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Human Digestion -Ch. 21.1. 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.

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Human Digestion -Ch. 21.1

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Human Digestion -Ch. 21.1

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

  • Ingestion: taking in food

  • Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells

  • Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules

  • 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)


Mouth

  • Functions

    • mechanical digestion

      • teeth

        • break up food

    • chemical digestion (saliva)

      • amylase enzyme

        • digests starch

      • mucus

        • protects soft lining of digestive system

        • lubricates food for easier swallowing

      • buffers

        • neutralizes acid to prevent tooth decay

      • anti-bacterial chemicals

        • kill bacteria that enter mouth with food

All thatin spit!


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


mouth

break up food

digest starch

kill germs

moisten food


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


Swallowing (& not choking)

  • Epiglottis

    • flap of cartilage

    • closes trachea (windpipe) when swallowing

    • food travels down esophagus

  • Peristalsis

    • involuntary muscle contractions to move food along


Stomach

  • Functions

    • disinfect food

      • hydrochloric acid = pH 2

        • kills bacteria

    • food storage

      • can stretch to fit ~2L food

    • digests protein

      • pepsin enzyme

But the stomach is made out of protein!

What stops the stomach from digesting itself?

mucus secreted by stomach cells protects stomach lining


stomach

kills germs

break up food

digest proteins

store food

mouth

break up food

digest starch

kill germs

moisten food

sphincter

sphincter


Ulcers

Free of H. pylori

Colonized by H. pylori

  • Used to think ulcers were caused by stress

    • tried to control with antacids

  • Now know ulcers caused by bacterial infection of stomach

    • H. pylori bacteria

    • now cure with antibiotics

inflammation of stomach

inflammation of esophagus

H. pylori

cell damaging proteins

(VacA)

inflammatory proteins

(CagA)

cytokines

helper T cells

neutrophil cells

white blood cells


Small intestine

  • Functions

    • digestion

      • digest carbohydrates

        • amylase from pancreas

      • digest proteins

        • trypsin & chymotrypsin from pancreas

      • digest lipids (fats)

        • bile from liver & lipase from pancreas

    • absorption

      • nutrients move into body cells by:

        • diffusion

        • active transport

This iswhere all thework is done!


Absorption in Small Intestines

  • Absorption through villi & microvilli

    • finger-like projections

    • increases surface area for absorption

SMALL INTESTINES6 meters long,but can stretchto cover a tennis court


small intestines

breakdown food

- proteins

- starch

- fats

absorb nutrients

mouth

break up food

digest starch

kill germs

moisten food

stomach

kills germs

break up food

digest proteins

store food

liver

produces bile

- stored in gall bladder

break up fats

pancreas

produces enzymes to

digest proteins & starch


Pancreas ~ accessory organ

  • Produces digestive enzymes

    • digest proteins

      • trypsin, chymotrypsin

    • digest starch

      • amylase

    • digest lipids

      • lipase

  • Buffers

    • neutralizes acid from stomach

smallintestine

pancreas


pancreas

produces enzymes to

digest all foods

mouth

break up food

digest starch

kill germs

moisten food

stomach

kills germs

break up food

digest proteins

store food


Liver & Gall Bladder ~accessory organs

  • Produces bile

    • breaks up fats

    • gallbladder only stores bile

      • that’s why you can have your gall bladder removed

bile contains colors from old red blood cells collected in liver =

iron in RBC rusts & makes feces brown


liver

produces bile

- stored in gall bladder

break up fats

mouth

break up food

digest starch

kill germs

moisten food

stomach

kills germs

break up food

digest proteins

store food

pancreas

produces enzymes to

digest proteins & starch


Large intestines (colon)

  • Function

    • re-absorbs water

      • use ~9 liters of water every day in digestive juices

        • if don’t reabsorb water would die of dehydration

      • > 90% of water re-absorbed

        • not enough water re-absorbed

          • diarrhea

          • can be fatal!

        • too much water re-absorbed

          • constipation

      • reabsorb by diffusion


You’ve got company!

  • Living in the large intestine is a community of helpful bacteria

    • Escherichiacoli:E.coli

      • digest cellulose

        • digests fruits & vegetables

      • produce vitamins

        • vitamin K & B vitamins

      • BUT generate gases

        • by-product of bacterial metabolism

        • methane, hydrogen sulfide

        • STINKY!

PEE-YOO!


large intestines

absorb water

mouth

break up food

digest starch

kill germs

moisten food

stomach

kills germs

break up food

digest proteins

store food

liver

produces bile

- stored in gall bladder

break up fats

small intestines

breakdown food

- proteins

- starch

- fats

absorb nutrients

pancreas

produces enzymes to

digest proteins & carbs


Rectum

  • Last section of large intestines

    • eliminate feces through anus

    • what’s left over?

      • undigested materials

        • mainly cellulose from plants

        • called roughage or fiber

        • keeps everything moving & cleans out intestines

      • masses of bacteria

So don’t forget to wash your hands!


Appendix

Vestigial organ


SomeDigestive 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


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