The Reproductive System and DevelopmentChapter 25 – Lecture Notes

to accompany

Anatomy and Physiology: From Science to Life

textbook by

Gail Jenkins, Christopher Kemnitz, Gerard Tortora

Chapter Overview

25.1 Sperm Production

25.2 Male Reproductive System

25.3 Female Reproductive System

25.4 Vagina and Mammary Glands

25.5 Ovarian and Uterine Cycle

25.6 Implantation of Blastocyst

25.7 Embryonic to Fetal Period

Chapter Overview

25.8 Maternal Changes During Pregnancy

25.9 Labor

25.10 Milk Production and Ejection

Essential Terms

gamete germ cells with haploid number of chromosomes

fertilization occurs when sperm unites with secondary oocyte

pregnancy sequence of events resulting in birth of child

gonads male testes and female ovaries which secrete

hormones and produce gametes

IntroductionSexual Reproduction

1. Males and females differ anatomically to produce gametes and support a fetus

2. Fertilization is the result of male and female gametes joining

3. Pregnancy begins with fertilization and usually results in birth of a child

4. Gonads produce gametes and hormones

Concept 25.1

Sperm Production

Male Reproductive System

1. Testes – System of Ducts• Epididymis, ductus deferens, ejaculatory ducts,

and urethra

2. Accessory glands• Seminal vesicles, prostate, and bulbourethral

glands

3. Supporting Structures• Scrotum and penis

Figure 25.1a

Figure 25.1b

Scrotum

Scrotal location and muscle contraction regulate temperature of testes

Normal sperm production occurs 2-3°C lower than core body temperature

Response to cool temperatures Cremaster muscles contract to pull testes close to

body Dartos muscles contract to tighten scrotum

Response to warm temperatures Reverse of above actions

Figure 25.2

Testes

One testes in each sac of scrotum Descend during seventh month of fetal

development Tunica albuginea is located deep to tunica

vaginalis and forms 200-300 lobules Lobules contain seminiferous tubules

Spermatogenesis carried out by seminiferous tubules of testes

Figure 25.3a

Figure 25.3b

Figure 25.3c

Testes

Spermatogenic cells Begin sperm production at puberty

Sertoli or sustentacular cells Junctions form blood-testis barrier Nourish spermatogenic cells Carry out phagocytosis Control spermatogenic movement Produce fluid for transport Secrete hormone inhibin

Leydig (interstitial) cells Secrete testosterone

Figure 25.4a

Figure 25.4b

Spermatogenesis

Begins with spermatogonia and diploid number of chromosomes

Some pass through blood-testis barrier Primary spermatocytes also diploid

Figure 25.5

Spermatogenesis

Meiosis I Crossing-over during metaphase I Secondary spermatocytes result Each with haploid number

Meiosis II Results in four spermatids Each with haploid number

Spermatogenesis

Cytoplasmic bridges link the four daughter cells

Spermiogenesis Transformation of spherical spermatids into

elongated sperm Formation of arcosome Flagellum develop Mitochondria multiply

Sperm

300 million per day produced Survive 48 hours in female reproductive tract Sperm Parts Head

Nucleus Arcosome

Tail Neck Middle piece Principal piece End piece

Figure 25.6

Hormonal Control of Testes

Negative feedback loops control testosterone release and spermatogenesis

Gonadotropin-releasing Hormone (GnRH) Increased production at puberty Stimulates secretion of LH and FSH

Luteinizing hormone (LH) Stimulates Leydig cells

Follicle-stimulating hormone (FSH) Stimulates Sertoli cells to secrete ABP

Figure 25.7

Hormonal Control of Testes Testosterone

Principal androgen Synthesized from cholesterol Suppresses LH and GnRH secretion Converted to DHT in prostate and seminal vesicles

Dihydrotestosterone (DHT) Stimulates development of external genitals

Androgen-binding Protein (ABP) Binds to and keeps testosterone levels high

Inhibin Inhibits FSH secretion

Effects of Testosterone and Dihydrotestosterone

Prenatal development Development of male sexual characteristics Development of sexual function Stimulation of anabolism

Figure 25.8

Concept 25.2 Male Reproductive System

Reproductive System Ducts in Males Ducts of testis

Seminiferous tubules Straight tubules Rete testis Efferent ducts Ductus epididymis

Epididymis Site of sperm maturation and storage Consists of ductus epididymis Head – superior portion formed by efferent ducts of testis Body Tail – continues as ductus (vas) deferens

Ductus Deferens

Terminal portion is the ampulla Conveys sperm from epididymis toward

urethra Storage and reabsorption of sperm

Figure 25.9

Spermatic Cord

Supporting structure ascends out of scrotum Comprised of several structures

Ductus deferens Testicular artery Pampiniform plexus Autonomic nerves Lymphatic vessels Cremaster muscles

Ejaculatory Ducts

Formed by duct of seminal vesicle and ampulla of ductus deferens

Eject sperm and seminal vesicle secretions from urethra to exterior

Urethra

Shared by reproductive and urinary systems 3 subdivisions

Prostatic urethra Membranous urethra Spongy (penile) urethra

Accessory Sex Glands

Produce fluids to protect semen and facilitate their movement

Seminal vesicles Prostate Bulbourethral or Cowper’s glands

Seminal Vesicles

Alkaline fluid Fructose Prostaglandins Clotting proteins Approximately 60% of semen volume

Prostate Gland

Citric acid Proteolytic enzymes – prostate-specific

antigen (PSA) Pepsinogen Lysozyme Amylase Hyaluronidse Milky, acidic fluid (pH ~ 6.5) Approximately 25% semen volume

Bulbourethral / Cowper’s Glands

Pea sized glands active during sexual arousal

Alkaline fluid Secrete lubricating mucus

Semen

Combination of sperm and seminal fluid 2.5 – 5 mL per ejaculation 50 – 150 million sperm/ml Alkaline pH ~ 7.2 – 7.7 Seminalplasmin – antibiotic

Penis

Contains urethra Passage for sperm and urine 3 Parts

Root Body Glans penis

Erection maintained by parasympathetic fibers

Ejaculation, a sympathetic reflex, releases semen to exterior

Figure 25.10a

Figure 25.10b

Concept 25.3 Female Reproductive System

Figure 25.11a

Figure 25.11b

Figure 25.12

Figure 25.13

Figure 25.14a

Figure 25.14b

Figure 25.15

Concept 25.4 Vagina and Mammary Glands

Concept 25.5 Ovarian and Uterine Cycle

Concept 25.6 Implantation of Blastocyst in Endometrium

Concept 25.7 Embryonic to Fetal Period

Concept 25.8 Maternal Changes During Pregnancy

Concept 25.9 Labor

Concept 25.10 Milk Production and Ejection