biology 20 excretory

Kidneys

Filter blood, remove nitrogenous waste (urea), regulate pH, water balance, and ions

Liver

Detoxifies harmful substances, converts toxic ammonia into urea for safe excretion

Lungs

Excrete carbon dioxide (CO₂), a byproduct of cellular respiration

Skin

Excretes small amounts of urea, water, and salts through sweat

Bladder / Ureters / Urethra

Transport and store urine until voluntary excretion

Filtration

High pressure forces water, ions, glucose, amino acids, and small molecules into nephron; blood cells/proteins stay

Reabsorption

Vital solutes (Na⁺, glucose, amino acids) and 85% water reabsorbed into blood via active/passive transport

Secretion

Drugs, H⁺, toxins, and NH₃ actively secreted from blood into nephron to maintain pH and remove extra waste

Bowman's Capsule

Collects filtrate from high-pressure glomerulus capillaries

Proximal Tubule

Major reabsorption of nutrients, water, and ions (active and passive transport)

Loop of Henle

Establishes osmotic gradient—water reabsorbed (descending), salts (ascending)

Distal Tubule

Selective reabsorption and secretion; site of hormone action (ADH, ALD)

Collecting Duct

Final water reabsorption; delivers urine to renal pelvis

ADH

Increases permeability of distal tubule & collecting duct to water

Aldosterone

Promotes Na⁺ reabsorption → water follows → increases blood volume/pressure

Buffer System

HCO₃⁻ + H⁺ ⇌ H₂CO₃ ⇌ CO₂ + H₂O (maintains blood pH ~7.4)

Kidney Compensation

Secretes H⁺ ions; reabsorbs HCO₃⁻ into bloodstream to buffer acidity

Linked to Respiration

CO₂ levels influence H⁺ concentration; kidneys help balance respiratory pH load

Urea

Deamination of amino acids (ammonia + CO₂ → urea)

Uric Acid

Breakdown of nucleic acids (DNA, RNA)

Ammonia (NH₃)

Highly toxic byproduct of protein metabolism; converted to urea

CO₂

Waste from aerobic respiration (mitochondria)

Bile Pigments

Breakdown of hemoglobin (bilirubin, biliverdin)

Lactic Acid

Anaerobic respiration product (muscles during O₂ shortage)

Diabetes Mellitus

Lack of insulin → excess glucose in blood & nephron

Diabetes Insipidus

Lack of ADH → inability to reabsorb water

Nephritis

Inflammation of glomerulus (due to infection/toxins)

Kidney Stones

Crystallized solutes (e.g., calcium, uric acid)

Kidney Failure

Chronic damage or disease

Hemodialysis

Blood filtered via machine; removes wastes via semipermeable membrane

Peritoneal Dialysis

Dialysis fluid in abdominal cavity filters wastes across peritoneum membrane

Kidney Transplant

Surgical replacement of damaged kidney with donor kidney

Nephron

Functional Unit of the kidney (~1 million/kidney)

Bladder capacity

600 mL

Strong urge to urinate

400 mL