Topic 7 - Animal Coordination, Control and Homeostasis

Question 1

7.1 - What are hormones?

Answer 1

It is part of the response system called the hormonal system, which uses chemical messenger called hormones.
These hormones are carried through the blood, so take time to reach body parts.
Hormones are released by endocrine glands such as the pituitary and the thyroid gland.

Question 2

7.1 - Where are different hormones produced?

Answer 2

The pituitary gland releases hormones such as FSH, LH, ACTH and growth hormone.
The thyroid gland produces thyroxine.
Pancreas have cells that produce insulin and some that produce glucagon.
The ovaries produce the sex hormones oestrogen and progestrone.
The adrenal glands release adrenalin.
The testes release the sex hormone testosterone.

Question 3

7.1 - What are target organs?

Answer 3

An organ affected by a specific hormone is a target organ.
Different organs can be a target organ of the same hormone.
Hormones change what the target organ does. ( Growth hormone stimulates cells to divide )
Some endocrine glands are target organs for other hormones.
For example, oestrogen released by the the ovaries can stimulate the pituitary gland to produce growth hormone.
As there is an increase in sex hormones during puberty, growth increases. This is why puberty increases growth rate.

Question 4

7.2 - What is adrenalin and its target organs?

Answer 4

Adrenalin is a hormone released from the adrenal glands.
In frightening or exciting situations, there are more impulses from neurones in the spinal cord to the adrenal glands, which releases large amounts of adrenalin.
Adrenalin has many target organs, this includes the liver, where glycogen ( storage of glucose in polymers ) is broken down into glucose which is released into blood to provide additional glucose for respiration.
Together, all the effects prepare the body for the fight or flight response.

Question 5

7.2 - What are the effects of adrenalin on its target organs?

Answer 5

Heart muscle cells contract more rapidly, which increases heart rate and leads to higher blood pressure.
Diameter of blood vessels leading to muscles widen, increasing blood flow to muscles.
Diameter of blood vessels leading to other organs narrow, reducing blood flow to those organs and increasing blood pressure.
Liver cells convert glycogen to glucose and it is released into the blood, increasing blood sugar concentration.
This prepares the body for the fight or fight response.

Question 6

7.3 - What is metabolic rate and resting metabolic rate and what affects it?

Answer 6

Metabolic rate is the rate at which energy in food is transferred through chemical reactions to keep the body alive.
Resting metabolic rate is measured with a person at rest, in a warm room and long after the person has eaten.
Thyroxine affects metabolic rate, released from the thyroid gland.
This is because when absorbed by cells, it causes heart cells to contract more rapidly and increase the rate of breakdown of proteins and carbohydrates in cells.

Question 7

7.3 - What is negative feedback?

Answer 7

The amount of thyroxine produced by the thyroid gland is controlled by the hypothalamus that releases TRH and the pituitary gland which releases TSH.

A decrease in thyroxine concentration causes the hypothalamus to send signals to the pituitary gland to release TSH into the bloodstream.
TSH signals the thyroid gland to release more thyroxine into the blood.
The increase in thyroxine is detected by the hypothalamus, preventing the release of TSH from the pituitary gland.

An increase in thyroxine concentration causes the hypothalamus to release TRH into the bloodstream.
TRH signals the thyroid gland to release less thyroxine into the blood.
The decrease in thyroxine is detected by the hypothalamus, which then triggers TSH again to increase the thyroxine concentration in blood.
This is the negative feedback cycle.

Question 8

7.4 - What is the menstrual cycle?

Answer 8

The menstrual cycle is a cycle of changes in a woman’s reproductive system, lasting 28 days.
The cycle prepares the woman’s body for the fertilisation of an egg cell and continues from puberty at 12 to menopause at 50.

Question 9

7.4 - What are the stages of the menstrual cycle?

Answer 9

Days 1-5 - Menstruation happens, this is when the uterus lining breaks down and is lost with an unfertilised egg cell.
Days 6-12 - Menstruation ends and the uterus lining starts to thicken again.
Days 13-15 - Ovulation happens, this is when the ovary releases the egg.
Days 16-28 - Fertilisation and pregnancy is more likely as the uterus lining continues to thicken and the egg travels along the oviduct to the uterus.
The cycle starts again.

Question 10

7.4 - What are the roles of the hormones oestrogen and progestrone in the menstrual cycle?

Answer 10

As the concentration of oestrogen in the blood increases the uterus wall thins.
As the concentration of progesterone in the blood increases the uterus wall thickens.
Oestrogen concentration is highest between days 10 to 22, causing the uterus lining to grow again.
Progesterone concentration is highest between 16-28, maintaining the lining of the uterus and supports a pregnancy if egg is fertilized.

Question 11

7.5 - Explain the interactions of oestrogen, progesterone, FSH and LH

Answer 11

FSH ( follicle-stimulating hormone ) and LH ( lutenising hormone ) are released from the pituitary gland.
FSH stimulates growth and maturation of egg follicle, these maturing follicles stimulate oestrogen production.
LH surge triggers ovulation, when the egg follicle becomes the corpus luteum, which releases progesterone.
When oestrogen and progesterone fall at the cycle’s end this triggers menstruation.
Low levels of progesterone allow FSH to be released.
High levels of oestrogen release more LH

Question 12

7.6 - How does hormonal contraception influence the menstrual cycle and prevent pregnancy?

Answer 12

Contraception is the prevention of fertilisation.
Hormonal contraception uses a progesterone-like hormone to inhibit FSH and LH from being produced.
This prevents the fall of hormone concentration at the end of the cycle.

Question 13

7.7 - Evaluate hormonal and barrier methods of contraception

Answer 13

Male condom - placed over penis and prevents sperm entering vagina.
Diaphragm - placed over cervix to prevent sperm entering the uterus.
Hormone pill - Releases hormones to prevent ovulation and thickens mucus at cervix, making sperm hard to pass through.

Abstaining from intercourse can ensure the egg isn’t fertilised.
Condoms and diaphragms can tear and let sperm through.
Hormone pill can lead to mood swings and depression.

Question 14

7.8 - Explain the use hormones in ART including IVF and clomifene therapy

Answer 14

Problems with conception can be overcome using ART ( Assisted Reproductive Technology ) , which uses hormones and other techniques to increase likelihood of pregnancy.
Clomifene therapy is used in women who rarely or never release egg cells during their menstrual cycles. Clomifene is a drug used to help increase concentration of FSH and LH in the blood.
Another ART technique is IVF ( in vitro fertilisation ). This can overcome problems like blocked oviducts or if the make produces few healthy sperm cells.

Question 15

7.8 - Explain how IVF is carried out

Answer 15

Egg follicle maturation stimulated by hormones.
Egg cells released and taken from the ovary.
This is combined with sperm cells from the man on petri dishes.
One or two healthy embryos are placed in the uterus.

Question 16

7.9 - What is homestasis?

Answer 16

Maintaining a constant internal environment in response to internal and external change.
Examples of homeostasis in the body include temperature control and control of water content.

Question 17

7.10B - Explain the importance of homeostasis via thermoregulation and osmoregulation

Answer 17

Thermoregulation is the control of the body temperature, keeping the temperature of major organs at 37°C.
A temperature above 38°C is a fever.
A temperature below 36°C causes hypothermia.
Both of these affect how well enzyme work in the body to catalyse reactions.

Osmoregulation is the control of the balance of water and mineral salts in the body.
If this balance is wrong then cells may take in or lose too much water by osmosis.
This imbalance can damage cells as water is needed for molecules to move for reactions and to maintain the cell shape.

Question 18

7.11B - How does thermoregulation take place when the body is hot?

Answer 18

The hypothalamus is a small part of the brain that constantly monitors temperature.
It can detect temperature changes in the brain and blood by receiving information from temperature receptors in the dermis of the skin.

If the body temperature exceeds 37°C, the hypothalamus detects this and the sweat gland secretes sweat.
Sweat spreads out as a thin layer over the epidermis, it then evaporates, transferring energy from the skin to the surroundings, cooling the skin.
The hypothalamus also increases blood flow near to the skin surface transferring the energy from blood to the surroundings, cooling the skin.
Erector muscles are relaxed so hair is flat.

Question 19

7.11B - How does thermoregulation take place when the body is cold?

Answer 19

If the hypothalamus detect blood or brain temperatures below 37°C it causes changes in the body. Temperature receptors on the epidermis gives these signals to the hypothalamus that cause the changes in the body.

Shivering happens, where muscles contract and relax rapidly, some of the energy from cell respiration of muscles are used as heat energy for the body.

Contraction of erector muscles in the dermis of the skin lead to body hairs standing upright. This is less effective in humans but in mammals, it traps air next to the skin for insulation.

There is also a reduction in the blood flow near the skin, keeping the warm blood deeper in the body. This reduces energy transfer of heat to the air.

Question 20

7.11B - How does thermoregulation happen via the changes in blood flow near the skin?

Answer 20

When it is cold, the hypothalamus sends nerve impulses to blood vessels deep in the skin, making them narrow, this is vasoconstriction.
This reduces blood flow near the skins surface and energy transfers to the air.
When it is hot, the hypothalamus causes blood vessels to widen, this is vasodilation.
This increases blood flow through blood vessels, bringing warm blood nearer to the skins surface and increases energy transfers to the surrounding, cooling the body.

Question 21

7.13 - How does insulin control blood glucose concentration?

Answer 21

When food is digested, glucose is released from carbohydrates.
This is absorbed from the small intestine into the blood and then into cells where it is used during respiration.
Cells take time to take in glucose released by digestion meaning there is a risk that glucose can reach high concentration in blood.
High blood glucose levels can lead to damaged organs, however, this doesn’t happen in most people as the blood glucose levels are controlled.

As blood glucose rises, it stimulates cells in the pancreas to release insulin.
Insulin causes cells in the liver and other organs to take in glucose and store it as glycogen, decreasing its concentration back to normal levels.

Question 22

7.14 - Explain how blood glucose concentration is regulated by glucagon

Answer 22

If blood glucose concentration falls too low, glucagon is released from other pancreatic cells.
Glucagon causes liver cells to convert glycogen back into glucose, which is released into the blood.
As blood glucose concentration increases, the amount of glucagon released from the pancreas falls.

Question 23

7.15 - Explain the cause of type 1 diabetes and how it is controlled

Answer 23

Type 1 diabetes is when pancreatic cells that should produce insulin do not.
This is due to the body’s immune system destroying these cells, this means they cannot control their blood glucose levels.
When blood glucose concentration is high, glucose is detected urine, this is the first test for type 1 diabetes.

Question 24

7.16 - Explain the cause of type 2 diabetes and how it is controlled

Answer 24

Type 2 diabetes is caused by insulin-releasing cells not producing enough insulin or by target organs not responding properly to the hormone.
People with type 2 diabetes may have some response to insulin so are treated differently to those with type 1 diabetes.
For some people, eating healthily and keeping sugar low controls their glucose.
For severe conditions, they are given medicine to reduce the amount of glucose the liver releases into the blood and to increase sensitivity of target organs responding to insulin.

Question 25

7.17 - How are body mass and type 2 diabetes correlated?

Answer 25

As the cases of type 2 diabetes has increased, so has body mass.
Scientists believe that more body fat means likely chances of type 2 diabetes.
Taller people have a larger mass, so scientists need to take into account height.
This is done by calculating the BMI ( body mass index ) : mass/height squared.

Question 26

7.17 - How are waist:hip ratio and type 2 diabetes correlated?

Answer 26

Waist:hip ratio is calculated as the waist measurement divided by hip measurement.
This is useful, because as people gain weight, they develop more fat around their hips.
As people increase their waist:hip ratio they increase their likelihood of developing type 2 diabetes.

Question 27

7.18B - Describe the structure of the urinary system

Answer 27

The urinary system removes excess amounts of substances from the blood, like mineral salts, it also removes waste products like urea.
Urea is produced in liver cells from the breakdown of amino acids, this is carried to the kidneys.

Renal arteries carry blood from body to the kidneys.
Renal veins carry blood with wastes removed back to the body.
The kidneys remove substances from the blood and make urine.
The bladder stores urine and a muscle keeps the exit closed until urination.
Urine flows through the urethra to outside of the body.

Question 28

7.19B - How do nephrons form urine?

Answer 28

Each kidney has thousands of microscopic tubes called nephrons.
Urine is made in the nephron through stages.

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 through small molecules from the blood like water and urea.
Large molecules such as proteins stay in the blood, this is filtration.

The filtration fluid flows along the blood. Selective reabsorption of useful substances from the filtration fluid happens, this includes glucose and minerals.
The useful substances are pumped through cell membranes of the firs convoluted tube into the blood by active transport. No glucose is left in urine.

Water is also reabsorbed by osmosis, depending on how much the body needs.
This happens in the loop of Henle and collecting duct.
At the end of the nephron the remaining fluid containing excess water and urea flows into the ureter, it is now urine.

Question 29

7.19B - How is a nephron adapted to its function?

Answer 29

Large SA of contact between nephron and blood capillaries.
Cell membrane of first convoluted tube has microvilli to increase SA:V.
Cells with protein pumps for the useful substances contain many mitochondria.

Question 30

7.20B - Explain the effect of ADH on nephrons

Answer 30

Kidneys help to control water content.
When the pituitary gland detects there is too little water in the blood, it releases ADH ( antidiuretic hormone ).
This increases the permeability of the collecting duct in nephrons and increases the concentration of urine.
When collecting duct is permeable, water is absorbed by osmosis by the blood .
When there is higher water concentration, the pituitary gland stops releasing ADH.

Question 31

7.21B - Describe treatments for kidney failure

Answer 31

he body can manage with one healthy kidney, although some people suffer kidney failures, where both kidneys stop working.
This is fatal, as the waste substances in the blood increase in concentration.

Due to this, someone with a kidney failure would need kidney dialysis every few days.
This is when blood carrying wastes passes into the machine from a vein.
It moves past dialysis fluid which has a partially permeable membrane to it.
Due to this the wastes will diffuse across the membrane while glucose will diffuse into the blood.
This blood with no wastes returns to the vein.

Another treatment method is organ donation. When a kidney of another person is put into the patients body.
This involves hours of surgery, which may be hard for weak patients.
Kidney cells have antigens on them, the patients immune system would attack the antigens on the donors kidney. This can cause rejection.
So antigens on the kidney must match those on the patients cells. This may take a long time.
Even with a good match, the patient would need life-long medication to prevent rejection, the medication can make the body catch infections easily.

Question 32

7.22B - How is urea produced?

Answer 32

By the breakdown of excess amino acids in the liver.