SB7: Animal Coordination, Control and Homeostasis

Question 1

SB7a
1) State where hormones are produced (in endocrine glands).
2) Describe the general role of hormones in the body.
3) Describe how hormones are transported around the body.
4) What is the endocrine system?

Answer 1

1) Hormones are produced in: the thyroid, adrenal, ovaries, testes and pancreas.
2) A hormone is a chemical substance, produced by a gland and carried in the bloodstream, which alters the activity of specific target organs.
Hormones can control the body, and the effects are much slower than the nervous system, but they last for longer.
3) Hormones are transported around the body in the bloodstream, more specifically in the blood plasma.
4) The endocrine system secretes hormones into the bloodstream from glands throughout the body. Hormones travel in the blood stream to specific target organs, where they have an effect.

Question 2

SB7a
1) Describe the production and release of some common hormones from their endocrine glands (pituitary gland, thyroid gland, pancreas, adrenal glands, ovaries and testes).
2) Identify the target organs of some common hormones (ADH, Adrenaline, and insulin)
3) In what ways does the endocrine system differ from the nervous system?

Answer 2

1) The pituitary gland: produces lots of hormones that regulate the conditions within the body. This releases hormones that tells the other glands when to release hormones. This is why it is known as the master gland.
The Thyroid: This produces thyroxine, which helps to control the rate of metabolism, temperature and heart rate.
The Pancreas: This produces a chemical called insulin which regulates blood glucose levels.
The adrenal gland: This gland produces adrenaline, which helps to prepare the body and mind for fight or flight responses.
The ovaries (in females): These produce oestrogen which help to control the menstrual cycle in women.
The testes (in males): These produce testosterone which help to control sperm production.
2) The target organ of insulin is the liver.
Adrenaline targets several organs including organs in the respiratory and circulatory systems, such as the liver, heart and muscle cells.
ADH (anti-diuretic hormone) which comes from the pituitary gland has the target organ of the kidneys.
3) The endocrine system uses hormones rather than electrical impulses. In the endocrine system messages travel via the blood rather than via neurones. The effects of the endocrine system last longer.

Question 3

SB7b
1) Describe the effects of adrenalin on the body.
2) Explain how adrenalin prepares the body for fight or flight.
3) Define metabolic rate.

Answer 3

1) The adrenal glands release the hormone adrenaline. Adrenaline increases your heart rate, increases blood pressure, increases blood flow to the muscles and increases the blood glucose level.
The adrenal glands increase blood glucose levels by releasing adrenaline which binds to the receptors in the liver. This causes the liver cells to convert glycogen into glucose, and then release the glucose into the bloodstream.
2) Adrenaline targets vital organs, increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.
3) The metabolic rate is the amount of energy used by an organism within a given time period.

Question 4

SB7b
1) Describe the effect of thyroxine on metabolic rate.
2) Describe how a negative feedback mechanism works.

Answer 4

1) The more thyroxine that is produced the higher the metabolic rate is.
2) A negative feedback control system responds when conditions change from the ideal or set point and returns conditions to this set point. There is a continuous cycle of events in negative feedback. In general this works by: if the level of something rises, control systems reduce it again, and if the level of something falls, control systems raise it again.

Question 5

SB7b
1) Explain how negative feedback controls the production of thyroxine.
2) Explain why negative feedback mechanisms are important in living organisms.

Answer 5

1) Thyroxine levels are controlled due to negative feedback. The hypothalamus, pituitary gland and thyroid glands are involved in this.
When thyroxine levels are low:
Low levels of thyroxine stimulate the hypothalamus to release Thyrotropin Releasing Hormone (TRH). The TRH causes the pituitary gland to release Thyroid Stimulating Hormone (TSH). The TSH travels in the blood and acts on the thyroid gland to produce thyroxine. Thyroxine levels increase. Thyroxine helps to regulate metabolic rate. Metabolism provides energy for movement.
When thyroxine levels are normal or high:
The thyroxine levels inhibit the release of TRH and the production of TSH, causing the thyroxine levels to decrease.
2) It is how the body keeps conditions within it constantly at the optimum level.

Question 6

SB7c
1) Describe what happens during the menstrual cycle.
2) Describe the function of oestrogen in the menstrual cycle.
3) Describe the function of progesterone in the menstrual cycle.

Answer 6

1) The menstrual cycles is approximately 28 days. Stage 1 is called menstruation, which is the period of bleeding caused by the breakdown of the uterus lining. Stage 2 is when the lining starts to build up to prepare for the fertilised egg. Stage 3 is called ovulation, which is when the eggs are released. Stage 4 is maintaining the lining of the uterus.
2) Oestrogen is produced by the ovary gland. The hormone that stimulates oestrogen production is the follicle-stimulating hormone (FSH). Oestrogen causes the uterus lining to thicken and grow.
3) Progesterone is produced by the corpus luterm. Progesterone maintains the uterus lining.

Question 7

SB7c
1) Explain how barrier methods can be used as contraception.
2) Explain how hormones can be used as contraception.

Answer 7

1) Barrier methods include a condom (for a male) and diaphragm (for a female). The barrier methods prevent a sperm from meeting an egg.
2) Chemical methods such as the birth control pill is the most effective method of contraception. The pill contains oestrogen and progesterone, which is used to tactically interfere with the release of an ovum from the ovary. It inhibits FSH production so that no eggs mature. However, there may be side effects such as: change in weight, blood pressure, mood, and levels of oestrogen. Additionally, it does not prevent STIs.

Question 8

SB7c
Compare, contrast and evaluate hormonal and barrier methods of contraception.

Answer 8

Advantages of barrier methods include:
- Some barrier methods (condoms) can protect gainst sexually transmitted infections (STIs), unlike hormonal methods.
- Barrier methods don’t have unpleasant side-effects, such as headaches or mood changes or acne, like hormonal methods can.
Advantages of hormonal methods include:
- Hormonal methods are generally more effective at preventing pregnancy than barrier methods when used correctly.
- Hormonal methods mean the couple don’t have to think about contraception each time they have intercourse, unlike with barrier methods.

Question 9

SB7d
1) Describe how changes in hormones affect the uterus wall, ovulation and menstruation.
2) Explain how oestrogen, progesterone, FSH and LH interact in the menstrual cycle.

Answer 9

1) The oestrogen causes growth and repair of the lining of the uterus wall. Oestrogen inhibits FSH. When oestrogen rises to a high enough level it causes a surge in LH from the pituitary which causes ovulation where an egg is released from the follicle (Day 14 of the cycle).
Progesterone maintains the uterus lining (the thickness of the uterus wall). If the egg has not been fertilised, progesterone levels drop. This causes menstruation, where the uterus lining breaks down - this is known as having a period.
2) Several hormones are involved in the menstrual cycle of a woman: follicle stimulating hormone (FSH) causes the maturation of an egg in the ovary. Luteinising hormone (LH) stimulates the release of the egg. Oestrogen is involved in repairing and thickening the uterus lining, progesterone maintains the uterine lining.
FSH stimulates the production of oestrogen. Oestrogen inhibits FSH, but oestrogen stimulates LH, which results in ovulation. Progesterone inhibits both LH and FSH.

Question 10

SB7d
1) State examples of Assisted Reproductive Technology (ART)
2) Explain how clomifene is used to stimulate ovulation.
3) Explain how hormones are used in IVF treatment.

Answer 10

1) Examples include IVF (in vitro fertilisation) and clomifene therapy.
2) Clomifine therapy is useful for women who rarely or never release an egg cell during their men’s trail cycle. Clomeifene is a drug that helps to increase the concentration of FSH and LH in the blood.
3) IVF (in vitro fertilisation) can overcome problems such as blocked oviducts in the woman, or if the man produces very few healthy sperm cells.
IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs. The eggs are collected from the mother and fertilised by sperm from the father in a dish in the laboratory (in vitro literally means ‘in glass’). The fertilised eggs develop into embryos.
Hormones are used to stimulate the production of eggs.

Question 11

SB7e
1) Define homeostasis.
2) Explain why a constant internal environment is important.
3) Explain the role of insulin in regulating blood glucose concentration.

Answer 11

1) Homeostasis means maintaining a constant internal environment.
2) Enzymes will only function properly under a small range of certain conditions, such as preferred pH and temperature. If any conditions are outside their specific range then the enzymes cannot function. This could cause the organism to die.
3) The pancreas monitors and controls blood glucose concentration by releasing the hormone insulin. The blood glucose concentration starts increasing as glucose (for example from food) is absorbed into the blood. The pancreas detects a high blood glucose concentration and secretes insulin. Insulin causes the blood glucose concentration to fall back to normal.

Question 12

SB7e
1) Explain the role of glucagon in regulating blood glucose concentration.
2) Explain how type 1 diabetes is caused.
3) Explain how type 1 diabetes can be controlled.

Answer 12

1) Glucagon increases the concentration of glucose in the blood because it causes glycogen stores in the liver and muscles to be converted to glucose, which is released into the blood.
2) Type 1 diabetics is where the pancreatic cells that should produce insulin do not. This is because the cells have been destroyed by the body’s immune system.
3) People with type 1 diabetics have to inject insulin into the fat layer below the skin, where it can enter the blood, causing blood glucose concentration to fall.

Question 13

SB7f
1) Explain how type 2 diabetes is caused.
2) Explain how type 2 diabetes can be controlled.

Answer 13

1) In type 2 diabetes the person’s body cells no longer respond to insulin produced by the pancreas.
2) Type 2 diabetes can be controlled by doing the following: eating a healthy diet, getting regular excercise, losing weight and taking medication or insulin injections.
Controlling your diet allows you to reduce the levels of carbohydrates or glucose in the diet. This ensures that the blood glucose levels do not rise too high too quickly, so that the insulin can cope.
Controlling your diet also allows you to reduce weight. This allows your body to produce more insulin, so that the cells respond to insulin.

Question 14

SB7f
1) Explain how BMI and waist : hip ratio are related to body mass.
2) Evaluate the correlation between body mass and type 2 diabetes.
3) What is the formula for BMI and the waist : hip ratio?

Answer 14

1) A patient’s mass and height may be measured to calculate their BMI. A BMI of over 30 is considered obese, and this is associated with an increased risk of developing type 2 diabetes.
A patient’s waist and hip circumference may be measured to calculate their waist to hip ratio. A high waist : hip ratio is associated with an increased risk of developing type 2 diabetes.
2) There is a correlation between rising levels of body mass in the general population and increasing levels of type 2 diabetes. Body fat affects the body’s ability to use insulin. Obesity is associated with an increased risk of developing type 2 diabetes.
3) BMI is calculated as: mass (kg) / ((height (m)) squared)
Waist:hip ratio is calculated by dividing your waist measurement (in cm) by your hip measurement (also in cm).

Question 15

SB7g
1) Define the term ‘thermoregulation’.
2) Explain the importance of thermoregulation in enzyme activity.
3) Explain the role of the skin in thermoregulation [blood flow in dermis, sweating and hair erection in epidermis].

Answer 15

1) Thermoregulation is the control of body temperature, which keeps the temperature of the major organs close to 37C most of the time.
2) It is important that the core body temperature remains around 37C so that enzymes can work effectively. 37C is the optimum temperature for enzymes in the human body. Above this temperature they may start to denature and below this temperature they slow down.
3) The dermis contain sweat glands which produce sweat. The epidermis contains pores to release the sweat onto the surface of the skin. When sweat evaporates from the surface of the skin, it transfers energy to the environment, which cools the body down.
When the temperature is high, hair erector muscles in the skin relax, causing hairs to lie flat. This stops them from forming an insulating layer by trapping air and allows air to circulate over skin and heat to leave by radiation.
Also, vasodilation happens, which is the increase in diameter of the skin arterioles to increase blood flow and increase heat loss by radiation.

Question 16

SP7g
1) Explain the role of the hypothalamus in thermoregulation.
2) Explain the role of muscles in raising low body temperature.
3) Explain the role of changing blood vessel diameter in thermoregulation.

Answer 16

1) Body temperature is monitored and controlled by the thermoregulatory centre in the hypothalamus, which is a structure within the brain.
2) If the body temperature is too low, shivering occurs, which is when muscles contract automatically. This generates heat, which transfers more energy to the body, increasing its temperature.
If the body temperature is too high, the hair erector muscles relax. If the body temperature is too low, hair erector muscles contract and skeletal muscles contract (shiver).
3) When the body is cold, vasoconstriction narrows the blood vessels’ diameter. This means that less blood flows near the surface of the skin, so less energy is transferred to the environment, which helps to keep the body warm.
When the body is warm, vasodilation widens the blood vessels’ diameter. This means that more blood flows near the surface of the skin, so more energy is transferred to the environment, which helps to cool the body down.

Question 17

SB7h
1) Describe the structure of the urinary system. What are the two key functions of the kidneys?
2) State how urea is formed.
3) Define the term ‘osmoregulation’.

Answer 17

1) Two key functions of the urinary system are: to filter waste products from the blood and expel it from the body as urine, and to control the water levels of the body (osmoregulation).
The urinary system consists of two kidneys (found at the back of the abdomen) joined to the bladder by two tubes called the ureters
Another tube, the urethra, carries urine from the bladder to outside the body.
Each kidney is also connected to: the renal artery which comes from the aorta and delivers oxygenated blood to the kidney.
The renal vein which delivers the deoxygenated blood from the kidney to the vena cava.
2) Urea is produced in the liver from the breakdown of excess amino acids.
3) Osmoregulation is a homeostatic process that controls the amount of water in body fluids (e.g. blood).

Question 18

SB7h
1) Describe how kidney failure is treated [kidney dialysis, organ donation]
2) Explain why osmoregulation is important.

Answer 18

1) In a dialysis machine, waste substances, excess ions and excess water are filtered out of the blood. The dialaysis fluid must have the same concentration of dissolved substances as healthy blood. This is so that useful substances won’t be lost from the person’s blood during dialysis. Dialysis is not a cure for kidney failure.
A cure for kidney failure is a kidney transplant. Reasons why someone may remain on dialysis include: they may have to wait a long time for a kidney donor with a tissue type that closely matches their own.
2) If the water concentration of the blood became too high, then water would move into the cells by osmosis, which would cause the cells to lyse (burst). If the water concentration of the blood became too low then water would move out of the cells by osmosis, which would cause the cells to shrink. Therefore, osmoregulation is needed to make sure that there is the correct concentration of water in the blood.

Question 19

SB7i
Describe the parts of a nephron.

Answer 19

a. Blood flows through a network of capillaries called a glomerulus, which runs inside the Bowman’s capsule of each nephron. The Bowman’s capsule and glomerulus are adapted to let very small molecules, such as water, urea and glucose, through into the nephron. Large molecules such as proteins, and blood cells, stay in the blood. This process is called ultrafiltration.
b. The filtration fluid flows along inside the nephron. Selective reabsorption of useful substances that the body needs occurs here. This includes glucose and some mineral ions. Reabsorption takes place as blood travels through the proximal convoluted tubal into the loop of Henle. These substances are pumped through proteins in the cell membranes in the first convoluted tubule of the nephron, by active transport. No glucose is normally left in urine.
c. Water is reabsorbed by osmosis, depending on how much the body needs. This happens in the loop of Henle and in the collecting duct.
d. At the end of the nephron the remaining fluid flows into the bladder. The fluid contains excess water that the body does not need, plus urea and other substances. It is now called urine. Urine production occurs in the collecting duct.

Question 20

SB7i
1) Explain how the structure of the nephron supports reabsorption of glucose.
2) Explain how the structure of the nephron supports reabsorption of water.
3) Explain the role of ADH in controlling body water content.

Answer 20

1) Glucose moves from the liquid in a nephron into the blood by the process of selective reabsorption. This takes place as the blood travels through the proximal convoluted tubal into the loop of Henle. When glucose moves from the nephron back into the blood, it moves against the concentration gradient. In a healthy person, all of the glucose that enters the nephron is reabsorbed into the blood.
2) These are the ways that the structure of the nephron supports reabsorption of water:
- There is a large surface area of contact between the nephron and capillaries.
- The cell membrane of the cells lining the first convoluted tubule has tiny folds called microvilli. These increase the surface area : volume ratio of the cells.
- Cells that have protein pumps in their cell membranes contain many mitochondria.
3) When the pituitary gland detects that there is too little water in the blood, it releases the hormone ADH (antidiuretic hormone). ADH changes the permeability of the collecting duct in nephrons and increases the concentration of the urine. If the collecting duct is permeable, water is absorbed by osmosis from the collecting duct back into the blood. When there is plenty of water in the blood, the pituitary gland stops releasing ADH.

Question 21

SB7i
1) State what urine contains.
2) Explain how the structure of the nephron allows filtration.

Answer 21

1) Urine contains water, urea and salts.
2) The blood is under high pressure at the start of the nephron, which aids the filtration of the blood.