Biology: Reproductive System

Asexual Reproduction = No gametes, identical offspring

• Binary fission

• Budding

• Regeneration

• Parthenogenesis

Binary fission

DNA replicates, cell splits (prokaryotes, bacteria)

Budding

New organism forms from outgrowth (yeast, hydra)

Regeneration

Fragment regrows (planaria, fungi)

Parthenogenesis

Unfertilized egg becomes organism (honeybees: males haploid, females diploid)

Spermatogenesis (Sperm Formation)

• Location: Seminiferous tubules in testes

• Process: Spermatogonia → sperm (haploid) via meiosis

• Structure:

  • Head: nucleus + acrosome (enzymes)

  • Midpiece: mitochondria (ATP)

  • Tail: flagellum (movement)

Pathway of sperm (SEVEn UP)

Seminiferous tubules → Epididymis → Vas deferens → Ejaculatory duct → Urethra → Penis

Seminiferous tubules

Site sertoli (spermatogenesis)

Epididymis

Sperm maturation

Vas deferens

Move sperms

Ejaculatory duct

Propels

Male: FSH

Stimulates sperm and Sertoli cells (support, inhibin)

Male: LH

Stimulates Leydig cells → testosterone

Male: Testosterone

Maturation and male traits

Oogenesis (Egg Formation)

• Ovary: Produces egg (ovum)

• Pathway: Ovary → fimbriae → fallopian tube → uterus

Female: FSH

Matures follicle, increases estrogen

Female: LH

Triggers ovulation, forms corpus luteum

Female: Estrogen/Progesterone

Maintain endometrium and cycle

Egg Arrest

• Arrested Before puberty: Prophase I

  • Primary oocytes: Prophase 1: resume puberty

• Arrested After ovulation: Metaphase II

  • Secondary oocytes: Metaphase 2: resume: fertilization

• Follicles release : estrogen and progesterone

Menstrual Cycle

• Follicular Phase

• Ovulation

• Luteal Phase

• Fertilization

• No fertilization

Follicular Phase

FSH stimulates follicle growth → estrogen thickens endometrium

Ovulation

LH spike → egg released

Luteal Phase

Corpus luteum → estrogen &  progesterone thickening(maintains lining FSH & LH)

Fertilization

hCG maintains corpus luteum → progesterone stays high → no menstruation

No fertilization

Hormones drop → menstruation

Positive and Negative Feedback Loops

• Positive: Prolactin (milk), oxytocin (release & birth)

• Negative: Estrogen/progesterone inhibit FSH/LH

Fertilization

• Capacitation

• Acrosomal Reaction

• Blocks to Polyspermy:

  • Fast block: Na⁺ influx (depolarization) 

  • Slow block: Cortical reaction (hard shell)

• Meiosis II completed after sperm entry

Capacitation

Sperm matures in uterus

Acrosomal Reaction

Sperm binds ZP3 on egg vitelline layer → enzymes digest egg coat

Twins

• Monozygotic: One zygote → splits (identical)

• Dizygotic: Two eggs fertilized 2 (fraternal)

Embryogenesis

1. Cleavage

2. Stages:

   1. Meroblastic: uneven 

   2. Holoblastic: even

Zygote then goes through its process

3. Germ Layers

Cleavage: Rapid divisions, same total size

• Radial: vertical (deuterostomes) 

• Spiral: spiral (protostomes)

• Indeterminate (regulative) (totipotent: turn into anything) 

• Mosaic: Determinate (fixed fate)

Zygote: Morula 

Solid ball blastomere

Zygote: Blastula

Hollow ball (fluid filled) blastocoel

Zygote: Gastrula

3 germ layers trilaminar embryo 

Germ Layer: Ectoderm

Nervous system, skin, hair, enamel, adrenal medulla, mammary glands

Germ Layer: Mesoderm

Muscles, bones, heart, gonads, notochord

Germ Layer: Endoderm

Linings, pancreas, liver, thyroid

Stem cells

Undifferentiated cells with the potential (potency) to develop in many different ways

Totipotent

Stem cell that is capable of developing into a complete embryo or differentiating into any cell type

Pluripotent

Stem cells that can differentiate into any of the three germ layers

Multipotent

Stem cells that can differentiate into any cell type within a particular lineage

Differentiated

Differentiated cells are fully specialized and can only reproduce cells of their own type

Neurulation

• Notochord (mesoderm) → induces neural plate (ectoderm)

• Neural plate → neural tube → CNS

Extraembryonic Membranes

Amnion, Chorion, Allantois, Yolk sac

Amnion

Cushions embryo with fluid

Chorion

Forms placenta (in mammals)

Allantois 

Waste transport, umbilical cord for mammals

Yolk sac

Early nutrients, blood formation

Embryonic induction

Organizers influence nearby cells

Homeotic genes (HOX)

Set body layout (head-tail)

Homeobox

DNA similar with different species with homeotic genes

Egg cytoplasm

Animal vs vegetal poles uneven guide cleavage

Apoptosis

Programmed cell death shapes development

Temperature-dependent sex

• Turtles: warm = female

• Crocodiles: medium = male

Oviparity

Egg

Viviparity

Inside

Ovoviviparity

Eggs inside and birth