Reproduction quiz

Reproductive System Overview

• The reproductive system is a fundamental characteristic of life, responsible for creating new individuals.
• Sex describes biological characteristics.
• Gender differentiates masculinity and femininity.
• Gametes are reproductive cells (sperm and egg).

Gametogenesis

• Gametogenesis is the production of gametes.
• Females produce ova (eggs) through oogenesis. Oogenesis takes ~300 days and begins around the 5th week of embryonic development.
• Males produce sperm (spermatozoa) through spermatogenesis. Spermatogenesis takes ~74 days and begins around the 5th week of embryonic development.
• Primordial germ cells (PGCs) initially migrate to genital ridges and then divide mitotically. These cells will differentiate into either ova or spermatozoa.

Spermatogenesis

• Spermatogenesis is a process that occurs in the seminiferous tubules from puberty onward.
• Begins with spermatogonia.
• Spermatogonia undergo mitosis to maintain stem cell population (Type A) to produce Type B spermatogonia.
• Type B spermatogonia undergo mitosis, duplicating the pool of germ cells entering the next steps.
• Meiosis I and meiosis II occur, leading to the formation of spermatids.
• Spermatids undergo spermiogenesis, a process of organelle and cytoplasm modification.
• The final product is spermatozoa.
• The spermatogenic cycle takes approximately 74 days.

Anatomy of Spermatozoon

• Spermatozoa are self-propelled, swimming cells.
• Components include head (nucleus, acrosome, centrioles), mid-piece (mitochondria), and tail (flagellum).

Oogenesis

• Oogenesis begins during embryogenesis and continues into puberty.
• At birth, 600,000 to 7,000,000 oocytes are present.
• Meiosis begins but arrests during prophase I during embryonic development.
• At puberty, the process is resumed in select oocytes.
• The oocyte will complete meiosis I and II during the release of the oocyte.

Male Reproductive Tract

• Structures include the testes (produce sperm), epididymis (store sperm), ductus deferens (transport sperm), ejaculatory duct (mixes sperm and seminal fluid), and urethra (conducts semen).

Male Reproductive Tract: Testis

• Testes are paired ovoid gonads housed in the scrotum.
• Surrounded by the tunica vaginalis and tunica albuginea.
• The tunica albuginea divides the testis into ~200 distinct tubules.

Male Reproductive Tract: Seminiferous Tubules

• Formed by interconnected Sertoli cells.
• Sertoli cells nourish and support developing sperm.
• Sertoli cells also scavenge debris and produce fluid.
• They also produce inhibin and androgen-binding protein (ABP).

Male Reproductive Tract: Epididymis

• Epididymis: long, thin, convoluted tube lying against the testis.
• A series of tubes converges into a single duct, coiling down to ~1/2000th of its actual size.
• The tubes maintain tight junctions and transport sperm.

Male Reproductive Tract: Ductus Deferens

• Structural continuation of the epididymis within the spermatic cord.
• Passes through the pelvic cavity to form the ampulla before connecting with the seminal vesicle.
• Has three layers (outer adventitia, middle muscularis, inner mucosa).

Male Reproductive Tract: Ejaculatory Duct and Urethra

• Ejaculatory ducts connect the vas deferens to the urethra.
• The urethra mixes sperm with seminal plasma.
• The male urethra is divided into prostatic, membranous, and spongy segments, collectively conducting semen.

Male Accessory Sex Glands

• Accessory glands include seminal vesicles, prostate, and bulbourethral glands.

Male Accessory Sex Glands: Seminal Vesicles

• Each seminal vesicle has an excretory duct.
• The duct joins the vas deferens to form the ejaculatory duct.
• The lumen consists of convoluted mucosa (increased surface area).
• Surrounded by two smooth muscle layers.

Male Accessory Sex Glands: Prostate Gland

• Largest male accessory sex gland, consisting of many lobules.
• Lobules open into the prostatic urethra.
• Secretes ~30% of seminal fluid (with ingredients such as citric acid, prostate-specific antigen, zinc).

Male Accessory Sex Glands: Bulbourethral Glands

• Two cm-long ducts join the spongy urethra.
• Secretions make up ~5% of ejaculate, typically pre-ejaculate.
• The fluid is clear, alkaline, and contains lubricating proteins and neutralizing mucins.

Male External Genitalia

• Includes the penis and scrotum.

Male External Genitalia: Penis

• Elongates during sexual arousal, with roots attaching to the pelvic girdle, body containing urethra and corpora cavernosa.
• The glans is highly sensitive.

Male External Genitalia: Scrotum

• Maintains testicular temperature at 34°C for spermatogenesis.
• Suspended at the base of the pelvis.
• Bisected at midline into two compartments.
• Monitored by thermoreceptors.

Female Reproductive System

• Includes ovaries, uterine tubes, uterus, and vagina.

Female Reproductive System: Ovaries

• Positioned on either side of the uterus via the mesovarium.
• Ovarian arteries, veins, and nerves pass through the hilum.
• Outer cortex has dense connective tissue with ovarian follicles (developing germ cells).
• Inner medulla has areolar connective tissue (blood vessels, lymphatics).

Female Reproductive System: Folliculogenesis

• The process of ovarian follicle development, including primordial, primary, secondary, and tertiary follicles.
• Oogenesis begins during embryogenesis and continues at puberty.
• Theca cells produce androgens, and granulosa cells convert androgens to estrogen.

Female Repro System:Ovarian Follicle

• Tertiary follicle develops, displacing the oocyte to one side of the antrum.
• Specialized granulosa cells form the corona radiata.
• Other granulosa and theca cells form luteal cells.

Female Repro System: Corpus Luteum

• Transient endocrine organ formed from granulosa and thecal cells.
• If pregnancy occurs, the corpus luteum persists and secretes hormones.
• If pregnancy does not occur, the corpus luteum degenerates and is replaced by the corpus albicans.

Female Repro System: Uterus

• Structurally divided into fundus, body, isthmus, and cervix.
• Function: support, nurture, and nourish developing embryo.
• Anchored by ligaments.

Female Repro System: Uterine Layers

• Perimetrium: outer serosa layer.
• Myometrium: three layers of smooth muscle.
• Endometrium: inner layer, site of implantation. Basal layer is permanent; functional layer is hormone-responsive.

Female Repro System: Cervix and Vagina

• Cervix: dome-like structure protruding into the vagina.
• Functions include copulation, passageway of menstrual flow, birth canal.
• Vagina: three-layered canal (outer adventitia, middle muscularis, inner mucosa). Natural home to several microorganisms.

Female External Genitalia

• Vulva: Mons pubis, labia majora and minora, pudendal cleft.
• Vestibule: area between labia minora, encompassing clitoris, urethral orifice, and vaginal orifice. Hymen may be present.
• Clitoris: erectile tissue homologous to the male penis.

Hormonal Regulation of Reproduction

• Hypothalamic-pituitary-gonadal axis regulates gametogenesis in both sexes.
• GnRH from hypothalamus stimulates the anterior pituitary to release LH and FSH.
• Gonadotropins (LH and FSH) stimulate gametogenesis and steroidogenesis in the gonads.
• Steroid hormones (androgens, estrogens, progesterone) regulate reproductive processes (e.g. spermatogenesis, oogenesis, menstrual cycle).

Male Reproductive Endocrinology

• The hypothalamic-pituitary-gonadal axis is responsible for the regulation of testicular function.
• This process involves GnRH stimulation of LH and FSH secretion from the anterior pituitary, which act on the testes to regulate spermatogenesis.
• Sertoli cells produce inhibin B and ABP, and Leydig cells secrete testosterone, DHT and estrogens. These hormones support sperm production and development and help regulate secondary sexual characteristics.

Menstrual Cycle

• A complex series of hormonal changes that result in the cyclical preparation of the endometrium (uterine lining) for potential pregnancy.
• The ovarian cycle involves the maturation of ovarian follicles and ovulation.
• The uterine cycle involves changes in the uterine lining. There are phases (follicular, ovulation, and luteal phases) in both cycles.
• Various hormones (FSH, LH, estrogen, progesterone) influence the ovarian and uterine cycles throughout the phases.

Puberty

• Puberty is the developmental period when reproductive function begins.
• Triggered by increased production of adrenal cortex and gonadal hormones.
• Results in sexual maturation and the development of secondary sexual characteristics in males and females.

Reproductive System Aging

• Reduced hormone levels (testosterone in males, and estrogen in females) result in decreased reproductive function over time.
• Termination of reproductive years is referred to as the climacteric in reproductive physiology.
• In males, this leads to reduced testosterone production, diminished sex drive and potential symptoms such as erectile dysfunction. In females, this leads to a decrease in circulating estrogen, depletion/absence of follicles, and/or menstruation.