Psych 337: Homeostasis and Eating
human physiological response to heat
Accelerated respiration Perspiration Dilation of cutaneous vessels
what is leptin
Adipokine (hormone produced by adipose cells)
why is diabetes problematic (both type 1 and 2)
Both result in higher-than-usual glucose in the blood, which can be damaging, while starving cells of energy
behavioral control of body temperature for ectotherms (and endotherms, but mostly ectotherms)
Change exposure of body surface (expose body to sun) Change external insulation - Nesting, burrowing (going underground) Change surroundings (moving into a shaded area for example)
how do ectotherms generate heat
Ectotherms get most of their heat from the environment (can't generate heat from within)
how does leptin affect 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
what type of processes do endotherms use to control body temperature
Endotherms can use internal and behavioral processes to control body temperature
how do endotherms generate heat
Endotherms generate their own heat through internal processes (like humans)
how is excess energy stored and when are these stores used
Excess energy is stored in the form of adipose tissue (or fat) These fat stores can then be tapped later when fuel after a meal wanes
levels of PYY3-36 and food intake
Its levels are low before eating but rise rapidly after a meal It also acts in opposition to ghrelin, acting as an appetite suppressor
what is the role of kidneys in conserving water
Kidneys use sodium to conserve water
leptin and POMC/NPY neurons
Leptin activates POMC neurons but inhibits NPY neurons, so leptin works to suppress hunger
where are leptin receptors
Leptin receptors are in the periphery as well as brain regions, especially in the arcuate nucleus of the hypothalamus
(During well fed state) Hormonal involvement in the postabsorptive phase: insulin
Levels rise and promote uptake of glucose into tissues (insulin is required as a transporter for glucose in the body - but not the brain) Stimulates the conversion of glucose into glycogen, a stored form of sugar Facilitates the transport of glucose into muscle and fat cells, and transport of amino acids into muscle cells
what leads to parasympathetic signaling via hypothalamus for food intake
Meal anticipation: smell, sight of food; time of day; environmental factors
what do the NPY neurons produce and what is the role of these neurons
NPY neurons produce neuropeptide Y (NPY) and agouti-related peptide (AgRP) These neurons stimulate appetite and lower metabolism, promoting weight gain
what is the primary homeostatic mechanism
Negative feedback systems are the primary homeostatic mechanisms
role of hormones in osmotic thirst
Neurons signal to paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus to release vasopressin (ADH) - This acts to help conserve water as the blood moves through the kidneys Aldosterone is released from the adrenal glands and causes kidneys to conserve Na+ (to help retain water) - Having more salt in an area helps hold onto more water
what cells secrete PYY3-36
Secreted by cells in the intestines
how is shorter term energy balance reported
Shorter-term energy balance - presence or absence of food in the gut - is reported by hormones from the digestive organs
Homeostasis
The maintenance of a steady state within an organism by means of physiological or behavioral feedback control mechanisms
what does the dual control after osmotic thirst allow for?
This dual control allows physiological water-saving systems to be engaged prior to behavioral responses, freeing us from having to drink frequently
osmosis
This movement of water to an area of higher concentration
relationship between leptin and food intake
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, but it is now thought to be a "starvation" signal to increase food intake when leptin levels fall
Type 2 diabetes (these people still have insulin in their bodies!)
When tissues are no longer sensitive, or do not respond to, insulin (receptors not responding) Used to be called adult-onset diabetes, but since it is being seen among younger kids it no longer applies
what happens when water use exceeds water intake
When water use exceeds water intake, the body conserves water by reducing the amount excreted from kidneys
what happens when physiological water conservation can no longer compensate for water use and loss
behavioral mechanisms kick in so the animal seeks out water sources
two hormones important for appetite control
ghrelin and PYY3-36
emergency system for metabolism in fasting state
gluconeogenesis - the production of glucose from amino acids
what is the motivation to seek out and ingest food
hunger
what are the peripheral signals in control of food intake
leptin, PYY3-36
how has stored fat enhanced survival for animals over the course of evolution
likely enhanced survival in environments where energy availability fluctuated, helping animals to survive especially harsh winters, droughts, or famine Also allowed individuals to engage in courtship, mating, gestation, lactation, and other reproductive behaviors that conflict with foraging, hoarding, and eating
what cells synthesize PYY3-36
released by intestinal cells
how does the number of mechanisms to promote eating compare with those to stop eating
there are more mechanisms to promote eating and weight gain (hunger signals) than there are to stop eating (satiety signals)
Type 1 diabetes (insulin-dependent diabetes)
B-cells of the pancreas produce very little (if any) insulin Requires individuals to exogenously deliver insulin
how does balance between energy stored in body, energy expenditure and energy intake compare with that of water and salt
Balance between the amount of energy stored in the body, energy expenditure, and energy intake is controlled but not as highly "regulated" as with water and salt or temperature
how is hypovolemic thirst detected
Baroreceptors in major blood vessels detect pressure drop from fluid loss
what is basal metabolism used for?
Basal metabolism is energy used for heat production, maintenance of membrane potentials, and life-sustaining processes (however, basal metabolism is super energetically costly)
during well fed state: Metabolic interactions among the major components of energy balance
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
Homeostasis in humans
For humans, we maintain an optimal body temperature between 36-38 degrees celsius There are also optimal concentrations of sugars, proteins, sodium, potassium, blood pH
what cells synthesize ghrelin
Ghrelin - synthesized and released by endocrine cells of stomach
what type of neurons do ghrelin and PYY3-36 mainly act on
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 appetite PYY3-36 inhibits the cells, reducing appetite
during the fasting state: metabolic interactions among the major components of energy balance
Glucagon is released from the pancreas Glycogenolysis breaks down stored glycogen in the liver Lipolysis in adipose tissue releases free fatty acids and glycerol "Liberated" glucose and ketone bodies power the brain
processes of metabolism during fasting state
Glycogenolysis breaks down stored glycogen from the liver to provide a rapid supply of glucose via glucagon (hormone) Lipolysis 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)
what two states signal a need for water
High extracellular solute concentration, or very salty fluids, stimulate osmotic thirst - Increased salt on the outside causes water from inside cells to move out, which leads to a drop in fluid of intracellular space Low extracellular volume from a loss of bodily fluids stimulates hypovolemic thirst (this is triggered by significant reduction in overall volume)
important of homeostasis in ensuring a continuous supply of fuel for organism
Homeostatic mechanisms in place to ensure a continuous supply of fuels without organisms having to eat constantly
what does the hypovolemia (drop in blood pressure) from hypovolemic thirst stimulate
Hypovolemia (drop in blood pressure) also stimulates angiotensin II production via action of renin (from the kidneys) Angiotensin → vasoconstriction Also causes release of aldosterone (from adrenal gland, helps with sodium retention in the kidneys) and vasopressin (to constrict blood vessels), and stimulates drinking behavior at the OVLT and SFO
when does compensatory action begin
If a desired value, the set point, is deviated from too much, the compensatory action begins
human physiological response to cold
Increased thyroid activity (increases production of thyroid hormone which increases metabolism) Metabolism of brown fat Constriction of cutaneous blood vessels Shivering of muscles
process of gluconeogensis
Occurs 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) → less efficient, need more to do the same kind of job Too many ketone bodies in the blood can change blood pH and may be dangerous for some individuals (such as diabetics with uncontrolled blood sugar levels)
how is the increased osmolarity in osmotic thirst detected
Osmosensory neurons in the hypothalamus detect increased osmolarity of extracellular fluid (higher extracellular solute concentration), which draws water out of intracellular compartment
how do POMC and NPY neurons module food intake
POMC and NPY neuron projections leave the arcuate and make connections with hypothalamic structures
what are the two sets of neurons that the arcuate appetite system relies on
POMC neurons and NPY neurons (and they have opposing effects)
what do the POMC neurons produce and what is the role of these neurons
POMC neurons produce the peptides proopiomelanocortin (POMC) and cocaine- and amphetamine-related transcript (CART) These neurons inhibit appetite and raise metabolism when stimulated, promoting weight loss
peripheral versus central signals in control of food intake
Peripheral signals are endocrine signals that come from outside the nervous system, while central signals are those that originate from within the nervous system
thermoregulatory systems in the rat
Preoptic area (POA): responsible for the physiological response to cold, such as shivering and constriction of the blood vessels (POA is in the hypothalamus) Lateral hypothalamus: controls behavioral regulation of temperature, such as turning on heat lamps or cooling fans
ghrelin levels and food intake
Reach high levels before eating and drop off after eating Works as an appetite stimulant
PYY3-36 levels and food intake
Reaches high levels after eating Works as an appetite suppressant
basic mammalian thermoregulatory system -- where are the receptors and how does the temperature return to the set zone
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
importance of sodium in movement of water
Sodium is also important for movement of water between the two major fluid compartments in the body: the intracellular and extracellular compartments Sodium helps to maintain the osmolarity between the two compartments
is homeostasis physiological processes or behavioral processes?
Some homeostatic systems are completely physiological processes, some utilize only behavioral processes, and some combine both
how must the body change its activities during the fasting state
The body must shift from putting energy into store to getting it out of storage
osmolarity and osmoregulation
The concentration of solutes in a solution is its osmolarity the control of this osmotic concentration is called osmoregulation
what does the extracellular fluid indicate
The extracellular fluid indicates the state of the intracellular space and is monitored by the nervous system
what is the set zone and why is it important
The set zone refers to the range of tolerance in a system This makes it so that the system isn't going on and off too frequently
Complications with study of energy balance
There are many different systems sending many different signals Different hormones have different effects Many other substances may indirectly affect food intake by doing something else (ex: Orexin increases general arousal and reduces sleep, resulting in animals eating more) In humans, many different things influence eating such as our biological clock, social events, etc.
appetite centers in the hypothalamus
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)
dynamics between sodium and water in balancing intracellular and extracellular fluid levels
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
how is water lost
Water is constantly lost through perspiration, respiration, and urination and must be continuously replaced (we don't have a store of it in the same way that we have food stores)
what happens if the release of ADH and aldosterone doesn't fix the dehydration?
a signal is sent from the OVLT and SFO (brain regions right around the ventricles) to stimulate drinking behavior - In this situation, you want to be drinking water not gatorade etc. - OVLT: organum vasculosum of the lamina terminalis - SFO: subfornical organ
what other parts of body does hypothalamus signal
intestine, stomach, pancreas
what happens when hypovolemic thirst is detected
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 (for this type of thirst you need to drink something that replenishes the electrolytes also)
issues with energy metabolism
type 1 and type 2 diabetes
