Water metabolism (lecture)

Lecture 6: Typical Disorders of Water Balance

Importance of Water

• Composition of the Human Body:

  • Newborn baby: 80% water

  • Adult man: 60% water

  • Adult woman: 55% water

• Functions of Water:

  • Medium for dissolution and transport of compounds

  • Essential for biochemical reactions, digestion, and nutrient absorption

  • Removes waste products of metabolism

• Origin of Life:

  • Development of life on Earth is believed to have occurred in aquatic environments.

Division of Body Water

• Intracellular vs. Extracellular Water:

  • Total body water divided into:

    • Extracellular water: 31% of mass

    • Intracellular water: 22% of mass

  • States of Intracellular Water:

    • Free (mobile)

    • Bound (to electrolytes, proteins, nucleic acids, polysaccharides)

    • Examples of water binding capacity:

      • 1 g DNA holds 0.6 ml,

      • 1 g protein holds 1.5 ml,

      • 1 g glycogen holds 3 ml.

• Extracellular Fluid Compartment:

  • Divided into three compartments:

    1. Intravascular Fluid (Plasma) - 4% of mass (2-2.5 liters)

    2. Interstitial Fluid - 18% of mass (12 liters)

    3. Transcellular Fluid - 1.5% of mass (includes gastric and intestinal juices, cerebrospinal fluid, synovial fluid, etc.)

• Barriers between Compartments:

  • Histohematic barrier separates the intravascular from interstitial fluid.

  • Transcellular fluid encased in epithelial membranes.

  • Different compositions and gradients of ions and pressures essential for physiological functions.

Regulation of Water Metabolism

• Importance of Regulation:

  • Maintaining the volume and concentration of dissolved substances in body water compartments is crucial.

• Intravascular Fluid Volume Regulation:

  • Volumoreceptors detect volume changes located in carotid sinuses, aortic arch, renal vessels.

  • Activation of Neurohumoral Regulatory Mechanisms:

    • Sympathetic Nervous System Response:

      • Increased cardiac output and blood pressure.

      • Activation of Renin-Angiotensin-Aldosterone System (RAAS).

    • Renin-Angiotensin-Aldosterone System (RAAS):

      • Activators include renal blood flow reduction and sympathetic tone increase.

      • Renin Release from juxtaglomerular cells:

        • Converts angiotensinogen to angiotensin I, then to angiotensin II, which constricts blood vessels and stimulates aldosterone release.

    • Aldosterone Effects:

      • Retains Na+ and water leading to increased intravascular volume.

      • Factors increasing aldosterone secretion: angiotensin II, increased plasma K+, decreased plasma Na+, increased ACTH.

    • Natriuretic Peptides:

      • Produced by atrial myocardium when intravascular volume increases, causing vessel dilation and decreased RAAS activity.

    • Thirst Mechanism:

      • Triggered by dehydration factors; plasma osmolality increase, lower intravascular volume, and dry mucous membranes.

      • ADH release increases reabsorption of water in kidneys.

Water Balance

• Components of Water Balance:

  • Water intake through food and beverages.

  • Water produced metabolically (endogenous water).

  • Water excretion through kidneys, lungs, skin, and feces.

• Daily Water Balance Example:

  • Total intake: 2.2 - 2.7 liters

  • Total excretion: 2.2 - 2.7 liters

• Pathological Variants of Water Balance:

  • Negative water balance (hypohydration) - deficit in body water.

  • Positive water balance (hyperhydration) - excess accumulation of water.

Hypohydration (Dehydration)

• Definition:

  • Characterized by loss of water exceeding intake.

• Causes of Hypohydration:

  • Insufficient Intake:

    • Water starvation, swallowing disorders, lack of thirst, etc.

  • Excessive Losses:

    • Prolonged polyuria, gastrointestinal disorders, vomiting, diarrhea, etc.

• Consequences:

  • Hypovolemia, circulatory failure, tissue hypoxia, possible fatality with severe dehydration (loss of 7-12% body weight can be fatal).

Clinical Signs of Dehydration

• Dry skin and mucous membranes, decreased tissue turgor, thirst, decreased blood pressure, rapid thready pulse.

• Classifications of Hypohydration by osmolality:

  • Hypoosmolal: Salt losses dominate; symptoms include intracellular hyperhydration.

  • Hyperosmolal: Fluid losses exceed salt losses; symptoms include cellular hypohydration.

  • Isoosmolal: Equivalent loss of salts and water.

Hyperhydration

• Definition:

  • More water intake than excreted, resulting in positive water balance.

• Types of Hyperhydration:

  • Hypoosmolal Hyperhydration: Low osmolality; fluid enters cells.

  • Hyperosmolar Hyperhydration: High osmolality; fluid leaves cells.

  • Isoosmolal Hyperhydration: Na+ and water excess with normal osmolality.

Edema and Watering

• Definition:

  • Edema: Excessive accumulation of fluid in interstitial spaces.

  • Hydrops: Excess fluid accumulation in body cavities.

• Types of Edema:

  • Localized or systemic. Examples: cardiac, renal, hepatic, allergic, inflammatory.

• Mechanism of Edema Development:

  • Hydrostatic, oncotic, osmotic, membranogenic, and lymphogenic mechanisms involved.

Starling's Hypothesis

• Transcapillary Water Exchange:

  • Fluid exchange mechanism between blood and tissues based on hydrostatic and oncotic pressures.

• Hydrostatic Pressure: Squeezes fluid out from vessels.

• Colloid-Osmotic Pressure: Retains water within vessels.

Clinical Implications of Edema

• Pathogenic Effects:

  • Disturbance between blood and cells, possible nutrient deficiencies, connective tissue changes, and disruptions in circulation.

  • Compression of vital organs due to excessive fluid can lead to severe systemic issues.

Treatment Principles for Water Disorders

• Goal: Address underlying causes of imbalance and regulate fluid dynamics through appropriate therapies like infusion, diuretics, and electrolyte corrections.

Lecture 6: Typical Disorders of Water Balance

Importance of Water

Water is crucial for the human body, with its composition varying significantly by age. A newborn baby is composed of 80% water, while adult men typically consist of 60% water, and adult women about 55% water. Water serves as a medium for the dissolution and transport of compounds, is essential for biochemical reactions, aids in digestion and nutrient absorption, and plays a key role in removing metabolic waste products. The development of life on Earth is believed to have occurred in aquatic environments, highlighting the foundational role of water in sustaining life.

Division of Body Water

The total body water is divided into two primary compartments: extracellular water, which constitutes 31% of body mass, and intracellular water, making up 22% of body mass. Intracellular water exists in two states: free (mobile) water and bound water, which is associated with electrolytes, proteins, nucleic acids, and polysaccharides. For instance, one gram of DNA can hold 0.6 ml of water, one gram of protein can hold 1.5 ml, and one gram of glycogen can hold 3 ml. The extracellular fluid compartment is further divided into three compartments: intravascular fluid (plasma) at 4% of body mass, interstitial fluid at 18% of body mass, and transcellular fluid at 1.5% of body mass, including gastric and intestinal juices, cerebrospinal fluid, and synovial fluid. Various barriers, such as the histohematic barrier, separate these fluid compartments and maintain different compositions and gradients of ions and pressures crucial for physiological functions.

Regulation of Water Metabolism

Maintaining the volume and concentration of dissolved substances across body water compartments is vital for overall health. Intravascular fluid volume is regulated by volumoreceptors located in the carotid sinuses, aortic arch, and renal vessels, which detect volume changes. This regulation activates neurohumoral mechanisms, including the sympathetic nervous system's response, which increases cardiac output and blood pressure, along with activating the Renin-Angiotensin-Aldosterone System (RAAS). The RAAS is stimulated by reduced renal blood flow and increased sympathetic tone. Renin, released from juxtaglomerular cells, converts angiotensinogen to angiotensin I and then to angiotensin II, prompting blood vessel constriction and stimulating aldosterone release. Aldosterone helps retain Na+ and water, thus increasing intravascular volume. It is secreted in response to factors such as angiotensin II, increased plasma K+, decreased plasma Na+, and increased ACTH. Natriuretic peptides, produced when intravascular volume increases, lead to vessel dilation and reduced RAAS activity. The thirst mechanism is triggered by dehydration factors like increased plasma osmolality, lower intravascular volume, and dry mucous membranes, resulting in the release of ADH, which promotes water reabsorption in the kidneys.

Water Balance

Water balance involves components such as water intake from food and beverages, metabolic water production, and water excretion through kidneys, lungs, skin, and feces. For example, total daily water intake typically ranges from 2.2 to 2.7 liters, with an equal total excretion amount. Pathological variants of water balance include negative water balance (hypohydration), which indicates a deficit of water, and positive water balance (hyperhydration), reflecting excess water accumulation.

Hypohydration (Dehydration)

Hypohydration is characterized by the loss of water exceeding intake. Causes include insufficient intake due to factors like water starvation, swallowing disorders, and lack of thirst, as well as excessive losses from prolonged polyuria and gastrointestinal disorders like vomiting and diarrhea. The consequences can lead to hypovolemia, circulatory failure, tissue hypoxia, and can be fatal if the body loses 7-12% of its weight due to severe dehydration. Clinical signs include dry skin and mucous membranes, decreased tissue turgor, thirst, decreased blood pressure, and a rapid thready pulse. Hypohydration can be classified by osmolality into hypoosmolal (with salt losses dominating), hyperosmolal (where fluid losses exceed salt losses), and isoosmolal (where salt and water losses are equivalent).

Hyperhydration

Hyperhydration occurs when water intake exceeds excretion, resulting in a positive water balance. It includes three types: hypoosmolar hyperhydration, which presents low osmolality and causes fluid to enter cells; hyperosmolar hyperhydration, characterized by high osmolality and fluid leaving cells; and isoosmolal hyperhydration, where there is an excess of Na+ and water with normal osmolality.

Edema and Watering

Edema refers to an excessive accumulation of fluid in interstitial spaces, and hydrops pertains to excess fluid in body cavities. Edema can be localized or systemic, with examples including cardiac, renal, hepatic, allergic, and inflammatory edema. Mechanisms for edema development include hydrostatic, oncotic, osmotic, membranogenic, and lymphogenic processes. Starling's Hypothesis outlines the fluid exchange mechanism between blood and tissues, driven by hydrostatic and oncotic pressures: hydrostatic pressure pushes fluid out of vessels, while colloid-osmotic pressure helps retain water within vessels.

Clinical Implications of Edema

The pathogenic effects of edema involve disturbances between blood and cells, potentially leading to nutrient deficiencies, connective tissue changes, and circulation disruptions. Compression of vital organs due to excessive fluid accumulation can cause severe systemic issues.

Treatment Principles for Water Disorders

The treatment of water disorders focuses on addressing the underlying causes of imbalances and regulating fluid dynamics through appropriate therapies, such as fluid infusion, diuretics, and corrections of electrolyte imbalances.

Lecture 6: Typical Disorders of Water Balance

Importance of Water

Water is crucial for the human body, with its composition varying significantly by age. A newborn baby is composed of 80% water, while adult men typically consist of 60% water, and adult women about 55% water. Water serves as a medium for the dissolution and transport of compounds, is essential for biochemical reactions, aids in digestion and nutrient absorption, and plays a key role in removing metabolic waste products. The development of life on Earth is believed to have occurred in aquatic environments, highlighting the foundational role of water in sustaining life.

Division of Body Water

The total body water is divided into two primary compartments: extracellular water, which constitutes 31% of body mass, and intracellular water, making up 22% of body mass. Intracellular water exists in two states: free (mobile) water and bound water, which is associated with electrolytes, proteins, nucleic acids, and polysaccharides. For instance, one gram of DNA can hold 0.6 ml of water, one gram of protein can hold 1.5 ml, and one gram of glycogen can hold 3 ml. The extracellular fluid compartment is further divided into three compartments: intravascular fluid (plasma) at 4% of body mass, interstitial fluid at 18% of body mass, and transcellular fluid at 1.5% of body mass, including gastric and intestinal juices, cerebrospinal fluid, and synovial fluid. Various barriers, such as the histohematic barrier, separate these fluid compartments and maintain different compositions and gradients of ions and pressures crucial for physiological functions.

Regulation of Water Metabolism

Maintaining the volume and concentration of dissolved substances across body water compartments is vital for overall health. Intravascular fluid volume is regulated by volumoreceptors located in the carotid sinuses, aortic arch, and renal vessels, which detect volume changes. This regulation activates neurohumoral mechanisms, including the sympathetic nervous system's response, which increases cardiac output and blood pressure, along with activating the Renin-Angiotensin-Aldosterone System (RAAS). The RAAS is stimulated by reduced renal blood flow and increased sympathetic tone. Renin, released from juxtaglomerular cells, converts angiotensinogen to angiotensin I and then to angiotensin II, prompting blood vessel constriction and stimulating aldosterone release. Aldosterone helps retain Na+ and water, thus increasing intravascular volume. It is secreted in response to factors such as angiotensin II, increased plasma K+, decreased plasma Na+, and increased ACTH. Natriuretic peptides, produced when intravascular volume increases, lead to vessel dilation and reduced RAAS activity. The thirst mechanism is triggered by dehydration factors like increased plasma osmolality, lower intravascular volume, and dry mucous membranes, resulting in the release of ADH, which promotes water reabsorption in the kidneys.

Water Balance

Water balance involves components such as water intake from food and beverages, metabolic water production, and water excretion through kidneys, lungs, skin, and feces. For example, total daily water intake typically ranges from 2.2 to 2.7 liters, with an equal total excretion amount. Pathological variants of water balance include negative water balance (hypohydration), which indicates a deficit of water, and positive water balance (hyperhydration), reflecting excess water accumulation.

Hypohydration (Dehydration)

Hypohydration is characterized by the loss of water exceeding intake. Causes include insufficient intake due to factors like water starvation, swallowing disorders, and lack of thirst, as well as excessive losses from prolonged polyuria and gastrointestinal disorders like vomiting and diarrhea. The consequences can lead to hypovolemia, circulatory failure, tissue hypoxia, and can be fatal if the body loses 7-12% of its weight due to severe dehydration. Clinical signs include dry skin and mucous membranes, decreased tissue turgor, thirst, decreased blood pressure, and a rapid thready pulse. Hypohydration can be classified by osmolality into hypoosmolal (with salt losses dominating), hyperosmolal (where fluid losses exceed salt losses), and isoosmolal (where salt and water losses are equivalent).

Hyperhydration

Hyperhydration occurs when water intake exceeds excretion, resulting in a positive water balance. It includes three types: hypoosmolar hyperhydration, which presents low osmolality and causes fluid to enter cells; hyperosmolar hyperhydration, characterized by high osmolality and fluid leaving cells; and isoosmolal hyperhydration, where there is an excess of Na+ and water with normal osmolality.

Edema and Watering

Edema refers to an excessive accumulation of fluid in interstitial spaces, and hydrops pertains to excess fluid in body cavities. Edema can be localized or systemic, with examples including cardiac, renal, hepatic, allergic, and inflammatory edema. Mechanisms for edema development include hydrostatic, oncotic, osmotic, membranogenic, and lymphogenic processes. Starling's Hypothesis outlines the fluid exchange mechanism between blood and tissues, driven by hydrostatic and oncotic pressures: hydrostatic pressure pushes fluid out of vessels, while colloid-osmotic pressure helps retain water within vessels.

Clinical Implications of Edema

The pathogenic effects of edema involve disturbances between blood and cells, potentially leading to nutrient deficiencies, connective tissue changes, and circulation disruptions. Compression of vital organs due to excessive fluid accumulation can cause severe systemic issues.

Treatment Principles for Water Disorders

The treatment of water disorders focuses on addressing the underlying causes of imbalances and regulating fluid dynamics through appropriate therapies, such as fluid infusion, diuretics, and corrections of electrolyte imbalances.