Renal Physiology: Nephrons, Urine Concentration, and ADH

Cortical Nephrons

85% of nephrons located in cortex.

Juxtamedullary Nephrons

15% of nephrons with long loops.

Nephron Loops

Deeply invade medulla, crucial for urine concentration.

ADH

Hormone increasing water channels in collecting ducts.

Collecting Ducts

Extend into medulla, affecting urine osmolarity.

Osmolarity

Concentration of solutes in urine, up to 1200 mOsm/L.

Plasma Osmolarity

Normal level around 300 mOsm/L; affects ADH secretion.

Dilute Urine

Produced when ADH is absent, osmolarity as low as 100 mOsm/L.

Urea Recycling

Process enhancing medullary osmotic gradient for urine concentration.

Proximal Tubule

Site for sodium and bicarbonate reabsorption.

HCO3- Reabsorption

Occurs in proximal tubule and collecting duct.

Loop of Henle

Structure involved in urine concentration and dilution.

Thin Descending Limb

Permeable to water, impermeable to salts.

Thin Ascending Limb

Impermeable to water, allows salt reabsorption.

Thick Ascending Limb

Active salt reabsorption, impermeable to water.

Distal Convoluted Duct

Further regulates sodium and water reabsorption.

Cortical Collecting Duct

Final site for sodium reabsorption and potassium secretion.

Outer Medullary Collecting Duct

Involved in final urine concentration adjustments.

Renin-Angiotensin-Aldosterone

Hormonal system regulating blood pressure and fluid balance.

Glucose Transport

Mechanism for reabsorbing glucose in kidneys.

Micturition Reflex

Neural control of bladder emptying.

H+ Secretion

Proximal tubule & collecting duct adjust H+ levels.

Carbonic Acid

Source of secreted H+ in renal tubules.

Electrochemical Balance

Na+ reabsorbed for each H+ secreted.

Phosphate Buffer System

Weak base HPO4^2- regulates pH in kidneys.

Type A Intercalated Cells

Secrete H+ and generate new HCO3-.

NH4+ Excretion

Generated from glutamine metabolism in PCT.

Bicarbonate Ion Excretion

Occurs via type B intercalated cells.

Renin-Angiotensin System

Pathway for aldosterone secretion regulation.

Aldosterone Secretion

Triggered by high K+ or low Na+ levels.

Addison's Disease

Adrenal insufficiency leading to low aldosterone.

Hypoaldosteronism

Condition of insufficient aldosterone production.

Hypovolemia

Low blood volume risk in Addison's patients.

Hyperkalemia

High potassium levels due to aldosterone absence.

Adrenocortical Tumor

Excess aldosterone causing low ECF potassium.

Principal Cell

Cell type involved in Na+ and K+ handling.

Furosemide

Diuretic affecting Na+ reabsorption in kidneys.

Thiazides

Diuretics that inhibit Na+ reabsorption.

Ouabain

Inhibitor of Na+/K+ ATPase pump.

Barium

Blocks potassium channels affecting renal function.

HCO3-/Cl- Antiport

Mechanism for bicarbonate reabsorption in kidneys.

Micturition

Process of urination or voiding urine.

Detrusor Muscle

Muscle that contracts to expel urine.

Internal Urethral Sphincter

Muscle controlled by ANS to retain urine.

External Urethral Sphincter

Muscle controlled by somatic nervous system.

Micturition Reflex

Involuntary urination response triggered by bladder distension.

Stretch Receptors

Sensors activated by bladder distension during micturition.

Parasympathetic Neurons

Nerve fibers stimulating detrusor contraction.

Urinary Incontinence

Inability to control urination, often due to muscle weakness.

Stress Incontinence

Urine leakage due to increased abdominal pressure.

Overflow Incontinence

Urine dribbles when bladder is overfilled.

Urinary Retention

Inability to expel urine from the bladder.

Fluid Compartments

Different areas of body where fluids are distributed.

Intracellular Fluid (ICF)

Fluid within cells, primarily composed of water.

Extracellular Fluid (ECF)

Fluid outside cells, includes interstitial and blood plasma.

Water Balance

Equilibrium between water intake and output.

Thirst Mechanism

Physiological response to dehydration signaling need for water.

Antidiuretic Hormone (ADH)

Hormone regulating water retention in kidneys.

Sodium Balance

Regulation of sodium levels in the body.

Aldosterone

Hormone influencing sodium reabsorption in kidneys.

Body Water Content

Percentage of water in the human body.

Total Body Water

Average water content in adults, ~40 L.

Adipose Tissue Hydration

Least hydrated tissue type in the body.

Osmotic Pressure

Pressure from solutes causing water movement.

Hydrostatic Pressure

Pressure exerted by fluids in compartments.

ECF Osmolality

Concentration of solutes in extracellular fluid.

Thirst Mechanism

Physiological drive to consume water.

Hypothalamic Thirst Center

Brain region regulating thirst sensation.

Osmoreceptors

Cells detecting changes in plasma osmolality.

Metabolic Water

Water produced during cellular metabolism.

Water Intake

Total water consumed, ~2500 ml/day.

Water Output

Total water excreted, mainly via urine.

Dehydration

Loss of water from extracellular fluid.

Hypotonic Hydration

Excess water intake causing cellular swelling.

Hyponatremia

Low sodium concentration in blood.

ADH Release

Hormone release in response to high osmolality.

Oliguria

Production of abnormally small urine amounts.

Cerebral Edema

Swelling of brain cells due to excess water.

Edema

Abnormal fluid accumulation in body tissues.

Pitting Edema

Swelling caused by fluid leakage from vessels.

Insensible Water Loss

Unnoticeable water loss through skin and lungs.

Electrolyte Loss

Loss of ions essential for body function.

Fluid Homeostasis

Balance of fluid intake and output.

Inhibitory Feedback Signals

Body signals that reduce thirst sensation.

Interstitium

Space between cells where fluid accumulates.

Interstitial Fluid Accumulation

Excess fluid in interstitial space causing tissue swelling.

Antidiuretic Hormone (ADH)

Hormone regulating water reabsorption in kidneys.

ADH Release Effects

Increased ADH leads to concentrated urine.

Decreased ADH Effects

Leads to dilute urine and reduced body fluid.

Hypothalamic Osmoreceptors

Senses ECF solute concentration to regulate ADH.

Central Diabetes Insipidus

Inadequate ADH release causing dilute urine production.

Polyuria

Excretion of large volumes of dilute urine.

Exogenous ADH Infusion

Corrects Central Diabetes Insipidus symptoms.

Syndrome of Inappropriate ADH (SIADH)

Excess ADH causing water retention and hypoosmotic fluids.

Nephrogenic Diabetes Insipidus (NDI)

Decreased AQP-2 expression leads to dilute urine.

Pyelitis

Infection of renal pelvis and calyces.

Pyelonephritis

Infection/inflammation of the entire kidney.

Dysuria

Painful urination often associated with infections.

Urethritis

Inflammation of the urethra.

Cystitis

Inflammation of the bladder.