1st Year Physiology Midterm PDF

-------------------------------------------------------------------------------------------------1st year.Physiology systems is the regulation of blood sugar (glucose). Blood glucose levels are normally maintained at about 90 mg/dL and supply all of our cells with energy. If glucose levels fall very...

-------------------------------------------------------------------------------------------------1st year.Physiology systems is the regulation of blood sugar (glucose). Blood glucose levels are normally maintained at about 90 mg/dL and supply all of our cells with energy. If glucose levels fall very much below this level, the hormone glucagon is released from the pancreas, stimulating the release of glucose from glycogen stores in the liver. Before glucose can be utilized by the cells, the hormone insulin must be secreted from the pancreas to stimulate glucose uptake by the cells. In addition, as blood is filtered in the kidney, the kidney tubules must efficiently reabsorb glucose so that it is not lost in the urine. As this example illustrates, simply maintaining the concentration of a single solute in the blood requires the coordinate function of the digestive system (liver), endocrine system (insulin and glucagon in the pancreas), cardiovascular system (blood), and the urinary system (kidneys). Homeostasis: As the above example illustrates, many of the parameters in our bodies are maintained within fairly narrow limits, through a process of homeostasis. Homeostasis is a dynamic constancy or equilibrium of the parameters of our bodies. The parameters include factors such as blood glucose concentrations, blood pH, body temperature, and blood ion concentrations 2 -------------------------------------------------------------------------------------------------1st year.Physiology NUTRITION What Is Nutrition? As we expect, food = energy. But nutrition not just a food source, it is a way of prevention of disease. So food is taken for metabolic function, energy, and to reduce the risk of disease. Foods not only have energy but nutrients. It is divided into; a. Macronutrients =Nutritional calories derived from carbohydrates, fats, and proteins b. Micronutrients = Substances responsible for proper metabolism of the macronutrients, as they activate the enzymes necessary to metabolize the macronutrients (vitamins & minerals). I. Nutrients Components: Carbohydrates: These are compounds that consist of carbon, hydrogen, and oxygen. Their primary function in the body is to supply energy. When a person ingests more carbohydrates than his or her body needs at the moment, the body converts the excess into a compound known as glycogen. It then stores the glycogen in the liver and muscle tissues, where it remains, a potential source of energy for the body to use in the future, though if it is not used soon, it may be stored as fat. The carbohydrate group comprises sugars, starches, cellulose. Lipids: In the body, lipids supply energy much as carbohydrates do. Lipids also protect the organs from shock and damage and provide the body with insulation from cold, and other threats. 3 -------------------------------------------------------------------------------------------------1st year.Physiology Proteins: Proteins are large molecules built from long chains of amino acids, which are organic compounds made of carbon, hydrogen, oxygen, nitrogen, and (in some cases) sulphur-bonded in characteristic formations. Proteins serve the functions of promoting normal growth, repairing damaged tissue and making enzymes. (An enzyme is a protein material that speeds up chemical reactions in the bodies of plants and animals). Vitamins: These are organic molecules required in the diet in small quantities (0.01 to 100 mg/day). Vitamins work together with enzymes and release energy from digested food and regulate the billions of chemical activities that occur in the body every minute of every day. They are classified as either, water-soluble (B- complex and C), meaning that they dissolve easily in water, or fat-soluble (A, D, E and K), which are carried through the body by fat, absorbed through the intestinal tract with the help of lipids and stored in fat tissue. Getting too much can be harmful. In general, water-soluble vitamins are readily excreted from the body. Vitamins generally are compounds that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation, immune system, helps maintain healthy teeth and gums. It helps the body to absorb iron & calcium, for proper neuronal formation, as an antioxidant, acts as antisterile agent, prevent bleeding and other proper healthy functioning. Minerals: Minerals are often divided into major and minor categories depending on the amount required. The major minerals follow with an example of their uses:  Sodium: most common extracellular cation.  Potassium: most common intracellular cation. 4 -------------------------------------------------------------------------------------------------1st year.Physiology  Calcium: required by enzyme systems, second messenger, synaptic transmission, muscle contraction, bone formation.  Phosphorus: part of DNA, often part of energy molecules such as ATP  Magnesium: required by many enzyme systems, muscle & nerve relaxation. Minor minerals include the following:  Manganese: required by enzyme systems.  Iron: in heme group, cytochrome oxidases.  Iodine: required only to make hormones, thyroxin and triiodothyronine  Cobalt: found only in vitamin B12, cyanocobalamin.  Copper, Zinc & Selenium: used by some enzyme systems and prevent oxidation. 5 -------------------------------------------------------------------------------------------------1st year.Physiology FOOD ASSIMILATION Digestion & Absorption The digestive system performs its specialized function of digestion which is the process of breaking down food into simpler parts so that it can be absorbed and used within the body then packaging the residue for waste disposal. Digestion involves mechanical and chemical processes. An enzyme is a protein that speeds up a chemical reaction; digestive enzymes speed up the breakdown of food. The structure and function of the digestive system: Mouth: The mouth is the beginning of the digestive tract; and, in fact, digestion starts here when taking the first bite of food. Chewing breaks the food into pieces that are more easily digested. Chemical digestion also starts in the mouth when saliva mixes with food – saliva contains an enzyme called “amylase” that starts breaking down carbohydrates into a form that a body can absorb and use. Oesophagus: Located in the throat near the trachea, the oesophagus receives food from the mouth when it is swallowed. By means of a series of muscular contractions called peristaltic waves. By the oesophagus a ball of food, called a “bolus,” is delivered to the stomach. Stomach: The stomach is a hollow organ, or "container," that performs both mechanical and chemical digestion. It holds food while it is being mixed with enzymes that continue the process of breaking down food into a usable form. Cells in the lining of the stomach secrete strong acid and powerful enzyme called “pepsin” that starts breaking down protein. Once food has been digested 6 -------------------------------------------------------------------------------------------------1st year.Physiology in the stomach, it passes on to the small intestine as a thick liquid called “chyme.” Small intestine: Made up of three segments, the duodenum, jejunum and ileum. The small intestine is a 22-foot long muscular tube that breaks down food using enzymes released by the pancreas and bile from the liver. Peristalsis also is at work in this organ, moving food through and mixing it with digestive secretions from the pancreas and liver. Several kinds of chemical digestion occur in the small intestine by digestive enzymes including “lipase,” which helps digest fat by breaking the bonds between glycerol and the fatty acids, another amylase to break down starches into sugar, and two protein digesting enzymes called, trypsin and chymotrypsin. The liver makes “bile” which increases the pH and helps the digestion and absorption of fats by converting them into emulsion to be easily digested. The small intestine itself has digestive enzymes on its surface that help break down proteins and carbohydrates. The small intestine does most of the absorbing of adequately digested food. Because absorption requires particles to come in contact with the surface of the intestine, the small intestine has finger-like projections called “villi” (on the individual cells are called microvilli) that increase its surface area. The duodenum is largely responsible for the continuous breaking-down process, with the jejunum and ileum mainly responsible for absorption of nutrients into the bloodstream. Contents of the small intestine start out semi-solid, and end in a liquid form. Water, bile, enzymes, and mucous contribute to the change in consistency. What is not absorbed in the small intestine passes onto the large intestine, where water is reabsorbed. The remainder is stored in the rectum until a bowel movement. 7 -------------------------------------------------------------------------------------------------1st year.Physiology Pancreas: The pancreas secretes digestive enzymes into the duodenum (the pancreatic juice). These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolizing sugar. Liver: The liver has multiple functions, but its main function within the digestive system is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. In addition, the liver is the body’s chemical "factory." It takes the raw materials absorbed by the intestine and makes all the various chemicals the body needs to function. The liver also detoxifies potentially harmful chemicals. It breaks down and secretes many drugs. Gallbladder: The gallbladder stores and concentrates bile, and then releases it into the duodenum to help absorb and digest fats. Colon (large intestine): The colon is a 6-foot long muscular tube that connects the small intestine to the rectum. The large intestine is made up of the ascending (right) colon, the transverse (across) colon, the descending (left) colon, and the sigmoid colon, which connects to the rectum. The large intestine is a highly specialized organ that is responsible for processing waste so that emptying the bowels is easy and convenient. Rectum: The rectum (Latin for "straight") is an 8-inch chamber that connects the colon to the anus. Absorption: It is the passage of substances through the intestinal mucosa into the blood or lymph. Amino acids and glucose get into the bloodstream. Lipids go into the lymphatic system. Water can pass by simple diffusion. Other molecules require more complex transport systems. For example, glucose is a relatively large molecule. Glucose passes by secondary active transport (by carrier & with energy) from the intestinal lumen into the bloodstream. Glucose 8 -------------------------------------------------------------------------------------------------1st year.Physiology binds to Na which is being pumped. Amino acids are thought to be transported in the same way. Fatty acids and monoglycerides are transported with the aid of bile salts. These form minute droplets called micelles which pass through the epithelial wall by diffusion, once inside, fatty acids reunite with triglycerides to form another type of micelle called a chylomicron. These are water-soluble and are taken up by the lymph. Regulation of Digestion: Mechanical and chemical activators are regulated somehow at the appropriate time when food is in the stomach through three phases: a. Cephalic phase (stimulatory): Regulating gastric secretions and motility. The thought of food causes an increase in secretions (HCl and pepsinogen) and increases motility, mediated by the vagus nerves (parasympathetic innervations) to the stomach and causes an increase in secretions and an increase in motility. b. Gastric phase (stimulatory): The stretching of the stomach by swallowing and putting food into the stomach causes an increase in motility and an increase in secretions. c. Intestinal phase (Inhibitory): The presence of food and acid chyme stuff comes out of the stomach causes the enterogastric reflex which decreases gastric motility because a lot of food in the small intestines means more food doesn’t need to be dumped into the small intestines because digestion couldn’t be completed. Hormonal control of Digestion: Gastrin: Polypeptides or alcohol in the pyloric stomach stimulate its release. Gastrin, in turn, stimulates hydrochloric acid secretion from oxyntic cells. A pH below 2 in the stomach will stop the process. 9 -------------------------------------------------------------------------------------------------1st year.Physiology Secretin: Acid in the duodenum stimulates its release from the intestinal mucosa. Secretin causes HCO3- secretion and synthesis of bile in the liver. It also inhibits gastric motility slowing emptying of the stomach. Cholecystokinin (CCK): Fats in the duodenum stimulate its release from the intestinal mucosa. It causes the release of pancreatic enzymes and contraction of the gall bladder. Gastric Inhibitory Polypeptide (GIP): Monosaccharides and fats in the duodenum stimulate its release from the intestinal mucosa. GIP inhibits gastric secretions and motility. Metabolism Metabolism is the array of chemical reactions occurring in the cell and helps maintain homeostasis in a changing environment. End products of metabolism are ATP, H2O, and CO2. It consists of anabolism: biosynthetic reactions and catabolism: decomposition reactions. I- Glucose Metabolism Glucose is a key metabolite in human metabolism, and we will study an overview on the several pathways that are concerned with the utilization, storage, and regeneration of glucose. I-Fates of dietary glucose: Glucose in the body undergoes one of three metabolic fates:  it is catabolised to produce ATP: This occurs in all peripheral tissues, particularly in brain, muscle and kidney.  it is stored as glycogen: This storage occurs in liver and muscle.  it is converted to fatty acids: Once converted to fatty acids, these are stored in adipose tissue as triglycerides. 10 -------------------------------------------------------------------------------------------------1st year.Physiology Glycolysis: Glucose will be oxidised by all tissues to synthesise ATP. The first pathway which begins the complete oxidation of glucose is called glycolysis. This pathway cleaves the six carbon glucose molecule (C6H12O6) into two molecules of the three carbon compound pyruvate (C3H3O3-). This oxidation is coupled to the net production of two molecules of ATP/glucose molecule. One oxidation reaction occurs in the latter part of the pathway. It uses NAD as the electron acceptor. This cofactor is present only in limited amounts and once reduced to NADH, as in this reaction, it must be re-oxidised to NAD to permit continuation of the pathway. This re-oxidation occurs by one of two methods: Aerobic metabolism of glucose: Pyruvate is transported inside mitochondria and oxidised to a compound called acetyl coenzyme A (CoA). This is an oxidation reaction and uses NAD as 11 -------------------------------------------------------------------------------------------------1st year.Physiology an electron acceptor. By a further series of reactions collectively called the citric acid cycle (Kreb’s cycle or TCA), acetyl co-enzyme A is oxidised ultimately to CO2. These reactions are coupled to a process known as the electron transport chain which has the role of harnessing chemical bond energy from a series of oxidation/reduction reactions to the synthesis of ATP and simultaneously re- oxidising NADH to NAD. Anaerobic glycolysis: Pyruvate is reduced to a compound called lactate. This single reaction occurs in the absence of oxygen (anaerobically) and is ideally suited to utilisation in heavily exercising muscle where oxygen supply is often insufficient to meet the demands of aerobic metabolism. The reduction of pyruvate to lactate is coupled to the oxidation of NADH to NAD. Accumulation of lactate (actually lactic acid) also causes a reduction in intracellular pH. The lactate formed is removed to other tissues and dealt with by one of two mechanisms: 1- it is converted back to pyruvate which is then proceeds to be further oxidised by the second mechanism described above, finally producing a large amount of ATP. 2- it is converted back to glucose in the liver, in a process called gluconeogenesis. Gluconeogenesis: It the conversion of lactate to glucose, uses some of the reactions of glycolysis (but in the reverse direction) and some reactions unique to this pathway to re-synthesise glucose (from fatty acids & amino acids). This pathway requires an energy input (as ATP) but has the role of maintaining a circulating glucose concentration in the bloodstream (even in the absence of dietary supply) and also maintaining a glucose supply to fast twitch muscle fibres. 12 -------------------------------------------------------------------------------------------------1st year.Physiology Glycogenolysis (glycogen breakdown): Glycogen is a highly branched polymer of glucose. It is stored as aggregates of glycogen molecules within cells with up to 70% of the aggregate being water. The energy yield from the hydrolysis of stored glycogen and the subsequent oxidation of the released glucose is the same in muscle and liver. When glycogen is hydrolysed, the product is glucose 1-phosphate. This is easily converted to glucose 6-phosphate (these are molecules with the phosphate group attached to different carbon atoms on the glucose). Glucose 6-phosphate is the first product in the glycolysis pathway and its formation from glucose requires the expenditure of 1 ATP molecule/glucose. As glucose 6-phosphate is formed directly from glycogen hydrolysis, glucose that is derived from glycogen and enters the glycolysis pathway (rather than starting as monomeric glucose) yields a net production of 3 ATP/glucose rather than just 2 ATP, so there is a 50% increase. Role of glucose 6-phosphatase Muscle and liver have different metabolic needs. Liver supplies other organs with glucose so must be able to export glucose released from glycogen hydrolysis. Muscle is a major consumer of glucose and thus does not export glucose. Glucose 6-phosphate formed as described in the previous section is highly polar and cannot cross the cell's cytoplasmic membrane. To leave the cell it must be converted to glucose. This reaction is catalysed by an enzyme, glucose 6- phosphatase. glucose 6-phosphate glucose + phosphate glucose 6-phosphatase Liver possesses this enzyme, so glucose released from liver glycogen can be exported to other tissues. It is very important to be aware that muscle does 13 -------------------------------------------------------------------------------------------------1st year.Physiology not possess glucose 6-phosphatase so it does not export glucose released from its glycogen stores, but rather uses it as a fuel to power muscle contraction. II-Lipid metabolism Lipolysis is carried out by lipases. Once freed from glycerol, free fatty acids can enter blood and muscle fiber by diffusion. Beta (β) oxidation splits long carbon chains of the fatty acid into Acetyl CoA, which can eventually enter the citric acid cycle. With each one Acetyl CoA, one FADH2 & one NADH are formed, this cycle repeats until the FFA has been completely reduced to Acetyl- CoA. Fatty acids must be activated before they can be carried into the mitochondria, where fatty acid oxidation occurs. This process occurs in two steps catalyzed by the enzyme fatty acyl-CoA synthetase. Once activated, the acyl CoA is transported into the mitochondrial matrix. Fatty acids, stored as triglycerides in an organism, are an important source of energy because they are both reduced and anhydrous. The energy yield from a gram of fatty acids is approximately 9 kcal (39 kJ), compared to 4 kcal/g (17 kJ/g) for proteins and carbohydrates. The breakdown of fat stored in fat cells is known as lipolysis (Release from adipose tissue). During this process, free fatty acids are released into the bloodstream and circulate throughout the body. Ketones are produced, and are found in large quantities in ketosis (an adaptive metabolic state that occurs when insufficient carbohydrates are present in the diet). The glycerol also enters the bloodstream and is absorbed by the liver or kidney where it is converted to glycerol 3-phosphate. Hepatic glycerol 3- phosphate is mostly converted into Dihydroxyacetone phosphate (DHAP) and then glyceraldehyde 3-phosphate (G3P) to rejoin the glycolysis and gluconeogenesis pathway. 14 -------------------------------------------------------------------------------------------------1st year.Physiology III-Protein metabolism Uses of amino acids: Amino acids are used in three ways in the body:  Protein synthesis: The synthesis of new proteins is very important during growth. In adults new protein synthesis is directed towards replacement of proteins as they are constantly turned over.  Synthesis of a variety of other compounds: e. g. purines and pyrimidines (components of nucleotides), catecholamines (adrenaline and noradrenalin), neurotransmitters (serotonin), histamine, porphyrins (the central oxygen binding component of haemoglobin)  As a biological fuel: About 10% of energy production in humans is from amino acids. The percentage is much higher in carnivores, whose diet is almost entirely protein. Amino acid catabolism The other biological fuels discussed (carbohydrates & fats) contain only the elements carbon, hydrogen and oxygen. Amino acids contain nitrogen as well. The first step in amino acid catabolism is the removal of the nitrogen (the amino group). Deamination: The removal of the amino groups of all twenty amino acids begins with the transfer of amino groups to just one amino acid - glutamic acid (or glutamate ion). This is catalysed by transaminase enzymes which transfer the amino group from amino acids to a compound called alpha-ketoglutarate. The product is an alpha-keto acid formed from the amino acid and glutamate (formed from the addition of the amino group to alpha-ketoglutarate. 15 -------------------------------------------------------------------------------------------------1st year.Physiology Once the amino groups have all been "collected" in the form of the one amino acid, glutamate, this amino acid has its amino group removed, this reaction reforms alpha-ketoglutarate with the other product being ammonia (NH4+). Ammonia and urea: Ammonia is toxic to the nervous system and its accumulation rapidly causes death. Therefore, it must be detoxified to a form which can be readily removed from the body. Ammonia is converted by urea (ornithine) cycle in the liver to urea, which is water soluble and is readily excreted via the kidneys in urine. Amino acid carbon skeletons: The remainder of the amino acid after deamination is referred to as the "carbon skeleton". Depending on the amino acid being catabolised, it will be converted to;  acetyl CoA: Those carbon skeletons which end up as acetyl CoA are committed to energy production. They will either be immediately oxidised via the citric acid cycle or they may be converted to ketone bodies. Because the amino acids whose carbon skeletons yield acetyl CoA are potentially a source of ketone bodies, they are referred to as ketogenic amino acids. 16 -------------------------------------------------------------------------------------------------1st year.Physiology  or pyruvate, or a citric acid cycle intermediate: Those carbon skeletons which end up as either pyruvate or a citric acid cycle intermediate may be used for energy production or they may be used to synthesis glucose by the pathway known as gluconeogenesis. Because the amino acids whose carbon skeletons yield pyruvate or a citric acid cycle intermediate are potentially a source of glucose, they are referred to as glucogenic amino acids. Catabolism summary Amino acid synthesis Amino acids are divided into two classes depending on whether they can be synthesised in the human body or whether they must be supplied in the diet. The former group is referred to as non-essential and the latter group as essential. Non-essential amino acids are synthesised from the products of their catabolism. The essential amino acids are synthesised in micro-organisms (bacteria and yeasts) and passed through the food chain until reaching us in diet. 17 -------------------------------------------------------------------------------------------------1st year.Physiology CIRCULATORY SYSTEM The circulatory system includes cardiovascular system and lymph system. The cardiovascular system consists of blood, a heart, and blood vessels (arteries, arterioles, blood capillaries, venules and veins). Functions of the Circulatory System The circulatory system functions with other body systems to provide the following (Figure 1): 1) Transport of materials: Gasses transport: Oxygen is transported from the lungs to the cells. CO2 (a waste) is transported from the cells to the lungs. Transport other nutrients to cells - For example, glucose, a simple sugar used to produce ATP, is transported throughout the body by the circulatory system. Immediately after digestion, glucose is transported to the liver. The liver maintains a constant level of glucose in the blood. Transport other wastes from cells - For example, ammonia is produced as a result of protein digestion. It is transported to the liver where it is converted to less toxic urea. Urea is then transported to the kidneys for excretion in the urine. Transport hormones - Numerous hormones that help maintain constant internal conditions are transported by the circulatory system. 2) It contains cells that fight infection (immunity) 3) Helps stabilize the pH and ionic concentration of the body fluids. 4) It helps maintain body temperature by transporting heat. This is particularly important in homeothermic animals such as birds and mammals. Figure 1: Functions of circulatory system 20 -------------------------------------------------------------------------------------------------1st year.Physiology Types of Circulatory System Animals may have: No circulatory system (Protozoa, Parazoa, Coelenterata, Platyhelminthes). Open circulatory system (Arthropoda and Mollusca). Closed circulatory system (Annelida, Echinodermata and Chordata). Open and close Circulatory System In an opened circulatory system, blood is pumped from the heart through blood vessels but then it leaves the blood vessels and enters body cavities, where the organs are bathed in blood, or sinuses (spaces) within the organs. Blood flows slowly in an open circulatory system because there is no blood pressure after the blood leaves the blood vessels. The animal must move its muscles to move the blood within the spaces. In a closed system, blood remains within blood vessels, pressure is high, and blood is therefore pumped faster. Evolution of Vertebrate Circulatory System (from amphibians to mammalians) Circulatory System of Amphibians Amphibians have a 5-chambered heart with two atria, one ventricle, sinus venosus and truncus arteriosus Venous system The deoxygenated blood is collected from all regions of the body and is poured into sinus venosus by three main veins right anterior vena cava, left anterior vena cava and posterior vena cava. The anterior vena cava, on each side, collects blood from three veins external jugular, innominate and subclavian veins. The sinus venosus opens into right atrium while blood from the lungs 21 -------------------------------------------------------------------------------------------------1st year.Physiology (pulmonary flow) goes to the left atrium through pulmonary vein. Blood from the body (systemic flow) goes to the right atrium. Both left atrium (which receive oxygenated blood from pulmonary veins) and right atrium (which receives deoxygenated blood from the three vena cava via sinus venosus) empty into the ventricle where mixing between oxygenated blood and deoxygenated blood occurs (to give mixed blood). In addition to the previously described venous system proper, there is a venous portal system which includes hepatic portal and renal portal systems. In the hepatic portal circulation, the blood from the mesentery of small intestine is collected by hepatic portal vein that enters into liver. The blood comes out from liver by hepatic vein which joins the posterior vena cava. Thus, the blood enters liver by two pathways through hepatic artery and hepatic portal vein and goes out from liver through single pathway, hepatic vein. Similarly, the blood enters kidneys through two pathways (renal portal veins and renal arteries) while it goes out from kidney by single pathway (renal veins) that joins posterior vena cava. Arterial system The mixed blood is pumped from the ventricle to truncus arteriosus that have 3 arches on each side; these are carotid, systemic and pulmocutaneous arches. The pulmonary artery is branched from pulmocutaneous arch and transport mixed blood to the lung for gas exchange (as part of pulmonary circulation). The rest of mixed blood in the three arches is pumped to all regions of the body (systemic circulation) for exchange of gases between organ cells and mixed blood in blood capillaries. As a result, the mixed blood is transformed into deoxygenated blood collected into veins. Circulatory System of Some Reptiles In reptiles except crocodiles, the ventricle is partially divided. This reduces mixing of oxygenated and unoxygenated blood in the ventricle. The circulatory 22 -------------------------------------------------------------------------------------------------1st year.Physiology system is more developed in reptiles than amphibians. The reptiles have reduced sinus venosus and have not truncus arteriosus. Circulatory System of Crocodilians, Birds, and Mammals Birds and mammals (also crocodilians) have a four-chambered heart which acts as two separate pumps. There are no sinus venosus or truncus arteriosus. After passing through the body, blood is pumped under high pressure to the lungs. Upon returning from the lungs, it is pumped under high pressure to the body. The high rate of oxygen-rich blood flow through the body enables birds and mammals to maintain high activity levels. Circulatory system in human Types of circulations within the body of human (Figure 2) Three types of blood circulation are found in the human body 1- Systemic circulation [left ventricle → aorta → all parts of the bodies through different arteries → arterioles (oxygenated blood) → blood capillaries in organs → venules deoxygenated blood) → veins → superior and inferior vena cavae → right atrium]. 2- Pulmonary circulation [right ventricle → pulmonary arteries (deoxygenated blood) → lungs → pulmonary veins (oxygenated blood) →left atrium]. 3- Hepatic portal circulation [hepatic portal vein collects blood from the region of small intestine → liver → hepatic vein that opens inferior vena cava] 4- Coronary circulation [right and left coronary arteries from aorta → smaller branches into cardiac wall → arterioles → capillaries → venules → veins (right great, left small and middle cardiac veins) → coronary sinus that opens into right atrium]. They have a very small diameter and may become blocked, producing a heart attack. 23 -------------------------------------------------------------------------------------------------1st year.Physiology 5- There is no renal portal circulation in mammals. Figure 2: Heart of human beings Blood Vessels heart → arteries → arterioles → capillaries → venules → veins → heart Differences between arteries and veins Arteries carry blood away from the heart while veins carry blood towards the heart. Arteries carry oxygenated blood except for pulmonary arteries while veins carry deoxygenated blood except for pulmonary veins. The arteries walls are thicker and more elastic than veins as the blood pressure is higher in arteries than veins. The wall of arteries stretches and recoils in response to pumping, thus peaks in pressure are absorbed and there is pulsation in arteries but not in veins. The elastic layer of artery is surrounded by circular muscle to control the diameter and thus the rate of blood flow. The blood pressure in the veins is low 24 -------------------------------------------------------------------------------------------------1st year.Physiology so valves in veins help prevent backflow. The arteries maintain pressure in the circulatory system much like a balloon maintains pressure on the air within it. The arteries therefore act as pressure reservoirs by maintaining (storing) pressure. The contraction of skeletal muscle during normal body movements squeezes the veins and assists with moving blood back to the heart. The vena cava returns blood to the right atrium of the heart from the body. In the right atrium, the blood pressure is close to 0. Veins act as blood reservoirs because they contain 50% to 60% of the blood volume. Smooth muscle in the walls of veins can expand or contract to adjust the flow volume returning to the heart and make more blood available when needed. Valves Valves allow blood to flow through in one direction but not the other. They prevent backflow. Atrioventricular valves are located between the atria and the ventricles. They are held in place by fibers called chordae tendinae. The left atrioventricular valve is often called the bicuspid or mitral valve; the right one is also called the tricuspid valve. The semilunar valves are between the ventricles and the attached aorta (aortic valve) and pulmonary artery (pulmonary valve). The heartbeat sound is produced by the valves closing. Cardiac cycle As the atria relax and fill, the ventricles are also relaxed. When the atria contract, the pressure forces the atrioventricular valves to open and blood in the atria is pumped into the ventricles. The ventricles then contract, forcing the atrioventricular valves closed. The pulmonary artery carries blood from the right ventricle to the lungs. The aorta carries blood from the left ventricle to the 25 -------------------------------------------------------------------------------------------------1st year.Physiology body. Cardiac cycle consists of periods of systole (0.4 seconds) and diastole (0.4 seconds). The systole includes atrial systole (0.1 seconds) and ventricular systole (0.3 seconds). Heart Sounds Heart Sounds are clearly heard by stethoscope which magnifies heart sounds. Two sounds are heard. Lubb is louder and is due to closure of atrioventricular valves during the contractions of two ventricles. Dup is softer and is due to closure of pulmonary and aortic valves during the relaxations of the two ventricles. Lubbdup are heard 74 times / minutes during normal resting state. Conducting system of the heart The heart does not require outside stimulation. The sinuatrial (SA) node is a bit of nervous tissue that serves as the cardiac pacemaker. Stimulation from this node causes both of the atria to contract at the same time because the muscle tissue conducts the stimulation rapidly. The contraction doesn't spread to the ventricles because the atria and ventricles are separated by connective tissue. As a wave of stimulation (depolarization) spreads across the atria resulting in their contraction, another bit of nervous tissue called the atrioventricular (AV) node also becomes stimulated (depolarized). It conducts the action potential slowly to the ventricles. The slow speed is due to the small diameter of the neurons within the node. The slow speed of conduction within the AV node ensures that the ventricles contract after the atria contract. The bundle of His then transmits impulse rapidly from the AV node to the ventricles. When cardiac impulses reach the network of Purkinje fibres at the apex of the two ventricles, a contraction wave begins to move from the apex toward the atrioventricular valves (Figure 3). 26 -------------------------------------------------------------------------------------------------1st year.Physiology Conducting system of the heart Figure 3: Conducting system of the heart Nervous control of heart beating rate - Sympathetic N. S. causes tachycardia - Parasympathetic N. S. causes bradycardia Blood Pressure As the blood is pumped in aorta and its branches, it produces pressure on the wall of arteries. The units of measurement are millimeters of mercury (mm Hg). For example, 120 mm Hg/80 mm Hg is considered to be normal blood pressure. The top number is referred to as the systolic pressure; the bottom number is the diastolic pressure. 27 -------------------------------------------------------------------------------------------------1st year.Physiology Electrocadiogram (ECG): Electrical changes are recorded on the screen of oscilloscope. Wave P is due to electrical changes in heart during contraction of the two atria. Wave QRS coincides with the electrical changes during the contraction of the two ventricles. Wave T coincides with the electrical changes during the relaxation of the two ventricles (Figure 4). Figure 4: ECG Lymph System Lymph flows from small lymph capillaries into lymph vessels that are similar to veins in having valves that prevent backflow. Lymph vessels connect to lymph nodes, lymph organs, or to the cardiovascular system at the thoracic duct and right lymphatic duct. 28 -------------------------------------------------------------------------------------------------1st year.Physiology RESPIRATION AND RESPIRATORY SYSTEM Respiration aims to provide cells of organism with oxygen used in oxidation of glucose and fatty acids to produce energy and to get ride of carbon dioxide produced from these processes. Different ways of respiration in animal kingdom In animal kingdom the respiration can be performed by different ways which are: 1- Direct exchange of gases between cells of the animal and environment. This way is found in Phyla: protozoa, porifera (sponges), coelentrata and platyhelminthes. 2- Direct exchange of gases between blood in peripheral blood vessels and environment. This way is found in phylum: annelida. 3- Respiration through spiracles leading to tracheas that are branched within the body into tracheoles as in arthropods like insects. These spiracles are covered with tracheal gills in nymph of mayfly as it lives in water. The respiration takes place though siphon at the end of the abdomin in the larvae of mosquitoes. 4- Exchange of gases through gills viz in fish. Exchange of gases take place between water currents and blood capillaries within the gills. 5- Exchange of gases through lungs viz in land vertebrates. Exchange of gases take place between air and blood capillaries within the lungs. 30 -------------------------------------------------------------------------------------------------1st year.Physiology Direct exchange of gases between cells of the Direct exchange of gases between blood in animal and environment peripheral blood vessels and environment Spiracles leading to trachea Siphon and tracheal tube in larvae of mosquitoes Exchange of gases through gills Exchange of gases through lungs 31 Figure 1: Gas Exchange Systems -------------------------------------------------------------------------------------------------1st year.Physiology Types of respiration (Figure 2) - External respiration: It is exchange of gases between the lungs and blood. - Internal respiration: It is exchange of gases between the body cells and blood. - Cellular respiration: the use of oxygen by the body cells in oxidation of food stuffs to produce energy. Lungs Organs Figure 2: Types of respiration Structure of the respiratory system (Figure 3): The Nose - Usually air will enter the respiratory system through the nostrils. The nostrils then lead to open spaces in the nose called the nasal passages. The nasal passages serve as a moistener, a filter, and to warm up the air before it reaches the lungs. The hairs existing within the nostrils prevents various foreign 32 -------------------------------------------------------------------------------------------------1st year.Physiology particles from entering. Different air passageways and the nasal passages are covered with a mucous membrane. Many of the cells which produce the cells that make up the membrane contain cilia. Others secrete a type a sticky fluid called mucus. The mucus and cilia collect dust, bacteria, and other particles in the air. The mucus also helps in moistening the air. Under the mucous membrane there are a large number of capillaries. The blood within these capillaries helps to warm the air as it passes through the nose. The nose serves three purposes. It warms, filters, and moistens the air before it reaches the lungs. You will obviously lose these special advantages if you breath through your mouth. Pharynx and Larynx - Air travels from the nasal passages to the pharynx, or more commonly known as the throat. When the air leaves the pharynx it passes into the larynx, or the voice box. The voice box is constructed mainly of crtilage, which is a flexible connective tissue. The vocal chords are two pairs of membranes that are stretched across the inside of the larynx. As the air is exspired, the vocal chords vibrate. Humans can control the vibrations of the vocal chords, which enables us to make sounds. Food and liquids are blocked from entering the opening of the larynx by the epiglottis to prvent people from choking during swallowing. Trachea - The larynx goes directly into the trachea or the windpipe. The trachea is a tube approximately 12 centimeters in length and 2.5 centimeters wide. The trachea is kept open by rings of cartilage within its walls. Similar to the nasal passages, the trachea is covered with a ciliated mucous membrane. Usually the cilia move mucus and trapped foreign matter to the pharynx. After that, they leave the air passages and are normally swallowed or removed by sneezing and coughing. The respiratory system cannot deal with tabacco smoke very keenly. Smoking stops the cilia from moving. Just one cigarette slows their motion for about 20 minutes. The tabacco smoke increases the amount of 33 -------------------------------------------------------------------------------------------------1st year.Physiology mucus in the air passages. When smokers cough, their body is attempting to dispose of the extra mucus (Figure 4). Bronchi - Around the center of the chest, the trachea divides into two cartilage- ringed tubes called bronchi. Also, this section of the respiratory system is lined with ciliated cells. The bronchi enter the lungs and spread into a treelike fashion into smaller tubes called bronchial tubes. Bronchioles - The bronchial tubes divide and then subdivide. By doing this their walls become thinner and have less and less cartilage. Eventually, they become a tiny group of tubes called bronchioles. Lungs - The lungs are effectively enclosed in a box, formed from the diaphragm at the base and the ribs at the sides. The diaphragm is a muscular membrane connected to the inside wall by tendons, which separates the thoracic and abdominal cavities. It plays an important part in inspiration and expiration, and also in the cough reflex and hiccups (though whether one thinks hiccups themselves are important is another matter). The 12 pairs of ribs not only provide protection, but are essential for inspiration. The intercostal muscles in their relation to the ribs provide a means of changing the volume of the thorax. There are two sets of internal intercostal muscles - the intercostalis intimus, nearest to the lungs, and the intercostalis internus, furthest from the lungs and lying immediate inside the ribs. There is also a single set of external intercostal muscles - the intercostalis externus located on the outer surface of the ribs. These pull the rib cage up and out, increasing the volume of the thorax. The two internal intercostals pull the ribs in, reducing the volume. The right-hand lung has three lobes, while the left has two. The lobes are determined by creases, or fissures: two on the right lung and one on the left. The left lung is smaller because of the location of the heart; the cardiac notch is the groove in the left lung where the heart sits. There is also an indent at the base, the hepatic notch, where the liver sits. There are approximately 600-700 million 34 -------------------------------------------------------------------------------------------------1st year.Physiology alveoli in an adult human, giving a total surface area of about 100 square metres, equivalent to one third of the area of a tennis court. This large surface area greatly facilitates gaseous exchange. Number of alveoli in human lungs range from 600-700 million/two lungs which form a surface area of about 50-90 m2 Figure 3: Anatomy and structure of respiratory system Figure 4: Inner wall of trachea 35 -------------------------------------------------------------------------------------------------1st year.Physiology Mechanism of External Respiration (Inspiration and Exhalation): During resting state: Inspiration – Ribs are pushed to outside and upward by the contraction of external intercostal muscles. – Diaphragm contracts and moves downwards. – Thoracic cavity increases in size and lung space increases – Pressure gradient causes gas to flow into the lungs Expiration – External intercostal muscles and diaphragm relax and return to normal position decreasing the size of thoracic cavity and decreasing lung space. – Pressure gradient causes air to flow to outside. In other words During inspiration, the diaphragm and the external intercostal muscles contract. The diaphragm moves downwards increasing the volume of the thoracic (chest) cavity, and the external intercostal muscles pull the ribs up expanding the rib cage and further increasing this volume. In contrast to inspiration, during expiration the diaphragm and intercostal muscles relax. This returns the thoracic cavity to its original volume, increasing the air pressure in the lungs, and forcing the air out (Figure 5). Inspiration Expiration Figure 5: Mechanism of inspiration and expiration 36 -------------------------------------------------------------------------------------------------1st year.Physiology Mechanisms of forceful inspiration and expiration during exercise: During strenuous exercise, more energy is required and excess oxygen must be supplied and the excess carbon dioxide produced must be removed from the body. Thus, more ventilation of two lungs or overdrive mechanisms are required to compensate these needs. During strenuous exercise, the respiratory rate is increased, the period of inspiration increases at the expense of expiration time and the lungs are more ventilated. During active inspiration: Scalenes and sternocleidomastoid muscles contract in addition to the contraction of external intercostal muscles leading to more moving of ribs outward and upward. This results in more increase in the size of thoracic cavity and more stretching of the two lungs permitting entering of bigger amount of air (Figure 6). During active Expiration: Contraction of internal intercostal muscles pulling ribs more inward and downward. In addition, abdominal muscles contract pushing diaphragm more upward. These two events result in more decrease in the size of thoracic cavity and more shrinkage of the two lungs permitting expelling of bigger amount of air than normal (Figure 6). ----- Figure 6: Quiet and active external respiration 37 -------------------------------------------------------------------------------------------------1st year.Physiology Transport of O2 and CO2 in the blood Oxygen is transported in two forms 1- 98% binds with haemoglobin (Hb) to form oxy haemoglobin. 2- 2% is physically dissolved in blood plasma. Carbon dioxide is transported in three forms 1- Less than one third (about 25%) enters RBCs and combine with Hb to form carbaminohaemoglobin (carboxy Hb). 2- About two thirds (about 67%) enter RBCs and form bicarbonate 3- 8% are physically dissolved in the blood plasma. Nervous control of external respiration (Figure 7): The dorsal respiratory group (DRG) is responsible for normal quiet inspiration. At usual blood gas levels, DRG generates action potentials spontaneously about 15 times per minute. The output from these is mainly to the diaphragm and external intercostal muscles and is responsible for inspiration during quiet breathing. The DRG can be considered the main respiratory pacemaker at rest. Dorsal Respiratory Group—Quiet inspiration Ventral Respiratory Group—Forceful inspiration and active expiration Pneumotaxic Center—Influences inspiration to shut off Apneustic Center—Prolongs inspiration Figure 7: Respiratory centres in the brain 38 -------------------------------------------------------------------------------------------------1st year.Physiology Respiratory volumes and capacities (Figure 8) The measurement of air that comes in and out of the lungs is known as spirometry and the apparatus used is known as spirometer (Figure 9) Tidal air volume (VT) (the volume of air that enters the lungs during normal inspiration or leaves the lungs during expiration)= 500 ml Complemental air volume (CV) (inspiratory reserve volume; IRV) (excess volume of air inhaled above tidal air volume during forceful respiration) or in other words, it is the additional amount of air entering the lungs during forced inspiration = 3000 ml Supplemental air volume (SV) (expiratory reserve volume; ERV) (excess volume of air exhaled above tidal air volume during forceful respiration) = 1000 -1200 ml. Residual air volume (RV) (the amount of air that remains in lungs after deep expiration) = 1200 ml Functional residual capacity (FRC) (the amount of air that remains in lungs after resting expiration) Total lung capacity (TLC) = VT + IRV + ERV +RV Vital capacity = VT + IRV + ERV Inspiratory capacity (IRC) = VT + IRV Expiratory capacity (ERC) = VT + ERV Figure 8: Lung volumes and lung capacities 39