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The breakdown of fatty acids, called fatty acid oxidation    or beta (β)-oxidation    , begins in the cytoplasm, where fatty acids are converted into fatty acyl CoA molecules. This fatty acyl CoA combines with carnitine to create a fatty acyl carnitine molecule, which helps to transport the fatty acid across the mitochondrial membrane. Once inside the mitochondrial matrix, the fatty acyl carnitine molecule is converted back into fatty acyl CoA and then into acetyl CoA ( [link] ). The newly formed acetyl CoA enters the Krebs cycle and is used to produce ATP in the same way as acetyl CoA derived from pyruvate.

Breakdown of fatty acids

This figure shows the reactions that break down fatty acids. The top panel shows the conversion of fatty acids into carnitine. The bottom panel shows the conversion of carnitine into acetyl-CoA.
During fatty acid oxidation, triglycerides can be broken down into acetyl CoA molecules and used for energy when glucose levels are low.

Ketogenesis

If excessive acetyl CoA is created from the oxidation of fatty acids and the Krebs cycle is overloaded and cannot handle it, the acetyl CoA is diverted to create ketone bodies    . These ketone bodies can serve as a fuel source if glucose levels are too low in the body. Ketones serve as fuel in times of prolonged starvation or when patients suffer from uncontrolled diabetes and cannot utilize most of the circulating glucose. In both cases, fat stores are liberated to generate energy through the Krebs cycle and will generate ketone bodies when too much acetyl CoA accumulates.

In this ketone synthesis reaction, excess acetyl CoA is converted into hydroxymethylglutaryl CoA (HMG CoA)    . HMG CoA is a precursor of cholesterol and is an intermediate that is subsequently converted into β-hydroxybutyrate, the primary ketone body in the blood ( [link] ).

Ketogenesis

This pathway shows the production of beta-hydroxybutyrate from acetyl-CoA.
Excess acetyl CoA is diverted from the Krebs cycle to the ketogenesis pathway. This reaction occurs in the mitochondria of liver cells. The result is the production of β-hydroxybutyrate, the primary ketone body found in the blood.

Ketone body oxidation

Organs that have classically been thought to be dependent solely on glucose, such as the brain, can actually use ketones as an alternative energy source. This keeps the brain functioning when glucose is limited. When ketones are produced faster than they can be used, they can be broken down into CO 2 and acetone. The acetone is removed by exhalation. One symptom of ketogenesis is that the patient’s breath smells sweet like alcohol. This effect provides one way of telling if a diabetic is properly controlling the disease. The carbon dioxide produced can acidify the blood, leading to diabetic ketoacidosis, a dangerous condition in diabetics.

Ketones oxidize to produce energy for the brain. beta (β)-hydroxybutyrate    is oxidized to acetoacetate and NADH is released. An HS-CoA molecule is added to acetoacetate, forming acetoacetyl CoA. The carbon within the acetoacetyl CoA that is not bonded to the CoA then detaches, splitting the molecule in two. This carbon then attaches to another free HS-CoA, resulting in two acetyl CoA molecules. These two acetyl CoA molecules are then processed through the Krebs cycle to generate energy ( [link] ).

Questions & Answers

Capillary permeability
what do you want to know about it?
Ramsin
Hello, I want to search about the topic, information and pictures
syncitium is the property of which of the following muscle
Shahab Reply
can I get the questions of human physiology that is present in HSC 2nd semester
Sai Reply
i now madam
irpa
ha can u please send me the PDF of questions
Sai
it's important to me to have that information please send as fast as u can
Sai
me too if possible?
Ramsin
If a molecule can only pass through a membrane with the assistance of a membrane protein, but the direction of its travel is controlled only by its concentration, the process is called?
osmosis
chozen
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column.
Isaac
a. What probably caused the IV disc herniation? b. What cause IV disc degeneration? c. What are the result of disc degeneration?
Isaac
b
Mirasol
Describe the neural control of erection and ejaculation.
Nana Reply
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column. a)What probably caused the IV di
Isaac
a) What probably caused the IV disc herniation? b) What cause IV disc degeneration? c) What are the result of disc degeneration?
Isaac
iv disc herniation compress the nerve cause numbness tingling sensation even paralysis in severe cases...
Khawaja
explain more
DANIELLA Reply
yes
Ramzan
function of skeleton
Josiah Reply
- for movement - blood production by the bone marrow
Daniel
production of calsium and phosphorus
Juma
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. 8. What fossa related the perineal swelling? 9. Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac
what is heart
Subhajit Reply
it is the tissue..which pump blood to the all parts of body
GRAY
the heart is a conical , hollow, muscular organ which works continuously through out the life of a person ,it is about the size of a clenched fist and weighs about 300 grams and also the heart is in the chest just behind the breast bone and between the two lungs
Mary
a hollow muscular organ that pumps blood through the circulatory system by regular contractions
Johnny
is a muscular organ that pumps blood lungs and other body tissues through vessels
Nolosha
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. 8. What fossa related the perineal swelling? 9. Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. 8. What fossa related the perineal swelling? 9. Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac Reply
inguinal fossa femoral vein?
Jeen
if you dont the answer by now you should seek another line of work. as a professor it is my duty to let you know about your lacking.
Arif
branches of brachial plexus
Arooj Reply
musculocutaneous, median, ulnar, axillary, and radial nerves.
Shakerah
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. a.What fossa related the perineal swelling? b.Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac
What is great Auricular nerve?
ZUBAIR Reply
it originates from the cervical plexus that provides sensory innervation to the skin.
Daniel
why it is called Auricular nerve
Amber
is any payment is needed to use this app
Suprith Reply
is it a question?
Samenjo
doubt about this app
Suprith
which lines divide the body into nine quadrant
Julius Reply
nine regions of abdomen can b marked using two horizontal & two vertical lines...the vertical lines are the mid clavicular lines taken from the mid point of each clavicle. the upper horizontal lines is the subcostal line taken from the inferior parts of the lowest costal cartilage...
Khawaja
to get a better understanding for the function
Rashana Reply
anatomy and physiology work closely together
Rashana
anatomy to you about the structure of the while physiology is the the study of the body function
Rashana
what is the difference between negative and positive feedback
Rashana
The key difference bewteen positive and negative feedback is their response to change. Positive feedback amplifies change while negative reduces change.
ladychen
negative feed back produces a response that brings back to normal while positive feed back produces a response that stimulates
Julius
examples of the body structure
Naki Reply
body's structure
Naki

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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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