digestive system - mount carmel area school districthome.mca.k12.pa.us/~farronatoa/digestion.pdf ·...
TRANSCRIPT
Digestive System
CHAPTER 14
Digestive System
http://media.pearsoncmg.com/bc/bc_marieb_ehap_8/activities/chapter14/Act14A.html
Functions of Digestion
� Ingestion - intake of food� Propulsion
� a. Peristalsis - alternating contracting & relaxation
� b. Segmentation - movement of food back & forth across an organ mixing with digestive juices
� Mechanical Digestion - breaking food into smaller fragments� mouth & stomach
� mastication- chewing
� Chemical Digestion - breakdown large molecules into their building blocks; occurs in mouth, stomach & small intestine
� Polysaccharides –Starch – composed of monosaccharides(glucose)
� Lipids – Fatty Acids & Glycerol
� Proteins – Amino Acid Chains
� Nucleic Acids –Nucleotide chains
� Absorption - transport of nutrients into the blood
� Defecation - elimination of waste in a solid form (feces)
Divisions of Digestive System
� Alimentary Canal or Gastrointestinal Tract (GI)
� coiled hollow tube with 2 openings
� mouth, pharynx, esophagus, stomach, small intestine, large intestine
� Accessory Organs -assist in breakdown of molecules
� teeth, tongue, salivary glands, pancreas, liver, gall bladder
Organs of the Alimentary Canal
� 1. Mouth or oral cavity� lips (labia) - protect oral cavity opening
� cheeks - forms lateral walls� hard palate - forms anterior roof
� soft palate - forms posterior roof� uvula - fleshy fingerlike projection; closes
nasal cavity when swallowing� vestibule - area between lips & cheeks and
teeth & gums
� 2. Pharynx - common throat� oropharynx - posterior
to oral cavity� nasopharynx - part of
respiratory passageway� laryngopharynx -
continues to esophagus; larynx -voice box
� 3. Esophagus - gullet; runs from pharynx through the diaphragm to the stomach
� 25 cm long� smooth muscle� propels food to stomach
through peristalsis� http://www.westga.edu/~
lkral/peristalsis/
� 4. Stomach � A. Structure
� Cardiac – surrounds junction between esophagus & stomach
� Fundus – superior portion� Body – main portion; lined with folded walls
called rugae that disappear when stomach is full
� Pylorus – terminal portion
� B. Valves or sphincters� Cardioesophageal (cardiac) – leads food
into stomach� Pyloric – leads partial digested food
(chyme) into small intestine
C. Curvatures:� Greater – outer (lateral) curve� Lesser – inner (medial) curve
� C. Mechanical Digestion
� 3 muscle layers
� segmentation of food� 1st – longitudinal� 2nd – circular� 3rd – oblique
p. 416 Fig 14.4
� D. Chemical digestion� Walls lined with gastric pits that lead to the
gastric gland� Gastric gland contains 3 types of cells� 1. Mucus neck cells – secrete alkaline sticky
mucus to protect stomach walls� 2. Parietal cells – produces HCl which
activates enzyme production� 3. Chief cells – produce protein digestive
enzymes called pepsinogen (inactive form of pepsin)
� Sequence of events:� 1. food enters stomach� 2. Parietal cells secrete HCl which
lowers pH � 3. low pH triggers chief cells to produce
pepsinogen� 4. pepsinogen converted to its active
form of pepsin
� 5. Small Intestine� A. Structure� Extends from the pyloric sphincter to the
ileocecal valve� 7 m long� Mesentary – web like membrane that
coils small intestine & holds it intact
� 3 subdivisions:� Duodenum – curves
around the pancreas; receives chyme from stomach, enzymes from pancreas & bile from liver
� Jejunum – middle portion; bulk of digestion & absorption
� Ileum – terminal portion
� B. Chemical Digestion� 1. pyloric sphincter controls amount of food entering
from stomach� 2. pancreas produces enzymes that are secreted to
small intestines through pancreatic duct� 3. Bile formed in liver is secreted through bile duct� 4. Pancreatic & bile ducts join to form
hepatopancreatic ampulla� 5. together enzymes,bile and bicarbonate (neutralize
acids) enter duodenum through duodenal papilla
� C. Absorption � Peyer’s Patches –
collection of lymphatic tissue that increases toward end of small intestine that prevents absorption of bacteria
� Surface area increased by 3 structures:� Circular folds
(plicae circularis) –deep folds of inner walls
� Villi – fingerlike projections that contain bv & lymphatic duct called the lacteal
� Microvilli – “brush border”; projections of the cell membrane that give a fuzzy appearance
Chemical Influences� Carbohydrates – sugars & starches� Salivary amylase – mouth
� Pancreatic amylase – produced by pancreas & sent to duodeum
� Brush border enzymes – dextrinase, glucoamylase
� Lactase (lactose), maltase (maltose), sucrase (sucrose)
� Produced & act in small intestine
� Proteins� Begins in stomach with pepsin & rennin
(more abundant in children)� Pancreas – trypsin, chymotrypsin,
carboxypeptidase
� Brush border – aminopeptidase, carboxypeptidase & dipeptidase
� Fats� Bile emulsifies fats
� Pancreatic lipases sent to small intestine to complete fat digestion
� Nucleic Acids� Pancreas produces nucleases to
breakdown nucleic acids (DNA, RNA)
� inhibits secretion of gastric juicesChyme from stomachDuodenumGASTRIC INHIBITORY PEPTIDE (GIP)
�Release of pancreatic juices & bile�Relaxes duodenal papillae
Chyme from stomachDuodenumCHOLECYSTOKININ (CCK)
�Release of pancreatic juices & bileChyme from stomachduodenumSECRETIN
�Inhibits secretion of gastric & pancreatic juices�Inhibits emptying of stomach & gall bladder
Food in stomachstomachSOMATOSTATIN
� activates parietal cellsFood in stomachStomachHISTAMINE
� release of gastric juice�Mobility of small intestine�Relaxes ileocecal valve
Food in stomachStomachGASTRIN
ACTIONSTIMULUSSOURCEHORMONE
� 6. Large Intestine
� Extends from ileocecal valve to anus� Absorption of water & elimination of waste
� No villi� Lined with goblet cells that produce mucus for
lubrication
� Outer walls puckered with haustra which aids in contraction
� Cecum – 1st portion ; ileocecal valve that allows indigestible material from sm. Intestine
� Appendix – sac extending from cecum
� Ascending colon –travels up right side of abdominal cavity ; turns at the hepatic flexure
� Transverse colon –travels across the abdomin; turns at the splenic flexture
� Descending colon –travels down left side of abdomen
� Sigmoid colon – S shaped
� Rectum – storage chamber
� Anal sphincter – external & internal; voluntary & involuntary muscles; opens during defecation
ACCESSORY ORGANS
� PANCREAS
� Gland that extends across abdomen from spleen to duodenum
� Located retroperitoneal – behind parietal peritoneum
� Functions: � produces enzymes in a alkaline fluid� Produces insulin ( breaks down glucose) and
glucagon hormone that raises glucose level)
PANCREAS
� LIVER� Largest gland ; 4 lobes� Suspended from diaphragm by falciform
ligament� Produces bile – yellow/green water solution
containing bile salts, bile pigments (bilirubin), cholesterol, phospholipids and electrolytes
� Bile emulsifies fat into small globules� Right & left hepatic ducts collect bile � Fuse into the common hepatic duct
� GALL BLADDER� Green sac within lobes of liver� When not digesting food bile backs up
into the cystic duct & is stored in gall bladder
� Bile becomes concentrated in gall bladder due to water absorption
� Gallstones – results from too much water absorption and cholesterol crystallizes
� Jaundice – results from blockage of common hepatic or bile ducts, hepatitis(inflammation of liver) or cirrhosis(hardening of liver)
� SALIVARY GLANDS� Parotid – lies anterior to ears; largest� Submandibular – below jaw� Sublingual – beneath tongue� Empty secretions in floor of mouth� Saliva – mixture of mucus (moistens &
binds food into bolus), amylase (digest starch) and antibodies (inhibit bacteria)
� TEETH� Massication of food� Deciduous teeth – 1st set; 20� Permanent teeth – 2nd set; 32
� Incisors – front; chisel shaped for cutting
� Canines – corner fangs; puncture & pierce
� Premolars / bicuspids –sides; grinding
� Molars – rear; crush & grind
� Crown – exposed area; above gum
� Root – beneath the gum
� Neck – connect root to crown
� Gingiva – gums
� Enamel – hard outer covering of crown
� Dentin – bone like material under enamel; composes bulk of tooth
� Cementum – glue like substance on outer root surface
� Pulp cavity – contains pulp – blood vessels, nerves & connective tissue – provides nutrients to tooth & sensations
� Root canal – extension of pulp into root
� Peridontal ligament –holds tooth in socket