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Digestive System and Metabolism

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Greg Horesovsky

on 13 September 2013

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Transcript of Digestive System and Metabolism

The Digestive System and Metabolism LARGE INTESTINE 5 feet long
Absorption of water, Vits K and B, electrolytes, elimination of feces
Cecum - Ileocecal valve separates ileum from cecum
Anal Canal
Anal sphincters Prepares urea, the chief waste product of protein metabolism
Stores vitamins A, D, and B complex
Breaks down hormones no longer useful to the body
Removes old red blood cells and recycles iron content LIVER/ACCESSORY ORGAN OF DIGESTION Functions of the liver
Manufactures bile which is necessary for fat digestion
Produces and stores glucose in the form of glucogen
Detoxifies alcohol, drugs and other harmful substances
Manufactures blood proteins LIVER/ACCESSORY ORGAN OF DIGESTION A hollow, muscular, pear-shaped organ that stores and concentrates bile
Releases bile to the small intestine
Bile aids in the digestion of lipids Gall Bladder Pancreas
Connects to the Duodenum via the pancreatic duct
Pancreatic juice
HCO3 (bicarbonate) to neutralize HCl
Trypsin – proteins to AA
Amylase – Carbs to sugars
Lipase – Fats to fatty acids
Insulin and glucagon
Gall bladder
Bile – continues fat breakdown Pancreas The small intestine receives and raises the pH of materials arriving from the stomach.
It then absorbs water, ions, vitamins, and the chemical products released by action of digestive enzymes secreted by intestinal glands and exocrine glands of the pancreas. Small Intestine:Big Picture The third segment
Longest (about 12 ft)
Ends at the ileocecal valve
A sphincter that controls flow of material from the ileum into the large instestine SMALL INTESTINE: Ileum Layers of the digestive system Section closest to stomach
About 10-12 inches in length
This is where the bile duct and pancreatic duct connect to small intestine .
Presence of chyme stimulates secretion of intestinal hormones like secretin and cholecystokinin (CCK)
Stimulate pancreatic enzyme production (insulin) and raise pH. SMALL INTESTINE: Duodenum Food is stored in the stomach while it is physically broken down in preparation for chemical digestion.

Protein digestion begins in the acid environment of the stomach through the action of pepsin.

Carbohydrate digestion begins in the mouth with the release of salivary amylase. BIG PICTURE Although digestion occurs in the stomach, nutrients are not absorbed there because
1) The epithelial cells are covered by a thick layer of mucous and are not directly exposed to Chyme
2) The epithelial cells lack the transport function of intestinal cells
3) the gastric lining in not permeable to water
4) digestion has not proceeded to completion by the time chyme leaves the stomach Stomach Contains shallow depressions called gastric pits
Fundus and body of stomach
Cells in gastric pits secrete gastric juice
Parietal Cells secrete:
Hydrochloric acid HCl- lowers the pH of stomach keeping it acidic (about 1.5- 2.0)
Converts Pepsinogen to Pepsin (protein digestion)
Intrinsic factor – facillitates absorption of Vitamin B12
Chief Cells secrete:
Converted to pepsin by stomach acid
Rennin – only found in infants and children
Prepares milk for further digestion

Chyme – semi-fluid mixture of food particles and gastric juices The Gastric Wall Swallowing Muscular tube
Pharynx to stomach
Behind trachea
Upper esophageal sphincter
Lower esophageal sphincter
Usually in active condition to keep stomach contents from backflow into esophagus ESOPHAGUS Salivary glands
Parotid – amylase (begins to digest carbohydrate)
Submandibular – mucin and ptyalin (like amylase)
Sublingual – Only secretes mucus and H2O
Moistens and lubricates food
Contains enzymes
Ptyalin Mouth: Salivary Glands Upper Gastrointestinal Tract
Lower Gastrointestinal Tract
Small intestines
Large intestines ORGANS OF DIGESTION Peristalsis Peritoneum - serous membrane
a smooth membrane consisting of a thin layer of cells which secrete serous fluid

Parietal peritoneum/Mesentery - part that attaches to posterior wall of abdominal cavity
Visceral peritoneum/Greater omentum - anterior portion that protects abdominal organs
Adipose and fat
Lesser omentum – btx liver and stomach LINING OF THE
DIGESTIVE SYSTEM Layers of the digestive system Serosa
Membrane that covers the muscularis externa along most of the digestive tract
In some areas digestive tract is suspended by mesenteries
Double sheets of the serous membrane
Stabilize the positions of attached organs
Serosa is NOT present in the oral cavity, pharynx, esophagus, and rectum. LAYERS OF DIGESTIVE SYSTEM ORGANS Muscularis Externa
Smooth muscle cells
Circular muscle and longitudinal muscle
Responsible for peristalsis
Autonomic reflex movements LAYERS OF DIGESTIVE SYSTEM ORGANS Mucosa
Inner lining of the digestive tract
Mucous membrane
Epithelium, loose connective tissue, smooth muscle
Secretes mucus LAYERS OF DIGESTIVE SYSTEM ORGANS Components of the digestive system Break food into smaller pieces (ingestion, mechanical processing (mastication)
Change food chemically into fat, carbohydrates, and protein
Secretion of water acids and enzymes to breakdown food into small organic fragments
Absorb nutrients into blood capillaries of small intestines, water and vitamins in large intestine
Eliminate waste products of digestion FUNCTIONS OF THE
DIGESTIVE SYSTEM The large intestine stores digestive wastes and reabsorbs water.

Bacterial residents of the large intestine are an important source of vitamins, especially Vitamin K, B and biotin. Big Picture: Large Intestine About 8 ft long
This is where most chemical digestion and nutrient absorption take place SMALL INTESTINE: Jejunum 2.5 cm diameter; 20’ long
Finishes digestion: absorbs nutrients and passes residue to Large intestine
Site of most absorption
Plicae – Folds that increase surface area
Villi – Fingerlike extensions of plicae

Three main sections: Duodenum, Jejunum, Ileum SMALL INTESTINE Stomach is divided into 3 portions
Fundus - upper part
Greater curvature (body) - middle
Pylorus - lower portion
Pyloric sphincter
Rugae (wrinkles)
Majority of digestion occurs here STOMACH Throat
Extends from base of skull to level of C6
Serves as both respiratory and digestive system
Opens into larynx and esophagus
Epiglottis PHARYNX Teeth
Composed of a bone-like material called dentin
Hard and soft palate (soft palate keeps food from entering nasal cavity)
Multi-layered skeletal muscles
Lingual frenulum
Papillae (site of taste buds) MOUTH Submucosa
The second layer, directly beneath the Mucosa
Loose connective tissue with blood vessels, lymphatic vessels, nerves, glands
Involved in controlling and coordinating contractions of the Muscularis Externa LAYERS OF DIGESTIVE SYSTEM ORGANS The Digestive System Metabolism Food Groups and MyPyramid Plan
A balanced diet contains all components needed to maintain homeostasis:
Substrates for energy generation
Essential amino acids and fatty acids
Minerals and vitamins
Must also include water to replace urine, feces, evaporation Nutrition Homeostasis can be maintained only if digestive tract absorbs enough fluids, organic substrates, minerals, and vitamins to meet cellular demands
Nutrition is the absorption of nutrients from food
The body’s requirement for each nutrient varies Nutrition Disassemble to nucleotides
Sugar (ribose) and cytosine and uracil can be catabolized and enter TCA
Adenine and guanine are not catabolized
Deaminized to uric acid for excretion:
gout DNA/RNA Catabolism Protein Synthesis
The body synthesizes half of the amino acids needed to build proteins
Nonessential amino acids:
Amino acids made by the body on demand

Ten essential amino acids:
Eight not synthesized:
isoleucine, leucine, lysine, threonine, tryptophan, phenylalanine, valine, and methionine
Two insufficiently synthesized:
arginine and histidine Amino Acids and Protein Synthesis Kahn Academy: Citric Acid Cycle (Krebs Cycle)

http://www.khanacademy.org/science/biology/v/krebs---citric-acid-cycle Summary If other energy sources are inadequate
Mitochondria generate ATP by breaking down amino acids in TCA cycle
Not all amino acids enter cycle at same point, so ATP benefits vary Protein Metabolism The body synthesizes 100,000 to 140,000 proteins
Each with different form, function, and structure
All proteins are built from the 20 amino acids
Cellular proteins are recycled in cytosol
Peptide bonds are broken
Free amino acids are used in new proteins Protein Metabolism Lipid Catabolism (also called lipolysis)
Breaks lipids down into pieces that can be:
Converted to pyruvic acid
Channeled directly into TCA cycle
Hydrolysis splits triglyceride into component parts:
One molecule of glycerol
Three fatty acid molecules Lipid Metabolism Lipid molecules contain carbon, hydrogen, and oxygen
In different proportions than carbohydrates
Triglycerides are the most abundant lipid in the body Lipid Metabolism Summary: ATP Production
For one glucose molecule processed, cell gains 36 molecules of ATP:

2 from glycolysis
4 from NADH generated in glycolysis
2 from TCA cycle
28 from ETS Energy Yield of Glycolysis and Cellular Respiration For most cells, reaction pathway
Begins with glucose
Ends with carbon dioxide and water
Is main method of generating ATP Energy Yield of Glycolysis and Cellular Respiration The Electron Transport System (ETS)
Also called respiratory chain
Is a sequence of proteins (cytochromes):
embedded in inner membrane of mitochondrion
surrounds pigment complex
Pigment complex:
contains a metal ion (iron or copper) Energy Production Within Mitochondria The Electron Transport System (ETS)
Is the key reaction in oxidative phosphorylation
Is in inner mitochondrial membrane
Electrons carry chemical energy:
Within a series of integral and peripheral proteins Energy Production Within Mitochondria Oxidative Phosphorylation and the ETS
Is the generation of ATP:
Within mitochondria
In a reaction requiring coenzymes and oxygen
Produces more than 90% of ATP used by body
Results in 2 H2 + O2 2 H2O Energy Production Within Mitochondria The TCA Cycle (Krebs cycle) The TCA Cycle
Acetyl-CoA is released to bind another acetyl group
One TCA cycle removes two carbon atoms:
Regenerating 4-carbon chain
Several steps involve more than one reaction or enzyme
H2O molecules are tied up in two steps
CO2 is a waste product
The product of one TCA cycle is:
One molecule of ATP Energy Production Within Mitochondria If oxygen supplies are adequate, mitochondria absorb and break down pyruvic acid molecules:
H atoms of pyruvic acid are removed by coenzymes and are a primary source of energy gain
C and O atoms are removed and released as CO2 in the process of decarboxylation Energy Production Within Mitochondria Glucose Breakdown
Occurs in small steps:
Which release energy to convert ADP to ATP
One molecule of glucose nets 36 molecules of ATP
(although 38 ATP are made, we have to spend 2 in glycolysis)
Breaks down glucose in cytosol into smaller molecules used by mitochondria
Does not require oxygen: anaerobic reaction
Aerobic Reactions:
Also called aerobic metabolism or cellular respiration
Occur in mitochondria, consume oxygen, and produce ATP Glycolysis Generates ATP and other high-energy compounds by breaking down carbohydrates:

glucose + oxygen --> carbon dioxide + water  Carbohydrate Metabolism Organic Compounds
Most abundant storage carbohydrate
A branched chain of glucose molecules
Most abundant storage lipids
Primarily of fatty acids
Most abundant organic components in body
Perform many vital cellular functions Metabolism In energy terms
Anabolism is an “uphill” process that forms new chemical bonds Metabolism Catabolism
Is the breakdown of organic substrates
Releases energy used to synthesize high-energy compounds (e.g., ATP)
Is the synthesis of new organic molecules Metabolism The Nutrient Pool
Contains all organic building blocks the cell needs:
To provide energy
To create new cellular components
Is source of substrates for catabolism and anabolism Metabolism Cellular Metabolism Metabolism refers to all chemical reactions in an organism
Cellular Metabolism
Includes all chemical reactions within cells
Provides energy to maintain homeostasis and perform essential functions Metabolism Body chemicals
Cardiovascular system:
Carries materials through body
Materials diffuse:
From bloodstream into cells Metabolism Cells break down organic molecules to obtain energy
Used to generate ATP
Most energy production takes place in mitochondria Introduction to Nutrition and Metabolism For each 2-carbon fragment removed from fatty acid, cell gains
2 ATP from acetyl-CoA in TCA cycle
5 ATP from NADH
Cell can gain 144 ATP molecules from breakdown of one 18-carbon fatty acid molecule
Fatty acid breakdown yields about 1.5 times the energy of glucose breakdown Lipids and Energy Production Alternative Catabolic Pathways The TCA Cycle (tri-carboxylic acid or the citric acid cycle) Also known as the KREBS cycle
The function of the citric acid cycle is:
To remove hydrogen atoms from organic molecules and transfer them to coenzymes
In the mitochondrion:
Pyruvic acid reacts with NAD and coenzyme A (CoA)
Producing 1 CO2, 1 NADH, 1 acetyl-CoA
Acetyl group transfers:
From acetyl-CoA to oxaloacetic acid
Produces citric acid Energy Production Within Mitochondria Glycolysis
Breaks 6-carbon glucose
Into two 3-carbon pyruvic acid
Ionized form of pyruvic acid Glycolysis Nutrient Use in Cellular Metabolism Carbohydrates Lipids Protein Nutrition Nutrition Water-Soluble Vitamins
Are components of coenzymes
Are rapidly exchanged between fluid in digestive tract and circulating blood:
Excesses are excreted in urine Nutrition Vitamin A
A structural component of visual pigment retinal
Vitamin D
Is converted to calcitriol, which increases rate of intestinal calcium and phosphorus absorption
Vitamin E
Stabilizes intracellular membranes
Vitamin K
Helps synthesize several proteins, including three clotting factors Nutrition Fat-Soluble Vitamins
Vitamins A, D, E, and K:
Are absorbed primarily from the digestive tract along with lipids of micelles
Normally diffuse into plasma membranes and lipids in liver and adipose tissue Nutrition Nutrition Nutrition Are essential components of the diet
The body does not synthesize minerals
Cells synthesize only small quantities of a few vitamins:
Ions such as sodium and chloride determine the osmotic concentration of body fluids.
Ions in various combinations play major roles in important physiological processes.
Ions are essential cofactors in a variety of enzymatic reactions. Minerals, Vitamins, and Water The MyPyramid Plan Your body is made up of approximately 100 trillion human cells and 1,500 trillion microbes. By numbers you are little more than 10% you.
However, eukaryotic cells are significantly larger than prokaryotic cells, so those 1,500 trillion microbes only make up between 2 and 5 pounds of your weight.
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