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A Level - Biology > 16: Homeostasis > Flashcards

16: Homeostasis Flashcards

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1
Q

What is homeostasis?

A

Maintenance of a constant internal environment in restricted limits in organisms

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2
Q

What is tissue fluid?

A

Liquid which bathes each cell

Supplies nutrients and removing wastes

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3
Q

What does homeostasis do?

A

Maintains optimum point

Does not prevent changes from occurring

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4
Q

What things are homeostasis important for?

A

Enzymes
Water potential
Geographical range

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5
Q

Why is homeostasis important for enzyme function?

A

Sensitive to changes in pH and temperatures
Any changes can cause them to denature and not be effective
Allows reactions to occur at the same rate

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6
Q

Why is homeostasis important for water potential?

A

Could cause cells to shrink and expand due to osmosis
Affected by glucose concentration
This could kill the cells

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7
Q

Why is homeostasis important for geographical range?

A

Constant internal environment means animal is more independent of external changes in environment
Gives wider geographical range

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8
Q

What are the stages of self-regulating systems?

A 
Optimum point
Receptor
Coordinator
Effector
Feedback mechanism
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9
Q

What is the optimum point stage in a self-regulating system?

A

Point at which the system operates best

Monitored a receptor

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10
Q

What is the receptor stage in a self-regulating system?

A

Monitoring system which detects any deviation from optimum point
Informs the coordinator

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11
Q

What is the coordinator stage in a self-regulating system?

A

Coordinates information from receptors

Sends instruction to an appropriate effector

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12
Q

What is the effector stage in a self-regulating system?

A

Thing which causes a change returning system to optimum point
Often muscle or gland

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13
Q

What occurs in feedback control?

A

Process by which a response to a stimulus is created in the form of a change to the system
This is brought about by the effector and caused by a receptor

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14
Q

What are the two types of feedback mechanisms?

A

Negative feedback

Positive feedback

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15
Q

When does negative feedback occur?

A

When the change produced by control mechanism which turns the system off

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16
Q

When does positive feedback occur?

A

When the change produced involves an even greater deviation from normal

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17
Q

Are there many or one receptors and effectors in a control system?

A

Many receptors and effectors per control system

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18
Q

Why do control systems have multiple receptors and effectors?

A

Separate mechanisms

Allows greater degree of control of particular factor being regulated

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19
Q

When does negative feedback occur?

A

Stimulus causes corrective measures to be turned off

Returns system to optimum level

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20
Q

Where are hormones produced?

A

Glands

Secrete hormone directly into blood

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21
Q

What are hormones carried in?

A

Blood plasma

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22
Q

How are only certain cells affected by hormones?

A

Hormones act only on target cells with specific receptors on cell-surface membrane
Receptor is complementary to a specific hormone

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23
Q

How long do hormones affect systems?

A

Effective in very low concentrations

Often widespread and long-lasting effects

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24
Q

What is a second messenger model?

A

Extracellular hormone binds to receptor

Causes an intracellular process to start by producing a secondary messenger

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25
Q

How does adrenaline affect liver cells?

A

Adrenalin binds to receptor on liver cell
Makes receptor protein to change shape on inside membrane
Activates adenyl cyclase enzyme in cytoplasm which converts ATP to cAMP
cAMP binds to protein kinase, changing its shape and activating it
This catalyses conversion of glycogen to glucose which moves out of liver cells

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26
Q

What is cAMP?

A

Cyclic AMP

Acts as a secondary messenger in liver cells

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27
Q

How does glucose leave liver cells?

A

Facilitated diffusion into the blood through channel proteins

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28
Q

Where is the pancreas located?

A

Upper abdomen

Behind the stomach

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29
Q

What is the pancreas?

A

Large, pale-coloured gland
Produces enzymes for digestion
Produces hormones for regulating blood glucose conc

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30
Q

What enzymes are produced by the pancreas?

A

Protease
Amylase
Lipase

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31
Q

What hormones are produced by the pancreas?

A

Insulin

Glucagon

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32
Q

What are islets of Langerhans?

A

Groups of hormone-producing cells in pancreas

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33
Q

What cells are found in the islets of Langerhans?

A

α cells

β cells

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34
Q

What do α cells produce?

A

Larger cells

Produces glucagon hormone

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35
Q

What do β cells produce?

A

Smaller cells

Produces insulin hormone

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36
Q

What are the name of cells found in the liver?

A

Hepatocyte

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37
Q

What are the three processes regulating blood sugar in the liver?

A

Glycogenesis
Glycogenolysis
Gluconeogenesis

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38
Q

What is Glycogenesis?

A

Conversion of glucose to glycogen

Removes glucose from blood

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39
Q

When does Glycogenesis occur?

A

Occurs when blood glucose conc is higher than normal

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40
Q

How much glycogen can the liver store?

A

75-100 grams of glycogen

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41
Q

What is Glycogenolysis?

A

Breakdown of glycogen to glucose
Diffuses into blood
Increases glucose conc in blood

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42
Q

When does Glycogenolysis occur?

A

When the blood glucose conc is lower than normal

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43
Q

What is the process of Gluconeogenesis ?

A

Production of glucose from sources other than carbohydrate

Glycerol and amino acids

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44
Q

When does Gluconeogenesis occur?

A

When supply of glycogen is exhausted

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45
Q

What occurs if glucose conc of the blood falls too much?

A

Substrate for respiration

Lack means not enough energy produced and animal dies

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46
Q

What occurs if the glucose conc of the blood increases too much?

A

Lowers Ψ of blood

Creates osmotic problems

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47
Q

What is the normal concentration of blood glucose?

A

5 mmol/dm3

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48
Q

What sources does blood glucose come from?

A

Directly from the diet
Hydrolysis of glycogen in small intestine and glycogenolysis to store it
Gluconeogenesis

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49
Q

Which hormones are responsible for blood glucose regulation?

A

Insulin
Glucagon
Adrenaline

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50
Q

Why are blood glucose hormones needed?

A

Fluctuates due to varying amounts of respiration at different times

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51
Q

Where is insulin produced?

A

β cells in the islets of Langerhans

Found in the pancreas

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52
Q

How do β cells know to release insulin?

A

Receptors that detect stimulus of rise in blood glucose conc

Responds to secrete insulin into blood plasma

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53
Q

What is insulin?

A

Globular protein made of 51 amino acids

Hormone

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54
Q

Which body cells have receptors which bind to insulin?

A

Nearly all cells

Except some such as red blood cells

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55
Q

What receptors are found on cells for detecting insulin?

A

Glycoprotein

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56
Q

What does increasing insulin cause in cells after binding to receptors?

A

Change in 3° structure of glucose transport carrier proteins, causing them to open
More carrier proteins put into membrane as vesicles with them fuse with membrane
Activation of enzymes to convert glucose to glycogen and fat

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57
Q

How is the blood glucose conc decreased due to insulin?

A

Increased rate of glucose absorption into cells
Increase rate of respiration
Increase glycogenesis (glucose to glycogen)
Increase glucose to fat

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58
Q

Why does an increased rate of respiration lower blood glucose conc ?

A

Cells use more glucose

Increases uptake of glucose from the blood

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59
Q

What type of feedback is the use of insulin?

A

Negative feedback

Lowers conc to normal

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60
Q

In which cell is glucose absorbed into most when insulin is present?

A

Muscle cells

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61
Q

Which cells store glycogen?

A

Liver and muscle cells

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62
Q

What occurs to the β cells when the blood glucose conc decreases?

A

Reduces secretion of insulin

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63
Q

Which hormone do α cells produce?

A

Glucagon

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64
Q

When do α cells produce glucagon?

A

After detecting a fall in blood glucose conc

65
Q

What is glucagon secreted into?

A

Blood plasma

66
Q

What are the actions of glucagon?

A

Attaches to specific protein receptor on cell-surface membrane of hepatocytes
Activates membrane for glycogen to glucose
Activates enzymes for gluconeogenesis (alternative sources for glucose production)

67
Q

What is the overall effect of glucagon?

A

Increases conc of glucose in the blood to optimum

68
Q

What type of feedback is the use of glucagon?

A

Negative feedback

Raises conc back to normal

69
Q

What occurs to α cells when [glucose] increases in the blood?

A

Reduce the secretion of glucagon

70
Q

Which hormone other than glucagon raises blood glucose conc?

A

Adrenaline

71
Q

How does adrenaline raise blood glucose conc?

A

Attaches to protein receptors on cell-surface membrane of target cells
Activates enzymes causing glycogenolysis in liver (glycogen to glucose)

72
Q

How do glucagon and insulin act with respect to eachother?

A

Antagonistically
Insulin decreases [glucose]
Glucagon increases [glucose]

73
Q

Why does the blood glucose conc fluctuate?

A

Negative feedback
Insulin and glucagon production determined by conc present
Only more produced if reaches threshold value

74
Q

What is diabetes?

A

Metabolic disorder
Unable to control blood glucose conc
Either lack of insulin or lack of response to it

75
Q

What are the two types of diabetes?

A 
Type I (insulin dependent)
Type II (insulin independent)
76
Q

How is type I diabetes formed?

A

Autoimmune response

Body attacks β cells

77
Q

What is type I diabetes?

A

Body is unable to produce insulin

Symptoms develop quickly

78
Q

What are the signs of diabetes?

A

High blood [glucose]
Glucose present in urine
Weight loss
Tiredness

79
Q

How does type II diabetes form?

A

Glycoprotein receptors on body cells being lost/losing responsiveness to insulin
or
Inadequate supply of insulin

80
Q

Who usually develops type II diabetes?

A

People over 40

Increasingly in younger due to obesity

81
Q

How is type I diabetes controlled?

A

Injections of insulin
2 to 4 times a day
Dose matched to glucose intake

82
Q

Why is insulin injected?

A

Protein

Would be digested into amino acids

83
Q

Why are insulin injections matched to glucose intake?

A

Too much leads to low blood glucose conc

Results in unconsciousness

84
Q

How are insulin injections matched to blood glucose levels?

A

Biosensors monitor blood glucose conc

85
Q

How is type II diabetes controlled?

A

Regulating intake of carbohydrate depending on exercise

Could use injections of insulin if not enough produced

86
Q

What is osmoregulation?

A

Homeostatic control of water potential in the blood

87
Q

Where are kidneys found?

A

Two kidneys
Back of abdominal cavity
Each side of spinal cord

88
Q

What is the kidney made of?

A 
Fibrous capsule
Cortex
Medulla
Renal pelvis
Ureter
Renal artery
Renal vein
89
Q

What does the fibrous capsule do in a kidney?

A

Outer membrane which protects the kidney

90
Q

What does the cortex contain in the kidney?

A

Lighter coloured outer region

Contains Bowman’s capsule, convoluted tubules and blood vessels

91
Q

What does the medulla contain in the kidney?

A

Darker coloured inner region

Loops of Henle, collecting ducts and blood vessels

92
Q

What is the renal pelvis in the kidney?

A

A funnel-shaped cavity that collects urine into teh ureter

93
Q

What does the ureter in the kidney?

A

A tube that carries urine to the bladder

94
Q

What does the renal artery do in the kidney?

A

Supplies kidney with blood from heart via aorta

95
Q

What does the renal vein do in the kidney?

A

Returns blood to the heart via the vena cava

96
Q

Where are nephrons found?

A

One million tiny tubular structures in each kidney

Found in cortex and medulla

97
Q

What is the nephron structure?

A

Functional unit of the kidney

Up to 14mm long, closed at one end, with two twisted regions separated by a long hairpin loop

98
Q

What is the nephron made of?

A 
Renal (Bowman's) capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
99
Q

What is the Bowman’s capsule?

A

Closed end at start of nephron

Cup-shaped and surrounds a mass of blood capillaries called a glomerulus

100
Q

What is the inner layer of the renal capsule?

A

Podocytes

101
Q

What is the structure of the proximal convoluted tubule?

A

Series of loops surrounded by blood capillaries

Made of epithelial cells which have microvilli

102
Q

What is the structure of the Loop of Henle?

A

Long, hairpin loop that extends from the cortex into the medulla of kidney
Surrounded by blood capillaries

103
Q

What is the structure of the distal convoluted tubule?

A

Series of loops surrounded by blood capillaries

Wall of epithelial cells, less capillaries than proximal

104
Q

What is the collecting duct?

A

Tube which many distal convoluted tubules from many nephrons empty

105
Q

What is the structure of the collecting duct?

A

Lined by epithelial cells

Increasingly wide as it empties into pelvis of the kidney

106
Q

Which blood vessels are found in the nephron?

A

Afferent arteriole
Glomerulus
Efferent arteriole
Blood capillaries

107
Q

What is the afferent arteriole?

A

Tiny vessel which comes from renal artery

Supplies nephron with blood

108
Q

Where does the afferent arteriole enter the nephron?

A

Enters renal capsule of the nephron

109
Q

What is the glomerulus?

A

Many-branched knot of capillaries from which fluid is forced out of the blood

110
Q

What does the glomerulus capillaries recombine to form?

A

Efferent arteriole

111
Q

What is the efferent arteriole?

A

Tiny vessel that leaves renal capsule

Carries blood away from the renal capsule to form blood capillaries

112
Q

What is the size of the efferent and afferent arteriole?

A

Efferent arteriole has a smaller diameter than the afferent arteriole

113
Q

Why is the efferent diameter smaller than afferent?

A

Increases blood pressure within the glomerulus

114
Q

Where are blood capillaries used in the kidney?

A

Conc network surrounding proximal and distal convoluted tubule, as well as loop of Henle
Merge together to form venules which merge to form a renal vein

115
Q

What are blood capillaries used for in the kidney?

A

Reabsorb mineral salts, glucose and water

116
Q

What are the four stages of osmoregulation in the kidney?

A

Ultrafiltration
Selective re-absorption
Concentrating Na+ in medulla
Water re-absorption

117
Q

Where does ultrafiltration occur in the kidney?

A

Glomerulus

118
Q

Where does selective reabsorption occur in the kidney?

A

Proximal convoluted tubule

119
Q

Where does the concentrating of Na+ in the medulla occur?

A

Loop of Henle

120
Q

Where does water reabsorption occur in the kidney?

A

Distal convoluted tubule

Collecting duct

121
Q

Where does the nephron start in the kidney?

A

Cortex

122
Q

What surrounds the glomerulus?

A

Bowman’s capsule

123
Q

What is ultrafiltration?

A

Fluid is pushed from capillaries into Bowman’s capsule under high pressure

124
Q

What is filtered out of the blood in ultrafiltration?

A 
Water
Amino acids
Glucose
Urea
Inorganic ions (Na+,Cl-,K+)
125
Q

What is not filtered out of the blood in ultrafiltration?

A

Blood cells

Proteins

126
Q

What occurs to the blood itself in ultrafiltration?

A

Water potential is lowered

Allows water to reabsorb at a later stage

127
Q

What causes the glomerulus to have a high pressure?

A

Efferent arteriole has a smaller diameter than the afferent, creates high hydrostatic pressure
Twisting capillaries into a knot increases pressure

128
Q

What is and isn’t reabsorbed from the proximal distal tubules?

A

85% of water
All glucose
All amino acids
No urea

129
Q

Where are molecules reabsorbed to in selective reabsorption?

A

Surrounding capillaries

130
Q

How are the cells in the proximal convoluted tubule adapted to selective reabsorption?

A

Microvilli provide large SA
Opposite membrane next to capillaries folded to increase SA
Cell cytoplasm has many mitochondria producing ATP for active transport

131
Q

What prevents the removal of filtrate from the glomerulus?

A

Capillary and renal capsule epithelial cells
Connective tissue and epithelial cells of blood capillary
Hydrostatic pressure of fluid in renal capsule space
Low water potential of blood in glomerulus

132
Q

How is it ensured that fluid leaves the glomerulus using permeability?

A

Podocytes line inner layer of renal capsule

Endothelium of glomerular capillaries have spaces

133
Q

How do podocytes increase permeability?

A

Cells have spaces between them

Allows only filtrate to pass through gaps

134
Q

How are things selectively reabsorbed into the proximal tubule?

A

Na+ actively transported out into blood capillaries
Na+ diffuse down conc gradient from lumen of PCT into epithelial cells through special carrier proteins by facilitated diffusion
Carrier proteins specifically transport another molecule with Na+ (co-transport)
Molecules co-transported into cells then diffuse into the blood

135
Q

Which molecules are co-transported with sodium into the epithelium of the proximal tubule?

A

Glucose
Amino acids
Inorganic ions etc.

136
Q

What does the Loop of Henle consist of?

A

Descending limb - into medulla

Ascending limb - back out to cortex

137
Q

What is the ultimate function of the loop of Henle?

A

Produce concentrated urine

138
Q

What is a feature of the descending limb?

A

Narrow and thin walls

Highly permeable to water

139
Q

What is a feature of the ascending limb?

A

Wider and thicker walls

Impermeable to water

140
Q

How does the Loop of Henle produce conc urine?

A

Salt leaves ascending limb - actively transported into medulla
Lowers water potential of medulla between two limbs
Water leaves descending limb by osmosis which then enters capillaries
Fluid in descending limb becomes more conc as it descends into medulla
Water leaves collecting duct due to low water potential of the medulla

141
Q

What are aquaporins?

A

Channel proteins which are specific to water

142
Q

What is the acronym for anti-diuretic hormone?

A

ADH

143
Q

What does the distal convoluted tubule do?

A

Actively transports water and salts into capillaries

Used to alter pH of the blood

144
Q

How does the distal convoluted tubule change to absorb more?

A

Permeability increases to cause more to diffuse into

Caused by various hormones

145
Q

What is the counter-current multiplier in the kidney?

A

Filtrate in collecting duct meets interstitial fluid that has a lower water potential

146
Q

Why is the counter-current multiplier important in the kidney?

A

Water potential gradient between collecting duct stays constant for the length of the duct

147
Q

What do hormones affect in the kidney to affect water concentration?

A

Distal convoluted tubule

Collecting duct

148
Q

What does the water potential of the blood depend on?

A 
Conc of:
Glucose
Proteins
Sodium chloride
Other minerals
149
Q

What causes the rise in solute conc and lowering in water potential?

A

Too little water consumption
A lot of sweating
Large amounts of ions (salt) intake

150
Q

What detects water potential?

A

Osmoreceptor cells

151
Q

Where are osmoreceptors located?

A

Hypothalamus of the brain

152
Q

How do osmoreceptors work?

A

Water is lost from osmoreceptors by osmosis
Cells shrink and causes hypothalamus to produce ADH
Moved to pituitary gland

153
Q

Where is ADH secreted from and to?

A

Pituitary gland to capillaries

154
Q

How does ADH work?

A

ADH binds to protein receptors on cells on wall of the DCT and collecting duct
Activates phosphorylase in the cell causing vesicles to move to and fuse with cell membrane
Vesicles contain aquaporins and increase water channels increasing permeability in DCT
ADH increases permeability to urea in CD which passes out, lowering water potential around it
More water leaves CD and into blood

155
Q

How does the ADH affect the water potential of the blood?

A

Does not increase water potential as reabsorbed from blood

Prevents it from lowering

156
Q

What is the use of ADH an example of feedback?

A

Negative feedback

Rise in water potential means osmoreceptors detect it and produce less ADH

157
Q

What causes the water potential of the blood to increase?

A

Large volume of water consumed

Salts used in metabolism or excreted

158
Q

How does the body respond to a rise in water potential?

A

Osmoreceptors detect it and decreases frequency of nerve impulse
Reduces amount of ADH released by pituitary
Less ADH means decreased permeability of collecting ducts to water and urea
Less water reabsorbed so more urine produced, lowers water potential

159
Q

How long does ADH last for?

A

Slowly broken down

Half life of around 20 minutes

A Level - Biology (22 decks)

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