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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

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
what are the layers of the skin
Helen Reply
It is made up of three layers, the epidermis, dermis, and the hypodermis, all three of which vary significantly in their anatomy and function. The skin's structure is made up of an intricate network which serves as the body's initial barrier against pathogens, UV light, and chemicals, and mechanical
Omer
what is diabetes?
Ifeoluwa
Diabetes is a chronic (long-lasting) health condition that affects how your body turns food into energy. Your body breaks down most of the food you eat into sugar (glucose) and releases it into your bloodstream. When your blood sugar goes up, it signals your pancreas to release insulin. Insulin act
Omer
what is gastric lavage and their implications
Ifeoluwa
what is velium
chizzy
what is a purpose
chizzy
what's fibroid
Kizito
what are disorders of connective tissue
Ester Reply
Rheumatoid arthritis (RA) Scleroderma. Granulomatosis with polyangiitis (GPA) Churg-Strauss syndrome. Lupus. Microscopic polyangiitis. Polymyositis/dermatomyositis. Marfan syndrome.
Omer
arthritis vasculitis
Enitan
what is cardiac output
Okoye Reply
(CO) amount of blood pumped by each ventricle during one minute; equals HR multiplied by SV
AI-Robot
what is SV and HR stand for
David
SV- Stroke Volume HR- Heart Rate
Ebelechukwu
Cardiac output is the amount of blood pumped by the heart in one minute. It's calculated by multiplying the heart rate (the number of times the heart beats in one minute) by the stroke volume (the amount of blood pumped out by the heart with each beat). So, cardiac output = heart rate x stroke volum
Dickson

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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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