HSCI 100 Reproductive System

Scrotum

Sacs that hold the testes

– Help regulate the temperature of the testes: 37oC is too warm and

inhibits spermatogenesis

Testes

Paired organs that produce sperm and male sex hormones

– Composed of seminiferous tubules where sperm are produced

continuously from puberty and includes process of meiotic cell division

– Sertoli cells help nourish sperm and regulate the

process of sperm production

– Leydig cells, between seminiferous tubules. Produce the male

hormones (androgens, e.g. testosterone

Epididymis

stores and matures sperm

Most sperm do not survive

Spermatogenesis

- Process of making sperm in Homo sapiens males

– From meiosis, all 4 haploid cells generate sperm

– A continual process after puberty

– A healthy male produce an avg 100 million sperm daily, and an ejaculate contains between 40 and 300 million sperm

Oogenesis

– Process of making eggs in females

– During meiosis 1 egg and 3 polar bodies are formed

– Polar bodies hold discarded chromosomes and disintegrate

– Female Homo sapiens are born with all their follicles

– 6-7 million follicles in fetuses, reduced to 1-2 million at birth

and to 400,000 ova) by puberty

– Normally 1 egg per month is released and ~400 during the

entire reproductive cycle

follicles

contains an unfertilized egg

Sperm production

Sperm are produced within the seminiferous tubules of the testes

• Sertoli cells help nourish sperm and regulate spermatogenesis

• Sperm are stored and mature in the epididymis

(spermiogenesis, cell differentiation

pathway)

Sperm anatomy

3 parts:

– Head: covered by a cap called the acrosome which stores enzymes needed to penetrate the egg

– Middle piece: contain mitochondria to make energy (ATP)

– Tail: A flagellum that provides movement for the sperm

3 glands that contribute to semen

Seminal vesicles

Prostate gland

Bulbourethral glands

Seminal vesicles

produces a fluid with fructose that provides energy to sperm

Prostate gland

produces an alkaline fluid to help buffer the acidic pH in the vagina

– May enlarge with age and this cuts off flow from the urethra

– Most of the time benign and curab

Bulbourethral glands

produces a clear fluid that lubricates the urethra

negative feedback 

regulatory mechanism that helps maintain homeostasis by adjusting hormone levels

The endocrine control of male reproduction is regulated by negative feedback mechanisms involving testosterone and inhibin, which inhibit the release of hormones (GnRH, LH, and FSH) from the hypothalamus and anterior pituitary gland when their levels are sufficient.

Penis

-Erection: A response to visual, auditory, olfactory, or

tactile stimuli

This stimulus causes a release of NO which causes the arteries to relax, triggering a signal transduction cascade that produces

(cGMP) which activates protein kinase G(PKG).

PKG phosphorylates target proteins and ion

channels, which lead to:

– Inhibition (Ca²⁺) entry into the smooth muscle cell.

– Sequestration of intracellular Ca²⁺ by the ER

– Opening of potassium (K⁺) channels, causing the cell membrane to hyperpolarize.

Cavernous bodies (made of erectile tissue) fill with blood,

compressing veins and slowing

blood returns; causing an erection.

Erectile dysfunction

When Cavernous bodies don’texpand enough to compress veins.

• Viagra blocks the phophodiesterase that breaks down cGMP, prolonging erections

Female anatomy: Genital tract

Ovaries

Uterus

Cervix

Vagina

Clitoris

Ovaries

produce eggs and sex hormones

Fallopian tubes (oviducts)

transports egg from ovary to uterus and the site of fertilization

Uterus

site of embryo implantation and fetal development

Cervis

opening to the uterus

Vagina

organ for sexual intercourse and birth canal

Clitoris

-erectile organ and site of intense sexual feeling

-clirotal erection follows similar path to penis erection

The Ovary

-contains many follicles

-ovarian waves: when multiple follicles develop, but only one matures and lead to ovulation

-these cycles occur in avg every 29 days (‘monthly cycle’) from puberty until the end of ovarian and uterine cycles (menopause)

Ovulation is the monthly release of an immatur egg (oocyte) from the ovary when a follicle ruptures.

The Ovarian Cycle

Controlled by GnRH from the hypothalamus

Anterior pituitary secretes gonadotropic hormones; follicle

stimulating hormone (FSH) and luteinizing hormone (LH)

Two phases:

-Follicular phase:

lasts 14 days

FSH promotes development of a follicle that secretes estrogen

Estrogen spike leads to surge in LH and ovulation on day 14

the released egg or follicle survives for around 24 hrs

- Luteal phase:

Occurs after ovulation

corpus luteum forms from the follicle that released the egg and produces progesterone to prepare the uterus for a potential pregnancy

If pregnancy does not occur, then menstruation begins

Menstruation

the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina

Hormonal control of the ovaries

similar to male, except it follows a monthly cycleand the ovaries make more progesterone and estrogen than testosterone

Uterine cycle

29-day cyclic event in the uterus

days 1-5: low levels of estrogen and progesterone, causing endometrium to disintergrate and menstruation occurs.

days 6-13: increase in estrogen causing the

endometrium to thicken

day 14: ovulation

Days 15-29: higher progesterone causes endometrium to further thicken in preparation for developing embryo.

If the egg is not fertilized, then the corpus luteum naturally

regresses and the endometrium breaks down

If the egg is fertilized and implants, human chorionic gonadotropin

(HCG) is made by the embryo and this maintains corpus luteum

and endometrium (n.b. hCG is what pregnancy tests detect)

Fertilization and Pregnancy

Fertilization: when a sperm and an egg combine to form a zygote

Pregnancy: begins with implantation into the endometrium, usually

6-12 days after fertilization