Chapter 46
Animal Reproduction
Reproduction
• sexual reproduction
• Asexual reproduction
Whose genes all come from one parent
Mechanisms of Asexual Reproduction
• Many invertebrates reproduce asexually by fission
– The separation of a parent into two or more individuals of approximately the same
size
Asexual and sexual
• Hydra
• Sexual reproduction presents a special problem for certain organisms
– That seldom encounter a mate
• One solution to this problem is hermaphroditism
– In which each individual has both male and female reproductive systems
Figure 46.2 Sexual behavior in parthenogenetic lizards
sequential hermaphroditism
• Another remarkable reproductive pattern is sequential hermaphroditism
– In which an individual reverses its sex during its lifetime
External fertilization intrenal fertelization
Figure 46.x2 Sea urchin sperm fertilizing an egg
Figure 46.5 Parental care in an invertebrate
Figure 46.6 Reproductive anatomy of a parasitic flatworm
Figure 46.7 Insect reproductive anatomy
Reproductive anatomy(and functions) of the human male
• Prostate gland
• Seminal vesicle
•
Bulbourethral gland
•
Testes
•
Epididymis
•
Scrotum
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Figure 46.8 Reproductive anatomy of the human male
Production of normal sperm
Cannot occur at the body temperatures of most mammals
Structure of a human sperm cell
• Semen (3-5 ml)
– 150-300 million sperm
– Fructose & prostaglandins (seminal vesicles)
– Buffers (prostate gland)
– Mucus-rich fluid (bulbourethral/cowpers gland)
–
Function:
• Nutrients
• Stimulates flagellum action and uterus contraction
–
Sperm in semen:
24-72 hour lifespan
Semen in the female reproductive tract
• Once in the female reproductive tract
– A number of processes, including contractions of the uterus, help move the sperm
up the uterus
Penis
• The human penis
– Is composed of three cylinders of spongy erectile tissue
• During sexual arousal
– The erectile tissue fills with blood from the arteries, causing an erection
Spermatogenesis
• Takes place in seminioferous tubule
-Stem cells
-Sertoli cells
provides nutrient
-Leydig cells
produce testosterone
Androgen secretion and sperm production
• Are both controlled by hypothalamic and pituitary hormones
Male Hormones
Figure 46.11x Spermatogenesis: Seminiferous tubules (left), sperm in semen
(right)
Reproductive anatomy of the human female
• Clitoris
– Responsive to sexual stimuli
• Vagina
– Organ of sexual intercourse; serves as birth canal
Reproductive anatomy of the human male
• Endometrium
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– Inner lining of uterus; site of implantation
• Myometrium
– Thick muscle layer of uterus that stretches during pregnancy
Anatomy of human overy
Oogenesis
• At birth, 2 million oocytes are present
• At age 7, there are 300,000
• 400-500 mature in a lifetime
Oogenesis
• The reproductive cycle of the human female
Menstrual cycle verses estrous cycles
• Humans and other primates have menstrual cycles
– While other mammals have estrous cycles
• In both cases ovulation occurs at a time in the cycle
– After the endometrium has started to thicken in preparation for implantation
Fertilization in mammals
Figure 46.16 Formation of the zygote and early postfertilization events
Figure 46.15 The reproductive cycle of the human female
Figure 46.10 Ovulation
Figure 46.17 Placental circulation
Placental circulation function
Figure 46.18 Human fetal development
The first trimester is the main period of organogenesis
– The development of the body organs
Second Trimester
• During the second trimester
– The fetus grows and is very active
– The mother may feel fetal movements
– The uterus grows enough for the pregnancy to become obvious
Third Trimester
• During the third trimester
– The fetus continues to grow and fills the available space within the embryonic
membranes
The three stages of labor
Figure 46.19 Hormonal induction of labor
Chapter 47
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Animal Development
•
•
As recently as the 18th century, the prevailing theory was called preformation
Preformation is the idea that the egg or sperm contains a miniature infant, or
“homunculus,” which becomes larger during development
Development is determined by the zygote’s genome
Cell differentiation is the specialization of cells in structure and function
Morphogenesis is the process by which an animal takes shape
After fertilization, embryonic development proceeds through cleavage, gastrulation, and
organogenesis
• Important events regulating development occur during fertilization and the three stages
that build the animal’s body
Fertilization
• Fertilization brings the haploid nuclei of sperm and egg together, forming a diploid
zygote
• The sperm’s contact with the egg’s surface initiates metabolic reactions in the egg that
trigger the onset of embryonic development
The Acrosomal Reaction
• The acrosomal reaction is triggered when the sperm meets the egg
• This reaction releases hydrolytic enzymes that digest material surrounding the egg
•
•
•
•
Gamete contact and/or fusion depolarizes the egg cell membrane and sets up a fast
block to polyspermy
The Cortical Reaction
• Fusion of egg and sperm also initiates the cortical reaction
• This reaction induces a rise in Ca2+ that stimulates cortical granules to release their
contents outside the egg
• These changes cause formation of a fertilization envelope that functions as a slow
block to polyspermy
Activation of the Egg
• The sharp rise in Ca2+ in the egg’s cytosol increases the rates of cellular respiration
and protein synthesis by the egg cell
• With these rapid changes in metabolism, the egg is said to be activated
• In a sea urchin, a model organism, many events occur in the activated egg
Fertilization in Mammals
• In mammalian fertilization, the cortical reaction modifies the zona pellucida as a slow
block to polyspermy
Cleavage
• Fertilization is followed by cleavage, a period of rapid cell division without growth
• Cleavage partitions the cytoplasm of one large cell into many smaller cells called
blastomeres
• Cleavage partitions the cytoplasm of one large cell
– Into many smaller cells called blastomeres
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Gastrulation
• Gastrulation rearranges the cells of a blastula into a three-layered embryo, called a
gastrula, which has a primitive gut
•
The three layers produced by gastrulation are called embryonic germ layers
– The ectoderm forms the outer layer
– The endoderm lines the digestive tract
– The mesoderm partly fills the space between the endoderm and ectoderm
Organogenesis
• During organogenesis, various regions of the germ layers develop into rudimentary
organs
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