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How Do Humans Reproduce?

By: Puneet N. 9-4

MEIOSIS

- Meiosis is the process in which haploid gametes are formed

- Becoming haploid means with only one set of unpaired chromosomes

- In the reproductive system, this form of cell division is employed to create haploid gametes, which are male & female sex cells

- Meiosis guarantees that each gamete has 23 chromosomes

WHAT ARE GAMETES?

- The reproductive cells of an organism are called gametes.

- These cells are also known as sex cells.

- Females and males each have their own.

- Each gamete is made of 23 chromosomes.

- Only cells in the human body that are not produced by mitosis.

GAMETES

MALE

THE MALE GAMETE

- Male Gametes, known as sperm cells, are formed in the testis of a male reproductive system

FEMALE

THE FEMALE GAMETE

- Within the female reproductive system, an ovary releases female gametes known as egg cells on a regular basis.

- The more scientific term for the egg cell is oocyte.

THE JOURNEY OF THE MALE GAMETE

SCROTUM

contains

TESTIS

produces

(stored in vas deferans)

male gamete

MALE REPRODUCTIVE SYSTEM

SPERM

EPIDIDYMIS

travels through

travels through seminal vesicle and prostate glands

SEMEN

travels through

URETHRA

exits through

PENIS

THE JOURNEY OF THE FEMALE GAMETE

OVARIES

contains

FOLLICLES

each follicle contains an egg

mature egg breaks off it's follicle

OVULATION

FEMALE REPRODUCTIVE SYSTEM

EGG

goes through

egg travels through

FALLOPIAN TUBE (OVIDUCTS)

moves towards

(the egg is now fertilized)

UTERUS

FERTILIZATION

- Fertilization is when the gametes from two parents combine to form one single cell. (sperm penetrates egg)

- When the egg is fertilized, it continues on its journey through the fallopian tube to the uterus as a zygote.

FERTILIZATION

WHAT IS A ZYGOTE?

ZYGOTE

- The fertilized egg is considered a zygote.

- First cell in the body

- As a zygote, you have 43 chromosones, 23 chromosomes from your dad, 23 chromosomes from your mom

- The process of mitosis begins after you are considered a zygote, which means your cells begin to rapidly divide.

- A zygote is a diploid cell that results from the union of two haploid genes.

INTERPHASE

- During interphase, the cells prepare for mitosis. DNA replication occurs.

INTERPHASE

WHAT ARE CHROMOSOMES?

- A chromosome is a DNA molecule that looks like a double-stranded thread and that is bundled very tightly.

- Chromosomes are inside of the nucleus

- Chromosomes are scattered/diffused

CHROMOSOMES

G1 - First stage of interphase

- This is the period of cell growth before the DNA is duplicated.

- Begins in daughter cells

G1

S - Second Stage of Interphase

S

- During the second stage of interphase, the DNA is duplicated (chromosomes are duplicated)

- DNA synthesis

G2 - Last Stage of Interphase

- Cells prepare for division during the last stage of interphase, after the cells have been divided.

G2

MITOSIS - THE PROCESS CELL DIVISION

- Mitosis is the process where one parent cell divides into two daughter cells.

- Each daughter cell recieves a complete set of chromosomes from the parent cell.

- Mitosis plays an important role in the development of embryos.

- This process allows the body to grow and replace cells.

MITOSIS

PROPHASE

- Prophase is the first stage of cell division.

- The chromatin which were scattered in interphase, condense into paired chromatids.

- Each chromosome has duplicated and now consists of two sister chromatids.

- At the end of prophase, the nuclear envelope disappears.

- Spindle fibers begin to form from centrioles.

PROPHASE

METAPHASE

- Second stage of mitosis

- Chromosomes align at the equitorial plate (sometimes called metaphase plate) and are held in place by microtubules called spindle fibers

- Spindle fibers are attached to the centromere

METAPHASE

ANAPHASE

- The third phase of mitosis

- Spindle fibers contract and shorten by pulling the centromere apart

- Sister chromatids, which are one of each of the replicated stands, seperate and move towards their corresponding poles

- During this stage, the cell elongates.

ANAPHASE

TELOPHASE

- Telophase is the last phase of mitosis

- Daughter chromosomes have arrived at their corresponding poles

- Spindle fibers disappear

- Chromosomes decondense to chromatin

- The nuclear envelope reappears

TELOPHASE

CYTOKINESIS

- During cytokinesis, the cytoplasm splits, the cell membrane pinches inwards, eventually resulting in the formation of two daughter cells.

- There are now two distinct nuclei in the same cell, therefore the cell must break in half.

- The two daughter cells will continue the cell cycle and eventually begin interphase again.

CYTOKINESIS

BLASTOCYST

- At this stage, the cells are arranged into inner and outer layers.

- The outer layer later aids in the formation of the placenta

BLASTOCYST

ENDOMETRIUM

- The endometrium is known as the lining of the uterus.

- The endometrium plays a very important role in the reproduction process, because the blastocyst adheres to it (implantation).

- If the blastocyst is unsuccessful in adhering to the endometrium, the pregnancy will be unsuccessful.

ENDOMETRIUM

EMBRYO

- 4 weeks after fertilization, you are considered an embryo.

- The limbs, eyeballs, and spine start to take shape.

- At this point, your heart has evolved enough that it begins to beat.

EMBRYO

FETUS

- When an embryo forms its first bone cells, it is considered a fetus.

- This happens at about 8 weeks of pregnancy

FETUS

PREGNANCY

WHAT IS DIFFERENTIATION?

PREGNANCY

- Differentiation is the process through which generalist cells become specialized to perform the different tasks of various tissues and organs in the body.

- During differentiation, three layers in the grastula develop into different parts of the body.

- The human gestation period, which lasts about 38 weeks, can be divided into 3 blocks of time, based on the formation of different tissues and organs.

- The placenta is a blood-vessel rich organ that is present only during pregnancy.

FIRST TRIMESTER (weeks 1-12)

- At 4 weeks, what begins to form is the limbs, eyes, and spine.

- At 8-9 weeks, the embryo begins to form its first bone cells, and is now considered a fetus.

- By the end of 12 weeks, all the major organs have begun their development, the fetus has the beginning of its liver, stomach, brain, and heart, along with a noticeable head and limbs.

- The fetus has a length of 100 mm

- Using ultrasound technology, the sex of the fetus can be identified

FIRST TRIMESTER

SECOND TRIMESTER (weeks 12-24)

SECOND TRIMESTER

- At 16 weeks, the placenta moves to one side because it is too small to surround the fetus.

- The skeleton begins to form, the brain grows rapidly, and the nervous system begins to function.

- The mother begins to feel the movements of the fetus as it moves and flexes its new muscles.

- At 24 weeks, the fetus is about 300 mm long, most organs are fully formed but not fully developed, therefore the fetus has little chance of survival if born prematurely.

- Premature birth can be accompanied by bleeding for the mother.

THIRD TRIMESTER (weeks 24-38)

- During the third trimester, the fetus rapidly increases in size and begins to move around in its amniotic sac, stretching and kicking.

- The immune system develops, and proper nutrition is more important than ever for the mother, mainly for the building of vital brain tissue.

- By the 8th month, the fetus opens its eyes, and by the end of the third trimester, the fetus has grown to an average length of 500 mm and an average wieght of between 2700 and 4100 grams.

THIRD TRIMESTER

LABOUR

- Labour is a sequence of muscle contractions that open up the cervix in preperation for childbirth.

LABOUR

3 STAGES OF BIRTH

DILATION STAGE

- Uterine contractions and oxytocin cause the cervix to open, or dilate.

- Amnion breaks, amiotic fluid is released throughout vagina.

- Lasts an average of 2-20 hours.

EXPULSION STAGE

- Contractions become very forced, causing the baby to be pushed through the cervix to the birth canal, which takes from 0.5-2 hours.

- The baby's head rotates as it moves through the birth canal, which makes it easier for the baby to pass through the birth canal.

PLACENTAL STAGE

- The placenta and umbilical cord are expelled from the uterus, which happens within 10-15 minutes after the baby is born.

- This expelled placenta is called after birth.

Problems than can occur during labour:

- Mother's pelvis is too small for the baby to pass through the birth canal

- The baby is not in the correct position for birth

- In many of these problem cases, the baby is delivered through a process called Cesarean section

COMPLICATIONS

CESAREAN SECTION

- A cesarean section is an alternative method of child birth

- In a c-section, doctors remove the baby, through an incision in the mother's abdomen and uterus

BIRTH HORMONES

Hormones play an important role in pregnancy.

BIRTH HORMONES

PROGESTERONE:

- Keeps the uterine lining in place and stops the menstrual flow.

- High levels maintain the pregnancy.

ESTROGEN & PROGESTERONE:

- A sharp drop in levels of pregesterone and estrogen cause contractions in the muscles of the uterus.

OXYTOCIN:

- Oxytocin is secreted by the pituitary gland

- Stimulates contractions and opens the birth canal, inducing labour.

BABY PUNEET

BABY

TODDLER PUNEET

TODDLER

ADOLESCENT PUNEET

As an adolescent, you now have the chance to reproduce.

ADOLESCENT

YOUNG ADULT

LOVE HORMONES

- Romantic love can be distinguished into three types, according to Dr. Helen Fisher and her team of experts in the study of the science behind lust, attraction, and attachment.

- Each group is characterized by its own set of hormones produced by the brain.

LOVE

HORMONES

LUST

TESTOSTERONE & ESTROGEN:

- These are the sex hormones, meaning your sexual desire (libido) is boosted.

- These hormones drive a desire for sexual gratification, and the need to reproduce.

ATTRACTION

- Attraction is much like an addiction to another human being.

DOPAMINE:

- Dopamine is released when we do things that make us feel joyful.

- Dopamine can be released during intimate moments of a relationship.

NOREPINEPHRINE:

- During attraction, norepinephrine is released

- Make us feel excited, can even cause a lack of sleep or appetite

SEROTONIN:

- Attraction causes decrease of serotonin, which is the hunger and mood hormone.

ATTACHMENT

OXYTOCIN:

- The hormone behind the feel-good, socialable affects that chemicals like; MDMA, GHB, which are party drugs, produce.

VASOPRESSIN:

- Released when getting affection.

Spermatogenesis & Oogenesis

SPERMATOGENESIS & OOGENESIS

SPERMATOGENESIS:

- Hormones involved in production of sperm in the male:

- FSH (follicle stimulating hormones), reaches the testes, promotes the development of sperm-producing tubes in the testes, and sperm cells

- Other cells in the testes start to produce the hormone testosterone.

OOGENESIS:

- Hormones involved in the production of eggs in the female:

- When FSH reaches the ovaries, they are stimulated to become maturing and releasing eggs.

- FSH also stimulates the ovaries to produce estrogen (reproductive hormone)

Hormones in the Menstrual Cycle:

MENSTRUATION

Hormones produced by the pituitary gland, and ovaries co-ordinate:

- Pituitary hormones "tell" the ovaries what to do

- Ovarian hormones "tell" the uterus what to do

The co-ordination between the hormones is called feedback. Positive feedback means the actions are stimulated. or begun. Negative feedback occurs when actions are inhibited, or prevented

- LH (luteinising hormone): progesterone, released by the pituitary gland, by a structure in the ovary called the corpus luteum.

- The uterine lining is shed from the body - menstruation.

- Decling progesterone levels cause the uterine lining to break down.

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