Physiology of Digestive System April 11

Question 1

Vomiting can be stimulated from which four main sites?

Answer 1

1. Chemoreceptor trigger zone / Area postrema
2. Vestibular system
3. Gastrointestinal tract and heart
4. Central Nervous System

Question 2

What is the chemoreceptor trigger zone/Area postrema stimulated by ?

Answer 2

• Stimulated by emetogenic stimuli in blood or cerebrospinal fluid

Question 3

What is the Vestibular system stimulated by ?

Answer 3

• Stimulated by disturbances in the balancing system of the body e.g. motion sickness

Question 4

What is the Gastrointestinal tract and heart stimulated by ?

Answer 4

• Stimulated by substances that cause gastric irritation and myocardial infarction

Question 5

What is central nervous system stimulated by ?

Answer 5

• Stimulated by psychiatric disorders, stress , anticipatory vomiting prior to cancer treatment or surgery

Question 6

What is Basal Metabolic Rate?

Answer 6

• energy body needs for essential activities. e.g. HR, kidney function , breathing etc.

Question 7

What are some factors affecting metabolic rate (MR)?

Answer 7

1. SNS activation - increases MR
2. Hormones - Increases MR
3. Body temp rise - increases MR
4. Exercise - Increases MR
5. Food ingestion - increases MR
6. Sleep - decreases MR

Question 8

Why do we eat and what sometimes interrupts our state of hunger?

Answer 8

• 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

Question 9

What does the brain use to know the status of the stored energy ?

Answer 9

• It uses glucose levels as a thermostat for eating

Question 10

What are some factors that help regulate food intake and energy balance ?

Answer 10

1. Role of CNS
   
   • Gut Brain interaction
   • Several peptides and proteins are identified that regulate food intake
2. Pre- gastric factors
3. Post gastric
4. Long term controls

Question 11

What is known as the hunger centre and what are its two main function ?

Answer 11

• It is Lateral Hypothalamus
  1. Stimulation of feeding behaviour
  2. Arousal

Question 12

What neurons does the lateral hypothalamus contain and what do they respond to and stimulate ? what can the loss of these neurons cause ?

Answer 12

• They contain Orexin neurons
• They respond to neuropeptide Y
• They stimulate wakefulness
• Loss of Orexin neurons causes narcolepsy ( sleepiness and lack of muscle weakness)

Question 13

What is the satiety centre of the hypothalamus and what neurons does it contain ?

Answer 13

• The ventro medial hypothalamus is known as the satiety centre
• it contains orexin receptor positive neurons

Question 14

What does the Ventro medial hypothalamus do ?

Answer 14

• 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

Question 15

What does the pre gastric factors help take in consideration to food ?

Answer 15

• Food appearance
• How does it taste
• learned preferences
• Psychologic factors ( do you eat more when happy or sad?)

Question 16

In gastrointestinal and post absorptive factors, what role does the vagus nerve play ?

Answer 16

• 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

Question 17

What is the source of ghrelin ? and where is the ghrelin receptor found ?

Answer 17

• mainly stomach
• hypothalamus
• small amount by intestine , placenta , kidney and pituitary gland
• Receptor found in anterior pituitary cells

Question 18

When do ghrelin levels increase ?

Answer 18

• It increases during food deprivation in animals and prior to meals in human

Question 19

What does Leptin do and where is it found?

Answer 19

• 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

Question 20

Where are leptin receptors found?

Answer 20

• Highly expressed in areas of hypothalamus known to be important in regulating body weight, in T lymphocytes and vascular endothelial cells

Question 21

What are physiologic effects of leptin?

Answer 21

• Regulation of food intake
• Energy expenditure and body weight
• regulation of gonadotropins

Question 22

What does injection of leptin in mice cause ?

Answer 22

• Enhances lipolysis and causes decreased food intake and weight loss

Question 23

When do you have low and high levels of leptin ?

Answer 23

• the more fat= the more leptin
• Low body fat= low leptin levels
• low leptin also interferes with onset of puberty

Question 24

What can sharp increase in leptin before puberty in boys cause?

Answer 24

• Results in increased androgens and decreased fat and increased muscle mass

Question 25

What does lack of leptin cause ?

Answer 25

• Obesity
• failure to achieve puberty

Question 26

What are some signs that show insensitivity to leptin ?

Answer 26

• when blood concentrations of leptin increase in obese human showing they are insensitivity