Review Sheet 1 for Test #3 Biology 2213 Dr. James Adams
The Digestive System -- Chapter 23
The overall function is to breakdown foodstuffs and absorb
materials
Anatomy
The digestive system organs can be separated into to groups:
I. Alimentary Canal/Gastrointestinal
(GI) Tract -- digests and absorbs;
continuous series of coiled, muscular, tubular organs.
Lumen is
technically outside of body (it is a harsh environment)
II. Accessory Organs
-- aid in process of digestion (teeth, tongue, salivary glands,
liver, pancreas, etc.)
Digestive Processes
1.Ingestion (and
mastication); 2. Propulsion
(peristalsis, segmentation,etc.); 3. Physical
(Mechanical)/Chemical digestion;
4. Absorption; 5. Defecation
The Coverings -- The
peritoneum (doubled serosae, pathways for vessels/nerves)
Mesenteries (also falciform ligament and greater/lesser omentum, mesocolons
[pgs.
885, 894, 901, 907–909]); know the terms intra-/retroperitoneal
Adventitia
The Wall (GI tract
organs) --
Tunics: mucosa, submucosa, muscularis
(circular/longitudinal layers), serosa.
Nerve plexuses* (submucosal, myenteric [between
circular/longitudinal muscles])
Know epithelial linings (as always!)
Some of control intrinsic
(enteric hormones, local nerve plexuses* [short reflexes]):
receptors in GI tract organs respond to:
1. stretch, 2. osmolarity/pH, 3. digestive end products
The short reflexes initiated in response, along nerve plexuses in organ walls; hormones
also released from some organs which also control digestive processes
Some of control also extrinsic: long reflexes involving vagus nerve
and CNS centers
Parasympathetic stim. increases secretory activity and
motility; sympathetic decreases
Basically, anything that increases secretory activity
also increases motility
The Functional Anatomy of the
Digestive System
I. Mouth (Oral, Buccal Cavity)
-- Associated Structures:
A. Lips and
cheeks (red margin, frenula)
B. Palate
(hard/soft with uvula)
C.
Accessory organs:
1. Tongue (frenulum,
papillae): taste, mechanical dig., propulsion (swallowing)
2. Salivary
glands
-- Parotid, Submandibular, Sublingual, Intrinsic
Secrete saliva: 97% H2O,
ions, amylase (hydrolyzes starch into disaccharides),
lysozyme and Ab's (disinfection), mucin (mucus);
KNOW serous/mucus cells
Salivation control
-- parasympathetic
nervous stimulation in response to stimulation
of mouth chemo- (esp. acid) and pressoreceptors;
1 to 1.5 liter/day
Sympathetic stimulation reduces
output -- thick saliva
3. Teeth:
principle organ of mechanical digestion; KNOW different teeth types
and adult human dental formula -- I-2, C-1, P-2, M-3
Digestive processes of mouth -- mastication, initiation of swallowing, amylase
(for
digestion of polysaccharides
-- starch [amylose] to maltose)
II. Pharynx (Oro-, laryngopharynx only) -- mainly propulsive
III. Esophagus -- in mediastinum, 25cm to stomach (through
hiatus in diaphragm)
also mainly propulsive (peristalsis); swallowing involves 22 separate muscle
groups;
mucosa has mucus-secreting esophageal glands
Wall has numerous distensible folds with fibrous adventitia (no
serosa)
Passage of food: 4
- 8 seconds for solids, 1 - 2 seconds for liquids
Ends at gastroesophageal (cardiac) sphincter
IV. Stomach
-- Storage and secretion; cardiac sphincter controls entry
from esophagus
Rugae make stomach distensible; allow for physical digestion
Regions:
cardia, fundus, body, pylorus; ends at pyloric sphincter.
Lesser/ greater curvatures, with
lesser/greater omenta.
Microscopic
Anatomy -- three muscles layers; additional oblique layer (innermost)
Mucosa:
Simple Columnar Epithelium (virtually all goblet cells), with gastric pits
Pits have secretory cells:
1. Mucus neck
-- thick, protective mucus
2. Parietal -- HCl and
intrinsic factor (only vital function of stomach; why?)
Be able to explain HCl production and blood's alkaline tide (leaving stomach)
3. Chief -- pepsinogen (activated by HCl; digests 15% of proteins), also lipases
4. Enteroendocrine
-- hormones+ (Table
23.1, pg. 888) secreted into capillaries
Phases of Gastric Secretion
-- Cephalic, gastric, intestinal (enteric) (Fig.
23.19, pg. 890)
+Understand functions of: gastrin, histamine, intestinal
gastrin,
cholecystokinin (CCK),
secretin (all functions of these hormones: Table 23.1), and acetylcholine
Total volume of gastric juice: 2 - 3
liters/day
Gastric accommodation and contraction (in response to significant stretch);
contrac-
tion powerful in pyloric region (any active amylase digested here);
slow, rhythmic
contraction (3/min.)
-- the BER (basic electrical rhythm); to a point, the more food
in the stomach, the more mixing and more rapid the emptying will be
Gastric emptying (avg. 4 hrs.): liq. rapid, lipids slowest (6 hrs.) WHY?
Chyme --
lipids on top going into small intestine
Ulcers -- Helicobacter pylori
Accessory Organs of Small Intestine:
1. Liver and Gallbladder
-- Accessory organs; main digestive function -- bile secretion
Liver 4-lobed; supported by falciform ligament, ligamentum teres
Microscopic Anatomy:
hepatocytes
Hexagonal liver lobules:
triad
(at corners) with branches of hepatic artery/portal vein/hepatic bile duct
bile canaliculi
central vein leading into hepatic vein to inferior vena cava
Sinusoidal capillaries with
Kupffer cells (macrophages)
Gallbladder mainly storage organ for bile,
though can concentrate bile (gall stones)
Ducts: cystic, hepatic, common bile.
Total bile production: 0.5 - 1 liter/day
Know bile composition; main function is
emulsification of lipid droplets (mechanical
digestion using salts and
phospholipids); secretion controlled mainly by CCK release
2. Pancreas –– Accessory digestive and endocrine organ
Principal digestive enzyme producing organ
(see enzyme handout); enzymes
released
into small intestine
Head, tail, duct cells, acini (secretory units:
enzymes [zymogen granules, alkaline
NaHCO3], pancreatic duct, hepatopancreatic duct
Secretion mainly controlled by hormones: secretin
--> bicarbonate-rich, CCK-->
enzyme-rich pancreatic juice; 1.2
to 1.5 liters/day
V. Small Intestine -- 6 meters; duodenum, jejunum, ileum;
lined with enterocytes
Know hepatopancreatic duct/sphincter (see pancreas/liver, gall bladder)
Modifications of wall: plicae circulares, villi
, microvilli (with
brush border enzymes)
Absorptive simple columnar epithetlium (tight junctions);
turnover: 5 - 6 days
Goblet cells
(increase along length of S.I.), crypts (decrease along length;
secrete watery
mucus/lysozyme, a few enzymes); 1 - 2 liters/day
Specialized duodenal (Brunner's) glands (alkaline secretions)
Enteroendocrine
cells
Lacteals (and don't forget
Peyer's
Patches)
Digestive processes occurring
in small intestine: *chemical (see Enzyme handout)
Most chemical digestion and absorption takes place in small intestine
Motility of Small Intestine
-- segmentation; peristaltic contractions weak,
until after
most absorption. Gastroileal reflex; enhanced by
gastrin.
VI. Large Intestine
-- cecum (w/ appendix), ascending/transverse/descending/sigmoid
colon (ascending and descending
retroperitoneal), rectum (with valves), anal canal,
internal/external anal sphincters, teniae coli, haustra
Bacterial flora (make B/K vitamins, which are absorbed in L.I.; also
methane [flattus])
Keeping
pathogenic bacteria in check (see page 909)
Haustral contractions/mass movements/defecation reflex
(remember Valsalva Maneuver)
Some absorption of water,
but most water absorbed in small intestine
Chemical Digestion -- See handout/text; understand names (eg., lipase); brush border enzymes
Absorption -- Up to 10 liters of food, drink, GI secretions per day, only 0.5
- 1 liter
reaches L.I., of which only approximately 150 ml becomes feces.
Most nutrients absorbed by active transport across
S.I. mucosa.
Carbohydrates: most monosaccharides co-transported with Na+; fructose by
factilitated diffusion
Proteins: several dif. carriers for amino acids, co-transported with Na+ also.
Some active carriers for di- and tripeptides.
Lipids: bile salts important for absorption as well; lipases digest neutral lipids to
two fatty acids and monoglycerides; these and cholesterol form micelles, which
passively cross mucosa. Triglycerides resynthesized in
epith. sER. Chylomicrons
released to
lacteals. Redigested at tissue cap. endothelium.
Nucleic Acids: Active transport of pentose sugars, PO4–3, nitrogenous bases.
Vitamins: Most (both fat/water soluble) diffuse; vitamin B12 requires intrinsic fac.
Electrolytes: Na+ actively pumped (many anions [Cl–, HCO3–] and water follow
passively), however, Cl– &
HCO3– exchanged in ileum (double-pump); K+
diffuses; Fe and Ca have special mechanisms
-- KNOW (ferretin, vitamin D, PTH)
NUTRITION -- Chapter 24
Nutrient -- a substance in food used for any bodily function; building
blocks and energy.
Major nutrients -- carbohydrates,
lipids, proteins, and water
(Micro) nutrients -- vitamins
and minerals; needed, but in small amounts
Most foods offer combinations of these; energy measure --
Calories
Note: recommended daily allowances (RDA's); see
Table 24.1, pg. 930
Essential nutrients -- nutrients the body cannot manufacture; MUST be
obtained in the diet
Some 45 to 50+ of the nutrients you take in are essential;
the rest you need can be
made from the essentials (as long as the essentials are
provided)
The essential nutrients include:
(1. A certain minimal amount of carbohydrates)
2. Two fatty acids: linoleic and linolenic acids (two
of the most abundant, so no big deal)
3. Eight (ten in infants) of the amino acids
4. Most vitamins (but not D & K)
5. All minerals
(6. A certain amount of water)
Technically, the carbohydrates and water are not actually
essential, as we can manufacture
some of both carbohydrates and water, but we cannot live without some intake of
both.
For each major nutrient, know dietary sources and basic uses in
the body
Although not responsible for the precise amounts of each, you
should understand the
concept of "recommended daily allowances/requirements"
For the vitamins, know importance in the body of all fat
soluble vitamins (A, D, E, K),
and know the importance of the following water soluble
vitamins --
C, B2, nicotinamide
(niacin), B5, B12, and folic acid
(see Table 24.2, pgs. 932)
For the minerals, know the importance in the body of all seven
major minerals (Ca, Cl, S,
K, Na, Mg, and P), and for the following trace minerals (F,
I, Fe, Zn)
(see Table 24.3, pgs. 933)