Energy Metabolism Flashcards
(34 cards)
1
Q
To main processes that govern energy metabolism
A
- Anabolism → use the nutrient pool to synthesize functional storage and components (macro nutrients)
- Catabolism → Breaking down the macronutrients to make ATP
2
Q
NUtrient pool
A
Form used by cells to generate ATP
- fatty acids
- glucose
- amino acids
3
Q
Macronutrients
A
Structural, functional and sotrage components
- triacylglycerides
- glycogen
- proteins
4
Q
When does anabolic vs. catabolic prevail?
A
- In times of nutrient excess in bloodstream anabolic will prevail
- times of stress or low macro the catabolic processes will take over
5
Q
Forms of energy throughout the body
A
6
Q
Absorptive State
A
- 3–4 hours following meal
- Nutrients in bloodstream plentiful from absorption
- Glucose serves as the primary fuel for the cells
- Energy derived from the macros are stored for later use or as structural building blocks
7
Q
Postabsorptive state
A
- Between meals → breaking down energy stores occurs about 6-8 hours after meal
- Energy stores must be mobilized → macros broken down from the storage sites
- Fatty acids are the primary fuel
8
Q
Carbohydrates’ absorptive state
A
- Glucose = primary fuel
- Glycogen synthesis and storage (glycogenesis)
- Conversion of excess glucose to triglycerides and storage in fat
9
Q
Carbohydrate post absorptive state
A
- Glycogen breakdown (glycogenolysis) → released as glucose into the blood
- Glucose synthesized (gluconeogenesis) → glucose made from scratch, liver utilizes these processes to make glucose in blood stream
10
Q
What is glycogen break down mainly used for?
A
Predominantly used by the muscles
11
Q
Where is glycogen stored?
A
liver and muscle
- Only liver is really capable of breaking down glucose to be used by other parts of body especially brain and muscle
12
Q
Where does glucose come from?
A
Glucose comes from the food we eat and alternatively can enter bloodstream from the liver or can make it from scratch to increase amount of glucose. Can be transported into cells by glucose transporters. Once enters cell can be used as energy (2) or other metabolic pathways (3)
13
Q
Proteins absorptive state
A
- Protein synthesis → amino acids to make structural and functional proteins for cellular function and make enzymes for catalysis
- Conversion of excess amino acids to triglycerides and storage as fat
14
Q
Proteins post-absorptive state
A
- Protein breakdown
- Amino acids are used for gluconeogenesis by liver
- only converted to energy in extreme conditions but not an ideal fuel
- Amino acids are used for gluconeogenesis by liver
15
Q
Protein pathways/ uses
A
- Broken down to peptides and aa and carried mostly in blood as aa and can be taken into cells to synthesize new proteins (2).
- Proteins inside cell can be broken down to aa and then used intercellularly to make other proteins or aa can be released (4).
- Or used as energy (3) but not a good idea because this would often usually only happen under starvation because this reaction used structural components of cells, which explains muscle wasting and heart problems when starving.
- Aa can also be taken up by liver and used in synthesis of glucose
16
Q
Lipid absorptive state
A
Triglyceride synthesis and storage (lipogenesis)
- building block for triacylgylcerides from fats, carbs and proteins in excess
17
Q
Lipid post-absorptive state
A
- Triglyceride breakdown (lipolysis)
- Fatty acids primary fuel
- yields glycerol (converted to glucose by liver) and FA (converted to ketones)
- Glycerol can be converted to glucose
- Fatty acids can be converted to ketones
18
Q
Processing fat for body cells
A
- Broken down in GI by bile acids and pancreatic enzymes, and enterocytes in SI absorb these as monoglycerides and FA and then packaged into chylomicrons, which is a transport vehicle since fats do not mix with water, and they are a form of lipoproteins, they carry fats in the bloodstream.
- Lipoproteins can also be secreted by the liver (LDL) and transported to the rest of the body.
- Once lipoproteins reach the target cell needs an enzyme, lipoprotein lipase (LPL), to hydrolyze triglycerides in lipoprotein and glycerol as well as FA. So breaks down triglyceride and yields substrates to be used by the cell as a source of energy.
- FA can undergo beta oxidation (in mitochondria) in order to produce ATP.
- Additionally mono can be taken up by liver.
19
Q
processing fat for fat cells
A
- Carried by lipoproteins in blood and LPL will hydroxylate the triacylglyceride to free up FA which can be taken up by fat cells.
- LPL is found in the endothelium of capillaries (gas exchange and nutrients).
- FA enter fat cells and are used as energy for fat cells themselves or undergo beta-oxidation to generate ATP in mitochondria.
- Alternatively, FA (4) can be re-esterified to form tri again, and stored in fat cells, which is the safe storage of fat.
- FA free in fat cells is toxic.
- IF haven’t eaten for a while or increase in energy demand then stored triglycerides can be broken down to glycerol and FFA to be used as fuel when released to the bloodstream. (5)
- the liver can take these substrates up and they are also a site for fat storage
- (too much in the liver though is not a good thing, a pathological condition known as fatty liver disease)
20
Q
When are ketones used as a fuel for the brain?
A
in times of starvation
21
Q
How is fat safely stored in fat cells?
A
In there triacylgyceride form
- FFA are toxic in fat cell
22
Q
What are the pancreatic hormones
A
- insulin → from the beta cells
- glucagon → from the alpha cells
23
Q
Where are the pancreatic hormones secreted from
A
the islet of Langerhans cells which have both the alpha and beta cells
24
Q
What kind of hormone is insulin?
A
peptide hormone → hydrophilic so receptors on the cell membrane
25
When is insulin secretion increased?
secretion increased during the absorptive state
stimuli:
* increased glucose in plasma
* increased amino acids in plasma
* increased parasympathetic activity (rest and digest function)
* incretins (e.g. GLP-1, GIP) act on pancreas to secrete insulin
26
When is insulin secretion decreased?
Secretion decreased during postabsorptive state
* secretion inhibited by epinephrine → stress hormone which stimulates glucose production
* secretion inhibited by somatostatin → released by delta cells and allows for paracrine, local effect, of insulin secretion
27
Overall effect of insulin
* Promotes synthesis of energy storage molecules (anabolism)
* promotes glycogen storage in the liver, triacylglyderide storage in adipose tissue and protein synthesis in muscle
* Promotes glucose uptake by body cells
* Helps to lower blood glucose level into various cells and inhibit uptakew of glucose by the liver
28
Regulation of blood glucose by insulin
* An Increase in blood glucose, such as after eating (absorptive state), and activates beta cells to secrete insulin causing a rise in insulin being circulated and has effects on different tissues
* In adipose and muscle stimulates the uptake of glucose. Insulin removes glucose from blood and allows these cells to bring in more glucose.
* Insulin will suppress output of glucose by liver by inhibiting liver production of glucose by suppressing glyconeogensis and glycogenlysis.
29
Insulin signalling
* Hydrophilic so receptor at cell surface and is enzyme linked tyrosine kinase receptor and binding to ligand (insulin) triggers a chain of phosphorylation reactions that involves activation of several protein kinases and leads to translocation of vesicles containing glucose transporters.
* Vesicles take glucose transporters to cell surface.
* At rest vesicles contain glucose transporters.
* Upon stimulation by insulin and activation of pathway the vesicles can then insert into cell membrane.
* They can then help with diffusion of glucose into the cell (glucose transporter 4 / GLUT 4)
* Lowers blood glucose levels by pulling out of blood and into cells
30
Action of increased insulin
promotes synthesis of energy storage/anabolism and inhibits catabolism
31
Action of decreased insulin
32
Glucose regulation via glucagon
* Main stimulus is drop in plasma glucose, opposite to insulun
* beginning of post absorptive state and need to start breaking stuff down for energy
* Helps to restore blood glucose once fallen
33
Actions of glucagon
**Stimuli**
* decreased glucose in plasma
* increased amino acids in plasma\*
* increased sympathetic activity
* epinephrine → part of stress response and want more glucose in blood stream
**Inhibitors**
* somatostatin (paracrine effects)
* insulin (paracrine effects)
* increased glucose in plasma
34
How do amino acids stimulate glucagon?
This stimulus is common to stimulating glucagon and insulin. So if we have a meal with protein we are less likely to get large fluctuations in plasma glucose levels because of way aa can stimulate both these hormones. Carbohydrate rich would be large fluctuation because of differential effect it has on these hormones. Why we eat sugary meal we will get sugar crash vs more balanced meal.
