Animal Reproduction and Development Chapter 38 Modes of

Animal Reproduction and Development Chapter 38

Modes of Reproduction • Sexual reproduction – Meiosis, gamete formation, and fertilization – Offspring show genetic variation • Asexual reproduction – Single parent produces offspring – Offspring are genetically identical

Stages of Development Gamete formation Fertilization Cleavage Gastrulation Organ formation Growth, tissue specialization

Development Overview

Male Reproductive System bladder seminal vesicle vas deferens prostate gland bulbourethral gland urethra epididymis scrotum testis penis

Spermatogenesis • Spermatogonium (2 n) divides by mitosis to form primary spermatocyte (2 n) • Meiosis produces haploid spermatids • Spermatids mature to become sperm

Testicular Cells • Sertoli cells – Line the seminiferous tubules – Nourish the developing sperm • Leydig cells – Lie between the seminiferous tubules – Secrete testosterone

Female Reproductive Organs oviduct ovary uterus oviduct vagina cervix

Menstrual Cycle • The fertile period for a human female occurs on a cyclic basis • Menstrual cycle lasts about 28 days

Fertilization • Sperm penetrates to egg cytoplasm • Egg nucleus and sperm nucleus fuse to form diploid zygote

Pregnancy • Averages 38 weeks from fertilization • Takes two weeks for blastocyst to form • Weeks 3 to 8 are embryonic period • Weeks 9 to birth are fetal period

Early Divisions • Cleavage begins within 24 hours of fertilization Day 1 Day 2 Day 3 Day 4 (morula)

Day 5 - Blastocyst Forms • Cell secretions produce a fluid-filled cavity in center of ball of cells • Layers of blastocyst inner cell mass – Inner cell mass – Trophoblast – Blastocoel Trophoblast- The outer layer of cells of the mammalian blastocyst that gives rise to the placenta.

Implantation Begins • Blastocyst attaches to endometrium (UTERUS) ; begins to burrow into maternal tissues Uterine cavity blastocoel inner cell mass trophoblast

Extraembryonic Membranes • The amniotic membrane will enclose embryo • Yolk sac forms • Chorion begins to form fingerlike villi chorionic villi chorion amniotic cavity connecting stalk yolk sac DAY 14 chorionic cavity

Human Chorionic Gonadotropin (HCG) • Hormone secreted by the blastocyst • Stimulates corpus luteum to keep making progesterone and estrogens • This maintains endometrium, prevents menstruation • Can be detected by week 3 with a home pregnancy test

Gastrulation - Day 15 • Primitive streak forms along one axis of the inner cell mass • Cells migrate inward here to form endoderm and mesoderm

Gastrulation • Sphere of cells is a blastula • During gastrulation, some cells move inward • Produces a threelayer embryo

Vertebrate Body Plan Emerges paired neural folds pharyngeal arches somites

4 weeks The Placenta at full term • Interlocking fetal and maternal tissues • Performs digestive, respiratory, and urinary functions for the fetus • Materials exchanged across membrane that separates bloodstreams 8 weeks 12 weeks

Embryonic Period Week 4 • Weeks 3 to 8 • By the close of embryo period – Appears human Weeks 5 -6 Week 8

Fetal Period • Weeks 9 to birth • Fetus is initially about 1 inch long • Fetus born before 22 weeks cannot survive • Survival is poor before 28 weeks because lungs are not fully formed • By 36 weeks, survival is 95 percent

Fetal Nutrition • All nutrients for fetal growth and development must be delivered via the placenta • Mother’s diet affects fetal health • Smoking may affect ability to absorb nutrients and to pass them to fetus

Birth (Labor) • Cervical canal dilates • Amniotic sac ruptures • Uterine contractions drive fetus from uterus • Placenta is expelled as afterbirth

Lactation • During pregnancy, progesterone and estrogen stimulate gland development • After birth, prolactin induces synthesis of enzymes for milk production • Oxytocin triggers contractions

Stages of Human Development - Prenatal • Zygote - Single cell • Morula - Solid ball of cells • Blastocyst - Ball with fluid-filled cavity • Embryo - 2 weeks to 8 weeks • Fetus - 9 weeks to birth

• Newborn - First 2 Stages of weeks after birth • Infant - 2 weeks to 15 Human months Development • Child - 10 -12 years Postnatal • Pubescent - At puberty • Adolescent - Puberty to maturation • Adult • Old age -

Birth Control Options Prevent fertilization Prevent ovulation Block implantation

Sexually Transmitted Diseases (STDs) • Worldwide epidemic of STDs • Women are most affected • Can cause infertility, pain, and even death

Causative Agents of STDs • Viruses – AIDS (HIV) – Genital herpes (Herpes simplex) – Genital warts (HPV) • Bacteria – Gonorrhea (Neisseria gonorrhoeae) – Syphilis (Trepnema pallidum) – Chlamydial infections

In Vitro Fertilization • Conception outside the body • Woman receives hormone injections to stimulate ovulation • Oocyte is removed and combined with sperm in petri dish • After fertilization and a few divisions, ball of cells is implanted in uterus

Abortion • Removal of blastocyst, embryo, or fetus • First trimester abortions are painless, and relatively complication free • Later abortions are more difficult and more controversial