Respiratory

Ch 23 Urinary system

• Functions of the kidneys- Filter blood and remove wastes (urea, creatinine)

Regulate water balance

Maintain electrolyte balance (Na⁺, K⁺, Ca²⁺)

Regulate blood pH (acid–base balance)

Control blood pressure (via renin)

Produce hormones (erythropoietin, activate vitamin D)

• Normal composition of urine - Water (~95%)

Urea (major waste product)

Creatinine

Uric acid

Electrolytes (Na⁺, K⁺, Cl⁻)

• Name the different parts of the nephron (renal corpuscle (aka Bowman's capsule, PCT, Loop of Henle, CT, collecting duct)and know what takes place in each section - Renal corpuscle (glomerulus + Bowman’s capsule)

• Function: Filtration

• Blood pressure forces water and small solutes into capsule

• Proteins and cells stay in blood

Proximal convoluted tubule (PCT)

• Function: Bulk reabsorption

• Reabsorbs:

  • Glucose

  • Amino acids

  • Na⁺, water

• Secretes some wastes/drugs

Loop of Henle

Descending limb

• Permeable to water

• Water leaves → filtrate becomes concentrated

Ascending limb

• Impermeable to water

• Actively transports Na⁺, K⁺, Cl⁻ out

• Filtrate becomes dilute

Distal convoluted tubule (DCT)

• Fine-tuning of electrolytes

• Regulated by hormones (aldosterone, PTH)

Collecting duct

• Final concentration of urine

• Controlled by ADH → increases water reabsorption

• What factors affect glomerular filtration rate? - Blood pressure (main factor)

Afferent arteriole diameter (incoming)

Efferent arteriole diameter (outgoing)

Plasma protein concentration

Hormones (renin, angiotensin II)

• What is meant by transport maximum and what happens when transporters in the kidney tubules (nephrons) are at their maximum? - The maximum rate at which substances can be reabsorbed

When exceeded:

• Transporters become saturated

• Excess substance stays in urine

👉 Example: In diabetes → glucose appears in urine

• What is the countercurrent multiplier? What is its function? What is secreted from the Descending loop? From the ascending limb into the medullary space? - A system in the Loop of Henle that creates a concentration gradient in the kidney medulla.

Function:

• Allows kidneys to produce concentrated urine

• Helps conserve water

What moves where:

• Descending limb:

  • Water leaves into medullary space

• Ascending limb:

  • Na⁺, K⁺, Cl⁻ are pumped out into medulla

  • No water leaves 

• Name the muscle that makes up the urinary bladder - Detrusor muscle trigone

• Smooth muscle that contracts to expel urine

• What is an antiport? What is a symport? Give examples of each - Symport

• Moves two substances in the same direction

• Example: Na⁺ + glucose reabsorption in PCT

Antiport

• Moves substances in opposite directions

• Example: Na⁺/H⁺ exchanger in PCT

• What is the function of the countercurrent multiplier? - Builds a salt gradient in the medulla

• Enables water reabsorption in collecting duct

• Produces concentrated urine 

• Understand the three ways of controlling FR: autoregulation (myogenic and juxtaglomerular

• What is the countercurrent multiplier? What is its function? What is secreted from the Descending loop? From the ascending limb into the medullary space? - A. Autoregulation (intrinsic control)

1. Myogenic mechanism

• Afferent arteriole stretches when BP increases → constricts

• When BP drops → dilates
  👉 Keeps GFR stable

2. Juxtaglomerular apparatus (JGA)

• Macula densa senses NaCl levels

• Low NaCl → signals to increase GFR (via renin release)

• High NaCl → reduces GFR

• B. Neural control

• Sympathetic nervous system

• During stress → vasoconstriction of afferent arteriole
  👉 Decreases GFR (conserves blood for vital organs)

C. Hormonal control

• Renin–angiotensin–aldosterone system (RAAS)

• Angiotensin II constricts efferent arteriole → maintains GFR

• Works with aldosterone and ADH to regulate fluid balance 

• How do aldosterone and ADH affect urine output - ldosterone

• Increases Na⁺ reabsorption

• Water follows → less urine, higher BP

ADH (antidiuretic hormone)

• Increases water reabsorption in collecting duct

• Produces concentrated urine

• Glucose in the urine is indicative of what disease? glycosuria

• Where do nitrogenous wastes come from and which organs system excretes nitrogenous wastes? - Where they come from:

• Breakdown of proteins and nucleic acids

• Mainly in the liver (forms urea)

Which system excretes them:

• Urinary system (kidneys)

• What are the 4 stages of urine formation?

Filtration

• In renal corpuscle

Reabsorption

• Useful substances returned to blood

Secretion

• Additional wastes added to filtrate

Excretion

• Urine leaves body