Sexual Reproduction (11.4)
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Notes:HORMONES, HOMEOSTASIS & REPRODUCTION (HL)Core Topic:
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Egg and Sperm CellS
Egg CellEgg Dimensions
Diameter of cell = 110mm Corona Radiate: remaining follicle cells from the follicle in the ovary
Zona pellucida: layer of glycoproteins that prevents polyspermy Cortical Granules: contain digestive enzymes used to degrade sperm receptors on cells |
SpERM CellSperm Dimensions
Head - 3mm wide & 4mm long Mid piece- 7mm long Tail - 40mm long Acrosome: contains enzymes to digest the zona pellucida
Helical mitochondria: at give energy to power the tail in swimming |
Spermatogenesis & Oogenesis Overview
Spermatogenesis is the development of the sperm in the testes. Oogenesis is the development of the ovum (egg) in the ovary.
- Both processes use meiosis and should be thought about in terms of meiosis development. (Please see Topics 3.3 and 10.1 for a review of this process).
- While the creation of the sperm and egg are generally the same the two processes occur very differently in terms of timing and production.
- Spermatogenesis occurs beginning at puberty and continues to death and men can produce millions of sperm a day until they die.
- In contrast, oogenesis begins during fetal development, then finishes meiosis I during the menstrual cycle. An egg does not complete meiosis II unless fertilized.
Oogenesis
The maturation and release of the ovum is linked directly to the Menstral cycle. (See Topic 6.6) This is controlled primarily by FSH and LH. However, the follicle cells themselves control the release of estrogen and progesterone in case of pregnancy.
Stages of oogenesis:
Stages of oogenesis:
- Primary follicles are developed during fetal development. Follicles consist of follicle cells that surround a single primary oocyte cell which will undergo meiosis.
- Most women are born with about 400,000 follicles between two ovaries,
- The primary oocytes are arrested in Prophase I of Meiosis I at the time of birth. This basically means the nucleus has undergone crossing over but not much else.
- Begining at puberty, each month a single follicle (sometimes two) are stimulated to begin growing and dividing (FSH).
- The primary ovum will undergo the rest of meiosis I, becoming a secondary oocyte.
- At ovulation, the follicle is ruptured releasing the secondary oocyte, now called an ovum, which is directed into the fillopian tube for the possibility of fertilization and to reach the uterus.
- If fertilization occurs, the ovum will undergo meiosis II and fuse with the sperm nucleus.
- If fertilization does not occur, the ovum will be shed with the uterus lining during mensus
- Once the follicle is ruptured and releases the ovumn, the remaining follicle cells are now called the corpus luteum.
- The corpus luteum will produce estrogen and progesterone but slowly begins to degrade.
- If pregnancy occurs, the corpus luteum will be stimulated to remain active until the placenta can take over the production of hormones.
- If pregnancy does not occur, it will disappear and mensus will begin, starting the menstral cycle all over again.
- This process repeats (from step 2), changing ovaries every month and stops when there are no more follicles left, which results in menopause.
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Spermatogenesis
Spermatogenesis occurs in the testes and begins at puberty and never really stops.
- The cells designated to become sperm cells are called germinal cells.
- These are diploid cells which can undergo mitosis, dividing continually.
- At puberty, these germinal cells triggered to grow larger and are called primary spermatocytes. Note that they are still diploid cells.
- Primary Spermatocyte goes through meiosis 1 to create the secondary spermatocyte (haploid)
- Secondary Spermatocyte goes through meiosis 2 to create immature spermatids (haploid).
- With the help of the Sertoli cells, sermatids develop into mature sperm called spermatozoa.
- Spermatozoa (Sperm) are then released into the seminiferous tubule to be used during ejaculation.
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Types of Fertilization
Fertilization is dependent on the species. There are two types: Internal and External Fertilization.
Internal vs External Fertilization- Boundless Biology
Internal vs External Fertilization- Boundless Biology
Internal Fertilization- release of gametes directly into female body (generally terrestrial organisms) results in fertilization
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External Fertilization – release of gametes directly into the water (generally aquatic organisms) resulting in fertilization outside the female body
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Fertilization of egg
Fertilization = the union of egg + sperm
Once the sperm reach the egg the following things must occur:
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Implantation & Pregnancy
Pregnancy does not occur until the blastocyst is implanted in the endometrium.
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hCG Hormone
Pregnancy is dependent upon the maintenance of the endometrium of the uterus. Which means it is dependent upon high levels of estrogen and progesterone. (See Menstral cycle in Topic 6.6)
By 9th week of pregnancy = the placenta secretes large enough quantities of estrogen and progesterone to sustain pregnancy and hCG production decreases.
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the placenta
The Placenta allows for nutrient exchange between mother and child, and contains both fetal and maternal components.
Transport across the placenta How does nutrients get from placenta to fetus? |
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From Fertilization to Birth
Here are some facts about when specific functions begin to develop:
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Birthing Process
Birthing processing is initiated by the secretion of oxytocin by the pituitary gland
Hormones and Birth Oxytocin and Positive Feedback Hormones of pregnancy and labor |
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Animal Size and Gestation
Larger the body mass the longer the gestation period.
Mammals have two development strategies:
Humans are generally considered altricial species
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