BIOLOGY 12 Reproductive System

Introduction to the Reproductive System http://www.youtube.com/watch?v=444fTSTuhjg&feature=related

Introduction We humans like all mammals, have internal fertilization and development. This requires specialized organs for both sexes.

Male Reproductive System

Testis – 2 oval shaped glands outside the body sperm and hormone production Seminiferous tubules – 3 coiled tubes approx. 250m in length which carry out meiosis spermatogenesis / sperm production Interstitial cells cuboidal cells surrounding the seminiferous tubules which are responsible for producing testosterone Scrotum – thin layer of skin (sac) containing testis Epididymis – tube just outside the testes where sperm is stored and matures. Testis

Seminiferous Tubules

Vas deferens (ductus deferens) small muscular tube leaving the testicles conducts semen from epididymis Seminal vesicle, prostate gland, and Cowpers gland (bulbourethral gland) – all three are glandular organs PROSTATE (largest) contribute to seminal fluid (contents of semen to be discussed later) Penis – erectile tissue (spongin) copulatory organ Glans penis – end of the penis containing large number of sensory receptors stimulation Foreskin – thin layer of skin over glans protection Urethra – muscular tube conducts semen and urine Corpus cavernosum – contains spongin becomes engorged with blood when vein is constricted Urinary bladder – hollow muscular organ holds urine

The Sperm Cell Smallest cell in the body - contains three regions: A. The head: made of the acrosome and the haploid nucleus. B. The Mid Piece: containing many mitochondria. C. The Tail: - a flagellum (9 x 2 pattern of microtubules).

Male Hormone Regulation The Interstitial cells between the seminiferous tubules begin to secrete Testosterone from puberty on. This is responsible for male secondary sex traits and the male sexual responses.

HORMONE CONTROL Two pituitary hormones regulate male reproductive physiology: 1) Follicle Stimulating Hormone (FSH) FSH is released from the anterior pituitary and targets the seminiferous tubules initiating spermatogenesis.

2. Lutenizing Hormone (LH) Also released by the anterior pituitary but it targets the Interstitial (Leydig) cells to produce testosterone. Both pituitary hormones are regulated by negative feedbacks.

Negative Feedback LOOP Gonadotropic releasing hormone Follicle stimulating hormone Increases sperm production Leutenizing hormone Increases testosterone

TESTOSTERONE The effects of testosterone are: Increase penis growth Facial, body, pubic and axillary hair Enlarged larynx Bone and muscle growth Increased sex drive Acne

The Female System The female system is actually a dual system: reproduction and providing an environment for development of the fetus

Human Ovary and Fallopian Tube

Human Uterus: l.s.

FEMALE REPRODUCTIVE SYSTEM

Female Reproductive Organs

ANATOMY / PHYSIOLOGY Ovaries – glandular organs (gonads) size of small lemons developing eggs (oogenesis), and produces sex hormones Uterus – strong muscular organ, holds the developing fetus Endometrium ( uterine lining) nourishes the developing embryo Cervix – opeining to the uterus forms a plug holding in the amniotic fluid during pregnacy Vagina – muscular organ copulation and birth canal

Clitoris – organ of stimulation similar to the glans penis in males Fimbrae – sweep egg up into fallopian tubes when the ovary ruptures and releases egg Fallopian tubes (oviducts) lined with tiny ciliated cells which sweep egg and usually site of fertilization Urethra – conducts urine from bladder

Ovarian cycle is divided into 2 phases; Follicular Phase where the egg matures and is released from the ovary Luteal Phase following the release of the egg, the corpus luteum forms and continues to release the hormone progesterone which is responsible for maintaining the endometrium lining.

OVARIAN CYCLE 1. Primary follicle containing an “oocyte” egg begins to produce sex hormone estrogen 2. Secondary follicle containing primary oocyte continues to develop. 3. Graafian follicle matures 4. Ovulation occurs when the Graafian follicle ruptures releasing the oocyte. 5. Corpus luteum produces the sex hormone progesterone and estrogen. 6. Corpus luteum gradually disinterates if the egg is not fertilized.

Menstrual cycle: changes that occur in the uterus. The Reproductive Cycle of the Human Female Menstrual cycle: changes that occur in the uterus. Day 1: the first day of menstruation. Menstrual flow phase. Menstrual bleeding. Usually lasts for a few days. Proliferative phase. Regeneration and thickening of the endometrium. About 1 – 2 weeks in duration.

Secretory phase. Continued endometrial thickening, increased vascularization of the endometrium, endometrium develops glands that secrete a glycogen-rich fluid, and a duration of about 2 weeks. If, by the end of the secretory phase, an embryo has not implanted in the uterus a new menstrual flow commences. Fig. 46.15d

Hormonal Control

Hormonal coordination of the menstrual and ovarian cycles involves five hormones. Gonadotropin releasing hormone (GnRH) secreted by the hypothalamus. Follicle-stimulating hormone (FSH) secreted by the anterior pituitary. Luteinizing hormone (LH) secreted by the anterior pituitary. Estrogens secreted by the ovaries. Progesterone secreted by the ovaries.

GnRH stimulates secretion of small amounts of FSH and LH. FSH stimulates the growth of immature ovarian follicles. The growing follicles secrete small amounts of estrogens. Inhibits secretion of FSH and LH. FSH and LH levels remain relatively low.

The rate of secretion of estrogens by the growing follicle rises steeply. Stimulates the secretion the GnRH. Stimulates the secretion of FSH and LH. LH secretion is especially high. LH induces the final maturation of the follicle and ovulation. The follicular phase of the ovarian cycle is coordinated with the proliferative phase of the menstrual cycle. Secretion of estrogens during the follicular phase stimulates endometrial thickening.

Negative feedback Loop

Estrogen / Progesterone Secondary Sex Characteristics Breast growth Mensturation Pubic hair Widening of hips Distribution of fat

Developing Oocyte

The Female System B. Fertilization Occurs in the top one third of the Fallopian tubes. Once ovulated, the egg is only viable for about 24 hours if not fertilized. Events of fertilization will be studied in detail when we do development next.

The Female System 3. Implantation and Pregnancy After fertilization, the zygote continues to move down the fallopian tube. As it does, development begins (details later). It takes the embryo 7 - 12 days to get to the uterus and implant in the endometrium.

Implantation

The Female System As it implants, it secretes a hormone called Human Chorionic Gonadotropin (HCG). This acts like LH and continues to stimulate the corpus luteum to secrete progesterone. If this didn’t happen, menstruation would happen with the loss of the endometrium and the embryo in it. HCG can be detected in the mothers urine.

The Female System Progesterone also triggers other anatomical and physiological changes in the mother. This includes: breast development, uterine growth, and placental development.

Postive Feed back loop during LABOUR