Lesson 1: Homeostasis Concepts
Fluid, Electrolyte, and Acid-Base Balances
Homeostasis is the body's ability to maintain a stable internal environment
despite changes in external conditions. It is essential for maintaining
optimal physiological health because it ensures that critical bodily functions
operate within a narrow range, preventing damage to cells and organs.
Distribution of Body Fluids
Intracellular Fluid (ICF): Fluid within cells, accounting for about 60% of
total body water.
Extracellular Fluid (ECF): Fluid outside cells, including interstitial fluid
(between cells) and plasma (in blood vessels).
Total Body Water (TBW): Varies by body weight, fat content, and age.
Higher fat content and older age typically reduce TBW percentage.
Mechanisms of Hydrostatic and Osmotic Pressure Maintaining Fluid
Balance
Osmotic Pressure: The force exerted by solutes drawing water across a
semipermeable membrane.
Oncotic Pressure: A form of osmotic pressure exerted by proteins, especially
albumin, in the blood plasma.
Hydrostatic Pressure: The pressure exerted by a fluid against a vessel wall,
promoting the movement of water out of capillaries.
Edema
,Occurrence: Edema occurs when excess fluid accumulates in the interstitial
space.
Mechanisms: Increased hydrostatic pressure pushes fluid out of capillaries.
Decreased oncotic pressure (e.g., low albumin levels) reduces the
reabsorption of fluid back into capillaries.
Correlation with Albumin: Low albumin levels reduce oncotic pressure,
leading to fluid retention in the interstitial space and causing edema.
Hormones and Fluid Balance
Antidiuretic Hormone (ADH): Regulates water balance by increasing water
reabsorption in the kidneys.
Renin-Angiotensin-Aldosterone System (RAAS):
Trigger: Low blood pressure or low sodium levels.
Steps:
Renin Release: Kidneys release renin.
Angiotensin I Formation: Renin converts angiotensinogen (from the liver) to
angiotensin I.
Angiotensin II Formation: Angiotensin I is converted to angiotensin II by the
enzyme ACE (in the lungs).
, Aldosterone Secretion: Angiotensin II stimulates aldosterone secretion from
the adrenal glands.
Sodium and Water Retention: Aldosterone increases sodium reabsorption
in the kidneys, leading to water retention and increased blood pressure.
Basic Concepts of Acid-Base Balance
pH: Measure of hydrogen ion (H⁺) concentration; normal blood pH ranges
from 7.35 to 7.45.
Hydrogen Ion Concentration: An inverse relationship with pH; as H⁺
concentration increases, pH decreases (more acidic).
Buffers
Role: Buffers maintain pH by neutralizing excess acids or bases.
Types: Carbonic Acid-Bicarbonate Buffering: Neutralizes strong acids and
bases.
Protein Buffering: Proteins, such as hemoglobin, act as buffers.
Respiratory Buffering: Lungs regulate CO₂ levels to maintain pH.
Renal Buffering: Kidneys excrete or reabsorb H⁺ and bicarbonate to
regulate pH.
Lungs and Kidneys
Regulation: Work together to maintain pH within the range of 7.35-7.45.
Fluid, Electrolyte, and Acid-Base Balances
Homeostasis is the body's ability to maintain a stable internal environment
despite changes in external conditions. It is essential for maintaining
optimal physiological health because it ensures that critical bodily functions
operate within a narrow range, preventing damage to cells and organs.
Distribution of Body Fluids
Intracellular Fluid (ICF): Fluid within cells, accounting for about 60% of
total body water.
Extracellular Fluid (ECF): Fluid outside cells, including interstitial fluid
(between cells) and plasma (in blood vessels).
Total Body Water (TBW): Varies by body weight, fat content, and age.
Higher fat content and older age typically reduce TBW percentage.
Mechanisms of Hydrostatic and Osmotic Pressure Maintaining Fluid
Balance
Osmotic Pressure: The force exerted by solutes drawing water across a
semipermeable membrane.
Oncotic Pressure: A form of osmotic pressure exerted by proteins, especially
albumin, in the blood plasma.
Hydrostatic Pressure: The pressure exerted by a fluid against a vessel wall,
promoting the movement of water out of capillaries.
Edema
,Occurrence: Edema occurs when excess fluid accumulates in the interstitial
space.
Mechanisms: Increased hydrostatic pressure pushes fluid out of capillaries.
Decreased oncotic pressure (e.g., low albumin levels) reduces the
reabsorption of fluid back into capillaries.
Correlation with Albumin: Low albumin levels reduce oncotic pressure,
leading to fluid retention in the interstitial space and causing edema.
Hormones and Fluid Balance
Antidiuretic Hormone (ADH): Regulates water balance by increasing water
reabsorption in the kidneys.
Renin-Angiotensin-Aldosterone System (RAAS):
Trigger: Low blood pressure or low sodium levels.
Steps:
Renin Release: Kidneys release renin.
Angiotensin I Formation: Renin converts angiotensinogen (from the liver) to
angiotensin I.
Angiotensin II Formation: Angiotensin I is converted to angiotensin II by the
enzyme ACE (in the lungs).
, Aldosterone Secretion: Angiotensin II stimulates aldosterone secretion from
the adrenal glands.
Sodium and Water Retention: Aldosterone increases sodium reabsorption
in the kidneys, leading to water retention and increased blood pressure.
Basic Concepts of Acid-Base Balance
pH: Measure of hydrogen ion (H⁺) concentration; normal blood pH ranges
from 7.35 to 7.45.
Hydrogen Ion Concentration: An inverse relationship with pH; as H⁺
concentration increases, pH decreases (more acidic).
Buffers
Role: Buffers maintain pH by neutralizing excess acids or bases.
Types: Carbonic Acid-Bicarbonate Buffering: Neutralizes strong acids and
bases.
Protein Buffering: Proteins, such as hemoglobin, act as buffers.
Respiratory Buffering: Lungs regulate CO₂ levels to maintain pH.
Renal Buffering: Kidneys excrete or reabsorb H⁺ and bicarbonate to
regulate pH.
Lungs and Kidneys
Regulation: Work together to maintain pH within the range of 7.35-7.45.
