Download Lesson 15.4 Pregnancy - Ms. McKenzie`s Class

McKenzie
Health Science 20
NAME:_________________
Lesson 15.4 Pregnancy
Objectives:
1. Describe how a zygote develops and implants in the uterus.
2. Describe the physiological changes that occur in the mother and developing child during pregnancy.
3. Explain the sequence of events involved in childbirth.
4. Explain how breast milk is produced and secreted.
Saskatchewan Outcome:
“I can analyze the anatomy and physiology of a healthy human”
Saskatchewan Indicators:
“I can describe the anatomy (structure) and physiology (function) of the reproductive system”
Before this lesson, try to answer the following questions:
1. Where is the oocyte fertilized and where does it go after it’s fertilized?
ANSWER:____________________________________________________________________
2. What is the placenta, and how does it help the embryo and fetus develop?
ANSWER:____________________________________________________________________
3. What are the stages of labour?
ANSWER:____________________________________________________________________
Key Terms:
 Amniotic fluid
 Dilation
 Fetus
 lactation
 placenta
References:
 Notes & handouts
 Textbook Pages: 550 – 559
 Study Guide Pages: 231 – 233
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Blastocyst
Embryo
hCG
let-down reflex
prolactin
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Delivery of the placenta
Expulsion
implantation
oxytocin
Umbilical chord
McKenzie
Health Science 20
NAME:_________________
Reproduction 5:
Pregnancy
Out of a total of about 400 million ejaculated from the penis, only about 3000 make it to the
oviduct. Of these 3000, only about 50 will make it to the mature egg. The egg is only
fertile for 10 to 15 hours and a sperm lives for about 48 hours. Only one sperm can fertilize
an egg and fertilization occurs in the OVIDUCTS.
The sperm and egg are gametes which contain 23 chromosomes. (Normal body cells have
46). When the nuclei of the gametes fuse, a ZYGOTE with 46 chromosomes is formed.
The zygote undergoes a number of mitotic divisions to become an EMBRYO which travels
down the oviduct to the uterus. Inside the uterus, the embryo will undergo
IMPLANTATION. Implantation marks the beginning of PREGNANCY. During
implantation, the PLACENTA forms. The placenta not only provides the embryo with
nourishment and oxygen and removes metabolic wastes, but it also produces HUMAN
CHORIONIC GONADOTROPIC HORMONE.
HUMAN
CHORIONIC
GONADOTROPIC
HORMONE
 prevents the degeneration of the
CORPUS LUTEUM

The corpus luteum remains in the ovary and secretes even larger quantities of ESTROGEN and
PROGESTERONE.

The maintenance of high levels of estrogen and progesterone provide negative feedback and prevent the
secretion of GONADOTROPIC RELEASING HORMONE. This effectively “shuts down” the anterior
pituitary and maintains low levels of FOLLICLE STIMULATING HORMONE and LEUTEINIZING
HORMONE.

Low levels of FSH and LH prevent follicular maturation, ovulation and menstruation.

The corpus luteum will eventually degenerate (after about 5 months). Estrogen and progesterone
production is taken over by the maturing placenta.
McKenzie
Health Science 20
NAME:_________________
Oxytocin: Positive feedback control.
Recall: Oxytocin is a hormone produced in the HYPOTHALAMUS but stored and secreted
by the POSTERIOR PITUITARY gland.
Oxytocin has two functions:
1. Stimulation of uterine contractions.
2. Release of milk by the mammary glands.
Uterine Stimulation

The number of oxytocin receptors in the uterus increase substantially during pregnancy.

Although there is no increase in the amount of oxytocin in the blood, the increased number of receptors
eventually makes the uterus so sensitive to oxytocin, strong uterine contractions begin.

Strong, coordinated uterine contractions exert a POSITIVE FEEDBACK effect by stimulating the
hypothalamus which signals the posterior pituitary to release more oxytocin.

More oxytocin causes more contractions which cause more oxytocin secretions (positive feedback) until
childbirth occurs.
Milk Let-Down


Milk LET-DOWN does not refer to milk
production. Milk is secreted into sacs called
ALVEOLI. However, milk must be moved into
the MAMMARY DUCTS that lead to the
nipples. This is milk let-down.

Milk let-down is accomplished by contraction
of the cells surrounding the alveoli. These
cells are stimulated to contract by OXYTOCIN.

The baby suckling the breast stimulates
nerves in the breast. These nerve impulses
travel to the hypothalamus which stimulates
oxytocin release by the posterior pituitary.
More oxytocin promotes more milk let-down
which makes the baby happier. The baby
suckles more and POSITIVE FEEDBACK occurs.
Complete the Lesson
1. VIDEO: Watch https://www.healthyfamiliesbc.ca/home/articles/video-about-labour-and-birth
2. Read p. 550 – 558
3. Complete #1-10, p. 558
4. Study Guide pages 231 and 233 (handout)