Animal Coordination, Control and Homeostasis

Question 1

What is the endocrine system?

Answer 1

The endocrine system sends hormones (chemical messengers) around the body. When they reach a target tissue they produce a response. It is made up of glands which secrete hormones directly into the bloodstream.

Question 2

Explain the different hormones glands secrete

Answer 2

Pituitary gland – Secretes hormones into the blood to either have an effect on the body or act on other glands to stimulate them to produce different hormones.

Pancreas – Secretes insulin. Controls blood glucose levels

Thyroid – Secretes thyroxine. Controls metabolic rate (how quickly reactions occur), heart rate and temperature.

Adrenal gland – Secretes adrenalin. Involved in the ‘fight or flight’ response (the body’s response to stressful situations).

Ovary – Secretes oestrogen. Is involved in the menstrual cycle and the development of female secondary sexual characteristics.

Testes – Secretes testosterone. Is involved in the production of sperm and the development of male secondary characteristics.

Question 3

What are the aspects of the fight or flight response? (4)

Answer 3

Increased heart rate: this allows oxygen to reach the muscles more quickly, so we can move out of danger.

Increased blood pressure: same as above

Increased blood flow to muscles: blood vessels dilate (widen) to allow more blood to reach them. This allows them to contract with greater strength, and more quickly.

Increased blood sugar levels: the liver is stimulated to break down glycogen (a storage molecule) into glucose, which muscles can use to contract.

Question 4

Explain how thyroxine levels are kept balanced?

Answer 4

Thyroxine regulates metabolic rate. It is also important in growth and development.
Low levels of thyroxine, stimulate production of a hormone called TRH in the hypothalamus. TRH causes the release of TSH from the pituitary gland. TSH acts on the thyroid gland to produce thyroxine.
When the thyroxine levels have reached the normal level, thyroxine inhibits the release of TRH, which stops the production of TSH.
The levels of thyroxine are controlled by negative feedback.
When the levels increase, it is detected by receptors in the brain. This inhibits the release of TSH. This inhibits the release of thyroxine so levels of thyroxine fall.

Question 5

Explain the menstrual cycle

Answer 5

The menstrual cycle is the process the body undergoes each month to prepare for a potential pregnancy.

It begins with the lining of the uterus breaking down, and the women has her period. The layer then builds up again, until ovulation (day 14) occurs and an egg is released from the ovary and moves to the uterus via the fallopian tube.
If a fertilised egg has not been embedded in the lining after 28 days, it begins to break down and the cycle continues.

The events of the cycle are controlled by four hormones.

Question 6

Describe the stages of the menstrual cycle (4)

Answer 6

1. Follicle stimulating hormone (FSH)
   Causes the maturation of an egg in the ovary, within a structure called a follicle.
   Produced in the pituitary gland.
   Stimulates the ovaries to produce oestrogen.
2. Oestrogen
   Causes the lining of the uterus to grow again.
   Produced in the ovaries.
   Secreted as a result of FSH.
   Stimulates the production of LH and
   inhibits the results secretion of more FSH.
3. Luteinising hormone (LH)
   Produced in the pituitary gland.
   Produced as a result of oestrogen.
   Its release results in ovulation.
4. Progesterone
   Produced in the ovaries and secreted from the egg follicle.
   Maintains the lining of the uterus, and support of a pregnancy if the egg is fertilised.
   Inhibits the release of both FSH and LH.

Question 7

Describe some hormonal methods of contraception

Answer 7

The contraceptive pill must be taken regularly or the bodies own hormones will be released, leading to an egg maturing.

The mixed pill contains oestrogen and progesterone. This means the oestrogen levels are constantly high, inhibiting FSH so no egg matures. The lining also stops developing and the mucus in the cervix becomes thick so sperm cannot move through.

The contraceptive implant – releases a continuous amount of progesterone. This prevents the ovaries from releasing the egg, thickens the mucus in cervix so sperm cannot swim and stops fertilised eggs from embedding in the uterus. It lasts for 3 years.

The contraceptive injection – Is made up of progesterone. Same effect as the implant. lasts for 2-3 months.

The plastic intrauterine device (IUD) – Releases progesterone. Same effect as the implant. T-shaped, inserted into the uterus. Lasts for 5-10 years.

Question 8

Describe non-hormonal methods of contraception

Answer 8

Chemical methods involve spermicides. These kill or disable sperm, but are only 70% to 80% effective.

• Barrier methods include condoms and diaphragm’s:

Condoms are either worn over the penis or are placed inside the vagina. They prevent the individual from contracting sexually transmitted diseases.

A diaphragm is a plastic cup which is positioned over the cervix. It is used with spermicide.

The copper intrauterine device works by killing sperm in the uterus and stopping any fertilised embryos from implanting in the uterus lining.

Question 9

What are fertility drugs used for?

Answer 9

Fertility drugs are used to increase the chance of pregnancy.
The main hormones used are FSH and LH because they stimulate the maturation and release the egg and become pregnant naturally.

Another drug used is called clomiphene. This increases the amount if FSH and LH released from the hypothalamus, increasing the chance that a woman will ovulate.

Question 10

What is In Vitro Fertilisation (IVF)?

Answer 10

The individual is given FSH and LH to encourage the release and maturation of eggs. These are then extracted from the mother and fertilised in the lab using sperm. The fertilised eggs develop into embryos and then one or two are inserted in the uterus.

Question 11

Describe some cons to In Vitro Fertilisation (IVF)? (3)

Answer 11

1. Can be expensive if the process needs to be repeated.
2. Success rate for IVF is 26%.
3. Side reactions to the hormones.

Question 12

What is homeostasis?

Answer 12

Homeostasis is the maintenance of a constant internal environment. Homeostasis is important to maintain enzyme activity and cell functions – including growth, replication and controlled cell death.

In the human body, homeostasis controls: blood glucose concentration, body temperature and water levels.

Question 13

What happens if the temperature gets too high?

Answer 13

If temperature becomes too high:

o Sweat (evaporates from skin surface resulting in increased energy transfer away from body)is produced from sweat glands, located in the dermis layer of the skin. The sweat is released onto the surface of the epidermis.
o Vasodilation means more blood flows closer to the surface of the skin, resulting in increased energy transfer from the body.

Question 14

What is thermoregulation?

Answer 14

Thermoregulation is the act of keeping internal body temperature constant This is important because if the temperature exceeds the optimum level of 37 degrees Celsius, enzymes will gradually become less effective and eventually denature.

The thermoregulatory centre which monitors and controls body temperature is found in the hypothalamus of the brain.
o Has receptors that monitor the temperature of the blood
o Has receptors in the skin that send impulses to the thermoregulatory centre

Question 15

What happens if temperature gets too low?

Answer 15

If temperature decreases too much:
o Sweating stops
o Skeletal muscles contract rapidly (shivering) to generate heat from respiration.
o Hairs strand on end to create an insulating layer, trapping warm air in.
o Vasoconstriction means blood does not flow close to the surface, resulting in less heat lost.

Question 16

What is osmoregulation?

Answer 16

Osmoregulation is the act of keeping the concentration of the blood at a constant level. If the blood becomes too dilute, water will move into cells by osmosis, and they will swell eventually busting under the pressure.

If the blood becomes too concentrated, water will move out of cells, and they will shrink. In either case they cannot perform their function, so it is vital that the blood remains the same concentration via osmoregulation.

Question 17

What happens if blood glucose levels are too high?

Answer 17

If glucose levels are too high, the pancreas produces the hormone insulin. Insulin binds to cell in target organs (muscles and liver) causing:

o Glucose to move from the blood into muscle cells for respiration.
o Excess glucose to be converted into glycogen which is stored in the liver.
The blood glucose concentration is reduced.

Question 18

What happens if blood glucose level decreases?

Answer 18

Exercise uses glucose for respiration and therefore there is less in the blood.

If glucose levels decrease, the pancreas produces the hormone glucagon. Glucagon binds to the liver cells causing glycogen to be broken down into glucose. Glucose is released into the blood, increasing the blood glucose concentration.
Blood glucose concentration is kept constant through using these two hormones. They work in a negative feedback.

Question 19

What is type 1 diabetes?

Answer 19

Type 1 diabetes: the pancreas cannot produce enough insulin. This condition is congenital (usually from birth/a young age).
o Blood glucose level can rise to a fatal amount.
o Glucose is excreted with urine.
o Treated with insulin injections at mealtimes, resulting in glucose being taken up from the bloodstream.
o Advised to limit the intake of simply carbohydrates which contains lots of glucose.

Question 20

What is type 2 diabetes?

Answer 20

Type 2 diabetes: the body cells no longer respond to insulin. This condition usually occurs later in life.
o Blood glucose levels can rise to a fatal amount.
o Obesity is a risk factor for this disease.
o Treatments include reducing the number of simple carbohydrates in diet, losing weight and increasing exercise.

Question 21

Describe what the urinary system does and the route that blood takes to be purified

Answer 21

The Urinary system is the bodily system that removes impurities and waste products from our blood.

The route that blood takes to be purified:

o Blood containing impurities travels in the renal artery to the kidneys.
o The kidneys regulate the levels of salt, ions and urea (produced from the breakdown of excess amino acids in the liver) in the blood. Any excess is sent to the ureter for excretion, and eventually the bladder.
o The purified blood returns to the circulation by way of the renal vein.

Question 22

Describe the function and structure of the nephron (3)

Answer 22

1. Filtration – Occurs in the glomerulus, a collection of capillaries at the start of the nephron. Urea, water, ions and glucose are small enough to pass out of the capillaries into the Bowman’s capsule however proteins and cells are too large and remain in the blood.
2. Selective reabsorption of glucose and ions – The substances in the Bowman’s capsule move into the tubule. At a point called the proximal convoluted tubule as much glucose as was lost during filtration is selectively reabsorbed in the blood.
3. Reabsorption of water and ions – Water and ions are absorbed at the Loop of Henle and collecting duct areas of the tubule. This process is tightly controlled according to the osmotic pressure of the blood.

Question 23

Describe the ADH hormone

Answer 23

ADH is a hormone produced from the pituitary gland and released into the bloodstream and travels from the brain to the kidney. It has special effects on the collecting duct of the nephron that relate to the water potential of the blood.

o If water potential of the blood is too high, less ADH is released from the pituitary gland and the collecting duct becomes less permeable to water. This leads to more water being released in urination.

o If water potential of the blood is too low, more ADH is released from the pituitary gland and the collecting duct becomes more permeable to water. This leads to less water remaining in the tubule and more entering blood vessels surrounding the tubule. Less water I released in urination.

Question 24

Treatments for kidney failure: Dialysis

Answer 24

o Type of therapy where a machine outside of the body filters out urea and other waste substances and reabsorbing sugar, water etc.

o Blood is taken from a vessel in the arm and is mixed with an anticoagulant to prevent the blood clotting and clogging up the machine.

o The machine contains dialysis fluid, which is separated from blood via a partially permeable membrane (allows some things to travel across it, but not others).

o Dialysis fluid contains a similar level of glucose and ions as is found in the blood, which means these substances remains in the blood and return to the body.

o Dialysis fluid contains no urea; therefore, urea diffuses out of the blood into the dialysis fluid down a concentration gradient.

Question 25

Treatments for kidney failure: Transplant

Answer 25

o Less restrictive than a dialysis machine, as regular visits are not required.

o A risk of rejection of the donor kidney, which occurs if specific antigens on the kidney cells do not match those of the host.

o Immunosuppressive drugs – they suppress the immune system and must be taken for the rest of the patient’s life. Prevent an immune rejection from occurring, but they also cause the immune system to be weak against pathogens.