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digestive system

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digestive system
organ system that processes food, extracts nutrients from it, and eliminates the residue. does this in five stages
five stages of digestion
1) ingestion 2) digestion 3) absorption 4) compaction 5) defecation
ingestion
the selective intake of food
digestion
the mechanical and chemical breakdown of food into a form usable by the body
absorption
the uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and the lymph
compaction
absorbing water and consolidating the indigestible residue into feces
defecation
the elimination of feces
2 stages of digestion
mechanical and chemical
mechanical digestion
is the physical breakdown of food into smaller particles. achieved by the cutting and grinding action of the teeth and churning contractions of the stomach and small intestines.
chemical digestion
is a series of hydrolysis reactions that break down dietary macromolecules in their monomers(residues)
digestion: polysaccharides
are broken down into monosaccharides
digestion: proteins
are broken down into amino acids
digestion: fats
are broken down into monoglycerides and fatty acids
digestion: nucleic acids
are broken down into nucleotides
2 divisions of the digestive system
1) the digestive tract 2) the accessory organs
the digestive tract
is a muscular tube extending from the mouth to anus. measuring about 9m (30 ft) long in the cadaver. aka the alimentary canal.
the accessory organs
are the teeth, tongue,salivary glands, liver, gallbladder, and pancreas.
tissue layers of the digestive tract from inner to outer
MUCOSA=epithelium, lamina propria. muscularis mucosae, SUBMUCOSA, MUSCULARIS EXTERNA= inner circular layer, outer longitudinal layer, SEROSA=arelolar tissue, mesothelium
the mucosa (mucus membrane)
lining the lumen consists of an inner epithelium , a loose connective tissue layer called the LAMINA PROPRIA, and a thin layer of smooth muscle called the MUSCULARIS MUCOSAE.
the submucosa
is a thicker layer of loose connective tissue containing blood vessels, lymphatic vessels, a nerve plexus, and in some places, glands that secrete lubricating mucus into the lumen.
the muscularis externa
consists of 2 layers of muscle near the outer surface. cells of the inner layers encircle the tract while those of the outer layer run longitudinally. in some places, the circular layer is thickened to form valves (sphincters) that regulate the passage of material through the tract. the longitudinal layer is responsible for the motility that propels food and residue through the digestive tract.
the serosa
is composed of a thin layer of areolar tissue topped by a simple squamous mesothelium. it begins in the lower 3 to 4 cm of the esophagus and ends just before the rectum.
enteric nervous system
the esophagus, stomach, and intestine have a nervous network called the ________ __________ ________, which regulates digestive tract motility, secretion, and blood flow. this system is thought to have over 100 million neurons--more than the spinal cord. it can function completely independently of the CNS, although the CNS usually exerts a significant influence on its action.
the enteric nervous system is composed of 2 networks of neurons:
1) the submucosal plexus (meissner) 2) the myenteric plexus (auerbach)
the submucosal plexus (meissner)
network of neurons in the submucosa
the myenteric plexus (auerbach)
a network of neurons of the parasympathetic ganglia and nerve fiber between the 2 layers of the muscularis externa. controls peristalsis and the other contractions of the muscularis externa and the submucosae and glandular secretion of the mucosa.
mesenteries
connective issue sheets that stabilize the positions of the attached organs and prevent the intestines from becoming entangled. also provide passage for the blood vessels and nerves that supply the digestive tract, and contain many lymph nodes and lymphatic vessels
dorsal mesentery
the parietal peritoneum that lines the wall of the abdominal cavity, along the posterior midline(dorsal) of the body in turns inward and forms the _________ _________, a translucent 2-layered membrane extending to the digestive tract.
ventral mesentery
may hang freely in the abdominal cavity or attach to the anterior (ventral) abdominal wall or other organs
lesser omentum
a ventral mesentery, it extends from the stomach to the liver.
greater omentum
hangs from the left inferior margin (greater curvature) of the stomach and loosely covers the small intestine like an apron.
neural, hormonal, and paracrine mechanisms
the motility and secretion of the digestive tract are controlled by __________ ___________ __________.
the neutral controls:
short and long autonomic reflexes.
short (myenteric) reflexes
stretching and chemical stimulation of the digestive tract act through the myenteric nerve plexus to stimulate contractions in nearby regions of the muscularis externa, such as the peristaltic contractions of swallowing .
long (vagovagal) reflexes
act through autonomic nerve fibers that carry sensory signals from the digestive tract to the CNS and motor commands back to the digestive tract.
gastrin and secretin
hormones produced by the digestive tract.the hormones are secreted into the blood and stimulate relatively distant parts of the digestive tract
histamine and prostaglandins
paracrine secretions that stimulate digestive function. the paracrine secretions diffuse through the tissue fluids and stimulate nearby target cells
the mouth
is also known as the oral or buccal cavity.
function of the mouth
include ingestion(food intake) taste, and other sensory responses to food, chewing, chmical digestion (starch is partially digested in the mouth) swallowing, speech,and respiration.
the mouth is enclosed by:
cheeks, lips, palate, and tongue.
oral fissure
mouth's anterior opening between the lips.
fauces
mouth's posterior opening in to the throat.
the mouth is lined with:
stratifies squamous epithelium. this epithelium is keratinized in area subject to greatest food abrasion, such as the gums and hard palate, and non-keratinized in other areas, such as the floor of the mouth, soft palate, and the inside of the check and lips.
the cheeks and lips:
retain food and push it between the teeth for chewing. are essential for articulate speech, and for sucking and blowing action. their fleshiness is due to the subcutaneous fat, the buccinator muscles of the cheek , and the orbicularis oris muscle of the lips
labial frenulum
attaches each lip to the gum, between the anterior incisors.
vestibule
the space between the the cheeks or lips and the teeth--the space where you insert a toothbrush when brushing your teeth.
3 areas of the lips
1) the cutaneous area 2) the red area (vermillion) 3) the labial mucosa
the cutaneous area
is colored like the rest of the face and has hair follicles and sebaceous glands, on the upper lip,this is where the mustache grows.
the red area (vermillion)
is the hairless region where the lips meet (where some apply lipstick)
the labial mucosa
is the inner surface of the lip, facing the gum and teeth.
the tongue
although muscular and bulky, is a remarkably agile and sensitive organ. it manipulates food between the teeth while it avoids being bitten, it can extract food particles from the teeth after a meal, and it is sensitive enough of feel a stray hair in a bite of food.
the tongue surface
is covered with nonkeratinized stratified squamous epithelium
lingual papillae
bumps and projections, that are the site of the taste buds.
tongue: body
the anterior 2/3 of the tongue, it occupies the oral cavity.
tongue: root
the posterior 1/3, that occupies the oropharynx.
vallate papillae
v-shaped row of papillae that marks the boundary between the body and root of the tongue
terminal sulcus
a groove behind the vallate papillae
lingual frenulum
the body of the tongue is attached to the floor of the mouth by a median fold called the _______ __________.
intrinsic muscles
the muscles of the tongue, which compose most of it's mass, contained entirely within the tongue, produce the relatively subtle tongue movements of speech.
extrinsic muscles
GENIOGLOSSUS, HYOGLOSSUS,PALATOGLOSSUS, STYLOGLOSSUS with origins elsewhere and insertions in the tongue, produce the stronger movements of food manipulation.
hard (bony) palate
is supported by the palatine processes of the maxillae and by the smaller palatine bones
soft palate
has a more spongy texture and is composed mainly of skeletal muscle and glandular tissue , but no bone.
uvula
conical medial projection of the soft palate, helps to retain food in the mouth until one is ready to swallow.
dentition
the teeth are collectively known as ______________.
function of the teeth
they serve to masticate the food, braking it into smaller pieces. this not only makes food easier to swallow, but also exposes more surface ares to the action of the digestive enzymes and thus speeds up chemical digestion.
number of teeth
adults normally have 16 teeth in the mandible and 16 in the maxilla
incisors
are chisel-like cutting teeth use to bite off a piece of food.
canines
are more pointed and act to to puncture and shred
premolars and molars
have relatively broad surfaces adapted for crushing and grinding
alveolus
each tooth is embedded in a socket called an ____________.
gomphosis
each tooth and socket forms a joint called a ________________.
periodontal ligament
the alveolus is lined by a , a modified periosteum whose collagen fibers penetrate into the bone on one side and into the tooth on the other.
gingiva
the gum or __________ covers the alveolar bone. regions are defined by their relationship top the gingiva
the crown
is the portion above the gum.
the root
is the portion below the gum
the neck
is the point where the crown, root and gum meet.
gingival sulcus
the space between the tooth and the gum is the _____.
dentin
most of a tooth consists of hard yellowish tissue called ___________.
enamel
covers the crown and neck and CEMENTUM in the root. dentin and cementum are living conncetive tissues with cells and cell processes embedded in a calcifies matrix.
enamel
is not a tissue but a cell free secretion produced before the tooth erupts above the gum. damaged dentin and cementum can regenerate, but damaged enamel cannot--it must be artificially repaired.
pulp cavitiy
a tooth has a dilated _________ in the crown and a narrow root canal in the lower root these spaces are occupied by pulp--a mass of connective tissue, blood and lymphatic vessels and nerves.
apical foramen
these nerves and vessels enter the tooth thru a pore called the _____________. at the basal end of each root canal.
occlusion
the meeting of the teeth when the mouth is closes is called _____________, and the surfaces where they meet are called the occlusal surfaces.
cusps
the occlusal surface of a premolar has 2 rounded bumps called _____, thus the premolars are also known as bicuspids. the molars have 4 or 5 _____._____ of the upper and lower premolars and molar mesh when the jaws are closed and slide over each other as the jaw make lateral chewing motions.
erupt
teeth develop beneath the gums and __________ (emerge) in predictable order.
deciduous teeth
20_______________(milk teeth or baby teeth) erupt from the ages 6-30 mo, beginning with the incisors.
permanent teeth
between 6 and 25 years of age, these are replaced by the 32 _______________.
wisdom teeth
the third molars erupt around ages 17 to 25 if at all.
impacted
over the course of human evolution, the face became flatter and the jaws shorter, leaving little room for the third molars. they often remain below the gum and become ____________ so crowed against neighboring teeth and bone that they cannot erupt.
mastication
(chewing) breaks food into pieces small enough to be swallowed and exposes more surface to the action of digestive enzymes. it is the first step in chemical digestion. ____________ requires little thought because food stimulates receptor that trigger an involuntary chewing reflex. the tongue buccinator and orbicularis muscles manipulates the food and push it between the teeth.
functions of saliva
moisten the mouth, digest a little starch and fat, cleanses the teeth, inhibits bacterial growth, dissolves molecule so they can stimulate the taste buds, and moistens food and binds particles together to aid in swallowing. it is a hypotonic solution of 97.0%-99.5 % water and solutes
solutes in the saliva
1) salivary amylase 2) lingual lipase 3) mucus 4) lysozyme 5) immunoglobulin A (IgA) 6) electrolytes
salivary amylase
solute found in saliva, an enzyme that begins starch digestion in the mouth
ligual lipase
an enzyme that is activated by stomach acid and digests fats after the food is swallowed.
mucus
bind and lubricates food mass and aids in swallowing
lysozyme
and enzyme that kills bacteria.
immunoglobulin A (IgA)
an antibody that inhibits bacterial growth
electrolytes
including sodium, potassium, chloride, phosphates and bicarbonate salts
pH of saliva
6.8-7.0
saliva begins
to digest starch before the food is swallowed and fat after it is swallowed.
2 kinds of salivary glands
intrinsic and extrinsic
intrinsic salivary glands
LINGUAL GLANDS, LABIAL GLANDS, BUCCAL GLANDS are an indefinite number of small glands dispersed amid the other oral tissues, they include the lingual glands in the tongue, labial glands on the inside of the lips, and buccal glands on the inside of the cheek
extrinsic salivary glands
PAROTID GLANDS, SUBMANDIBULAR GLANDS, SUBLINGUAL GLANDS are three pairs of larger. more discrete organs located outside the oral mucosa. that communicate with the oral cavity by way of ducts.
the parotid gland
is located just beneath the skin anterior to the earlobe. its duct passes superficially over the masseter, pierces the buccinator and opens into the mouth opposite the second upper molar tooth. MUMPS is an inflammation and swelling of the parotid gland caused by a virus.
the submandibular gland
is located halfway along the body to the mylohyoid muscle. its ducts empties into the mouth at the papilla on the side of the lingual frenulum, near the lower central incisor.
the sublingual gland
is located in the floor of the mouth. it has multiple ducts that empty into the mouth posterior to the papilla of the submandibular duct.
salivation
the extrinsic salivary glands secrete about 1.0-1.5 l of saliva per day.
salivary nuclei
food stimulates tactile, pressure, and taste receptors in the mouth, which transmit signals to a group of _________ ________ in the medulla oblongata and pons.
bolus
salivary amylase begins to digest starch as the food is chewed, while the mucus in the saliva binds food particles into a soft, slippery. easily swallowed mass called a ______. without mucus, one must drink a much larger volume of fluid to swallow food.
the pharynx
is a muscular funnel that connects the oral cavity to the esophagus, as well as connecting the nasal cavity to the larynx, thus , it is a point where the digestive and respiratory tract intersect.
pharyngeal constrictors
Superior, middle and inferior. The circular muscles that forces food downward during swallowing:
upper esophageal sphincter
made of smooth muscle at the superior end of the esophagus; relaxes so food and drink can be channeled into the esophagus, then closes once food and drink is in the esophagus, not an anatomical feature, disappears at death.
esophagus
is a straight muscular tube 25-30 cm long.
esophageal hiatus
after passing downward, through the mediastinum, the esophagus penetrates the diaphragm at an opening called the ________ _______, continues another 304 cm, and meets the stomach at the level of the t7 vertebra.
cardiac orifice
where the esophagus meet the stomach. it is named this because of its proximity to the heart.
lower esophageal sphincter
a physiological sphincter that briefly slows down food before it enters the stomach . it also acts to prevent stomach contents from regurgitating into the esophagus, thus protecting the esophageal mucosa from the corrosive effect of the stomach acid.
deglutition
process of swallowing, complex action involving over 22 muscles in th mouth, pharynx, and esophagus, coordinated by the swallowing center
buccal phase
The first phase in swallowing, the tongue collects food, presses it against the palate to form a bolus, and pushes it back into the oropharynx. the bolus stimulates the tactile receptors and activates the next phase
pharyngo-esophageal phase
2nd phase of swallowing is under involuntary control, 3 actions block food and drink from reentering the mouth ot entering the nasal cavity or larynx: 1) root of the tongue blocks the oral cavity 2)the soft palate rises and blocks the nasopharynx 3)the infrahyoid muscles pull back they larynx up to meet the epiglottis while the vestibular fold adduct to to close the airway
peristalsis
rhythmic muscular contractions that squeeze food through the esophagus into the stomach, liquid reach the stomach in 1-2 seconds, a food bolus in 4-8 seconds
stomach
large muscular sac that is located in the upper left abdominal cavity immediately inferior to the diaphragm. continues the mechanical and chemical digestion of food, internal volume of 50 ml when empty, 1.0-1.5 l after a typical meal, can expand up to 4l.
chyme
a semiliquid mass of partially digested food that passes from the stomach through the pyloric sphincter into the duodenum
lesser curvature
the smaller inside curve of the stomach between the entrance of the esophagus and the pylorus (10 cm)
greater curvature
referring to the outer and longer curve of the stomach (40 cm)
4 regions of the stomach
cardiac, fundus, body, and pylorus
cardiac region
an area of the stomach that is surrounding the cardiac orifice through which food enters the stomach from the esophagus
fundus region
a rounded portion at the top of the stomach
body region
central main portion of the stomach
pylorus region
pyloric sphincter and pyloric orifice, right before entering duodenum of small intest.
pyloric sphincter
the sphincter muscle of the pylorus that separates the stomach from the duodenum, controls the movement of chyme from the stomach to the small intestines
gastric rugae
Folds formed in the interior gastric mucosa of the stomach
gastric pits
gastric mucosa is pocked with depressions which are lined with the the same columnar epithelium as the surface. they are continually producing new epithelial cells, Channels that open into gastric glands located between the columnar cells of the mucosa
cardiac glands
gastric gland located in the cardiac region of the stomach
pyloric glands
Located between fundus and pylorus region. gastric gland
gastric glands
Glands in the gastric mucosa composed of mucous cells, chief cells, and parietal cells
mucus cells
secrete mucus that protects stomach lining from hydrochloric acid
regenerative cells
cells that divide rapidly and produce a continued supply of new cells...they are found in the base of the pit and neck of the glands
parietal cells
Cells found in gastric glands that secrete hydrochloric acid (for hydrolysis of ingested food) and gastric intrinsic factor (for absorption of vitamin B-12) and a hunger hormone called ghrelin
chief cells
A cell of the gastric glands that secretes pepsinogen (breaks down protein) and gastric lypase
enteroendocrine cells
cells that secrete hormones and paracrine messengers that regulate digestion.
gastric juice
digestive secretions of the stomach glands composed mainly of water, hydrochloric, and pepsin, stomach produces 2-3 L per day
hydrochloric acid
Substance produced by the stomach; necessary for digestion of food. pH as low as 0.8, could cause burns to the skin.
functions of stomach acid
1) activates the enzyme pepsin and lingual lipase 2) breaks up connective tissue and plant cell walls, helping to liquify food 3) converts ingested ferric ions to ferrous ions, a form of iron that can be absorbed and used for hemoglobin synthesis4) contributes to nonspecific disease resistance by destroying most ingested pathogens
zymogens
Digestive enzymes are released in inactive forms, necessary to prevent the digestive enzymes from autodigesting the cells that produce them
pepsinogen
The inactive form of pepsin that is first secreted by specialized (chief) cells located in gastric pits of the stomach, reacts with HCl to create pepsin
pepsin
Breaks down proteins into amino acids
auto-catalytic
as some pepsin is formed, it coverts pepsinogen into more pepsin
gastric lipase
Secreted by glands in the stomach, this enzyme plays minor role responsible for 10-15% of fat digestion, rest take place in the sm intestine
intrinsic factor
glycoprotein secreted by parietal cells necessary for absorption of vitamin B12 in the sm intestine. w/o vit B12, hemoglobin cannot be synthesized and pernicious anemia develops
receptive-relaxation response
as you begin to swallow, the swallowing center of the medulla oblongata signals the stomach to relax, thus preparaing it to recieve food. the arriving food stretches the stomach and activates the ________-________ ___________ of smooth muscle. soon the stomach shows a rhythmic peristaltic
gastric motility
Controlled locally and centrally: Combination of mixing waves (80%) and peristaltic waves (20%) ;Both esophageal and pyloric sphincters are closed; store, mix chyme then empties; only allows small amount of chyme at a time via Pyloric sphincter
30ml
amount of chyme the antrum can hold
3 ml
amount of chyme squirted into the duodenum at a time.
4 hrs
amount of time it takes a typical meal to empty from the stomach.less time if meal is more liquid, as much as 6hrs if meal is high in fat.
vomiting
forcible or involuntary emptying of the stomach through the mouth., Emesis
emetic center
vomiting involves multiple muscular actions intergarted by the ______ _______ of the medulla oblongata, commonly induced by over stretching of the stomach or duodenum. alcohol , bacterial toxins can activate the ______ _______ reverse peristalis
retching
rhytmic action of respiratory muscles preceding vomiting and consisiting of contration of ab intercost and diapharmatic msucles against a closed glottis, create a pressure difference that dilates the esophagus. often accompanied by tachycardia, profuse salivation, and sweating.
projectile vomiting
vomiting that occurs with great force, and is sudden with no prior nausea or retching, may be caused by neurological lesions, common in infants after feeding.
chronic vomiting
can cause dangerous fluid, electrolyte and acid/base imbalances
bulimia
repeated binge eating, usually followed by vomiting, tooth enamel becomes eroded,
stomach absorbs
aspirin and some lipid-soluble drugs, does not absorb any significant amount of nutrients
3 way the stomach is protected from acid and enzymes
1) mucuos coat 2) tight junctions 3) epithelial cell replacement
mucuos coat
thick, highly alkaline mucus resists the action of acid and enzymes
tight junctions
(forms a gasket, like the seal on a refridgerator), the membranes of neighboring cells are actually fused at tight junctions forming a seal that prevents the leakage of extracellular fluid across a membrane(important in digestive system)
epithelial cell replacement
epithelial cells live only for 3-6 days and are then sloughed off into the chyme and digested with the food
all phases of gastric function
overlap and all 3 can occur simultaneously
cephalic phase
Earliest phase of digestion when the brain thinks about and prepares the digestive organs for the consumption of food
gastric phase
a phase in which swallowed food and semidigested protein (peptides and amino acids) activate gastric activity
intestinal phase
third phase of gastric activity; begins when chyme enters the small intestine; the duodenum controls gastric activity through hormones and nervous refelexes.
gastritis
inflammation of the stomach lining
peptic ulcer
another name for gastric or duodenal ulcer
h pylori
acid resistant bacterial infection that has been increasingly recognized as being involved in the development of peptic ulcers
entrogastric reflex
the duodenum send inhibitory signals to the stomach by way of the enteric nervous system, and send signals to the medulla that 1) inhibit the vagal nuclei, thus reducing vagal stimulation of the stomach. 2) stimulates sympathetic neurons, which send inhibitory signals to the stomach, chyme also stimulates duodenal enteroendocrine cells to release secretin and cholecystokin
(gip) glucose-dependent insulinotropic peptide
inhibits gastrin secretion AND reduces the rate and force of gastric contractions; stimulated by the arrival of chyme into the duodenum (specifically lipids and carbs)
the liver
where lactic acid is converted back into pyruvic acid, Largest glandular organ., The digestive function of the liver is to produce bile.Bacteria and expended red and white blood cells are broken down. is the place where the majority of gluconeogenesis occurs weights about 3 lbs,
right lobe
Large lobe on the right of the liver
left lobe
Smaller lobe on the left of liver
falciform ligament
a ligament that attaches part of the liver to the diaphragm and the abdominal wall
round ligament
A structure that attaches the umbilicus to the liver as a result of the collapse of the umbilical vein that occurs after birth; also known as the ligamentum teres
quadrate lobe
inferior to caudate lobe, between left lobe and gallbladder
caudate lobe
tail-like lobe posterior to the quadrate lobe
porta hepatis
Is the region where the hepatic artery and the portal vein enter and the hepatic ducts leave the liver., this structure separates the caudate and quadrate lobes
bare area
area of liver not covered by peritoneum to allow room for IVC to enter the chest
hepatic lobules
small functional units of the liver, made of many hepatic cells organized around a central vein
central vein
Each hepatic lobule consists of plates of epithelial cells radially arranged around a blood vessel called the _______________.
hepatocytes
major functional cells of the liver; make up 80% of the volume; functions: metabolic, secretatory, endocrine: active in synthesis of proteins and lipids for export
hepatic sinusoids
vascular channels of the liver that receive nutrient rich blood from the hepatic portal vein
hepatic macrophages
in the hepatic sinusoids, specialized phagocytic cells which remove bacteria and debris from the blood.
hepatic triad
(1) branch of hepatic portal vein (2) branch of hepatic artery proper (3) small branch of bile duct
bile canaliculi
narrow channels between opposing membranes of adjacent liver cells; extend outward through liver lobule away from central vein, connect with fine bile ductules
bile ductules
connect with bile canaliculi; carry bile ultimately into the right and left heptatic duct
common hepatic duct
joins the cystic duct (goes to gallbladder) to form common bile duct
cystic duct
where the neck of the gallbladder taper and how bile leaves the gallbladder, a duct draining bile from the gallbladder; merges with the common hepatic duct to form the common bile duct
bile duct
the hepatic duct, which joins with the cystic duct to form the common bile duct opening into the duodenum.
hepatopancreatic ampulla
bulb-like joining of ducts at the duodenum, which they empty their products into the duodenal lumen through the major duodenal papilla. where pancreas and gall bladder deliver their secretions.
major duodenal papilla
an oriface that empties the products of the hepatopancreatic ampulla into the lumen.
hepatopancreatic sphincter
aka sphincter of Oddi, the muscular valve with contols the major duodenal papilla
gallbladder
a pear-shaped, muscular sac attached to the liver that secretes bile and stores it until needed for digestion, about 10 cm long
bile
fluid secreted by the liver and passed into the duodenum where it aids digestion especially in the emulsification and absorption of fats, yellowish-brown or green fluid produced by the liver, stored in the gallbladder, and secreted into the small intestine. liver secrete 500-1000 ml of ___/daily,
bilirubin
Orange-yellow pigment in bile. It is formed by the breakdown of hemoglobin when red blood cells die., principal pigment released by the liver in the bile
urobilinogen
a chromogen formed in the intestine from the breakdown of bilirubin, gives feces brown color
bile acids (bile salts)
steroids, synthesized from cholesterol in liver, stored in gallbladder, release stimulated by fat in duodenum, along with lecithin aid in fat digestion and absorption. 80% of bile acids are reabsorbed in the ileum and returned to the liver.
gallstones
When bile contains either insufficient biles salts or lecithin or excessive cholesterol, the cholestorol may crystallize to grow in size and number; may casue minimal, intermittent, or complete obstruction to the flow of bile from the gallbladder into the duodenum
the pancreas
produces enzymes that flow into the small intestine and help break down starches, proteins, and fats., Responsible for the secretion of glugagon, insulin, and gylcogen, produces enzymes that flow into the small intestine and help break down starches, proteins, and fats. 99% of the pancreas is exocrine tissue
pancreatic juice
exocrine secretion that digests carbohydrates, lipids and proteins and produces bicarbonate, 1200-1500ml clear juice produced daily, buffers HCL arriving from the stomach
pancreatic duct
conducts pancreatic juice from pancreas to duodenum of small intestine
zymongen granules
vesicles filled with secretions
accessory pancreatic duct
may branch from pancreatic duct before leaving pancreas; will empty into duodenum at lesser duodenal papilla
minor duodenal papilla
The opening of the accessory pancreatic duct into the duodenum proximal to the major duodenal papilla, present only if there is an accessory pancreatic duct
trypsinogen
precursor of the digestive enzyme trypsin. comes from the acinar cells in the pancreas and is activated by autocatalysis or by enterokinase.
chymotrypsinogen
precursor of the digestive enzyme chymotrypsin. comes from the acinar cells in the pancreas and is activated by autocatalysis or by trypsin (the active form of trypsinogen)
procarboxypeptidase
inactive form of carboxypeptidase; secreted by pancrease; breaks down proteins into amino acids
trypsin
a pancreatic enzyme responsible for breaking some peptide bonds; secreted as trysinogen, activated by enterokinase in the small intestine
pancreatic amylase
Enzyme in pancreatic juice that digests starch
pancreatic lipase
Enzyme in pancreatic juice that breaks down triglycerides (fats and oils), creating fatty acids and monoglycerides
ribonuclease
secreted by the pancreas, breaks down RNA
deoxyribonuclease
secreted by the pancreas, breaks down DNA
acetylcholine
causes the pancreas to produce pancreatic juice, even before food is swallowed.
cholecystokinin
hormone from the duodenum that stimulates release of pancreatic enzymes and bile from the gallbladder, in response to fats in the small intestine
secretin
A hormone secreted by the small intestine (duodenum) in response to low pH (e.g., from stomach acid). It promotes the release of bicarbonate from the pancreas to act as a buffer.
small intestine
20 feet starts with duodenum which adds digestive juices to chyme including bile from liver via gall bladder, pancreas also adds digestive juices to chemically break down food so it can be absorbed. Chyme goes on to jejunum & ileum and it is lined with villi, organ that completes the chemical digestion of food and absorbs the nutrients
duodenum
the first nine to the ten inches of the small intestine, signals the secretion of pancratic enzymes and bile relase from gall bladder
jejunum
The middle (approximtely 40%) of the small intestine., middle portion of small intestine where chemical digestion ends and absorption begins
ileum
The final section (approximately 55%) of the small intestine. characterized by Peyer's patches, Has a larger bacterial population.
ileocecal junction
This is where the ileum joints the cecum
ileocecal valve
controls the progeress of substances into the large intestine
200m2
surface area of small intestines
circular folds
deep folds of the mucosa and submucosa that extend completely or partially around the circumference of the small intestine
villi
finger-like projections that increase the surface area and increase absorption, contain blood capillaries and lacteals
absorptive cells
cells of the small intestine mucosal lining microvilli that absorb nutrients
goblet cells
Mucus secreting cells in mucous membranes
lacteal
Dietary lipids are taken up by a lymphatic capillary called the _____ in each villus of the small intestine
brush border enzymes
enzymes in microvilli plasma membrane which complete final stages of enzymatic digestion
intestinal crypts
crypts of lieberduhn tubular pits at base of villi secrete intesinal juice carries nutirents absorbed from chyme
paneth cells
cells at the base of the intestinal crypts that secrete bactericidal (bacteria-killing) enzyme, lysozyme
duodenal glands
secrete bicarbonate rich mucous which neutralizes acidity of chyme.
intestinal juice
1-2 L produced a day; contains water and mucous; pH=7.6; provides liquid medium aiding absorption from chyme
3 functions of intestinal contractions
1) to mix chyme with intestinal juice, bile and pancreatic juice, allowing these fluids to neutralize acids and digest nutrients more effectively 2) to churn chyme and bring it into contact with the mucosa for contact digestion and nutrient absorption 3) to move residue toward the large intestine.
segmentation
alternating ring-like constriction and relaxation; mixes chyme and spreads it over length of small intestine
gastroileal reflex
distension of the stomach causes increased peristalsis which moves chyme from the ileum to the cecum. This reflex also relaxes the ileocecal sphincter, and caused the secretion of gastrin
starch
a carbohydrate, the main food energy source for human beings
carbohydrate digestion
amylase acts upon starch and water (and it becomes maltose); pancreatic juices act upn it in small intestine (and it is now glucose); absorbed into blood stream by villi, starts in the mouth, completed in the small intestine, 2 Phases: 1) Carbohydrases from salivary glands & pancreas 2) Brush border enzymes (maltase to maltose) (Sucrose to Sucrose) (Lactase to Lactose) Enterokinase (protein)carboxypeptidase
dextrinase
in brush border/sm. intestine, digests oligosaccharides
glucoamylase
in brush border/sm. intestine, digests oligosaccharides
sucrase
produced in the brush border of the SI- catalyzes the splitting of sucrose into glucose and frutose
lactase
brush border enzyme that catalyzes the breakdown of lactose into glucose and galactose
carbohydrate absorption
are absorbed as the monosaccharides glucose, fructose and galactose. Both glucose and galactose are moved by active transport, but fructose is moved by facilitated diffusion.
solvent drag
When water carries with it a variety of dissolved solutes through the epithelium, it is called:
3 sources of amino acids absorbed in the SI
1) dietary protein 2) digestive enzymes digested by each other 3)sloughed off epithelial cells, digested by enzymes
proteases
enzymes that break down proteins
carboxypeptidase
Released by the pancreas into the small intestine, this enzyme hydrolyzes terminal peptide bond at the carboxyl end.
aminopeptidase
removes amino acid at N terminus, brush border enzyme that catalyzes the breakdown of peptides into individual amino acids
dipeptidase
brush border enzyme that catalyzes the splitting of dipeptides into 2 individual amino acids, splits dipeptides in the middle, breaking them into individual free amino acids
lipases
general name for enzymes that work on lipids
lingual lipase
enzyme secreted by lingual glands that act on triglycerides, becomes activated in acidic environment of stomach
gastric lipase
secreted by the chief cells in the stomach, hydrolyzes triglycerides into fatty acids and monoglycerides
pancreatic lipase
pancreatic juice enzyme; triglycerides into fatty acids and glycerol
emulsification droplets
large fat globules are broken up into smaller________ _________ by bile salts and lecithin.
micelles
small droplets with a single layer of phospholipids arranged so the interior is filled with hydrophobic side and hydrophilic side on the outside and accessible to lipid-digesting enzymes
chylomicrons
fat droplets covered in protein that diffuse into capillaries in small intestine
nucleic acids
DNA and RNA, macromolecule containing hydrogen, oxygen, nitrogen, carbon and phosphorus, that store and transmit genetic information
nucleases
pancreatic juice enzymes that digest nucleic acids into nucleotides
nucleosidases
in the small intestine brush border and works there to decompose dna and rna into procucts that can be trans ported to the bloodstream for the body's use.
phosphatases
in the small intestine brush border, any of a number of enzymes that removes a phosphate group from a protein,
vitamins
Essential nutrients that do not yield energy, but that are required for growth and proper functioning of the body.
fat-soluble
vitamins A,D,E,K. not absorbed unless fat is present
water-soluble
vitamins b complex and c, absorbed by simple diffusion
minerals
inorganic nutrients that the body needs, are absorbed along the entire length of the small intestine
iron and calcium
are absorbed in proportion to the body's need, other minerals are absorbed in fairly constant rates and excess is secreted
calbindin
protein that keeps the intracellular calcium concentrations low, maintaining the gradient factors that favor calcium up take by cells.
9 L water
amount of water, the digestive system receives every day, .7 in food,1.6 in drink. 6.7 in gastointestinal secretions,8l of this is absorbed by the small intestines .8 by large intestine= .2 eliminated in feces
diarrhea
frequent discharge of liquid stool, occurs when large intestine absorbs too little water, can occur when lining is irritated by bacteria
constipation
Hard, slow stools that are difficult to eliminate; ocurs when large intestine absorbs too much water,often a result of too little fiber in the diet
500 ml
amount of indigestible food residue that the large intestine received per day, reduces it to 150 ml of feces by absorbing water and salts
the large intestine
measured 5ft long in the cadaver, reabsorbs water and stores and eliminates undigested food : contains abundant bacteria and intestinal flora, _ main functions are to absorb water and to eliminate undigested food, absorbes water
cecum
blind U-shaped pouch that is the first portion of the large intestine
appendix
a blind 2 in log tube extension on the lower end of the cecum; contains a large amount of lymphocytes that contribute to immunity
colon
portions of the large intestine extending from the cecum to the rectum, identified by direction or shape
ascending colon
the part of the large intestine that ascends from the cecum to the transverse colon
right colic flexure
aka the hepatic flexure, the right-angle turn that continues from the ascending colon
transverse colon
the part of the large intestine that extends across the abdominal cavity and joins the ascending to the descending colon
left colic flexure
aka the splenic flexure, the region of the colon takes a left-turn, it is a continuation from the transverse colon
descending colon
the part of the large intestine that descends from the transverse colon to the sigmoid colon
sigmoid colon
the s-shaped curve between the descending colon and the rectum
rectum
The last part of the digestive tract, through which stools are eliminated
rectal valves
Used to delay feces in procession to anus. enables rectum to retain feces while passing gas
anal canal
the last 2 or 3 cm of the rectum; opens to the exterior through the anus
anal columns
Vertical folds in the mucosal lining of the anal canal
anal sinuses
depressions between the anal columns
hemorroidal veins
large veins that form on the superficial plexuses in the anal columns and around the orifice.
taenia coli
The longitude muscle of the colon arranged into three distinct bands.
haustra
pouches that form in the large intestine when the longitudinal muscles are shorter than the colon
internal anal sphincter
smooth muscle (involuntary) anal sphincter
external anal sphincter
voluntary sphincter to control waste while exiting the body
epiploic appendages
aka omental appendages fat filled peritoneal bodies hanging from the outer walls of the large intestine, of unknown significance
no circular folds or villi
in the large intestine there are _____________.
there are more in the large intestine
intestinal crypts, they are deeper and have more goblet cells , they only secrete mucus.
bacterial flora
what populates the large intestine allowing fermentation of cellulose and other undigested carbohydrates and synthesizing vitamins B and K? harbors 800 species of bacteria.
flatus
intestinal gas, expells about 500 ml a day, reabsorbing the rest
12-24 hrs
amount of time it takes for the large intestine to reduce the residue of a meal to feces. does not chemically change the residue, but reabsorbs water and electrolytes from it
feces
semi solid waste material excreted from the large intestine expelled thru the anus; made of undigested food, water, bacteria, mucus, and shed intestinal cells, excreted from the large intestine 75% water 25% solids consist of: 30% bacteria,30% undigested dietary fiber, 10-20% fat smaller amounts of protein
haustral contractions
short, slow segmenting movements that propel feces forward into the subsequent haustra
defecation reflexes
caused by the stretching of the rectum, and accounts for the urge to defecate
intrinsic defecation reflex
operates entirely within the myenteric nerve plexus. stretch signals travel through the plexus to the muscularis of the descending and sigmoid colon and the rectum
the parasympathetic defecation reflex
is a spinal reflex, it's principal events are that stretching signals are transmitted to the spinal cord. and rthe motor signals return by way of the pelvic nerves to intensiify peristalsis in the descending and sigmoid colon and rectum and to relax the internal sphincter.
parietal cells
Secretes hydrochloric acid (HCL) and intrinsic factor (aids in absorption of B12) and ghrelin
chief cells
secretes pepsinogen (breaks down protein) and gastric lypase (breaks down fat)
enteroendocrine cells
aka G cells, produce hormones known as Gastrin, histamine, serotonin, somatostatin that regulate the digestive system
sodium bicarbonate
chemical compound released by the pancreas into the small intestine which neutralizes the acidity of the chyme
zymogens
are inactive precursors of enzymes, like pepsinogen, trypsinogen, procarboxypeptidase, chymotrysinogen (often has -gen ending)
trypsinogen
precursor of the digestive enzyme trypsin. comes from the acinar cells in the pancreas and is activated by autocatalysis or by enterokinase. digest proteins
chymotrypsinogen
precursor of the digestive enzyme chymotrypsin. comes from the acinar cells in the pancreas and is activated by autocatalysis or by trypsin (the active form of trypsinogen) digest proteins
procarboxypeptidase
inactive form of carboxypeptidase; secreted by pancrease; breaks down proteins
obesity
a condition in which a person's weight is 20 percent more than is recommended for his or her height 30% of us pop is obese. 35% is overweight
ghrenlin
secreted by an empty stomach; tells the brain you're hungry
peptide YY
from the enteroendocrine cells, signal that you are full, stop eating.
cholecystokinin
from the enteroendocrine cells in the small intestinal when fat is present in Chyme. This then stimulates the gallbladder to contract and release bile. signals to stop eating.
leptin
A protein produced by fat cells, when released into the bloodstream, signals the hypothalamus that the body has had enough food and reduces the appetite while increasing the feeling of being full,
insulin
a hormone produced by the pancreas and released in response to high blood glucose following a meal. Insulin promotes the use and storage of glucose by the body's tissues.
neuropeptide Y
from Arcuate nucleus of secreted in response to appetite regulators that increase appetite
melanocortin
from Arcuate nucleus of secreted in response to appetite regulators, signals decreased eating
fuel
a substance that provides energy as the result of a chemical change