APHY 102- ch 22-23

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Meiosis

22.1 Meiosis

  • Gonads: Produce hormones and gametes (sex cells).

    • Male: Testes (male gonads) produce sperm.

      • A sperm cell has 23 chromosomes

    • Female: Ovaries (female gonads) produce ova (eggs/oocytes).

      • An egg cells have 23 chromosomes

  • Genetic Composition:

    • Gametes have one set of 23 chromosomes (haploid).

    • Body cells have two sets (diploid).

    • Normal body cells have 23 types of chromosomes, of those there are 2 copies, making 46 chromosomes total, 1 paternal copy, 1 maternal copy- diploid

  • Fertilization: Unites sperm and egg, restoring 46 chromosomes.

  • Meiosis: Produces gametes through two successive divisions.

  • Homologous Chromosome: the same type of chromosome but have a paternal and maternal one, same genes but different genetic code

  • Sister Chromatids: copy one of the chromosomes, and have two of them together, exact same pair/copy of chromosomes in a set of two

Meiosis Stages

Before Meiosis:

  • Sperm (23) + Egg (23) = 46 chromosomes

  • DNA replication = 46 chromosomes

    • why? - counting centromeres not chromatids

  • each chromosome replicates and contains 2 DNA strands, called chromatids, connected by the centromere

Meiosis I

  • separates homologous pairs of chromosomes

    • results in haploid cells - contain 1 set of chromosomes: 23 chromosomes total, one from each homologous pair

  • Four Phases in Meiosis 1- PMAT

    • Result: 2 haploid daughter cells, each one containing 23 chromosomes w/ 2 chromatids

Meiosis II

  • cells are still haploid, but chromosomes now have 1 chromatid

  • Four Phases in Meiosis 2- PMAT

    • Result: 2 daughter cells, each one w/with 23 chromosomes and 1 chromatid

  • END RESULT OF MEIOSIS 1 AND 2 IS HAPLOID

  • WHEN EGG AND SPERM ARE INTRODUCED THEY BECOME DIPLOID CELLS AND CHROMOSOMES ARE NOW PAIRED

Male Reproductive System

  • Gonads: Testes produce testosterone and spermatozoa.

  • Accessory Organs: Transport sperm, including seminal vesicles, prostate gland, and bulbourethral glands.

    • Epididymis: store/mature sperm

    • Ductus Defrens: tube to epididymis to Ejactulatory duct

    • Seminal Vesicle: produce alkaline fluid, fructose, prostaglandin

    • Prostate: release alkaline and prostaglandin

    • Bulbourethral gland: neutralizes urethra and secretes alkaline substance, provides lubrication.

  • Semen: combo of sperm, seminal vesicles, prostate gland, and bulbourethal glands. alkaline. avg. 120 million sperm cells/mL of semen.

  • Dartos Muscle: contracts/relaxes scrotum/testis in response to temp.

  • Penis: shaft contains 3 erectile tissues: 2 corpora cavernosa and 1 corpus spongiosum

  • Erection: parasympathetic event, nerve impulses release nitric oxide which dilates arteries in penis, penis swells and elogates

  • Orgasm: physiological and psychological release, dependent on sympathetic nerve impulses

    • Emission: movement of semen into the urethra

    • Ejaculation: movement of semen out of the urethra

Testes

  • In fetal development, testes descend into the scrotum due to testosterone influence.

  • Gubernaculum: Aids in descent through inguinal canal.

  • The tunica albuginea encloses each testis

  • Seminiferous tubules: sperm is developed here

  • Interstitial cells (Leydig cells): Produce testosterone.

  • Seminal Vesicles: Secrete alkaline fluid rich in fructose.

  • Prostate Gland: Produces thin, milky fluid that enhances sperm motility.

Sperm Cell

  • Head: contains nucleus, acrosome (enzymes that penetrate layers around oocyte)

  • Midpiece: contains mitochondria

  • Tail: contains microtubules

Hormones:

  • Hypothalamic Hormone

    • GnRH: regulates secretion of gonadotropins of anterior pituitary gland

  • Anterior Pituitary Hormones:

    • Interstitial Cell Stimulating Hormone (LH): development of interstitial cells in testes, secretes male sex hormones

    • Follicle stimulating hormone: stimulates cells of testes to mature, proliferate, and respond to testosterone

  • Androgens- male sex hormones- testosterone - produce some as baby then stop until puberty

    • Secondary sex characteristics:

      • increased growth of body hair, decreased growth of scalp hair

      • enlargement of larynx

      • thickening of skin

      • increased muscular growth

      • thickening/strengthening of bones

Female Reproductive System

Female Reproductive System

  • Primary Gonads: Ovaries produce oocytes and hormones (estrogen and progesterone).

  • Accessory Organs: Include uterine tubes, uterus, and vagina, facilitating fertilization and gestation activities.

Ovaries

  • Ovarian Medulla: inner layer

  • Ovarian Cortex: outer layer: granular appearance, tiny masses of cells called ovarian follicles (oocytes develop inside these follicles).

  • Fallopian/Uterine Tubes: connect ovaries to the uterus

    • Layers: inner mucosa, middle muscularis, outer peritoneum

Vagina: passage way for penis, menstuation, and childbirth.

Mammary Glands: feed offspring, develop in puberty due to estrogen being released, accessory organ.

External Accessory Organs: - all together are called Vulva

  • Labia Majora: skin like layers, outer layer

  • Labia Minora: skin like layer, inner layer

  • Clitoris: 2 erectile columns, sensory structures that aid in sexual stimulation

  • Vestibule: everything inside labia minora, encloses vaginal and urethal opening

    • vestibular glands: secrete mucus during sexual stimulation

Erection: in clitoris and around vaginal entrance

Lubrication: vestibular glands

Orgasm: clitoris responds to sexual stimulation, a physiological and psychological release

Uterus:

  • Body: upper 2/3rds

  • Cervix: lower 1/3rd

  • Layers: Endometrium, Myometrium, Perimetrium

Primary Follicles:

  • primordial germ cells give rise to oogonia

  • Oogonia develop into primary oocytes

  • flat epithelial cells called follicular cells form primordial follicles

  • primary oocytes begin (in fetal development) but don’t finish meiosis until puberty

  • Primordial follicles are never produced again

Oogenesis

  • primary oocytes- haploid

  • unequal division, primary oocyte and secondary oocyte- outcome is secondary oocyte and polar body

  • polar body function- to contain DNA

  • secondary oocyte gets to keep all cytoplasm and organelles

Hormones

  • Gonadotropin-Releasing Hormone (GnRH): Triggers FSH and LH from the anterior pituitary, regulating ovarian function.

  • Estrogens and Progesterone: Control reproductive cycle, secondary sex characteristics, and pregnancy preparation.

    • breast and mammary gland duct development

    • increased adipose tissue in breasts, thighs, butt

    • increased vascularization of skin

Menstrual Cycle Phases

  1. Follicular Phase: Dominant follicle matures.

  2. Ovulation: Triggered by LH surge.

  3. Luteal Phase: Corpus luteum forms and degenerates if no fertilization occurs.

  • corpus albicans: oocyte degenerates, scar tissue

  • corpus luteum: prepares uterus for implantation - follicular cells left after ovulation

  • FSH, LH, and Estrogen peak BEFORE ovulation

  • Progesterone peaks AFTER ovulation

Birth Control:

  • Coitus Intrruptus: withdrawing penis before ejactulation- not very effective

  • Rhythm Method: paying attention to cycle- not very effective

  • Mechanical Barriers: condoms, can work well if used properly

  • Chemical Barriers: creams, foams, etc,- most effective

  • Hormonal contraceptive: estrogen or progesterone based

  • IUD: causes inflammation by releasing copper

  • Emergency Contraceptive: stops ovulation

  • Sterilization: vasectomy and/or tubal ligation

  • Chlamydia, Gonorrhea: bacterial infection, can result in infertility, pelvic disease.

Chapter 23- Growth and Development

  • Growth: increase in size, or number of cells

  • Development: growth and aging, continuous process

    • prenatal: fertilzation-birth

    • postnatal: birth-death

  • Fertilization occurs in the fallopian tubes

  • corona radiata: sperm invades here first, layer of follicular cells that surround oocyte

  • zona pellucida: next sperm digest this glycoprotein layer that closely surrounds the oocyte

  • only 1 sperm shall win the heart of the oocyte and penetrate its membrane

  • Once sperm enters, secondary oocyte completes meiosis 2, producing tiny polar body and a large cell that contains nucleus w/female’s chromosomes

    • pronuclei: nuclei of sex cells until united

  • pronuclei now unite, completing fertilization> fertilized egg is now a zygote= 46 chromosomes

Pregnancy:

  • developing offspring in uterus, lasts about 38wks

  • three stages: pre-embryonic, embryonic, and fetal

    • Pre-Embryonic Stage: fertilzation-2/3wks

      • Cleavage: rapid cell division

        • blastomeres are the cells produced

      • Morula: when 16 cells have been developed, moved into uterus

      • Blastocyst: hollow ball of cells, attached to endometrium of uterus

        • inner mass cells: gives rise to embryo

        • trophoblast: produces hCG- maintains corpus luteum and prevents immune system from attacking, develops into structures that assist embryo

          • Chorion: will develop into embryonic portion of placenta

          • Amnion: membrane that develops around embryo, provides suitable environment for embryo to develop in

          • Yolk Sac: provides nutrients to embryo while placenta is forming

      • Embryonic Stage: 3rd wks-8th wk

        • Gastrulation: movement of cells within the embryonic disc to form multiple layers

        • primary germ layers:

          • Ectoderm: nervous system

          • Mesoderm: muscle, bone, blood, and reproductive system

          • Endoderm: resp. tract and digestive system

        • Gastrula: an embryo that has gone through gastrulation and contains all 3 germ layers

      • Fetal Stage: 8wks-birth

        • rapid growth stage

  • Fetal Hemoglobin is more efficient at carrying oxygen than adult hemoglobin