Honors Anatomy & Physiology Chapter 27 Part 2

© 2013 Pearson Education, Inc. Spermatogenesis Sperm (spermatozoa) production in seminiferous tubules most body cells have 46 chromosomes - diploid chromosomal number (2n) 2 sets (23 pairs) of chromosomes one maternal, one paternal – homologous chromosomes gametes have 23 chromosomes - haploid chromosomal number (n) only one member of homologous pair

© 2013 Pearson Education, Inc. Meiosis gamete formation involves meiosis differs from mitosis: 2 consecutive cell divisions (meiosis I and II); only one round of DNA replication produces 4 daughter cells functions of meiosis # of chromosomes halved (from 2n to n) genetic diversity

© 2013 Pearson Education, Inc. Meiosis Sources of Genetic Diversity random alignment of homologous pairs in meiosis I  variability of gametes crossing over (Prophase I)  variability of gametes ~ no 2 gametes exactly alike ~ all genetically different from original cells

© 2013 Pearson Education, Inc. Spermatogenesis Spermatogenic cells give rise to sperm Mitosis of spermatogonia (stem cell) forms two spermatocytes (2n) Meiosis spermatocytes  secondary spermatocytes  spermatids 2 ◦ spermatocytes (n) Spermiogenesis spermatids become sperm

© 2013 Pearson Education, Inc. Figure 27.8c Spermatogenesis. Type A daughter cell remains at basal lamina as a precursor cell Type B daughter cell Primary spermatocyte Secondary spermatocytes Early spermatids Late spermatids Spermatozoa Basal lamina Spermatogonium (stem cell) Cytoplasm of adjacent sustentocytes Tight junction between sustentocytes Sustentocyte cell nucleus Cytoplasmic bridge Lumen of semini- ferous tubule Adluminal compartment Basal compartment A portion of the seminiferous tublule wall, showing the spermatogenic cells surrounded by sustentocytes (colored gold)

© 2013 Pearson Education, Inc. Mitosis of Spermatogonia Spermatogenesis begins at puberty

8/animation__spermatogenesis__quiz_1_.html

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 2 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus 1

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 3 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles 12

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 3 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles 12

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 4 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles Microtubules Flagellum 12 3

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 5 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles Microtubules Flagellum Mitochondria

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 6 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles Microtubules Flagellum Mitochondria Acrosome Nucleus Excess cytoplasm

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 7 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles Microtubules Flagellum Mitochondria Acrosome Nucleus Excess cytoplasm

© 2013 Pearson Education, Inc. Figure 27.9 Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 1 Approximately 24 days Golgi apparatus Acrosomal vesicle Spermatid nucleus Centrioles Microtubules Flagellum Mitochondria Acrosome Nucleus Excess cytoplasm Midpiece Head Tail

© 2013 Pearson Education, Inc. Role of Sustentocytes large supporting cells (Sertoli cells) extend through wall of tubule and surround developing cells provide nutrients and signals to dividing cells move cells along to lumen secrete testicular fluid into lumen for sperm transport phagocytize faulty germ cells and excess cytoplasm produce chemical mediators to regulate spermatogenesis

© 2013 Pearson Education, Inc. Role of Sustentocytes tight junctions divide tubule into two compartments basal compartment—spermatogonia and primary spermatocytes adluminal compartment—meiotically active cells and tubule lumen

© 2013 Pearson Education, Inc. Type A daughter cell remains at basal lamina as a precursor cell Type B daughter cell Primary spermatocyte Secondary spermatocytes Early spermatids Late spermatids Spermatozoa Basal lamina Spermatogonium (stem cell) Cytoplasm of adjacent sustentocytes Tight junction between sustentocytes Sustentocyte cell nucleus Cytoplasmic bridge Lumen of semini- ferous tubule Adluminal compartment Basal compartment A portion of the seminiferous tublule wall, showing the spermatogenic cells surrounded by sustentocytes (colored gold) Figure 27.8c Spermatogenesis.

© 2013 Pearson Education, Inc. Role of Sustentocytes tight junctions form blood testis barrier prevents sperm antigens from escaping into blood  activation of immune system important - sperm not formed until puberty, absent during immune system development, would not be recognized as "self"

© 2013 Pearson Education, Inc. Spermatogenesis takes 64 – 72 days if conditions hospitable pressure of testicular fluid pushes immotile sperm into epididymis  motility and fertilizing power

© 2013 Pearson Education, Inc. Homeostatic Imbalance Infertility gradual decline in male fertility past 50 years Xenobiotics (alien molecules) may be cause environmental toxins, PVCs, phthalates, pesticides, herbicides, compounds with estrogenic effects, antibiotics (tetracyclines), radiation, lead, marijuana also, lack of selenium, excessive alcohol, lack of specific Ca 2+ channel, anatomical obstructions, hormonal imbalances, oxidative stress, fevers, hot tubs

© 2013 Pearson Education, Inc. Hormonal Regulation of Male Reproductive Function sequence of hormonal regulatory events involving hypothalamus, anterior pituitary gland, and testes Hypothalamic-Pituitary-Gonadal (HPG) axis regulates production of gametes and sex hormones through 3 interacting sets of hormones GnRH indirectly stimulates testes via FSH & LH FSH & LH directly stimulate testes Testosterone & Inhibin – negative feedback on hypothalamus and anterior pituitary

© 2013 Pearson Education, Inc. HPG Axis Testosterone  1. sex organ maturation, 2. development/maintenance secondary sex characteristics, 3. libido rising testosterone levels  feedback inhibition on hypothalamus to inhibit GnRH and on pituitary to inhibit gonadotropin release

HPG Inhibin (released when sperm count high) – inhibits GnRH and FSH release

© 2013 Pearson Education, Inc. HPG Axis 3 years to achieve balance, then testosterone and sperm production fairly stable throughout life without GnRH and gonadotropins  testes atrophy; sperm and testosterone production cease

© 2013 Pearson Education, Inc. Male Secondary Sex Characteristics features induced in nonreproductive organs by male sex hormones (mainly testosterone) appearance of pubic, axillary, and facial hair enhanced growth of chest hair; deepening of voice skin thickens and becomes oily bones grow, increase in density skeletal muscles increase in size and mass boosts basal metabolic rate basis of sex drive (libido) in males

© 2013 Pearson Education, Inc. Male Secondary Sex Characteristics Testosterone masculinizes embryonic brain continues to exert effect well into adulthood adrenal glands produce androgens in small amounts – insufficient to maintain normal testosterone- mediated functions