Urinary, digestive, and fluid acid balance

Intracellular Fluid (ICF)

Fluid within cells, accounting for 2/3 of total body fluid.

Extracellular Fluid (ECF)

Fluid outside cells, accounting for 1/3 of total body fluid.

Interstitial Fluid

Fluid surrounding tissue cells, accounting for 80% of ECF.

Plasma

The liquid component of blood, accounting for 20% of ECF.

Plasma Membrane

A barrier that separates intracellular fluid from interstitial fluid.

Blood Vessel Walls

A barrier that divides the interstitial fluid from blood plasma.

Capillary Walls

Thin barriers allowing crucial exchange of water and solutes between blood plasma and interstitial fluid.

Lean Adult Female (Fluids)

Accounts for 55% of total body mass.

Lean Adult Male (Fluids)

Accounts for 60% of total body mass.

Daily Water Balance

Approximately 2500 mL, with average daily water gain equaling average daily water loss.

Ingested Liquids (Daily)

Accounts for approximately 1600 mL of daily water gain.

Ingested Foods (Daily)

Accounts for approximately 700 mL of daily water gain.

Metabolic Water

Water produced as a byproduct of metabolic reactions, approximately 200 mL daily.

Kidneys (Water Loss)

The primary route of water loss, approximately 1500 mL daily as urine.

Skin (Water Loss)

Accounts for approximately 600 mL daily, including insensible perspiration.

Lungs (Water Loss)

Accounts for approximately 300 mL daily as exhaled vapor.

Gastrointestinal Tract (Water Loss)

Accounts for approximately 100 mL daily in feces.

Dehydration

A condition triggered by decreased fluid volume, leading to decreased saliva flow, increased blood osmolarity, and decreased blood volume/pressure.

Blood Osmolarity

Increased during dehydration, detected by osmoreceptors in the hypothalamus.

Osmoreceptors

Sensory receptors in the hypothalamus that detect changes in blood osmolarity.

Thirst Center

A region in the hypothalamus stimulated by dry mouth, activated osmoreceptors, and increased angiotensin II, leading to increased water intake.

Angiotensin II

Increases in dehydration, contributing to the sensation of thirst; also a potent vasoconstrictor and stimulates aldosterone release.

Increased Saline (NaCl) Intake

Leads to increased plasma sodium/chloride, causing osmosis of water into plasma and increased blood volume.

Atrial Natriuretic Peptide (ANP)

Released due to increased blood volume stretching the atria, leading to decreased renin, angiotensin II, and aldosterone.

Renin

Its release is decreased by ANP and increased blood volume, suppressing angiotensin II formation.

Aldosterone (Increased Saline Intake)

Its release is decreased by ANP and increased blood volume, reducing Na+ and water reabsorption.

Glomerular Filtration Rate (GFR)

Increased by ANP and increased blood volume, promoting fluid loss.

Natriuresis

Increased loss of Na+ and Cl- in urine, caused by ANP and associated hormonal changes.

Hormones Regulating Renal Na+ and Cl-

Angiotensin II, Aldosterone, and Atrial Natriuretic Peptide (ANP).

Aldosterone (Function)

Increases Na+ (and thus water) reabsorption and K+ secretion in the kidneys.

Antidiuretic Hormone (ADH) / Vasopressin

Major hormone regulating water loss, increasing water reabsorption by the kidneys.

Electrolytes

Ions in body fluids that control osmosis, maintain acid-base balance, carry electrical current, and serve as cofactors.

Control Osmosis (Electrolyte Function)

Regulate the movement of water between fluid compartments.

Maintain Acid-Base Balance (Electrolyte Function)

Act as buffers or contribute to pH regulation.

Carry Electrical Current (Electrolyte Function)

Essential for nerve impulse transmission and muscle contraction.

Serve as Cofactors (Electrolyte Function)

Many enzymes require specific ions as cofactors for their activity.

Sodium (Na+)

Most abundant ions in extracellular fluid, crucial for impulse transmission, muscle contraction, and fluid balance. Regulated by aldosterone, ADH, and ANP.

Potassium (K+)

Most abundant cation in intracellular fluid, involved in fluid volume regulation, impulse conduction, muscle contraction, and pH balance.

Calcium (Ca2+)

Most abundant ion in the body, primary structural component of bones/teeth, essential for blood coagulation, neurotransmitter release, and muscle tone. Regulated by PTH and calcitriol.

Magnesium (Mg2+)

An intracellular cation, activates enzymes in carbohydrate/protein metabolism, vital for myocardial function, neurotransmission, and Na+-K+ pump operation.

Chloride (Cl-)

Major extracellular anion, helps regulate osmotic pressure, forms HCl in the stomach. Primarily controlled by aldosterone.

Bicarbonate (HCO3-)

Important plasma ion, a major component of the plasma acid-base buffer system, essential for maintaining blood pH. Regulated by kidneys.

Hydrochloric Acid (HCl)

Formed by chloride in the stomach, essential for digestion.

Plasma Acid-Base Buffer System

A system where bicarbonate ions act as a major component to maintain blood pH.

Parathyroid Hormone (PTH)

A hormone that regulates calcium and phosphate levels in plasma.

Calcitonin

A hormone that regulates calcium levels in plasma.

Na+-K+ Pump

Its proper operation is vital for magnesium's functions.

Phosphate (HPO4 2-, inorganic)

Primarily occurs as calcium phosphate salt in bones and teeth; crucial component of the buffer system for pH regulation and ATP/RNA/DNA structure.

Normal Blood pH Range

Arterial blood pH is tightly maintained between 7.35 to 7.45.

Buffer Systems

Mechanisms that rapidly convert strong acids or bases into weaker ones to maintain acid-base balance.

Exhalation of Carbon Dioxide

The respiratory system's method of adjusting CO2 levels to influence blood pH, maintaining acid-base balance.

Kidney Excretion of H+

The renal system's method of excreting excess hydrogen ions and conserving bicarbonate, providing long-term pH regulation.

Protein Buffer System

Most abundant buffer in intracellular fluid and blood plasma, utilizing carboxyl and amino groups of proteins.

Carboxyl Groups (-COOH)

Groups in proteins that dissociate to release H+ when pH rises, acting like an acid.

Amino Groups (-NH2)

Groups in proteins that accept H+ when pH falls, acting like a base.

Amphoteric Substances

Substances like proteins that can act as both acids and bases.

Hemoglobin as a Buffer

Plays a crucial role in buffering H+ generated from carbon dioxide transport within red blood cells.

Carbonic Acid (H2CO3)

Formed from CO2 and water in blood, dissociates into H+ and HCO3-; a weak acid component of the carbonic acid-bicarbonate buffer system.

Bicarbonate Ion (HCO3-)

A weak base component of the carbonic acid-bicarbonate buffer system, removes excess H+ to prevent pH drop.

Carbonic Acid-Bicarbonate Buffer System

A buffer system based on bicarbonate ion (weak base) and carbonic acid (weak acid).

Phosphate Buffer System

Functions similarly to the carbonic acid-bicarbonate system, important in intracellular fluid and renal tubules.

Dihydrogen Phosphate (H2PO4-)

A component of the phosphate buffer system, acting as a weak acid.

Monohydrogen Phosphate (HPO4 2-)

A component of the phosphate buffer system, acting as a weak base.

Hyperventilation

Excessive CO2 exhalation that decreases blood CO2 levels, consumes H+, and raises blood pH (alkalosis).

Hypoventilation

CO2 retention that increases blood CO2 levels, produces more H+, and drops blood pH (acidosis).

Kidneys (Acid-Base Role)

The most powerful, although slowest, regulators of blood pH, by secreting H+ and regulating bicarbonate.

Ammonium (NH4+)

Formed from ammonia (NH3) in renal tubular cells to trap H+ in urine for removal during acidosis.

New Bicarbonate Generation

A renal mechanism during acidosis where the kidneys synthesize and return more HCO3- to the blood, raising pH.

Acidosis

A condition where blood pH falls below 7.35.

Alkalosis

A condition where blood pH rises above 7.45.

Respiratory Acidosis

Blood pH drops due to excessive retention of CO2, leading to carbonic acid accumulation, often from hypoventilation.

Respiratory Alkalosis

Blood pH rises due to excessive loss of CO2, often during hyperventilation from anxiety or high altitude.

Metabolic Acidosis

Arterial blood levels of bicarbonate (HCO3-) fall significantly, caused by HCO3- loss (e.g., severe diarrhea) or accumulation of non-carbonic acids.

Metabolic Alkalosis

Arterial blood levels of bicarbonate (HCO3-) rise, caused by excessive H+ loss (e.g., prolonged vomiting) or ingestion of alkaline substances.

Diabetic Ketoacidosis

A cause of metabolic acidosis due to the accumulation of non-carbonic acids.

Lactic Acidosis

A cause of metabolic acidosis due to the accumulation of non-carbonic acids.

Increased H+ Secretion (Kidneys)

A renal response to acidosis where kidneys actively pump more hydrogen ions into the urine for excretion.

Decreased Bicarbonate Reabsorption (Kidneys)

A renal response to alkalosis where more HCO3- is left in the urine to be excreted.

Decreased Renin Release (Increased Saline Intake)

A physiological response to increased blood volume and ANP, leading to decreased angiotensin II.

Urinary system

System that maintains homeostasis by regulating blood volume and composition and eliminating wastes.

Kidney

Primary organ of the urinary system; filters blood, forms urine, regulates ions and pH.

Right kidney

Kidney located on the right side of the body.

Left kidney

Kidney located on the left side of the body.

Renal artery

Artery delivering oxygen-rich blood to the kidney.

Renal vein

Vein carrying filtered blood away from the kidney.

Ureter

Tube transporting urine from kidneys to the bladder via peristalsis.

Urinary bladder

Muscular sac storing urine; capacity ~700–800 mL.

Urethra

Tube through which urine is excreted from the body.

Hilum

Entrance/exit point for renal artery, vein, ureter, nerves, and lymphatics.

Renal capsule

Fibrous outer covering of the kidney.

Adipose capsule

Layer of fat around the kidney protecting and anchoring it.

Renal fascia

Connective tissue that anchors kidney to surrounding structures.

Renal cortex

Outer region of the kidney containing the glomeruli and tubules.

Renal medulla

Inner region of the kidney containing renal pyramids.

Renal pyramid

Cone-shaped sections within the renal medulla that house collecting ducts.

Renal papilla

Tip of a renal pyramid where urine drains into a calyx.

Nephron

Functional unit of the kidney that filters blood and forms urine.

Glomerulus

Capillary network where blood is filtered.

Bowman’s capsule

Cup-like capsule surrounding the glomerulus that collects filtrate.

Proximal convoluted tubule

First segment of the renal tubule; major site of reabsorption.