Chapter 22 Male Reproductive system + Meiosis

Meiosis

gonads produce hormones and gametes (sex cells)

testes

male gonads that produce sex cells called sperm

ovaries

female gonads that produce sex cells called ova (oocytes, eggs)

Sex cells have

1 set of genetic instructions on 23 chromosomes

Other body cells have

2 sets on 46 chromosomes in other body cells

When sperm and egg unite at fertilization

genetic information carried on 46 chromosomes is restored

Meiosis consists of

2 divisions; meiosis 1 then meiosis 2

Prior to meiosis

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

Cells in meiosis are

diploid; containing 2 sets of chromosomes in 23 pairs

Meiosis 1

separates homologous pairs of chromosomes

Meiosis 1 results in

haploid cells, which contain 1 set of chromosomes; 23 chromosomes, 1 from each homologous pair

Meiosis 2

separates chromatids

Meiosis 2 results in

haploid cells, whose chromosomes now have 1 chromatid; each chromatid is considered a chromosome

Four phases of Meiosis 1

prophase 1, metaphase 1, anaphase 1, telophase 1

Prophase 1 of Meiosis 1

involves synapsis and crossover occurs

Synapsis

pairing of homologous chromosomes

Crossover

exchange of genetic material between homologous chromosomes, to produce chromosomes with genetic information from both parents

Metaphase 1 of Meiosis 1

chromosome pairs line up on midline of spindle; alignment is random, w/ respect to maternal or paternal origin

Anaphase 1 of Meiosis 1

Homologous chromosome pairs separate, each replicated member migrating to a different pole

Anaphase 1 in Meiosis 1 results in

each daughter cell receives only 1 replicated member of each chromosome pair; this reduces the chromosome number by half

Telophase 1 of Meiosis 1

cell divides completely, forming 2 new haploid daughter cells; each new cell contains 23 chromosomes w/ 2 chromatids

Meiosis 2 four phases

Prophase 2, Metaphase 2, anaphase 2, telophase 2

Prophase 2 of meiosis 2

chromosomes condense and reappear, still replicated

Metaphase 2 of Meiosis 2

Replicated chromosomes attach to spindle fibers along midline

Anaphase 2 of meiosis 2

centromeres separate, and chromatids migrate to opposite poles; chromatids are now considered chromosomes

Telophase 2 of meiosis 2

each 2 cells produced in meiosis 1 divides into 2 daughter cells

Each cell entering meiosis could produce

4 gametes; this occurs in sperm, not in eggs, only 1 egg cell matures and the others degenerate

Primary sex organs (gonads) are the 2 testes

produce sperm cells or spermatozoa and produce male sex hormones

Secondary (accessory) sex organs

other internal and external sex organs, secrete male sex hormones, and transport sperm and secretions to outside of body

In male fetus, testes originate from

masses of tissue behind the parietal peritoneum, near the kidneys

1 to 2 months before birth in the descent of testes process

testosterone produced by the developing testes triggers their descent into the scrotum

Gubernaculum

fibrous cord aids descent through inguinal canal

After the descent of testes

spermatic cord contains the ductus deferens, blood vessels, and nerves

Structure of testes

tunica albuginea, lobules, seminiferous tubules, interstitial cells, rete testis, and epididymis

Tunica albuginea

tough, fibrous capsule enclosing each testis

Lobules

compartments in testis, separated by connective tissue septa

Seminiferous tubules

highly coiled tubules inside lobules; lined w/ a special stratified epithelium containing spermatogenic cells that give rise to sperm cells

Interstitial cells (cells of leydig)

lie between seminiferous tubules; produce and secrete male sex hormones

Rete testis

channels that transport from testis to epididymis

Epididymis

coiled tube on surface of testis, that transports sperm from rete testis to ductus deferens

Male internal accessory organs

nature and transport sperm cells

Male internal accessory organs consist of

epididymis, ductus deferens, ejaculatory duct, seminal vesicles, prostate gland, bulbourethral gland, urethra

Ductus (vas) deferens

muscular tubes, part of spermatic cord, extends from the epididymis to the ejaculatory duct

Seminal vesicles (glands)

attached to a ductus deferens, secretes alkaline fluid, fructose, prostaglandins and empties into the ejaculatory duct

Prostate gland

secretes a thin, milky alkaline fluid enhancing sperm motility contributing to semen

Bulbourethral glands (cowper)

secretes mucus-like fluid into urethra and released in response to sexual stimulation lubricating end of penis

Semen is transported by

urethra to outside of the body during ejaculation

Semen contains

contains sperm from testes, secretions of seminal vesicles prostate gland and bulbourethral glands, prostaglandins and nutrients

Semen pH

slightly alkaline, 7.5

sperm begin to swim as they

mix with secretions of accessory glands

Sperm cannot fertilize egg until

they undergo capacitation in female tract, which weakens acrosome (cap over sperm head)

Male infertility

inability of sperm cells to fertilize an oocyte

Causes of male infertility

failure of testes to descent, inflammation of testes (mumps), poor quality sperm, low sperm count

Computer-aided sperm analysis (CASA)

technique used to evaluate a man’s fertility; analyzes sperm count, sperm motility, size and shape of sperm parts

Male external reproductive organs

scrotum and penis

Scrotum

pouch of skin and subcutaneous tissue behind penis, lacks fat

Dartos muscle

contracts and relaxes in response to temp changes to keep testes at optimal temp for sperm production and survival

Medial septum divides into 2 chambers

each chamber is lined w/ serous membrane and houses a testis and epididymis

Penis

conveys urine and semen through urethra to outside of body; specialized to become erect for insertion

Body (shaft) contains 3 columns of erectile tissue

2 corpora cavernosa, 1 corpus spongiosum which surrounds urethra

Prepuce (foreskin)

covering of glans penis; removed during circumcision

Erection

during sexual stimulation, parasympathetic nerve impulses release nitric oxide, which dilates arteries of penis

Erection causes

pressure of arterial blood compresses veins, blood accumulates in erectile tissues, and penis swells and elongates

Orgasm

culmination of sexual stimulation, pleasurable feeling of physiological and psychological release accompanied by emission and ejaculation

Emission

movement of semen into urethra

Ejaculation

movement of semen out of urethra; dependent on sympathetic nerve impulses

Spermatogenesis

formation of sperm cells; combined processes of meiosis and spermiogenesis

Sustentacular (sertoli) cells

support and nourish spermatogenic cells throughout their development into sperm

Sperm formation proceeds in this sequence

Spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, spermatozoa

Spermiogenesis

development of spermatids into sperm

Spermatogenesis produces

4 sperm cells from meiosis of 1 primary spermatocyte

during spermatogenesis spermatogonia

replenish themselves, giving rise to spermatocytes which develop into sperm

As the stages of spermatogenesis continue

the developing sperm migrate from the outer edge of the seminiferous tubule to the lumen

Sperm structure

tiny tadpole-shaped structure that contains a head, midpiece (body), and tail (flagellum)

Head of sperm

nucleus contains 23 chromosomes, acrosome caps nucleus which contains enzymes that penetrate the egg

Midpiece (body) of sperm

contains many mitochondria, which provide ATP for swimming

Tail (flagellum) of sperm

contains many microtubules enclosed in extension of cell membrane; lashing movement propels sperm toward egg

Male reproductive functions

controlled by hormones secreted by hypothalamus, anterior pituitary gland, and testes

Functions of hormones in male reproductive parts

initiate and maintain sperm cell production; oversee development and maintenance of male secondary sex characteristics

Hypothalamic hormone

gonadotropin-releasing hormone (GnRH) regulates secretion of gonadotropins from anterior pituitary gland

Anterior pituitary hormones (gonadotropins)

interstitial cell stimulating hormone (luteinizing hormone, LH, ICSH) and follicle stimulating hormone (FSH)

Interstitial cell stimulating hormone

causes development of interstitial cells in testes, which secrete male sex hormones (testosterone)

Follicle stimulating hormone (FSH)

stimulates sustentacular cells of testes to mature, proliferate, and respond to testosterone

In presence of FSH and testosterone

sustentacular cells stimulate spermatogenesis in spermatogenic cells

Negative feedback controls

reproduction and hormone production

Androgens (testosterone) prevents

over secretion of GnRH and LH

Inhibin from sustentacular cells

prevents over secretion of FSH

Androgens

male sex hormones produced by interstitial cells of testes and adrenal cortex (little)

most important androgen

testosterone

Testosterone secretion begins during

fetal development and continues until weeks after birth, after secretion stops during childhood (begins again in puberty and continues)

Dihydrotestosterone (DHT)

Androgen derivative of testosterone acts on cells in prostate gland, seminal vesicles, and external accessory organs

Actions of testosterone prior to birth

development of male reproductive organs, descent of testes into scrotum

Actions of testosterone during puberty

enlargement of testes and accessory organs of male reproductive system; development of secondary sex characteristics