Lecture 30

Digestion

• Nutrients: Any ingested material that takes part in normal metabolism
  
  • Carbohydrates (CHO), Proteins, Lipids (Fats), Vitamins, Minerals, H20
    
  • Carbohydrates proteins and lipids undergo enzymatic degredation in order to be absorbed in the intestine – places that secrete enzymes to do this are the salivary glands, intestinal mucosa (creates enzymes), stomach, pancreas
    
• Salivary Enzymes – role is not to do any great amount of digestion – made to extract nutrients from not typical foods
  
  • Salivary Alpha amylase – activated by chlorine but inactivated by pH of stomach - thus only works in mouth and esophagus – is turned off in stomach very shortly – breaks 1-4 alpha amyl bonds off carbohydrate – Produces maltose, maltotriose and alpha limit dextrons
    
  • Lingual lipase – will act on triglycerides breaking off 1-3 fatty acids - will stay active in the stomach – we use this for survival to extract energy from non regular sources
    
• Stomach secretions – role of stomach is for food storage and activation of food proteins- pH of stomach between 1-3 – achieves this by secreting HCl
  
  • ATP powered H+ ion in and K+ out
    
  • Bicarb is exchanged – chlorine comes in and bicarb goes out
    
  • At a ph of 1-3 enzymes cant function so they cant hurt you
    
  • Pepsinogen is secreted and changes pepsin in the stomach by HCl – extremely active – only active in pH of 1-3 – breaks proteins up into things that cant harm you
    
  • Newborn infants will secrete rennin and gastric lipase – gastric lipase will digest fat – rennin digests milk proteins
    
• Pancretatic enzymes – produced by the aceners of the pancreas – and are then kicked out into the lumen of the small intestine (specifically the duodenum) are mixed with food
  
  • Trypsin – is secreted as tripsinogen – is then activated – activated by a small intestine enzyme called enteropeptidase – created by the small intestine – tripsin cant be activated until it gets out into duodenum – tryprsin breaks only peptide bonds - Breaks down proteins disabled by stomach
    
  • Chymotrypsin is secreted as trypsinogen – will be activated by tripsin – will also change polypeptides to peptides
    
  • Elactase – is secreted as proelastase – activated by tripsin
    
  • Carboxypetidases A and B – (each protein has amine end and carboxy end) eats off amino acids one at a time from the carboxy end – elastase only works on protein elastin and releases peptides - protein digesters do digest each other
    
  • Pancreatic alpha amalyze is activated by chlorine – is identical to one in the mouth which was salivary alpha analyze – does and creates same things
    
  • Colipase – activated by tripsin – does not do any digesting itself – creates a interface – triglycerides come down and water comes down and salts – and this colipase forms an interface and forms an anchor for the lipase
    
  • Pancreatic lipase – secreted as an active enzyme – acts on triglycerides to produced 2 monogylcerides –
    
  • Phospholipase A2 – this is activated by trypsin – breaks down phospholipids – a phospholipids has 2 fatty acids and a phosphoro group – breaks off the number 2 prefatty acid – creates a 1 lysophospholipid
    
  • Cholesterol ester hydrolase – comes out already active – acts on cholester esthers – to produce cholesterol and free fatty acids
    
  • Ribonucelase – already activated – acts on RNA to form nucleotides
    
  • Deoxyribonuclease – already activated - works on DNA to form nucleotides – breaks down DNA and RNA
    

    **Trypsin very important to digestive system – if this gets interfered with its bad – soy beans interfere with it – it is an antitrypsin factor
    

• Small intestine hormones - not secreted – produced by enterocytes of small intestine – not secreted into lumen – put on surface of microvilli and they stay there – must come in contact with microvilli to interact
  
  • Enteropeptidase – main function is to activate trypsin
    
  • Aminopeptidase – eat from one end of a protein breaking amino acids from amine side
    
  • Carbodypeptidases – eat from other side "hug noses"
    
  • Dipeptidase- digests the dipeptides that the above 2 cant
    
  • Maltase – acts on maltose, malto triose and alphalimidextrose  to produce glucose – works on the malto and malto triose mainly
    
  • Lactase – acts on sugar lactose to produce glucose and galactose – once lactase disappears never comes back again
    
  • Sucrase and Alpha limidextranase – sucrose will digest sucrose – alpha limidextronase works on maltose, maltotriose and mostly alphalimidextrose – this is one protein with two different active sites on it
    
  • Carbohydrates you cant digests à Cellulose, lignin, non digestible carbohydrates, fiber, high fiber diet
    
  • Nucleotidase – will act on nucleptides to produce phosphic acid in the nucleoside – nuclease acts on nucleosides to produce a sugar and a base – these two may be one enzymes
    
  • Some enzymes produced by entoterocye are not presented at the surface of the microvilli – they have within their cytoplasm di/tri/ and tetra preptiedases – can break stuff down into amino acids
    

Absorption

• Carbohydrates and Proteins
  
  • Glucose, glactose and fructose – glucose and glactose share transport into mucosal cell – this is a cotransport with sodium – same transport found in the nephron – the first place blood goes is to liver – changes any fructose or glactose to glucose – glucose is only thing seen in circ system – some glactose and fructose pass by simple diffusion to the liver where they are changed
    
  • Pentose Sugars  - Ribose/ dioxyribose - are absorbed by passive diffusion – sugars flow freely in the blood
    
  • Aminio Acids - Are transported into cell by many active and facilitated transport – cotransported with Na+ but sometimes other amino acids – amino acids will enter – by passive and facilitated diffusion – amino acids flow freely
    
• Lipids and fats – follow pathway around body
  
  • Exogenous pathway – actually gets fat into body
    
    • Monoglycerides, glycerol, free fatty acids – these are found in the myicelle which is a droplet formed by biosalts, H20 and fat - this is micelle will be filled with products of digestion of fat - will bump up against enterocyte – fats will enter through simple passive diffusion – micelle can do the same again
      
    • Inside - smaller free fatty acids (less than 10-12 C)can pass directly into blood – but larger ones are resynthesized to triglyceride – these TG are mixed with phospholipids and cholesterol – what happens is TG and cholesterol inside phospholipids – these are making a single layer membrane encasing it – making a globule of fat inside a cell and that globule of fat is called a chylomicron
      
    • The cell puts markers at the surface of the chylomicron called apoproteins and these are E,C, and B48 – we find those at the surface of chylomicrons – chylomicrons enter into interstium by exocytosis - taken up by lacteals – these are the capillaries of the lymphatic system - the chylomicrons will follow lymph system back to blood circulation – once they get into blood circulation through the lymph system – they cycle through the system until endothelial binds to C - when bound will hold on tight and drain TG from chylomicron
      
    • Inside of the endothelial cell – these TG's will be broken down into free fatty acids and glycerol and then kicked back out into adipose tissue
      
    • Chylomicrons is released with out C – this is called chylomicron remnant (only E and B48) – this will be picked up by the liver however this is nothing more than a sack of cholesterol
      
  • Endogenous pathway – starts at the liver
    
    • The liver is going to create a droplet of fat very similar to a chylomicron and it will secret this filled with TG cholesterol and surrounded by phospholipids – is called VLDL (very low density lipo protein) this has apoprotein in it and these are GC, B100 (not 48)
      
    • The fate of the VLDC is the same as the chylomicron - it will circulate through the tissues until endothelial cells grabs to c and then will drain TG until sack of cholesterol and release without C – all cell left is E and B100 – called IDL (intermediate density lipoprotein)
      
    • Them 50% of the IDL will taken up by the liver, the other 50% lose the E and become LDL, LDL supplies cholesterol to cell – this is needed – we make hormones with cholesterol – this will go to tissues and passes cholesterol to cell whether it needs it or not – if there is a lot of LDL the excess cholesterol leaves back into blood stream as free cholesterol – LDL can eventually be taken up by the liver or it maybe eaten by a macrophage
      
    • HDL has one of the 3 high density lipoproteins at its surface – it has an A, I or AIV only one HDL will pick up free cholesterol from blood (this is good) – can either pass free cholesterol IDL or it can just be taken up by the liver
      
• Nucleic acids – bases and phosphates break down and are actively transported into broken down into mucosal cell