CIRCULATORY SYSTEM - CVA.pdf

CHAPTER 12 THE CIRCULATORY SYSTEM ambient temperatures during the day, and Introduction their body temperatures can exceed 45°C Reporter: Roentgen Gapol (113°F). THE HUMAN CIRCULATORY SYSTEM...

CHAPTER 12 THE CIRCULATORY SYSTEM ambient temperatures during the day, and Introduction their body temperatures can exceed 45°C Reporter: Roentgen Gapol (113°F). THE HUMAN CIRCULATORY SYSTEM In large measure, humans and animals can The Circulatory system helps with the adjust to changes in activity and physical transport of gases between the sites of stress because of adjustments orchestrated external and internal respiration, while also by the circulatory system. adjusting to changes in pressure on or within the body, and transporting hormones BLOOD to target organs and waste products to the kidneys. Cells produced by hemopoietic tissues usually enter the circulation to become the In a more simple approach, the Circulatory peripheral or circulating blood, which is then System of Vertebrates is a set of connecting comprised of plasma and formed elements. tubes and pumps that move fluid, referring to the ability of an organism to adjust to Plasma: Fluid component, acts as immediate physiological changes in physical the ground substance of blood. and metabolic activity. Formed Elements: Cellular components including: Lastly, it provides oxygen, nutrients, and Red Blood Cells (Erythrocytes): hormones to muscles, tissues and organs ○ Transport oxygen via throughout our body. hemoglobin. ○ Mammalian erythrocytes lack Parts Of Circulatory System nuclei. ○ Sizes vary from 8 μm The Circulatory System, or can be also (humans) to 80 μm (some called as the Vascular or Cardiovascular salamanders). System if consisted of various parts--- the ○ Live 3-4 months in circulation Heart, Blood, & Blood Vessels. before replacement. White Blood Cells (Leucocytes): Additionally, the Circulatory System also Defend against infection and includes the Lymph Vascular System that is disease. made up of Lymphatic Vessels and lymph, Platelets: Involved in clotting by and the fluid they circulate. releasing factors that lead to thrombus formation. Did You Know? Red blood cells vary in individual size, from Whales can dive from the surface to depths 8 μm in humans, to 9 μm in elephants, to 80 of over 2,000 m or over 6560 ft (the μm in some salamanders. equivalent of 2 and a half Burj Khalifa) and feed there for up to an hour. During that Functions of blood time, they experience immense pressures on their bodies, over 16 million Pascal Respiration: Oxygen transport. (about 2,300 psi) per square meter of body Disease Protection: Immune surface. response. Nutrition: Carries carbohydrates, Animals such as the Oryx, an African fats, proteins. antelope, can be exposed to searing  Excretion: Removes spent their tunica media and the presence of metabolites. one-way valves in veins. Temperature Regulation: Distributes heat. Blood Vessel Structure Water Balance: Maintains hydration. Hormone Transport: Delivers 1.) General Structure hormones throughout the body. Three Layers: BLOOD VESSELS ○ Tunica Intima: Innermost layer with endothelial cells Blood vessels are essential components of lining the lumen. the circulatory system, responsible for ○ Tunica Media: Middle layer transporting blood throughout the body. with smooth muscle and They come in three principal types: arteries, elastic fibers. veins, and capillaries. ○ Tunica Adventitia: Outermost layer with fibrous connective 1. Arteries tissue. - Carry blood away from the heart 2.) Arteries vs. Veins - Typically high in oxygen (exception: Arteries: pulmonary artery) ○ Tunica Media has more elastic fibers and some 2. Veins smooth muscle. ○ No one-way valves. - Carry blood toward the heart Veins: ○ Tunica Media has more - Typically low in oxygen (exception: smooth muscle and fewer pulmonary vein) elastic fibers. ○ Contains one-way valves to 3. Capillaries prevent backflow. - Tiny vessels connecting arteries and veins 3.) Small Vessels - Facilitate exchange of oxygen and Arterioles and Venules: nutrients ○ Thin Tunica Adventitia. ○ Tunica Media consists mostly Blood vessel classification is based on the of smooth muscle. direction of blood flow relative to the heart, ○ Similar in structure. not the oxygen content. Muscle Function Of Blood Vessel Blood Vessel Illustration The thickness and size of blood vessel walls Blood vessels, including arteries and veins, vary by type. Large arteries have a thick have complicated structures that enable tunica media with many elastic fibers and them to perform their functions effectively. membranes to handle the pulse from the By understanding their layers and heart. They also have small vessels, called differences, we can comprehend their roles vasa vasorum, that supply blood to their in the circulatory system. The key walls. differences between arteries and veins lie in Smooth Muscle Function in Blood Vessels:  Smooth Muscle Sheets: Surround ○ Characterized by hardening arteries and veins. and loss of elasticity in Vasoconstriction: Contraction of arteries. smooth muscles narrows the vessel. ○ Impaired expansion and Vasodilation: Relaxation of smooth recoil lead to higher blood muscles allows vessels to widen, pressure in smaller vessels. often assisted by residual blood ○ Increased risk of vessel pressure and oblique muscle rupture, especially in critical orientation. organs like the brain, which can be fatal. HEMODYNAMICS OF CIRCULATION Capillaries are tiny blood vessels with very thin walls that allow for the The pressures and flow patterns of the exchange of gases, nutrients, water, blood circulating through vessels constitute ions, and heat. the hemodynamics of circulation. Because They lack a tunica media and tunica of their different hemodynamics, the blood adventitia, consisting only of the pressures associated with the arterial and endothelial layer. venous sides of the circulation are Capillary beds, made up of networks considerably different. of capillaries, adjust blood flow to tissues based on activity levels by Understanding blood pressure involves opening or closing different sets of recognizing the two key measurements: overlapping capillary beds. systolic and diastolic pressures. These measurements reflect the force of blood ARTERIES against the arterial walls during different phases of the heart's pumping cycle. Just like with the Veins from previous slides, Arteries can be identified in various forms. Systolic Pressure: Peak force They vary in structure based on their size, produced when heart ventricles which influences their function in the contract. circulatory system. Diastolic Pressure: Lowest pressure in blood vessels between Structure And Function heartbeats, sustained by arterial elastic recoil. Large Arteries: Blood Pressure Notation: Systolic ○ Contains many elastic fibers. pressure recorded first, followed by ○ Expand to accommodate diastolic (e.g., 120/80 in young blood surges from adults). heartbeats. Disease Indication: Elevated blood ○ Elastic recoil between pressure can signal arterial disease heartbeats helps smooth and structural changes in arteries. blood flow. Giraffe Blood Pressure: ○ Pulse felt in wrist or neck. Exceptionally high at 260/160 to Small Arteries and Arterioles: maintain brain blood flow; drops to ○ Few or no elastic fibers. about 120/70 in the brain due to ○ Direct blood to local tissues. gravity. ○ Smaller arteries and arterioles manage blood flow VEINS from larger arteries. Arterial Disease: Because VEINS return blood to the heart, ○ Local: Autoregulation based they are collecting tubes. At any one on tissue activity. moment, up to 70% of the circulating blood Blood Flow Adjustment: Capillary within the body may reside in veins. During beds adjust blood flow to match times of stress, slight vasoconstriction of tissue needs; shunts can bypass strategic veins effectively decreases certain areas. “reserve” volume and moves some blood from this reservoir to the arterial side of the The microcirculation includes the capillary circulatory system. beds as well as the arterioles supplying and venules draining them. The usual flow of Veins have one-way valves to prevent blood to, through, and from a capillary bed backward blood flow and help manage low is diagrammed (solid arrows). Smooth blood pressure. External forces, like muscle muscles of the walls of the arterioles form contractions or pressure changes, squeeze small bands, the precapillary sphincters, the veins to assist blood movement toward that control blood flow to the capillary bed. A the heart. In veins without these external direct shunt running from the arterial to the forces, such as those in bones or the brain, venous side of circulation allows for major blood flow relies on remaining pressure and diversions of blood (open arrows). gravity. For example, as an animal lowers its head One-way valves in veins. to drink from a stream, blood pressure within its tissues changes quickly. Quick The one-way valves within the lumina of adjustments in the microcirculation serve to veins prevent retrograde movement of blood equalize and distribute these temporary and ensure its return flow toward the heart pressure fluctuations to prevent undue (vertical arrow). The pressure that drives stress on especially sensitive organs such blood flow (horizontal solid arrows) comes as the brain and spinal cord. from surrounding organs, usually muscles, that impinge upon and squeeze veins. Additionally, as posture changes, the head Dissected view of hindleg of a lion is shown. and extremities are raised or lowered relative to the heart. A giraffe lowering its MICROCIRCULATION head to drink quickly experiences increased pressure within its brain and cranial tissues. The microcirculation is crucial for regulating Adjustments in the microcirculation are one cell metabolism by controlling blood flow way to prevent such pressures from through capillary beds. It involves the creating a problem. smallest blood vessels and is tightly regulated by various mechanisms to ensure Microcirculation plays a key role in heat adequate nutrient and oxygen delivery to distribution. During activity, increased blood tissues. flow through skin capillaries helps release excess heat, causing flushed skin. In cold Microcirculation Components: weather, reduced peripheral blood flow Includes capillary beds, arterioles minimizes heat loss to maintain core (supply), and venules (drain). temperature. Emotional states can also Blood Flow Regulation: Controlled increase peripheral blood flow, leading to by smooth muscles in arterioles, blushing. venules, and precapillary sphincters. Control Mechanisms: ○ Global: Nervous and hormonal systems. BLOOD ALLOCATION The microcirculation is also involved in induces shock, helping the snake to allocating blood to active organs. Capillaries dispatch its meal quickly. are so small that it would take an hour for just a few drops of blood to pass through a SINGLE AND DOUBLE CIRCULATION single one. Yet, collectively, capillary beds represent an extensive volume, their linear Blood travels in one of two general patterns. extent being somewhere around 96,500 km Most fishes have a single circulation pattern (about 60,000 miles) of microtubing in all. in which blood passes only once through No animal has enough ready blood volume the heart during each complete circuit. With to fill all its capillaries at once. this design, blood moves from the heart to the gills to the systemic tissues and back to If all capillaries opened at once, major blood the heart. vessels would empty and the circulatory system would fail. Instead, blood is Amniotes have a double circulation pattern selectively directed to active organs, in which blood passes through the heart ensuring only the needed amount reaches twice during each circuit, traveling from the those tissues. However, sometimes the heart to the lungs, back to the heart, out to microcirculation may not provide enough the systemic tissues, and back to the heart blood to meet tissue demands. a second time. For example, if there are more active (a) The single circulation of fishes includes organs than available blood, then the heart, gills, and systemic capillaries in microcirculation gives preference to some series with one another (arrows indicate and not to others. If strenuous exercise is path of the blood flow). undertaken soon after a large meal, then the digestive system and skeletal muscles (b) The double circulation of most amniotes compete for blood to support their activities. includes heart, lungs, and systemic Preference is given to the skeletal muscles as more capillary beds open in them and capillaries. Blood passes twice through the the stomach receives less blood. heart before completing one route. This places lungs and systemic tissues in Humans who exercise might complain of separate circuits that parallel each other. “side cramps.” This results from Ischemia, a localized lack of sufficient blood to the stomach to meet metabolic expectations. Following severe injury or trauma, the microcirculation may fail to regulate blood distribution. When this happens, a condition called Shock, properly hypotensive shock, results from a cascade of events. Too many vessels open, not enough blood is available, pressure drops, and circulation fails. If shock is not quickly reversed, death can soon follow. The chemical arsenal in some snake venoms takes advantage of this general physiological feature of the cardiovascular system. When injected into prey, the venom PHYLOGENY OF THE aorta to supply the viscera. These are the CARDIOVASCULAR SYSTEM celiac, supplying the liver, spleen, stomach, Reporter: Cherrie O. Garcia and part of the intestines; the anterior mesenteric, supplying most of the small The vessels of the cardiovascular system intestine; and the posterior mesenteric, are as varied as the diverse organs they supplying the large intestine. supply. However, these variations are based on modifications of a fundamental plan of Embryonic heart formation organization common to vertebrates. Chick embryo in successive stages of incubation (25, 27, 29 hrs, respectively). Blood leaving the heart first enters an Ventral (left) and corresponding unpaired ventral aorta and courses forward cross-sectional (right) views of heart below the pharynx. Anteriorly, the ventral formation are illustrated. aorta divides into the external carotids, which carry blood into the ventral region of A. Angiogenic cells emerge from the the head. Before producing these external epimyocardium, a thickened carotids, however, the ventral aorta gives off splanchnic mesoderm. a series of aortic arches, which pass B. Angiogenic cells differentiate into a dorsally within the branchial arches between pair of primordial endocardial tubes. pharyngeal slits. Above the pharynx, these C. This pair of endocardial tubes fuses aortic arches meet a paired dorsal aorta. medially into the single endocardial Sprouting from the anterior end of the dorsal tube, the future lining of the heart. aorta are the internal carotids, which carry The thickened epimyocardium forms blood forward into the head and usually the thin peritoneum on the surface of penetrate the braincase to supply the brain. the heart, and the extensive The dorsal aorta itself, however, carries myocardium forms the muscular wall blood posteriorly. of the heart. At about the level of the liver, the paired Growth of the chick heart vessels of the dorsal aorta unite to form the The four-chambered heart consists of sinus unpaired aorta, which distributes blood to venosus, atrium, ventricle, and bulbus the posterior part of the body and eventually cordis. Once it forms, subsequent folding extends into the tail as the caudal artery. and enlargement shift the relative positions Along the way, the dorsal aorta gives off of these chambers. This process does not numerous small parietal arteries to the alter the route of blood flow through the local body wall, as well as several major functioning embryonic heart. arteries, usually paired, to somatic tissues. Paired subclavian arteries supply the Basic Vertebrate Circulatory Pattern anterior appendages (fins or limbs) and Illustrated in Shark usually branch from the dorsal aorta, as do The heart pumps blood to the ventral aorta, the caudal iliac arteries, which supply the from which it is distributed to the paired posterior appendages. The gonads receive aortic arches and then to the single dorsal blood from paired genital arteries (ovarian aorta. From the dorsal aorta, blood flows or spermatic). Paired renal arteries to the forward to the head and posteriorly to the kidneys are large, major branches from the body, where major branches carry it to dorsal aorta. This ensures that the kidneys visceral and somatic tissues. receive blood early in the arterial circuit while blood pressure is still relatively high, a Renal circulation feature of the hemodynamics that aids renal filtration. Typically in vertebrates, three Blood Return in Primitive Vertebrates: unpaired arteries depart from the dorsal  Common Cardinal Vein (or Sinus): ○ Gills replaced by lungs, ○ Major vein for blood return to leading to pulmonary the heart. circulation. ○ Receives blood from: ○ Cardinal veins become less Anterior Cardinal Vein prominent. (precardinal) - drains ○ Development of: anterior body regions. Postcava (Posterior Posterior Cardinal Vena Cava): Drains Vein (postcardinal) - posterior body. drains posterior body Precava (Anterior regions. Vena Cava): Drains ○ Tributaries include: anterior body. Subclavian Vein - from anterior ARTERIAL VESSELS appendage. Lateral Abdominal Reporter: Cherrie O. Garcia Vein - from lateral body wall and posterior appendage. Primitive Aortic Arches: Portal Systems: Debate on the exact number; some ostracoderms had up to 10 pairs. Hepatic Portal System: Lampreys: 8 pairs; Hagfishes: 15 ○ Blood flows from digestive pairs; Sharks: 10-12 pairs. tract capillaries to liver via Most gnathostome fishes and all the hepatic portal vein. tetrapods typically have 6 pairs in ○ Directly transports nutrients embryonic development. to the liver for processing. Renal Portal System: Numbering and Terminology: ○ Blood from tail or hindlimbs capillaries travels via renal Basic pattern: 6 aortic arches, portal veins to kidneys. designated by Roman numerals ○ Functions (not fully (I–VI). understood): Variations in numbering: May help in delivering ○ Some authors use up to 10 metabolic by-products arches based on presumed to kidneys. primitive numbers. Possibly aids in ○ Others number arches as kidney filtration by found in adults (e.g., 1, 2, 3). providing low-pressure blood Frog flow. ○ Absent in mammals but has Larval Stage: a low-pressure network in the mammalian kidney for similar ○ Internal gills on aortic arches functions. III–VI. ○ Pulmonary artery buds from Phylogenetic Modifications: arch VI. Transition from water to land: Metamorphosis:  ○ Losses: Internal gills, carotid Aortic Arches in Mammals: Up to six aortic duct, and all of arch V. arches form in the mammalian embryo, but only three persist as major arteries in adults: Persisting Arches: carotid arteries, pulmonary arch, and systemic arch. Carotid Arteries: Arise from Arch III: Becomes internal carotid. the paired aortic arches (III) and parts of the Arch IV: Joins the dorsal aorta, ventral and dorsal aortae. Form from the supplying the body. same components as in reptiles. Pulmonary Arch VI: Loses connection to the Arch: Forms from the bases of the paired dorsal aorta, forms the sixth arch and its branches, similar to pulmocutaneous artery. reptiles. Pulmocutaneous Artery: Systemic Arch: Develops from the left aortic arch (IV) and the left dorsal aorta, resulting Pulmonary Branch: Enters the lungs. in a left systemic arch in mammals. Cutaneous Branch: Supplies blood Brachiocephalic Artery: Common carotids to the skin. may originate together from the brachiocephalic artery or branch Carotid Arteries: independently from the aortic arch. Subclavian Arteries: Left subclavian artery Common Carotid: Section of ventral departs from the left systemic arch. Right aorta between arches III and IV. subclavian includes parts of the right aortic Carotid Body: Sensory cluster at the arch (IV), adjoining right dorsal aorta, and internal carotid root. arteries extending into the right limb. Misconceptions: Early views suggested inefficient VENOUS VESSELS blood flow with mixing of oxygenated and deoxygenated blood, but Reporter: Cherrie O. Garcia minimal mixing actually occurs. In vertebrates with an established double Mammals circulation, there are two general functional systems of venous circulation: the systemic Aortic Arches in Mammals: Up to six aortic system draining the general body tissues, arches form in the mammalian embryo, but and the pulmonary system draining the only three persist as major arteries in adults: lungs. Within the systemic system, hepatic carotid arteries, pulmonary arch, and portal veins serve the liver, renal portal systemic arch. veins serve the kidneys, and general body veins drain the remaining systemic tissues. Carotid Arteries: Systemic System Arise from the paired aortic arches (III) and parts of the ventral and Early Development: Three major paired dorsal aortae. veins develop: vitelline veins (yolk sac), Form from the same components as cardinal veins (embryo body), and lateral in reptiles. abdominal veins (pelvic region). Pulmonary Arch: Forms from the bases of Vitelline Veins: the paired sixth arch and its branches, similar to reptiles. Among the first to appear; arise over the yolk and follow the yolk stalk into the embryo.  Continue along the gut and enter the Transports absorbed end products of sinus venosus. digestion from the digestive tract to Liver growth breaks up vitelline veins the liver. into hepatic sinusoids; remaining Common to all vertebrates. sections become hepatic veins. Development: Cardinal Veins: Arises mostly from the embryonic Anterior Cardinal Veins: Drain blood subintestinal vein, originating in the from the head; consist of parts that caudal vein. receive tributaries from the brain, The subintestinal vein loops around cranium, and neck. the anus, extends forward along the Posterior Cardinal Veins: Return ventral wall of the intestine, and blood from the body, primarily collects blood. developing as vessels for the Passes through the liver and joins embryonic kidneys. the left vitelline vein. Both unite into common cardinal The vitelline veins in the liver veins that open into the sinus become hepatic sinusoids, into venosus. which the subintestinal vein empties blood. Lateral Abdominal Veins: Transformation: Present in fishes, but usually merged or absent in tetrapods. The posterior end of the In fishes, they join the iliac vein and subintestinal vein regresses and become the subclavian vein, which loses contact with the caudal vein. enters the common cardinal vein. The modified subintestinal vein In tetrapods, the subclavian returns becomes the hepatic portal vein. separately to the heart, and the Collects blood from the intestines, lateral abdominal veins enter the stomach, pancreas, and spleen, liver. delivering it to the liver’s vascular In amphibians, they may unite into sinusoids. the ventral abdominal vein; absent in alligators, birds, and mammals. General Body Veins Venous Development: Primitive Vertebrates: Involves changes in early paired Retain the basic embryonic pattern vessels, including anastomoses, where blood from anterior and atrophy, and new embryonic posterior systemic tissues is vessels. returned via anterior and posterior Results in asymmetrical adult cardinal veins. venous routes for blood return to the Both pairs of cardinal veins unite in heart. common cardinal veins near the heart. Hepatic Portal Vein Derived Vertebrates: Hepatic Portal Vein Function: Cardinal veins appear during embryonic development but usually persist only in the embryo.  In adults, they are functionally return route, eventually enlarging to replaced by alternative venous form the adult postcava. systems. Precava and Postcava: Precava Formation: Both are mosaics of preceding Begins with the development of embryonic vessels, which are anterior, posterior, and common repurposed during development to cardinal veins in the embryo. form the definitive adult veins that Small intersegmental veins enlarge drain the anterior and posterior parts into subclavian veins, which empty of the body. into the anterior cardinals. An intercardinal anastomosis forms Pulmonary System between the anterior cardinals, especially on the right side, aiding in Many fishes have supplementary blood return from the head. air-breathing organs, but only fishes with The right common cardinal vein lungs possess a pulmonary system. Among enlarges and becomes the precava living fishes, only dipnoans have true lungs. in adults; the left regresses to a If the ancient placoderms had lungs, a small vein near the heart. possibility mentioned earlier, then the pulmonary system would have evolved early Postcava Formation: in vertebrate evolution. Initially, paired posterior cardinal Pulmonary Veins veins return blood from the embryonic body. The pulmonary veins return blood from the Consolidation of parts of the paired lungs to the heart. Before entering hepatics, subcardinals, and the heart, they usually unite into a single supracardinals, along with vein. Embryologically, the pulmonary vein anastomoses between them, shifts does not arise by conversion of existing blood flow to a single medial vascular channels. Instead, numerous small channel. vessels originate separately page 471 within This channel, formed from merging and drain the embryonic lung buds. They parts of several veins, eventually then converge into several common vessels becomes the postcava. that become the pulmonary veins entering the left atrium. Development involves: Lung Evolution Posterior Cardinal Veins: Drain early embryonic kidneys. Head Drainage: Subcardinal Veins: Connect through a subcardinal anastomosis. Paired anterior cardinal veins and Supracardinal Veins: Provide small inferior jugular veins drain the additional drainage. head. Right Vitelline Vein: Joins the right These veins join the common subcardinal anteriorly. cardinal veins before emptying into New Connections: Form posteriorly the sinus venosus of the heart. between subcardinals and supracardinals. Appendage Drainage: As these vessels consolidate, the medial channel becomes the primary  Subclavian and iliac veins drain the Blood Flow Rates: appendages via the lateral abdominal vein, both joining the Dogfish Shark: 7.5 liters per hour. common cardinal. Resting Hen: 24 liters per hour. Human: 280 liters (about 75 gallons) Posterior Cardinal Modification: per hour. Giraffe: Nearly 1,200 liters per hour. In most fishes, blood from the tail is diverted to flow through the kidneys Heart Rate Effects: before reaching the remaining sections of the posterior cardinal. Tachycardia: Can increase blood flow up to fivefold. Hepatic Portal Vein: Bradycardia: Can significantly decrease blood flow, e.g., a turtle's Transports blood from the digestive cardiac output can drop to less than tract to the liver, where it flows 1/50 during a dive. through capillaries and then to the heart via the hepatic veins. Heart Functions: Actinopterygians: Pumps blood and channels deoxygenated and oxygenated Lateral abdominal veins are usually blood to prevent mixing. lost; pelvic fins are drained by the posterior cardinal. Next Steps: Blood from gas bladders empties into the hepatic or common cardinal Examination of the heart's structure veins. in vertebrates. Lungfishes: Basic Vertebrate Heart Similar venous return to other fishes, Four-Chambered Hearts: but the right posterior cardinal vein enlarges and is called the postcaval Birds and Mammals: Both have vein. four-chambered hearts. Paired lateral abdominals fuse into Fish Heart Evolution: Original four an unpaired ventral abdominal vein, chambers are reduced to two major draining the pelvic fins and emptying chambers (atrium and ventricle), into the sinus venosus. which are divided into left and right Blood from the lungs enters the compartments in birds and atrium of the heart directly. mammals. HEART Evolutionary Context: Reporter: Cherrie Garcia Tetrapods: Birds and mammals descended from early tetrapods, but The heart is a pump that moves blood their four-chambered hearts evolved through vessels both by pushing blood independently. through the circulatory system and also by Amphibians and Reptiles: Positioned aspiration—creation of negative pressure between early tetrapods and modern that sucks blood into the heart vertebrates; their hearts should be studied for their current functional  roles, not just as evolutionary Pulmonary Blood Flow: intermediates. ○ When Air-Breathing: Increased Pulmonary FISHES Flow: When a lungfish surfaces to Reporter: Cherrie Garcia breathe air, pulmonary blood flow Fish hearts. (a) Shark. (b) Teleost. Blood to the lungs leaves the shark heart through the muscular increases. conus arteriosus, a chamber that is absent Shunting Oxygenated in many teleost fishes. Instead, in the Blood: Oxygenated teleost heart, the base of the ventral aorta is blood returning from swollen, creating the elastic bulbus the lungs is shunted arteriosus. through aortic arches III and IV (which lack Lungfishes gills) and directed straight to systemic The lungfish heart is modified from that of tissues. other bony fishes. Systemic Blood: Deoxygenated blood Sinus Venosus: returning from systemic tissues is Receives returning blood. In shunted through Australian lungfish (Neoceratodus), arches V and VI and it receives blood from the lungs, directed to the lung while in South American for oxygenation. (Lepidosiren) and African lungfish (Protopterus), it connects directly to 2. Spiral Valve and Aortic Arches: the left atrial chamber. Separation of Blood Streams: Atria: ○ Spiral Valve: The spiral valve within the conus arteriosus The atrium is partially divided helps separate oxygenated internally by an interatrial septum and deoxygenated blood. (pulmonalis fold), creating a larger ○ Arch Pathways: right atrial chamber and a smaller Oxygenated Blood: left atrial chamber. Travels through the Pulmonary Veins: anterior set of aortic ○ In Australian lungfish, they arches. empty into the sinus Deoxygenated Blood: venosus. Passes through ○ In South American and posterior arches and African lungfish, they empty is directed to the directly into the left atrial lungs. chamber. Lungfish possess unique cardiovascular 3. Adaptation to Low Oxygen Conditions: adaptations that allow them to thrive in varying oxygen conditions. Avoiding Oxygen Loss: ○ Directing Oxygenated Blood: Cardiovascular Adaptations About 95% of oxygenated  blood from the lungs is directed to systemic tissues through anterior aortic arches, minimizing dilution by deoxygenated blood. ○ Secondary Shunt Mechanism: Thick, muscular arteries can bypass gill capillaries to prevent exposure of oxygenated blood to water low in oxygen. ○ Physiological Benefits Efficient Oxygen Uptake: ○ Separation of Blood Streams: Keeps oxygenated and deoxygenated blood separate, allowing efficient oxygen uptake in the lungs and preventing dilution of oxygenated blood. Protection from Oxygen Loss: ○ Avoiding Oxygen Loss: By not directing oxygenated blood through gills, the lungfish avoids losing oxygen to water that is low in oxygen.