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By the end of this section, you will be able to:
  • Explain how energy can be derived from fat
  • Explain the purpose and process of ketogenesis
  • Describe the process of ketone body oxidation
  • Explain the purpose and the process of lipogenesis

Fats (or triglycerides) within the body are ingested as food or synthesized by adipocytes or hepatocytes from carbohydrate precursors ( [link] ). Lipid metabolism entails the oxidation of fatty acids to either generate energy or synthesize new lipids from smaller constituent molecules. Lipid metabolism is associated with carbohydrate metabolism, as products of glucose (such as acetyl CoA) can be converted into lipids.

Triglyceride broken down into a monoglyceride

The top image shows the chemical formula for a triglyceride, and the bottom panel shows the formula for a monoglyceride.
A triglyceride molecule (a) breaks down into a monoglyceride (b).

Lipid metabolism begins in the intestine where ingested triglycerides    are broken down into smaller chain fatty acids and subsequently into monoglyceride molecules    (see [link] b ) by pancreatic lipases    , enzymes that break down fats after they are emulsified by bile salts    . When food reaches the small intestine in the form of chyme, a digestive hormone called cholecystokinin (CCK)    is released by intestinal cells in the intestinal mucosa. CCK stimulates the release of pancreatic lipase from the pancreas and stimulates the contraction of the gallbladder to release stored bile salts into the intestine. CCK also travels to the brain, where it can act as a hunger suppressant.

Together, the pancreatic lipases and bile salts break down triglycerides into free fatty acids. These fatty acids can be transported across the intestinal membrane. However, once they cross the membrane, they are recombined to again form triglyceride molecules. Within the intestinal cells, these triglycerides are packaged along with cholesterol molecules in phospholipid vesicles called chylomicrons    ( [link] ). The chylomicrons enable fats and cholesterol to move within the aqueous environment of your lymphatic and circulatory systems. Chylomicrons leave the enterocytes by exocytosis and enter the lymphatic system via lacteals in the villi of the intestine. From the lymphatic system, the chylomicrons are transported to the circulatory system. Once in the circulation, they can either go to the liver or be stored in fat cells (adipocytes) that comprise adipose (fat) tissue found throughout the body.

Chylomicrons

This figure shows a chylomicron containing triglycerides and cholesterol molecules as well as other lipids.
Chylomicrons contain triglycerides, cholesterol molecules, and other apolipoproteins (protein molecules). They function to carry these water-insoluble molecules from the intestine, through the lymphatic system, and into the bloodstream, which carries the lipids to adipose tissue for storage.

Lipolysis

To obtain energy from fat, triglycerides must first be broken down by hydrolysis into their two principal components, fatty acids and glycerol. This process, called lipolysis    , takes place in the cytoplasm. The resulting fatty acids are oxidized by β-oxidation into acetyl CoA, which is used by the Krebs cycle. The glycerol that is released from triglycerides after lipolysis directly enters the glycolysis pathway as DHAP. Because one triglyceride molecule yields three fatty acid molecules with as much as 16 or more carbons in each one, fat molecules yield more energy than carbohydrates and are an important source of energy for the human body. Triglycerides yield more than twice the energy per unit mass when compared to carbohydrates and proteins. Therefore, when glucose levels are low, triglycerides can be converted into acetyl CoA molecules and used to generate ATP through aerobic respiration.

Questions & Answers

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Hussein Reply
mention two processes of bone formation
Ngopiro Reply
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Ngopiro
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Justine Reply
what are the importance of studying anatomy and physiology?
Justine Reply
bones and structures
Nkechi Reply
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Cb
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Cb
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patrick
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King
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Abdi
what are the Hodgkin's disease
Mwasiti Reply
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Mwasiti Reply
Heart Blood Blood Vessel
Md
what are the components of the bone
Ngopiro
what is Hodgkin's disease
Mwasiti Reply
What is anatomy
Munira Reply
anatomy is a study of physical and structural functions of human body parts
Mohd
is the study of structure of the body and physical relationship involve between the body system
Mwasiti
is the study of structure of the body and physical relationship involve between the body system
Mwasiti
why simple columnar support peristalisis
Camilius Reply
why when sex of an individual is determined by y chromosome found in male therefore why there is many women than male
pamfili Reply
I'm not sure if I fully understand your question.
are you sure it is more
samir
i don't remember what I said.
I'm not sure if I fully understand your question.
roughly taking a lead.
samir
Muscle of mastication
JIMOH Reply
what is anatomy
Akanle
Sorry....it's the study of human body and it's functions.
Irene
Anatomy is the study of human organs
Kity
what is serum protein?
Salum
what is anatomy
Akanle
Anatomy is the study of human organs
Kity
Who is a bovin
Kity
Who is a bovin
Kity
Why do you ask tough questions I'm in JHS 3
Kity
pls does broken bones get healed
Desmond
yes
Belinda
how
Desmond
by surgery or medication
Desmond
Medication
Irene
why do a bovin not menstruate unlike women?
patrick
Why do you ask tough questions I'm in JHS 3
Kity
Anatomy is the study of structure of the human body
Belinda
yes
Belinda
medication
Belinda
yes
Belinda
animals within that group include cows as well as others.
ihope that was helpful
aaa,kity.bovin is a terminology used by veteranians to refer a cow.for dogs its carnine,cats it's ferline...etc
patrick
i believe if you look up the classification of Bovin , it tell clarify more for you.
ihope that was helpful
i don't think my first message about taxonomy sent
i don't think my first message about taxonomy sent
difference between seminiferous tubules and ejaculatory duct
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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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