Chapter 8: Digestion

Structure and Functions of Digestive OrgansMacronutrients

Digestive Enzymes

What organisms need Digestion?Heterotrophs - rely on ingestion of organic molecules for production of energy

- consumers!!

Autotrophs - able to produce organic molecules themselves

- plants/producers!!

What are steps of Digestion?

Ingestion

Digestion

Absorption

Egestion

Assimilation

What are types of Digestion?

Digestion is both mechanical and chemical

Mechanical - chewing, mashing, softening, mixing ect

Chemical - acids and enzymes

How do we turn foods into energy?

How many parts of the digestive system can you name?

Primary Organs:

MouthPharynx

EsophagusStomach

Small IntestineLarge Intestine

Anus

Accessory Organs:

Salivary glandsPancreas

LiverGall Bladder

Mouth - Function

Teeth and Tongue - chewing and mixing of food

Saliva - softens food and contains enzymes

Food is formed into a ball

“bolus” to be swallowed

Mouth - Secretions

Salivary Glands - secret up to 2L of saliva a day

Saliva contains: Water - moisten food

Amylase - enzyme which breaks down starches

Pharynx

Area at back of mouth

- sorts food/liquids into the esophagus

- keeps food/liquid out of airways (nasal cavity and trachea)

Sorting is controlled by

a flap = EPIGLOTTIS

Esophagus

Connects pharynx to stomach by passing through middle of thorax(chest)

Moves food by wave-like contractions and relaxations of muscular walls = PERISTALSIS

Stomach - structure

J- shaped muscular pouch

Connected to esophagus by the LOWER ESOPHAGEAL SPHINCTER(LES)

small intestine by the PYLORIC SPHINCTER

Sphincters are ring-like muscles which contract to close the opening and relax to open.

They control movement of food through the parts of the digestive system

Stomach - functionStrong muscular contractions mix food with secretions to break-down molecules (mechanical and chemical digestion)

Gastric folds allow the stomach to stretch and move food along

Stomach - secretions

Gastric Fluid: up to 500mL can be produced during a meal

Hydrochloric Acid (HCl) -

creates acidic environment in the stomach (pH 1-2)

kills pathogens (bacteria, fungus) in food

Begins chemical digestion of proteins by denaturation

Activates pepsinogen into pepsin

Stomach - secretions

Pepsin - protein-digesting enzyme

is secreted as pepsinogen (inactive-form) and activated into pepsin by a low pH (HCl acid)

*This a safety measure to protect cells from having their proteins digested!

Mucus - lubricates food material

lines stomach to protect tissue from HCL and pepsin

Ulcers - when gastric fluid goes wrong

Small Intestine - function/strucureComplete the digestion of food by mixing with secretions from liver and pancreas (chemical digestion)

Begin absorption of nutrients into the bloodstream

Up to 7m in length

Divided into 3 sections:

DuodenumJejunumIleum

Small Intestine- structure

The inside of the small intestine is covered with millions of tiny finger-like projections called villi- each villus has an outer layer of of microvilli- The villi and microvilli increase surface area for

absorbing nutrients into the blood

Small intestine - Pancreas

The pancreas secretes Sodium Bicarbonate and many digestive enzymes into the small intestine.

Sodium Bicarbonate - neutralizes the acidic stomach contents when they enter the small intestine

Small intestine - Pancreas

Amylase - breakdown of carbohydrate molecules

Lipase - breakdown lipids (fats) into fatty acids and glycerol

Trypsinogen and Ereprsin - breakdown proteins into amino acids

Trypsingoen(inactive form) is converted to trypsin (active form) by enterokinases in the small intestine

Small intestine - Liver/Gall Bladder

The liver:

- Stores glycogen (form of glucose) and vitamins- Detoxifies harmful substances in the body

- Ex. alcohol, urea, hemoglobin

- Produces Bile which is stored in the Gallbladder until released into the small intestine through the bile duct

Bile contains:

Bile salts - emulsifies fat into small droplets

Pigments - gives feces their brown colour

Small intestine - Liver/Gall Bladder

Bile salts break down fat into smaller pieces by emulsification which is a type of physical digestion, NOT chemical digestion! (no chemical bonds are broken!)

Large Intestine- Structure

3 main parts: Colon and Rectum

Large Intestine - Function

2 parts: Colon and Rectum

Colon - resorbs water and some minerals/vitamins

indigestible material (such as fibre) accumulates and adds bulk for easier passing

Rectum - final storage site of waste materials

has sensory nerves to control bowel movements

material exits through the anus

Hormone Control of Digestion

Hormones are chemicals secreted into the blood stream to deliver a “message”

Gastrin - released from stomach when it extends with food

stimulates secretion of HCl acid by stomach

Hormone Control of Digestion

Secretin - released from small intestine when HCl acid enters from the stomach

Stimulates release of pancreatic secretions

Hormone Control of Digestion

Enterogastrone and Cholecystokinin(CCK)

- both released from small intestine in presence of high fat

Enterogastrone slows down intestinal movement to allow more time for digestion

CCK stimulates release of bile from gall bladder