Digestive System Chapter 23 Flashcards
1
Q
Alimentary canal aka gastrointestinal tract
A
- gut–continuous muscular tube that winds through the body from the mouth to the anus
- it digests food and absorbs the digested fragments through the lining into the blood
- organs of alimentary: mouth, pharynx, esophagus, stomach, small intestine, and large intestine
- in cadaver, the alimentary canal is approximately 9 m but in living person it is shorter b/c of muscle tone
2
Q
Accessory digestive organs
A
-teeth, tongue, gallbladder, salivary glands (and other digestive glands), liver, and prancreas
3
Q
Ingestion
A
-simply taking food in to the digestive tract
4
Q
Propulsion
A
- moving food through the alimentary canal
- swallowing is voluntary
- peristalsis is involuntary
5
Q
Mechanical breakdown of food
A
- increases surface area of food, preparing it for digestion by enzymes
- chewing, mixing food w/ saliva by tongue
- churning food in the stomach
- segmentation (rhythmic local constriction) of small intestine
6
Q
Digestion
A
-series of catabolic steps in which enzymes secreted into the lumen of the alimentary canal break down complex food molecules to their chemical building blocks
7
Q
Absorption
A
-passage of digested end products and vitamins, minerals, and water from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph
8
Q
Defecation
A
-eliminates indigestible substances from the body via the anus in the form of feces
9
Q
What does stimulating receptors in the GI tract do?
A
- activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood
- stimulates smooth muscle of the GI tract walls to mix lumen contents and move them along the tract
10
Q
Intrinsic controls of digestive activity–“gut brain”
A
- nerve plexuses and hormone producing cells
- gut brain–consists of enteric nerve plexuses spread like chicken wire along the entire length of the GI tract and regulates digestive activity all along the tract
11
Q
Short reflexes of GI
A
-mediated by the local enteric plexuses in response to stimuli in the GI tract
12
Q
Long reflexes of GI
A
-initiated by stimuli arising inside or outside the GI tract and involve CNS centers and extrinsic autonomic nerves
13
Q
Visceral peritoneum
A
covers external surfaces of most digestive organs and is continuous with the parietal peritoneum
14
Q
Parietal peritoneum
A
-lines the body wall
15
Q
Peritoneal cavity
A
- b/t the two peritoneums
- slitlike potential space containing slippery fluid secreted by serious membranes
- lubricates the mobile digestive organs allowing them to glide across one another and along the body wall to carry out their activites
16
Q
Mesentary
A
- double layer of peritoneum
- sheet of 2 serous membranes fused back to back
- extends to digestive organs from the body wall
- provide routes for blood vessels, lymphatics and nerves to reach the digestive viscera
- holds organs in place
- stores fat
17
Q
Retroperitoneal organs
A
- organs become retroperitoneal during development b/c some regions of the small intestine adhere to the abdominal wall and lose their mesentary
- most of the pancreas, duodenum, parts of large intestine
18
Q
Peritonitis
A
- inflammation of the peritoneum
- usually happens from a burst appendix that sprays feces all over the peritoneum
19
Q
Splanchnic circulation
A
- arteries that branch off abdominal aorta to serve the digestive organs and the hepatic portal circulation
- arteries: branches of celiac trunk supply the spleen, liver, and stomach ; mesentarics supply the small and large intestines
- hepatic portal circulation: collects nutrient rich venous blood draining from the digestive viscera and delivers it to the liver
20
Q
Alimentary canal
A
- from esophagus to anus
- has same four layers: mucosa, submucosa, muscularis externa, and serosa
21
Q
Mucosa
A
- innermost layer
- moist epithelial membrane
- secretes mucus, digestive enzymes and hormones
- absorbs the end products of digestion in the blood
- protects against infectious disease
22
Q
Layers of the mucosa
A
- lining epithelium
- lamina propria
- muscularis mucosae
- -mouth, esophagus, and anus are stratified squamous
- -the rest of the canal is simple columnar epithelium
23
Q
Lamina propria of the mucosa
A
- under the epithelium
- loose areolar connnective tissue
- its capillaries nourish the epithelium and absorb digested nutrients
- defend us against bacteria and other pathogens that easily get to the digestive tract
- large collections of lymphoid follicles in the pharynx and appendix
24
Q
Muscularis mucosae of the mucosa
A
- external to lamina propria
- produces local movement of the mucosa
25
Submucosa
- external to mucosa
- aerolar connective tissue
- contains rich supply of blood and lymphatic vessels, lymphoid follicles and never fibers
- supply the surrounding tissues of the GI tract wall
- elastic fibers enable the stomach to regain its normal shape after storing a meal
26
Muscularis externa
- surrounds submucosa
- responsible for segmentation and peristalsis
- has internal circular layer and external longitudinal layer of smooth muscle cells
- at some points the circular layer thickens and forms sphincters (prevent backflow)
27
Serosa
- outermost layer of intraperitoneal organs (visceral peritoneum)
- areolar connective tissue covered with mesothelium and a single layer of squamous epithelial cells
- in the esophagus, the serosa is replaced by an adventitia--fibrous connective tissue that binds the esophagus to surrounding structures
- -retroperitoneal organs have serosa and adventitia
28
Enteric neurons
- regulate digestive system activity
- semiautonomous
- constitute the bulk of the intrinsic nerve plexuses: the submucosal and myenteric
- provide the major nerve supply to the GI tract wall and control GI tract motility
29
Submucosal nerve plexus
-occupies the submucosa
30
Myenteric nerve plexus
-lies b/t circular and longitudinal muscle layers of the muscularis externa
31
Enteric nervous system is linked to the central nervous system by what?
- afferent visceral fibers
- sympathetic and parasympathetic branches of the autonomic nervous system that enter the intestinal wall and synapse w/ neurons in the intrinsic plexuses
- -sympathetic: inhibits digestive activity
- -parasympathetic: enhance digestive activities
32
What type of tissue is in the mouth?
- stratified squamous epithelium
| - the gums, hard palate, and dorsum of the tongue are keratinized for extra protection against abrasion
33
Obicularis oris muscle
-forms the fleshy lips
34
Buccinator
-forms the cheeks
35
Hard palate
- underlain by palatine bones and palatine processes of the maxillae
- mucosa on either side of the midline ridge (raphe) is corrugated to help create friction
36
Soft palate
-closes off nasopharynx when we swallow
37
How is the soft palate anchored to the tongue? The oropharynx?
- by the palatoglossal arches
- palatopharyngeal arches
- these two pairs of arches form the fauces
38
Fauces
- created by the palatoglossal arches and palatopharyngeal arches
- it is the arched area of the oropharynx that contains the palantine tonsils
39
Intrinsic muscles of the tongue
- confined in the tongue and aren't attached to bone
| - allow tongue to change its shape as needed for speech and swallowing
40
Extrinsic muscles of the tongue
- extend to the tongue from their points of origin on bones of the skull or soft palate
- alter tongues position: protrude it, retract it, and move it from side to side
41
Papillae of the tongue
- filiform—whitish, give the tongue roughness and provide friction
- fungiform—reddish, scattered over the tongue
- circumvallate (vallate)—V-shaped row in back of tongue
- -----these three house taste buds
- foliate—on the lateral aspects of the posterior tongue
42
Buccal salivary glands (intrinsic)
- scattered in the oral mucosa
- secretes saliva
- cleans the mouth
- moistens and dissolves food chemicals
- aids in bolus formation
- contains enzymes that begin the breakdown of starch
43
Parotid gland (extrinsic)
- anterior to the ear, external to the masseter muscle
| - opens into the vestibule next to second upper molar
44
Submandibular gland (extrinsic)
- medial to the body of the mandible
| - duct opens at the base of the lingual frenulum
45
Sublingual gland (extrinsic)
- anterior to the submandibular gland under the tongue
| - opens via 10–12 ducts into the floor of the mouth
46
Saliva composition
-secreted by serous and mucous cells
-97–99.5% water, slightly acidic solution containing
electrolytes—Na+, K+, Cl–, PO4 2–, HCO3–
-digestive enzymes: salivary amylase and lingual lipase
-proteins: mucin, lysozyme and IgA
-metabolic wastes—urea and uric acid
-lysozyme, IgA, defensin, and a cyanide compound protect against microorganisms
47
Control of saliva
-intrinsic glands continuously keep the mouth moist
-extrinsic salivary glands produce secretions when
ingested food stimulates chemoreceptors and mechanoreceptors in the mouth
-salivatory nuclei in the brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX
-strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)
48
Tooth
- enamel covered crown and cement-covered root
- most is dentin which surrounds the central pulp cavity
- a periodontal ligament secures the tooth to th ebony alveolus
49
Gingivitus
- plaque calcifies to form calculus (tartar)
- calculus disrupts the seal between the gingivae and the teeth
- anaerobic bacteria infect gums
- infection reversible if calculus removed
50
Pharynx
- oropharynx and laryngopharynx
- allow passage of food, fluids, and air
- stratified squamous epithelium lining
- skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors
51
Esophagus
- flat muscular tube from laryngopharynx to stomach
- pierces diaphragm at esophageal hiatus
- joins stomach at the cardiac orifice
- esophageal mucosa contains stratified squamous epithelium which changes to simple columnar at the stomach
- esophageal glands in submucosa secrete mucus to aid in bolus movement
- skeletal superiorly and smooth inferiorly
- adventitia instead of serosa
52
Deglutition
- involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups
- buccal phase--voluntary contraction of the tongue
- pharyngeal-esophageal phase--nvoluntary
- control center in the medulla and lower pons
53
Chewing
- break down food, tongue mixes it w/ saliva and forms a bolus
- digestion of starch begins
- 5th cranial nerve innervates muscles of mastication
- chewing is voluntary but also involves stretch receptors that are involuntary
54
Buccal phase
- occurs in mouth and is voluntary
- form bolus and force it into the oropharynx
- food stimulates tactile receptors in the pharynx and involuntary relax activity occurs
55
Pharyngeal-esophageal phase
- uvula and larynx rise to prevent food from entering respiratory passageways
- upper esophageal sphincter relaxes, allowing food to enter the esophagus
- constrictor muscles of pharynx contract, forcing food into the esophagus
- upper esophageal sphincter closes after food enters
- peristalsis moves food through the esophagus to the stomach
- gastroesophageal sphincter surrounding the cardial oriface opens and food enters the stomach
56
Swallowing center-Medulla
- sensory input from pharnyx and esophagus
- coordinates activity from vagal nuclei with other centers (e.g. inhibits respiratory center)
- food in pharynx--afferent sensory input via vagus/glossopharyngeal nerve
- swallowing center-brain stem nuclei-efferent input to pharynx.
57
Esophageal pressures
-high resting pressures in upper esophageal sphincter and lower esophageal sphincter
UES - keeps air from entering esophagus
LES - prevents acid reflux into esophagus
58
Dysphagia from a stroke or cranial nerve damage
- aspiration - UES and pharyngeal contractions are not coordinated
- secondary peristalsis is still functional
59
GERD
-heartburn/acid indigestion (1/10 people)
-backwash of acid, pepsin, and bile into esophagus
Can lead to -
stricture of esophagus (scar tissue)
asthma (aspiration)
chronic sinus infection (reflux into throat)
Barrett’s esophagus (squamous replaced by goblet cells--strongly correlated w/ cancer)
60
Achalasia and Megaesophagus
- motility disorder affecting lower 2/3 of esophagus
- LES fails to relax - LES pressure is high
- organized peristaltic contractions are absent
- myenteric plexus issues (neurological)
- after months/years causes megaesophagus develops
- the esophagus can hold > 1 liter of food
- esophageal ulceration, rupture, and death can occur
61
Gross anatomy of stomach
- cardiac region (cardia)--surrounds the cardiac orifice
- fundus--dome-shaped region beneath the diaphragm
- pyloric region: antrum, pyloric canal, and pylorus--continuous with the duodenum through the pyloric valve (sphincter)
- lesser omentum--from the liver to the lesser curvature
- greater omentum--drapes from greater curvature, anterior to the small intestine
62
Autonomic nervous system nerve supply to stomach
- sympathetic via splanchnic nerves and celiac plexus
| - parasympathetic via vagus nerve
63
Blood supply of stomach
- celiac trunk--gastric and splenic branches
| - veins of hepatic portal system which ultimately drain into the hepatic vein
64
Tunics of the stomach
- four tunics
- three layers of smooth muscle
- inner oblique layer allows stomach to churn, mix, move, and physically break down food
65
Mucosal barrier in the stomach
- protects it from itself
- simple columnar epithelial cells with gastic pits that lead to gastic glands
- thick coating of bicarbonate-rich mucus builds up on stomach wall
- epithelial cells of the mucosa are joined together by tight junctions that prevent gastric juice from leaking into underlying tissues
- damaged epithelial mucosal cells are shed and quickly replaced by undifferentiated stem cells that reside where gastric pits join the gastric glands
66
Secretory cells in the gastric glands
- cheif cells--produce pepsinogen which activates protein digesting enzyme pepsin
- parietal cells--secrete hydrochloric acid--needed for activating pepsin and acid helps break down cell walls of food, and intrinsic factor--needed for absoprtion of B12 in the small intestine
- mucous neck cells--produce mucous
- enteroendocrin cells--secrete hormones to target digestive system organs
67
Cephalic phase of gastric secretion
- occurs before food enters stomach and it triggered by the smell, taste, or sight of food
- sensory inputs form olfactory receptors and taste buds are relayed to the hypothalamus which stimulates the vagal nuclei of the medulla oblongata--this sends motor impulses via the vagus nerves to the parasympatheic ganglia--the neurons here stimulate the stomach glands
- depression or no appetite suppresses this reflex
68
Gastric phase of gastric secretion
- ACh, histamine, and gastrin stimulate parietal cells
- all three are necessary for maximum HCl secretion
- antihistamines block H2 receptors and decrease HCl release
69
Intestinal phase of gastric secretion
-brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones)
70
Gastric contractile activity
- peristaltic waves move toward the pylorus at the rate of 3 ml per minute
- basic electrical rhythm initiated by pacemaker cells (cells of Cajal)
- distension and gastrin increase force of contraction
- most vigorous near the pylorus
- chyme is either delivered in 3 ml spurts to the duodenum, or forced backward into the stomach
71
Regulation of gastric emptying
- as chyme enters the duodenum receptors respond to stretch and chemical signals
- enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling
- carbohydrate-rich chyme moves quickly through the duodenum
- fatty chyme remains in the duodenum 6 hours or more
72
Duodenum
- contains the bile duct and main pancreatic duct--they join at the hepatopancreatic ampulla
- enter the duodenum at the major duodenal papilla
- controlled by the hepatopancreatic sphincter
73
What increases the surface area of the small intestine?
- circular folds of the mucosa and submucosa--force chyme to spiral through so it takes longer and more nutrients can be absorbed
- villi-motile fingerlike extensions of the mucosa--villus epithelium is simple columnar absorptive cells (enterocytes) and goblet cells
- mircovilli-projections (brush border) of absorptive cells--brush border has enzymes that complete digestion of carbs and proteins in sm. intestine
74
Intestinal crypts
- epithelial cells are secretory cells that produce intestinal juice
- enteroendocrine cells
- intraepithelial lymphocytes (IELs)--release cytokines that kill infected cells
- paneth cells--secrete antimicrobial agents (defensins and lysozyme)
- stems cells that differentiate
75
Peyer's patches
-protect against bacteria
76
Duodenal glands
- produce alkaline mucus barrier that helps neutralize acidic chyme moving in from the stomach
- erosion causes duodenal ulcers
77
Intestinal juice
- secreted in response to distension or irritation of the mucosa
- slightly alkaline and isotonic with blood plasma
- largely water, enzyme-poor, but contains mucus
- facilitates transport and absorption of nutrients
78
Liver lobes
-right, left, caudate, quadrate
79
Liver ligaments
- falciform ligament--separates the (larger) right and (smaller) left lobes and suspends liver from the diaphragm and anterior abdominal wall
- round ligament (ligamentum teres)--remnant of fetal umbilical vein along free edge of falciform ligament
80
Liver vascularture
-hepatic artery and vein enter the liver at the porta hepatis
81
Ducts associated with the liver
- common hepatic duct leaves the liver
- cystic duct connects to gallbladder
- bile duct formed by the union of the above two ducts
82
Liver lobules
- hexagonal structural and functional units
- filter and process nutrient-rich blood
- composed of plates of hepatocytes (liver cells) that radiate outward from the longitudinal central vein
83
Portal triad
- each of the 6 corners of a lobule is a portal triad
| - contains a branch of the hepatic artery, a branch of the hepatic portal vein, and a bile duct
84
Liver sinusoids
-leaky capillaries between hepatic plates
85
Kupffer cells aka stellate macrophages
-hepatic macrophages in liver sinusoids
86
Hepatocyte functions
- process bloodborne nutrients
- store fat-soluble vitamins
- perform detoxification
- produce ~900 ml bile per day
87
Bile
- yellow-green, alkaline solution containing
- -bile salts: cholesterol derivatives that function in fat emulsification and absorption
- -bilirubin: pigment formed from heme
- -cholesterol, neutral fats, phospholipids, and electrolytes
88
Enterohepatic circulation
-recycles bile salts
89
Gall bladder
- thin-walled muscular sac
- stores and concentrates bile by absorbing its water and ions
- releases bile via the cystic duct, which flows into the bile duct
90
Pancreas
- pancreatic islets secrete insulin and glucagon
- acini (clusters of secretory cells) secrete pancreatic juice
- zymogen granules of secretory cells contain digestive enzymes
91
Pancreatic juice
- watery alkaline solution (pH 8) neutralizes chyme
- has electrolytes (primarily HCO3–)
- enzymes--amylase, lipases, nucleases are secreted in active form but require ions or bile for optimal activity
- proteases secreted in inactive form--activated in duodenum where they do their work---trypsinogen is activated to trypsin by brush border enzyme enteropeptidase---procarboxypeptidase and chymotrypsinogen are activated by trypsin
92
What is bile secretion stimulated by?
- bile salts in enterohepatic circulation
| - secretin from intestinal cells exposed to HCl and fatty chyme
93
What stimulates the gallbladder contraction?
-gallbladder contraction is stimulated by
cholecystokinin (CCK) from intestinal cells exposed to proteins and fat in chyme
-vagal stimulation (minor stimulus)
-CKK also causes the hepatopancreatic sphincter to relax (Sphinctor of Oddi)
94
Regulation of pancreatic secretion
- CCK induces the secretion of enzyme-rich pancreatic juice by acini
- secretin causes secretion of bicarbonate-rich pancreatic juice by duct cells
- vagal stimulation also causes release of pancreatic juice (minor stimulus)
95
Digestion and absorption requirements for the small intestine
- slow delivery of hypertonic chyme
- delivery of bile, enzymes, and bicarbonate from the liver and pancreas
- mixing
96
Segmentation (motility of the sm. intestine)
- initiated by intrinsic pacemaker cells
- mixes and moves contents slowly and steadily toward the ileocecal valve
- intensity is altered by long and short reflexes
- wanes in the late intestinal (fasting) phase
97
Peristalsis (migrating motor complex)
- initiated by motilin in the late intestinal phase
- each wave starts distal to the previous (the migrating motility complex)
- meal remnants, bacteria, and debris are moved to the large intestine
- local enteric neurons coordinate intestinal motility
- cholinergic sensory neurons may activate the myenteric plexus
- causes contraction of the circular muscle proximally and of longitudinal muscle distally
- forces chyme along the tract
98
Ileocecal control (motility in the sm. intestine)
- ileocecal sphincter relaxes and admits chyme into the large intestine when--gastroileal reflex enhances the force of segmentation in the ileum and gastrin increases the motility of the ileum
- ileocecal valve flaps close when chyme exerts backward pressure
99
Large intestine
- teniae coli--three bands of longitudinal smooth muscle in the muscularis
- haustra--pocket like sacs caused by the tone of the teniae coli
- epiploic appendages--fat-filled pouches of visceral peritoneum
100
Colon
- part of lg intestine
- ascending colon and descending colon are retroperitoneal
- transverse colon and sigmoid colon are anchored via mesocolons (mesenteries)
101
Rectum and anus
- part of lg intestine
- three rectal valves stop feces from being passed with gas
- -anal canal--the last segment of the large intestine
- -sphincters--internal anal sphincter—smooth muscle and external anal sphincter—skeletal muscle
102
Microscopic anatomy of the lg intestine
- mucosa of simple columnar epithelium except in the anal canal (stratified squamous)
- abundant deep crypts with goblet cells--mucus produced by goblet cells eases the passage of feces and protects the intestinal wall form irritating acids and gases
- superficial venous plexuses of the anal canal form hemorrhoids if inflamed
103
Bacterial flora
- enter from the small intestine or anus
- colonize the colon, ferment indigestible carbohydrates, release irritating acids and gases, synthesize B complex vitamins and vitamin K
104
Large intestine functions
- vitamins, water, and electrolytes are reclaimed
- major function is propulsion of feces toward the anus
- colon is not essential for life
105
Haustral contractions
- slow segmenting movements
| - haustra sequentially contract in response to distension
106
Gastrocolic reflex
- initiated by presence of food in the stomach
| - activates three to four slow powerful peristaltic waves per day in the colon (mass movements)
107
Defication
- mass movements force feces into rectum
- distension initiates spinal defecation reflex
- parasympathetic signals stimulate contraction of the sigmoid colon and rectum and relax the internal anal sphincter
- conscious control allows relaxation of external anal sphincter
108
Digestion of carbohydrates
-digestive enzymes--salivary amylase, pancreatic amylase, and brush border enzymes (glucoamylase, dextrinase, lactase, maltase, and sucrase)
109
Absorption of carbohydrates
- secondary active transport (cotransport) with Na+
- facilitated diffusion of some monosaccharides
- enter the capillary beds in the villi
- transported to the liver via the hepatic portal vein
110
Digestion of proteins
- enzymes: pepsin in the stomach
- pancreatic proteases--trypsin, chymotrypsin, and carboxypeptidase
- brush border enzymes--aminopeptidases, carboxypeptidases, and dipeptidases
111
Absorption of proteins
-absorption of amino acids is coupled to active transport of Na+
112
Digestion of lipids
- pre-treatment—emulsification by bile salts
| - enzymes—pancreatic lipase
113
Absorption of lipids
- glycerol and short chain fatty acids
- --absorbed into the capillary blood in villi
- --transported via the hepatic portal vein
- monoglycerides and fatty acids
- --cluster with bile salts and lecithin to form micelles
- --released by micelles to diffuse into epithelial cells
- --combine with proteins to form chylomicrons
- --enter lacteals and are transported to systemic circulation
114
Amphipathic nature enables bile salts to perform what two functions essential for fat digestion and absorption?
- emulsification of lipids - detergent action causes fat globules to break down into microscopic droplets allowing them to be digested effectively.
- transport of lipids - bile salts carry lipids (monoglycerides, fatty acids, cholesterol, others) to intestinal wall in the form of micelles.
115
Digestions of nucleic acids
-enzymes--pancreatic ribonuclease and deoxyribonuclease
116
Absorption of nucleic acids
-active transport--transported to liver via hepatic portal vein
117
Vitamin absoprtion
- in small intestine...
- water-soluble vitamins (vitamin C and B vitamins) are absorbed by diffusion or by passive or active transporters.
- fat-soluble vitamins (A, D, E, and K) are carried by micelles and then diffuse into absorptive cells
- vitamin B12 binds with intrinsic factor, and is absorbed by endocytosis
- vitamin K, biotin, and B vitamins from bacterial metabolism are absorbed
118
Water-soluble vitamins
- wash out of foods/body easily, less easily stored.
- B1/Thiamine Deficiency--Beri-Beri--Wernicke Korsakoff syndrome
- B12/cyanocobalamin, Niacin, Folacin
119
Fat-soluble vitamins
Deficiencies
A-poor absorption cue to diet, bowel disease, bile flow. Night blindness, xerophthalmia
D-softening of bones. renal stones from toxicity
Ricketts, osteomalacia
E-interfere w/ hormone action, clotting,
K-Hemolytic anemia, kernicterus (bili in the brain) and poor clotting
-toxicity more likely
120
Electrolyte absorption
-mostly along the length of small intestine
Iron and calcium are absorbed in duodenum
Na+ is coupled with absorption of glucose and amino acids
Ionic iron is stored in mucosal cells with ferritin
K+ diffuses in response to osmotic gradients
Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH)
121
Water absorption
95% is absorbed in the small intestine by osmosis
Net osmosis occurs whenever a concentration gradient is established by active transport of solutes Water uptake is coupled with solute uptake
122
Malabsorption of nutrients
-Causes--anything that interferes with delivery of bile or pancreatic juice and damaged intestinal mucosa (e.g., bacterial infection)
-Gluten-sensitive enteropathy (celiac disease)
Gluten damages the intestinal villi and brush border
Treated by eliminating gluten from the diet (all grains but rice and corn)
