Urinary System

pe test 2

What are the two main roles of the kidney in blood filtration?

Removes toxins, metabolic wastes, excess ions from plasma; returns filtered nutrients and important ions to blood.

What are the three major functions of the kidney system?

1. Excretion (remove wastes),

2. Elimination (discharge wastes),

3. Homeostatic regulation (of blood volume & solute concentration).

How does the urinary system regulate blood volume and pressure?

By adjusting water loss in urine and releasing erythropoietin and renin

How are plasma ion concentrations regulated by the urinary system?

By controlling excretion of ions like Na⁺, K⁺, Cl⁻ and producing calcitriol to manage Ca²⁺.

How does the urinary system help stabilize blood pH?

By controlling the excretion of hydrogen and bicarbonate ions in urine.

What nutrients does the urinary system conserve?

Glucose, amino acids, and other valuable substances.

How does the urinary system assist the liver?

In detoxifying poisons and performing gluconeogenesis during fasting.

What are the four main organs of the urinary system?

Kidneys, ureters, urinary bladder, and urethra.

What is micturition?

The process of urination, involving contraction of the bladder to expel urine through the urethra.

What are the physical characteristics of the kidneys?

Bean-shaped, ~10cm long, 5.5cm wide, 3cm thick, retroperitoneal.

What three layers protect the kidney?

1. Renal fascia,

2. Perinephric fat capsule,

3. Fibrous capsule.

What hormones do the adrenal glands produce?

Adrenaline, noradrenaline, cortisol, aldosterone, and weak sex hormones.

What are the functions of cortisol and aldosterone?

Cortisol affects metabolism and immunity; aldosterone helps regulate blood pressure.

What are the three main internal regions of the kidney?

Renal cortex (outer), renal medulla (middle), renal pelvis (inner).

What is the function of renal pyramids and calyces?

Collect and channel urine to the renal pelvis.

What percentage of cardiac output do kidneys receive?

20–25%, or ~1200 mL/min.

What artery supplies each kidney?

The renal artery.

What is the nephron and how many are in each kidney?

It’s the functional unit of the kidney; ~1 million per kidney.

What are the two main parts of the nephron?

Renal corpuscle and renal tubule.

What structures make up the renal corpuscle?

Bowman's capsule and the glomerulus.

What is the function of the renal corpuscle?

Produces a protein-free filtrate from plasma.

What are afferent and efferent arterioles?

Afferent brings blood in; efferent carries filtered blood away.

What are the three parts of the renal tubule?

Proximal convoluted tubule (PCT), nephron loop, distal convoluted tubule (DCT).

Where does urine go after leaving the renal tubule?

Collecting duct → renal pelvis → ureter → bladder → urethra → voided

What happens to the filtrate as it passes through the renal tubule?

Valuable substances are reabsorbed into blood; wastes are secreted into the tubule for excretion.

What are the three functions of the renal tubule?

1. Reabsorb nutrients,

2. Reabsorb 90% of water,

3. Secrete waste products and excess ions.

What are the 3 basic steps of urine formation?

• Glomerular filtration – filters blood to make filtrate (no cells or proteins).

• Tubular reabsorption – useful substances (like glucose, water, Na⁺) move back into blood.

• Tubular secretion – wastes (like H⁺, K⁺, drugs) move from blood into the tubule to be excreted.

What happens during glomerular filtration?

Blood pressure forces water and small solutes from blood into Bowman's capsule. No proteins or blood cells get through.

What makes up the filtration membrane?

1. Fenestrated capillaries
2. Basement membrane
3. Podocytes with slit pores

What is GFR and what affects it?

GFR = amount of filtrate made per minute (~125 mL/min). It's affected by:

• Filtration pressure

• Membrane surface area

• Membrane permeability

• Blood vessel diameter (changed by nerves/hormones)

What is the purpose of reabsorption?

To return useful substances from filtrate into blood (like water, glucose, Na⁺, amino acids).

Where does reabsorption happen?

In all parts of the nephron except the glomerulus.

What happens in the PCT (proximal tubule)?

Reabsorbs ~70% of filtrate:

• All glucose & amino acids

• Most Na⁺, Cl⁻, water

What happens in the nephron loop?

• Descending limb: reabsorbs water

• Ascending limb: reabsorbs Na⁺, K⁺, Cl⁻

• Helps concentrate urine

What happens in the DCT (distal tubule)?

Hormone-controlled reabsorption of Na⁺ (aldosterone), Ca²⁺ (PTH), and water.

What hormones control water and salt in the collecting ducts?

• ADH: increases water reabsorption → ↑ blood volume & pressure

• Aldosterone: increases Na⁺ (and water) reabsorption, lowers K⁺

• ANP: causes Na⁺ and water loss → ↓ blood volume & pressure

What is tubular secretion and what gets secreted?

Transfer of waste from blood into filtrate (mostly in the DCT):

• K⁺, H⁺, NH₄⁺, drugs, creatinine, acids

• Helps remove toxins, balance pH, and regulate K⁺ levels

How does filtrate become urine?

• Filtrate = blood plasma without proteins/cells

• Urine = filtrate minus water, glucose, ions (reabsorbed) + wastes (secreted)

• Final urine forms in DCT & collecting ducts → flows to renal pelvis → ureter → bladder → urethra

What should normal urine contain?

95% water, no glucose, no protein, no amino acids. Yellow colour from urochrome pigment.

What are the roles of the ureters, bladder, and urethra?

• Ureters: carry urine from kidneys to bladder via muscle contractions

• Bladder: stores urine (~400–500 mL), stretches as it fills

• Urethra: releases urine during urination (longer in males)

What is a pyelogram?

An X-ray of the urinary system using dye to show kidneys, ureters, and bladder.

What is micturition?

The act of urinating — bladder contracts, sphincters relax, urine exits body.

What is GFR?

glomerular filtration rate

The amount of filtrate both kidneys produce each minute.

How is GFR controlled?

By intrinsic (local) and extrinsic (external) mechanisms.

How does intrinsic regulation work?

It adjusts the afferent arteriole size to keep GFR steady despite blood pressure changes.

What happens if blood pressure rises?

Afferent arteriole constricts to lower GFR.

What if blood pressure falls?

Afferent arteriole dilates to raise GFR.

What is the JGC?

Juxtaglomerular Complex (JGC)

A kidney structure that helps control filtration and blood pressure.

What are its main parts?

• Mesangial cells (sense stretch)

• Macula densa (sense salt levels)

• Juxtaglomerular cells (release renin)

When is extrinsic regulation used?

During stress or low blood pressure (like bleeding).

What systems are involved?

• Sympathetic nervous system (fast, causes vasoconstriction)

• RAAS hormone system (slow, raises blood volume and pressure)

What triggers RAAS?

Low blood pressure causes kidneys to release renin.

What does renin do?

Starts a chain that creates angiotensin II, which raises blood pressure.

How does angiotensin II raise blood pressure?

• Causes aldosterone release to save sodium and water → increases blood volume.

• Constricts efferent arteriole → raises pressure in the kidney filter.

• Promotes ADH release → saves water in kidneys.

How do kidneys keep blood pH normal?

• If too acidic → remove H⁺, keep bicarbonate

• If too basic → keep H⁺, remove bicarbonate

What makes kidneys produce red blood cells?

Low oxygen → kidneys release erythropoietin (EPO) → bone marrow makes more RBCs.

How is red blood cell production controlled?

Low oxygen → more EPO → more RBCs → oxygen rises → EPO stops.