6.6 Hormones, Homeostasis and Reproduction

Question 1

How does the pancreas work?

Answer 1

The pancreas is effectively two glands in one organ. Most of the pancreas is exocrine glandular tissue that secretes digestive enzymes into ducts leading to the small intestine. There are small regions of endocrine tissue called islets of Langerhans dotted through the pancreas that secrete hormones directly into the blood stream. The two cell types in the islets of Langhans secrete different hormones:

• Alpha cells synthesise and secrete glucagon if the blood glucose level falls below the set point. The hormone stimulates the break down of glycogen into glucose in liver cells and its release into the blood, increasing the concentration.
• Beta cells synthesise insulin and secrete it into the blood when the concentration of glucose is too high. It stimulates the uptake of glucose of various tissues.

Question 2

Where is insulin produced?

Answer 2

beta cells of the pancreas

Question 3

Where is glucagon produced?

Answer 3

Alpha cells of the pancreas

Question 4

What is diabetes?

Answer 4

A condition where a person has consistently elevated blood glucose levels, leading to the presence of glucose in the urine. It impairs water re-absorption and therefore leads to dehydration and damage of tissues.

Question 5

What are the two types of diabetes?

Answer 5

Type 1 - an inability to produce insulin so you cannot store glucose. It results from a destruction of the beta cells in the pancreas.

TREATMENT - injections of insulin when blood glucose is about to get high.

Type 2 - characterised by an inability to process or respond to insulin because of a deficiency of insulin receptors or glucose transporters on target cells.

TREATMENT - adjusting diet, little and often, high fibre, more exercise.

Question 6

What is thyroxin?

Answer 6

Thyroxin is secreted by the thyroid gland (in neck) to regulate the metabolic rate and help control body temperature. A major component of it is iodine and so if you are iodine deficient that may give you a problem with thyroxin.
If your body is cold, thyroxin will increase in your body, increasing metabolic rate and producing heat for you.

Question 7

Problems with lack of thyroxin?

Answer 7

• Lack of energy (metabolism too slow)
• Feeling cold
• Forgetfulness and depression
• Weight gain (as less respiration happening)
• Constipation because less contractions in the gut.

Question 8

What is leptin?

Answer 8

Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.
If adipose tissue increases then it releases leptin to stop the person feeling hungry and acts of the hypothalamus to inhibit appetite.

However if you are really fat and have really really high levels of leptin your brain may become resistant to it, and so injecting it may not help. This however is only a small number and caused by mutations in genes. Leptin has also been shown to negatively affect the reproductive system so injections are not suitable in children and young adults.

Question 9

What is melatonin?

Answer 9

Melatonin is secreted by the pineal gland to control circadian rhythms.
It is controlled by the hypothalamus and the concentration of melatonin increases in the evening, and drops to a low level at dawn as the hormone is removed from the blood by the liver, blood concentrations rise and fall rapidly in response to these changes in secretion.
A special type of ganglion cell in the eye detects light and passes impulses to cells in the SCN. This indicates the timings of dawn and dusk so the cycle can adjust.

Question 10

How can melatonin be used artificially?

Answer 10

If it is taken when you would normally sleep it can help solve jet lag.

Question 11

How is sex determined in males?

Answer 11

If the gene SRY is present, the embryonic gonads develop into testes. This gene is located on the Y chromosome, so it is only present in 50% of embryos. SRY codes for a DNA-binding protein called TDF (testis determining factor). TDF stimulates the expression of other genes that cause testis development.

Question 12

What is testosterone?

Answer 12

Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.

Question 13

How is sex determined in females?

Answer 13

Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty.
The embryonic gonads develop into ovaries as there is not SRY. Progesterone and oestrogen are always present in pregnancy. At first they are secreted by the mother’s ovaries and then later by the placenta.

Question 14

DIAGRAM OF FEMALE AND MALE REPRODUCTIVE SYSTEMS

Answer 14

NEED TO DO

Question 15

What do the testis do?

Answer 15

Produce sperm and testosterone

Question 16

What does the scrotum do?

Answer 16

Hold testes at lower than body temperature

Question 17

What does the epididymus do?

Answer 17

Store sperm till ejaculation

Question 18

What does the sperm duct do?

Answer 18

Transfer sperm during ejaculation

Question 19

What does the seminal vesicle and prostate gland do?

Answer 19

Secrete fluid containing alkali, proteins and fructose that is added to sperm to make semen.

Question 20

What does the urethra do?

Answer 20

Transfer semen during ejaculation and urine during urination

Question 21

What does the penis do?

Answer 21

Penetrate the vagina for ejaculation of semen near cervix

Question 22

What does the ovary do?

Answer 22

Produce eggs, oestrogen and progesterone

Question 23

What does the oviduct do?

Answer 23

Collect eggs at ovulation, provide a site for fertilisation and then move the embryo into the uterus.

Question 24

What does the uterus do?

Answer 24

Provide for the needs of the embryo and then foetus during pregnancy.

Question 25

What does the cervix do?

Answer 25

Protect the foetus during pregnancy and then dilute to provide the birth canal.

Question 26

What does the Vagina do?

Answer 26

Stimulate penis to cause ejaculation and provide a birth canal

Question 27

What does the Vulva do?

Answer 27

Protect internal parts of the female reproductive system.

Question 28

What is the follicular phase of the menstrual cycle?

Answer 28

The first half because a group of follicles is developing in the ovary. In each follicle an egg is stimulated to grow. At the same time the lining of the uterus (endometrium) is repaired and starts to thicken. The most developed follicle breaks open, releasing its egg into the oviduct. The other follicles degenerate.

Question 29

What is the luteal phase of the menstrual cycle?

Answer 29

The second half of the cycle is called the luteal phase because the wall of the follicle that released an egg becomes a body called the corpus luteum. Continued development of the endometrium prepares it for the implantation of an embryo. If fertilisation does not occur the corpus luteum in the ovary breaks down and is shed during menstruation.

Question 30

How is FSH produced?

Answer 30

By the pituitary gland - it is a protein hormone

Question 31

How is LH produced?

Answer 31

By the pituitary gland - it is a protein

Question 32

Where does FSH go?

Answer 32

Binds to FSH receptors in the membranes of follicle cells

Question 33

Where does LH go?

Answer 33

Binds to LH receptors in the membranes of the follicle cells.

Question 34

Where is oestrogen produced?

Answer 34

ovarian hormones produced by the fall of the follicle and the corpus luteum.

Question 35

Where is progesterone produced?

Answer 35

ovarian hormones produced by the wall of the follicle and the corpus luteum.

Question 36

How does the menstrual cycle work?

Answer 36

1. FSH rises to a peak towards the end of the menstrual cycle and stimulates the development of follicles, each containing an oocyte and follicular fluid. FSH stimulates the secretion of oestrogen by the follicle wall.
2. Estrogen rises to a peak towards the end of the follicular phase. It stimulates the repair and thickening of the endometrium after mensuration and an increase in the FSH receptors that make the follicles more receptive to FSH boosting oestrogen production even more. When it reaches him levels oestrogen inhibits the secretion of FSH and stimulates LH secretion.
3. LH rises to a sudden and sharp peak towards the end of the follicular phase. It stimulates the completion of meiosis in the oocyte and partial digestion of the follicle wall allowing it to burst open at ovulation. LH also promotes the development of the follicle after ovulation into the corpus luteum which secretes estrogen and progesterone.
4. Progesterone levels start to rise at the start of the luteal phase reach a peak and then drop back to a low level by the end of this phase. Progesterone promotes the thickening and maintenance of the endometrium. It also inhibits FSH and LH secretion by the pituitary gland.

Question 37

What is IVF?

Answer 37

Outside the body fertilisation
The woman takes a drug each day to stop FSH and LH production, and because FSH makes oestrogen secreted and LH makes progesterone secreted they are all stopped. This means the doctors can control it
The woman is then injected with FSH and LH and this stimulates follicles to develop. They inject much more FSH than normal and so more follicles develop. This is why it is called super-ovulation. Then when the follicles have grown big enough another injection of HCG, another hormone that is normally secreted by the embryo. A pipette is used to wash eggs out of the follicles, each egg is then mixed with 50,000 sperm cells and incubated. It is then implanted back in.