physiol psych exam 3

glucose

the principal sugar used for energy, especially in the brain

glycogen

complex carbohydrate made of glucose molecules; stored for a short term in the liver and muscles

glycogenesis

converting glucose to glycogen; regulated by the pancreatic hormone insulin

glycogenolysis

converting glycogen to glucose; controlled by the pancreatic hormone glucagon

lipids

fats for longer-term storage; deposited in adipose (fat) tissue

prolonged deprivation

• first/ongoing: gluconeogenesis to convert fat and proteins to glucose

• then: ketogenesis produces ketones from fat as a form of fuel

where does the body need insulin

glucose transporters in the cell membrane must have insulin to function, except in the brain

diabetes mellitus

caused by a lack of insulin

type I diabetes mellitus

juvenile-onset; the pancreas stops producing insulin

type II diabetes mellitus

adult-onset; primarily a consequence of reduced sensitivity to insulin; associated with obesity; leads to further health problems such as increased risk of heart disease and stroke

what is basal metabolism?

processes of heat production, maintenance of membrane potentials, and all other basic life-sustaining processes

basal metabolism

• metabolism adjusted in response to under- or over-nutrition, so resist losing or gaining eight

• at the start of a diet (less nutrition), the basal metabolic rate will fall to prevent losing weight

metabolic adaptation

decrease in basal metabolism following weight loss

the 2 centers in the outdated dual-center model of appetite control

• ventromedial hypothalamus (VMH)

• lateral hypothalamus (LH)

ventromedial hypothalamus (VMH)

lesions cause hyperphagia and obesity; suggests satiety center

lateral hypothalamus (LH)

lesions cause aphagia; suggests hunger center

why the dual-center hypothesis is too simple

• both VMH- and LH-lesioned rats eventually stabilize at a new body weight, even with excessive feeding or food deprivation

• research shows that the hypothalamus has a role in larger appetite control network

the role of the arcuate nucleus in appetite control

arcuate nucleus of hypothalamus contains an appetite controller (integrates satiety and hunger signals) governed by several hormones

hormones that govern the arcuate nucleus

• insulin

• ghrelin - hunger

• leptin - satiety

• PYY_3-36 - satiety

• GLP-1 - satiety

the only hormone that governs the arcuate nucleus in appetite control that signals hunger

ghrelin

what insulin is essential for in terms of glucose

• insulin is a pancreatic hormone that is essential for the uptake and storage of glucose

• the brain integrates insulin and glucose levels with other information to regulate feeding behavior

the 3 sequential stages insulin is released in

• cephalic stage

• digestive phase

• absorptive phase

cephalic phase of insulin release

sensory stimuli related to food (ex. taste, smell, sight) causes the conditioned release of insulin in anticipation of ingestion/glucose

digestive phase of insulin release

food enters the stomach and intestines → release of gut hormones → stimulation of insulin release from pancreas

absorptive phase of insulin release

glucodetectors in the liver detect glucose entering blood → send info via vagus nerve to the nucleus of solitary tract (NST) → hypothalamus → stimulate insulin release from pancreas

ghrelin - hunger

• released by endocrine cells in stomach during fasting

• acts in brain

• also linked to foraging and hoarding (not just consuming food)

ghrelin: released by endocrine cells in stomach during fasting

• suppressed if animal eats or food is infused into stomach

• not suppressed if nutrients delivered to blood

• so, influenced by contents of digestive system, not solely the availability of nutrients

ghrelin: acts in brain

• activates “hunger neurons” in hypothalamus (NPY/AgRP → LH)

• activates of mesolimbic reinforcement pathway (dopamine release from VTA → NAc)

ghrelin is not just linked to hunger, its also linked to…

foraging & hoarding - not just consuming food

leptin - satiety

• hormone released by fat cells

• leptin receptors in the brain (hypothalamus, cortex)

• negative feedback signal regarding body fat (ex. signal regarding energy reserves) - leads to a decreased food intake and increased metabolism

• homozygous mutant gene ob/ob mice are 3x ormal weight

leptin: homozygous mutant gene ob/ob mice are 3x normal weight

• lack leptin

• eat more, store more fat (slow metabolism)

• develop diabetes in adulthood

• daily leptin injections can help regulate behavior and physiology

PYY_3-36 - satiety

• from cells in intestines

• eat → levels rise → satiety

• injection (peripheral or directly into arcuate) → stop eating

• acts as an appetite-suppressor (in opposition to ghrelin)

GLP-1 - satiety

• from cells in intestines

• eat (especially fats and carbs) → autonomic system as well as nutrients in the intestinal tract signal GLP-1 levels to rise → stimulates insulin release

• receptors also in hypothalamus

  • blocks effects in ghrelin

  • activation of GLP-1 system →

    • decrease appetite and eating

    • alter reward aspect of food

    • slows digestion

arcuate nucleus of hypothalamus contains an appetite controller governed by several hormones

• leptin, ghrelin, and other hormones circulate in blood and reach hypothalamus and NST of medulla

• vagus and spinal nerves carry additional sensory information to NST of medulla

• neurons of NST of medulla communicate with hypothalamus

the arcuate appetite system relies on two sets of neurons with opposing effects

• POMC/CART neurons inhibit appetite and raise metabolism, promoting weight loss

• NPY/AgRP neurons stimulate appetite directly and inhibit POMC neurons

POMC/CART neurons and NPY/AgRP neurons make connections with second-order hypothalamic sites

• orexigenic neurons of the lateral hypothalamus (LH) act to increase appetite and food intake

• anorexigenic neurons of the paraventricular nucleus (PVN) act to decrease appetite and feeding

POMC/CART are co-released but POMC → _____

α-MSH

POMC/CART (co-releasing) neurons project to the LH

release α-melanocyte-stimulating hormone (α-MSH) works at melanocortin type 4 receptors (MC4Rs) to cause a decrease in appetite

NPY/AgRP (co-releasing neurons) project to PVN and LH

• inhibits anorexigenic PVN neurons to increase appetite

• NPY/AgRO signals compete with α-MSH (ex. blocks α-MSH, thus increasing appetite)

orexin

peptide produced in the LH that also increases feeding

many intestinal hormones release in response to nutrients cholecystokinin (CCK)

• peptide hormone released by the gut (duodenum) after high intake

• promotes meal termination

• signals to brain via CCK receptors on vagus nerve

• rodents with no CCK receptors eat large meals and become obese

what cranial nerve is used to convey information regarding satiety

the vagus nerve (10th cranial nerve) sends sensory signals from the gastric intestine (GI) tract to the brain

gastric distention

• mechanical stretch receptors

• vagal afferent signal to the brain

• most relevant at larger volumes

which neurotransmitter system plays a role in food motivation and enjoyment

dopamine and endogenous opioids in the mesolimbic reward system play a role in motivation for food and enjoyment of food

how does the endocannabinoid system affect appetite

the endocannabinoid system regulates appetite and feeding primarily by stimulating hunger

what functions have been linked to the microbiome

mood, stress, social behavior, and cognitive functioning including neurological conditions including autism, schizophrenia, bipolar disorder, multiple sclerosis, and parkinson’s disease

what is fecal transplantation used for

• fecal transplantation is an effective treatment for certain intestinal infections and may be effective in various diseases including inflammatory disease and type II diabetes

• findings suggest that fecal transplants improve metabolic function and other digestive processes in obese people and can play a role in aging

• a donor’s healthy enterotype establishes itself in the recipients

enterotype

a personal combination of different species of gut microbiota; reflects the history of your gut including substantial changes in your diet or the use of antibiotics to treat infections

key features of anorexia nervosa

• severe food restriction

• respond to food with normal/high levels of insulin but deny feeling hungry

• often a mismatch between their physiology and cognition

• distorted body image

• difficult to treat because it appears to involve a combination of genetic, endocrine, personality, cognitive, and environmental variables

• can be fatal due to a lack of proper nutrition, which damages organ systems

bulimia

• marked by periodic gorging and purging by vomiting or laxatives

• can be fatal due to a lack of proper nutrition, which damages organ systems

binge eating

• gorging on more food than is necessary to satisfy hunger

• strong pleasure associated with food activates opiate and DA reward

• dysfunction of MC4R

how is obesity defined

obesity, based on body mass index (BMI), is an epidemic in the US, exacerbated by sedentary lifestyles

why is obesity an epidemic

• a little before 1980, medical recommendations to avoid dietary fats became widespread

• the replacement of fat calories were carbohydrates, esp. sugar

• researchers believe the replacement of fat with carbs is the leading cause of obesity

• over 38 years, the prevalence of obesity has tripled

what health disorders accompany obesity

cardiovascular disease, diabetes, and other illness

can parental obesity affect offspring

parental obesity may program metabolic disadvantages in their children by epigenetic transmission

how can drugs target the arcuate nucleus systems

treatment with PYY_3-36 (via nasal spray) or a drug that mimics its actions may directly act on arcuate neurons to reduce appetite

• appetite suppressants: α-MSH agonists and PYY_3-36

• GLP-1 receptor agonists increase POMC/CART and decrease NPY/AgRP

what are GLP-1 agonists

drugs that mimic GLP-1’s to regulate blood sugar, reduce appetite, and slow digestion; effective for treating type II diabetes and promoting weight loss

how do GLP-1 agonists work

target receptors in the body to release insulin, lower glucagon, slow digestion, and suppress appetite

homeostasis

maintenance of a relatively stable, balanced internal environment

motivation

psychological process that induces or sustains a particular behavior - specifically behavior that seems purposeful and goal driven

drive

involves a state of tension that pushes (or motivates) behaviors to meet a need; physiological or psychological requirements that must be maintained at some baseline or constant state

set point

desired value

thermoregulation

regulation of body temperature around a set value

any mismatch between actual internal state and regulated state…

produces a drive to restore balance

drive-reduction theory

suggests that maintaining homeostasis motivates us to meet biological needs

homeostatic mechanisms are primarily negative feedback systems

deviation from a desired value (set point) triggers a compensatory action of the system; restoring the desired value turns off the response (like a home thermostat)

ectotherms

• get most of their heat from the environment

• regulate body temperature by behavior

endotherms

• produce their own heat by metabolic processes

• enhanced capacity for oxygen utilization sustains greater muscular activity

the specific set point for humans

98.6^oF (36.8^oC)

what things could cause the set point in humans to fluctuate

• fluctuates in circadian rhythm (by about 0.9^o)

• fluctuates across he menstrual cycle

body heats vs. body cools

body heats → mechanism for dissipating heat

body cools → mechanism for warming up

what happens at low temperatures

at low temperatures, reactions slow down; cell membranes are damaged - except for species that produce “antifreeze”

redundancy in the context of thermoregulation

the body has multiple systems for regulating the internal environment; allows for compensation if one monitoring system fails

redundancies for thermoregulation

1. preoptic area of the anterior hypothalamus (POA/AH) has…

• both warm-sensitive and cold-sensitive neurons

• warm-sensitive neurons actually outnumber cold-sensitive neurons in the POA/AH (~3.5:1)

2. posterior hypothalamus also contains cold-sensitive neurons involved in coordinating responses

redundancy detectors

• there are central detectors (hypothalamic) and some brainstem/spinal cord cells (but these are less know)

  • peripheral detectors (skin) and viscera

examples of physiological systems for generation of heat and cooling

• shivering

• sweating

• burning fat

• changing blood flow

posterior hypothalamus vs. POA/AH (preoptic area of the anterior hypothalamus) in thermoregulation

• posterior hypothalamus detects cold and warms you up (red)

  • metabolism of brown fat

  • constriction of cutaneous blood vessels

  • shivering of muscles

• POA/AH detects heat and cools you off (blue)

  • accelerated respiration

  • perspiration

  • dilation of cutaneous vessels

how do ectotherms regulate temperature, even to produce a fever when needed?

• many ectotherms have specialized behaviors to regulate body temperature

• when infected by bacteria, ectotherms, such as iguanas, produce a ever through behavioral means to help fight the infection such as moving around

what is the role of thermogenic brown fat in endotherms

to generate heat

physiological and behavioral homeostatic mechanisms are often integrated

• the young of many endotherms lack the ability to create heat or regulate temperature

• newborn rat pups huddle together to reduce heat loss

• many generate heat via thermogenic brown fat deposits

• prominent yellow “hot spot” between the shoulder blades overlies a deposit of thermogenic brown fat

behavioral strategies used for temperature regulation

• changing exposure of body exposure

• change external insulation

• change surroundings (go to sun, shade, etc.)

allostasis

many physiological systems shift responses, depending on the nature of the stressors and prior experience

how allostasis differs from homeostasis

• homeostatic response: your bodies systems adjust in response to a change in environment

• allostasis: anticipatory; before you do something or enter a certain region your body adjusts in anticipation of the following activity (like a compensatory conditioned response)

how a fever can be considered an example of allostasis

fevers can be considered allostasis because the body is adaptively changing its regulated variable to meet a challenge (infection)

infection → cytokines → prostaglandins

• the hypothalamus raises set point → you feel cold and shiver because your body temp is lower than hypothalamus says it should be → body temp goes up

• when fever breaks, the hypothalamus lowers the set point → you feel hot and sweat because your body temp is higher than hypothalamus says it should be → back down to 98.6

basic elements of mammalian thermoregulatory systems

afferents → neural regions → effectors

afferents

• skin surface

• body core

• hypothalamus/POA

neural regions

• spinal cord

• brainstem

• hypothalamus/POA

effectors

behavioral responses: heat-seeking/avoiding behaviors

autonomic responses: vasoconstriction/dilation; sweating; respiration; brown-fat stimulation; thyroid hormone secretion

diffusion

• passive spread of molecules of one substance among molecules of another substance until uniform concentration is achieved

• salt molecules will passively spread through water because of the random jiggling and movement of the molecules until they are uniformly distributed

osmosis

movement of water molecules through a semipermeable membrane, to equalized concentration of two solutions

osmolality

the concentration of solute in a solution

isotonic salt solution

about 0.9% or 0.15M (physiological saline); the same as in mammalian fluids

aquaporins and their function

specialized channels that assists the movement of water in and out of cells

osmotic pressure

the tendency of a solvent to move through a membrane in order to equalize the concentration of solute

isotonic salt solutions: hypertonic vs. hypotonic solution

• hypertonic solution: has more salt

• hypotonic solution: has less salt

what does the constancy of salt osmolality across species suggest?

• we are constantly using and replenishing water and salts

• most organisms have evolved homeostatic mechanisms to ensure that the composition of their body fluids closely resembles dilute seawater

• despite many years of evolution, the salt concentration of extracellular fluid has remained constant among many animals

what percentage of the mammalian body is water?

water constitutes 70% of the mammalian body

the main fluid compartments and their subdivisions

• intracellular compartment

• extracellular compartment

two sets of receptors that monitor fluid balance

osmosensory neurons and baroreceptors

why is fluid balance highly regulated in the mammalian body

fluid balance is highly regulated because the concentration of solutes in water determines the rate of all chemical reactions in the body