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Sex and Reproduction

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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

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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.

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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.

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Mammals

• 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

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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 ~ 34oC

Leydig Cells

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Human Male Reproductive System

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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.

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Testis and Sperm

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Male Reproductive System

• Male accessory sex organs– epididymis– vas deferens– seminal vesicles– prostate gland– urethra– erectile tissue

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B. Vas deferens -

• tube where some sperm are stored and connects to the urethra at the base of the urinary bladder

vas deferens

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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)

seminalvesicle

prostate

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

urethra

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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

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Human Female Reproductive System

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Female Reproductive System

• Female accessory sex organs– fallopian tubes (oviducts)– uterus– cervix– vagina

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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.

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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

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Journey of an Egg

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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

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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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VII. The Menstrual Cycle

2 4 6 8 10 12 14 16 18 20 22 24 26 28

2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

A. Days 1 - 14

1. Uterine activity

a. 1-4 - menstrual phase

b. 5-7 - repair phase

c. 7-14 - 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

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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

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2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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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.

2 4 6 8 10 12 14 16 18 20 22 24 26 28

2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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Menstrual Cycle (cont.)

B. Days 14 -20

1. Uterine activity Walls of uterus continue to proliferate (build up) under influence of progesterone

2 4 6 8 10 12 14 16 18 20 22 24 26 28

2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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Menstrual Cycle (cont.)

Days 14-20

2. Ovarian activity -old Graffian follicle becomes corpus luteum and secretes a hormone, LH (luteinizing hormone) which keeps levels of progesterone high.

2 4 6 8 10 12 14 16 18 20 22 24 26 28

2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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3. Hormones - days 14-20

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

2 4 6 8 10 12 14 16 18 20 22 24 26 28

2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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C. Days 20 - 28

1. Uterine Activity - continued increase in proliferation until day 28

2. Ovarian activity - continued secretion of LH - to maintain high levels of progesterone - to maintain walls of uterus

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2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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C. Days 20 - 283. 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

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2 4 6 8 10 12 14 16 18 20 22 24 26 28

Follicular Phase Luteal Phase

ProgesteroneEstrogen

FSH

LH

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Birth Control

• abstinence• sperm blockage

– condom– cervical cap

• sperm destruction– jellies or foams

• prevention of ovulation– oral contraceptives

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Birth Control

• Prevention of embryo implantation– intrauterine devices (IUD)– morning after pill

• Sterilization– vasectomy– tubal ligation

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Sex Determination in Mammals

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