Topic 3 - Homeostasis Flashcards
(89 cards)
1
Q
What is homeostasis?
A
The process by which the body maintains a relatively constant internal environment, despite changes to the external environment.
2
Q
What are positive feedback loops?
A
A response that reinforces or enhances the original stimulus.
3
Q
What are negative feedback loops?
A
A response that counteracts the original effects of the stimulus.
4
Q
What is a stimulus?
A
Is the change in the environment that causes the system to operate.
5
Q
What is a receptor?
A
Detects the change in the internal condition of the body through receptors.
6
Q
What is a modulator?
A
Is a control centre responsible for processing information received from the receptor and for sending information to the effector.
7
Q
What is a effector?
A
Carries out a response counteracting or enhancing the effect of the stimulus.
8
Q
What is a response?
A
Restores the body to its original state through an action taken.
9
Q
What is a set point?
A
The point at which conditions fluctuate?
10
Q
What is meant by steady state?
A
The body regulates its function to keep the internal conditions as stable as possible.
11
Q
What is a dynamic equilibrium?
A
It is dynamic because it is constantly adjusting to the changes that the systems encounter. It is in equilibrium because body functions are kept within a normal range, with some fluctuations around a set point for the processes.
12
Q
What are tolerance limits?
A
Refer to the range within which an organism can maintain its internal environment to ensure survival and proper functioning.
13
Q
What is the word equation for cellular respiration?
A
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)
14
Q
What is glycogenesis (decreases glucose)?
A
The process of converting excess glucose into glycogen for storage in the liver and muscles, stimulated by insulin.
15
Q
What is glycogenolysis (Increases glucose)
A
The process of converting breaking down stored glycogen back into glucose in the liver, stimulated by glucagon.
16
Q
What is gluconeogenesis (increases glucose)?
A
The production of glucose from lipids and amino acids in the liver.
17
Q
What is lipogenesis (decreases glucose)?
A
The conversion of glucose into lipids (fat) in adipose tissue for long term storage.
18
Q
What is lipolysis (provides fuel and supports gluconeogenesis)?
A
The breakdown of lipids into fatty acid for energy.
19
Q
How is insulin released?
A
Insulin is released when blood glucose levels are high and helps lower blood glucose levels back to the normal range. The beta cells in the Islets of Langerhans (in the pancreas) detects this rise.
20
Q
What is insulins role in glucose regulation?
A
- Increases glucose uptake by body cells to use for energy.
- Stimulates glycogenesis
- Stimulates lipogenesis
- Stimulates protein synthesis (helps make proteins from glucose when needed).
21
Q
How is glucagon released?
A
Glucagon is released when blood glucose levels are low and helps increase blood glucose back to normal. The alpha cells in the Islets of Langerhans (in the pancreas) detect the low glucose.
22
Q
What is glucagons role in glucose regulation?
A
- Stimulates glycogenolysis
- Stimulates gluconeogenesis
- Stimulates lipolysis
23
Q
What is the role of the liver in blood glucose regulation?
A
The liver can store and take up glucose and:
- Use it for energy in liver function.
- Allow it to continue to circulate in the blood.
- Convert excess glucose into fat.
- Convert glucose into glycogen for storage.
24
Q
What is the role of the pancreas in glucose regulation?
A
The pancreas is the main control centre for blood glucose:
- Contains alpha cells (release glucagon) and beta cells (release insulin) in the Islets of Langerhans.
- Controls whether the body stores or releases glucose.
25
What is the role of the adrenal medulla in glucose regulation?
Releases adrenaline which stimulates:
- Glycogenolysis (glycogen → glucose)
- Stimulates production of lactic acid from glycogen in muscle cells (used for energy or converted back to glucose by the liver).
26
What is the role of the adrenal cortex in glucose regulation?
Releases cortisol which stimulates:
- Gluconeogenesis (fats/proteins → glucose).
- Increases glycogenolysis (glycogen → glucose).
- Mobilises fatty acids from adipose tissue for energy.
- Protein breakdown to supply materials for gluconeogenesis.
- Cortisol also helps reduce insulin action, so glucose stays available during stress.
27
What is the negative feedback loop for low blood glucose look like?
Stimulus: Blood glucose level falls.
Receptor: Chemoreceptors in the islets of Langerhans (pancreas) which are the alpha cells.
Modulator:
- Alpha cells produce glucagon
- Hypothalamus stimulates the secretion of cortisol (via adrenocorticotropic hormone travelling to the adrenal cortex)
- Hypothalamus stimulates the adrenal medulla to secrete adrenaline via sympathetic nerves
Effector:
- Liver
- Skeletal muscles
Response:
* Glycogenolysis in the liver.
* Gluconeogenesis in the liver.
* Increased lipolysis.
* Protein breakdown.
Feedback: Blood glucose level rises (homeostasis is restored).
28
What is the negative feedback loop for high blood glucose look like?
Stimulus: Blood glucose level rises.
Receptor: Chemoreceptors in the islets of Langerhans (pancreas) which are the beta cells.
Modulator: Beta cells produce insulin.
Effector:
- Liver
- Body cells
Response:
- Increased transport of glucose into body cells.
- Glycogenesis in the liver and skeletal muscles.
- Increased protein synthesis.
- Lipogenesis in adipose tissue.
Feedback: Blood glucose level declines (homeostasis is restored).
29
What is thermoregulation and how does it maintain homeostasis?
Thermoregulation is the process of keeping the core body temperature around 36.8–37°C. It maintains homeostasis by balancing heat gain and heat loss so cells can work properly even when the environment changes.
30
How does the body produce heat (metabolic rate)?
Heat is mainly produced by metabolic processes:
- The body breaks down food to release energy, mostly as heat.
- Exercise, stress, and body temperature increase the metabolic rate.
- The thyroid hormone (thyroxine) also increases metabolic rate long-term.
- Adrenaline & Noradrenaline (from adrenal medulla) has a short-term increase in metabolic activity.
31
How is heat gained by the body?
- Metabolism (Main source)
- Shivering:
Due to an increase in skeletal muscle tone, producing rhythmic muscle tremors that occur at a rate of around 10 to 20 per second. As no work is being done, that heat produced by the muscles is released as heat.
* Radiation from the environment
* Conduction from warm surfaces.
32
How is heat lost by the body?
1) Conduction
2) Convection
3) Radiation
4) Evaporation
33
What is conduction?
Is the transfer of heat by direct contact between particles.
34
What is convection?
Is the transfer of heat by the movement of a liquid or gas. (Air/Water movement)
35
What is radiation?
Is the transfer of heat by infrared radiation being emitted by objects. (Body emitting heat)
36
What is evaporation?
Is the process of a liquid forming a gas which absorbs heat energy. (Sweating)
37
How is low body temperature regulated through a negative feedback loop?
Stimulus: Decreased body temperature.
Receptors: Thermoreceptors (peripheral and central).
Modulator: Hypothalamus.
- Sends impulses via the sympathetic neural pathway to the skin and blood vessels.
- Sends impulses to the part of the brain responsible for muscle tone.
- Stimulates the adrenal medulla via sympathetic nerve pathway.
Effectors:
- Skin blood vessels
- Skeletal muscles
- Anterior lobe of the pituitary
- Adrenal medulla
Response:
1) Physiological:
- Skeletal muscles (Shivering): Rhythmic, oscillating muscle tremors generate heat.
- Vasoconstriction: Blood vessels constrict reducing the amount of blood flow to skin.
- Hair erector muscles (causing goosebumps which trap warm air close to the skin)
- Adrenaline: Adrenal medulla increases the secretion of adrenaline and noradrenaline.
- Thyroxine: Thyroid gland is stimulated to secrete more thyroxine, increasing metabolic rate.
2) Behavioural:
- Put on jumper
- Shelter from external elements
Feedback: Feedback is negative as body temperature increases.
38
How is high body temperature regulated through a negative feedback loop?
Stimulus: Rising body temperature.
Receptors: Thermoreceptors (peripheral and central).
Modulator: Hypothalamus.
- Sends impulses via the sympathetic neural pathway to the skin blood vessels.
- Sends impulses to the sweat glands.
- Secretes TSH inhibiting factors.
Effectors
- Skin blood vessels
- Sweat glands
- Anterior lobe of the pituitary
Response:
1) Physiological:
- Vasodilation in skin: Blood vessels dilate increasing the amount of blood flow to the skin.
- Increased sweating: Sweat glands secrete sweat that evaporates, releasing heat energy.
- Reduced thyroxine: Thyroid gland releases less thyroxine, decreasing metabolic rate of the body and the amount of heat produced.
2) Behavioural:
- Take jumper off
- Turn on fan/AC
Feedback: Help lower body temperature and restore homeostasis.
39
What are central thermoreceptors?
Found in the hypothalamus and internal organs and detect blood and internal temperature.
40
What are peripheral thermoreceptors?
Found in skin and mucous membranes and detect external temperature.
41
What is intracellular fluid?
Fluid inside cells (cytosol) which makes up about 66% of total body water.
42
What is extracellular fluid?
Fluid outside cells (includes plasma and tissue fluids).
43
What are the 3 different types of extracellular fluid?
1) Intravascular fluid
2) Interstitial fluid
3) Transcellular fluid
44
What is intravascular fluid?
The plasma within blood vessels.
45
What is interstitial fluid?
Fluid between cells.
46
What is transcellular fluid?
Fluid in specific body regions like the brain, eyes, joints, and around the heart.
47
What is osmotic concentration?
Osmotic concentration is the amount of dissolved substances (solutes) in a solution. It determines water movement by osmosis.
48
What is osmotic pressure?
Osmotic pressure is the tendency of a solution to attract water across a membrane. The higher the osmotic concentration, the higher the osmotic pressure.
49
What is excretion and what organs are involved?
Excretion is the removal of metabolic waste from the body.
- Lungs: Excrete carbon dioxide and water.
- Sweat glands: Excrete water, salts, urea.
- Alimentary canal: Excretes bile pigments.
- Kidneys: Excrete urea and regulate water and salt levels
50
What is the structure of a nephron?
1) Glomerulus – Filters blood.
2) Bowman’s Capsule – Collects filtrate.
3) Proximal Convoluted Tubule – Reabsorbs nutrients and water.
4) Loop of Henle – Concentrates urine.
5) Distal Convoluted Tubule – Fine-tunes water and salt reabsorption.
6) Collecting Duct – Carries urine to ureters
51
What are osmoreceptors and where are they located?
Osmoreceptors are sensory cells that detect changes in osmotic pressure (water concentration) of blood. They are located in the hypothalamus.
52
What is the main function of the kidneys in regulating water?
The kidneys regulate water loss to maintain fluid balance.
53
What is selective reabsorption of water?
It is the process where the kidneys reabsorb water from the filtrate back into the bloodstream.
54
Where does water reabsorption by osmosis occur?
In the proximal convoluted tubule and loop of Henle.
55
Where does water reabsorption by active transport occur?
In the distal convoluted tubule and collecting duct.
56
How does ADH control water reabsorption?
ADH changes the permeability of the distal convoluted tubule and collecting duct to water.
57
What happens when ADH levels are high?
High permeability → more water reabsorbed → smaller, concentrated urine.
58
What happens when ADH levels are low?
Low permeability → less water reabsorbed → larger, dilute urine.
59
When is aldosterone released?
When sodium levels are low or blood pressure is low.
60
What does aldosterone do?
It promotes sodium reabsorption and potassium secretion in the kidneys.
61
How does aldosterone help retain water?
Water follows reabsorbed sodium by osmosis, increasing water retention and blood volume.
62
What is the role of the thirst centre and the thirst reflex?
Stimulus: High osmotic pressure in the blood (low amount of water).
Receptor: Osmoreceptors in the thirst centre of the hypothalamus stimulated.
Modulator: Hypothalamus sends nerve impulse to cerebral cortex and a conscious feeling of thirst occurs.
Effector: Skeletal muscles respond to behaviour and actively seek a drink.
Response: Drink a glass of water.
Feedback: Water absorbed into blood lowering osmotic pressure.
63
What does a negative feedback loop for increase in osmotic pressure/decrease in water concentration look like?
Stimulus: Decrease in water (increased osmotic pressure).
Receptor: Osmoreceptors in the hypothalamus stimulated.
Modulator:
- Hypothalamus sends nerve pulses to the posterior lobe of the pituitary gland to release ADH.
- Adrenal cortex secretes aldosterone.
- Thirst centre of the hypothalamus sends impulses to the cerebral cortex.
Effector:
- Distal convoluted tubule and collecting ducts of the nephron in the kidneys.
- Cerebral cortex coordinates the muscles of the arms, hands etc. to drink.
Response:
- ADH increases the permeability of nephron tubules (DCT and collecting duct) in the kidney.
- Aldosterone causes the increase of Na absorption and K secretion, which indirectly allows more water to be reabsorbed due to the movement of osmosis.
- Voluntary movement of the body to drink results in water being consumed and absorbed through the alimentary canal.
Feedback: Increased water reabsorption = decreased osmotic pressure.
64
What does a negative feedback loop for decrease in osmotic pressure/increase in water concentration look like?
Stimulus: increase in water (decreased osmotic pressure).
Receptor: Osmoreceptors in the hypothalamus stimulated.
Modulator:
- Hypothalamus reduces the release of ADH into the bloodstream by stimulating the posterior pituitary gland less.
Effector:
- Distal convoluted tubule and collecting ducts of the nephron in the kidneys.
Response:
- ADH decreases the permeability of nephron tubules (DCT and collecting duct) in the kidney. As a result, less water is reabsorbed into the body.
Feedback: Increased water reabsorption = decreased osmotic pressure.
65
What happens if there is too much water?
Water intoxication:
- Too much water.
- Body fluids become too dilute.
- Cells take in too much water and may swell or burst.
66
What happens if there is too little water?
Dehydration:
- Too little water.
- Cells shrink.
- If untreated, can be fatal.
Symptoms include:
- Thirst
- Dizziness
- Low blood pressure
67
How do the lungs control breathing?
Allow gas exchange (Oxygen enters the blood, and carbon dioxide is removed).
68
How do the diaphragm control breathing?
Is a dome-shaped muscle that separates the chest cavity from the abdomen.
- When it contracts, it flattens, increasing chest volume and drawing air into the lungs.
- When it relaxes, it pushes up, decreasing chest volume and forcing air out.
69
How do the intercostal muscles control breathing?
The intercostal muscles are located between the ribs. They assist in expanding and compressing the rib cage during breathing.
70
How does the medulla oblongata control breathing?
Contains the respiratory centre that controls breathing rate and depth of breathing.
71
How does the respiratory centre control breathing?
- Has areas for inspiration and expiration.
- Sends nerve signals to breathing muscles.
72
How does the peripheral nerves control breathing?
Peripheral nerves carry signals from the respiratory centre to the muscles:
- Phrenic nerve: Stimulates/activates the diaphragm.
- Intercostal nerves: Stimulate intercostal muscles.
73
How do the aortic and carotid bodies (peripheral chemoreceptors) control breathing?
Peripheral chemoreceptors are located in the aortic and carotid bodies and detect changes in oxygen, carbon dioxide, and hydrogen ion (pH) levels. They send signals to the respiratory centre to adjust breathing when gas concentrations deviate from normal.
74
What are central chemoreceptors and how do they control breathing?
Central chemoreceptors are located in the medulla oblongata and are highly sensitive to carbon dioxide and hydrogen ions. They send signals to the respiratory centre to adjust breathing when gas concentrations deviate from normal.
75
What is the main chemical trigger for breathing control?
Carbon dioxide (CO₂).
76
How does carbon dioxide affect breathing?
Even small increases significantly raise breathing rate and depth.
77
How does the body detect and respond to carbon dioxide levels?
- Detected by central (medulla) and peripheral chemoreceptors.
- Signals sent to the respiratory centre → stimulates diaphragm & intercostals → faster, deeper breathing to remove excess CO₂.
78
How do hydrogen ions affect breathing?
CO₂ forms carbonic acid, increasing H⁺ (lowers pH), which increases breathing rate.
79
How are hydrogen ions detected and how does the body respond?
- Detected by central and peripheral chemoreceptors.
- Increases breathing rate to lower CO₂ and H⁺ → restores pH.
80
When does oxygen affect breathing rate?
Only when oxygen levels drop significantly.
81
How is low oxygen detected and how does the body respond?
- Detected by peripheral chemoreceptors.
- Stimulates respiratory centre → increases breathing rate.
82
What controls voluntary breathing and what can it allow?
- Controlled by the cerebral cortex (conscious brain).
- Allows temporary control of breathing (e.g., holding breath, speaking, blowing candles).
83
What is a limitation of voluntary control of breathing?
If CO₂ builds up too much, the respiratory centre overrides voluntary control and forces breathing.
84
What changes occur during exercise that affect breathing?
- Cells use more oxygen.
- Produce more CO₂.
- Blood pH drops (more H⁺).
- Chemoreceptors detect these changes.
85
How does the respiratory centre respond during exercise?
- Increases breathing rate.
- Increases depth of breathing.
- Brings in more oxygen and removes CO₂.
86
How is carbonic acid formed?
1) Carbon dioxide (CO₂) dissolves in blood plasma.
2) It reacts with water (H₂O) to form carbonic acid (H₂CO₃)
3) Increases H⁺ concentration → lowers pH (more acidic).
4) Detected by central and peripheral chemoreceptors.
5) Triggers faster, deeper breathing to remove excess CO₂ and restore pH balance.
87
How does aldosterone regulate blood pressure and water concentration in the body?
1) Trigger: Low blood pressure or low sodium levels are detected.
2) Hormone Release: The adrenal cortex releases aldosterone.
3) Target Site: Aldosterone acts on the distal convoluted tubule and collecting duct of the kidney.
4) Sodium Movement: It causes 3 Na⁺ ions to be reabsorbed into the bloodstream.
5) Potassium Movement: At the same time, 2 K⁺ ions are secreted into the urine.
6) Water Follows: Water follows sodium by osmosis, increasing blood volume.
7) End Result: Blood pressure increases due to higher water and sodium concentration in the blood.
88
What does a negative feedback loop for a decrease in blood oxygen levels look like?
Stimulus: Oxygen levels decrease.
Receptor: Peripheral chemoreceptors in the aortic and carotid bodies.
Modulator: Respiratory centre of the medulla oblongata sends impulses along the phrenic and intercostal nerves.
Effector:
- Diaphragm (stimulated by the phrenic nerves)
- Intercostal muscles (stimulated by the intercostal nerve)
Response:
Diaphragm and intercostal muscles contract to increase the rate and depth of breathing, so more oxygen enters the bloodstream.
Feedback:
Feedback is negative as the amount of oxygen in the blood increases.
89
What does a positive feedback loop for a decrease in blood oxygen levels look like?
Stimulus:
- Increase in CO₂ levels
- Increase in hydrogen ion concentration
- Decrease in blood pH
Receptor:
- Peripheral chemoreceptors in the aortic and carotid bodies
- Central chemoreceptors in the medulla
Modulator: Respiratory centre of the medulla oblongata sends impulses along the phrenic and intercostal nerves.
Effector:
- Diaphragm (stimulated by the phrenic nerves)
- Intercostal muscles (stimulated by the intercostal nerve)
Response:
Diaphragm and intercostal muscles contract to increase the rate and depth of breathing, so more carbon dioxide is breathed out of the body.
Feedback:
Feedback is negative as the CO₂ and H⁺ levels decrease and the blood pH increases.
