1 Sex and Reproduction

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3 Sexual and Asexual Reproduction Sexual reproduction occurs when a new individual is formed through the union of two sex cells (gametes). – produce zygote gametes formed by meiosis in sex organs (gonads). Asexual reproduction occurs when genetically identical cells are produced from a single parent cell by mitosis. – fission or budding

4 Fertilization and Development Vertebrate sexual reproduction evolved in the ocean before vertebrates colonized land. – External fertilization - Males generally release sperm into water where the union of the free gametes occurs.

5 Fertilization and Development Three strategies of Internal fertilization: – Eggs are fertilized internally and deposited outside mother’s body to complete development. – Fertilized eggs are retained within mother to complete development, but all nourishment gained from yolk sac. – Young develop within mother and obtain nourishment directly from mother’s blood.

6 Mammals – Females generally undergo reproductive cycles (estrous cycles). (In Heat or Breeding season)  periodic release of mature ovum  Changes in secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) by pituitary gland drive cycle. – induced ovulators - Females ovulate only after copulation as a result of LH secretion.  cats and rabbits

7 Male Reproductive System Sperm are produced in seminiferous tubules. In adult male 100 to 200 million sperm per day – Leydig cells, located in interstitial tissue between seminiferous tubules, secrete testosterone.  Converts indifferent structures into male external genitalia (penis and scrotum).  Secondary sexual characteristics – In an adult, each testis is composed primarily of seminiferous tubules.  testes descend into scrotum  maintains slightly lowered temperature ~ 34 o C Leydig Cells

8 Human Male Reproductive System

9 Male Reproductive System Production of sperm – Wall of seminiferous tubule consists of germinal cells which become sperm, by meiosis, and supporting Sertoli cells. – Each parent cell undergoes mitosis, and one of the two daughter cells then undergoes meiosis to form sperm.

10 Testis and Sperm

11 Male Reproductive System Male accessory sex organs – epididymis – vas deferens – seminal vesicles – prostate gland – urethra – erectile tissue

12 B. Vas deferens - tube where some sperm are stored and connects to the urethra at the base of the urinary bladder vas deferens

13 C. Accessory glands 1. Prostate gland - large gland behind urinary bladder and produces seminal fluid. 2. Seminal vesicles - paired glands at bases of vas deferentia and produce seminal fluid. * Seminal fluid serves as a lubricant, pH buffer, and nutrient (high in sugars) seminal vesicle prostate

14 D.Urethra and penis - urethra is tube exiting the urinary bladder and extending the length of the penis, the male intromittent organ. urethra

15 Female Reproductive System Female embryo develops a clitoris and labia majora. – Ovaries contain ovarian follicles which each contain an egg cell and smaller granulosa cells.  At puberty, estrogen triggers menarche and the formation of secondary sexual characteristics.  breast development, pubic hair

16 Human Female Reproductive System

17 Female Reproductive System Female accessory sex organs – fallopian tubes (oviducts) – uterus – cervix – vagina

18 Female Reproductive System Menstrual and estrous cycles – At birth, a female’s ovaries contain approximately 2 million follicles.  Some follicles are stimulated to develop each cycle.  Human menstrual cycle lasts approximately one month, and is commonly divided into a follicular phase and a luteal phase.

19 Female Reproductive System Follicular phase – A few follicles are stimulated to grow under FSH stimulation, but only one achieves full maturity as a tertiary, Graafian, follicle. – Ovulation  Increasing level of estrogen in the blood stimulates the anterior pituitary gland to secrete LH about midcycle.  follicle bursts releasing secondary oocyte

20 Journey of an Egg

21 Female Reproductive System - phase1 second half of menstrual cycle  Corpus luteum secretes estrogen and progesterone. - phase2 of the endometrium  Endometrium becomes more vascular, glandular, and enriched with glycogen.  secretory phase

22 Female Reproductive System – In absence of fertilization, corpus luteum triggers its own atrophy toward the end of the luteal phase.  menstrual phase

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24 VII.The Menstrual Cycle Follicular Phase Luteal Phase Progesterone Estrogen FSH LH A. Days Uterine activity a menstrual phase b repair phase c proliferative phase - walls of uterus increase as a result of build-up of tissue and blood vessels - Preparation to receive fertilized egg for implantation into wall of uterus

25 The Menstrual Cycle 2. Ovarian activity - Graffian follicle begins to develop during this 14-day period OVULATION OCCURS ON OR ABOUT DAY 14 - Slight increase in body temperature and increase flow of mucus Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

26 3. Hormones - a. Estrogen gradually increases - Prompts build-up of uterine walls; stimulates pituitary to produce FSH - follicle stimulating hormone - follicular development b. Progesterone - gradually increases to prepare uterus for pregnancy Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

27 Menstrual Cycle (cont.) B. Days Uterine activity Walls of uterus continue to proliferate (build up) under influence of progesterone Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

28 Menstrual Cycle (cont.) Days Ovarian activity - old Graffian follicle becomes corpus luteum and secretes a hormone, LH (luteinizing hormone) which keeps levels of progesterone high Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

29 3. Hormones - days a. estrogen - decreases b. progesterone - highest levels to maintain walls of uterus and blocks FSH c. luteinizing hormone (LH) from ovarian follicle high and maintains levels of progesterone Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

30 C.Days Uterine Activity - continued increase in proliferation until day Ovarian activity - continued secretion of LH - to maintain high levels of progesterone - to maintain walls of uterus Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

31 C.Days Hormones a. progesterone begins to decrease if pregnancy has not occurred. b. LH decreases as old corpus luteum loses secretory function Walls of uterus sloughed away as tissue and blood Follicular Phase Luteal Phase Progesterone Estrogen FSH LH

32 Birth Control abstinence sperm blockage – condom – cervical cap sperm destruction – jellies or foams prevention of ovulation – oral contraceptives

33 Birth Control Prevention of embryo implantation – intrauterine devices (IUD) – morning after pill Sterilization – vasectomy – tubal ligation

34 Sex Determination in Mammals

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