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What is the main function of the urinary system?
What is the main function of the urinary system?
The right kidney is located higher than the left kidney.
The right kidney is located higher than the left kidney.
False
What is the approximate size and shape of a kidney?
What is the approximate size and shape of a kidney?
Bean-shaped, about 11 cm long, 6 cm wide, and 3 cm thick
The functional unit of the kidney is called the __________.
The functional unit of the kidney is called the __________.
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Match the following kidney structures with their functions:
Match the following kidney structures with their functions:
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What condition is described as an inferior displacement of the kidneys?
What condition is described as an inferior displacement of the kidneys?
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The kidney's role includes regulating blood volume and blood pressure.
The kidney's role includes regulating blood volume and blood pressure.
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What is found in the urine that kidneys produce?
What is found in the urine that kidneys produce?
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What is the main function of diuretics?
What is the main function of diuretics?
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The urinary bladder has a capacity of approximately 500-600 mL.
The urinary bladder has a capacity of approximately 500-600 mL.
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What triggers the micturition reflex when the bladder fills?
What triggers the micturition reflex when the bladder fills?
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The __________ is the triangular area formed by the openings in the floor of the urinary bladder.
The __________ is the triangular area formed by the openings in the floor of the urinary bladder.
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Match the following structures with their functions:
Match the following structures with their functions:
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Which hormone increases the reabsorption of water in the kidneys?
Which hormone increases the reabsorption of water in the kidneys?
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The inner lining of the bladder, when empty, is arranged in folds called rugae.
The inner lining of the bladder, when empty, is arranged in folds called rugae.
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The contraction of the __________ muscle in the bladder is responsible for expelling urine.
The contraction of the __________ muscle in the bladder is responsible for expelling urine.
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What is the normal bladder capacity?
What is the normal bladder capacity?
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The female urethra is longer than the male urethra.
The female urethra is longer than the male urethra.
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What triggers the micturition reflex?
What triggers the micturition reflex?
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The ________ sphincter is a smooth involuntary muscle at the beginning of the urethra.
The ________ sphincter is a smooth involuntary muscle at the beginning of the urethra.
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Match the following conditions with their definitions:
Match the following conditions with their definitions:
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What is a common cause for urinary tract infections (UTIs) in women?
What is a common cause for urinary tract infections (UTIs) in women?
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Micturition can only happen voluntarily.
Micturition can only happen voluntarily.
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What might cause temporary urinary incontinence?
What might cause temporary urinary incontinence?
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What percentage of solute reabsorption occurs in the proximal convoluted tubule?
What percentage of solute reabsorption occurs in the proximal convoluted tubule?
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The ascending limb of the nephron loop is permeable to water.
The ascending limb of the nephron loop is permeable to water.
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What hormone is responsible for increasing the reabsorption of water in the DCT and collecting duct?
What hormone is responsible for increasing the reabsorption of water in the DCT and collecting duct?
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Reabsorption of sodium and water is increased by __________, which is secreted by the adrenal cortex.
Reabsorption of sodium and water is increased by __________, which is secreted by the adrenal cortex.
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Match the following hormones with their actions:
Match the following hormones with their actions:
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What happens when there is a high concentration of solutes in the blood?
What happens when there is a high concentration of solutes in the blood?
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Secretion in the kidneys helps control blood pH.
Secretion in the kidneys helps control blood pH.
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What role does negative feedback play in the secretion of aldosterone?
What role does negative feedback play in the secretion of aldosterone?
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What is the main function of the renal tubule?
What is the main function of the renal tubule?
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Less than 1% of the filtrate produced daily becomes urine.
Less than 1% of the filtrate produced daily becomes urine.
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What is the composition of the filtrate produced during filtration?
What is the composition of the filtrate produced during filtration?
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The _____ is responsible for the movement of fluid from the glomerular capillary across the filtration membrane.
The _____ is responsible for the movement of fluid from the glomerular capillary across the filtration membrane.
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Match the following pressures with their contributions to filtration:
Match the following pressures with their contributions to filtration:
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Which of the following substances are NOT typically filtered into the nephron?
Which of the following substances are NOT typically filtered into the nephron?
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Capsular hydrostatic pressure (CHP) tends to facilitate the movement of fluid into the Bowman’s capsule.
Capsular hydrostatic pressure (CHP) tends to facilitate the movement of fluid into the Bowman’s capsule.
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How much filtrate is produced daily by the kidneys?
How much filtrate is produced daily by the kidneys?
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What is the outer light-red region of the kidney called?
What is the outer light-red region of the kidney called?
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The renal pyramids are located in the renal cortex.
The renal pyramids are located in the renal cortex.
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What is the primary function of nephrons in the kidney?
What is the primary function of nephrons in the kidney?
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The cavity that collects urine from the major calyx is called the __________.
The cavity that collects urine from the major calyx is called the __________.
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Match the kidney structures with their descriptions:
Match the kidney structures with their descriptions:
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Where do nephrons receive their blood supply from?
Where do nephrons receive their blood supply from?
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Nephrons can be replaced if damaged.
Nephrons can be replaced if damaged.
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What does the renal plexus supply to the kidney?
What does the renal plexus supply to the kidney?
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Study Notes
Learning Outcomes
- Students should be able to identify organs associated with the kidneys
- Students should be able to state the functions of the kidneys
- Students should be able to outline the gross structure of the kidneys
- Students should be able to describe the structure of a nephron
- Students should be able to explain urine formation
- Students should be able to explain the structure of the ureter, urinary bladder, and urethra in the urinary system
- Students should be able to explain the process of micturition
Urinary System Overview
- The urinary system is the main excretory system
- It plays a vital role in maintaining water and electrolyte homeostasis
- Urine contains carbon dioxide, ammonia, urea, uric acid, creatinine, and inorganic salts
- The urinary system consists of two kidneys, two ureters, a urinary bladder, and a urethra
Kidneys
- Location: posterior abdominal wall, on each side of the vertebral column, extending from the 12th thoracic vertebra to the 3rd lumbar vertebra, behind the peritoneum, and below the diaphragm. The right kidney is slightly lower than the left due to the liver occupying space there.
- Shape: bean-shaped organs, approximately 11 cm long, 6 cm wide, 3 cm thick and weigh 150 gm.
- Gross structure: Renal hilum (where renal artery, nerves enter, and renal vein and ureter exit), renal sinus (cavity filled with fat and loose connective tissue), renal cortex (outer light-red region), renal medulla (darker red-brown inner region), renal pyramids (cone-shaped in the renal medulla), renal columns (extension of the renal cortex), renal papillae (base of renal pyramids pointing towards the center of the kidney), minor calyces (surround renal papillae, collecting urine from that pyramid), major calyces (formed from several minor calyces), renal pelvis (cavity collecting urine & continuous with the ureter)
- Adipose capsule: protects the kidney from trauma and acts as cushioning
- Renal fascia: thin layer of connective tissue anchoring the kidney to surrounding structures and abdominal wall
Clinical Application: Nephroptosis
- Nephroptosis is inferior displacement of the kidneys
- More common in thin people
- Dangerous because ureters may kink and block urine flow
Microscopic Structure of the Kidney
- Internally, kidneys consist of cortex, medulla, pyramids, papillae, columns, calyces, and renal pelvis
- Renal cortex and renal pyramids constitute the functional portion or parenchyma of the kidney
- Nephron: the functional unit of the kidney
Nephron
- Functional unit of the kidney
- When damaged, they are not replaced
- Consists of two parts: renal corpuscle and renal tubule
- Functions: glomerular filtration, tubular reabsorption, tubular secretion
Renal Corpuscle
- Filters blood plasma
- Located in the cortex of the kidney
- Glomerulus: a network of tiny arterial capillaries
- Glomerular (Bowman's) capsule: surrounds the glomerulus
Renal Tubule
- Carries filtered fluid away from the glomerular capsule
- Consists of: Proximal convoluted tubule (PCT), Descending and ascending loop of Henle (nephron loop), Distal convoluted tubule (DCT)
Clinical Application: Glomerulonephritis (GN)
- Inflammatory condition of glomerulus
- Impaired glomerular filtration
- Symptoms include oliguria, hypertension, hematuria, and uraemia
Clinical Application: Nephrotic Syndrome
- Increased permeability of glomerular membrane resulting from glomerular damage
- Plasma proteins pass into the filtrate
- Symptom: edema
Proximal Convoluted Tubule (PCT)
- Arise from glomerular capsule
- Filtrate passes first
- Great absorption occurs here (glucose, amino acids, water, salts)
Loop of Henle
- A long U-shaped portion of the renal tubule
- Contains descending limb and ascending limb
- Active transport of salt
Distal Convoluted Tubule (DCT)
- Short & less coiled compared to the PCT
- End of nephron
Collecting Ducts
- Receive fluids from the DCT of several nephrons
- Fluid flows from collecting ducts into the minor calyces
Juxtaglomerular Apparatus
- Specialized structure near the glomerulus
- Juxtaglomerular cells: ring of smooth muscle in the afferent arteriole where the latter enters Bowman's capsule; produce renin for blood pressure regulation
- Macula densa: specialized tubule cells of the distal tubule that monitors sodium in the urine
Overview of Renal Physiology (Urine Formation)
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Filtration
- Movement of fluid from blood through glomerulus across filtration membrane into the Bowman's capsule
- Filtrate: Water, ions, and small molecules
- Not filtered: Plasma proteins, blood cells, and platelets
- Filtration pressure: pressure gradient responsible for filtration
- Pressures contributing to filtration pressure: Glomerular capillary pressure (GCP), Capsular hydrostatic pressure (CHP), Blood colloid osmotic pressure (BCOP).
- Glomerular filtration rate (GFR): the amount of filtrate formed in all the renal corpuscles of both kidneys each minute.
Renal Autoregulation
- Protect renal blood flow & glomerular filtration
- Involves changes of constriction in afferent arterioles
- Systemic blood pressure increases, afferent arterioles constrict and prevent increase in renal blood flow
- Juxtaglomerular apparatus detects if there is increased rate of blood flow of filtrate past cells of macula densa, causing afferent arteriole constriction
- In severe dehydration or hemorrhage, sympathetic simulation constricts small arteries & afferent arterioles, decreasing renal blood flow & filtrate formation. Renin, secreted from juxtaglomerular cells, stimulates vasoconstriction and maintains GFR.
- Tubuloglomerular feedback: mechanisms used to maintain a consistent GFR (glomerular filtration rate).
Reabsorption
- Return of most filtered water and solutes to the bloodstream (about 99%)
- Primarily in the PCT, the walls are lined with microvilli to increase surface area for absorption
- Use active and passive processes
- Sodium reabsorption is key to creating osmotic and electrical gradients for water reabsorption.
Reabsorption...cont
- Passive process: diffusion and osmosis
- Active process: Using energy to transport molecules; carrier proteins bind to molecules
- Reabsorption of glucose, amino acids, vitamins, minerals, and some H2O back into blood within PCT and DCT occur.
- Location of reabsorption: 65% in proximal convoluted tubule, 15% in nephron loop, 19% in distal tubule, and 1% excreted as urine.
- Most solutes are reabsorbed by active transport mechanism using carrier molecules.
Secretion
- Removing substances from blood into renal tubules
- Helps control blood pH and eliminate substances from body
- Takes place along the renal tubules and collecting ducts
- Occurs via both passive diffusion and active transport
Hormonal Actions
- Parathyroid hormone: Secreted by parathyroid gland; works with calcitonin to regulate Ca2+ & phosphate reabsorption in the DCT to maintain blood levels.
- Aldosterone: Secreted by the adrenal cortex; increased by renin action on angiotensin I converting to angiotensin II; increased reabsorption of Na+ and H2O, excretion of K+. Regulated via negative feedback mechanism
- Antidiuretic hormone (ADH): Secreted by the anterior pituitary. Increases water reabsorption in the DCT and collecting duct; decreases urine volume and maintains normal blood volume and blood pressure
- Atrial natriuretic peptide (ANP): Secreted from cardiac muscle in right atrium of the heart when BP increases; decreases reabsorption of Na+ and H2O in PCT and collecting ducts; regulated via negative feedback.
Urine Concentration and Dilution
- Kidneys change urine volume and osmolality by concentrating or diluting as per body needs
- Hypothalamus: sensitive to blood composition
- If solute concentration is high, kidneys secrete small amounts of concentrated urine to conserve water and eliminate solutes
- By diluting urine, kidneys conserve solutes and remove excessive water.
Urine Transportation, Storage, & Elimination
- Ureters: transport urine from the renal pelvis of the kidneys to the urinary bladder (approximately 25 to 30 cm long, 3 mm diameter) using peristaltic waves, hydrostatic pressure, and gravity. No anatomical valve prevents backflow.
- Urinary Bladder: hollow, distensible muscular organ located in the pelvic cavity; storage of urine (700-800ml capacity).
- Micturition: discharge of urine from the bladder; combination of involuntary and voluntary muscle contractions. When volume increases, stretch receptors send signals to the spinal cord, triggering a micturition reflex, stimulating involuntary detrusor muscle contraction and relaxation of the internal urethral sphincter.
- Wall of the bladder has a mucosal membrane that folds into rugae, allowing expansion.
- Trigone: triangular area formed by the openings of two ureters and one urethra
- Urethra: tube exiting the bladder (male: ~20cm, female: ~3-4cm)
- Contains internal urethral sphincter (smooth involuntary muscle) and external urethral sphincter (skeletal voluntary muscle).
Clinical Application: Urethra
- Urinary tract infections (UTIs) are common in women due to the short length and proximity of the urethra to the anal opening, allowing easier access for intestinal bacteria
- Urethritis: UTI of the urethra. Cystitis: UTI of the urinary bladder
Micturition Reflex
- Accumulation of urine in the bladder triggers stretch receptors in the bladder wall
- This activates sensory impulses that are transmitted to the spinal cord
- Spinal reflex initiates involuntary contraction of the detrusor muscle & relaxation of the internal urethral sphincter
- Urine enters the urethra, and micturition occurs.
- When bladder control is established, sensory impulses from the bladder are transmitted upward to the brain.
- Consciousness of passing urine, as bladder fills (300–400ml), can contract the external sphincter (voluntary) & muscle of the pelvic floor, inhibiting micturition (in adult)
- Overdistention bladder causes involuntary relaxation to occur.
Composition of Urine
- Urine is clear and amber due to urobilinogen (bile pigment altered in the intestines)
- Characteristics:
- Volume: 1-2 liters per 24-hours (average 1500 ml/day)
- pH: 4.6–8.0 (average 6)
- Specific Gravity: 1.001-1.035
- Color: Yellow due to urochrome
- Composition: 95% water, 5% solutes (primarily urea).
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Test your knowledge on the urinary system with this quiz. Questions cover kidney functions, anatomy, and related physiological processes. Perfect for students studying biology or health sciences.
