Digestion, Absorption, and Metabolism

Anotações:

• atoms -> molecule -> cells -> tissues-> organs -> organ system -> organism 

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• The human body contains four types of tissue: muscle, nerve, epithelial, and connective. These tissues are organized in varying combinations into organs, which are discrete structures that perform specialized functions in the body 

1. nervous

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   • Brain, Spinal cord, and associated nerves
   • What it does: Responds to stimuli from the external and internal environments; conducts impulses to activate muscles and glands; integrates activities of other systems
2. respiratory

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   • lungs, trachea, and air passageways 
   • what it does; supplies the blood with oxygen and removes carbon dioxide 
3. urinary

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   • kidneys and their associated structures
   • what it does: eliminates wastes and regulates the balance of water, electrolytes and acid in the blood. 
4. reproductive

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   • testes, ovaries, and their associated structures 
   • what it does: produces offspring
5. cardiovascular

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   • heart and blood vessels
   • what it does: transports blood, which carries oxygen, nutrients and wastes 
6. lymphatic/immue

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   • lymph and lymph structures, white blood cells
   • what it does: defends against foreign invaders: picks up fluid leaked from blood vessels; transports fat- soluble nutrients 
7. muscular

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   • skeletal muscles 
   • what it does: provide movement and structure
8. skeletal

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   • bones and joints 
   • what it does: protects and supports the body: provides a framework for the muscles to use for movement 
9. endocrine

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   • pituitary, adrenal, thyroid, pancreas and other ductless glands
   • what it does; secretes hormones that regulate processes such as growth, reproduction and nutrient use
10. integumentary

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    • skin, nails, hair, and sweat glands
    • what it does: covers and protects the body; helps control body temperature 
11. digestive

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    • mouth, pharynx, esophagus, stomach, intestines, pancreas, liver and gall bladder
    • Ingest and digests food; absorbs nutrients into the blood; eliminates unabsorbed food residues

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• it has two functions: digestion and absoption. 
• digestion: the process of breaking food into components small enough to be absorbed into the body
• absorption: the process of taking substances into the interior of the body. 

1. gastrointestinal tract (GI tract)

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   • a hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. 
   1. mouth

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      • chews food and mixes it with saliva then moves to salivary galnds
   2. salivary glands

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      • produces saliva, which contains a starch-digesting hormone
   3. pharynx

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      • swallows chewed food mixed with saliva
   4. esophagus

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      • moves food to the stomach
   5. stomach

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      • churns and mixes food; secretes acid and a protein-digesting enzyme
   6. liver

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      • makes bile, which aids in digestion and absorption of fat. 
   7. pancreas

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      • releases bicarbonate to neutralize intestinal contents; produces enzymes that digest carbohydrate, protein and fat. 
   8. gallbladder

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      • stores bile and relaeases it into the small intestine when needed
   9. small intestine

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      • completes digestion; absorbs nutrients into blood or lymph
   10. large intestine

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       • absorbs water and some vitamins and minerals; home to intestinal bacteria; passes waste material- includes the colon and rectum
   11. anus

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       • opens to allow waste to leave the body. 
2. structure of the gut wall

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   • contains four layers of tissue. lining the lumen is the mucosa, a layer of mucosal cells that serves as a protective layer and is responsible for the absorption of the end products of digestion. 
   • surrounding the mucosa is a layer of connective tissue containing nerves and blood vessels. this layer provides support, delivers nutrients to the mucosa and provides the nerve signals that control secretions and muscle contractions. 
   • layers of smooth muscle surround the connective tissue and mixes food, breaks it into smaller particles and propels it through the digestive tract.
   • the final, external layer is also made up of connective tissue and provides support and protection
3. digestive secretions

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   • digestion inside the lumen of the GI tract is aided by digestive secretions. One of these secretions is mucus, a viscous material produced by the cells in the mucosal lining in the gut.  Mucus moistens, lubricates, and protects the digestive tract. 
   1. enzymes

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      •  another component of digestive system secretions, are protein molecules that speed up chemical reactions without themselves being consumed or changed by the reactions
      • In digestion, enzymes accelerate the breakdown of nutrients. Different enzymes are needed for the breakdown of different nutrients.
4. barrier function

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   • the protective rile that the gastrointestinal cells have in limiting the absorption of harmful substances and disease-causing organisms. 
   •     Phagocytes – first immune response, targets invaders -       Lymphocytes – produce and create antibodies
   1. antigen

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      • a foreign substance (almost always a protein) that, when introduces into the body, stimulates an immune response.  
   2. anti bodies

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      • proteins produced by cells of the immune system that destroy of inactivate foreign substances in the body. 

1. salivary amylase

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   • found in the mouth: breaks starch (a larger carb molecule) into smaller carbohydrate molecules 
2. rennin

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   • found in the stomach: causes the milk protein casein to curdle
3. pepsin

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   • breaks proteins into polypeptides and amino acids
4. trypsin

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   • found in the pancreas: breaks proteins and polypeptides into shorter polypeptides
5. chymotrypsin

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   • Breaks proteins and polypeptides into shorter polypeptides.
6. carboxypeptidase

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   • Breaks polypeptides into amino acids.
7. Pancreatic lipase

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   • Breaks triglycerides into monoglycerides, fatty acids, and glycerol.
8. pancreatic amylase

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   • Breaks starch into shorter glucose chains and maltose.
9. Carboxypeptidase, aminopeptidase, and dipeptidase

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   • found in the small intestine: breaks polypeptides into amino acids
10. lipase

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    • breaks monoglycerides into fatty acids and glycerol
11. sucrase

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    • breaks sucrose into glucose and fructose 
12. lactase

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    • breaks lactose into glucose and galactose 
13. maltase

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    • breaks maltose into glucose
14. dextrinase

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    • breaks short chains of glucose into individual glucose molecules 

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• nerve signals help regulate the GI tract. The sight and smell of food, as well as the presence of food in the gut, stimulate nerves throughout the GI tract. 
• Nerve signals cause muscle contractions that churn, mix, and propel food through the gut at a rate that allows  for optimal absorption of nutrients, 
• the nerves can also communicate with the brains so digestive activity can be coordinated with other body needs 

1. hormones

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   • produced both by cells lining the dddigestive tract and by a number of accessory organs. 
   •  Chemical messengers that are produced in one location, released into the blood, and elicit responses at other locations in the body.
   1. Gastrin

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      • comes from the stomach mucosa: it stimulate the secretion of HCL and pepsinogen by gastric glands in the stomach and increases gastric motility and emptying 
   2. somatostatin

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      • comes from the stomach and duodenal mucosa: it inhibits the following stomach secretion, motility, and emptying, pancreatic secretion, absorption in the small intestine; gallbladder contraction and bile release
   3. secretin

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      • comes from the duodenal mucosa\; it inhibits gastric secretion and motility; increase output of water and bicarbonate from the pancreas' increase bile output from the liver
   4. cholecystokinin (CCK)

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      • stimulates contraction of the gallbladder to expel bile; increase output of enzyme-rich pancreatic juice. 
   5. gastric inhibitory peptide

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      • inhibits gastric secretion and motility.