liver but a large proportion takes place in the kidneys especially during a long fast.

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5
Q

Describe the “system approach” to kidney function (how does it contribute to the body as a system?)

A

Kidney’s relationship to extrarenal environment (the rest of the body)…

Excretion of:

  • Metabolic waste products
  • Foreign substances

Adjustment of:

  • Fluid volume
  • Solute concentration

Elaboration of endocrine hormones

Gluconeogenesis

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6
Q

Describe the role of the body in signaling the kidney in this “system approach” to kidney function

A
  • Blood pressure and volume
  • Plasma composition
  • Neuroendocrine
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7
Q

Describe the intrarenal processes of the “system approach” (does not interact with the body, is just the kidney’s own functions)

A

Basic kidney process

Local control:

  • Renal auto-regulation
  • Autocrine/paracrine systems
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8
Q

Describe the basic physiological anatomy of the kidney

A

The two kidneys lie on the posterior wall of the abdomen

The ureter carries the final urine from the kidney to the bladder

In a bisected kidney, from
top to the bottom, the two major regions visualized are the cortex (outer region) and medulla (inner region)

The medulla is divided in multiple cone-shaped masses of tissue called renal pyramids

The base of each pyramid terminates in the papilla, which projects into the space of the renal pelvis

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9
Q

Describe the basic tubular segments of the nephron

A
  • Each kidney in the human contains about 1 million
    of nephrons
  • The nephron is the functional
    unit of the kidney
  • Each nephron contains a
    glomerulus and long tubule
  • The glomerulus contains a
    collection of capillary (glomerular
    capillary), through which large
    amount of fluid is filtered from the blood
  • The glomerulus is incased in the Bowman’s capsule
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10
Q

Describe the structure of the glomerulus

A

The glomerular capillary membrane is similar to that of other capillaries, except that it has three (instead of the usual two) major layers:

  • Endothelium of the capillary
  • A basement membrane
  • A layer of epithelial cell (podocytes)
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11
Q

What do these layers of the glomerulus make up?

A

These layers make up the filtration barrier which filters fluid and solute with high filtration rate

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12
Q

Describe the filtration rate across the glomerular capillary

A

The high filtration rate across the glomerular capillary is supported by:

  • The perforation of the endothelium (fenestrae)
  • Meshwork of the basement membrane
  • The long foot-like processes of the podocytes
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13
Q

Describe where the fluid goes after it is filtered in the glomerular capillaries

A

Fluid filtered from the glomerular capillaries flows into the Bowman’s capsule and, then, into the renal tubule

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14
Q

What happens in the renal tubule?

A

The tubule is where the filtered fluid is converted in urine

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15
Q

What are all the segments of the renal tubule?

A
  • Proximal Tubule
  • Loop of Henle
  • Distal Tubule
  • Connecting Tubule
  • Collecting Tubule
  • Collecting Duct
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16
Q

Describe the vasculature in kidney

A
  • The renal artery enters the kidney and, then, branches progressively
  • The venous system run parallel to the arteriolar vessels
  • The vascular structures supplying the juxtamedullary nephron differ from those supply the cortical nephrons
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17
Q

What are the regional differences we see in nephron types?

A

There are two types of nephrons

  • Cortical nephrons
  • Juxtamedually nephrons
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18
Q

Describe cortical nephrons

A

Nephrons that have glomeruli located in the outer cortex and short Loop of Henle

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19
Q

Describe juxtamedullary nephrons

A

Nephrons that have glomeruli located deep in the cortex and long Loop of Henle (20-30%)

Only 20-30% of all nephrons are juxtamedullary, the rest are cortical

20
Q

Describe the microcirculation of the nephron in the cortical nephrons

A
  • The cortical nephrons are
    surrounded by an extensive
    network of peritubular capillaries
  • The renal circulation
    is unique in that it has two capillary beds, the glomerular and peritubular capillaries
  • The glomerular and peritubular capillaries are arranged in series and separated by the efferent arteriole

** Arranged IN SERIES - important for regulation and flexibility **

21
Q

Describe the microcirculation of the nephrons in juxtamedullary nephrons

A
  • The juxtamedullary nephrons
    are surrounded by specialized
    peritubular capillaries (vasa recta)
  • The vasa recta extend downward into the medulla, lying side by side with the Loop of Henle
  • This specialized network of capillaries in the medulla plays an essential role in the formation of concentrated urine
22
Q

Describe the basic 4 steps for urine formation

A

1 - Glomerular filtration
2 - Reabsorption of stubstance from the renal tubules into the blood
3 - Secretion of substances from the blood into the renal tubules
4 - Urinary excretion

23
Q

How can you calculate or determine the amount of excretion of urine?

A

EXCRETION = FILTRATION - REABSORPTION + SECRETION

** know this ***

24
Q

What is the process of glomerular filtrate production?

A
  • Urine formation begins with filtration of large amounts of fluid through the glomerular capillaries into Bowman’s capsule
  • Filtrated fluid is essential protein-free and devoid of cellular elements
  • The concentration of other constituents of the glomerular filtrate, including salts and organic molecules is similar to the concentration in the plasma
25
Q

What are the exceptions in this process of glomerular filtrate production?

A

Exceptions to this generalization include a few molecular-weight substances, such as calcium and fatty acid that are bound to plasma proteins

26
Q

How do you determine the glomerular filtration rate (GFR)?

A

The Glomerular Filtration Rate (GFR) is determined by the net filtration pressure and glomerular capillary filtration fraction coefficient

27
Q

How do you determine the net filtration pressure?

A

The net filtration pressure is determined by the sum of the following across the glomerular:

  • Hydrostatic Forces (Pressure)
  • Colloid Osmotic Forces (Pressure)
28
Q

What is hydrostatic pressure>

A

Hydrostatic pressure is the pressure that the fluid exerts on the walls of its container

In the capillary it is the force that is exerted by a fluid against the capillary wall

29
Q

What is colloid osmotic pressure (oncotic pressure)

A

Osmotic pressure is the pressure required to prevent the solvent migration across a semipermeable membrane via osmosis

In the capillaries it is the pressure exerted by proteins in the plasma

30
Q

Give a summary of the forces and pressures that cause filtration by the glomerular capillaries

A

Forces and pressures that FAVOR filtration
- Glomerular hydrostatic pressure

Forces and pressures that OPPOSE filtration

  • Glomerular colloid osmotic pressure
  • Bowman’s capsule pressure
31
Q

What is the effect of vasoconstriction of afferent arterioles on GFR?

A

Vasoconstriction of afferent arteriole (AA) leads to a decreased GFR

32
Q

What is the effect of vasoconstriction of the efferent arterioles on GFR?

A

Vasoconstriction of efferent arteriole (EA) leads to an increased GFR

33
Q

What is the effect of vasodilation of efferent arterioles on GFR?

A

Vasodilation of efferent arteriole (EA) leads to a decreased GFR

34
Q

What is the effect of vasodilation of afferent arterioles on GFR?

A

Vasodilation of afferent arteriole (AA) leads to an increased GFR

35
Q

Describe how tubular re-absorption/secretion is highly selective

A
  • The kidney controls the rate of tubular re-absorption or secretion of solutes independently of one another
  • This capacity of the kidney is essential for precise control of the composition and volume of the body fluid
  • The selectivity of tubular re-absorption/secretion is due to the luminal membrane and tight junctions permeability
36
Q

How does the function depend on structure?

A
  • Proximal tubule: tall cell with a lot of membrane allows for a lot of reabsorption and secretion ***
  • Thick ascending loop of Henle: also very tall, also a lot of reabsorption and secretion ***
  • Thin descending loop of Henle: no resorption of ions, just water
  • Distal tubule and collecting duct: intercalated cells are important for the absorption and secretion of potassium

* Important concepts*

37
Q

Describe reabsorption of filtered fluid and solutes from the tubular lumen into the blood

A

Two options…

  • Transcellular pathway = Through the cells (diffusion or active transport)
  • Paracellular pathway = Around the cells (diffusion)
38
Q

Describe the transcellular (through the cells) pathway

A

Uses primary and secondary ACTIVE transport

  • Metabolic substrates such as glucose, amino acid and fatty acid
  • All if these various fuels are converted in energy ATP
  • Electrochemical gradients such as low cell sodium and negative voltage drive a whole array of transport processes
39
Q

What are the net reabsortive forces

A
  • Hydrostatic forces
  • Colloid osmotic forces

Calculate this by taking the sum of forces favoring reabsorption minus the sum of the forces opposing reabsorption

40
Q

Give a summary of key concepts

A
  • The kidneys have a very large blood flow relative to their mass that is regulated for functional reasons rather metabolic demand
  • Glomerular filtration proceeds trough a 3-layered barrier that restrict filtration of large molecules such as proteins
  • Glomerular Filtration Rate (GFR) is determined by the permeability of the filtration barrier and net re-absorptive forces
  • Control of the resistances of the afferent and efferent arterioles permits independent control of GFR and renal blood flow
  • The kidneys moves solutes across membranes by multiple transport mechanisms
41
Q

What are the percentages of substrates reabsorbed from the urine back into the blood?

A

Sodium = 1-2%
Amino acids = 1%
Glucose = 1%
Potassium = 12%

42
Q

How do you calculate fractional excretion?

A

Amount excreted/Amount filtered

43
Q

Which substances have the same level of excretion (out of body) as initially secreted (into urine ) - NO reabsorption?

A

This means the fractional excretion is 1 in FEEF (fractional excretion = amount excreted/amount filtered =1)

Creatinine

44
Q

Which substances have LESS excretion (out of body) than initially secreted (into urine ) - there is REABSORPTION?

A

FEEF

45
Q

Which substances have NO excretion and all of the substrate is reabsorbed?

A

FEEF = 0

Examples: amino acids, oligopeptides, glucose
carboxylates

46
Q

Which substances have MORE excretion (out of body) than was initially secreted (into the urine)?

A

FEEF >1

Examples: potassium, proton
organic acids and basis
urea, urate

GI and Renal Exam 1 (16 decks)

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