The Digestive System How does it work? Human Anatomy The Digestive System How does it work?

Digestion Humans are Heterotrophs We have a gastrointestinal tract (GI) which is one way Peristalsis- Muscular contractions that push food through the GI tract. These contractions work in a rhythmic fashion. It is like squeezing a tube of toothpaste

The System The oral cavity or mouth- Contains teeth, tongue and salivary glands which secrete saliva Saliva contains amylase which breaks down STARCH. The tongue aides in chewing and mixing saliva with food, as well as helping you swallow. Chewing = Mechanical Digestion Saliva = Chemical Digestion 1 a- In pharynx

Digestive System

The System 2. Esophagus- Peristalsis moves food from the mouth to the stomach. Starch Digestion continues here, from the amylase in the mouth. 3. Stomach- A muscular sac in which food is mixed and liquefied. Gastric glands in the stomach lining secrete hydrochloric acid (HCL) and the enzyme gastric protease. HCL provides the proper Ph for gastric protease to begin digesting proteins. *Chemical Digestion*

Digestive System

The System 4. Small Intestine- A long, twisty tube in which most digestion occurs. It is lined with intestinal glands which secrete several different enzymes. These digest proteins, lipids and disaccharides. The liver, gall bladder and pancreas secrete substances into the small intestine. The liver: Produces bile which mechanically breaks down fat into tiny droplets. This is called emulsification and bile is an emulsifier. The gall bladder: Stores bile, small ducts take bile from the gall bladder into the small intestine The pancreas: Secretes pancreatic juice which contains protease, lipase and amylase

The System The end products of digestion including Amino acids (digested_________________) Fatty acids (digested_________________) Glycerol (digested____________________) Glucose (digested____________________) Are absorbed by the lining of the small intestine.

The System The surface area of the intestine is increased by its lining being folded into finger-like projections called villi (singular villus). Each villus contains a: Lacteal: a small lymphatic vessel which absorbs fatty acids and glycerol. They are transported in the lymph and added to blood. Capillaries: Absorb glucose and amino acids, transported to the liver for temporary storage and into the blood. Excess glucose in blood is removed and stored by the liver as glycogen; an insoluble polysaccharide.

The System When blood glucose levels drop, glycogen is broken down into glucose and returned to the blood. This is an adaptation of the body for maintenance of a constant blood glucose level.

The System 5. Large intestine- Undigested, indigestible foods and water enter. Water is re-absorbed from undigested food into capillaries (intestine wall). This conserves water. The remaining waste feces. Human nitrogenous waste: urea (in urine only)

Digestive System

The System 6. Rectum- Temporary storage of feces 7. Egestion through anus

Digestive Disorders Ulcer: An open sore in the lining of the stomach or intestines. Caused by excess HCL which erodes mucus. Bacteria also cause or contribute to ulcers. When severe enough, ulcers can eat through the blood vessels in the stomach lining, causing a bleeding ulcer. Constipation: Difficulty eliminating feces, due to too much H20 removed, reduction of peristalsis, or lack of roughage (fiber).

Digestive Disorders Diarrhea: Frequent elimination of watery feces due to lack of absorption in large intestine and increased peristalsis. Can lead to dehydration. Appendicitis: An inflammation of the appendix a small pouch located at the beginning of the large intestine. Gallstones: Small, hard cholesterol deposits that sometimes form in the gall bladder. They can enter the bile duct and block the flow of bile…… OUCH!