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2/7/18
1
Chapter 6
� The smallest cell in the human body
¡ Only 0.002 inches in length
� Travel about 1 inch per hour
¡ Akin to a human traveling 1 – 2 mph (i.e., slow walking speed)
� Once in fallopian tube, sperm typically travel 3 “sperm miles” to reach the egg
¡ Takes about 1 – 2 hours
¡ Sperm can live in the vagina for up to 5 days
� Ejaculate has 80 million sperm
¡ 25% are already inactive (“dead”)
¡ 50% drain out the vagina
¡ Many are killed by acidity of vagina
¡ Only 1 – 2% make it through the cervix
¡ 50% enter the wrong fallopian tube
¡ Only 1 - 2% of the remaining find the egg
� In the end, typically only 3,000 (about 1 in 25,000) make it to the egg!
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� How many sperm does it take to impregnate an egg?
�Hundreds of sperm are necessary in order to implant an egg
¡ Sperm release chemicals that weaken the “zona” (shell) of the egg, allowing one to enter
¡ Once one sperm enters egg, it releases enzymes¢ Causes zona to
instantly harden
¢ Halts other sperm from entering
¡ It takes a village for one hero to emerge!
� Males often compete with their sperm, known as “gamete selection”¡ Producing more sperm to “out
number” other males
¡ “Shovel” shape of penis evacuates competitor’s sperm
¡ In some animals, some sperm cells only used to kill competing sperm (“glatiator” sperm)
¡ In some animals, sperm tangle with each other around egg to create defensive barrier, blocking egg from competing sperm
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� Recent studies find men’s sperm counts have been drastically lowering
¡ Sperm counts have dropped 60% in last 40 years
¡ Similar decreases have been seen in sperm quality (sperm viability, life span, swimming capacity)
¡ Replicated in samples across North and South America, Europe, Asia, and Africa
� Standards were established in 1980s for what constituted “satisfactory” sperm donation
Percent of men giving “satisfactory” donations
82%
56%
18%
0%
10%20%30%40%50%
60%70%80%90%
1990 2000 2015
� What is causing lowered sperm counts?¡ Endocrine disrupting chemicals
¢ Commonly found in plastics, pesticides, and even sunscreen and other cosmetics
¢ Interrupts production of testosterone and other hormones, especially among pregnant women
� Likely also the cause of recent increases in…¡ Insufficient testosterone levels among infants¡ Undescended testicles and other genital disorders
¡ Need for assisted reproductive technology (e.g., in vitro fertilization)
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�Most women experience first symptoms of pregnancy about 2 weeks after conception¡ Once placenta has formed, the body produces
high levels of estrogen and progesterone
� This causes most symptoms of pregnancy¡ Headaches
¡ Fatigue
¡ Swelling and water retention
¡ Breast tenderness
¡ Nausea (not just in the mornings)
¢ Although 33% don’t experience nausea
�At this time, pregnancy tests can be used¡ Detects chemical changes caused by pregnancy
� Many women use home pregnancy tests
�Poll: How accurate are home pregnancy tests?
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�Tests at the doctor’s office: 98% accurate¡ Test multiple hormone patterns for higher
accuracy
¡ Costs more ($200 - $400) but covered by insurance
¡ Can sometimes (1 – 2%) result in false negative if administered too early
�Home pregnancy tests have an accuracy rating of 50 – 65%!
* 99% accurate “if administered once per week for 4 weeks”
� Humans are the only animals known to get nauseous and vomit during pregnancy
� Why do women get morning sickness?¡ Human fetus is extremely sensitive
to toxins, bacteria, and parasites
¡ Nausea most common after eating meat or bitter-tasting vegetables¢ Most likely to contain toxins or micro-
organisms that can damage fetus
¡ Morning sickness usually stops around time fetus becomes less vulnerable to toxins (1st trimester)
�Second Trimester
¡Most experience relief of negative symptoms
¡Worst symptom now is water retention and swelling
¢ Particularly around the ankles and feet
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�Third Trimester
¡Women really begin to feel the weight!
¢ Pregnancy results in increase of 25 – 40 lbs.
¡ Can experience “pseudo” contractions
¢ Painless contractions meant to “train” the uterine muscles
� First Stage: Labor
¡ Contractions begin, separated by 15 – 20 minutes
¡ These start to efface (thin out) and dilate (open) the cervix
¡ Women should go to the hospital when contractions are 5 minutes apart
¢ Usually takes 5 – 18 hours after first contraction
¢ At this time, cervix is dilated 3 – 4 inches
� Second Stage: Delivery
¡ Begins when cervix is fully dilated (4 – 5 inches)
¢ Baby begins to move down birth canal
¡ Within a few hours, the baby “crowns”
¡ Doctors then sometimes perform an episiotomy
¢ Cutting the perineum
¢ Usually painless, because pressure from baby’s head blocks nerve signals