Homeostasis Flashcards

All 55 cards in this deck

What is homeostasis?

The maintenance of a constant internal environment inside the body, despite internal and external changes.

Why must the body keep its internal conditions constant?

So that cells and enzymes work at their optimum, and cells are not damaged.

Name three conditions in the human body that are controlled by homeostasis.

Body temperature, blood glucose concentration and the water content of the blood.

True or false? Homeostasis only responds to changes outside the body.

False. It responds to internal changes too, e.g. exercise raising body temperature and using up blood glucose.

What is the normal core body temperature of a human?

About $37^\circ$C.

Why must body temperature be kept close to $37^\circ$C?

It is the optimum temperature for enzymes; if the body gets too hot enzymes denature, and if too cold reactions become too slow.

Which part of the brain is the thermoregulatory centre?

The hypothalamus — it monitors the temperature of the blood.

What is the role of the epidermis in thermoregulation?

It is the outer layer: sweat reaches the surface through pores in it and evaporates, and hairs on it can trap an insulating layer of air.

What are the steps in the body's response to becoming too hot?

e.g. exercising on a hot day

1. The hypothalamus detects a rise in blood temperature.
2. Sweat glands in the dermis release more sweat and vasodilation occurs.
3. Thermal energy is lost by evaporation and radiation, so body temperature falls back to $37^\circ$C.

What is vasodilation and what effect does it have?

Blood vessels near the skin surface widen, so more blood flows near the surface and more thermal energy is lost — it cools the body down.

What is vasoconstriction and what effect does it have?

Blood vessels near the skin surface narrow, so less blood flows near the surface and less thermal energy is lost — it keeps the body warm.

True or false? During vasodilation the blood vessels move closer to the skin surface.

False. Blood vessels cannot move; they widen so that more blood flows through the vessels near the surface.

True or false? Vasoconstriction happens when the body is too hot.

False. Vasoconstriction happens when the body is too cold, to reduce heat loss.

What effect does shivering have on body temperature, and why?

It raises it — muscles contract and relax rapidly, increasing respiration, which releases thermal energy.

Iguanas have no sweat glands and pant with their mouths open when too hot. What cools them down?

Water evaporates from the mouth, removing latent heat (thermal energy) so their temperature falls.

What is osmoregulation?

The control of the water (and dissolved solute) content of the blood and body fluids.

What happens to an animal cell if the blood plasma around it becomes too dilute?

Water enters the cell by osmosis, so the cell swells and may burst.

What happens to an animal cell if the blood plasma around it becomes too concentrated?

Water leaves the cell by osmosis, so the cell shrinks and cannot function properly.

True or false? An animal cell is protected from bursting in a dilute solution by its cell wall.

False. Animal cells have no cell wall, so they can burst if too much water enters by osmosis.

Which organs carry out osmoregulation in humans?

The kidneys — they adjust how much water is reabsorbed into the blood.

Name the parts of the urinary system in the order urine passes through them.

Kidney $\rightarrow$ ureter $\rightarrow$ bladder $\rightarrow$ urethra.

True or false? The urethra carries urine from the kidney to the bladder.

False. The ureter carries urine from the kidney to the bladder; the urethra carries urine out of the body.

What are the steps of filtration in the nephron?

e.g. blood arriving at a glomerulus

1. Blood in the glomerulus is under high pressure.
2. Small molecules (water, glucose, urea, ions) are forced through the membrane into the Bowman's capsule as filtrate.
3. Blood cells and proteins are too large to pass through, so they stay in the blood.

True or false? Proteins in the blood are filtered into the Bowman's capsule.

False. Proteins (and blood cells) are too large to pass through the membrane, so they remain in the blood.

Where in the nephron is glucose reabsorbed, and by what process?

In the first coiled tubule, by active transport back into the blood (selective reabsorption).

Why does the urine of a healthy person contain urea but no glucose?

All the glucose is selectively reabsorbed into the blood, but urea is a waste product and is not reabsorbed.

Which hormone regulates the water content of the blood, and which gland releases it?

ADH (anti-diuretic hormone), released by the pituitary gland.

What effect does ADH have on the collecting duct?

It makes the collecting duct more permeable to water, so more water is reabsorbed into the blood.

What are the steps in the response to the blood becoming too concentrated?

e.g. after sweating a lot on a hot day

1. The hypothalamus detects that the blood is too concentrated.
2. The pituitary gland releases more ADH.
3. The collecting duct becomes more permeable, so more water is reabsorbed and a small volume of concentrated urine is made.

What happens to ADH release and urine after drinking a large volume of water?

Less ADH is released, so the collecting duct is less permeable and a large volume of dilute urine is produced.

True or false? Releasing more ADH increases the volume of urine produced.

False. More ADH means more water is reabsorbed, so a smaller volume of more concentrated urine is produced.

What are the two treatments for kidney failure?

Kidney dialysis and a kidney transplant (organ donation).

What happens to the blood inside a dialysis machine?

e.g. a patient with a high blood urea concentration

1. Blood is pumped through tubes surrounded by dialysis fluid, separated by a partially permeable membrane.
2. Urea and excess salts and water diffuse out of the blood into the dialysis fluid.
3. The cleaned blood is returned to the patient.

Why does dialysis fluid contain glucose and salts at the same concentration as healthy blood?

So there is no concentration gradient for them, and they are not lost from the blood by diffusion.

Give two advantages of a kidney transplant over dialysis.

No need for regular, time-consuming dialysis sessions, and fewer restrictions on diet and fluid intake (also cheaper long term).

Give two disadvantages of a kidney transplant.

The donor kidney may be rejected, so immunosuppressant drugs must be taken for life; there is also a shortage of donors and risks from surgery.

True or false? Dialysis cures kidney failure.

False. It only removes wastes temporarily, so it must be repeated regularly, e.g. three times a week.

Where in the body is urea produced, and what is it made from?

In the liver, from the breakdown of excess amino acids.

What is deamination?

The breakdown of excess amino acids in the liver, producing urea.

Which organ removes most of the urea from the blood?

The kidney — urea is excreted in urine.

True or false? Urea is produced in the kidneys.

False. Urea is produced in the liver; the kidneys remove it from the blood.

Which organ monitors blood glucose concentration, and which two hormones does it release?

The pancreas; it releases insulin and glucagon.

What are the steps by which insulin lowers blood glucose concentration?

e.g. after a carbohydrate meal

1. The pancreas detects high blood glucose and releases insulin.
2. Insulin makes liver and muscle cells take up glucose from the blood.
3. The glucose is converted to glycogen for storage, so blood glucose falls to normal.

What are the steps by which glucagon raises blood glucose concentration?

e.g. several hours after eating

1. The pancreas detects low blood glucose and releases glucagon.
2. Glucagon makes the liver convert stored glycogen back into glucose.
3. The glucose is released into the blood, so blood glucose rises to normal.

What is glycogen and where is it stored?

The storage carbohydrate made from glucose; it is stored in the liver and muscles.

True or false? Glucagon and glycogen are two names for the same substance.

False. Glucagon is a hormone from the pancreas; glycogen is the storage carbohydrate in the liver and muscles.

What happens to blood glucose concentration during exercise, and why?

It falls, because muscle cells take up and respire more glucose to release energy.

What is the cause of type 1 diabetes?

The pancreas stops producing enough insulin, so blood glucose concentration can rise dangerously high.

How is type 1 diabetes controlled?

By insulin injections, together with a controlled carbohydrate diet and regular exercise.

What is the cause of type 2 diabetes?

Body cells (in the liver and muscles) become resistant to insulin, so they no longer take up glucose properly.

How is type 2 diabetes controlled?

By a controlled carbohydrate diet, losing weight and regular exercise; drugs may also be used.

True or false? Type 2 diabetes is caused by the pancreas failing to make insulin.

False. In type 2 diabetes insulin is still made, but the body's cells are resistant to it.

Which two calculations are used to link body mass to the risk of type 2 diabetes?

$BMI = \frac{\text{mass (kg)}}{(\text{height (m)})^2}$ and waist:hip ratio = waist circumference $\div$ hip circumference.

True or false? A positive correlation between BMI and rates of type 2 diabetes proves that obesity causes type 2 diabetes.

False. A correlation shows the risk increases with BMI, but it does not on its own prove cause.

True or false? The concentration of glucose in the filtrate in the Bowman's capsule is the same as its concentration in the blood plasma.

True. Glucose molecules are small enough to be filtered through, so they pass into the filtrate and are only removed later by selective reabsorption.