Absorptive and Post-absorptive states Flashcards
Absorptive and post-absorptive states
Absorptive state refers to the pattern of energy metabolism due to high concentration of the nutrients in the blood as a result of absorption of the nutrients.
In this case, some of the nutrients are used to meet immediate energy needs while the excess are stored for energy later.
Post-absorptive state is a pattern of energy metabolism adopted between meals or during fasting.
Changes in the pattern of energy metabolism depends on the changes in the blood concentration of insulin and other hormones.
Absorptive state
In the absorptive state, the absorbed nutrients are hexose sugars and amino acids.
These nutrients go through the liver into circulation.
Other nutrients go into adipose tissues, muscles and other tissues.
Lipids -> small intestines -> lymph (chylomicrons) -> venous blood -> adipose tissue
Control of absorptive state
Absorptive state
Feeding
Uptake of glucose
↑Blood sugar
Glucose > Enters pancreas > GLUT2 > ↑ATP
β-cells (Islets of Langerhans)
↑ATP causes K+ channels to close
Membrane depolarisation
↑ Ca2+ intracellular > Insulin exocytosis
Pompeii disease
Glycogen is synthesised in the liver or muscles
A disorder with glycogen storage cause accumulation of glycogen or change in structure of glycogen.
Pompeii disease is an autosomal recessive disorder which affects the functioning of lysosomal acid α-glucosidase due to mutation of GAA gene. This causes cellular damage.
In healthy individuals, glycogen accumulates in the cytoplasm of liver and muscle cells. However, patients with Pompeii disease have glycogen accumulated in the lysosome of these cells instead.
Insulin
Insulin- a hormone secreted by in the pancreas.
Insulin largely influences the pattern of metabolism observed
The release of insulin is stimulated by fed state and inhibited by fasted state.
High concentration of glucose/amino acids in the blood stimulates the release of insulin (fed state).
Hormones and neurotransmitters also influence insulin secretion.
GLUT4- found in adipose tissues and straited muscle
GLUT2- used in liver cells
Insulin in post-absorptive state
The brain and RBC largely depend on glucose for energy. Lack of glucose = brain damage, coma, death
In the post-absorptive state plasma levels of glucose is maintained by glucose-supplying and glucose sparing reactions.
Therefore, when insulin secretion is impaired, the pattern of metabolism = post-absorptive state.
glucose supplying reactions
-glycogen , glycogenolysis , gluconeogenesis
glucose sparing reactions
- fatty acids , ketone bodies
Starvation
In famine, starvation is prevalent.
What are the metabolic processes that would have been occurring to enable people to maintain their plasma glucose concentration?
Depletion of carbohydrate precursors
Increased gluconeogenesis (amino acids glycerol)
After about 48 hrs, energy is supplied by ketone bodies and free fatty acids
Prolonged starvation initiates protein catabolism (organ system dysfunction)
Glycogenolysis in liver,
Glycogenolysis in muscle, which would provide glucose indirectly via lactate production and
Gluconeogenesis in liver, which would provide glucose from amino acids, lactate and glycerol.
Insulin would be at basal level
Diabetes mellitus
Diabetes mellitus has two forms
Type 1
Young onset
Loss of β cells
Cannot utilise glucose > Other fuels
Weight loss, ketoacidosis (ketones)
Type 2
Prevalence ↑age
↑insulin but resistance
Weight loss, ketoacidosis
Effect of diabetes on tissues
↑ Glycogenolysis (Glycogen breakdown) - in liver
Gluconeogenesis from protein break down - in muscle
↑ fatty acids in circulation - in fatty tissue
↑ risk of non-alcoholic fatty liver disease - in liver
Muscle wasting - in muscle
Excess ketone - in fatty tissue
Tests for diabetes
The concentration of insulin in the plasma should vary based on the level of plasma glucose.
The glucose tolerance test is commonly used to diagnose diabetic states. The test relies on the metabolic pattern in absorptive state.
Fasting blood sugar test is also used to diagnose diabetic states. The test relies on the metabolic pattern in post-absorptive state.
Obesity causes slower uptake of glucose insulin resistance ↑ plasma glucose.
Haemoglobin A1C (HbA1C) is considered a more reliable test for the diagnosis and management of diabetes
GLP-1 agonists
Glucagon-like peptide-1 (GLP-1) agonists are in current use for the management of type 2 Diabetes Mellitus.
GLP-1 is a peptide produced by the cleavage of proglucagon in pancreatic islet α-cells.
They work by activating GLP-1 receptors in the pancreas -> ↑ insulin release -> ↓ glucagon release -> ↓ gastric emptying
Impact of chronic diabetes
Elevated glucose react with proteins
Maillard reaction (non enzymatic browning)
This is also why food goes brown when cooking
Makes this taste good
Here is alters enzyme / protein function
AGE (Advanced glycation end products)
Impact of chronic diabetes
Retinopathy
Growth of poor-quality new blood vessels in the retina
Macular oedema
Which can lead to severe vision loss
Blindness
Neuropathy
Decreased sensation in hands and feet
Damages blood vessels
Diabetic foo ulcers
Delayed healing > Secondary infection > Amputation
