Study sets, textbooks, questions
Upgrade to remove ads
DIGESTION AND NUTRIENTS
Lecture 3 Part 1
Terms in this set (62)
What are the 3 major learning objectives for this lecture topic?
1) Understand the major types of macronutrients.
2) Understand the digestive processes for carbohydrates, proteins and lipids
3) Understand the activities, locations, and roles of the major enzymes involved in the digestion of carbohydrates, proteins and lipids
What is the function of saliva?
Function of Saliva:
Lubrication, Protection & Digestion
What are the 3 key components of saliva?
Key Saliva components:
3) Lingual lipase (Van Ebner Glands)
What are the 2 types of mucosa produced by the stomach?
1) Oxyntic mucosa
2) Pyloric Mucosa
Describe oxyntic mucosa - where it comes from and what it does
Oxyntic mucosa (Fundus & Body (upper 80%)
Oxyntic glands secretes Gastric Acid (Parietal cells), Pepsinogen (Peptic or Chief cells), protective mucus (Neck cells).
Describe pyloric mucosa - where it comes from and what it does
Pyloric Mucosa: Antrum (lower 20%)
Synthesizes and releases Gastrin
What are the basic 5 Oxyntic gland products?
1) Gastric Acid: Parietal Cells
2) Pepsinogen: Peptic/ Chief Cells
3) Gastric Lipase: Peptic/ Chief Cells
4) Mucus: Neck Cells
5) Intrinsic Factor: Parietal Cells
Describe Gastric acid and its role as an oxyntic gland product
Gastric Acid: (Parietal Cells)
HCl (NaCl/KCl) 150-160 mEq/L (mM), pH 1-2
Protein denaturing (Digestion, B12 release)
Solubilization of iron and the maintenance of reduced states
Describe pepsinogen and its role as an oxyntic gland product
Pepsinogen: (Peptic/ Chief Cells)
(45kD) autoconverted (+ acid) to pepsin (35kD)
Initiates protein digestion
Describe Gastric lipase and its role as an oxyntic gland product
Gastric Lipase: (Peptic/ Chief Cells)
Acidic lipase similar to lingual lipase
Emulsifier and coactivator independent lipase
Describe mucus and its role as an oxyntic gland product
Mucus: (Neck Cells)
Together with HCO3- protects gastric mucosa from HCl and pepsin.
Describe instrinic factor and its role as an oxyntic gland product
Intrinsic Factor: (Parietal Cells)
Mucoprotein of 55 kD
Only indispensable component of gastric juice.
Vitamin B12 capture for later absorbtion in the ileal mucosa.
What is the basic functionality of the exocrine pancreas?
1) Aqueous Bicarbonate Secretion (buffering)
2) Serous Enzyme secretion
What are the Primary Enzymes by Substrate Group coming from the pancreas to break up protein, fat, and starch?
1) Proteins: Trypsin, Chymotrypsin, Elastase and Carboxypeptidases (A1, A2, B) secreted as Proenzymes (Zymogens)
2) Fat: Pancreatic lipase (bile salt dependent) and Colipase.
Phospholipase A2 (as proenzyme)
3) Starch: a-Amylase (identical to the enzyme secreted by the salivary gland)
On the most basic level, how does the pancreas work?
as an Exocrine and endocrine organ
Can the pancreas be removed, and if so what would happen?
The pancreas can be removed (e.g. due to chronic pancreatitis or pancreatic cancer), but enzymes have to be replaced in addition to treatment of the resulting diabetis.
What is a heterotopic pancreas?
Heterotopic pancreas is rare but results in pancreatic tissue (both exo and endocrine) that is not connected to the main organ. Mostly in the stomach, duodenum, and jejunum.
Describe the products and work of the pancreas (Hint: separated into 3 points)
1) Products are both aqueous (Bicarbonate & Water)
and proteinaceous (Digestive (Pro)enzymes)
2) The pancreas is under endocrine control (Secretin & CCK) and ANS control (Vagus). Triggers are food and gastric acid.
3) The degree of coupling and cellular source of aqueous secretions may vary with the mode of stimulation
What are the 4 different cells of the pancreas?
1) Acinar cells
2) Centroacinar cell
3) Zymogen granules
4) Intercalated duct
In the process of Fluid and Electrolyte Secretion by the Pancreas, what happens with Cl and Bicarbonate?
The exchange of Chloride for Bicarbonate matches overall
The current model for HCO3- - and water secretion is based what 4 observations?
1) HCO3- is actively secreted against electrical and chemical gradients.
2) HCO3- secretion is blocked by Ouabain.
3) HCO3- secretion involves both secondary active transporters (exchangers) for Na+/H+ and Cl- /HCO3-
4) Lack of extracellular Cl- reduces HCO3- secretion. (efflux of Cl- into the lumen depends on a cAMP regulated Cl- channel (CFTR, Cystic Fibrosis Transmembrane conductance Regulator)
What do aquaporins do in this model for HCO3?
Aquaporins facilitate the flow of water and may be regulated by CFTR activity
Which cells are adapted to high rates of protein secretion?
Acinar Cells in the pancreas
Which enzymes of the pancreas are inactivate in their granular storage form?
Proenzymes and Carboxypeptidases (A1, A2, B)
What actions do the Liver/Gallbladder do?
-> emulsification of lipids of the diet into mixed micelles
-> Contact facilitation with Enterocyte brushborder for diffusion of transporter mediated lipid uptake
What 4 actions does the Duodenum (pH 7-10) perform?
1) Regulation of gastric emptying, gastric and pancreatic secretion, and bile release
2) Mucus production (Brunner's glands)
3) Pancreatic Zymogen activation to active proteases
4) Primary sites of digestion of food through secreted enzymes and brushborder enzymes
What actions does the Jejunum/Ileum perform?
1) Uptake of digested products by absorbtion, facilitated diffusion, or active uptake
2) Active uptake mechanisms increase from jejunum to the ileum (e.g. bile acids or B12)
3) Goblet cells -> Mucus
High density of immune cells in the Ileum (Peyer's Patches)
What actions does the colon perform?
Colon: Water & electrolyte recovery,
Feces Storage, Microbe assisted fermentation
What is the Average Daily Macronutrient Utilization for a 70 kg man?
100g of Fat --> 450L of CO2
300g of Carbs Urea, NH3 ~15g
100g of Protein H2O 320g
500L of O2
In an OVERVIEW OF CARBOHYDRATE DIGESTION, give the 4 basic stages by identifying products
1) Dietary carbs - starch, glycogen, sucrose, lactose
2) Polysaccharides, sucrose, lactose, and maltose
4) Monosaccharides in bloodstream
What enzymes are individually capable of 75% of starch digestion?
Lingual and pancreatic a-amylase
- they are unstable at acidic pH
What does Maltase (a Brushborder Enzyme) help produce?
Maltose --> Glucose + Glucose
via HYDROLYSIS OF GLYCOSIDIC BONDS
What does Brushborder Sucrase help produce?
Sucrose --> Glucose + Fructose
What does Brushborder Lactase help produce?
Lactose --> Galactose + Glucose
In the Digestion of Disacharides at the intestinal Brushborder, what is the consequence of the insufficiency of Sucrase or Lactase (β-D-galactosidase)?
its results in similar intolerance Manifestations
In an OVERVIEW OF LIPID DIGESTION, give the 4 basic stages by identifying products
1) Dietary Lipids
2) TG, Mono and Di glycerides - phospholipids, Cholesterol (esters)
3) Free Fatty Acids, Monoacylglycerol - Cholesterol, Lysophospholipids
4) Reesterfication and export to the lymph via chylomicrons - return to lumen for some cholesterol
What are the Key Lipases used in the lipid absorption of Triglycerides?
1) Lingual Lipase, Gastric Lipase
2) Pancreatic Lipase & Colipase*
3) (Monoacylglyceride lipase [minor])
* Colipase (not the Apoenzyme) and Phospholipase A2
are secreted as Proforms and activated by Trypsin
What percentage of dietary lipids are Triglycerides?
What are the products of Triglyceride lipid absorption?
What are the Key Lipases used in the lipid absorption of Phospholipids?
1) Phospholipase A2*
2) (Lysophospholipase [minor])
What are the products of phospholipid lipid absorption?
What are the Key Lipases used in the lipid absorption of Cholesterol esters?
1) Carboxyl ester lipase
2) Cholesterol Esterase/ nonspecific esterase
What are the products of Cholesterol esters lipid absorption?
Describe the Enzymatic activity of acidic and basic lipases
In contrast to (basic) Pancreatic Lipase,
1) (Acidic) Lingual/Gastric Lipase
- Accounts for up to 30% of fat hydrolysis shortly after ingestion. More in neonates.
- Activity is independent of surface active detergents/emulsifiers (e.g. bile salts).
- Acidic lipase with low pH optimum (4.5-5.4). Active throughout the stomach and intestine.
Describe the INTESTINAL ABSORPTION OF LIPIDS
Absorption of lipids from a mixed micelle into a mucosal cell.
Briefly describe the contents of a Mixed Micelle (Hint: 5 things are present)
1) Bile Salts/Acid
2) Free Fatty Acids
What is the Primary fate of Long chain fatty acids - a lipid derived building block during assimilation?
Captured by Fatty Acid Binding proteins prior to activation and coupling through the Monoglyceride or Phosphatidic acid pathway
What is the Primary fate of Short chain fatty acids - a lipid derived building block during assimilation?
Recoupled (esterification) or direct diffusion to blood stream
What is the Primary fate of Cholesterol - a lipid derived building block during assimilation?
Converted back into esters inside cytoplasm or exported actively back into the lumen by LXR regulated ABCG5/ABCG8
What is the Primary fate of 2-Monoglyceride - a lipid derived building block during assimilation?
Converted back to triglycerides
What is the Primary fate of Glycerol - a lipid derived building block during assimilation?
Metabolized or diffusion to blood stream
What is the Primary fate of Lysophospholipid - a lipid derived building block during assimilation?
Intracellular captured by Fatty Acid Binding proteins. Converted back or used extracellularly as emulsifier. Tightly regulated. If both fatty acids are removed, the glycerophosphoryl base stays behind in the lumen
What is an important thing to note in the Primary fate of lipid derived building blocks during assimilation?
Enterocytes do not have glycerol kinase activity
What are the 5 steps of Chylomicron metabolism?
1) Intestinal rich mucosal cells secrete nascent TG-rich chylomicrons produced primarily from dietary lipids
2) Apo C-II & apo E are transferred from HDL to the nascent CM
3) Extracellular lipoprotein lipase, activated by apo C-II, degrades TG into CM
4) Apo C-II is returned to HDL
5) CM remnants bind to specific receptors on the liver where they are endocytosed
Describe a little bit of Enterohepatic Circulation and Net Flow of Cholesterol and Bile salts/acid
- Note that most of the Cholesterol is ultimately not absorbed. Hence, Cholesterol in the Bile (and some of the Bile acid/salts) are the only way of eliminating Cholesterol from the body.
- Netuptake efficiency is regulated by Oxysterol regulated levels of ABCG5/G8 , a cholesterol and phytosterol exporter
In an OVERVIEW OF PROTEIN DIGESTION, give the 4 basic stages by identifying products
1) Dietary Protein
2) Denatured and partially hydrolyzed proteins and larger peptides
3) Amino acids and small peptides
4) Release of amino acids to bloodstream and some reincorporation into new proteins
Describe the relative role of proteins in the diet
1) Protein is fundamentally distinct from fats and carbohydrates in that there is no dedicated storage form.
2) Protein metabolism is fundamentally designed to maintain homeostasis
What are the three, broad categories of clinically relevant problems of protein deficiency?
1) Protein wasting due to overall under nutrition leading to protein-energy malnutrition (Marasmus)
2) Protein wasting due to imbalanced diet or lack of essential amino acids (Kwashiorkor), and pathological deregulation of protein metabolism (Chachexia)
3) Genetic disorders due to problems in protein processing, uptake or reabsorption.
What is the Mode of protein digestion?
1) The basic catalytic activity of proteases involves the hydrolysis of the protein peptide bond.
2) The nature of the adjacent residues R1 and/or R2 define the substrate specificity of the protease.
3) The optimal pH for function classifies them as acidic, neutral and basic and is defined by the catalytic core of the enzyme as well as the interaction with R1 and R2.
**The mode of action distinguishes exopeptidases (cleavage from the end) and endopeptidases (cleavage within a peptide chain).
What is one of the most important things to remember about the Mode of protein digestion?
The appearance of gastric, pancreatic and intestinal mucosa peptidases progresses from endopeptidases to exopeptidases and hydrophobic to charged.
In the mode of protein digestion, what does the digestion of protein involve?
A combination of initial acid denaturation and enzymatic cleavage. All three isoforms of pepsin operate best under acidic conditions (pH1-3) and are denatured above pH 7. That is effectively the reverse profile of "normal proteins". Its substrate specificity ensures that it cuts infrequently (large products) and preferentially in the core of proteins.
What happens to metabolites and sodium gradient in the ABSORPTION OF AMINO ACIDS & PEPTIDES?
1) Many metabolites (including amino acids) are interconverted directly in the mucosa cells before delivery to the plasma.
2) Initial uptake makes use of the Na+ gradient between the lumen and enterocyte.
Sets with similar terms
Nutrition Ch. 6 - The Proteins and Amino Acids
Proteins EXAM 1
Unit 7 NSC 101
HUN1201 Chapter 6
Other sets by this creator
Cardiovascular Pressures & Fluid Balance
Pumps and Transport
OVERVIEW OF LIPIDS & LIPID METABOLISM