Chapter 24 - Digestive System Flashcards
pharynx
Muscular driving of materials into the esophagus
esophagus
transport of materials to stomach
stomach
– Mechanical digestion with muscular contractions
– chemical digestion by acid and enzymes
small intestine
Enzymatic digestion and absorption of water, organic substrates, vitamins, and ions
large intestine
indigestible materials prepares for elimination
Integrated processes of digestive system
–Ingestion –Mechanical digestion and propulsion –Chemical digestion –Secretion –Absorption –Defecation
villi
fingerlike projections from surface of certain membranous structures
mucosa
glands and the gastric pits, mucous membrane layer of the stomach
submucosa
layer of areolar connective tissue under mucous membrane
Enteroendocrine cells
Secrete hormones that coordinate activities of digestive tract and accessory glands
regulation of digestive functions
– Local factors
– Neural mechanisms
– Hormonal mechanisms
visceral motor neurons
Control smooth muscle contraction
Short reflexes (local reflexes)
- Control small segments of digestive tract
* outside of CNS control - enteric nervous system
long reflexes
- in CNS
- Provide higher level control
- Stimulate large-scale peristalsis
- Parasympathetic motor fibers synapse in myenteric plexus
hormonal mechanisms
enteroendocrine cells:
– Enteroendocrine cells in digestive tract produce many peptide hormones
• Affect almost every aspect of digestion
– Travel through bloodstream to reach target organs
chyme
Partially digested food mixed w acidic secretions of stomach
rugae
wrinkles/gastric folds
gastric glands
– In fundus and body of stomach
– Each gastric pit communicates w/ several gastric glands
• Parietal cells
• Chief cells
– Secrete about 1500 mL of gastric juice each day
parietal cells
– Secrete intrinsic factor
• Glycoprotein - absorb vitamin B12
– secrete hydrochloric acid (HCl)
chief cells
– Secrete pepsinogen (an inactive proenzyme)
• Pepsinogen is converted to pepsin (an active proteolytic enzyme) by HCl
things absorbed in stomach
alcohol, ibuprofen
chemical digestion in stomach
digestion of carbohydrates (by salivary amylase) and lipids (by lingual lipase)
As stomach contents become more fluid,
• pH approaches 2.0
• digestion of proteins by pepsin increases
– Nutrients are not absorbed in stomach
exocrine cells
– Secrete alkaline pancreatic juice into small intestine
• About 1000 mL per day
• Contains digestive enzymes, water, and ions
pancreatic enzymes
– Pancreatic alpha-amylase - starch
– Pancreatic lipase -
– Nucleases - dna
– Proteolytic enzymes - proteins
liver secretes bile
(gall bladder)
• Into a network of narrow channels (bile canaliculi)
– Right and left hepatic ducts
– Liver has over 200 functions in three categories
- Metabolic regulation
- Hematological regulation
- Bile production
liver cells
- removes nutrients or toxins from blood
- removes and stores excess nutrients (C loading)
Regulatory activities of liver affect
– Carbohydrate metabolism – Lipid metabolism – Amino acid metabolism – Waste removal – Vitamin storage – Mineral storage – Drug inactivation
Liver receives about ?? of cardiac output
25%
– Largest blood reservoir in body
Hematological regulation by liver involves
removal of antibodies
removal or storage of toxins
bile salts
break lipid droplets apart
Enterohepatic circulation
Cycling of bile salts between liver and small intestine
Duodenum
– Segment of small intestine closest to stomach
– “Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver
Jejunum
– Middle segment of small intestine
– Site of most chemical digestion and nutrient absorption
ileum
– Final segment of small intestine
• Sphincter that controls flow of material from ileum
into cecum of large intestine
lacteal
Transports chylomicrons that are too large to enter blood capillaries
Intestinal glands (intestinal crypts)
- Stem cells produce new epithelial cells
- Paneth cells at base function in innate immunity
- Contain enteroendocrine cells
intestinal juice
1.8 L every day
• Moistens chyme
• Assists in buffering acids
• Keeps digestive enzymes and products of digestion in solution
Neural mechanisms involving CNS
– Prepare digestive tract for activity (parasympathetic)
– Inhibit gastrointestinal activity (sympathetic)
– Coordinate movement of materials along digestive tract
• Through reflexes
– Motor neuron synapses in digestive tract release neurotransmitters
gastrin
- Secreted by G cells in duodenum
- Promotes increased stomach motility, acids and enzymes
secretin
- Released when chyme arrives in duodenum
– Increases secretion of buffers by pancreas and bile by liver
– Reduces gastric motility and secretory rates
Cholecystokinin (CCK)
– Secreted when chyme arrives in duodenum
– Accelerates pancreatic production and secretion of digestive enzymes
cecum
– Expanded pouch
– Receives and stores materials arriving from ileum appendix
internal anal sphincter
– Smooth muscle cells
– Not under voluntary control
external anal sphincter
– Skeletal muscle fibers
– Under voluntary control
large intestine
– Lacks villi
– Mucus provides lubrication for fecal material
– Large lymphoid nodules present
Functions of large intestine
– Absorption or reabsorption of:
- Water
- Nutrients (less than 10 percent)
- Bile salts
- Organic wastes
- Vitamins and toxins produced by bacteria
microbiome
– Microbes (bacteria, fungi, and viruses) that live in and on human body
• Including stuff in large intestine
vitamins
- cofactors or coenzymes in metabolism
– Normal bacteria in colon make three vitamins
Vitamins produced by bacteria in colon
– Vitamin K (fat soluble)
• Required by liver for producing four clotting factors
– Biotin (water soluble)
• Imp in glucose metabolism
– Vitamin B5 (pantothenic acid; water soluble)
• steroid hormones
Bacteria convert
bilirubin to urobilinogens and stercobilinogens
• Some urobilinogens are absorbed into bloodstream and excreted in urine
Urobilinogens and stercobilinogens remaining in
colon are converted
to urobilins and stercobilins
– By exposure to oxygen
– Bacteria break down
peptides in feces and generate
• Ammonia, as soluble ammonium ions
• Indole
• H2S
Bacteria feed on indigestible carbohydrates
Produce flatus (intestinal gas) in large intestine
a balanced diet contains
- Carbohydrates
- Lipids
- Proteins
- Vitamins
- Minerals
- Water
digestive enzymes
• breakdown of Carbohydrates, proteins, lipids, and nucleic acids called hydroysis
Digestive enzymes
– Secreted by
- Salivary glands
- Tongue
- Stomach
- Pancreas
maltase
splits bonds between maltose
sucrase
breaks apart sucrose
lactase
hydrolyzes lactose
– Insufficient lactase leads to lactose intolerance
Absorption of monosaccharides
– Via facilitated diffusion and cotransport, which differ in
• ATP requirement
pancreas makes its own
amylase
lipid digestion
• Interact with bile salts to form micelles (lipid–bile
salt complexes)
• Join with steroids, phospholipids, vitamins, and
proteins to form chylomicrons (big)
protein digestion and absorption
– Complex and time consuming
– Involves mechanical digestion, hydrochloric acid, and proteases
Dipeptidases in epithelial surfaces of small intestine
Break short peptide chains into individual amino acids
Nucleic acid digestion and absorption
– Nucleic acids are broken down into nucleotides
– digest nucleotides into sugars, phosphates, and nitrogenous bases
• Absorbed by active transport
water absorption
– Cells cannot actively absorb/secrete water
–involves passive water flow down osmotic gradients
calcium ion absorption
- Involves active transport at epithelial surface
* Rate is increased by calcitriol
Water-soluble vitamins
vitamins B and C
Fat-soluble vitamins
Vitamins A, D, E, and K
