Animal Reproduction Overview

Animal Reproduction

• Animal reproduction exists in many forms
• Sexual reproduction involves sperm and egg fertilization creating offspring.
• Asexual reproduction creates offspring without the joining of gametes.
• Some animals exhibit sex reversals.
• Reproduction is key to a population's survival.

Asexual Reproduction

• Many invertebrates reproduce asexually via fission, separating into two or more similar-sized individuals.
• Budding creates new individuals as outgrowths of existing organisms.
• Fragmentation involves breaking the organism into pieces, some or all of which can develop into new organisms.
• Regeneration lets lost body parts regrow.
• Parthenogenesis is the development of a new individual from an unfertilized egg.

Sexual Reproduction

• Sexual reproduction involves the fusion of a male gamete (sperm) and a female gamete (egg) to create a zygote.
• A crucial advantage of sexual reproduction is the increase in genetic variation among offspring.
• Increased variation leads to greater reproductive success in changing environments, and a faster rate of adaptation.

Reproductive Cycles and Patterns

• Ovulation is the release of mature eggs.
• Many animals have reproductive cycles tied to changing seasons, influenced by hormones and environmental factors.
• Some organisms can reproduce sexually or asexually, depending on conditions.
• Hermaphroditism is a reproductive strategy in which an individual has both male and female reproductive systems.
• This can be helpful when encountering a mate is difficult.
• Some hermaphrodites can self-fertilize.

Fertilization

• External fertilization occurs when eggs are shed, and sperm fertilizes them outside the female's body.
• Internal fertilization involves sperm being deposited inside or near the female's reproductive tract.
• Fertilization mechanisms ensure that sperm and eggs from the same species combine.
• Behavioral interactions, pheromones,and/or courtship behaviors often play crucial roles in fertilization.

Ensuring Offspring Survival

• Internal Fertilization is often related to fewer gametes produced but higher survival rates of zygotes.
• Mechanisms protecting embryos and parental care are important factors.
• Some embryos develop within eggs, while others are retained in the female.
• Parental care for offspring is common in many species.

Gamete Production and Delivery

• Gametes are produced in gonads, but some animals develop gametes from undifferentiated tissue.
• In many species, elaborate systems using accessory tubes and glands carry, nourish, and protect the developing embryos.
• Many insects have complex reproductive systems.
• The female typically has a spermatheca to store sperm during copulation.
• A cloaca is a common opening for reproduction, excretion, and defecation in many non-mammalian vertebrates.

Male Reproductive Anatomy

• The male's external reproductive structures include the scrotum and penis.
• Internal organs in males include gonads (producing sperm and hormones) and accessory glands.
• Accessory glands' secretions combined with sperm form semen.

Female Reproductive Anatomy

• The external female reproductive structures include the clitoris and the labia.
• The internal organs include gonads (ovaries) and a system of ducts and chambers for carrying gametes to house the embryo.
• These chambers and ducts also support development.

Ovaries

• Ovaries house follicles containing oocytes which develop into an ovum.
• Ovulation is the release of an egg cell from a follicle.
• Once an egg releases, the cells produce estradiol, contributing to pregnancy.
• If the egg is not fertilized, the corpus luteum degenerates.

Oviducts and Uterus

• Oviducts or fallopian tubes transport the egg from the ovary to the uterus (womb).
• Cilia aid in the transport of the egg.
• The uterus has a lining called the endometrium with many blood vessels.
• The uterus narrows at the cervix and then opens into the vagina.

Vagina and Vulva

• The vagina is a thin-walled chamber, receiving sperm and serving as the birth canal.
• The vulva is an external area with labia majora, labia minora, hymen, and clitoris.

Mammary Glands

• Mammary glands aren't reproductive systems but essential for mammals.
• Secrete milk within sacs of epithelial tissue.

Monogamy

• Males/females of some species have mechanisms decreasing mating with others.
• Females may influence reproductive success of their mates; eg. choosing mates.

Hormonal Control of Female Reproductive Cycles

• Hormones coordinate the uterine and ovarian cycles, influencing the development and preparation of the endometrium (uterine lining).
• Ovulation releases an egg.
• Prior to ovulation, the endometrium thickens (preparing for implantation).
• If not fertilized, the endometrium sheds leading to menstruation.
• Reproduction involves the interplay of tropic and sex hormones from hypothalamus, pituitary gland, and gonads.

Ovarian Cycle

• The sequential release of hormones, GnRH, FSH, and LH, initiates follicle growth.
• Follicles grow initially and increase Estrogen levels.
• The follicular phase ends with ovulation, releasing a secondary oocyte.

Uterine (Menstrual) Cycle

• The cycle involving the uterus is hormonally coordinated with the ovarian cycle.
• The proliferative phase thickens the uterine lining.
• The secretory phase secretes nutrients.
• The menstrual flow phase sheds the lining (menstruation).

Menopause

• Menopause in females marks the cessation of ovulation and menstruation.

Menstrual Versus Estrous Cycles

• Humans have menstrual cycles (periodic shedding of the uterine lining) while other mammals exhibit estrous cycles (mating periods during specific times).

Hormonal Control of the Male Reproductive System

• FSH stimulates Sertoli cells to support sperm development.
• LH stimulates Leydig cells to secrete testosterone, promoting spermatogenesis.

Conception, Embryonic Development, and Birth

• Conception, is also known as fertilization, occurs when sperm fertilizes an ovum.
• Zygote divides through mitosis (cleavage), forming a blastocyst, a ball-like structure.
• In placental mammals, the embryo develops fully within the uterus.
• Development relies on signaling molecules and hormones to direct proper processes.

First Trimester

• Initial development of major body organs.
• The embryo is called a fetus by week eight.
• The growing endometrium protects and supports an implanting embryo.

Second Trimester

• The fetus grows rapidly and becomes active.
• The growing uterus and the fetal movements are obvious signs of pregnancy.

Third Trimester

• Fetus grows and fills the uterine space.
• The complex interplay of hormones and regulators manages labor, which leads to childbirth.

Labor

• Labor involves the thinning and opening of the cervix (dilation).
• Expulsion of the baby, and the placenta are involved in childbirth.

Post-Natal

• Delivery of the baby and the placenta are involved in childbirth.
• Lactation (milk production) is a unique mammalian trait.

Maternal Immune Tolerance

• A woman's acceptance of her offspring is not fully understood.
• Possible mechanisms include suppression of immune responses in the uterus.

Infertility

• Modern technology provides assisted reproductive technologies (in vitro fertilization, ICSI).

Detecting Disorders During Pregnancy

• Methods like amniocentesis and chorionic villus sampling allow genetic analysis of the fetus.

Contraception and Abortion

• Various methods prevent pregnancy: preventing release of eggs or sperm, keeping gametes apart, preventing implantation.
• Abortion is the termination of a pregnancy and is a complex issue involving social and medical factors. A health care provider should be consulted.