Reproduction 11.4

Reproduction 11.4IB STANDARDS PART II

Bianca arguillaBrea alotaya

Natasha guenther

IB STANDARDS

11.4.1: Annotate a light micrograph of testis tissue to show the location and function of interstitial cells (leydig cells), germinal epithelium cells, developing cells, developing spermatozoa, and Sertoli cells

Parts to know on the testis tissue: › wall of

seminiferous tubule› Fluid inside

seminiferous tubule› Blood vessel› Interstitial cells

(Leydig cells) secrete testosterone


Interstitial Cells (Leydig cells): adjacent to the seminiferous tubules in the testicle. They can secrete testosterone and are often closely related to nerves. Leydig cells have round vesicular nuclei and an eosinophilic cytoplasm› Leydig cells release a class of hormones called androgens. They

secrete testosterone, androstenedione and dehydroepiandrosterone (DHEA), when stimulated by the pituitary hormone LH. LH increases cholesterol desmolase activity, leading to testosterone synthesis secretion by Leydig cells.

› FSH increases the response of Leydig cells to LH by increasing the number of LH receptors expressed on Leydig cells.

Germinal epithelium (male): innermost layer of the testicle› cellular covering of internal and external surfaces of the body,

including the lining of vessels and other small cavities. It consists of cells joined by small amounts of cementing substances


Developing cells: are able to revert back into an embryonic-like stem cell state, which could then be driven into chosen cell types; can continue to produce sperm› In science today, testis tissues have been found to be “stem-

like” cells that are capable of being harvested and used in the future

developing spermatozoa: aka sperm› Spermatogenesis is the production of spermatozoa and

occurs in the narrow tubes called seminiferous tubules in the testes

Sertoli cells: a 'nurse' cell of the testes which is part of a seminiferous tubules; nurtures developing sperm cells through spermatogenesis› It is activated by FSH and has FSH receptors on its

membranes.

11.4.2: OUTLINE THE PROCESSES INVOLVED IN SPERMATOGENESIS WITHIN THE TESTIS, INCLUDING MITOSIS, CELL GROWTH, THE TWO DIVISIONS OF MEIOSIS, AND CELL DEFFERENTIATION


6 Stages total:› 1. An outer layer called the germinal epithelium cells [2n]

divide endlessly by MITOSIS to produce more diploid cells› 2. Diploid cells GROW larger and are then called primary

spematocytes [2n]› 3. Each primary spermatocyte carries out the FIRST DIVISION

OF MEIOSIS to produce two secondary spermatocytes [n]› 4. Each secondary spermtocyte carries out the SECOND

DIVISION OF MEIOSIS to produce two spermatids [n]› 5. Spermatids become associated with nurse cells, sertoli

cells, which help the spermatids to develop into spermatozoa [n]. This is CELL DIFFERENTIATION.

› 6. Sperm detach from sertoli cells and eventually are carried out of the testis by the fluid in the centre of the seminiferous tubule.

11.4.3: STATE THE ROLE OF LH, TESTOSTERONE, AND FSH IN SPERMATOGENESIS

Hormone Source RoleFSH Pituitary Glands Stimulates primary

spermatocytes to undergo the first

division of meiosis, to form the secondary

spermatocytesTestosterone Interstitial cells in the

tubulesStimulates the development of

secondary spermatocytes into

mature spermLH Pituitary Glands Stimulates the

secretion of testosterone by the

testis

11.4.4: ANNOTATE A DIAGRAM OF THE OVARY TO SHOW THE LOCATION AND FUNCTION OF GERMINAL EPITHELIUM, PRIMARY FOLLICLES, MATURE FOLLICE, AND SECONDARY OOCYTE

Parts to know on the ovary:› Region where blood

vessels enter and leave› Outer layer of germinal

epithelium cells› Cortex [containing

primary follicles]› Secondary oocyte

inside a mature follicle› Medulla [containing

blood vessels]

11.4.4: ANNOTATE A DIAGRAM OF THE OVARY TO SHOW THE LOCATION AND FUNCTION OF GERMINAL EPITHELIUM, PRIMARY FOLLICLES, MATURE FOLLICE, AND SECONDARY OOCYTE

Germinal Epithelium: surface of the ovary covered by a layer of simple cuboidal cells› These cells are derived from the mesoderm during

embryonic development and are closely related to the mesothelium of the peritoneum. The germinal epithelium gives the ovary a dull gray color as compared with the shining smoothness of the peritoneum; and the transition between the mesothelium of the peritoneum and the columnar cells which cover the ovary is usually marked by a line around the anterior border of the ovary.

› The germinal epithelium gives rise to primary follicles Primary Follicles: Located inside the cortex; develop

receptors to FSH at this time, but they are gonadotropin-independent up until the latter stages

11.4.4: ANNOTATE A DIAGRAM OF THE OVARY TO SHOW THE LOCATION AND FUNCTION OF GERMINAL EPITHELIUM, PRIMARY FOLLICLES, MATURE FOLLICLE, AND SECONDARY OOCYTE

Mature Follicle: contains secondary oocyte; bursts open and releases the egg with increased levels of LH, starting ovulation

Secondary Oocyte: An oocyte in which the first meiotic division is completed. The second meiotic division usually stops short of completion unless fertilization occurs; b/w first and second maturation development

11.4.5: OUTLINE THE PROCESSES INVLOVED IN OOGENESIS WITHIN THE OVARY, INCLUDING MITOSIS, CELL GROWTH, THE TWO DIVISIONS OF MEIOSIS, THE UNEQUAL DIVISION OF CYTOPLASM, AND THE DEGENERATION OF POLAR BODY


8 STEPS:› 1. In the ovaries of a female fetus, germinal epithelium cells [2n] divide by

MITOSIS to form more diploid cells [2n]› 2. Diploid cells GROW into larger cells called primary oocytes [2n]› 3. Primary oocytes start the FIRST DIVISION OF MEIOSIS but stop during the

prophase I. The primary oocyte and a single layer of follicle cells around forma primary follicle

› 4. When a baby girl is born the ovaries contain about 400,000 primary follicles› 5. Every menstrual cycle a few primary follicles start to develop. The primary

oocyte completes the first division of meiosis, forming two haploid nuclei. The cytoplasm of the primary oocyte is DIVIDED UNEQUALLY forming a large secondary oocyte [n] and a small polar cell [n]

› 6. The secondary oocyte starts the SECOND DIVISION OF MEIOSIS but stops in prophase II. The follicle cells meanwhile are proliferating and follicular fluid is forming.

› 7. When the mature follicle bursts, at the time of ovulation, the egg that is released is actually still a secondary oocyte.

› 8. After fertilization the secondary oocyte completes the second division of meiosis to form an ovum, [with a sperm nucleus already inside it] and a second polar cell or body. The first and second polar bodies do not develop and eventually DEGENERATE.

11.4.6: DRAW AND LABEL A DIAGRAM

OF A M

ATURE SPERM AND EGG

FEATURES TO LABEL: HEAD, ACROSOME, HAPLOID NUCLEUS, MID-PIECE, TAIL, PROTEIN FIBERS TO STRENGTHEN TAIL, MICROTUBULES IN A 9+2 ARRANGEMENT, HELICAL MITOCHONDRIA, CENTRIOLE, PLASMA MEMBRANE

Click icon to add picture

11.4.6: DRAW AND LABEL A DIAGRAM

OF A M

ATURE SPERM AND EGG

FEATURES TO LABEL: TWO CENTRIOLES, FIRST POLAR CELL, PLASMA MEMBRANE, LAYER OF FOLLICLE CELLS [CORONA RADIATA], LAYER OF GEL COMPASED OF GLYCOPROTEINS [ZONA PELLLUCIDA], CORTICAL GRANULES, CYTOPLASM/YOLK CONTAINING DROPLETS OF FAT, HAPLOID NUCLEUS

11.4.7: OUTLIHNE THE ROLE OF THE EPiDIDYMIS, SEMINAL VESICLE, AND PROSTATE GLAND IN THE PRODUCTION OF SEMEN

The three main structures: Epididymis, Seminal vesicles, and Prostate gland› When sperm first arrive in the epididymis from the testes,

they are unable to swim› While in epididymis, sperm matures and learn to swim› The prostate gland and two seminal vesicles produce and

store fluids that are later expelled during ejaculation› The fluid them mixes with them sperm and increased the

volume of the ejaculate The fluid from the seminal vesicle contains nutrients, like

fructose, for the sperm and a muscus to protect it in the vagina

The fluid from the prostate gland has mineral ions and protects the sperm from the vagina’s acidic conditions due to its alkalinity.

COMPARE THE PROCESSES OF SPERMATOGENESIS AND OOGENESIS, INCLUDING THE NUMBER OF GAMETES AND THE TIMING OF THE FORMATION AND RELEASE OF GAMETES

Similarities:› Both start with the proliferation of cells by mitosis› Both involve the cell growth before mitosis› Both involve the two divisions of meiosis

Differences:Spermatogenesis OogenesisMillions produced daily One produced every 28 daysReleased during ejaculation Released on about day 14 of menstrual

cycle by ovulationSperm formation starts during puberty in boys

The early stages of egg production happen during fetal development in females

Sperm production continues throughout the adult life of men

Egg production becomes irregular and then stops at the menopause in women

Four sperm are produced per meiosis Only one egg is produced per meiosis

11.4.9: DESCRIBE THE PROCESS OF FERTILIZATION, INCLUDING THE ACROSOME REACTION, PENETRATION OF THE EGG MEMBRANE BY A SPERM AND THE CORTICLE RXN


6 steps total:› 1. Arrival of sperm: Sperm attracted by a chemical signal

and swim up the oviducts to reach the egg. Fertilization is only successful if many sperm reach the egg {sperm tries to push through the layers of follicle cells around the egg}

› 2. Binding: The 1st sperm to break through the layers of follicle cells binds to the zona pellucida. This triggers the acrosome reaction.

› 3. Acrosome Reaction: The contents of the acrosome are released by the separation of the acrosomal cap from the sperm. Proteases from the acrosome digest a route for the sperm through the zona pellucida, allowing the sperm to reach the plasma membrane of the egg


Fertilization continued› 4. Fusion: The plasma membrane of the sperm and egg

fuse and the sperm nucleus enters the egg and joins the egg nucleus. Fusion causes the cortical reaction.

› 5. Cortical Reaction: Small vesicles called cortical granules move to the plasma membrane of the egg and fuse with it, releasing their contents by exocytosis. Enzymes from the cortical granules cause the cross linking glycoproteins in the zona pellucida, making it hard and preventing the entry of anymore sperm

› 6. Mitosis: The nuclei from the sperm and the egg do not fuse together. Instead, both nuclei carry out mitosis using the same centrioles and spindle of microtubules. A 2-celled embryo is produced

Figure 47.5 Fertilization in mammals

11.4.10: OUTLINE THE ROLE OF HCG IN EARLY PREGNANCY

HCG: human chronic gonadotrophin; prevents degeneration of the corpus luteum.› Estrogen and progesterone are needed throughout pregnancy

to stimulate the development of the uterus lining. During the first few days after ovulation, the corpus luteum secretes these hormones whether or not there has been fertilization. After implanting in the uterus wall, the embryo starts to secrete HCG.

› HCG stimulates the corpus luteum to grow and to continue secretion of estrogen and progesterone. This is essential to allow the pregnancy to continue.

› By the middle of the pregnancy, the corpus luteum starts to degenerate, but by then the cells in the placenta are secreting estrogen and progesterone and these cells secrete increasing amounts until the end of the pregnancy.

11.4.11: OUTLINE THE EARLY EMBRYO DEVELOMPENT UP TO THE IMPLANTATION OF THE BLASTOCYST

Fertilization: Fusion of the egg and the sperm› During copulation, or sexual intercourse, semen is

ejaculated into the vagina. Sperm swim through the cervix, up the uterus and into the oviducts. If there is an egg in the oviducts, the sperm can fuse with it to produce a zygote

Zygotes produced in the oviduct = new individual› Zygote starts to divide by mitosis and forms a 2-cell

embryo, and then a 4-cell embryo and so on until a blastocyst, or a hollow ball of cells, is formed

› During these stages embryo is transported down the oviducts to the uterus {at about 7 days old the embryo implants itself into the wall of the uterus to continue development}.

11.4.12: EXPLAIN HOW THE STRUCTURE AND FUNCTIONS OF THE PLACENTA, INCLUDING ITS HORMONAL ROLE IN SECRETION OF ESTROGEN AND PROGESTERONE, MAINTAIN PREGANCY

Placenta: a disc-shaped structure, 185 mm in diameter and 20 mm thick when fully grown.

Placentile Villi: small projections that give a large surface area, 14 m^2, for gas exchange and exchange of other materials. Fetal blood flows through the capillaries in the villi

Inter-villous Spaces: Maternal blood flows through these spaces, brought by the uterine arteries and carried away by the uterine veins.

Myometrium: muscular wall of the uterus used during childbirth. Oxygenated Fetal Blood: flows back to the fetus from the

placenta along the umbilical vein De-oxygenated Fetal Blood: flows from the fetus to the placenta

along the umbilical arteries Endometrium: the lining of the uterus which the placenta grows

11.4.13: STATE THAT THE FETUS IS SUPPORTED AND PROTECTED BY THE AMNIOTIC SAC AND AMNIOTIC FLUID

The fetus develops an amniotic sac containing amniotic fluid around it.

The fetus floats in and is supported by the amniotic fluid b/c the fluid acts as a shock absorber (such as everyday events, or accidents that impacts the mother’s abdomen)

Figure 46.17 Placental circulation

11.4.14: STATE THAT MATERIALS ARE EXCHANGED BETWEEN THE MATERNAL AND FETAL BLOOD IN THE PLACENTA

Background Info› 8 weeks+, embryo starts to develop tissue,

becoming a “fetus.” The placenta and umbilical also develop. The placenta has many projections called placenta

villi embedded in the uterine wall. In the placenta, the blood of the fetus flows close to

the blood of the mother in the uterus wall.› Materials are exchanged between the maternal

and fetal blood Ex: Oxygen passes from maternal to fetal blood and

Carbon Dioxide passes from fetal to maternal blood

11.4.15: OUTLINE THE PROCESS OF BIRTH AND ITS HORMONAL CONTROL, INCLUDING THE CHANGES IN PROGESTERONE AND OXYTOCIN LEVELS AND POSITIVE FEEDBACK

Over 9 months of pregnancy, progesterone ensure that the uterus develops and sustains the growing fetus

Levels are increasingly high until end of pregnancy in which a rapid decrease of the hormone occurs.

This causes secretion of oxytocin which causes the muscles of the uterus wall to contract

The uterine contractions then become stronger and stronger due to increase of oxytocin, creating a positive feedback

John Jacob Jingle Heimer Schmitt, his name was my name, too!

Figure 46.19 Hormonal induction of labor

Reproduction 11.4

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