Digestion

THE PROCESS OF LIPID ABSORPTION Getting to the Intestinal Wall

1. Fatty acids and monoglycerides are carried to the intestinal wall by Micelles 2. Fatty acids and Monoglycerides leave the micelle and diffuse into the intestinal epithelial cells 3. Micelles go back and pick up more fatty acids and monoglycerides

The esophagus is __ inches long and runs from the __ to the __

10, laryngopharynx to the stomach

It takes __ hrs for the intestine to turn wastes feces

12 to 24

How many new ATPs are made? (Hint-How many ADPs are converted to ATP).

2 ATPs are generated directly during this stage. (One is generated for each Acetyl CoA.

Complete this chemical equation for this phase

2 Acetyl CoAs 2ATPs + 6 NADH + H+ + 2FADH2

How many FADH2s are generated?

2 FADH2s s are generated at this stage.

How many NADH + H+ s are generated?

2 NADH + H+ s are generated at this stage. (One is generated for each pyruvic acid. Only one is shown in figure 26.4)

Complete this chemical equation for this phase

2 Pyruvic acids 2 acetyl CoA + 2 NADH + H+ + 2 CO2

With 10 NADH + H+s and 2 FADH2s entering the chain, how many total ATPs will be made?

34 ATPs are made.

How many NADH + H+ s are generated?

6 NADH + H+ s are generated at this stage.

Saliva has a pH of

6.8-7.0

Around __ of water enter the digestive tract every day.

9.3 liters (9.5 quarts)

What if the intestinal wall were flat? How do the presence villi and microvilli increase the amount of absorption that takes place?

A flat wall has less surface area. The villi and microvilli create much more surface over which things can be absorbed. In fact if you could lay out the entire surface of the small intestine, it would extend 2200 square feet! (That's as big as the entire floor space of a two story house.)

What is the cause of abdominal swelling in a person with Kwashiorkor?

A lack of protein reduces the amount of albumen (a plasma protein) produced in the liver. The lack of plasma proteins in the blood causes • A drop in blood osmotic pressure. This causes • The net flow of fluid during capillary exchange to move out of the blood into the tissues. • The tissues become edmic or swollen

When added to the 4 ATPs made directly, how many total ATPs are generated through cell respiration of glucose?

A total of 38 ATPs are generated.

ATP (Adenosine Triphosphate)

A way in which the body stores small amounts of energy. A molecule of ATP readily releases this energy wherever it is needed by chemical reactions throughout the body. The process of cell respiration occurs in many small steps, with each step • Breaking another carbon-hydrogen bond • Releasing a small amount of energy • Generating a few ATPs.

Things That Affect BMR

A wide verity of factors effect the BMR. They include hormones, moods, food, and body temperature. When the body requires more energy it increases the BMR. When the body requires less energy it lowers the BMR.

• Fat soluble vitamins include

A, D, E and K o These vitamins must be absorbed with fats

METABOLIC STATES The body switches between

ABSORPTIVE and POSTABSORPTIVE STATES

Chemical Digestion

After the food has been chewed and mixed with the saliva it becomes a bolus and is swallowed. It then enters the esophagus

PROTEIN CATABOLISM

Amino acids can also be used for cell respiration • One amino acid yields around 36 ATPs but o Proteins more difficult to breakdown then lipids or carbohydrates o Breakdown produces toxic ammonia which must be converted to urea in liver • Proteins are needed by cells for other reasons Amino acids are only used when other sources of energy are not available.

Why do fat droplets need to be emulsified in order to be properly digested?

An enzyme can only work on the uncharged surface of a fat droplet. It's charge prevents it from mixing into the center of the droplet.

Chemical Stimuli in stomach wall

An increase in pH caused by the presence of peptides in the stomach These buffer the acids in the stomach and raise the pH Response The stomach releases gastrin The stomach increases contractions and enzyme secretions

• Water soluble vitamins include

B complex and vitamin C o Most of these are absorbed by simple diffusion o Vitamin B12 must be absorbed with intrinsic factor This is produced in the stomach

Fat digestion continues in the small intestine with the help of

Bile • Emulsifies fat droplets o Big fat droplets are broken up into many small ones Pancreatic lipase • Deposited into the duodenum • Same as lingual lipase

Bile Release

Bile is released into the duodenum of the small intestine. Specific foods in the small intestine stimulate release of CCK • CCK stimulates the release of bile

What effects do these hormones have on the stomach?

Both of these hormones inhibit stomach secretions and motility. Just the opposite of their effects on the intestine.

The formula for glucose breakdown is:

C6H12O6 + 6O2 6CO2 + 6H20 + 36ATPs

The Goals of Carbohydrate Digestion

Carbohydrates are broken down by hydrolysis to form: • Monosaccharides These can then be absorbed in the small intestine.

Some coenzymes act as

Carriers. They • Pick up hydrogen from one reaction and • Move it to another where it is used it to make ATP

Can you think of a situation when the cells would run out of oxygen leading to lactic acid build up?

During active muscle use, the muscle cells rapidly use up oxygen supplies and must depend on glycolysis only for energy. This a factor contributing to muscle fatigue.

Why does cell respiration need to take place in many small steps? Why not split a molecule of glucose in one quick step?

During cell respiration energy is released from chemical bonds. Some of this energy can be saved in other chemical bonds, some will be lost as heat. • If this reaction occurred in one step Most of the energy generated would be lost as heat • Instead glucose and other molecules are broken down in many small steps Small amounts of energy are released at each step Most of this energy is easily stored as ATP

GLYCOLYSIS

During glycolysis glucose, which is a 6-carbon molecule, is split into two 3-carbon molecules of pyruvic acid. Glycolysis: • Takes place in the cytoplasm of the cell • Is Anaerobic (no oxygen is required) • Requires input of ATP. o Some ATP is needed in the first three steps, to begin the process of glucose breakdown. • Makes a small amount of ATP • Makes a small amount of NADH + H+ o This will be used in the electron transport step to make more ATP

What kinds of food would act as a trigger for release of bile?

Fats in duodenum

The structure of fats

Fats or triglycerides are made up of a molecule of glycerol bound to three fatty acid chains.

What kinds of foods include large amounts of starches?

Foods which are high in starch include: Potatoes, rice, pasta, and bread

2. How many new ATPs are made? (Hint-How many ADPs are converted to ATP)

Four ATPs are made in glycolysis, two in step 6 and two in step 7.

3. What is the total number of ATPs generated in this stage?

Four ATPs are made, but two ATPs are used up. Thus, a net total of two ATPs are generated in glycolysis.

Food storage takes place in the __ in the upper part of the stomach. There are __ in this region and food remains here for ___ hours

Fundus, few mixing waves, 2-6 hrs

The most important organic molecule for cell respiration is

Glucose

Complete this chemical equation for glycolysis

Glucose 2 pyruvic acids + 2ATP + 2NADH + H+

How are the monosaccharides absorbed into and out of the cells?

Glucose and Galactose are absorbed into the epithelial cells by • Facilitated diffusion with Na+ Fructose is absorbed by • Facilitated diffusion using a different carrier All monosaccharides move out of the epithelial cell by • Facilitated diffusion

How does hydrochloric acid denature proteins?

HCl dissociates or splits into H+ and Cl-. The H+ gets in between the charges that form the hydrogen bonds and sulfur-sulfur bonds on the peptide chains of the proteins and breaks the bonds.

What do you think happens to them in the absence of bile salts?

In the absence of bile salts : • Much of the fat that enters the intestine does not get exposed to the lipases in the intestinal juices and • Most does not get digested • It will, instead be excreted with the feces

ELECTRON TRANSPORT

In the final step in cell respiration, the 10 NADH + H+s and 2 FADH2s move to the electron transport chain, where they will be used to generate ATPs. Electron transport: • Takes place on the mitochondrial membrane • Uses oxygen • Uses hydrogen atoms to make ATP

How are these cells designed to speed absorption?

Intestinal cells have fingerlike projections or villi and microscopic projections on the villi called microvilli. These create a very large surface area for absorption.

Intestinal enzymes - produced by? Which enzymes do they include?

Intestinal enzymes are produced mainly by the epithelial cells that form the brush boarder (Microvilli) of the intestine . These enzymes include: • Maltase, Sucrase, Lactase • Peptidases • Nucleosidases

What does HCl do to proteins?

It denatures them, breaking apart their quarternary, tertiary and secondary structures.

FUNCTIONS OF THE LIVER

It has numerous functions that are critical to life. They include: • Metabolism (breakdown and synthesis) of all organic molecules • Synthesis of Bile • Excretion of Bilirubin • Storage Of Vitamins and Minerals • Detoxification of blood

What would increased contraction of the pyloric sphinctor do?

It would slow the movement of food going from the stomach to the small intestine.

Because lipids are not soluble in the water portion of the blood, they must be transported bound to proteins in a molecule known as a

LIPOPROTEIN

After the monosaccharides have been absorbed, they travel to the

LIVER

Fat digestion begins with the enzyme

Lingual lipase which catalyzes the breakdown of • Triglycerides monoglycerides and fatty acids

LIPID CATABOLISM

Lipids such as fatty acids can be used for cell respiration • One fatty acid yields 144 ATP molecules • Lipids thus provide more energy than glucose but o Lipids are more difficult to break down • Lipids are thus used by cells with modest energy needs o These include resting skeletal muscle cells

Minutes after food enters the stomach weak peristaltic waves called ___ start and they ___

MIXING WAVES • Mix and breakdown food forming a liquid called chyme • Most mixing takes place in the body of the stomach

The disaccharides include:

Maltose • Glucose + Glucose Sucrose • Glucose + Fructose Lactose • Glucose + Galactose

Which foods remain in the stomach the longest?

Meals that are high in fat remain in the stomach for the longest amount of time. Liquids move out most rapidly.

Secretions of the Large Intestine

Mucus

How many new ATPs are made?

No ATPs are generated directly during this stage.

Oxidation-Reduction Reactions

Oxidation • Loss of an electron Reduction • Gain of an electron

Pancreatic Juice

Pancreatic juice is released into the duodenum of small intestine. It is made up of • Sodium Bicarbonate o This creates a pH of 7.1 - 8.2 • Pancreatic amylase o Turns carbohydrates into disaccharides • Trypsin, Chymotrypsin and Carboxypeptidase o Turns proteins into peptides • Lipase o Turns lipids into monoglycerides and fatty acids

BREAKDOWN OF PROTEINS The Intestine

Protein-digesting enzymes from both the pancreas and the small intestine are deposited in the small intestine. The pancreatic enzymes include: • Trypsin and Chymotrypsin. These continue the process of converting Proteins to peptides • Carboxypeptidase this coverts Peptides to amino acids The intestinal enzymes include • Peptidases. These convert Peptides to amino acids

Fatty Acids and Glucose in the Intestine

Response • Release of hormones produced in the small intestine o Secretin, CCK (cystokinin), GIP (gastric inhibitory peptide) Causes decreased contractions and secretions of the stomach • The Medulla stimulates the sympathetic nervous system (same as the stretching response). o Causes decreased contractions and secretions of the stomach o Increased contraction of pyoric sphinctor Thus food in the intestine causes all activity in the stomach to SLOW DOWN.

Stretching of the stomach wall

Response • Stretch receptors in the stomach stimulate the medulla o The medulla stimulates the parasympathetic nervous system o Causes increases in contractions and secretions

Stretching of the Intestinal Wall

Response • The Medulla stimulates the sympathetic nervous system o Causes decreased contractions and secretions of the stomach o Increased contraction of pyloric sphinctor

Carbohydrate breakdown begins in the mouth with the enzyme

Salivary amylase which catalyzes the breakdown of Starch Maltose

Segmentation

Segmentation involves localized ring-like contractions. It mixes chyme and moves it against the walls of the small intestine.

What are the four main functions of the stomach? If a person has their stomach stapled which of these functions will be totally gone?

Storage of food Mechanical breakdown of food Chemical digestion of some foods Absorption of some foods A person with no stomach would no longer be able to: Store food o Food storage takes place only in the stomach. Mechanically breakdown large chunks of food. o Limited mechanical breakdown takes place in the mouth, but most break down occurs in the stomach.

Can you think of five things that would increase the BMR and three things that would lower it?

The BMR would be increased by: • Pregnancy • Anxiety • Fever • Eating • Cold The BMR would be lowered by: • Apathy • Starvation • Weight loss

What vessel transports blood directly from the small intestine to the liver?

The Hepatic Portal Vein

Can you think of three conditions when the body would the body turn to lipids for energy?

The body turns to lipids during periods when it runs out of glucose: • Fasting • Diabetes • Starvation

When the Body Runs Out of Blood Glucose

The body turns to stores • The major source of stored glucose is o Liver glycogen This lasts for around 4 hours • Other sources of glucose include o Glycerol from lipids o Muscle glycogen

Which foods begin their chemical breakdown in the mouth?

The bread, peach, and potatoes all contain carbohydrates and thus all begin their chemical breakdown in the mouth. The bacon, chicken breast and egg are protein and fat and are not broken down in the mouth.

Fatty acids need micelles to get to the intestinal cells. Why don't they need them to cross the cell membrane?

The cell membrane has a phospholipid backbone. Thus any lipids diffuse easily across.

BREAKDOWN OF PROTEINS The Stomach

The chemical breakdown of proteins begins in the stomach. Here the acid pH of 2 allows activation of protein-digesting enzymes. The stomach wall produces • HCl (hydrochloric acid) which • Denatures proteins • Pepsin which catalyzes the breakdown of • Proteins to peptides (chains of amino acids)

Why don't the chylomicrons get deposited directly into the blood capillaries instead getting transported through the lymphatic system?

The chylomicrons are relatively large and cannot get through the spaces between the epithelial cells of the blood capillaries. Lymph capillaries are larger than blood capillaries and more permeable. Chylomicrons can readily penetrate these vessels.

CITRIC ACID (KREBS) CYCLE

The citric acid cycle begins with a molecule of acetyl CoA and ends with a molecule of oxaloacetic acid. This phase: • Takes place in the mitochondria • Requires O2 • Goes around 2x for each glucose

What Happens to the Electrons?

The electron-transport chain is made up of a series of enzymes. The electrons get passed from one enzyme to another, down the electron-transport chain. At the end of the chain: • Oxygen picks up the electrons • Oxygen binds to H+ to form H2O

Can you guess why fructose is absorbed more slowly (and raises blood sugar more slowly) than the glucose and galactose?

The fructose uses a different carrier protein, which moves fructose more slowly across the membrane.

THE GASTRIC STAGE

The gastric stage begins when food enters the stomach.

What do you think determines whether glucose is stored as glycogen or fat?

The liver and muscle cells have only a limited amount of space to store glycogen. Once this space is filled, all excess glucose, lipid or amino acid is turned into fat and stored in fat cells.

Protein Metabolism

The liver manages all aspects of amino acid use. • It synthesizes plasma proteins • It turns amino acids into glucose, when needed • Plays a role in amino acid breakdown • It stores excess amino acids as fats.

Lipid Metabolism

The liver manages all aspects of lipid use. • It synthesizes o Lipoproteins o Cholesterol • It stores lipids • It breaks down lipids for energy

Why is a liver disease such as cirrhosis associated with distension or swelling of the abdomen and increased bleeding?

The liver manufactures the plasma protein albumen. • This adds solutes to the blood • Lack of albumen upsets the osmotic balance, causing fluid to move from the blood (where there are fewer solutes) to the interstitial fluid of the abdomen (where there are more solutes), making it swell. The liver manufactures clotting factors. • Lack of these causes increased bleeding

What Happens to the H+ Ions?

The mitochondrial membrane is only permeable to H through pores • Energized H+s scoot through these pores to get back to the outside of the membrane. o In the process they make ATP

How important do you think the mouth phase is in all of fat digestion? Explain your reasoning.

The mouth phase of fat digestion is not very important because: • Food only spends a very short time in the mouth • Food undergoes much of its mechanical breakdown in the stomach. After this it becomes easier for enzymes to mix with the food.

gastric pits

The mucosa of the stomach is lined with deep grooves. At the end of the pits are tubular gastric glands.

Carbohydrate does not take place in the stomach. Can you guess why?

The pH of the stomach, at 2, is too acidic for the enzymes that breakdown carbohydrates to work.

Factors Which Turn Off The Satiety Center

The satiety center is NORMALLY TURNED ON so a person is not hungry (This probably seems hard to believe, because we have so many things that make us think we need to eat.) Factors that turn it off and turn on the hunger center are numerous.

What kind of stimuli from the food would trigger a response?

The sight, smell, taste or thought of food all act to stimulate a response.

The sites of Carbohydrate Digestion

The sites of carbohydrate digestion are the: • Mouth and • Small Intestine

What functions of the stomach and mouth are not found in the small intestine?

The small intestine plays no role in mechanical breakdown of food. • Food is already a semi-liquid chyme by the time it gets to the small intestine. The small intestine plays no role in food storage.

What is the advantage of having only very small amounts of chyme enter the intestine at a time?

The small intestine, the major site of chemical breakdown can only handle small amounts of food at any one time. If too much go in, most of it won't get digested.

G cells

These are endocrine cells located at the very base of the gastric glands They produce the hormone Gastrin o Gastrin regulates digestion

Peristalsis

These are weak waves of contraction that slowly transport food down the intestine Food remains in the small intestine for 3-5 hours

• Chylomicrons

These carry digested lipids from the digestive tract to the liver and other tissues

Parietal Cells

These cells are also found in the gastric glands of the stomach They produce: Intrinsic factor -This chemical is critical for absorption of vitamin B12 HCl (Hydrochloric acid) -This makes the pH of stomach very acidic, 2 HCl has several important functions in the stomach. It: o It kills microbes o It activates pepsinogen o It helps to break down proteins

Mucus cells

These cells are located in the gastric pits. They produce mucus This protects stomach wall

Why don't long-chain fatty acids and monoglycerides mix with intestinal juices?

These uncharged molecules cannot mix with the water in intestinal juices. They need to be wrapped in charged bile salts to mix in.

What would be the purpose of having stomach activity slow down when food enters the intestine?

This ensures that the stomach empties slowly enough for the intestines to digest all the food that enters.

PREPARATION FOR KREBS CYCLE

This second step in the cell respiration process begins with two 3-carbon pyruvic acids and leads to the formation of two 2-carbon acetyl CoAs. This phase: • Takes place in the mitochondria • Requires 02 • Yields NADH + H+

1. How many ATPs are used up? (Hint-How many ATPs are converted to ADP)

Two ATPs are used up in glycolysis, one in step 1 and one in step 3.

. How many NADH + H+ s are generated?

Two NADH + H+ s are generated in step 5 of glycolysis

. METABOLIC RATE

When a cell breaks down a molecule of food (glucose, amino acids or fatty acids), energy is released. The amount of energy released in the body per unit of time is known as the METABOLIC RATE. Metabolic rate • Is measured in Kcal/hr • Can be determined by measuring o The amount of heat given off by the body or o Amount of oxygen consumed/unit time

Carbohydrate metabolism

When blood glucose is low, the liver makes more glucose from: • Glycogen • Amino acids • Lactic acid • Fructose + Galactose When blood glucose is high, the liver makes glucose into • Glycogen • Lipids For storage

How might olestra create a problem for nutrient absorption? The fat substitute olestra (used in some potato chips and other foods) is neither digested nor absorbed in the intestine.

When olestra leaves the body it carries off fat soluble A,D,E, K vitamins. These will then be eliminated with the feces.

The small intestine is the major site of

absorption

Excess fat is stored in

adipose tissue is stored in adipose tissue throughout the body.

Bile is transported through

bile ducts and stored in concentrated form in the gall bladder

During cell respiration, the cell

breaks down organic molecules to make ATP.

Energy is defined as the

capacity to do work.

What happens to the other monosaccharides absorbed

converted to glucose or other molecules by the liver.

The process by which two monosaccharides bind together is known as

dehydration synthesis. Dehydration is the loss of water. This means that when two monosaccharides bind together they lose a molecule of water. What is the chemical equation for this reaction? C6H12O6 + C6H12O6 C12H22O11 + H2O

The Pancreas serves as both an __ and an __ organ

endocrine and exocrine

Carbohydrates are absorbed by the

epithelial cells of the small intestine.

The intestinal stage begins when

food enters the small intestine

Chief Cells

found at this base of the gastric pits. They produce: • Gastric lipase in infants -Digests fats • Renin in infants -Curdles milk • Pepsinogen throughout life -An inactive form of an enzyme that helps to breakdown proteins into peptides (chains of amino acids) , Pepsinogen is activated as pepsin only in presence of HCL

80% of the absorbed monosaccharides are which type of monosaccharide

glucose

Lipids are compounds that are either partially or completely

hydrophobic (not soluble in water) They are hydrophobic because they are uncharged and cannot mix with charged water molecules.

Food intake is regulated in the

hypothalamus. There are two centers • A Satiety Center o Inhibits food intake • A Hunger center o Stimulates food intake

The intestinal crypts produce

intestinal juice that contains some of the chemicals needed for breakdown. These include: • Water • Mucus • Enzymes

The large intestine is populated with

kinds of symbiotic (helpful) bacteria. These function to • Synthesize B vitamins, Vitamin K • Break down remaining amino acids and form o Odor causing Indole, skatols, and hydrogen sulfide

The wall of the small intestine is designed to

maximize absorption

Stomach secretions and contractions are regulated through both __ and __ mechanisms

nervous and endocrine

As a molecule is formed or broken down

o Energy is transferred from one group of chemical bonds between atoms to another

Lipids are used by the cells in a number of ways.

o Fatty acids provide energy for resting muscle and other tissues o Cholesterol is used to form cell membranes, steroids, and bile

• Short-chain fatty acids

o Fatty acids with only 10-12 carbons o Move into intestinal cells by simple diffusion

THE CEPHALIC STAGE -- The Stimulus

o Food in the mouth

What are the functions of mucus in the large intestine

o It lubricates and binds feces o It protects the walls of the large intestine

• Long-chain fatty acids and monoglycerides

o Need bile salts to get to the intestinal wall o Otherwise they won't mix in intestinal juices

There are two kinds of stimuli in the intestine. They are:

o Stretching of the intestinal wall o Chemical stimuli

There are two kinds of stimuli from the food in the gastric stage. They are:

o Stretching of the stomach wall o Chemical stimuli

THE CEPHALIC STAGE -- The response

o The medulla stimulates the parasympathetic nervous system o It increases gastric secretions

pyloric sphincter

o The sphincter opens briefly only allowing a very small amount of food to enter the small intestine o Most of the chyme is squirted back into the stomach

• High-density lipoproteins (HDLs)

o These are 13% cholesterol, 37% trigylcerides, 50% proteins o They remove excess cholesterol from cells and take it to the liver for removal o Large amounts of HDLs are considered healthy for the cardiovascular system

Very low-density lipoproteins

o These are 20% cholesterol, 70% triglycerides, 10% proteins o They transport triglycerides to adipocytes (fat cells) for storage o After transporting some triglycerides, they are converted to LDLs

Low-density lipoproteins (LDLs)

o These are 55% cholesterol, 20% triglycerides, 25% proteins o They deliver cholesterol to body cells for use in repair of cell membranes and synthesis of steroids and bile. o As they move through the blood vessels LDLs can deposit cholesterol on the vessel walls o Large amounts of LDLs are considered to be unhealthy for the cardiovascular system

Current health guidelines state that healthy numbers are as follows

o Total Cholesterol (LDLs and HDLs)-should be 200 mg/dL or less o LDLs- should be 130 mg/dL or less o HDLs- should be 40 mg/dL or more

The stomach is not the major site of nutrient of absorption. However, it does absorb:

o Water o Lipid-soluble drugs o Aspirin

Saliva contains

o Water, mucus, salts o Salivary amylase This enzyme helps turn starches to maltose o Lingual lipase This enzyme helps turn triglycerides into fatty acids and monoglycerides It must be activated in the stomach and works after swallowing

Breakdown continues in the small intestine with enzymes from both the

pancreas and the small intestine.

Amino acids bind together through dehydration synthesis to form

peptides

It moves the bolus by

peristalsis A WAVE OF CONTRACTION that moves down the length of the tube

The stomach plays an important role in the chemical breakdown of foods, particularly ___

proteins

The mixing waves move food towards the

pyloric sphincter

Vitamins are absorbed in the

small intestine

The pits and associated glands contain

special cells that produce gastric juices critical to chemical digestion of food.

The polysaccharides include

starch, glycogen, and cellulose. Polysaccharides are all built from • Chains of glucose arranged in different ways.

After the chylomicrons enter the blood they get transported through

the capillaries to the tissues.

Monosaccharides must first be absorbed into

the epithelial cell. Then they must be absorbed from the epithelial cell into the blood.

After food is absorbed in the SI, it is carried to the __ and what happens to it here

the liver. The liver either stores or releases nutrients or creates new molecules depending on the body's needs.

The gastrocolic reflex is

the mass movement of feces from the transverse colon to the rectum. • It occurs 2-3 times per day • It is triggered by: o Food in the stomach or duodenum o Thoughts of food • It is a strong peristaltic wave • It triggers the defecation reflex

The digestive tract is a tube that runs from

the mouth to the anus.

Bioenergetics

the process of generating energy through cell respiration.

Amino acids are absorbed in

the small intestine

The final stages of chemical breakdown of food takes place in

the small intestine.

When two monosaccharides combine

they form disaccharides.

A monosaccharide always contains (chemically)

two hydrogens and one oxygen for every carbon. Thus, the formula for a six-carbon monosaccharide is C6H12O6.

After the three stages of cell respiration are completed, the total numbers of energy generating molecules produced are as follows:

• 10 NADH + H+ • 2 FADH2 • 4 ATPs

Storage sites for adipose tissue in the body are:

• 50% subcutaneous (under the skin) • 12% kidneys • 10-15% omenta • 20% genitals • 5-8% muscles

What changes in blood chemistry turn on the hunger center?

• A drop in blood glucose levels is the main trigger for the hunger center • A drop in amino acids also acts as a trigger

Storage Of Vitamins and Minerals

• A, B12, D, E, K • Iron, copper

It contains two types of cells

• Acini (exocrine) o These make up 99% of the pancreas o Exocrine cells which produce digestive enzymes • Islets of Langerhans (ducts) o Endocrine cells which produce Insulin and Glucagon

They are absorbed by

• Active transport with Na+ into the intestinal cell • Facilitated diffusion out of the intestinal cell

Amino Acids in the absorptive state

• Amino acids are absorbed by cells o These are used in protein synthesis o Can be converted to glucose o Excess amino acids is converted to glycogen or lipids

Once the satiety center has been turned off several factors turn it back on. These include:

• An increase in fatty acids • Warm temperatures • Distension of G.I. Tract • The intestinal hormone CCK

Excretion of Bilirubin

• Bilirubin is absorbed from heme of broken down red blood cells • It is excreted with bile o It is responsible for the yellow-green color of bile o When the liver is not functioning properly, bilirubin accumulates in membranes of the skin and eyes giving them a yellowish tint (Jaundice)

The release of pancreatic juices is increased in all digestive three phases. How is it stimulated and what is the result in each stage

• CEPHALIC and GASTRIC PHASES Stimulation of the Parasympathetic nervous system Stimulates increased secretions of pancreatic juice. • INTESTINAL PHASE Food in the small intestine Stimulates release of Secretin and CCK Increases pancreatic secretions

Chylomicrons

• Can dissolve in water • Won't clump • Can be transported and used by cells

Chemical structure of amino acids

• Carbon • Hydrogen • Oxygen • Nitrogen • Sulfur

Lipids are made up of:

• Carbon • Oxygen • Hydrogen • Phosphate and Nitrogen (some lipids)

Simple sugars or monosaccharides chemical makeup

• Carbon • Hydrogen • Oxygen

Biochemical processes body include

• Catabolism o Breakdown of organics o Causes release of energy • Anabolism o Synthesis of new molecules o Used for maintenance and repairs o Growth o Secretory products o Uses energy

There are three stages of regulation

• Cephalic stage When food is in the mouth • Gastric stage When food is in the stomach • Intestinal stage When food is in the small intestine

The small intestine has two major functions in digestion.

• Chemical breakdown • Absorption o 90% of digestion of breakdown products are absorbed here.

The specialized cells of the stomach include the:

• Chief cells • Parietal cells • Mucus cells • G cells

Types of Lipoproteins

• Chylomicrons • Very low-density lipoproteins • Low-density lipoproteins (LDLs) • High-density lipoproteins (HDLs)

what happens to the chylomicrons in the tissue

• Chylomicrons and triglycerides are broken down by a capillary wall enzyme, lipoprotein lipase • The newly formed fatty acids Diffuse into the liver and fat cells -Here they recombine with glycerol and Form triglycerides for storage Diffuse in to muscle cells -Here they are used by resting cells for energy

Chylomicrons Absorption into the Blood

• Chylomicrons leave the epithelial cell and enter the lacteal of villus • The lymphatic system carries chylomicrons to the blood

Micelles are a

• Cluster of bile salts • Polar on outside only • Fatty acids and monoglycerides dissolve in nonpolar core

What changes in body temperature turn on the hunger center?

• Cold temperatures turn on the hunger center. The body needs to obtain extra fuel to break down and generate heat.

Digestion of proteins requires

• Denaturation o Breakdown of the secondary, tertiary, and quaternary structure • Hydrolysis o Splitting of the bonds between amino acids

Proteins are digested to form

• Dipeptides • Amino acids

The small intestine includes three regions the:

• Duodenum o The first 25 cm (10 inches) o The major cite of chemical digestion • Jejunum o The next 2.4 m (8 feet) • Ilium o The last 3.6 m (12 feet)

THE END RESULT OF GLUCOSE METABOLISM

• Each NADH + H+ produces o 3 ATPS • Each FADH2 produces o 2 ATPs

Bile functions to

• Emulsify fats (break up fat droplets) • Enhance fat absorption

If needed by the cells, glucose is released into the blood and enters the __ with help of __. It is then _____

• Enters the cells with help of insulin here it is • Metabolized for ATP

Cell Respiration Requires

• Enzymes • Coenzymes • Trace elements • ATP coenzymes

Lipids include

• Fats (triglycerides) • Steroids • Phospholipids • Ecosinoids

Fats in the absorptive state

• Fats are absorbed by cells o If needed by cells for energy Glycerol or Fatty acids can be broken down but Lipids are difficult to break down Glucose is preferred by most tissues Used by resting skeletal muscles o They are used for formation of phospholipids Some of these are used to build cell membranes

Once lipids have entered the intestinal epithelial cells the

• Fatty acids and glycerol recombine to form tryglycerides • The triglycerides o Combine with phospholipids and cholesterol o Become coated with polar proteins o Now called CHYLOMICRONS

The small intestine wall includes:

• Finger-like projections called Villi • The surface of each villus is covered with microscopic finger-like projections called Microvilli o These create a surface that's fuzzy like a carpet called the brush boarder

Mechanical Digestion

• Food that enters the mouth is masticated or chewed and mixed with saliva

Functions of the Large Intestine

• Formation of feces • Absorption of water and salts • Synthesis of vitamins

Six-carbon monosaccharides include:

• Glucose • Galactose • Fructose

Glucose in the absorptive state

• Glucose is absorbed by the cells o Glucose is oxidized by cells for energy o Excess glucose is stored as glycogen or lipids o

CELL RESPIRATION-STEPS

• Glycolysis • Prep for Krebs • Krebs cycle (TCA) • Electron transport

Movements of the Large Intestine

• Haustral churning o Ring-like contractions of the large intestine o Occur every 30 minutes o Moves feces against walls for reabsorption of water • Mass propulsion o A strong peristaltic wave that moves feces along the intestine o Occurs 3 times per day

What Happens to the Hydrogen Atoms During electron transport:

• Hydrogen atoms are released from NAD and FAD • Hydrogen ions are then separated from their electrons o Remember that a hydrogen atom is nothing more than one proton in the nucleus and one electron in an outer shell. The hydrogen ions are o Pumped into the space between mitochondrial membranes The electrons o Remain on the outside of the membrane This creates an electrical and chemical gradient o The H+s are concentrated on the inside (Thus the inside is more positive) o The e-s are concentrated on the outside (Thus the outside is more negative)

ANAEROBIC FERMENTATION

• If oxygen is not available to the cell o The process stops after glycolysis • In this case, pyruvic acid is converted to lactic acid.

Why is important for pepsin to be released into the lumen (space) of the stomach in an inactive form? (What would happen if it were active inside the chief cells?)

• If pepsin were released from the chief cells in active form, it would digest the membrane of the cells and create a hole in the stomach wall. • The wall of the stomach is protected by a layer of mucus, so the pepsin, once activated can't go back and digest it. • If something destroys this mucus coating (such as bacteria) the pepsin will digest the wall and produce ulcers.

It receives secretions from accessory organs the:

• Liver • Pancreas • Salivary glands

The intestinal enzymes work on disaccharides. They include

• Maltase Maltose to glucose + glucose • Sucrase Sucrose to glucose + fructose • Lactase Lactose to glucose + galactose

Can you guess which organic molecules are broken down in the presence of each of these enzymes? (Hint. Their names should give it away.)

• Maltase, Sucrase, Lactase o Turn carbohydrates into monosaccharides • Peptidases o Turn proteins into amino acids • Nucleosidases o Turn nucleic acids into nucleotides

There are two digestive processes that take place in the mouth. They are:

• Mechanical digestion • Chemical digestion

Basal Metabolic Rate

• Metabolic rate when you are awake and relaxed o This is the rate 12 hours after last meal o The body would be in a postabsorptive state • The basal metabolic rate of an average adult male is o 2000 kcal/day o It can go up to 5000 kcal/day

During digestion fats are split into:

• Monoglycerides (glycerol and one fatty acid chain) • Fatty acids

Absorption of water takes place throughout the digestive tract.

• Most in the duodenum- 8.3 liters • A small amount in the large intestine-0.5-1 liters Around 0.1 liter is excreted in the feces

There are two coenzymes used as carriers

• NAD -niacin • FAD-riboflavin (B2) NAD picks up two hydrogens. It becomes NADH + H+. This means that it binds • One Hydrogen atom and • One Hydrogen ion (A hydrogen that has lost its one electron) FAD picks up one hydrogen. It becomes FADH2.

Cell Respiration Involves

• Oxidation of glucose • Reduction of oxygen

The pancreatic enzymes include

• Pancreatic Amylase. This is just like salivary amylase. It turns Starch to maltose

Two kinds of movement occur in the small intestine.

• Segmentation • Peristalsis

Carbohydrates include:

• Simple sugars • Starches • Cellulose Found in the cell walls of plants Humans do not digest cellulose, but instead pass it through the system as roughage • Glycogen The compound used by the body to store carbohydrates

Fats are then absorbed in the

• Small intestine

• If not needed by cells, glucose is

• Stored as glycogen in liver or muscle • Stored as fat in liver or fat cells

There are two factors that trigger release of intestinal juices in the small intestine. They are:

• Stretching • The presence of an acid chyme Response These stimuli cause the release of two intestinal hormones • Secretin • Cholecystokinin (CCK) Both of these hormones cause increased release of intestinal juice from the intestinal wall.

When Lipid Stores Run Down

• The body switches to proteins from muscle • Only during fasting o Person can fast several weeks with water and maintain glucose at 25% normal range

Organisms get energy from

• The chemical bonds in food by o Cellular respiration

Detoxification of blood

• The liver converts NH3 (ammonia) into nontoxic Urea o Ammonia is produced during amino acid breakdown • It also breaks down alcohol and drugs

Proteins are large molecules that have four levels of structure

• The primary structure The chains of amino acids that form the proteins • The secondary structure The twisting of the protein chain • The tertiary structure The coiling of the twisted protein chain • The quaternary structure The fitting together of two or more coiled, twisted protein chains. The secondary, tertiary and quaternary structures of the protein chain result from • Hydrogen bonds (shown in figure 3.14) and sulfur-sulfur bonds

The small intestine is a coiled tube that extends from

• The pyloric sphincter of the stomach to • The ileocecal junction where it joins the cecum of the large intestine

THE DEFECATION REFLEX

• The rectum distends and stimulates stretch receptors • This triggers a Parasympathetic reflex causing o Mass movement from descending colon o Relaxation of the internal anal sphincter o Voluntary relaxation of external anal sphincter o Defecation

When Glucose Stores Run Down

• The remaining glucose is saved for the nervous system • Other tissues switch to lipids (fatty acids)

In babies, some fat digestion takes place in the stomach with the enzyme

• This enzyme is the same as lingual lipase • It has minimal function in adults

Amino acids are carried to the liver where they may be:

• Used to form plasma proteins • Stored as lipids • Used for energy o If other energy sources are used up or o If amino acid levels are high • Converted to glucose

Bile is made up of:

• Water, Bile salts, Cholesterol

The absorptive state

• When digestive end products are being absorbed into the blood • These nutrients are used for energy and molecule production and stored for later use.\ This state occurs around 4 hours after eating. During this time • Nutrients from the G.I. Tract enter the blood This nutrient uptake is regulated by insulin

The postabsorptive state

• When stored nutrients are being used for energy and molecule production The postabsorptive state occurs several hours after eating, during the late morning, afternoon, evening. The goal of the body during this time is to: • Maintain normal blood glucose levels to brain o 90 - 100 mg/100ml blood