🫁Honors Anatomy and Physiology Unit 15 – Reproductive System

Key Structures and Functions

• Reproductive system consists of organs and structures involved in producing offspring
• Primary reproductive organs include testes in males and ovaries in females which produce gametes (sperm and eggs)
• Secondary reproductive organs include ducts, glands, and external genitalia that transport and nurture gametes
• Accessory glands secrete fluids that support and protect gametes
  • In males, seminal vesicles and prostate gland contribute to semen production
  • In females, Bartholin's glands secrete mucus to lubricate the vagina
• Reproductive system is closely linked to the endocrine system for hormonal regulation
• Puberty marks the onset of reproductive maturity and is characterized by the development of secondary sexual characteristics (pubic hair, breast development)
• Reproductive system functions to ensure the survival and perpetuation of the species

Male Reproductive System

• Testes are the primary male reproductive organs that produce sperm and testosterone
• Scrotum is a sac of skin that holds the testes outside the body cavity to maintain optimal temperature for sperm production
• Epididymis is a highly coiled tube where sperm mature and are stored until ejaculation
• Vas deferens is a muscular tube that transports sperm from the epididymis to the ejaculatory ducts
• Seminal vesicles and prostate gland secrete fluids that mix with sperm to form semen
  • Seminal fluid provides nutrients and protection for sperm
• Urethra serves as a common passage for both semen and urine, although not simultaneously
• Penis is the male copulatory organ that becomes erect during sexual arousal to facilitate the delivery of semen into the female reproductive tract

Female Reproductive System

• Ovaries are the primary female reproductive organs that produce eggs (ova) and female sex hormones (estrogen and progesterone)
• Fallopian tubes (oviducts) transport eggs from the ovaries to the uterus and serve as the site of fertilization
  • Fimbriae are finger-like projections that sweep the egg into the fallopian tube
• Uterus is a muscular organ that houses and nourishes the developing fetus during pregnancy
  • Endometrium is the inner lining of the uterus that thickens in preparation for implantation and is shed during menstruation if pregnancy does not occur
• Cervix is the narrow, lower portion of the uterus that connects to the vagina and dilates during childbirth
• Vagina is a muscular canal that serves as the receptacle for the penis during sexual intercourse and forms part of the birth canal
• External genitalia include the labia, clitoris, and vaginal opening, which are collectively known as the vulva

Hormonal Regulation

• Hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• In males, FSH stimulates sperm production in the testes, while LH stimulates testosterone production by Leydig cells
  • Testosterone is responsible for the development and maintenance of male secondary sexual characteristics and supports spermatogenesis
• In females, FSH stimulates follicle development in the ovaries, while LH triggers ovulation and the formation of the corpus luteum
  • Estrogen is produced by developing follicles and promotes the development and maintenance of female secondary sexual characteristics
  • Progesterone is produced by the corpus luteum and prepares the uterus for implantation and maintains pregnancy
• Negative feedback loops regulate hormone levels to maintain homeostasis
  • High levels of testosterone, estrogen, and progesterone inhibit the release of GnRH, FSH, and LH

Gametogenesis and Fertilization

• Gametogenesis is the process of producing haploid gametes (sperm and eggs) from diploid germ cells through meiosis
• Spermatogenesis occurs in the seminiferous tubules of the testes and involves the differentiation of spermatogonia into mature spermatozoa
  • Spermatogonia undergo mitosis to maintain their population and produce primary spermatocytes
  • Primary spermatocytes undergo meiosis I to form secondary spermatocytes, which then undergo meiosis II to form spermatids
  • Spermatids differentiate into mature spermatozoa through the process of spermiogenesis
• Oogenesis occurs in the ovaries and involves the development of primary oocytes into mature ova
  • Primary oocytes are formed before birth and remain arrested in prophase I until puberty
  • Each menstrual cycle, a primary oocyte completes meiosis I to form a secondary oocyte and a polar body
  • The secondary oocyte is released during ovulation and will complete meiosis II if fertilized by a sperm
• Fertilization occurs when a sperm penetrates the zona pellucida of an egg and their genetic material combines to form a zygote
  • Capacitation is a process that occurs in the female reproductive tract, which enables sperm to fertilize an egg
  • The acrosome reaction involves the release of enzymes from the sperm head to digest the zona pellucida and allow the sperm to enter the egg

Pregnancy and Fetal Development

• Pregnancy begins with the implantation of the blastocyst (early embryo) into the uterine wall, typically 6-7 days after fertilization
• The placenta develops from the chorionic villi of the blastocyst and serves as the interface between maternal and fetal circulation
  • Allows for the exchange of nutrients, oxygen, and waste products between the mother and fetus
  • Produces hormones (human chorionic gonadotropin, estrogen, and progesterone) to maintain pregnancy
• Fetal development is divided into three trimesters, each lasting approximately three months
  • First trimester: rapid cell division and differentiation, formation of major organ systems
  • Second trimester: continued growth and development, fetal movements become detectable
  • Third trimester: rapid fetal growth, organs mature in preparation for life outside the womb
• Parturition (childbirth) is initiated by a complex interplay of hormones, including increased levels of oxytocin and prostaglandins
  • Stages of labor include dilation of the cervix, expulsion of the fetus, and delivery of the placenta

Common Disorders and Diseases

• Infertility is the inability to conceive after 12 months of regular, unprotected sexual intercourse
  • Causes include hormonal imbalances, structural abnormalities, and genetic factors
• Polycystic ovary syndrome (PCOS) is a hormonal disorder characterized by irregular menstrual cycles, excess androgen production, and the presence of multiple cysts on the ovaries
• Endometriosis is a condition in which endometrial tissue grows outside the uterus, causing pelvic pain and infertility
• Sexually transmitted infections (STIs) such as chlamydia, gonorrhea, and human papillomavirus (HPV) can lead to pelvic inflammatory disease, infertility, and certain cancers (cervical cancer)
• Erectile dysfunction is the inability to achieve or maintain an erection sufficient for sexual intercourse
  • Causes include cardiovascular disease, diabetes, and psychological factors
• Prostate cancer is the most common cancer in men and is often detected through prostate-specific antigen (PSA) screening
• Ovarian and breast cancer are common malignancies in women, often associated with genetic predisposition (BRCA1 and BRCA2 mutations)

Clinical Applications and Current Research

• Assisted reproductive technologies (ART) such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) help individuals with infertility conceive
  • IVF involves fertilizing an egg with sperm in a laboratory dish and transferring the resulting embryo to the uterus
  • ICSI involves injecting a single sperm directly into an egg to overcome male factor infertility
• Contraceptive methods include hormonal (birth control pills, patches, and injections), barrier (condoms and diaphragms), and intrauterine devices (IUDs)
  • Emergency contraception (Plan B) can prevent pregnancy if taken within 72 hours of unprotected intercourse
• Prenatal testing and screening help detect genetic disorders and congenital abnormalities
  • Amniocentesis and chorionic villus sampling (CVS) are invasive procedures that allow for genetic testing of fetal cells
  • Non-invasive prenatal testing (NIPT) analyzes fetal DNA in maternal blood to screen for chromosomal abnormalities
• Stem cell research holds promise for the treatment of reproductive disorders and infertility
  • Spermatogonial stem cells could potentially be used to restore spermatogenesis in men with infertility
  • Induced pluripotent stem cells (iPSCs) derived from adult cells could be used to generate gametes or study early embryonic development
• Oncofertility is an emerging field that focuses on preserving fertility in cancer patients undergoing gonadotoxic treatments
  • Options include sperm banking, oocyte and embryo cryopreservation, and ovarian tissue freezing