Reproduction in Humans
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Transcript of Reproduction in Humans
Reproduction in Humans
Introduction
• Male and female reproductive systems • Function together to produce offspring • Female reproductive system nurtures
developing offspring • Produce important hormones
MALE REPRODUCTIVE SYSTEM
Male reproductive System
• Essentially 4 parts:• Testes
• Gonads, in scrotum; make gamates and releases sex hormones
• Ducts• Epididymis, sperm ducts
• Glands• Seminal vesicles, prostate gland
• Penis• Urethra and erectile tissue. Arousal leads to filling
of the tissue with blood erection. Enables it to function as a penetrating organ in intercourse
Male Reproductive System (cont.)
• Sperm cells• Head
• Nucleus with 23 chromosomes• Acrosome – enzyme-filled sac
− Helps sperm penetrate ovum
• Midpiece• Mitochrondria that generate cell’s energy
• Tail• Flagellum that propels sperm forward
Male Reproductive System: Erection, Orgasm, and Ejaculation
• Erection• Parasympathetic nervous system stimulates erectile
tissue • Become engorged with blood
• Orgasm• Sperm cells propelled out of testes into urethra• Secretions from accessory organs also released into
urethra
• Ejaculation• Semen is forced out of urethra• Sympathetic nerves then stimulate erectile tissue to
release blood • Penis returns to flaccid state
FEMALE REPRODUCTIVE SYSTEM
Female reproductive System I• Function is to:
• Produce gamates (ova)• Receive the male gamates• Provide a suitable environment for:
• fertilisation• Development of fetus
• Provide a means of expelling the developed fetus during parturition (birth)
Female reproductive System II• Consists of:
• Ovaries• Produce Ova, secrete progesterone + oestrogen
• Oviducts (Fallopian Tubes)• Uterus
• Hollow, pearshaped, muscular. Lining – endometrium – undergoes cyclical changes. Cervix part of uterus that projects thru’ from vagina
• Vagina• Muscular tube adapted for reception of the penis
and passage of baby out during birth.
Internal Female Organs
GAMETE PRODUCTION
Production of Gametes
• Production of Gametes – Gametogenesis• Involves special cell division –
meiosis
• Spermatogenesis• Oogenesis
Spermatogenesis 1
• Each testis is packed with seminiferous tubules
• In these Spermatogenesis takes place
• Spermatogonia (germ cells) line the tubules dividing my mitosis to give more spermatogonia (Type A and Type B)
Spermatogenesis 2
• Type B Spermatogonia will undergo meiosis to eventually form spermatozoa
• Type B also known as primary spermatocytes
• After the first meiotic division they become secondary spermatocytes
Spermatogenesis 3
• Secondary spermatocytes rapidly under go the second meiotic division to form spermatids
• Spermatids undergo development into spermatozoa
Spermatogenesis 4
Spermatogenesis 5
• During spermatogenesis, cells are supported by Sertoli Cells
• Testes also produce testosterone from Leydig cells• Controls rate of sperm production and
male characteristics
Spermatogenesis 6
Spermatogenesis 6• Testes controlled by the anterior
pituitary gland• Follicle stimulating hormone (FSH)• Interstitial Cell Stimulating Hormone (ICSH)
• ICSH stimulates leydig cells to secrete testosterone inhibits FSH and ICSH secretion. Negative feedback.
Oogenesis 1
• The process primordial germ cells (oogonia) become ova
• Begins in fetus – oogonia divide by mitosis
• By 4 or 5months, some are enlarged – potential to become gametes
• Now called primary oocyte
Oogenesis 2
• Primary oocytes begin first stage of meiosis
• By month 7 they are surrounded by follicular cells to form primary follicles
• Then Meiosis stops until puberty
Oogenesis 3• Once a month some of the primary
oocytes continue meiosis• move to surface of ovary• One reaches maturity, others
degenerate• First meiotic division finishes –
secondary oocyte• Ovulation follicle ruptures, oocyte
released (once released called ovum)• 2nd Meiotic division doesn’t occur until
the head of a spermatozoan enters the ovum
Oogenesis 4
Oogenesis 5• After ovulation, the ruptured
follicle fills with a blood clot• Cells enlarge• temporary endocrine structure,
the corpus luteum• Grows for 7 – 8 days secreting
progesterone and oestrogen• If fertilisation/implantation don’t
occur, corpus luteum degenerates after 12 – 14 days.
Oogenesis 6
FERTILISATION & PREGNANCY
Pregnancy: Fertilisation
• Pregnancy – condition of having a developing offspring in the uterus
• Fertilisation – process in which a sperm cell unites with an ovum; results in pregnancy
• Only one sperm cell penetrates the follicular cells and the zona pellucida that surround the ovum’s cell membrane
Acrosome reaction
• After fertilization, ovum releases enzymes that cause the zona pellucida to become impenetrable to other sperm
• Zygote forms from union of ovum and sperm • Contains 46 chromosomes
Fertilisation & Implantation
Pregnancy: The Prenatal Period
• Time before birth• Zygote – undergoes rapid mitosis
• First week after fertilization• Cleavage – rapid cell division• Morula – ball of cells resulting from cleavage
• Travels down fallopian tube to uterus• Becomes blastocyst which implants in endometrial
wall • Blastocyst
• Some cells (inner cell mass) become embryo• Others, along with cells from uterus, form placenta
Fertilisation & Implantation (brief)• Sperm motile – 1mm/min• With muscular movements of uterus get
through cervix into oviducts• Fertilisation takes place (diploid)• Fertilised ovum – zygote – begins
mitosis• 3 days – morula – 16 cells, enters uterus• Fluid enters morula, cells rearrange to
become hollow – blastocyst• Blastocyst implants into endometrium –
total 10 days
Pregnancy: Hormonal Changes
• Embryonic cells secrete human chorionic gonadotropin (HCG)• Maintains the corpus luteum
• Estrogen and progesterone• Secreted by corpus luteum and placenta• Functions
• Stimulate uterine lining to thicken, development of mammary glands, enlargement of female reproductive organs
• Inhibit release of FSH and LH from anterior pituitary gland (preventing ovulation) and uterine contractions
Pregnancy Testing Kits
• These use monoclonal antibodies to test for hormone hCG
• hCG produced by placenta• The test relies on the reaction
between hCG and antibodies bound to coloured latex beads