Lecture 5: Homeostasis, Metabolism & Eating Disorders Flashcards
homeostasis
the maintenance of an internal stable environment within the body, despite the changing external environment
- e.g. body temperature, glucose level, oxygen level, blood pressure
gastrointestinal tract
the part of the digestive tract where food is broken down and absorbed so that the nutrients can be mobilized and used as energy sources
eating habits before eating
- prior to the act of eating, the body begins the digestive process
- once the food is in the mouth, saliva and chewing are used to prepare the food to be swallowed
eating habits during eating
- chewed food is formed into a moist ball (bolus), and enters the oesophagus and is collected in the stomach
- hydrochloric acid breaks down the food
eating habits after eating
- pepsin initiates the breakdown of protein molecules into amino acids
- stomach empties through the pyloric sphincter, slowly into the duodenum
- enzymes from the gallbladder and pancreas are added to the food pulp
- division into smaller particles allows the elements to be small enough to pass through the lining of the duodenum into the bloodstream
- once in the bloodstream, they are processed by the liver
emulsification
fats are broken down by bile, which is made by the liver and stored in the gallbladder
- fat molecules won’t pass through the wall of the duodenum, and therefore transported through small tubes in the lymphatic system
lipids
fatty acids or derivatives thereof
- insoluble in water
amino acids
simple organic compounds that compose protein when assembled into long chains
glucose
a sugar and energy source
- a simple sugar broken down from carbohydrates
where energy is stored
- fats (main storage system)
- glycogen (converted to glucose): a substance deposited in body tissues as a store of carbohydrates
- proteins
three processes/phases in energy metabolism
- cephalic or reflex phase
- gastric or absorption phase
- intestinal or fasting phase
cephalic or reflex phase
involves preparatory processes for feeding, in which the sensory stimulus for food activates the digestive system
- the cephalic phase stops when nutrients are absorbed into the bloodstream
gastric or absorption phase
occurs when the body’s immediate needs are attended to and nutrients are absorbed into the bloodstream
- takes 3-4 hours
- the physical relaxation caused by food in the stomach activates stretch receptors that promote the parasympathetic version of ACh
- ACh increases the secretion of gastric juices
- increasing pH stimulates the release of gastrin by enero-endocrine cells
gastrin
a peptide hormone that causes the stimulation of hydrochloric acid (HCL)
- HCL creates an acidic environment for protein digestion
- also responsible for smooth muscle contractions and the movement of food
enero-endocrine cells
specialized cells of the endocrine system located in the gastrointestinal tract and pancreas
intestinal or fasting phase
occurs when nutrients no longer provide immediate energy and the body mobilizes previously stored nutrients
- end of the fasting phase precedes the beginning of the cephalic phase
insulin
an important hormone in the digestive process
released by the pancreas for:
- the use of glucose
- the conversion of glucose to glycogen and fat for storage
- the conversion of amino acids into proteins for storage
- the storage of glycogen in the liver and muscles
- the storage of fat in adipose tissue
- the storage of proteins in the muscles
glucagon
a peptide hormone released by the pancreas when glucose levels become lower
- converts stored glycogen into glucose
- promotes the release of fatty acids from adipose tissue and stimulates the conversion of these fatty acids into ketones
ketones
used by muscles as an energy source
satiety
the feeling of being full
vagus nerve
connects the digestive system to the neural system
- transmits the focus of eating behavior to the brain
biomolecules
molecules derived from substances that occur naturally in an organism
- e.g. amino acids, triglycerids, and glucose
catabolism
the breakdown of complex molecules to release energy
disaccharide
a molecule made up of two monosaccharides
- e.g. sucrose (table sugar) made up of glucose and fructose
anabolism
the creation of complex molecules from simple ones to store energy
glycogen
a multiple-branched polymer of glucose, which serves as energy storage in animals
- polysaccharide
storage of fats
in the cytoplasm of body cells
- the tissue in which fat is stored is called adipose tissue
lipoproteins
transport units for fats secreted by the liver
- a combination of protein, triglycerides, and cholesterol in a phospholipid membrane
catabolized units
when glycerol and fatty acids are attached together forming a long chain
anabolized
when phospholipids (membrane) and triglycerides (body fat) are attached together
cholesterol
promotes cell membrane fluidity and can be metabolized into steroid hormones, such as estrogen
LDL (low-density lipoprotein) and HDL (high-density lipoprotein)
ratio between them is important for cardiovascular health, as LDL promotes plaque formation in cell walls
lipogenesis
the making of fats
absorptive state
glucose can be stored as glycogen, used for energy, or adipose tissue can convert glucose into fats (lipogenesis)
- fatty acids are taken up by adipose tissue and combine with a-glycerol phosphate to form triglycerides
post-absorptive state
the body is in this phase after 4 hours without food
- glycogenolysis
- gluconeogenesis
glycogenolysis
occurs when glucose is released from glycogen
- can be in the liver or the muscles
gluconeogenesis
new glucose is generated from amino acids or fats
- during this phase, there are high values of glucagon and low values of insulin
cellular respiration
glucose is eventually converted into ATP in a cell
- requires oxygen and water
- delivers ATP, heat, and CO2
hypoglycemia
when glucose levels in the blood are low
A-cells and B-cells
- A-cells add glucose to the bloodstream via glucagon
- B-cells bring down glucose levels via insulin
hypothalamus
made up of separate nuclei
- lateral hypothalamus (LH) and the ventromedial hypothalamus (VMH) emphasized in relation to hunger
- LH considered the hunger center
- VMH considered the satiety center
lesions of the ventromedial hypothalamus (VMH)
lesions of the VMH is rats let to hyperphagia (overeating)
2 types of hyperphagia
- dynamic phase: during which the rats gained most of their weight, which occurred immediately after surgery
- static phase: during which the rats ate enough to become obese
lesions of the lateral hypothalamus
caused aphagia in rats and cats: they stopped eating
- accompanied by adipsia: they stopped drinking
glucoreceptors
receptors for glucose in the VMH
2 areas of the brain which stand out in motivational eating behaviors
ventral tegmental area (VTA) and nucleus accumbens (NAcc)
- dopamine is released in these areas when primary reinforcers are presented
- food, a primary reinforcer and essential for survival, increases dopamine outflow from the NAcc
anorexia nervosa
a condition of restricted food intake, leading to severe weight loss
- occurs mainly in women
- strive for a body image that they often see on social media
regions playing important role for anorexia
insula and cingulate cortex
cingulate cortex
underlies motivation, goal-directed behavior, and emotional processes
insula
involved in emotion and disgust
- considered the central mechanism uderlying anorexia nervosa
serotonin and dopamine in anorexia patients
serotonin and dopamine levels are reduced among anorexia patients, which may be linked to changes in motivation and reinforcement
- main treatment drug is SSRIs
bulimia nervosa
patients with bulimia nervosa binge eat and then purge by vomiting or laxatives to control their weight
- fluoxetine (Prozac) is a 5-HT agonist used to treat bulimia nervosa
metabolic rate
the speed at which the body uses energy to perform basic functions
average kcal requirement for men and women
- 2500 kcal for men
- 2000 kcal for women
basal metabolic rate (BMR)
the amount of energy expressed in calories that a person needs to maintain body functions at rest
leptin
a hormone that suppresses the feeling of hunger
hypothyroidism
insufficient thyroid hormone
- associated with fatigue, depression, libido loss, a decreased metabolic rate, and a slower heart rate (bradycardia)
- anorexia nervosa is related to hypothoyroidism
hyperthyroidism
too much thyroid hormone
- related to hyperactivity, insomnia, libido loss, an increased metabolic rate, and a faster heart rate (tachycardia)
- adrenaline can have a diminished function
2 fluid-filled compartments in the body
intracellular fluid (in the cytoplasm) and extracellular fluid
- include intravascular fluid (blood plasma), interstitial fluid (between cells) and cerebrospinal fluid (CSF)
types of thirst
- osmotic thirst
- hypovolemic thirst
osmotic thirst
occurs when the dissolved concentration of extracellular fluid increases, triggered by loss of volume in the intracellular fluid stores
- it becomes saltier and absorbs water from the intracellular fluid, which can compromise cells)
osmoreceptors
possibly located in the anterior hypothalamus and other areas, detect changes in the concentration of interstitial fluid
hypovolemic thirst
occurs when intravascular fluid decreases
- a loss of blood volume is detected by baroreceptors and also by receptors in the kidneys
renin
secreted by the kidneys during times of low blood flow
- helps the production of angiotensin
angiotensin
a hormone that increases drinking
- activates 2 other hormones: aldosterone and vasopressin
aldosterone
retains salt and water, and constricts blood vessels
vasopressin
reduces the amount of fluid going to the bladder
- conserves water, while aldosterone conserves salt until more is consumed
