Reproduction and Growth

Chapter 13

Male Reproductive Structures and Glands

Spermatogenesis:• In testis

– Seminiferous tubules

– Spermatogenesis occurs here

• Other structures:– Epididymis– Vas deferens– Glands

• Prostate• Seminal vesicles

Spermatogensis• Each seminiferous

tubule is lined with a layer of germinal epithelium which consist of primordial germ cells

• Each cells undergo to produce diploid spermatogonia (2n)

• Each spermatogonium develops into primary spermatocyte (2n)

• At meiosis I, each spermatocyte divides to produce 2 secondary spermatocytes (n)

• At the end of meiosis II, two spermatids are formed

• Therefore, each spermatogonium develops to form 4 sperms

GROWTHMEITOSIS I,

CYTOPLASMIC DIVISIONMEIOSIS II,

CYTOPLASMIC DIVISION

cell differentation, sperm formation (mature, haploid male gametes)

spermatids (haploid)

secondary spermatocytes

(haploid)

primary spermatocyte

(diploid)

spermato-gonium

(diploid male reproductive

cell)

Spermatogenesis:

Fig. 45.4, p. 787

Sertoli cell

spermatogonium (diploid)

primary spermatocyte

MITOSIS MEIOSIS I MEIOSIS IIpart of the lumen of a seminiferous tubule

late spermatid

secondary spermatocyte early spermatids

head (DNA in enzyme-rich cap)

midpiece with mitochondria

tail (with core of microtubules)

Female Reproductive Structures

Oogenesis:

ovary (where eggs develop)

vagina

• Regulated by the menstrual cycle

• Ovary– Oogenesis

occurs here

• Other structures:– Fallopian tubes

or oviducts– Uterus– Vagina

Oogenesis• The ovary wall consists a layer of germinal

epithelium which is made up of primordial germ cells.

• In foetal stage, each germ cells divide by mitosis to form diploid oogonia (2n)

• Each oogonium develops into primary oocyte (2n), surrounded by a layer of follicle cells to form a primary follicle

• At birth, a baby girl has millions of primary oocytes, which undergoes meiosis I and stop at Prophase I until puberty

…continue from previous slides

• At puberty, 1 primary oocyte completes meiosis I to form 2 haploid cells; 1 secondary oocyte (n) and a polary body (n)

• The secondary oocyte is surrounded by secondary follicle cells, which further develops into Graafian follicle the side of ovarian wall

• During ovulation, the Graafian follicle bursts and releases the secondary oocyte into Fallopian tube

• When fertilisation occurs, the secondary oocyte undergoes complete meiosis II to form a polar body (n) and an ovum (n)

Oogenesis:

Fig. 10.9 p. 169

GROWTHMEITOSIS I,

CYTOPLASMIC DIVISIONMEIOSIS II,

CYTOPLASMIC DIVISION

ovum (haploid)

primary oocyte (diploid)

oogonium (diploid

reproductive cell) secondary

oocyte haploid)

first polar body

haploid)

three polar bodies

haploid)

Hormonal Control in the Menstrual Cycle:• Hypothalamus

– GnRH

• Anterior Pituitary– FSH– LH

• Ovaries– Estrogen– Progesterone

Changes in the Ovary and Uterus

Hormonal changes Ovarian and Uterine changes

Fig. 45.9, p. 792

hypothalamus

anterioir pituitary

FSH LH midcycle peak of LH (triggers ovulation)

Blood levels of FSH (purple) and LH (lavender)

FSH LH LH

estrogens progesterone, estrogen

estrogens progesterone, estrogen

Blood levels of estrogens (light blue) and progesterone (dark blue)

growth of follicle

FOLLICULAR PHASE OF MENSTRUAL CYCLE

LUTEAL PHASE OF MENSTRUAL CYCLE

menstruation

endometrium of uterus

Days of one menstrual cycle (using 28 days as the average duration)

hypothalamus

anterior lobe of pituitary

gland

ovulationcorpus luteum

GnRH

Menstrual Cycle Overview

• Follicular Phase– Menstruation

– Endometrium breakdown and buildup

– Maturation of oocyte

• Ovulation– Release of oocyte from ovary

• Luteal Phase– Corpus luteum

– Endometrium gets ready for pregnancy

Overview regulation of menstrual cycleDay Hormone

secretionHormone level Follicle Endometrium

thickness

1-5 FSH (Pituitary) Increasing Stimulates development of primary oocyte

Breaks down

6-14 a. FSH

b. Oestrogen (Follicle cells in ovary)

c. LH (Pituitary)

Continues until the 6th day

Stimulated by FSH. Level increases until the 12th day, stimulating LH secretion during its highest level

LH increases on the 10th until the 14th day

Follicle develops until becomes matured Graafian follicle

Graafian follicle bursts on 14th day and release secondary oocyte. Remaining Graafian follicle becomes corpus luteum

Oestrogen repairs and thickens endometrium

14-28 Progrestrone (Corpus lutuem in ovary)

Increasing from the 14th until 25th day

Corpus luteum degenerates on 25th day if no fertilization occurs

Thickness maintain until 25th day if no fertilisation occurs

Effects of Menstrual Hormonal Imbalance in Woman

• Hormonal imbalance affect a woman physiologically, emotionally and well-being

• Type of disorders caused by hormonal imbalances:– Prementrual syndrome (PMS): combination of

physical and emotional symptoms related to menstrual cycle due to changes in level of oestrogen and progestrone. Emotional symptoms such as tension, depresion, confusion, oversensitivity, mood swings, lack of concentration; physical symptoms such as headaches, fatigue, feeling bloated, breast tenderness, abdominal pain, appetite, sleep disturbance

…continue from previous slide

– Micarriage: Progestrone maintains endometrium thickness for zygote implantation. Failure in production cause the reduction of thickness, hence embryo cannot be embedded securely in endometrium

– Menopause: Occur between age 45 to 55 when menstruation stops for 12 months in a row, causing less FSH and LH to be produced. Due to limited development of follicle, ovaries produce less progestrone and oestrogen. Experiencing symptoms such as hot flushes, night sweats, sleeping disorders, osteoporosis, mood changes, weight gain and hair loss. Can be treated with oestrogen through Hormone Replacement Therapy (HRT)

Fertilization:

• Sperm surround ovum

• Cap releases acrosomal enzyme

• One sperm penetrates

• Oocyte completes meiosis II

• Sperm and egg nuclei fuse– Zygote

Formation of the Early Embryo:

First week of development

Oocyte(fertilization)zygote4-cell stage (2 days) morula (ball)blastocysteinner cell mass (embryo)

Trophoblast villi (extraembronic membranes)

From oocyte to blastocyst

• Mitosis forming zygote with 2 cells

• Both cells divide into 4 cells, then 8 cells, 16 cells and into a few hundreds of cells called morula

• Morula then transformed into a fluid-filled sphere called blastocyst, consisting of outer layer (later develop into placenta) and inner cell mass (develop into embryo)

Implantation of Blastocyst

• Outer layer of blastocyst attaches to endometrium using its extended projections called trophoblast villi

• The villi secretes enzymes to dissolve the cells at uterine wall, forming cavity that allows blastocyst to embed into

• Villi with rich supply of blood capillaries extend into the endometrium to implant the blastocyst

Early Embryo and Implantation:

Maternal and Fetal Blood Circulation:

• Diffusion of O2, CO2 and other solutes

Placental Development:

Embryo at 4 Weeks:

Fetus at 16 Weeks:

• Reflex actions

• Limb

differentiation

Birth:

• Labor

• Oxytocin

• Uterine

contractions

What Can Affect Development?

• Nutrition– Diet

– Extra vitamins

– Increased

calories

• Infections– Bacteria

– Rubella virus

• Prescription drugs– Tranquilizers

– Barbiturates

– Anti-acne

medication

– Antibiotics

• Alcohol

• Cocaine

• Cigarettes

Functions of the Uterus

• During embryo development– Protect the embryo– Provide a constant environment for the

embryo to develop– Allow placenta to attach on

• During birth of baby– Push the baby out by muscular contraction

Functions of the Amniotic Fluid

• To keep the foetus moist to prevent dessication

• As a water cushion to – support the foetus– allow it to move freely– absorb shock– protect the foetus from mechanical injuries

• To reduce temperature fluctuation• To lubricate the vagina during birth

The Placentaoxygenated blood

from mother’s artery

villus

umbilical vein

umbilical artery

deoxygenated blood to mother’s vein

Functions of the placenta

Immune protection: protective molecules cover the surface of the early placenta “hiding” it from the maternal immune system so it is not rejected as ‘non-self’ due to the presence of the paternal genes.

Functions of the placenta

Barrier: limits the transfer of blood components from the maternal to foetal system. Cells of the maternal immune system do not cross so reducing risk of immune rejection. (The placenta is not a barrier to heavy metals, nicotine, HIV, heroin or other toxins)

Functions of the placenta

Immune protection: protective molecules cover the surface of the early placenta “hiding” it from the maternal immune system so it is not rejected as ‘non-self’ due to the presence of the paternal genes.

Site of exchange of many solutes between maternal and foetal systems. Oxygen (aided by foetal haemoglobin), glucose, amino acids are all selective transported. CO2, urea and other waste materials diffuse the other way. Some antibodies pass from the mother during later pregnancy.

Functions of the placenta

Barrier: limits the transfer of blood components from the maternal to foetal system. Cells of the maternal immune system do not cross so reducing risk of immune rejection. (The placenta is not a barrier to heavy metals, nicotine, HIV, heroin or other toxins)

Endocrine function – the placenta takes over the production of oestrogen and progesterone as the corpus luteum degenerates ensuring the endometrium is maintained.

Adaptations of the Placenta1. Finger-like villi

– to increase the surface area for efficient diffusion

2. Maternal blood and foetal blood flows in opposite direction– to speed up diffusion of materials between

them

3. Maternal blood capillaries and foetal blood capillaries are separated by thin membrane – to shorten the distance of diffusion of materials

4. Maternal blood is separated from foetal blood by capillary wall– to prevent high pressure of maternal blood to

break the delicate foetal blood vessels– to prevent harmful substances to enter the

foetus– to prevent clotting of maternal and foetal

blood if their blood groups are incompatible

Formation of TwinsIdentical Twins

• 1 ovum + 1 sperm• Zygote divides after

fertilization• Both foetus share 1

placenta• Both carry the same sex• Twins look alike and

genetically identical

Fraternal twins

• 2 ova + 2 sperms• Zygote does not divide• Each has its own

placenta• Twins may carry different

sex• Twins may have some

similarities, but not genetically identical

Formation of Siamese twins• Also known as conjoined twins, as certain parts

of the body are joined together• Can be separated through operation, if parts are

separatable

Birth Control• Human

population increases exponentially– leads to

shortage of resources

– problem of pollution becomes more serious

– overcrowding

Control of Human Fertility:

Techniques in Birth Control1. Natural Method

a) Rhythm Method: Period counting

b) Withdrawal Method: Withdraw before ejaculation

2. Physical Method: involve devices to avoid pregnancy

3. Chemical Method: use of chemical to prevent pregnancy

4. Sterilisation Method: operation that will result permanent sterility

5. Abortion: removing of embryo of foetus before 28th week

Rhythm Method• Prevent copulation during 7 days before and

after ovulation (fertile period)

Physical 1: Condom• Male and female condom• As a barrier to prevent sperms from

entering the vagina

Physical 2: Diaphragm

• Fitted over the cervix• To be used together with spermicides

Physical 3: Intrauterine Device• Prevent implantation of zygote on the uterus

Chemical 1: Contraceptive Pills

• Contains hormones which inhibit ovulation• Must be taken regularly• May have side effect

Chemical 2: Spermicides

• Chemical that can kill sperms

• To be rubbed on vaginal wall before sexual intercourse

• Unreliable protection against pregnancy when used alone

Sterilisation MethodsVasectomyCutting and tying of sperm ducts

Fallopian Tube ligationCutting and tying of oviducts

Abortion Method

Overcoming Sterility1. Sperm bank: provide healthy sperms for couples who have

inability sperms

2. Artificial insemination: transferring sperms vagina of wife during ovulation. Due to sperm infertility or low count

3. In vitro fertilisation (IVF): Fertilisation outside the body due to blockage or damage of Fallopian tube. Babies borned in this technique is known as test-tube babies

4. Intrafallopian transfer: transfer of gamete or zygote into Fallopian tube

5. Embryo transfer: Transfer embryo from secondary oocyte donor woman into the uterus of receiver

6. Surrogate mother: Woman hired to carry a baby for full term

7. Cloning: Replacing the nucleus of body cell from the target with the unfertilised ovum of a donor and implanted in a surrogate mother

Procedures in IVF1. Ovarian hyperstimulation

– Patient injected with hormones to stimulate multiple follicle production in the ovaries

2. Egg Retrieval– The eggs are retrieved from the patient using a

transvaginal technique involving an ultrasound-guided needle piercing the vaginal wall to reach the ovaries.

3. Egg and sperm preparation– Selected oocytes prepared by stripping of surrounding

cells; Sperm prepared by by removing inactive cells and seminal fluid in a process called sperm washing.

4. Fertilisation– incubated together at a ratio of about 75,000:1 in the

culture media for about 18 hours on a petri dish

5. Embryo culture– Typically, embryos are cultured until having reached

the 6–8 cell stage three days after retrieval.– In some programmes, embryos are placed into an

extended culture system with a transfer done at the blastocyst stage at around five days after retrieval.

6. Embryo selection– Spefici grading methods are used to judge oocyte

and embryo quality

7. Embryo transfer– The "best" are transferred to the uterus through a

thin, plastic catheter, which goes through her vagina and cervix.

– Several embryos may passed into to improve chances of implantation and pregnancy.