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Chapter 5: Nutrition - Coggle Diagram

- - - - Transports absorbed water-soluble foods (sugars and amino acids) from the ileum to the liver in nutrient-rich but deoxygenated blood
      - Blood capillaries that supply the small intestine unite to form this vein
      - What happens to the absorbed sugar in the liver?
        
        Most of the sugars are converted to glycogen and stored
        
        Glucose is transported by the hepatic vein to different parts of the body
    - - Transports deoxygenated, nutrient-poor blood with waste products away from the liver
    - - Transports oxygenated but nutrient-poor blood from the aorta to the liver
  - - - Excess glucose is converted back into glycogen and stored in the liver
      - The glycogen is converted back into glucose when the body needs energy or if the blood sugar level is low
      - Further excess glucose is stored as fats in the adipose tissue
      - Also used in cellular respiration
    - - Partially stored in the adipose tissue
      - Used in the synthesis of the cell membrane
      - Used in respiration when glucose and glycogen is used up
      - Fats stored under the skin and around organs act as energy stores and insulation
    - - Used in the synthesis of proteins, enzymes and hormones
      - Used for growth and development
      - Excess amino acids are not stored in the body, but broken down and deaminated in the liver to form urea and glucose
  - - - High (after meals)
        
        If the blood glucose level rises above a set point, the pancreas secretes insulin
        
        Insulin stimulates the liver to convert excess glucose into insoluble glycogen which is stored
        
        Insulin ensures the entry of glucose into body cells
        
        Insulin promotes the synthesis of fatty acids from glycogen and glucose in the liver
        
        Thus, blood glucose levels fall
      - Low (after exercise)
        
        If blood glucose levels fall below a set point, the pancreas secretes glucagon
        
        Glucagon stimulates the liver to convert glycogen to glucose which enters the blood
        
        Glucagon converts excess amino acids into glucose
    - - Emulsifies fats
      - Assists in fat digestion
    - - Haemoglobin from destroyed red blood cells in the spleen is broken down, and the iron ion (Fe2+) is stored in the liver
      - The protein component of haemoglobin is converted to bile pigments
      - The spleen acts as a blood filter to remove old/damaged red blood cells and to fight off infections
    - - Removal of the amino groups (NH2) from excess amino acids and converted into urea, and excreted in kidneys as urine
      - The carbon component of amino acids is converted in glucose in the liver
    - - Synthesis of proteins (albumins, globulins, fibrinogen) from amino acids
    - - Removal or conversion of harmful substances in blood into harmless substances
      - Alcohol into aldehydes by alcohol dehydrogenase enzyme
- - - - Amylase
      - Lipase
      - Proteases
    - - Insulin
      - Glucagon
- - - - These 2 layers of muscles cause rhythmic, wave-like contractions of the gut walls, known as peristalsis.
  - - - When the circular muscles contract, the longitudunal muscles relax
        
        The wall of the gut constricts, becoming narrower and longer
        
        Food in the gut is squeezed or pushed forward
      - When the longitudunal muscles contract, the circular muscles relax
        
        The wall of the gut dilates, becoming wider and shorter
        
        This widens the lumen for the food to enter
- - - - In the mouth (chewing of food)
      - In the stomach (churning breaks up the food particles and mixing with digestive enzymes)
  - - - Breaking down of large molecules in food, like proteins, starch, and fats into smaller soluble molecules which can be absorbed
      - Involves hydrolytic reactions catalysed by digestive enzymes
    - - Food in the mouth stimulates the salivary glands to secrete saliva
      - Saliva is mixed with the food
      - Mucin in saliva helps to soften the food
      - Saliva contains an enzyme called salivary amylase, which digests starch to maltose
      - The pH of saliva is neutral (around pH7 - salivary amylase is active at)
      - Chewing breaks the food up into smaller pieces
      - Increases the surface area : volume ratio for salivary amylase to work on
      - The tongue rolls the food into small, slippery, round masses or boli (bolus)
    - - The boli/bolus are swallowed and pass down the oesophagus via the pharynx
      - Peristalsis in the walls of the oesophagus pushes each bolus of food down into the stomach
      - Gravity also helps the food to pass down the oesophagus
    - - Food passes into the stomach
      - The presence of food in the stomach stimulates the gastric glands to secrete gastric juice into the stomach cavity
      - Peristalsis in the stomach walls churns and breaks the food up, mixing the food well with gastric juice
      - Gastric juice is a dilute solution of hydrochloric acid (about pH 2), and 2 enzymes - pepsin and rennin
      - The dilute hydrochloric acid
        
        Stops the action of the salivary amylase by denaturing it
        
        Changes the inactive forms of the enzymes - pepsinogen and prorennin, in the gastric juice, into the active forms, pepsin and rennin
        
        Provides an acidic medium suitable for the action of gastric enzymes
        
        Kills certain potentially harmful microorganisms in food
      - The proteases - pepsin and rennin, act on proteins
        
        Pepsin digests proteins into polypeptides or peptones
        
        Rennin clots or curdles milk proteins, by converting the soluble protein caesinogen into soluble caesin
        
        This is necessary because milk proteins would pass through the duodenum as easily as water and would not be digested by pepsin
        
        Insoluble caesin would remain long enough in the stomach to be digested properly by pepsin
      - Food normally remains in the stomach for about 3-4 hours
      - The partially digested food becomes liquefied, forming chyme
      - Chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes and opens
    - - Chyme enters the small intestine
      - Chyme stimulates...
        
        Intestinal glands to secrete intestinal juice
        
        Pancreas to secrete pancreatic juice, which passes through the pancreatic duct into the duodenum
        
        Gall bladder to release bile, which does not contain any enzymes, passing through the bile duct into the duodenum
        
        All 3 fluids are alkaline
        
        The alkalis neutralises the acidic chyme, providing a suitable alkaline medium for the action of pancreatic and intestinal enzymes
      - Pancreatic juice contains...
        
        Amylase which digests starch into maltose
        
        Trypsin which digests proteins into polypeptides
        
        Trypsinogen needs to be activated by the enterokinase enzyme found in the intestinal juices
        
        Lipase which digests fats into glycerols and fatty acids
      - Intestinal juice contains...
        
        Enterokinase which activates trypsinogen
        
        Disaccharidases (maltase, sucrase, lactase) which digests disaccharides into monosaccharides
        
        Peptidase and erepsin which digest polypeptides into amino acids
        
        Lipase which digests fats into glycerols and fatty acids
      - What does bile do?
        
        In the small intestine, bile salts emulsify fats
        
        They lower the surface tension of the fats, reducing the attractive forces between the fat molecules
        
        This causes the fats to break up into tiny fat droplets suspended in water, forming an emulsion
        
        This is just a physical break-up, and no chemical digestion of fat molecules has occurred yet
        
        Emulsification increases the surface area : volume ratio of fats, speeding up their digestion by lipase
        
        Emulsified fats are digested by lipases from the pancreatic and intestinal juices into fatty acids and glycerol
        
        Digested fats - fatty acids and glycerol, can pass through the cell membrane of villi cells in the ileum
        
        Fat molecules are formed again and transported by exocytosis, as chylomicrons, out of the cells into the lacteals of the villi in the ileum
      - Adaptations
        
        Length
        
        Longest part of the alimentary canal
        
        Internal surface area
        
        Internal walls are folded to increase surface area for absorption
        
        Villi
        
        Further increases surface area for absorption
        
        Microvilli
        
        Villus covered with epithelial cells
        
        Plasma membrane of each cell has minute finger-like projections to further increase surface area
        
        Movement
        
        Villi move back and forth independently
        
        Motion is faster after meals
        
        Absorption rate increases
        
        Membrane
        
        Absorption across a thin membrane (epithelium is 1-cell thick)
        
        Either by diffusion or active transport
        
        Capillary network
        
        Dense capillary network close to epithelium
        
        Carry away absorbed food particles quickly
        
        Maintains a steep concentration gradient between ileum and blood capillaries to aid diffusion
      - Absorption of Nutrients
        
        Amino acids and simple sugars mainly use active transport and diffusion to the capillaries and the hepatic portal vein, leading to the liver
        
        Fatty acids and glycerols are absorbed into the lacteal to be transported to the lymphatic system
        
        Blood capillaries network
        
        Helps to transport amino acids and glucose to the body
        
        Lacteals/lymphatic capillaries
        
        Help to transport fats to the body
        
        How are nutrients absorbed in the small/large intestines?
        
        Diffusion
        
        Glucose and amino acids diffuse into the blood capillaries
        
        Glycerols and fatty acids diffuse into the epithelium, combining to form minute fat globules which then enter the lymphatic capillary
        
        Active Transport
        
        Glucose and amino acids are absorbed by active transport
        
        Thus, intestinal cells need to be equipped with many mitochondria
        
        What happens to the undigested and unabsorbed matter?
        
        They are stored temporarily in the rectum and later discharged as faeces through the anus
        
        The discharging of faeces from the body is known as egestion