Osmoregulation and Body Fluid Composition

Osmoregulation

• Osmotic pressure is the pressure needed to offset the movement of pure solvents (e.g., water) across a semipermeable membrane.
• Hydrostatic pressure is the pressure exerted by a fluid on its surroundings.
• Blood pressure on vessel walls contributes to hydrostatic pressure.
• Pressure in fluid increases with depth.

Ionic Concentration and -tonic Solutions

• Ionic concentration refers to the concentration of ions in a solution.
• Semipermeable membranes allow certain substances to pass through.
• Initially, there is a net movement of water from one side to the other. 
• At equilibrium, there is no net movement of water.

Electrolyte Composition of Body Fluids

• Serum and ECF (extracellular fluid) have similar electrolyte compositions.
• Key electrolytes like Na+, K+, Ca2+, and Cl- are listed along with their respective concentrations in different body fluids.
• Active transport and diffusion are methods used during metabolism in maintaining the electrolyte balance in the body.

Homeostasis Challenges

• Animals maintain homeostasis depending on their environment.
• Blood concentration relative to the environment influences urine concentration and osmoregulatory mechanisms.
• Different animals have varied strategies like drinking seawater or excreting excess salt.
• Examples include marine elasmobranchs, marine teleosts, freshwater teleosts, amphibians, and marine reptiles.

Water Gain and Loss

• Mammals, including kangaroo rats, maintain balance between water gain and loss in their environment.
• Water gain pathways and losses include intake of water, drinking, and metabolic water production.
• Water loss pathways include urine, feces, evaporation/perspiration, and respiration.

Respiratory Evaporative Water Loss

• Respiratory water loss is affected by relative humidity, air temperature, and breathing rate.
• Inhaled air warms and humidifies as it passes through the nasal passages and lungs.
• Exhaled air cools and loses moisture, which is a form of evaporative loss.
• There is a correlation between water loss through respiration and ambient air temperature.

Mammalian Kidney Adaptation

• Kidney structure relates to environment.
• Beaver's have short loops of Henle, while desert dwelling animals like kangaroo rats have long loops of Henle.
• These adaptations reflect their respective environment's water availability.

Metabolic Water

• By definition, metabolic water is water produced as a result of metabolic processes, rather than from food intake or external sources.
• Oxidation of foodstuffs in the body produces metabolic water.
• Carbohydrates produce the most metabolic water (0.56 g of water per gram).
• Lipids are more water-efficient than Carbohydrates and proteins in producing metabolic water.

Fat and Protein Stores as Water Sources

• Migratory birds rely on stored fat for energy and water.
• Fat stores can release more water than glycogen stores.
• Protein degradation can release bound water.
• The need for energy and water is balanced with storage mechanisms in organs.

Hummingbirds and Dehydration

• Contrary to some assumptions, hummingbirds' dehydration regulation is not a daily problem.
• Frequent water intake and maximum glucose reabsorption offset urine dilution.
• Concentrated glucose absorption has significant roles in water retention.

Carb Absorption

• Carbohydrate absorption in the intestine involves several stages.
• Maltose is broken down to glucose.
• Glucose is absorbed via active transport with Na+ entering the cell.
• Glucose then leaves enter the blood by facilitated transport.

Glucose Re-absorption

• Active transport, facilitated diffusion, and sodium-potassium pumps assist in glucose reabsorption within the kidneys.

Type II Diabetes

• Hyperglycemia (high sugar) is a common symptom.
• Sweet-tasting urine was an historical diagnostic indicator.

Blood pH Regulation

• Blood pH is regulated by maintaining appropriate levels of bicarbonate and hydrogen ions.
• The kidneys and carbonic anhydrase play a role in maintaining an appropriate balance between these.
• The kidneys help maintain an internal equilibrium of these levels.

Urine Acidification

• Ammonia and phosphates act as buffers for urine.
• Urine pH is generally lower than blood pH.
• The protein in our diet affects the acidity of urine.

Vasopressin

• Also known as antidiuretic hormone (ADH), vasopressin regulates water reabsorption in the kidneys.
• Released in response to high plasma osmolarity or low blood pressure.
• Stimulates aquaporins which are proteins, to increase water permeability in collecting ducts, allowing more water to be absorbed.
• High blood osmolality or low blood pressure stimulates vasopressin production and release.

Hypertension

• Body regulates blood osmotic pressure by adjusting sodium levels in the kidneys.
• Excess sodium intake can lead water to be retained in the blood, which increases blood pressure.
• Medications such as ACE inhibitors and Angiotensin Receptor blockers can be used to manage high blood pressure.

Renin-Angiotensin-Aldosterone (RAA) Pathway

• Juxtaglomerular cells release renin in response to low blood pressure or low glomerular filtration rate (GFR).
• Renin converts angiotensinogen to angiotensin I, and then to angiotensin II , which has various effects on the cardiovascular system, including vasoconstriction and secretion of aldosterone.
• Aldosterone promotes sodium and water retention, while raising blood pressure.

Test your knowledge on osmoregulation, ionic concentration, and the electrolyte composition of body fluids. This quiz covers important concepts related to osmotic pressure, hydrostatic pressure, and the role of semipermeable membranes in fluid movement. Challenge yourself and see how well you understand these essential biological processes.