Chapter 23
- Urinary system rids the body of metabolic Waste products
- The urinary system is closely associated with the
reproductive system
- Shared embryonic development and adult anatomical relationship
- Consist of 6 organs: two kidneys, two ureters, urinary bladder and urethra
- Normal concentration of blood urea is 10 to 20 mg/dL
- Excretion- separation of wastes from body fluids and the elimination of them.
- Renal artery divides into segmental arteries
- zKidneys account for only 0.4% of body weight, they receive about 21% of the cardiac output (re
- Each kidney has about 1.2 million nephrons
- PCT (proximal convoluted tubule)- arises from glomerular capsule
- Nephron loop- long U shaped portion of renal tubule
- DCT 9 distal convoluted tubule)- begins shortly after the ascending limb reenters the vortex
- Collecting duct- recovered fluid form the DCts f severa; nephrons as it passes back into the med
- PCT reabsorbs about 65% of glomerular filtrate, removes some substances from the blood, and
- Abundant mitochondria provide ATP for active transport
- Kidneys reduce 180L of glomerular filtrate to 1 or 2 L urine each day
- Urea, uric acid, bile acids, ammonia, catecholamines, prostaglandins, and a little creatinine are
reabsorption earlier in PCT
- Clears blood of pollutants, morphine, penicillin, aspirin, and other drugs
Segment Main Job Reabsorbed Secreted
PCT Bulk reabsorption Na+, K+, Cl-, H+, drugs, NH₄⁺
(~65-70%) HCO₃⁻, water,
glucose, amino
acids, urea
Loop of Henle Concentrates urine Descending: Water; —
Ascending: Na+,
K+, Cl-
DCT Fine-tuning Na+, Cl-, Ca²⁺ H+, K+
(electrolytes, Ca²⁺) (PTH)
,Collecting Tubule Final concentration Na+, water (ADH), H+, K+
(ADH, aldosterone) urea (in medulla)
Nephron Reabsorption Table:
Nephron Segment Main Components Energy Usage Notes
Reabsorbed
Glomerulus Forms filtrate (water, Passive (filtration) No reabsorption here;
Na+, K+, Cl-, HCO₃⁻, just passive filtration
glucose, amino acids, of plasma minus
urea, creatinine, etc.) proteins/cells
Proximal Convoluted ~65-70% of Na+, Cl-, Highest energy use Uses active transport
Tubule (PCT) K+, HCO₃⁻, water; (Na+/K+ ATPase);
100% of glucose & bulk reabsorption;
amino acids major site of energy
consumption
Loop of Henle Descending limb: Moderate Water reabsorbed
water; Ascending passively; ascending
limb: Na+, K+, Cl- limb reabsorbs ions
actively (thick
segment)
Distal Convoluted Na+, Cl- (via Low-Moderate Hormonal regulation
Tubule (DCT) symporter), Ca²⁺ (e.g., PTH for Ca²⁺);
(stimulated by PTH) continues adjusting
electrolyte balance
Collecting Tubule / Na+ (aldosterone), Moderate (hormone- Final urine
Duct water (ADH), urea driven) concentration;
(medulla only) responds to body
needs via hormones
, (ADH, aldosterone)
Hormones Acting on the Urinary System
Hormone Stimulus for Site of Action Main Effect(s)
Release
ADH (Antidiuretic ↑ Plasma Collecting ducts Inserts
Hormone) osmolality aquaporins → ↑
(dehydration) or water
↓ blood reabsorption → ↓
volume/pressure urine volume, ↑
blood volume
Aldosterone ↓ Na+, ↑ K+, or DCT and Collecting ↑ Na+
↓ blood pressure tubule reabsorption, ↑
(via RAAS K+ secretion → ↑
activation) blood
volume/pressure
ANP (Atrial ↑ Blood Collecting duct, ↑ Na+ and water
Natriuretic Peptide) volume/pressure afferent/efferent excretion
(atria stretch) arterioles (natriuresis),
dilates afferent &
constricts
efferent → ↑ GFR
Parathyroid ↓ Serum calcium PCT, DCT ↓ phosphate
Hormone (PTH) reabsorption
(PCT), ↑ Ca²⁺
reabsorption
(DCT), stimulates
vitamin D
- Urinary system rids the body of metabolic Waste products
- The urinary system is closely associated with the
reproductive system
- Shared embryonic development and adult anatomical relationship
- Consist of 6 organs: two kidneys, two ureters, urinary bladder and urethra
- Normal concentration of blood urea is 10 to 20 mg/dL
- Excretion- separation of wastes from body fluids and the elimination of them.
- Renal artery divides into segmental arteries
- zKidneys account for only 0.4% of body weight, they receive about 21% of the cardiac output (re
- Each kidney has about 1.2 million nephrons
- PCT (proximal convoluted tubule)- arises from glomerular capsule
- Nephron loop- long U shaped portion of renal tubule
- DCT 9 distal convoluted tubule)- begins shortly after the ascending limb reenters the vortex
- Collecting duct- recovered fluid form the DCts f severa; nephrons as it passes back into the med
- PCT reabsorbs about 65% of glomerular filtrate, removes some substances from the blood, and
- Abundant mitochondria provide ATP for active transport
- Kidneys reduce 180L of glomerular filtrate to 1 or 2 L urine each day
- Urea, uric acid, bile acids, ammonia, catecholamines, prostaglandins, and a little creatinine are
reabsorption earlier in PCT
- Clears blood of pollutants, morphine, penicillin, aspirin, and other drugs
Segment Main Job Reabsorbed Secreted
PCT Bulk reabsorption Na+, K+, Cl-, H+, drugs, NH₄⁺
(~65-70%) HCO₃⁻, water,
glucose, amino
acids, urea
Loop of Henle Concentrates urine Descending: Water; —
Ascending: Na+,
K+, Cl-
DCT Fine-tuning Na+, Cl-, Ca²⁺ H+, K+
(electrolytes, Ca²⁺) (PTH)
,Collecting Tubule Final concentration Na+, water (ADH), H+, K+
(ADH, aldosterone) urea (in medulla)
Nephron Reabsorption Table:
Nephron Segment Main Components Energy Usage Notes
Reabsorbed
Glomerulus Forms filtrate (water, Passive (filtration) No reabsorption here;
Na+, K+, Cl-, HCO₃⁻, just passive filtration
glucose, amino acids, of plasma minus
urea, creatinine, etc.) proteins/cells
Proximal Convoluted ~65-70% of Na+, Cl-, Highest energy use Uses active transport
Tubule (PCT) K+, HCO₃⁻, water; (Na+/K+ ATPase);
100% of glucose & bulk reabsorption;
amino acids major site of energy
consumption
Loop of Henle Descending limb: Moderate Water reabsorbed
water; Ascending passively; ascending
limb: Na+, K+, Cl- limb reabsorbs ions
actively (thick
segment)
Distal Convoluted Na+, Cl- (via Low-Moderate Hormonal regulation
Tubule (DCT) symporter), Ca²⁺ (e.g., PTH for Ca²⁺);
(stimulated by PTH) continues adjusting
electrolyte balance
Collecting Tubule / Na+ (aldosterone), Moderate (hormone- Final urine
Duct water (ADH), urea driven) concentration;
(medulla only) responds to body
needs via hormones
, (ADH, aldosterone)
Hormones Acting on the Urinary System
Hormone Stimulus for Site of Action Main Effect(s)
Release
ADH (Antidiuretic ↑ Plasma Collecting ducts Inserts
Hormone) osmolality aquaporins → ↑
(dehydration) or water
↓ blood reabsorption → ↓
volume/pressure urine volume, ↑
blood volume
Aldosterone ↓ Na+, ↑ K+, or DCT and Collecting ↑ Na+
↓ blood pressure tubule reabsorption, ↑
(via RAAS K+ secretion → ↑
activation) blood
volume/pressure
ANP (Atrial ↑ Blood Collecting duct, ↑ Na+ and water
Natriuretic Peptide) volume/pressure afferent/efferent excretion
(atria stretch) arterioles (natriuresis),
dilates afferent &
constricts
efferent → ↑ GFR
Parathyroid ↓ Serum calcium PCT, DCT ↓ phosphate
Hormone (PTH) reabsorption
(PCT), ↑ Ca²⁺
reabsorption
(DCT), stimulates
vitamin D
