16: Homeostasis Flashcards
1
Q
What is homeostasis?
A
Maintenance of a constant internal environment in restricted limits in organisms
2
Q
What is tissue fluid?
A
Liquid which bathes each cell
Supplies nutrients and removing wastes
3
Q
What does homeostasis do?
A
Maintains optimum point
Does not prevent changes from occurring
4
Q
What things are homeostasis important for?
A
Enzymes
Water potential
Geographical range
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
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
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
8
Q
What are the stages of self-regulating systems?
A
Optimum point Receptor Coordinator Effector Feedback mechanism
9
Q
What is the optimum point stage in a self-regulating system?
A
Point at which the system operates best
Monitored a receptor
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
11
Q
What is the coordinator stage in a self-regulating system?
A
Coordinates information from receptors
Sends instruction to an appropriate effector
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
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
14
Q
What are the two types of feedback mechanisms?
A
Negative feedback
Positive feedback
15
Q
When does negative feedback occur?
A
When the change produced by control mechanism which turns the system off
16
Q
When does positive feedback occur?
A
When the change produced involves an even greater deviation from normal
17
Q
Are there many or one receptors and effectors in a control system?
A
Many receptors and effectors per control system
18
Q
Why do control systems have multiple receptors and effectors?
A
Separate mechanisms
Allows greater degree of control of particular factor being regulated
19
Q
When does negative feedback occur?
A
Stimulus causes corrective measures to be turned off
Returns system to optimum level
20
Q
Where are hormones produced?
A
Glands
Secrete hormone directly into blood
21
Q
What are hormones carried in?
A
Blood plasma
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
23
Q
How long do hormones affect systems?
A
Effective in very low concentrations
Often widespread and long-lasting effects
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
25
How does adrenaline affect liver cells?
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
26
What is cAMP?
Cyclic AMP
| Acts as a secondary messenger in liver cells
27
How does glucose leave liver cells?
Facilitated diffusion into the blood through channel proteins
28
Where is the pancreas located?
Upper abdomen
| Behind the stomach
29
What is the pancreas?
Large, pale-coloured gland
Produces enzymes for digestion
Produces hormones for regulating blood glucose conc
30
What enzymes are produced by the pancreas?
Protease
Amylase
Lipase
31
What hormones are produced by the pancreas?
Insulin
| Glucagon
32
What are islets of Langerhans?
Groups of hormone-producing cells in pancreas
33
What cells are found in the islets of Langerhans?
α cells
| β cells
34
What do α cells produce?
Larger cells
| Produces glucagon hormone
35
What do β cells produce?
Smaller cells
| Produces insulin hormone
36
What are the name of cells found in the liver?
Hepatocyte
37
What are the three processes regulating blood sugar in the liver?
Glycogenesis
Glycogenolysis
Gluconeogenesis
38
What is Glycogenesis?
Conversion of glucose to glycogen
| Removes glucose from blood
39
When does Glycogenesis occur?
Occurs when blood glucose conc is higher than normal
40
How much glycogen can the liver store?
75-100 grams of glycogen
41
What is Glycogenolysis?
Breakdown of glycogen to glucose
Diffuses into blood
Increases glucose conc in blood
42
When does Glycogenolysis occur?
When the blood glucose conc is lower than normal
43
What is the process of Gluconeogenesis ?
Production of glucose from sources other than carbohydrate
| Glycerol and amino acids
44
When does Gluconeogenesis occur?
When supply of glycogen is exhausted
45
What occurs if glucose conc of the blood falls too much?
Substrate for respiration
| Lack means not enough energy produced and animal dies
46
What occurs if the glucose conc of the blood increases too much?
Lowers Ψ of blood
| Creates osmotic problems
47
What is the normal concentration of blood glucose?
5 mmol/dm3
48
What sources does blood glucose come from?
Directly from the diet
Hydrolysis of glycogen in small intestine and glycogenolysis to store it
Gluconeogenesis
49
Which hormones are responsible for blood glucose regulation?
Insulin
Glucagon
Adrenaline
50
Why are blood glucose hormones needed?
Fluctuates due to varying amounts of respiration at different times
51
Where is insulin produced?
β cells in the islets of Langerhans
| Found in the pancreas
52
How do β cells know to release insulin?
Receptors that detect stimulus of rise in blood glucose conc
| Responds to secrete insulin into blood plasma
53
What is insulin?
Globular protein made of 51 amino acids
| Hormone
54
Which body cells have receptors which bind to insulin?
Nearly all cells
| Except some such as red blood cells
55
What receptors are found on cells for detecting insulin?
Glycoprotein
56
What does increasing insulin cause in cells after binding to receptors?
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
57
How is the blood glucose conc decreased due to insulin?
Increased rate of glucose absorption into cells
Increase rate of respiration
Increase glycogenesis (glucose to glycogen)
Increase glucose to fat
58
Why does an increased rate of respiration lower blood glucose conc ?
Cells use more glucose
| Increases uptake of glucose from the blood
59
What type of feedback is the use of insulin?
Negative feedback
| Lowers conc to normal
60
In which cell is glucose absorbed into most when insulin is present?
Muscle cells
61
Which cells store glycogen?
Liver and muscle cells
62
What occurs to the β cells when the blood glucose conc decreases?
Reduces secretion of insulin
63
Which hormone do α cells produce?
Glucagon
64
When do α cells produce glucagon?
After detecting a fall in blood glucose conc
65
What is glucagon secreted into?
Blood plasma
66
What are the actions of glucagon?
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
What is the overall effect of glucagon?
Increases conc of glucose in the blood to optimum
68
What type of feedback is the use of glucagon?
Negative feedback
| Raises conc back to normal
69
What occurs to α cells when [glucose] increases in the blood?
Reduce the secretion of glucagon
70
Which hormone other than glucagon raises blood glucose conc?
Adrenaline
71
How does adrenaline raise blood glucose conc?
Attaches to protein receptors on cell-surface membrane of target cells
Activates enzymes causing glycogenolysis in liver (glycogen to glucose)
72
How do glucagon and insulin act with respect to eachother?
Antagonistically
Insulin decreases [glucose]
Glucagon increases [glucose]
73
Why does the blood glucose conc fluctuate?
Negative feedback
Insulin and glucagon production determined by conc present
Only more produced if reaches threshold value
74
What is diabetes?
Metabolic disorder
Unable to control blood glucose conc
Either lack of insulin or lack of response to it
75
What are the two types of diabetes?
```
Type I (insulin dependent)
Type II (insulin independent)
```
76
How is type I diabetes formed?
Autoimmune response
| Body attacks β cells
77
What is type I diabetes?
Body is unable to produce insulin
| Symptoms develop quickly
78
What are the signs of diabetes?
High blood [glucose]
Glucose present in urine
Weight loss
Tiredness
79
How does type II diabetes form?
Glycoprotein receptors on body cells being lost/losing responsiveness to insulin
or
Inadequate supply of insulin
80
Who usually develops type II diabetes?
People over 40
| Increasingly in younger due to obesity
81
How is type I diabetes controlled?
Injections of insulin
2 to 4 times a day
Dose matched to glucose intake
82
Why is insulin injected?
Protein
| Would be digested into amino acids
83
Why are insulin injections matched to glucose intake?
Too much leads to low blood glucose conc
| Results in unconsciousness
84
How are insulin injections matched to blood glucose levels?
Biosensors monitor blood glucose conc
85
How is type II diabetes controlled?
Regulating intake of carbohydrate depending on exercise
| Could use injections of insulin if not enough produced
86
What is osmoregulation?
Homeostatic control of water potential in the blood
87
Where are kidneys found?
Two kidneys
Back of abdominal cavity
Each side of spinal cord
88
What is the kidney made of?
```
Fibrous capsule
Cortex
Medulla
Renal pelvis
Ureter
Renal artery
Renal vein
```
89
What does the fibrous capsule do in a kidney?
Outer membrane which protects the kidney
90
What does the cortex contain in the kidney?
Lighter coloured outer region
| Contains Bowman's capsule, convoluted tubules and blood vessels
91
What does the medulla contain in the kidney?
Darker coloured inner region
| Loops of Henle, collecting ducts and blood vessels
92
What is the renal pelvis in the kidney?
A funnel-shaped cavity that collects urine into teh ureter
93
What does the ureter in the kidney?
A tube that carries urine to the bladder
94
What does the renal artery do in the kidney?
Supplies kidney with blood from heart via aorta
95
What does the renal vein do in the kidney?
Returns blood to the heart via the vena cava
96
Where are nephrons found?
One million tiny tubular structures in each kidney
| Found in cortex and medulla
97
What is the nephron structure?
Functional unit of the kidney
| Up to 14mm long, closed at one end, with two twisted regions separated by a long hairpin loop
98
What is the nephron made of?
```
Renal (Bowman's) capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
```
99
What is the Bowman's capsule?
Closed end at start of nephron
| Cup-shaped and surrounds a mass of blood capillaries called a glomerulus
100
What is the inner layer of the renal capsule?
Podocytes
101
What is the structure of the proximal convoluted tubule?
Series of loops surrounded by blood capillaries
| Made of epithelial cells which have microvilli
102
What is the structure of the Loop of Henle?
Long, hairpin loop that extends from the cortex into the medulla of kidney
Surrounded by blood capillaries
103
What is the structure of the distal convoluted tubule?
Series of loops surrounded by blood capillaries
| Wall of epithelial cells, less capillaries than proximal
104
What is the collecting duct?
Tube which many distal convoluted tubules from many nephrons empty
105
What is the structure of the collecting duct?
Lined by epithelial cells
| Increasingly wide as it empties into pelvis of the kidney
106
Which blood vessels are found in the nephron?
Afferent arteriole
Glomerulus
Efferent arteriole
Blood capillaries
107
What is the afferent arteriole?
Tiny vessel which comes from renal artery
| Supplies nephron with blood
108
Where does the afferent arteriole enter the nephron?
Enters renal capsule of the nephron
109
What is the glomerulus?
Many-branched knot of capillaries from which fluid is forced out of the blood
110
What does the glomerulus capillaries recombine to form?
Efferent arteriole
111
What is the efferent arteriole?
Tiny vessel that leaves renal capsule
| Carries blood away from the renal capsule to form blood capillaries
112
What is the size of the efferent and afferent arteriole?
Efferent arteriole has a smaller diameter than the afferent arteriole
113
Why is the efferent diameter smaller than afferent?
Increases blood pressure within the glomerulus
114
Where are blood capillaries used in the kidney?
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
What are blood capillaries used for in the kidney?
Reabsorb mineral salts, glucose and water
116
What are the four stages of osmoregulation in the kidney?
Ultrafiltration
Selective re-absorption
Concentrating Na+ in medulla
Water re-absorption
117
Where does ultrafiltration occur in the kidney?
Glomerulus
118
Where does selective reabsorption occur in the kidney?
Proximal convoluted tubule
119
Where does the concentrating of Na+ in the medulla occur?
Loop of Henle
120
Where does water reabsorption occur in the kidney?
Distal convoluted tubule
| Collecting duct
121
Where does the nephron start in the kidney?
Cortex
122
What surrounds the glomerulus?
Bowman's capsule
123
What is ultrafiltration?
Fluid is pushed from capillaries into Bowman's capsule under high pressure
124
What is filtered out of the blood in ultrafiltration?
```
Water
Amino acids
Glucose
Urea
Inorganic ions (Na+,Cl-,K+)
```
125
What is not filtered out of the blood in ultrafiltration?
Blood cells
| Proteins
126
What occurs to the blood itself in ultrafiltration?
Water potential is lowered
| Allows water to reabsorb at a later stage
127
What causes the glomerulus to have a high pressure?
Efferent arteriole has a smaller diameter than the afferent, creates high hydrostatic pressure
Twisting capillaries into a knot increases pressure
128
What is and isn't reabsorbed from the proximal distal tubules?
85% of water
All glucose
All amino acids
No urea
129
Where are molecules reabsorbed to in selective reabsorption?
Surrounding capillaries
130
How are the cells in the proximal convoluted tubule adapted to selective reabsorption?
Microvilli provide large SA
Opposite membrane next to capillaries folded to increase SA
Cell cytoplasm has many mitochondria producing ATP for active transport
131
What prevents the removal of filtrate from the glomerulus?
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
How is it ensured that fluid leaves the glomerulus using permeability?
Podocytes line inner layer of renal capsule
| Endothelium of glomerular capillaries have spaces
133
How do podocytes increase permeability?
Cells have spaces between them
| Allows only filtrate to pass through gaps
134
How are things selectively reabsorbed into the proximal tubule?
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
Which molecules are co-transported with sodium into the epithelium of the proximal tubule?
Glucose
Amino acids
Inorganic ions etc.
136
What does the Loop of Henle consist of?
Descending limb - into medulla
| Ascending limb - back out to cortex
137
What is the ultimate function of the loop of Henle?
Produce concentrated urine
138
What is a feature of the descending limb?
Narrow and thin walls
| Highly permeable to water
139
What is a feature of the ascending limb?
Wider and thicker walls
| Impermeable to water
140
How does the Loop of Henle produce conc urine?
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
What are aquaporins?
Channel proteins which are specific to water
142
What is the acronym for anti-diuretic hormone?
ADH
143
What does the distal convoluted tubule do?
Actively transports water and salts into capillaries
| Used to alter pH of the blood
144
How does the distal convoluted tubule change to absorb more?
Permeability increases to cause more to diffuse into
| Caused by various hormones
145
What is the counter-current multiplier in the kidney?
Filtrate in collecting duct meets interstitial fluid that has a lower water potential
146
Why is the counter-current multiplier important in the kidney?
Water potential gradient between collecting duct stays constant for the length of the duct
147
What do hormones affect in the kidney to affect water concentration?
Distal convoluted tubule
| Collecting duct
148
What does the water potential of the blood depend on?
```
Conc of:
Glucose
Proteins
Sodium chloride
Other minerals
```
149
What causes the rise in solute conc and lowering in water potential?
Too little water consumption
A lot of sweating
Large amounts of ions (salt) intake
150
What detects water potential?
Osmoreceptor cells
151
Where are osmoreceptors located?
Hypothalamus of the brain
152
How do osmoreceptors work?
Water is lost from osmoreceptors by osmosis
Cells shrink and causes hypothalamus to produce ADH
Moved to pituitary gland
153
Where is ADH secreted from and to?
Pituitary gland to capillaries
154
How does ADH work?
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
How does the ADH affect the water potential of the blood?
Does not increase water potential as reabsorbed from blood
| Prevents it from lowering
156
What is the use of ADH an example of feedback?
Negative feedback
| Rise in water potential means osmoreceptors detect it and produce less ADH
157
What causes the water potential of the blood to increase?
Large volume of water consumed
| Salts used in metabolism or excreted
158
How does the body respond to a rise in water potential?
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
How long does ADH last for?
Slowly broken down
| Half life of around 20 minutes
