The Endocrine Pancreas COPY Flashcards
What parts of the hypothalamus determine the energy balance?
Feeding centre
Satiety centre
What controls the feeding and satiety centres?
Nutrients in plasma
What is the glucostatic theory
Food intake is determined by [BG]
As [BG] increases the drive to eat decreases
What is the lipostatic theory?
Food intake determined by fat stores
Leptin release by fat stores depresses feeding centre
What are the 3 elements of metabolism?
- Extracting nutrients from food
- Storing extracted energy
- Using the energy to do work
What are the 2 major types of metabolic pathway?
Anabolic
Catabolic
Describe anabolic?
Build up
Synthesises large molecules from smaller constituents
Stores
Describe catabolic?
Breaks down
Breaking down of larger molecules into smaller constituents
Uses stores
What is the absorptive state?
Follows after a meal
- Ingested nutrients are used to supply energy demands
- Excess energy is stored
- Anabolic
What is the post absorptive stage?
Fasted state between meals and overnight
- Body demands are reliant on stores
- Catabolic
What is an obligatory glucose user and name one?
Tissue that can only utilise glucose as energy
The brain
What can the brain utilise in extreme starvation?
Ketones
What is normal [BG]?
4.2 - 6.3mM
How many Islets of Langerhans are there in the average pancreas?
1.2 million
What are the 4 types of cells in the islets of langerhans?
Alpha
Beta
Delta
F cells
What do alpha cells secrete?
Glucagon
What do beta cells secrete?
Insulin
What do delta cells secrete?
Somatostatin
What do F cells secrete?
Pancreatic Polypeptide
What is control of [BG] dependent on?
The insulin:glucagon balance
What is the only hormone that lowers [BG]?
Insulin
How is insulin secreted from beta cells?
- Have specific KATP ion channel
- [BG] ^ causes glucose to enter the cells through a GLUT 2
- Metabolism increases and the KATP channels are activated
- K+ enters the cells
- Cell depolarises
- Ca2+ channels open and calcium enters
- Calcium dependent exocytosis of insulin vesicles occurs
What is the half life of insulin?
About 5 minutes
What happens when [BG] is low to beta cells?
The cell hyperpolarises so calcium dependent exocytosis can’t occur
What is the main role of insulin??
Stimulates glucose uptake by muscles and adipose tissue (insulin sensitive tissue)
What is the process of glucose uptake by insulin sensitive tissue?
- Insulin binds to tyrosine kinase receptors on the cell membrane
- GLUT 4 transporters mobilised and migrated to the membrane
- Allows glucose to enter the cell
- When insulin release stops the tyrosine kinase receptor and the insulin molecule are endocytosed and destroyed
- GLUT 4 transporters return to cytoplasmic pool
What are the other non insulin dependent GLUT transporters?
GLUT 1 - Basal glucose in many tissue (brain, kidney, RBCs)
GLUT 2 - beta pancreatic cells and liver
GLUT 3 - same as GLUT 1
What other pathways are promoted by insulin?
Glycogen synthesis
Increases amino acid uptake and therefore promotes protein synthesis
TAG synthesis
K+ entry via the sodium potassium pump
What processes are inhibited by insulin?
Gluconeogenesis
Permissive effect on GH
What stimuli increase insulin release?
High [BG]
High [AA]
Glucagon
Incretin hormones
Vagal nerve activity
What incretin hormones stimulate insulin release?
Gastrin
CCK
GLP-1
GIP
How does vagal nerve activity stimulate insulin release?
- Stimulates release of major GI incretin hormones
What stimuli inhibit insulin release?
- Low [BG]
- Somatostatin
- Sympathetic A2 effects
- Stress (e.g. hypoxia)
GLUCAGON QUESTIONS
What type of hormone is glucagon?
Peptide hormone
What cells produce glucagon?
Alpha cells of islets
What is the primary purpose of glucagon?
Maintain [BG] in the fasted state
- Acts on the liver
How does glucagon raise [BG] in the fasted state?
Involved in the glucose counter regulatory control system (along with cortisol and GH)
- Binds to GPCRs liked to cAMP
- Phosphorylates specific liver enzymes resulting in
1. Increase glycogenolysis
2. Increased gluconeogenesis
3. Formation of ketones from FA’s
When is glucagon secreted?
Relatively constantly
- Increases when [BG] < 5.6mM
- Ratio of glucagon:insulin most significant
What other processes stimulate the release of glucagon?
- High [AA]
- Low [BG]
- Sympathetic B2 innervation
- Cortisol
- Stress
What inhibits glucagon release?
- High [BG]
- FFAs
- Ketones
- Insulin
- Somatostatin
How do amino acids regulate [BG] after a meal?
Release both insulin and glucagon to ensure that hypoglycaemia doesn’t occur
- Also ensures that obligatory glucose utilisers get enough glucose
What is the parasympathetic effect on islets?
- Vagus
- Increases insulin release
- Increases glucagon release (to a lesser effect)
During what phase does the vagus act?
Cephalic phase
What is the effect of the sympathetic phase on islets?
- Promotes glucose release
- Increases glucagon
- Increases epinephrine
What type of hormone is somatostatin?
Peptide hormone
What cells secrete somatostatin?
D cells
Hypothalamus
What are the functions of somatostatin?
- Slow down GI tract (i.e. reduce absorption of nutrients to prevent plasma spikes)
- Strongly suppresses the release of both insulin and glucagon
What stimuli promote somatostatin release?
- [BG] high
- [AA] high
What effect does insulin have during exercise?
- Glucose enters muscle more in exercise even without insulin
- Insulin sensitivity is increased so GLUT 4 mediated transport increases
- This allows the muscle to get better energy supply
What happens to adipose tissue during starvation?
- Broken down into FFAs
- These can be readily used by most tissue but brain requires Glc/Ketones
- Brain adapts
- This spares protein so muscle wasting doesn’t occur
- Protein is used after fat stores are depleted
