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🟥 Chapter 1:- 

🟥 Cellular Physiology:-

- Introduction.

1. Volume and Composition of Body Fluids 🌊  

2. Characteristics of Cell Membranes 🧬  

3. Transport Across Cell Membranes 🚧  

4. Diffusion Potentials and Equilibrium Potentials ⚖️  

5. Resting Membrane Potential ⚡️  

6. Action Potentials 🔋  

7. Synaptic and Neuromuscular Transmission 🔄  

8. Skeletal Muscle 💪  

9. Smooth Muscle 🌀

🟥 Chapter 1: Cellular Physiology:-

📌 الدرس الأول:-

📌 Volume and composition of the body fluids compartment:-

📌 عناوين الدرس:-

💊 Distribution of water in the body fluid compartments

💊 Composition of the fluid compartments:

   💢 Units for measuring solute compartments

   💢 Electroneutrality of body fluid compartments

   💢 Composition of Intracellular fluid and Extracellular fluid

   💢 Creation of concentration differences across the cell membrane 

   💢 Concentration differences between plasma and interstitial fluids 

🔰 عندك العلامة دي 📌 معناها العنوان الرئيسي للدرس اما 💊 للعناوين بتاعت الدرس و 💢 العناوين المتفرعة من العناوين الرئيسية.

- Understanding the functions of the organ systems requires profound knowledge of basic cellular mechanisms. 🧠⚙️  

- Although each organ system differs in its overall function, all are undergirded by a common set of physiologic principles. 💡⚖️  

- The following basic principles of physiology are introduced in this chapter: body fluids, with particular emphasis on the differences in composition of intracellular fluid and extracellular fluid; creation of these concentration differences by transport processes in cell membranes. 💧🧬  

- The origin of the electrical potential difference across cell membranes, particularly in excitable cells such as nerve and muscle. ⚡️💪  

- Generation of action potentials and their propagation in excitable cells. 🚀🔋  

- Transmission of information between cells across synapses and the role of neurotransmitters. 📡💭  

- The mechanisms that couple the action potentials to contraction in muscle cells. 💡💪  

- These principles of cellular physiology constitute a set of recurring and interlocking themes. 🔄⚙️  

- Once these principles are understood, they can be applied and integrated into the function of each organ system. 🧠🔑

📌 Volume and composition of body fluids:-

  💊 Distribution of water 🌊 in the body compartments:-

- In the human body, water constitutes a high proportion of body weight. 💧  

- The total amount of fluid or water is called total body water, which accounts for 50% to 70% of body weight. 📊💧  

- For example, a 70-kilogram (kg) man whose total body water is 65% of his body weight has 45.5 kg or 45.5 liters (L) of water (1 kg water ≈ 1 L water). 📏💦  

- In general, total body water correlates inversely with body fat. 📉🍔  

- Thus, total body water is a higher percentage of body weight when body fat is low and a lower percentage when body fat is high. 📊🏋️‍♂️  

- Because females have a higher percentage of adipose tissue than males, they tend to have less body water. 👩‍🦰💧  

- The distribution of water among body fluid compartments is described briefly in this chapter and in greater detail in Chapter 6. 📚💡  

- Total body water is distributed between two major body fluid compartments: intracellular fluid (ICF) and extracellular fluid (ECF). 🧬💧  

- The ICF is contained within the cells and is two-thirds of total body water; the ECF is outside the cells and is one-third of total body water. 🧬➗  

- ICF and ECF are separated by the cell membranes. 🔄🧬  

- ECF is further divided into two compartments: plasma and interstitial fluid. 🩸💧  

- Plasma is the fluid circulating in the blood vessels and is the smaller of the two ECF subcompartments. 💉🩸  

- Interstitial fluid is the fluid that actually bathes the cells and is the larger of the two subcompartments. 🛁🧬  

- Plasma and interstitial fluid are separated by the capillary wall. 🏗🩸  

- Interstitial fluid is an ultrafiltrate of plasma, formed by filtration processes across the capillary wall. 🔬💧  

- Because the capillary wall is virtually impermeable to large molecules such as plasma proteins, interstitial fluid contains little, if any, protein. 🛡🔒  

- The method for estimating the volume of the body fluid compartments is presented in Chapter 6. 📏📚

💊 Composition of body fluid compartments:-

- The composition of the body fluids is not uniform. 💧⚖️  

- ICF and ECF have vastly different concentrations of various solutes. 🧬💧  

- There are also certain predictable differences in solute concentrations between plasma and interstitial fluid that occur as a result of the exclusion of protein from interstitial fluid. 🩸⚛️  

💢 Units for Measuring Solute Concentrations:-

- Typically, amounts of solute are expressed in moles, equivalents, or osmoles. ⚖️🧮  

- Likewise, concentrations of solutes are expressed in moles per liter (mol/L), equivalents per liter (Eq/L), or osmoles per liter (Osm/L). ⚖️  

- In biologic solutions, concentrations of solutes are usually quite low and are expressed in millimoles per liter (mmol/L), milliequivalents per liter (mEq/L), or milliosmoles per liter (mOsm/L). 📏💧  

- One mole is 6 × 10²³ molecules of a substance. 🧬  

- One millimole is 1/1000 or 10⁻³ moles. 📉🧪  

- A glucose concentration of 1 mmol/L has 1 × 10⁻³ moles of glucose in 1 L of solution. 🍬⚗️  

- An equivalent is used to describe the amount of charged (ionized) solute and is the number of moles of the solute multiplied by its valence. ⚛️➗  

- For example, one mole of potassium chloride (KCl) in solution dissociates into one equivalent of potassium (K⁺) and one equivalent of chloride (Cl⁻). 🧪🧬  

- Likewise, one mole of calcium chloride (CaCl₂) in solution dissociates into two equivalents of calcium (Ca²⁺) and two equivalents of chloride (Cl⁻). ⚛️⚖️  

- Accordingly, a Ca²⁺ concentration of 1 mmol/L corresponds to 2 mEq/L. 📏  

- One osmole is the number of particles into which a solute dissociates in solution. 🧬  

- Osmolarity is the concentration of particles in solution expressed as osmoles per liter. 🧮💧  

- if a solute does not dissociate in solution (e.g., glucose), then its osmolarity is equal to its molarity. 🍬⚗️  

- If a solute dissociates into more than one particle in solution (e.g., NaCl), then its osmolarity equals the molarity multiplied by the number of particles in solution. 🧬⚗️  

- For example, a solution containing 1 mmol/L NaCl is 2 mOsm/L because NaCl dissociates into two particles. ⚛️  

- pH is a logarithmic term that is used to express hydrogen (H⁺) concentration. 📉🧪  

- Because the H⁺ concentration of body fluids is very low (e.g., 40 × 10⁻⁹ Eq/L in arterial blood), it is more conveniently expressed as a logarithmic term, pH. 📏💧  

- The negative sign means that pH decreases as the concentration of H⁺ increases, and pH increases as the concentration of H⁺ decreases. 📉🧬

💢 Electroneutrality of Body Fluid Compartments  

- Each body fluid compartment must obey the principle of macroscopic electroneutrality; that is, each compartment must have the same concentration, in mEq/L, of positive charges (cations) as of negative charges (anions). ⚖️  

- There can be no more cations than anions, or vice versa. 🚫⚖️  

- Even when there is a potential difference across the cell membrane, charge balance still is maintained in the bulk (macroscopic) solutions. ⚡️🔄  

- (Because potential differences are created by the separation of just a few charges adjacent to the membrane, this small separation of charges is not enough to measurably change bulk concentrations.) 📉🔌  

💢 Composition of Intracellular Fluid and Extracellular Fluid:-

- The compositions of ICF and ECF are strikingly different, as shown in Table 1.1. 📊  

- The major cation in ECF is sodium (Na⁺), and the balancing anions are chloride (Cl⁻) and bicarbonate (HCO₃⁻). 🔋  

- The major cations in ICF are potassium (K⁺) and magnesium (Mg²⁺), and the balancing anions are proteins and organic phosphates. ⚛️  

- Other notable differences in composition involve Ca²⁺ and pH. 📏  

- Typically, ICF has a very low concentration of ionized Ca²⁺ (≈10⁻⁷ mol/L), whereas the Ca²⁺ concentration in ECF is higher by approximately four orders of magnitude. 📈  

- ICF is more acidic (has a lower pH) than ECF. 🔴  

- Thus substances found in high concentration in ECF are found in low concentration in ICF, and vice versa. 🔄  

- Remarkably, given all of the concentration differences for individual solutes, the total solute concentration (osmolarity) is the same in ICF and ECF. 🌊  

- This equality is achieved because water flows freely across cell membranes. 💧  

- Any transient differences in osmolarity that occur between ICF and ECF are quickly dissipated by water movement into or out of cells to reestablish the equality. 🔄💧

💢 Creation of Concentration Differences Across Cell Membranes:-   

- The differences in solute concentration across cell membranes are created and maintained by energy-consuming transport mechanisms in the cell membranes. ⚡️🔄  

- The best known of these transport mechanisms is the Na⁺-K⁺ ATPase (Na⁺-K⁺ pump), which transports Na⁺ from ICF to ECF and simultaneously transports K⁺ from ECF to ICF. 🔄🔋  

- Both Na⁺ and K⁺ are transported against their respective electrochemical gradients; therefore an energy source, adenosine triphosphate (ATP), is required. ⚡️🔋  

- The Na⁺-K⁺ ATPase is responsible for creating the large concentration gradients for Na⁺ and K⁺ that exist across cell membranes (i.e., the low intracellular Na⁺ concentration and the high intracellular K⁺ concentration). 🔄⚖️  

- Similarly, the intracellular Ca²⁺ concentration is maintained at a level much lower than the extracellular Ca²⁺ concentration. ⚖️  

- This concentration difference is established, in part, by a cell membrane Ca²⁺ ATPase that pumps Ca²⁺ against its electrochemical gradient. ⚡️🔄  

- Like the Na⁺-K⁺ ATPase, the Ca²⁺ ATPase uses ATP as a direct energy source. 🔋  

- In addition to the transporters that use ATP directly, other transporters establish concentration differences across the cell membrane by utilizing the transmembrane Na⁺ concentration gradient (established by the Na⁺-K⁺ ATPase) as an energy source. 🔄💧  

- These transporters create concentration gradients for glucose, amino acids, Ca²⁺, and H⁺ without the direct utilization of ATP. 🍬⚛️  

- Clearly, cell membranes have the machinery to establish large concentration gradients. ⚙️  

- However, if cell membranes were freely permeable to all solutes, these gradients would quickly dissipate. 🚫⚖️  

- Thus it is critically important that cell membranes are not freely permeable to all substances but, rather, have selective permeabilities that maintain the concentration gradients established by energy-consuming transport processes. 🧬🔍  

- Directly or indirectly, the differences in composition between ICF and ECF underlie every important physiologic function, as the following examples illustrate: 🔄⚖️  

- (1) The resting membrane potential of nerve and muscle critically depends on the difference in concentration of K⁺ across the cell membrane; ⚡️🧠  

- (2) The upstroke of the action potential of these same excitable cells depends on the differences in Na⁺ concentration across the cell membrane; ⚡️🔄  

- (3) Excitation-contraction coupling in muscle cells depends on the differences in Ca²⁺ concentration across the cell membrane and the membrane of the sarcoplasmic reticulum (SR); 💪⚡️  

- (4) Absorption of essential nutrients depends on the transmembrane Na⁺ concentration gradient (e.g., glucose absorption in the small intestine or glucose reabsorption in the renal proximal tubule). 🍞💧

💢 Concentration Differences Between Plasma and Interstitial Fluids  

- As previously discussed, ECF consists of two subcompartments: interstitial fluid and plasma. 💧  

- The most significant difference in composition between these two compartments is the presence of proteins (e.g., albumin) in the plasma compartment. 🧪  

- Plasma proteins do not readily cross capillary walls because of their large molecular size and therefore are excluded from interstitial fluid. 🚫🔬  

- The exclusion of proteins from interstitial fluid has secondary consequences. ⚠️  

- The plasma proteins are negatively charged, and this negative charge causes a redistribution of small, permeant cations and anions across the capillary wall, called a Gibbs-Donnan equilibrium. ⚖️  

- The redistribution can be explained as follows: 📚  

- The plasma compartment contains the impermeant, negatively charged proteins. ⚛️  

- Because of the requirement for electroneutrality, the plasma compartment must have a slightly lower concentration of small anions (e.g., Cl⁻) and a slightly higher concentration of small cations (e.g., Na⁺ and K⁺) than that of interstitial fluid. ⚡️  

- The small concentration difference for permeant ions is expressed in the Gibbs-Donnan ratio, which gives the plasma concentration relative to the interstitial fluid concentration for anions and interstitial fluid relative to plasma for cations. 🔄  

- For example, the Cl⁻ concentration in plasma is slightly less than the Cl⁻ concentration in interstitial fluid (due to the effect of the impermeant plasma proteins); the Gibbs-Donnan ratio for Cl⁻ is 0.95, meaning that [Cl⁻]plasma/[Cl⁻]interstitial fluid equals 0.95. 📉  

- For Na⁺, the Gibbs-Donnan ratio is also 0.95, but Na⁺, being positively charged, is oriented the opposite way, and [Na⁺]interstitial fluid/[Na⁺]plasma equals 0.95. 🔄  

- Generally, these minor differences in concentration for small cations and anions between plasma and interstitial fluid are ignored. 🔍

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