Modules 10-16.pdf - Respiratory System module 10 Functions of the Respiratory System Transport of oxygen from air into the blood and Removal of carbon

Modules 10-16.pdf - Respiratory System module 10 Functions...

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Unformatted text preview: Respiratory System module 10 Functions of the Respiratory System • Transport of oxygen from air, into the blood and Removal of carbon dioxide from the blood, into the air • Control of blood acidity (pH) • Temperature regulation • Forming a line of defense to airborne particles • Anatomy of the Lungs • Located in the thoracic cavity • Airways and mouth join at the pharynx, leads to the larynx (voicebox), becomes the trachea (windpipe) • Trachea eventually splits into right and left bronchioles, which continually divide and become alveoli • The pulmonary artery supplies deoxygenated blood to the lungs, branches and forms many capillary beds that surround each alveolus, and oxygenated blood flows back in via the pulmonary vein • Characteristics which maximize gas exchange: o Thin endothelial walls o Large total cross-­‐sectional area o Very low blood velocity Structure of an Alveolus • There are roughly 300 million alveoli in a healthy lung, each with a 0.3mm diameter • Alveolar epithelial cells (Type I) walls of the alveoli that are 1 cell thick o • Alveolar epithelial cells (Type II) Secrete surfactant which lines the alveoli o • Respiratory membrane Region between the alveolar space and o the capillary lumen This is where gas exchange takes place o • Macrophages and Lymphocytes Protects the body from airborne particles that make their way into the alveoli o • Elastin and collagen Present in alveolar walls, around blood vessel and bronchi o Pressures of the Lungs Two thin pleural membranes: • Parietal pleura – against the ribs • Visceral pleura – against the lungs The interpleural space formed between these two contains 10-­‐15mL of pleural fluid, which reduces friction between the two membranes during breathing 1 Jenna Le Due to the nature of the structures, ribs always want to move outwards, & the lungs always want to collapse. Alveolar pressure / Intrapulmonary pressure – pressure located inside the lungs Intrapleural pressure – pressure in the interpleural space Atmospheric pressure (760mmHg)– pressure outside the body • Between breaths, alveolar and atmospheric pressures remain the same (760mmHg) but interpleural space is lower (756mmHg) o This difference is due to the different pulls of the lungs and ribs Transpulmonary pressure – the difference between the alveolar and the intrapleural pressures Equation 1: Transpulmonary = Alveolar pressure – Intrapleural Pressure • This difference in pressure holds the lungs open Transpulmonary = 760 mmHg – 756 mmHg = +4mmHg Pneumothorax • In a healthy set of lungs, TPP is positive (outward) and keeps and alveoli open • If TPP = 0, lungs would collapse, producing a pneumothorax • This usually occurs when the interpleural space is punctured • Generally, only one lung collapses because each intrapleural space is isolated from the other. Boyle’s Law When a volume of a container decreases, the pressure inside increases (and vice versa) • Pressure varies inversely with volume: Ventilation • Moving air into and out of lungs requires an air pressure gradient • To move air into the lungs, we need high pressure outside and low pressure inside (in alveoli) • To move air out of the lungs, we need low pressure outside and high pressure inside 2 Mechanisms of Inspiration • To decrease alveolar pressure, lung volume increases • To do this: (active process) i. diaphragm contracts, moving downward ii. external intercostal muscles (of the rib) contract, lifting the rib cage up and out • These movements drop alveolar pressure to 759 mmHg Mechanisms of Expiration • At rest: (passive process) i. Diaphragm and external intercostals simply relax ii. Volume decreases, pressure rises to 761 mmHg • During exercise: (active process) o Contraction of abdominal muscles and internal intercostal muscles o Creates a larger pressure gradient, 763 mmHg Pulmonary Compliance • The stretchability of the lungs (increased compliancy with increased stretchability) • PC determines the ease of breathing o Low compliance – difficult to inflate, easy to deflate o High compliance – easy to inflate, difficult to deflate Two major factors: • Amount of elastic tissue found in alveoli, blood vessels, and bronchi walls o o • Pulmonary fibrosis § Causes a decrease in compliance § Caused by inhaling small particles, e.g. asbestos (immune cells cannot destroy them) § Large amounts of collagen deposited and leave fibrous scars Normal aging & pulmonary emphysema § Causes an increase in compliance § Destruction of elastin fibers in lungs, which help to recoil and exhale the lungs Surface tension of liquid lining all alveoli Elastic tissue components • Elastin and collagen are arranged in a special geometric pattern that allows for: o Elastin to be easily stretched o Collagen not easily stretched 3 o • Found within alveolar walls, blood vessel walls, and bronchial walls This arrangement contributes to 1/3 of total compliance Surface Tension • ST of film of liquid surrounding alveoli collapses the alveoli, decreasing compliance o • ST -­‐ Due to the attractive forces between water molecules Contributes to the other 2/3 of elastic behaviour Pulmonary Surfactant • Lipoprotein substance produced by type II alveolar cells (mostly phospholipids) • Surfactant balances out the attractive forces in surface tension • This is how the ST is regulated by our lungs • Pulmonary surfactant is released from type II cells during deep breathing o • Can be difficult for those post-­‐surgery Infant Respiratory Distress Syndrome o Premature babies (before 36 weeks) do not produce proper amounts of surfactant o Alveoli collapse often, making it difficult to inhale which uses lots of energy o Infants can die from this exhaustion, surfactant is dosed directly into lungs at birth Lung Volumes • Max amount is roughly 5 liters, but depends on health, age, level of activity • Spirometer – device used to measure lung capacities, useful in diagnosing pulmonary diseases Tidal volume: (500mL) • Volume entering/leaving lungs during one breath Inspiratory reserve volume: (2500mL) • Max amount of air that can enter the lungs (in addition to tidal volume) Expiratory reserve volume: (1000mL) • Max amount of air that can be exhaled (beyond the tidal volume) Residual volume: (1200mL) • Remaining air in lungs after max exhale Inspiratory capacity: (TV + IRV = 3000mL) • Max amount of air that can be inhaled after exhaling tidal volume Functional residual capacity (ERV + RV = 2200mL) • Amount of airs still in lungs after exhalation of TV Vital capacity: (IRV + TV + ERV = 4000mL) • Max amount of air that can be exhaled after maximum inhalation 4 Total lung capacity: (VC + RV = 5200mL) Max amount of air the lungs can hold • Pulmonary Ventilation (VE) • • The amount of air that enters all of the conducting and respiratory zones in one minute o Conducting zone – no gas exchange takes place (trachea, primary bronchi, smaller bronchi, bronchioles o Respiratory zone – region where alveoli are located (alveoli) Determines the amount of air, and oxygen available to the body (similar to Cardiac output = stroke volume x Heart rate) • VE = 500 mL/breath x 15 breaths/min = 7500 ml/min (at rest) • But not all of this air is available for gas exchange Alveolar Ventilation (VA) • Volume of air entering only the respiratory zone each min (disregards dead space) • Represents the volume of fresh air available for gas exchange • Anatomical dead space volume is usually equal to the person’s weight in pounds Partial Pressures of Gases • PP is the pressure exerted by one gas in a mixture of gases • Our air contains = 21% oxygen, 78% nitrogen & other, 0.03% carbon dioxide Equation: Partial pressure = Total pressure of all Gases x Fractional Concentration of one Gas • PO2= 760 x 0.2093 = 159 mmHg and PCO2= 0.3 mmHg However, within our lungs, gas exchange takes place and these values are different: o PO2= 105 mmHg o PCO2= 40 mmHg 5 • Oxygen and carbon dioxide move across membranes and down a partial pressure gradient Movement Across the Alveoli • • • • Blood entering the lungs have: o PPO2 = 40mmHg o PPCO2= 46mmHg Alveoli have: o PO2= 105 mmHg o PCO2= 40 mmHg As the blood move past the alveoli, oxy and CO2 will diffuse down their partial pressure gradients o Oxygen moves from the alveolar space into the blood stream o Carbon dioxide will move from the blood to the alveolar space By the time the blood leaves the alveolus, pressures are the same as that of the alveolar air Movement Across Circulatory System a. Blood leaving lungs has high PO2 (100 mmHg) and low PCO2 (40 mmHg). b. Blood returns to heart and is pumped into circulatory system c. Tissue beds have the same pressures as the blood d. BUT cells have low PO2 (40mmHg) and high PCO2 (46mmHg) e. Blood flows through capillaries and oxy and co2 diffuse down the gradients with the cells f. Blood leaving the tissue has same pressure as cells (40, 46) g. Blood returns to heart and is refilled in lungs Remember that partial pressures of oxy and carbon dioxide refer to amount of gases dissolved in plasma 6 Oxygen Transport • Other than very little being dissolved in plasma, oxygen is also carried in red blood cells (erythrocytes) o Specifically, by hemoglobin • Plasma transfer only makes up 1.5% of total oxygen transported in blood, Hemoglobin is the 98.5% • Each molecule of hemoglobin carries 4 oxygen molecules The Red Blood Cell • Males have more RBC due to the effect of testosterone on RBC production • Lifespan of 120 days, 250 million RBCs produced and die each day • Erythropoiesis – production of red blood cells which takes place in bone marrow o • Requires amino acids, iron, folic acid, and vitamin B12 RBCs are broken down in the liver/spleen Erythropoietin (EPO) • Control of erythrocyte production require erythropoietin hormone (EPO) • 90% EPO secreted by kidneys, 10% by the liver, stimulated by drop in oxygen levels o Decrease in cardiac output, lung disease, high altitudes, or a decrease in the number of RBCs and/or total hemoglobin content. • Testosterone stimulates secretion of EPO in kidneys (accounts for larger amounts of RBC in males) • EPO was once used in blood doping to increase RBC levels in atheletes o Increased RBC leads to increased blood viscosity, decreased blood flow, increased resistance Hemoglobin • Each person contains around 2g of hemoglobin • 4 subunit molecule, one heme per subunit and an iron central atom • Each heme carries 1 oxygen molecule which is attached to iron • Reversible reaction occurs between the hemoglobin and oxygen o Oxygen + Hemogobin ßà oxyhemoglobin Oxygen-­‐Hemoglobin Dissociation Curve • Shows the unloading of oxygen from hemoglobin at different blood PO2 Things to note: • At alveoli, PO2 is high (100mmHg), and Hb is 95% saturated with Oxy At tissues, PO2 is low (40mmHg), less oxy is bound to Hb, more is dissociated. Temperature and acidity also affect the dissociation of oxygen Exercise causes the body to heat up and working muscles to produce lactic acid, this increases the acidity of the blood These effects increase unloading of oxygen from Hb 7 Carbon Dioxide Transport 3 forms of Transport: a. Dissolved and carried directly in plasma b. Carried as a bicarbonate ion (HCO3-­‐) c. Attached to proteins in the blood, forming carbamino compounds Dissolving in Plasma • 40mmHg on arterial side (away from lungs), and 46mmHg on venous side (away from tissue) • Always some amount of CO2 in the arterial blood – this heals maintain blood flow by keeping arterioles dialated! Bicarbonate Ion • 70% of total CO2 in blood is carried as this ion • Carbonic anhydrase enzyme is found inside RBCs o First step of this reaction occurs mainly here o Second step is rapid dissociation also in RBCs (H+ binds with Hb) • Reaction is reversible, if there is more CO2 or more HCO3 the rx could go left or right • Chloride Shift: o H+ binds with hemoglobin, (does not diffuse into blood to change pH) o Bicarbonate diffuses out of RBC into plasma, acts as a pH buffer! o Bicarbonate leaving RBC charges the cell positively, so chloride ions (Cl-­‐) diffuse into the cell to take its place Carbamino Compounds • 20-­‐23% of CO2 transported is attached to blood proteins, forming carbamino compounds • can attach to globin of Hb and form carbamino hemoglobin o • CO2 + Hb ß à HbCO2 once back in the lungs, CO2 will detach and diffuse into alveolar space o when this happens, Oxygen will attach to heme portion instead Loading and Unloading of Carbon Dioxide • High PCO2 in the tissue will cause reaction to move to the right • Low PCO2 in the lungs will cause reaction to reverse (and CO2 will diffuse out of the RBC into alveoli) 8 Respiring Cells vs Alveolar Cells Origin of Respiration • Spontaneous respiration o Originates in medulla oblongata of the brain stem, rhythmic neuron activity similar to pacemaker of the heart • Voluntary center o Originates in cerebral cortex, capable of overriding the brainstem’s instructions Inhalation (Active process) • In the medulla oblongata: o Inspiratory center – activates inspiratory muscles o Expiratory center – activates expiratory muscles • Inspiratory center inhibits expiratory when it is active • Involves contraction of external intercostal muscles and diaphragm Exhalation (Passive process) • Involves relaxation of muscles • Force exhalation – originate from expiratory center in medulla • Expiratory center inhibits inspiratory when it is active • Requires contraction of abdominals and internal intercostal muscles Regulation by the Pons • Respiration as a whole is regulated to ensure there is sufficient oxygen and carbon dioxide • Of the Pons: o Pneomotaxic center – regulates the rate of breathing o Apneustic center – controls depth of inhalation and exhalation Voluntary Center 9 • Cerebral cortex affects signals originating in apneustic or pneotaxic center Regulation of Respiration • Hyperventilation o Causes decrease in CO2 in the blood and blood vessels to vasoconstrict o Decreases blood flow, decreasing blood flow o the brain resulting in fainting Negative Feedback System: Sensors are also known as Chemoreceptors Chemoreceptors • Special receptors that detect concentrations of oxygen, carbon dioxide, or hydrogen ions in the blood Two groups in the body: Peripheral Receptor – Located in the aortic arch and carotid sinus (similar to baroreceptors) • Primarily sensitive to oxygen concentrations, slightly sensitive to carbon dioxide • Changes are reported to respiratory center in the brain Central group – Located in medulla of brain stem • Primarily sensitive to H+ ion levels in the interstitial spaces of the brain • Gases must cross the blood brain barrier to reach these medulla sensors o But this is permeable by CO2, not H+ Once CO2 crosses BBB into brain interstitial fluid, it diffuses down into bicarbonate and H+… • This H+ is detected by the central receptors • So an increase in blood CO2 leads to increased H+ past the BBB o Signal to respiratory center is sent to increase ventilation 10 Renal System and Water/Electrolyte Balance module 11 Renal System includes: • Kidneys, ureters, bladder, urethra Principle functions include: • Regulation of water balance, electrolyte levels, pH of the blood, long-­‐term reg of arterial pressure Functions of the Kidney • To remove non-­‐essential substances from the plasma! o • Including waste metabolites, excess water, and electrolytes To recover any essential substance o Like glucose • Important part in regulating water levels, chemical concentrations of body fluid, and pH of blood • Kidneys do not produce water or electrolytes, but conserve them by controlling amount removed from body • To act as an endocrine gland to produce hormones and components of hormone system o E.g. Erythropoietin, renin, vitamin D, stanniocalcin Anatomy of the Kidneys • Outer renal cortex, Middle Renal medulla, Inner calyces drain into Renal Pelvis • Renal Pelvis drains into Ureter • Functional unit of the kidney: nephron o Located in the Renal Pyramids o Drains into a small collecting duct Blood Supply of the Kidneys • Flows from the renal artery o Branches into interlobar arteries § Branches into arcuate arteries (supplies nephron) § o • Returns through arcuate vein Returns through interlobar veins Returns through renal vein Anatomy of the Nephron • Functional unit of the kidney, more than 1 million in each kidney • Filters blood, reabsorbs essential substances, excretes non essential molecules and waste • Composed of coiled tubes surrounded by blood supply/network i) Glomerular / Bowman’s Capsule • surrounds Glomerulus (small, permeable capillary bed) 11 o Together these are known as the renal corpuscle ii) Proximal convoluted tubule • Highly coiled iii) Descending and Ascending limbs of the Loop of Henle iv) Distal convoluted tubule v) Collecting duct Glomerular Capsule Interlobu lar artery Afferent Arteriole Glomerul -­‐us Proximal Convoluted Tubule Descending limb Efferent Arteriole Ascending limb Distal convoluted tubule Peritubular capillaries Collecting duct Interlobu lar vein The Renal Corpuscle • Glomerular capsule and Glomerulus • The site where blood is filtered via Glomerular filtration • Fluid filtered from the blood into the capsule is called filtrate • Facilitated by highly permeable capillary endothelium, surrounded by podocytes • Large diameter afferent arteriole and smaller diameter efferent arteriole also enhance filtration 12 Renal vein Filtration Reabsorption Secretion -­‐ Movement of fluid -­‐ Movement of substance -­‐ Movement of a substance -­‐ Removal of substance through glomerular from lumen back into from the blood into lumen capillary blood -­‐ Hydrostatic Pressure -­‐ Creates filtrate (water + small blood solutes) Excretion from the body Excretion = Filtration + Secretion -­‐ Reabsorption Glomerular Filtration • Bulk flow of fluid from blood into glomerular capsule • Creates fluid, called the filtrate containing same substances as plasma o • With the exception of large proteins and red blood cells Podocytes surrounding capillaries have large filtration slits (formed between pedicles) which increase filtration Affected by: • Extremely permeable capillaries that make up the glomerulus • Starling forces Starling Forces • Blood hydrostatic pressure is roughly 60 mmHg (almost twice that in regular capillary) o • Colloid osmotic pressure is roughly -­‐32 mmHg (due to plasma proteins) o • Causes reabsorption of fluid into the plasma Capsular hydrostatic pressure is roughly -­‐18 mmHg o • Due to the different diameters between afferent (large) and efferent (small) arterioles Also causes reabsorption of fluid There is no colloid osmotic force in the glomerular capsule, since few proteins are filtered • As a result, BHP + COP + CP = Net filtration pressure 60 + (-­‐32) + (-­‐18) = +10mmHg – the pressure is outwards Glomerular Filtration Rate and Filtered Load • Kidneys filter roughly 180 L/day • GFR -­‐ The volume of fluid filtered during a certain time period • Filtered Load = the amount of other substances filtered by the kidneys per day • A good point to know: This can tell doctors if your kidneys are healthy o E.g. Glucose is filtered by the glomerulus, but completely reabsorbed by the nephron in health individuals. 13 § • You shouldn’t pee out glucose unless something is wrong. The opposite goes for sodium Also important to know the urine concentration of a substance and amount of solute excreted Urine concentration – amount of the solute that is excreted per unit volume (g/L) Amount of solute excreted – actual amount (in g) of solute in urine Amount reabsorbed – amount of filtered substance taken back up by kidneys Fraction excreted Tubular Transport Mechanisms Blue – Reabsorption Pink – Secretion Over 99% of substances filtered in the Glomerulus are reabsorbed back into circulation. Na+ Reabsorption: H2O reabsorption K Reabsorption H Secretion Glucose and Amino -­‐ Proximal tubule, -­‐Proximal tubule, -­‐Proximal tubule, -­‐Proximal tubule, Acids Reabsorp...
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