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Ketone oxidation

This figure shows the reactions in which ketone is oxidized to acetyl-CoA.
When glucose is limited, ketone bodies can be oxidized to produce acetyl CoA to be used in the Krebs cycle to generate energy.

Lipogenesis

When glucose levels are plentiful, the excess acetyl CoA generated by glycolysis can be converted into fatty acids, triglycerides, cholesterol, steroids, and bile salts. This process, called lipogenesis    , creates lipids (fat) from the acetyl CoA and takes place in the cytoplasm of adipocytes (fat cells) and hepatocytes (liver cells). When you eat more glucose or carbohydrates than your body needs, your system uses acetyl CoA to turn the excess into fat. Although there are several metabolic sources of acetyl CoA, it is most commonly derived from glycolysis. Acetyl CoA availability is significant, because it initiates lipogenesis. Lipogenesis begins with acetyl CoA and advances by the subsequent addition of two carbon atoms from another acetyl CoA; this process is repeated until fatty acids are the appropriate length. Because this is a bond-creating anabolic process, ATP is consumed. However, the creation of triglycerides and lipids is an efficient way of storing the energy available in carbohydrates. Triglycerides and lipids, high-energy molecules, are stored in adipose tissue until they are needed.

Although lipogenesis occurs in the cytoplasm, the necessary acetyl CoA is created in the mitochondria and cannot be transported across the mitochondrial membrane. To solve this problem, pyruvate is converted into both oxaloacetate and acetyl CoA. Two different enzymes are required for these conversions. Oxaloacetate forms via the action of pyruvate carboxylase, whereas the action of pyruvate dehydrogenase creates acetyl CoA. Oxaloacetate and acetyl CoA combine to form citrate, which can cross the mitochondrial membrane and enter the cytoplasm. In the cytoplasm, citrate is converted back into oxaloacetate and acetyl CoA. Oxaloacetate is converted into malate and then into pyruvate. Pyruvate crosses back across the mitochondrial membrane to wait for the next cycle of lipogenesis. The acetyl CoA is converted into malonyl CoA that is used to synthesize fatty acids. [link] summarizes the pathways of lipid metabolism.

Lipid metabolism

This figure shows the different reactions that take place for lipid metabolism.
Lipids may follow one of several pathways during metabolism. Glycerol and fatty acids follow different pathways.

Chapter review

Lipids are available to the body from three sources. They can be ingested in the diet, stored in the adipose tissue of the body, or synthesized in the liver. Fats ingested in the diet are digested in the small intestine. The triglycerides are broken down into monoglycerides and free fatty acids, then imported across the intestinal mucosa. Once across, the triglycerides are resynthesized and transported to the liver or adipose tissue. Fatty acids are oxidized through fatty acid or β-oxidation into two-carbon acetyl CoA molecules, which can then enter the Krebs cycle to generate ATP. If excess acetyl CoA is created and overloads the capacity of the Krebs cycle, the acetyl CoA can be used to synthesize ketone bodies. When glucose is limited, ketone bodies can be oxidized and used for fuel. Excess acetyl CoA generated from excess glucose or carbohydrate ingestion can be used for fatty acid synthesis or lipogenesis. Acetyl CoA is used to create lipids, triglycerides, steroid hormones, cholesterol, and bile salts. Lipolysis is the breakdown of triglycerides into glycerol and fatty acids, making them easier for the body to process.

Questions & Answers

starnd of MRI and ?why
ruha Reply
what is haploid
Sonnie Reply
half of diploid(2n) n no of chromosomes I.e human have 46 no of chromosomes and its haploid is 23
Sayed
Half of diploid
ruha
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Sayed
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ruha
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Sayed
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ruha
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Sayed
2endyear
ruha
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Sayed
what are oxygen free radical
Fateemah Reply
are very reactive molecules that can react with every cellular component
Irene
is a molecule that contains atleast one unpaired electron
kevin
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is the study of structure of the body
Saifullah
is the study of the structure and function of the human body
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Sayed Reply
yes
Andrei
yes
Irene
yes
MONISH
what is anatomy
Eunice Reply
describe how penile erection occurs
Eunice
the study of the parts of an organism
Ayisi
is the study of the bones
Zainab
that's osteology
Ayisi
Ok
Emmanuel
How many hair do we have
Emmanuel
hair?
christine
why it's not advisable to not to give an intramuscular
Jamila Reply
well l think intramuscular injection takes a long time to get to the cells of the body for action whislt an intravenous injection goes straight to the heart and then pump to the cells /tissues quickly.So in a nutshell, intramuscular is slower and takes a longer time to work
Anna
it depends on the route of administration of drugs in an instance where the drugs to be given needs a fast action then intravenous is given but if opposite then intramuscular is advised
Deborah
Some times it is not fast in action, and again due to some complications of IM such as injection abcess, and pain.
Idris
why in IM ingestion should not be more than 2ml
Fatou
because of tissues inflammation the high dose of more than 2mls may cause
Clifford
TSH secretion is inhibited by stress and cortisol
Hadi Reply
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Hello my friend. What do you want to chat about?
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mehmet
why it's not advisable to not to give an intramuscular injection on the shoulder more than 2ml
Fatou
what are the factor that stimulates bile secretion
Linda Reply
secretin ,gestrin , glucagon, cholecytokinin-pancreozymin,
Leila
bile secretion is stimulate by secretin . bile secrete in to gall bladder .gall bladder store and concentrate bile...
Anoop
what happens to the rate of breathing during acidosis? why?
Rachael Reply
the breathing rate increases
Azapa
The breathing rate decreases due to accumalative amounts of carbondioxide. Or un balanced amounts of oxygen and carbondioxide
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explain on the cellular respiration
Racheal Reply
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The founder of anatomy is called herophilos
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is the study of the human body
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does blood moves through the heart
Ezeonu Reply
yes
Chifuniro
yape
LifeLine
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LifeLine
No 👎.
ring
Since dendrites are at the terminal end of a sensory neurone allowing it to transmit impulses to the relay neurone... what is at the other terminal end of the sensory neurone that connects it to the sensory organ?
Emmanuel Reply
The sensory organs have receptors which detect the stimulus then transmits impulses to the neurones via synaptic transmission. Meaning dendrites connect the sensory neurones to the receptors in the organ.
Cindah

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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