The ovarian & menstrual cycle

HBS 2B

Cell division

1. What type of division is shown here – meiosis or mitosis?2. How can you tell?3. Name the stages shown in each diagram.4. Is this likely to be happening in a male, a female or people of either sex?5. How can you tell?

Cell division

1. What type of division is shown here – meiosis or mitosis?2. How can you tell? 2 divisions & 4 cells are produced3. Name the stages shown in each diagram.4. Is this likely to be happening in a male, a female or people of either sex?5. How can you tell? 4 gametes are produced

Prophase 1 Metaphase 1 Anaphase 1 Telophase 1

Prophase 2 Metaphase 2 Anaphase 2 Telophase 2

The ovarian and menstrual cycleEvery month, one of the follicles in an ovary starts

to develop. Each follicle consists of an immature ovum

surrounded by a layer of follicular cells. As it develops the follicle gets larger and fills with

fluid. After 10 –14 days the mature follicle bursts,

expelling the ovum towards the uterine tube. This is called ovulation. The follicular cells develop into a structure called

the corpus luteum. The ovum is wafted by movement of the fimbriae

into the uterine tubes. Movement of cilia and muscular folds in the tubes

cause the ovum to travel down the tubes towards the uterus.

Fertilisation takes place in the uterine tubes. If fertilisation takes place then the zygote will

divide and move down into the uterus where it will implant, resulting in pregnancy.

If fertilisation does not take place, then the uterus will shed its lining (menstruation) and a new cycle will begin

Control of the cycle

The reproductive system is controlled by special chemicals called hormones.

Hormones are chemicals released into the blood stream that control the activity of target cells (cells with receptors for that hormone)

They are made in endocrine glands, which are collections of cells that secrete into body cavities or blood stream

They act by travelling in the blood until they reach a target organ, where it causes a change in activity.

Follicle Stimulating Hormone (FSH)Luteinising Hormone (LH)OestrogenProgesterone

Changes during the cycle

Reproductive hormonesThe main endocrine glands

associated with reproduction are the hypothalamus, pituitary gland, ovaries and testes.

The placenta in a pregnant woman also acts as an endocrine gland.

The hypothalamus is located at the base of the brain and is important because it controls many of the body’s activities as well as the ovarian/menstrual cycle

The pituitary gland is located just below the hypothalamus and is important because it secretes many hormones that control the body’s activities – including the gonadotrophins that control the ovarian/menstrual cycle

Reproductive hormones 2

Hormonal regulation and gametogenesis in males is not cyclic as in females. Sperm are produced continually from puberty onwards.

Males and females produce some hormones in common eg follicle stimulating hormone and luteinising hormone

Each sex produces small amounts of hormones we associate with the opposite sex, but we consider some hormones to be mainly male eg testosterone, and some to be mainly female eg oestrogen and progesterone.

Hormone Where made Effects

Oestrogen F________ and c______ l______ in o__________

Progesterone C______ L________and p____________

Testosterone

FSH male:female:

LH male:female: causes ovulation and development of corpus luteum leading to

HCG

Prolactin

Oxytocin

Name Where made Effects

Oestrogen follicle and corpus luteum in ovaries

Is responsible for female secondary sexual characteristics (eg breasts, rounder body shape, etc). It is also involved with endometrial repair after menstruation.

Progesterone corpus luteum in ovaries and placenta

Is responsible for development and maintenance of the endometrium (ie hormone of pregnancy).

Testosterone Testes Is responsible for male secondary sexual characteristics (eg facial and body hair, squarer body shape, deeper voice, etc).

Follicle stimulating hormone (FSH)

Pituitary gland Stimulates spermatogenesis in the male, and stimulates the development of the follicle containing an ovum in the female.

Luteinising hormone (LH)

Pituitary gland Stimulates the production of testosterone in the male, and stimulates ovulation and the formation of the corpus luteum (which then secretes oestrogen and progesterone) in the female.

HCG Placenta Maintains the corpus luteum during early pregnancy. This keeps the corpus luteum secreting progesterone and preventing the start of a new cycle.

Prolactin Pituitary gland Stimulates the production of milk in the mammary glands.

Oxytocin Pituitary gland Stimulates the contraction of the uterus (during childbirth) and the contraction muscles in the mammary glands (which causes milk to flow during breast feeding)

Cyclic control of the cycle1. The hypothalamus controls release of gonadotrophins

from anterior pituitary by the use of releasing and inhibiting factors

2. Release of Follicle Stimulating Hormone (FSH) from anterior pituitary causes the development of a follicle in the ovary

3. The developing follicle releases oestrogen, which acts on the uterus to repair the endometrium

4. High levels of oestrogen stimulate hypothalamus to release FSH IF & LH RF, which causes anterior pituitary to decrease secretion of FSH and increase secretion of LH.

5. Luteinising Hormone (LH) acts on the follicle to induce ovulation, and the development of the corpus luteum.

6. The corpus luteum secretes oestrogen and progesterone, which act on the uterus to prepare it for pregnancy (increased size and number of glands & blood vessels).

High levels of oestrogen and progesterone inhibit the release of FSH RF and LH RF from the hypothalamus.

7. If no pregnancy occurs, the corpus luteum degenerates, and levels of oestrogen and progesterone fall.

This causes the uterine lining to shed (a process called menstruation), and the hypothalamus to release FSH RF, thus starting a new cycle.

Hormonal control of spermatogenesis

Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the anterior pituitary gland to secrete two hormones.

Follicle-Stimulating Hormone (FSH) acts on Sertoli cells, which nourish developing sperm.

Sertoli cells also secrete Inhibin, which reduces FSH secretion by negative feedback.

Luteinizing Hormone (LH) acts on Leydig cells (interstitial cells), which produce androgens, chiefly testosterone.

Testosterone regulates production of the brain hormones by negative feedback

Sample test questions 1

a) Name structures:A GB HC ID J

E KF

b) Give the function of:i) Eii) Fiii) Giv) I

Sample test questions 1

a) Name structures:A bladder G ovaryB urethra H uterine tubeC penis I uterusD vas deferens J bladder

E testes K vaginaF scrotum

b) Give the function of:i) E makes sperm and testosteroneii) F protects testes and maintains them at a cooler temperature for spermatogenesisiii) G makes ova and female hormonesiv) I protects and nourishes the embryo/foetus during pregnancy

Sample test questions 2

1. Look at the diagram above:

Sperms A and B carry different sex chromosomes:

A has an X chromosome B has a Y chromosome

(a) What sex chromosome will the ovum contain? (1 mark)

(b) If sperm A fertilises the ovum, what sex will the baby be? (1 mark)

(c) What is the total number of chromosomes in sperm B? (1 mark)

(d) As far as the sex chromosomes are concerned, why are there 2 sorts of sperms, but only one type of ova? (3 marks)

Sample test questions 2

1. Look at the diagram above:Sperms A and B carry different sex chromosomes:A has an X chromosome B has a Y chromosome

(a) What sex chromosome will the ovum contain? X (1 mark)

(b) If sperm A fertilises the ovum, what sex will the baby be? female (1 mark)

(c) What is the total number of chromosomes in sperm B? 23 (1 mark)

(d) As far as the sex chromosomes are concerned, why are there 2 sorts of sperms, but only one type of ova? Females are XX, so can only give the ovum an X chromosome. Males are XY, so will produce 2 types of sperm – half will have the X and half the Y (3 marks)