Physiology of Digestive System April 11 Flashcards
Vomiting can be stimulated from which four main sites?
- Chemoreceptor trigger zone / Area postrema
- Vestibular system
- Gastrointestinal tract and heart
- Central Nervous System
What is the chemoreceptor trigger zone/Area postrema stimulated by ?
- Stimulated by emetogenic stimuli in blood or cerebrospinal fluid
What is the Vestibular system stimulated by ?
- Stimulated by disturbances in the balancing system of the body e.g. motion sickness
What is the Gastrointestinal tract and heart stimulated by ?
- Stimulated by substances that cause gastric irritation and myocardial infarction
What is central nervous system stimulated by ?
- Stimulated by psychiatric disorders, stress , anticipatory vomiting prior to cancer treatment or surgery
What is Basal Metabolic Rate?
- energy body needs for essential activities. e.g. HR, kidney function , breathing etc.
What are some factors affecting metabolic rate (MR)?
- SNS activation - increases MR
- Hormones - Increases MR
- Body temp rise - increases MR
- Exercise - Increases MR
- Food ingestion - increases MR
- Sleep - decreases MR
Why do we eat and what sometimes interrupts our state of hunger?
- To generate energy for immediate metabolic needs
- To store fat for future use during starving
- State of hunger can sometimes be interrupted by inhibitory impulses
What does the brain use to know the status of the stored energy ?
- It uses glucose levels as a thermostat for eating
What are some factors that help regulate food intake and energy balance ?
- Role of CNS
- Gut Brain interaction
- Several peptides and proteins are identified that regulate food intake
- Pre- gastric factors
- Post gastric
- Long term controls
What is known as the hunger centre and what are its two main function ?
- It is Lateral Hypothalamus
1. Stimulation of feeding behaviour
2. Arousal
What neurons does the lateral hypothalamus contain and what do they respond to and stimulate ? what can the loss of these neurons cause ?
- They contain Orexin neurons
- They respond to neuropeptide Y
- They stimulate wakefulness
- Loss of Orexin neurons causes narcolepsy ( sleepiness and lack of muscle weakness)
What is the satiety centre of the hypothalamus and what neurons does it contain ?
- The ventro medial hypothalamus is known as the satiety centre
- it contains orexin receptor positive neurons
What does the Ventro medial hypothalamus do ?
- so orexin is produced when you feel hungry and you eat when there is a rise of the orexin and your body doesn’t need it anymore the ventro medial hypothalamus helps to contain orexin as we are not hungry anymore
What does the pre gastric factors help take in consideration to food ?
- Food appearance
- How does it taste
- learned preferences
- Psychologic factors ( do you eat more when happy or sad?)
In gastrointestinal and post absorptive factors, what role does the vagus nerve play ?
- it Stimulates all three of these :
- CCK–> decrease in meal size –>decrease appetite
- Glucagon like peptide-1(GLP1) secreted from intestine and when arrive in the brain decreases appetite
- Ghrelin a potent stimulator of appetite
What is the source of ghrelin ? and where is the ghrelin receptor found ?
- mainly stomach
- hypothalamus
- small amount by intestine , placenta , kidney and pituitary gland
- Receptor found in anterior pituitary cells
When do ghrelin levels increase ?
- It increases during food deprivation in animals and prior to meals in human
What does Leptin do and where is it found?
- It is a satiety factor that stops you from eating
- mostly expressed in adipocytes and smaller amounts in the epithelium of the stomach and the placenta
Where are leptin receptors found?
- Highly expressed in areas of hypothalamus known to be important in regulating body weight, in T lymphocytes and vascular endothelial cells
What are physiologic effects of leptin?
- Regulation of food intake
- Energy expenditure and body weight
- regulation of gonadotropins
What does injection of leptin in mice cause ?
- Enhances lipolysis and causes decreased food intake and weight loss
When do you have low and high levels of leptin ?
- the more fat= the more leptin
- Low body fat= low leptin levels
- low leptin also interferes with onset of puberty
What can sharp increase in leptin before puberty in boys cause?
- Results in increased androgens and decreased fat and increased muscle mass
What does lack of leptin cause ?
- Obesity
- failure to achieve puberty
What are some signs that show insensitivity to leptin ?
- when blood concentrations of leptin increase in obese human showing they are insensitivity
