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Slide 2.1
Human AnatomyHuman Anatomy
CELLULAR METABOLISMCELLULAR METABOLISM
Pavemedicine.comPavemedicine.com
Slide 14.46
Processes of the Digestive SystemProcesses of the Digestive System
Figure 14.11
Slide 14.47a
Control of Digestive ActivityControl of Digestive Activity
Mostly by reflexes via the parasympathetic division
Chemical and mechanical receptors trigger reflexes
Slide 14.47b
Control of Digestive ActivityControl of Digestive Activity
Stimuli include: Stretch of the organ pH of the contents Presence of breakdown products
Slide 14.47b
Control of Digestive ActivityControl of Digestive Activity
Reflexes include: Activation or inhibition of glandular
secretions Smooth muscle activity
Slide 14.55
Digestion and Absorption in the Digestion and Absorption in the StomachStomach
Proteases act on:
Pepsin –protein digestion
Rennin –milk protein digestion
Absorption of:
Water, alcohol and aspirin
Slide 14.57a
Digestion in the Small IntestineDigestion in the Small Intestine
Pancreatic enzymes provide… Complete digestion of starch
Amylase Other carbohydrases
About half protein digestion (trypsin, etc.)
Slide 14.57b
Digestion in the Small IntestineDigestion in the Small Intestine
Pancreatic enzymes, cont…
Fat digestion (lipase)
Nucleic acid digestion (nucleases)
Alkaline content neutralizes acidic chyme
Slide 14.58
Stimulation of the Release of Pancreatic Stimulation of the Release of Pancreatic JuiceJuice
Vagus nerve
Local hormones
Secretin
Cholecystokinin
Figure 14.15
Slide 14.59
Absorption in the Small IntestineAbsorption in the Small Intestine
Water
Products of digestion
Most molecules absorbed by active transport
Lipids absorbed by diffusion
Nutrients transported to the liver
Slide 14.63
NutritionNutrition Nutrient – substance used by the body
for growth, maintenance, and repair Categories of nutrients
Carbohydrates Lipids Proteins Vitamins Mineral Water
Slide 14.67
Cellular MetabolismCellular Metabolism
“All the chemical reactions necessary to maintain life”
Anabolism: a constructive process during which larger molecules are built from smaller ones
Usually involves condensation
AKA dehydration synthesis
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…
•Carbohydrates
•Monosaccharides = simple sugars
•Glucose, fructose
•Disaccharides = Combinations of monosaccharides, removal of water
•Sucrose, lactose, maltose
• Polysaccharides: usually polymers of glucose
•Starch, cellulose, chitin
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Lipids
•1 glycerol + 3 fatty acids neutral fat + 3 H2O
•These are triglycerides
•Further modifications produce:
•Phospholipids (cell membrane)
•glycolipids (cell membrane)
•Lipoproteins (cell membrane, blood)
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Proteins
•Two amino acids a dipeptide + H2O
•Covalent bond formed is a peptide bond
•Unique to proteins
•Polypeptides: 2-100 amino acids
•Protein: >100 amino acids
•Require additional modification to become functional
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Proteins
•Modification occurs on four levels
•Primary: string of amino acids
•Secondary: helix or “pleat” structures
•Tertiary: 3-D folding
•Quarternary: two or more 3-D proteins that act as a functional unit
•i.e., hemoglobin, collagen
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Proteins
•Recall from Chemistry: •Proteins each have a unique 3-D shape
•Shape determines function
•Loss of shape leads to loss of function
•“denaturing” proteins with heat, pH changes
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Proteins
•May be structural or functional
•Structural:
•Play a role in cellular architecture
•Collagen, fibrin, actin, myosin, etc.
•Functional:
•Play a role in cell metabolism
•Enzymes, neurotransmitters, antibodies, etc.
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Enzymes:
•Biological catalysts
•Highly specific for a substrate
•Substrate: substance upon which an enzyme acts
• i.e., peptidases act only on peptide bonds in small polypeptides
•Produced only in presence of substrate
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…
•Enzymes:
•Huge protein molecules
•Alter shape to conform to shape of substrate (“wrap around” effect)
•Average 1500/cell (>5000 in liver cells)
•Most require co-enzymes
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Enzymes:
•Recognize substrate by shape of binding site
•Serve to lower energy required for reaction to occur (activation energy)
•therefore speed up reactions
•Not changed or used up during reaction
Slide 14.67
Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Co-Enzymes:
•Required to activate enzymes
•Facilitate enzymatic reactions
•May be a metal ion (Zn++, Cu++, Fe++)
•May be a vitamin
•Vitamins are co-enzymes
•Only function if “their” enzyme is available
Cellular Metabolism Catabolism: substances are broken down into molecules
“destructive” process
Large molecules broken down into smaller molecules
Usually by hydrolysis
“splitting with water”
Adds H2O back into molecule
Breaks covalent bonds
Cellular Metabolism Catabolism
Energy is released when bonds break
Reverse of dehydration synthesis (condensation)
Hydrolysis = chemical digestion
Occurs simultaneously (and continuously) with anabolism
Processes controlled by enzymes
Cellular Energy Cellular energy is chemical energy
Derived from breaking chemical bonds
~ ½ Energy is stored as ATP
~ ½ Energy is released as heat
Helps maintain body temperature
Enzymes control in the process
Cellular EnergyAll nutrient molecules are ultimately
degraded or converted to glucoseOnly glucose can be used to make
ATPOxidation: cellular process of
chemically breaking apart a glucose molecule to release energy
Cellular EnergyGlucose oxidation occurs in 2 phases
Anerobic metabolismOccurs in cytoplasmWithout oxygenAKA glycolysisSplits glucose into two 3-Carbon
molecules: pyruvate
Cellular EnergyGlycolysis
Process also produces 2 ATPsIn yeast, plant cells:
Pyruvate can undergo alcoholic fermentation
In bacteria, animal cells:Pyruvate can produce lactic acid
Cellular EnergyAerobic metabolism
Uses oxygenAKA Kreb’s Cycle or Citric Acid
cycle or Tricarboxylic Acid (TCA) Cycle
Occurs in mitochondriaMakes more ATP than anerobic
processes
Cellular EnergyAerobic metabolism
CO2 and H2O are waste products
CO2:
Diffuses out of cellsDissolves in plasmaProduces HCO3
- in blood
Exhaled from lungs
Cellular EnergyAerobic metabolism
H2O:
“metabolic” waterExhaled from lungs
Final products of glucose oxidation:CO2, H2O, ATP
Cellular EnergyAerobic metabolism
For each molecule of glucose:2 ATP formed in glycolysis36 ATP formed in TCA cycleEnergy stored in phosphate
bondsA reversible reaction
Metabolic Pathways“A particular sequence of enzymatic
reactions” Such as glycolysis, TCA cycle
Carbohydrate pathwaysCarbos should comprise most of
our diet (~ 50% complex carbs)Used as a primary energy sourceProduce 4kcal/gm
Metabolic PathwaysCarbohydrate pathways
Excess carbs converted to energy storage formsGlycogen (muscle, liver)Adipose tissue (hips)Process is anabolism
Metabolic PathwaysLipid pathways
Metabolism controlled by liverShould comprise <30% of calories
in dietGet 9 kcal/gm (more ATP!)Must be degraded into glycerol,
fatty acids, then pyruvateA reversible catabolic process
Metabolic PathwaysProtein pathways
Proteins should comprise ~30% of diet
Get 4 kcal/gmCatabolism is more complex
Proteins contain nitrogen
Metabolic PathwaysProtein pathways
Deamination: removal of nitrogen from amino acidsOccurs in liverNitrogen is converted to urea
A nitrogenous waste product
Sent to kidneys for excretion
Metabolic PathwaysProtein pathways
After deamination: amino acid “skeleton” is
processed in TCA cycleMay produce CO2, H2O, ATP
May form glucose or fat
Metabolic PathwaysProtein pathways
Glucose formed from amino acid skeletons may be re-converted to amino acids
“Essential” amino acids: Body cannot make theseMust obtain in the diet
Regulation of Metabolic Pathways
Enzyme “saturation”Too much substrate for number of
enzyme moleculesReaction rate cannot increaseA single enzyme can control an
entire metabolic pathway“rate limiting” enzyme
Slide 14.92b
Digestive System: DisordersDigestive System: Disorders
Ulcers: bacterial infection with H. pylori
Vomiting: controlled by center in medulla oblongata
Activity of tract slows in old age Fewer digestive juices Peristalsis slows Diverticulosis and cancer more common
Slide 14.92b
Digestive System: DisordersDigestive System: Disorders
IBS: irritable bowel syndrome Crohn’s disease (autoimmune) Constipation Diarrhea Colitis Colon polyps/cancers
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