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  4. The digestive system
  5. Chemical digestion and absorption

23.7 Chemical digestion and absorption: a closer look

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By the end of this section, you will be able to:
  • Identify the locations and primary secretions involved in the chemical digestion of carbohydrates, proteins, lipids, and nucleic acids
  • Compare and contrast absorption of the hydrophilic and hydrophobic nutrients

As you have learned, the process of mechanical digestion is relatively simple. It involves the physical breakdown of food but does not alter its chemical makeup. Chemical digestion, on the other hand, is a complex process that reduces food into its chemical building blocks, which are then absorbed to nourish the cells of the body ( [link] ). In this section, you will look more closely at the processes of chemical digestion and absorption.

Digestion and absorption

This diagram identifies the functions of mechanical and chemical digestion and absorption at each organ. Next to each organ, a callout identifies which steps of digestion take place in that particular organ.
Digestion begins in the mouth and continues as food travels through the small intestine. Most absorption occurs in the small intestine.

Chemical digestion

Large food molecules (for example, proteins, lipids, nucleic acids, and starches) must be broken down into subunits that are small enough to be absorbed by the lining of the alimentary canal. This is accomplished by enzymes through hydrolysis. The many enzymes involved in chemical digestion are summarized in [link] .

*These enzymes have been activated by other substances.
The Digestive Enzymes
Enzyme Category Enzyme Name Source Substrate Product
Salivary Enzymes Lingual lipase Lingual glands Triglycerides Free fatty acids, and mono- and diglycerides
Salivary Enzymes Salivary amylase Salivary glands Polysaccharides Disaccharides and trisaccharides
Gastric enzymes Gastric lipase Chief cells Triglycerides Fatty acids and monoacylglycerides
Gastric enzymes Pepsin* Chief cells Proteins Peptides
Brush border enzymes α-Dextrinase Small intestine α-Dextrins Glucose
Brush border enzymes Enteropeptidase Small intestine Trypsinogen Trypsin
Brush border enzymes Lactase Small intestine Lactose Glucose and galactose
Brush border enzymes Maltase Small intestine Maltose Glucose
Brush border enzymes Nucleosidases and phosphatases Small intestine Nucleotides Phosphates, nitrogenous bases, and pentoses
Brush border enzymes Peptidases Small intestine
  • Aminopeptidase: amino acids at the amino end of peptides
  • Dipeptidase: dipeptides
  • Aminopeptidase: amino acids and peptides
  • Dipeptidase: amino acids
Brush border enzymes Sucrase Small intestine Sucrose Glucose and fructose
Pancreatic enzymes Carboxy-peptidase* Pancreatic acinar cells Amino acids at the carboxyl end of peptides Amino acids and peptides
Pancreatic enzymes Chymotrypsin* Pancreatic acinar cells Proteins Peptides
Pancreatic enzymes Elastase* Pancreatic acinar cells Proteins Peptides
Pancreatic enzymes Nucleases Pancreatic acinar cells
  • Ribonuclease: ribonucleic acids
  • Deoxyribonuclease: deoxyribonucleic acids
 Nucleotides
Pancreatic enzymes Pancreatic amylase Pancreatic acinar cells Polysaccharides (starches) α-Dextrins, disaccharides (maltose), trisaccharides (maltotriose)
Pancreatic enzymes Pancreatic lipase Pancreatic acinar cells Triglycerides that have been emulsified by bile salts Fatty acids and monoacylglycerides
Pancreatic enzymes Trypsin* Pancreatic acinar cells Proteins Peptides

Questions & Answers

Discuss the differences between taste and flavor, including how other sensory inputs contribute to our  perception of flavor.
John Reply
taste refers to your understanding of the flavor . while flavor one The other hand is refers to sort of just a blend things.
Faith
While taste primarily relies on our taste buds, flavor involves a complex interplay between taste and aroma
Kamara
which drugs can we use for ulcers
Ummi Reply
omeprazole
Kamara
what
Renee
what is this
Renee
is a drug
Kamara
of anti-ulcer
Kamara
Omeprazole Cimetidine / Tagament For the complicated once ulcer - kit
Patrick
what is the function of lymphatic system
Nency Reply
Not really sure
Eli
to drain extracellular fluid all over the body.
asegid
The lymphatic system plays several crucial roles in the human body, functioning as a key component of the immune system and contributing to the maintenance of fluid balance. Its main functions include: 1. Immune Response: The lymphatic system produces and transports lymphocytes, which are a type of
asegid
to transport fluids fats proteins and lymphocytes to the blood stream as lymph
Adama
what is anatomy
Oyindarmola Reply
Anatomy is the identification and description of the structures of living things
Kamara
what's the difference between anatomy and physiology
Oyerinde Reply
Anatomy is the study of the structure of the body, while physiology is the study of the function of the body. Anatomy looks at the body's organs and systems, while physiology looks at how those organs and systems work together to keep the body functioning.
AI-Robot
what is enzymes all about?
Mohammed Reply
Enzymes are proteins that help speed up chemical reactions in our bodies. Enzymes are essential for digestion, liver function and much more. Too much or too little of a certain enzyme can cause health problems
Kamara
yes
Prince
how does the stomach protect itself from the damaging effects of HCl
Wulku Reply
little girl okay how does the stomach protect itself from the damaging effect of HCL
Wulku
it is because of the enzyme that the stomach produce that help the stomach from the damaging effect of HCL
Kamara
function of digestive system
Ali Reply
function of digestive
Ali
the diagram of the lungs
Adaeze Reply
what is the normal body temperature
Diya Reply
37 degrees selcius
Xolo
37°c
Stephanie
please why 37 degree selcius normal temperature
Mark
36.5
Simon
37°c
Iyogho
the normal temperature is 37°c or 98.6 °Fahrenheit is important for maintaining the homeostasis in the body the body regular this temperature through the process called thermoregulation which involves brain skin muscle and other organ working together to maintain stable internal temperature
Stephanie
37A c
Wulku
what is anaemia
Diya Reply
anaemia is the decrease in RBC count hemoglobin count and PVC count
Eniola
what is the pH of the vagina
Diya Reply
how does Lysin attack pathogens
Diya
acid
Mary
I information on anatomy position and digestive system and there enzyme
Elisha Reply
anatomy of the female external genitalia
Muhammad Reply
Organ Systems Of The Human Body (Continued) Organ Systems Of The Human Body (Continued)
Theophilus Reply
what's lochia albra
Kizito
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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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