Lose It--And It Finds Its Way Back

1. Humans have adipose tissue (fat cells) to store food reserves.
   1. The amount of storage can become a problem of too much (obesity) or too little (anorexia).
   2. Maintaining a certain weight is a long-term commitment.
2. Nutrition and digestion describe the range of processes that supply the body with its needs.

The Nature of Digestive Systems

1. Incomplete and Complete Systems
   
   1. An incomplete digestive system (for example, in a flatworm) has one opening.
      
   2. A complete digestive system is a tube with two openings allowing food to move in one direction through the lumen; it performs six  tasks:
      1. Ingestion food enters mouth
      2. Mechanical processing and motility is the breaking up, mixing, and transporting of food material.
      3. Secretion is the release of needed enzymes and hormones.
      4. Digestion is the chemical breakdown of food matter to molecules small enough to cross the gut lining.
      5. Absorption is the passage of digested nutrients into the blood and lymph.
      6. Elimination is the expulsion of undigested and unabsorbed residues at the end of the gut.
   
   
2. Correlations With Feeding Behavior
   1. The digestive system is an internal space or tube with specialized regions for food transport, processing, and storage.
   2. Regional specializations correlate with feeding behavior.
      1. Birds store meals in a stretchable crop and grind the food in a gizzard.

      

      1. Ruminants (for example, cows) can eat grass almost continuously and have multiple stomachs to digest cellulose.

      

Visual Overview of the Human Digestive System

1. The human digestive system is a tube with two openings.
   1. Stretched out, it would extend more than 20 feet.
   2. An epithelium lines all the surfaces facing the lumen.

    

2. The human digestive system has many specialized regions.
   1. Food enters through the mouth and proceeds through the esophagus to enter the gut.
   2. The gut starts at the stomach and extends through the small intestine, colon, and rectum, to the anus.
   3. Accessory glands include the salivary glands, liver (with gallbladder), and pancreas.

Into the Mouth, Down the Tube

1. Mechanical breakdown of food and its mixing with saliva begin in the mouth.
   1. Teeth chew the food.
      1. Each has an enamel coat, a dentine core, and an inner pulp.
      2. Incisors bite off chunks, canines tear, and premolars and molars grind food.

      

      
      
   2. Saliva (from salivary glands) contains salivary amylase to begin carbohydrate digestion, bicarbonate to neutralize acids, and mucins to lubricate.

    

2. The tongue pushes the ball of food into the pharynx where receptors initiate the swallowing reflex into the esophagus and then into the stomach; the epiglottis closes off the trachea to prevent choking.

Choking

CPR and Heimlich

How do you know if someone is choking and how do you help?

Most people who are choking will exhibit the universal sign of choking.  You should always seeks the person's consent to help by asking them if you can help, if it is a minor you should ask the parent or if no parent is around consent is implied.  Infants will not exhibit this sign, therefore you must recognize the infant is agitated, making funny breathing sounds, cannot cry etc.  Call 911 or EMS immediately, at anytime the person could become unconscious and their heart could stop beating.

 

 

How Do You Help Someone Who is Conscious and Choking?

• If they can make breath sounds, speak or cough, do nothing except encourage them to keep coughing.

• If you are sure the airway is completely blocked perform the Heimlich as described in the following pictures.

 

The Heimlich Maneuver for CHOKING
A choking victim can't speak or breathe and needs your help immediately. Follow these steps to help a choking victim:

1. From behind, wrap your arms around the victim's waist.
2. Make a fist and place the thumb side of your fist against the victim's upper abdomen, below the ribcage and above the navel.
3. Grasp your fist with your other hand and press into their upper abdomen with a quick upward thrust. Do not squeeze the ribcage; confine the force of the thrust to your hands.
4. Repeat until object is expelled.

UNCONSCIOUS VICTIM, OR WHEN RESCUER CAN'T REACH AROUND VICTIM:
Place the victim on back. Facing the victim, kneel astride the victim's hips. With one of your hands on top of the other, place the heel of your bottom hand on the upper abdomen below the rib cage and above the navel. Use your body weight to press into the victim's upper abdomen with a quick upward thrust. Repeat until object is expelled. If the Victim has not recovered, proceed with CPR.
The Victim should see a physician immediately after rescue.

Don't slap the victim's back. (This could make matters worse.)

The Heimlich Maneuver for CHOKING INFANTS A choking victim can't speak or breathe and needs your help immediately. Follow these steps to help a choking infant: Lay the child down, face up, on a firm surface and kneel or stand at the victim's feet, or hold infant on your lap facing away from you. Place the middle and index fingers of both your hands below his rib cage and above his navel. Press into the victim's upper abdomen with a quick upward thrust; do not squeeze the rib cage. Be very gentle. Repeat until object is expelled. If the Victim has not recovered, proceed with CPR. The Victim should see a physician immediately after rescue. Don't slap the victim's back. (This could make matters worse.)

The Heimlich Maneuver for CHOKING
When you choke, you can't speak or breathe and you need help immediately. Follow these steps to save yourself from choking:

1. Make a fist and place the thumb side of your fist against your upper abdomen, below the ribcage and above the navel.
2. Grasp your fist with your other hand and press into your upper abdomen with a quick upward thrust.
3. Repeat until object is expelled.

Alternatively, you can lean over a fixed horizontal object (table edge, chair, railing) and press your upper abdomen against the edge to produce a quick upward thrust. Repeat until object is expelled.

See a physician immediately after rescue.

Digestion in the Stomach and Small Intestine

1. The Stomach
   1. The stomach is a muscular sac that stores and mixes food, secretes substances that dissolve and degrade food, and controls the rate at which food enters the small intestine.
      
      

      The stomach is famous for its secretion of acid, but acid is only one of four major secretory products of the gastric epithelium, all of which are important either to the digestive process or to control of gastric function: Mucus: The most abundant epithelial cells are mucous cells, which cover the entire lumenal surface and extend down into the glands as "mucous neck cells". These cells secrete a bicarbonate-rich mucus that coats and lubricates the gastric surface, and serves an important role in protecting the epithelium from acid and other chemical insults.   Acid: Hydrochloric acid is secreted from parietal cells into the lumen where it establishes an extremely acidic environment. This acid is important for activation of pepsinogen and inactivation of ingested microorganisms such as bacteria.   Proteases: Pepsinogen, an inactive zymogen, is secreted into gastric juice from both mucous cells and chief cells. Once secreted, pepsinogen is activated by stomach acid into the active protease pepsin, which is largely responsible for the stomach's ability to initiate digestion of proteins. In young animals, chief cells also secrete chymosin (rennin), a protease that coagulates milk protein allowing it to be retained more than briefly in the stomach.   Hormones: The principle hormone secreted from the gastric epithelium is gastrin, a peptide that is important in control of acid secretion and gastric motility. A number of other enzymes are secreted by gastric epithelial cells. One secretory product of considerable importance in man is intrinsic factor, a glycoprotein secreted by parietal cells that is necessary for intestinal absorption of vitamin B12.

    

   Peristaltic contractions churn the chyme and keep the sphincter of the stomach's exit closed, but small amounts are released at regular intervals into the small intestine.

   
   
2. The Small Intestine

   
   
   

   1. The three regions are: duodenum, jejunum, and ileum.
   2. Secretions from the pancreas, liver, and gallbladder enter via a common duct.     
      
      
   3. Digestion is completed and most nutrients are absorbed in the small intestine.
      1. Trypsin and chymotrypsin digest proteins to peptide fragments.
      2. Carboxypeptidase and aminopeptidase degrade the fragments to amino acids.
      3. Bicarbonate from the pancreas buffers the acid from the stomach.
   
   
3. The Role of Bile in Fat Digestion

   Bile is a complex fluid containing water, electrolytes and a battery of organic molecules including bile acids, cholesterol, phospholipids and bilirubin that flows through the biliary tract into the small intestine. There are two fundamentally important functions of bile in all species:

   • Bile contains bile acids, which are critical for digestion and absorption of fats and fat-soluble vitamins in the small intestine.
   • Many waste products are eliminated from the body by secretion into bile and elimination in feces.

   Adult humans produce 400 to 800 ml of bile daily, and other animals proportionately similar amounts.

   The gall bladder stores and concentrates bile during the fasting state. Typically, bile is concentrated five-fold in the gall bladder by absorption of water and small electrolytes - virtually all of the the organic molecules are retained.

   Secretion into bile is a major route for eliminating cholesterol. Free cholesterol is virtually insoluble in aqueous solutions, but in bile, it is made soluble by bile acids and lipids like lethicin.

   Their amphipathic nature (that is, they contain both hydrophobic (lipid soluble) and polar (hydrophilic) faces) enables bile acids to carry out two important functions:

    

   • Emulsification of lipid aggregates: Bile acids have detergent action on particles of dietary fat which causes fat globules to break down or be emulsified into minute, microscopic droplets. Emulsification is not digestion per se, but is of importance because it greatly increases the surface area of fat, making it available for digestion by lipases, which cannot access the inside of lipid droplets.
      
   • Solubilization and transport of lipids in an aqueous environment: Bile acids are lipid carriers and are able to solubilize many lipids by forming micelles - aggregates of lipids such as fatty acids, cholesterol and monoglycerides - that remain suspended in water. Bile acids are also critical for transport and absorption of the fat-soluble vitamins
   
   
4. Controls Over Digestion
   
   1. Distention of the gut wall after a meal stimulates mechanoreceptors and their neurons, which respond with muscle action and enzyme secretion.
   2. Four gastrointestinal hormones play roles.
      1. Gastrin, produced by the stomach lining, stimulates secretion of acids into the stomach.
      2. Secretin, from the intestinal lining, stimulates insulin secretions from the pancreas.
      3. Cholecystokinin (CCK) enhances the actions of secretion and stimulates gallbladder contractions.
      4. GIP (glucose insulinotropic peptide), released in the presence of glucose and fat, stimulates insulin secretion also.

Absorption From the Small Intestine

1. Structure Speaks Volumes About Function
   1. The intestinal wall consists of several layers:

      
      
      

      1. The mucosa is the epithelial lining that faces the lumen of the gut; connective tissue underlies it.
      2. The submucosa contains blood and lymph vessels plus nerve networks.
      3. A muscle layer (longitudinal and circular) is covered with the outermost serosa.
   2. Absorptive surface area is increased by fingerlike projections of the intestinal lining called villi, the cells of which bear even smaller microvilli.
   
   
2. What Are the Absorption Mechanisms?

   
   
   

   1. Repeated segmentation contractions create an oscillating movement that mixes the food.
   2. Monosaccharides (glucose) and amino acids cross the gut lining by active transport and enter the bloodstream.
   3. The products of fat digestion are absorbed using a series of steps:

      

      1. First the products combine with bile salts to form micelles.
      2. Diffusion gradients favor movement of products out of the micelles and into the epithelial cells of the mucosa.
      3. Triglycerides combine to form chylomicrons that leave the cell by exocytosis to enter the lymph vessels mainly.

Disposition of Absorbed Organic Compounds

1. Nutrient molecules are shuffled and reshuffled once they have been absorbed.
   1. Shortly after a meal, the level of carbohydrates rises; some are converted to fat for storage, and others are converted to glycogen in the liver and muscle tissue.
   2. Between meals, glucose levels are maintained by breakdown of glycogen reserves in the liver and amino acids are converted to glucose; fatty acids from fats can be used directly by cells for energy.
2. The liver is a valuable organ for conversion of nutrients and detoxification of chemicals.

The Large Intestine

1. The large intestine (colon) stores and concentrates feces--undigested and unabsorbed material, water, and bacteria.
   1. The large intestine begins as a cup-shaped pouch at its junction with the small intestine (appendix attached here).
   2. It is draped across the lower abdomen and ends in a rectum (feces storage) that opens to the outside through the anus.
2. Colon Functioning
   1. Sodium is actively transported out of the colon and water follows.
   2. The slow movement of the materials through the colon favors growth of bacteria.
   3. The nervous system controls the progression of the material through the colon and its eventual expulsion at the anus.
   
   
3. Colon Malfunctioning
   1. Fiber ("bulk") in the diet is important in moving material in the feces through the large intestine at the proper speed.
   2. Delayed defecation can result in constipation.
   3. Fecal material lodged in the appendix can lead to the complications of appendicitis.
   4. Colon cancer is related to diet and the speed at which materials move through the colon.