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A-Level Biology Component 3 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis?

A

The maintenance of a constant internal environment within a living organism irrespective of the external conditions

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2
Q

What are cells provided with so they can function efficiently, independently of fluctuations in the conditions of external environment?

A

they are provided with constant conditions, even during different levels of activity of the organism.

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3
Q

What are examples of homeostatic control?

A

-Regulation of blood glucose levels
-Regulation of solute potential e.g. when water is lost via excretion, sweating and expiration
-regulation of core body temp and pH

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4
Q

What is the set point?

A

the desired level, or norm, at which the system operates

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5
Q

What does homeostasis use negative feedback to do?

A

to return the body to the set point

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6
Q

What is the set point determined by?

A

a control centre

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7
Q

What are deviations from
the set point corrected by?

A

negative feedback so the set point is restores

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8
Q

What does negative feedback use?

A

-detector/receptor- which monitors the condition and provides output to the control centre/coordinator- which evaluates the information and provides output to an effector, which makes a response designed to take away the deviation, i.e. restore the set point/norm

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9
Q

What is the definition of negative feedback?

A

-A receptor detects any deviation from a set point.
-Information is sent to a control centre which coordinates a response to return levels back to the set point.

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10
Q

What do some systems in the body operate by?

A

positive feedback, in which an effector increases a change.

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11
Q

What is an example of positive feedback (in pregnancy)?

A

-Oxytocin stimulates the contraction of the uterus at the end of pregnancy. -The contractions stimulate the production of more oxytocin, which increases the stimulus.

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12
Q

What is another example of positive feedback?

A

-When the skin is cut, the first stage of clot formation is that platelets adhere to the cut surface.
-They secrete signalling molecules, which attract more platelets to the site

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13
Q

What is thermoregulation?

A

The restoration of the core body temperature back to the norm

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14
Q

Where is the control centre of thermoregulation?

A

The hypothalamus in the brain

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15
Q

What is the specific receptor, control centre and effector involved in thermoregulation?

A

-Set point- 37
-Receptors- Thermoreceptors and cutaneous receptors
-Control centre- Hypothalamus in the brain
-Effector- Smooth muscle in wall of arterioles and muscle tissue

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16
Q

Why is a tall, thin swimmer more likely to suffer suffer from hypothermia than a short, stout swimmer of the same body mass?

A

-larger surface area to volume ratio;
-less insulation / steeper thermalgradient;
-more heat loss by conduction;

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17
Q

What are 2 functions of the kidney?

A

-Nitrogenous excretion
-Osmoregulation (water regulation)

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18
Q

What is nitrogenous excretion?

A

Amino acids cannot be stored and surplus amino acids, not used for the synthesis of proteins and other nitrogenous compounds, are deaminated in the mammalian liver.

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19
Q

What is the meaning of deamination?

A

to remove the amino group from (a compound)

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20
Q

What is the process of nitrogenous excretion?

A

1.Amine group is removed
2. The removed amine group is converted to ammonia
3. With the addition of CO2, less toxic urea is formed and transported in the blood plasma to kidneys.
4. Urea is removed by the kidneys and excreted in the urine

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21
Q

What is osmoregulation?

A

-the control of the water content and solute composition of body fluids, e.g. blood, tissue fluid and lymph.
-Osmoregulation is the homeostatic balance between water gain and water loss

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22
Q

What do humans gain water from (osmoregulation)?

A

•Food and drinks
•Respiration (metabolic water)

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23
Q

What do humans lose water by (osmoregulation)?

A

•Urination and egestion of faeces
•Sweating
•Exhalation (need to keep exchange surfaces moisture)

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24
Q

What are the parts of the human urinary system?

A

-kidney
-ureter
-urethra
-sphincter
-bladder

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25
Q

What is are the kidneys?

A

Organs that filter waste products from the blood

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26
Q

What is the function of the ureter?

A

Convey urine to the bladder

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27
Q

What is the function of the Urethra?

A

carries urine to outside for elimination

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28
Q

What is the sphincter?

A

A muscle that allows conscious control of urine release

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29
Q

What is the function of the Bladder?

A

stores urine prior to elimination

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30
Q

What is ultrafiltration?

A

is filtration under pressure that separates small soluble molecules from the blood plasma

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31
Q

What is the general process of ultrafiltration?

A

-The small molecules (water, glucose, urea and salts) are filtered from the knot of capillaries (the glomerulus) to form a filtrate in the Bowman’s capsule.
-High hydrostatic pressure is generated in the glomerulus because the afferent arteriole diameter is wider than the efferent arteriole

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32
Q

What is blood entering the glomerulus separated from the bowman’s capsule by?

A

two cell layers and a basement membrane

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33
Q

What are water and small molecule uses forces through to be separated from the blood plasma to form filtrate in the Bowman’s capsule (ultrafiltration)?

A

•Pores in the endothelial cells of glomerulus capillary wall.
•The basement membrane - which acts as a molecular sieve.
•Filtered between the feet of the podocytes (epithelial cells of the Bowman’s capsule)

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34
Q

What passes into the glomerular filtrate in ultrafiltration?

A

-Water + amino acids, fatty acids, small proteins
-Salts (Na+ and Cl-)
-Glucose
-urea (excreted in urine)

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35
Q

What remains in the blood in ultrafiltration?

A

-RBC’s
-WBC’s
-Platelets
-Large Plasma Proteins

36
Q

What is selective reabsorption? (in the Proximal Convoluted Tubule)

A

the process by which useful products, such as glucose and salts, are reabsorbed back into the blood as the filtrate flows along the nephron

37
Q

What is the filtrate at the end of the proximal convoluted tubule?

A

Isotonic to blood plasma

38
Q

What products are selectively absorbed?

A

-all of the glucose and amino acids
-most of the mineral ions
-most of the water
-some filtered proteins and urea

39
Q

What mechanism are all the glucose and amino acids selectively reabsorbed by?

A

Secondary active transport using a co-transport mechanism with Na+

40
Q

What mechanism are most of the mineral ions selectively reabsorbed by?

A

Active transport/co-transport

41
Q

What mechanism is most of the water selectively reabsorbed by?

A

By osmosis down a water potential gradient

42
Q

What mechanism are some filtered proteins and urea selectively reabsorbed by?

A

diffusion

43
Q

What are the adaptations of the structures the proximal convoluted tubule (PCT) in relation to selective reabsorption?

A

Large surface area (due to its length and large number per kidney)
•Cuboidal epithelial cells with microvilli to provide large surface area and basal channels
•Numerous mitochondria to provide ATP for active transport
•Tight junctions to prevent seepage of reabsorbed materials back into the filtrate, and close association with peritubular capillaries.

44
Q

What is osmosis?

A

the diffusion of water from an area of higher water potential to an area of lower water potential across a selectively permeable membrane. It is a passive process so does not require ATP.

45
Q

What is water potential?

A

(Ψ) is the tendency for water to leave a solution by osmosis, and is measured in KPa. (The greater the number of free water molecules in a solution, the higher the water potential).

46
Q

What is pure water?

A

has the greatest potential energy to move and it is therefore given the highest value of 0 kPa

47
Q

What happens as you add a solute to water? (e.g. sugar or salt)

A

-the potential energy of the water decreases and therefore the water potential becomes more negative
-e.g. a dilute solution may have a water potential of -50kPa, whereas a more concentrated solution may have a water potential of -100kPa

48
Q

What is solute potential?

A

-(Ψs) is due to the solutes in the cytoplasm.
-It is the lowering of water potential due to the presence of solute molecules.

49
Q

What is Hypotonic?

A

If the water potential of the external solution is less negative (higher) than the solution inside the cell, it is hypotonic to the cell and water flows into the cell.

50
Q

What is Hypertonic?

A

If the water potential of the external solution is more negative (lower) than the solution inside the cell, it is hypertonic to the cell and water flows out of the cell.

51
Q

What is Isotonic?

A

If the water potential of the external solution is the same as the solution inside the cell, it is isotonic to the cell and there is no net movement of water.

52
Q

What does the loop of henle do?

A

-Concentrates Na+ in the tissue fluid of the medulla, causing an osmotic flow of water out of the collecting ducts and distal convoluted tubules.
-This water can then be reabsorbed into the blood stream via the capillaries of the vasa recta.
-This concentrates the urine and makes it hypertonic to the blood (lower water potential).

53
Q

What is the order in the loop of henle?

A

-Bowman’s Capsule
-Proximal Convoluted Tubule
-Descending limb
-Ascending limb
-Distal Convoluted tubule
-Collecting duct

54
Q

What is the first part of the loop?

A

Descending limb and is permeable to water

55
Q

What is the second part of the loop?

A

-ascending limb and is impermeable to water
-loop of Henle easier to understand if we start here

56
Q

When will water also leave the permeable collecting ducts by osmosis to be reabsorbed into the capillaries?

A

As the loop of Henle creates a high Na+ concentration in the tissue fluid of the medulla

57
Q

What affects the permeability of the collecting duct walls?

A

Anti diuretic hormone

58
Q

What does ADH do?

A

enables more concentrated urine to be formed by making plasma membranes of the distal convoluted tubule cells and collecting duct walls more permeable

59
Q

What is the ADH negative feedback (summary)?

A

-Detectors- Osmoreceptors in the hypothalamus (brain) detect changes in the water potential of the blood
(nerve impulse)
-Coordinator- Cells of posterior lobe of pituitary gland secrete more or less ADH
(ADH in blood)
-Effector- Cells of distal convoluted tubules and collecting ducts become more or less permeable to water

60
Q

What is NF summary if a person is dehydrated?

A

-Decrease in WP detected by osmoreceptors in the hypothalamus
-More ADH released from posterior
pituitary
-Collecting duct walls more
permeable
-More water reabsorbed into blood (and and less urine produced) -Increase in water potential of blood

61
Q

What in the NF summary if a person has just drunk 2 litres of water and is well hydrated?

A

-Increase in WP detected by osmoreceptors in the hypothalamus
-Less ADH released from posterior
pituitary
-Collecting duct walls less
permeable
-Less water reabsorbed into blood (and and more urine produced) -Decrease in water potential of blood

62
Q

What do different animals produce?

A

Different forms of nitrogenous waste (this is directly like with the environment in which they live)

63
Q

What form of nitrogenous waste do aquatic animals excrete?

A

-Excrete ammonia, which is highly toxic.
-Ammonia is very soluble in water and can diffuse quickly across the gills of fish into the water where it is diluted to a non-toxic level.

64
Q

What form of nitrogenous waste do birds, reptiles and insects produce?

A

-Excrete uric acid which is almost insoluble in water.
-They use a lot of energy to excrete this waste but very little water is needed.
-Therefore, these animals can survive in dry environments.

65
Q

What form of nitrogenous waste do mammals produce?

A

-Excrete urea.
-This requires a lot of water, but it is less toxic than ammonia so body tissues can tolerate it in higher concentrations for short periods of time.

66
Q

What form of nitrogenous waste do desert mammals produce?

A

-survive with very little water.
-Water is produced from the breakdown of food during respiration in the cells (metabolic water).
-They may live in underground burrows which are cooler to reduce water loss by evaporation

67
Q

The kangaroo rat Dipodomys spectabilis, lives in desert regions of North America.
Why does it have a longer than average loop of Henle?

A

-longer the Loop of Henle=more opportunity there is to pump ions into medulla tissue fluid
-When ions are pumped from the ascending limb, the concentration of ions in the tissue fluid of the medulla increases.
-This low water potential in the medulla tissue fluid enhances water reabsorption from the descending limb and from the collecting duct, resulting in more concentrated urine.

68
Q

What is the loop of henle concerned with?

A

water reabsorption

69
Q

What the the longer the loop mean?

A

the greater the water potential in the medulla

70
Q

What is the loop of henle like in a beaver (aquatic)?

A

-length- short
-position in kidney- doesn’t extend into medulla
-consequence of water reabsorption- minimal reabsorption of water from collecting duct

71
Q

What is the loop of henle like in a rabbit (terrestrial/land)?

A

-length- Intermediate
-position in kidney-extends into medulla
-consequence of water reabsorption-
Moderate reabsorption of water from collecting duct

72
Q

What is the loop of henle like in a kangaroo rat (desert)?

A

-length- long
-position in kidney-extends deeply into medulla
-consequence of water reabsorption-
maximum reabsorption of water from collecting duct

73
Q

What would the volume and concentration of urine be for each mammal?

A

-Beaver – Larger volume of dilute urine (520 mOsmol/l)
-Human – Medium volume of intermediate concentration (3100 mOsmol/l)
-K rat - Very small volume of concentrated urine (5500mOsmol/l)

74
Q

What are symptoms of kidney failure?

A

Fatigue
Shortness of breath
Nausea
Confusion
Coma

75
Q

What are causes of kidney failure?

A

Diabetes –
•Raised blood pressure – damages structure of epithelial cells and basement membrane of glomerulus, preventing ultrafiltration
•Auto-immune disease
•Kidney infections –
•Genetic conditions – polycystic kidney disease
•Crushing injuries

76
Q

What do kidney problems do?

A

affect the rate at which blood is filtered in Bowman’s capsule

77
Q

What can treatments for kidney problems be used to do?

A

to balance the fluids in blood and reduce the concentration of waste products

78
Q

What are the kidney treatments?

A

-Dialysis
-Transplant
-Medication to control blood potassium and calcium levels
-Reduce the intake of protein in diet to reduce urea formation
-Use of drugs to reduce blood pressure

79
Q

What is dialysis?

A

The process of removing excess water, inorganic ions, and urea from the blood in people whose kidneys can no longer perform these functions naturally.

80
Q

What is the process of dialysis?

A

-The dialysate runs in counter-current flow next to the blood to be cleaned, this maintains a concentration gradient.
-Blood and dialysate are separated by a selectively permeable membrane to prevent loss of (plasma) proteins.
-Replacement with fresh dialysate further maintains a concentration gradient

81
Q

What is the concentration and water potential of glucose, na ions, amino acids, water and urea in the blood? (dialysis)

A

Glucose- same
Sodium Ions- higher
Amino Acids- same
Water- higher
Urea- higher

82
Q

What is the concentration and water potential of glucose, na ions, amino acids, water and urea in the dialysis fluid? (dialysis)

A

Glucose- same
Sodium Ions- lower
Amino Acids- same
Water- lower
Urea- lower

83
Q

What substances will diffuse out of the blood across the membranes and why? (dialysis)

A

inorganic ions, water and urea down their concentration gradients.

84
Q

Why should the temperature change f the dialysate be maintained at 37 degrees?

A

To increase rate of diffusion, maintains patient temperature, prevents temperature shock

85
Q

What can a big problem be due to a kidney donor?

A

Rejection- Antigens on the donor organ differ from antigens on the cells of the recipient and the immune system is likely to recognise this. -Immunosuppressant medicines must be taken for the rest of their life.

86
Q

What is the disadvantage of dialysis instead of transplant?

A

Dialysis is only a stepping stone treatment and restricts an individuals life, only with a transplant would they get the freedom back.

87
Q

What are the disadvantages of transplant over dialysis?

A

-Transplant lists are long and even if there is a match it could potentially be rejected.
-Having a transplant does not last forever – 12-20 years from a living donor, only 8-12 years from a deceased donor.
-Taking a kidney from a live individual increase the stress on their remaining kidney increasing risk of further transplants in the future.

A-Level Biology Component 3 (12 decks)

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