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