Animal Reproduction

Chapter 46

Reproduction in the Animal Kingdom Sexual Asexual

FissionBuddingFragmentation & RegenerationParthenogenesis egg develops without

being fertilized

Parthenogenesis Development of an unfertilized egg

honey bees drones = males produced through

parthenogenesis haploid workers & queens = females produced from

fertilized eggs diploid

queen worker drone

Reproductive Cycles and Patterns

Most animals exhibit cycles in reproductive activity Often related to changing seasons

Reproductive cycles Are controlled by hormones and

environmental cues

Fertilization Plays an important part in sexual

reproduction Joining of egg & sperm

external usually aquatic animals

internal usually land animals

Patterns of Sexual Reproduction

External fertilization, external development

Internal Fertilization, External Development

Internal Fertilization, Internal Development

Hermaphrodites

Certain Organisms seldom encounter a mate

Solution hermaphroditism In which each

individual has both male and female reproductive

Sequential Hermaphroditism

An individual reverses its sex during its lifetime

Figure 46.4

Male Reproductive System

Male Reproductive System Testicles

produces sperm & hormones Scrotum

sac that holds testicles outside of body Epididymis

where sperm mature Vas deferens

tubes for sperm to travel from testes to penis Prostate, seminal vesicles,

Cowper’s (bulbourethal) glands nutrient rich fluid to feed & protect sperm buffer to counteract acids in vagina

Male reproductive system Sperm production

over 100 million produced per day!

~2.5 million released per drop!

Testes & epididymis sperm production &

maturation Glands

seminal vesicles, prostate, bulbourethal

produce seminal fluid = nutrient-rich

SpermatogenesisEpididymis Testis

Coiledseminiferoustubules

Vas deferens

Cross-section ofseminiferous tubule

Spermatozoa

Spermatids(haploid)

2°spermatocytes

(haploid)

1°spermatocyte

(diploid)

Germ cell (diploid)

MEIOSIS II

MEIOSIS I

Female Reproductive System

Female Reproductive System

Ovaries produces eggs & hormones

Uterus nurtures fetus; lining builds up each month

Fallopian tubes tubes for eggs to travel from ovaries to uterus

Cervix opening to uterus, dilates 10cm (4 inches) for

birthing baby Vagina

birth canal for birthing baby

Female Reproductive System

Oogenesis

Meiosis 1 completed

during egg maturation

Meiosis 2 completedtriggered by

fertilization

ovulation

What is the advantage of this development system?

The reproductive cycle of the human female The Ovarian Cycle The Uterine (Menstrual) Cycle Menopause

Female Hormones FSH & LH

release from pituitary stimulates egg development & hormone release peak release = release of egg (ovulation)

Estrogen released from ovary cells around developing egg stimulates growth of lining of uterus lowered levels = menstruation

Progesterone released from “corpus luteum” in ovaries

cells that used to take care of developing egg stimulates blood supply to lining of uterus lowered levels = menstruation

The Ovarian Cycle In the ovarian cycle

Hormones stimulate follicle growth, which results in ovulation

Following ovulation The follicular tissue left behind

transforms into the corpus luteum

Figure 46.13a–e

Control by hypothalamus Inhibited by combination of estrogen and progesterone

Stimulated by high levelsof estrogen

Inhibited by low levels ofestrogen

Hypothalamus

Anterior pituitary

GnRH

FSH LH

Pituitary gonadotropinsin blood

LH

FSH

FSH and LH stimulatefollicle to grow

LH surge triggersovulation

Ovarian cycle

Growing follicle Maturefollicle

Corpusluteum

Degenerating corpus luteum

Estrogen secretedby growing follicle inincreasing amounts

Progesterone andestrogen secretedby corpus luteum

Follicular phase Luteal phaseOvulation

Ovarian hormonesin blood

Peak causes LH surge

Estrogen Progesterone

Estrogen levelvery low

Progesterone and estro-gen promote thickeningof endometrium

Uterine (menstrual) cycle

Endometrium

Menstrual flow phase Proliferative phase Secretory phase

0 5 10 14 15 20 25 28

Da

ys

1

(a)

(b)

(c)

(d)

(e)

3

6

7 8

4

5

2

10

9

The Uterine (Menstrual) Cycle

Occurs when the endometrium is shed Three Phases

Mentrual Flow Phase endometrium is shed and mentrual bleeding occurs

Proliferative Phase endometrium regenerates & thickens

Secretory Phaseendometrium thickens, if an embryo has not implanted by the end of this phaseA new menstrual flow commences

Menopause

After about 450 cycles, human females undergo menopause The cessation of ovulation and

menstruation

Fertilization

Placental Mammals Human Chorionic Gonadotropin

Secreted by embryo; acts like LH to maintain the Corpus Luteum

Excreted in urine Parturition

Birth; in late pregnancy; estrogen increases

This stimulates oxytocin receptorsOxytocin from fetus and mother

stimulate contractions

Hormonal Control of the Male Reproductive System

Testosterone and other androgens Are directly responsible for the primary

and secondary sex characteristics of the male

Androgen secretion and sperm production controlled by hypothalamic and pituitary hormones

Stimuli from otherareas in the brain

Hypothalamus

GnRH from thehypothalamus reg-ulates FSH and LH

release from theanterior pituitary.

FSH acts on theSertoli cells of the

seminiferoustubules, promotingspermatogenesis.

LH stimulates the Leydig cells to maketestosterone, whichin turn stimulatessperm production.

Anteriorpituitary

Negativefeedback

Leydig cellsmake

testosteronePrimary andsecondary sexcharacteristics

Sertoli cells

Spermatogenesis TestisFigure 46.14

Conception, Pregnancy and Birth

Blastocyst Implants by burrowing;

endometrium grows over

Provides nutrients first 2-4 weeks

Placenta Derived from both maternal and fetal cells produce progesterone Materials exchange across membranes

Human fetal development The fetus just spends much of the 2nd &

3rd trimesters just growing …and doing various flip-turns & kicks inside amniotic fluid

Week 20

Human fetal development 24 weeks (6 months; 2nd trimester)

fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix

Human fetal development

30 weeks (7.5 months)

umbilical cord

Getting crowded in there!!

32 weeks (8 months)

The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

BirthHormone induction

positive feedback

Intestine

Placenta

Umbilicalcord

Wall ofuterus

VaginaCervix

Birth (36 weeks)

Bladder

The end of the journey!

Mechanisms of some contraceptive methods

RU486

Progesterone analog Blocks progesterone receptors in

uterus; lining is shed Prostaglandins also taken

Reproductive Technologies

Ultrasound Amniocentesis Chorionic Villi Sampling (CVS) In Vitro Fertilization (IVF) or GIFT