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Regulation of Metabolism and Body Temperature Part2

Terms in this set (105)

Insulin stimulates:
lipogenesis and storage in adipose tissue (spares fat utilization)
promotes glucose transport through the cell membrane into adipose cells thus formation of glycerol that combines with FFA to form TG (↑ TG synthesis)
↑ FFA transport into adipose tissue
Effect of insulin on Protein Metabolism
transport of AAs into the cells
protein synthesis
↑ translation of mRNA (insulin "turns on" the ribosomal machinery)
Over the long term - ↑ the rate of transcription of DNA
protein catabolism
Glucagon released from the cells of Langerhans is stimulated in response to:
declining blood glucose levels
rising amino acid levels
Glucagon and other hormones stimulate
lipolysis
Diabetes mellitus (DM) is a group of metabolic diseases characterized by
high levels of blood glucose resulting from defects in insulin production, insulin action, or both.
Complex disorders of CHO, fate and protein metabolism
Type 1 DM
autoimmune destruction of b-cells
absolute insulin deficiency
Type 2 DM
insulin resistance = relative insulin deficiency
eg interference with insulin binding to target tissue (receptor)
DM pathophysiology in brief
glucose transport from blood to target tissues requires insulin
No insulin = no transport glucose accumulates in the blood
Blood glucose concentration = Hyperglycemia
Functions of the liver
Metabolism
carbohydrates, lipids and proteins
Storage of:
carbohydrates (glycogen)
vitamins (A, B12, D, E, K)
minerals (iron and copper)
Detoxification/deactivation of:
poisons, drugs and hormones
eg converting NH3 to uruea
Excretion of bilirubin to the bile
Synthesis of:
bile salts
most of the clotting factors
lipoproteins
Phagocytosis (Stellate macrophages cell) of:
old RBC, leukocytes and some bacteria
Cholesterol
Not used as an energy source
Structural basis of bile salts, steroid hormones, and vitamin D
Major component of plasma membranes
15% is ingested, the rest made in body, primarily by liver
Lost from body when catabolized or secreted in bile salts that are lost in feces
Transported in lipoprotein complexes containing triglycerides, phospholipids, cholesterol, and protein
Cholesterol Transport
Transport of exogenous & de novo cholesterol requires a diversity of lipoproteins and proteins
Lipoproteins
transport water-insoluble cholesterol and TGs through blood
Regulate lipid entry/exit at target cells
All contain triglycerides, phospholipids, cholesterol, and protein
The higher the percentage of lipids, the lower the density
VLDLs (very low density lipoproteins)
Mostly triglycerides with low density of proteins
LDLs (low-density lipoproteins)
Highest cholesterol content
HDLs (high-density lipoproteins)
The highest protein content
VLDLs
Transport
TG to peripheral tissues (mostly adipose)
LDLs ("bad cholesterol")
Transport
cholesterol to peripheral tissues for membranes, storage, or hormone synthesis
High levels increase risk of heart attack, stroke etc
HDLs ("good cholesterol")
Transport
excess cholesterol from peripheral tissues to the liver to be broken down and secreted into bile (reverse transport)
Also provide cholesterol to steroid-producing organs
Factors Regulating Blood Cholesterol levels
The liver produces cholesterol at a basal level regardless of dietary cholesterol intake
Restricting dietary cholesterol does not markedly reduce blood cholesterol levels
More important effect is relative amounts of saturated and unsaturated fatty acids
Saturated vs Unsaturated fats
Saturated fatty acids stimulate liver synthesis of cholesterol and inhibit cholesterol excretion from body

Unsaturated fatty acids enhance excretion of cholesterol into bile salts
Trans fats can occur when
healthy oils are chemically transformed into solids (example: margarine)
Worse effect on cholesterol levels than saturated fats; increase LDL and reduce HDL
. Unsaturated omega-3 fatty acids (found in cold-water fish)
have
lower proportions of saturated fats and cholesterol
Make platelets less sticky and help prevent spontaneous clotting
Have antiarrhythmic effects on heart
Can lower blood pressure
Stress & cigarette smoking
lower HDL levels
Aerobic exercise & estrogen
↑ HDL levels & ↓ LDL levels
"Apple": fat
carried on upper body is correlated with high cholesterol and LDL levels
Pear": fat
carried on hips and thighs is correlated with lower cholesterol and LDL levels
triglyceride breakdown (dialysis) -->
increased release of free fatty acids (ffa) and their utilization for energy production
Kentone bodies production (ketoacidosis)
due to insufficient amount of acceptor for acetyl-coA (oxaloacetate) used for glucose production
pH of blood is lowered if
ketoacidosis is severe
if ketoacidosis is severe
Can disrupt many processes, including heart activity and o2 transport, leading to coma and death
catabolism of body proteins (gluxoneogenesis)
^utilization of body proteins for energy production
^protein degradation
^urea production (protein breakdown byproduct)
^muscle wasting and loss of muscle mass
type 2 dm: metabolic consequences
insulin resistance / relative insulin deficiency
lipolysis dm 2
lack of glucose transport to cells
mobilization of ffas needed for energy
Can lease to build up of fatty acid metabolites (ketone bodies) in the blood
t4 (thyroxine)
major form that consists of two tyrosine molecules with four bond iodine atoms
t3 (triiodothyronine)
form that has two tyrosines with three bound iodine atoms

must be converted to t4 at tissue level
t4 and t3 are both
iodine containing amine hormones
effects of thyroid hormone include
^bmr and heat production
regulates tissue growth and development
- critical for normal skeletal and NS development and reproductive capabilities
maintains bp
- increases adrenergic receptors in blood vessels
physiological functions of thyroid hormone
increase cellular metabolic processes

affect growth in children

stimulate other specific body mechanisms

^t3 and t4 = anxiety and paranoia
t3 and t4 ¿ = sluggishness
iodine ingested in the form of iodine is necessary for the formation of
t3 and t4
synthesis of thyroid hormone
1. thyroglobulin
2. iodine trapping
3. iodine oxidation
4. iodine attached to tyr
5. iodinated tyr linked
6. thyroglobulin endocytosed
7. t3/t4 released into blood stream
Thyroid gland stores hormone extracellularly in follicle lumen until triggered by TSH to release
Seven steps involved in synthesis of TH:
Thyroglobulin is synthesized &
discharged into follicle lumen
Iodide is trapped
iodide ions (I-) are actively taken into cell and released into lumen
Iodide oxidized
electrons are removed, converting it to iodine (I2)
Iodine is attached to tyrosine: mediated by peroxidase enzymes
Monoiodotyrosine (MIT): formed if only one iodine attaches
Diiodotyrosine (DIT): formed if two iodines attach
Iodinated tyrosines link together to
form T3 and T4
MIT + DIT = T3
DIT + DIT = T4
Colloid is endocytosed by
follicular cells
Vesicle is then combined with a lysosome
Lysosomal enzymes cleave T3 and T4 from
- thyroglobulin
Hormones are secreted into bloodstream
Mostly T4 secreted, but T3 is also secreted; T4 must be converted to T3 at tissue level
T4 & T3 transported by thyroxine-binding globulins (TBGs)
Both bind to target receptors, but T3 is 10 times more active than T4
Peripheral tissues have enzyme that to convert T4 to T3 (- 1 iodine)
Negative feedback regulation of TH release
Rising TH levels provide negative feedback inhibition on release of TSH

Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback during pregnancy or exposure to cold
TH Hyposecretion in adults can lead to
myxedema
myxedema
Symptoms include low metabolic rate, thick and/or dry skin, puffy eyes, feeling chilled, constipation, edema, mental sluggishness, lethargy
If due to lack of iodine, a goiter may develop
↑ synthesize of unusable thyroglobulin causes thyroid to enlarge
Hyposecretion in infants leads to
cretinism
cretinism
Symptoms include intellectual disabilities, short and disproportionately sized body, thick tongue and neck
Endemic goiter
Places where goiters are especially common
soil is iodine poor
Lack of access to iodine rich seafood
Hashimoto's thyroiditis (chronic autoimmune thyroiditis)
autoimmune destruction of thyroid hormones producing cells
is the most common cause of hypothyroidism in iodine-sufficient areas of the world
Its prevalence increases with age
Hyperthyroidism
increased production of TH
Hyperthyroidism
Autoimmune disease
Symptoms include:
metabolic rate
sweating
rapid & irregular heartbeats
Nervousness
weight loss despite adequate food. Why?
Exophthalmos may result
eyes protrude as tissue behind eyes becomes edematous and fibrous
Energy intake
energy derived from absorbable foods = energy liberated during food oxidation
Energy output
Immediately lost as heat (~60%)
Used to do work (driven by ATP)
Stored as fat or glycogen
Nearly all energy from food is eventually converted to heat, which cannot be used to do work, but it
Warms tissues and blood
Helps maintain homeostatic body temperature
Allows metabolic reactions to occur efficiently
Energy balance depends on:
genetic makeup (127 candidate genes)
dietary intake and dietary habits
environmental conditions
lifestyle
Body Mass is maintained when energy intake (consumed) =
energy expenditure (used)
Body mass index (BMI) is a formula used to determine
obesity based on a person's weight relative to height
The arcuate nucleus (ARC) area
release neuropeptide Y (NPY) and agouti-related peptides that enhance appetite
release proopiomelanocortin (POMC) & cocaine-amphetamine regulated transcript (CART) which suppress appetite
Lateral hypothalamic area (LHA) neurons promote hunger when stimulated by
neuropeptides (e.g., NPY)
Ventromedial neurons(VMN) cause satiety through release of
corticotropin-releasing hormone (CRH) when stimulated by appetite-suppressing peptides (e.g., POMC and CART)
Neural signals from digestive tract
High protein content of meal increases and prolongs afferent vagal signals
Distension sends signals along vagus nerve that suppress hunger center
Bloodborne nutrients related to body energy stores
Increased nutrient levels in blood depress eating
Rising blood glucose levels
Elevated blood amino acid levels
Blood levels of fatty acids during the absorptive stage ↓appetite
Hormones
Gut hormones (e.g., insulin and CCK) depress hunger
Glucagon and epinephrine stimulate hunger
Ghrelin (Ghr) from stomach stimulates appetite; levels peak prior to mealtime
Leptin
secreted by fat cells in response to ↑ body fat mass
Indicator of total energy stores in fat tissue
Protects against weight loss in times of nutritional deprivation
Acts on ARC neurons in hypothalamus
↓ secretion of NPY- potent appetite stimulant
↑ expression of appetite suppressants (e.g., CART peptides)
Rising leptin level causes some weight loss but is no "magic bullet" for obese patients
Obese people have high leptin levels but seem to be resistant to its action
Theory on function of leptin is that it helps prevent weight loss during times of nutritional deficiency
Additional factors in regulation of food intake
Temperature: cold activates hunger
Stress: depends on individual
Psychological factors
Adenovirus infections
Sleep deprivation
Composition of gut bacteria
Metabolic rate:
total heat produced by chemical reactions and mechanical work of body
Metabolic rate Can be measured:
Directly: calorimeter measures heat liberated into water chamber
Indirectly: respirometer measures oxygen consumption (directly proportional to heat production)
BMR: energy body needs to perform its most essential activities
Measured in postabsorptive state (12-hour fast)
reclining position
relaxed mentally & physically
room temperature 20-25C
BMR depends mainly on:
Body surface area
Age
Gender
Body temperature
higher temperature increases BMR
Environmental temperature
heat and cold (?) increase BMR
Thyroid status
hyperthyroidism increases BMR
Stress
increases BMR
Pregnancy and lactation
increase BMR
Male sex hormones
increase BMR
Growth hormone
increases BMR
Sleep
decreases BMR
Malnutrition
decreases BMR
At rest,
the liver, heart, brain, kidneys & endocrine organs generate most heat
During exercise
heat production from skeletal muscles increases dramatically
Body temperature reflects
the balance between heat production and heat loss
Only ~ 40% of energy released by catabolism can be
captured by ATP; the rest is lost as heat
Cannot be used to do work
Warms the tissues and blood
Helps maintain the homeostatic body temperature
The main objective of thermoregulation
is to prevent core body temperature from rising or falling excessively
Radiation:
loss of heat by infrared rays ; objects are not in contact
Conduction
heat transfer between molecules of objects in direct contact
Convection:
heat transfer to surrounding air
Evaporation
heat loss due to evaporation of water from body surfaces; heat absorbed by water during evaporation is known as heat of vaporization
Insensible heat loss
accompanies insensible water loss from lungs, oral mucosa & skin
Loss ~ 10% of basal heat production
Sensible
heat loss - when body temperature rises and sweating increases water vaporization
Thermoregulatory centers
preoptic region of hypothalamus is main integrating center for thermoregulation
Two thermoregulatory centers
Heat-loss center
Heat-promoting center
Hypothalamus receives afferent input from:
Peripheral thermoreceptors in shell (skin)
Central thermoreceptors in core (some in hypothalamus)
Initiates appropriate heat-loss and heat-promoting activities
Constriction of cutaneous blood vessels
Regulated by sympathetic nervous system
Shivering
Heat from skeletal muscle activity
Enhanced release of thyroxine
Seen only infants
Increases in metabolic rate
Chemical (nonshivering) thermogenesis: via epinephrine and norepinephrine stimulated by cold temperatures
Mechanism seen in infants
Brown adipose tissue in infants and adults
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