digestion Flashcards
What is the alimentary canal?
the digestive tract
also known as
GI tract
gut
includes: mouth, esophagus, stomach, small and large intestine
give some examples of accessory organs.
teeth, tongue, salivary glands, liver, gall bladder, pancreas
What are the two main groups of organs in the digestive system?
Alimentary canal
Accessory organs
List the 5 essential activities of the digestive system
1) eating
2) propulsion and mixing
3) digestion
4) absorption
5) elimination
What are the two types of receptors in the digestive system? What do they respond to?
MECHANORECEPTORS: respond to stretch
CHEMORECEPTORS: respond to changes in osmolarity, pH, chemical comp
What do the reflexes stimulated by chemoreceptors in the digestive system do?
1) stimulate smooth muscle to mix and move lumen contents
2) activate or inhibit digestive glands
What are the two types of control of the digestive system?
EXTRINSIC control: from without
INTRINSIC control: from within
Describe the two forms of extrinsic controls of the digestive system
NEURAL:
- LONG reflexes in response to stimuli inside or outside the GI tract that involve CNS centers and autonomic nerves
HORMONAL:
- endocrine gland secretes hormones that influence GI activities
Describe the two forms of intrinsic controls of the digestive tract
NEURAL:
- SHORT reflexes from one part of DT (digestive tract) to another. Enteric nerve plexuses (gut brain) send these in response to stimuli in the gut
HORMONAL:
- enteric hormones from enteroendicrine cells in stomach and small intestine stimulate target cells in the same or different organs
What is the peritoneum?
the serous membranes of the abdominal membrane
Describe the three components that make up the peritoneum.
1) Parietal layer: lines body wall
2) Visceral layer: covers the organs
3) serous fluid between layers acts as lubricator
What are mesenteries?
extensions of the peritoneal wall
What do mesenteries do?
- anchor organs to the wall
- carry nerve fibers and blood and lymph vessels
- store fat
Describe the two possible locations of DS organs
1) INTRAPERITONEAL: organs are inside peritoneal cavity (most DS organs)
2) RETROPERITONEAL: organs lie posterior to the peritoneum embedded in the body wall. Anterior surface covered by peritoneum, posterior by adventitia
give an example of a few retroperitoneal organs
most of the duodenum
pancreas
parts of colon
What are the two blood supplies for the DT, what do they supply?
SPLANCHNIC circulation: hepatic, splenic, left gastric, and mesenteric arteries (supply O2 and nutrients)
HEPATIC PORTAL system: carries blood from DT to liver for processing of nutrients
What are the four tunics of the DT wall?
outer to inner
SEROSA
MUSCULARIS EXTERNA
SUBMUCOSA
MUCOSA
Describe the serosa layer of the DT
= visceral peritoneum
- areolar CT + squamous ep
- joined to mesenteries
- produces serous fluid
What is the adventitia. Do organs that have adventitia also have serosa
Adventitia is the tissue that surrounds the esophagus and the body wall side of retroperitoneal organs. Acts as anchor
yes, they have both
Describe the muscularis externa layer of the DT
Smooth muscle in 2 layers: inner circular, outer longitudinal
- responsible for peristalsis (movement) and segmentation (mixing)
- contains myenteric nerve plexus (part of the gut brain)
- sphincters are formed by the circular layer to keep movement unidirectional.
Describe the submucosa layer of the DT
made of elastic CT
- supplies mucosa with blood, lymph vessels, and nerves
- has glands that secrete into lumens (ex mucus)
- contains submucosal nerve plexus
What is the role of the mucosa layer of the DT?
to carry out digestion and absorption
What are the 3 sublayers of the mucosa layer of the DT? describe each.
LINING EPITHELIUM: varies from strat. squamous to simple columnar with mucus. Has hormone and enzyme secreting cells
LAMINA PROPRIA: loose areolar CT with capillaries and lymph nodules to protect against infection
MUSCULARIS MUCOSAE: thin layer of smooth muscle that causes local movement of mucosa; pulls mucus into folds
What is the enteric nervous system?
the intrinsic nervous system entirely within the gut that regulate activities via short reflexes
What are the 2 components of the enteric nervous system?
SUBMUCOSAL NERVE PLEXUS: regulates glands and smooth muscle in the mucosa
MYENTERIC NERVE PLEXUS: in muscularis externa - controls contraction of muscularis externa (motility)
How is the enteric nervous system linked to the CNS
linked by long reflexes of autonomic branch of nervous system
SYMPATHETIC fibers: inhibit digestion
PARASYMPATHETIC fibers: stimulate digestion
What are the functions of the mouth?
ingestion, mastication, beginning of chem digestion
What is mastication?
chewing
What are the 5 parts in the mouth that assist with its processes?
MUCOSA: lined with stratified squamous ep (protection) release defensins when dmgd
LIPS: assist with moving food, holds it in
HARD PALATE: tongue forces food against it in forming bolus
SOFT PALATE: uvula blocks nasopharynx during swallowing
TONGUE: moves and mixes food with saliva.
What is a bolus?
a ball of chewed food
What are the four types of papillae on the tongue?
FILIFORM papillae: smallest and most numerous. Generates friction
FUNGIFORM papillae: reddish and scattered over tongue - have taste buds
CIRCUMVALLATE papillae: V shaped row on back of tongue - have taste buds
FOLIAATE papillae: on lateral aspects of posterior tongue - have taste buds
What are the types of salivary glands?
intrinsic (buccal) glands: small and scattered in mucosa. produce small amounts of saliva continuously
Extrinsic glands - large and paired, empty through ducts into mouth.
PAROTIDS: contain only serous cells
SUBMANDIBULAR & SUBLINGUAL: open under tongue, have serous and mucus cells
Describe the chemical composition of saliva
- pH 6.75 - 7.00
- mostly water
- has ions
- salivary amylase
- mucin
- small amounts of metabolic waste
- defensive compounds
What are the functions of saliva?
1) clean mouth
2) dissolve taste chemicals
3) moisten and compact food
4) begin digestion of carbs
5) releases protection against bacteria
What are some examples of protection against bacteria found in the saliva?
IgA
lysozyme
Cyanide compound
Defensins
Describe the control of the two types of salivary glands.
Extrinsic: by parasympathetic fibres in the autonomic nervous system (can have reflex response)
Intrinsic: active all the time, but inhibited during stress by sympathetic NS
What are deciduous teeth?
teeth that are formed in childhood and fall out as permanent teeth develop
How many deciduous teeth are there?
20
How many permanent teeth are there?
32
What are the 3 classes of teeth?
INCISORS: chisel shaped for cutting (I)
CANINES: fanglike for tearing/piercing (C)
PREMOLARS, MOLARS: broad crowns with rounded cusps for grinding/crushing (PM, M)
What is the dental formula?
shorthand way of indicating the number of teeth and relative position of teeth
deciduous:
2 I, 1 C, 2M
(so five left top x 4 = 20)
permanent:
2 I, 1 C, 2PM, 3M
so 8x4 = 32
Describe the structure of the teeth.
Enamel: composed of Ca salts
Dentin: bone-like material under enamel
Pulp cavity: cavity surrounded by dentin
Pulp: CT blood vessels, and nerves
Root canal: extends from pulp cavity to the root
What is the hardest material in the body?
enamel on teeth
What does the pharynx do?
connects mouth and esophagus.
divided into naso, oro, and laropharynx
lined with sq ep and goblet cells
2 skeletal muscle layers: contract to move food to esophagus by peristalsis
What is the esophagus?
10 inch tube through mediastinum and diaphragm to abdomen
connects laryngopharynx to stomach
What are the 2 sphincters in the esophagus?
UPPER ESOPHAGEAL: closed except during swallowing
GASTROESOPHAGEAL: prevents backflow from stomach
Describe the wall structure of the esophagus
has same 4 walls as DT, but adventitia instead of serosa
- Mucosa: strat sq ep
- Submucosa: glands that secrete mucus
- Muscularis externa: upper 1/3 skeletal, lower 1/3 smooth muscle, middle is mixture of both
What is the function of the pharynx and esophagus?
swallowing of bolus and transport to stomach
What is deglutition?
swallowing
What are the two phases of deglutition (swallowing)?
1) Buccal phase: voluntary control - tongue pushes food into pharynx
2) PHARYNGEAL-ESOPHAGEAL phase: involuntary
Describe the process of the pharyngeal-esophageal phase of deglutition (swallowing)
1) bolus stretches wall -> stimulates receptors in pharynx -> impulse to swallowing center in medulla and pons -> motor impulse sent through vagus nerve -> muscles contract
2) upper esophageal sphincter relaxes
- uvula blocks nasal cavity
- tongue blocks mouth
- epiglottis blocks glottis
3) bolus enters esophagus -> peristalsis to stomach -> gastroesophageal sphincter relaxes -> bolus enters stomach
what is another name for the gastroesophageal sphincter?
cardiac sphincter
Describe the stomachs volume when full and empty
50 mL empty
4000 mL full
Describe the gross anatomy of the stomach.
CARDIAC region: superior. right below esophagus
FUNDUS: dome shaped region at top
BODY: mid portion
PYLORIC REGION: from right to left; antrium, canal, sphincter
GREATER CURVATURE: convex lateral surface
Lesser curvature: convex medial side
what is the difference between the muscularis externa of the stomach and that of the basic structure of the DT
Has 3 layers instead of 2
circular, longitudinal and oblique
What are the 2 mesenteries associated with the stomach?
LESSER OMENTUM: hangs from liver to lesser curvature of stomach
GREATER OMENTUM: hangs from greater curvature of stomach
What is the surface epithelium of the stomach made up of? what do they do?
simple columnar epithelium with goblet cells.
secrete mucus layer that traps alkaline fluid beneath it (counteracts acid)
Explain how gastric juice is released into the stomach?
gastric glands produce the juice which flows into gastric pits then the stomach
What are the 4 types of cells found in the gastric glands of the stomach?
Parietal cells
Chief cells
Enteroendocrine cells
Mucous neck cells
What do mucous neck cells in the gastric glands?
role is not understood
secrete a slightly acidic mucus
What do parietal cells in the gastric glands produce?
produce:
- intrinsic factor (for B12 absorption)
- HCL (pH 1.5-3.5)
What is the purpose of the HCL produced by parietal cells in the gastric glands?
- activates pepsinogen
- kills bacteria
- denatures protein fibres
- breakdown of plant cell walls
What do chief cells in the gastric glands produce?
inactive enzyme pepsinogen
- does not become active until it comes into contact with HCL or pepsin (pos feedback loop)
- becomes pepsin when activated
- begins protein digestion
What do enteroendocrine cells produce?
enteric hormones into the blood
regulate various parts of DT
What are some examples of enteric hormones and what do they do?
gastrin, histamine and serotonin inc gastric activity
somatostatin dec gastric activity
Explain the stomach’s methods for protection against self-digestion.
Mucosa:
- produces thick layer of alkaline mucuus
- tight junctions between cells
- cell membranes impermeable to HCL
- stem cells at entrance to gastric pits that undergo rapid mitosis to replace damaged cells
Pepsinogen: pepsin is released in inactive form (so not to digest bodies proteins)
How often are the surf ep cells replaced in the stomach?
every 3-6 days
What is gastritis?
inflammation caused by anything that breaches the mucosal barrier
What are gastric ulcers?
erosion of the stomach wall
most caused by a bacteria helicobacter pylori
What is pernicious anemia?
caused by lack of intrinsic factor and therefore can’t absorb B12 which is required for iron absorption
Describe the digestive processes in the stomach.
1) storage of food
2) physical digestion (churning)
3) prepares food to enter intestine (converts to chyme)
4) beginning of chem digestion of proteins
6) little absorption, but some lipid soluble substances like alcohol and aspirin
Describe how the chemical digestion process is started in the stomach.
HCL denatures proteins and breaks meat fibres
pepsin converts polypeptides to polypeptide fragments
How much secretion does the stomach output in a day?
up to 3L
Explain how gastric secretion is regulated.
both neural and hormonal control
stimulated or inhibited by stimuli from head, stomach, small intestine
What are the 3 phases of regulation of gastric secretion?
Cephalic
Gastric
Intestinal
Describe what happens during the cephalic phase of stimulation?
Long reflexes triggered by thought, smell, taste
stimuli -> brain -> vagus nerve -> enteric ganglia -> gastric glands -> increase secretion
Describe what happens during the gastric phase of stimulation?
long and short reflexes and hormonal controls triggered by FOOD ENTERING stomach
1) Distension: stretching of wall
stretch receptors -> vagus nerve -> medulla -> vagus nerve -> gastric glands -> increased secretion
distension also intrinsically causes gastric glands to secrete
2) Chemoreceptors: presence of proteins, caffeine, rise in pH
G cells in gastric glands -> gastrin into blood -> parietal cells -> secrete HCL
Describe what happens during the intestinal phase of stimulation.
triggered by chyme entering the intestine
intestinal cells secrete gastrin -> briefly stimulates gastric activity
further distension with protein fragments, acid, etc initiates ENTEROGAStRIC reflux (inhibits activity
What is the enterogastric reflex?
reflex that inhibits gastric secretion and stimulates closing of pyloric sphincter
How does the enterogastric reflex close the pyloric sphincter?
1) inhibits vagal nuclei in medulla
2) inhibits local reflexes
3) stimulates sympathetic fibers that close the valve
What is the purpose of the enterogastric reflex?
to allow time for the chyme to be processed in small intestine before more is released
What is the process of gastric motility?
1) receptive relaxation - in response to thought, taste
2) adaptive relaxation - muscle relaxes in response to distension
3) plasticity - smooth muscle can be stretched without increasing tension
4) peristalsis:
- peristalsis is gentler at top inc towards pylorus
- pylorus acts like a pump squirting 3mL chyme into duodenum at a time
- pacemaker cells set rhythm of contraction (3/min)
- intensity of contraction is controlled by amount of food present
inc volume -> inc stretch receptors -> inc force -> inc G cells -> inc gastrin
What is a G cell?
cell in the duodenum and stomach that secretes gastrin
How long does it take for the stomach to empty?
3-4 hrs
What factors of the chyme exiting the stomach affect gastric emptying?
1) as chyme enters the duodenum: receptors respond to stretch and chem signals and enterogastric reflex inhibits gastric secretion and emptying
2) Large volume, carbohydrate, or more liquid chyme moves quickly through duodenum (speeds emptying)
3) fatty or high protein chyme remains in the duodenum longer (6hrs or more) slows gastric emptying
What is emesis?
vomiting
emetic center in medulla is stimulated by irritation or extreme stretching of stomach/small intestine
stimulates contraction of diaphragm and abdominal muscles with relaxation of cardiac sphincter
How long is the small intestine?
2-4 m long
what are the three subdivision of the small intestine?
Don’t Jump In
Duodenum
Jejunum
Ilieum
Describe the structures that receive secretions from the gall bladder, liver, and pancreas into the duodenum.
bile duct receives from liver and gall bladder
pancreatic duct from the pancreas
these two ducts join at the hepatopancreatic ampulla
enter at the major duodenal papilla
are controlled by the sphincter of Oddi
What are the three modifications in the small intestine that give it a large surface area?
Plicae circularis (circular folds)
Villi
Microvilli
What are the plicae circularis
they are circular folds of mucosa and submucosa in the small intestine
they:
- force chyme to slowly spiral through the lumen
- slows flow to facilitate digestion
What are the villi of the small intestine?
motile fingerlike extensions of the mucosa
have:
- lacteal and capillaries inside
- smooth muscle in core to allow for local movements
What are the microvilli of the small intestine?
outfoldings on the apical surface of cell membranes on villi that form brush border where enzymes are attached.
What types of cells make up the mucosa of the small intestine?
simple columnar ep with microvilli and many goblet cells
also have:
scattered enteroendocrine cells
intra ep lymphocytes: release cytokines that attack antigens
What are intestinal glands?
crypts between the villi that produce intestinal juice
Describe the components of the intestinal glands (crypts)
SECRATORY cells: secrete 1-2L/day of slightly alkaline juice
- mostly water and mucus that aids in carrying and absorbing nutrients
- some free enzymes, most are brush border
STEM cells: in base of crypts rep ep every 3-6 days
- ep cells migrate up the villi and are shed from tip
PANETH cells: secrete defensins and lysozyme
What is the stimulus for release from the intestinal glands (crypts)
distension or irritation of the mucosa by acidic chyme
What are brush border enzymes?
they are attached to luminal surface of ep cells
complete digestion of carbs and proteins
What is the role of the lamina propria in the mucosa?
contains massive network of capillaries for absorption
What are peyer’s patches?
lymphoid tissue that prevents bacteria from entering blood
located in the submucosa
What are Brunner’s glands?
located in the submucosa
secrete alkaline mucus to protect against acid
What does the slowing of the release of chyme from the stomach by the enterogastric reflex allow proper processing for?
allows the duodenum to:
- lower pH so enzymes can function properly
- bile to be mixed in for emulsification of fats
- and for enzymes to be mixed in
What is segmentation?
the most common type of movement in the SI
- mixes contents and moves slowly along toward ileocecal valve
- controlled by pacemakers
- different rates in different parts
What is true peristalsis?
type of movement in SI that occurs only after nutrients have been removed
controlled locally by enteric neurons
What is the migrating mobility complex?
peristaltic waves move distally to transport undigested food, bacteria and debris to the large intestine
2 hrs from duodenum to ileocecal valve
controlled by local reflexes
What is opening of the ileocecal sphincter controlled by?
in response to increased activity in ileum
controlled by:
1) long reflex (gastroileal reflex)
food enters stomach -> inc gastric activity -> cns -> vagus nerve -> inc activity of ileum -> ileocecal valve opens
2) gastrin secretion by stomach
gastrin into blood -> ileum -> inc activity of ileum -> ileocecal valve opens
What prevents back flow of the ileocecal valve?
back pressure
What is the largest gland in the body?
the liver
What are the 2 ligaments that support the liver?
falciform ligament - suspends liver from diaphragm
lesser omentum - anchors to stomach
How is the liver supplied with blood?
hepatic artery and hepatic portal vein
explain how bile is drained from the liver
common hepatic duct from liver and cystic duct from gall bladder
join to form bile duct that drains into duodenum through hepatopancreatic sphincter and ampulla
Describe the microscopic anatomy of the liver.
made up of hexagonal functional units called lobules
Central vein (in middle duh)
PORTAL TRIADS at edge of lobule:
- arteriole: O2 rich blood from hepatic artery
- venule: nutrients from hepatic portal
- bile duct: drains from the canaliculi
SINUSOIDS: leaky capillaries
- filter blood from arteriole and venule to central vein
- has KUPFFER cells; fixed macrophages
HEPATOCYTES: line the sinusoids
What is a hepatocyte?
a functional liver cell
What are the functions of hepatocytes?
1) produce 500-1000mL of bile/day from old RBCs
2) process nutrients from DT
3) store fat soluble vitamins (ex A,D)
4) detoxify blood
What are the ways that hepatocytes process nutrients from the DT?
excess glucose converted to glycogen and stored
make plasma proteins from amino acids
makes non-essential amino acids
packages fatty acids for storage and transport
What is hepatitis?
inflammation of the liver caused by viral infection
What is cirrhosis?
death of hepatocytes because of abuse
ex alcohol, drugs
Is bile acidic or alkaline?
alkaline
What does bile contain?
HCO3- (bicarbonate ion): neutralizes chyme
bile salts (derived from cholesterol) and phospholipids - act as detergent
bile pigments (bilirubin) - biproduct of hemoglobin breakdown
Cholesterol - bile is the major route for getting rid of this
What are the only 2 contents of the bile that aid digestion?
bile salts and phospholipids
they emulsify fats to enhance pancreatic lipase
What is enterohepatic circulation?
route by which bile salts are recycled
bile salts -> duodenum -> reabsorbed from ileum -> hepatic portal blood -> liver - secreted into bile
What does the gall bladder do?
stores and concentrates bile up to 10x by absorbing water and ions
Where is the gall bladder located?
ventral surface of the liver
What hormone causes bile to be released from the bile duct?
CCK
What duct does bile enter from the gall bladder?
goes into the cystic duct which flows into the bile duct
explain the two ways that release and production of bile is controlled
1) if fatty chyme in duodenum enteroendocrine cells secrete:
CCK into blood -> GB walls contract -> bile expelled into cystic duct -> bile duct -> sphincter of oddi opens -> major duodenal papilla -> duodenum to emulsify fats
SECRETIN into blood -> liver produces more bile
2) if no chyme in duodenum:
liver hapatocytes -> bile canaliculi -> bile ducts -> common bile duct -> sphincter of Oddi is shut -> bile backs up cystic duct into GB for storage
What are gall stones?
result of too much cholesterol or not enough bile salts in the bile resulting in:
cholesterol no longer being kept in solution (normally held in by bile salts, but there is an imbalance) and crystalizing. Very painful when GB contracts
What are the two functions of the pancreas?
ENDOCRINE secretion: insulin and glucagon
EXOCRINE secretion: essential for digestion
describe the process of exocrine secretion in the pancreas.
this is the process that makes pancreatic juice
1) duct cells produce alkaline fluid (bicarbonate ion)
2) acinar cells produce enzymes
3) juice drains from small ducts to main pancreatic duct through pancreatic sphincter into hepatopancreatic ampulla
4) released into duodenum by opening of sphincter of Oddi
What are some of the enzymes that are in the pancreatic juice?
FAT digesting: lipase
CARB digesting: pancreatic amylase
PROTEIN digesting: proteases; chymotrypsinogen, trypsinogen, procarboxipeptidase, etc
NUCLEIC acid digesting: nucleases
How are the proteases secreted into the duodenum by the pancreas?
in inactive form to prevent self digestion
How do the proteases become activated?
TRYPSINOGEN is activated by brush border enzyme ENTEROPEPTIDASE to become TRYPAIN
TRYPSIN then activates the rest
Explain the 2 ways that pancreatic secretion is regulated
HORMONAL:
secretin: acid chyme in duodenum -> release of secretin -> duct cells -> secrete alkaline fluid
CCK: protein and fat in duodenum -> release of CCK -> acinar cells secrete enzymes
NEURAL: vagus nerve - parasympathetic division - long reflex
When do neural impulse cause release of pancreatic juice?
during cephalic and gastric phases of gastric stimulation
What are the 8 parts of the large intestine (colon)?
1) cecum
2) appendix
3) ascending, transverse, and descending sigmoid colon
4) rectum
5) anal canal
6) anus
What parts of the colon are retroperitoneal?
ascending and descending colon
What are the three unique features of the colon?
TENIA COLI: longitudinal muscle reduced to 3 strands (like worms)
HAUSTRA: pocket like that form the tone of tenia coli
EPIPLOIC appendages on outside: fat
Describe the structure of the mucosa in the colon?
simple columnar except in the anal canal where it is strat sq
has abundant deep crypts with goblet cells
NO circular folds, villi, or microvilli
What are the 2 types of movement in the colon?
HAUSTRAL contractions: local, move contents from one haustrum to the next
- occur every 30 mins
- response to distension
MASS movements: 3-4 daily
- long slow peristalsus
- triggered by gastrocolic reflex (food entering stomach)
What are the four major functions of the colon?
1) transport of waste
2) absorbs water
3) reabsorbs bile salts and ions
4) houses bacteria
What are some of the purposes of the bacterial flora in the colon?
cause gas from the fermenting of undigested carbs
make vitamins like K and B complex needed for the liver to make clotting proteins
What are the 2 sphincters in the anal canal of the rectum?
internal: made of smooth muscle and is involuntary
external: made of skeletal muscle and is voluntary
Describe the defecation reflex.
1) mass movements force feces into rectum
2) distension initiates spinal defecation reflex
3) parasympathetic signals
4) stimulate contraction of the sigmoid colon and rectum
5) internal anal sphincter relaxes
6) conscious control allows relaxation of external anal sphincter
Why is chemical digestion necessary?
because most of the food that we eat are large polymers and need to be broken down into monomers to be able to penetrate the membranes.
What does chemical digestion involve?
catabolic hydrolysis: reactions in which H20 molecules are inserted and break bonds
What are the 3 types of molecules In Polysaccharides (carbs)
monosaccharides - need no digestion
ex glucose, fructose
disaccharides - need only by hydrolyzed to mono
ex sucrose, lactose, maltose
polysaccharides and oligosaccharides- need multi step hydrolysis process
ex glycogen and starch
Where does polysaccharide/carbohydrate digestion occur?
in the mouth and small intestine
What are polypeptides and where are they digested?
they are proteins
monomer is amino acid
occurs in stomach and small intestine
What are lipids and where does their digestion occur?
fatty acids
only in the small intestines
Describe the process for carbohydrate digestion
mouth:
SALIVARY AMYLASE
poly -> oligosaccharides
stomach: no digestion
small intestine
SALIVARY AMYLASE
poly to oligo and oligo to disaccharides
BRUSH BORDER (dextrinase, glucoamylase) oligo -> disaccharides
BRUSH BORDER DISACCHARASES (maltase, sucrose, lactase)
di -> monosaccharides
mono can now be absorbed
Describe the process of protein/polypeptide digestion
mouth: no digestion
stomach
HCL
meat fibers -> fragments
pepsinogen -> pepsin
PEPSIN
polypeptides -> peptide fragments
peptide fragments -> some amino acids
duodenum
TRYPSIN and CHYMOTRYPSON
peptide fragments -> small peptides
pancreatic CARBOXYPEPTIDASE
brush border AMINO and DIPEPTIDASES
small peptides -> amino acids
Describe the digestion process of lipids.
mouth: no digestion
stomach: no digestion
duodenum:
Liver -> bile
lipid globules -> emulsified fat droplets
pancreatic LIPASE
lipid droplets -> monoglycerides and free fatty acids
How are monosaccharides absorbed?
Mainly in DUODENUM & JEJUNUM
1) into cells by FACILITATED or COTRANSPORT with Na
2) carrier proteins in membrane
3) cross cell by simple diffusion
4) facilitated diffusion into capillaries
5) some di and tri can be absorbed and hydrolyzed in cells
How are amino acids absorbed?
mainly in DUODENUM & JEJUNUM
1) cotransport with Na
2) facilitated diffusion into capillaries
3) some di and tripeptides are actively absorbed and dissolved in cell
EXACT same as monosaccharides
How are lipids absorbed?
mainly in ILEUM
1) monoglycerides and free fatty acids form micelles with bile salts and lecithin
2) micelles move to microvilli
3) lipids leave micelles
4) resynthesized into tryglycerides, formed to chylomicrons by binding to proteins
5) chylomicrons extruded from cell -> enter lacteals -> lymph vessels -> thoracic duct -> into blood at vena cava
6) in blood lipoprotein lipase converts tri back to basic form which then diffuse through capillary walls into tissue cells
7) remainder of chylomicron is converted to lipoproteins in liver (used for cholesterol transport)
How are vitamins absorbed?
from diet by small intestine
formed by bacteria from large intestine
fat soluble with fat into micelles
water soluble by diffusion
vitamin B12 needs intrinsic factor and is absorbed by active transport
