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Week 27 Flashcards

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1
Q

What is homoeostasis?

A

Maintenance of a stable internal environment despite changes in external conditions.

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2
Q

What is the goal of homoeostasis?

A

To maintain internal conditions within a narrow optimal range. If conditions deviate, control systems bring them back.

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3
Q

What is a negative feedback loop?

A

A mechanism that reverses a deviation from the set point. Sensor detects change, control center processes info, effector makes correction.

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4
Q

What are examples of homeostatic variables?

A

Temperature, blood gas concentrations, ion concentrations, hunger, pH, water balance, glucose levels.

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5
Q

What are the 3 key elements of homeostatic control and regulation?

A
  1. Receptor (sensor) – detects change 2. Control center – receives signal, sends command 3. Effector – responds to restore balance.
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6
Q

What are the behavioural responses to temperature changes?

A

Seeking shelter, adjusting clothing, moving to warmer/cooler environments.

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7
Q

What are the physical responses to cold temperatures?

A

Vasoconstriction, shivering, hair erection (in furry animals).

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8
Q

What are the metabolic responses to cold?

A

Increased cellular respiration, non-shivering thermogenesis, hormonal stimulation of metabolism.

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9
Q

What are the molecular responses to cold?

A

Upregulation of uncoupling proteins, expression of cold-shock proteins.

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10
Q

What happens when core temperature drops?

A

Detected by hypothalamus; hormonal responses include increased T3, T4, epinephrine, and cortisol.

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11
Q

What are the effects of increased T3, T4, epinephrine, and cortisol during cold exposure?

A

Increased metabolic rate and heat production.

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12
Q

What hormone signals hunger?

A

Ghrelin – produced in the stomach, increases before meals, stimulates appetite.

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13
Q

What hormone signals satiety (fullness)?

A

Leptin – produced by adipose tissue, inhibits hunger, regulates long-term energy balance.

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14
Q

What are the effects of ghrelin and leptin on hunger regulation?

A

Ghrelin stimulates eating; leptin reduces food intake and increases energy expenditure.

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15
Q

How do ghrelin and leptin affect metabolism and behaviour?

A

They influence hypothalamic centres and affect feeding behaviour and energy storage.

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16
Q

How does temperature regulation affect different biological levels?

A

Cellular: enzyme activity; Tissue: vasodilation/constriction; Organ: shivering; Organism: behavioural changes.

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17
Q

How does hunger regulation affect different biological levels?

A

Cellular: nutrient sensing; Tissue: adipose tissue signalling; Organ: stomach and hypothalamus; Organism: eating behaviour.

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18
Q

What are some practical examples of homeostatic regulation?

A

Thermoregulation in cold weather, hormonal control of appetite, body responses to stress or starvation.

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19
Q

Ghrelin pathway?

A

1) Reduced blood sugar levels and low stomach content promotes the releases of Ghrelin into the bloodstream

2) Ghrelin travels to the hypothalamus and binds to GHSR and promotes AMPK phosphorylation

3) AMPK activation promotes insulin retention and resistance and alters behaviour to seek out food.

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20
Q

Leptin pathway?

A

1) Leptin is releases by adipose tissue cells into the bloodstream, therefore increased adipose cells, increased leptin concertation

2) Leptin reaches the lateral hypothalamus counteracting the hunger promotion of Neuroprotein Y and Anandamide, and in the medial hypothalamus promote α-MSH synthesis (a hunger-suppressor)

3) Reduced blood sucrose concertation promotes the breakdown of brown adipose tissue (BAT) utilising lipids as a source of energy

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21
Q

What conditions do plants need to maintain via homeostasis?

Study These Flashcards
A

Overall water concentration → maintaining turgidity, gas exchange, fuelling chemical processes

Oxygen/Carbon Dioxide Balance → balancing photosynthesis and respiration

Temperature → preventing thermal damage to plant material

Nutrient balance → preventing saturation or starvation

Photon Absorption → preventing excessive damage to leaf
material while maintaining photosynthetic efficiency

Wound response → preventing infection and resource loss

22
Q

What are some methods by which plants maintain physical or internal conditions via homeostasis?

Study These Flashcards
A

Physical Response - Changes in trophism
Behavioural Response - Opening/Closing stomata
Molecular Response - Promoting/Inhibiting transcription genes
Metabolic Response - Alteration of Carotenoid Content within leaves

23
Q

What are specific plant responses used to regulate homeostasis?

Study These Flashcards
A

Opening/Closing of stomata
Alteration of carotenoid content within leaves
Changes in trophism-based growth
Promotion and inhibition of transcription of genes

24
Q

What are the three mechanisms required for homeostasis in plants?

Study These Flashcards
A

A mechanism for detection of the change in a variable
A pre-set limit for that condition
A mechanism to return the changed variable back to the pre-set limit

25
What roles does ABA (abscisic acid) play in plant homeostasis?
Seed development Dormancy Germination Vegetative growth Adapting to environmental stresses
26
Where is ABA produced, and what triggers its activation?
ABA is a zeaxanthin-derived phytohormone synthesised in almost all plant tissues First committed reaction step: Zeaxanthin to violaxanthin (ZEP) Stored in chlorenchyma cells as an inactive form (ABA-Glucose-Ester, ABA-G-E) Activated and released in response to environmental stressors: increased heat, increased soil salinity, and decreased water concentration
27
What are the effects of ABA in plant homeostasis?
Induces stomatal closure in drought conditions (antitranspirant) Promotes and activates antiviral immune response Inhibits additional cellular growth by preventing kinetin synthesis Promotes root growth in response to low atmospheric humidity Reduces endodermis growth in roots exposed to salt Inhibits seed germination Downregulates photosynthetic enzyme production in high light, low water stress conditions Inhibits fruit ripening in stressful conditions
28
What is the ABA activation pathway?
Zeaxanthin Violaxanthin Neoxanthin Xanthoxin ABA-Aldehyde ABA Enzymes: ZEP, NSY, NCED, ABA2, AAO/MCSU ABA-G-E Activated in response to drought or increased soil salinity Promoted transcription Phosphoprotein cascade Response
29
Why must transpiration be minimized under low water stress conditions?
If more water is lost than gained through roots, the plant risks: Reduced cellular turgidity Reduced metabolic water Reduced transport media
30
How does ABA mediate water retention (Part 1)?
ABA is released in response to dehydration stress and imported into stomatal guard cells via ABCG40 ABA binds to PYR/PYL receptor and induces dissociation of regulatory proteins OST1 is inhibited; it is a key ion influx/efflux regulator KAT1 (K⁺ influx transporter) is inactivated to prevent K⁺ entry into guard cells KUP6 (K⁺ efflux transporter) is activated and shuttles K⁺ out of guard cells SLAC1 (anion efflux transporter) is activated and shuttles anions out of guard cells Anion flow causes depolarisation, activating GORK (voltage-gated K⁺ efflux transporter) Water flows out of vacuole, reducing turgidity, shrinking guard cells, and causing stomata to close
31
How does soil salinity affect root growth and ABA activity?
High soil salinity risks water imbalance and reduced turgidity/metabolism Root growth is reduced in high salinity to prevent excessive Na⁺ and Cl⁻ uptake ABA is released in endodermal cells when excessive ions are detected, reducing root length and lateral development
32
What is the role of the Casparian strip and ABA in detecting salt stress?
Casparian strip forces water and ions into endodermal cells (from apoplastic pathway) Allows detection of Na⁺ and Cl⁻ ions ABA release reduces root development ABA activates: SOS1 (pumps Na⁺ out of cells) HKT1 (pumps K⁺ into vacuoles to promote water uptake)
33
Why is ABA considered a highly conserved regulatory molecule?
ABA is fundamental for homeostatic regulation Utilised by almost all plant species Zeaxanthin to violaxanthin is the first committed step in its production
34
What is the effect of a ZEP mutation in orange pepper plants?
ZEP mutation reduces activity, causing accumulation of orange carotenoid Occurs in ripe/unripe fruit, roots, leaves, stems Reduced ZEP activity lowers ABA levels Diminished response to environmental stressors
35
What are the risks of genetic modifications that reduce ABA production?
Altered carotenoid/vitamin content can reduce stress responses May impair crop growth in changing climates
36
What is the function and location of the kidneys?
Filter the blood and produce urine Found in the retroperitoneal space (back of abdominal cavity) Located between T12 and L3 vertebrae Right kidney is lower due to the liver Protected by lower ribs and a fat capsule
37
What structures make up the nephron?
Bowman’s capsule Proximal convoluted tubule Loop of Henlé Distal convoluted tubule Collecting duct Each kidney contains ~1 million nephrons
38
How does Bowman’s capsule function in filtration?
Afferent arteriole brings blood into glomerulus Efferent arteriole is narrower, creating high pressure High pressure forces small molecules (water, glucose, ions, urea) into capsule Large molecules (proteins, blood cells) do not pass through
39
Which molecules and ions are filtered into the nephron?
Water Glucose Amino acids Ions (Na⁺, Cl⁻) Urea
40
Which substances are not filtered through the glomerulus?
Blood cells Plasma proteins
41
What determines net filtration pressure in the glomerulus?
Net Filtration Pressure = Glomerular pressure − (Osmotic pressure + Capsular pressure) Maintains flow of filtrate into the nephron
42
How is glomerular filtration rate (GFR) regulated?
Intrinsic control (renal autoregulation) Extrinsic control (neural and hormonal)
43
What mechanisms are involved in intrinsic control of GFR?
Myogenic mechanism: afferent arteriole constricts/dilates in response to pressure Tubuloglomerular feedback: Macula densa detects NaCl concentration Signals afferent arteriole to constrict if NaCl is high
44
What mechanisms are involved in extrinsic control of GFR?
Sympathetic nervous system: vasoconstriction reduces GFR to conserve fluid Hormonal control: RAAS system
45
What is selective reabsorption, and where does it occur?
Occurs mainly in proximal convoluted tubule Microvilli increase surface area Reabsorbs glucose, amino acids, ions, water Uses active and passive transport
46
How does the loop of Henlé contribute to water reabsorption?
Descending limb: permeable to water, impermeable to ions Ascending limb: impermeable to water, actively transports ions out
47
What is the countercurrent multiplier system?
Function of the loop of Henlé Creates osmotic gradient in medulla Facilitates water reabsorption from collecting ducts
48
How does the brain regulate water balance via the kidneys?
Hypothalamus osmoreceptors detect water potential Low water potential triggers ADH release from posterior pituitary
49
What is the role of ADH in kidney function?
ADH (antidiuretic hormone) travels to kidneys via blood Increases collecting duct permeability to water
50
How do collecting ducts respond to ADH?
ADH binds to receptors on duct cells Aquaporins inserted into membrane Water reabsorbed into blood
51
What happens when water potential rises?
Less ADH is released Aquaporins are removed from membrane Less water reabsorbed More dilute urine is produced

Organ systems (9 decks)

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