11:Digestive System

Nutrients

Chemical compounds that make up foods and which are essential to life

• carbohydrates, lipids, proteins, vitamins, minerals

organic compounds

large molecules that always contain the element carbon bonded to hydrogen

• carbohydrates, amino acids, proteins, lipids and nucleic acids

in-organic compounds

large molecules that don’t contain the element carbon bonded to hydrogen.

• water, oxygen, carbon dioxide, minerals

carbohydrates

used mainly as an energy for cellular respiration.

may also be used to form glycoproteins in the cell membrane and can also be stored in the liver and muscle cells as glycogen.

Monosaccharides (simple sugars)

single sugar molecules

• glucose, fructore, galactose, ribose

disaccharides

carbohydrates formed by joining two monosaccharides through a glycosidic linkage releasing a water molecule (are water soluble)

used for energy

• sucrose, maltose, lactose

polysaccharides

long chains of simple sugars

• starch: produced by most plants as energy storage.

• glycogen: produced by animals as energy storage (aka “stored glucose”)

• cellulose: makes up plant cell walls.

sugars

relatively small carbohydrate molecules

starch

a carbohydrate that is produced by most plants as energy storage

glycogen

a carbohydrate produced by animals as energy storage.

lipids (fats)

used mainly as an energy source and for energy storage. They contain as much energy as carbohydrates. can also be used for insulation, protection of organs, structural functions

fatty acids and glycerol

foundational building blocks of lipids commonly stored as triglycerides in the body for energy

triglycerides

one glycerol molecule attached to three fatty acid molecules

saturated fats

fatty acid molecule is “saturated” with hydrogen atoms

• red meat, butter, cream, hot chips

unsaturated fats

fatty acid molecules are not saturated with hydrogen atoms.

• avocado, olives, seeds

essential fatty acids

cannot be prepared within an organism by any known chemical pathways and therefore must be obtained from the diet.

• omega 3, omega 6

proteins

many functions:

• metabolic

• structural

• oxygen transport

• protection

• energy source

amino acids (monomers)

building block of protein, 20 different types, joined together by a peptide bond

peptides and polypeptides

10 or more amino acids bonded together

essential amino acids

nine amino acids that cannot be produced by the body and must therefore be obtained from the diet

vitamins

organic substances essential in small quantities for normal health. Most act as coenzymes which help to regulate metabolic processes.

Minerals

chemical elements rewuired by living organisms, in addition to the four elements C,H,N,O

digestive system

GI system, alimentary canal

A group of organs working together to convert food into energy, and the basic nutrients needed to feed the entire body.

basic functions of the digestive system

• ingestion of food and water

• mechanical digestion of food

• chemical digestion of food

• movement of food along the alimentary canal

• absorption of food and water into the blood and lymph

• elimnation of material that is not absorbed

digestive tract

alimentary canal or gastrointestinal tract

the pathway by which food enters the body and solid wastes are expelled.

accessory organs

organs that are not part of the digestive tract but aid in the digestive process

mouth

oral/buccal cavity

mechanical digestion by teeth, chemical digestion of starch by saliva.

salivary glands

three pairs of glands produce saliva, which dissolved food so it can be tasted. Saliva contains mucus that lubricates the mouth and food and holds food in a lump (bolus) for swallowing. It also contains the enzyme salivary amylase, which begins starch digestion.

pharynx

throat

by moving upwards and backwards, the tongue pushes food into the pharynx for swallowing.

oesophagus

carries food from the mouth to the stomach. it passes through the diaphragm into the abdominal cavity.

stomach

mechanical digestion by churning action; chemical digestion by pepsin, which begins protein digestion.

liver

produces bile, which is stored and concentrated in the gall bladder. Bile emulsifies lipids (breaks down)

gall bladder

stores bile and releases it into the small intestine, where the bile emulsifies lipids.

pancreas

produces pancreatic juice containing enzymes for digesting proteins, lipids and nucleic acids.

small intestine

about 6m long. Its lining secretes intestinal juice, which contains many enzymes. The internal surface is lined with villi for absorption of digested food.

large intestine

no chemical digestion, absorbs water and vitamins; stores faeces; defecation

rectum

final part of large intestine in which faeces are formed

anus

open surrounded by the anal sphincter, a muscle that can be voluntarily controlled.

digestion

process in which carbohydrate, protein and fat molecules are broken down to products small enough to be absorbed into the blood and into the cells.

mechanical digestion

physical breakdown of food particles and aims to break the food down into smaller pieces so that the total surface area increases. This allows more effective chemical digestion, as the chemicals can access more of the food.

chemical digestion

chemicals breakdown large complex molecules into smaller, simpler molecules. These smaller molecules are then small enough to be absorbed into the bloodstream.

ingestion

intake of food

bolus

ball of food and saliva mass

swallowing

tongue moves up and back → food is pushed to pharynx

saliva

secreted into oral cavity by three pairs of salivary glands, contains digestive enxyme of salivary amylase

salivary glands

3 glands secretes saliva that moistens and lubricates food.

salivary amylase

breaks down starch (carbohydrates-polysaccharides) into simple sugars (disaccharides and monosaccharides)

incisors

chisel shaped teeth that aids in biting and cutting (x4)

canines

conical shaoed teeth that are used in tearing (x2)

premolars

moderate crowns and rounded cusp shaped teeth that crush and grind food (x4)

molars

broad crowns and rounded cusp shaped teeth that crush and grind food

epiglottis

flap of tissue that covers the trachea when swallowing. Stops food from entering the trachea

mucus lining

protects stomach from acidic chyme and bacteria. Prevents nutrient transfer at this stage of the alimentary canal. also known as mucosa lining.

peristalsis

circular muscle behind bolus contracts and pushes bolus forward, and then the longitudinal muscles ahead of the bolus contracts shortening and widening the tube to receive the bolus.

rugae

series of ridges produced by folding of the organ wall

mucosa

internal lining of the stomach, specialised for the secretion of gastric juices which are secreted by gastric glands in the mucosa lining.

gastric juices

gastric juice is a highly acidic fluid produced by glands in the stomach lining, with approximately1.5-3 litres secreted daily to aid digestion. It consists primarily of HCl acid, pepsinogen (activated to pepsin for protein digestion), gastric lipase, and mucus. It breaks down food and acts as a defence against pathogens.

churning

waves of muscular contractions that move along the stomch wall (mechanical digestion)

chyme

a soupy liquid of partially digested food and stomach juices.

• contains HCl acid, mucus, and digestive enzymes

gastric protease (pepsin)

enzyme that works in very acidic solutions; needs stomach acid to work. Protease breaks down protein to make polypeptides and then later dipeptides and amino acids.

Hydrochloric acid

Allows gastric protease to work and kills bacteria that enters stomach

stomach mucus

protects stomach from acidic chyme and bacteria.

Prevents nutrient transfer at this stage of the alimentary canal.

pepsinogen

inactive form of the enzyme gastric protease. HCl activates pepsinogen, converting it into gastric protease (pepsin)

pyloric sphincter

ring of muscle which contracts to regulate food movement into small intestine.

duodenum

First part of the small intestine. Only 25 cm. extends from the bottom end of the stomach in a curve around the pancreas. Most of the chemical digestion occurs here before the chyme moves further along the small intestine.

jejunum

Middle section. 2.5 metres. The lining allows effective absorption of carbohydrates and proteins

ileum

Final part of small intestine. Vitamin B12, bile salts, and any remaining products of digestion are absorbed.

intestinal juice

Watery secretion released from the glands and mucous membrane lining of the small intestine. Contains many enzymes that complete digestion of carbohydrates, proteins and lipids.

• Peptidase to break down peptides into amino acids

• Sucrase, lactase and maltase to break down sucrose, lactose, and maltose, into monosaccharides glucose, fructose and galactose

  • Lipases to break down lipids into fatty acids and glycerol

duodenum mucus

Secreted by glands in the mucosa; alkaline mucus

• Neutralises hydrochloric acid

• Creates a suitable pH level for chemical digestion in small intestine

• Protects wall of duodenum

• Lubricates small intestine.

bile

Produced by liver, stored in and released by the gall bladder.

Liquid that physically breaks down fat into smaller units

bile salts

Emulsifies fats: breaks down fat into small droplets and does not contain digestive enzymes

pancreatic juice

Helps to neutralise the acid that has come with the material from the stomach and contains many of the enzymes involved in the digestion of food

• Pancreatic amylase breaks down starch into the disaccharide maltose

• Trypsin, which splits proteins into peptides

• Pancreatic lipases breaks down fats into fatty acids and glycerol

• Ribonuclease and deoxyribonuclease - enzymes that digest RNA and DNA.

amylase

breaks down starch/carbohydrates into monosaccharides (glucose)

protease

breaks down proteins/polypeptides into amino acids

lipase

breaks down fat into fatty acids and glycerol