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Questions and Answers
Which mechanism is NOT an intrinsic method of regulating the glomerular filtration rate (GFR)?
What is the primary effect of the renin-angiotensin II system on the efferent arteriole?
Which of the following is a characteristic of the myogenic mechanism in GFR regulation?
Which parameter primarily influences the glomerular filtration rate (GFR)?
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What effect do natriuretic peptides have on glomerular filtration?
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What is the role of the tubulo-glomerular feedback mechanism?
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How does the glomerular hydrostatic pressure affect filtration?
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What happens to GFR if the Bowman’s capsule hydrostatic pressure increases?
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What is the primary function of the kidneys in the urinary system?
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Which component of the nephron is involved in the filtration of blood?
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What hormone produced by the kidneys stimulates erythrocyte production?
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How does the urinary system help maintain blood osmolarity?
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Which is NOT a function of the urinary system?
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What effect does the secretion of renin have on blood pressure?
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What is the total number of nephrons present in one kidney?
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Which of the following correctly describes the structure of Bowman’s capsule?
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What is the role of natriuretic peptides in kidney function?
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What triggers the myogenic mechanism in the kidneys?
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How does the tubulo-glomerular feedback mechanism function to regulate GFR?
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What is the primary effect of sympathetic stimulation on the afferent arteriole?
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Which part of the nephron contains the macula densa?
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How does increased glomerular hydrostatic pressure affect GFR?
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What effect does adenosine have in the context of renal blood flow regulation?
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What is the primary function of juxtaglomerular cells?
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Study Notes
Urinary System Anatomy
- Composed of two kidneys, two ureters, one urinary bladder, and one urethra
- Kidneys are bean-shaped organs located on the posterior wall of the abdomen, to either side of the vertebral column
Kidney Weight
- Approximately 150g in males
- Approximately 135g in females
Functions of the Urinary System
-
Excretion of wastes and foreign substances:
- Nitrogenous wastes (urea, creatinine, and uric acid)
- Toxins
- Drugs
-
Maintenance of blood osmolarity:
- Maintains plasma osmolarity at 300 mOsm
- Regulates water balance
- Regulates blood electrolyte levels (sodium, potassium, etc.)
- Regulates blood glucose levels
-
Regulation of blood volume:
- Conserves water in case of need (e.g. fasting)
- Eliminates excess water (e.g. after drinking lots of water)
-
Regulation of blood pressure:
- Secretes renin, which promotes the production of angiotensin, increasing blood pressure
-
Regulation of blood pH:
- Excretes excess H+ ions
- Conserves bicarbonate ions (HCO3-)
- Production of erythropoietin: Stimulates erythrocyte production in bone marrow
- Activation of vitamin D: Allows calcium uptake from the gastrointestinal tract to the blood
The Nephron
- The basic functional unit of the kidney
- Approximately 1 million nephrons per kidney
- Filters blood and forms urine
- Composed of two components:
- Renal corpuscle
- Renal tubule
Renal Corpuscle
- Composed of two parts:
- Glomerulus: a network of fenestrated capillaries located between two arterioles
- A large afferent arteriole for incoming blood (mixed with wastes)
- A narrow efferent arteriole for outgoing blood (filtered and free of wastes)
- Bowman's capsule: a double-walled structure of epithelial cells that forms a cup surrounding the glomerulus
- Glomerulus: a network of fenestrated capillaries located between two arterioles
Glomerular Filtration
- Movement of water, solutes, and ions out of the glomerular capillary into Bowman's capsule
- Filters everything except red blood cells and proteins
- Depends on net filtration pressure (NFP), determined by the following forces:
- Glomerular hydrostatic pressure: Pushes water and solutes out (from the capillary into Bowman's capsule), approximately 60 mm Hg
- Bowman's capsule hydrostatic pressure: Pushes water and solutes in (from Bowman's capsule into the capillary), approximately 18 mm Hg
- Glomerular colloid osmotic pressure: Pulls water and solutes in (from Bowman's capsule into the capillary), approximately 32 mm Hg
Glomerular Filtration Rate (GFR)
- The volume of plasma filtered by the glomeruli of both kidneys per minute
- Normal value of GFR = 125 ml/min (7.5 L/h, 180 L/day)
- GFR is auto-regulated by the following mechanisms:
- Extrinsic mechanisms:
- Hormonal mechanisms:
- Renin-Angiotensin II system
- Natriuretic peptides
- Neural mechanism
- Hormonal mechanisms:
- Intrinsic mechanisms:
- Myogenic mechanism
- Tubulo-glomerular feedback mechanism
- Extrinsic mechanisms:
Extrinsic Mechanisms of GFR Regulation (Outside of the Kidney)
-
Hormonal Mechanisms:
-
Renin-Angiotensin II System:
- Cause vasoconstriction of the efferent arteriole
- If blood pressure decreases, angiotensin II increases and causes efferent vasoconstriction to:
- Increase glomerular capillary hydrostatic pressure and maintain GFR so the kidney continues functioning
-
Natriuretic Peptides:
- Made by the heart in case of increased blood volume and blood pressure
- Cause vasodilation of the afferent arteriole to increase the GFR and water excretion
- ANP (Atrial Natriuretic Peptide)
-
Renin-Angiotensin II System:
-
Neural Mechanism:
- Sympathetic stimulation causes vasoconstriction of the afferent arteriole
- Decreases renal blood flow (RBF), which is important in shock to reduce blood flow to the kidney and maintain blood flow to other organs
Intrinsic Mechanisms of GFR Regulation (Inside the Kidney)
-
Myogenic Mechanism:
- Increases afferent resistance
- Increased renal blood flow (RBF) stretches the afferent arteriole leading to smooth muscle contraction, decreasing RBF
-
Tubulo-glomerular Feedback Mechanism:
- Mediated through the juxtaglomerular apparatus
- The juxtaglomerular apparatus is located between the afferent arteriole, efferent arteriole, and distal convoluted tubule of the same nephron
- Composed of:
- Macula densa: Modified cells in the distal convoluted tubule that act as chemoreceptors sensitive to changes in Na+ content of the fluid in the distal convoluted tubule
- Juxtaglomerular cells: Modified cells in the afferent arteriole as it enters the glomerulus that act as baroreceptors and respond to decreased blood pressure or hypovolemia by secreting renin
Juxtaglomerular Apparatus
- Located at the point where the afferent arteriole makes contact with the distal convoluted tubule
Tubulo-glomerular Feedback Mechanism
- In case of increased pressure: (GFR is high and must be decreased)
- Increased glomerular hydrostatic pressure leads to increased GFR and increased Na+ delivery to the macula densa
- The macula densa secretes adenosine (a vasoconstrictor)
- Adenosine causes vasoconstriction of the afferent arteriole
- This decreases glomerular hydrostatic pressure and decreases GFR
Tubular Component
- Formed by a single layer of epithelial cells
- Allows filtrate to pass through the nephron and is the site of tubular secretion and reabsorption
- Begins with Bowman's capsule and consists of:
- Proximal convoluted tubule
- Loop of Henle:
- Descending limb
- Ascending limb
- Distal convoluted tubule
- Collecting duct
Types of Nephron
- There are two types of nephrons
Urine Formation Steps
- Glomerular Filtration: Movement of water, solutes, and ions from the glomerular capillary into Bowman's capsule
- Tubular Reabsorption: The process of reclaiming essential substances from the filtrate back into the bloodstream
- Tubular Secretion: The process of moving substances from the blood into the filtrate
- Urinary Excretion: The process of eliminating waste products from the body in the form of urine
Decrease Peritubular Capillary Hydrostatic Pressure
- Decreasing peritubular capillary hydrostatic pressure facilitates more water absorption in these capillaries
Summary of Mechanisms Regulating GFR:
- Overall Goal: To maintain a constant GFR despite fluctuations in blood pressure
- Extrinsic Mechanisms: Primarily involve hormonal and neural signals impacting blood flow to the kidneys
- Intrinsic Mechanisms: Focus on autoregulation within the kidney, primarily through adjustments in the diameter of the afferent arteriole and the juxtaglomerular apparatus.
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Description
This quiz explores the anatomy and functions of the urinary system, including the roles of the kidneys, ureters, bladder, and urethra. It covers topics such as waste excretion, blood osmolarity maintenance, volume regulation, and blood pressure regulation. Test your knowledge of how this system contributes to overall health.
