Lecture 3: General Physiology - The Body Fluids PDF

General Physiology Dr.Ahmed talib Lect. 3 The Body Fluids Isotonic, hypotonic and hypertonic fluids. Isotonic:- the solutions on either side of a cell membrane are isotonic if the concentration of solute...

General Physiology Dr.Ahmed talib Lect. 3 The Body Fluids Isotonic, hypotonic and hypertonic fluids. Isotonic:- the solutions on either side of a cell membrane are isotonic if the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. In this case the cell neither swells nor shrinks because there is no concentration gradient to induce the diffusion of large amounts of water across the cell membrane and the water concentration in the intracellular and extracellular fluids is equal and the solutes cannot enter or leave the cell. Such a solution is said to be isotonic. Examples of isotonic solutions include a 0.9 % solution of sodium chloride or a 5 % glucose solution. These solutions are important in clinical medicine because they can be infused into the blood without the danger of upsetting osmotic equilibrium between the intracellular and extracellular fluids. Hypotonic:- If a cell is placed into a hypotonic solution that has a lower concentration of impermeant solutes water will diffuse into the cell, causing it to swell water will continue to diffuse into the cell,diluting the intracellular fluid while also concentrating the extracellular fluid until both solutions have about the same osmolarity. Example is 0.3% sodium chloride solution. Hypertonic:- If a cell is placed in a hypertonic solution having a higher concentration of impermeant solutes, water will flow out of the cell into the extracellular fluid, concentrating the intracellular fluid and diluting the extracellular fluid. In this case, the cell will shrink until the two concentrations become equal. Example is 2% sodium chloride solution. 1 \ Edema:- Edema is defined as the swelling caused by excessive accumulation of fluid in the tissues. It may be generalized or local. Edema that involves the entire body is called generalized edema. Local edema is the one that occurs is specific areas of the body such as abdomen, lungs and extremities like feet, ankles and legs. Accumulation of fluid may be inside or outside the cell. Types of Edema Edema is classified into two types, depending upon the body fluid compartment where accumulation of excess fluid occurs: 1. Intracellular edema 2. Extracellular edema. Intracellular Edema Intracellular edema is the accumulation of fluid inside the cell. It occurs because of three reasons: 1. Malnutrition 2. Poor metabolism 3. Inflammation of the tissues. 1- Edema due to Malnutrition Malnutrition occurs because of poor intake of food or poor circulatory system, through which the nutritive substances are supplied. Due to the lack of nutrition, the ionic pumps of the cell membrane are depressed leading to poor exchange of ions. Especially, the sodium ions leaking into the cells cannot be pumped out. Excess sodium inside the cells causes endosmosis, resulting in intracellular edema. 2- Edema due to Poor Metabolism Poor metabolism is caused by poor blood supply. Poor blood supply leads to lack of oxygen. It results in poor function of cell membrane and edema, as explained above. 2  3- Edema due to Inflammation of Tissues During inflammation of the tissues, usually the permeability of cell membrane increases. This causes the movement of many ions, including sodium into the cells resulting in endosmosis and intracellular edema. Extracellular Edema Extracellular edema is defined as the accumulation of fluid outside the cell. Causes for extracellular edema 1. Abnormal leakage of fluid from capillaries into interstitial space. 2. Obstruction of lymphatic vessels that prevents fluid return from interstitium to blood. Conditions which lead to extracellular edema 1. Heart failure. 2. Renal disease. 3. Decreased amount of plasma proteins. 4. Lymphatic obstruction. 5. Increased endothelial permeability. 1- Edema due to Heart Failure Edema occurs in heart failure because of various reasons such as: A- Failure of heart to pump blood: Failure of the heart to pump blood from veins to arteries increases venous pressure and capillary pressure. This leads to increased capillary permeability and leakage of fluid from blood into interstitial fluid, causing extracellular edema.2- B- Fall in blood pressure during heart failure: It decreases the glomerular filtration rate in the kidneys, resulting in sodium and water retention. So, the volume of blood and body fluid increases. This in turn increases the capillary hydrostatic pressure. These two factors together increase the accumulation of fluid causing extracellular edema. C-Low blood supply to kidneys during heart failure: It increases renin secretion, which in turn increases aldosterone secretion. Aldosterone increases the reabsorption of sodium and water from renal tubules into ECF resulting in the development of extracellular edema. Pulmonary Edema Pulmonary edema is the accumulation of fluid in pulmonary interstitium. In left heart failure, the blood is easily pumped into pulmonary circulation by right ventricle. However, the blood cannot return from lungs to left side of the heart because of weakness of this side of the heart. This increases pulmonary vascular pressure leading to leakage of fluid from capillaries into pulmonary interstitium. It causes pulmonary edema which can be life threatening. 3  2- Edema due to Renal Diseases - Generalized Edema In renal disease, the kidneys fail to excrete water and electrolytes particularly sodium, leading to retention of water and electrolytes. So, the fluid leaks from blood into interstitial space causing extracellular edema. Initially, the edema develops in the legs, but later it progresses to the entire body (generalized edema). 3- Edema due to Decreased Amount of Plasma Proteins When the amount of plasma proteins decreases, the colloidal osmotic pressure decreases. Because of this, the permeability of the capillary increases, resulting in increased capillary filtration. So, more amount of water leaks out of the capillary. It accumulates in the tissue spaces resulting in extracellular edema. Amount of plasma proteins decreases during the conditions like malnutrition, liver diseases, renal diseases, burns and inflammation. 4- Edema due to Lymphatic Obstruction – Lymphedema Lymphedema is the edema caused by lymphatic obstruction. It is common in filariasis. During this disease, the parasitic worms live in the lymphatics and obstruct the drainage of lymph. Accumulation of lymph along with cellular reactions leads to swelling that is very prominent in legs and scrotum. Repeated obstruction of lymphatic drainage in these regions results in fibrosis and development of elephantiasis. Elephantiasis Elephantiasis is a disorder of lymphatic system, characterized by thickening of skin and extreme enlargement of the affected area, most commonly limbs (legs), genitals, certain areas of trunk and parts of head. 5- Edema due to Increased Endothelial Permeability The permeability of the capillary endothelium increases in conditions like burns, inflammation, trauma, allergic reactions and immunologic reactions, which lead to oozing out of fluid. This fluid accumulates leading to development of edema. Edema fluid in the potential spaces is called ―Effusion‖. Some examples of "potential spaces" are pleural cavity, pericardial cavity, peritoneal cavity, and synovial cavities, including both the joint cavities and the bursae. Virtually all these potential spaces have surfaces that almost touch each other, with only a thin layer of fluid in between, and the surfaces slide over each other. To facilitate the sliding, a viscous proteinaceous fluid lubricates the surfaces. When edema occurs in the subcutaneous tissue adjacent to the potential spaces, edema fluid usually collects in the potential space as well, and this fluid is called effusion fluid. The abdominal cavity is especially prone to collect effusion fluid, and in this instance, the effusion is called ascites. 4  Organization of the Cell A typical cell, as seen by the light microscope, is shown in figure below. Its two major parts are the nucleus and the cytoplasm. The nucleus is separated from the cytoplasm by a nuclear membrane, and the cytoplasm is separated from the surrounding fluids by a cell membrane, also called the plasma membrane.The different substances that make up the cell are collectively called protoplasm. Protoplasm is composed mainly of five basic substances: water, electrolytes, proteins, lipids, and carbohydrates. -Water. The principal fluid medium of the cell is water, which is present in most cells, except for fat cells, in a concentration of 70 to 85 %. Many cellular chemicals are dissolved in the water. Others are suspended in the water as solid particulates. Chemical reactions take place among the dissolved chemicals or at the surfaces of the suspended particles or membranes. -Ions. The most important ions in the cell are potassium, magnesium, phosphate, sulfate, bicarbonate, and smaller quantities of sodium, chloride, and calcium. The ions provide inorganic chemicals for cellular reactions. Also, they are necessary for operation of some of the cellular control mechanisms. For instance, ions acting at the cell membrane are required for transmission of electrochemical impulses in nerve and muscle fibers. -Proteins. After water, the most abundant substances in most cells are proteins, which normally constitute 10 to 20 per cent of the cell mass. These can be divided into two types: 1. Structural proteins. 2. Functional proteins. 5  Structural proteins are present in the cell mainly in the form of long filaments that themselves are polymers of many individual protein molecules. A prominent use of such intracellular filaments is to form microtubules that provide the “cytoskeletons” of such cellular organelles as cilia, nerve axons, the mitotic spindles of mitosing cells, and a tangled mass of thin filamentous tubules that hold the parts of the cytoplasm and nucleoplasm together in their respective compartments. Extracellularly, fibrillar proteins are found especially in the collagen and elastin fibers of connective tissue and in blood vessel walls, tendons, ligaments, and so forth. functional proteins are an entirely different type of protein, usually composed of combinations of a few molecules in tubular-globular form. These proteins are mainly the enzymes of the cell and, in contrast to the fibrillar proteins, are often mobile in the cell fluid. Also, many of them are adherent to membranous structures inside the cell. The enzymes come into direct contact with other substances in the cell fluid and thereby catalyze specific intracellular chemical reactions. For instance, the chemical reactions that split glucose into its component parts and then combine these with oxygen to form carbon dioxide and water while simultaneously providing energy for cellular function are all catalyzed by a series of protein enzymes. -Lipids. Lipids are several types of substances that are grouped together because of their common property of being soluble in fat solvents. Especially important lipids are phospholipids and cholesterol, which together constitute only about 2 percent of the total cell mass. The significance of phospholipids and cholesterol is that they are mainly insoluble in water and, therefore, are used to form the cell membrane and intracellular membrane barriers that separate the different cell compartments. In addition to phospholipids and cholesterol, some cells contain large quantities of triglycerides, also called neutral fat. In the fat cells, triglycerides often account for as much as 95 percent of the cell mass. The fat stored in these cells represents the body’s main storehouse of energy-giving nutrients that can later be dissoluted and used to provide energy wherever in the body it is needed. -Carbohydrates. Carbohydrates have little structural function in the cell except as parts of glycoprotein molecules, but they play a major role in nutrition of the cell. 6  Most human cells do not maintain large stores of carbohydrates; the amount usually averages about 1 per cent of their total mass but increases to as much as 3 per cent in muscle cells and, occasionally, 6 percent in liver cells. However, carbohydrate in the form of dissolved glucose is always present in the surrounding extracellular fluid so that it is readily available to the cell. Also, a small amount of carbohydrate is virtually always stored in the cells in the form of glycogen, which is an insoluble polymer of glucose that can be depolymerized and used rapidly to supply the cells’ energy needs. Physical Structure of the Cell The cell is not merely a bag of fluid, enzymes, and chemicals; it also containshighly organized physical structures, called intracellular organelles. The physicalnature of each organelle is as important as the cell’s chemical constituents for cell function. For instance, without one of the organelles, the mitochondria, more than 95 per cent of the cell’s energy release from nutrients would cease immediately.The most important organelles and other structures of the cell are shown in figure below Cell membrane. The cell membrane (also called the plasma membrane), which envelops the cell, is a thin, pliable, elastic structure only 7.5 to 10 nanometers thick. It is composed almost entirely of proteins and lipids. The approximate composition is proteins, 55 percent; phospholipids, 25 percent; cholesterol, 13 percent; other lipids, 4 percent; and carbohydrates, 3 percent. Lipid Barrier of the Cell Membrane :- Membranes contain three predominant types of lipid: phospholipids, cholesterol, and glycolipids. All are amphipathic in nature, meaning that they have a polar (hydrophilic) region and a nonpolar (hydrophobic) region. The polar region is referred to as the head group (hydrophilic). The( hydrophobic)or non polar region is usually composed of fatty acid ―tails‖ of variable length. When the membrane is assembled, the lipids naturally gather into a continuous bilayer as in the Figure. The polar head groups gather at the internal and external surfaces where the two layers interface with ICF and ECF, respectively. The hydrophobic tail groups dangle down from the head groups to form the fatty membrane core. Although the two halves of the bilayer are closely apposed, there is no significant lipid exchange between the two membrane leaflets. Cell Membrane Proteins:- There are two types of cell membrane proteins: integral proteins that protrude all the way through the membrane and peripheral proteins that are attached only to one surface of the membrane and do not penetrate all the way through. 7  Integral proteins:- 1-Many of the integral proteins provide structural channels (or pores) through which water molecules and water soluble substances, especially ions, can diffuse between the extracellular and intracellular fluids.These protein channels also have selective properties that allow preferential diffusion of some substances over others. 2-proteins act as carrier proteins for transporting substances that otherwise could not penetrate the lipid bilayer. 3-proteins can also serve as receptors for water-soluble chemicals, such as peptide hormones, that do not easily penetrate the cell membrane. Peripheral proteins:- often attached to the integral proteins These peripheral proteins function almost entirely as. 1-Enzymes. 2-controllers of transport of substances through the cell membrane "pores". The Membrane CarbohydratesThe Cell “Glycocalyx.” :- Membrane carbohydrates occur in combination with proteins or lipids in the form of glycoproteins or glycolipids. most of the integral proteins are glycoproteins, and about one tenth of the membrane lipid molecules are glycolipids. he “glyco” portions of these molecules almost invariably protrude to the outside of the cell, Thus, the entire outside surface of the cell often has a loose carbohydrate coat called the glycocalyx. It has several important functions : (1) Have a negative electrical charge, (2) The glycocalyx of some cells attaches to the glycocalyx of other cells. (3) Act as receptor substances for binding hormones. (4) Some carbohydrate types enter into immune reactions 8  Cytoplasm and Its organelles. The cytoplasm is filled with both minute and large dispersed particles and organelles. The clear fluid portion of the cytoplasm in which the particles are dispersed is called cytosol; this contains mainly dissolved proteins, electrolytes, and glucose. Dispersed in the cytoplasm are neutral fat globules, glycogen granules, ribosomes, secretory vesicles, and five especially important organelles: the endoplasmic reticulum, the Golgi apparatus, mitochondria, lysosomes, and peroxisomes. - Endoplasmic reticulum. Network of tubular and flat vesicular structures in the cytoplasm; this is the endoplasmic reticulum. The tubules and vesicles interconnect with one another. Also, their walls are constructed of lipid bilayer membranes that contain large amounts of proteins, similar to the cell membrane. The total surface area of this structure in some cells the liver cells, for instance can be as much as 30 to 40 times the cell membrane area. - Ribosomes and the granular endoplasmic reticulum. Attached to the outer surfaces of many parts of the endoplasmic reticulum are large numbers of minute granular particles called ribosomes. Where these are present, the reticulum is called the granular endoplasmic reticulum. The ribosomes are composed of a mixture of RNA and proteins, and they function to synthesize new protein molecules in the cell. - Agranular endoplasmic reticulum. Part of the endoplasmic reticulum has no attached ribosomes. This part is called the agranular, or smooth, endoplasmic reticulum. The agranular reticulum functions for the synthesis of lipid substances and for other processes of the cells promoted by intra reticular enzymes. - Golgi apparatus. The Golgi apparatus, shown in Figure below, is closely related to the endoplasmic reticulum. It has membranes similar to those of the agranular endoplasmic reticulum. It usually is composed of four or more stacked layers of thin, flat, enclosed vesicles lying near one side of the nucleus. This apparatus is prominent in secretory cells, where it is located on the side of the cell from which the secretory substances are extruded. The Golgi apparatus functions in association with the endoplasmic reticulum. As shown below, small “transport vesicles” (also called endoplasmic reticulum vesicles, or ER vesicles) continually pinch off from the endoplasmic reticulum and shortly thereafter fuse with the Golgi apparatus. In this way, substances entrapped in the ER vesicles are transported from the endoplasmic reticulum to the Golgi apparatus. The transported substances are then processed in the Golgi apparatus to form lysosomes, secretory vesicles, and other cytoplasmic components. 9  Lysosomes Lysosomes, shown in the figure above, are vesicular organelles that form by breaking off from the Golgi apparatus and then dispersing throughout the cytoplasm. The lysosomes provide `an intracellular digestive system that allows the cell to digest: (1) Damaged cellular structures. (2) Food particles that have been ingested by the cell. (3) Unwanted matter such as bacteria. The lysosome is quite different in different types of cells, but it is usually 250 to 750 nanometers in diameter. It is surrounded by a typical lipid bilayer membrane and is filled with large numbers of small granules which are protein aggregates of as many as 40 different hydrolase (digestive) enzymes. A hydrolytic enzyme is capable of splitting an organic compound into two or more parts by combining hydrogen from a water molecule with one part of the compound and combining the hydroxyl portion of the water molecule with the other part of the compound. For instance, protein is hydrolyzed to form amino acids, glycogen is hydrolyzed to form glucose, and lipids are hydrolyzed to form fatty acids and glycerol. Ordinarily, the membrane surrounding the lysosome prevents the enclosed hydrolytic enzymes from coming in contact with other substances in the cell and, therefore, prevents their digestive actions. However, some conditions of the cell break the membranes of some of the lysosomes, allowing release of the digestive enzymes. These enzymes then split the organic substances with which they come in contact into small, highly diffusible substances such as amino acids and glucose. - Peroxisomes Peroxisomes are similar physically to lysosomes, but they are different in two important ways. 1- they are believed to be formed by self-replication (or perhaps by budding off from the smooth endoplasmic reticulum) rather than from the Golgi apparatus. 2- they contain oxidases rather than hydrolases. Several of the oxidases are capable of combining oxygen with hydrogen ions derived from different intracellular chemicals to form hydrogen peroxide (H2O2). Hydrogen peroxide is a highly oxidizing substance and is used in association with catalase, another oxidase enzyme present in large quantities in peroxisomes, to oxidize many substances that might otherwise be poisonous to the cell. For instance, about half the alcohola person drinks is detoxified by the peroxisomes of 10 the liver cells in this manner.  - Secretory Vesicles One of the important functions of many cells is secretion of special chemical substances. Almost all such secretory substances are formed by the endoplasmic reticulum–Golgi apparatus system and are then released from the Golgi apparatus into the cytoplasm in the form of storage vesicles called secretory vesicles or secretory granules. Figure below shows typical secretory vesicles inside pancreatic acinar cells; these vesicles store protein proenzymes (enzymes that are not yet activated). The proenzymes are secreted later through the outer cell membrane into the pancreatic duct and thence into the duodenum, where they become activated and perform digestive functions on the food in the intestinal tract. Mitochondria The mitochondria, shown in figures below are called the “powerhouses” of the cell. Without them, cells would be unable to extract enough energy from the nutrients, and essentially all cellular functions would cease. Mitochondria are present in all areas of each cell’s cytoplasm, but the total number per cell varies from less than a hundred up to several thousand, depending on the amount of energy required by the cell. Further, the mitochondria are concentrated in those portions of the cell that are responsible for the major share of its energy metabolism. They are also variable in size and shape. Some are only a few hundred nanometers in diameter and globular in shape, whereas others are elongated as large as 1 micrometer in diameter and 7 micrometers long; still others are branching and filamentous. Mitochondria are self- replicative, which means that one mitochondrion can form a second one, a third one, and so on, whenever there is a need in the cell for increased amounts of ATP. Cell Cytoskeleton—Filament and Tubular Structures:- The fibrillar proteins of the cell are usually organized into filaments or tubules. These originate as precursor protein molecules synthesized by ribosomes in the cytoplasm. The precursor molecules then polymerize to form filaments. General Cell Structure & Function:- Component Structure Function Nucleus: control center of the cell - Nuclear envelope Double-layered membrane that Supports nucleus & controls passage of surrounds nucleus, composed of materials b/w nucleus & cytoplasm protein & lipid molecules -Nucleolus Dense nonmembranous mass Produces ribosomal RNA for ribosomes composed of protein & RNA molecules Contains genetic code that determines -Chromati Fibrous strands composed of protein which proteins (including enzymes) will & DNA be manufactured by the cell 11  Plasma (cell) Membrane composed of double layer Surrounds, holds cell together & gives its membrane of phospholipids in which proteins are form; controls passage of materials into & embedded out of cell Cytoplasm Fluid, jellylike substance b/w cell Serves as matrix substance in which membrane & nucleus in which chemical reactions occur. organelles are suspended Endoplasmic System of interconnected membrane- Agranular (smooth) ER metabolizes reticulum forming canals & tubules nonpolar compounds & stores Ca2+ in striated muscle cells; granular (rough) ER assists in protein sysnthesis Ribosomes Granular particles composed of Synthesize proteins protein & RNA Golgi complex Cluster of flattened membranous sacs Synthesizes carbohydrates & packages molecules for secretion. Secretes lipids & glycoproteins Lysosomes Membranous sacs Digest foreign molecules & damaged organelles Peroxisomes Spherical membranous vesicles Contain enzymes that detoxify harmful molecules & break down hydrogen peroxide Mitochondria Membranous sacs with folded inner Release energy from food molecules & partitions transform energy into usable ATP Centrosome Nonmembranous mass of 2 rodlike Helps to organize spindle fibers & centrioles distribute chromosomes during mitosis Vacuoles Membranous sacs Store & release various substances within the cytoplasm Microfilaments & Thin, hollow tubes Support cytoplasm & function as microtubules cytoskeleton, transport materials within the cytoplasm Cilia & flagella Minute cytoplasmic projections that Move particles along cell surface, or move extend from the cell surface the cell 12