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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