Urinary system A&P test 2

1. What are the organs of the urinary system?

Kidneys, ureters, urinary bladder, and urethra. The kidneys filter blood and produce urine, the ureters transport urine to the bladder, the bladder stores urine, and the urethra eliminates it from the body.

2. What are the primary functions of the kidneys?

The kidneys regulate blood composition by filtering waste, balance electrolytes, control blood pressure through the renin-angiotensin system, produce erythropoietin for red blood cell production, and regulate pH.

3. How do the kidneys contribute to the maintenance of body fluid volume, pH, and composition?

The kidneys adjust water and electrolyte excretion to maintain fluid balance, regulate pH by excreting hydrogen ions and reabsorbing bicarbonate, and filter metabolic waste while selectively reabsorbing necessary nutrients.

4. What roles do the ureters, urinary bladder, and urethra play in urine transport and elimination?

The ureters transport urine from the kidneys to the bladder using peristalsis. The bladder stores urine until elimination. The urethra carries urine from the bladder to the exterior of the body, with sphincters controlling release.

5. How would you describe the size, shape, and color of the kidneys?

The kidneys are bean-shaped, reddish-brown, about 10-12 cm long, 5-7 cm wide, and 3 cm thick.

6. Where are the kidneys located, and what does it mean that they are retroperitoneal?

The kidneys are located on either side of the spine at the level of T12-L3, behind the peritoneum, meaning they are retroperitoneal and not within the abdominal cavity.

7. Why is the left kidney usually positioned slightly higher than the right?

The right kidney is slightly lower due to the presence of the liver on the right side of the body.

8. What is the function of the fibrous renal capsule, renal fat, and renal fascia surrounding the kidney?

The renal capsule provides protection, renal fat cushions and insulates, and renal fascia anchors the kidney in place.

9. What are the main regions of the kidney (renal cortex, renal medulla, and renal sinus), and what is their significance?

The renal cortex contains nephrons for filtration, the medulla houses renal pyramids for urine collection, and the renal sinus contains renal pelvis and blood vessels.

10. What are nephrons, and why are they considered the functional units of the kidney?

Nephrons are microscopic structures that filter blood and form urine through filtration, reabsorption, and secretion.

11. How is the structure of a nephron organized (renal corpuscle and renal tubule)?

The renal corpuscle (glomerulus and Bowman’s capsule) filters blood, and the renal tubule (proximal tubule, loop of Henle, distal tubule, and collecting duct) processes the filtrate.

12. What is the difference between cortical nephrons and juxtamedullary nephrons, and why is this distinction important?

Cortical nephrons are in the outer cortex and handle most filtration. Juxtamedullary nephrons extend deep into the medulla and help concentrate urine.

Cortical nephrons:

Make up 85% of nephrons.

Located in the renal cortex.

Involved in regular filtration and urine production.

Juxtamedullary nephrons:

Make up 15% of nephrons.

Extend into the renal medulla.

Play a key role in producing concentrated urine by creating an osmotic gradient​ 

13. What is the route of blood flow to and through the kidney starting with the renal artery?

Renal artery → segmental artery → interlobar artery → arcuate artery → cortical radiate artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta → cortical radiate vein → arcuate vein → interlobar vein → renal vein.

14. How do the afferent and efferent arterioles function in glomerular filtration?

The afferent arteriole supplies blood to the glomerulus, and the efferent arteriole carries filtered blood away, maintaining pressure for filtration.

15. What is the role of the glomerulus in filtering blood?

The glomerulus allows water and small solutes to pass while retaining larger proteins and blood cells.

16. How do the peritubular capillaries support the processes of tubular reabsorption and secretion?

These capillaries surround nephrons, reabsorbing essential nutrients and secreting waste into the tubules.

17. What are the three major processes involved in urine formation?

Glomerular Filtration – Blood is filtered in the glomerulus, allowing water, ions, and small molecules to enter the renal tubule.

Tubular Reabsorption – Essential substances (e.g., glucose, amino acids, water) are reabsorbed from the filtrate back into the blood.

Tubular Secretion – Additional waste products and excess ions are secreted from the blood into the renal tubule for excretion​

.

18. What happens during glomerular filtration, and what factors determine the glomerular filtration rate (GFR)?

The glomerulus filters blood plasma, with GFR influenced by blood pressure, filtration membrane permeability, and hydrostatic pressure.

19. How do hydrostatic pressure, colloid osmotic pressure, and capsular hydrostatic pressure interact to affect filtration?

Hydrostatic pressure pushes fluid out, colloid osmotic pressure pulls it back in, and capsular hydrostatic pressure opposes filtration.

20. What substances are typically filtered into the renal tubule during glomerular filtration?

Water, glucose, amino acids, ions, urea, and small solutes.

21. What is tubular reabsorption, and which segments of the nephron are most active in reabsorption?

The proximal tubule reabsorbs most water, glucose, and ions. The loop of Henle and distal tubule adjust urine concentration.

Tubular reabsorption: Movement of water and solutes from the nephron back into the blood.

Most active sites:

Proximal convoluted tubule (PCT) – Major site for glucose, amino acids, sodium, and water reabsorption.

Loop of Henle – Water reabsorption in descending limb; sodium reabsorption in ascending limb.

Distal convoluted tubule (DCT) and collecting duct – Hormone-regulated reabsorption (e.g., ADH and aldosterone influence water and sodium balance)​

What are the mechanisms (passive and active transport) by which substances like glucose, amino acids, and ions are reabsorbed?

Passive transport: Diffusion and osmosis (water moves due to osmotic gradients).

Active transport: Requires ATP to move substances against their concentration gradient (e.g., sodium-potassium pumps for sodium reabsorption, glucose transport via sodium-glucose symporters)​

What is tubular secretion, and how does it complement reabsorption in forming urine?

Tubular secretion: The active transport of substances (e.g., hydrogen ions, potassium, ammonia, drugs) from the blood into the nephron.

Purpose: Helps remove toxins, balance pH, and eliminate excess ions​

Which substances are actively secreted into the tubular fluid, and why is secretion necessary?

Actively secreted substances: Hydrogen ions (pH balance), potassium (electrolyte balance), creatinine, drugs (e.g., penicillin).

Importance: Prevents toxic buildup, regulates blood pH, and maintains electrolyte balance​

29. How is the glomerular filtration rate (GFR) maintained relatively constant through autoregulation?

The kidneys adjust afferent and efferent arteriole diameters to stabilize filtration.

Myogenic Mechanism – Afferent arteriole constricts when blood pressure rises, reducing GFR; dilates when BP drops, increasing GFR.

Tubuloglomerular Feedback – The macula densa cells detect NaCl levels in the distal tubule and signal afferent arteriole adjustments​

30. What is tubuloglomerular feedback, and how do the macula densa and juxtaglomerular apparatus regulate GFR?

The macula densa detects NaCl levels and signals changes in arteriole diameter to maintain GFR.

31. How do changes in the diameter of the afferent and efferent arterioles affect GFR?

Dilation of the afferent arteriole increases GFR, while constriction reduces it.

Afferent arteriole constriction → Decreases blood flow → Decreases GFR.

Afferent arteriole dilation → Increases blood flow → Increases GFR.

Efferent arteriole constriction → Increases glomerular pressure → Increases GFR.

Efferent arteriole dilation → Decreases glomerular pressure → Decreases GFR​

38. What is the typical composition of urine, and how does it differ from plasma and glomerular filtrate?

Urine contains water, urea, creatinine, and electrolytes but lacks proteins and glucose.

What role does the renin-angiotensin-aldosterone system (RAAS) play in regulating GFR and systemic blood pressure?

RAAS is activated when BP is low, helping restore blood volume and GFR:

Juxtaglomerular cells release renin.

Renin converts angiotensinogen to angiotensin I.

ACE (angiotensin-converting enzyme) converts angiotensin I to angiotensin II.

Angiotensin II effects:

Vasoconstriction (raises BP).

Stimulates aldosterone release (increases sodium and water retention).

Stimulates ADH release (promotes water reabsorption)​

How do the kidneys regulate urine concentration and volume?

Controlled by hormonal signals (ADH and aldosterone).

Countercurrent mechanisms in the nephron loop create a gradient that allows for water reabsorption.

Urine concentration depends on hydration status:

Dehydration → More ADH → More water reabsorbed → Concentrated urine.

Overhydration → Less ADH → Less water reabsorbed → Dilute urine​

What is the countercurrent multiplier mechanism, and how does it help concentrate urine?

Occurs in the loop of Henle to create a high solute concentration in the medulla.

Process:

Descending limb: Permeable to water, but not solutes → Water exits, increasing filtrate concentration.

Ascending limb: Impermeable to water, actively transports NaCl out → Creates a medullary osmotic gradient.

Importance: Enables the collecting duct to reabsorb water efficiently, concentrating urine when needed​

How does antidiuretic hormone (ADH) influence water reabsorption in the distal tubule and collecting ducts?

ADH (vasopressin) is released from the posterior pituitary when dehydration is detected.

Effects of ADH:

Increases permeability of the collecting ducts by inserting aquaporins.

More water is reabsorbed, reducing urine volume and increasing urine concentration​

What is the typical composition of urine, and how does it differ from plasma and glomerular filtrate?

Urine Composition:

95% water, 5% solutes (urea, uric acid, creatinine, ions: Na+, K+, Cl-, Ca2+, H+).

May contain small amounts of hormones, drugs, or metabolites.

Comparison:

Plasma: Contains proteins, glucose, amino acids, and formed elements (RBCs, WBCs, platelets) – these are absent in normal urine.

Glomerular filtrate: Initially similar to plasma without large proteins but undergoes reabsorption and secretion to form urine​

39. How is renal clearance defined, and what substances (e.g., inulin, creatinine) are used to measure it?

Renal clearance measures how efficiently a substance is cleared; inulin and creatinine are standard markers.

Renal Clearance: The volume of plasma completely cleared of a substance per unit time (mL/min).

Common markers:

Inulin: Most accurate for GFR measurement (freely filtered, not reabsorbed or secreted).

Creatinine: Used in clinical settings as an estimate of GFR (slightly secreted by tubules, so it slightly overestimates GFR)​

34. What is the pathway of urine from its formation in the nephrons to its elimination from the body?

Nephrons → Urine forms in the renal tubules.

Collecting ducts → Urine is concentrated.

Renal papillae → Drain urine into minor calyces.

Minor calyces → Merge into major calyces.

Major calyces → Funnel urine into the renal pelvis.

Renal pelvis → Leads urine into the ureters.

Ureters → Transport urine to the urinary bladder.

Urinary bladder → Stores urine until excretion.

Urethra → Conducts urine out of the body​

How do the ureters use peristalsis to transport urine?

Ureters use peristaltic contractions (wave-like muscle movements) to push urine from the kidneys to the bladder.

Smooth muscle in the ureter walls contracts rhythmically, independent of gravity.

Prevents urine backflow due to one-way valves at the bladder entrance​

.

What are the structural features of the urinary bladder that enable it to store urine?

Detrusor muscle: A smooth muscle layer that contracts during urination.

Transitional epithelium: Allows the bladder to expand and contract.

Rugae (folds in the bladder wall): Expand to accommodate more urine.

Trigone region: A triangular area that funnels urine toward the urethra when the bladder contracts​

.

How do the internal and external urethral sphincters contribute to urinary control?

Internal urethral sphincter (involuntary, smooth muscle):

Located at the bladder-urethra junction.

Prevents urine leakage until micturition reflex activates it.

External urethral sphincter (voluntary, skeletal muscle):

Located in the pelvic floor.

Under conscious control, allowing voluntary delay of urination​

How does micturition (urination) occur, and what neural mechanisms control it?

Micturition reflex involves spinal cord and brain control.

Steps:

Bladder fills, stretching receptors activate.

Signals sent to the spinal cord and brainstem (pons).

Parasympathetic nerves stimulate detrusor muscle contraction, relaxing the internal sphincter.

If convenient, somatic nerves relax the external sphincter → urination occurs.

If not, the brain suppresses the reflex until appropriate​

What is glomerulonephritis, and how does it affect kidney function?

Glomerulonephritis is inflammation of the glomeruli, often due to infection, autoimmune disorders, or toxins.

Effects on kidney function:

Decreased filtration rate: Damaged glomeruli cannot filter blood efficiently.

Proteinuria & hematuria: Proteins and blood cells leak into urine.

Edema & hypertension: Fluid retention due to poor filtration​

What are the differences between acute and chronic glomerulonephritis?

Acute glomerulonephritis:

Sudden onset, often after infections (e.g., streptococcal throat infection).

Usually resolves with treatment but can progress if untreated.

Chronic glomerulonephritis:

Develops slowly, leading to progressive kidney damage.

Can result in chronic kidney disease (CKD) and require dialysis or transplant​

.

Acute glomerulonephritis:

Sudden onset, often after infections (e.g., streptococcal throat infection).

Usually resolves with treatment but can progress if untreated.

Chronic glomerulonephritis:

Develops slowly, leading to progressive kidney damage.

Can result in chronic kidney disease (CKD) and require dialysis or transplant​

42. What characterizes nephrotic syndrome, and how does it lead to edema?

Nephrotic syndrome involves excessive protein loss in urine, reducing blood osmotic pressure and causing fluid retention (edema).

What are kidney stones composed of, and what are common causes of their formation?

Composition: Kidney stones are hard mineral and salt deposits, often made of:

Calcium oxalate (most common)

Uric acid

Struvite (magnesium ammonium phosphate)

Cystine (rare, genetic condition)

Causes:

Dehydration (concentrated urine encourages crystal formation).

High calcium, oxalate, or uric acid levels in urine.

Urinary tract infections (UTIs) (struvite stones).

Genetics & metabolic disorders​

44. What is chronic kidney disease (CKD), and what are the potential treatment options?

CKD is progressive kidney function loss, treated with dialysis or transplantation.

 What developmental abnormalities can occur in the urinary system (e.g., horseshoe kidney, renal agenesis)?

Horseshoe kidney: The kidneys fuse during development, forming a single U-shaped kidney.

Renal agenesis: One or both kidneys fail to develop (unilateral is survivable, bilateral is fatal).

Polycystic kidney disease (PKD): Genetic disorder causing fluid-filled cysts, leading to kidney enlargement and failure.

Duplication of ureters: Can lead to urinary reflux or infections​

How can urinalysis provide clues to systemic diseases or kidney disorders?

Urinalysis detects abnormalities in urine composition.

Findings & Possible Causes:

Proteinuria → Kidney damage (glomerulonephritis, CKD).

Hematuria → Infection, kidney stones, trauma.

Glucose in urine → Diabetes.

Ketones in urine → Starvation, uncontrolled diabetes.

Leukocytes & nitrites → Urinary tract infection (UTI).

Crystals → risk of kidney stones

46. How does kidney function change with age, particularly regarding the glomerular filtration rate (GFR)?

Decline in GFR:

By age 40, GFR starts declining at about 1% per year due to reduced nephron number and renal blood flow.

This decreases the kidneys’ ability to filter waste, leading to a higher risk of toxin buildup (uremia) in older adults.

Reduced ability to concentrate urine:

Aging kidneys have difficulty conserving water, increasing dehydration risk.

Slower drug clearance:

Medications that are excreted by the kidneys (e.g., antibiotics, NSAIDs) may accumulate, increasing toxicity risk​

What structural changes occur in the kidneys and urinary tract as part of aging?

Kidney changes:

Decreased kidney mass due to nephron loss.

Thickening of glomerular and tubular membranes, reducing filtration efficiency.

Urinary tract changes:

Bladder wall elasticity decreases, leading to reduced bladder capacity.

Weakened urethral sphincters, increasing the risk of urinary incontinence.

Prostate enlargement (in men) can obstruct urine flow, leading to difficulty urinating and increased infection risk​