2.3 Sexual Reproduction in Humans

What is the function of the ovaries?

• produces female gametes

• Secretes hormones; oestrogen and progesterone

How big is the ovary in diameter?

3-4cm wide

What is the function of the uterus?

• compact, muscular organ made up of 3 layers

• Nourishes and protects the growing foetus

What is the function of the cervix?

• neck of the uterus

• Muscular ring which closes the entrance to the uterus

• Dilates during birth

What is the function of the fallopian tubes?

• connects the ovaries to the uterus

• Ciliates epithelial cells convert the secondary oocyte to the uterus

What is the function of the endometrium?

• innermost layer of the uterus which is supplied with blood.

• Embryo becomes implanted here

• Internal surface is shed each month if not fertilised (menstruation)

What is the function the bladder.

• Storage of urine.

What is the function of the urethra (female)?

• connects to bladder, allowing passage of urine.

What is the function of the vagina?

• muscular tissue that leads to the outside of the body

What is the function of the seminal vesicle?

• glands that secrete a mucus into the vas deferens

• contains nutrients which are respired by sperm for energy

What is the function of the vas deferens?

• tube that takes the sperm from the testis to the urethra during ejaculation

What is function of the prostate gland?

• gland found at the base of the bladder

• produces an alkaline secretion which neutralises urine left in the urethra

• aids in sperm mobility

What is the function of the urethra (male)?

• tube that connects the bladder to outside

• passes through penis and transfers semen and urine to outside (not at the same time)

What is the function of the epididymus?

• sperm collect and mature here

What is the function of the seminiferous tube?

• tubes found in testis

• site of sperm production

What is the function of the testis?

• produces the male gametes (spermatozoa)

What is the function of the scrotum?

• external sac that holds the testes outside of the body

• gives an optimum temperature of 35 degrees for sperm production

What is the function of the penis?

• organ used to pass semen into the reproductive system

What is spermatogenesis?

The production of haploid spermatozoa from diploid spermatogonia.

Takes place in the seminiferous tubules of the testis.

How long does spermatogenesis occur for?

Until death.

What are the 4 steps in spermatogenesis?

1. MULTIPLICATION

2. GROWTH

3. MATURATION

4. DIFFERENTIATION

What happens during the multiplication stage of SPERMATOGENESIS?

Many diploid spermatogonia multiply via mitosis from a germinal epithelium on the outer layer of the seminiferous tubule.

What happens during the growth stage of SPERMATOGENESIS?

The spermatogonia grow into primary spermatocytes.

What happens during the maturation stage of SPERMATOGENESIS?

• The diploid primary spermatocytes under go meiosis 1 to produce secondary spermatocytes.

• These then undergo meiosis 2 to produce haploid spermatids

What happens during the differentiation stage in SPERMATOGENESIS?

The haploids spermatids differentiate into spermatozoa - they form their mid piece and tails.

What do sertoli cells do?

Secrete a fluid which nourishes the spermatids and protects them from the male immune system.

What do leydig cells do?

Secrete testosterone.

What are the parts of a spermatozoa?

Acrosome + nucleus in head

Neck

Mitochondria in the midpiece

Flagellum + plasma membrane in tail

What does the acrosome contain?

hydrolytic enzymes

How many chromosomes does a sperm contain?

23

Where does oogenesis take place?

Ovary

What happens during oogenesis before birth?

• germinal epithelial cells (2n) divide by mitosis into OOGONIUM. Also divide to form follicle cells that surround primary oocyte to produce the PRIMORDIAL FOLLICLE

• OOGONIUM divide by mitosis and growth to form PRIMARY OOCYTES

• 1ARY OOCYTES start meiosis 1 but stop at prophase 1

What happens during oogenesis during puberty?

• Hormones stimulate follicles to develop every month, but only 1 matures into a fully developed GRAAFIAN FOLLICLE

• 1ary oocyte completes meiosis 1 to become a SECONDARY OOCYTE + a POLAR BODY

• 2ary oocyte begins meiosis 2 but stops in METAPHASE 2

• Graafian follicle migrates to surface of ovary and the secondary oocyte is released (ovulation)

What happens during ovulation in oogenesis?

Graafian follicle migrates to the surface of the ovary and the secondary oocyte is released.

What happens during oogenesis in fertilisation stage?

Meiosis 2 is completed to form an OVUM and a second polar body.

When does puberty start in the female?

11-13 years old

How long does oogenesis last for?

Each month from puberty to menopause.

How many gametes are produced from each germ cell?

Oogenesis: 1

Spermatogenesis: 4

Number of polar bodies produced from each germ cell?

Oogenesis: 2/3

Spermatogenesis: 0

Name of accessory cell involved?

Oogenesis: follicle cells

Spermatogenesis: Sertoli cells

How does spermatogenesis increase genetic variation in the offspring?

• random assortment of homologous chromosomes in metaphase 1

• Crossing over in prophase 1

• Independent assortment of chromatids in metaphase 2

• Fusion of 2 haploid gametes - one from male, one from female

What are the full names of LH and FSH?

LH - luteinising hormone

FSH - follicle stimulating hormone

What happens during the follicular phase of the menstrual cycle?

• day 0 is the first day of menstruation

• Concentration of all 4 hormones is LOW

• Hypothalamus secretes gonadotrophic releasing hormone (GnRH) which stimulates the anterior pituitary gland to release FSH

• FSH stimulates the development of (5/6) primary follicles in the ovary into 1 Graafian follicle

• FSH also stimulates thecal cells of the Graafian follicle to produce oestrogen

What is the function of Oestrogen in the menstrual cycle?

• causes the rebuilding of the endometrium

• Inhibits the secretion of FSH to stop any more follicles from developing (negative feedback)

• Stimulates LH secretion (positive feedback)

What happens during ovulation in the menstrual cycle?

• main role of LH: induce ovulation

• day 14 - high conc of it causes Graafian follicles at the surface of the ovary to release the secondary oocyte

What happens during the secretory phase in the menstrual cycle?

• after ovulation, the Graafian follicle is retained in the ovary as the corpus luteum produces both progesterone and oestrogen

• Progesterone + oestrogen both inhibit the production of FSH + LH, reducing their conc.

• No new follicles produced

• Progesterone stimulates the endometrium to THICKEN (increased no. of blood vessels) and remain in place

What happens during breakdown of the menstrual cycle?

• no implantation = falling conc of FSH + LH cause corpus luteum to break down

• Occurs within 14 days if no embryo is present

• Breakdown of corpus luteum means progesterone production declines, causing endometrium to shed

• Oestrogen low - FSH production no longer inhibited so menstrual cycle will restart

What is the menstrual cycle?

• uterus preparing for fertilised egg

• Repeating series of changes in the endometrium

• From birth to menopause

What counts as the menopause?

When you haven’t had your cycle for a year. Typical in women aged 51+