Digestive System

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Anonymous
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15426
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Digestive System
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2010-04-21 03:27:45
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HAP II
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HAP II DIGESTIVE SYSTEM
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  1. How does Breakdown occur in the Digestive System
    • Ingestion put food in
    • Mastication Chewing
    • Propulsion & Mixing peristalsis and segmentation
    • Digestion enzymatic breakdown of food- secretion of enzymes, acids, buffers
    • Absorption of nutrients, vitamins, and electrolytes across the gut wall
    • Compaction of waste material into feces
    • Elimination excretion of solid waste
  2. The Lining of the Digestive Tract plays a defensive role, protects against?
    1) corrosive effect of acids

    2) Protects against abrasion

    3) pathogens: pH of 1-3; Peyer's patches in ileum
  3. What is included in the Accessory Organs of the digestive tract?
    1) Salivary glands

    2) Liver

    3) Gall bladder

    4) Pancreas
  4. Four Major layers of the GI Tract
    1) Internal Mucosa (Innermost layer)

    2) Submucosa

    3) Muscularis Externa

    4) Serosa
  5. WHat goes on within the Internal Mucosa?
    innermost layer

    • has MUCOUS EPITHELIUM: Goblet cells
    • has Lamina propria
    • Muscularis mucosa
  6. What occurs within the submucosa?
    made of thick connective tissue

    contains nerves, blood vessels, small glands

    nerves of this layer form the submucosal plexus- A parasympathetic ganglionic plexus; some sympathetic input too

    exocrine glands that secrete buffers and enzymes
  7. Whats important of the Muscular Externa?
    2 layers of muscle; myenteric plexus lies between (has parasympathetic and symp response)

    • (inner layer- circular smooth muscle)
    • (outer layer - longitudinal muscle)
  8. Intramural Plexus? What consists of it? WHy is it important?
    The intramural Plexus consists of the Submucosal and Myenteric PLexus.

    Important in the control of movement and secretion!!!
  9. Serosa? which of the 4 layers? IMportance??
    Serosa= Visceral Peritoneum= ADVENTITIA

    formed of serous membrane and loose connective tissue
  10. Importance of Mesenteries in the stomach
    Mesenteries is a double layered membrane firmed by the visceral and parietal peritoneum.

    Mesenteries provide a route for blood vessels, nerves, and lymphatics.

    7 liters a day of serous fluid is secreted by peritoneal lining to lubricate the peritoneum
  11. Importance of Smooth Muscle in the Digestive Tract
    Found throughout the GI tract

    IMportant in movement of the food through peristalsis, and mechanical breakdown

    shorter than skeletal muscle

    single nucleus, centrally within the cell

    actin and myosin are present, but the are not arranged in sarcomeres- therefore NO striations

    muscle fibers twist like corkscrew

    Ca++ triggers the contraction, as in skeletal and cardiac muscle

    Most of the Ca++ enters through the extracellular fluid
  12. what does plasticity of smooth muscle mean??
    Smooth muscle can function over a wide range of lengths- this is plasticity.

    a "stretched" muscle adapts and can still contract

    this stretch is difference from cardiac and skeletal- plasticity is important for digestive organs bc they undergo volume changes
  13. Where are the pacemaker cells located? What are they?
    Located within the muscularis mucosa and the muscularis externa

    Pacemaker cells "pacesetter cells" depolarize spontaneously
  14. Deglutition?
    Swallowing

    moves the food from the oral cavity to the esophagus
  15. Segmental contractions?
    Mixing contractions that occur in the small intestine
  16. Functions of Secretions?
    Secretions serve to lubricate, liquefy, and digest the food.

    Secretions include:

    • 1) Mucus- which is secreted through the food tube
    • 2) WATER
    • 3) enzymes
  17. Propulsion vs. Perstalsis
    Propulsion- takes about 24-36 hrs to move the food the entire length of the food tube.

    Peristalsis- method of which food is moved through the tube
  18. Methods of Peristalsis
    Peristalsis is stimulated by chemical Ach or physical actions, stretch.

    Local peristalsis is stimulated by sensory receptors in wall of GI tract (myenteric reflexes)

    1) CIrcular Contractions: pushes the food forward

    Stretch receptors trigger relaxation ahead to allow the food to move forward.

    2) Longitudinal Muscles- contract and shorten the tube (behind)
  19. What is common stimulus for GI tract?
    STRETCH

    Stretch before a sphincter---------> Relaxation up ahead

    Stretch after a sphincter--------------> Contract the sphincter behind it
  20. Where does Segmentation occur? WHat is Segmentation?
    Occurs in the small intestine

    Churning of the food assure a thorough mixing of the contents

    NO NET DIRECTIONAL MOVEMENT IN SEGMENTATION

    accomplished by circular muscles of the muscularis externa
  21. Function of Secretions within the GI Tract?
    Mucus is secreted and present throughout the entire tract

    lubricates the food and helps protect the lining of the tube from abrasion and acidity

    large amount of water is added to liquify the food

    water moves into the GI tract by osmosis

    Enzymes are secreted in the:

    Mouth, stomach, and pancreas
  22. Digestion: What happens?
    • Breakdown into small, absorbable fragments
    • -Mechanical: mastication
    • -Enzymatic- uses enzymes; occurs mostly in small intestines

    • carbohydrates----> monosaccharides
    • proteins-------------> amino acids
    • lipids------------------> glycerol and fatty acids
  23. Types of Absorptions?
    (Four processes)
    1) Simple DIffusion: Movement from [high} to [low}

    2) Facilitated Diffusion: Involves a carrier protein; still passive

    3) Active Transport: ATP used; moves from [low] to [high]

    4) Cotransport: 2 molecules are transported together in the same direction
  24. How are the nutrients transported?
    1) Circulatory system: amino acids and monosaccharides

    2) Lacteals: fatty acids and lipids
  25. Oral Cavity: Functions and what it consists of...
    Functions:

    1) analysis of material before swallowing

    2) mastication: carried out by teeth, tongue, and parietal surface

    3) lubrication: mucus and salivary secretions

    4) digestion: of carbs by amylase

    CONSISTS OF:

    ORAL CAVITY, LABIA, PALATE, VESTIBULE, UVULA, TONGUE, LINGUAL FRENULUM
  26. NAME THE 3 PAIRS OF SALIVARY GLANDS, AND WHERE LOCATED?
    LOCATED WITHIN THE ORAL CAVITY

    1) Parotid- The largest, has Amylase; serous secretions

    2) Submandibular: under the mandible; some amylase; serous and mucous secretions

    3) Sublingual: Under the tongue; mostly mucus secretions; no enzymes
  27. 3 Phases of Deglutition/Swallowing
    1) Voluntary: the bolus is pressed against the hard palate----> pharynx

    • 2) Pharyngeal : Soft palate is elevated, closing off the nasopharynx (uvula)
    • The epiglottis closes and the vocal folds shuts the glottis; the larynx is elevated.

    THis phase is unconscious and is stimulated by tactile receptors in the oropharynx

    3) Esophageal - journey through esophagus to the entry of the stomach

    bolus must be lubricated to travel down the esophagus (peanut butter)

    Intramural plexus (submucosal plexus and myenteric plexus) initiates peristalsis
  28. What is the Swallowing Center and what cranial nerves are involved with swallowing?
    Medulla is the swallowing center

    Trigeminal (V)

    Glossopharyngeal (IX)

    Vagus (X)

    Accessory (XII)
  29. Name the 2 muscles of the Pharynx, and explain the function of the Pharynx.
    The common passageway that leads to the digestive tract, via the esophagus, and to the lungs, via the trachea

    • Muscles:
    • Pharyngeal constrictors- bolus movement

    Laryngeal elevators: elevate the larynx
  30. Purpose of the Esophagus?
    The food tube that leads from the mouth to the stomach

    Passes through the esophageal hiatus (opening) of the diaphragm (hiatal hernia)

    1 ft long, 5-8 sec. to pass through

    contains smooth and skeletal muscle!
  31. Functions of the Stomach?
    1) BULK STORAGE: Rugae (pleats) allow for distension

    2) Mechanical breakdown: CHURNING- TURNS FOOD INTO CHYME- A SOUPY MIXTURE MIXED WITH STOMACH ACIDS AND ENZYMES

    3) Limited Digestion: via acid secretions and enzymes (Parietal Cells- release HCL)

    4) Produce Intrinsic Factor: binds vitamin B12 to allow for absorption

    5) PRODUCES FOOD INTO CHYME- food is turned into a "soupy" mixture once it leaves the stomach
  32. **********GASTRIC WALL************
    CONTAINS GASTRIC PITS; LINED WITH GOBLET CELLS

    MUCUS PROTECTS THE LINING OF THE STOMACH FROM EFFECTS OF THE ACIDS AND ENZYMES

    • CONTAINS FOUR TYPES OF GASTRIC GLANDS
    • (PARIETAL, CHEIF, ENDOCRINE, MUCOUS)
  33. Gastric Glands (4 Cell Types)
    1) parietal cells- secrete HCL and intrinsic factors

    2) chief cells- secrete pepsinogen an inactive form of pepsin

    3) endocrine cells- secrete GASTRIN

    4) Mucous cells- secrete mucous
  34. Parietal Cells
    parietal cells- secrete HCL and intrinsic factors (Allows absorption for vitamin B12)
  35. Function of Parietal Cells
    Parietal cells- secretes HCL and intrinsic factors (B12 absorption)

    INTRINSIC FACTORS:

    facilitates absorption of B12 in the gut wall

    B12 is necessary for DNA synthesis and RBC formation
  36. Function of Chief Cells
    Function of Chief cells is to secrete pepsinogen- an inactive form of pepsin, which acts on proteins
  37. Function of Endocrine Cells
    SECRETES GASTRIN

    ******* GASTRIN STIMULATES PARIETAL AND CHIEF CELLS

    ******* GASTRIN INCREASES SECRETIONS AND MOTILITY

    ******* GASTRIN ALWAYS PROMOTES DIGESTION
  38. Function of Mucous cells
    Secretes Mucus!
  39. Function of HCL in the stomach
    HCL is released by parietal cells

    Histamine is released by endocrine cells- stimulates teh HCL release

    Also activates pepsinogen to denature the proteins

    Stops the carbohydrate breakdown of amylase which begun in the mouth
  40. Phases of Gastric Secretion (3)
    1) Cephalic Phase- thoughts, smell, taste stimulates para symp.- leads to an increase in motility and secretions

    2) Gastric Phase- Arrival of food in the stomach- causes muscular reflexes- Gastrin is secreted

    • 3) Intestinal Phase- arrival of chyme in the duodenum
    • **** Stimulate gastric response if pH is above 3
    • ***** Chyme inhibits gastric secretions if pH is below 2
  41. What is the Pyloric Pump?
    Stretch is an IMPORTaNT stimulus in the GI tract

    *** The pyloric sphincter usually remains partially closed. Peristaltic contractions force chyme through the sphincter. This contraction is referred to as the pyloric pump
  42. What promotes motility and relaxes the pyloric sphincter?
    STRETCH, CNS reflexes, Gastrin
  43. Functions of the Small Intestine AND 3 subdivisions?
    MOST OF THE DIGESTION AND ABSORPTION OF NUTRIENTS OCCURS IN THE SMALL INTESTINE.

    1) Duodenum- 12in long

    2) Jejunum- middle region; lots of villi

    3) Ileum- last part; leads to the colon
  44. Specialization of Duodenum?
    1st part of Small Intestine

    receives the acidic chyme from the stomach

    has abundant muscle glands

    has short villi
  45. Specialization of Jejunum?
    MOST ABSORPTION OCCURS HERE

    Plicae and Villi are prominent over the first half and decrease as you approach the colon
  46. What is the specialization of the Ileum?
    PEYER's PATCHES- clusters of lymph nodes found here

    Most abundant as you approach the colon
  47. WHat are Plicae and where are they located?
    PLicae is located in the inner lining of the small intestine.

    Plicae have villi- villi are columnar epithelium and are covered with many microvilli for absorption

    Each villus is supplied with blood vessels, nerve endings, and terminal lymphatics called LACTEALS
  48. Function of Lacteals?
    Fatty acids which do not cross capillary walls are absorbed into the lacteals
  49. WHere does mitosis of the villi occur ?
    In the INTESTINAL CRYPTS/INTESTINAL GLANDS ( ALONG THE GASTRIC PITS)

    UPON EXFOLIATION, ENTEROKINASE IS RELEASED
  50. WHAT IS ENTEROKINASE?
    ENTEROKINASE - Is an intracellular enzyme released during exfoliation of mitosis

    ENTEROKINASE activates proenzymes of the pancreas- these then dump into the duodenum
  51. Intestinal Sections... What Regulates??
    1.8L a day

    Most of the fluid moves by osmosis out of the mucosa and into the lumen

    *** Activity of intestinal glands occurs in response to stretch

    Regulated by hormones and ANS

    Parasymp increases (vagus nerve X); Symp decreases
  52. Important Hormones to Know; Intestinal Hormones released by Small Intestine
    (4 Hormones of the Intestines: G.S.C.G)
    1) Gastrin- ALWAYS PROMOTES MOVEMENT AND DIGESTION. Increases enzymatic activity and motility. Release is triggered by Stretch

    2) Secretin- Causes RELEASE of HCO from the pancreas; release is triggered by arrival of acidic chyme from stomach into the duodenum

    3) CKG- CHOLECYTOKININ - Causes gallbladder to contract and release bile AND release of pancreatic enzymes; inhibitory to stomach

    4) GIP- Gastric Inhibitory Peptide; Inhibit Gastric Secretions
  53. THE LIVER AND ITS FUNCTIONS
    (3 MAIN FUNCTIONS)
    1) METABOLIC REGULATION

    2) HEMATOLOGICAL REGULATION

    3) BILE PRODUCTION
  54. METABOLIC REGULATION IN THE LIVER
    (7 FUNCTIONS)
    1) Storage of glucose as glycogen

    2) Maintain normal amino acid and fatty acid concentrations

    3) Interconversion of nutrients

    4) Makes and releases Cholesterol

    5) Inactivation of TOxins: AMonia is converted to urea

    6) Storage of IRON reserves

    7) Storage of fat solubles (Vit A, D, E)
  55. HEMATOLOGICAL REGULATION OF LIVER
    (9 FUNCTIONS)
    1) Synthesis of plasma proteins (albumins)

    2) Synthesis of clotting factors

    3) Synthesis of angiotensinogen

    4) Synthesis of compliment proteins

    5) Synthesis of Heparin

    6) Phagocytosis of inefficient RBC's by Kupffer cells

    7) BLOOD RESERVOIR (1L)

    8) Absorption and breakdown of circulating hormones

    9) Absorption and inactivation of lipid soluble drugs
  56. BILE PRODUCTION WITHIN THE LIVER
    (4 FUNCTIONS)
    1) Bile emulsifies fat

    2) Bile contains H20, Ions, Bilirubin, Lipids

    3) Bile helps buffer chyme entering the duodenum

    4) Bile salts are derived from cholesterol... recycled 90%
  57. Circulation through the Liver
    RECEIVES BLOOD:

    1) Hepatic Artery (1/3)

    • 2) Hepatic Portal Vein (2/3)
    • All Blood LEAVES Hepatic Portal Vein, then joins inferior Vena Cava

    Blood flows slowly through the liver aloowing time for absorption by the hepatocytes.
  58. WHat is a TRIAD?
    At the corners of 6 lobules.

    consists of:

    • 1) Hepatic Portal Vein
    • 2) Bile Duct
    • 3) Artery
  59. HOW DOES THE FLOW OF BILE OCCUR?
    Bile flows to the hepatic duct----> Cystic Duct--------> Gall bladder to be stored

    Bile flows in the opposite direction from the flow of blood
  60. Function of the Gall Bladder?
    Not an Enzyme!!!!!!!!

    Stores and modifies Bile

    a muscular organ

    CKG stimulates release of Bile (relaxes the sphincters and gall bladder contracts)

    Always release bile when food enter the duodenum; more is ALWAYS act on Fatty Foods

    Emulsifies fat into droplets to increase the surface area for lipases to work
  61. Functions of Pancreas... What Are the 2 Components?
    Function is to produce pancreatic juice

    • Has Exocrine and Endocrine Functions
    • 2 components:

    1) Aqueous Component- Mostly bicarbonate ions (H20)

    2) Enzymatic Component- Produced by Acinar Cells---> THE DIGESTIVE ENZYMES
  62. Exocrine Functions of Pancreas?
    Acini cells (digestive enzymes)
  63. Endocrine Functions of Pancreas?
    Contain Islet cells:

    1) Alpha cells- Secrete Glucagon

    2) Beta Cells- Secrete Insulin
  64. Enzymes of The Pancreas
    1) Lipases: act on lipids

    2) Carbohydrases: Act on Carbs

    3) Proteolytic: Act on proteins

    • a) Protinases- breakdown proteins to peptide fragments
    • b) Peptidases: Act on peptides--> amino acide, dipeptides, tripeptides

    4) Nucleases: Act on nucleic acids (DNA, RNA)
  65. How do the Pancreatic Secretions Occur???
    Pancreatic Secretions occur in response to hormones (CKG and Secretin) released from the duodenum
  66. How is Secretin Released and what causes it?
    Secretin is released from the arrival of acidic chyme into the duodenum and releases HCO3- and buffers from the pancreas
  67. What does CKG release? WHat Causes CKG?
    CKG causes gallbladder to release bile and release pancreatic enzymes, inhibitory to stomach

    1) Amylase is enzyme released in mouth

    2) Pancreatic Lipase

    3) Nucleases

    • 4) Protinases: 70% Released as proenzymes and are converted to active form after secretion.
    • a) Trypsin ( ACTIVATES ALL THE OTHER ENZYMES)
    • b) Chymotrypsin
    • c) Carboxypeptidase
    • d) Elastase
  68. FUNCTIONS OF THE COLON
    (3)
    1) COMPACT FECES

    2) ABSORPTION OF VITAMINS

    3) STORES FECES PRIOR TO DEFECATION
  69. FEATURES OF THE COLON?
    (6)
    1) HAUSTRAE: POUCHES SEEN EXTERNALLY

    2) EPIPLOIC APPENDAGES: FAT FILLED POUCHES

    3) CECUM- BLIND ended pouch at the very beginning of the colon "cul de sac"

    4) Taenia coli- 3 longitudinal bands of muscle seen on external structure

    5) Appendix- Hangs of the cecum at the juncture of the small intestine and the colon; HAS LYMPHATIC TISSUE

    6) Ileocecal valve: At the entry of the colon
  70. Both the stomach and colon are lined with what??
    Gastric Pits!

    HOWEVER---> The COLON ALSO HAS CRYPTS...

    These crypts have MANY goblet cells (Mucus)

    Crypts with goblet cells are known as INtestinal Glands
  71. THE MASS MOVEMENT!!!
    Powerful peristaltic movement that occur a few times/day.

    THE STIMULUS IS DISTENSION OF THE STOMACH AND TEH DUODENUM.

    INTESTINAL NERVE PLEXUSES RELAY THE SIGNAL.

    THIS MASS MOVEMENT FORCES CHYME INTO THE RECTUM WHICH PRODUCES THE URGE TO DEFECATE!!!!
  72. THE RECTUM; 2 Sphincters
    Last 5-6 inches

    External Sphincter- Skeletal Muscle and under voluntary control

    Internal Sphincter- is smooth muscle and under involuntary control

    (When feces passes through the internal sphincter, the external sphincter automatically shuts and voluntary action is required to open the external sphincter to pooh)
  73. Digestion of Carbohydrates
    Begins in mouth with salivary amylase.

    Digestion is completed in the small intestine

    Glucose uptake is facilitated by insulin
  74. Digestion of Proteins
    Begins in stomach with pepsin

    Most of the digestion of proteins occurs in the small intestine- many proteases and peptidases

    Using Cotransport mechanisms, amino acids, dipeptides, and tripeptides are the final end product that are absorbed across the gut.

    once inside the gut wall, tripeptides and dipeptides are broken down into amino acids
  75. Lipid Digestion
    Lipids are emulsified by bile salts in the small intestine to form micelles.

    Lipases breakdown the lipids to free fatty acids and glycerol.

    When the micelles contact cell membrane, fatty acids and glycerol, triglcerides diffuse into the epithelial cells

    once inside, triglycerides gain a protein coat and are now called chylomicrons

    then the chylomicrons leave the epithelial cells and enter the lacteals in the villi (too large to enter the capillaries in the villi)

    LIPIDS ARE NOT WATER SOLUBLE- THUS ARE TRANSPORTED IN THE BLOOD WITH A PROTEIN COAT
  76. WHAT ARE THE TWO BEST KNOWN LIPID TRANSPORTERS IN THE BLOOD?
    LDL "bad" low density lipoproteins; transports cholesterol to the cells. If the cells are full. the cholesterol stays in circulation and can produce plaques

    HDL "good" high density lipoproteins; takes cholesterol out of blood

    GENETICALLY PREDETERMINED
  77. UP-Regulation vs DOWN-Regulation with cholesterol
    UP-Regulation: when cholesterol is in short supply, the cell up regulates its cholesterol receptors ( takes out of the blood)

    DOWN-Regulation- when a cell has an abundance of cholesterol, the cell DOWN-Regulates its cholesterol receptors

    DIET PLAYS AN IMPORTANT ROLE IN REGULATION OF THE NUMBER OF CHOLESTEROL RECEPTORS A CELL EXPRESSES
  78. Vitamins in Digestion
    All water soluble vitamins (EXCEPT B12) Are easily absorbed

    B12 REQUIRES INTRINSIC FACTOR -FROM parietal cells

    Fat soluble vitamins are absorbed in micelles

    Colonic Bacteria are an important source of some vitamins, especially vitamin K, which is important with blood clotting
  79. IONS in Digestion
    Na, K, Mg, and PO are ACTIVELY TRANSPORTED into the small intestine

    CL can move passively or if alone may be actively transported

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