11.4 Reproduction Higher

A mature Sperm

http://www.bmu.unimelb.edu.au/resources/illustrations/images/sperm_thumb.gif

You need to know the top diagram. The bottom ones are included for interest only!

http://images.google.com.ph/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Complete_diagram_of_a_human_spermatozoa.svg/180px-Complete_diagram_of_a_human_spermatozoa.svg.png&imgrefurl=http://en.wikibooks.org/wiki/Human_Physiology/The_male_reproductive_system&usg=__zSltk3LvardHYMqGrfqBWtXJjxo=&h=176&w=180&sz=18&hl=en&start=3&tbnid=U7gKJCUpYC4dmM:&tbnh=99&tbnw=101&prev=/images%3Fq%3Dspermatazoa%2Bdiagram%26gbv%3D2%26hl%3Den

A mature ovum

Nucleus

Nucleolus

Cytoplasm containing lipid granules

Zona pellucida

Membrane with cortical granules

www.gettyimages.com/detail/BC8592-001/Stone

http://etc.usf.edu/clipart/50700/50718/50718_ovum_lg.gif

Fertilisation• 2 reactions occur in fertilization. The

acrosome reaction and the cortical reaction

http://images.google.com.ph/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/2/26/Acrosome_reaction_diagram.svg/440px-Acrosome_reaction_diagram.svg.png&imgrefurl=http://en.wikibooks.org/wiki/Human_Physiology/The_male_reproductive_system&usg=__X1gzuaYckkk_8BRocULr7-jhhEY=&h=310&w=440&sz=72&hl=en&start=2&tbnid=wvYtqlT1PP6GVM:&tbnh=89&tbnw=127&prev=/images%3Fq%3Dspermatazoa%2Bdiagram%26gbv%3D2%26hl%3Den

As the sperm approaches the zona pellucida of the egg,

which is necessary for initiating the acrosome

reaction, the membrane surrounding the acrosome

fuses with the plasma membrane of the

sperm, exposing the contents of the acrosome. The

contents include surface antigens and numerous

enzymes which are responsible for breaking through the egg's tough

coating and allowing fertilization to occur.

• The cortical reaction, also known as the zona reaction, occurs when a sperm cell unites with the egg's plasma membrane, altering the zona pellucida which prevents other sperm from binding to and entering the egg.

• The cortical reaction is exocytosis of the egg's cortical granules. Cortical granules are secretory vesicles that reside just below the egg's plasma membrane. When the fertilizing sperm contacts the egg plasma membrane, it causes calcium to be released from storage sites in the egg, raising the intracellular free calcium concentration. This triggers fusion of the cortical granule membranes with the egg plasma membrane, liberating the contents of the granules to the extracellular space. Fusion begins near the site of sperm contact, and then as the wave of calcium release sweeps around the egg, a wave of cortical granule fusion results. The contents of the granules vary with the species, and are not fully understood.

http://en.wikipedia.org/wiki/Cortical_reaction

http://www.kumc.edu/instruction/medicine/anatomy/histoweb/male/male04.htm

http://faculty.southwest.tn.edu/rburkett/A&P2_r7.jpg

• The small cells at the base of the seminiferous epithelium are spermatogonia.

• The ones with the largest are nuclei are primary spermatocytes.

• There are spermatids (round & elongating) about to be released into the lumen.

SpermatogenesisA. Spermatogonia push their way

through the tight junctions between adjacent Sertoli cells and become primary spermatocytes.

B. In the first meiotic division each of the 46 chromosomes doubles up and then forms a pair with another doubled up chromosome during which time there is exchange of genetic material (crossing over). The cell divides and each daughter cell contains one of the pairs of chromosomes. In the second meiotic division each double chromosome simply separates producing genetically identical secondary spermatocytes.

http://faculty.southwest.tn.edu/rburkett/A&P2_r8.jpg

http://click4biology.info/c4b/11/11.4/comparison.gif

Roles of HormonesFemale Male

FSH •stimulates ovary to produce steroids ovary will produce estradiol during follicular phase and progesterone during luteal phase •surge at midcycle, with LH, triggers ovulation

•stimulates Sertoli cells to produce androgen-binding protein (ABP), thereby stimulating spermatogenesis•FSH also stimulates Sertoli cells to produce inhibin, which provides negative feedback to the anterior pituitary to decrease FSH secretion

LH •stimulates ovary to produce steoroids.•surge at midcycle triggers ovulation remember, luteinizing hormone turns the follicle into the corpeus luteum by triggering ovulation

•stimulates Leydig cells to produce testosterone •testosterone provides negative feedback to anterior pituitary and hypothalamus

HCG Human Chorionic Gonado-trophin

•maintains progesterone production by the corpus luteum; •maintains the endometrium for the first trimester;•stimulates fetal gonad development and androgen synthesis by the fetal testes; •stimulates the secretion of oestrogen and development of the placenta.

Testosterone •Initiates the process of spermatogenesis•Stimulates the maturation of secondary spermatocytes through meiosis and differentiation to spermatozoa.

The first week of pregnancy.

http://stemcells.nih.gov/StaticResources/info/scireport/images/figurea2.jpg

Use this diagram for the timings. The labels are beyond your IB requirements.

http://mcb.berkeley.edu/courses/mcb135e/Difficult%20Slides/Fertilization%201.jpg

The embryo goes through its cleavage stages while it is migrating along the fallopian tube. As a blastocyst it reaches the uterine cavity at the end of the 5th day. There, the hatching and the embedding into the endometrium occur on the 6th day.

The morula, a collection of around 30 cells (blastomere), is created at about 96 hours. Because these cells arise only through the cleavage of the zygote and all are found inside the pellucid zone, which cannot expand, no growth is seen. Every new cell is thus only half as large as the cell from which it derives. The name of this stage comes from its resemblance to a mulberry, since it really looks like a collection of spherical cells.

http://www.embryology.ch/anglais/evorimplantation/furchung01.html

A blastocystThe blastocyst comes into being through compaction of the cells and the accumulation of intercellular fluid, leading to the formation of the blastocyst cavity. At this point, the embryoblast that lies inside (hump on the left side) consists of roughly 12 cells. At the same time, the enveloping trophoblast, made of a single cellular layer, contains around a hundred cells.

Hatching Around the end of the fifth day the embryo frees itself from the enveloping pellucid zone. Through a series of expansion-contraction cycles the embryo bursts the covering. This is supported by enzymes that dissolve the pellucid zone. The rhythmic expansions and contractions result in the embryo bulging out of and emerging from the rigid envelope. This "first birth" is called hatching.

Implantation

http://mcb.berkeley.edu/courses/mcb135e/Difficult%20Slides/Implantation%203.jpg

Having ‘hatched’ the blastocyst nows burrows into the endometrium. The inner mass (embryoblast) starts to develop into the embryo. The trophoblast develops into the amniotic sac and placenta.

Early embryoAfter 4 weeks Implantation site. The basic structure of the placenta has been formed with maternal blood being delivered to the forming placenta via spiral arteries while being drained away via uterine veins. Like the roots of a tree, the developing chorionic villi remain immersed in a space filled with the nutrient rich maternal blood.

http://www.med.yale.edu/obgyn/kliman/placenta/articles/EOR_Placenta/Trophtoplacenta.html

The amnion secretes amniotic fluid that protects the baby. It acts as a physical shock absorber and due to its high water content (and the high Spec.Heat.Cap. of the water) as a thermal buffer.

The placenta allows exchange of materials between the mother and embryo without allowing the blood to mix. It also produces Progesterone and oestrogen.

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Pregnancy week by week

Stretch receptors in the uterus send a signal to the pituitary gland to release oxytocin into the blood stream.

Oxytocin causes the muscles of the uterus to contract. And prepare the mammary glands to secrete milk.

This is called Positive feedback.

The hormonal control of birth.

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Birth

http://www.healthsquare.com/fgwh/wh1c2601.jpg

Now watch these videos….

• http://www.pbs.org/wgbh/nova/miracle/program.html