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Biol211, W07 Clara Tsui Lecture 14 – Muscle Somatic (from myotomes and mesenchyme) - axial, appendicular, branchial, hypobranchial - myotomes #: o eye: 1, 2, 3, 5 o mandibular: 4 o hyoid: 6 o 1st branchial arch: 7 Visceral - heart, smooth muscles of skin, gut, organs Muscle Types 1. Smooth: small, spindle-shaped, involuntary 2. Cardiac: branched, striated, involuntary; intercalated disks 3. Skeletal a. Tonic: slow contraction, unable to propagate stimulus (local contraction) b. Twitch: fast, brief contraction along entire length of fibre i. Slow: high myoglobin content (red), fatigue slowly ii. Fast 1. fatigable: white; responsible for bursts of movement 2. fatigue-resistant: red; moderate contraction speed - axial musculature in fish and lower tetrapods directs side-to-side movement in tetrapods, appendicular musculature increases at expense of axial o trunk muscles become more dorsal o trunk movement becomes dorso-ventral (not lateral) Biol211, W07 Clara Tsui Lecture 15 – Digestive System Coelom and Gut Undivided coelom/peritoneal cavity, or with partial septum Separate pericardial cavity behind gills; separated by transverse septum Heart moves beneath lungs; pleuripericardial membrane separates heart and lungs Lungs are ventral in a separate pleural cavity and surround the heart; membrane is called mediastinum; pleuroperitoneal membrane houses the diaphragm Hagfish, sharks Fishes, Amphibia Reptiles Mammals Mouth - invagination meets the gut; called the stomodeum - nasal epithelium and hypophyseal pouch develop on or dorsal to stomodeum - in Agnatha, they develop on the head adjacent to it Gut - mucosa and submucosa are derived from the endoderm muscular layers and serous membrane are from (splanchnic) hypomere absorptive part of gut needs lots of surface area – folds, villi o shark – spiral valve o trout – pyloric caeca o tetrapods – long small intestine Foregut - ahead of small intestine - absorption is favoured - slow - allows for re-chewing (cud) - protection adaptation – grab food and run Liver - Hindgut - below small intestine - faster throughput - coprophagus – poo-eating largest organ in the body digestive – produces bile acids (stored in gallbladder) metabolic – metabolize carbs and proteins, store fats detoxification, blood cell formation, stores iron and vitamins Pancreas - exocrine glands in acinous cells from ventral pancreas produce zymogens - endocrine glandsin islets of Langerhans from dorsal pancreas produce insulin and glucagon - it is not a discrete organ in most fishes Biol211, W07 Clara Tsui Lecture 16 Respiratory Systems External respiration requires: (1) large surface area (2) thin barrier between blood and fluid (3) flow or exchange of air/water (4) favourable diffusion gradient between blood and fluid - each visceral arch (6) between the gill openings contains a branch of the ventral aorta gas exchange takes place in gill filaments Lamprey Shark Teleost Pouched gills 7 gill openings, tubular 5 gill openings; 4 ½ gills Covered by gill septa that separate and protect filaments Spiracle = opening ahead of hyoid arch 4 arches Gill filaments are free, covered by operculum Lungs - dorsal in fish; ventral in tetrapods - gas bladders maintain neutral buoyancy o gas is added via the red body, and removed via the oval body - mammalian lungs have large surface area, but are inefficient o air flow is tidal - avian lungs are small, constant-volume, associated with hollow air sacs o sternum and muscles act on air sacs o air low is unidirectional (not tidal) o countercurrent gas exchange is used o extremely efficient, for flying at high altitudes Lectures 17 & 18 Circulation Blood vascular system Lymphatic system Sites of hemopoiesis - blood islands - guts and organs - spleen, thymus (usually degenerates), lymph nodes - leuocytes - red bone marrow Circulation in the Shark - heart pumps blood to gills - it gets oxygenated - internal carotid arteries and dorsal aorta distribute it around body Biol211, W07 Clara Tsui - returning blood is collected via paired anterior and posterior cardinal veins - tail circulation returns to kidneys via renal portal vein Example of recapitulation in circulatory system of vertebrates: - all vertebrate embryos have circulatory systems with six aortic arches on each side of the pharynx - major arteries and veins are paired o except dorsal and ventral aorta, and vessels of the gut - then... they develop by deleting unnecessary portions of the embryonic system o becomes asymmetric in tetrapods Example of parallel evolution (but opposite): - birds lose the left 4th aortic arch while mammals delete the right 4th arch - birds: 4R = dorsal aorta; 4L = brachiocephalic artery - mammals: 4R = subclavian artery; 4L = dorsal aorta - veins also become asymmetric - right hepatic vein + right hepatic portal vein = postcava - anterior cardinal vein = precava Heart Development - in embryos it is a linear pump - parts: 1. sinus venosus - receives blood returning via common cardinal veins 2. atrium - delivers blood to... 3. ventricle - main pump 4. conus - has semilunar valves that prevent backflow to ventricle - in fish, atrium lies dorsal to ventricle; conus is elastic and called the bulbus arteriosus Flexible Hearts - lungfish can direct blood to gills or lungs - conus is divided; ventricle is partly divided - when lungs are not in use, resistance prevents circulation and redirects blood - frog uses skin primarily to breathe, but can direct a variable fraction of blood to lungs if they are in - there's no mixing of blood from the two sides - turtles cannot skin breathe - undivided ventricle and divided conus - when diving, oxygenated blood goes only to 4R (head and limbs) Inflexible Hearts - mammals and birds have fully divided atria and ventricles - no mixing or shunting - highly efficient; appropriate for endotherms with high and constant metabolic rates Biol211, W07 Clara Tsui Lecture 19 Excretory System Functions: 1. Maintain salt/water balance 2. Eliminate toxins Evolution of the nephron = recapitulation - pronephros - may persist and have glandular function in fish - mesonephros = opisthonephros o drained by (opistho)nephric ducts directly into cloaca or out - metanephros - develops in amniotes o drained by ureters that grow toward kidney o allantois becomes urinary bladder o the duct is the urethra o nephric duct persists in male amniotes as part of reproductive system Blood supply - filtration is minimal in fishes, reptiles, birds - renal portal vein is present; carries deoxygenated blood - mammals undergo maximal filtration Mammalian Nephron Function 1. Filtration. Water and low molecular weight substances enter renal capsule. 2. Reabsorption of water and Cl- in proximal tubule by active transport of Na+. 3. Loop of Henle acts as "counter-current sodium multiplier". Active transport of Na+ happens along ascending limb. High salt content of surrounding tissue drives passive water reclamation along descending limb. 4. In distal tubule, K+ is recovered, pH is altered, secretion occurs. 5. Excretion to pelvis of kidney. Human Kidney Function - contain 2 million nephrons - capsules have 1/2 of body's surface area - 125 mL/min passes through glomerulus Osmoregulation in vertebrates - birds and reptiles have small renal corpuscles - convert ammonium to uric acid (solid) so they don't have to produce urine - birds have a Loop of Henle - excess salt is secreted through specialized glands of eye, nasal area, mouth - mammals are less effective at water conservation - they secrete ammonium as urea so they must produce urine - Loop of Henle minimizes water loss - marine mammals produce urine that is more saline than seawater (b/c they can't drink fresh water) Biol211, W07 Clara Tsui Hyperosmotic - freshwater fish - gain water and salt through gills and in feeding - large renal corpuscle = copious dilute urine - ammonium is lost through gills - sharks - accumulate urea and retain it in their flesh - large renal corpuscle is large - excess salt is excreted through rectal gland Hyposmotic - saltwater fish - tend to lose water through gills - gain salt in feeding; excrete it via the gills - small renal corpuscle; almost don't pee at all - ammonium or urea is lost through gills Lecture 20 Reproductive System dioecious - produce only one type of gamete sequentially hermaphroditic - one sex for awhile; the other, later simultaneously hermaphroditic - has both M and F sex organs; rarely self-fertilize parthenogenesis - reproduce from unfertilized eggs (genetically unfavourable) sexually dimorphic - M and F have different characteristics