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