Evolutionary y trends in the circulatory system 1) Conversion from a single circuit to u circuit: u a double – Fishes: single circuit: • To g gill capillaries p and body y capillaries. p – Lungfishes and sarcopterygians: • Pulmonary y circuit: to lung g capillaries. p • Systemic circuit: to body capillaries. Evolutionary trends in the circulatory i l t system t 2) Corresponding conversion of heart from a single pump to a double pump: – Single pump: • Fishes. – Partially subdivided pump: • Lungfishes and coelacanths. coelacanths • All amphibians. • Turtles, lizards & snakes. – Double pump: • Crocodilians and birds. • Mammals. Mammals Evolutionary trends in the circulatory system 3) Modification and reduction of aortic arches. 4) Addition of subcircuits. – For example: portal systems. 5)) Reduction u and loss of f other basic elements. m . – For example: • Truncus arteriosus. • Sinus venosus. General pattern of circulation in a fish Carotid arteries Heart • Muscular tube. • Divided into series of chambers: – Each chamber formed from separate blood island. – Formed d within h splanchnic l h hypomere. h • Composed of thick wall of cardiac muscle (m c dium): (myocardium): – Lined with epithelium tissue (= endocardium). – Surrounded by thin membrane of connective tissue (= epicardium). – Lies within fluid-filled p pericardial cavity. y • Partitioned from coelom. Heart • Why is the heart considered to be a center of emotion (with thanks to Aristotle)? I give i you my h heart. t You broke my heart. I’ve given my heart to another. She has a soft heart. It comes from the heart. g with your y head rather than your y heart. You’re thinking • Cardiac muscle is intrinsically contractile. • Rate of contractions mediated by vagus and autonomic nerves. Heart is a peristaltic pump with valves Heart • Two main pumping chambers: h – Atrium: • Receives blood returning to heart. heart • Pumps anteriorly to ventricle. – Ventricle: • Pumps P blood bl d anteriorly t i l to t ventral t l aorta. t • Two accessory chambers: – Sinus venosus (posterior): • Stores blood returning to heart from veins. – Truncus arteriosus (anterior): • Strong St valves l s tto resist sist b back-pressure k ss f from bl blood d vessels. • Equivalent to conus arteriosus of sharks and bulbus arteriosus of bony fishes. fishes • Valves between chambers prevent back-flow. Development of the heart Heart cycle • Systole: – Atrium relaxes, fills with blood. – Ventricle contracts contracts, blood pumped into aorta. • Diastole: – Atrium contracts, blood pumped into ventricle ventricle. – Ventricle relaxes, fills with blood. Systole y Diastole Development of heart • Chambers ham rs develop op from ant anterior r or to posterior. Each new w chamber m beats more m rapidly. p y. • E – Anterior chambers speed up to synchronize. • Sinus venosus becomes final regulator. – Higher vertebrates: sinoatrial (SA) node. • Located in posterior wall of right atrium. • “Pacemaker”. Major trends in the heart • Longitudinal L it di l di division i i b by septa, t posterior t i to anterior. • Strengthening of internal valves. • Subdivision of truncus arteriosus into separate trunks (arteries). • Reduction of sinus venosus to cluster of pacemaker cells (sinoatrial node, SA). Aortic arches • Six aortic arches develop p between seven primitive pharyngeal arches (pouches): – – – – From ventral aorta, around pharynx. To pair of radices. Continue posteriorly to form dorsal aorta. Continue anteriorly to form internal carotid arteries. • Basic pattern from which can derive all patterns of aortic arches in vertebrates. Ductus caroticus Ductus arteriosus Modified circulation in some airair-breathing fishes Major trends in the aortic arches • • • • Isolation of carotid subcircuit. Systemic circuit taken over by arch #4. #4 Pulmonary circuit taken over by arch #6. Pulmonary circuit isolated by loss of ductus arteriosus. Fetal circulation in mammals • Lungs not functional in fetus: – Blood shunted away from lungs. – To T and nd f from m the th placenta pl nt via i umbilical mbili l vessels: ss ls: • Umbilical artery to placenta from iliac artery. placenta to inferior vena cava • Umbilical vein from p (post caval vein). – Placenta forms from chorion and uterine tissue. – Exchange of gases gases, nutrient molecules molecules, and urea by diffusion across walls of chorionic villi. – Oval opening between atria in heart shunts oxygenrich blood from right to left atrium. atrium – Any blood entering right atrium and pulmonary artery shunted to aorta via the arterial duct (d (ductus arteriosus). i ) • At birth: – Flow through umbilical artery and vein cut off, usually ll b by mother th biting biti umbilical bili l cord. d • Remnants of umbilical blood vessels become connective tissue. – Oval opening in heart closes via a flap (valve), which permanently attaches to the atrial wall. – Arterial duct (ductus arteriosus) closes. – Aquatic A ti organism i b becomes a tterrestrial t i l organism. Cardiovascular (circulatory) system • Blood-vascular Bl d l system: t – Closed circulatory system. • Lymphatic system: – Returns interstitial fluid to bloodvascular system. Lymphatic system • Functions: – Provides for the return of fluids to the bloodvascular s l ssystem. st • 99% of fluid that leaves the blood at the arterial end p y bed re-enters the capillaries p at the of a capillary venous end. • Function of blood pressure vs osmotic pressure. • Remaining 1% returned to blood by lymphatic vessels. vessels – Route of absorption of fats from the digestive tract. f lymphocytes. ymp y . – Source of • Presence in vertebrate groups: – Absent in agnathans g and chondrichthyans. y – Present in bony fishes and all tetrapods. Lymphatic Lymphat c system • Lymphoid y p masses (“lymph y p glands”): g – Enlargements of lymph tissue. • Include thymus gland, adenoids, tonsils, spleen • Functions: F – – – – Filter bacterial and other foreign materials. Lymphocyte production. production Antibody production. Spleen p associated with erythrocytes. y y • Destroys old cells, recovers iron. • Excretes hemoglobin as bilirubin. Endothermic E m f fishes • Most fishes are ectothermic. – About the h same temperature as the h surrounding water. • Some S me fishes are endothermic. end thermic – Able to maintain an elevated body temperature temperature. • Endotherms often have higher rates of: – Metabolism, Metabolism growth, growth reproduction. reproduction – Neural and visual function. – Swimming speed, speed endurance. endurance Endothermic E m f fishes • Endothermic fishes maintain elevated body temperatures by conserving heat generated by active swimming muscles. – Countercurrent system: rete mirabile. – Blood from gills shunted to cutaneous vessels near body surface. – From there carried through heatexchanging system en route to warm the swimming i i muscles. l Rete of the tuna Endothermic fishes • Examples: – Tunas m maintain temperatures mp from f m 3-21°C above ambient. – Mackerel sharks and thresher sharks maintain i t i 3 3-7°C 7°C above b ambient. bi t – Marlins, sailfishes and swordfishes have “brain brain heaters heaters”:: • Maintain elevated brain and eye temperatures. • Superior p rectus losses contractile filaments,, can generate heat without contracting. • Hunt in cold water without decrease in brain and visual functions. functions Marlin, Makaira Sailfish, Istiophorus h Brain coolers in mammals Evolutionary y trends in the circulatory system 1) Conversion from a single circuit to u circuit: u a double – Fishes: single circuit: • To g gill capillaries p and body y capillaries. p – Lungfishes and sarcopterygians: • Pulmonary circuit: to lung capillaries. • Systemic circuit: to body capillaries. Evolutionary y trends in the circulatory system 2) C Corresponding di conversion i of f heart h t from f a single pump to a double pump: – Single pump: • Fishes. – Partially subdivided pump: • Lungfishes and coelacanths. • All amphibians. • Turtles, Turtles lizards & snakes. snakes – Double pump: • Crocodilians and birds. • Mammals. Evolutionary trends in the circulatory system 3) Modification and reduction of aortic arches. 4) Addition of subcircuits. – For example: portal systems. 5)) Reduction u and loss of f other basic elements. m . – For example: • Truncus arteriosus. • Sinus venosus.