G9 BIOLOGY: DIGESTION AND ABSORPTION

alimentary canal

long tube from mouth to anus, part of digestive system; walls contain muscles that contract and relax to let food pass through; each part of the canal has a role: digestion, absorption, egestion

mouth structure

teeth mechanically ingest food into small pieces, tongue mixes food with saliva which forms into a bolus; has epiglottis, a flap-like structure closing over trachea to prevent food from entering it, located in the pharynx

oesophagus

20 cm long; secretes mucus; uses peristalsis to move food from throat to stomach; sphincter guards entrance to stomach

oesophagus - peristalsis

muscle movement

oesophagus - sphincter

ring of muscle

stomach walls

strong, muscular; has goblet cells to secrete mucus; cells produce protease enzymes or hydrochloric acids

stomach muscles

contract and relax to churn food and mix w/ enzymes and mucus; mixture = chyme

stomach ability

stomach can store food for long duration; 1-2 hours, sphincter at the bottom of stomach opens and lets chyme into duodenum

small intestine location

5m long; part of alimentary canal between stomach and colon; ileum is near colon; some enzymes are secreted into the duodenum and made in the pancreas

pancreatic juice enzymes

amylase, protease, lipase; they dont work well in acid environments; contains sodium hydrogencarbonate that partially neutralizes the acid

bile

yellowish green, alkaline, watery liquid; helps neutralize acidic mixture from stomach; made in liver, stored in gallbladder; doesnt contain enzymes, does emulsification;

emulsification

breaks down large drops of fat into minuscule ones

bile pigment

made by hemoglobin; yellowish pigments made by liver when it breaks down old red blood cells; pigments are not needed, so theyre excreted

villi

semipermeable; microvilli increase the internal surface area allowing increased intestinal wall area available for absorption

villi: increased absorption area

useful because digested nutrients pass into the villi through diffusion, only effective at short distances

longitudinal section through a villus: thin epithelium

1 cell thick to increase diffusion rate

longitudinal section through a villus: lacteal

tiny lymphatic vessels absorb fatty acids & glycerol

blood capillary

absorbs glucose & amino acids

cells covering the villi make enzymes

they dont come out into the lumen of the small intestine, but stay close to the cells that make them

carbohydrase enzyme maltase

break down maltose to glucose

protease

break down polypeptides to amino acids

lipase

break down fats to fatty acids & glycerol

passive transport

monosaccharides, amino acids, some electrolytes (chloride ions): absorbed by diffusion

facilitated transport

fructose and some amino acids are absorbed by carrier ions (sodium)

active transport

glucose, amino acids, electrolytes (sodium) are reabsorbed into the blood

Na+

sodium

large intestine (colon and rectum)

wider tubes than duodenum and ileum

undigested food

travels through caecum, past the appendix, to the colon

colon

more water and minerals are absorbed

egestion (removing indigestible food)

roughage, bacteria, some dead cells inside alimentary canal form feces pass out at intervals in anus