BIO Chapter 27

Gonads - Definition

Primary reproductive organs that produce gametes (sex cells) and sex hormones

Gonads - Male

Gonads in males: testes – produce sperm and testosterone

Gonads - Female

Gonads in females: ovaries – produce eggs (ova) and estrogen/progesterone

Gametes - Definition

Specialized reproductive cells used in sexual reproduction; haploid (half chromosomes of body cells)

Sperm - Definition

Male gamete produced in testes; haploid, motile with flagellum; fertilizes egg to form zygote

Sperm - Key Point

Sperm is specialized for movement and delivering genetic material

Egg (Ovum) - Definition

Female gamete produced in ovaries; haploid, non-motile, large, nutrient-rich; can be fertilized to form zygote

Egg (Ovum) - Key Point

Provides genetic material and resources for the developing embryo

Zygote - Definition

Single cell formed when sperm fertilizes an egg; diploid (full set of chromosomes)

Zygote - Function

Undergoes cell division and differentiation to develop into an embryo; first stage of new organism

Gametes vs Body Cells

Key points: gametes are haploid; body cells are diploid; sperm small/mobile, eggs large/nutrient-rich; zygote formation begins development

Primary Sex Organs

Organs directly involved in reproduction; produce gametes and sex hormones; male = testes, female = ovaries

Secondary Sex Organs

Support reproduction but do not produce gametes; male: penis, vas deferens, epididymis, seminal vesicles, prostate; female: uterus, fallopian tubes, vagina

Secondary Sex Characteristics

Traits appearing at puberty; distinguish males and females; male: facial/body hair, deep voice, muscle mass, Adam’s apple; female: breast development, widened hips, fat distribution, pubic/underarm hair

Sex Chromosome

Chromosome determining biological sex; humans have X and Y; female = XX, male = XY; carry some genes unrelated to sex

Autosome

Chromosome not involved in sex determination; humans have 22 pairs (44 total); control most body traits

Sex Chromosomes vs Autosomes

Total human chromosomes = 46 (23 pairs): 22 autosomes + 1 pair sex chromosomes; sex chromosomes = gender, autosomes = other traits

Offspring Sex Determination

Females always contribute X; males contribute X → daughter, Y → son; male gamete determines sex; fertilization determines XX (female) or XY (male)

Sexual Differentiation Timeline

Weeks 0–6: undifferentiated gonads, bipotential sexual structures; Weeks 6–7: Y/SRY → testes, no Y → ovaries; Weeks 8–12: internal organs develop; Weeks 12–16: external genitalia form; puberty: secondary sex characteristics appear

Y Chromosome

Contains SRY gene; triggers testes formation; without Y/SRY → female development

Testosterone

Produced by developing testes; drives development of male internal organs (vas deferens, seminal vesicles, prostate) and external genitalia (penis, scrotum); influences male secondary sex characteristics

Descent of Testes

Develop near kidneys; descend through inguinal canal to scrotum around 7 months gestation; guided by gubernaculum; proper descent important for sperm production; incomplete descent = cryptorchidism

Scrotum - Definition

Sac of skin and smooth muscle housing testes; protects and maintains ~2–3°C below body temperature for sperm production

Spermatic Cord

Connects testis to body; contains vas deferens, testicular artery & pampiniform plexus, nerves, lymphatic vessels

Scrotum Compartments

Divided into 2 compartments by median septum

Thermal Regulation Mechanisms

Cremaster muscle – raises/lowers testes; Dartos muscle – wrinkles/relaxes skin; Pampiniform plexus – cools arterial blood via countercurrent heat exchange

Seminiferous Tubules

Site of spermatogenesis; highly coiled tubes inside testes; hundreds per testis

Sertoli (Sustentacular) Cells

Located inside seminiferous tubules; support/nourish developing sperm; produce inhibin; form blood-testis barrier

Blood-Testis Barrier

Tight junctions between Sertoli cells; separates sperm from immune system; maintains controlled environment for spermatogenesis

Interstitial (Leydig) Cells

Located between seminiferous tubules; produce testosterone for sperm development and male secondary sex characteristics

Spermatic Ducts - Efferent Ductules

Carry sperm from rete testis to epididymis; lined with ciliated cells to move sperm

Spermatic Ducts - Epididymis

Long, coiled duct on posterior testis; functions: sperm maturation, storage, removal of defective sperm

Spermatic Ducts - Vas Deferens

Muscular tube carrying sperm from epididymis to ejaculatory duct; thick smooth muscle for peristalsis; travels through spermatic cord, joins seminal vesicle duct

Spermatic Ducts - Ejaculatory Duct

Formed by union of vas deferens and seminal vesicle duct; ~2 cm; passes through prostate, empties into urethra; mixes sperm with seminal fluid

Spermatic Ducts - Urethra

Final duct for semen; shared by urinary/reproductive systems (not simultaneously); regions: prostatic, membranous, spongy; sperm pathway: seminiferous tubules → rete testis → efferent ductules → epididymis → vas deferens → ejaculatory duct → urethra → out

Accessory Glands - Seminal Vesicles

Posterior to bladder; produce fructose-rich fluid (energy) and prostaglandins (stimulate uterine contractions); ~60% semen volume

Accessory Glands - Prostate

Gland around prostatic urethra; slightly acidic fluid with enzymes/nutrients to enhance motility; ~25–30% semen volume

Accessory Glands - Bulbourethral (Cowper’s) Glands

Inferior to prostate; produce clear mucus pre-ejaculation; lubricates urethra, neutralizes acidic urine; <5% semen volume

Accessory Glands Key Points

Secrete fluids that nourish, protect, transport sperm; together form seminal fluid (semen)

Endocrine Control of Puberty

Hypothalamus releases GnRH → anterior pituitary secretes LH (stimulates sex hormone production) & FSH (stimulates sperm/egg production); rising sex hormones trigger secondary sex characteristics; negative feedback regulates GnRH, LH, FSH

Male Climacteric

Gradual decline in male reproductive function (~40–50 yrs); testosterone decreases; effects: reduced sperm/fertility, muscle/bone loss, decreased libido, mood/fatigue; sperm still produced but gradually declines

Meiosis - Overview

Cell division producing haploid gametes from diploid cells; reduces chromosome number; increases genetic variation

Meiosis I (Reduction Division)

Homologous chromosomes pair & separate; produces 2 haploid cells with one chromosome from each pair

Meiosis II (Equational Division)

Sister chromatids separate; produces 4 haploid gametes with single set of chromosomes

Mitosis vs Meiosis - Number of Divisions

Mitosis: 1; Meiosis: 2 (I & II)

Mitosis vs Meiosis - Chromosome Number

Mitosis: diploid; Meiosis: haploid

Mitosis vs Meiosis - Genetic Variation

Mitosis: identical; Meiosis: unique due to crossing over & independent assortment

Mitosis vs Meiosis - Purpose

Mitosis: growth, repair, asexual reproduction; Meiosis: gamete production

Mitosis vs Meiosis - Daughter Cells

Mitosis: 2; Meiosis: 4

Spermatogenesis - Overview

Production of sperm in seminiferous tubules; begins at puberty; continues lifelong

Spermatogenesis - Spermatogonia

Diploid stem cells along basement membrane; divide by mitosis or differentiate into primary spermatocytes

Spermatogenesis - Primary Spermatocytes

Undergo Meiosis I; homologous chromosomes separate → 2 secondary spermatocytes (haploid)

Spermatogenesis - Secondary Spermatocytes

Undergo Meiosis II; sister chromatids separate → 4 spermatids (haploid)

Spermatogenesis - Spermatids

Immature round cells; undergo spermiogenesis → mature sperm

Spermatogenesis - Spermatozoa

Mature motile gametes; structure: head (nucleus & acrosome), midpiece (mitochondria), tail (flagellum)

Spermatogenesis - Role of Sertoli Cells

Nourish sperm, form blood-testis barrier, secrete inhibin to regulate sperm production

Spermatogenesis - Key Points

Reduces diploid → haploid sperm; takes ~64–72 days; testosterone essential

Sperm Structure - Head

Contains nucleus with haploid DNA; acrosome with enzymes for egg penetration

Sperm Structure - Midpiece

Packed with mitochondria; provides ATP for tail movement

Sperm Structure - Tail

Flagellum; propels sperm toward egg

Sperm Structure Key Points

Head = genetic delivery, midpiece = energy, tail = movement; sperm specialized for motility/fertilization

Semen Sources - Seminal Vesicles

~60% semen volume; fructose-rich fluid + prostaglandins

Semen Sources - Prostate

Gland fluid ~25–30% semen; slightly acidic, enzymes/nutrients for motility

Semen Sources - Bulbourethral Glands

Semen Sources - Sperm (Testes/Epididymis)

~5–10% semen volume; haploid gametes for fertilization

Semen Key Points

Semen = sperm + accessory gland fluids; each contributes nutrition, protection, motility, transport

Components of Semen - Sperm

Male gametes from testes; haploid; fertilize egg

Components of Semen - Seminal Fluid (~60%)

From seminal vesicles; fructose + prostaglandins; stimulates female reproductive tract

Components of Semen - Prostatic Fluid (~25–30%)

From prostate; slightly acidic, enzymes & nutrients enhance sperm motility

Components of Semen - Bulbourethral Fluid (<5%)

Clear mucus; lubricates urethra, neutralizes acidic urine; protects sperm

Components of Semen Key Points

Each component contributes to nutrition, protection, motility, transport of sperm