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Lecture 8

Lecture 8 (Ch.6 - Sexual Development).docx

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Ayesha Khan

NOTE: DUE TO POTENTIAL COPYRIGHT INFRINGEMENTS, THE SLIDES HAD BEEN TAKEN OUT BY OWNER. Lecture 8 (Ch:6 – Sexual Development) SLIDE 1 - Genes guide development of structure of the fetus - What are the steps and sequence that occurs - Listing series of steps and how things get differentiated SLIDE 2 - FERTILIZATION - sperm must go through 2 important processes: - Capacitation: sperm carries a lot of protein (head of sperm has lots of protein); the fallopian tubes have a lot of enzymes; if it’s a capacited sperm, it means protein surrounding the head of the sperm gets removed and allows the sperm to swim faster and forcefully; the danger with this is that it can only live for a few hours - Not all sperm capacitate at the same time; tends to vary by time; once capacitated, it has to have a good sense of where the egg is and the egg sends out chemical attraction to - Acrosome reaction: when sperm reaches outer layer of the egg; acrosome have lots of digestive enzymes and allow sperm to enter ___ to egg?; if not enough digestive enzymes, then the sperm can not penetrate the layer of the egg SLIDE 3 - Increase in calcium ions - There’s going to be mixing of genetic material between sperm and egg - What allows for sperm to continue to habitate in the egg is the increase of calcium ions in the conceptus stage - Increase of calcium ions means allowing genetic material exchange to occur - Allow for cell division - In order to figure if healthy fertilization has occur, need to see multiple cell division - Start off with conceptus and see if genetic material starts to induce cell division SLIDE 4 - Start to see genes that become activated then goes to 16 cell stage and see conceptus become mass of cells and then it goes to 4 days cell - There’s a predictable timeline and if something is not right, you’ll see developmental delays in the 4 or 8 cell stage - 4 day is important SLIDE 5 - When 32 cell stage, then it’s called blastocyst - 6 days later, conceptus starts to secrete hCG and signals to mom’s body that implantation has occurred SLIDE 6 - It wasn’t induced, it was spontaneous - Pregnancy can occur but it may not carry on several weeks later - Perhaps the hormonal environment (estrogen) - Increase of estrogen have impact? Looking at the chromosomal abnormality? - Suspected the number of genes might be terminating implantation - Signals that block implantation such as nicotine (can impact some individuals); interfere with docking signals that occur between conceptus and endometrium SLIDE 7 - Three layers; give rise to skin and the nervous system - Ectoderm: eventually form skin and nervous system - Mesoderm: give rise to cardiovascular, muscular and skeletal system - Endoderm: formation of guts and lungs - The mesoderm and the endoderm are the things that develop on the fetal side of the placenta and that’s important because exchange of hormones between fetus and mother - If mother’s ovaries have something wrong, then the fetus can produce it’s own progesterone and NOTE: DUE TO POTENTIAL COPYRIGHT INFRINGEMENTS, THE SLIDES HAD BEEN TAKEN OUT BY OWNER. estrogen - Maternal side of the placenta is coming from endometrium SLIDE 8 - Fetus wants to take control of hormonal - The corpus luteum exist; major source of where progesterone gets released - Progesterone is also released from fetal side of placenta and at the same time, the fetal adrenal glands has capacity to produce testosterone and convert it to estrogen - Levels of hormones in pregnancy tend to be very high because of the mother’s production along with the fetus’s production - Lungs of developing fetus is different in function along side of heart; a lot of blood pump from heart is going towards the lung; the amount of blood flow is very little in the fetus compare to newborn; also mean hemoglobin structure is different in developing fetus compared to newborn - Air is not required to same extent as the newborn - Not a lot of flow, different hemoglobin structure; the fetus is focus on development and structure - Development of placenta and there’s functions of it right away compared to cardiovascular system that might not function right away SLIDE 9 - Hormones production are different based on genetic sex - How and what makes a difference of development of male and female? - Male development depend on gene complex that trigger development of gonads; the concept goes back to structure and function - Testes in the fetus start producing testosterone and the testosterone goes to work right away in the internal reproductive structures - Testosterone get into blood supply of fetus and then goes toward the brain and has consequence there in terms of structure of the brain (actual nuclei are being affected) and this is what male and females different - Female fetus does not have testes to produce testosterone and therefore brain structure is very different - Concept of sex differentiation is that males get exposure on androgens and impact on the brain SLIDE 10 - Removed ovaries in females and removed testes in males - Looking at the behavour - When ovaries were removed, what you look at is the sexual behaviour and compare - The females were not interested in sex (neutral) with a receptive male - Male fetus with testes removed and that they still continue to be males, but their behaviour changes where their mounting and start showing female sexual behaviour - genetic sex didn’t change but the adult behaviour was similar; fetus with testes removed exhibit no mounting or show female behaviours - It tells us that testosterone was driving the mounting behaviour SLIDE 11 - SRY: sequence of genes - DAX-1 important in ovary development SLIDE 12 - IMPORTANT - The basics of how everything start to form - Sex chromosomes of XX or XY that have different gene functions - In XY, although they have DAX-1, it doesn’t mean there’s development of ovaries because there’s a strong SRY gene that indicates to make testes - Developing fetus is really squished so that its structure is very close together - The aorta develops eventually close to the heart, and next to aorta there’s a cluster of cells and they make up the genetic ridge (mesodermal cells) and these mesonephros cells - Both testes and ovaries develop from genetic ridges despite the fact that - Mesonephros will donate tissue to the genetic ridges which eventually form testes and ovaries - Genetic ridge contributes to making gonads themselves NOTE: DUE TO POTENTIAL COPYRIGHT INFRINGEMENTS, THE SLIDES HAD BEEN TAKEN OUT BY OWNER. - When these genes become activated, that’s when further development of testes and ovaries will happen - In males, when this system become activated (donation of cells) and then there’s activation of SRY gene (not the other around); the cell division around genital ridge and donation of cells from mesonephros and then it activates the SRY gene; - When SRY gene is activated, the sertoli cells start to develop and found within genetic ridges and assist in further development of the testes; - When SRY gene is absent, the production of granulosa cells happen for mechanisms that are not clear SLIDE 13 - Where do sperm and egg originate from? From the yolk sac SLIDE 14 - Yolk sac have premordial germ cells and then it will migrate to genetic ridges and then it will differentiate to eggs or sperms depending on the sex - Chemical signal that is coming from genetic ridge to tell the premordial germ cells to migrate in that direction; the eggs will start to develop right away, in males, there’s a lot of stem cells and these stem cells later on life will change to sperm cells SLIDE 15 - 6 weeks after fertilization, two sets of ducts running from each gonads to the future site of external genitals - Both males and females have Wolffian ducts and Mullerain ducts - Ultimately, Wolffian ducts that give rise to male reproductive system and Mullerian ducts give rise to female reproductive system SLIDE 16 SLIDE 17 - initially, males and females have both ducts SLIDE 18 - in order for differentiation to occur, need further development first
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