Biology - Nutrition in Humans Flashcards
What are the processes of nutrition?
Feeding/ingestion: Food is taken into the body
Digestion: Large food molecules broken down to be absorbed into body cells
Absorption: Nutrients move from small intestines into bloodstream
Assimilation: Nutrients used by cells to provide energy or to make new cytoplasm for growth
Egestion: Undigested matter is removed from the body
The mouth and the buccal cavity
Physical digestion takes place.
- teeth break up food into smaller pieces (inc. SA:V)
- saliva flows into the buccal cavity via salivary ducts (tubes)
- salivary glands produce saliva containing salivary amylase (hydrolyses starch into maltose) and lysozyme (kills bacteria and microorganisms) and mucus that moisten and lubricate food
- muscular tongue mixes food with saliva, rolls it into compact mass bolus pushed to back of mouth to swallow
- taste buds identify and select suitable foods
What is the process of swallowing?
- voluntary
- food is pushed into pharynx 🡪 connects buccal cavity to oesophagus & larynx (voice-box)
- epiglottis (small flap) bent downwards by weight of the food, closes entrance to windpipe
- food passes through larynx to oesophagus
What is the oesophagus/gullet?
- narrow muscular tube 🡪 passes through the thorax (chest) and diaphragm to join stomach
- wall contains 2 layers of muscles: longitudinal muscles (outside), circular muscles (inside)
- food moves through peristalsis (which continues in stomach to the intestines)
What is peristalsis?
- rhythmic wavelike contractions that propel contents of the alimentary canal forward
- pair of antagonistic muscles which alternates in their contraction
- mixes food with digestive juices
What is the stomach?
- muscular organ, no absorption
- sphincter muscle at the end of oesophagus controls the entry of food into it
- gastric glands secrete gastric juice, contains mucus (protect stomach walls), proteases (inactive)
- hydrochloric acid - activates proteases, provides acidic environment for enzymes to work, stops action of salivary amylase and kills bacteria
What processes occur in the stomach?
- food is physically broken by churning of stomach muscular wall
- churning also mixes food with gastric juices, forming an acidic semi-liquid called chyme
- HCl denatures salivary amylase, activates pepsinogen to pepsin, provides acidic condition for pepsin, kills microorganisms in food
- protease digests proteins into short peptides (then hydrolysed into shorter peptide chains)
- food remains for about 3-4 hours
Chyme passes into the duodenum in small
amounts 🡪 controlled by pyloric sphincter
What is the small intestine?
- long coiled tube adapted for absorption of digested food
- lining of the walls contains glands that secrete digestive enzymes
- consists of duodenom (secretes intestinal juice, receives chyme from stomach and digestive juices from accessory organs), jejunum (where chemical digestion is completed and absorption begins) and ileum (much coiled portion where absorption also occurs)
- ileum is coiled and highly folded with villi, nutrients are absorbed into blood and transported to the liver via the hepatic portal vein to be assimilated
What are the accessory organs and their functions?
Liver:
- produces bile which is stored in the gall bladder and
released into duodenum via a bile duct
- bile speeds up fat digestion by breaking up fat
droplets (emulsification)
Pancreas:
- releases pancreatic juice (contains many digestive enzymes) into duodenum to neutralise acidic chyme
What does the intestinal juice in the small intestine do?
- Proteases digest the short peptides into amino acids
- Amylase hydrolyses starch to maltose
- Carbohydrases split disaccharides into monosaccharide
components
Sucrase (sucrose 🡪 glucose + fructose)
Maltases (maltose 🡪 glucose + glucose)
Lactases (lactose 🡪 glucose + galactose) - Lipases digest fats into glycerol and fatty acids
What processes occur in the small intestine?
- peristalsis moves the chyme from stomach towards the pyloric sphincter which controls the entry of chyme into the small intestine
- bile salts are produced by the liver and stored in the gall bladder before release into the duodenum via the bile duct for emulsification of fats:
- increases the surface area for lipase –> bile (greenish fluid) speeds up fat digestion
What is the large intestine?
- comprises of caecum (junction between small
intestine & colon), colon and rectum - no villi
- no digestion occurs
- appendix🡪 Attached to the caecum 🡪 no
specific function in humans - when undigested food passes through the caecum and first portion of the colon, water and minerals are absorbed 🡪 becomes solid or semi-solid 🡪 faeces
- Fibre in the faeces provides bulk for muscle contractions
- Faeces is eventually emptied into and stored temporarily in rectum before being passed out through the anus
What are the characteristics of the liver?
- located below diaphragm
- three blood vessels attached to the surface; hepatic portal vein, hepatic vein, hepatic artery
- produce and secrete bile containing bile salts that aid in emulsification
What are the characteristics of the gall bladder?
- attached to liver
- bile stored temporarily
- when contracting, bile flows via bile duct into the duodenum
What are the characteristics of the pancreas?
- connected to the duodenum by the pancreatic duct (which is joined by the bile duct)
- produces pancreatic juice (amylase, lipase, protease)
- secretes the hormones insulin and glucagon, which help regulate the blood sugar concentration in the body
