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Hormones and Behavior > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is homeostasis?

A

the maintenance of a steady state within an organism by means of physiological or behavioral feedback control mechanisms
- for humans, we maintain an optimal body temperature between 36-38C
Some homeostatic systems are completely physiological processes, some utilize only behavioral processes, and some combine both

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2
Q

Describe how the thermostat is a common homeostatic device

A

there is a set zone for stasis on the thermostat, and once the temperature goes outside that zone, it either sets off the air conditioner to cool off or the heater to warm it up. This is all through negative feedback

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3
Q

What is the set zone?

A

the range of tolerance in a system that makes it so the system isn’t going on and off too frequently

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4
Q

What are endotherms?

A

Generate their own heat through internal processes

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5
Q

What are ectotherms?

A

They get most of their heat from the environment

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6
Q

How do endotherms maintain temperature?

A

thermoregulatory systems show redundancy–they are monitored by more than one mechanism
the POA and the Lateral hypothalamus

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7
Q

How does the POA help in endotherm maintenance?

A

Responsible for the physiological responses to cold, such as shivering and constriction of the blood vessels–> pulls from skin so as not to loose heat

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8
Q

How does the Lateral Hypothalamus help in endotherm maintenance?

A

Controls behavioral regulation of temperature, such as turning on heat lamps or cooling fans

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9
Q

How can endotherms use internal and behavioral processes to control body temperature?

A
  • Receptors in the skin, body core, and hypothalamus detect temperature and transmit that information to the spinal cord, brainstem, and hypothalamus
  • If body temperature is outside of the set zone, these neural regions can initiate behavioral and physiological responses to return temperature to the set zone
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10
Q

What are some brain responses to being cold?

A

increased thyroid activity
metabolism of brown fat
constriction of cutaneous blood vessels
shivering of muscles

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11
Q

What are some brain responses to heat?

A

Accelerated respiration
perspiration
dilation of cutaneous vessels

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12
Q

What are the three strategies in behavioral control of body temperature in both endotherms and ectotherms?

A

Change exposure of the body surface
Change external insulation (nesting, burrow)
Change surroundings (moving to shade)

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13
Q

What is fluid balance and why is it important?

A

Water is important for virtually all metabolic processes: mammals are approximately 67% water
Water also serves as the solvent for sodium, chloride, potassium, sugars, amino acids, proteins, vitamins and others
Water is constantly lost through perspiration, respiration and urination and must be continuously replaced, so very little is stored in the body
When use exceeds intake, the body conserves water by reducing the amount excreted from kidneys, and then triggers behavioral mechanisms to seek water sources

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14
Q

Why is sodium important in homeostasis?

A

The kidneys use sodium to conserve water
Sodium is also important for the movement of water between the two major fluid compartments in the body: the intracellular and the extracellular compartments

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15
Q

How do the dynamics between sodium and water balance intracellular and extracellular fluid levels?

A
  • Water can pass freely through semipermeable biological membranes, but many solutes (chemical substances dissolved in the water) cannot
  • When one compartment has a greater concentration of solutes than the other, the water will redistribute itself so the solute concentration is more even
  • This movement of water to an area of higher concentration is called osmosis
  • The concentration of solutes in a solution is its osmolality, and the control of this osmotic concentration is called osmoregulation
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16
Q

What makes us thirsty?

A

The extracellular fluid indicates the state of the intracellular space and is monitored by the nervous system
Two states signal a need for water
- High extracellular solute concentration, or very salty fluids, stimulates osmotic thirst
- Low extracellular volume from a loss of bodily fluids stimulates hypovolemic thirst

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17
Q

What is osmotic thrist?

A
  • Osmosensory neurons in the hypothalamus detect increased osmolality of extracellular fluid, which draws water out of intracellular compartment
  • These neurons signal to the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) of the hypothalamus to release vasopressin (AVP); this acts to help conserve water as blood moves through the kidneys
  • Aldosterone is released from the adrenal glands and causes kidneys to conserve Na+ (to help retain water)
  • If that doesn’t fix the dehydration, a signal is sent from the OVLT and SFO to stimulation drinking behavior
    -This dual control allows physiological water-saving systems to be engaged prior to behavioral responses, freeing us from having to drink frequently
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18
Q

What brain structures are involved in the mediation of thirst and water intake?

A

Circaventricular organs
- Subfornical organ
- Supraoptic nuclei
- Organum vasculosum of the lamina terminalis (OVLT)
- Lateral preoptic area
- Paraventricular nuclei
- Area postrema

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19
Q

What is hypovolemic thirst?

A
  • Baroreceptors in major blood vessels detect pressure drop from fluid loss
  • This also triggers ADH which also acts as a vasoconstrictor to increase blood pressure and reduce water flow to bladder
  • The baroreceptors in the heart also signal to the brain directly via the vagus nerve to stimulate thirst (replenish not just water but also SaH)
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20
Q

What does hypovolemic thirst trigger?

A
  • Hypovolemia (drop in blood pressure) also stimulates angiotensin II production via action of renin (from the kidneys)
    • Angiotensin II causes vasoconstriction; will also constrict blood vessels
    • It also causes release of aldosterone (from the adrenal gland, helps with sodium retention in the kidneys) and vasopressin (to constrict blood vessels), and stimulates drinking behavior at the OVLT and SFO
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21
Q

How does nutrient regulation help prepare for future homeostasis?

A

Aside from obtaining energy from ingested food, nutrients are needed for growth, maintenance, and repair of the body
Because of its importance, there are homeostatic mechanisms in place to ensure a continuous supply of fuels without organisms having to eat constantly

22
Q

What is basal metabolism?

A

Energy used for heat production, maintenance or membrane potentials, and life-sustaining processes (super energetically costly!)

23
Q

How do fluctuations in energy requirements relate to fat storage?

A

There is always a persistent need for energy, but fluctuations in requirements
- rate of energy use varies throughout the day and with different seasons
- There are also fluctuations in energy acquisition
The balance between the amount of energy stored in the body, energy. expenditure, and energy intake is controlled but not as hightly regulated as with water and salt or temp
Stored fat likely enhanced survival in environments, helping animals to survive

24
Q

What is adipose tissue?

A

Excess energy is stored as fat, which can be tapped later when fuel after a meal wanes

25
Q

What mechanisms are there more of when it comes to eating?

A

There are more mechanisms to promote eating and weight gain (hunger signals) than there are to stop eating (satiety signals)

26
Q

What complications are there with the study of energy balance?

A

There are many different systems sending many different signals
Lots of different homrones have lots of different effects
Additionally, many other substances may indirectly affect food intake by doing something else
In humans, many different things influence eating (access to food, smells, activity/boredom, sttress/guilt)

27
Q

What are the two phases of energy utilization and storage after a meal?

A

The postprandial phase
The postabsorptive phase

28
Q

What is the Postprandial phase?

A

Occurs immediately after ingestion of food when the supply of metabolic fuels in he form of glucose, fatty acids, and amino acids enters the blood stream almost immediately

29
Q

What is the Postabsorptive phase?

A

The storage of the excess energy from the meal

30
Q

How does insulin relate to the postabsorptive phase?

A
  • Levels rise and promote the uptake of glucose into tissues
  • Stimulates the conversion of glucose to glycogen, a stored form of sugar
  • Facilitates the transport of glucose into muscle and fat cells, and transport of amino acids into muscle cells
31
Q

Describe metabolic interactions during the well-fed state

A
  • Food is broken down into glucose, free fatty acids, and amino acids. Glucose powers the brain and muscles
  • Insulin is released from the pancreas to facilitate transport of glucose
  • Excess glucose is converted to glycogen and stored in the liver and muscles
32
Q

Describe metabolism during the fasting state

A

The body must shift from putting energy into storage to getting it out of storage:
glucagon is released from the pancreas
Glycogenolysis breaks down glycogen in liver
Lipolysis breaks down triglycerides from fat
“Liverated” glucose and ketone bodies power the brain
Body needs energy, but does it before you HAVE to eat

33
Q

What is Glycogenolysis?

A

It breaks down stored glycogen from the liver to provide a rapid supply of glucose via glucagon

34
Q

What is Lipolysis?

A

It acts to breakdown triglycerides stored in adipose tissue into free fatty acids and glycerol, which can be used in the periphery (also done by glucagon)

35
Q

What is an emergency system for metabolism during the fasting state?

A

Gluconeogenesis–production fo glucose from amino acids
- takes place in liver, resulting in production of ketone bodies as a side reaction, called ketosis
- Ketone bodies are used as fuel instead of glucose (including in the brain)
- Too many ketone bodies in the blood can change blood pH and may be dangerous for some individuals

36
Q

What is type 1 diabetes?

A

(also called insulin-dependent diabetes)
- B-cells of the pancreas produce very little (if any) insulin
- Requires individuals to exogenously deliver insulin
Results in higher-than-usual glucose in the blood, which can be damaging, while starving cells of energy

37
Q

What is type 2 diabetes?

A
  • When tissues are no longer sensitive, or do not respond, to insulin
  • Used to be called adult-onset diabetes, but since it is being seen among younger kids it no longer applies
    Results in higher-than-usual glucose in the blood, which can be damaging, while starving cells of energy
38
Q

What is hunger?

A

A strong motivation to seek out and ingest food

39
Q

What are peripheral signals?

A

Endocrine signals that come from outside the nervous system

40
Q

What are central signals?

A

Those that originate from within the NS

41
Q

What is satiety?

A

The feeling of fullness that will suppress/inhibit food intake

42
Q

Describe Leptin as a peripheral signal for homeostasis

A
  • Adipokine (hormone produced by adipose cells)
  • When stored fat is being used for energy, the blood levels of leptin fall faster than the levels of fat being metabolized
  • This drop in leptin signals for increase in food intake
  • Used to be considered a “satiety” signal, it is now though to be a “starvation” signal to increase food intake when leptin levels fall
  • Leptin receptors are in the periphery as well as brain regions, especially in the arcuate nucleus of hypothalamus
  • Leptin also affects sexual motivation
  • Elevated leptin levels signal to hypothalamus that fat stores are increased and to inhibit eating, and signals to reproductive system that enough energy is around to support reproduction
43
Q

What is PYY3-36?

A

Secreted by. cells in the intestines
- Its levels are low before eating but rise rapidly after a meal
- It also acts in opposition to ghrelin, acting as an appetite suppressor
- Eating quickly makes itt harder for brain to release this hormone/detect fullness

44
Q

What is reported from hormones in the digestive organs?

A

Shorter-term energy balance–presence or absence of food in the gut

45
Q

What are two important hormones for appetite control and what do they do?

A
  • Ghrelin: synthesized and released by endocrine cells of the stomach; reaches high levels before eating and drops off after eating; works as an appetite stimulant
  • PYY3-36: released by intestinal cells; reaches high levels after eating and works as an appetite suppressant
46
Q

How do GI hormones serve as satiety signals that converge on the dorsal hindbrain?

A

Outside signals (such as nutrients, memory, time of day, etc) go through the hypothalamus, ARC and pituitary and through to the hindbrain. Satiety signals go to the dorsal hindbrain and food intake results from signals in the ventral hindbrain

47
Q

What is the hypothalamus important for in homeostasis?

A

No single brain region has control of apptetie, but the hypothalamus is important to regulation of: metabolic rate, food intake, and body weight

48
Q

What are the “appetite centers” in the hypothalamus?

A
  • Ventromedial hypothalamus (VMH) is a satiety center
  • Lateral hypothalamus (LH) is a hunger center
  • The arcuate nucleus of the hypothalamus contains an appetite controller governed by hormones, like insulin
49
Q

What are the two sets of neurons that the arcuate appetite system relies on?

A
  • POMC neurons produce the peptides pro-opiomelanocortin (POMC) and cocaine-and amphetamine-related transcript (CART)
    • these neurons inhibit appetite and raise metabolism when stimulated, promoting weight loss
  • NPY neurons produce neuropeptide Y (NPY) and agouti-related peptide (AgRP)
    • These neurons stimulate appetite and lower metabolism, promoting weight gain
      POMC and NPY neuron projections leave the arcuate and make connections with hypothalamic structures, ultimately modulating food intake
50
Q

How do the GI hormones interact with POMC and NPY?

A
  • Leptin activates POMC neurons but inhibits NPY neurons, so leptin works to suppress hunger
  • Ghrelin and PYY3-36, act mainly on NPY neurons, work in opposition to provide short term appetite control
    • Ghrelin stimulates the cells, leading to an increase in appetits
    • PYY3-36 inhibits the cells, reducing appetite

Hormones and Behavior (12 decks)

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