9. Endocrine System 5 Flashcards
Why is maintaining blood glucose important?
- too low:
- glucose only nutrient that normally can be used by the brain, retina and germinal epithelium of the gonads - too high:
- cellular dehydration due to osmotic pressure exerted by plasma glucose
List four things that stimulate insulin release and four things that inhibit its release.
stimulate:
1. increased blood glucose
2. increased blood free fatty acids
3. increased blood amino acids
4. gastrointestinal hormones
inhibit:
1. decreased blood glucose
2. fasting
3. somatostatin
4. a adrenergic activity
Describe how insulin release is initiated by high glucose levels. Indicate how insulin has its effect at the target tissues.
1.Glucose entry into b cells via glucose transporters
2.Glucokinase phosphorylates glucose to become g6p
3.G6pis oxidized to make atp
4.Inhibits atp-sensitive potassium channels in b-cell
5.Depolarization of b cell and opens votlage gated calcium channels
6.Calcium influx
7.Fusion of insulin vesicles with cell membrane
8.Release of insulin to bloodstream through exocytosis
- Binds with enzyme linked receptors to activate tyrosine kinase
Describe how insulin has it’s effects on carbs
- 80% of the cells start taking in a lot more glucose
- Conversion of glucose to glycogen in muscle
- Increase in glucose uptake by liver cells and increased conversion of glucose to glycogen in liver
- Inhibits gluconeogenesis
Describe how insulin has it’s effects on fats
Promotes fat synthesis and storage
1. promotes fatty acid synthesis in liver
2. activates lipoprotein lipase
3. inhibits hormone-sensitive lipase
4. increased glucose transport into adipose cells
Describe how insulin has it’s effects on proteins
Promotes protein synthesis and storage
1. stimulates transport of many of the amino acid into cells
2. increases translation of mRNA
3. increases rate of transcription of selected DNA genetic sequences
4. inhibits catabolism of proteins
5. depresses rate of gluconeogenesis which uses amino acids as precursors
What stimulates glucagon release and what inhibits glucagon release from the cells of the
pancreas?
stimulates:
1. decreased blood glucose
2. high blood amino acids - glucagon allows these amino acids to be used in gluconeogenesis
3. exercise - increased circulating amino acids, b adrenergic stimulation
inhibits:
1. increased blood glucose
2. somatostatin
What are the effects of glucagon?
- Causes glycogenolysis in the liver - increases blood glucose concentration within minutes and uses the cAMP second messenger system
- increase the uptake of amino acids by the liver
- increased activity of enzymes for gluconeogenesis
What hormone is released by the delta cells of the pancreas?
Somatostatin
What stimulates somatostatin release and what
are its actions?
Stimulated:
increased blood glucose
increased amino acids
increased fatty acids
increased gastrointestinal hormones
actions:
1. inhibits secretion of insulin and glucagon
2. inhibits secretion of motility of the stomach, duodenum, gallbladder
3. decreases both secretion and absorption in the GIT
4. extends the period of time over which food nutrients are assimilated
5. decreases the utilization of absorbed nutrients by tissues - prevents rapid exhaustion of nutrients
What is the role of parathyroid hormone?
- Increases calcium and phosphate absorption from bone
- Increases renal tubule reabsorption of calcium
- decreases renal tubule reabsorption of phosphate
- indirectly increases calcium and phosphate absorption from the intestines
- result of activating Vitamin D
Demonstrate how Vitamin D is activated.
- converted in liver via negative feedback to intermediate form
- converted to active form in kidneys
- What is the effect of the active form of Vitamin D?
- Promotes intestinal absorption of calcium and phosphorous
- increases calcium and phosphate reabsorption from renal tubules (minor effect)
- increases bone calcification
What is the role of calcitonin in calcium metabolism?
- Increased secretion of calcium in urine
- Inhibits action of osteoclasts
