Ch6. NUtrition

• Modes of nutrition

  1. Holozoic: take in complex food and digest inside body eg humans
  2. Saprophytic: break down food outside the body and absorb the nutrients into the body eg. Fungi
  3. Parasitic: live on or inside other organisms and obtain food from them eg. Tapeworms
• Nutrition process

  1. Ingestion
  2. Digestion
  3. Absorption
  4. Assimilation
  5. Egestion
• Alimentary canal

  1. Mouth cavity
  2. Pharynx
  3. Oesophagus
  4. Stomach
  5. Small intestine ( ileum and duodenum)
  6. Large intestine (caecum, appendix, colon, rectum)
  7. Anus
• ingestion

  • Mastication: process of chewing food
  • Teeth: incisors, canines, molars, premolars
  • Incisors: biting and cutting food (chisel-shaped with flat sharp edges, one root)
  • Canine: tearing flesh (pointed and curved, one root)
  • Premolars: crushing and grinding food (broad top and cusps, two root)
  • Molars: crushing and grinding food (broad top with cusps, two or three roots)
• Milk teeth: 2102/2102 (incisor,canine,premolars,molar) 20 teeth

  Permanent teeth: 2123/2123 32 teeth
• Structure of teeth

  1. Crown: enamel , dentine, pulp cavity
  2. Neck: nerve fibres, gums
  3. Root
• Enamel:

  • Outermost layer of crown
  • Non-living and made of calcium salts
  • Hardest tissue in our body, protects the tooth from wearing down
  • Replaced by cementum around the roots, which attaches the tooth to the jawbone through the periodontal membrane
• Dentine:

  • bone-like substance containing calcium salts, not as hard as enamel
  • Living tissue containing strands of cytoplasm
• Pulp cavity:

  • Contains living cells, blood vessels, and nerve fibres
  • Blood vessels supply oxygen and nutrients to the tooth and removes waste from it
  • Nerve fibres detect temperature and pressure
• Digestion:

  • Physical: breaking down food into smaller pieces eg. chewing, churning, emulsification by bile
  • Chemical: carbohydrates, lipases, proteases etc.
• Digestion in mouth

  -physical: chewing

  -chemical: salivary amylase
• saliva:

  -salivary amylase: break down starch into maltose

  -mucus: moisten and lubricate food

  -water: dissolve soluble substances
• stomach

  -physical: churning

  -chemical: pepsin
• gastric juice

  -pepsin: break down protein into peptides

  -hydrochloric acid: provide acidic medium for pepsin to work, kill most harmful microorganisms

  -mucus: protect stomach wall from being digested
• duodenum

  -physical: bile ( produced in liver, stored in gallbladder)

  -bile salts: emulsify lipids into small oil droplets

  -bile pigment: contain metabolic waste

  -sodium hydrogen carbonate: neutralise hydrochloric acid

  -pancreatic amylase, lipase, protease:break down peptides into amino acids
• ileum (intestinal juice)

  -no enzymes

  -epithelium of small intestine: protease, carbohydrase
• when we swallow food, the larynx rises so the epiglottis covers the opening to the trachea, preventing bolus from entering the trachea
• wall of alimentary canal:

  longitudinal muscle—>circular muscle—>connective tissues—>epithelium—>lumen
• peristalsis

  behind bolus: longitudinal muscles relax and circular muscles contract to make the lumen smaller

  in front of bolus: longitudinal muscles contract and circular muscles relax to make the lumen larger
• stomach

  cardiac sphincter: contracts to prevent food from flowing back into oesophagus

  pyloric sphincter: relaxes to release food into the duodenum, prevents overload and allows for time for digestion
• small intestine wall

  -long : for complete digestion and absorption of food

  -inner wall is highly folded to increase the surface area to increase rate of absorption

  -villi: small finger-like projections, has a lacteal surrounded by network of capillaries

  -epithelium: one-cell thick, cell membrane has large number of microvilli
• villi

  -finger-like projections: increase surface area for increased absorption of digested food

  -lacteal and network of capillaries: allow absorbed food molecules to be carried away rapidly, maintaining a steep concentration gradient of food molecules, increasing rate of diffusion of food molecules
• peristalsis brings digested food molecules into close contact with villi for absorption , and keeps a steep concentration gradient of food molecules to increase rate of diffusion
• epithelium is one-cell thick to shorten the diffusion distance of food molecules into the blood, increasing the rate of absorption
• abundance of mitochondria in epithelial of small intestine

  -to carry out more respiration to release more energy for active transport of digested food
• absorption of digested food into villi

  -water-soluble food molecules: through diffusion and active transport into capillaries

  -lipid-soluble food molecules: diffusion along the concentration gradient and recombining into lacteal
• Assimilation

  Transport of absorbed food

  -water-soluble food molecules: carried by blood to the liver through the hepatic portal vein, then to the heart through the hepatic vein and vena cava, then transported to other parts of the body through the aorta

  -lipid-soluble: carried by lymph to the lymph vessel, then enter the blood and are carried to the heart through the vena cava, then t the body through the aorta
• if remains of food pass through colon too slowly, more water is absorbed, resulting in hard faeces and constipation. if remains pass too quickly, more water remains in the faeces, leading to diarrhoea
• lactose intolerance:

  lack lactase to break down lactose, lactose remains in lumen, lowering the water potential of chyme. there is net movement of water into lumen by osmosis leading to a large amount of water into lumen, stimulating peristalsis. the time for chyme to stay inside small intestine decreases, so less water is absorbed, causing watery faeces
• fates of absorbed food

  glucose: broken down in respiration to release energy, excess is converted into glycogen in liver and muscles or lipids

  lipids: used to make cell membranes and hormones, act as energy reserve, excess is stored in adipose tissues around organs and under skin

  amino acids: used to make proteins for growth and repair, used to release energy, excess are broken down in liver through deamination
• liver

  -regulated blood glucose level

  -main site for storage of glycogen

  -converts carbohydrates and amino acids into lipids

  -break down excess amino acids ( amino groups become urea to be excreted in urine, other parts are converted into carbohydrates or lipids)

  -breakdown old red blood cells , stores iron

  -stores and produces vitamins

  -produces bile

  -detoxification( break down alcohol,drugs)
• Faeces

  -contain dietary fibre, bacteria, secretions, dead cells, water

  -brown because of bile pigments

  Egestion: anal sphincter relaxes and rectum muscles contract to push faeces out