5.1.2 Pregnancy and Birth in Mammals Flashcards
Placental Mammals
Types of Mammals
A uterus provides nourishment and protection (through the placenta and umbilical cord) to the embryo until birth, after which they are nourished with milk.
Marsupial Mammals
Types of Mammals
The offspring is birthed prematurely before being protected and nourished in an eternal pouch.
Monotreme Mammals
Types of Mammals
Lay leathery eggs (oviparous) to be hatched and then protected and nourished by its mother’s milk.
ONLY platypus and echidna
Scrotum
Male Reproductive System
A sac that houses the testes and epididymis.
Testicle
Male Reproductive System
The site of sperm production, composed of several lobes of seminiferous tubules which are filled with Leydig cells and Sertoli cells.
Leydig Cells
Male Reproductive System: Testicles
Produce testosterone
Sertoli Cells
Male Reproductive System: Testicles
Produces androgen-binding protein (ABP)
Androgen - hormone that binds to testosterone to promote the production of sperm when signalled by the anterior pituitary gland in the brain by sending the hormones gonadotropins.
Luteinizing Hormone
Male Hormones
Stimulates Leydig cells to produce testosterone binding protein.
Follicle-Stimulating Protein
Male Hormone
Stimulates Sertoli cells to produce androgen binding protein.
Epididymis
Male Reproductive System
Structure that lines the outside of the testicles to store, mature and transport sperm into the net stage.
Vas Deferens/Ductus Deferens
Male Reproductive System
Transports sperm around the bladder to the seminal vesicle gland.
Seminal Vesicle
Male Reproductive System: Spermatic Cord
Produces two-thirds of the liquid of semen, including fructose, the energy source for sperm.
Prostate
Male Reproductive System
A gland below the bladder that includes the merged urethra from the bladder and the ejaculatory duct carrying semen.
Penis
Male Reproductive System
A structure made up of spongiform tissue for transporting sperm into the female reproductive system.
Erection
Male Reproductive System: Penis
The parasympathetic nervous system that causes the blood vessels in the penis to dilate.
Ejaculation
Male Reproductive System: Penis
The sympathetic nervous system causes the spermatic cord to contract and force the semen through.
Vulva
Female Reproductive System
The eternal genitalia of the female reproductive system, including the mons pubis and labia.
NEED TO FINISH FEMALE REPRODUCTIVE SYSTEM
Spermatogenesis
Stages of Mammalian Reproduction
The male productive system is required to produce and supply sperm, which occurs inside the testes.
- When signals come from the pituitary glands, the antiunitary gland will release gonadotropin (including luteinising hormone and follicle-stimulating hormone), which stimulate the Leydig and Sertoli cells to produce testosterone and androgen-binding protein respectively.
- These products bind to promote sperm production through meiosis
- These mature sperm will be stored in the epididymis, then the vas ductus/deferens.
Ovarian/Menstrual Cycle
Stages of Mammalian Reproduction
While males continually produce sperm, females are born with immature egg cells, which arrest at prophase 1.
Once the organism reaches maturity, the ovarian cycle commences, continuing meiosis until fertilisation occurs. Meiosis only completes after fertilisation.
Follicular Phase (Days 1-12)
Stages of the Ovarian/Menstrual Cycle
Under the influence of follicle stimulating hormone (FSH), one or more of the oocytes will resume its meiotic division up to metaphase II and matures within a group of nutrivitie cells called a follicle.
Only one egg forms from each oocyte during meiosis. When the oocyte is maturing it grows much larger by adding nutrients and extra organelles. The nutrients are stored in the cytoplasm for use after fertilisation, when cleavage begins and rapid mitotic division forms new smaller cells.
- Menstruation: The endometrium of the uterus breaks down after the previous reproductive cycle over about four days.
- Pre-Ovulation: A new endometrial lining will form over 5-12 days.
- 10-20 primordial follicles begin to develop into primary follicles by surrounding themselves with follicle cells for nourishment.
- The hypothalamus releases gonadotropin releasing hormone, which stimulate the anterior pituitary gland to release gonadotropin. The released gonadotropins, which include follicle-stimulating hormones and luteinizing hormones. The follicle-stimulating hormone allows the primary follicle to develop into a secondary follicle, which has surrounded itself with a zona pellucida, granular cells and theca cells.
- The granular cells and theca cells both produce estrogen. The hormone estrogen stimulates the uterus to prepare its uterine lining (endometrium) for implantation. It will become thicker, softer and richly supplied with blood vessels.
- The secondary follicle develops into a mature follicle, or a graafian follicle. This has the zona pellucida, thicker granular cells, and theca cells. These begin to protrude on the edges of the ovary and produce even more estrogen.
- The overproduction of estrogen feeds back to the hypothalamus to stop the production of FSH. As even more estrogen produces, a positive surge of FSH and especially luteinizing hormone, which then drops quickly.
Ovulation (Days 13-15)
Stages of the Ovarian/Menstrual Cycle
- A watery mucus is secreted by the glands of the endometrium, cervix and uterine tubes.
- The spike in luteinizing hormone begins to weaken the wall of the ovary, causing the mature follicle to protrude out. The ovum is released from the follicle and drawn by fluid currents and fimbriae into the fallopian tubes and oviduct, leaving a cluster of cells, the corpus luteum.
- The oviduct contracts and moves in synchronisation with the cilia to propel the egg towards the uterus.
Luteinising Phase
Stages of the Ovarian/Menstrual Cycle
- The corpus luteum, now without the egg inside, enlarge and changes colour in order to build up the protein lutein. This stimulates the secretion of both progesterone and estrogen, causing the uterus to thicken its endometrial wall even further and vascularise (blood vessels). This hormone release continues to occur for 10 days.
- If after 10 days, the oocyte has not been fertilised, the corpus luteum will begin to break down, dropping progesterone levels. The built-up vascularised tissue of the uterus and egg begin to fall off and bleed out of the vaginal opening.
Fertilisation: If the ovum does become fertilised, pregnancy results. Progesterone and estrogen maintain constant secretion in order to maintain the uterine wall and a placenta forms to attach the embryo. The pregnancy is also maintained by human chorionic gonadotropin (HCG).
Fertilisation
Stages of Mammalian Reproduction
the fusion of two haploid gametes (egg and sperm) to form a single diploid zygote cell. The zygote contains equal genetic information of both the sperm and the egg. In humans this is called conception.
The male is required to insert his penis into the female’s vagina, and ejaculate semen from the urethra into her vagina. The sperm’s flagellum allows it to travel through the cervix and into the oviduct, where fertilisation occurs as it penetrates the egg. Fertilisation also depends on timing as this must occur during the female’s ovulation phase, but the sperm can survive for 3-5 days.
Four steps:
- The sperm uses enzymes in the acrosome to dissolve and penetrate the protective layer (zona pellucida) surrounding the egg to reach the cell membrane.
- Molecules on the sperm surface bind to receptors on the egg’s cell membrane to ensure that a sperm of the same species fertilises the egg, then the nucleus of the sperm enters the cytoplasm in the egg cell.
- Changes at the surface of the egg occur to prevent the entry of multiple sperm cells.
- Fusion of the haploid egg and sperm nuclei result in a diploid zygote cell.
