The Digestive System The Physiology

Function of the Digestive System 6 processes Ingestion: Propulsion Digestion Mechanical digestion Chemical digestion Absorption Defecation These processes occur more or less in order from start to finish (lucky for you!), although the different organs can carry out more than one of these functions

Ingestion Food must be placed in the mouth

Propulsion Moving food from one digestive organ to the next Swallowing Peristalsis Wave-like contraction and relaxation to move food through a tube

Digestion: Mechanical Mixing of food in the mouth Tongue and teeth! Mixing of food in the stomach Stomach churning Mixing of food in the small intestine Segmentation: moving of foodstuff back and forth across the organ walls

Digestion: Chemical Enzymes break down foodstuff Carbohydrates  simple sugars (monosaccharides) Proteins  amino acids Fats  fatty acids and glycerides

Absorption Digested foods must enter the blood or lymph vessels Active transport Passive transport

Defecation Elimination of indigestible substances from the body Feces (poo)

Here’s how we are going to play… From here on out, we are going to go through the passage of food, from mouth to anus, and will connect the functions back to those 6 processes on the previous slide Get ready!

The Mouth Predict: The mouth would perform which of the 6 functions? Ingestion That is the food’s first stop! Propulsion (aka peristalsis) We have to swallow to move the food to the next organ Wait….what is the next organ? The esophagus!  Mechanical digestion We masticate our food Means that we chew it and mix it with saliva using our tongue and teeth “I was distracted by the half-masticated cow rolling around in your wide-open trap!” --Miss Congeniality

The Mouth Once the food is masticated, it is called a bolus Chemical digestion Carbohydrates are broken down Saliva Saliva is secreted by salivary glands Contains an enzyme called salivary amylase Once the food is masticated, it is called a bolus

Esophagus Predict: What functions would the esophagus perform? Peristalsis There are layers of smooth muscle to help deliver the bolus to the stomach

Stomach Predict the functions Functions Peristalsis Has to get the food to the SI Mechanical digestion Your stomach churns to further break up the food Chemical digestion There are many enzymes that can help break down food Once the stomach has churned the food, it is called chyme http://www.youtube.com/watch?v=o18UycWRsaA

Small Intestine Predict the functions Functions Peristalsis Mechanical Digestion Segmentation: mixing food back and forth Predict the functions Functions Peristalsis Move the food along! Chemical digestion Break the macromolecues down further With the help of: Pancreas Digestive enzymes Liver/gall bladder Liver produces bile Bile is stored in the gall bladder Bile helps to break down fat Absorption Nutrients are absorbed so the body can use them Carbs, proteins, and fats are absorbed

Large Intestine Predict the functions Functions Chemical digestion There are no digestive enzymes in the LI, only bacteria Absorption Mostly absorb water Propulsion Moving it along!! Defecation Poo!

Interesting The bacteria in our large intestines are vital to our survival Symbiotic relationship (mutualism) If we ingest too many antibiotics from misuse or a prolonged infection, we can decrease the amount of good bacteria in our colon and can lead to an increase in the bad bacteria Can lead to colitis (inflammation of colon), constipation, irritable bowel syndrome Treatment? Fecal bacteriotherapy This means that feces from a healthy person is transplanted into the patient This will transfer that good bacteria into your system http://www.voanews.com/content/fecal-transplants-used-to-cure-intestinal-disorders/1723974.html YUM!

Let’s make a table ingestion propulsion Mechanical digestion Chemical digestion absorption defecation Mouth mouth Color code the different organs within our GI tract and list them under the correct function. The mouth has been done for you.