Test 4 Flashcards
What is homeostasis?
Process by which body’s substances and characteristics (such as temperature and glucose level) are maintained at their optimal level
What is ingestive behaviour?
Eating or drinking
What is a system variable?
variable that is controlled by a regulatory mechanism
- Ex: temperature in a heating system
What is set point?
optimal value of the system variable in a regulatory mechanism
What is a correctional mechanism?
In regulatory process, mechanism that is capable of changing value of system variable
- Provides negative feedback: process whereby the effect produced by a correctional mechanism serves to diminish or terminate the corrective action
What is a satiety mechanism?
brain mechanism that causes cessation of hunger or thirst, produced by adequate and available supplies of nutrients or water
When does thirst occur?
- Not enough blood circulating in the body (volumetric thirst)
- There is too much salt in the blood (osmometric thirst)
What is hypovolemia?
• When there is not enough blood circulating in the body
What does low blood flow cause?
Causes the release of renin, which triggers a hormone signalling cascade that promotes thirst, among other things, by activating hypothalamic neurons near the anteroventral tip of the third ventricle (the AV3V region), where the blood brain barrier is weak
- Hormones in the blood can seep into the CSF
What is tonicity?
The relative concentration of dissolved solutes (ex: salt) on either side of a semipermeable membrane
- It is used to describe the direction and extent of water diffusion across the membrane
What is an isotonic solution?
similar solute concentrations are present inside and outside the cell
- The cell will neither gain nor lose water
What is a hypotonic solution?
solute is less concentrated outside the cell than in, so water will enter the cell
- Because only water can move, water begins to enter the cell to try to equilibrate the concentration
What is a hypertonic solution?
solute is more concentrated outside the cell than in, so water will leave the cell
- Water will leave the cell to try to dilute the solution outside the cell
What are osmoreceptors?
neurons that detect changes in cell size, which corresponds to interstitial solute concentration
- The membrane potential and release of NT from osmoreceptor cells relates to the volume of these cells
What is glycogen?
Polysaccharide referred to as animal starch
- constitutes the short-term store of nutrients
What is insulin?
Pancreatic hormone that facilitates conversion of glucose into glycogen, entry of glucose and amino acids into cells of the body, and transport of fats into adipose tissue
What is glucagon?
Pancreatic hormone that promotes conversion of liver glycogen into glucose and conversion of adipose triglycerides into fatty acids
What is a triglyceride?
Form of fat storage in adipose cells (fat cells)
- Constitutes the long-term store of nutrients
What is glycerol?
Substance (also called glycerine) derived from breakdown of triglycerides, along with fatty acids
- Can be converted by liver into glucose
What is a fatty acid?
Substance derived from breakdown of triglycerides, along with glycerol
- Can be metabolized into sugars by most cells of body except for brain
What is grehlin?
Peptide hormone released by the empty stomach that increases eating
- also produced by neurons in the brain
What is the duodenum?
First portion of small intestine attached directly to the stomach
- the presence or absence of food in the duodenum regulates the release of grehlin from the stomach
What is leptin?
A circulating hormone that is secreted by adipocytes (fat cells)
- Thought to signal the size of peripheral energy stores in the body
- As fat cells grow, there is a concomitant increase in leptin levels in the blood stream
- The leptin provides a negative homeostatic feedback signal that decreases hunger
- Exogenous administration of leptin temporarily decreases meal size in healthy people
What is glucoprovation?
Dramatic fall in amount of glucose available to cells (detected in liver and brainstem)
- Can be caused by excess insulin signalling or by drugs that inhibit glucose metabolism
- Creates intense hunger
What is lipoprivation?
Dramatic fall in level of fatty acids available to cells (detected in liver and brain)
- Usually caused by drugs that inhibit fatty acid metabolism, but it can also relate to too little body fat
What is hypoglycemia?
Low blood sugar
- When the brain senses that it does not have enough glucose (sugar) to support normal brain function (via glucose-sensing neurons in various regions of the brain), it launches an emergency cascade of effects
What is hyperglycemia?
When disruptions in insulin signalling can cause high blood sugar, because sugar is not being converted int glycogen or fat
- If left untreated, this causes ongoing weight loss and loss of body fat
What are AGRP/NPY neurons?
They are orexigenic (their activity promotes hunger)
- These neurons are inhibited by leptin and activated by ghrelin
What are POMC/alpha-MSH neurons?
Anorexigenic (their activity inhibits hunger)
- These cells are activated by leptin and inhibited by ghrelin
What is the arcuate nucleus of the hypothalamus?
Nucleus in the base of hypothalamus that contains neurons highly sensitive to circulating levels of leptin
- contains AGRP/NPY neurons and POMC/alpha-MSH neurons, which are involved in feeding and metabolic rate
What is the paraventricular nucleus of the hypothalamus?
Nucleus of hypothalamus that receives inputs from arcuate nucleus
- Contains oxytocin neurons that signal the body has adequate levels of leptin (fat)
What is Prader-Willi syndrome?
a rare chromosomal abnormality in which up to 7 genes are deleted from chromosome 15
- One of these genes is critical for the development/survival of oxytocin-containing neurons in the PVN
- People with this syndrome are born with very low muscle mass and have little interest in eating
- But later, between 2 and 8 years old, these people develop into having no sensations of satiety to tell them to stop eating or to throw up, so they can accidentally consume enough food in a single binge to fatally rupture their stomach
What is leptin resistance?
When people have an elevated leptin set point that they are trying to maintain, and they have a blunted response to increases in leptin levels
What is bariatric surgery?
Aimed at the stomach, small intestine, or both
- The most effective form of bariatric surgery is special form of gastric bypass called the RYGB
- With RYGB surgery, the jejunum is cut and upper end is attached to stomach pouch
- The stomach is physically smaller
What is memory retrieval?
Accessing memories
What is neural plasticity?
the ability of the nervous system to change and adapt
What is intrinsic plasticity?
:The number of action potentials a neuron exhibits in response to an influx of positive current
- Determined by the number and type of ion channels (leak channels and voltage-gated channels) expressed by the neuron
- More action potentials = more excitable
What is synaptic strength?
the amount of positive (or negative) current that enters the postsynaptic neuron when the presynaptic cell has an action potential
- Enduring changes in synaptic strength are referred to as long-term potentiation (LTP) or long-term depression (LTD)
- Can involve pre or postsynaptic changes (in vesicle release and receptor activity)