Renal Anatomy, Physiology, and Urine Production Flashcards

1
Q

Renal system

A

Maintain a stable internal environment for optimal cell and tissue metabolism by:

  1. Balancing solute and water transport
  2. Excreting metabolic waste products
  3. Conserving nutrients
  4. Regulating acids and bases
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2
Q

Additional renal functions

A

Endocrine functions (secrete hormones):

  1. Renin
  2. Erythropoietin
  3. 1,25-dihydroxy-vitamin D3

Gluconeogenesis (synthesize glucose from amino acids)

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3
Q

Urinary system

A

Formation of urine is achieved within the kidney through the process of (1) glomerular filtration, (2) tubular reabsorption, and (3) tubular secretion

Urinary bladder: stores urine received from the kidney by way of the ureters

Urine is removed from the body through the urethra

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4
Q

Kidney anatomy

A

The kidneys are paired, retroperitoneal organs located in the posterior region of the abdominal cavity, behind the peritoneum

Renal capsule: tight adhering capsule that surrounds each kidney

Cortex: outer layer of the kidney that contains glomeruli, most PCTs, and some segments of DCTs

Medulla: inner layer of the kidneys consisting of regions called pyramids

Apex (ends) of pyramids project into minor and major calyces (cup-shaped cavities) to form the renal pelvis

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5
Q

Nephron

A

Functional unit of kidney

Contains:

  1. Renal corpuscle (glomerulus, Bowman’s capsule, and mesangial cells)
  2. PCT
  3. Loop of Henle
  4. DCT
  5. Collecting duct
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6
Q

Glomerulus

A

Tuft of capillaries that loop into Bowman’s capsule; structurally supported by mesangial cells

Synthesizes NO (vasodilator) and endothelin-1 (vasoconstrictor) to regulate blood flow and GFR

Fenestrae: endothelial cells with pores that line the capillaries and allow filtration of fluid, plasma, solutes, and small proteins; prevent filtration of RBCs, WBCs, and platelets

JGA is formed by the afferent arteriole and portion of DCT; juxtaglomerular cells produce renin to regulate renal perfusion and GFR

Macula densa: specialized Na and Cl-sensing cells in between afferent and efferent arterioles (in a portion of the DCT)

Podocytes: cells that adhere to the capillaries of the GBM; gaps allow filtration

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7
Q

Renal blood flow

A

GFR: the filtration of the plasma per unit of time; directly related to renal perfusion

Controlled by:

  1. Autoregulation
  2. Neural regulation
  3. Hormonal regulation
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8
Q

Autoregulation

A

Maintain constant renal perfusion and GFR despite increasing/decreasing range of systolic BP

Mechanisms:
1.) Increasing/decreasing arteriole resistance (increased resistance with increased BP)

2.) Tubuloglomerular feedback:
Pathway:
1. Decreased arterial pressure
2. Decreased glomerular hydrostatic pressure and GFR
3. Macula dense sense lack of Na and Cl in DCT
4. JGA releases renin, and formation of angiotensin
5. Vasoconstriction and increased resistance
6. Increase glomerular hydrostatic pressure and GFR

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9
Q

Neural regulation

A

Afferent arterioles are innervated by SNS fibers

  1. Decreased arterial pressure
  2. Sensed by aortic baroreceptors
  3. Increase sympathetic output of epinephrine
  4. Afferent arteriole (renal) vasoconstriction
  5. Decreased GFR (initially)
  6. Increase sodium and water reabsorption
  7. Increases plasma blood volume, BP, and GFR
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10
Q

Hormonal regulation

A
  1. Decreased BP, ECF, renal perfusion, serum Na OR increased urine Na
  2. Renin (formed in the JGA) is released
  3. Stimulates angiotensinogen production (in liver)
  4. Renin and angiotensinogen form angiotensin I
  5. Angiotensin I is converted into angiotensin II (by ACE)
  6. Angiotensin II stimulates: (1) vasoconstriction of arterioles and (2) aldosterone secretion (from adrenal cortex)
  7. Aldosterone: (1) retains sodium and water in kidneys and (2) stimulates ADH secretion (and thirst)
  8. Increases ECF, BP, and GFR
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11
Q

Nephron function

A

Filters plasma at glomerulus for (1) excretion, and (2) reabsorption and (3) secretion along the tubules

Ultrafiltration: protein-free filtrate, that helps maintain body fluid volume, pH, and electrolyte balance

Functions:

  1. Tubular reabsorption: movement of fluid and ions from renal tubules to capillary
  2. Tubular secretion: movement from capillaries to renal tubules
  3. Excretion: elimination of a substance in the final urine
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12
Q

Function of nephron segments

A

PCT: active reabsorption of most ions (Na+, Ca2+, K+, Mg2+, Cl-, HCO3-, H2O, amino acids, glucose)

Loop of Henle (THIN descending): highly permeable to water (osmosis); no ions

Loop of Henle (THICK ascending): active reabsorption of ions (Na+, Ca2+, K+, Cl-)

DCT: active reabsorption of Na+, Ca2+, Cl-, HCO3-, H2O and secretion of K+, H+ NH4+

Collecting duct:

  1. Principle cells reabsorb Na+ and H2O, and secrete K+
  2. Intercalated cells reabsorb K+, and secrete H+
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13
Q

Concentration and Dilution of Urine

A

Occurs mainly in the Loop of Henle, DCT, and collecting ducts

Concentrated urine is produced by a concurrent mechanism in the Loop of Henle; the longer the loop, the more concentrated urine can become

Aldosterone stimulates the release of ADH (from the pituitary gland) which increases the permeability and reabsorption of water in the DCT and collecting ducts (concentrates urine)

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14
Q

Problems with renal failure

A

HTN (inability to regulate BP)

Edema (nephrotic syndrome)

Anemia (EPO deficiency)

Hypocalcemia, vitamin D deficiency, and hyperphosphatemia (1,25-dihydroxy vitamin D3 deficiency)

Hypoglycemia (impaired gluconeogenesis)

Accumulation of toxic metabolites (inability to excrete toxins)

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15
Q

Diuretics

A

Enhance urine flow; decrease renal sodium reabsorption, and as a result, decrease ECF

Types of diuretics:
1. Osmotic: act on PCT and the descending Loop to inhibit reabsorption of water and sodium

  1. Loop: act on ascending Loop and DCT to inhibit reabsorption of Na+, Ca2+, K+, and Cl-
  2. Thiazide: act on DCT to inhibit reabsorption of Na+ and Cl-; promotes Ca2+ reabsorption
  3. Potassium-sparing: act on end of DCT and collecting duct to promote reabsorption of K+
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16
Q

Urine dipstick

A

Glucose: normally entirely reabsorbed

Leukocyte esterase: enzyme in WBCs; normally not present in urine (present in UTI, infections)

Nitrates: positive with some bacteria

Ketones: by-product of fat breakdown; positive in starvation/fasting and diabetic ketoacidosis

Albumin: positive in glomerular failure (large protein)

Hgb: positive in RBC breakdown

Myoglobin: positive in muscle breakdown

17
Q

Urine sediment/cytology

A

A microscopic analysis that can identify crystals, casts, RBCs, WBCs, and urothelial cells (that are commonly found in CA)

Can also identify: blood, bacteria

18
Q

Blood Urine Nitrogen (BUN)

A

Inversely reflects urine concentrating ability and GFR; BUN (normally 10-20 mg/dL) increases as GFR drops

Elevated BUN indicates dehydration, HF, AKD/CKD

A less specific indicator of kidney function and is a reflection of ingested protein and muscle catabolism

19
Q

Plasma Creatine

A

Inversely reflects GFR; creatine (normally 0.7-1.2 mg/dL) increases as GFR drops

Most useful in long-term monitoring; less useful in AKD (takes 7-10 days for creatine to stabilize with GFR decline)

Creatine clearance (kidneys ability to handle creatine): estimates GFR = Urine creatine x Urine volume/Plasma creatine