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 Name the structures that are unique to the male reproductive system.

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 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.

Female Reproductive System Name the structures that are unique to the female reproductive system.

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

Zygote forms from union of ovum and sperm 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