Digestive System

http://www.youtube.com/watch?v=0gY-zXsUYgs

Humans as HeterotrophsHetero=another Trophe= nutrition

As heterotrophs we cannot convert carbon therefore we ingest carbon in our food.

All of our cells require nutrition for;

1)Growth

2)Repair

3)Maintenance

Functions of the Digestive System

1. Break down of food into nutrients.

2. Nutrients absorbed in the body.

3. Transported throughout the circulatory system.

Nutrients in the cell can be used as a

source of energy

OR

Used for the synthesis of chemical compounds

Stages of the Digestive System

1. Ingestion

2. Digestion

3. Absorption

4. Egestion

1. Ingestion

Ingestion occurs when food enters the mouth.

It is mechanically broken down by teeth

1. Ingestion: Cont.

Chewing stimulates the release of saliva from the salivary organs.

Saliva contains a mixtures of water, mucus and enzymes.

1. Ingestion: Amylase

Enzyme that breaks starch down into simple sugars.

1. Ingestion: Bolus

Food that has been chewed and mixed with saliva becomes a bolus.

The epiglottis, a flap of skin directs food down the esophagus.

1. Ingestion: Peristalsis

When the bolus has entered the esophagus muscle contractions (peristalsis) move it towards the stomach.

2. Digestion:

Stomach

Digestion occurs initially in the stomach.

The stomach is J-shaped, it stores food, and has a capacity of 1.5 L

2. Digestion: Sphincters

Food enters and exits the stomach through sphincters.

Sphincters are muscles surrounding a tube-like structure

The bolus enters the stomach when the cardiac sphincter relaxes.

2. Digestion: Gastric Juice

The stomach contains gastric juice secreted by the stomach lining.

Gastric juice contains a mixture of:HCL (hydrochloric acid) EnzymesMucus

2. Digestion: Gastric Juice

HCLBreaks down fibres & Bacteria

MucusProtect stomach lining from HCL

If stomach lining is destroyed ulcers form.

Heliobacter pylori

2. Digestion

The stomach absorbs: Water Alcohol Some medications (Aspirin)

2. Digestion: Chyme

Chyme travels out of the stomach by the pyloric sphincter into the small intestine.

Chyme is a mixture of:WaterDigested foodGastric Juices

2. Digestion: Small

Intestine

After the pyloric sphincter chime enters the duodenum

Duodenum is first 25cm of the small intestine.

7m in length, 2.5m in diameter.

2. Digestion: Duodenum

Majority of digestion occurs here.

Secretions from pancreas and duodenum enter via a duct.

2.Digestion: Liver

Has four functions in digestion:

1.Synthesis

2.Breakdown

3.Detoxification

4.Storage

Synthesis

Produces bile which breaks down fats. Bile is stored in the gallbladder

1. Synthesis: Bile

Bile is an emulsifier (a compound used to mix immiscible substances)

This allows for the breakdown of fats and for travel through the digestive system.

1. Synthesis: Gallstones

Gallstones occur when too much bile or concentrated bile is produced in the gallbladder.

The bile will crystalize into gallstones blocking the gallbladder.

2. Breakdown

Process of removing Nitrogen group from Amino Acids to create urea.

2. Breakdown: Jaundice

When there is a blockage of the gallbladder Jaundice can occur (yellowing of the skin).

3. Detoxification

Removes toxins from the body including

AlcoholChemicals

4. Storage

Vitamins and carbohydrates are stored in the liver.

Pancreas

Increases the pH of chyme from 2.5 to 9 due to the production of sodium bicarbonate.

Secretes enzymes for digestion

Lipase (fats)Trypsin (proteins)

Small Intestine Secretes

Maltase (maltose - > glucose)

Peptidase (protein breakdown)

Duodenum (beginning), Jejunum (middle), Ileum (end).

Food & Enzymes

Carbohydrates -> Glucose (amylase & maltase)

Proteins -> Amino Acids (pepsin & peptidase)

Fats (triglycerides) -> Fatty Acids & Glycerol

(bile & lipase)

3. Absorption

The jejunum and ileum contain villi (finger like projections) which increase the surface area.

The villi help with absorption ofGlucoseAmino AcidsFatty AcidsGlycerol

3. Absorption

Once nutrient are absorbed through the villi they enter the blood stream and are dispersed throughout the body

Digestive System

3. Absorption: Large Intestine

Water absorptionBacteria living in colon releasing Vitamin K & B, also absorbed.

4. Egestion

Cellulose aids in the ejection of material from the bowels.

Lack of cellulose in the diet can lead to colon cancer.

Digestive System

The entire process takes 24-36 hours.

Homeostasis

The ability of the body to regulate according to the fluctuating internal and external environment

Digestion & Homeostasis

Nervous and hormonal system aid digestion before we eat.

Seeing, smelling and tasting food stimulates production of gastric secretions.

Digestion & Homeostasis Cont.

Swallowing stimulate the production of gastric juices.

Gastrin (hormone) stimulates the release of gastric juice before food arrives.

Digestion

Speed of Digestion:Large meals with digest quickly due to strong stomach contractions and faster emptying. Fatty meals slow down digestion due to a hormone response from the small intestine.

Homeostasis

Receptors in the body sense:Blood Sugar levelsBody TOxygen levelDisruption in homeostasis -> Signal to brain for correction

Homeostasis: Blood Sugar

Blood SugarConcentration crucial to well beingToo low body shuts down (coma)Eating increases blood sugar (glucose)

Homeostasis: Blood Sugar

Body releases insulin from pancreas to bring glucose inside cells.

Extra glucose taken by liver cells and convert to glycogen and stored.

Homeostasis: Blood Sugar

Decrease in blood sugar pancreas will be activate to release glucagon

Glucagon (hormone) will convert glycogen (in liver), back to glucose, which will be released into the blood.

normal glucose

normal glucose

high glucose

food

low glucose

insulin release (pancrea

s)

cells take up excess glucose, liver makes glycogen

glucagon

release (pancre

as)

glycogen release

as glucose (liver)