Urinary System Part 2: Renal Physiology
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Questions and Answers

What does the urinary system regulate?

The urinary system regulates the volume and composition of blood.

How concentrated is urine?

Urine is concentrated to 855-1355 mOsm/L.

What is Urea?

Urea is the most abundant organic waste in the body and is a by-product of amino acid breakdown.

What is Creatinine?

<p>Creatinine is a by-product of creatine phosphate breakdown in muscles.</p> Signup and view all the answers

What is Uric acid?

<p>Uric acid forms during the recycling of nitrogenous bases of RNA.</p> Signup and view all the answers

Which of the following are processes involved in urine formation?

<p>All of the above (D)</p> Signup and view all the answers

Glomerular filtration happens ONLY in the glomerulus.

<p>True (A)</p> Signup and view all the answers

What is the resulting fluid that enters the capsular space during filtration called?

<p>Glomerular filtrate</p> Signup and view all the answers

What structure allows filtration to occur?

<p>Filtration membrane</p> Signup and view all the answers

Which of these is NOT a part of the filtration membrane?

<p>Peritubular capillaries (A)</p> Signup and view all the answers

What does Net Filtration Pressure depend on?

<p>Net Filtration Pressure (NFP) depends on Glomerular Blood Hydrostatic Pressure (GBHP), Capsular Hydrostatic Pressure (CHP), and Blood Colloid Osmotic Pressure (BCOP).</p> Signup and view all the answers

NFP dictates how much fluid moves in which direction during filtration.

<p>True (A)</p> Signup and view all the answers

What happens to GFR if GBHP drops below 45 mmHg?

<p>Filtration stops if GBHP drops below 45 mmHg.</p> Signup and view all the answers

What is the process of calculating Filtration Fraction (FF)?

<p>Filtration Fraction (FF) is the fraction of Renal Plasma Flow (RPF) that becomes glomerular filtrate.</p> Signup and view all the answers

What is the normal glomerular filtration rate per minute?

<p>The normal glomerular filtration rate is 105-120 ml/min.</p> Signup and view all the answers

GFR is directly related to NFP.

<p>True (A)</p> Signup and view all the answers

An eGFR of <15 indicates kidney failure.

<p>True (A)</p> Signup and view all the answers

What are the three mechanisms to maintain relatively consistent GFR?

<p>All of the above (D)</p> Signup and view all the answers

Where are mesangial cells located?

<p>Mesangial cells lie between adjacent glomerular capillaries.</p> Signup and view all the answers

What is the main function of the Juxtaglomerular Apparatus?

<p>The Juxtaglomerular Apparatus (JGA) regulates blood pressure and the filtration rate of the glomerulus.</p> Signup and view all the answers

What are the two types of renal autoregulation?

<p>The two types of renal autoregulation are myogenic mechanism and tubuloglomerular feedback.</p> Signup and view all the answers

The myogenic mechanism is faster than tubuloglomerular feedback.

<p>True (A)</p> Signup and view all the answers

What does the tubuloglomerular feedback mechanism rely on?

<p>The tubuloglomerular feedback mechanism relies on the juxtaglomerular apparatus.</p> Signup and view all the answers

When BP is increased, GFR is decreased due to vasoconstriction of the afferent arterioles.

<p>False (B)</p> Signup and view all the answers

What is the main purpose of neural regulation of GFR?

<p>Neural regulation of GFR primarily serves to conserve blood flow to vital organs during stressful situations.</p> Signup and view all the answers

Neural regulation of GFR can cause the release of renin.

<p>True (A)</p> Signup and view all the answers

What is the role of Angiotensin II in the regulation of GFR?

<p>Angiotensin II acts as a vasoconstrictor, narrowing afferent and efferent arterioles, which reduces GFR and helps maintain blood pressure.</p> Signup and view all the answers

What is the main function of ANP?

<p>ANP primarily relaxes mesangial cells, increasing the surface area of the glomerulus, and ultimately increasing GFR.</p> Signup and view all the answers

ANP suppresses secretion of ADH and aldosterone.

<p>True (A)</p> Signup and view all the answers

What is the role of PTH in regulating GFR?

<p>Parathyroid hormone (PTH) increases blood calcium levels by stimulating reabsorption of calcium in the early distal convoluted tubule.</p> Signup and view all the answers

What is the role of calcitonin in regulating GFR?

<p>Calcitonin, released by parafollicular cells, acts to decrease blood calcium levels by inhibiting reabsorption of calcium in the distal tubule.</p> Signup and view all the answers

What are the two types of water reabsorption?

<p>The two types of water reabsorption are obligatory water reabsorption and facultative water reabsorption.</p> Signup and view all the answers

Obligatory water reabsorption occurs in the PCT and descending limb of the nephron loop.

<p>True (A)</p> Signup and view all the answers

Facultative water reabsorption occurs in the DCT and collecting duct.

<p>True (A)</p> Signup and view all the answers

What is the normal volume of urine produced in a day?

<p>The normal volume of urine produced per day is about 1200 mL.</p> Signup and view all the answers

What is the normal osmotic concentration of urine?

<p>The normal osmotic concentration of urine is 600-1500 mOsm/L.</p> Signup and view all the answers

Dilute urine is produced in the absence of ADH.

<p>True (A)</p> Signup and view all the answers

Concentrated urine is produced in the presence of ADH.

<p>True (A)</p> Signup and view all the answers

The Countercurrent Multiplication System is a system in the nephron loop of juxtamedullary nephrons.

<p>True (A)</p> Signup and view all the answers

The thick ascending limb is impermeable to water.

<p>True (A)</p> Signup and view all the answers

The Countercurrent Exchange System involves the vasa recta.

<p>True (A)</p> Signup and view all the answers

Urea recycling helps maintain the osmotic gradient in the renal medulla.

<p>True (A)</p> Signup and view all the answers

Diabetes insipidus is a rare condition that affects about 1 in 25,000 people worldwide.

<p>True (A)</p> Signup and view all the answers

Which of the following are causes of Central Diabetes Insipidus?

<p>All of the above (D)</p> Signup and view all the answers

Which of the following are causes of Nephrogenic Diabetes Insipidus?

<p>Medications like lithium or tetracycline (A), Inherited genetic mutations (B)</p> Signup and view all the answers

Treatment for Central Diabetes Insipidus can include Desmopressin.

<p>True (A)</p> Signup and view all the answers

Thiazide diuretics are used to treat Nephrogenic Diabetes Insipidus.

<p>True (A)</p> Signup and view all the answers

The prognosis for Diabetes Insipidus is generally good if managed well and affected individuals drink enough water.

<p>True (A)</p> Signup and view all the answers

Study Notes

Urinary System Part 2: Renal Physiology

  • The urinary system maintains homeostasis by regulating blood volume and composition.
  • Urine is concentrated to 855-1355 mOsm/L.
  • The system excretes solutes, mainly metabolic wastes.

Renal Physiology: Normal Laboratory Values

  • Ions (mEq/L):
    • Sodium (Na+): 135-145 in plasma, 40-220 in urine
    • Potassium (K+): 3.5-5.0 in plasma, 25-100 in urine
    • Bicarbonate (HCO3-): 20-28 in plasma, 1.9 in urine
  • Metabolites and Nutrients (mg/dL):
    • Glucose: 70-110 in plasma, 0.009 in urine
    • Lipids: 450-1000 in plasma, 0.002 in urine
    • Proteins: 6.0-8.0 g/dL in plasma, 0.000 in urine
  • Nitrogenous Wastes (mg/dL):
    • Urea: 8-25 in plasma, 1800 in urine
    • Creatinine: 0.6-1.5 in plasma, 150 in urine
    • Uric acid: 2-6 in plasma, 40 in urine
    • Ammonia: <0.1 in plasma, 60 in urine

Renal Physiology: Metabolic Wastes

  • Urea: The most abundant organic waste, a byproduct of amino acid breakdown.
  • Creatinine: A byproduct of creatine phosphate breakdown in muscles.
  • Uric acid: Formed during the recycling of RNA's nitrogenous bases.

Renal Physiology: Urine Formation

  • There are three processes involved in urine formation:
    • Filtration: Blood hydrostatic pressure forces water and solutes across glomerular capillaries into the capsular space.
    • Reabsorption: Water, ions, and other substances are reabsorbed from renal tubules into peritubular capillaries.
    • Secretion: Substances like wastes, drugs, and excess ions are secreted from peritubular capillaries into renal tubules.

Glomerular Filtration

  • Filtration: Blood hydrostatic pressure forces water and solutes through the glomerular capillaries into the capsular space.

  • Filtration membrane:

    • Fenestrations of endothelial cells allow small molecules to pass through.
    • Basement membrane (collagen fibers and proteoglycans; large negatively charged proteins cannot fit).
    • Filtration slits between podocytes, regulating the size of substances passing through

  • Net Filtration Pressure (NFP): The driving force for filtration determined by:

    • Glomerular blood hydrostatic pressure (GBHP) - opposing: Capsular hydrostatic pressure (CHP) and Blood colloid osmotic pressure (BCOP)
    • Calculating NFP: GBHP - CHP - BCOP = 10mmHg (under normal circumstances)

  • Normal filtration fraction (FF) = 16-20%.

  • Daily glomerular filtrate = 150L-180L.

  • 99% of filtrate reabsorbed back into the blood

  • Glomerular Filtration Rate (GFR)

    • Amount of filtrate formed per minute in both kidneys (normal 105-120 ml/min)
    • Directly related to NFP; eGFR used to test kidney function

  • The body carefully monitors GFR to maintain homeostasis.

  • High GFR: Needed substances pass too quickly through the renal tubules, and are lost in urine

  • Low GFR: Metabolic wastes are not filtered from the blood into the renal tubules.

Renal Autoregulation

  • Mesangial cells: Located between adjacent glomerular capillaries. They control capillary diameter and filtration rate.
  • Juxtaglomerular apparatus (JGA): Includes specialized cells in the distal tubules and glomerular arterioles that regulate blood pressure and filtration rate.
    • Macula densa cells detect changes in tubule NaCl concentration.
    • Juxtaglomerular cells (granular cells) secrete renin in response to low blood pressure.
  • Two types of myogenic mechanism:
    • Myogenic: Stretch receptors in afferent arterioles respond to increased or decreased blood pressure.
    • Tubuloglomerular feedback: Macula densa cells detect changes in tubular Na+ and Cl− concentrations, which affects renin release
  • GFR can be regulated by nervous and hormonal systems

Hormonal Regulation:

  • Angiotensin II: Part of the Renin-Angiotensin-Aldosterone System (RAAS). Aldosterone causes more Na+, Cl- and H2O reabsorption.
  • Antidiuretic hormone (ADH): Responds to low blood volume or high blood osmolarity; principal cells increase aquaporin numbers to reabsorb more water.
  • Atrial natriuretic peptide (ANP): Responds to increased blood pressure; inhibits Na+ reabsorption and lowers blood pressure

Reabsorption & Secretion (Proximal Convoluted Tubule/PCT):

  • PCT: The most important site of reabsorption.
    • Active transport: 100% of glucose, amino acids, HPO42-, SO42-, and lactic acid, and 85-90% of filtered bicarbonate
    • Passive transport: 65% of filtered water, 65% of filtered sodium, potassium, 50% of filtered chloride, urea
  • PCT: Secretion
    • Active transport: elimination of H+ (blood pH regulator) and other substances e.g. NH4+ and medications
  • Overview:
    • Reabsorption: 100% Glucose, amino acids, phosphate, lactate
    • Reabsorption: 85-90% bicarbonate
    • Secretion: NH4+, drugs

Reabsorption & Secretion (Nephron Loop):

  • Reabsorption: (descending limb/ascending limb):
    • Some water, 20-30% salt, 35% chloride, and variable amounts of Mg2+, C2+, and bicarbonate in loop of Henle.
  • 15% of filtered water reabsorbed only in the descending limb.
  • Lots of reabsorption. Very little secretion.

Reabsorption & Secretion (Early Distal Convoluted Tubule):

  • Reabsorption:
    • 10-15% water; mostly passive
    • 5% of Na+ and Cl- (active transport)
    • PTH acts to reabsorb calcium

Reabsorption & Secretion (Late Distal Convoluted Tubule and Collecting Duct):

  • Reabsorption:
    • Principal cells: Reabsorb Na+ and H2O; controlled by ADH and aldosterone.
    • Intercalated cells: Reabsorb K+ and HCO3-; regulate pH.
  • Secretion:
    • Principal cells: Secrete K+
    • Intercalated cells: Secrete H+
    • Urea:
  • 90-95% of remaining filtered solutes and water reabsorbed or secreted based on body needs

Hormonal Regulation of Tubular Reabsorption:

  • Many hormones play a role:
    • Renin-Aldosterone-Angiotensin System (RAAS)
    • Antidiuretic hormone (ADH)
    • Atrial natriuretic peptide (ANP)
    • Parathyroid hormone (PTH)
    • Calcitonin

Diabetes Insipidus (DI):

  • Definition: Inadequate response to or production of ADH
    • Types:
      • Central DI: Posterior pituitary or hypothalamus defect impacting ADH production or release.
      • Nephrogenic DI: Kidneys are resistant to ADH.
    • Symptoms: Excessive excretion of dilute urine, dehydration, thirst, fatigue.
    • Treatment: - Desmopressin (synthetic ADH) for Central DI or
      • Thiazides for Nephrogenic DI

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Urinary System Lecture 2 2023 - PDF

Description

Explore the essential concepts of renal physiology in this quiz. Learn how the urinary system functions to maintain homeostasis, regulate blood composition, and excrete metabolic wastes. Additionally, familiarize yourself with normal laboratory values for ions and metabolites.

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