DIGESTIVE SYSTEM Mechanical and chemical breakdown of

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Transcript DIGESTIVE SYSTEM Mechanical and chemical breakdown of

DIGESTIVE SYSTEM
Mechanical and chemical breakdown of foods and
the absorption of the resulting nutrients by cells.
Chapter 15
SENSE OF SMELL AND TASTE
• Smell and taste receptors are chemoreceptors
(receptors stimulated by binding of certain
chemicals).
• Aid in food selection
Sense of smell
• 12 million olfactory receptors
• Yellowish-brown masses of epithelium
• Upper portion of nasal cavity
• Bipolar neurons
• Stimulated by odorant molecules
• Send impulses to olfactory bulbs, are analyzed
and travel along olfactory tracts to the
temporal lobe
• Anosmia is the complete or partial loss of
smell.
Sense of taste
• 10,000 taste buds located on the surface of the tongue; 1,000
on roof of mouth and throat (found within papillae: tiny
elevations on tongue)
• Taste buds contain 50-150 taste cells that are replaced every 3
days
• Tongue has taste pores and taste hairs
• 5 primary taste sensations:
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Sweet (tip of tongue)
Sour (sides of tongue)
Salty
Bitter (back of tongue)
Umami (delicious)
(6.) Alkaline
(7.) Metallic
• Pathway to brain:
• taste cells
facial, glossopharygeal, vagus nerves
medulla
thalamus
Digestion
• Mechanical digestion: breaks large pieces into
smaller ones without altering their chemical
composition.
• Chemical digestion: breaks food into simpler
chemicals.
• 2 parts of digestive system (pg. 403)
• Alimentary canal: tube that extends mouth to anus
• Muscular tube about 8 meters long
• Wall has 4 layers
• Mucosa: contains tiny projections (lumen) that increase
absorption area; has glands to secrete mucus to protect
other layers
• Submucosa: contains blood vessels that nourish
• Muscular: produces movements
• Serosa: serous fluid lubricates tube outer surface
• Peristalsis: wavelike motion that propels food down the tube
• Accessory organs: secrete substances in canal to
digest
MAIN DIGESTIVE ORGANS AND FUNCTIONS
• MOUTH: mastication (pg. 406)
SPECIAL
STRUCTURES
FUNCTION
DESCRIPTION
LIPS
Sense texture and temp of food
Skeletal muscle sensory
receptors
CHEEKS
Expression, chewing
Skin & fat
TONGUE
Mix (bolus), taste, friction (papillae)
PALATE
Hard- bony anterior roof
Soft- muscular posterior roof (covers nasal
cavity)
UVULA
Gag reflex
Cone shaped projection in back
FRENULUM
Connects tongue to floor of mouth
Membranous fold
TONSILS
Protect against infection
Lymphatic tissue/tonsillitis
TEETH : break down food to increase surface area
for enzymes to be effective (pg. 407)
• Primary teeth (deciduous)
• Acquired from 6 months-2 years
• 20 teeth total
• Roots are reabsorbed before next set come in
• Secondary teeth (permanent)
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32 teeth total
Incisors: bite off pieces of food
Canine: grasp or tear food
Premolars/Molars: grind food particles
• 2 portions (pg. 408)
• Crown: part that projects beyond gum
• Is covered by enamel-contains Ca salts; strongest substance in body; if
damaged it does not come back
• Root: anchored to jaw
• Dental caries (cavities): caused by bacteria that release acid that
decay enamel
SALIVARY GLANDS
• Secrete saliva that moistens food particles, binds them, and
begins chemical digestion of carbohydrates. It is also a solvent
that aids in tasting food and cleanse mouth and teeth. (pg. 410)
• 2 types of secretory cells
• Serous cells: produce a watery fluid that includes amylase (enzyme
that splits starch and glycogen molecules into disaccharides)
• Mucous cells: secretes mucus that binds food particles and lubricates
food during swallowing.
• Parasympathetic nerve impulse elicit saliva secretion or
inhibits it if food smells good or bad.
• Major Glands
• Parotid - largest; anterior to ear; secretes amylase
• Submandibular – floor of mouth; serous and mucus
• Sublingual – smallest; inferior floor of mouth; mucous
PHARYNX
• Passageway posterior to mouth whose muscular walls aid in
swallowing. It connects the nasal and oral cavities with the
larynx and esophagus.
• Structure
• Nasopharynx- airway
• Oropharynx- food down and air up
• Laryngopharynx- food down
• Peristalsis starts here
ESOPHAGUS
• Food passageway that aids in swallowing.
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Straight, collapsible tube about 25 cm long
Leads from pharynx to stomach
Posterior to trachea
Penetrates diaphragm at the esophageal hiatus
Esophageal sphincter: area where stomach and
esophagus meet; contains circular smooth muscle that
stays closed to prevent contents from regurgitating into
the esophagus. When peristaltic waves reach the
stomach, the muscle fibers temporarily relax and allow
the food to enter.
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SWALLOWING MECHANISM
Soft palate raises preventing food from entering
nasal cavity.
Hyoid bone and larynx are elevated. Epiglottis
(flap like structure) closes off the top of the
larynx so that food is less likely to enter the
trachea.
Tongue is pressed against the soft palate,
sealing off the oral cavity from the pharynx.
Longitudinal muscle in the pharyngeal wall
contract, pulling the pharynx upward toward
the food.
STOMACH
• Structure
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J-shaped, pouchlike organ that hangs inferior to diaphragm
Upper left portion of abdomen
1 liter capacity
40 million cells line the stomach and can secrete 2 to 3 liters of
gastric juice per day
• Contains rugae (thick folds)
• Functions
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Receives food from esophagus
Mixes food with gastric juice
Initiates protein digestion
Limited absorption (water, salts, alcohol)
Moves food to small intestine
• Regions of stomach
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Cardiac: small area near esophageal opening
Fundic: temporary storage area
Body: main portion
Pyloric: narrow canal to small intestine
Pyloric sphincter: muscle valve that controls gastric emptying
• Problems
• Ulcers: an open sore in mucous membrane from
tissue breakdown
• Hiatal Hernia: portion of the stomach protrudes
through a weakened area of the diaphragm.
Gastric secretions (pg. 413 )
• Gastric glands line the inner stomach which is thick with
mucus
• 3 types of secretory cells
• Mucous: mucus; to prevent products of these stomach from
digesting itself ;produce gastric juice
• Parietal: secrete HCL acid
• Chief: digestive enzymes
• Gastric juice
• Pepsin: most important digestive enzyme; begins the digestion of
protein
• Intrinsic factor: helps small intestine absorb vitamin B12
• Gastrin: increase secretory activity of gastric glands and stimulates
cell growth
• Chyme: paste of food particles and gastric juice
• Structure
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LIVER
upper right quadrant of abdominal cavity
reddish-brown with many blood vessels
heaviest organ in body; 3 lbs.
2 lobes (large right/smaller left) separated by hepatic
lobules
• Functions (pg. 418)
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Carbohydrate metabolism
Lipid metabolism
Protein metabolism
Storage
Blood filtering
Detoxification
Secretion of bile (yellow-green liquid secreted from hepatic
cells)
• Problems
• Jaundice: yellow eyes and skin due to a buildup of
bile, blocked bile duct, diseased liver
• Hepatitis: inflammation of the liver; Types A-G (pg
419)
PANCREAS
• Structure
• Near posterior abdominal wall in the C-shaped curve of
duodenum
• Contains pancreatic acinar cells that produce pancreatic juice
• Pancreatic duct: connects with duodenum at same place the
bile duct of liver and gallbladder joins
• Hepatopancreatic sphincter: controls the movement of
pancreatic juices into duodenum
• Function
• Secretes pancreatic juice that contains enzymes that
digest carbohydrates, fats, nucleic acids and proteins
• Problems
• Pancreatitis: results from blockage in release of
pancreatic juice
• Cystic Fibrosis: excessive production of mucus
blocking the release
of digestive enzymes.
• Structure
GALL BLADDER
• Pear shaped sac on inferior surface of liver
• Connects to cystic duct which joins hepatic duct to
form common bile duct
• Function
• Stores bile between meals
• Reabsorbs water to concentrate bile
• Releases bile into small intestine
• Problems
• Gall stones: cholesterol in bile forms crystals and
blocks flow in cbd; painful
• Structure
SMALL INTESTINE
• 3 parts (5-6 meters long)
• Duodenum: about 25 cm long/5cm in diameter; most fixed portion
• Jejunum
• Ileum
• Mesentery
• double-layered fold of peritoneal membrane
• suspends jejunum and ileum from posterior wall
• supports the blood vessels, nerves, and lymphatic vessels that supply
intestinal wall
• Greater Omentum
• Drapes from stomach over intestines and within folds
• Fat accumulation occurs here
• Intestinal villi
• Greatly increase surface area to absorb
• Ileocecal sphincter
• Joins the ileum to the large intestine
• Function
• Receives secretions from pancreas and liver
• Completes digestion of the nutrients in chyme
• Absorbs the products of digestion (*most important
absorbing organ)
• Transports the residues to the large intestine
• Chyme takes 3-10 hours to pass through
• Problems
• Diarrhea: organ becomes irritated and a strong
peristaltic rush passes contents through without any
absorption
• Celiac disease: reaction to gluten that causes
malabsorption
• Lactose intolerance: not producing sufficient lactase to
adequately digest lactose causing diarrhea, cramping
and bloating
LARGE INTESTINE
• Structure
• Greater diameter than small intestine
• 1.5 meters long
• Parts
• Cecum
• Appendix (consists of lymphatic tissue but has no known
digestive function) hangs from this area
• Colon
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Ascending – goes upward
Transverse – longest, most movable, goes across
Descending – goes down
Sigmoid – S curve
• Rectum – lies by sacrum
• Anal canal
• Anus – 2 sphincters
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Internal – involuntary control
External – voluntary control
• Function
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Little or no digestive function
Absorbs water and electrolytes from chyme remaining
Forms and stores feces
Includes materials not digested or absorbed
About 75% water
Color derives from bile pigments
Odor is produced by bacteria
Secretes mucus to protect wall, bind feces and control pH
Slower peristaltic waves only 2 to 3 times a day
• Problems
• Hemorrhoids – enlarged and inflamed branches of the rectal vein
that cause itching, pain, and bleeding. Caused by pressure.
• Crohn’s disease – inflammation in digestive tract