Flashcards in Physiology 2 - Endocrine Pancreas Deck (29):
The energy of the body is the energy input - the energy output. What determines our food intake?
Glucostatic Theory - Feeding centres suppressed/satiety centres promoted as blood [Glc] rises.
Lipostatic Theory - Fat stores decrease the drive to eat.
How does increasing fat stores reduce the urge to eat?
Leptin (a peptide hormone) is released from fat stores and depresses the feeding centre.
Disruption of this hormone can lead to obesity
What are the categories of energy output?
Mechanical Work (Both muscular and intracellular)
Define Anabolic vs Catabolic Pathways?
Anabolic refers to synthesis of large molecules, largely for storage
Catabolic refers to breakdown of large molecules, largely for energy
Define the absorptive & Post-absorptive state?
Absorptive State occurs after eating, ingested nutrients supply energy and the excess is stored.
Post-Absorptive (Fasting) occurs between meals where body stores are used for energy
Describe and give examples of obligatory Glucose utilisers?
The Brain is the major Obligatory Glucose Utiliser.
It means it can't use fats, carbs or protein for energy, hence why we require a constant blood Glucose level.
What is the normal range of Blood Glucose?
Hypoglycaemia is considered below 3mM
What hormones are responsible for regulating Blood glucose and where are they made?
Insulin & Glucagon are the major ones.
Made in Islets of Langerhans of the pancreas
Describe the 4 cell types of the Islets of Langerhans?
Alpha cells - make glucagon
Beta cells - Make insulin
Delta cells - Make Somatostatin (GHIH)
F cells make Pancreatic Polypeptide
What class of hormone are insulin/glucagon?
In short what is the function of insulin vs glucagon?
Insulin reduces Blood Glucose
Glucagon Increases Blood Glucose
Therefore they are both stimulated by the opposite level of blood glucose.
How does Glucose trigger Insulin secretion by Beta Cells?
B cells contain ATP sensitive K+ channels.
1) High blood glucose enters cell
2) Metabolises to ATP
3) ATP closes K+ Channels, causing cell to depolarise
4) Voltage Dependant Ca2+ channels open & Ca2+ triggers Insulin-Vesicle Exocytosis
Other than high blood [Glc] what else triggers insulin release?
- Increased plasma [amino acids]
- Incretin Hormones e.g. CCK, Secretin, GIP & Gastrin
- Vagal Activity
Glucagon has the opposite effect to insulin so why would it trigger insulin release?
Glucagon creates more glucose in the blood. Insulin is required for glucose uptake by cells so is needed for the new glucose to be used.
Why do incretin hormones trigger insulin release?
So that the glucose being absorped from the gut doesn't trigger a dangerous spike in blood [Glc]
What are the 8 actions of insulin?
1) Increased Glc uptake in muscle/adipose
2) Increased Glycogenesis
3) Inhibits Gluconeogenesis
4) Increased TAG synthesis in adipose/liver
5) Increased Amino acid uptake in muscle
6)) Increased protein synthesis in muscle
7) Promotes K+ entry to cells
8) permissive effect on growth hormone
How does insulin cause increased Glc uptake?
Insulin-Sensitive Tissues (muscle/adipose) have specific Tyrosine Kinase Receptors for insulin.
These stimulate GLUT-4 transporters to take up Glc
The liver isn't an Insulin-sensitive tissue, but it's Glc uptake is still affected by insulin, how?
Insulin activates Hexokinase within the liver, this turns Glc to Glc-6-phosphate, creating a conc. gradient for Glc to enter the cell.
What trigger's release of Glucagon?
1) Low blood Glucose
2) High blood [amino acids]
3) Sympathetic innervation/Epinephrine on B2 receptors
5) Stress e.g. Exercise
Why does a rise in blood amino acids trigger a release of both insulin & Glucagon?
Amino acids cause insulin release because it makes muscles take up more amino acids and form more proteins.
They also trigger glucagon release to counter the insulin so that it doesn't cause hypoglycaemia
How does Glucagon raise Blood Glc?
Triggers phosphorylation of enzymes responsible for:
How is the ANS involved in the Islet cells?
Parasympathetic activity (via Vagus) during the anticipatory stage of digestion triggers insulin (and some glucagon) release.
Sympathetic innervation promotes glucagon & epinephrine while inhibiting insulin as part of the fight/flight response
4 hormones are involved in the Glucose Counter-Regulation, what are they and how do they regulate glucose?
Glucagon - Liver glycogenolysis, Lipolysis and Gluconeogenesis
Epinephrine - Muscle/liver glycogenolysis, Gluconeogenesis & Lipolysis
Cortisol - Gluconeogensis, inhibits Glc uptake, lipolysis & Protein Catabolism
GH - Gluconeogenesis, Inhibition of Glc uptake & Lipolysis
What is somatostatin?
A peptide hormone produced by delta cells in the pancreas and hypothalaus (aka GHIH)
What does somatostatin do?
1) Slows absorption of nutrients in the gut to reduce blood Glc spikes
2) Suppresses insulin/glucagon in a paracrine fashion
3) Inhibits secretion of GH from Ant Pituitary
We have described how blood glucose is controlled in the steady state, what happens during exercise?
Exercise does 2 things:
1) increases insulin sensitivty of muscle
2) Induces insulin-independant increase in GLUT-4 transporters
This effect lasts hours and regular exercise can cause prolonged increases in insulin sensitivity
We have described how blood glucose is controlled in the steady state, what happens during starvation?
During starvation glucose drops.
In response the body breaks down adipose tissue to Fatty acids.
The liver converts FAs to Ketone bodies which the brain can adapt to use for energy.
Summary of Insulin
Reduces Glucose levels in the blood as well as promoting Amino acid uptake and protein synthesis.
A peptide hormone produced in B cells in the pancreas