Digestive/Nutrition & Metabolism Flashcards
(300 cards)
0
Q
what is ingestion?
A
introduction of solids & liquids in the oral cavity
1
Q
What are the 6 main functions of the digestive system?
A
ingestion motility secretion digestion absorption elimination
2
Q
what is motility?
A
voluntary & involuntary muscle contractions for mixing & moving materials through GI tract
3
Q
what is secretion in the digestive process?
A
process of producing & releasing fluid products like digestive enzymes, acid, and bile into GI tract
facilitates digestion
4
Q
what is digestion?
A
the breakdown of ingested food into smaller structures that can be absorbed from GI tract.
5
Q
what are the 2 types of digestion?
A
mechanical - physically breaking down materials by chewing & mixing without changing chemical structure
chemical - enzymes break chemical bonds - change larger molecules into smaller molecules that can be absorbed
6
Q
what is absorption?
A
can be passive movement and active transport of digested molecules, electrolytes, vitamins & water from GI tract into blood or lymph
7
Q
what is elimination?
A
expulsion of indigestible components
8
Q
What are the 2 categories of organs in the digestive system?
A
those composing the GI tract (form a continuous tube - oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus)
accessory digestive organs - accessory digestive glands produce secretions (salivary glands, liver & pancreas), other organs (teeth, tongue, gallbladder - concentrates & stores secretions of the liver)
9
Q
what is the GI tract tube composed of?
A
tunics from inner to outer mucosa submucosa muscularis adventitia (or serosa)
10
Q
What are the layers of the mucosa?
A
epithelium
lamina propia
muscularis mucosae (thin layer)
11
Q
what kind of epithelium lines the GI tract?
A
simple columnar for stomach, small intestine & large intestine (allows for secretion & absorption)
areas where abrasion may occur (esophagus) are lined by nonkeratinized stratified squamous epithelium
12
Q
what is the lamina propia of the GI tract composed of?
A
areolar connective tissue
small blood vessels
nerves
lymphatic capillaries
13
Q
what is the muscularis mucosae and what is its function?
A
thin layer of smooth muscle deep to lamina propia in mucosa tunic
causes slight movements in mucosa which
1) facilitate release of secretions from mucosa into the lumen
2) increase contact of materials w/in lumen w/mucosa - shakes stuff up
14
Q
what is the submucosa composed of?
A
areolar and dense irregular CT
large blood vessels
lymph vessels
nerves
15
Q
what is the submucosal nerve plexus?
A
fine branches of nerves that extend into mucosa along w/their associated ganglia
also called Meissner plexus
innervate smooth muscle and glands of mucosa and submucosa
16
Q
what is in the areolar CT of lamina propia of mucosa and submucosa?
A
MALT mucosa-associated-lymphatic tissue
17
Q
what are Peyer patches?
A
aggregates of lymphatic nodules in submucosa of last region of small intestine (in the ileum)
18
Q
what is the function of MALT?
A
helps prevent ingested microbes from crossing GI tract wall & entering body
19
Q
what composes the muscularis?
A
2 layers of smooth muscle
inner circular layer - oriented circumferentially around GI tract
outer longitudinal layer - oriented lengthwise
axons and ganglia between these 2 layers - called myenteric nerve plexus (or Auerbach plexus) - control smooth muscle contractions
20
Q
what is the enteric nervous system?
A
submucosal nerve plexus and myenteric nerve plexus
sensory neurons in these plexuses detect changes in GI tract wall & chemical makeup of contents of lumen
21
Q
what kind of neurons compose the enteric nervous system?
A
sensory and motor neurons of the autonomic nervous system
22
Q
what is a sphincter?
A
closes off the lumen along the GI tract to control the movement of materials in the next section of tract
a greatly thickened area in the inner circular muscular layer
23
Q
what is the function of the muscularis?
A
to mix & propel contents w/in GI tract
24
what do contractions of the circular layer and of the longitudinal layer of the muscularis do?
circular layer contractions constrict lumen of tube
| longitudinal layer contractions shorten tube
25
what are the 2 primary modes of motility?
peristalsis
| mixing
26
what is peristalsis?
alternating contraction sequence of inner circular and outer longitudinal muscle layers to propel ingested materials through GI tract
27
what is mixing?
back & forward (kneading) motion - occurs at any point in time w/in different regions - no directional movement.
purpose is to blend ingested materials with secretions w/in GI tract
28
what is the difference between an adventitia and a serosa?
adventitia - composed of areolar CT w/collagen & elastic fibers - found outside peritoneal cavity
serosa - same composition as adventitia AND completely covered by a visceral peritoneum - found w/in peritoneal cavity
29
How does the stomach differ from typical pattern of tunics?
it has 3 layers of smooth muscle in the muscularis
30
what serous membranes are associated with the abdominal cavity?
```
parietal peritoneum (serous membrane that lines inside surface of body wall)
visceral peritoneum (serous membrane that reflects over & covers surface of internal organs)
```
31
what is the peritoneal cavity?
space between parietal peritoneum and visceral peritoneum.
| potential space w/small volume of lubricating serous fluid that is secreted by both peritoneal layers
32
what is the function of serous fluid in the peritoneal cavity?
lubricates internal body wall & external organ surfaces
allows organs to move freely
reduces friction resulting from movement
33
what are intraperitoneal organs?
organs within abdomen that are completely surrounded by visceral peritoneum
34
what are the intraperitoneal organs?
stomach
most of small intestine
parts of large intestine
35
what are retroperitoneal organs?
organs where only the anterolateral portions are covered w/peritoneum - typically lie directly against posterior abdomen wall
most of duodenum (1st part of small intestine)
pancreas
ascending and descending colon (parts of large intestine)
rectum
36
What is mesentery?
double-layer of peritoneum that supports, suspends and stabilizes the intraperitoneal GI tract organs.
37
what is housed in between the folds of the mesentary?
blood vessels, lymph vessels, and nerves ---> supply the digestive organs
38
what is the greater omentum?
the mesentery that extends inferiorly like an apron from inferolateral surface of stomach
also called fatty apron because it often accumulates lots of adipose tissue. ick
39
what is the lesser omentum?
the mesentery that connects the superomedial surface of the stomach & proximal end of duodenum to liver
40
what is the falciform ligament?
the mesentery that attaches the liver to the internal surface of the anterior abdominal wall
41
what is the mesentery proper?
sometimes referred to as the mesentery
fan-shaped fold of peritoneum that suspends most of the small intestine from the internal surface of the posterior abdominal wall
42
what is the mesocolon?
mesentery that attaches parts of the large intestine to the internal surface of the posterior abdominal wall.
has distinct sections named for portion of colon it suspends
(transverse mesocolon, sigmoid mesocolon...)
43
List the mesenteries
```
greater omentum
lesser omentum
falciform ligament
mesentery proper
mesocolon
```
44
What are the 2 types of general receptors?
mechanoreceptors (detect either stretch or pressure)
| chemoreceptors (detect specific chemicals)
45
where does sensory input from mechanoreceptors and chemoreceptors go?
CNS
46
which nerves convey autonomic motor output to digestive system mechanoreceptors and chemoreceptors?
3 cranial nerves
facial
glossopharyngeal
vagus
47
what are long reflexes?
coordinated secretory and smooth muscle contractions involved in digestive responses controlled by autonomic interactions of the central nervous system
48
what are short reflexes?
digestive reflexes that do not involve the CNS. occur only within neurons of enteric nervous system that are housed in GI tract wall.
49
what are the hormones that participate in the regulation of digestion?
gastrin (released from stomach)
| secretin and cholecystokinin (released from small intestine)
50
what structures are considered part of the upper gastrointestinal tract?
```
oral cavity
salivary glands
pharynx
esophagus
stomach
duadenum (1st part of the small intestine)
```
51
what is the function of the oral cavity in digestion?
mechanical digestion begins here. salivary glands excrete saliva to mix with food to form wet mass called bolus
saliva contains salivary amylase, a hydrolytic enzyme that initiates digestion of starch (amylose)
52
what is bolus?
wet mass of food plus saliva
53
what is the function of the pharynx in digestion?
where swallowing of the bolus occurs
| upper part secretes mucus (as do salivary glands in saliva) to help w/swallowing
54
what is the function of the esophagus in digestion?
secretes mucus to lubricate passage of bolus. Bolus comes here from pharynx and then goes to stomach
55
what is the function of the stomach in digestion?
smooth muscle of stomach wall secrete gastric juice as they contract --> mixes with bolus. secretions are produced by epithelial cells of stomach mucosa. include HCl, digestive enzymes and mucin
forms acidic puree called chyme
56
what are the regions of the oral cavity?
vestibule (buccal cavity) - space b/t gums, lips & cheesk
oral cavity proper - central to the teeth and bound laterally by cheeks, anteriorly by teeth & lips & posteriorly by oropharynx
57
what are the muscles of the cheeks & what are their function?
buccinator muscles
| compress cheeks against teeth to hold solid materials in place during mastication
58
what forms the lips?
orbicularis oris muscle
59
why are lips red?
lots of superficial blood vessels & less keratin in outer skin
60
what are gums?
gingivae
61
how are lips attached to the gums?
labial frenulum
| thin mucosa fold in the midline of lips
62
what forms the roof of the oral cavity and what is its function?
the palate
| separates the oral cavity from the nasal cavity
63
what is the hard palate?
anterior 2/3 of palate
| formed by palatine processes of maxillae and horizontal plates of palatine bones
64
what are the ridges on the hard palate and what is their purpose?
transverse palatine folds - friction ridges
| assist tongue in manipulating ingested materials prior to swallowing
65
what is the uvula?
extends inferiorly from posterior part of soft palate - conical projection
66
what prevents food from entering nasal region during swallowing?
soft palate and uvula elevate & close off posterior entrance into nasopharynx during swallowing
67
what are the openings between the oral cavity and the oropharynx?
fauces
bound by paired muscular folds
palatoglossal arch (anterior) and
palatopharyngeal arch (posterior)
68
what is housed in between the palatoglossal arch and the palatopharyngeal arch?
palatine tonsils
69
what is the tongue made out of?
skeletal muscle
| extrinsic and intrinsic muscles
70
what are the bumps on the tongue?
papillae
| involved in sense of taste
71
what else is on the tongue besides papillae?
lingual tonsils - round masses of lymphatic tissue on posteroinferior region
72
how is the tongue attached to the bottom of the oral cavity?
lingual frenulum
| thin vertical mucous membrane
73
what is the histology of the oral cavity?
epithelial lining is stratified squamous epithelium - protects against abrasion during mechanical digestion
nonkeratinized except for lips, parts of the tongue & small part of hard palate
74
what are intrinsic salivary glands?
unicellular glands including buccal glands of cheek, lingual glands of tongue & labial glands of lips --> contribute to production of saliva --> secretions include lingual lipase enzyme
75
where is most saliva produced?
multicellular exocrine glands outside of oral cavity called extrinsic salivary glands
76
What are the pairs of multicellular salivary glands?
parotid
submandibular
sublingual
77
describe the parotid salivary glands
largest
located anterior & inferior to ear - partially overlaying masseter muscle
produce about 25-30% of saliva
conducted through parotid duct to oral cavity
78
how are the parotid glands attached to the oral cavity?
through parotid duct - extends from the gland, across the external surface of the masseter muscle, penetrate the buccinator muscle & opens into the vestibule of oral cavity near 2nd molar
79
describe the submandibular salivary glands
inferior to the floor of oral cavity & medial to body of mandible
produce most of saliva - 60-70%
connected to oral cavity through submandibular duct - opens from each gland through a papilla in the floor of the oral cavity on the lateral sides of the lingual frenulum
80
describe the sublingual salivary glands
inferior to tongue, medial and anterior to submandibular salivary glands, internal to oral cavity mucosa
connected by multiple tiny sublingual ducts that open onto inferior surface of oral cavity, posterior to submandibular duct papilla
contribute 3-5% total saliva
81
what is the histology of paired salivary glands?
they have mucous cells and serous cells
mucous cells secrete mucin (forms mucus with water)
serous cells secrete watery fluid containing electrolytes and salivary amylase
also have salivary ducts
82
what types of secretions do each of the salivary glands produce?
parotid - only serous secretions
| submandibular and sublingual - both serous and mucus secretions
83
what is the production rate of saliva?
1 - 1.5 L/day
84
what are the components of saliva?
salivary amylase, lingual lipase (from intrinsic salivary glands), mucin, ions (Na+, K+, Cl-, HCO3-), lysozyme (antibacterial), immunoglobulin A (from plasma cells)
85
what is the pH range of saliva?
slightly acidic 6.4-6.8
| 99.5% water, the rest are solutes
86
What are the functions of saliva?
moistens food & helps it become bolus
initiates chemical breakdown of starch (salivary amylase)
food molecules dissolved in it so taste receptors can be stimulated
cleanses oral cavity structures
helps inhibit bacterial growth b/c it contains lysozyme & IgA
87
what regulates salivary secretion?
salivary nuclei within the brainstem
basic level is maintained by parasympathetic stimulation to make sure oral cavity is moist
input to salivary nuclei received from chemoreceptors or mechanoreceptors in upper GI tract when stimulated by substances in oral cavity (esp. acid), arrival of food in stomach lumen (esp. spicy or acid)
higher brain centers send input in response to though, smell or sight of food
stimulation of salivary nuclei ---> increased parasympathetic output relayed along facial nerve to submandibular & sublingual salivary glands & along glossopharyngeal nerve to parotid salivary glands
88
how does sympathetic stimulation affect salivary secretions?
occurs during exercise, excitement or anxiety ---> more viscous saliva by decreasing water content because sympathetic stimulation constricts capillaries of salivary glands & so decreases fluid added to saliva
89
what is mastication?
mechanical digestion in the oral cavity
| chewing
90
what controls mastication?
coordinated by nuclei within medulla oblongata & pons: the mastication center
91
what is the primary function of chewing?
to reduce bulk of food into smaller particles
92
does chewing affect digestion & absorption?
not much
| surface area of food is increased - so that does affect exposure to enzymes
93
what kinds of medications can be absorbed in the mouth?
small, nonpolar molecules that go under the tongue, pass through oral cavity epithelium by diffusion & absorb into blood
94
what is another word for teeth?
dentition
95
what are the parts of a tooth?
crown, neck, root
96
how are the teeth connected?
roots fit into dental alveoli (sockets) in alveolar processes of maxillae and mandible
bound by periodontal ligament to form gomphosis joint
97
what forms the primary mass of a tooth?
dentin - harder than bone
| covered by enamel - hardest substance in the body, composed of calcium phosphate crystals
98
what is in the middle of a tooth?
pulp cavity full of pulp (connective tissue)
99
what is the apical foramen?
opening in root of tooth from pulp cavity where blood vessels & nerves connect with body.
100
what surrounds the root of teeth?
cementum
| hard material
101
what are deciduous teeth?
baby teeth (milk teeth)
102
how many deciduous teeth are there & when do they arrive?
20 - usually start between 6 -30 months
103
how many permanent teeth are there?
32
104
name the teeth
from middle out
incisors (central and lateral) (slicing & cutting)
canines (puncturing & tearing)
premolars (1st & 2nd) - cusps crush and grind, 1-2 roots
molars (1st, 2nd & 3rd) 3+ roots - grinding & crushing
105
what are gums?
gingivae
composed of dense irregular CT
nonkeratinized stratified squamous epithelium covers alveolar processes of upper & lower jaws & surrounds neck of teeth
106
what forms the walls of the pharynx?
3 skeletal muscle pairs
| superior, middle & inferior pharyngeal constrictors
107
what lines the walls of the pharynx?
oropharynx & laryngopharynx are lined with nonkeratinized stratified squamous epithelium - protection against abrasion
108
describe the esophagus
normally collapsed
10 inches long in adult
begins at level of cricoid cartilage of larynx
anterior to vertebral bodies until it goes through diaphragm through esphageal hiatus & connects to stomach
109
describe the sphincters of the esophagus
superior esophageal sphincter (pharyngoesophageal): circular skeletal muscle ring where esophagus & pharynx meet - closes during inhalation
inferior esophageal sphincter (esophageal gastric or cardiac sphincter): ring of circular smooth muscle - not strong enough to prevent backflow so diaphragm muscles contract to help
110
what lines the mucosa of the esophagus?
nonkeratinized stratified squamous epithelium
111
describe the submucosa of the esophagus
thick
lots of elastic fibers so it can stretch during swallowing
lots of mucous glands that provide thick mucus for epithelium (lubrication) - ducts project through mucosa & open into lumen
112
describe the muscularis of esophagus
has both skeletal & smooth muscles
2 layers in top third are skeletal (not smooth), because skeletal contracts more quickly than smooth so food can get down before next inhalation
middle third has both
bottom third has just smooth - beginning of continuous smooth muscle muscularis that goes through stomach, small & large intestines, to anus
113
what is the outer most layer of the esophagus?
adventitia
114
what is another name for swallowing?
deglutition
115
what are the 3 phases of swallowing?
voluntary
pharyngeal
esophageal
116
describe the voluntary phase of swallowing
controlled by cerebral cortex
| bolus is pushed by tongue against hard palate & moves toward oropharynx
117
describe the pharyngeal phase of swallowing
involuntary
initiated by arrival of bolus at entryway to oropharynx
stimulates sensory receptors around fauces. nerve signals relayed to effectors to cause: entry of bolus into oropharynx, elevation of soft palate & uvula to block passageway b/t oropharynx & nasopharynx, elevation of larynx by hyoid muscles in neck to move epiglottis to cover laryngeal opening (so food doesn't go into larynx & trachea), inhibition of respiratory center in medulla oblongata so that breath isn't taken during swallowing
118
how long is the pharyngeal phase of swallowing?
about 1 second as pharyngeal constrictors contract from top to bottom, creating pressure difference & forcing food down into esophagus
119
describe the esophageal phase of swallowing
involuntary
bolus goes from esophagus into stomach - 5-8 seconds
presence of bolus in lumen of esophagus stimulates sequential peristaltic waves of muscular contraction
pressure difference moves bolus down
120
when do superior & inferior esophageal sphincters open & close?
closed at rest
relax when bolus is swallowed
after bolus passes inferior esophageal sphincter, nerve signals cause it to contract
121
what kind of digestion occurs in the stomach?
mechanical and chemical
| chemical digestion of protein & fat begin here
122
how many liters of stuff enter stomach each day?
3-4 liters of food, drink & saliva
123
how long does stuff stay in the stomach?
between 2-6 hours
| fatty stuff takes longest to empty
124
what kinds of things absorb in the stomach?
small nonpolar substances that come in contact with mucosa
| alcohol & aspirin
125
what are the regions of the stomach?
greater & lesser curvature
cardia (entryway into stomach lumen from esophagus)
cardiac orifice - internal opening where cardia meets esophagus
fundus - top of the stomach above esophageal opening
body - main part
pylorus - funnel shaped pouch at the end of the stomach
pyloric orifice - opening of pylorus into duodenum
pyloric sphincter - thick ring of circular smooth muscle around pyloric orifice
126
what does the pyloric sphincter do?
regulates entry of material into small intestine
127
what is the gross anatomy of the inside of the stomach
full of gastric folds or rugae
128
what is the purpose of the gastric folds?
allow it to expand greatly when full of food
129
what membranes are associated with the stomach?
greater and lesser omentum
greater omentum extends inferiorly from greater curvature of stomach forming fatty apron that covers anterior surface of abdominal organs
lesser omentum extends superiorly from the lesser curvature of stomach & duodenum to liver
130
describe the histology of the stomach
thin mucosa 1.5mm at thickest - lined by simple columnar epithelium supported by lamina propia, indented by gastric pits
gastric glands extend deep into mucosa from base of each gastric pit - surrounded by muscularis mucosa that helps expel gastric gland secretions
muscularis had 3 smooth muscle layers (rather than 2 in rest of GI tract), inner oblique, middle circular, outer longitudinal. gets thicker as it goes from body to pyloris
serosa is outer layer - visceral peritoneum (stomach is intraperitoneal)
131
what is the purpose of the 3 layers of muscularis in the stomach?
churning and blending of bolus to help mechanically digest food
132
What are the types of secretory cells of the gastric epithelium?
```
surface mucous cells
mucous neck cells
parietal cells
chief cells
G-cells
```
133
describe surface mucous cells
line the stomach lumen & extend into gastric pits
secrete alkaline product that contains mucin onto gastric surface
mucin + water makes 1-3mm thick mucus layer - helps prevent ulceration of stomach lining w/high acidity of gastric fluid & gastric enzymes
134
how much gastric juice is produced a day?
3L
135
describe mucous neck cells
located immediately deep to the base of the gastric pit & interspersed among parietal cells
produce acidic mucin - helps maintain acidic conditions - lubricating properties to help protect lining from abrasion & mechanical injury
136
describe parietal cells
also called oxyntic cells
add intrinsic factor - a glycoprotein - only essential function performed by stomach. required for absorption of B12 in ileum - B12 is necessary for erythrocyte production
adds HCl - forms from H+ and Cl- secreted across parietal cell's surface - creates low pH in stomach
137
what is the function of HCl in the stomach?
converts inactive enzyme pepsinogen into active pepsin & provides optimal pH for pepsin activity
kills most microorganisms
contributes to breakdown of plant cell walls & animal CT
denatures proteins - facilitating chemical digestion by enzymes
138
describe chief cells
also called zymogenic cells or peptic cells
most numerous secretory cells w/in gastric glands
produce & secrete packets of zymogen granules primarily containing pepsinogen (inactive form of proteolytic enzyme pepsin) - has to be produced inactive form to prevent destruction of chief cell proteins
produce gastric lipase - small role in fat digestion (about 10-15% of fats)
139
what happens to pepsinogen in the stomach?
activated by HCl and other active pepsin molecules
| chemically digests denatured proteins into smaller peptide fragments (oligopeptides)
140
describe G-cells
enteroendocrine cells
widely distributed in gastric glands
secrete gastrin hormone into blood
141
what does gastrin do?
a hormone that stimulates stomach secretions and motility
142
what is a peptic ulcer?
chronic, solitary erosion of a portion of the lining of either the stomach or the duodenum
gastric ulcers are in the stomach
duodenal ulcers are in the superior part of the duodenum
143
what is the purpose of smooth muscle activity in the stomach?
mixing bolus with gastric juice to form chyme
| emptying chyme from stomach into small intestine
144
describe steps of gastric mixing & emptying
1. contractions of smooth muscle mix bolus with gastric secretions to form chyme
2. peristaltic wave results in pressure gradient that moves stomach contents toward pylorus sphincter
3. pressure gradient increases force in pylorus against pyloric sphincter
4. pyloric sphincter opens, small amount of chyme enters duodenum (3mL)
5. pyloric sphincter closes & retropulsion occurs
145
what is retropulsion?
when pyloric sphincter closes, stomach contents are squeezed back toward stomach body --> additional mixing of contents to further reduce size of food particles
146
how are the digestive processes in the stomach regulated?
pacemaker cells in stomach wall spontaneously depolarize less than 4X/min. - establishes rhythm of muscular contraction
electrical signals spread via gap junctions
regulated by both nervous reflexes and hormones, which alter force but not rate of contractions (constant)
secretory of gastric glands is also altered
3 phases
147
what are the 3 phases of digestion?
cephalic phase
gastric phase
intestinal phase
148
describe the cephalic phase of digestion
involves the cephalic reflex initiated by thought, smell, sight or taste of food
nerve signals from higher regions of brain are sent to hypothalamus --> relays nerve signals to medulla oblongata ---> increases vagal stimulation of stomach by increasing parasympathetic output along vagus nerve to stomach, ---> increase in contractile force in gastric wall (increasing motility) & secretory activity of gastric glands (stomach growling)
149
describe the gastric phase of digestion
happens when bolus reaches stomach
regulated by nervous system via gastric reflex and endocrine system by release of gastrin hormone
gastric reflex initiated as food enters stomach - baroreceptors in stomach wall detect stretch, chemoreceptors detect protein and increase in pH of gastric contents. nerve signals relayed to medulla oblongata resulting in same effect as cephalic reflex - increase in stomach motility & secretory activity
150
during gastric phase, what hormone does the presence of food stimulate?
release of gastrin from enteroendocrine cells
gastrin enters blood & circulates back to stomach to stimulate contractile activity & increase HCl release from parietal cells
also stimulates contraction of pyloric sphincter to slow stomach emptying giving enough time for digestive activities w/in stomach
151
describe the intestinal phase of the stomach
processes following chyme reaching small intestine
regulated by nervous system and endocrine system
involves intestinal reflex & release of 2 hormones: cholecystokinin (CCK) and secretin
152
how are the intestinal reflex, gastric reflex & cephalic reflex related?
intestinal reflex opposes other 2 reflexes
153
what is the function of the intestinal reflex?
protects small intestine from being overloaded with chyme
initiated w/entry of acidic chyme into duodenum --> initiates inhibitory nerve signals to medulla oblongata --> vagal stimulation to stomach is decreased ---> decrease in motility & secretory activity of the stomach
154
what do cholecystokinin & secretin do?
decrease stomach motility & secretory activity
inhibit release of gastrin
slows down emptying of stomach
155
what comprises the lower GI tract?
```
small intestine (duodenum, jejunum, ileum - duodenum is considered part of upper GI tract)
accessory organs
large intestine
```
156
what is the purpose of accessory organs in the lower GI tract?
they secrete bile & pancreatic juice. Bile is produced by liver, stored concentrated & released by gallbladder. pancreatic juice has numerous digestive enzymes produced & released by pancreas.
157
how much stuff enters the small intestine?
9-10 L of food, water & digestive system secretions / day
158
how long does stuff spend in the small intestine?
at least 12 hours
159
what is the function of the small intestine?
finishes chemical digestion process, absorbes most of the nutrients & a large percentage of water & electrolytes
absorbs vitamins
160
how long is the small intestine?
6 meters on cadaver - shorter in living person due to muscle tone
161
Describe the duodenum
duodenum - 1st segment, 10" long C-shape around pancreas & meets jejunum @ duodenojejunal flexure
most is retroperitoneal, proximal part is intraperitoneal & connected to liver by lesser omentum
receives accessory gland secretions from liver, gallbladder & pancreas
162
what are the sections of the small intestine?
duodenum
jejunum
ileum
163
describe the jejunum
middle region
7.5 feet - 2/5 of total length of small intestine
primary region for chemical digestion & nutrient absorption
intraperitoneal & suspended in abdomen by mesentery
164
describe the ileum
last region of small intestine
10.8' long
3/5 of small intestine
distal end terminates at ileocecal valve - sphincter that controls entry of material into large intestine
intraperitoneal & suspended in abdomen by mesentery
absorption of digested material continues in ileum
165
describe the mucosal & submucosal tunics on the small intestines
```
internal circular folds called plicae
increase surface area for nutrient absorption
speed bumps to slow down chyme
most numerous in duodenum & jejunum
least numerous in ileum
```
166
describe the histology of the small intestine
length of muscularis mucosae is shorter than two layers internal to it ---> makes villi - larger & more numerous in jejunum
epithelium is glove covering the lamina propria finger
villus has arteriole, capillary network (absorbs most nutrients), venule, lacteal (absorbs lipids & lipid-soluble vitamins too large to be absorbed by blood capillaries)
microvilli - extensions of plasma membrane on simple columnar epithelial cells lining small intestine - look fuzzy so called brush border
167
what is in the brush border?
enzymes that complete chemical digestion - called brush border enzymes
also embedded w/in membrane are required proteins for transport of digestion products
168
where are intestinal glands located and what is their purpose?
between intestinal villi - invaginations of mucosa
also called intestinal crypts
mucosal cells that secrete intestinal juice
extend to base of mucosa (slightly resemble gastric glands of stomach)
169
what are the types of intestinal glands?
goblet cells - produce mucin that forms mucus with water - lubricates & protects intestinal lining - increase in number from duodenum to ileum because more lubrication needed as nutrients are absorbed & undigested stuff left behind
unicellular gland cells - synthesize enteropeptidase
enteroendocrine cells - release hormones like CCK and GIP
170
what kind of gland is housed in the submucosa only in the proximal duodenum?
submucosal or duodenal gland (Brunner gland)
| produces viscous, alkaline mucus that protects duodenum from acidic chyme
171
what are the functions of smooth muscles in small intestine?
mixing chyme with accessory gland secretions
moving chyme continually against new areas of brush border
propelling contents through small intestine toward large intestine
172
what are the two types of muscle processes in the small intestine?
segmentation & peristalsis
segmentation (more prevalent at entry of small intestine) mixes chyme with accessory gland secretion through back & forth motion
peristalsis propels material w/in lumen by alternating contraction of circular and longitudinal muscle layers in small regions - rhythm of contractions is more frequent in duodenum than ileum so net movement of intestinal contents is toward the large intestine
173
what is the gastroileal reflex?
moves contents from ileum to cecum in response to food entering stomach
ileocecal sphincter usually is constricted, but activity in ileum during digestion makes it relax to allow small intestine contents to enter large intestine
contraction of sphincter closes passage to decrease backflow into ileum
174
What are the accessory organs associated with the duodenum?
liver
gallbladder
pancreas
175
what delivers secretions of accessory organs to duodenum?
biliary apparatus
network of thin ducts:
right & left hepatic duct drain left & right lobes of liver --> merge to form common hepatic duct --> merges with cystic duct (from the gallbladder) to form common bile duct that extends inferiorly to duodenum
176
what is the hepatopancreatic ampulla?
swelling on posterior duodenal wall where common bile duct and main pancreatic duct merge & pierce duodenal wall
177
what is the area called where common bile duct & main pancreatic duct merge & enter duodenum?
hepatopancreatic ampulla
178
what does the hepatopancreatic sphincter do?
regulates movement of bile & pancreatic juice into duodenum
179
what is the projection called within the duodenum where the bile & pancreatic juice enter through the ducts
major duodenal papilla
180
what is an alternative way for small amounts of pancreatic juice to enter duodenom?
accessory pancreatic duct - penetrates duodenal wall & forms the minor duodenal papilla
181
what is the liver's main function in digestion?
production of bile
182
what is the gross anatomy of the liver?
covered by CT capsule & layer of visceral peritoneum (except for small region on diaphragmatic surface called bare area)
4 partially separated lobes, supported by 2 ligaments right & left lobe (right is bigger - separated from left by falciform ligament, a peritoneal fold that holds liver to anterior abdomen wall)
caudate lobe & quadrate lobes are within the right lobe
caudate is adjacent to inferior vena cava
quadrate lobe is adjacent to gall bladder
183
how is blood supplied to the liver?
dual supply - 1 oxygenated, 1 deoxygenated
hepatic artery is branch of celiac trunk that carries oxygenated blood to liver
hepatic portal vein is part of hepatic portal system - carries blood from capillary beds of GI tract, spleen & pancreas - brings 75% of blood volume to liver - rich in nutrients but poor in O2
blood mixes as it passes into & through hepatic lobules
184
what are the structural & functional units of the liver?
hepatic lobules
formed by CT capsule that branches throughout the organ forming septa that partition it into thousands of small polyhedral lobules
185
what are liver cells called?
hepatocytes
186
what is a portal triad and where is it?
at periphery of liver lobule
| composed of hepatic duct bile ductule and branches of hepatic portal vein & hepatic artery
187
what is in the middle of each liver lobule?
central vein - drains blood flow from lobule
| merge throughout liver to form hepatic veins that eventually empty into the inferior vena cava
188
what are hepatic sinusoids?
thin-walled capillaries w/large gaps b/t cells - more permeable than other capillaries
venous blood of hepatic portal system & arterial blood mix w/in sinusoids & flow slowly toward central vein
nutrients absorbed from sinusoids into hepatocytes
sinusoids also lined with reticuloendothelial cells (Kupffer cells) - star-shaped - macrophages that eat harmful substances from blood
189
what is between each cord of hepatocytes in the liver lobules?
bile canaliculus
| channel that conducts bile that is produced by hepatocytes to hepatic duct in portal triad
190
what is bile?
alkaline fluid that contains mostly water, bicarbonate ions, bile salts (formed from cholesterol), bile pigments, cholesterol, lecithin (a phospholipid) and mucin
produced by liver
.5-1 L/day
191
what is the function of bile salts & lecithin?
function in mechanical digestion of lipids, making more efficient chemical digestion of triglycerides
192
where is the gallbladder?
attached to inferior surface of liver
193
what is the function of the gallbladder?
stores, concentrates & releases bile that liver produces
194
what is the structure of the gallbladder?
3 tunics: inner mucosa, middle muscularis, external serosa
| mucosa is folded to permit distension of wall as it fills with bile
195
what connects the gallbladder to the common bile duct?
cystic duct
196
what is at the neck of the gallbladder?
sphincter valve that controls flow of bile into & out of gallbladder
bile enters when hepatopancreatic sphincter closes & bile backs up through common bile duct & cystic duct into gallbladder.
can hold 40-60mL of concentrated bile
197
what kinds of functions does the pancreas have?
endocrine & exocrine
198
what are the endocrine functions of the pancreas?
producing & secreting hormones like insulin & glucagon
199
what are exocrine cells of the pancreas called? and what do they do?
acinar cells
| produce pancreatic juice to assist with digestive activities
200
describe the gross anatomy of the pancreas
retroperitoneal
touches the spleen
has a wide head adjacent to curvature of duodenum
body projects toward left lateral abdominal wall
tail tapers as it approaches the spleen
201
what is the histology of the pancreas?
modified simple cuboidal epithelial cells (acinar cells) arranged in saclike acini which are organized into large clusters - lobules
202
what do acinar cells of the pancreas do?
produce & release hydrolytic enzymes
small ducts lead from each acinus to larger ducts---> to pancreatic ducts ---> to duodenum
pancreatic ducts are lined by simple cuboidal epithelial cells & secrete alkaline HCO3- fluid
203
what is pancreatic juice & what cells produce it?
acinar cells & cells that line the pancreatic ducts produce it
alkaline fluid most water, HCO3- & hydrolytic enzymes:
pancreatic amylase (digest starch)
pancreatic lipase (digest fats)
inactive proteases (trypsinogen, chymotrypsinogen, procarboxypeptidase) that digest protein when activated
nucleases (digest nucleic acids - DNA RNA)
204
what activates the pancreas to release pancreatic juice?
vagal stimulation during cephalic & gastric phase
205
what does CCK do?
cholecystokinin
hormone released from small intestine - mostly in response to fatty chyme
stimulates smooth muscle of gallbladder to contract --> releasing concentrated bile
stimulates pancreas to release pancreatic juice
relaxes smooth muscle w/in hepatopancreatic ampulla so bile & pancreatic juice can enter small intestine
inhibits stomach motility & release of gastric secretions
206
what does secretin do?
released from small intestine in response to chyme acidity
causes release of alkaline solution that contains HCO3- form liver & ducts of pancreas - helps neutralize acidic chyme
inhibits gastric secretions & motility
207
list the hormones that control digestion
gastrin
cholecystokinin
secretin
208
what secrets the digestion hormones?
gastrin - G cells in stomach
CCK - enteroendocrine cells of small intestine
secretin - enteroendocrine cells of small intestine
209
what is the stimulus for release of each of the digestion hormones?
gastrin - bolus in stomach - especially if it has proteins
CCK - chyme w/amino acids & fatty acids entering small intestine
secretin - acidic chyme entering small intestine
210
what are the targets & effects of the digestion hormones?
gastrin: parietal cells: stimulates secretion of HCl - chief cells: stimulates secretion of pepsinogen - pyloric sphincter: stimulates contraction
CCK: stomach: inhibits motility & gastric secretion - gallbladder: stimulates release of bile - pancreas - stimulates release of pancreatic juice - hepatopancreatic sphincter: causes relaxation
secretin: stomach: inhibits gastric secretion & motility - pancreas: stimulates secretion of alkaline solution from pancreatic ducts - liver: stimulates secretion of alkaline solution
211
how much material enters large intestine daily?
about 1 L
212
what does the large intestine absorb?
water, electrolytes (mostly Na+ and Cl-)
| only 100mL water that enters large intestine is lost in feces daily
213
describe the anatomy of the large intestine
2.5" diameter, 5' long
originates at ileocecal junction, terminates at anus
3 regions: cecum, colon and rectum
214
what is the cecum
1st portion of the large intestine
right lower abdominal quadrant
extends inferiorly from ileocecal valve
vermiform appendix pokes down - lined w/lymphocyte-filled lymphatic nodules
cecum & appendix are intraperitoneal organs
215
where does chyme enter the large intestine?
from the ileum into the ileocecal valve
216
describe the colon
begins at level of ileocecal valve - forms the U-shape of large intestine
partitioned into 4 segments:
ascending colon - retroperitoneal b/c posterior wall adheres to posterior abdominal wall
transverse colon - intraperitoneal
descending colon - retroperitoneal
sigmoid colon - intraperitoneal
217
what are the bends in the colon called?
right colic flexure (hepatic flexure) from ascending colon to transverse colon (as it approaches anterior surface of liver)
left colic flexure (splenic flexure) from transverse to descending as it approaches spleen in upper left quadrant of abdomen
sigmoid flexure where sigmoid originates - bend at bottom of descending
218
describe the rectum
retroperitoneal
rectal valves - thick transverse folds hold poo in while passing gas
anal canal - last few centimeters of large intestine - lined by stratified squamous epithelium - terminates at anus - thing longitudinal ridges called anal columns in between are anal sinuses that release mucin during pressure from poo
at bottom are internal anal sphincter (involuntary smooth muscle) and external anal sphincter (voluntary skeletal muscle)
219
what features are unique to the large intestine?
```
teniae coli - thin, longitudinal bundles of smooth muscle that act like elastic in a waistband
haustra - many sacs - the teniae coli bunch the large intestine into these sacs
epiploic appendages (omental appendages) - fat lobules that hang off external surface of haustra. gross
```
220
what is the histology of the large intestine?
lined by simple columnar epithelium w/many goblet cells
mucosa is smooth - no villi but does have intestinal glands (crypts) that extend inward toward muscularis mucosae
glands secrete mucin
lots of lymphatic nodules & lymphatic cells are in lamina propia
muscularis of cecum & colon has 2 layers of smooth muscle, but outer longitudinal don't surround all the way - they form the teniae coli
221
what are the normal bacterial flori of the large intestine called?
indigenous microbiota
222
what do normal bacterial flori do in large intestine?
chemical breakdown of complex carbohydrates, proteins & lipids that are still in chyme
bacterial action produces CO2, H+, methane etc - partly accounting for smelly poo
also produce B vitamins, vitamin K which is absorbed from large intestine into blood (also absorbed in small intestine from food we eat)
223
what types of movement happen in the large intestine?
peristaltic movements: weak & sluggish but resemble small intestine peristaltic movement
haustral churning: happens after relaxed haustrum fills with stuff - distention stimulates reflex contractions in muscularis - increase churning & move material to more distal haustra
mass movement: powerful peristaltic-like contractions involving teniae coli - propel fecal material toward rectum. contraction wave begins in middle of transverse colon - forcing stuff into descending colon, sigmoid colon, & rectum
usually happens 2-3 times a day
224
what reflexes are associated with motility in large intestine?
gastrocolic reflex - initiated by stomach distension to cause mass movement
defecation reflex - filling of rectum initiates urge to poo - stimulus results in transmission of nerve signals from receptors to spinal cord, parasympathetic output increases to sigmoid colon & rectum & decreases to internal anal sphincter
225
what does essential nutrients mean?
stuff we need to eat to survive
226
what are the essential nutrients?
```
carbohydrates
lipids
proteins
minerals
vitamins
water
```
227
how are carbohydrates classified?
monosaccharides (glucose, fructose, galactose)
disaccharides (sucrose, maltose, lactose)
polysaccharides (starch, cellulose)
228
what does chemical digestion of carbohydrates consist of?
1) breakdown of starch into individual glucose molecules
2) breakdown of disaccharides into individual monosaccharides that compose them
oral cavity & small intestines main sites
229
where does the digestion of starch begin?
oral cavity - catalyzed by salivary amylase --> breaks down chemical bonds between glucose molecules
salivary amylase is inactivated by low stomach pH - usually w/in 15-20 minutes after bolus enters stomach
230
how are carbohydrates broken down in small intestine?
(no new enzymes for carbohydrate digestion enter stomach)
pancreatic amylase - synthesized & released by pancreas - digests starch into shorter strands of glucose
brushborder enzymes complete the breakdown of starch: dextrinase & glucoamylase and maltase
lactase (lactose to glucose & galactose), sucrase (sucrose to glucose & fructose)
glucose fructose & galactose are absorbed across small intestinal epithelial lining into blood --> hepatic portal vein to liver --> converted to glucose
cellulose is not digested - facilitates movemetn along GI tract
231
what are proteins?
amino acid subunits linked by peptide bonds
232
what does digestion do to proteins?
releases individual amino acids so body can use them to build its own proteins
233
how do enzymes work on proteins?
either break peptide bonds between specific adjacent amino acids or release amino acids from either end of a protein
all are released as inactive enzymes so that they won't destroy the proteins within the cells that produce them
234
describe protein breakdown in the stomach
begins with pepsin - formed from pepsinogen that is released by chief cells
HCl (released from parietal cells) causes low stomach pH that activates pepsinogen to pepsin, denatures protein to make breakdown easier
235
describe protein breakdown in small intestines
pepsin inhibited by high pH
pancreas releases inactive trypsinogen, chymotrypsinogen & procarboxypeptidase into small intestine
enzyme enteropeptidase (synthesized and released by small intestine) activates trypsinogen to trypsin. trypsin activates other trypsinogen & activates chymotrypsinogen to chymotrypsin & procarboxypeptidase to carboxypeptidase
trypsin & chymotrypsin break specific bonds, carboxypeptidase frees amino acid at end
brush border enzyme dipeptidase breaks final bond between dipeptide
aminopeptidase frees amino acids from amino end of protein
amino acids absorbd across small intestine epithelial lining & enter blood
236
what are lipids?
not water-soluble
triglycerides (glycerol molecule & 3 fatty acids - enzymes need t break bonds between glycerol & fatty acids) & cholesterol (doesn't have to be digested to be absorbed)
237
describe lipid digestion in stomach
lingual lipase is component of saliva in oral cavity - not activated until it reaches stomach
in stomach lingual lipase & gastric lipase (produced by chief cells) digest some triglycerides 30% to diglyceride & fatty acid. don't need bile salts
238
describe lipid digestion in small intestine
pancreatic lipase (released in duodenum) digests triglyceride into monoglyceride & 2 free fatty acids
emulsification (action of bile salts) separates big lipid droplets so that lipase can digest - make micelles
last portion of ileum, bile salts are recovered by active transport & recycled to liver for reuse
new bile salts synthesized by hepatocytes
239
describe bile salts
amphipathic molecules - polar head & nonpolar tail
nonpolar tails surround fat & make micelle
no brushborder enzymes required for breakdown of triglycerides
240
describe lipid absorption
micelles transport lipids to simple columnar epithelial lining of small intestine
enter epithelial cells (ball salts remain)
inside epithelial cells, fatty acids are reattached to monoglyceride to re-form triglycerides
triglycerides, cholesterol & other lipid molecules wrapped with protein to form chylomicron - released by exocytosis --> enter lacteals (too big to enter blood capillaries)
241
describe nucleic acid breakdown in small intestine
nucleases synthesized & released by pancreas start digestion of nucleic acid
brush border enzymes (phosphatase breaks phosphate bond and nucleosidase breaks bond b/t sugar & N base)
all components are absorbed across epithelium of small intestine to blood: phosphate, sugar, nitrogenous bases
242
how much water is required daily by the body?
2-3L
243
what are the nutrient biomolecules?
carbohydrates, lipids & proteins
| nucleic acid not considered nutrients because they aren't required in our diet for survival
244
what are carbohydrates?
simple sugar monomers (monosaccharides), disaccharides, and polysaccharides
245
what is the function of carbohydrates?
glucose --> broken down to generate energy for life processes
glycogen (polymer of glucose molecules) stored in liver & skeletal muscle tissue
246
what is the function of lipids?
triglycerides store energy
phospholipids compose cell membranes
steroids are components of plasma membranes, serve as hormones & precursors for synthesis of bile salts
eicosanoids are local hormones
247
what is the function of proteins?
structural & functional components of the body
248
what is the function of vitamins?
```
coenzymes in chemical reactions
participate in CT synthesis
part of visual pigment in eye
enhance Ca absorption
aid in bone formation
```
249
what is the function of minerals?
required in bone formation, nerve & muscle formation
| component of nucleic acids, ATP and part of hemoglobin
250
what is the function of water?
support life - cohesion, adhesion, surface tension, high specific heat, high heat of vaporization
251
what are proteins?
formed by 20 different amino acids & contain nitrogen in the amine group
nonessential amino acids can be made in the body
8 essential amino acids must come from food
can be categorized as complete (supply all essential amino acids) or incomplete (do not supply all essential amino acids)
252
what are the fat soluble vitamins?
K - leafy green vegetables - clotting
A - liver, milk products, green vegetables - eyes
D - cod liver oil, dairy products, UV rays - Ca absorption
E - leafy greens, seeds, butter - cell membrane & fatty acid protection from oxidation
253
how are fat soluble vitamins absorbed in body?
w/in lipid micelles - enter lacteals
| excess is stored w/in body fat & can be toxic
254
name the minerals required by humans
Major: CaClCo MgMnP KNaS
Minor: CrCuF IFe SeZn
255
what is the function of iron?
present in hemoglobin w/in erythrocytes (binds O2) & w/in mitochondria in e- transport system (binds e-'s)
256
what is the function of calcium?
required for formation & maintenance of skeleton, blood clotting, exocytosis of neurotransmitters
257
what is the function of sodium & potassium?
maintain resting membrane potential in excitable cells
| required to generate Action Potential
258
what is the function of iodine?
needed to produce thyroid hormone
259
what is the function of zinc?
roles in protein synthesis & wound healing
260
how do we get minerals?
from food
261
what is the difference between major minerals & minor minerals
major minerals - we need more than 100mg/day
| minor (trace) - we need less
262
what are sources of carbohydrates?
starch (potatoes breads rice grains)
lactose (milk)
sucrose (sugar, maple syrup, fruits)
disaccharides (maltose in cereal), monosaccharides (fructose & glucose), high fructose corn syrup
263
what is our source of lipids?
fats & oils
cholesterol (component of all animal-based products b/c it is wi/in plasma membrane of animal cells) - also synthesized by liver
264
what is our source of protein
meat, dairy, beans nuts
| also supply nitrogen - needed for N- bases of DNA & RNA
265
what is nitrogen balance?
equilibrium b/t dietary intake & loss in urine & feces
positive N balance when we absorb more N than excrete (when growing, pregnant or recovering from injury)
negative N balance - more N excreted than absorbed (malnutrition or blood loss)
266
what affects how much of each nutrient you need?
age, sex, body mass, level of physical activity, health, pregnancy
267
how is my plate divided?
half is fruits & vegetables
half is proteins & grains
milk is a cup on the side
268
what is the absorptive state?
time you are eating, digesting & absorbing nutrients
lasts about 4 hours after meal
concentrations of glucose, triglycerides & amino acids are increasing in blood as they are absorbed from GI tract
269
what is the ideal blood glucose level?
70-110mg/dL
270
what hormone is released during absorptive state?
insulin
271
what does insulin do to regulate blood nutrient levels?
stimulates liver cells & muscle cells to form glycogen from glucose (glycogenesis)
causes adipose connective tissue to increase uptake of triglycerides from blood, stimulates lipogenesis & inhibits lipolysis
stimulates most cells to increase amino acid uptake --> accelerated rate in protein synthesis
decrease in all energy-releasing molecules in blood, increase in storage of glycogen & triglycerides & formation of protein w/in body tissues
272
what is the postabsorptive state?
time between meals when body relies on stores of nutrients b/c no absorption of nutrients is happening
273
what is the major regulating hormone during the postabsorptive state?
glucagon
274
what effects does glucagon have?
stimulates liver cells to catabolize glycogen to glucose - increase glycogenolysis and gluconeogenesis (formation of glucose from noncarbohydrate sources)
causes adipose CT to break down triglycerides to glycerol & fatty acids by stimulating lipolysis
glucose released from liver, fatty acids released from fat storage
glucagon has no effect on body proteins because there is no storage of amino acids or proteins in cells
275
what is the functional unit of the liver?
liver lobule
microscopic
composed of cords of hepatocytes that radiate out from a central vein
sinusoids are located between cords (capillaries)
oxygenated blood from hepatic artery & deoxygenated (nutrient-rich) blood from hepatic portal vein travel through liver sinusoids toward central vein
bile canaliculi are b/t each cord of hepatocyte & get bile synthesized by hepatocyte - bile drains eventually to small intestine
276
describe cholesterol synthesis
fatty acids go from blood to sinusoid to hepatocyte
broken down into 2 C units to form acetyl CoA through beta oxidation process
Acetyl CoA molecules are used to synthesize cholesterol in enzymatic pathway using enzyme called HMG-CoA reductase
basal level of cholesterol production adjusts according to intake
277
what happens to cholesterol after it is synthesized?
1) released into blood as component of very-low-density lipoproteins (VLDLs) OR
2) synthesized into bile salts & released as part of bile into small intestine -10% bile salts go out w/poo - way of eliminating excess cholesterol & lowering blood cholesterol levels
278
how are lipids transported in blood?
lipids are hydrophobic, so they are wrapped in water-soluble protein --> lipoprotein - contain triglycerides, cholesterol & phospholipids inside protein wrapper
279
what is a chylomicron?
triglycerides & some cholesterol wrapped in protein - formed in epithelial cells lining small intestine so that they can be absorbed into a lacteal & transported w/in lymph until it enters venous blood at junction of jugular & subclavian vein
280
what are the 3 categories of lipoproteins formed in the liver?
1) very-low-density lipoproteins (VLDL) - contain the most lipid
2) low-density lipoproteins (LDL) somewhat less lipid
3) high-density lipoproteins - least amount of lipid
all 3 transport lipids between liver & peripheral tissues
281
which lipoproteins transport lipids from liver to peripheral tissues?
VLDLs - mostly deliver lipids to adipose CT - after delivery become LDL
LDLs - have high amounts of cholesterol - deliver cholesterol to cells. bind to LDL receptors & are engulfed into cell where cholesterol is used in plasma membrane or by certain tissues
282
which lipoproteins transport lipids from tissues to liver?
HDLs
proteins are formed in liver & released into blood w/out additional lipid
circulate in blood & fill w/lipids from peripheral tissues & inner lining of arterial walls. transport lipids to liver
excess cholesterol is converted to bile salts w/in liver
HDL's also make cholesterol available to steroid-producing tissues (like LDL's) but HDLs are not engulfed by cell when cholesterol is removed.
283
which are the good cholesterols?
HDLs because they remove cholesterol from arterial walls, LDLs deposit it there
284
what are the main categories of liver function?
```
carbohydrate metabolism
protein metabolism
lipid metabolism
transport of lipids
storage & drug detoxification
```
285
how does the liver function in carbohydrate metabolism?
1) monosaccharides absorbed from small intestine into blood, enter hepatocytes, converted to glucose
2) noncarbohydrates converted to glucose by gluconeogenesis
3) glucose molecules are bonded together to form glycogen by glycogenesis
4) glucose molecules are released from glycogen by glycogenolysis
286
how does the liver function in protein metabolism?
1) deamination (amine group removed from amino acids) NH2 converted to urea & enters blood where eliminated by kidney. remaining components oxidized in cellular respiration to generate ATP from liver
2) amino acids used to form proteins, including plasma proteins
3) transamination: amino acids converted from one form to another
287
how does the liver function with lipid metabolism?
1) fatty acids joined with glycerol to form triglycerides (lipogenesis)
2) fatty acids released from triglycerides (lipolysis)
3) fatty acids broken down into acetyl CoA (beta oxidation)
4) acetyl CoA changed to ketone bodies (water-soluble molecules) - released into blood, transported to other cells - can be oxidized in cell respiration pathways
5) acetyl CoA used in cholesterol synthesis - cholesterol released into blood w/in VLDL & some used to form bile salts
288
how does the liver function with lipid transport?
transports both triglycerides & cholesterol w/in VLDLs and LDLs from liver to peripheral tissues
empty HDLs pick up lipids from peripheral tissues & blood & return as full HDLs to liver
289
what are other functions of the liver?
absorption of bilirubin (derived from heme group of hemoglobin) and eliminated as component of bile
storage site for vitamins (ADB) and minerals (Fe,Zn,Cu,Mg,Mn)
detoxification of drugs
hormone breakdown
290
what are the four stages of cellular respiration?
glycolysis
intermediate stage
citric acid cycle
electron transport system
291
describe glycolysis
```
anaerobic
cytoplasm of cell
glucose oxidized to 2 pyruvate molecules
2 ATP molecules formed
2 NAD+ molecules turn into 2 NADH molecules
```
292
describe the intermediate stage
multienzyme step
pyruvate converted to acetyl CoA
molecule of CO2 is formed by decarboxylation
1 molecule of NADH is produced
293
describe the citric acid cycle
acetyl CoA binds to oxaloacetic acid to form citric acid
2 C released as part of CO2 by decarboxylation
1 ATP, 1FADH2, and 3 NADH molecules are produced per turn
intermediate stage & citric acid cycle happen TWICE because there are 2 pyruvate molecules formed from oxidation of each glucose molecule entering glycolysis
294
describe the electron transport system
transfer of H and an e- from coenzymes NADH and FADH2. ATP formation occurs through oxidative phophorylation.
295
how can amino acids be used in cellular respiration?
must be deaminated in liver first
then can enter pathway of glycolysis, intermediate stage, or at specific points in the citric acid cycle
amine group is converted to urea & peed out
296
where does glycerol enter the pathway of cellular respiration?
glycolysis
it is converted to glucose through gluconeogenesis w/in liver
carbons of fatty acids are moved two at a time to form CoA which then enters citric acid cycle
297
what is the basal metabolic rate?
amount of energy used when an individual is at rest & not eating
298
what is total metabolic rate?
amount of energy used by the body, including energy needed for physical activity
BMR + metabolism associated w/physical activity
299
In the pancreatic islet, what are the cells
Alpha cells - secrete glucagon
| Beta cells - secrete insulin
