*Reproductive System (Pt 1)

Ch 28

Common elements of the 2 systems

• Both females and males have primary reproductive organs, gonads

• Ovaries in females; testes in males

• Produce sex cells called gametes

  • Unite at fertilization to initiate formation of new indv

• Produce large amts of sex hormones

  • Affect maturation, dvlpmt, activity of reproductive organs

• Both sexes also have accessory reproductive organs

• Ex. ducts to carry gametes away from gonads

  • Toward site of fertilization (females)

  • Toward outside of body (males)

Common elements: puberty

• Puberty

• Onset during adolescence

• External sex characteristics dvlp

  • Ex. breast enlargement in females

  • Ex. pubic hair growth

• Gametes begin to mature

• Gonads start to secrete sex hormones

Puberty hormones

• Hormones initiating puberty:

• Hypothalamus begins to secrete gonadotropin-releasing hormone (GnRH)

• Stimulates ant. pituitary to release 2 hormones

  • Follicle-stimulating hormone (FSH)

  • Luteinizing hormone (LH)

  • Gonads begin to produce significant levels of sex hormones

  • Start process of gamete and sexual maturation

Common elements: gametes

• Gametes

• Produced by males and females

• Female produces and releases singly gamete monthly

  • Oocyte/ovum

• Male produce large numbers of gametes

  • Sperm

  • 100 million/day

  • Store for short time only

  • If not expelled from body, resorbed

Common elements: anatomy

• Perineum

• Diamond-shaped area between thighs

• Forms the urogenital and rectal triangles

• Provides support for lower pelvic organs

  • Bladder, uterus, vagina, rectum

• Contains locations for muscles involved in urinary and bowel continence

Anatomy of the perineum

• Triangle regions of perineum:

• Divided into 2 triangle bases

  • Imaginary horizontal line btwn ischial tuberosities of ossa coxae

  • Anterior triangle, urogenital triangle

    • Females: urethral and vaginal orifices

    • Males: base of penis and scrotum

    • Both: muscles surrounding external genitalia

      • Partly anchored by perineal body, dense CT structure (perineal body)

  • Posterior triangle, anal triangle

    • Location of anus, surrounded by external anal sphincter

A brief review of heredity (pt 1)

• Heredity information:

• Carried on 23 pairs of chromosomes in human body cells

  • 22 pairs of autosomes, 1 pair of sex chromosomes

• Autosomes

  • Contain genes that code for cellular functions

  • Determine most human characteristics

    • Ex. eye and hair color, height, skin pigmentation

  • A pair of matching autosomes, homologous chromosomes

A brief review of heredity (pt 2)

• Hereditary information (continued)

• Sex hormones

  • Two X chromosomes or one X and one Y

  • Female (XX) or male (XY)

  • Also, some genes code for other functions

• One member of chromosome pair inherited from each parent

A brief review of heredity (pt 3)

• How many pairs of chromosomes inherited in cells can vary btwn species

• Diploid cell

  • 23 pairs of chromosomes (46 indv chromosomes)

• Haploid cell

  • 23 chromosomes (not 23 pairs)

  • Gametes from either sex

    • Ensures offspring do not receive two sets of paired chromosomes

An overview of cell division (pt 1)

• Mitosis

• Somatic cell division

• Produces 2 daughter cells genetically identical to parent cell

• Diploid daughter cells

• No crossing over

An overview of cell division (pt 2)

• Meiosis

• Sex cell division

• 4 daughter cells genetically different from parent cell

• Haploid daughter cells

• Includes crossing over

  • Genetic material exchanged btwn homologous chromosomes

  • Get genes from both parents on one chromosome

Meiosis creates gametes

• Meiosis

• Starts w/diploid parent cell

• Produces haploid daughter cells, gametes

• Begins w/diploid parent cell in gonad (ovary or testis)

  • 23 chromosomes from organism’s mother

  • 23 chromosomes from organism’s father

  • Must undergo meiosis to produce haploid gametes

Meiosis I (pt 1)

• Meiosis I

• Begins after interphase

• Homologous pairs of chromosomes separate when cell divides

• 4 phases plus cytokinesis

• Results in 2 cells

  • Each w/23 chromosomes of replicated sister chromatids held together at centromere

  • Meiosis II separates sister chromatids

Meiosis (pt 2)

Meiosis II: separation of sister chromatids

• Meiosis II

• After meiosis I

  • 2 daughter cells, each w/23 replicated chromosomes w/2 connected sister chromatids

• Second mitotic division

  • Chromatids separate

  • Become single chromosomes in haploid cells

• Produces 4 haploid daughter cells

  • 22 autosomes

  • 1 sex chromosome (X or Y)

  • Mature into secondary oocytes in females

  • Mature into sperm in males

Meiosis II

Gametogenesis creates egg and sperm

GAMETOGENESIS: production of gametes

• Females: oogenesis; produces an ovum; takes 300 days to complete

• Males: spermatogenesis; produce a spermatozoa; takes 74 adys to complete

• Gametogenesis begins around 5th week of embryonic dvlpmt

• Begins w/cell division, meiosis

  • Similar process in females and males, a few differences

The basic, shared steps of gametogenesis

Spermatogenesis

• Spermatogenesis

  • Process of sperm dvlpmt

  • Occurs w/in seminiferous tubule

  • Begins during puberty w/significant lvls of FSH and LH

• Spermatogonia

  • Primordial germ cells from which all sperm dvlp

  • Diploid cells near base of seminiferous tubule

  • Surrounded by cytoplasm of sustentacular cell

  • Divide by mitosis into new spermatogonium and primary spermatocyte

Spermatogenesis from puberty onward (pt 1)

Spermatogenesis

• Primary spermatocytes

  • Diploid cells that undergo meiosis

• Secondary spermatocytes

  • Two cells produced by primary spermatocyte from meiosis I

  • Haploid cells, 23 chromosomes only

  • Relatively closer to seminiferous tubule lumen

• Spermatid

  • Formed when secondary spermatocytes complete meiosis II

  • Haploid cell near seminiferous tubule lumen

  • Start off round and become elongated/oval in appearance

Spermatogenesis from puberty onward (pt 2)

Spermiogenesis

• Spermiogenesis

  • Final stage of spermatogenesis

  • Spermatid becomes mature spermatozoa, sperm

  • Excess cytoplasm shed and nucleus elongates

  • Acrosome cap forms over nucleus

    • Digestive enzymes to help penetrate secondary oocyte

  • Tail forms from organized microtubules in cell

    • Attached to midpiece region containing mitochondria and centriole

    • Mitochondria provide energy to move tail

Anatomy of the spermatozoon

• Spermatozoa: the only self-propelled, swimming cells of the human body

Spermatogenesis and spermiogenesis