6.2 - The alimentary canal

what is the alimentary canal

the continuous tube from mouth to anus

what is the digestive system

the alimentary canal with associated organs

what occurs in the mouth

ingestion of food and chewing (mastication

what is saliva secreted by and what does it do

secreted by salivary glands to lubricate food, and salivary amylase turns starch into maltose

name the all the teeth, how many there are of each, and what they do

four incisors - biting/cutting

two canines - conical for tearing

four premolars

six molars - crushing/grinding

what happens after chewing

tongue shapes food into bolus and pushes it into pharynx

how long is the oesophagus

20-25cm long

what are the two types of muscle in the oesophagus

circular muscle - muscle fibres in circle

longitudinal muscle - fibres along length of canal

how is food moved down the oesophagus and what is it lines with

muscular contractions behind the food in a wave like motion called perisalsis, lubricated by its mucus lining

how does mechanical digestion occur in the stomach

muscular contractions along wall with oblique muscles alongside the other two to churn food

what is food mixed with stomach juices called

chyme

how is gastric juice secreted

out of the gastric glans that are present in the stomachs mucosa lining

what is the composition of gastric juice

hydrochloric acid, mucus, and digestive enzymes

what is the pH of the gastric juice and how does the stomach protect from it

pH is 2-3 (acidic) so the mucus protects the stomach lining

what do the enzymes in the gastric juice do

turn pepsinogen into pepsin to break down proteins into shorter peptides

what is absorbed in through the stomach

alcohol and drugs like aspirin and caffeine

how does the stomach stop the contents from moving out

with contractions of the pyloric sphincter, after 2-8 hours contents are gradually passed through

how long is the small intestine

6-7m long, narrow tube

what are the three regions of the small intestine

duodenum - shortest section where most chemical digestion occurs

jejunum - middle section that absorbs carbohydrates and proteins

ileum - final section, absorbs B-12, bile salts, and remaining products

what liquids influence digestion in the small intestine and how are they secreted

pancreatic juice - secreted by pancreas through pancreatic duct

bile - produces by liver, stored in gallbladder, secreted via bile duct

intestinal juice - secreted by lining in the small intestine

what is the composition of pancreatic juice and what do they do

pancreatic amylase - breaks down starch to maltose

trypsin - splits proteins into peptides

pancreatic lipases - break down fats into fatty acids + glycerol

ribo/deoxyribonuclease - digests DNA/RNA

what does bile do

emulsifies fat into smaller droplets to increase surface area for lipases

what is the composition and function of the parts of intestinal juice

peptidase - peptides into amino acids

sucrase, lactase, maltase - turns sucrose, lactose, and maltose into glucose, fructose, and galactose

lipases - lipids into fatty acids + glycerol

how does mechanical digestion occur in the small intestine

segmentation - contraction of circular muscle to break up bolus and mix it with juices and bile

how is a large surface area for digestion in the small intestine achieved

long length

mucosa membrane has folds that extend inside (like uuuu)

villi project from musoca

microvilli project from villi

what is the structure of a villus

1mm long - covered by single layer of cells, have inner lymph capillary called lacteal that is surrounded by blood capillaries

how is absorption into villi enhanced

muscular contractions that bring villi into contact with all parts of small intestine contents

how does absorption occur

simple diffusion and active transport

how are amino acids and simple sugars absorbed

into blood capillaries via active transport

how are fatty acids and glycerol absorbed

diffuse into villi and recombine to form fats that enter lacteals

how are water soluble vitamins and water absorbed

diffuse into blood capillaries

where are substances diffused into the blood capillaries taken

taken in hepatic portal vein to liver

where are substances in lacteals taken

transported in lymph system and emptied into upper chest veins

how long is the large intestine

1.5m long but larger in diameter

what are the parts of the large intestine

caecum, colon, rectum, anus

what lines the large intestine

mucus

how long does it take for contents to move through the large intestine

18-24 hours

what happens in the large intestine

water is absorbed so contents become more solid

bacteria break down remaining organic compounds which are absorbed along with minerals

what is the composition of faeces

water, undigested food, bacteria, bile pigments, and cell fragments

is this excretion or elimination and what is the difference

it is elimination because excretion is the removal of metabolic wastes

what does the liver do

produces bile

what does the gall bladder do

stores bile

what does the appendix do

stores useful bacteria