Reproduction And Development

Reproduction and Development

Male Reproductive Anatomy 

In most mammalian species 



The internal organs 

36.1

The male’s external reproductive organs are the scrotum and penis Consist of the gonads, which produce sperm and hormones, and accessory glands

Reproductive anatomy of the human male

Seminal vesicle (behind bladder)

(Urinary bladder)

Prostate gland Urethra Scrotum

36.1

Glans penis

Bulbourethral gland Erectile tissue of penis Vas deferens Epididymis Testis

Reproductive anatomy of the human male

(Urinary bladder)

Seminal vesicle (Rectum)

(Pubic bone) Erectile tissue of penis

Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland

Urethra Vas deferens Epididymis Testis

36.1

Scrotum

Glans penis Prepuce

Testes 

The male gonads, or testes 



The tubes are seminiferous tubules 

36.1

Consist of many highly coiled tubes surrounded by several layers of connective tissue

Where sperm form

Sperm Production 

Production of normal sperm 

36.1

Cannot occur at the body temperatures of most mammals so the testis are held outside the body

Ducts 

From the seminiferous tubules of a testis 



The sperm pass into the coiled tubules of the epididymis

During ejaculation 

36.1

Sperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethra

Glands 

Three sets of accessory glands 



Add secretions to the semen, the fluid that is ejaculated

A pair of seminal vesicles 

36.1

Contributes about 60% of the total volume of semen

Glands 

The prostate gland 



The bulbourethral gland 

36.1

Secretes a clear fluid directly into the urethra through several small ducts Secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra

Semen in the Female Reproductive Tract 

Once in the female reproductive tract 

36.1

A number of processes, including contractions of the uterus, help move the sperm up the uterus

Penis 

The human penis 



Is composed of three cylinders of spongy erectile tissue

During sexual arousal 

36.1

The erectile tissue fills with blood from the arteries, causing an erection

Female Reproductive Anatomy 

The female external reproductive structures include  



The internal organs are a pair of gonads 

36.2

The clitoris Two sets of labia

And a system of ducts and chambers that carry gametes and house the embryo and fetus

Uterus Oviduct



(Urinary bladder) (Pubic bone)

Ovary

Reproductive anatomy of the human female (Rectum) Cervix Vagina

Urethra Shaft Glans

Bartholin’s gland

Figure 46.9

36.2

Clitoris

Prepuce

Vaginal opening

Labia minora Labia majora

Ovaries

Uterus

Oviduct

Uterine wall Endometrium

Cervix

Vagina

36.2

Follicles Corpus luteum

Ovaries 

The female gonads, the ovaries 



Each ovary 



Is enclosed in a tough protective capsule and contains many follicles

A follicle 

36.2

Lie in the abdominal cavity

Consists of one egg cell surrounded by one or more layers of follicle cells

Ovulation 

The process of ovulation 



The remaining follicular tissue then grows within the ovary 

36.2

Expels an egg cell from the follicle

To form a solid mass called the corpus luteum, which secretes hormones, depending on whether or not pregnancy occurs

Oviducts and Uterus 

The egg cell is released into the abdominal cavity 



Cilia in the tube 

36.2

Near the opening of the oviduct, or fallopian tube Convey the egg to the uterus

Vagina and Vulva 

The vagina is a thin-walled chamber 





The vagina opens to the outside at the vulva 

36.2

That is the repository for sperm during copulation That serves as the birth canal through which a baby is born

Which includes the hymen, vestibule, labia minora, labia majora, and clitoris

The Reproductive Cycles of Females 

In females 

36.3

The secretion of hormones and the reproductive events they regulate are cyclic

The Reproductive Cycles of Females

36.3

The Ovarian Cycle 

In the ovarian cycle 



Hormones stimulate follicle growth, which results in ovulation

Following ovulation 

The follicular tissue left behind transforms into the corpus luteum  

36.4

Produces estrogen and progesterone Causes endometrial thickening

The Uterine (Menstrual) Cycle 

Cycle after cycle 



The maturation and release of egg cells from the ovary are integrated with changes in the uterus

If an embryo does not implant in the endometrium 

36.4

A new menstrual flow begins

Conception, Embryonic Development, and Birth 

In humans and most other placental mammals 

36.5

Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus



Fertilization of an egg by a sperm, conception occurs in the oviduct 3 Cleavage (cell division) begins in the oviduct as the embryo is moved toward the uterus by peristalsis and the movements of cilia.

4 Cleavage continues. By the time the embryo reaches the uterus, it is a ball of cells. It floats in the uterus for several days, nourished by endometrial secretions. It becomes a blastocyst.

Ovary

2 Fertilization occurs. A sperm enters the oocyte; meiosis of the oocyte finishes; and the nuclei of the ovum and sperm fuse, producing a zygote.

5 The blastocyst implants in the endometrium about 7 days after conception.

Uterus

1 Ovulation releases a secondary oocyte, which enters the oviduct. (a) From ovulation to implantation Endometrium

Endometrium

Inner cell mass

Cavity

Blastocyst

36.5

(b) Implantation of blastocyst

Trophoblast



In fertilization, the cortical reaction modifies the zona pellucida to block polyspermy 1 The sperm migrates through the coat of follicle cells and binds to receptor molecules in the zona pellucida of the egg. (Receptor molecules are not shown here.)

2 This binding induces the acrosomal reaction, in which the sperm releases hydrolytic enzymes into the zona pellucida.

3 Breakdown of the zona pellucida 4 The nucleus and other by these enzymes allows the sperm components of the sperm to reach the plasma membrane cell enter the egg. of the egg. Membrane proteins of the sperm bind to receptors on the egg membrane, and the two membranes fuse.

Follicle cell

5 Enzymes released during the cortical reaction harden the zona pellucida, which now functions as a block to polyspermy. Zona pellucida Egg plasma membrane

Sperm basal Sperm Cortical granules body nucleus

Acrosomal vesicle EGG CYTOPLASM



After fertilization 

The zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium

First Trimester 

Human gestation 



Can be divided into three trimesters of about three months each

The first trimester 

36.6

Is the time of most radical change for both the mother and the embryo



During its first 2 to 4 weeks of development 



The embryo obtains nutrients directly from the endometrium

Meanwhile, the outer layer of the blastocyst 

36.6

Mingles with the endometrium and eventually forms the placenta



Blood from the embryo 

Travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein

Maternal arteries

Maternal veins

Placenta

Maternal portion of placenta Umbilical cord Chorionic villus containing fetal capillaries

Fetal portion of placenta (chorion)

Maternal blood pools Uterus

36.6

Fetal arteriole Fetal venule Umbilical cord

Umbilical arteries Umbilical vein



The first trimester is the main period of organogenesis 

The development of the body organs

(a) 5 weeks. Limb buds, eyes, the (b) 14 weeks. Growth and heart, the liver, and rudiments development of the offspring, of all other organs have started now called a fetus, continue to develop in the embryo, which during the second trimester. is only about 1 cm long. This fetus is about 6 cm long.

36.6

(c) 20 weeks. By the end of the second trimester (at 24 weeks), the fetus grows to about 30 cm in length.

Second Trimester 

During the second trimester   

36.6

The fetus grows and is very active The mother may feel fetal movements The uterus grows enough for the pregnancy to become obvious

Third Trimester 

During the third trimester 

36.6

The fetus continues to grow and fills the available space within the embryonic membranes

A complex interplay of local regulators and hormones 

Induces and regulates labor, the process by which childbirth occurs Estrogen from ovaries

Oxytocin from fetus and mother's posterior pituitary

Induces oxytocin receptors on uterus Stimulates uterus to contract Stimulates placenta to make Prostaglandins

36.7

Stimulate more contractions of uterus

Positive feedback





Birth, or parturition 



Is brought about by a series of strong, rhythmic uterine contractions

The process of labor has three stages

Placenta Umbilical cord Uterus Cervix 1

Dilation of the cervix

2

Expulsion: delivery of the infant Uterus Placenta (detaching) Umbilical cord

36.8

3

Delivery of the placenta