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IGCSE Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What happens when you’re too hot?

A
  • the hair erector muscle relates, making the hairs lie flat
  • sweat is produced by sweat glands and evaporates from the skin, removing heat
  • the blood vessels supplying the skin capillaries dilate, so more blood flows close to the surface of the skin
  • the vessels now have a larger surface area, which means more heat can be lost from the blood to the environment by radiation
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2
Q

What is the only way to cure kidney failure?

A
  • kidney transplant
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3
Q

How is ion content controlled?

A
  • ions are taken into the body in food, then absorbed into the blood
  • if the food contains too much of an ion, then the excess needs to be removed
  • some are lost through sweat, but the rest needs to be removed by the kidneys and got rid of in urine
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4
Q

Why may kidney failure result in death?

A
  • waste substances build up in the blood

- ability to control the levels of ions and water are lost

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5
Q

What is homeostasis?

A
  • the maintenance of internal environment (e.g. body temperature, mineral ion conc., water balance and blood glucose conc.)
  • at a constant level
  • despite change in external environment
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6
Q

What are the pros and cons of kidney transplant?

A

Pros:

  • no special diet
  • no sessions of dialysis
  • relative inexpensive after surgery
  • kidney works all the time
  • long-term solution (8-10 years)

Cons:

  • need donor
  • need tissue match
  • have to take immunosuppressant drugs
  • risk of surgery
  • danger of infection
  • surgery every ten years (risk/cost)
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7
Q

How is blood sugar level controlled?

A
  • eating foods containing carbohydrate puts glucose into the blood from the gut
  • the normal metabolism of cells removes glucose from the blood
  • insulin helps to maintain the right level of glucose in the blood, so cells get constant supply of energy
  • pancreas acts as the coordination centre
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8
Q

How is body temperature controlled?

A
  • enzymes within the human body work best at 37 degrees

- hypothalamus contains the thermoregulatory centre and it receives messages from receptors in the skin

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9
Q

How can water lost through sweat be replaced?

A
  • drink

- food

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10
Q

Explain what happens in the nephrons to filter blood

A
  1. Ultrafiltration:
    - In the glomerulus, blood is under high pressure, forcing some molecules, such as glucose, amino acids, urea and mineral ions out of the blood to pass through filter, into the Bowman’s capsule.
    - proteins and blood cells cannot pass through as they are too large.
    - a filtrate is formed
  2. Selective Reabsorption
    - as the liquid flows along the nephron, useful substances are reabsorbed back into the blood
    - all glucose is reabsorbed by active transport against the concentration gradient
    - sufficient ions are reabsorbed by active transport. excess ions are not.
    - some water is reabsorbed by osmosis, but excess water passes onto the collecting duct
    - urea is not reabsorbed as it is toxic
  3. Collecting Duct:
    - remaining substances continue out of the nephron, into the ureter and down to the bladder as urine.
    - if body is dehydrated, hypothalamus detects it, more anti-diuretic (ADH) hormone is produced by pituitary gland, allowing water to pass through by osmosis.
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11
Q

What happens when the glycogen stores are full?

A
  • excess glucose is stored as lipid in the tissues §
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12
Q

How can automatic control systems produce a response?

A
  • by using hormones
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13
Q

Explain deamination and detoxification

A
  • liver removes excess amino acids produced when we eat and digest protein. large amounts of amino acids can be damaging, so they must be broken down and excreted.
  • liver breaks down amino acids into ammonia by deamination
  • ammonia is converted to urea. some is lost through sweat, but most is removed in the urine by the kidneys
  • liver breaks down other harmful substances (alcohol, drugs etc) into less harmful substances, that are excreted in the urine. this is called detoxification
  • old blood cells are also removed from the blood in the liver. blood cells are broke down and iron is stored for use in the body
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14
Q

How is temperature controlled?

A
  • the hypothalamus (thermoregulatory centre) in the brain acts as a personal thermostat
  • it contains receptors that are sensitive to the temperature of the blood flowing through the brain
  • it also receives impulses from receptors in the skin, giving info about skin temperature
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15
Q

How is water content controlled?

A
  • body needs to constantly balance the water coming in against the water going out
  • water is taken into the body as food and drink and is lost through: skin as sweat, via lungs in breath, via kidneys as urine
  • hormones control body water content and brain is coordination centre
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16
Q

How does dialysis work?

A
  • the person’s blood flows between partially permeable membranes, surrounded by dialysis fluid. Like a kidney, ions and waste substances can pass, but proteins and blood cells cannot
  • dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood
  • meaning that useful dissolved ions and glucose won’t be lost from the blood
  • only waste substances, such as urea, and excess ions and water diffuse across the barrier
17
Q

How is glucose removed from the blood?

A
  • the normal metabolism of cells

- vigorous exercise removes much more glucose from the blood

18
Q

What are the internal conditions that need to be controlled?

A
  • temperature
  • the water content of the body
  • the ion content of the body
  • blood glucose levels
19
Q

What is excess glucose stores as?

A
  • glycogen

- in the liver and in the muscles

20
Q

What are the control systems?

A
  • cells called receptors, which detect stimuli
  • coordination centres that receive and process information from receptors
  • effectors, which bring about responses
21
Q

Why may someone have kidney failure?

A
  • damage by infections
  • genetic disorders
  • physical injury
22
Q

What do kidneys do?

A
  • filter the blood
  • reabsorb products that are needed: all glucose, any dissolved ions and any water needed
  • release urea, excess ions and excess water as urine
23
Q

What are nephrons?

A
  • the filtration units in the kidneys which filter the blood to produce urine
24
Q

Explain Type 1 diabetes

A
  • the pancreas produces little or no insulin (autoimmune destruction of beta cells in the pancreas)
  • the person’s blood glucose can rise to a level that can kill them
  • conditions can be partially controlled by having a controlled diet and taking regular exercise
  • insulin needs to be injected several times a day
25
Q

What three things determine the amount and concentration of urine?

A
  • heat: sweat causes water loss, causing a release of ADH so kidneys will reabsorb more water, so only a concentrated, small amount of urine will be produced
  • exercise: make you hot and sweat, so concentrated small amount of urine
  • water intake: not drinking enough water produced concentrated urine, drinking a lot produced dilute urine
26
Q

How is the glucose level kept steady when there is high blood sugar?

A
  • when glucose rises (such as after eating carbs), the Islet of Langerhans (receptor) in the pancreas, detects a rise in glucose.
  • the beta cells produce insulin, which stimulates glucose uptake in the blood and also stimulates glycogen production (glycogenesis), converting glucose into glycogen, lowering the blood sugar
27
Q

How is water content controlled by the kidneys?

A
  • it is controlled by a hormone called anti-diuretic hormone (ADH)
  • ADH makes the nephrons more permeable so water can be reabsorbed back into the blood
  • the hypothalamus detects water content and instructs the pituitary gland to release ADH:
  • if the water content of the blood is too low, ADH is released into the blood. the kidneys reabsorb more water and a more concentrated urine is produced
  • if the water content of the blood is too higher, less ADH is released into the blood. the kidneys reabsorb less water and a more dilute urine is produced.
28
Q

Why is it important to keep a constance concentration of water molecules in the blood plasma?

A
  • prevents too much water moving into our out of the tissues by osmosis
  • keeps the blood pressure constant
29
Q

Explain type 2 diabetes

A
  • a person becomes resistant to their own insulin
  • blood sugar rises to a dangerous level
  • being overweight increases the change of developing it
  • can be controlled by avoiding foods rich in simple carbohydrates e.g. sugars
  • exercise helps as the increased metabolism of cells during exercise removes more glucose
30
Q

Give examples of receptors found in organs

A
  • the eyes: sensitive to light
  • the ears: sensitive to sound, and to change in position
  • the tongue and in the nose: sensitive to chemicals
  • the skin: sensitive to touch, pressure, pain and to temperature changes
  • the brain: sensitive to blood temperature and the concentration of water in the blood
  • the pancreas: sensitive to the concentration of glucose in the blood
31
Q

What are the pros and cons of dialysis?

A

Pros:

  • machines usually available
  • no problems with tissue matching
  • no need for surgery
  • immediate treatment and life-saving

Cons:

  • has to happen at least twice a week
  • expensive in the long-term
  • diet has to be watched
  • substances build up in-between sessions
  • risk of blood clots so have to use anticoagulant drugs (excessive bleeding)
  • not a cure, just treatment
32
Q

What are hormones?

A
  • hormones are chemical substances secreted by glands (effectors)
  • they are carried in the blood to other parts of the body, but only affect particular cells (target cells) in particular places
33
Q

What is the liver responsible for?

A
  • deamination

- detoxification

34
Q

What happens when you’re too cold?

A
  • the hair erector muscles are erect, making hairs stand up, trapping an insulating layer of air
  • no sweat is produced
  • blood vessels supplying skin capillaries constrict to reduce the skin’s blood supply
  • the constriction of the blood vessels reduces the surface area of vessels. less heat is lost by radiation
  • you shiver as rapid muscle contraction releases heat. needs respiration which releases some energy to warm the body
35
Q

How is the glucose level kept steady when there is low blood sugar?

A
  • when glucose falls (such as after exercise), the Islet of Langerhans (receptor) in the pancreas detects the fall in glucose
  • the alpha cells produce glucagon, which stimulates glycogen breakdown (glycogenolysis) , releasing glucose and raising the blood sugar

IGCSE Biology (16 decks)

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