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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