Hormones That Effect Blood Glucose Levels Flashcards
(75 cards)
1
Q
What happens after a meal, in the fed / absorptive state?
A
- the levels of glucose in the intestinal circulation are high
- this nutrient rich blood is carried to the liver in the portal venous blood
- this is where the nutrients are processed - some are stored in the liver, some are going to the hepatic vein towards the rest of the body
- hormones process blood glucose for cellular use or storage
- the reactions = they lower blood glucose
2
Q
What happens in the fasted / post-absorptive state?
A
- blood glucose may be low
- reactions and processes that act to raise blood glucose predominate
3
Q
What are glucose lowering reactions - that happen in the fed state?
A
- glucose uptake by cells
- glucose breakdown for energy
- glucose storage as glycogen
- glucose conversion to non-carbohydrate forms
4
Q
What is glucose uptake by cells?
A
- glucose is a water soluble molecule, it does not pass easily through the lipid cell membrane
- the barrier is overcome by glucose carrier proteins in cell membranes, which allow facilitated diffusion of glucose into the cytoplasm
- if plasma concentrations are higher than those inside the cell
5
Q
What is glucose breakdown for energy?
A
- the energy stored within the glucose molecule is released in two series of reactions:
- glycolysis occurs within the cytoplasm, leading to the formation of pyruvate and small amounts of ATP
- the pyruvate can be converted to lactate - especially in anaerobic conditions
- or it can be transported to the mitochondria where it is fully oxidised in the citric acid cycle
- producing much larger amounts of ATP
- along with carbon dioxide and water as byproducts
6
Q
What is glucose storage in the form of glycogen?
A
- glycogen synthesis occurs within muscle cells & hepatocytes
7
Q
What is glucose conversion to non-carbohydrate forms?
A
- glucose may be used as a substrate for the synthesis of amino acids, or fatty acids
8
Q
Glucose in the liver:
A
- fatty acids
- amino acids
- glycogen
- glycolysis
- pyruvate / lactate
9
Q
Glucose in the muscle:
A
- glycogen
- pyruvate / lactate (by glycolysis)
10
Q
What are the main glucose raising reactions?
A
- use of non-carbohydrate energy sources
- release of glucose from glycogen
- formation of glucose from non-carbohydrate sources
11
Q
What is the use of non-carbohydrate energy sources to raise glucose?
A
- degradation of other substrates, such as the beta-oxidation of fatty acids
- provides cells with necessary ATP, whilst sparing the glucose
- this can’t occur in the brain - metabolism is strictly glucose dependent
12
Q
What is the release of glucose from glycogen in glucose raising reactions?
A
- glycogen breakdown is called glycogenolysis
- it happens in the liver
- allows the release of glucose into the circulating plasma
- muscle glycogen cannot be used to maintain plasma glucose directly
- as glucose-phosphate that is formed during the breakdown of glycogen can’t be converted to glucose, in the muscle
- any lactate formed in the muscle via glycolysis can be used as a gluconeogenic substrate in the liver
- so it contributes to maintaining the blood glucose
13
Q
What is the formation of glucose from non-carbohydrate sources mean in raising blood glucose?
A
- gluconeogenesis from other substrates, like amino acids released from the breakdown of proteins
- and glycerol released by the breakdown of triglycerides
- happens in the liver
14
Q
What is the concentration of glucose in the blood normally in a fasted individual?
A
- 5mmol L/-1
15
Q
Why does blood glucose rise after a meal?
A
- due to absorption of glucose and other nutrients from the intestine
- in the absorptive state
16
Q
What do blood glucose levels normally fall to then, what happens?
A
- they do not normally rise above 10mmol L/-1
- they fall back towards normal within 2 hours, after absorption has stopped
17
Q
What do the absorptive features and tendencies depend on?
A
- active regulation of the concentration of glucose within the circulation
- if this regulation does not happen, glucose levels fluctuate at a greater level
- they rise to much higher levels during absorption
- and fall to lower levels during fasting for longer than 3-4 hours
18
Q
What does insulin do?
A
- decrease blood glucose levels
19
Q
What increases blood glucose levels?
A
- glucagon
- glucocorticoids
- catecholamines
- growth hormone
20
Q
When is insulin the dominant hormone?
A
- during the fed state
21
Q
What is insulin’s actions balanced or opposed by?
A
- the group of hormones that elevate or maintain blood glucose under fasting conditions
- these hormones = glucagon, glucocorticoids, catecholamines, growth hormone
22
Q
What is the source of insulin?
A
- synthesis and release of digestive enzymes by the exocrine pancreas is an important component of gastrointestinal function
- the pancreas plays an important endocrine role = it secretes hormones which are important for control of plasma glucose concentration
23
Q
What are the small groups of cells specialised for endocrine secretion into the blood?
A
- they are between exocrine structures
- they form the islets of langerhans
24
Q
What are the three main cell types within the islets?
A
- alpha
- beta
- sigma
- they each produce a different hormone
25
What is insulin secreted by?
- beta cells
- consists of two peptide chains linked by two disulphide bridges
- survives for a relatively short time in circulation, broken down approximately after 10 minutes - in the liver & kidney
- the rapid turnover means = insulin levels drop rapidly if the beta-cell stops secreting them
26
What is insulin’s main role?
- to regulate cellular absorption & use glucose in a way to reduce plasma glucose concentration, when the levels raise way above normal
27
What is the most important factor that helps regulate insulin secretion?
- plasma concentration of glucose
28
What does elevation of the plasma glucose concentration do?
- stimulates a rapid rise in insulin secretion
- insulin levels are low at normal fasting glucose concentrations - BUT
- rise as glucose is absorbed immediately after a meal
- as insulin reduces the amount of glucose in the extracellular fluid, this acts as a negative feedback system
- which limits any increase in plasma glucose
29
What happens beta cells secretion as glucose levels decline?
- it decreases
- so insulin falls back to a low concentration in the fasting state 3-4 hours after a meal
30
What is insulin secretion also stimulated by?
- increased amino acid concentrations
- promoting their cellular uptake for protein synthesis
31
What inhibits insulin release?
- somatostatin from islet sigma cells
32
What type of hormone is insulin?
- major ANABOLIC hormone
- affecting carbohydrate, protein & lipid metabolism
33
How does insulin affect carbohydrate metabolism?
- insulin stimulates glucose uptake by several body tissues
- promotion of glucose influx by insulin is important in skeletal muscle, cardiac muscle & adipose tissue
- the liver & brain cells are permeable to glucose, in the absence of insulin
- cerebral metabolism is highly dependent on glucose
- so a maintenance of an adequate supply of plasma glucose is crucial
34
How does insulin promote glycogen storage?
- through increased glycogen synthesis = glycogenesis
- and decreases glycogen breakdown = glycogenolysis
- this is an important mechanism, allowing carbohydrate storage during the absorption of a meal
- insulin stimulates the use of glucose for energy by stimulating = glycolysis
35
What does insulin do for protein metabolism, what does insulin promote protein accumulation in cells by?
- stimulates amino acid uptake, particularly in muscle
- stimulates protein synthesis and stops protein breakdown
- inhibits the conversion of amino acids to glucose = gluconeogenesis
- increasing substrate availability for protein synthesis
36
What does insulin do to lipid metabolism?
- promotes the deposition of triglycerides in lipid body stores
37
How does insulin do this to triglycerides?
- inhibitng the breakdown of stored lipid by lipase
- stimulating fatty acid synthesis from glucose, in the liver
- promoting the release of fatty acids from triglycerides in lipoprotein complexes
- the fatty acids can then be stored as lipids in the adipose tissue
- promotes glycerol synthesis in lipid cells
- promotes carbohydrate metabolism so that fat is spared
- example = muscle oxidise fatty acids for energy but after a meal, when glucose & insulin levels are high = it switches to carbohydrate
38
What is glucagon?
- catabolic peptide hormone that raises plasma sugar levels
39
Where is glucagon secreted from?
- the alpha-cells of the pancreatic islets
40
What is glucagon stimulated by?
- low plasma glucose concentrations = glucagon levels rise in the fasting state after a meal
- high levels of circulating amino acids = important in maintaining normal plasma glucose levels during absorption of a protein meal
- as the amino acids stimulate insulin secretion
- this might be cause hypoglycaemia in the absence of action on carbohydrate metabolism
41
What are glucagon’s metabolic actions?
- oppose insulins
- mainly in the liver
1. Carbohydrate metabolism
2. Lipid metabolism
42
How does glucagon affect carbohydrate metabolism?
- hepatic output of glucose to the plasma is promoted by:
- increased glycogenolysis
- increased formation of glucose from amino acids & glycerol = gluconeogenesis
- glucose sparing via beta-oxidation of fatty acids for energy = leads to formation of ketone bodies
43
How does glucagon affect lipid metabolism?
- glucagon favours an increase in plasma levels of fatty acids & glycerol, by the activation of lipase
44
What is the source and secretion of catecholamines (adrenaline and noradrenaline)?
- they are amines released from the central portion of the adrenal gland = the medulla
- low levels of blood glucose activate sympathetic nerves in the CNS
- this results in stimulation of catecholamines release from the adrenal medulla, by the preganglionic sympathetic nerves
45
What are the main metabolic actions of catecholamines?
- increased metabolism and heat production
- increased glycogenolysis
- increased gluconeogenesis
- decreased glucose uptake and use in muscle
- increased fat breakdown by lipase, increased fatty acid oxidation & ketone production
46
What does activation of the adrenal medulla do?
- activated due to stress or hypoglycaemia
- favours a rise in blood glucose
47
What else do catecholamines stimulate the release of?
- pancreatic glucagon
- which tends to elevate blood glucose levels
48
What is growth hormone?
- peptide hormone secreted from the anterior pituitary
- stimulates growth during childhood & adolescence
49
When is growth hormone secreted?
- in increased concentrations in a response to hypoglycaemia = low blood sugar
50
What effects does growth hormone have?
- it is ANABOLIC, glucose raising effects
- decreases glucose uptake and utilisation in the body, increases hepatic glucose production
- promotes protein synthesis, stops protein breakdown
- increases fat breakdown
51
Where are glucocorticoids secreted?
- from the cortex of the adrenal glands
- play a major role in the control of blood glucose and metabolism
52
What is the dominant glucocorticoid?
- cortisol = hydrocortisone
53
What do glucocorticoids do?
- assist glucagon to prevent blood glucose from falling below normal
54
What type of hormone is cortisol, what does it do?
- CATABOLIC
- promotes protein breakdown
- promotes glucose synthesis from amino acids = gluconeogenesis
- promotes glycogen storage
- promotes oxidation of fatty acids for free energy use, so it preserves cell glucose
55
When are the effects of glucocorticoids important?
- preventing hypoglycaemia during the fasting state
- especially if it is a prolonged fast
56
What doesn’t occur when cortisol is absent?
- increases in amino acids and gluconeogenesis in fasted individuals
57
What is important when glycogen stores are diminished?
- stimulation of glycogenolysis by glucagon & adrenaline is important in response to hypoglycaemia
- it has limited benefit when there is less glucocorticoids
- glucocorticoids also stimulate appetite
58
All of insulins effects:
- increased glucose uptake
- increased glycogen stores
- decreased gluconeogenesis
- increased protein synthesis
- decreased protein breakdown
- increased triglyceride stores
- decreased fatty acid oxidation
59
All of glucagons effects:
- decreased glucose uptake
- decreased glycogen storages
- increased gluconeogenesis
- decreased triglyceride storage
- increased fatty acid oxidation
60
All of catecholamines’ effects:
- decreased glucose uptake
- decreased glycogen storage
- increased gluconeogenesis
- decreased triglyceride storage
- increased fatty acid oxidation
61
All of growth hormones effects:
- decreased glucose uptake
- decreases glycogen stores
- increased gluconeogenesis
- increased protein synthesis
- decreases protein breakdown
- decreased triglyceride storage
- increased fatty acid oxidation
62
All of glucocorticoids actions:
- decreased glucose uptake
- increased glycogen storages
- increased gluconeogenesis
- decreases protein synthesis
- increased protein breakdown
- decreased triglyceride storage
- increased fatty acid oxidation
63
What is the main cause of diabetes mellitus?
- inadequate effect of insulin
64
First way diabetes mellitus can arise:
- primary deficiency of insulin = type 1 diabetes
- beta cells are damaged, fail to secrete insulin
65
Second way:
- insulin resistance
- overweight patients
- type 2 non-insulin dependent diabetes
66
What is the last reason for diabetes mellitus - sometimes?
- not due to a defect in insulin,
- excess secretion of cortisol, growth hormone or very rarely = glucagon
67
How many consequences of diabetes mellitus are there?
Three
68
First consequence:
- problems due to abnormal carbohydrate metabolism
- decreased glucose uptake - leads to hyperglycaemia
69
What does hyperglycaemia lead to?
- plasma glucose is filtered in the kidney
- but is normally completely reabsorbed within the convoluted tubules
- abnormally high levels of glucose lead to saturation of the tmax renal transport mechanisms
- the excess is excreted in the urine
- this occurs when plasma glucose is raised above the normal renal threshold for glucose excretion
70
What does elevated glucose within renal tubules cause?
- osmotic retention of water, so there is an increased rate of urine production
- this is osmotic diuresis
71
Why do thirst and drinking increase?
- due to dehydration resulting from renal fluid loss
72
What do reductions in amino acids uptake and protein synthesis lead to?
- negative nitrogen balance
- impaired growth in children
- weight loss with muscle wasting in adults
73
Problems due to abnormal lipid metabolism:
- weight loss, increased fatty acid plasma levels
- low levels of glucose uptake, beta-oxidation of fatty acids is increased, so ketones are formed - leading to metabolic acidosis
- increased ventilation due to respiratory compensation
74
Treatment for diabetes mellitus:
- restriction of carbohydrate intake
- regular insulin injections
75
Causes and consequences of excess insulin:
- reduction in plasma glucose levels
- activates the sympathetic nervous system
- tremor, sweating, increased heart rate
- must be reversed by glucose / glucagon to prevent brain damage
