In-Depth Notes on Homeostasis and Water-Salt Balance

Housekeeping

• Quiz number 12 is now open until just before the final exam.
• Final exam (Exam 3) scheduled for Saturday, 01:30 to 04:30, in Seaton Auditorium C.
• Important to attend the correct row due to alternating classes.
• Content covered: Digestive system and renal system, not purely cumulative but building on previous knowledge.

Overview of Homeostasis and Water-Salt Balance

• Homeostasis: Regulation of bodily functions to maintain stable internal conditions.
• Importance of ion (e.g., sodium, potassium, calcium) concentrations for physiological functions, particularly in the cardiac and nervous systems.
• Crucial for establishing resting and threshold potentials in neurons.
• Disturbances in water-salt balance affect multiple physiological functions.

Kidney Function in Water-Salt Balance

• Kidneys regulate water balance through reabsorption:
• Producing hypo-osmotic urine (high volume, low sodium) to eliminate excess water.
• Producing hyperosmotic urine (low volume, high sodium) to retain water.
• Fluid compartments in the body: Intracellular fluid (ICF) vs. extracellular fluid (ECF).
• ICF has lower sodium concentration compared to ECF to maintain cellular function.

Obligatory Water Loss and Recovery

• Water Loss: Unavoidable losses occur through respiratory loss, skin evaporation, etc.
• Obligatory Water Loss:
• Respiratory Water Loss: Water is lost via exhaled humid air.
• Transdermal Water Loss: Skin loses water even without sweating.
• Strategies for Water Recovery:
• Consuming safe drinking water is essential.
• Food sources of water (fruits, vegetables) play an important role.

Consequences of Dehydration

• Dehydration leads to reduced physiological functions, confusion, muscle twitching, convulsions, and potential coma.
• Signs: Headaches, thirst, fatigue.
• Elderly and sick individuals may not exhibit clear dehydration signs until severe.

Fluid and Mineral Balance

• High water loss can lead to mineral imbalance; urine always contains some salt.
• Minerals like potassium, sodium, calcium must be replenished via diet.
• Essential to monitor intake of electrolytes, particularly in situations of sweat and illness (vomiting, diarrhea).

Renal Function and Ion Balance

• Nephron Function: Different parts (ascending and descending limbs) have unique permeabilities:
• Ascending limb: Actively pumps out sodium while being impermeable to water.
• Descending limb: Permeable to water but not solutes.
• Importance of the osmotic gradient in the renal medulla to facilitate water reabsorption through collecting ducts, modulated by hormones (e.g., ADH).

Digestive Process

• Lipid digestion begins in the stomach; most absorption occurs in the small intestine.
• Stomach cells convert lipids into lipoproteins for transport via exocytosis into the bloodstream.

Clinical Considerations

• Severe dehydration or electrolyte imbalances can lead to critical conditions, including potential coma.
• Body's responses to dehydration include hormone release to stimulate thirst and retention of water.