GCSE Biology- Reproductive Hormones and Negative Feedback

Primary Sexual Characteristics

The presence of male or female sex organs

What controls the development of secondary sexual characteristics in males?

Testosterone (secreted from testes)

What controls the development of secondary sexual characteristics in females?

Oestrogen (secreted by ovaries)

When do secondary sexual characteristics develop?

During Puberty

Function of Testes

Make sperm and testosterone

Function of Sperm Ducts

Carries sperm towards the penis

Function of Seminal Vesicle

Secretes alkaline fluid and nutrients

Function of Prostate Gland

Adds more fluid and nutrients to sperm to form semen

Function of Urethra (males)

Passes semen containing sperm to the penis

Function of penis

Becomes erect during arousal to enter the vagina and deliver semen

Function of Ovaries

Makes eggs, also secretes oestrogen and progesterone

Function of Oviducts (Fallopian Tubes)

Moves the egg towards the uterus, lined with cilia

Uterus

Muscular organ that both stretches exponentially to accommodate a growing foetus and contracts to push a baby out during childbirth.

Cervix

Ring of muscle at bottom of uterus, holds baby in place during pregnancy and dilates to allow childbirth.

Vagina

Receives the penis during sexual intercourse, holds the sperm until they pass into the uterus

Where are ova (eggs) made?

in the ovaries

Where is sperm made?

In the testes

What type of nucleus do sperm and egg cells have?

Haploid

Why do egg cells have haploid nuclei and vice versa?

Because the sperm cell has the other half of the genetic information

What does the acrosome contain and why?

Contains digestive enzymes to break down the walls of the egg cell

Why do sperm cells have so many mitochondria?

To release lots of energy so it can swim

How many chromosomes are in a haploid cell?

23

How many chromosomes are in a diploid cell?

46 chromosomes in 23 pairs

What is a fertilised egg called?

Zygote

Key functions of the menstrual cycle:

Co-ordinates the release of one egg per month from the ovary, stops the egg release if fertilisation occurs, provide a suitable environment for embryo development if fertilisation occurs.

Where is FSH made?

Pituitary Gland

What is the function of FSH?

Stimulates one egg cell to mature, stimulates ovaries to produce oestrogen

Where is oestrogen made?

Ovaries

What is the function of oestrogen?

Stimulates repairing and thickening of uterus wall, inhibits FSH production, stimulates release of LH

Where is LH made?

Pituitary Gland

What is the function of LH?

Stimulates ovulation, controls growth of corpus luteum

Corpus Luteum

empty egg follicle in ovaries

Where is progesterone made?

Corpus luteum

What is the function of progesterone?

Maintains uterus lining, inhibits FSH and LH (stops eggs maturing and ovulating)

What happens at the start of the menstrual cycle?

Uterine lining sheds, FSH increases and causes ovum to start developing, FSH stimulates oestrogen production, and oestrogen rises until ovulation

What happens during ovulation?

Oestrogen inhibits FSH production and stimulates LH, which causes ovulation to occur. Progesterone then maintains uterine lining and inhibits maturing of the egg by stopping LH and FSH.

Why is the pituitary gland known as the master gland?

Because it produces several hormones which act on other glands to stimulate release of other hormones.

Where is TSH produced?

Pituitary gland.

What is the function of TSH?

To stimulate the thyroid to make thyroxine

Negative Feedback

A process that reverses a change in the internal environment in order to maintain a steady, optimal state in the body

Where is adrenaline secreted from?

Adrenal Glands

What are adrenaline’s target organs?

Heart, Liver, Eyes, Brain, Lungs, Digestive System

What are the functions of adrenaline?

Increase HR and BR, convert glycogen in liver to glucose for respiration, dilate pupils to let in more light, decrease mental awareness, divert blood away from digestive system to big muscles and limbs

Where is thyroxine secreted from?

Thyroid gland

What are thyroxine’s target organs?

Cells all over the body

What are the functions of thyroxine?

Controls basal metabolic rate (how quickly substances are broken down and built up, and how much oxygen tissues use)

How are the effects of adrenaline also an example of negative feedback?

Because the mechanisms are switched off when the danger is gone, if they weren’t your body would be in a state of constant anxiety.

Why is it important that negative feedback occurs?

It is crucial to maintain a stable internal environment (homeostasis)

Why may people have difficulty conceiving?

Lack of female hormones, damaged oviducts, lack of sperm in semen, age, obesity, eating disorders

What does IVF stand for?

In-Vitro Fertilisation

What does IVF do?

Allows people who can’t get pregnant by having sex the change to have a baby (e.g. same sex couples)

How expensive is IVF?

Expensive for NHS and individuals

Ethical Concerns of IVF

Destruction of unused embryos, designer babies, using embryos for research/stem cells, religious views on moral status of embryos

Step 1- IVF

Fertility drugs are used to make lots of eggs mature at the same time for collection from the ovary.

Step 2- IVF

The eggs are collected and placed in a special solution in a petri dish

Step 3- IVF

A sample of semen is collected and the sperm and eggs are mixed in the petri dish

Step 4- IVF

The eggs are checked to make sure they have been ferilised and the embryos are developing properly

Step 5- IVF

When the fertilised eggs have formed tiny balls of cells, 1 or 2 of the tiny embryos are placed in the mother’s uterus. Then, if all goes well, at least 1 baby will grow and develop

How does artificial FSH work?

Artificial FSH stimulates eggs in the ovaries to mature, which triggers oestrogen production

How does artificial LH work?

Artificial LH can be used to trigger ovulation

Advantages of contraceptive injections

Lasts 12 weeks, slow release of progesterone

Advantages of contraceptive implant

Lasts up to 3 years, slow release of progesterone, 99.95% effective

What hormones are in the contraceptive patch?

Oestrogen and Progesterone

Advantage of contraceptive patch

Hormones absorbed directly into blood

Disadvantages of contraceptive patch

must be replaced every seven days

Advantages of condoms

Prevents sperm reaching egg, no side effects, protection against some STDs

Disadvantages of condoms

Easily damaged

What does a diaphragm/cap do?

prevents sperm entry

Disadvantages of diaphragm/cap

needs to be fitted by a doctor initially, needs to be positioned correctly, lets sperm through if fitted incorrectly

What does an IUD do?

Prevents implantation of an embryo

Advantages of IUD

lasts for 3-5 years

Disadvantages of IUD

Must be fitted by a doctor each time

What do oral contraceptives do?

Makes sure no eggs mature by inhibiting FSH

Disadvantages of oral contraceptives

Need to be taken regularly, can cause raised blood pressure

What do spermicidal agents do?

Kill or disable sperm

Disadvantages of Spermicidal Agents

Ethical Concerns

Abstinence

If people do not have sex, they will not get pregnant. A rhythm method is sometimes used.

Disadvantages of abstinence and rhythm method

rhythm method can sometimes be unreliable

Vasectomy (males)

When sperm ducts are cut or tied, preventing sperm from entering semen.

Vasectomy (females)

When oviducts are cut or tied, preventing eggs from reaching the uterus

Disadvantages of Vasectomies

Permanent and require surgery