PHGY 209 Midterm (Body Water & Transport)
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Questions and Answers

What is the primary factor that causes the variation in body water percentage among individuals?

  • Amount of muscle mass
  • Dietary habits
  • External environmental conditions
  • Age and fat distribution (correct)

    • Which type of fluid surrounds cells and acts as a transitional medium between the cell and its external environment?

  • Intracellular fluid
  • Cytoplasm
  • Extracellular fluid
  • Interstitial fluid (correct)

    • What happens if the body cannot establish a new homeostasis in response to stress?

  • Symptoms of stress increase
  • The organism may die (correct)
  • Homeostasis is automatically restored
  • The body enters a state of hyperactivity

    • How does gender affect body water percentage?

    <p>Women generally have lower % body water because of fat distribution</p> Signup and view all the answers

    Which of the following is NOT a function of body water?

    <p>Building muscle mass</p> Signup and view all the answers

    What is the total body water (TBW) of a person weighing 70 kg with 60% body water?

    <p>42 L</p> Signup and view all the answers

    Which component makes up the largest portion of extracellular fluid (ECF)?

    <p>Interstitial fluid</p> Signup and view all the answers

    How much water loss is typically considered as insensible loss per day?

    <p>1 L</p> Signup and view all the answers

    What happens during water intoxication?

    <p>Hyponatremia (low Na+ in blood)</p> Signup and view all the answers

    What is the primary method of water intake for the body?

    <p>Oral fluid and food</p> Signup and view all the answers

    During which conditions is sensible water loss most likely to increase?

    <p>Heavy exercise and hot environments</p> Signup and view all the answers

    What is the primary role of plasma in the body?

    <p>To transport nutrients and waste</p> Signup and view all the answers

    What is the primary reason for the higher protein concentration in plasma compared to interstitial fluid?

    <p>The large size of proteins hinders their transport through cell membranes.</p> Signup and view all the answers

    Which fluid compartment contains the highest concentration of sodium ions?

    <p>Extracellular Fluid</p> Signup and view all the answers

    Which of the following is NOT a component of extracellular fluid (ECF)?

    <p>Intracellular Fluid</p> Signup and view all the answers

    What percentage of body mass is typically represented by plasma?

    <p>5%</p> Signup and view all the answers

    How can physiological saline (0.9% NaCl) be used in relation to extracellular fluid?

    <p>It serves as a substitute for extracellular fluid.</p> Signup and view all the answers

    What method is NOT suitable for measuring compartment volumes in animals?

    <p>Using the direct measurement of species before and after desiccation</p> Signup and view all the answers

    Which property must an indicator have to adequately measure compartment volumes using the indirect method?

    <p>It must be non-toxic and distribute evenly throughout compartments.</p> Signup and view all the answers

    Which of the following forces is primarily responsible for driving fluid from the capillary into the interstitial fluid space?

    <p>Hydrostatic pressure difference</p> Signup and view all the answers

    What percentage of total body mass does blood represent?

    <p>7%</p> Signup and view all the answers

    Which component constitutes approximately 55% of blood volume?

    <p>Plasma</p> Signup and view all the answers

    The term hematocrit refers to what measurement in blood analysis?

    <p>The height of red blood cell column relative to the total blood column height</p> Signup and view all the answers

    What role does blood play in the human body?

    <p>It transports nutrients, gases, wastes, hormones, and regulates temperature.</p> Signup and view all the answers

    What percentage of blood volume do red blood cells typically constitute?

    <p>45%</p> Signup and view all the answers

    What is the primary function of albumins in the plasma?

    <p>Carrying lipids, minerals, and hormones</p> Signup and view all the answers

    Which plasma protein is crucial for blood clotting?

    <p>Fibrinogens</p> Signup and view all the answers

    Where are y-globulins primarily produced?

    <p>In the lymph tissue</p> Signup and view all the answers

    How do plasma proteins contribute to colloidal osmotic pressure (C.O.P.)?

    <p>As non-diffusible solutes</p> Signup and view all the answers

    What distinguishes y-globulins from other plasma proteins in terms of synthesis?

    <p>Y-globulins are produced in the lymph tissue</p> Signup and view all the answers

    What drives the net fluid movement out of the blood plasma on the arterial end of the capillary?

    <p>Hydrostatic pressure</p> Signup and view all the answers

    What happens to the osmotic pressure as the hydrostatic pressure decreases along the capillary?

    <p>It draws fluid into the capillary on the venous end</p> Signup and view all the answers

    Which plasma protein contributes most significantly to colloidal osmotic pressure (C.O.P.)?

    <p>Albumin</p> Signup and view all the answers

    What is the hydrostatic pressure at the arterial end of the capillary?

    <p>33 mmHg</p> Signup and view all the answers

    How does an increase in colloidal osmotic pressure affect fluid movement in the capillaries?

    <p>It helps retain fluid within the blood</p> Signup and view all the answers

    What happens to large proteins during the filtration process in capillaries?

    <p>They remain in the capillary and do not enter the interstitial fluid</p> Signup and view all the answers

    Which of the following best explains the significance of capillary permeability in fluid movement?

    <p>It regulates the filtration and reabsorption of water and ions.</p> Signup and view all the answers

    What role do lymphatics play in fluid dynamics within the body?

    <p>They absorb excess fluid from the interstitial space.</p> Signup and view all the answers

    How does increased capillary permeability contribute to edema?

    <p>It causes plasma proteins to leak into the interstitial space.</p> Signup and view all the answers

    What primarily causes edema due to decreased oncotic pressure?

    <p>Proteins lost in urine</p> Signup and view all the answers

    Which condition could lead to increased hydrostatic pressure resulting in edema?

    <p>Prolonged immobility or traveling long hours</p> Signup and view all the answers

    Which of the following is a potential result of decreased lymphatic drainage?

    <p>Swelling post breast cancer surgery</p> Signup and view all the answers

    What effect does increased capillary permeability have on interstitial fluid?

    <p>Allows more fluid and proteins to escape into interstitial space</p> Signup and view all the answers

    What is one of the primary physiological reasons for the accumulation of fluid in tissues leading to edema?

    <p>Imbalance between hydrostatic and oncotic pressures</p> Signup and view all the answers

    Which laboratory method is used to separate proteins based on their size in a mixed sample?

    <p>Electrophoresis</p> Signup and view all the answers

    What type of plasma protein is primarily lost during renal disease due to filtration issues?

    <p>Albumin</p> Signup and view all the answers

    Which plasma protein type moves the fastest during electrophoresis?

    <p>Albumin</p> Signup and view all the answers

    What is the primary indication for ordering a plasma protein analysis?

    <p>To diagnose metabolic issues</p> Signup and view all the answers

    What condition could result in the loss of albumin in urine?

    <p>Renal disease</p> Signup and view all the answers

    Which technique is most effective for separating plasma proteins based on their size?

    <p>Electrophoresis</p> Signup and view all the answers

    In an electrophoresis gel, which type of plasma protein moves the slowest?

    <p>Fibrinogens</p> Signup and view all the answers

    What is a common reason for ordering a plasma protein analysis?

    <p>To diagnose liver dysfunction</p> Signup and view all the answers

    Which plasma proteins are primarily found closer to the bottom of an electrophoresis gel?

    <p>Albumins</p> Signup and view all the answers

    What is considered a major homeostatic organ responsible for regulating water balance in the body?

    <p>Kidney</p> Signup and view all the answers

    What type of water loss occurs independently of intake and is necessary for health?

    <p>Obligatory losses</p> Signup and view all the answers

    Which of the following accurately describes insensible water losses?

    <p>Losses through evaporation from skin and respiratory tract</p> Signup and view all the answers

    Which of the following statements about facultative water losses is correct?

    <p>They vary based on the amount of water consumed.</p> Signup and view all the answers

    What role does cholesterol play in the plasma membrane?

    <p>It enhances membrane fluidity and acts as a temperature buffer.</p> Signup and view all the answers

    Which component of the cell membrane is responsible for creating a hydrophobic core?

    <p>Phospholipid fatty acid tails</p> Signup and view all the answers

    Which function is NOT attributed to the glycocalyx in cell membranes?

    <p>Storage of nutrients</p> Signup and view all the answers

    What percentage of the plasma membrane's weight do proteins typically constitute?

    <p>25-75%</p> Signup and view all the answers

    What type of protein is known to be loosely associated with the cell membrane, typically on the cytoplasmic face?

    <p>Peripheral proteins</p> Signup and view all the answers

    Which type of molecules can easily diffuse through the cell membrane based on their concentration gradient?

    <p>Fat-soluble molecules</p> Signup and view all the answers

    What role do transporters play in cellular membrane function?

    <p>Allowing polar or charged molecules to cross the membrane</p> Signup and view all the answers

    What does the Fluid Mosaic model describe in terms of membrane structure?

    <p>Lateral diffusion of phospholipids and embedded proteins</p> Signup and view all the answers

    Which of the following best describes the permeability of very large molecules through the cell membrane?

    <p>They cannot cross the membrane and are impermeable</p> Signup and view all the answers

    What limitation is imposed on the diffusion of molecules within the membrane?

    <p>Cytoskeletal anchoring</p> Signup and view all the answers

    What is the primary role of membrane proteins that act as receptors?

    <p>Provide attachment sites for hormones and neurotransmitters</p> Signup and view all the answers

    Which membrane proteins are involved in the structural anchoring to the cytoskeleton?

    <p>Actin and microtubules</p> Signup and view all the answers

    Which type of junction allows for rapid transmission of signals between two cells?

    <p>Communication junctions</p> Signup and view all the answers

    What is the purpose of membrane proteins that facilitate cell-to-cell attachment?

    <p>To form connections that hold cell layers together</p> Signup and view all the answers

    Which of the following is an example of a receptor protein in the cell membrane?

    <p>G protein receptor</p> Signup and view all the answers

    What role do receptors in membrane proteins serve?

    <p>Act as attachment sites for hormones and neurotransmitters</p> Signup and view all the answers

    Which type of membrane protein facilitates the connection between adjacent cells?

    <p>Cell-to-cell adhesion proteins</p> Signup and view all the answers

    Which example is associated with communication junctions in membrane proteins?

    <p>Gap junctions</p> Signup and view all the answers

    Which of the following functions is NOT performed by membrane proteins?

    <p>Transporting nutrients into the cell</p> Signup and view all the answers

    What distinguishes structural anchors of membrane proteins from receptors?

    <p>They provide attachment to the cytoskeleton and strengthen the cell membrane</p> Signup and view all the answers

    What is the primary function of transporters in cellular membranes?

    <p>Facilitate the movement of specific substances</p> Signup and view all the answers

    Which of the following best describes the role of enzymes in cellular activity?

    <p>To catalyze reactions and break down molecules</p> Signup and view all the answers

    How do cell surface identity markers function in the immune system?

    <p>They display antigens to distinguish self from non-self cells</p> Signup and view all the answers

    What is a key function of the Na+/K+ ATPase pump in a cell?

    <p>Maintaining the electrochemical gradient</p> Signup and view all the answers

    Which component of the immune system is directly involved in cell-to-cell communication?

    <p>CD68 Monocytes</p> Signup and view all the answers

    What type of transport mechanism requires no energy and moves substances from high to low concentration utilizes protein carriers?

    <p>Facilitated diffusion</p> Signup and view all the answers

    Which transport mechanism directly involves the hydrolysis of ATP for energy?

    <p>Active transport</p> Signup and view all the answers

    Which of the following processes involves the infolding of the cell membrane to create a vesicle?

    <p>Endocytosis</p> Signup and view all the answers

    What distinguishes active transport from facilitated diffusion?

    <p>It moves substances against the concentration gradient</p> Signup and view all the answers

    Which statement about facilitated diffusion is incorrect?

    <p>It requires energy input.</p> Signup and view all the answers

    Which membrane transport mechanism requires energy to move substances against their concentration gradient?

    <p>Active transport</p> Signup and view all the answers

    What is the role of protein carriers in facilitated diffusion?

    <p>To allow specific polar or charged molecules to move through the membrane</p> Signup and view all the answers

    Which type of endocytosis involves the intake of large particles or cells?

    <p>Phagocytosis</p> Signup and view all the answers

    What distinguishes primary active transport from secondary active transport?

    <p>Number of steps involved</p> Signup and view all the answers

    What process is involved in the secretion of molecules such as hormones through vesicles released by the Golgi apparatus?

    <p>Exocytosis</p> Signup and view all the answers

    What occurs to the movement of individual molecules once chemical equilibrium has been reached during passive transport?

    <p>Individual molecules continue moving without net change</p> Signup and view all the answers

    What is a key characteristic of transport proteins or transporters regarding their function?

    <p>They have a maximum rate at which they can move substances</p> Signup and view all the answers

    Which type of molecules are primarily released during the process of exocytosis?

    <p>Hormones</p> Signup and view all the answers

    What would most likely happen if a transporter protein reaches its saturation point?

    <p>Further increases in substrate will not increase the rate of transport</p> Signup and view all the answers

    What determines the flux of molecules according to Fick's Law in membrane transport?

    <p>Permeability, area, and concentration gradient</p> Signup and view all the answers

    Which type of molecules can diffuse through the membrane solely based on their concentration gradient?

    <p>Nonpolar/lipid molecules</p> Signup and view all the answers

    What happens to the net flux of molecules when equilibrium is reached across a membrane?

    <p>The net flux becomes zero</p> Signup and view all the answers

    Which of the following substances cannot diffuse through the membrane without a protein channel?

    <p>Glucose molecules</p> Signup and view all the answers

    Which parameter does NOT influence the permeability of a substance through a membrane?

    <p>Presence of membrane proteins</p> Signup and view all the answers

    What characterizes facilitated diffusion in terms of energy usage?

    <p>It utilizes a transmembrane protein and does not require energy.</p> Signup and view all the answers

    How does the presence of transporters, like GLUT4 influenced by insulin, affect diffusion rates?

    <p>It increases the number of channels available for diffusion.</p> Signup and view all the answers

    Which factor is not affecting the movement of ions through protein channels?

    <p>The temperature of the surrounding environment.</p> Signup and view all the answers

    What role do ligand-gated channels play in facilitated diffusion?

    <p>They require a specific ligand to change conformation and allow diffusion.</p> Signup and view all the answers

    Which statement best describes electrochemical gradients in ion diffusion?

    <p>Ions move down both their concentration and electrical gradients.</p> Signup and view all the answers

    What happens when the transport maximum (Tm) is reached for a protein-mediated transporter?

    <p>All binding sites on the transporter are occupied</p> Signup and view all the answers

    Which characteristic of protein-mediated transport allows similar substances to influence each other's transport rates?

    <p>Competition</p> Signup and view all the answers

    What role does ATP play in active transport processes?

    <p>It provides chemical energy to move solutes against their concentration gradient</p> Signup and view all the answers

    Why might ions move slower through transporters compared to ion channels?

    <p>Transporters operate under a saturation limit</p> Signup and view all the answers

    What is a potential consequence of using metabolic inhibitors on protein-mediated transport?

    <p>Complete halt of active transport processes</p> Signup and view all the answers

    What is the net effect of the Na+/K+ ATPase pump in terms of ion transport?

    <p>3Na+ out, 2K+ in costs 1 ATP</p> Signup and view all the answers

    Which ATPase is responsible for maintaining low intracellular Ca2+ concentration for cell signaling?

    <p>Ca2+ ATPase</p> Signup and view all the answers

    What process occurs during the binding of ATP to the Na+/K+ ATPase pump?

    <p>ATP is hydrolyzed leading to a conformational change</p> Signup and view all the answers

    Which statement about the Na+/K+ ATPase pump is false?

    <p>It is not subject to competitive inhibition.</p> Signup and view all the answers

    What is the primary function of the H+/K+ ATPase pump in the stomach?

    <p>To acidify the stomach for enzyme activity</p> Signup and view all the answers

    What is the primary role of the Na+/K+ ATPase in secondary active transport within the digestive system?

    <p>To create a Na+ gradient for coupling with other substances</p> Signup and view all the answers

    How does sodium ions (Na+) facilitate the absorption of other solutes like glucose or amino acids in the intestine?

    <p>By enabling secondary active transport through symporters</p> Signup and view all the answers

    What is the consequence of a low intracellular Na+ concentration in terms of secondary active transport?

    <p>It allows for the establishment of a potential energy gradient for coupling transport</p> Signup and view all the answers

    Which statement best describes the function of a symporter in secondary active transport?

    <p>It transports two or more different solutes in the same direction</p> Signup and view all the answers

    What occurs during the process of secondary active transport in relation to glucose absorption?

    <p>Glucose moves against its concentration gradient with Na+ down its gradient</p> Signup and view all the answers

    Which type of secondary active transport involves the movement of substances in the same direction across a membrane?

    <p>Symporter</p> Signup and view all the answers

    In which manner does an antiporter function during secondary active transport?

    <p>It exchanges two molecules in opposite directions.</p> Signup and view all the answers

    What is a key characteristic of the receptor-mediated endocytosis process?

    <p>Specific ligands bind to receptors before vesicle formation.</p> Signup and view all the answers

    Which of the following is an example of a symporter?

    <p>Narglucose cotransporter</p> Signup and view all the answers

    What is the process by which larger particles are taken up by immune cells for destruction?

    <p>Phagocytosis</p> Signup and view all the answers

    Which mechanism involves the uptake of random small particles from the extracellular space?

    <p>Pinocytosis</p> Signup and view all the answers

    What triggers the process of receptor-mediated endocytosis?

    <p>Binding of extracellular ligands to membrane receptors</p> Signup and view all the answers

    What structure is formed when the cell membrane surrounds a particle during phagocytosis?

    <p>Phagosome</p> Signup and view all the answers

    What role does clathrin play in receptor-mediated endocytosis?

    <p>It forms a cage-like structure at the membrane</p> Signup and view all the answers

    What structure is formed during clathrin-dependent receptor-mediated endocytosis?

    <p>Clathrin-coated vesicle</p> Signup and view all the answers

    What is the primary function of potocytosis?

    <p>Vitamin uptake</p> Signup and view all the answers

    Which protein is responsible for linking receptors and ligands during clathrin-dependent endocytosis?

    <p>AP2 proteins</p> Signup and view all the answers

    What happens to receptors after the ligand is removed in clathrin-dependent endocytosis?

    <p>They are recycled back to the membrane</p> Signup and view all the answers

    What type of vesicles are utilized in potocytosis for transporting molecules?

    <p>Caveolae</p> Signup and view all the answers

    What type of exocytosis is an unregulated process that delivers proteins to the plasma membrane?

    <p>Constitutive Exocytosis</p> Signup and view all the answers

    What triggers regulated exocytosis in cells?

    <p>Increase in Ca²⁺ in the cytosol</p> Signup and view all the answers

    What type of molecules are typically released during regulated exocytosis?

    <p>Hormones and enzymes</p> Signup and view all the answers

    Which process is characterized by the fusion of an intracellular vesicle to the membrane to release contents to the extracellular fluid?

    <p>Exocytosis</p> Signup and view all the answers

    In the context of exocytosis, what occurs after a vesicle fuses with the plasma membrane?

    <p>The contents are released into the extracellular fluid</p> Signup and view all the answers

    What is the primary factor that determines osmotic pressure in a solution?

    <p>Concentration of the solute particles</p> Signup and view all the answers

    How is osmolarity calculated from molarity?

    <p>Molarity x (number of particles/mol)</p> Signup and view all the answers

    What happens to water movement during osmosis?

    <p>Water moves from areas of lower to higher solute concentration.</p> Signup and view all the answers

    Why is a semipermeable membrane crucial in osmosis?

    <p>It permits only the solvent to move while blocking solute.</p> Signup and view all the answers

    In the given example, how does 1 mole of NaCl produce an osmolarity of 2 Osm?

    <p>NaCl dissociates into sodium and chloride ions.</p> Signup and view all the answers

    What is the term used for the difference between calculated osmolarity and measured osmolality?

    <p>Osmolal gap</p> Signup and view all the answers

    Which of the following correctly defines osmolality?

    <p>Number of milliosmoles per kilogram of solvent</p> Signup and view all the answers

    What occurs when a membrane is permeable to both solute and solvent?

    <p>Both solute and solvent reach equal concentrations in compartments</p> Signup and view all the answers

    How many osmoles are produced from one mole of NaCl in solution?

    <p>2 osmoles</p> Signup and view all the answers

    When are osmolarity and osmolality considered equivalent?

    <p>When the concentration of solutes is low</p> Signup and view all the answers

    Study Notes

    Homeostasis

    • Physiology is the study of living organisms and their internal environment control.
    • Homeostasis refers to the balance of energy in metabolic reactions, maintaining stable internal conditions despite external changes.
    • Claude Bernard emphasized the difference between the external environment and the internal environment (Milieu Interieur) surrounding individual cells, which is maintained by homeostasis.

    Body Fluid Compartments

    • Interstitial fluid surrounds cells and acts as a transition between the cell membrane and the external environment.
    • Intracellular fluid (IC) is the fluid inside cells, also known as cytoplasm.
    • Extracellular fluid (ECF) is the fluid outside cells, including interstitial fluid (ISF) and blood plasma.

    Body Water

    • Standard Reference Individual (SRI): A 21-year-old white male, 70 kg (150 lbs) is the reference point for body composition calculations.
    • Body water composition: 45-75% of body mass (60% in SRI).
    • Leaner individuals have a higher percentage of body water.
    • Muscle mass, skin, and organs have a high water content (70-80%).
    • Bone contains 25% water.
    • Fat/adipose tissue contains only 10% water, influencing the overall body water percentage.
    • Body water percentage decreases with age due to fat gain and muscle loss.
    • Women have lower body water percentages due to breast and buttock fat deposition.
    • Functions of body water:
      • Provides a medium for dissolved solutes and reactions, like in cytoplasm.
      • Regulates body temperature.
      • Moistens tissues (eyes, mouth, nose).
      • Lubricates joints.
      • Protects organs and tissues.
      • Prevents constipation.
      • Dilutes toxins for excretion by liver and kidneys.

    Calculating Body Water

    • Total body water (TBW): Intracellular fluid + extracellular fluid.
    • TBW calculation: TBW (L) = (weight (kg) x % body water).
    • In the SRI (70 kg, 60% body water): TBW = 42L, ICF = 28L (2/3 of TBW), ECF = 14L (1/3 of TBW).
    • Interstitial fluid: 11L.
    • Plasma: 3L.

    Water Balance

    • Dynamic steady state: The body maintains a balance of water intake and output to keep solute concentrations and blood volume/pressure normal.
    • Water intake: Oral fluids (drinking), oral intake (food), and metabolic water produced from chemical reactions.
    • Water output:
      • Insensible/obligatory loss: ~1L/day.
        • Lungs (breathing out water vapor).
        • Skin (evaporation).
      • Sensible/Facultative loss: ~0.5L/day.
        • Kidneys (urine): obligatory and facultative.
        • Stool (feces).
      • Sweat: Not obligatory or facultative.
        • Insensible perspiration: Continuous, obligatory, entire skin surface, passive evaporation of pure water due to temperature and humidity.
        • Sweating: Only as needed, facultative, active secretion of electrolyte solution to cool the body when hot or actively working.

    Normal Turnover

    • Adults: 3-4% of total body weight per 24 hours.
    • Infants: ~10% of total body weight per 24 hours.
    • Infants have a higher surface area to volume ratio, increasing evaporation at the skin.
    • Underdeveloped kidneys reabsorb less water, leading to increased urine output.

    Negative Water Balance

    • Excess water loss: Gut (vomiting/diarrhea), sweat, dry air, or urine.
    • Reduced intake: Food/drinks leading to more loss than intake.

    Water Intoxication

    • Excess water intake: Leads to hyponatremia (low Na+ in blood).
    • Renal system failure (kidney failure): Inability to excrete urine.

    ### Body Fluid Compartments

    • Concentration differences exist between fluid compartments due to selectively permeable cell membranes.
    • Plasma and interstitial fluid have similar ion concentrations, but plasma has a higher protein concentration due to protein size.
    • Physiological saline (0.9% NaCl) can replace extracellular fluid (ECF).
    • Intracellular fluid (ICF) and ECF have significantly different ion concentrations.
    • ICF is high in potassium (K+), magnesium (Mg2+), and proteins. It constitutes 2/3 of total body water and 40% of body mass in a standard reference individual (SRI).
    • ICF is calculated by subtracting ECF from total body water.
    • ECF is high in sodium (Na+) and chloride (Cl-), making up 1/3 of total body water and 20% of body mass in an SRI.
    • ECF is accessible through the plasma and interstitial fluid, and includes lymph and transcellular fluid.
    • Plasma constitutes 5% of body mass and is the fluid part of blood, holding blood cells and platelets. It is held in capillaries and the circulatory system.
    • Interstitial fluid (ISF) makes up 15% of body mass and fills the spaces between individual cells. It's considered the internal environment ("milieu interieur"). ISF is calculated by subtracting plasma from ECF.
    • Lymph makes up 1-2% of body mass and is not directly measurable. It is approximately 10% of ISF and is filtered into the open lymph system. This system consists of permeable endothelial cells that line lymph vessels and collect fluid and proteins from ISF. Eventually, it mixes back into blood circulation near the heart through large veins.
    • Transcellular fluid is a smaller volume fluid compartment with various functions and locations, such as cerebrospinal fluid, synovial fluid, and aqueous humor.

    Measuring Compartment Volumes

    • Direct measurement involves measuring species before and after desiccation. This method cannot be used for animals as they die during the process.
    • Indirect methods use an indicator substance introduced into the blood supply to measure compartment volumes.
    • The indicator method involves introducing a non-toxic substance that distributes evenly throughout the compartments, doesn't affect water distribution, and is easily measured in blood plasma.
    • The indicator is introduced into a vein to avoid loss in urine and allowed to equilibrate throughout the body.
    • A known volume of blood plasma is then extracted and the concentration of the indicator is measured.
    • The volume of the compartment (V) can be calculated using the formula: V = Q/c where Q is the quantity of the indicator introduced and c is its concentration in blood plasma.
    • In clinical settings, adjustments for metabolism and excretion of the indicator are necessary.

    Capillary Fluid Transport

    • Capillaries, which contain 5% of the blood in circulation, facilitate fluid transport between the blood and interstitial fluid.
    • The single-layered endothelial cells of capillaries allow for the passage of substances in and out of the circulatory system.
    • Simple and facilitated diffusion are the primary modes of transport across cell membranes, facilitating movement of nutrients, gases, and waste products.
    • Facilitated diffusion may involve water-filled channels.
    • Transcytosis is a transport process where substances are taken in by endocytosis on the luminal membrane, migrate through the cell, and are released by exocytosis on the interstitial membrane.
    • Bulk flow, driven by hydrostatic pressure differences (Starling Forces), moves protein-free plasma from the capillary into the interstitial fluid space. The interstitial fluid (IS) volume is about 75%, while the plasma volume is 25% of the total extracellular (EC) volume.

    Blood

    • The blood pH is maintained between 7.35-7.45 and serves as a transport medium for nutrients, gases, wastes, and hormones.
    • Blood also plays a role in temperature regulation.
    • Blood constitutes approximately 7% of total body mass.
    • Hypovolemia refers to a lower than normal blood volume.

    Blood Composition

    • Plasma, comprising 55% of blood volume, represents approximately 5% of total body fluid mass.
    • Plasma contains nutrients (glucose, amino acids, lipids), gases, waste products (urea, lactate), and proteins (colloids).
    • Proteins make up about 7% of plasma volume.
    • Hematocrit is the percentage of blood volume occupied by red blood cells (RBCs) and is also known as Packed Cell Volume (PCV).
    • Hematocrit is calculated as the height of the RBC column divided by the total height of the blood column.
    • RBCs constitute approximately 45% of blood volume.
    • The buffy coat, located between the plasma and packed red blood cells, contains white blood cells (WBCs or leukocytes) and platelets.

    Plasma Proteins

    • Plasma proteins are essential components of blood plasma, playing vital roles in various bodily functions.
    • Albumins are the most abundant plasma proteins and act as carriers for lipids, minerals, and hormones.
    • Globulins, including immunoglobulins (Ig), are involved in the immune response by forming antibodies to detect infections.
    • Globulins also contribute to blood clotting and serve as carriers.
    • Fibrinogen is a crucial plasma protein for blood clotting.
    • While most plasma proteins are synthesized in the liver, γ-globulins (immunoglobulins) are produced in the lymph tissue.

    Microcirculation of Fluid in the Circulatory System

    • Plasma proteins, due to their inability to cross the capillary membrane, contribute significantly to the plasma's colloidal osmotic pressure (COP).
    • As non-diffusible solutes, plasma proteins create an osmotic pressure that draws fluid back into the capillaries.
    • The osmotic effect is determined by the concentration of solutes, regardless of their size or charge.

    Starling Forces

    • Four forces determine fluid movement across capillary walls: hydrostatic pressure, osmotic pressure, interstitial fluid hydrostatic pressure, and interstitial fluid osmotic pressure.
    • Hydrostatic pressure (blood pressure) pushes fluid out of the capillary.
    • Osmotic pressure (created by plasma proteins) pulls fluid into the capillary.
    • On the arterial end of the capillary, hydrostatic pressure is greater than osmotic pressure, resulting in net fluid movement out of the capillary and into the interstitial space (filtration).
    • On the venous end of the capillary, hydrostatic pressure is lower than osmotic pressure, resulting in net fluid movement from the interstitial space into the capillary (reabsorption).
    • Colloidal osmotic pressure (COP), also known as oncotic pressure, is determined by the number of osmotically active particles in the plasma and is inversely related to the molecular weight of the protein.
    • The average COP is 25 mmHg, with albumin contributing 20 mmHg, globulins contributing 5 mmHg, and fibrinogen contributing less than 1 mmHg.
    • Increased COP pulls water into the plasma, while decreased COP allows more water to exit into the interstitial fluid.
    • Hydrostatic pressure is 33 mmHg at the arterial end of the capillary and 15 mmHg at the venous end.
    • The decrease in pressure is due to increased resistance through the capillary bed.

    Capillary Dynamics

    • Capillaries experience a net fluid loss of approximately 10% to the interstitial space (IS).
    • This loss is influenced by hydrostatic pressure, colloid osmotic pressure (C.O.P.), capillary permeability, and lymphatic drainage.
    • The movement of fluid at any point along a capillary is determined by the balance of four Starling forces.
    • Filtration refers to the movement of fluid out of the capillary.
    • Reabsorption refers to the movement of fluid back into the capillary from the interstitial space.
    • Water and dissolved substances (ions) can pass through pores between endothelial cells lining a capillary, but large proteins cannot.

    Edema

    • Edema is the accumulation of excess interstitial fluid.
    • It can occur due to decreased venous return, often manifesting as swelling in the ankles and feet.
    • Causes of edema:
      • Increased capillary hydrostatic pressure: This can occur in conditions like heart failure or venous obstruction.
      • Increased capillary permeability: This allows plasma proteins to leak into the interstitial space, which increases interstitial osmotic pressure.
      • Blocked lymphatic drainage: This can result in a buildup of fluid in the interstitial space.
      • Decreased plasma protein concentration: This can be caused by conditions such as malnutrition or liver disease.

    Edema Examples

    • Kwashiorkor: A severe form of protein malnutrition characterized by edema (especially in the abdomen).
    • Elephantiasis: A painful condition caused by a parasitic infection that blocks lymphatic drainage.

    Edema

    • Edema is swelling caused by excessive fluid buildup in the interstitial space
    • Can occur due to imbalances in fluid pressure and movement

    Causes of Edema

    • Increased hydrostatic pressure: high pressure within blood vessels pushes fluid into surrounding tissues
      • Example: Long periods of standing or sitting can cause edema in the legs
    • Decreased oncotic pressure: low protein levels in the blood cause fluid to leak from blood vessels
    • Example: Kidney disease can cause protein loss in urine, leading to decreased blood protein levels and edema
    • Increased capillary permeability: damaged blood vessels leak fluid
      • Example: Infections or allergic reactions can increase capillary permeability
    • Decreased lymphatic drainage: impaired lymphatic system function prevents fluid removal
      • Example: Surgery or injury to lymph nodes can disrupt drainage and cause edema

    Plasma Protein Analysis

    • Plasma protein analysis may be requested to investigate metabolic issues, liver issues, kidney disease, an overactive immune system, or inflammation.
    • Liver issues can impact protein production, with a notable exception being the production of gamma globulins.
    • Kidney disease can lead to the loss of albumin in urine during filtration.
    • An active immune system (often due to infections) can cause a spike in gamma globulins.

    Separation of Plasma Proteins

    • Plasma proteins can be separated using various methods:
      • Differential precipitation by salt treatment: This method relies on the different solubilities of proteins in salt solutions.
      • Sedimentation by ultracentrifugation: This technique utilizes high-speed centrifugation to separate proteins based on their size and density.
      • Immunological characteristics: Determining the presence of specific globulins through immunochemical techniques.
      • Electrophoretic mobility: This method utilizes an electric current to separate proteins based on their size and charge, with the largest proteins moving slower.

    Electrophoresis

    • Electrophoresis is a technique that separates proteins based on their size (molecular weight, MW) and charge.
    • In electrophoresis, proteins are moved through a gel matrix using an electric current.
    • Negatively charged proteins migrate towards the positively charged electrode.
    • Larger proteins (such as fibrinogens) move slower through the gel.
    • Medium-sized proteins (such as globulins) move at an intermediate speed.
    • Smaller proteins (such as albumins) move faster and are typically found closer to the bottom of the gel.

    Plasma Protein Analysis

    • A plasma protein analysis can be ordered to diagnose metabolic, liver, renal, and inflammatory conditions
    • Liver issues can be identified by a low concentration of plasma proteins, except for gamma globulins
    • Renal disease can be diagnosed by a low concentration of albumin in plasma due to its loss in urine
    • A high concentration of gamma globulins in plasma indicates that the immune system may be active due to an infection or inflammation

    Plasma Protein Separation

    • Plasma proteins can be separated using different techniques
    • Differential precipitation by salt treatment can isolate specific plasma proteins
    • Sedimentation in ultracentrifugation separates proteins based on their size and density
    • Immunological characteristics can be used to identify specific globulins
    • Electrophoretic mobility can be used to determine the size of plasma proteins based on their migration through a gel

    Electrophoresis

    • Electrophoresis uses electrical current to separate proteins in a sample based on their molecular weight
    • Negatively charged proteins move through a gel based on their molecular weight (size)
    • Larger proteins move slower, like fibrinogen
    • Medium sized proteins, like globulins, are found in the middle of the gel
    • Smaller proteins, like albumin, move faster and are found at the bottom of the gel

    Water Intake

    • We obtain water through consuming foods, liquids, and the breakdown of nutrients.

    Water Loss

    • Water loss occurs through obligatory and facultative mechanisms.
    • Obligatory water loss is essential for maintaining health and occurs regardless of water intake.
      • Includes insensible losses from skin and respiratory tract through evaporation.
      • Also includes water lost in urine and stool.
    • Facultative water loss varies with water intake.
      • The kidneys play a crucial role in regulating water balance.
      • Increased water intake leads to increased urine production.

    Cell Membrane Structure

    • Cell membranes are approximately 6-10 nm thick and surround the entire cell.
    • The phospholipid bilayer creates a hydrophobic core due to the fatty acid tails, and a hydrophilic exterior due to the polar head groups.
    • The phospholipid head group is connected to the fatty acids via glycerol, and interacts with the intracellular fluid (IC or cytoplasm) and the extracellular fluid (ECF).
    • Amphipathic phospholipids constitute 40-50% of the plasma membrane's weight.
    • Cholesterol contributes to membrane fluidity by acting as a temperature buffer, ensuring optimal movement of membrane components.
    • Cholesterol is also involved in the formation of lipid rafts and vesicles.
    • Proteins account for 25-75% of the membrane's weight and can be integral (embedded with transmembrane domain) or peripheral (loosely associated to one side, typically the cytoplasmic face).

    Glycocalyx

    • The glycocalyx is an extracellular coating composed of glycans, glycoproteins, and glycolipids.
    • It plays several crucial roles, including cell communication, adhesion, protection, recognition, and control of fluid balance (vascular permeability).

    Membrane Transport Properties

    • Fat-soluble molecules, like fatty acids, steroid hormones, and non-polar gases, can easily pass through the cell membrane due to their chemical structure. They move down their concentration gradient.
    • Polar or charged molecules, such as sugars, amino acids, and ions, need help from transporters to cross the membrane. This allows for a concentration gradient to be maintained.
    • Very large molecules, such as RNA and proteins, cannot pass through the cell membrane.

    Fluid Mosaic Model

    • The fluid mosaic model explains the lateral movement of phospholipids and membrane proteins (integral proteins) within the membrane.
    • Membrane molecules are constantly in motion, similar to a "sea", allowing for diffusion throughout the membrane.
    • Anchoring to the cytoskeleton internally or the extracellular matrix (ECM) externally can restrict the movement of membrane molecules.

    Membrane Protein Functions

    • Receptors: Bind to signaling molecules like hormones and neurotransmitters, triggering cellular responses.
      • Examples include G protein receptors, insulin receptors, and acetylcholine (ACh) receptors.
    • Structural Anchors: Provide support and stability to the cell membrane by attaching to the cytoskeleton.
      • Proteins like actin, microtubules, and septins can anchor the cell membrane.
    • Cell-to-Cell Attachment: Connect cells together through interactions with proteins on opposing cell membranes.
      • Examples include cell adhesion molecules (CAMs), cadherins, and integrins, which help maintain tissue integrity.
    • Communication Junctions: Facilitate communication between cells through direct connections and signal transduction.
      • Sugars attached to proteins or the membrane itself can act as signals.
      • Gap junctions, found in cardiac muscle cells, allow rapid transmission of signals between cells.

    Receptor Proteins

    • Bind hormones and neurotransmitters
    • Examples: G protein receptors, insulin receptors, ACh receptors

    Structural Anchors

    • Cytoskeleton Attachment: Attach to the inner surface of the cell membrane to support, strengthen, and anchor cytoskeleton and cell organelles to the membrane.
      • Examples: Actin, microtubules, septins
    • Cell-to-Cell Attachment: Connect cells together to hold cell layers together. These proteins from each cell interact, connecting cells.
      • Examples: CAMs, cadherins, integrins

    Communication Junctions

    • Sugars attached to proteins or the membrane can act as signals.
    • Channels connecting the cytoplasm of two cells allow for rapid transmission of signals.
    • Example: Gap junctions between cardiac cells

    Transporters

    • Span across the cell membrane, acting as gates or channels that control the movement of specific substances into and out of the cell.
    • Examples include the Sodium channel (Na+) and the Glucose transporter (GLUT).

    Enzymes

    • Catalyze reactions or break down molecules within the cell.
    • An example is the Sodium-Potassium ATPase pump (Na+/K+ ATPase).

    Cell Surface Identity Markers

    • Present on the outer surface of the cell, using antigens or glycoproteins to display the cell's identity.
    • Proper markers protect the cell from the body's immune system.
    • Used in cell-cell communication.
    • Examples include:
      • CD T-cells (lymphocytes that activate the immune system)
      • CD45 Leucocytes
      • CD68 Monocytes

    Simple Diffusion

    • Molecules move randomly due to their thermal motion (kinetic energy).
    • Movement is from an area of high concentration to low concentration.

    Facilitated Diffusion

    • Specific proteins, carriers, or channels facilitate the movement of molecules.
    • Transports polar or charged molecules that cannot easily cross the membrane.
    • Requires NO energy.
    • Moves substances like glucose, ions, or water from high to low concentrations.

    Active Transport

    • Moves molecules AGAINST their concentration gradients.
    • Requires energy from ATP hydrolysis.
    • Proteins act as transporters.
    • Allows for the creation of concentration gradients or sequestration of molecules on one side of the membrane.
    • Includes primary and secondary active transport.

    Endocytosis

    • The cell membrane invaginates to form a vesicle.
    • This vesicle encloses extracellular molecules and brings them into the cell.
    • Types of endocytosis include:
      • Receptor-mediated endocytosis
      • Phagocytosis
      • Pinocytosis

    Simple Diffusion

    • Movement of molecules due to thermal motion (kinetic energy)
    • Random movement of molecules from high concentration to low concentration

    Facilitated Diffusion

    • Movement of molecules across the cell membrane with the assistance of transport proteins (carriers or channels)
    • Moves molecules down their concentration gradient (high to low)
    • Does not require energy
    • Transports polar and charged molecules, like glucose, ions, and water

    Active Transport

    • Movement of molecules against their concentration gradient (low to high)
    • Requires energy, obtained through ATP hydrolysis
    • Uses transport proteins
    • Creates a concentration gradient or sequesters molecules on one side of the membrane
    • Primary and Secondary active transport both require ATP, but differ in the number of steps

    Endocytosis

    • Cell membrane invaginates (folds inward) to create a vesicle that encloses an extracellular molecule
    • Brings molecules into the cell
    • Types include: receptor-mediated endocytosis, phagocytosis, and pinocytosis

    Exocytosis

    • Exocytosis is the process of cells secreting molecules, often hormones, through vesicles released by the Golgi apparatus.
    • These vesicles travel to the cell membrane, fuse with it, and release their contents outside the cell.
    • Passive transport relies on concentration gradients, and once equilibrium is reached, there is no net change in concentration. However, individual molecules continue to move.
    • Transporter proteins or channels can become saturated, meaning they have reached their maximum rate of transporting a substance.

    Simple Diffusion

    • Simple diffusion is the movement of molecules across a membrane from an area of high concentration to an area of low concentration.
    • This movement is driven by the concentration gradient, which is the difference in concentration between the two areas.
    • The rate of simple diffusion is determined by Fick's Law, which states that the flux (J) of a substance across a membrane is proportional to the permeability of the membrane (P), the surface area of the membrane (A), and the concentration gradient (Co - C).
    • At equilibrium, the net flux is zero, meaning there is no net change in concentration across the membrane.
    • Nonpolar or lipid molecules can diffuse through the membrane on their concentration gradient.
    • Small polar molecules such as water and alcohol can also pass through the bilayer.
    • Larger polar or charged molecules require the assistance of a transport protein to cross the membrane.

    Facilitated Diffusion

    • Uses transmembrane proteins to move polar or charged substances across the membrane.
    • Movement is down the concentration gradient, so no energy is required.
    • Hormones can influence the number of transporters in membranes, for example insulin increases GLUT4 transporters in muscle cells.

    Factors Affecting Diffusion Rate through Protein Channels

    • Affinity of transporter for solute: Higher affinity leads to faster transport.
    • Type of transporter: Channels are faster than carriers or pumps because they simply open and close, while carriers and pumps undergo conformational changes.
    • Solute concentration: A larger concentration gradient results in faster diffusion.
    • Number of channels: More open channels allow for faster diffusion.
    • Electrochemical gradient: Ions move down both their chemical and electrical gradients.
    • Channel conductance: Current flow depends on the amount of time the channel is open, and how frequently it opens.

    Ion Channel Conformation

    • Channels can exist in an open or closed state.
    • Ligand-gated channels: Open when a specific molecule binds to them.
    • Mechanically-gated channels: Open due to changes in shape, such as pressure on the skin.

    Protein-Mediated Transport Characteristics

    • Specificity: Transporters are designed to bind to specific molecules, allowing them to be selectively transported across cell membranes.
    • Ion Channels: While ion channels are also transmembrane proteins, they primarily act as channels that allow the rapid passage of specific ions, such as sodium or potassium. Transporters, on the other hand, are involved in the movement of a wider range of molecules, including glucose and amino acids.
    • Saturation: The rate of transport via protein transporters can be saturated. This means that when all binding sites on the transporter are occupied, the rate of transport will reach a maximum (Tm).
    • Competition: Molecules with similar chemical characteristics may compete for the same binding sites on a transporter. This competition can affect the rate of transport for each molecule.

    Active Transport

    • Energy Requirement: Unlike passive transport, active transport requires energy to move solutes across the cell membrane.
    • ATP Hydrolysis: Active transport utilizes the energy released from the hydrolysis of ATP to drive the movement of solutes against their concentration gradient.
    • Movement Against Gradient: This means that active transport can move molecules from a region of low concentration to a region of high concentration, which is the opposite of what occurs in passive transport (diffusion).
    • Regulation: The activity of active transporters can be regulated by various factors like metabolic inhibitors. This regulation ensures that the transport process is carefully controlled to meet the cell's needs.

    Primary Active Transport: The Sodium-Potassium Pump (Na+/K+ ATPase)

    • Specificity: Each transporter is designed for a specific molecule. For the Na+/K+ pump, it only moves sodium and potassium ions.
    • Competitive Inhibition: Other molecules that resemble the transported molecule can compete for the transporter's binding site.
    • Limited Transport Capacity: The transporter can be saturated. This means that there’s a limit to how much of a substance it can transport, even when there's a high concentration of that substance.
    • Net Effect: The Na+/K+ pump moves 3 sodium ions (Na+) out of the cell and 2 potassium ions (K+) into the cell using the energy from one ATP molecule. This results in a higher concentration of sodium outside the cell and a higher concentration of potassium inside the cell.
    • Steps in Transport:
      • ATP binds to the pump.
      • Sodium ions bind to the pump.
      • ATP is hydrolyzed, releasing ADP and phosphate.
      • This triggers a conformational change in the pump, causing the sodium ions to be released outside the cell.
      • Potassium ions bind to the pump.
      • The phosphate group is released, causing another conformational change, and potassium ions are released inside the cell.

    Other Important ATPases:

    • Calcium ATPase (Ca2+ ATPase): Plays a crucial role in maintaining a low concentration of calcium ions (Ca2+) inside the cell, which is essential for cell signaling processes.
    • Proton ATPase (H+ ATPase): Maintains a low pH in lysosomes by pumping protons (H+) into these organelles, ensuring optimal activity of lysosomal enzymes for cellular waste breakdown.
    • Hydrogen/Potassium ATPase (H+/K+ ATPase): Found in the stomach, responsible for the acidification of the stomach lumen, essential for digestion and the protection against invading pathogens.

    Secondary Active Transport

    • Requires energy indirectly, using an existing ion gradient established by a primary active transporter (e.g., Na+/K+ ATPase).
    • Two-step process:
      • Step 1: Primary active transporter (e.g., Na+/K+ ATPase) uses ATP to create an ion gradient (e.g., low intracellular Na+).
      • Step 2: This gradient is then used to move a second substance against its concentration gradient. The movement of the second substance is coupled to the movement of the first ion down its gradient.
    • Example: Digestive system utilizes a Na+/K+ ATPase to establish a low intracellular Na+ concentration. This gradient drives the movement of Na+ from the intestinal lumen (high concentration) into enterocytes (low concentration) via a symporter.
    • Symporter: A protein that transports two or more molecules in the same direction across a membrane.
    • Result: Both Na+ and other solutes, such as glucose or amino acids, are transported into the enterocytes and ultimately into the bloodstream.
    • Note: The passive transport step (step 2) is not possible without the active transport step (step 1) as the gradient established by the primary active transporter is crucial for the symporter to function.

    Secondary Active Transport

    • Types of secondary active transport:
      • Symport (cotransporter): Movement of two substances in the same direction
        • SGLT (Sodium-glucose cotransporter): Involved in glucose absorption in the digestive system
        • NBC (Na+/HCO3- cotransporter): Found in the kidney and other cell types, involved in regulating pH balance
      • Antiport (countercurrent exchange): Movement of two substances in opposite directions
        • NCX (Na+/Ca2+ exchanger): Found in cardiac cells, involved in calcium removal and regulating heart function
    • Receptor-mediated endocytosis:
      • Selective uptake of molecules into cells via receptors that bind specific ligands
      • Both the receptor and ligand are internalized within a vesicle that forms at the membrane

    Endocytosis

    • Membrane-involved intake using energy
    • Larger particles are specifically taken up as part of the immune system for destruction
    • Pseudopodia engulf particles and pinch off the membrane forming phagosomes inside the cell

    Phagocytosis

    • Phagosomes fuse to lysosomes for digestion of contents.
    • Defends against infection, removes dead or senescing cells (no longer dividing)

    Pinocytosis

    • Random small particle uptake from extracellular space, nonspecific and constitutive
    • Endocytotic vesicle engulfs whatever solute is present, bringing it into the cell and fusing with endosome/lysosome for processing

    Receptor-mediated endocytosis

    • Extracellular ligands bind cell membrane receptors (highly specific), which induces a conformational change in the protein receptor triggering membrane uptake

    Clatherin-dependent Receptor Mediated Endocytosis

    • Clatherin is recruited to the membrane where receptor/ligand are bound, linking by adaptor (AP2) proteins to form a cage-like structure that when the membrane invaginates forms a coated vesicle.
    • Example: LDL-cholesterol

    Receptor-Mediated Endocytosis

    • Cells take up substances by binding to specific receptors on the cell membrane.
    • This binding induces a conformational change in the receptor, triggering membrane uptake.

    Clathrin-Dependent Receptor Mediated Endocytosis

    • Clathrin proteins are recruited to the membrane where the receptor/ligand complex is bound.
    • Adaptor proteins (AP2) link clathrin to the membrane, forming a cage-like structure.
    • This structure invaginates, forming a "clathrin-coated vesicle" that detaches from the membrane.
    • Clathrin-coated vesicles bind to endosomes or lysosomes for processing.
    • They can also fuse with the opposite membrane (transcytosis).
    • Once the ligand is removed, the receptors are recycled back to the membrane by being transported in vesicles.
    • An example is the uptake of LDL-cholesterol.

    Potocytosis (Clathrin-Independent)

    • Molecules are taken up in tiny vesicles called caveolae.
    • These vesicles are clathrin-independent.
    • They release their contents into the cytoplasm, ER, other organelles, or the opposite membrane (transcytosis).
    • An example is the uptake of vitamins.

    Exocytosis

    • Process of releasing molecules like hormones and proteins to the extracellular fluid by fusing intracellular vesicles with the cell membrane.

    Constitutive Exocytosis

    • Occurs continuously and doesn't require specific activation signals.
    • Delivers proteins synthesized in the endoplasmic reticulum (ER) and processed in the Golgi apparatus to the cell membrane.

    Regulated Exocytosis

    • Triggered by a rise in intracellular calcium levels.
    • This rise in calcium is often caused by extracellular signals activating a signaling pathway.
    • Releases specific molecules stored inside intracellular vesicles, such as hormones, digestive enzymes, or neurotransmitters.

    Osmosis

    • Movement of water across a semi-permeable membrane in response to a solute concentration gradient
    • Water moves to dilute the more concentrated solution, moving towards the high concentration of solute where there is a lower concentration of water
    • Movement occurs through simple diffusion and facilitated diffusion with aquaporins (protein channels)

    Key Terms

    • Solute: Substance dissolved in a liquid (e.g., glucose, Na+)
    • Solvent: Liquid in which the solute is dissolved (e.g., water, alcohol)
    • Permeable membrane: Both solute and solvent can move through
    • Semi-permeable membrane: Only solvent can move

    Osmotic Pressure

    • The pressure applied to exactly oppose the osmotic movement of water, preventing movement.
    • Proportionate to the number of particles (solute) in solution (osmolarity), NOT related to the size/charge/configuration of the particles
    • Calculating Osmotic Pressure (mmHg): Osmolarity x 22.4 atm/Osm x 760 mmg/atm

    Osmolarity

    • Number of particles (ions or intact molecules) per liter of solution, expressed as osmol/L or Osm
    • Typically measured in milliosmoles per liter, mosmol/L or mOsm, for cells.
    • Remember that 500 mmol = 0.5 mol (1000x difference), the same applies to Osm/mOsm.
    • Knowing the concentration of the solute can be useful to predict osmosis.

    Calculating Osmolarity

    • (molarity) x (# of particles/mol)
    • Example: 1 mole NaCl → 2 Osm because Na+ and Cl- (ions will dissociate because they're not covalently bonded)
    • Example: 1 mole glucose → 1 Osm because sugar doesn't dissociate into C, H, and O in solution; it remains as C6H12O6, bonded together as a molecule.

    Membrane Permeability

    • If a membrane is permeable to both solute and solvent, both will move across the membrane until the concentrations and volumes are equal in both compartments.

    Osmotic Activity

    • Osmotic activity occurs when a solution with lower conductivity or mineral content passes through a semi-permeable barrier to dilute the concentration of a solution with higher conductivity or mineral content on the other side.

    Osmolarity vs Osmolality

    • Osmolality is the number of milliosmoles per kilogram of solvent (mOsm/kg), representing the concentration of dissolved particles in a fluid.
    • 1 mole of NaCl dissociates into Na+ and Cl-, resulting in 2 osmoles per kg of water.
    • The difference between calculated osmolarity and measured osmolality is known as the "osmolar gap."
    • When the solute concentration in a fluid is very low, osmolarity and osmolality are considered equivalent, with a difference of less than 1%.

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    Description

    Test your knowledge on homeostasis and the various body fluid compartments. This quiz covers the physiological aspects of how living organisms maintain internal balance and the significance of different fluid types within the body. Understand key concepts like interstitial fluid, intracellular fluid, and the role of body water composition.

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