Module 2.2- Hormones Regulating Metabolism Flashcards
Explain the role of insulin and glucagon in maintaining glucose homeostasis. Describe the physiological actions of growth hormone (GH)
What endocrine hormones does the pancreas produce?
Insulin, Glucagon, Stomatostatin, Amylin, Pancreatic Polypeptide.
Where is the pancreas generally located?
In the digestive tract, attached to the duodenum and gall bladder.
What hormone does an alpha cell of the Pancreas produce?
Glucogon
What hormones does an beta cell of the Pancreas produce?
Insulin, amylin
What hormone does an delta cell of the Pancreas produce?
Somatostatin
What hormone does an F cell of the Pancreas produce?
Pancreatic Polypeptide
Are there any non-endocrine functioning cells in the Pancreas? If so, what are they called?
Yes, Exocrine pancreatic cells are acinar cells and duct cells
How does the pancreas regulate glucose homeostasis?
High blood sugar promotes insulin release in pancreas which stimulates glucose uptake from blood into tissue and stimulates production of glycogen (glucose storage molecule) in the liver, lowering blood sugar levels.
Low blood sugar promotes Glucagon release in the pancreas which stimulates glycogen breakdown in the liver, releasing glucose into the blood and raising blood sugar levels.
Which pancreatic hormone predominates in the ‘fed’ absorptive state?
Insulin
Which pancreatic hormone predominates in the ‘fasted’ post-absorptive state?
Glucagon
What is the insulin receptor in a cell called?
Tyrosine Kinase
How does insulin work on insulin sensitive muscle and adipose cells?
Insulin binds to Tyrosine Kinase receptor -> Signal transduction cascade occurs -> Glut 4 protein performs exocytosis (becomes part of the cell wall) -> parts of glut 4 protein create channels or glucose to enter cell
What are some examples of insulin sensitive cells?
Muscle cells, adipocytes
How does insulin work on insulin sensitive Hepatocytes?
Insulin binds to Tyrosine Kinase receptor -> Signal transduction cascade occurs -> Hexokinase- mediated conversion of glucose to G-6-P keeps intracellular glucose concentrations low -> Glut 2 protein channels allow glucose to move into cell where glucose concentration is lower.
When insulin isn’t bound to Tyrosine Kinase (low blood sugar) the glucose (from glucose stores and gluconeogenesis) inside the cell moves though Glut 2 protein channels into extracellular fluid.
What effects does increased insulin have on the functions of adipose tissue?
Increase in fatty acid and triglyceride synthesis, decrease in Lipolysis.
What effects does increased insulin have on the functions of liver and muscle tissue?
Increase in glycogen synthesis, decrease in glycogenolysis
What effects does increased insulin have on the functions of only liver tissue?
Increase in fatty acid and triglyceride synthesis, decrease in gluconeogenesis.
Increases and decreases in what can stimulate beta cells of the pancreas to secrete insulin?
Increases in plasma glucose, plasma amino acids, GIP secretions, parasympathetic activity.
Decreases in sympathetic activity and epinephrine secretion.
What stimulates Glucagon release?
Decreases in blood glucose levels and increased plasma amino acids
What possibly inhibits Glucagon release?
Insulin
What does Glucagon stimulate?
Hepatic Glucogenolysis and Gluconeogenesis
Increases and decreases in what can stimulate alpha cells of the pancreas to secrete glucagon?
Decrease in plasma glucose, increase in plasma amino acids, increase in sympathetic activity, increase in epinephrine secretion.
What effects does increased glucagon have on the functions of liver tissue?
Increased glycogenolysis, keytone synthesis, protein breakdown and gluconeogenesis.
Decreased glycogen synthesis and protein synthesis.
What effects does increased glucagon have on the functions of adipose tissue?
Increased lipolysis.
Decreased triglyceride synthesis
What is the normal range of blood glucose levels?
70-110mg/dL
What happens when blood glucose levels fall below 70mg/dL?
Alpha cells secrete glucagon
->
increased breakdown of glycogen to release glucose, increased breakdown of fats to fatty acids, increased synthesis and release of glucose - >
blood glucose concentration rises and homeostasis is restored.
What happens when blood glucose levels rise above 110mg/dL?
Beta cells secrete insulin
->
increased rate of glucose transport into target cells, increased rate of glucose utilization and ATP generation, increased conversion of glucose to glycogen, increased amino acid absorption and protein synthesis, increased triglyceride synthesis
->
Blood glucose concentration falls and homeostasis is restored.
What is somatotrophin?
A peptide growth hormone produced in the anterior pituitary.
What hormone inhibits the production of the growth hormone somatotrophin?
Growth hormone inhibiting hormone (GHIH), aka stomatostatin
What hormone promotes the production of the growth hormone somatotrophin?
Growth hormone releasing hormone (GHRH), aka stomatocrinin
What cells produce the growth hormone stomatotrophin?
Stomatotroph cells in the anterior pituitary.
Are the actions of the hormones stomatostatin (GHIH) and stomatocrinin (GHRH) direct, indirect or both?
Both
Are the levels of growth hormones the same in the body over a day or do they change?
They change, peaking and falling 6-8 times over a 24hr period
How often do growth hormone levels peak over 24hrs in an average human?
6-8 times
Are the levels of growth hormones the same in the body over a lifetime or do they change?
They change with age.
When is the most intense period of release of growth hormone in a single day?
Soon after the onset of sleep
When is the most intense period of release of growth hormone in a lifetime?
During the teenage years
Does gender affect the levels of growth hormone found in a person?
Yes
What factors can affect levels of growth hormone found in the body (excluding any diseases or abnormalities)?
Gender, age, stress, exercise, nutrition and sleep
What are the indirect actions of growth hormones?
Growth hormones cause the liver to release IGFs which then bind to target tissues stimulating both hyperplasia and hypertrophy, causing growth.
What are the direct actions of growth hormones?
Stimulates stem cell divisions in connective tissues, increases breakdown of stored fats and glycogen and decreases uptake of glucose by muscles giving the overall effect of metabolising fat stores while conserving glucose for the brain.
What is the hormone pathway for the direct effects of growth hormone on the body?
Hypothalamus produces GHRH -> Produces Stomatotroph -> anti-insulin effects -> Fat cells undergo lypolysis forming Fatty acids and glycerol, carbohydrates/glucogen form glucose -> diabetogenic activity
What is the hormone pathway for the indirect effects of growth hormone on the body?
Hypothalamus produces GHRH ->
Produces Stomatotroph ->
Liver produces prolactin, placental lactogen, insulin->
Fat calls undergo lypogenesis, muscle cells undergo protein synthesis, condrocytes (in bones) for cartilage causing bone growth
What feedback mechanism are in place for the regulation of growth hormones?
The levels of growth hormones themselves and the livers production of stomatomedins as an inirect action of growth hormones both act to stimulate the hypothalamus into producing SST, which acts to reduce production of growth hormone in the stomatotroph cells
What is the functional unit of the thyroid gland?
A folicle
What do follicles of a thyroid gland enclose?
an inner lumen, making a colloid
What is a colloid in a thyroid gland?
Unique extracellular storage
What do parafollicular “C” cells in the thyroid produce?
calcitonin
What is the chief constituent of a colloid in a thyroid gland folicle?
Thyroglobulin
What does the Thyroglobulin in thyroid follicles do?
Synthesises Tetraiodothyronine (T4 or Thyroxine) and Tri-iodothyronine (T3)
What are the four products of the thyroid?
Tetraiodothyronine (T4 or Thyroxine)
Tri-iodothyronine (T3)
Monoiodotyrosine (MIT)
diiodotyrosine (DIT)
What are the basic ingredients for the synthesis of thyroid hormones?
Tyrosine and Iodine
What are the two thyroid hormones?
Monoiodotyrosine (MIT) and diiodotyrosine (DIT)
What hormones form Tetraiodothyronine (thyroxine, T4)
Two diiodotyrosine (DIT)
What hormones form Tri-iodothyronine (T3)?
One diiodotyrosine (DIT) and one Monoiodotyrosine (MIT)
Which is more potent in biological activity, Tri-iodothyronine (T3) or Tetraiodothyronine (thyroxine, T4)?
Tri-iodothyronine (T3) is four times more potent
Roughly what percentage of circulating Tri-iodothyronine (T3) is derived from Tetraiodothyronine (thyroxine, T4)?
Roughly 80%
What do the liver and kidneys do to most of the Tetraiodothyronine (thyroxine, T4) they encounter?
It’s activated and converted to Tri-iodothyronine (T3)
Proportionally, how much of both Tri-iodothyronine (T3) and Tetraiodothyronine (thyroxine, T4) are secreted by the Thyroid
Roughly 90% Tetraiodothyronine (thyroxine, T4)
10% Tri-iodothyronine (T3)
Are thyroid hormones lipophilic or lipophobic?
lipophilic
Where are the receptors for thyroid hormones found in target cells?
In the nucleus
What happens in a target cell when a thyroid hormone binds to the receptor site on the nucleus?
Alters the rate of mRNA transcription and thus the rate of protein synthesis.
How quickly do thyroid hormones take affect and how long does the effect last?
Hours to days to take affect and that effect can last for days.
What is the first degree action of thyroid hormones?
Increased Basal Metabolic Rate
What effect does thyroid hormones have on all cells of the body?
Increases the number and activity of mitochondria.
Increased movement of Na+/K+ through ATPase.
Increase in catecholamine receptors.
Increase in carbohydrate metabolism (Increase in: cell glucose uptake, glycolysis, glycogenolysis, GI reabsorption)
Increased fat metabolism (Increased lipid mobilisation aka lipolysis and hepatic excretion of cholesterol)
Increased cardiac output, rate and depth of respiration and increased skin and hair growth
How does the thyroid glad regulate it’s hormone output?
Using a negative feedback mechanism. Increased levels of T4 hormone works to reduce function of the hypothalamus and anterior pituitary
What is the basic anatomy of the adrenal gland?
Small pair of glands found sitting on top of each kidney (one per kidney), consists of the outer adrenal cortex (80%) and an inner adrenal medulla (20%).
What does the Adrenal gland produce?
Lipid-soluble hormones derived from cholesterol (steroids) and amine derivatives of catechol made from tyrosine.
What are the 4 regions of the Adrenal cortex (in order of furthest from the medulla to the closest)?
Capsule
Zona glomerulosa
Zona fasciculata
Zona reticularis
What are the specialised cells of the adrenal medulla called?
Chromaffin cells
What kind of specialised cells are Chromaffin cells in the adrenal medulla?
Post-ganglionic neurons
What do the Chromaffin cells of the adrenal medulla produce?
Catecholamines (adrenaline and noradrenaline) from tyrosine (aka epinephrine and norepinephrine)
How much of the circulating adrenaline is produced by the adrenal medulla?
All of it
What cells, other than the Chromaffin cells of the medulla, produce noradrenaline?
Postganglionic sympathetic neurons
What is the generalised ratio of adrenaline to noradrenaline in humans?
80% adrenaline, 20% noradrenaline but this does vary.
Where is adrenaline and noradrenaline stored in the body?
In secretory vesicles called chromaffin granules
How is adrenaline and noradrenaline released from the storage chromaffin granules and how do they circulate in the body?
Released by exocytosis and circulated in the blood
Other than catecholamines, what else stimulates the target organs of the adrenal gland?
Direct stimulation from the sympathetic nerves
What is the half life of catecholamines? Is this considered high or low?
15 seconds, low
how quickly do catecholamines take affect?
Almost immediately
What rough percentage is the uptake of catecholamines? is this low or high?
More than 90%, high uptake
What cells in the body have receptors for catecholamines?
Virtually all cells.
Where on cells are the receptors for catecholamines located?
On the surface membranes
What types of catecholamine receptors are there on cells?
Alpha and Beta
What are the biological effects of catecholamines?
Increased: Heart rate BP Cardiac contractility Cellular oxygen consumption Lipolysis Gluconeogenesis Glycodenolysis
And dilation of skeletal muscle blood vessels, pupils and airways
How does cortisol secretion effect adipose tissue?
Increased lipolysis
How does cortisol secretion effect muscle and other tissue?
Increase protein breakdown and Decreased protein synthesis
How does cortisol secretion effect the liver?
Increased gluconeogenesis
How does cortisol secretion effect many tissues (other than muscle, liver and adipose tissues)?
Decreased glucose uptake and decreased amino acid uptake
How does glucocorticoid secretion effect muscle tissue?
Increased protein degradation
Decreased protein synthesis, glucose utilisation and insulin sensitivity
How does glucocorticoid secretion effect fat?
Increased lipolysis
Decreased insulin sensitivity, glucose utilisation
How does glucocorticoid secretion effect liver tissue?
Increased glycogen storage, gluconeogenesis, enzyme amount and enzyme activity
