BIOL1003 Lecture Notes - Lecture 5: Pancreatic Lipase Family, Gastric Glands, Stomach
19 May 2018
School
Department
Course
Professor
Discuss the action of digestive enzymes and the processes involved in digesting a well-balanced meal
Contain C, H, O, N and most have sulfur
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Building blocks of proteins = amino acids
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Protein = many amino acids joined together to form polypeptide chain
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Ability of proteins to perform their functions depends on their shape. Ie H bonds maintaining shape are broken then protein i s
non-functional
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Change in shape = denaturation, caused by high temps or changes in pH or conc
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Proteins
Enzymes composed of proteins
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Enzyme = biological catalyst, speeds up a biochemical reaction
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Protein catalyst
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Enzyme is not permanently changed
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Enzymes = specific
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Increases rate of chemical reaction by lowering activation energy (energy needed to start a chem rxn)
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Lock and key model - shape of enzyme and reactants allow enzyme to easily bind. Enzymes very specific for reactions they
control
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Each enzyme controls only one type of chem rxn
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Enzymes reusable
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Enzymes
Hydrolytic enzymes = add water in rxns that break down complex molecules to simpler ones
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Salivary amylase - begins digestion of carbohydrates in the mouth
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Pancreatic amylase - in duodenum, continues digestion of carbs after passes through stomach. Absorption begins
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Amylases (chemical digestion) - break down polysaccharides to disaccharides (carbs)
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Digestive enzymes
Enzyme
substrate
What broken down
where
product
amylase
Starch and water
carbohydrates
Salivary glands in mouth
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Pancreatic secretions and small intestine
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maltose
proteases
proteins
Stomach
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Pancreatic secretions
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Small intestine
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disaccharidases
Maltose and water
Small intestine
glucose
pepsin
Protein and water
stomach
Polypeptides ( in stomach)
trypsin
Polypeptides and water
pancreas
Peptides (small intestine)
Peptidases
Peptides and water
Small intestine
Amino acids
RNA or DNA
nucleases
pancreas
Individual nucleotides
Lipases
Fats and water
Fats and lipids
Pancreatic secretions and small intestine
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Fatty acids and glycerol
Sodium bicarbonate - produced in pancreas and glands in wall of duodenum, acts in small intestine, neutralises acidic chyme released by stomach into the
duodenum so it does not damage the intestines
5a)
Friday, 31 March 2017
10:53 PM
5. Digestive system Page 1
Sodium bicarbonate - produced in pancreas and glands in wall of duodenum, acts in small intestine, neutralises acidic chyme released by stomach into the
duodenum so it does not damage the intestines
Activities of the digestive system (processes)
Ingestion of food into mouth
Sight and smell of food sends nerve impulses from brain to salivary glands (increase saliva
secretion) and stomach glands (start secretion of gastric juices)
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Mechanical and chemical digestion
Food goes down pharynx (throat, funnel shaped tube)
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Teeth chew food
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Muscular contractions of esophagus occur in peristaltic waves (relaxation and contraction),
pushing food towards stomach
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Food churned
○
Mixed with stomach secretions CHYME
○
Gradually moves by peristaltic waves into small intestine
○
In stomach
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In small intestine - mixing of chyme with enzymes
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Mechanical
HCl (from gastric glands, kills bacteria, softens fibres in food, activates
digestive enzymes
▪
Enzymes - from gastric glands, PEPSIN breaks down proteins to polypeptides),
secreted in inactive form pepsinogen (converted to pepsin by HCl)
▪
alkaline mucus - from mucus cells, protects stomach lining from HCl
▪
intrinsic factor - from gastric glands, secreted in presence of food, not
digestive, assists in absorption in small intestine, binds to Vit-B12
▪
Stomach wall secretes gastric juices
○
In stomach
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Cephalic (nervous) phase
1.
Sight, smell, taste, thought of food stimulate centres in medulla --> gastric juices
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Vagus nerve transmits singals brain --> stomach
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Initiat4es secretion of HCl, pepsinogen, mucous, intrinsic factor, gastrin (hormone)
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Gastric (stretching) phase
2.
Stomach expands when food enters --> stimulates stretch receptors
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Local and central nervous pathways activated --> further stomach secretion of
gastric juices
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Polypeptides produced from initial digestion stimulate release of gastrin hormone
from gastric glands --> increase stomach secretion of gastric juices
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Chyme moves continuously into small intestine
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Intestinal (hormonal) phase
3.
Inhibits gastric secretions
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Once all food digested chyme pH --> 2.0
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Chyme ph 2.0 -> duodenum, detected by chemoreceptors
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Duodenum releases secretin and cholecystokinin hormones
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Neural signals and local reflexes reduce gastric secretion
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3 phases of regulation (stomach actions/secretions)
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Enzymes released from lining
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Enzymes released from pancreas
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Bile produced in liver , released from gall bladder
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Mucosa of duodenum secretes mucus, ions, h20 lubricating and protecting
intenstinal wall from chyme
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Secretes digestive enzymes - peptidases, sucrase, lactase, maltase
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Small intestine
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digestive enzymes and bicarbonate
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Bicarbonate - neutralise acidic chyme
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Trypsin, chymotrypsin - polypeptides -> peptides
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Carboxypeptidase - peptides -> amino acids
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Pancreatic amylase - starch -> monosaccharides
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Pancreatic lipases - emulsified fat -> fatty acids and glycerols
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Nucleases - DNA and RNA -> component nucleotides
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Pancreas (pancreatic secretions into duodenum)
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Chemical
Digestion - produces bile, emulsifies fat, as small fat droplets more effectively digested by
enzymes
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Excretion - bilirubin in bile from RBC breakdown
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Nutrient storage - blood glucose -> glycogen, stores fat vitamins copper iron, mantains
blood glucose
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Nutrient conversion - amino acids-> lipids or glucose, Vit D to active form, detoxication of
blood - ammonia ->urea -> eliminated in urine, metabolism of poisons
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Synthesis of new molecules - makes blood proteins from absorbed amino acids
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Liver
•
Movement of food along the digestive
tract
Peristaltic waves of esophagus and stomach
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Absorption of digested food
By stomach - very limited abs through stomach wall, only substances of low molecular weight can
pass through (water, alcohol aspirin)
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Duodenum, jejunum, ileum
•
Parts to increase surface area - circular folds (mucosa/subcosa), villi (projections from
mucosa), microvilli (extensions of mucosal cells)
•
Water soluble nutrients e.g. monosaccharides, capillaries -> hepatic portal vein ->
liver
○
Fats/non water soluble nutrients e.g. fatty acids, lymphatic vessels -> blood
○
2 absorption routes across intestinal epithelium to other parts of body
•
92% h20 abs in small intestine
•
At end of ileum all remains is - water, indigestible food (cellulose), bacteria
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Small intestine
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Elimination of indigestible substances and
waste products via defecation
Colon - mucosal lining with tubular glands which contain mucus producing goblet cells
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Rectum - straight muscular tube
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Anal canal - thick, involuntary smooth muscle forms internal anal sphincter, voluntary
skeletal muscle forms external anal sphincter
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NO ENZYMES PRODUCED = No DIGESTION
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Water abs along with minerals and vitamins
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Waste stored before release (defecation)
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Synthesise Vit K (blood clotting) and vit B complexes
○
Microbes ferment some waste residues (food cannot digest) - by products: hydrogen
sulphide gas, methane gas
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Screen clipping taken: 8/04/2017 11:36 AM
Resident bacteria
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Large intestine
5. Digestive system Page 2
Identify the digestive organs and glands and discuss their functions
Food and water enter body through mouth
○
Ingestion of food
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Food is broken down from complex particles to smaller molecules that can be absorbed
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Digestion of food
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Epithelial cells that line lumen of small intestine absorb the small molecules of ntureints (amino acids, monosaccharides, fatty acids,
vitamins, minerals, water) that result from digestive process
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Absorption of nutrients
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Undigested material e.g. fibre, cellulose from food, plus waste products excreted into the digestive tract are eliminated in the faeces
○
Elimination of wastes
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Functions of the digestive system
Screen clipping taken: 8/04/2017 1:53 PM
Bounded by the lips and cheeks, and contains teeth and tongue
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Mouth/oral cavity
Teeth
32 in normal adult mouth
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Located in mandible and
maxillae
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Divided up into quadrants -
right upper, right lower, left
upper, left lower
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Each quadrant contains one
central and one lateral incisor,
on canine, 2 premolars, 3
molars
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Incisors - cutting
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Canines - piercing and tearing
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Premolars - cutting and
grinding
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Molars - grinding and crushing
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Mastication
Mechanical breakdown of food
by teeth
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Breaks large particles of food
into small ones, increasing SA,
increases efficiency of
digestion
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Frenulum
Tissue attaching floor of mouth
to tongue
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Palate and tonsils
Palate has 2 regions
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Hard palate = anterior rigid
hard region
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Soft palate = posterior soft
region
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Palate separates oral and nasal
cavity preventing food from
passing into nasal cavity
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Uvula = posterior extension of
soft palate
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Tonsils - located in laterial
posterior walls
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Screen clipping taken: 8/04/2017 2:14 PM
Salivary glands
3 major pairs - parotid,
submandibular, sublingual
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Produce saliva, which is a
mixture of serous and mucous
fluids
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Parotid glads - serious glands
located just anterior to each
ear
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Submandibular glands
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Screen clipping taken: 9/04/2017 3:21 PM
5b)
Saturday, 8 April 2017
11:48 AM
5. Digestive system Page 3
Document Summary
Discuss the action of digestive enzymes and the processes involved in digesting a well-balanced meal. Contain c, h, o, n and most have sulfur. Protein = many amino acids joined together to form polypeptide chain. Ability of proteins to perform their functions depends on their shape. Ie h bonds maintaining shape are broken then protein i s non-functional. Change in shape = denaturation, caused by high temps or changes in ph or conc. Enzyme = biological catalyst, speeds up a biochemical reaction. Increases rate of chemical reaction by lowering activation energy (energy needed to start a chem rxn) Lock and key model - shape of enzyme and reactants allow enzyme to easily bind. Each enzyme controls only one type of chem rxn. Hydrolytic enzymes = add water in rxns that break down complex molecules to simpler ones. Salivary amylase - begins digestion of carbohydrates in the mouth. Pancreatic amylase - in duodenum, continues digestion of carbs after passes through stomach.
