1.2 Sexual Reproduction in Humans

• How is HIV transferred?

  1. Through sexual intercourse

  - wear a condom (not 100% safe)

  
  

  2. Through blood contact

  - blood transfusion needs to be screened for HIV

  - sharing hypodermic needles

  - people who deal with accidents where there is a lot of blood

  
  

  3. From mother to child
• AIDS

  Acquired Immune Deficiency Syndrome

  - caused by HIV [human immunodeficiency virus]

  - infects T cells over a long period of time

  - after several years of infection, T cells cannot fight pathogens effectively

  - patient becomes vulnerable to diseases

  - can develop cancer, brain damage etc
• STI

  Sexually transmitted infections

  - pathogens passed from one partner to another during sexual intercourse
• Artificial Insemination


  Injecting semen into the uterus by artificial means

  - sperm donor (man has sperm problem, get sperm from donor)

  
  

  Fertility drugs

  - enhance reproductive fertility

  - in women stimulates follicle development

  - contain FSH an LH

  - side effect: multiple pregnancies

  
  

  In vitro fertilization [IVF]

  - ovum fertilized outside woman's body

  - fertilized ovum implanted into uterus
• Surgical birth control

  Vasectomy

  - sperm ducts are cut and tied

  - stops sperm from traveling from the testes to the penis

  
  

  Tubal ligation

  - oviducts are cut and tied

  - stops eggs from travelling down oviducts

  
  

  ADV:

  - sure method

  - no side effects

  
  

  DISADV:

  Tube cannot be reopened again.
• IUD

  Intrauterine Device

  - plastic coated copper coil

  - has a string to remove it out of the vagina

  - irritates uterus wall preventing implantation

  - can be left inside for months / years
• Diaphragm or cap


  - circular rubber

  - placed over the cervix

  - sperm deposited in vagina cannot get past the diaphragm

  - work well with spermicides

  - must be fitted by a doctor
• Condom


  - thin rubber sheath worn on a man's erect

  penis

  - also is a female version

  - traps semen as it is released to stop it from going into the vagina

  - safe if used correctly

  - prevents transfer of infection
• Mechanical birth control

  Condom

  Femidom

  Diaphragm or cap

  IUD
• Chemical birth control


  The pill or oral contraceptive

  - contains oestrogen and progesterone

  - stops egg production when woman gets pregnant

  - must be taken every day

  - may have unpleasant side effects

  
  

  Spermicide

  - chemical applied as a gel / cream / foam

  - kills sperm

  - easy to use

  - works best with combination of another method, e.g diaphragm
• Natural birth control

  A method of birth control that involves no devices or chemicals

  - woman keeps record of menstrual cycle so she can predict when the egg is likely to be present in oviducts

  - avoid intercourse for several days around that time

  - not 100% certain
• Birth control


  The practice of preventing unwanted pregnancies, typically by use of contraception.
• Corpus luteum


  Empty ovarian follicle that secretes progesterone after release of the egg cell

  - if not fertilized, will gradually disappear

  - no more progesterone, so uterus breaks down
• Hormones in menstrual cycle

  Oestrogen

  - secreted by ovaries

  - stops FSH being produced so that only 1 egg matures during a cycle

  - stimulates pituitary gland to release LH

  
  

  Progestogen

  - secreted by the ovaries

  - maintains lining of uterus

  - made during the middle part of the menstrual cycle and during pregnancy

  
  

  Follicle stimulating hormone [FSH]

  - secreted by pituitary gland

  - causes egg to mature

  - stimulates ovaries to release oestrogen

  
  

  Luteinizing hormone [LH]

  - secreted by pituitary gland

  - causes mature egg to release from ovary
• Menstrual cycle


  Regular sequence of events in which an egg develops and is released from the body

  - lasts 28 - 30 days (variable)

  
• Puberty

  Developmental stage at which a person becomes capable of reproduction.

  
  

  BOYS:

  - start producing sperm

  - facial and pubic hair

  - muscular development

  Hormone: testosterone [produces in testes]

  
  

  GIRLS:

  - pubic hair

  - breast development

  - pelvic girdle becomes broader

  - menstrual cycle begins

  Hormone: Oestrogen [produced in ovaries

  
  

  During puberty, a person is not fully an adult. Emotional development is not yet complete.
• Disadvantages of bottle feeding

  - baby more likely to develop illness (no antibodies)

  - risk of wrong mixture when making

  - expensive

  - bottle must be cleaned after every feeding to avoid infection
• Advantages of bottle feeding

  - less pain for mother

  - others can help feed baby, can help father develop bond with baby

  - contains supplement vitamins and minerals
• Disadvantages of breastfeeding

  - painful for mother, baby needs to suck hard

  - mother must be present at all times

  - mother might be unable to rest well - baby might need milk at night time

  - damage beauty of mother
• Advantages of breastfeeding

  - has antibodies in it, develop baby's immune system + less chance of infection

  - has nutrients correctly to the proportion of baby as it grows

  - correct temperature to feed baby
• Post-natal care


  Care of the infant after delivery

  1. Mother's breast glands will become large during pregnancy, in order to produce breast milk to feed baby.

  2. Baby must be kept warm at all times

  3. Baby must be cared for physically and emotionally.
• Ante-natal care


  Care before birth

  - ensure diet is rich in calcium and irons, as well as carbohydrates

  - exercise regularly

  - do not drink or smoke

  - avoid getting ill
• Birth

  1. Fetus lies down few week before birth, head over the cervix

  2. Uterus walls contract when birth starts [labour]

  3. Muscles slowly stretch open cervix

  4. When cervix is wide enough for baby's head to go through (hours later), muscles push baby out cervix and vagina

  5. Placenta is detached from walls and passes out through vagina after birth

  6. Umbilical cord is removed, point where baby is connected is clamped (painless)
• Development of embryo to fetus

  Week 6: All major organs begin to grow

  Week 8: Embryo will start to move slightly

  Week 10 - 11: All organs are now in place, embryo is now a fetus

  
  

  Fetus will grow until week 38 - 40, when it will be born
• Amnion

  Innermost membranous sac surrounding the developing fetus

  - amnion and chorion form amniotic sac

  - amniotic fluid made by amnion

  - fluid is used to support and protect fetus
• Umbilical cord


  A tube containing the blood vessels connecting the fetus and placenta
• Substances that diffuse across placenta

  1. Waste products from fetus

  2. Oxygen

  3. Carbon dioxide

  4. Glucose

  5. Amino acids

  6. Fatty acids

  7. Water

  8. Toxins (smoke, alcohol)

  9. Pathogens (viruses, rubella)
• Placenta


  A structure that allows an embryo to be nourished by the mother

  - embryo's life support

  - connects embryo to wall of uterus

  - soft and dark red

  - blood of embryo and blood of mother never mix

  - movement of molecules across placenta by diffusion [large surface area, thin walls]
• Uterus containing fetus

  - placenta

  - umbilical cord

  - amniotic fluid

  
• Implantation


  The process by which the zygote attaches to the uterine wall

  
• Fertilisation in humans

  When the nucleus of a sperm fuses with the nucleus of an egg

  1. Sperm swims towards egg

  2. Head of sperm enters egg - does this using digestive enzymes in acrosome to dissolve jelly surrounding egg cell

  3. Once sperm head enters egg, egg membrane stops other sperm from entering

  4. Nucleus of successful sperm fuses with egg nucleus
• Sexual intercourse

  1. Blood is pumped into spaces inside penis, so it becomes erect

  2. Penis is placed inside vagina of woman

  3. Sperm is pushed out into the vagina [ejaculation- one ejaculation can give over 1 million sperm]

  4. Semen is deposited near cervis
• How does sperm get from the testes to the urethra?

  1. Sperm is produced in testes

  2. Sperm is carried away in sperm duct.

  3. Sperm duct joins up with urethra just below bladder

  4. Prostrate gland provides fluid for sperm to swim in
• Male gamate


  sperm

  - produces in cell wall of tubules in the testes

  - made by meiosis

  - sensitive to heat - too hot, sperm will not develop properly

  - survive for up to 5 days

  
• Sperm duct


  Carries sperm from testes to urethra
• Penis


  Male organ used in sexual intercourse
• Scrotum


  External sac that contains the testes
• Testicles


  Two small, egg-shaped glands

  - produce sperm

  - produce testosterone
• Urethra


  Tube leading from the urinary bladder to the outside of the body

  - additional function of ejaculating semen (in males)
• Prostate gland


  A gland surrounding the neck of the bladder

  - releases prostatic fluid (additional fluid to sperm)