This document discusses digestion and absorption of food. It begins by outlining the biological and medical importance of digestion and absorption. The major sites of digestion in the gastrointestinal tract and the digestive juices involved are described. Carbohydrates, proteins, and lipids are broken down into smaller molecules so they can be absorbed. Carbohydrates are digested into monosaccharides like glucose and galactose. Proteins are digested into amino acids through the action of proteases. Lipids are broken into fatty acids and glycerol. The absorbed nutrients are then transported through the intestinal mucosa and into circulation. Clinical conditions related to deficiencies in digestion and absorption are also mentioned.
The chemistry of digestion is simple because, in the case of all three major types of food (carbohydrates, proteins and fats), the same basic process of hydrolysis is involved. The only difference lies in the types of enzymes required to promote the hydrolysis reactions for each type of food.
The chemistry of digestion is simple because, in the case of all three major types of food (carbohydrates, proteins and fats), the same basic process of hydrolysis is involved. The only difference lies in the types of enzymes required to promote the hydrolysis reactions for each type of food.
Digestion & absorption of carbohydrate.pptxABHIJIT BHOYAR
The goal of carbohydrate digestion is to break down all disaccharides and complex carbohydrates into monosaccharides for absorption, although not all are completely absorbed in the small intestine (e.g., fiber). Digestion begins in the mouth with salivary amylase released during the process of chewing.
Digestion and absorption, digestive secretions, their characteristic features: Digestion is the breakdown of food into particles small enough to cross the cellular barrier of the gastrointestinal (GI) system and be carried around the body in the circulation.
This occurs by both mechanical and chemical processes that begin in the mouth and generally end in the small intestine, where 90% of absorption takes place.
The other 10% takes place in the stomach and large intestine and often involves the help of the gut microbiota.
A small amount of absorption is also thought to take place in the mouth.
Mechanical digestion begins in the mouth with chewing and continues with segmental muscle contractions in the stomach and intestines.
Chemical digestion is primarily mediated by enzymes present in the secretions of the salivary glands, stomach and pancreas, and on the epithelial lining of the small intestine
Mechanical digestion is physical process in which food is broken into smaller pieces without chemically.
It begins with our first bite of food and continues as we chew food with our teeth into smaller pieces.
The process of mechanical digestion continues in the stomach. This muscular organ churns and mixes the food it contains, an action that breaks any solid food into still smaller pieces.
Chemical digestion is the biochemical process in which macromolecules in food are changed into smaller molecules that can be absorbed into body fluids and transported to cells throughout the body.
Substances in food that must be chemically digested include carbohydrates, proteins, lipids, and nucleic acids.
Carbohydrates must be broken down into simple sugars, proteins into amino acids, lipids into fatty acids and glycerol, and nucleic acids into nitrogen bases and sugars.
Some chemical digestion takes place in the mouth and stomach, but most of it occurs in the first part of the small intestine (duodenum).
Chemical digestion could not occur without the help of many different digestive enzymes. Enzymes are proteins that catalyze or speed up biochemical reactions.
Digestive enzymes are secreted by exocrine glands or by the mucosal layer of the epithelium lining the gastrointestinal tract.
In the mouth, digestive enzymes are secreted by salivary glands.
The lining of the stomach secretes enzymes, as does the lining of the small intestine.
Many more digestive enzymes are secreted by exocrine cells in the pancreas and carried by ducts to the small intestine
About 80 percent of digestible carbohydrates in a typical Western diet are in the form of the plant polysaccharide amylose, which consists mainly of long chains of glucose and is one of two major components of starch.
Additional dietary carbohydrates include the animal polysaccharide glycogen, along with some sugars, which are mainly disaccharides.
To chemically digest amylose and glycogen, the enzyme amylase is required. The chemical digestion of these polysaccharides begins in the mou
Digestive physiology of herbivorous fishMahendra Pal
The knowledge of food and feeding habits and the physiology of digestion of any organism is most essential for development of artificial feed in culture practices. Fish and shellfish belong to the poikilothermous animal. The digestion process is somewhat different than the terrestrial animals. Similarly the mechanism of digestion and absorption process is quite different in fishes and shellfishes. The basic function of digestive system is to dissolve foods by rendering them soluble so that they can be absorbed and utilized in the metabolic process. The system may also function to remove dangerous toxic properties of certain food substances.
Fish generally change their feeding habits depending upon availability of food. So according to their feeding fishes are classified into different categories viz., predators, grazers, strainers, suckers and parasites.
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
Lung Cancer: Artificial Intelligence, Synergetics, Complex System Analysis, S...Oleg Kshivets
RESULTS: Overall life span (LS) was 2252.1±1742.5 days and cumulative 5-year survival (5YS) reached 73.2%, 10 years – 64.8%, 20 years – 42.5%. 513 LCP lived more than 5 years (LS=3124.6±1525.6 days), 148 LCP – more than 10 years (LS=5054.4±1504.1 days).199 LCP died because of LC (LS=562.7±374.5 days). 5YS of LCP after bi/lobectomies was significantly superior in comparison with LCP after pneumonectomies (78.1% vs.63.7%, P=0.00001 by log-rank test). AT significantly improved 5YS (66.3% vs. 34.8%) (P=0.00000 by log-rank test) only for LCP with N1-2. Cox modeling displayed that 5YS of LCP significantly depended on: phase transition (PT) early-invasive LC in terms of synergetics, PT N0—N12, cell ratio factors (ratio between cancer cells- CC and blood cells subpopulations), G1-3, histology, glucose, AT, blood cell circuit, prothrombin index, heparin tolerance, recalcification time (P=0.000-0.038). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and PT early-invasive LC (rank=1), PT N0—N12 (rank=2), thrombocytes/CC (3), erythrocytes/CC (4), eosinophils/CC (5), healthy cells/CC (6), lymphocytes/CC (7), segmented neutrophils/CC (8), stick neutrophils/CC (9), monocytes/CC (10); leucocytes/CC (11). Correct prediction of 5YS was 100% by neural networks computing (area under ROC curve=1.0; error=0.0).
CONCLUSIONS: 5YS of LCP after radical procedures significantly depended on: 1) PT early-invasive cancer; 2) PT N0--N12; 3) cell ratio factors; 4) blood cell circuit; 5) biochemical factors; 6) hemostasis system; 7) AT; 8) LC characteristics; 9) LC cell dynamics; 10) surgery type: lobectomy/pneumonectomy; 11) anthropometric data. Optimal diagnosis and treatment strategies for LC are: 1) screening and early detection of LC; 2) availability of experienced thoracic surgeons because of complexity of radical procedures; 3) aggressive en block surgery and adequate lymph node dissection for completeness; 4) precise prediction; 5) adjuvant chemoimmunoradiotherapy for LCP with unfavorable prognosis.
These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
Prix Galien International 2024 Forum ProgramLevi Shapiro
June 20, 2024, Prix Galien International and Jerusalem Ethics Forum in ROME. Detailed agenda including panels:
- ADVANCES IN CARDIOLOGY: A NEW PARADIGM IS COMING
- WOMEN’S HEALTH: FERTILITY PRESERVATION
- WHAT’S NEW IN THE TREATMENT OF INFECTIOUS,
ONCOLOGICAL AND INFLAMMATORY SKIN DISEASES?
- ARTIFICIAL INTELLIGENCE AND ETHICS
- GENE THERAPY
- BEYOND BORDERS: GLOBAL INITIATIVES FOR DEMOCRATIZING LIFE SCIENCE TECHNOLOGIES AND PROMOTING ACCESS TO HEALTHCARE
- ETHICAL CHALLENGES IN LIFE SCIENCES
- Prix Galien International Awards Ceremony
ARTIFICIAL INTELLIGENCE IN HEALTHCARE.pdfAnujkumaranit
Artificial intelligence (AI) refers to the simulation of human intelligence processes by machines, especially computer systems. It encompasses tasks such as learning, reasoning, problem-solving, perception, and language understanding. AI technologies are revolutionizing various fields, from healthcare to finance, by enabling machines to perform tasks that typically require human intelligence.
Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
ASA GUIDELINE
NYSORA Guideline
2 Case Reports of Gastric Ultrasound
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
5. Digestion and Absorption of Food
Contents:
Biological Importance
Medical Importance
Digestion and Absorption – General Aspects
Digestion and Absorption of Carbohydrates
Digestion and Absorption of Proteins
Digestion and Absorption of Lipids
8. Biological Importance
• Absorption is
transport of molecules,
either digested products or
other small molecules which do not require
digestion,
from the intestinal lumen into
blood
across the
intestinal mucosal cells.
9. Medical Importance
• Lactose intolerance
deficiency of lactase
intake of milk causes diarrhea
• Hartnup’s disease
genetic defect in the absorption of
neutral amino acids,
especially tryptophan.
10. Medical Importance
• Steatorrhea
excess fat is excreted in feces and
is seen in diseases of
pancreas, biliary obstruction, etc.
• Chronic diarrhea can cause
malabsorption as seen in
celiac disease,
Sprue,
Crohn’s disease, etc.
11. Digestion – General Aspects
major foodstuffs
that require digestion
macromolecules
digestion
smaller molecules
carbohydrates,
monosaccharides
proteins
Amino acids
fats and oils
(triacylglycerol)
glycerol and fatty acids
12. Digestion – General Aspects
Digestion takes place in the aqueous medium of
various digestive juices –
Site of Digestion
Digestive Juices
Mouth
Saliva
Stomach
Gastric juice
Small intestinal lumen
Pancreatic juice,
Bile
Intestinal juice
13. Digestion – General Aspects
• Digestion
involves
action of enzymes
that are present in different
digestive juices.
• All digestive enzymes are
hydrolases
that hydrolyze the
anhydride linkages –
14. Digestion – General Aspects
anhydride linkages
carbohydrates,
Glycosidic linkage
proteins
Peptide linkage
fats and oils
(triacylglycerol)
Ester linkage
15. Digestion – General Aspects
• Bile,
synthesized in liver and
entering into duodenum,
• helps in fat digestion and
• neutralizes
acidic stomach contents when it enters
the duodenum.
16. Digestion – General Aspects
• Cooking
hydration of polysaccharides and
denaturation of proteins
helps digestion of these molecules.
• Mastication
helps in
breaking down of food particles
increases solubility and surface area for
enzyme action.
• Peristalsis
also important in
breaking down of food particles and
mixing them with enzymes.
17. Absorption– General Aspects
• small intestine
main absorptive organ.
About 90% of the ingested foodstuffs
absorbed
through the small intestine
• Considerably more water is absorbed
in the large intestine,
so that the contents,
gradually become more solid in the colon.
18. Absorption – General Aspects
Absorption of substances into mucosal cells involves
the passage across the plasma membrane
simple diffusion
carrier-mediated transports
passive
facilitated transport
(no energy expenditure)
(passive)
No carrier protein
active transport
(requiring energy expenditure)
19.
20. Absorption – General Aspects
two pathways for the transport of nutrients
absorbed by the intestine
water-soluble nutrients
hepatic portal blood
liver
lipid-soluble nutrients
lymphatic vessels
thoracic duct
blood
blood
22. Digestion and Absorption of Carbohydrates
Introduction
major carbohydrates in the diet
Monosaccharides
fructose (present in fruits)
Disaccharides
sucrose
lactose
maltose
Small amounts
(present in malt, beer)
Polysaccharides
starch
dietary fibers
Starch - more than 50% of carbohydrates
23. Digestion and Absorption of
Carbohydrates - Introduction
• Dietary fibers –
cellulose, hemicellulose, pectin, lignins, etc.
are
indigestible.
For ‘Dietary fibers’,
see Chapters –
‘Chemistry of Carbohydrates’ and
‘Nutrition’)
24. Digestion and Absorption of
Carbohydrates - Introduction
Human food also contains
small amounts of
• pentoses,
• glucose,
• trehalose
(disaccharide present in mushroom), and
• glycogen (present in liver in animal foods).
25. Digestion and Absorption of
Carbohydrates - Introduction
• All enzymes of carbohydrate digestion
cleave
glycosidic bonds by
hydrolysis.
• Disaccharides and polysaccharides are digested to
their respective constituent monosaccharides units and
absorbed in the small intestines
along with free monosaccharides present in the food
26. Digestion and Absorption of
Carbohydrates - Introduction
• The absorbed monosaccharides
hepatic portal circulation
liver cells
systemic circulation.
27. Digestion and Absorption of
Carbohydrates Introduction
Fructose
DIGESTION
ABSORPTION
(Small Intestine)
Fructose
Sucrose
FOOD
Starch
Glucose
Lactose
Galactose
28. Digestion of Starch1, 2
• Starch on complete digestion
yields
glucose
• Digestion of starch
takes place in
• mouth,
• small intestinal lumen and
• small intestinal brush border
(luminal surface of intestinal mucosal cells).
29. Digestion of Starch1, 2
• The enzymes and the steps of digestion of
glycogen are same as those of
amylopectin component of starch as
both have similar structure.
• Cooking hydrates the starch granules making it
more susceptible to digestion.
30. Digestion of Starch1, 2
Enzymes required for complete digestion of starch –
• amylase (salivary and pancreatic amylase),
• maltase and
• isomaltase.
• Amylase and maltase cleave
-1,4 glycosidic linkages and
isomaltase cleaves
-1,6 glycosidic linkages of
starch.
(Amylase hydrolyzes
internal -1,4 glycosidic linkages.)
31. Digestion of Starch
• Starch is mainly digested by
pancreatic amylase.
Contribution by
salivary amylase is very little
since the food remains in the mouth for
a very short period of time and
the enzyme is inactivated by
gastric HCl as it enters stomach.
• Maltase and isomaltase
are present on the
luminal surface of small intestinal epithelial cells
(brush border cells).
32. Digestion of
Starch
Starch (amylose and amylopectin)
Salivary amylase (in mouth)3
Or
Pancreatic amylase
(in small intestinal lumen
Small unbranched oligosaccharides
(e.g., Maltose, Maltotriose, etc)
Isomaltase
Maltase
(brush border cells)
(brush border cells)
Limit dextrins4
Maltase
Isomaltose
Glucose
Isomaltase (brush border cells)
33. Digestion of Starch
• Cl- is an activator of
Salivary amylase
(ptyalin)
• Limit dextrins
derived from
amylopectin component
by the action of amylase and
contain eight glucosyl units with
one or two branches with
α-1,6-glycosidic bonds.
34. Digestion of Disaccharides
Major disaccharides
present in the human diet are –
• sucrose and
• lactose
Small amounts of
• free maltose (present in malt, beer) and
• trehalose
(disaccharide present in mushroom)
35. Digestion of Disaccharides
• However, quantitatively
the major disaccharide digested in the gut is
maltose
• Most of the maltose in the gut is derived from
digestion of
starch.
• Isomaltose is another disaccharide
derived from starch and
is digested by
isomaltase.
(See ‘Digestion of Starch’).
36. Digestion of Disaccharides
• Disaccharidases are attached to the surface of
the small intestinal brush border cells.
• (For ‘digestion of maltose’, see ‘Digestion of
Starch’.)
37. Digestion of Disaccharides
Site of digestion of disaccharides – attached to the
small intestinal brush border
surface of the
small intestinal brush
border cells
disaccharides disaccharidases
sucrose
sucrase (also called invertase)
lactose
lactase
trehalose
trehalase
maltose
maltase
39. Absorption of Monosaccharides
The major monosaccharides
resulting from carbohydrate digestion are –
• D-glucose,
• D-galactose and
• D-fructose.
Absorption is
carrier mediated.
• Pentoses are absorbed by
simple diffusion.
• Monosaccharides are first transported
from the lumen to the small intestinal epithelial cells
and then into capillaries of portal venous system.
40. Absorption of Glucose
from the small intestinal lumen
into the intestinal epithelial cells by
carrier mediated mechanism
involving transporter proteins
situated on the luminal surface of
intestinal epithelial cells.
• Glucose is absorbed mainly by
• 1) Na+-dependent transporter
by secondary active transport and
to a less extent by
• 2) Na+-independent transporter
by passive transport.
41. Absorption of Glucose
from the small intestinal lumen
by carrier mediated mechanism
involving transporter proteins
1) Na+-dependent transporter
by secondary active transport
and to a less extent by
2) Na+-independent transporter
by passive transport
into the intestinal epithelial cells
42. 1. Na+-dependent transporter (SGLT)
• This carrier protein carries
glucose or galactose along with
sodium ion
from the lumen.
The driving force for the
Na+-dependent transport is
derived from the
maintenance of
low intracellular levels of Na+
by the action of the
Na+-K+ATPase
(secondary active transport).
44. Transport of glucose
from cells to portal venous capillaries:
Glucose is transported
from the
intestinal epithelial cells into
portal venous capillaries by
glucose transporter-2 (GLUT-2).
• It is a
uniport facilitated transport system,
which is sodium independent.
45. Absorption of Glucose
facilitated transport
Intestinal
Epithelial Cell
Glucose
GLUT-5
Glucose
secondary active transport
Na+
Intestinal Lumen
Na+-dependent transporter
(SGLT)
Na+ K+
ATP
ADP + Pi
GLUT-2
Glucose
Na+
Portal Capillary Blood
K+
Na+–K+ ATPase
47. Absorption of
Other Monosaccharides
• Fructose
facilitated trasporter
GLUT-5,
sharing with glucose.
• Galactose
Na+-dependant trasporter (SGLT)
secodary active transport
sharing with glucose
• Any pentose present in food is absorbed by
simple diffusion.
48. Absorption of
Other Monosaccharides
• Both
fructose and galactose
transported from the intestinal epithelial cells
into portal venous capillaries by
glucose transporter-2 (GLUT-2),
sharing with glucose.
49. Clinical Significance
Lactose Intolerance
• This is a common condition
gastrointestinal symptoms like
diarrhea, abdominal cramps and flatulence
after ingestion of
milk or milk-based foods
50. Clinical Significance
Lactose Intolerance
• Cause
deficiency of lactase1.
Deficiency may be due to
• genetic
(primary/inherited) or
• acquired
(secondaryto other causes)
The reason for
acquired lactose intolerance may be
damage to intestinal epithelial cells
due to
colitis, gastroenteritis, alcohol consumption or
sudden change into a milk-based diet.
51. Clinical Significance
Lactose Intolerance
• Cause
lactase enzyme
defective at
birth
early onset lactose intolerance
(inherited lactase deficiency).
A significant number of adults
exhibit
late onset lactase deficiency
(primary low lactase activity)
especially
Asian-, Native- and African-Americans.
52. Biochemical basis of Clinical Manifestation
Lactase deficiency
Accumulation of
lactose,
organic acids
and gases (CO2
and H2)
(Produced by action of bacteria on lactose
in the gut)
Osmotic movement of water
from the intestines to the lumen
flatulence
Abdominal cramps
diarrhea
54. Digestion and Absorption of Proteins
Contents:
• Digestion of protein – general aspects
• Reactions of protein digestion
• Absorption of amino acids
• Clinical significance
55. Digestion of Proteins – General Aspects
•
•
•
•
•
•
Contents:
Introduction
Sites of protein digestion, GIT juices and proteases
Endopetidases and exopetidases
Specificity of proteases
Proteases - zymogen form and activation
Role of HCl in protein digestion
56. Digestion of Proteins – General Aspects
Introduction
• Digestion of dietary proteins –
hydrolysis of peptide bonds
catalyzed by a group of
enzymes called
proteases or peptidases
in the gastrointestinal tract
•
• Complete digestion of proteins yields
amino acids.
57. Digestion of Proteins – General Aspects
Introduction
• Dietary proteins
denatured on cooking
and therefore,
cooked proteins
more easily digested1.
During the process of denaturation
unfolding of protein molecule takes place and thus
peptide bonds become
more accessible for
enzyme action.
58. Digestion of Proteins – General Aspects
Sites of Protein Digestion, GIT Juices and Proteases
Protein digestion takes place in
• stomach and
• intestinal lumen.
Enzymes of protein digestion are secreted in
• gastric juice,
• pancreatic juice and
• intestinal juice.
59. Digestion of Proteins – General Aspects
GIT Juices and Proteases
GIT Juices
Proteases Present
Gastric juice
Pepsin (chief cells of stomach), Rennin2
Pancreatic Juice
Trypsin
Chymotrypsin
Elastase
Carboxypeptidases
Intestinal Juice
Aminopeptidases Dipeptidases
Tripeptidases
60. Rennin
• Rennin,
a protease,
active in infants and
involved in
curdling of milk.
Rennin
denatures casein of milk to
paracasein irreversibly,
which then is acted upon by
pepsin.
61. Endopeptidases and Exopeptidases
Pepsin
Trypsin
Carboxypeptidases
carboxy terminal
Chymotrypsin
Elastase
Aminopeptidases
amino terminal
hydrolyze peptide bonds in the
interior of the protein chain to
cleave the protein molecule into
more than one
smaller polypeptides and peptides.
hydrolyze terminal bond
releasing one amino acid
at a time.
62. Digestion of Proteins – General Aspects
Specificity of Proteases
• Endopeptidases
hydrolyze
specific
peptide bonds
in protein molecules.
Specificity differs from
one protease to another3.
63. Specificity of Proteases
Enzyme
Hydrolysis of petide bonds formed by
carboxyl groups of
Pepsin
Phe, Tyr, Trp, Met
Trypsin
Arg, Lys (basic amino acids)
Chymotrypsin
Phe, Tyr, Trp, Val, Leu
(Aromatic, uncharged amino acids)
Elastase
Ala, Gly, Ser (small amino acid residues)
64. Digestion of Proteins – General Aspects
Proteases – Zymogen Form and Its Activation
Proteolytic enzymes are secreted as
inactive
zymogens/proenzymes,
which are converted to their
active form
in the intestinal lumen4.
65. Digestion of Proteins – General Aspects
Proteases – Zymogen Form and Its Activation
Activation of enzymes
involves
cleavage of
small peptides so that
active sites
are exposed.
prevents auto-digestion of the
secretory acini.
66. Digestion of Proteins – General Aspects
Proteases – Zymogen Form and Its Activation
Active Enzyme
Inactive Zymogen
Pepsin
Pepsinogen
Trypsin
Trypsinogen
Chymotrypsin
Carboxypeptidase
Elastase
Chymotrypsinogen
Procarboxypeptidase
Proelastase
67. Digestion of Proteins – General Aspects
Proteases – Zymogen Form and Its Activation
(Parietal cells of stomach)
Pepsinogen
HCl
Pepsin
Autoactivation
(a protease present on the intestinal
Enterokinase mucosal membranes)
Trypsinogen
Trypsin
Autoactivation
68. Digestion of Proteins – General Aspects
Proteases – Zymogen Form and Its Activation
Trypsin
Chymotrypsinogen
Proelastase
Procarboxypeptidase
Chymotrypsin
Elastase
Carboxypeptidase
69. Digestion of Proteins – General Aspects
Role of HCl in Protein Digestion
1) Activation of pepsinogen
2) Denaturation of dietary proteins and
3) Providing optimum pH (pH 2 to 3) for the
action of pepsin.
• (HCl also kills microorganisms present in food).
70. Reactions of Protein Digestion
(In Stomach and Small Intestinal Lumen)
Dietary Proteins
In Stomach
Pepsin
HCl
Gastric Juice
(polypeptides and
Proteoses + Peptones smaller polypeptides)
In
Small
Intestinal
Lumen
Trypsin
Chymotrypsin
Elastase
Small Polypeptides + Peptides
Pancreatic Juice
71. Dietary Proteins
In Stomach
Pepsin
HCl
Gastric Juice
(polypeptides and
Proteoses + Peptones smaller polypeptides)
In
Small
Intestinal
Lumen
Trypsin
Chymotrypsin
Elastase
Small Polypeptides+ Peptides
Pancreatic Juice
72. HCl
(polypeptides and
Proteoses + Peptones smaller polypeptides)
In
Small
Intestinal
Lumen
Trypsin
Chymotrypsin
Pancreatic Juice
Elastase
Small Polypeptides+ Peptides
In
Small
Intestinal
Lumen
Carboxypeptidases
Pancreatic Juice
Aminopeptidases
Dipeptidases
Amino acids
Intestinal Juice
73. Absorption of Amino Acids
absorbed from the intestine
into
portal blood.
•
transported by
a number of carriers
many by secondary active transport –
Na+-dependent carriers
similar to
glucose transporter system.
74. Absorption of Amino Acids
Different Na+-dependent carriers are:
• Neutral amino acid carrier
• Phenylalanine and methionine carrier
• Carrier specific for imino acids (proline and
hydroxy proline)
There are also Na+-independent carriers
specializing in the transport of
• Neutral and lipophilic amino acids (e.g.
Phe, Leu)
• Cationic amino acids (e.g. Lys)
75. Clinical Significance
• Allergy to certain food proteins
(milk, fish)
believed to result from absorption of
partially digested
proteins.
76. Clinical Significance
• Defect in non-tropical sprue is
located within the mucosal cells of the
intestine
and permits the polypeptides
(resulting from the peptic and tryptic digestion of
gluten,
the principal protein of wheat)
to be absorbed into the circulation and thus
elicit the production of
antibodies.
77. Clinical Significance
• Defect in the intestinal amino acid transport
systems
seen in
-- Hartnup’s disease,
[defect in intestinal neutral amino acid (Trp)
carrier], I
-- iminoglycinuria, cystinuria etc.
78. Clinical Significance
• Acute pancreatitis
(acute inflammation of pancreas)
caused by
autodigestion
of pancreas by its proteolytic enzymes
a life threatening disorder.
Autodigestion is
due to unusual conversion of
proenzymes into active enzymes by
trypsin.
79. Digestion of Fat (Triacylglycerols)
Contents
• Digestion of fat
• Digestion of other lipids
• Absorption of lipids
• Clinical significance
80. Digestion of Fat (Triacylglycerols)
main site
Small intestinal lumen
Hydrolysis of ester bonds
Fat
Lipases
Fatty acids
Glycerol
Monoacyl glycerols (MAGs)
main enzyme for digestion of most of the fat - Pancreatic lipase
other lipases
lingual
lipase, gastric their contribution is negligible
lipase and
intestinal lipase
Colipase cofactor
a proteinsalts
Bile secreted by pancreas digestion by emulsifying fat
help fat
81. Role of Bile Salts in Fat Digestion
Bile salts
present in the bile
lower the surface tension
– emulsify fat in the intestine.
– Intestinal peristalsis also helps in this.
Emulsification increases the surface area of
fat droplets
enabling more enzyme (lipase) molecules to
act
and thus
speeding up digestion
82. Reactions of Digestion of Fat (Triacylglycerol)1
Triacylglycerol (Fat)
Lipase
Pancreatic Juice
Colipase
Fatty Acid
Diacylglycerol (DAG)
Lipase
Colipase
Fatty Acid
Monoacylglycerol (MAG)
Lipase
Colipase
Fatty Acid
Glycerol
83. Reactions of Digestion of Fat (Triacylglycerol)1
Digestion of fat
requires another enzyme also
an isomerase
which isomerzes 2-MAG into 1-MAG,
as lipase cannot hydrolyze 2-MAG.
84. Reactions of Digestion of Fat
(Triacylglycerol)1
The major end products of
digestion of fat are –
• monoacylglycerols (MAGs),
• glycerol and
• fatty acids
85. Digestion of Other Lipids
Pancreatic secretion also contains
cholesterol esterase
cholesterol ester
cholesterol
Fatty acid
phospholipase A2
phospholipid
lysophospholipid
Fatty acid
87. Absorption of Digested Products of
Lipids
• Normally
over 98% of the dietary lipid is
absorbed.
88. Clinical Significance
• Steatorrhea
• Chyluria and Chylothorax
When daily excretion of fat in feces
more than 6g per day
• may be due to
defective digestion or
defective absorption of fat.
• - Defective digestion
may be due to absence of or deficiency of
pancreatic lipase
as in
chronic diseases of pancreas or
surgical removal of pancreas. bile salt
89. Clinical Significance
• Steatorrhea
• Defective absorption of fat occurs
when bile salts do not enter the intestine as in
biliary obstruction (e.g. due to biliary stone)
• - Defective absorption may also be due to
malabsorptive diseases
e.g. celiac disease,
Sprue,
Crohn’s disease, etc or
surgical removal of large lengths of the
intestine.
90. MCQS on Digestion and Absorption
1. All of the below are true about digestion,
EXCEPT,
A. All digestive enzymes are hydrolases.
B. Digestion ensures the absorption of
nutrients.
C. Sites of digestion in the GIT are mouth,
stomach, and the lumen of small and the
large intestines.
D. Vitamins, minerals, monosaccharides and
free amino acids do not need digestion.
91. 2. The anhydride linkages that are
broken during digestion are:
A.glycosidic, peptide and ester linkages
carbohydrates, proteins and fats, respectively.
of
B.ester, peptide and glycosidic linkages
carbohydrates, proteins and fats, respectively.
of
C.glycosidic, peptide and ester linkages
carbohydrates, fats and proteins, respectively.
of
D.peptide, glycosidic and ester linkages
carbohydrates, proteins and fats, respectively.
of
92. 3. Factors, other than enzymes that
help in digestion are the following,
EXCEPT,
A.Cooking
B.Exercise
C.Mastication
D.Peristalsis
93. 4. All the following are true about
absorption, EXCEPT,
A.Considerably more water is absorbed in the
large intestine than in the small intestines.
B.Absorption of all substances require carriermediated transports.
C.Water-soluble nutrients are absorbed through
hepatic portal system.
D.Lipid-soluble nutrients are absorbed through
the lymphatic vessels.
94. 5. The full set of enzymes required for
complete digestion of starch are –
A.amylase, maltase and isomaltase.
B.amylase, maltase and sucrase.
C.amylase, maltase, isomaltase and
sucrase.
D.amylase, sucrase and isomaltase.
•
95. 6. Contribution by salivary amylase in
digestion of starch is very little
because:
A.activity of the enzyme is very low.
B.the food remains in the mouth for a very short
period of time.
C.the food remains in the mouth for a very short
period of time and the enzyme is inactivated
by gastric HCl.
D.the enzyme is inactivated by gastric HCl.
96. 7. Which of the following is FALSE
about digestion of starch?
A.The enzymes and the steps of digestion of
glycogen are same as those of amylopectin
component of starch.
B.Cooking hydrates the starch granules making
it more susceptible to digestion.
C.Cl- is an activator of salivary amylase.
D.Limit dextrins are derived from amylose
component of starch by the action of amylase.
97. 8. Quantitatively the major
disaccharide digested in the gut is
A.sucrose
B.maltose
C.lactose
D.isomaltose
98. 9. The major monosaccharides resulting
from carbohydrate digestion are
A.glucose, galactose and ribose.
B.glucose, mannose and fructose.
C.glucose, ribose and fructose.
D.glucose, galactose and fructose.
99. 10. Glucose is absorbed mainly by
A.simple diffusion
B.Na+-dependent transporter
C.Na+-independent transporter
D.passive transport
•
100. 11. Enzymes of protein digestion are
secreted in
A.gastric juice, pancreatic juice and
intestinal juice.
B.saliva, gastric juice and pancreatic juice.
C.saliva, gastric juice and intestinal juice.
D.saliva, gastric juice and intestinal juice.
101. 12. Proteases secreted in the pancreatic
juice are
A.pepsin,
trypsin,
chymotrypsin
carboxypeptidases.
B.trypsin,
chymotrypsin,
elastase
carboxypeptidases.
C.trypsin,
chymotrypsin,
elastase
aminopeptidases.
D.trypsin, chymotrypsin, aminopeptidases
carboxypeptidases.
and
and
and
and
102. 13. HCl has following roles in protein
digestion, EXCEPT.
A.kills microorganisms present in food
B.activation of pepsinogen
C.denaturation of food proteins
D.providing optimum pH for the action of
pepsin
103. 14. Intestinal absorption of amino
acids involves all of the
following, EXCEPT,
A.simple diffusion
B.Na+-dependent transporter
C.Na+-independent transporter
D.passive transport
104. 15. Which of the following is false
about action of bile salts?
A.They help both in digestion of fat and
absorption of digested products of lipids.
B.They lower the surface tension and
emulsify fat in the intestine.
C.They stimulate pancreatic secretion.
D.Emulsification increases the surface area
of the fat droplets.
105. 16. Digestion of fat produces:
A.fatty acids, glycerol and diacyl
glycerols.
B.fatty acids and glycerol.
C.glycerol and monoacyl glycerols.
D.fatty acids, glycerol and monoacyl
glycerols.
106. 17. Lipases other than pancreatic lipase
present in the human GIT are:
A.salivary lipase, gastric lipase and intestinal
lipase
B.lingual lipase, gastric lipase and intestinal
lipase
C.lingual lipase, gastric lipase and hepatic lipase
D.gastric lipase, biliary lipase and intestinal
lipase
107. 18. Steatorrhea is a condition when
daily excretion of fat in feces is more
than:
A.6g
B.8g
C.10g
D.12g