Physiology Chapter 16

Absorptive Phase

period in which food is ingested and enters the blood form the GI tract

• takes about 4 hours after ingestion

• nutrients are absorbed and we start to store extra nutrients in the form of macromolecules designed for quick release during times of nutrient deprivation

Post-absorptive Phase

period in which the GI tract contains no nutrients

• body starts to breakdown energy stores (lipids, glycogen, proteins)

• not actively consuming energy (must obtain energy from what we’ve stored

• follows absorptive phase

VLDL and LDL

very low density lipoprotein and low density lipoproteins

• made in the liver and contain TAGs

• contain “bad” cholesterol

LDLs can accumulate throughout the body and cause plaques (reduces flow)

HDL

high density lipoprotein

• carry “good” cholesterol

• removes cholesterol from cells/tissues and brings it back to the liver where it is then targeted for removal

Cholesterol can be used to form what? What enzyme does this?

it forms primary bile acids via the CYP7A enzyme

-cholesterol can also be used to synthesize some steroid hormones too

Insulin

hormone secreted from pancreatic beta cells that regulates glucose

• main targets=muscle, adipose, and liver

• secreted in vesicles and released via exocytosis into the blood

• tyrosine kinase receptor

• promotes glucose uptake to decrease blood glucose levels (i.e. after a meal is ingested)

Type I vs Type II diabetes

Type I: immune depletion of beta cells; have to inject insulin because the body does not make it

• patients have a more susceptible immune system

Type II: insulin resistance (very selective in that some tissues recognize it and others do not)

• lock and key fit issue because receptor recognition doesn’t occur because it doesn’t bind properly

• more prevalent form

• can become Type I if not regulated

What are some neuronal and hormonal factors that oppose the action of insulin?

• glucagon (secreted from alpha cells of pancreas and involved in post-absorptive phase to promote breakdown of storage molecules; increases blood glucose levels)

• epinephrine

• cortisol

• growth hormone

• sympathetic stimulation

hormones of the GI tract are referred to as…

incretins

What is true of glucagon levels in Type I diabetes patients?

they are high

hyperglycemia vs hypoglycemia

hyperglycemia: blood glucose levels are too high

hypoglycemia: blood glucose levels are too low

Cortisol

increased concentrations of it causes:

• more protein catabolism

• gluconeogenesis

• decreased glucose uptake

• increased TAG breakdown

net result: increased plasma concentrations of amino acids, glucose, and free fatty acids

Growth Hormone

lesser effects but similar to cortisol

• increased responsiveness of adipocytes

• stimulation of gluconeogenesis

• reduced insulin ability (anti-insulin effects)

Fasting hypoglycemia

• an excess of insulin due to an insulin-producing tumor, drugs that stimulate insulin secretion, or taking to much insulin (if diabetic)

• a defect in one or more glucose-counterregulatory controls (i.e. inadequate gluconeogenesis due to liver deficiency)

symptoms include increased heart rate, dizziness, convulsions, coma, headaches, etc.

What percentage of energy released from organic molecules appears immediately as heat?

60 %

the rest is used for work

Internal energy liberated

ΔE=H+W

total energy expenditure=internal heat produced+external work performed + energy stored

What are some factors that can result in a decrease in metabolic rate?

-sleep (less sleep=lower rate)

-age (increased age=lower rate)

-sex (women have lower rate)

-fasting (decreases rate to conserve energy)

What are some factors that can increase metabolic rate?

-increasing body temperature

-increased muscular activity

-recent ingestion of food

-growth

-body surface area

-increased environmental temperature

-pregnancy

-hormones (i.e. thyroid)

Overweight

a state in which an increased amount of fat in the body results in a significant impairment of health from a variety of diseases and disorders (hypertension, heart disease, diabetes, and sleep apnea)

BMI=26-29

Obesity

a particularly large accumulation of fat that is extreme overweight

BMI=30+

anorexia nervosa

person becomes obsessed with their weight and body image; characterized by decreased food intake so severely that the person may die of starvation

bulimia nervosa

characterized by recurrent episodes of binge eating usually associated with regular self-induced vomiting, use of laxatives/diuretics, strict dieting/fasting, or vigorous exercise to lose weight/prevent weight gain

Effects of thyroid hormone levels on BMR

thyroid hormone increases BMR (calorigenic effect)

• increases oxygen consumption and heat production

• part of 3-hormone pathway

• levels decrease during starvation

Diet-induced thermogenesis

food ingestion increases BMR by 10-20% for a few hours after eating with protein having the greatest effect; increased heat production is due to processing of nutrients by the liver, energy used by the GI tract to digest and absorb nutrients, and energy used by adipose to store energy