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BIOL 211
Bill Taylor

NOTES FOR BIOL 211 INTRO TO VERTEBRATE ZOOLOGY PART 2 LECTURE 13-14 COELOMIC CAVITIES, MOUTH, AND DIGESTIVE SYSTEM Origin of the Coelom and Gut - organs of gut develop as evaginations of the gut into mesenteries - coelomic space is split in the hypomere - in hagfish, and some sharks --> the coelom and peritoneal cavity is undivided - in most fishes and amphibia --> heart in pericardial cavity is divided and separated from the peritoneal cavity by the transverse septum....heart behind gills - in reptiles --> heart is under lungs - in mammals --> lungs in pleural cavity...diagphram separates pleural and peritoneal cavities membrane separating pleural and pericardial cavity = mediastinum - the scrotum = extension of the peritoneal cavity Origin of the Mouth - mouth develops de novo in deuterostomes - invagination that creates the mouth and meets the gut = stomodeum - nasal epithelium and hypophyseal pouch develop on head (deuterostomes) - in cyclostomes, both remain on top of head and stomodeum is shallow - in fish, only the hypophyseal pouch is drawn into the stomodeum - in vertebrates with choanae or internal nares --> both hypophyseal pouch and nasal epithelium are drawn into the stomodeum Mouths in Sagittal Section - fish have no neck...heart is found in their pharyngeal region - changes in tetrapods --> include salivary glands, and larger and more mobile tongue Specialization of Homodont Dentition - although may vary greatly among fish and ectothermic tetrapods, generally the same within species --> chewing is minimal Heterodont Dentition of Mammals - have differentiated teeth 1) Incisors --> for cutting 2) Canines --> for stabbing 3) Premolars and molars (together = cheek teeth) --> for chewing - all teeth usually replaced once except for molars - carnassial teeth = molars specialized for shearing Adaptations for Herbivory - herbivores like deer have few to no incisors and canines --> but have high and deeply folded cheek teeth that resist wear Adaptations for tooth wear - Rodents --> have opening-rooted incisors that keep growing - Elephants --> use their 6 immense cheek teeth one at a time Gut Functions 1) Transportation and Storage 2) Physical treatment --> mixing and churning 3) Chemical treatment --> breakdown of macromolecules by acids, enzymes, microbes 4) Adsorption 5) Production of feces, reclamation of H2O General structure of the gut - muscularis externa and the serosa --> derived from splanchnic hypomere - mucosa and submucosa --> derived from endoderm - blood vessels and nerves to and from the gut use dorsal mesentery The Stomach - secretions include --> mucous, HCl, proteases, renin - fundic regions = glandular.............pyloric region = muscular Diversity of Vertebrae Stomachs - Vertebrate stomachs are rather similar - in birds --> pylorus and gizzard = muscular.........fundus and cardia = secretory - in ruminants --> esophagus is expanded as rumen The Rumen - rumen part of the esophagus...upstream from the stomach - allows ruminant animals to extract nutrition via microbial fermentation - methane gas production significant The Cecum - other vertebrate herbivores --> fermentation occurs in hindgut, in an enlarged cecum (homologous with human appendix) or large intestine Foregut vs Hindgut Fermentation Foregut: - kangaroos, sloth, hippos, ostrich - occurs ahead of small intestine --> absorption favoured --> allows for re-chewing..but slow Hindgut: - horses, rodents, rabbits - occurs below the small intestine, involves large intestine or cecum --> absorption limited but faster throughput - cannot regurgitate and re-chew - many are coprophagous --> eats feces Structure of the small intestine - internal surface is highly folded to increase surface area for nutrient absorption - has a rich blood supply Fish Guts - fish --> esophagus short and starts behind mouth, large intestine not distinct - shark and some Osteichthyes --> increased area for absorption via spiral valve - teleosts --> have pyloric ceca to increase absorptive area instead of spiral valve Tetrapod Guts - have distinct large intestine - have urinary bladder and cloaca - never have pyloric ceca or spiral valve --> small intestine instead longer and coiled rather than single loop - birds and reptiles lack urinary bladder --> instead have a gizzard, and birds have a crop - tetrapods increase absorptive area but lengthening the small intestine - amphibians have a short esophagus like fish - birds have a colic ceca Liver Functions - largest organ and quite universal in all vertebrates 1) Digestive - produces bile acids which emulsify fats. Bile acid stored in gall bladder 2) Metabolic - carbohydrate metabolism, stores fat, protein metabolism 3) also stores iron and vitamins, detoxifies toxins, phagocytosis, and blood cell formation in fish and embryos The Liver in Relation to the Circulatory System Liver Lobule in Transverse Section - liver functions occur as the blood from hepatic portal vein passes through liver lobules to collect in central veins and ultimately the hepatic vein Development of the Liver and Pancreas - pancreas develops from dorsal and ventral mesenteries that fuse during development Pancreas Functions 1) Exocrine gland (secretions to outside, gut lumen)--> produces proteolytic enzymes as zymogens or pro-enzymes (inactive) 2) Endocrine gland (secretions into body, the blood) --> secretes insulin (stimulates deposition of glycogen) and glucagon (stimulates release of glycogen) - although liver is universal in vertebrates....not the case for have tissue with pancreatic function scattered in mesentery adjacent to liver - some vertebrates --> dorsal and ventral pancreas are separate with separate ducts - other vertebrates (humans) --> dorsal and ventral pancreas are fused LECTURE 15 RESPIRATORY SYSTEMS AND GAS BLADDERS Respiratory Systems Requirements of external respiratory surfaces: 1) Large surface area 2) Thin barrier between blood and air or water 3) Flow or exchange of air or water 4) Favourable diffusion gradient between blood and air or water The Early Development of Gills - gill openings develop in the pharynx - each branchial arch contains an element of the splanchocranium and ventral aorta Gills - lampreys have pouched gills where the 7 openings are tubular - sharks have 5 gill openings covered by septa - have a half-gill on the hyoid arch + 4 holobranches - opening ahead of hyoid arch is the spiracle - teleosts have 4 branchial arches without septa, covered by the operculum External Gills - external gills are larval structures (found in Necturus) - larval fish have external gills that develop before pharyngeal gills (adaptation to low2O environments) - tetrapods and amphibia never have functional pharyngeal gills Holobranch of a shark - shark gills protected by the gill septa separating the two halves of the holobranch Teleost Gills - teleost gills do not have a gill septa - they are instead protected by the operculum - note that blood oxygenation travels in opposite direction of waterflow within the gill lamellae -- > better gas exchange - this is known as countercurrent gas exchange Why do fish have lungs? 1) Water saturated with dissolved O 2t 20C...decreases with increasing temp and altitude 2) Microbial respiration also depletes amount of dissolved oxygen 3) Air is about 20% O 2 easier to move over respiratory surface - therefore fish living in warm habitats develop lungs to obtain the available oxygen from the air above water Lungs in Fish - evaginations of anterior gut behind gills --> highly folded and vascularized for gas exchange - lungs and gas bladders in fish are dorsal in position while lungs in tetrapods are ventral Gas Bladders - teleosts give up lungs for neutral buoyancy - gas content of bladder is maintained by adding or removing gas from the circulatory system via the red body and the oval body, respectively - some fish can even use the gas bladder for sound reception (hearing) Respiratory Systems in Tetrapods Modern Amphibia - external gills (larvae) - cutaneous respiration - mouth breathing (when frogs throat bulge out) - lungs, ventilated pharynx Labyrinthodonts and Reptilia - mouth breathing - lungs ventilated via aspiration by ribs using intercostal muscles (to expand thorax to draw air in) Mammals - lungs ventilated via aspiration by ribs using intercostal muscles + diaphragm - lungs have large surface area due to complex internal structure of alveoli Birds - lungs, ventilated via sternum (lung not expanded by aspiration....but by action of sternum) - bird lungs are associated with hollow air sacs that take up space in the body and lighten it - birds don't have alveoli - air does not move in and out....but in a single direction through parabronchi - blood flows through in opposite direction - air flow is rather inefficient in mammals compared to the crosscurrent flow of birds - mixing pot of gas in the alveoli of mammals LECTURE 16&17 CIRCULATORY SYSTEM Circulatory System - distributes water, solutes, dissolved gases, heat, cells involved in damage repair, immune system 2 Parts: 1) Blood Vascular system - heart, arteries, veins, capillaries, blood 2) Lymphatic system - lymphatic vessels, lymph nodes, lymph hearts, lymph Vertebrate Blood and Lymph Blood has 2 components: 1) Plasma - water + dissolved components (ie: albumens, fibrinogens, globulins, salts, wastes) 2) Blood cells - erythrocytes (RBC) --> found in BV system only, contain hemoglobin for O an2 CO 2 transport - leucocytes --> found in BV and lymph systems --> involved in immune system - thrombocytes (platelets in mammals, biconcave without nuclei) --> involved in clotting response (repair) Early Development of the Circulatory System - mesoderm tissue forms "blood islands" on the yolk, that coalesce into vitelline vessels containing blood Hemopoiesis or blood cell formation Sites of hemopoiesis change during development and evolution: - blood islands --> first sites of hemopoiesis in amniotes and embryonic blood vessels - gut and organs of the gut in embryos and fishes - spleen --> but in mammals, it only produces leucocytes, and only stores/destroys erythrocytes - thymus --> produces leucocytes, development of the immune system - lymph nodes --> produce leucocytes - red bone marrow of ribs, centra, and epiphyses in tetrapods Components of the Circulatory System Arteries, Capillaries, Veins - blood pressure seems to decrease directionally from the aorta--> arterioles --> capillaries --> venules --> vein - shunt --> to direct blood somewhere else when certain capillaries don't need the blood Structure of Blood Vessels 3 Layers: 1) Tunica Externa --> external layer of fibrous connective tissue 2) Tunica Media --> muscular layer with smooth muscles and elastic cartilage 3) Tunica Interna --> includes the endothelial layer that lines vessel and comprises capillaries Circulation in the Shark - in fishes, the heart pumps blood to the gills where it is oxygenated, then the internal carotid arteries and the dorsal aorta distribute it around the body - returning blood is collected via paired anterior and posterior cardinal veins - tail circulation returns to the kidneys via the renal portal vein - most vessels are paired (dorsal and ventral versions, or left and right versions) - all vertebrate embryos' circulatory systems have 6 aortic arches on each side of pharynx except Agnatha (which typically have >6) - adult fishes have 4 - 5 aortic arches - major arteries and veins (except dorsal and ventral aorta, and vessels of gut) are paired unlike in adult amniotes --> example of recapitulation... our development echoes our ancestors (fish) The Primitive/Embryonic Arterial Arches - Agnatha have >6 pairs of arterial arches, but all other vertebrate embryos have 6 - during development into an adult....different arches are deleted Sharks - 5 aortic arches --> 1st one is deleted in development - ventral aorta extends forward as the external carotid artery Teleosts - 4 aortic arches, branch of 6th arch serves the lung - in living Sarcopterygii, the 3rd and 4th no longer serve gill tissue - they are direct connections between the ventral and dorsal aorta - this is so blood is shunted to and from ventral and dorsal aorta without going through lungs Amphibia - arches 1 and 2 are lost in development - 3rd arch carries blood to the head via the internal carotid artery - 5th may also be deleted - 4th arch always remains as a connection between the ventral and dorsal aorta taking blood to the posterior body - the dorsal aorta is usually not continuous, but disappears between the 3rd and 4th arches - 6th arch takes blood to the lungs Amniotes - arches 1, 2, and 5 are lost in development - 3rd arch carries blood to the head - 4th arch carries blood to the body - 6th arch carries blood to the lungs (pulmonary artery) - symmetry is lost! - reptiles --> left side serves body, right side serves head + body - birds --> left 4th arch is lost completely - mammals --> right 4th arch is lost completely - ductus arteriosus persists until birth....why? Increasing asymmetry, ventral view - common carotid arteries are derived from the ventral aortic arches - Subclavian arteries serve the forelimbs Summary: Evolution of the aortic arches - tetrapods lose arches 1, 2, and 5 - 6th arch contributes to the pulmonary arteries The major veins, as seen in embryos and adult fish - embryonic and fish major veins are symmetrical - in adult fish, caudal circulation returns to the heart via kidneys - the artery is the renal portal vein Venous System of Amphibia - caudal circulation also passes through kidneys - a new vein, the post cava takes over at least partly the circulation previously carried to the heart by the posterior cardinal veins (ie: posterior cardinal veins lost in adult) Venous System of Amniotes - venous system continues to simplify and lose its symmetry - postcava delivers all blood from the body to the heart Venous System of Mammals - further simplified --> loss of all embryonic paired cardinal veins - precava is the only vein carrying blood into the heart from the anterior, and is derived from the fusion of portions of several embryonic veins - venous circulation does not pass through kidney - kidney receives only arterial blood and removes blood via renal veins Early Development of the Heart - heart develops from splanchnic hypomere (specifically ventral mesenteries) - has 3 layers: endothelium, muscle, and connective tissue The Embryonic Heart - heart of vertebrate embryos = linear pump, sends blood through the ventral aorta to branchial arches 4 main parts: 1) Sinus venosus - receives blood returning via the common cardinal veins 2) Atrium - delivers blood into the main pump (ie: ventricle) 3) Ventricle - receives blood from atrium 4) Conus - with semilunar valves that prevent backflow of blood. Note also sinuatrial and atrioventricular valves (also prevents backflow) Fish Hearts - Adult fish hearts similar to embryonic except atrium lies above ventricle (blood flow ="S" pattern) - Teleosts have an elastic conus called the bulbus arteriosus - Ventricle = main pump Amphibians: vertebrates with different sites for gas exchange - amphibian atria are divided --> blood from lungs enter on the left and blood entering from the sinus venosus enter on the right - ventricle not divided --> but can still separate deoxygenated blood from body from oxygenated blood from lungs - can direct blood to body or lungs depending if lungs are in use or animal is relying on cutaneous respiration Lateral views of amphibian hearts and arches - in larval stages --> 3 sites of gas exchange - external gills, lungs, and skin Reptile Hearts - have fully divided atria + a 3-chambered ventricle - blood returns from lungs to left atrium which then flows to the cavum arteriosum - then passes through an interventricular canal to get to the cavum venosum - then sent to rest of body via left and right aortic arches - blood returning from body enters right atrium which then flows to the cavum pulmonale - then pumped to the lungs via pulmonary arches - if lungs are not used, blood can be stopped from crossing to the cavum pulmonale, and direct it back to the right aortic arch (i.e. diving in turtles) Mammal Heart - mammals and birds have fully divided atria and ventricles - right ventricle takes venous blood returning from body and sends it to the lungs via pulmonary arteries - left ventricle takes blood returning from the lungs and sends it to body - before birth, embryonic circulation uses the ductus arteriosus and an opening in the septum between the atria to bypass the lungs Conservation of Heat in Endotherms - can conserve or lose heat by altering their microcirculation patterns to heat the entire body or just the core (using counter-current circulation to warm the cold blood returning to the body) Nasal turbinates - turbinate bones above secondary palate aids to conserve moisture, heat in the cold, and cool the brain in hot weather - cooling brain is accomplished with assistance of a carotid rete, where arterial blood going to brain is cooled by blood returning from the nasal area Lymph vessels and nodes - carry lymph back toward the heart via lymph nodes LECTURE 18 EXCRETORY SYSTEM Excretory System Functions 1) Maintain salt/water balance - by releasing controlled amounts of both - under the influence of the endocrine system (adrenal and pituitary glands) 2) Eliminate toxic wastes - NH /3H . R4leased as NH in fis4 - NH 4onverted to urea in liver in some fishes + - NH 4onverted to uric acid by kidneys in reptiles and birds The Nephron - basic unit of the kidney Renal corpuscle - renal (Bowman`s) capsule + glomerulus Nephron - renal capsule + tubule (proximal, intermediate, distal) - renal corpuscle is where filtrate passes from the blood-vascular system to the capsule - tubule reclaims solutes from the filtrate and conducts urine towards the outside of the body Development of the Kidney - kidney tissue develops from mesomere, which swells to create a nephric ridge - first segments of mesomere produce one pair of glomeruli and nephrons per segment - this first kidney is called the pronephros - pronephros may have originally emptied into the coelom in hagfishes - otherwise, collects in the nephric duct that transports urine towards cloaca - pronephros is a functional kidney in larval cyclostomes (lampreys and hagfishes), many fishes, and amphibia - in amniotes, even in their embryonic stages, pronephros is there but never functional - in teleosts, pronephros may persist with a glandular role...referred to as head kidney - vertebrate kidneys develop from mesomere beginning with the pronephros - a second kind of kidney, behind pronephros, develops as the mesonephros - it has many corpuscles per segment - it becomes the adult kidney in non-amniotes --> called opisthonephros (tail kidney) - in amniotes, a third kidney develops as the metanephros - it does not share the archinephric duct, but rather a new duct emerges from the cloaca to meet it --> ie the ureter Amniote embryo illustrating all 3 kidney types Opisthonephric kidney of a (male) salamander - kidney is associated with the testis --> shares the duct for carrying sperm leading to cloaca Mammalian Kidney Function - blood supply to the glomerulus is from the renal artery - blood travels through glomerulus and through capillaries in the nephric tubules where water and solutes are re-gained - Na ions are actively removed, and Cl water follows passively - animals with low filtration have the renal portal system - intermediate part of tubule is site of active transport of Na into surrounding tissue, resulting in very high [Na ] in that tissue - Cl follows to maintain charge balance - water also follows and reclaimed as it passes down collecting tubule Human Metanephric Kidney - about 180 L/day passes into glomerulus, or about 125 mL per minute - kidney re-absorbs all but 1.5 L/d achieving 100x concentration of the filtrate - the corpuscles are in the cortex of the kidney, while loops of Henle in the medulla Bird Kidneys - birds and mammals are only vertebrates that can produce urine that has a salt concentration higher than their blood - organization of bird kidney is different than that of mammals - loops are short peripherally, and long centrally, in each lobule Osmoregulation and Excretion in Vertebrates - land animals face a problem of water loss - fish in freshwater tend to gain water and must conserve salt - hyperosmotic to environment - fish in salt water tend to lose water - hyposmotic to environment - some saltwater fish (sharks) are osmoconformers --> can vary their salt content to remain isosmotic Osmoregulation and excretion in different vertebrates Saltwater teleosts are hyposmotic - tend to lose water - renal corpuscle is small or absent --> therefore produce very little urine and minimum of water is lost + - NH 4urea, or salt is lost through gills Freshwater fish are hyperosmotic - tend to gain water and lose salt - actively transport salt in through gills to maintain salt concen+ration - renal corpuscle is large --> produce copious dilute urine. NH i4 lost through gills Osmoconformers - sharks accumulate urea until they are isosmotic with seawater - renal corpuscle is large to eliminate water - excess salt excreted through rectal gland Birds and reptiles - are water conservers
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