Reproductive System - Lecture notes provided by Professor Childress PDF

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Lecture notes provided by Professor Childress...

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Reproductive System Functions -

Provides means for sexual maturation Generates reproductive cells (gametes) Provides structures for fertilization Maintenance of the developing embryo

Cell Division -

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Nuclear division - Mitosis - Result: 1 parent cell produces 2 identical daughter cells (46 chromosomes) - Where: in somatic cells - Importance: growth and repairs - Steps: PMAT - Meiosis - Result: 1 parent cell produces 4 different haploid daughter cells (23 chromosomes) - Where: in reproductive cells (gametes) - Importance: allows to reproduce sexually - Steps: P1, M1, A1, T1 + P2, M2, A2, T2 Cytoplasmic division - Cytokinesis

Meiosis Goals -

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Reduces the number of chromosomes in half in order to maintain a normal number of chromosomes in a human offspring: - 23 maternal + 23 paternal = 46 normal human Creates a variety of gametes with different combinations of genes (recombination) achieved through: - Crossing over during P1 (exchange of the portions of homologous chromosomes) - Independent assortment of chromosomes during M1 (random sets of maternal and and paternal chromosomes are produced)

Female Reproductive System -

Ovaries: paired, oval organs located within the pelvic cavity lateral to uterus; slightly larger than an almond in an adult; anchored by cords and sheets of connective tissue - Germinal epithelium - Tunica albuginea: connective tissue capsule

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- Cortex: contains 6 types of ovarian follicles - Medulla: connective tissue with blood and lymph vessels, nerves Oocyte + follicular cells (granulosa cells) = follicle Ovarian structure

Type of oocyte

Anatomic characteristics

Time of first appearance

Primordial follicle

Primary oocyte (P1)

1.5 million at birth, 400,000 by puberty Single layer of flattened follicular cells

Fetus

Primary follicle

Primary oocyte (P1)

Multiple layers of granulosa cells that secrete estrogen

Puberty

Secondary follicle (20/month)

Primary oocyte (P1)

A fluid-filled space Puberty (antrum) develops Zona pellucida (protein coat) and corona radiata (innermost follicular cells) protective structures around oocyte

Vesicular follicle

Secondary oocyte (M2)

1/month will mature Many layers of granulosa cells, very large antrum Will rupture to release oocyte (ovulation)

Puberty

Corpus luteum

No oocyte

Secretes progesterone and estrogen that stimulate buildup of uterine lining preparing it for possible implantation of fertilized oocyte (lasts 10-13 days if egg is not fertilized)

Puberty

Corpus albicans

No oocyte

Whitish connective Puberty tissue scar, the remnant of a degenerated corpus luteum Most are completely reabsorbed

Human reproductive system is primarily non functional until puberty - Hypothalamus begins to secrete gonadotropin-releasing hormone (GnRH) - Anterior pituitary responds by releasing gonadotropins: - Follicle stimulating hormone (FSH) - Luteinizing hormone (LH) - Gonads start to produce significant levels of sex hormones that trigger sexual maturation and gametogenesis - Varying production of hormones creates: - Ovarian cycle (follicular, ovulation, luteal phases) - Uterine cycle (menstrual, proliferating, secretory phases)

Ovarian and Uterine Cycles -

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Hypothalamus secretes GnRH→ FSH and LH are released → increase follicular development Maturing ovarian follicles secrete increasing amounts of estrogen → inhibits hypothalamus and anterior pituitary while vesicular follicle formation is stimulated High level of estrogen → LH surge → ovulation - Only luteinizing hormone causes ovulation Corpus luteum forms and secretes large amounts of estrogen and progesterone → inhibits hypothalamus and anterior pituitary, builds uterine lining If secondary oocyte is not fertilized, corpus luteum starts degenerating 10 days after ovulation → levels of estrogen and progesterone decrease → uterine lining is shed (14 days after ovulation) If secondary oocyte is fertilized and implants: - Starts secreting human chorionic gonadotropin (hCG) - Corpus luteum is stimulated to produce estrogen and progesterone - Maintains and builds uterine lining - Regresses by end of third month (placenta producing its own progesterone and estrogen then)

Uterine Tubes (Fallopian Tubes) -

Fibromuscular passageways for secondary oocyte and sperm and site of fertilization Wall composition: - Mucosa: has cilia that draw oocyte into the tube toward the uterus - Muscularis: 2 layers; properly pre-embryo through the uterine tube toward uterus - Serosa: external membrane covering

Uterus -

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Pear shaped muscular organ that - Serves as an implantation site for the pre-embryo - Protects and nourishes developing embryo through the vascular connection (placenta) - Ejects fetus at birth - Contracts and sheds the lining if oocyte was not fertilized Uterus is partitioned into - Fundus - Body - Isthmus - Cervix Three tunics of the uterine wall - Perimetrium (a serosa) - Myometrium (three layers of smooth muscle) - Endometrium (a mucosa rich in uterine glands) - Two layers: - Basal layer - Functional layer - At puberty: grows from basal layer under influence of estrogen and progesterone; shed during menstruation

Uterine Cycle -

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Cyclical change in endometrial lining under the influence of estrogen and progesterone Consists of three distinct phases of development: - Menstrual phase (1-5): shedding of functional layer - Proliferative phase (6-14): development of new functional layer - Secretory phase (15-28): increased vascularization and uterine gland development due to the increased progesterone secretion from corpus luteum If fertilization does not occur - Degeneration of corpus luteum - Dramatic drop of progesterone - Shedding of functional layer

Vagina -

Thick walled fibromuscular tube that connects uterus with outside Functions: - A birth canal - Receives penis during intercourse - Passageway for menstruation

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Vaginal wall composition - Mucosa: highly folded - Produces acidic secretion helping to prevent infection; transverse fold near vaginal opening forms barrier (hymen) - Muscularis: 2 layers of smooth muscle - Adventitia: large amount of elastic fibers

Genitalia -

Functions: - Protection - Mons pubis (elevation of adipose tissue; covered with hair) - Labia majora and labia minora (folds) - Large number of sweat, sebaceous, mucous glands (chemical defense) - Assistance in sexual reproduction - Erectile bodies that increase in sensitivity and blood flow during sexual activity for pleasure (bulbs of the vestibule and clitoris) - Greater vestibular glands increase production of mucin during sexual intercourse - Removal of urine

Male Reproductive System -

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Scrotum: skin covered sac that protects testes and provides cooler environment needed for sperm development Testes: primary reproductive organs that produce sperm and androgens Structure: - Outer double layered serous membrane, tunica vaginalis - Fibrous capsule, tunica albuginea, that enters each testis and subdivides internal space with septa into 250 lobules - Each lobule carries 1-4 seminiferous tubules Seminiferous tubules contain 2 types of cells: - Continuously dividing germ cells producing sperm - Sustentacular cells (Sertoli cells) that create blood-testis barrier, nourish developing sperm, release hormone inhibin when sperm count is high that inhibits FSH secretion and adjusts sperm production - Interstitial cells (Leydig cells) surround seminiferous tubules and produce androgens (testosterone) in response to the luteinizing hormone Small amount of androgens are secreted by adrenal cortex

Hormones in Male Reproductive System -

Male reproductive system is primarily non functional until a time in adolescence puberty initiated by various hormones: - Hypothalamus secretes gonadotropin releasing hormone (GnRH) - Anterior pituitary responds by releasing gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH) - Gonads beginning to produce significant levels of sex hormones (androgens): - LH stimulates interstitial cells to secrete testosterone - FSH stimulates sustentacular cells to secrete androgen binding protein (ABP) that binds androgens in order to maintain high concentration of them in seminiferous tubules (testes)

Increased Testosterone Level has Multiple Effects: -

Facilitates spermatogenesis Stimulates development of the secondary sex characteristics (hair growth in axillary and pubic regions, deeper voice, facial hair) Stimulates libido

Influence of Testosterone -

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Skin - Growth of facial hair/body hair - Supports collagen Male sex organs - Sperm production - Prostate growth - Erectile function Muscle - Muscle mass and strength Brain - Sex drive - Positive feelings - Aids cognition and memory Bone marrow - Red blood cell production Bone - Bone density maintenance

Ducts -

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Spermatozoa enter epididymis to complete development and to be stored - If expelled too soon - not motile - If ejected too late - old sperm degenerate Ductus deferens (vas deferens): thick walled tube that sperm is propelled through after leaving epididymis; fuses with seminal vesicle to form ejaculatory duct Ejaculatory duct: opens into the prostatic urethra Urethra: transports semen outside

Semen -

2-5% sperm (200-500 million) + fluids from 3 glands: - Seminal vesicle contributes ~70% volume of semen - Alkaline fluid (to neutralize the acidic mucus of vagina) - Fructose (nourishment to sperm) - Prostaglandins (promoting widening of cervix) - Clotting enzyme that “gels” the ejaculate - Prostate gland secretes milky fluid that contains - Calcium - Zinc (antibacterial properties/preserves sperm DNA) - Citric acid (possibly, nutrient for sperm health) - Sminalplasmin, antibiotic combating urinary tract infection - Prostate specific antigen (PSA) enzyme to help liquify semen following ejaculation (15-30 min later) - Bulbourethral glands - Produce clear, viscous mucin that forms mucus to protect urethra and serves as lubricant during intercourse - Makes up pre-ejaculate

Penis -

Root: internally attached portion of penic Body: elongated movable portion Glans: tip of penis that contains external urethral orifice Prepuce (foreskin): circular fold of skin attached to the raised edge of the glans 3 cylindrical erectile bodies within penis shaft: - Paired corpora cavernosa - Corpus spongiosum (contains spongy urethra) - Root of penis

Fertilization -

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Combining male and female genetic material, restoring diploid number of chromosomes (46) Following ovulation, the secondary oocyte is viable in the uterine tube for no more than 24 hours - Sperm can remain in female reproductive tract an average of 3-4 days Of the millions of sperm deposited, only a few hundred will reach the secondary oocyte and only one is able to fertilize the oocyte It takes about 24 hours for a sperm cell to form a zygote When the sperm penetrates the egg, the surface of the egg changes so that no other sperm can enter The fertilized egg starts growing fast, dividing into many cells; leaves the fallopian tube; (tubal pregnancy/ectopic pregnancy); danger to mother 8-9 days after fertilization, the mass of cells implants into the endometrium After the implantation, some cells become the placenta while others become the embryo...