Human digestion _ch[1]._35
Transcript of Human digestion _ch[1]._35
Human Digestion -Ch. 35.1
Section Objectives:Interpret the different functions of the digestive system organs.
Outline the pathway food follows through the digestive tract.
Identify the role of enzymes in chemical digestion.
Human Digestion
This part of the life process of NUTRITION-> process by which an organism obtains and utilizes food
Overview: Food processing occurs in four stages
1. Ingestion: taking in food
2. Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells
3. Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules
4. Elimination: undigested material passes out of the digestive tract
Human Digestion~ a 2 part process that changes food into a form useable by the body cells
1. Mechanical digestion – physical breakdown of large pieces of food into smaller ones
2. Chemical digestion – hydrolysis – the splitting of large insoluble molecules in small, soluble molecules with the use of water and enzymes ( in other words; breaking complex molecules into simple ones)
The process of chemical digestion ( hydrolysis) is regulated by enzymes
Examples of chemical Digestion:
1. Carbohydrates+ water -> simple sugars (glucose for instance)
2. Proteins+ water -> amino acids 3. Lipids+ water -> 3 fatty acids +gylcerol
HUMAN DIGESTIVE SYSTEM
Human digestive tract = GI (gastrointestinal) Consists of a continuous one way food tube (mouth to anus)
HUMAN DIGESTIVE SYSTEM
1. Mouth: (oral cavity) ingests food
2. Teeth: function in mechanical breakdown of food, increases surface area of food for enzyme action
3.Tongue: acts as a plunger to push food back into the throat (pharynx) taste buds are located on the surface of the tongue
HUMAN DIGESTIVE SYSTEM
Salivary glands are located in the mouth Produce and secrete
salivary amylase which starts the chemical digestion of starch
Provides lubrication for the chewed food
Contains enzymes to kill harmful microbes
HUMAN DIGESTIVE SYSTEM 4. Pharynx: food is pushed by tongue to back of throat,
initiates swallowing – food is now in the form of a bolus Epiglottis: flap that prevents choking
5. Esophagus: muscular tube that moves food from mouth to the stomach by process of peristalsis: wave of muscular contractions that moves chewed food to stomach
HUMAN DIGESTIVE SYSTEM 6. Stomach: J-shaped,
sac-like , muscular organ that mechanically churns food into a liquid and begins chemical digestion of protein, lining secretes gastric juice, stomach empties in about 2-6hrs., food now liquid called chyme
HUMAN DIGESTIVE SYSTEM
Components of gastric juice: 1. water-solvent 2. mucus-lubrication 3. pepsin- protease
enzyme that begins chemical digestion of protein
4. hydrochloric acid (HCl) ph=2,activates pepsin
HUMAN DIGESTIVE SYSTEM
7. Small Intestine: the major organ of chemical digestion and nutrient absorption, long twisted tube with small diameter,
enzymes and fluids needed to complete chemical digestion come 3 separate sources: 1. intestine itself 2. pancreas-. Small intestine 3. liver-> gallbladder->small
intestine
Absorption 7. Small intestine: besides digestion being completed in the small
intestine, its other main function is absorption of the digested molecules into the blood
Villi: fingerlike projections that increase surface area of small intestine contain a network of capillaries for absorption of amino acids and simple sugars into blood, center contains lymph vessel called lacteal which absorbs fatty acids
Accessory organs
1. Pancreas: located near small intestine Produces juices,
enzymes, and fluids Produces sodium
bicarbonate that neutralizes HCl acid from stomach
Works best at neutral pH
Accessory organs
2. Liver: largest internal organ (has many functions outside digestion) Makes bile ~ bile NOT an
enzyme,) bile emulsifies lipids- breaks them into smaller droplets to increase the surface area for enzymes (lipases) to act on fats
3.Gallbladder: small storage sac for bile, carries bile to small intestine
HUMAN DIGESTIVE SYSTEM
8. Large Intestine: primarily a drying and storage organ. undigested and unabsorbed
material pass into LI through sphincter muscle
No digestion occurs in LI Functions:
1. reabsorption of water and salts
2. absorption of vitamins produced by bacteria that live in the LI
3. storage and elimination of fecal matter
9. Rectum: last part of the digestive system: feces are eliminated through the anus
Largeintestine(colon)
Smallintestine
Rectum
Anus
Endof smallintestine
Nutrientflow
Some Digestive Homeostasis Disorders 1.Constipation– person has uncomfortable or infrequent
bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)- may result from insufficient fiber in diet
2. Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration
3. Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain
4. acid reflux -backflow of stomach contents upward into esophagus
5. appendicitis- inflammation of appendix