Study sets, textbooks, questions
Upgrade to remove ads
Liver - Glucose Regulation, Fat metabolism
Terms in this set (51)
Describe the absorptive state
• Ingested nutrients in the GI tract absorbed into blood
• some CATABOLISED and used in metabolism
• excess converted + stored for later use
In absorptive state
glucose → metabolised to generate ATP
glucose → glycogen store
amino acids → proteins
FAs + glycerol → lipids
Describe the post-absorptive state
• GI track empty of nutrients
• Energy/nutrient stores MUST supply the energy needs of the body
In the post-absorptive state, glucose levels must be regulated.
• Glucose is no longer available for absorption from GI tract
• But plasma conc. of glucose MUST be maintained as the CNS relies on glucose for fuel
• Glucose must come from other sources
3 sources of glucose in post-absorptive state
1. Glycogen (glycogenolysis)
2. Lipids (gluconeogenesis)
3. Protein (gluconeogenesis)
• Where are body stores of glycogen
• Broken down to which monomer
• Liver & skeletal muscle
• Glucose-6-phosphate (not straight to glucose!!!)
Liver and skeletal muscle - does one contain more glycogen?
Both contain SAME amounts of glycogen
Hepatic glycogenolysis vs. skeletal muscle
Glycogen → glucose-6-phosphate
• Glucose-6P ENZYMATICALLY converted to glucose
• this glucose → blood
• Do not have enzymes for conversion of glucose-6P to glucose
• Glucose-6P undergoes GLYCOLYSIS → pyruvate, ATP, lactate
Body's FIRST LINE OF DEFENCE in maintaining plasma blood glucose conc. within homeostatic range:
• Hepatic glycogenolysis
• Begins within SECONDS of appropriate stimulus
• Such as SYMPATHETIC STIMULATION
However, the hepatic glycogen can only supply body's requirements for ...
Thus, glycogenolysis also occurs in ...
several hours before depletion
skeletal muscles (contain same amount of glycogen as liver)
Muscle glycogen is NOT a source of...
Glycogenolysis & subsequent ... in muscle forms ...
Fate of each product ...
Pyruvate, lactate, ATP
Pyruvate + ATP → directly used by muscle cell
LACTATE → some enters blood → liver → converted to GLUCOSE → blood
Thus, muscle cells contribute to blood glucose...
by way of liver processing lactate
- Hydrolysis of glycogen
- To glucose-6-phosphate monomers
- In liver and skeletal muscle
Lipids are broken down via..
• Hydrolysis of triglycerides to glycerol and fatty acids
• In adipose tissue
• Glycerol and fatty acids diffuse into blood → liver
• Glycerol can be ENZYMATICALLY converted to GLUCOSE through series of steps in liver
After ... of being in the post-absorptive state, protein must also become a source of glucose
Is this not dangerous?
• Large amounts muscle and tissues can be catabolised
• without significant cellular malfunction
(so initially ok)
Protein loss in short fast = ok
Continued protein loss in prolonged fast = dangerous
Disrupts cell function
Fate of protein in gluconeogenesis
• Protein broken down → amino acids → blood → liver
• Amino acids converted via the α-KETO ACID pathway → glucose
(transamination to pyruvate?)
• Glucose → blood
• Synthesis of new glucose molecules
• From non-carbohydrate precursors (amino acids, glycerol)
FOR 1 MOLECULE OF GLUCOSE FORMED ... MOLECULES OF ATP OF CONSUMED
1 GLUCSE FORMED : 6 ATP CONSUMED
Location of body fat stores
• Most in adipocytes, form adipose tissue
• Some in hepatocytes
Dietary lipids consists of 5 lipid forms:
• Triglycerides (95%) (TAGs/TGs)
• FFAs (free fatty acids)
• Fat-soluble vitamines (A,K,E,D)
Body's energy store is accounted for by
- TAGs = ..%
- Protein = ..%
- Carbohydrates = ..%
- TAGs = 78%
- Protein = 21%
- Carbohydrates = 1%
78% of energy stored in the body is stored in the form of triglycerides
• ESTERS of fatty acids and certain alcohol compounds
(many different types - fats/oils/waxes/steroids/hormones/phospholipids/cholesterol - fats only one type of lipid! All hydrophobic, non-polar and mostly made up of hydrocarbon chains)
• Energy store
• Structural component of cell membranes
• Steroid hormones
(also insulation, organ protection, solubilise fat-soluble vitamins
Lipids are hydrophobic.
How then are they transported in water of the blood or ecf?
What are lipoproteins?
• Means of transporting hydrophobic lipids in the blood (/ecf)
• Consist of single outer layer of phospholipids and cholesterol (hydrophilic ends facing outward)
• Hydrophobic/lipophilic ends point towards core of lipids
(apoproteins embedded in membrane to stabilise structure + determine its fate)
Lipoprotein 4 examples + site of synthesis:
1. HDL - liver
2. LDL - plasma
3. VLDL - liver
4. Chylomicrons - intestinal cells
HDL and LDL both carry ...
The main carrier being...
• HDL = 'good cholesterol'
• formed in liver
• REMOVE EXCESS cholesterol from blood & tissue to liver
• Liver secretes it in bile/converts it to bile salts
(remember they are still required for normal metabolism and life! But excess is bad)
• LDL = 'bad cholesterol'
• formed in plasma
• main cholesterol carrier
• DELIVER cholesterol to cells throughout the body
• LDL has protein component on surface that binds to receptors on the cell plasma membrane of cell → ENDOCYTOSIS of LDL into cell
Why LDL is considered "bad"
• Delivers cholesterol to cells
• High plasma concentrations of LDL
Associated with INCREASED DEPOSITION of cholesterol in ARTERIAL WALLS
Increased incidence of heart attack
LDL is still ESSENTIAL to cells however:
• Supplies them with cholesterol required for
• Cell membrane synthesis
• Steroid hormone synthesis in adrenal glands and gonads
- testosterone & oestrogen
- Synthesised where
• Liver hepatocytes
• Transport (endogenous) triglycerides (from glucose in liver) from liver → adipocytes
- Synthesised where
• Enterocytes (endoplasmic reticulum)
• Transport dietary lipids (exogenous) from GI tract → various tissues of the body such as adipose/caridac/skeletal
FATTY ACID CATABOLISM
Under resting conditions, around ... of the energy used by ....... comes from the CATABOLISM OF FA.
Muscles, liver, kidneys
Where is fat stored in body?
• Most cells do store some degree of fat
• But most is stored in ADIPOCYTES as SINGLE FAT DROPLET - almost fills the cytoplasm
• Clusters of adipocytes form ADIPOSE tissue
• Adipose tissue = underlying the skin / surrounding internal organs
Adipocyte function (absorptive + post-absorptive)
• Absorptive: synthesise and store TAGs
• Post-absorptive: breakdown TAGs
→ release glycerol and fatty acids into blood
→ transported by albumin
→ taken up by cells
→ used in metabolism to provide energy for ATP production
Adipocytes fat stores broken down.
Glycerol and fatty acids released into blood and taken up by cells.
Cells produce ATP from the fatty acids.
Involves ... of fatty acid followed by ...
This occurs in the ... of the cell
• Fatty acid activation
Describe the process
1. acetyl-CoA molecule attaches to end of FA at carboxyl group
2. ATP broken down → AMP + 2Pi
3. produces CoA derivative of the fatty acid
4. the coenzyme A derivative of the fatty acid proceeds through β-oxidation
5. each cycle cleaves off 2C from the FA → acetyl-CoA
and 2 pairs of H (one pair to FAD and one pair to NAD⁺)
- fate of H on coenzymes
- fate of acetyl CoA cleaved off
- fate of remaining fatty acid (acyl-CoA)
6. hydrogen atoms from the coenzymes are used in OXIDATIVE PHOSPHORYLATION to produce ATP
7. acetyl-CoA molecule used in KREB'S CYCLE
8. remaining acyl-CoA used again in cycle (but now 2C shorter)
• Fatty acid catabolised to produce acetyl-CoA for use in TCA cycle
• Acyl-CoA enters β-oxidation (fatty acid CoA derivative)
• 2 x 2H cleaved off
FAD → FADH₂
NAD⁺ → NADH + H⁺
• 2C cleaved off
→ acetyl CoA
Each passage through the β-oxidation sequence ...
SHORTENS the fatty acid chain by TWO CARBONS
until all the carbon atoms have been transferred to molecules of acetyl-CoA
Molecules produced in β-oxidation ... lead to the production of ... via ..
• Acetyl-CoA, FADH₂ and NADH
• production of CO₂ and ATP
• via Kreb's and oxidative phosphorylation
Other sets by this creator
FPHN week 1
FPHN week 9
FPHN week 8
FPHN week 7