Animal Development Chapter 46 & 47

Fig. 46-6

Vocabulary Zygote: Single diploid cell Fertilization: Sperm & egg combine Ovulation: Egg is released from the ovary Spermatogenesis: Formation of sperm Oogenesis: Formation of the egg

Anatomy

(Rectum) Cervix Vagina Vaginal opening Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) Urethra Clitoris Shaft Glans Prepuce Labia minora Labia majora

Fig b Ovaries Oviduct Follicles Corpus luteum Uterine wall Uterus Cervix Endometrium Vagina

Female Ovaries (at birth) Contain approximately 1 million follicles Primary oocyte Started meiosis Stopped at prophase I (diploid)

Female FSH Stimulates production of a follicle One follicle goes through Meiosis I Two daughter cells Secondary oocyte (starts Meiosis II) Polar body (disintegrates)

Female LH stimulates ovary Secondary oocyte leaves ovary Ovulation Fertilized then completes Meiosis II Ovum Polar body Travels fallopian tube Implants in uterus (approx. 5-6 days)

Fig g Primordial germ cell Mitotic divisions Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I Completion of meiosis I and onset of meiosis II Secondary oocyte, arrested at metaphase of meiosis II First polar body Ovulation, sperm entry Completion of meiosis II Second polar body Fertilized egg 2n2n 2n2n n n n n In embryo

Ovulation

Menstrual cycle GnRH FSH & LH released Stimulates follicle Estradiol released Follicle released (ovulation) LH increases

Menstrual cycle Corpus luteum releases progesterone & estridiol Corpus luteum disintegrates Lining sheds Endometriosis: Uterine lining in abdomen

Menstrual cycle

Anatomy

Fig b Seminal vesicle (Rectum) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland Vas deferens Epididymis Testis Scrotum (Urinary bladder) (Urinary duct) (Pubic bone) Erectile tissue Urethra Glans Prepuce Penis

Male Testes are in abdomen (at birth) Descend into scrotum Temperature of testes is cooler Normal sperm production Seminiferous tubules Contain spermatogonia or germ cells

Male Germ cells (diploid) Mitosis One undergoes meiosis Produce 4 haploid sperm Produce 100 to 200 million sperm a day Continues for life

Spermatogenesis

Fig b Epididymis Seminiferous tubule Sertoli cell nucleus Testis Cross section of seminiferous tubule Spermatogonium Primary spermatocyte Secondary spermatocyte Spermatids (two stages) Sperm Lumen of seminiferous tubule

Fig c Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell Mitotic divisions Spermatogonium Mitotic divisions Primary spermatocyte Meiosis I Secondary spermatocyte Meiosis II Early spermatid Differentiation (Sertoli cells provide nutrients) Sperm 2n2n 2n2n 2n2n n n n n n n n n n n

Gamete formation

Embryonic development Fertilization Cleavage Gastrulation Neurulation Organogenesis

Fertilization 1. Penetration Sperm digests cells surrounding egg Contains glycoprotein enzymes 2. Activation Membrane changes Prevents other sperm penetrating

Fertilization 2. Activation A. stimulates egg to complete division of Meiosis II B. stimulates movement of cytoplasm to prepare for cell division of zygote C. stimulates increase in protein synthesis

Fertilization 3. Nuclei fusion Sperm nucleus fuses with egg Egg is not activated Does not form zygote

Fertilization

Cleavage Rapid cell division Blastomeres: Smaller & smaller cells No increase in volume of cytoplasm Morula: Tight mass of approximately 32 cells

Fig (a) Fertilized egg(b) Four-cell stage(c) Early blastula(d) Later blastula

Cleavage Blastocyst (Blastula) Hollow ball of approx cells Blastocyst cavity Fluid filled Different regions in blastocyst Received differing amounts of cytoplasm Affects further development

Cleavage Trophoblast: Outer layer of cells Surround blastocyst (involved in placenta) Inner cell mass: Layer of dividing cells At one end of Blastocyst Becomes developing embryo

Fig Blastula (cross section) Blastocoel Animal pole 4-cell stage forming 2-cell stage forming Zygote 8-cell stage Vegetal pole 0.25 mm

Cleavage Implantation: Blastocyst attaches to endometrium 6 days after fertilization Human chorionic gonadotropin (HCG) Hormone released by trophoblast Maintains corpus luteum

Fig Trophoblast Hypoblast Maternal blood vessel Expanding region of trophoblast Epiblast

Gastrulation Turning inward of cells into blastocyst Forms germ layers Ectoderm: Epidermis/neural tissue Mesoderm: Muscle/skeletal/vasculature Endoderm: Gut lining, respiratory tract, liver

Fig ECTODERMMESODERMENDODERM Epidermis of skin and its derivatives (including sweat glands, hair follicles) Epithelial lining of mouth and anus Cornea and lens of eye Nervous system Sensory receptors in epidermis Adrenal medulla Tooth enamel Epithelium of pineal and pituitary glands Notochord Skeletal system Muscular system Muscular layer of stomach and intestine Excretory system Circulatory and lymphatic systems Reproductive system (except germ cells) Dermis of skin Lining of body cavity Adrenal cortex Epithelial lining of digestive tract Epithelial lining of respiratory system Lining of urethra, urinary bladder, and reproductive system Liver Pancreas Thymus Thyroid and parathyroid glands

Gastrulation

Chorion: Surrounds embryo Gas exchange Amnion: Encloses the embryo Protective amniotic fluid Yolk sac: Formation of blood cells

Gastrulation Yolk sac Mesoderm Amnion Chorion Ectoderm Extraembryonic mesoderm Atlantois Endoderm

Neurulation Development of dorsal nerve cord Notochord (spinal column) Forms from mesoderm soon after gastrulation Neural grove (spinal cord/brain) Crease down the axis of the embryo Neural tube (ectoderm) Hollow cylinder

Neural cord

Neurulation Neural crest Cells pinch off from neural tube Migrate to parts of embryo Peripheral nerves, teeth, skull bones

Fig b-4 Neural tube Neural crest cells Outer layer of ectoderm (b) Neural tube formation

Organogenesis Below neural tube Somitomeres: Small sections of mesoderm Somites Smaller sections of mesoderm Develop into muscles, vertebrae, connective tissues

Organogenesis Mesoderm surrounds the endoderm Separates into 2 layers One lines the inner body wall One lines the outside of the gut Between layers becomes body cavity

Human development 266 days divided into trimesters First trimester First cleavage 30 hours Second cleavage 60 hours Third cleavage 72 hours

Human development Gastrulation second week Neurulation third week Organogenesis Heart beats at 4 weeks (heard at end of first trimester) Fetus at 8 weeks All major organs are developed 5 cm in length

Fig a (a) 5 weeks

Human development Second trimester Large growth Baby about 30 cm in length Lanugo: fine hair covering body Placenta now controls progesterone levels

Fig b (b) 14 weeks

Fig c (c) 20 weeks

Human development Third trimester Large growth of fetus Developing nerves

Human development Birth Labor Estrogen stimulates the production of oxytocin receptors on the uterus Prostaglandins start labor Posterior pituitary releases oxytocin Uterine contractions expel fetus

Fig Estradiol Oxytocin from ovaries Induces oxytocin receptors on uterus from fetus and mother’s posterior pituitary Stimulates uterus to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus Positive feedback + +

Fig Expulsion: delivery of the infant 2

Fig Delivery of the placenta Uterus Placenta (detaching) Umbilical cord 3

Placenta

Fig Placenta Uterus Umbilical cord Chorionic villus, containing fetal capillaries Maternal blood pools Maternal arteries Maternal veins Maternal portion of placenta Fetal arteriole Fetal venule Umbilical cord Fetal portion of placenta (chorion) Umbilical arteries Umbilical vein