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Lecture 6

BIO270H1 Lecture Notes - Lecture 6: Ovoviviparity, Signal Transduction, Vitellogenin

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Chris Garside

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Lecture 6 (October 28, 2015): Reproduction
Signal Transduction and Endocrine regulation Continued
insulin and glucagon and secreted by the pancreas
beta cells = insulin
alpha cells = glucagon
insulin works via direct feedback loops
obeta cells function as the integrating center
ouses ATP gated K+ channels
continuum design
omany pathway interact and there are many controls on a single pathway
Insulin and Glucagon
antagonistic pairing
oopposing effects on a pathway
oincrease blood glucose, glucose enters beta cells of pancreas, accelerates the
metabolic pathway, increase in ATP, ATP gated K+ channels close, depolarization
of cells, opens voltage fates Ca2+ channels, Ca2+ enters beta cell, stimulates
docking of vesicles and exocytosis of vesicles using SNARE proteins, insulin
inside the vesicles
o the vesicles travel to the target cells and bind to insulin receptors
tyrosine kinase receptor
dimerization and autophosphorylation initiates phosphorylation
cascades that lead to glucose uptake
osecond order feedback loop
stretch receptor sends signal to integrating center to prepare for the
breakdown of food
the signal is then send to the pancreas to stimulate the release of insulin
oreceptors in digestive track respond to glucose by releasing CCK, which interacts
with beta cells to stimulate the release of insulin
othe increase of insulin has a negative feedback on glucose and when there is less
glucose, insulin decreases as well since it's not needed anymore
oinsulin turns off alpha cells, turning off the pathway
this causes the breakdown of glycogen
oarthropods have homeostatic control of glucose levels
crustaceans use more neurohormones than hormones because they lack the
the neurohormone is produced in X organ, is transported to the sinus
gland, and is stored in vesicles

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when blood glucose decreases, K+ channels close, depolarization, Ca2+
channels open, this stimulates the docking and exocytosis of CHH, CHH
then binds to receptors on the target cells and the cell releases glucose
Regulation of Hormone Actions
synthesis (release)/degradation
receptor regulation (up/down)
oresults in change in sensitivity
alteration of affinity of receptor
feedback regulation
alterations in signal transduction pathway
osame signal can bind to different receptors
interaction with other molecules
oscientist injects compounds into dogs
othere were different levels of glucose depending on which combinations of
compounds were given
o(1)additive effect
adds the effects of each individual compound alone because the
compounds use the same signal transduction pathway
ex: glucagon + epinephrine
combined effect is greater than the sum of the individual hormone effects
ex: glucagon + epinephrine + cortisol
uses different signal pathway
one hormone reduces the effect of another
one hormone permits another hormone to exert its full effect
ex: thyroid hormones are necessary for epinephrine to exert its full effect
o(2), (3), (4) occur physiologically through receptors
usually first hormone leads to the up/down regulation of the second
production of offspring through sexual or asexual processes to ensure a species continues
why is the reproduction system unique?
ounnecessary for organism's own survival
in some cases detrimental because of how costly it is
onot required for individual homeostasis
ophysiological systems are different between males and females

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osexual reproduction
2 parents contribute equal amounts of genetic material
offspring is a combination of that genetic material
variation occurs because...
(1)haploid gametes from diploid parents
(2)recombination creates hybrid chromosomes
(3)diploid offspring have unique genetic combinations of (1) and
creates a population of distinct genotypes, so organisms can exploit
diverse ecological niches
oasexual reproduction
in a constant, stable environment, asexual reproduction is advantageous
identical offspring
buds from somatic tissue
ex: hydra
a single individual can make a colony
oex: coral
only ova and female reproductive system is involved
no male gametes
ex: daphnia go through parthenogensis when environment is stable
oif unstable, then they undergo sexual reproduction
ex: aphids
Sex Determination
oY is the sex determining chromosome
oXY = heterogametic male
oXX = homogametic female
ofemales are heterogametic (ZW)
omales are homogametic (ZZ)
ofertilized eggs = diploid females
ounfertilized eggs = haploid males
environmental sex determination
oex: temperature dependent
common in reptiles
turtles, crocodiles
pivotal temperature
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