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Cheatsheet - Respiration and Gastrointestinal
Quantitative Physiology for Bioengineers (National University of Singapore)
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Lung Anatomy
- Lung space ~4l
- 1kg, 60% lung tissue, 40% blood
- Respiratory system begins at nose, ends at most distal alvelolus
- Nasal cavity, posterior pharynx, glottis, vocal cords, trachea are
divisions of tracheobronchial tree, all part of respiratory system
- Upper and Lower airways
- Vol. of air entering nares in order of 10,000 to 15,000
- Resistance to airflow in the nose during quiet breathing
accounts for ~50% of total resistance of respiratory system (~8cm
H20/L/sec)
-- Right lung (located in right hemithorax) divided into 3 lobes
(upper, middle and lower) by 2 interlobar fissures (oblique,
horizontal)
-- Left lung (left hemithorax) divided into 2 lobes (upper,
including the lingula, and lower) by a oblique fissure
-- Visceral pleura and parietal pleura
1. The trachea bifurcates into 2 main stem bronchi
2. Divide further into smaller and smaller bronchioles until
reaching alveolus
3. Bronchi and bronchiles differ in size and presence of cartilage,
type of epithelium and blood supply
4. Total surface area for that generation increases in size and no.
until the respiratory bronchiole terminates in an opening to a
group of alveoli
5. Cartilage Is a tough, resilient connective tissue that supports
the conducting airways of the lung and encircles about 8% of the
trachea
6. Conducting airwyas makes up 30% in volume while respiratory
airway 70%
7. An adult has ard 5x108 alveoli, composed of type I and II
epithelial cells, where under normal conditions, type I:type II =
1:1
- As part of pulmonary lobule, alveoli are delicate structures
coposed chiefly of type I alveolar cells, which allow for exchange
of gases with pulmonary capillaries (Alveoli make up large S.A.
750ft2
- Type II cells secrete surfactant prevents collapse of alveoli
during exhalation
- Lungs are separated from each other by the heart and other
structures in the mediastinum
- Each lung enclosed by double-layered pleural membrane
* Parietal pleura line walls of thoraic cavity
* Visceral pleura adhere tightly to surface of lungs themselves
Airway resistance as a function of the airway generation - Major site of resistance along
- Before inspirationn begins, the pleural pressure in normalbronchial tree is large bronchi.
individuals is ~-5cm H2O
The smallest airways
contribute very little to overall
- This -ve pressure is created by inward elastic recoil
pressure of lung and it acts to pull the lug away from the total resistance of bronchial
chest wall
tree
- With the onset of inspiration, alveolar pressure falls below- First, airflow velocity
zero, and when the glottis opens, gas moves into the
decreases substantially as the
effectivecross-sectional area
airways
- Note that at the resting volume of the lung (FRC), the
increases (i.e. Flow becomes
elastic recoil of the lung acts to decrease lung volume, but lamiar)
this inward recoil is offset by the outward recoil of the chest- Most importantly, the airway
wall, which acts to increase lung volume
generations exists in parallel
rather than in series
- During normal breathing,
~80% of the resistance to
airflow at FRC occurs in airways
with diameters greather than 2
Various lung volumes and capacities
mm
- Ratio of RV:TLC used to distinguish different types of
Determinants of maximal flow
pulmonary disease, where in normal individuals < 0.25
1. Factors responsible for max.
- An elevated ratio, secondary to an increase in RV out of
inspiratory flow include:
proportion to any increase in TLC, is seen in diseases
- Force generated by inspiratory
Changes inmuscles
alveolardecreases
pleural pressure
associated with airway obstruction, known as obstructive
as lung during a tidal
volume breath
pulmonary diseases
volume increases above RV
In
passive
breathing,
the
largest
- Could also be caused by a decrease in TLC, which is caused
- The recoil pressure of pressure
the lung difference
Surfactant
across lungs
occurs at
at the enf of inspiration,
by restrictive lung diseases
increases
as the
the point
lung volume
typically most
negative
in normal
breathing
increases
above
RV
- Max. point
happens
at the same
2. The
combination
of point in forced food
exhalation,inspiratory
but in the muscle
positveforce,
rangerecoil
Pressure
changes
during
Respiration
of the lung,
changes
in airway
resistance causes maximal
inspiratory flow to occur about
halfway between TLC and RV
3. Expiratory flow rates at lower
lung volumes are “effort
independent” and “flow limted”
- Lung vol. are determined by the balance between the
4. In contrast, events early in the
lung’s elastic properties and the properties of the chest wall
- If surfactant not present, alveoli will collpase,
expiratory maneuver are said to
- TLC occurs when the inspiratory chest wall muscels are
preventing gas exchange
be “effort dependent”
unable to generate the additional force needed to further
- Surfactant ensures large open area in the lungs for gas
distend the lung and chest wall
exchange to occur between the lungs and CV system
- RV occurs, when expiratory muscle force is insufficient to
- In healthy individual, always got some air in lung to
further reduce chest wall vol.
keep alveoli open but as lung age, got gradual increase in
- FRC, vol. of lung at the end of normal exhalation, is
no. of collapsed small airway
determined by the balance btwn. elastic recoil pressure
Surfactant and Laplace Law
Turbinates
- Pressure is directly proportional to surface tension and inversely generated by the lung parenchyma to become smaller
(inward recoil) and the pressure generated by chest wall to
propotional to radius of alveolus
become larger (outward recoil)
- Small alveoli would be at greater risk of collapse without
- When chest wall muscles are weak, FRC decreases (lung
surfactant
elastic recoil > chest wall muscle force). In the presence of
airway obstruction, FRC increases because of premature
Work of breathing
airway closure, trapping air in lungs
- Breathing requires the use of
Compliance of lung
respiratory muscles (diaphragm,
- CL = Lung volume/Translung pressure
intercostals, etc.), which expends
- Compliance of normal human lung = ~0.2L/cm H20, but
energy. Work is required to
varies with lung volume
overcome the inherent mechanical
- Compliance of lung is affected by several respiratory
Why is expiratory flow limited?
properties of the lung (i.e. elastic and
disorders
- Flow limitation occurs when the airways, which flow-resistive forces) and to moe
- In emphysema, an obstructive lung disease, usually of
are intrinsically floppy, distensible tubes, become both the lungs and chest wall
smokers, associated with destruciton of the alveolar septa
- Divide airway into 4 passages
compressed. The airways become compressed
and pulmonary capillary bed, the lung is more compliant
- Pseudostratified columnar, ciliated respiratory
when the pressure outside the airway exceeds the
- In contrast, in pulmonary fibrosis, a restrictive lung disease
epithelium with a thick vascular, and erectile glandular
pressure inside
is assoidated with increased collagen fibre deposition in the
tissue layer
- During expiration, the transmural pressure
interstitial space, the lung is noncompliant
- Airflow direction, humidification, heating and filtration
across the airways decreases as gas flows out of
- Sensors: airflow pressure and temperature-sensing
the alveoli
nerve receptors
- Airways toward the mouth become compressed
- Superior turbinates are smaller structures, connected to
when the pressure outside is greater than inside
the middle turbinates by nerve-endings, and serve to
(dynamic airway compression)
protect the olfactory bulb
- Then no amt. of effort will increase the flow
Fluids line the lung epithelium and play important
further because the higher pleural pressure tends
physiological role
to collapse the airway at equal pressure point
- Respiratory system is lined with 3 different and
- Hence, the expiratory flow is effort independent
highly significant fluids: pericilliary flui, mucus &
and flow limited
surfactant
Ventilation
- Respiratory tract to the level of bronchioles is lined
1. Process by which air moves in and out of the
by a pseudostratified, ciliated columnar epithelium
lung
- Goblet or suface secretory cells are interspersed
VE = f * TV
among the epithelial cells in a ratio of ~1 goblet sell
Where f -Frequency/No. of breaths per min; TVto 5 ciliated cells. They produce mucus in the airways
tidal vol. (Vol. of air inspired//exhaled per breath
and increase no. in response to chronic cigarette
2. Boyle’s law states that when temp. is constant,
smoke (and environmental pollutants) and thus
P and vol. are inversely proportional
Dead space: Physiological
combine to increased mucus and areway obstruction
3. Dalton’s law states that partial P of a gas in a
- Alveoli that are perfused but not ventilated are often
observed in smokers
gas mixture is the P that the gas exerts if it
found in diseased lungs. Total vol. of gas in each breath
- Alveoli lined with predominantly lipid-based
occupies the total vol. of mixture in the absence - OABCD: Work necessary to
that does not participate in gas exchange is
substance called surfactant that reduces surface
of the other components
physiological dead space ventilation
overscome elastic resistance
tension
4. Henry’s law states that conc. of a gas dissolved - AECF: Work necessary to overcome
- This vol. includes the anatomic dead space and the
in liquid is proportional to its partial P
dead space secondary to the ventilated but not
nonelastic resistance
prefused alveoli. The physiological dead space is always
1.0 = FN2 + FO2 + Fargon + other gases
- AECB: Work necessary to overcome
Perfusion and pulmonary circulation
at
least
as
large
as
the
anatomic
dead
psacwe,
and
in
nonelastic ressitance during
- Perfusion is the process by which deoxygenated blood passes through the lung and
Pb = PN2 + PO2 + Pargon + other gases
the presence of disease, it may be considerably larger
becomes reoxygenated
760mmHg = PN2 + PO2 + Pargon + other gases inspiration
- ABCF: Work necessary to overcome
- The arteries of the pulmonary circulation are the only arteries in the body that
O2 and CO2 transport
nonelastic resistance during
carry deoxygenated blood
- Gas movement throughout the respiratory system occurs
exhalation (Represents stored elastic
- The functions of the pulmonary circulation system are to:
predominantly via diffusion
energy from inspiration
(1) Reoxygenate the blood and despense with CO2
- Respiratory and circulatory system contain several unique
(2) Aid in fluid balance in the lungs
anatomic and physiological features to facilitate gas diffusion
(3) Distribute metabolic products to and from the lung
(1) Large S.A. for gas exchange (alveolar to capillary and capillary
- The arteries of the pulmonary circulation are thin-walled with minimal smooth
to tissue membrane barrrieris) with short distances to travel
muscle. They are 7x more compliant than systemic vessels, and are easily distensible
(2) Substantial partial pressure gradient differences
(3) Gases with advantageous diffusion properties
- Fick’s law states that diffusion of a gas (Vgas) across a sheet of
Ventilation-perfusion relationships
Distribution of pulmonary blood flow
tissue is ddirectly related to the S.A. (A) of the tissue, the diffusion
- The ventilation-perfusion ratio (V/Q ratio) is defined as the
- Pulmonary circulation is a low-pressure/low-resistance system
constant (D) of the specific gas and the partial pressure difference
ratio of ventilation to blood flow
and is influenced by gravity much more dramatically than the
(P1-P2) of the gas on each side of the tissue and is inverely related
- In a normal lung, the overall ventilation-perfusion ratio is
systemic circulation is
- In the blood, some O2 is dissolved in
to tissue thickness (T)
- In normal upright subjects at rest, blood flow increases from the about 0.8, but the range of V/Q ratios varies widely in
the plasma as a gas (~1.5%) the rest is
Vgas = A * D * (P1-P2)/T
different lung units
apex of the lung to the base of the lung, where it is the greatest
attached to Hb
- Different gases have different solubility factors
* When ventilation exceeds perfusion, V/Q > 1
- In a supine individual, blood flow is less in the uppermost
Equilibration
occurs
in
less
time
than
the
0.75s
that
RBC
spends
* When perfusion exceeds ventilation, V/Q < 1
(anterior regions and greater in the lower (posterior) regions
in the capillary bed (capillary transit time)
- On leaving the pulmonary artey, blood must travel against gravity - V/Q ratio varies in different areas of the lung. In an upright
- Diffusion of insoluble gases between alveolar gas and blood is
to the apex of the lung in upright subjects. For every 1cm increase subject, ventilation increases more slowly than blood flow
considered perfusion limited because the partial pressure of gas in
from apex of lung to base
in height above the heart, there is a decrease in hydrostatic
the blood leaving the capillary has reached equilibrium with
Oxygen transport
- Hence, V/Q ratio at apex is much >1 while that at base is
pressure equal to 0.74 mmHg
alveolar gas and is limted only by the amount of blood perfusing
- O2 is carried in blood in 2
much <1.
- This effect of gravity on blood flow affects arteries and veins
the alveolus
Hemoglobin
forms: dissolved and bound to
equally and results in wide variations in arterial and venous
Hgb
pressure from the apex to the base of the lung. These variations - Hgb is the major transport molecule for O2. The Hgb molecule is a - In contrast, a diffusion limited gas, such as CO, has low solubility
- Dissolved form is measured
will influence both flow and ventilation-perfusion relationships protein with 2 major components – 4 nonprotein heme group each in the alveolar-capillary membrance but high solubility in blood
containing iron in the reduced ferrous (Fe +++) form, which is the site because of its high affinity for hemoglobin (Hgb)
clinically in an arterial blood
of O2 binding + a globin portion conssiting of 4 polypeptide chains - Gases that are chemically bound to Hgb do not exert a partial
gas sample as PaO2. Only a
- Normal adults have 2 α-globin chains and 2 β-globin chains (HgbA) pressure in blood
small % of O2 in blood is in the
- High affinity of CO for Hgb enables large amounts of CO to be
- Binding of O2 to Hgb alters the ability of Hgb to absorb light
dissolved form and its
- Binding and dissociation of O2 with Hgb occur in milliseconds, thus taken up in blood with little or no appreciable inccrease in its prtial
contriibution to O2 transport
pressure
facilitating O2 transport because RBC spend 0.75s in capillaries
under normal conditions is
- There are ~280 million Hgb molecules per RBC, providing efficient - Equilibration for O2 and CO2 usually occurs within 0.25s. Thus, O2
almost negligible
and CO2 transfer is normally perfusion limited. Partial pressure of a
mechanism to transport O2
- Binding of O2 to Hgb to form
- Abnormalies of Hgb molecule occur with mutations in the amino diffusion limited gas (i.e.CO) does not reach equilibrium with the
oxyhemoglobin within RBC is
acid sequence (i.e. sickle cell disease) or in the spatial arrangement alveolar pressure over the time that it spends in the capillary
primary transport mechanism
Although
CO
has
a
greater
rate
of
diffusion
in
blood
than
O2
2
of the globin polypeptide chains and result in abnormal function
of O2. Hgb not bound to O2 is
- Compounds such as CO, nitrites [NO] and cyanides can oxidise iron does, it has a lower membrane-blood solubility ratio and
deoxyhemoglobin or reduced
Hgb. The O2-carrying capacity
molecule in heme group and change it from reduced ferrous state toconsequently takes approx. same amt of time to reach equilibrium
in blood
ferric state (Fe++++), reducing ability of O2 to bind to Hgb
of blood is enhanced about 65x
Major Respiratory Muscles
- Exhalation during normal breathing is passive but it
becomes active during exercise and hyperventilation
- Important muscles of exhalation are those of the
abdominal wall (rectus abdominis, internal and external
oblique, and transversus abdominis) and the internal
intercostal muscles
by its ability to bind to Hgb
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The Oxyhemoglobin dissociation curve
Physiological factors that shift the oxyhemoglobin
- In the alveoli, majority of O2 in plasma quickly diffuses dissociation curve
into RBC and chemically binds to Hgb. This process I
reversible such that Hgb gives up its O2 to the tissue
- The S-shape curve demonstrates the dependence of Hgb
saturation on PO2 especially at partial pressures lower than
60 mmHg
Carbon moxide
pH and CO2
- Increase in CO2 production by tissue and
+
release into blood results in generation of H
ions and decrease in pH, shfiting to right. This
has a beneficial effect by aiding in the release
of O2 from Hgb for diffusion into tissues
- Conversely, as blood passes through the
lungs, CO2 is exhaled, thereby resulting in an
increase in pH, causing a shift to the left in
oxyhemoglobin dissoication curve
Effect of body temperature
- Increased body temp. shifts to right,
enabling more O2 to be released to tissues
where needed as demand increases
- Shifted to right: affinity of Hgb for O2 decreases
- During cold weather > Decreased body
which enhances O2 dissociation
temp, especially at extremities, shifts O2 Bicarbonate and CO2 transport
- When affinity of Hgb for O2 increases, the curve is
dissociation curve to left (higher Hgb
- In blood, CO2 is transported in RBC primarily as
shifted to the left, reducing P 50. In this state, O2
affinity). In this instance, PaO2 may be bicarbonate (HCO3-) but also as dissolved CO2 and
dissociation and delivery to tissue are inhibited. Shifts normal, but release of O2 in thises
as caramino protein complexes (i.e. CO2 binds to
to the right or left of the dissociation curve have little extremeities is not facilitate. Hence,
plasma proteins and to Hgb)
effect when they occur at O2 partial pressures within these anatomical areas display a blush - Once CO diffuses through tissue and enters
2
the normal range (80-100mmHg). However, at O2
colouration with exposure to cold
plasma, it quickly dissolves. Reaction of CO2 with
partial pressures below 60mmKh (Steep part), shifts
H2O to form carbonic acid (H2CO3) provides the
in oxyhemoglobin dissociation curve can dramatically
major pathway for the generation of HCO 3- in RBC
influence O2 transport
+
- The clinical significance of the flat portion of the
exyhemoglobin dissociation curve (>60mmHg) is htat a
drop in PO2 over a wide range of partial pressures (100 to
60 mmHg) has only minimal effect on Hgb saturation, which
remains at 90% to 100%, a leel sufficient for normal O2
transport and delivery. The clinical significance of the steep
portion (<60 mmHg) shows that a large amount of O 2 is
released from Hgb with only a small change in PO2, which
facilitates the release and diffusion of O2 into tissue
CO2 transport
- CO2 is produced at ~200ml/min under healhty
conditions, and ~80 molecules of CO 2 will be expired by
ung for every 100 molcules of O2 that enter the capillary
bed
- Ratio of expired CO2: O2 uptake is referred to as the
respiratory exchange ratio and under normal
conditions, is 0.8
- The body has enhanced storage capabilies for CO2 as
compared with O2, and hence PaO2 is much more
sensitive to changes in ventilation than PaCO 2 is.
Whereas PaO2 is dependent on several factors, in
addition to alveolar ventilation, arterial PaCO2 is solely
dependent on alveolar ventilation, and CO 2 production
Barium
CO2 + H2O <-> H2CO3 <-> H + HCO3
GI Organs
Terminoloagy
- Mouth, esophagus, stomach,
- Visceral: Internal organs
small and large intestine
of the body
Accessory Organs
- Oral: mouth
- Salivary glands, teeth, pancrease,
- Lingual: Tongue
liver, gallbladder
- Gastric: Stomach
GI compartmentalisation
- Gut: Stomach and Intestines
- Sphincters:
- Bowel: Intestines
* Muscular sturctures under nervous and - Hepatic: Liver
hormonal control
* When constricted, prevents movement of
food
*Upper esophageal sphincter – Between
mouth and esophagus
* Lower – Between esophagus and stomach
* Pylorus - Barrier between stomach and
intestine
* Ileocecal sphincter - Barrier between small
and large intestine
* Sphincter of Oddi – Regulates juices from
liver and pancreas into duodenum
* Anal sphincter – At end of alimentary canal
Esophagus
- Submucosa – comes after mucous and houses a no. of glands
- Musculature: Some skeletal voluntary muscles but
- Muscularis externa – Most important muscles reside
majority smooth muscles
- Serosa – Very thinm layer of connective tissue that serves as
*Voluntary skeletal in most oral sections
protection for what is underneath
*Involuntary smooth in most aboral sections
- Nerves are from enteric nervous system (ENS)
- Highly regulated by neural inputs from swallowing
- This reaction normally proceeds quite slowly but
it is catalysed within RBC by enzyme carbonic
anhydrase. HCO3 diffuses out of RBC in exchange
for Cl-, the choride shift, helping the cell maintain
its osmotic equilibrium
- This chemical reaction is reversible and can be
shifted to the right to generate more HCO3 in
response to more CO2 entering the blood from
tissues or can be shifted to left as CO2 is exhaled in
lungs, reducing HCO3. The free H+ is quickly
buffered within RBC by binding to Hgb. Buffering of
H+ is critical to keep the reaction moving toward
the synthesis of HCO3; high levels of free H+ (low
pH will shift reaciton to the left)
Different types of muscles
In GI tract, smooth muscles almost
Types of contractions
everywhere except mouth, upper esophagus
- Phasic: Fast (sec) but
and terminal part of anus (where instead, a
still slower than
mix of smoooth and striated muscle is present
skeletal muscles
- Smooth muschle contract relatively slowly
- Tonic: Slow &
compared to skeletal muscles and are not
sustained (min to hr)
within our voluntary control
- Smooth muscle can
provide both types
Motility: Electrophysiology
- Interstitial cells of Cajal (ICC) generates slow waves,
established as pacemaker cells in the GI tract
- Network of ICC found in between circular and
longitudinal muscle layer
Concept of muscle contraction
Low waves + neural input  Opening of calcium
channels  Increased levels of intracellular calcium
 Activation of Myosin Light Chain Kinase (MLCK)
Types of GI secretions
 Myosin head phosphorylates  Cross-bridge
- Contains enzymes that directly break down
cycling where myosin and actin bind and slide on
big moecules
centre
Stomach
each other (Contraction)
Small intestine
- Make environment acidic to prevent
- Length varies with total body height - Musculature: Smooth only (f ~3/min)
- Note that slow waves not always  contractions
- Motility: Segmentation (mixing, shuffling of food back
bacterial colonisations and activate some
- Immediately after eating: Mixing,
- Slow waves happen all the time, contraction only
and forth) & Peristalsis (net movement of bolus, MMC)
specific enzymes that initiatte enzyme
grinding and emptying
when stimulus is present
- During fed state, segmentation prevails while fasting
digestion (e.g. pepsinogen  pepsin)
- Pyloric valve is closed most of the
- Stimulus is from ENS and vagal neurons from CNS
state, peristalsis prevails
pH = -log10 [H+] = log10 (1/[H+])
time (or slighty open when contraction Large intestine
- Signals can be excitatoy for contraction, inhibition
- Secretions that contain H+ wil decrease pH
wave reaches it)  Only allows very
- Musculature: Smooth muscle cells (Some
or relacation
- Secretions that contain HCO3 will increase
small particles and liquids to go
striated voluntary muscle cells in outer anal
- E.g. Acetylcholine (Excitatory) &
Gastric secretions
through. The rest is retaianed and
spincter)
nitric oxide (Inhibitory)
- Secretions come from rugae
Saliva
mixed further with digestive juices to - Appedix: Not part of large intestin eby
- Made of secretions from epithelial cells
- Control is exclusively neural and achieved by
be broken down into smaller particles clinically very relevant as it gets infected
and gastric glands
secretory galnds: SublingualBelow tongue),
- “Fasting state” – the Migrating Motor and needs to be removed urgently
- Production of H+ starts when CO2 from
Submandibular (Below mandible) & Parotid (near ear)
Complex (MMC) clears uo the stomach - Primary aim: Storage of food and rebloodstream combines with water to
- 4 main functions:
(~every 100 min) - 5-10 min of
absorption of fluids
create H2CO3 with activator carbonic
(1) Cleanse the mouth
luminally occlusive contractions
- MMC equivalent in large intestine = mass (2) Initiation of food breakdown (chemicals) for taste
anhydrase.H2CO3 splits to form H+ and
movement]Folds
of
large
intestine
called
HCO3-  H+ is pumped into lumen by a
(3)
Moistens
and
compact
food
into
a
bolus
Carbohydrates
- Primary peristalsis initiated by deglutition
“haustra”
proton pump (uses ATP) + HCO3- reenters
(4) Starts enzymatic breakdown of food
- Upon swallowing, musles in the pharynx contract
bloodstream by another membrane
Class
of
Major
enzymes
Where
and
how
Types
of
acinar
cells:
Mucous
cell
(Mucous)
&
Serous
to push the food down. The upper esohagus
carbohydrate
exchangers, bringing in Clcells (Water + enzymes)
sphincter contracts and as the food comes and
Disaccharides
Sucrase, lactase
Surface of small
- Gastric mucosal protecction system
- Composition: 97% water, salivary amylase, mucins
relaxes to let it through before contracting again
intestine (brush
- Intrinsic factor: Lack of this is not
(Constiuent
of
mucus),
lysozyme
(inhibit
bacterial
- At lower esophageal sphincter, it is moderately
border digestion)
compatible with life
growth), metabolic waste (urea) & electrolytes
Pancreatic amylase,
In lumen of small
contracted at the start. Upon swallowing, it relaxes Starch
Hepatic secretions
isomaltase, glucoamylase
intestine + surface
- Process:
so when the food reaches, it is allowed through
- Produces bile
Pancreatic
secretions
of
small
intestine
*Primary secretion: water plus Na+, K+, Cl-,
Proteins
continuously, stored and - Secreted by Acina cells
Exogenous bacteria
Colonic bacterial
HCO3-, occurs in acinar part
- Objective: Break the long peptide chains, folded Fibres
concentrated in gallbladder - Made of water (for
flora
* Secondary (in the ducts): Water reabsorbed,
in different ways, into either single amino acids or
- When acidic, fatty chyme lubrication) and enzyme
- Simple carbohydrate molecules are transported in the cell along
HCO3very short peptide chains
enters the duodenum  - Cells lining pancreatic
intestines by specific transporters  Na+/glucose transporters
+
- Saliva is hypotonic (Lower osmolarity than plasma)
- Proteins (Pepsin+H in gastric lumen)Large
duodenum epithelia releaseduct secrete HCO3-,
(SGLTI) co-transports glucose and Na+  Later Na+ is eliminated by
and slightly alkaline (due to presence of HCO3-)
peptide chains (Pancreatic juice in intestinal
cholecystokinin 
Na+-K+ pump
making solution alkaline
Absorption of nutrients
lumen)  Oligo-peptides (Oligo-peptidases on
Stimulates secretion of
- On the other side, facing interstitial space near the blood vessel,
to neutralise the acidic X-ray Fluoroscopy
- Products of proteains and carbohydrates digestion
membraneof cells along walls of lumen*brush
pancreatic juice + Oddi
glucose and fructose are actively transported into bloodstream
chyme from stomach - Input: Barium suplfate solution (contrast)
 Ferried into enterocyte  Exit enterocyte into
border*) Amino acids
- Output: Proportion of meal in stomach vs time + walls
Emulsification
sphincter opens +
- Produces insulin,
bloodstream (hepatic portal vein)
- Pepsingoen – Inactive; Pepsin - Active
- Fats form a separate layer on top of the watery content  To
gallbladder contracts
generated by islets of of GI organs
Lipids
- Products of lipid digestion  Easy entry into
Endoscopy
digest the lipids, we need the lipids to be in contact with enzymes
γ-Scintigraphy
Langerhans
- Classes: Triglycerides (vegetable oils and animal
enterocyte (lipophilic)  Re-esterifciation in
- Output: Observe the GI alls (also take tissues out for
- Bile is used to beak the fat layer into small dropets so that is can
- Input: Radiolabeled meal
fats), cholesterol (In food but also a component of
endoplastmic reticulum  “New” lipids +
be dispersed throughout the watery layer and coming into contact
- Output: Proportion of meal in the stomach vs time biosy, if necesarry)
bile), phospholipids (found in our cell membranes)
specialised proteins = chylomicron  Chylomicron
- Small intestineis hardest to reach anatomically
with the lipases
(gastric emptying)
- Gastric phase (gastric lipase): only 2 ester links in
taken up by lymphatic system (bypasses liver)
* Double balloon technique & Capsule technology
- Bile contain bile salts that will coat fat droplets and prevent the
- Siegel model
triglycerides, no cholesterol, no phospholipids
Defecation
Magnetic Resonance Imaging (MRI)
y(t) = 1/(1-e-kt)ᵝ
fromre-aggregating into a big fatty layer
- Intestinal phase: Pancreatic lipase breaks all ester
- As the rectum pushes down the solid mass, the
Input:
Contrast agent (water based)
- y(t) is fraction of food dtill in stomach; β and k are
- Process is facilitated by intestinal motility
links, cholesterol esterase (in pancreatic juice), Pyloric stenosis
external anal sphincter contracts to ‘seal’ the
- Output: Observe movement of the GI tract
patient-specific parameters; tlag is time taken to reach max.
phospholipase A2 (in pancreatic juice)
- Thickened pylorus  Food (milk) has difficuulties entering the small sphincter. The internal anal sphincter relaxes to
Electrogastrography/Magnetogastrography
emptying rate
Conditions
intestine. 1 in 250 infant boys affected. More rare in adults and females accommodate the mass
- Output: Dominant frequency of slow waves
- Achalasia (Failure to relax) – Failure of normal Ileus
Importance of steady blood glucose levels
0  t To
logβ/k
achieve stable blood sugar level (70-99mg/dl)
peristalsis and an inadequate lower esophageal - A temporary/permanent state of inhibited intestinal motlility in
- Extreme acute consequences of lack of insulin:
1.
Low
blood
glucose (hypoglycemia) stimulates alpha cells to
sphincter relaxation
absence of physical obstuction (intestinal pseudo-obstruction)
ketoacidosis (diabetic coma)  Body starts using lipids secrete glucagon
- GastroEsophageal Reflux Disease (GERD) – Lower
- Typically occurs after surgery (postoperative ileus)
for energy needs (reaction produces toxic ketones)
2.
Glucagon
acts
on hepatocytes (liver cells) to:
esophagus section becomes leaky  Acid content
- Typically treated with drugs
because of the inability to use glucose
* Convert glycogen to glucose (glycogenolysis)
of the stomach gets into the esophagus
Irritable bowel syndrome (IBS)
- Too much glcose remains in body  hyperglycemia
* Form glucose from lactic acid and cetain amino acids
Basics of insulin and glucagon
- A chronic condition that manifests itself with a combination
- Long-term consequences: Retinopathy; Neuropathy; (gluconeogenesis)
- Alpha cells secrete glucagon
of: abdominal pain (e.g. cramps), excessive gas, diarrhea
Cardiovascular disease; Gastroparesis; Kidney disease 3. Glucose released by hepatocytes raises blood glucose level to
- Beta cells secrete insulin
- Affects 7-21% of general population
Current treatment and care
normal
- Islets intertwined with acini
Drugs: Prokinetic agents
1. Injecting insulin (All type I and some II)
4. If blood glucose continues to rise, hyperglycemia inhibitis
1. Directly stimulate enteric neuronsto release more
2. Oral medication: Drugs that help lowering
release of glucagon
neurotransmitters (e.g. Acetylcholine)
glucose levels (Only for some Type II)
5. High blood gluscoe (hyperglycemia) stimulates beta cells to
2. Stimulate receptors in the chemoreceptor zone in the CNS (including vomiting centre)
Hypoglycemia
secrete insulin
- (Type I) Absence of decrease
Terminology
6. Insulin acts on various body cells to:
glucose usage by peripheral
- Endocrine: Secretion of hormones directly into bloodstream
* Accelerate facilitated diffusion of glucose into cells
tissues + Absence of glucagon
(e.g. Pancrease secretes insulin & glucagon)
* Speed conversion of glucose into glycogen (glycogenesis)
stimulated to create glucose +
- Exocrine: Secretion of enzymes through a duct into a surface
* Increase uptake of amino acids and increase protein synthesis
Absence of other minor
covered by epithelium (e.g. pancreas secretes pancreatic juic
* Speed synthesisof fatty acids (lipogenesis)
mechanisms + Brain cells are
into the duodenum)
* Slow glycogenolysis
unable to store glucose and need * Slow gluconeogenesis
- Paracrine: Secretion of hormones with effects only in the
glucose continuously
vicinity (e.g. a cell secretes a hormone to signal a neighbouring
7. Blood glucose level falls
= Injecting too much insulin might 8. If blood glucose continues to fall, hypoglyccemia inhibits
cell)
cause glucose levels to drop too
release of insulin
Algorithm used to calculate how much insulin to use
much  Very real and severe
- Proportional-Integral-Derivative (PID) algorithm
Diabetes
consequences to the brain (eg.
Ins(n) = P(n) + I(n) + D(n)
- Type I: Pancreas does not produce insulin (~5-10% of all cases)
Fainting/permanent brain
- P(n) = Kp(SG(n)-target); I(n) = I(n-1) + Ki(SG(n)-target); D(n) = Kd d (SG(n))/dt
- Type II: Insulin resistance; Impaired insulin productioon;
damaged/death)
- Kp, Ki, Kd ar patient specific constants  algorithm “calibration”
Increased rate of glucose production
d 2 y /dt 2
Downloaded by Derrick Jiang (djiang3@cps.edu)