Post-absorptive Mechanisms Flashcards
Absorptive state
During which ingested nutrients enter the blood from GI tract
Ingested, circulating nutrients provide the energy requirements
Excess is stored in post-absorptive state
Post-absorptive state
GI tract is empty
Nutrients come from body stores
How long can glycogen stores last
12 hours
How long can lipid stores last
3 months
When is tissue protein used as an energy source
After prolonged starvation
Which 2 organs require 40% of energy requirement at rest
Brain and liver
Energy requirements of brain
Glucose
Keton bodies
Energy requirements of muscle
Glucose, triacylglycerol, branched chain amino acids
Ketone bodies (at rest)
Energy requirements of liver
Amino acids
Fatty acids
Glucose
Alcohol
Why can’t ketone bodies be used by the liver
Produced here but have no thiolase
Energy requirements of kidney cortex
Glucose
Ketone bodies
Energy requirements of kidney medulla
Glucose
Energy requirements of small intestine
Ketone bodies (in starvation)
Glutamine
Energy requirements of large intestine
Short chain fatty acids
Glutamine
BMI and health
As BMI goes up mortality increases exponentially
Cancer/ heart disease/ musculoskeletal/ sleep apnea
Fed state
Fuels are oxidised to energy
Any excess is stored
Triglycerides in adipose
Glycogen in muscle or liver
Limited amount to how much glycogen can be stored in muscle and liver so more is converted into adipose
Insulin and the liver
Glucose to liver
Insulin promotes uptake of glucose into cells for storage as glycogen
Some glucose used to produce energy
Glucose and liver
Stored as glycogen
Used to produce energy = converted to acetyl-CoA to enter kreb’s cycle
Acetyl-CoA and liver
- Enters kreb’s cycle to produce ATP
- Make triglycerides that enter bloodstream as VLDLs
VLDLs
Very low density lipoprotein
Triglycerides that enter bloodstream from liver
High glucose = high VLDL levels
Glucose and erythrocytes
Glucose taken up but cannot be stored
Glucose converted to pyruvate which can diffuse out of cell or be converted into lactate
Lactate is released from the cell
Post-absorptive state and amino acids
Absorption through intestines
Converted into proteins (can be reversed)
Can make hormones and other molecules
Feed into kreb’s cycle to make ATP
Where are amino acids absorbed
Intestines
Glucose and adipocytes
Glucose taken up (promoted by insulin)
Used to make ATP or stored as triglycerides
Glucose and muscle
Glucose stored as glycogen
Uses insulin to promote uptake
Lipoproteins
LDL
HDL
VLDL
Absorption of triglycerides
Chylomicrons carry triglycerides and lipoproteins
Into the lymphatic system and then blood stream
Glucose and CNS
Converted to acetyl-CoA
Enters kreb’s cycle
No energy stored in brain
Fasting state
Maintaining blood glucose whilst not eating
Body breaks down its energy stores
Horus to overnight
Pathway of glucose
Broken down and absorbed in intestines
Passes through blood in liver
Reaches muscles, brain, erythrocytes and adipocytes
Pancreas
Endocrine and exocrine organ
Where is insulin produced
Pancreas
Where is glucagon produced
Pancreas
Insulin
Main anabolic hormone
Energy uptake into cells
Glycogen storage, fat storage and protein synthesis
Glucagon
Main catabolic hormone
Energy release
Glycogenolysis, gluconeogenesis, ketogenesis
Where is cortisol produced
Adrenal gland
Where is adrenaline/noradrenaline produced
Adrenal gland
Cortisol
Preparation for stress response
Lipolysis, protein breakdown, gluconeogenesis, glycogen storage
Adrenaline/noradrenaline
Fight or flight
Energy into blood stream to be used
Glycogenolysis, gluconeogenesis, lipolysis
Where is thyroxine produced
Thyroid gland
Thyroxine
Generally controls metabolism
Glycolysis, cholesterol synthesis, glucose uptake, protein synthesis, sensitises tissues to adrenaline
Where is growth hormone produced
Pituitary gland
Where is somatostatin produced
Pituitary gland
Growth hormone
Gluconeogenesis, glycogen synthesis, lipolysis, protein synthesis, decreased glucose use
Which hormones trigger Glycogenolysis
Glucagon
Adrenaline/noradrenaline
Which hormones trigger gluconeogenesis
Glucagon
Cortisol
Adrenaline/noradrenaline
Growth hormone
Which hormones trigger glycogen storage
Insulin
Cortisol
Growth hormone
What 2 hormones control appetite
Leptin and ghrelin
Where is leptin released from
Adipocytes
Where is ghrelin released from
Stomach
What does leptin act on
CNS to influence appetite
Leptin in normal weight
Suppresses appetite
Leptin in obesity
Leptin resistance due to continuous high leptin levels (stops responding)
Ghrelin
When empty ghrelin is released, goes to CNS to stimulate appetite
Release stopped upon stretch of stomach
Glycogenolysis
Breakdown of glucagon to glucose
Glucose - short fast
Glycogenolysis
Glucose primarily goes to brain and erythrocytes
Longer fast- alternative energy sources for gluconeogenesis to produce glucose
Amino acids (from muscles)
Lactate (from erythrocytes)
Glycerol (from adipocytes)
Site of gluconeogenesis
Liver
When does ghrelin release stop
Stretch of stomach
What hormone controls glycogenolysis
Glucagon
Lipolysis
Triglycerides stored in adipocytes
Break down triglycerides
Produces glycerol and fatty acids
Lipolysis- glycerol produced
Transported to liver to produce glucose
Lipolysis- produces fatty acids
Transported to kidneys, muscles and liver
In liver produce ketones
Which tissues can use ketones as an energy source
Muscles
CNS
Ketogenesis
Ketones released from liver
Produced from fatty acids
Protein degradation stops to preserve muscle
Which tissues can use ketones - prolonged fasting
CNS - during starvation
Muscles use less to preserve them for the brain
CNS decreases glucose use to preserve glucose for erythrocytes
Glucose-6-phosphate —> glycogen
Glycogenesis
Glycogen —> glucose-6-phosphate
Glycogenolysis
Pyruvate —> glucose-6-phosphate
Gluconeogenesis
Acetyl-CoA —>fats and lipids
Lipogenesis
Which substances can be measured in blood to give idea about health and disease
Glucose
Ketones
Insulin
Lactate
Triglycerides
Fats and lipids—> acetyl-CoA
Beta oxidation
Post-absorptive phase
CNS and many other tissues preferentially use glucose, produced from glycogen breakdown
Gluconeogenic phase
Protein catabolism is used to feed glucose to the CNS, while other tissue feed on ketones and fat
Protein conservation phase
Protein catabolism is decreased to a minimum, fatty acids are used everywhere and ketones instead of glucose fuel the CNS
Energy balance in
Food and drink
Energy balance out
Basal metabolic rate (BMR)
Diet induced thermogenesis (DIT)- energy used to break down food
Activity- uses the most energy
Stable weight
Energy in = energy out
Basal metabolic rate (BMR)
Minimum amount of energy to keep body alive
How is BMR measured
Using O2 consumption whilst awake, restful and fasted for 12 hours
How does age affect BMR
BMR decreases with age
Units of BMR
Kcal expended/hr/m^2
Factors contributing to obesity
Genetics
Environment
Energy dysregulation
Which enzyme converts glucose to glucose-6-phosphate in liver
Glucokinase
Which enzyme converts glucose-6-phosphate to glucose-1-phosphate in liver
Phosphoglucomutase
What is glucose-1-phosphate converted to in liver
UDP-glucose
Which enzyme adds UDP-glucose to glycogen chain
Glycogen synthase or branching enzyme
How much glycogen can be stored in the liver
100g
What is glucose-6-phosphate converted to in the liver
Glucose-1-phosphate
What is glucose-1-phosphate converted to in the liver
UPD-glucose
Lipolysis
Break down triglycerides
What are the products of lipolysis
Glycerol and fatty acids
Where is glycerol produced by lipolysis transported to
Liver to produce glucose
Where are fatty acids produced by lipolysis transported to
Kidneys, muscles and liver
In liver produce ketones
Which tissues can use ketones as energy
Muscles
CNS
Ketogenesis
Ketones released from liver
CNS uses ketones during starvation
Muscles use less ketones to preserve them for brain
CNS decreases glucose use
Preserves glucose for erythrocytes
What do erythrocytes give for gluconeogenesis
Lactate
What do muscles give for gluconeogenesis
Amino acids
What do adipocytes give for gluconeogenesis
Glycerol
Post-absorptive phase
The CNS and many other tissues preferentially use glucose, produced from glycogen breakdown
Gluconeogenic phase
Protein catabolism is used to feed glucose to the CNS, while other tissue feed on ketones and far
Protein conservation phase
Protein catabolism is decreased to a minimum, fatty acids are used everywhere and ketones instead of glucose fuel the CNS
Which glucose transporter is the primary transporter at the gastrointestinal brush border membrane in-between meals
SGLT-1
A 24-year-old woman is started on oral iron supplements as she is found to be iron deficient. This is her first time taking iron supplements in her lifetime. The patient has heard about many other medications, foods and drinks that can interfere with the absorption of iron.
What substance increases the absorption of the supplement the patient has been prescribed?
Vitamin C (ascorbic acid)
Carbohydrates are digested in a series of hydrolysis reactions in the gastro-intestinal tract. Starch/glycogen are hydrolysed by salivary and pancreatic amylase to produce disaccharides, which are further hydrolysed to monosaccharides. The absorption of which monosaccharide does NOT require energy from ATP?
Fructose
