Chapter 27-Reproduction

Testes

produce sperm & testosterone

Epididymis

sperm maturation & storage

Vas deferens

transports sperm

Accessory glands

• Seminal vesicles: alkaline fluid, fructose, prostaglandins (~70% semen).

• Prostate: milky acidic fluid, enzymes, antibacterial proteins (~25% semen).

• Bulbourethral glands: mucus for lubrication & neutralization.

Penis

delivers sperm into female tract

Meiosis & Role in Gametogenesis

cell division reducing chromosome number from diploid (2n) to haploid (n).

Produces gametes (sperm/eggs) with 23 chromosomes

• Ensures genetic diversity via crossing over

Differences in Male vs Female Meiosis (7+)

• Timing: males start at puberty, females begin before birth.

• Duration: males continuous; females arrest at prophase I until ovulation.

• Output: males → 4 viable sperm; females → 1 ovum + 3 polar bodies.

• Cell death: sperm production ongoing; most oocytes degenerate.

• Error rate: higher in oocytes (~20%) vs sperm (~3–4%).

• Arrest points: female oocytes pause at prophase I & metaphase II.

• Quantity: males produce ~400 million sperm/day; females release ~1 egg/month.

• Completion: female meiosis II only finishes if fertilization occurs.

Spermatogenesis

stem cells → spermatogonia → primary spermatocytes → secondary spermatocytes → spermatids → spermatozoa.

Spermiogenesis

spermatids mature into sperm (head, midpiece, tail)

Sperm structure

Head: nucleus (male DNA) + acrosome (contains enzymes required for fertilization)

Midpiece: Mitochondria ( for energy to swim to eggs

Tail: Flagella for locomotion to egg

Endocrine Regulation (Male)

• GnRH (hypothalamus) → stimulates anterior pituitary.

• FSH → Sertoli cells → ABP → supports spermatogenesis.

• LH → Leydig cells → testosterone.

• Inhibin: negative feedback on FSH.

Semen Formation & Composition

• Mix of sperm + secretions.

• Volume: 2–5 mL per ejaculation.

• Sperm count: 20–150 million/mL.

• Contains nutrients, clotting proteins, immune suppressors.

Pathway of Sperm

Seminiferous tubules → straight tubules →rete testes → efferent duct → ductus epididymis → ductus (vas) deferens → ejaculatory duct → urethra

Physiology of Erection

Erection Stimulation→ Sacral regional of spinal cord reflex→Parasympathetic neurons release vasodilator (NO)→Arteries leading into penis dilate→Corpora fill with blood→Penis stiffens→Filling of corpora put pressure on veins and prevent blood from leaving  (maintains erection)

Cavernosa

• provide stiffness and rigidity

Spongiosum

protects the urethra and forms the glans, ensuring sperm can be ejaculated.

Ejaculation

Stimulation reaches threshold level

Spinal reflex arc  send massive impulses through sympathetic neurons

Bladder sphincter constricts and smooth muscle in walls of reproductive ducts and accessory glands contract propelling sperm and secretions into the urethra

Ovaries

make eggs & hormones

Fallopian tubes

transport egg, site of fertilization

Uterus

Receives egg & nourishes fetus

Vagina

birth canal

Oocyte

eggs

Follicles

cells/tissues that surround the egg

Provide nutrient for egg

make hormones

protect egg

vulva (external genitalia)

protection & sensory

Oogenesis

Primordial follicles = egg arrested in prophase I and a single layer of surrounding follicle cells

Each month some (12 to 15) of these follicles start developing further

1° follicles = egg still in prophase I but it is enlarging, follicle cells multiply and thicken to cubodial cells

2° follicles = egg still in prophase I, follicular cells (now called granulosa cells) form layers around oocyte, clear layer of glycoprotein called zona pellucida (zp) forms between the egg and granulosa cells. 

Some granulosa cells remain attached to the zp (and are then called corona radiata cells), outer granulosa cells (called theca follicular cells) separate from them as a fluid filled antrum develops

Meiosis I completed results in 2 cells, one secondary oocyte and one polar body 

Graffian (Vesicular) follicle = secondary oocyte with mature follicle; follicle extends from the deepest part of the cortex and bulges from the surface

Corpus luteum 

secretes progesterone & estrogen it produces this after ovulation to prepare the uterine lining for a possible pregnancy

what if pregnancy doesn’t occur?

It forms a scar in the ovary known as a corpus albicans

FSH

promotes follicle growth 

LH

ovulation

Birth Control Methods

Barrier: Condoms

Hormonal: injection, pills, patches

IUDs: Prevents implantation

Sterilization: vasectomy, tubal ligation

Efffectiveness: hormonal/IUDs

• Chlamydia

bacterial; often asymptomatic, can cause infertility.

• Gonorrhea

bacterial; discharge, painful urination.

Genial Herpes

Virus

Estrogen 

secreted by follicular cells

• Breast cancer:

•Arises from epithelial cells of the smallest ducts

Prostate cancer

Normal aging causes blocks urine flow and can be painful

Meiosis starts with ______

one diploid cell

Meiosis ends with _______

4 haploid cells

purpose of Meiosis

produce gametes with 23 chromosomes

Meiosis I (interphase)

• DNA replicates.

• Cell prepares for division.

Prophase I

• Homologous chromosomes pair up → form tetrads.

• Crossing over occurs: chromatids exchange segments → genetic variation.

• Nuclear envelope breaks down.

Metaphase I

• Tetrads align randomly at the spindle equator.

Anaphase I

• Homologous chromosomes separate.

• Sister chromatids stay together (unlike mitosis).

Telophase I & Cytokinesis

• Two haploid daughter cells form.

• Chromosomes uncoil, nuclear membranes reform.

• No DNA replication before Meiosis II.

Meiosis II (prophase II)

Chromosomes condense again.

Spindle forms

Metaphase II

• Chromosomes align at the equator.

Anaphase II

Sister chromatids finally separate

Telophase II & Cytokinesis

• Four haploid cells form.

• Each is genetically unique.

Oogenesis (Primordial Follicle)

the oocyte arrested in prophase I of meiosis

Surround a single layer of flat follicle cells

Primary follicles 

Each month, 12-15 primordial follicles begin to develop

egg still in prophase I, but enlarges

Follicle cells become cuboidal and multiply forming a thicker layer

Secondary follicle

Egg still in prophase I

Follicle cells now called granulosa cells

zona pellucida forms

some granular cells stick to ZP called the corona radiata

outer granulosa cells become theca follicular cells

A fluid- filled cavity (antrum) begins to form

Secondary oocyte continues meiosis up to metaphase II and arrests (awaits to be fertilized)

Graafian (vesicular) follicle

secondary oocyte with mature follicle

bulges from the surface of the ovary

ready for ovulation

the follicle will rupture & release the egg