Midterm 3 Flashcards
What are the 2 main period of the cardiac cycle and what do they do?
systole: ventricle contraction
diastole: ventricle relaxation
Why do valves open passively?
due to pressure gradients
What valves open when atrial pressure is greater than ventricular pressure?
AV
What valves open when ventricular pressure is greater than atrial pressure?
semilunar
What are the 4 phases of the cardiac cycle?
- ventricular filling
- isovolumetric ventricular contraction
- ventricular ejection
- isovolumetric ventricular relaxation
What is the first phase of the cardiac cycle?
ventricular filling: when atria pressure is greater than the ventricles and AV valves are open
What is the second phase of the cardiac cycle?
isovolumetric ventricular contraction: increases pressure due to ventricle contraction, AV and semilunar valves are closed and no blood enters or exits. the ventricle
What is the third phase of the cardiac cycle?
ventricular ejection (pumping): ventricle pressure is greater than in the arteries, semilunar valves open
What is the fourth phase of the cardiac cycle?
isovolumetric ventricular relaxation: ventricle can relax which decreases pressure, AV and semilunar valves are closed and no blood enters or exits the ventricle
What is an active phase?
when no atria or ventricles contract
What is a passive phase?
when atria contract
When is heart sound 1 between?
atrial systole and isovolumetric ventricular contraction
When is heart sound 2 between?
ventricular ejection and isovolumetric ventricular relaxation
What is the fourth phase of the cardiac cycle?
isovolumetric ventricular relaxation: ventricle can relax which decreases pressure, AV and semilunar valves are closed and no blood enters or exits the ventricle
- pressure is less than aorta so aortic valve closes
When is ventricular filling passive until?
until the atrium contracts
How long does ventricular systole last and how long is the entire cycle?
systole: 0.3 seconds
entire: 0.8 seconds
(therefore diastole is 0.5 seconds)
What makes the sound “lubb”?
the closure of the tricuspid and mitral valves at the beginning of systole (AV valve)
What makes the sound “dubb”?
the closure of the aortic and pulmonary semilunar valves at the beginning of diastole
What is the dicrotic notch?
a brief rise in aortic pressure caused by back flow of blood rebounding off semilunar valves (closure of aortic valve at the end of systole)
What is systolic pressure?
the pressure in the aorta in the first phase (ventricles to aorta)
What is diastolic pressure?
the lowest pressure in the aorta when blood leaves it
What makes the sound “lubb”?
the closure of the tricuspid and mitral valves at the beginning of systole (AV valves close simultaneously)
- soft sound
What makes the sound “dubb”?
the closure of the aortic and pulmonary semilunar valves (SL valves simultaneously) at the beginning of diastole
- louder sound
What does the aorta do during systole/diastole?
stores E during systole as the walls expand then releases it during diastole as the walls recoil inwards
What is end diastolic volume?
the volume of blood left in the ventricle at the end of diastole = 130ml
What is end systolic volume?
the volume of blood left in the ventricle at the end of systole = 60ml
What is stroke volume?
the volume of blood ejected from the ventricles each cycle = 70ml (1 heart beat)
(equal to end diastolic volume minus end systolic volume)
What is the ejection fraction?
stroke volume / end diastolic volume = 70/130 = 0.54 (54%)
Why does the heart make sounds?
its due to turbulent flow when the valves close
What is cardiac output?
the volume of blood pumped by each ventricle per minute (= stroke volume x heart rate)
- affected by animal size, is 8% of body weight (higher for larger animals)
What is an average cardiac output?
5 liters/min at rest
What is an average amount of heart beats per minute?
about 72-75 ish
What is extrinsic regulation?
the regulation of any organ function from factors originating outside the organ (neural and hormonal regulation)
What is intrinsic regulation?
the regulation of an orgran function by factors originating within the organ (autoregulation)
What does the ANS innervate?
the conduction system and the heart muscle (myocardium) SNS
Which system affects the contraction of the heart?
SNS
What is the SA node intrinsic firing rate
100 AP/min
What hormones increase sympathetic activity (excitatory)
epinephrine and nerves
Which receptors receive the signal that sympathetic activity have increased?
beta 1
What opens when beta 1 receptors are activated?
calcium funny (If) channels
What receptors generate a resting state?
acetylcholine on M receptor (parasympathetic - decreases heart rate to rest)
Which receptors respond to increased parasympathetic activity and where?
muscarinic cholinergic receptors in the SA node
What nerve through which does the parasympathetic system activity increases?
vagus
What do muscarinic receptors do?
increase open state of potassium channels and closed state of calcium channels
What do open potassium and closed calcium channels do?
decreases rate of spontaneous depolarization and hyperpolarizes cell, therefore decreasing heart rate
How does parasympathetic activity affect levels of depolarization and repolarization?
Decreases depolarization, increases repolarization
How does sympathetic activity affect levels of depolarization and repolarization?
increases depolarization, decreases repolarization
How does sympathetic activity affect AV node?
increases conduction velocity through the nerve
How does parasympathetic activity affect AV node?
decreases conduction velocity through the nerve
What does epinephrine do (x2) and where is it released from?
increases frequency of action potentials at the SA node and increases velocity of AP conduction through the cardiac muscle fibers (same effect as SNS) – released by the adrenal gland
What hormones increase heart rate (force of contraction)?
glucagon, T3, T4 and insulin
- T3+T4 = thyroid hormones
How does glucagon increase heart rate?
it opens funny and calcium channels
What 3 factors affect stroke volume?
- ventricular contractility (the force)
- end diastolic volume
- afterload
What is afterload?
the resistance that ventricles encounter to pump blood into arteries
What are the 2 extrinsic controls of stroke volume?
- sympathetic drive to ventricular muscle fibers
2. hormonal control
What is the 1 intrinsic control of stroke volume?
changes in end diastolic volume
Whats a special feature of ventricles?
they never completely empty of blood
How do you increase cardiac contractility?
when norepinephrine binds to beta 1 adrenergic receptors in contractile cells (due to sympathetic innervation), which increases it
- parasympathetic innervation ain’t important/significant
What 4 things affect ventricular contractility?
- opening of calcium channels on the sarcolemma
- enhancing the release of calcium from the sarcoplasmic returuclm (SR)
- increasing the rate of ATPase activity and cross bridge cycling
- enhancing the rate of calcium-ATPase (pump) activity on the SR and reuptake of calcium
What does protein kinase do?
increases calcium binding (affecting cross bridge cycle binding)
What 4 things increase when sympathetic activity is increased?
- epinephrine release
- strength of contraction
- rate of contraction
- rate of relaxation (relaxation period is shorter)
What are pressure gradients?
they drive flow from high pressure to low pressure
How is mean arterial pressure determined?
its the pressure of the aorta - 85-90 mmHg
What type of system is the circulatory system?
a closed system
What is pressure?
the force exerted by blood (from the left ventricle)
Flow rate is proportional to what?
directly proportional to the difference between the pressures at the 2 ends of the pipe and inversely proportional to the resistance of the pipe
What is bulk flow?
flow due to pressure gradients
What must exist to maintain blood flow?
a gradient throughout the circulatory system
What is a pressure gradient?
driving force of fluid from high to low pressure (aka the pressure in pulmonary arteries minus pressure in pulmonary veins)
- greater in systemic than pulmonary circuits (but more resistance in pulmonary cause shorter distance)
What is central venous pressure?
the pressure of the vena cava, 0mmHg
What is the amount of flow comparing systemic vs pulmonary circuits
they receive equal flow
What is a pressure gradient?
driving force of fluid from high to low pressure (aka the pressure in pulmonary arteries minus pressure in pulmonary veins)
- greater in systemic than pulmonary circuits (but less resistance in pulmonary cause shorter distance)
What 3 factors affect resistance to flow?
- radius of vessel
- length of vessel
- viscosity of fluid (=n)
Which factor affects the length of the vessel
age is the only one
What creates higher resistance?
longer vessels
What is vasoconstriction?
the narrowing of arterioles and therefore increasing resistance
What is vasodilation?
the widening of arterioles and therefore decreasing resistance
What is total peripheral resistance?
the combined resistance of all blood vessels within the systemic circuit
What does resistance depend on?
resistance across a network of blood vessels depend on resistance of all vessels
What is microcirculation/
the vessels cannot be seen with our eyes, only with microscope (arterioles, capillaries and venules)
What do arteries and veins do?
arteries: carry blood away from the heart
veins: carry blood towards the heart
Where are endothelial cells located?
they line the inner layer of the blood vessels
What is collagen?
a tensile protein, enables blood vessels to withstand pressure (fibrous connective tissue)
What is elastin?
a stretchable protein, enables blood vessels to expand or contract (elastic connective tissue)
What are arteries?
they have the thickest wall, are stiff and have highly elastic pressure reservoirs (large diameter, little resistance) – walls contain elastic and fibrous tissue
What are arterioles?
they are muscular, well innervated blood vessels that serve as a contractile vessel
- connect arteries to capillaries or metarterioles
- part of microcirculation
What are arteries?
they have the thickest wall, are stiff and have highly elastic pressure reservoirs (large diameter, little resistance) – walls contain elastic and fibrous tissue
What are venules?
thin walled blood vessels that contain some smooth muscle, their only function is to return blood to the heart
What are veins?
thin walled blood vessels with a large internal diameter, are fairly muscular, highly distensible and can store blood in the body for use (have internal valves)
What is the basal lamina?
a thin extracellular layer that lies underneath epithelial cells and separates them from other tissues
What is the pericyte?
a stem cell that regenerates smooth muscle cells
What is an adipocyte?
a cell that stores fat
What are muscular arteries?
medium sized arteries that contain layers of smooth muscle allowing for involuntary control of vessel diameter, controlling blood flow – smooth muscle regulates radius
What is compliance?
the ability of a vessel to distend and increase volume with increasing transmural pressure (used as an indication of arterial stiffness)
Where is systolic blood pressure at its max?
in the aorta due to ejection of blood into it (diastolic is minimum in it too)
What happens to the arteries during diastole/systole?
systole: expand
diastole: recoil
Why is arteriole blood pressure never 0?
due to elastic recoil
What is arterial blood pressure?
the pressure in the aorta
What are metarterioles?
short vessels that link arterioles and capillaries; also act as bypass channels for times when precapillary sphincters constrict
What is systolic blood pressure?
the maximum pressure due to the ejection of blood into the aorta
What is diastolic blood pressure?
minimum pressure that isn’t 0 due to elastic recoil
What regulates radius / resistance in arterioles?
rings of smooth muscle (have alpha adrenergic receptors)
What provides greatest resistance to blood flow?
arterioles
What are precapillary sphincters?
close off capillaries in response to loca signals
What is arteriolar tone?
radius of the arteriole independent of extrinsic influences; typically, partially contracted
What does mean arterial pressure depend on?
on TPR which depends on the radius of arterioles
What is phosphatidyl inositol triphosphate?
the system that norepinephrine reacts with alpha adrenergic receptors on, causing vasoconstriction
What does norepinephrine bind to?
alpha adrenergic receptors
What does epinephrine bind to and what does it cause?
alpha: vasoconstriction
beta2: vasodilation
What is angiotensin 2?
synthesized from angiotensinogen and is responsible for vasoconstriction
- increases MAP
Where is angiotensinogen synthesized?
in the liver
What does renin do?
converts angiotensinogen to angiotensin 1
What does ACE (angiotensin-converting enzyme) do?
converts angiotensin 1 to angiotensin 2
What is another name for ADH?
vasopressin
What does ADH do?
comes from the hypothalamus (posterior pituitary), increases water reabsorption by the kidneys (minimizes water loss) which causes vasoconstriction
- increases MAP
Where does epinephrine come from and what effect does it have on MAP?
comes from the adrenal medulla (hormone) and increases MAP
What are capillaries?
sites of exchange between blood and tissue
- very close to cells
- pores
- slow blood velocity
- small diffusion barrier
Where are capillaries found?
in networks called capillary beds
What moves through pores between endothelial cells of capillaires?
protein free plasma
What are continuous capillaries?
most common capillaries, small gaps between endothelial cells that allow small water-soluble/lipid-soluble (fatty acids, steroids) through.
Where are continuous capillaries located?
located in skin, most nervous/connective tissue, muscle tissue
What are fenestrated capillaries?
capillaries with large gaps between endothelial cells forming pores/fenestrations; allow proteins and sometimes blood cells to move through.
Where are fenestrated capillaries located?
located in kidneys, endocrine glands, small intestine
What are sinusoidal capillaries?
capillaries that serve as discontinuous sheets of endothelium with very large pores; allow large molecules (proteins and cells) through capillary walls.
Where are sinusoidal capillaries located?
located in liver, lymphoid organs, bone marrow, spleen
What are sinusoids?
large blood filled spaces that function in the exchange of substances between blood and tissue
Where does blood cells move through in sinusoidal caps?
bone marrow and spleen
What 2 liver proteins are released into the blood through sinusoidal caps?
albumin and clotting factors
What are metarterioles?
intermediates between arterioles and capillaries that directly connect arterioles with venules
- shunts to bypass capillaries
What happens when metarterioles contract and relax?
contract: increases blood flow through capillaries
relax: decreases blood flow through capillaries
What are precapillary sphinctors?
rings of smooth muscle that surround capillaries on the arteriole end
- contract and relax due to local factors only
What happens when precapillary sphinctors contract and relax?
contract: constricts capillary and restricts blood flow
relaxes: increases blood flow
What pauses relaxation (vasodilation)?
CO2 and pH
What causes contraction (vasoconstriction)?
oxygen
What is a metabolite?
a specific product of a substance, formed by chemical processes in the body
What is the most common mechanism of exchange across capillary walls?
diffusion
What is transcytosis?
the movement of exchangeable proteins into, across, and then out of a cell
What is mediated transport?
the transport of specific proteins which takes place in the brain
What are the 4 pathways of exchanging material across a capillary wall?
- transcytosis (pinocytosis/endocytosis)
- diffusion (pressure driven bulk flow)
- diffusion via junctions and fenestrations
- diffusion across cells (lipid soluble molecules)
Filtration vs absorption
filtration: movement out of a capillary
absorption: movement into a capillary
What is the purpose of bulk flow?
to maintain balance between interstitial fluid and plasma (distribute ECF)
What is pinocytosis?
a type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
What is the hydrostatic pressure gradient?
forces due to fluid
What is osmotic pressure?
osmotic force exerted on water by non-permeating solutes (proteins)
What is oncotic pressure?
osmotic force of proteins
What are starling forces?
forces that drive movement of fluid into and out of capillaries
What is capillary hydrostatic pressure (Pcap)?
pressure due to the hydrostatic pressure of fluid inside the capillary (higher pressure at the arteriole end vs the venous end)
What is interstitial fluid hydrostatic pressure (Pif)?
pressure due to the hydrostatic pressure of fluid outside of the capillary
What is capillary osmotic pressure (Picap)?
pressure due to the presence of non-permeating solutes inside the capillary
What is interstitial fluid osmotic pressure (Piif)?
pressure due to the presence of non-permeating solutes outside the capillary
What does Pcap favour?
filtration
What does Pif favour?
reabsorption
What does Picap favour?
reabsorption
What does Piif favour?
filtration
What is the main determinant of oncotic pressure?
albumin (a protein)
What does the hydrostatic pressure gradient favour?
reabsorption
What does the osmotic pressure gradient favour?
reabsorption
What is net filtration pressure?
filtration pressure-absorption pressure
What does the arteriole end favour in net filtration?
filtration (more of it across the capillary)
What does the venous end favour in net filtration?
absorption
What does the lymphatic system do?
picks up excess filtrate and returns it to circulation
How much net filtration is there per day (amount of fluid left unabsorbed)?
3L
How much fluid is filtered in the body per day?
20L
What are venules?
- smaller than arterioles
- connect capillaries to veins
- single layer of endothelium and are porous (some exchange of material between blood and interstitial fluid)
What is the lymphatic system (open or closed)?
open
What is the lymphatic system composed of?
vessels, nodes and organs
What do vessels do?
are involved in returning excess filtrate to circulation
What is the colour of lympth?
yellow
What do lymphatic capillaries do and what do they have?
collect excess fluid from capillaries that is then returned to the veins (have valves)
Where does lymph enter?
enters veins near jugular veins and then into the right atrium
Which way does lymph move?
from capillaries to veins
What do lymph nodes do?
contain macrophages/immune cells that filter lymph flowing through
What is the size of veins?
have a large diameter but with thin walls
What are peripheral veins?
all veins outside the thoracic cavity
What are central veins?
all veins within the thoracic cavity
Where are there valves on veins?
in the peripheral veins, NOT central veins
What has a larger diameter, venae cavae or the aorta?
venae cavae (30 vs 12.5)
What is compliance?
property of veins that enables them to expand with little change in pressure
What is another vein function?
as a blood reservoir (readily available so that it can shift to the arterial side of the circulation)
What holds more blood: arteries or veins?
veins (at a given pressure)
What is a respiratory pump?
pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
How will inspiration affect the pressure in the thoracic and abdominal cavities?
decreases pressure in thoracic cavity, increases pressure in abdominal cavity
Pressure on veins in the abdominal cavity due to inspiration creates a gradient that favours blood movement to where?
thoracic cavity
What is central venous pressure?
venous blood pressure within the right atrium that influences the pressure in the large peripheral veins
What is venous return?
the amount of blood returned to the heart by the veins
How will expiration affect the pressure in the thoracic and abdominal cavities?
increases in thoracic, decreases in abdominal
What does expiration favour?
movement of blood to abdominal veins
Backwards flow to the abdomen is prevented by what?
closure of valves in the abdominal cavity
How does an increase in blood volume affect venous pressure?
it increases it
How does an decrease in blood volume affect venous pressure?
it decreases it
How is blood pressure regulated?
through blood volume
What is venomotor tone?
smooth muscle tension in the veins; caused by contraction of smooth muscle in the wall of the vein, which then constricts it
How does a decrease in blood volume affect the body?
it activates mechanisms in the kidneys to lower water output elimination through urine (maintains blood volume and venus pressure)
Where are alpha adrenergic receptors located?
receptors present in the smooth muscle of the walls of veins
Smooth muscles in the walls of veins is innervated by what?
by the SNS
What causes venous constriction?
when norepinephrine stimulates the contraction of smooth muscle
What causes increased cardiac output?
an increase in venous pressure caused by increase in venomotor tone, causing an increase in SV
What is blood?
a vehicle for transport
What is the average blood volume in the body?
8% of body weight
What are the 4 components of blood?
plasma, erythrocytes (RBC), leukocytes (WBC) and platelets
What is serum?
plasma from which fibrinogen and other clotting proteins have been removed
What is most dense in blood?
plasma
What is hematocrit?
the fractional contribution of erythrocytes to the blood (aka hct)
What proteins are in blood?
albumins (most concentrated), globulins and fibrinogen
What 3 things is plasma composed of?
mostly water, then proteins then electrolytes (mostly Na and Cl, minimal H, HCO3, K and Ca)
- nutrients, wastes, dissolved gasses and hormones
What colour is plasma?
a pale yellow
What dissolved gas is most concentrated in plasma?
nitrogen
What is synthesized in the liver?
albumins and fibrinogen
What is synthesized by lymphocytes?
globulins
What does fibrinogen get converted to?
to fibrin in the clotting process
When are lymphocytes more populated?
when animals have more stomachs
Animals with less stomachs have more what?
neutrophils
What is the average blood pH and that is ideal for protein/enzyme function?
7.4
What does albumin do?
it is a major contributor to plasma oncotic pressure and is a carrier for steroids, fatty acids and thyroid hormones
What is fibrinogen synthesized by?
the liver
What is the key to blood clot formation?
fibrinogen
What are alpha and beta globulins?
produced by the liver, they are carriers for lipids, steroids and other compounds and act as:
- clotting factors
- enzymes
- precursor proteins (angiotensinogen)
What are gamma globulins?
immunoglobulins that are part of the immune system
What do lymphocytes do?
produce specific immune responses directed against invaders
What do monocytes do?
develop into macrophages after migrating into tissues
What do neutrophils do?
they are mobile phagocytes (bacteria killing) that ingest foreign substances and pathogens
- red and blue staining
- predominant white blood cell
What do eosinophils do?
produce toxic compounds directed against invading pathogens
- red staining
What do basophils do?
aka mast cells, defend against large parasites by releasing toxic substances
- contribute to allergic reactions (histamine/heparin)
- blue staining
What is the shape of an erythrocyte and its name?
biconcave disk – has a large surface area and favours diffusion to enhance gas exchange
- lifespan is longer in larger animals
Why are erythrocyctes flexible (membrane)?
due to spectrin (forms hexagonal arrangements for maintenance and integrity)
What is the function of erythrocytes and what are they composed of?
are literally a bag of enzymes and hemoglobin (not efficient) – they transport oxygen and CO2
How is glucose metabolized in RBC’s and what is created?
metabolized by glycolysis yielding lactate which is excreted into the blood
How do red blood cells produce ATP?
glycolysis
What is necessary for generating energy needed to fuel active transport mechanisms involved in maintaining proper ionic concentrations within a red blood cell
glycolytic enzymes
What is essential for the transport of carbon dioxide?
carbonic anhydrase
What is a hemoglobin molecule composed of?
globin + 4 heme groups
What is hemoglobin?
an iron-containing protein in red blood cells that reversibly binds oxygen.
What is carbonic anhydrase?
its the enzyme inside of red blood cells that is essential for the transport of CO2, adds it to H20 to form H2CO3 for carrying
What is a globin?
4 chains of polypeptides
What is a heme?
an iron containing group
What 3 things can hemoglobin bind to?
CO, CO2 and H
What colour is oxygenated hemoglobin?
bright red (cause its in ferrous form)
What colour is deoxygenated hemoglobin?
dark red
Where do erythrocytes get produced and through what process?
in red bone marrow through erythropoiesis
Where do erythrocytes get filtered?
by the spleen and liver
What do macrophages do?
engulf old RBCs at the end of their lifespan through phagocytosis
What are hematopoietic stem cells?
cell in the bone marrow that gives rise to all types of blood cells
What is erythropoietin?
stimulates erythrocyte synthesis; secreted from kidneys under conditions of low oxygen levels in the blood flowing to the kidneys
- produces hemoglobin
What 3 substances are required for erythrocyte production?
folic acid, iron and vitamin B12
What does a lack of iron cause?
ammonia
Why are folic acid and vitamin B12 requirements?
for DNA replication and cell proliferation
What filters and removes old erythrocytes?
the spleen
What metabolizes byproducts from the breakdown of erythrocytes?
the liver
When is hemoglobin catabolized and by what?
after phagocytosis of red blood cells in the spleen by macrophages
What is heme turned into after iron is removed?
bilirubin (goes to the liver for further metabolism)
Where are products of bilirubin catabolism secreted?
in bile to the intestinal tract or released into the bloodstream and excreted in urine
How is iron transported in blood and where does it go?
bound to transferrin (from GI or liver to bone marrow)
Iron stored is bound to what and where is it (x3)?
bound to ferritin in the liver, spleen and small intestine
What are platelets?
cell fragments produced in the bone marrow from megakaryocytes; have no nucleus, but possess mitochondria, smooth ER, granules
What do platelets do?
stop blood loss, act as immune cells + mediators of inflammatory response
What are granules?
membrane bound vesicles filled with enzymes and proteins
What are leukocytes?
they function in defense of the body (immune system - defend against pathogens, identify and destroy cancer cells and the phagocytosis of debris from dead or injured cells)
Where are leukocytes found?
the bloodstream and in body tissues
What is a pressure gradient?
the force for air flow, created by changes in alveolar pressure
What are the 3 granulocytes (cytoplasmic granules)?
neutrophils, basophils and eosinophils
What are agranulocytes (no cytoplasmic granules)?
monocytes and lymphocytes
What 2 factors determine inter-alveolar pressure?
quantity of air and volume
What is a blood smear stained with and what does it reveal?
wrights stain and reveals different leukocytes
What does heparin do?
prevents blood clotting (released by basophil)
When is intra-alveolar pressure 0?
when air flow stops
What does histamine do?
dilates blood vessels (released by basophil)
What are monocytes?
phagocytes that make up a small portion of leukocytes, become macrophages
What are wandering macrophages?
mobile cell moving throughout the alveoli, ingesting foreign particles
What are fixed macrophages?
stationary phagocytic cell that engulfs cell debris and pathogens
What are lymphocytes?
agranulocyte. 30% of leukocytes and 99% of interstitial fluid cells;
What are the 3 types of lymphocytes?
- b lymphocytes (b cells)
- T lymphocytes (t-helper cells)
- null cells / natural killer cells
What are b cells?
associated with antibodies and becomes a plasma cell upon contact with an antigen
- have proteins on their membrane
What cell lacks membrane proteins?
natural killer cells
What are Cytotoxic T cells?
they directly damage foreign cells and contact+kill virally infected, mutant or transplanted cells
- have proteins on their membrane
How do T cells kills bad cells?
their secretory products form pores in the target cell membrane and water enters and they die
What are natural killer cells?
attack virus infected cells and cause lysis (early immune response)
What is a plasma cell?
secretes immunoglobulin antibodies that mark invaders for destruction
What class of antibody that marks bacteria for destruction?
IgM
What is the largest class of antibody and where is it found?
IgA – found on all epithelial layers
What does a T cell become and how?
becomes a cytotoxic t cell upon contact with a foreign cell
What activates B and T cells?
interleukin-2
How is a Th cell activated?
by contact with a macrophage
What does interleukin activate (x4)?
TH, B, TC, and NK cells
What are perforins?
proteins that poke holes in pathogens and allow toxins to enter
What is a memory B cell?
a B cell that responds to an antigen more strongly when the body is reinfected with an antigen than it does during its first encounter with the antigen
What is external respiration?
exchange of oxygen and carbon dioxide between atmosphere and body tissues
What is the function of oxygen?
generation of ATP in mitochondria and oxidative phosphorylation
What is internal respiration?
oxidative phosphorylation
What is pulmonary ventilation?
movement of air into and out of the lungs
What is pulmonary capillaries?
site of exchange between lungs and blood
What are systemic capillaries?
site of exchange between blood and body tissues
What is bulk flow?
the movement of air based on pressure gradients
What does upper airways refer to?
air passages in the head and neck
What are the 3 air passages of the head and neck?
nasal cavities, oral cavity and the pharynx
What is the larynx?
the voice box, contains vocal cords
Where does the respiratory tract go from?
in airways from pharynx to lungs
What is the respiratory tract composed of (x3)?
larynx, conducting and respiratory zone
Why is there less space on the left lung?
cause of the heart
What is the smaller lobe called on the lungs?
cranial lobe (top)
What is the larger lobe called on the lungs?
caudal lobe (bottom)
How many lobes do the right and left lungs have?
right: 4 // left: 2
What are the left lobes of a bovine lung?
cranial and caudal
What are the right lobes of a bovine, pig and dog lung?
cranial, middle, caudal and accessory lobes
What are the left lobes of a dog lung?
bilobed cranial and caudal
What are the left lobes of a pig lung?
divided cranial and caudal
What are the 3 structures of the conducting zone?
trachea, bronchi and secondary bronchi
What is the conducting zone?
includes respiratory passageways; serves as air passageway (dead space volume), increases air temperature to body temperature, humidifies air by adding water vapor until it reaches 100% humidity, filters inspired air through trachea and bronchi to prevent viruses, bacteria, and inorganic particles from reaching alveoli
What are bronchi?
two short branches located at the lower end of the trachea that carry air into the lungs
What are secondary bronchi?
branches of the primary bronchi that lead to each lobe of the lung; also called lobar bronchi
What marks the end of conducting zone?
terminal bronchioles (0.5mm)
What is the difference between the conducting and respiratory zones?
thickness of walls (determines whether gas exchange occurs)
What are tertiary bronchi?
branches of the secondary bronchi that divide into bronchioles; also called segmental bronchi. 16-23 orders of branching
What are bronchioles?
smallest branches of the bronchi; diameter <1mm
- have elastic fibers and smooth muscles
- prevent collapsing and help change diameter
What is the respiratory zone?
respiratory bronchioles and alveoli; site of gas exchange between air and blood via diffusion
What do goblet cells do?
they produce mucus that contain immunoglobulins
What happens when diameter of airways decrease?
the number of passageways increase
What is dead space?
when air does not participate in gas exchange with blood in a region
What is a cross sectional area?
a surface or shape exposed by making a straight cut through something at right angles to the axis
How does cross sectional area react to division of the airways?
it grows larger
What are ciliated cells?
they move particles towards the mouth (mucus containing trapped particles out of the lungs into the pharynx)
What is the mucus escalator?
it prevents mucus from accumulating in the airways and clears trapped foreign matter
What occurs if mucus accumulates?
infection might occur (due to bacteria colonizing)
What allows the mucus elevatory to function properly?
the secretion of a watery saline layer beneath mucus
What are the largest producers of mucus?
submucosal glands
What are respiratory bronchioles?
they are branches of the terminal bronchioles that subdivide into several alveolar ducts
What are the 4 structures of the respiratory zone?
respiratory bronchioles, alveolar ducts, alveoli and alveolar sacs
What is the respiratory membrane composed of?
epithelial cell layer of alveoli and an endothelial cell layer of capillary
What covers the majority of alveolar surface?
type 1 alveolar cells (used for gas exchange)
What do type 2 alveolar cells do?
they secrete surfactant which prevents collapsing of alveoli
What are alveolar macrophages?
they engulf foreign particles and pathogens
What are alveolar pores?
they connect adjacent alveoli and allow air to flow between alveoli which allows equilibration of pressure within the lungs
What are alveoli?
sites of gas exchange, over which capillaries form a sheet for a rich blood supply
What are the 3 barriers for diffusion between air and blood (on respiratory membrane)?
basement membranes, capillary endothelial cells and type 1 cells
What is the chest wall?
an air tight structure that protects the lungs
What is the chest wall composed of?
the ribcage and sternum
What are the 3 muscles in the thoracic cavity?
diaphragm, internal intercostals and external intercostals
What is the pleura?
a membrane lineing the lungs and chest wall
What surrounds each lung?
the pleural sac
What is intrapleural space filled with?
intrapleural fluid (15ml) – creates a negative pressure
What is the driving factor of bulk flow?
a pressure gradient (high to low)
How is the pressure in the lungs during inspiration?
less than the atmosphere
How is the pressure in the lungs during expiration?
greater than the atmosphere
What is atmospheric pressure?
the pressure caused by the weight of the atmosphere. ~760 mmHg at sea level, decreases as altitude increases, increases under water. other pressures are given relative to this
What is intra-alveolar pressure?
the pressure of the air in the alveoli; difference between this and atmospheric pressure drives ventilation
When is intra-alveolar pressure negative?
during inspiration
When is intra-alveolar pressure positive?
during expiration
What are the 4 primary pressures that are associated with ventilation?
Atmospheric, intra-alveolar, intrapleural and transpulmonary pressure
What is intrapleural pressure?
the pressure inside the pleural sac, always negative (under normal conditions) and less than intra-alveolar pressure – varies with phase of respiration and keeps lungs extended
What drives ventilation?
the difference between intra-alveolar and atmospheric pressure
What is elasticity
property of lungs and chest wall that results in the negative pressure of the intrapleural pressure
What is transpulmonary pressure?
difference between intrapulmonary and intrapleural pressure; represents distending pressures across the lung wall
What does an increase in transpulmonary pressure cause?
increases distending pressure across the lungs, causing them to expand (increases volume)
What is a pneumothorax?
air in the pleural cavity caused by a puncture of the lung or chest wall
What is a pressure gradient?
force for air flow; created by changes in alveolar pressure
What 2 factors of alveoli determine intra-alveolar pressure?
quantity of air and volume
What determines the direction of air movement?
changes in alveolar pressure
What is the equation for flow?
atmos - intra-a / R
What happens to the alveolar pressure and volume when the lungs expand?
volume increases and pressure decreases
What happens to the alveolar pressure and volume when the lungs contract?
volume decreases and pressure increases
What is boyle’s law?
an increase in volume will create a decrease in pressure and vv
When is intra-alveolar pressure 0?
When air flow stops
What do inspiratory muscles do and what are the 2?
they increase the volume of the thoracic cavity (diaphragm and external intercostals)
What do expiratory muscles do and what are the 2?
they decrease the volume of the thoracic cavity (internal intercostals and abdominal muscles)
How does expiration occur?
it is a passive process that happens when the lungs and chest wall recoil to their original positions once the inspiratory muscles stop contracting
What is active expiration?
when the contraction of expiratory muscles create a greater and faster decrease in volume of the thoracic cavity
How are oxygen. and carbon dioxide levels?
they remain relatively constant (move at the same time they are produced/consumed by cells)
What is the composition of air?
79% nitrogen and 21% oxygen
What is the pressure of nitrogen at 0% humidity?
600mmHg
What is the pressure of oxygen at 0% humidity?
160mmHg
What is the pressure of carbon dioxide at 0% air humidity?
0.23mmHg
What is the total pressure of a gas mixture equivalent to?
the sum of the pressures of the individual gases that make up the mixture
What is the pressure of nitrogen at 100% humidity?
563mmHg
What is the pressure of oxygen at 100% humidity?
149mmHg
What is the pressure of water at 100% humidity?
47mmHg
What is the pressure of CO2 at 100% humidity?
0.21mmHg
How do gas molecules exist?
in gas form or dissolved in liquid
What types of gases exert partial pressures and what are their partial pressures at eq?
vaporized and dissolved gases = equal at equilibrium
What is the solubility of oxygen like in water?
low solubility
What is the concentration of oxygen in water at 100mmHg partial pressure?
0.15mmoles/liter
What is the concentration of carbon dioxide in water at 100mmHg partial pressure?
3.0mmoles/liter
Is oxygen or carbon dioxide more soluble in water?
carbon dioxide is 20x more soluble in water and blood than oxygen
How do gases diffuse down gradients?
by partial pressure
Where is oxygen partial pressure = 100mmHg (x3)?
alveolar air, pulmonary veins and systemic arteries
Where is oxygen partial pressure less than or = 40mmHg?
in cells
Where is oxygen partial pressure 40mmHg (x2)?
pulmonary arteries and systemic veins
What is the partial pressure of oxygen in atmospheric air?
160mmHg
What is the partial pressure of CO2 in atmospheric air?
0.3mmHg
Where is the partial pressure of carbon dioxide 40mmHg (x3)?
alveolar air, pulmonary veins and systemic arteries
Where is the partial pressure of CO2 less than or equal to 46mmHg?
cells
Where is the partial pressure of CO2 46mmHg?
systemic veins and pulmonary arteries
What is the diffusion between alveoli and blood like?
very rapid since its a small diffusion barrier and very thin with a large SA
How long does it take for blood to equilibrate with alveolar air?
0.25 seconds
What concludes eq?
by the time blood has travelled 1/3 of the length of a capillary bed
How do oxygen and carbon dioxide diffuse?
oxygen: from blood to cells
carbon dioxide: from cells to blood
What is mixed venous blood?
a mixture of venous blood from the upper and lower extremities, complete
Where does venous blood get mixed and go to?
in the right ventricle and goes to the pulmonary artery
What is minute alveolar ventilation?
the volume of fresh air that reaches the alveoli each minute, similar to minute ventilation but air in anatomical dead space must be accounted for
What percentage of arterial blood oxygen is dissolved in plasma?
1.5%
What percentage of arterial blood oxygen is transported by hemoglobin?
98.5%
What is the law of mass action?
an increase in the concentration of the reactants drives the reaction to the right, resulting in the generation of more product
What is the max # of oxygen molecules that one hemoglobin can bind to?
4
How soluble is oxygen in plasma?
not very
Where is oxyhemoglobin formed and what is it?
oxygenated hemoglobin, formed in the lungs
Where is deoxyhemoglobin formed and what is it?
deoxygenated hemoglobin, formed in the tissues
How do you measure how much oxygen is bound to hemoglobin/
the saturation of hemoglobin
What is positive cooperativity?
the first substrate changes the shape of the enzyme allowing other substrates to bind more easily
How much oxygen does 1g of hemoglobin carry when 100% saturated?
1.34
What is 100% saturation?
a state in which all 4 binding sites on hemoglobin have oxygen bound to them
What are normal blood hemoglobin levels?
12-17gm/dL (150g/L)
What % of hemoglobin is saturated in venous blood?
75%
How much oxygen is released to the tissues?
250mL/min
What causes a rightward shift?
less loading of oxygen and more unloading
What causes a leftward shift?
more loading of oxygen and less unloading
How does high temperature affect oxygen loading?
causes a right shift
How do lower pH levels affect oxygen loading?
results in a right shift
What is the bohr effect
lower pH increases oxygen unloading
What happens when oxygen binds to hemoglobin?
certain amino acids in the protein release hydrogen ions
What happens when theres an increase in H+ ion concentration (decrease in pH)?
pushes the reaction leftward and oxygen dissociates (decreases the affinity of hemoglobin for oxygen)
What is the carbamino effect?
a decrease in the affinity of hemoglobin (conformation change) for oxygen when carbon dioxide binds to hemoglobin (caused by increased metabolic activity)
What is carbaminohemoglobin?
the compound formed by the union of carbon dioxide and hemoglobin (has a lower affinity for oxygen than normal hemoglobin)
What is 2,3-DPG?
is produced in red blood cells under conditions of low oxygen such as anemia and high altitude (decreases affinity of hemoglobin for oxygen, therefore enhancing oxygen unloading)
What is the synthesis of 2,3-DPG inhibited by?
oxyhemoglobin
What does hemoglobin have a greater affinity for (carbon monoxide or oxygen)
CO than O2 (that’s why it can kill you)
What does carbon monoxide do?
it prevents oxygen from binding to hemoglobin
Is CO2 concentrations higher in systemic arterial or venous blood?
in systemic venous blood
How much carbon dioxide transported is dissolved in plasma?
5-6%
How much carbon dioxide transported is bound to hemoglobin?
5-8%
Is CO2 more soluble in plasma or oxygen?
plasma
How is CO2 transported in plasma?
erythrocytes convert it to bicarbonate (86-90% transported)
What is carbonic anhydrase?
the fastest enzyme to convert CO2 and water to carbonic acid
What is the law of mass action/
an increase in carbon dioxide causes an increase in bicarbonate and hydrogen ions
Where does chloride go in the erythrocyte when CO2 goes to the alveoli
goes in (VV)
What is a chloride shift?
the movement of chloride ions into the RBCs as H ions move out to maintain the electrochemical eq
How does the urinary system regulate plasma ionic composition?
by regulating uptake/excretion of: Na, K, Ca, Mg, Cl, bicarbonate, H and phosphates
How does the urinary system regulate plasma volume and blood pressure?
by controlling the rate at which water is excreted in the urine, the kidneys regulate plasma volume and blood pressure
How does the urinary system regulate plasma osmolarity?
by regulating solute concentration (osmolarity) by regulation of water excretion
How does the urinary system regulate plasma pH
by regulating concentration of bicarbonate and hydrogen ions in the plasma they contribute to regulation of blood pH
How does the urinary system remove metabolic waste products and foreign substances from plasma?
the kidneys excrete waste and undesirable substances in the urine (ex. urea (proteins) / uric acid (nucleic acids) )
What are the 3 foreign substances that kidneys excrete in urine?
drugs, feed additives and pesticides
What does the secretion of erythropoietin stimulate?
erythrocyte production (RBC by bone marrow)
What does the secretion of renin do?
it raises blood pressure by influencing vasoconstriction – necessary for the production of angiotensin 2
What is calcitriol?
the active form of vitamin D that gets activated by the kidneys – regulates calcium and phosphorus metabolism (synthesized in skin)
What is gluconeogenesis?
formation of glucose from noncarbohydrate sources; supplies glucose to plasma by degrading certain amino acids and glycerol
What 6 things does the urinary system consist of?
2 kidneys, 2 ureters, a urinary bladder and the urethra
What do kidneys do?
form urine
What do ureters do?
transport urine from the kidneys to the bladder
What does the bladder do?
stores urine
What does the urethra do?
excretes urine from the bladder outside of the body
What lines the abdominal cavity?
a membrane called the peritoneum
What does retroperitoneal mean?
something located between the peritoneum and abdominal wall
What are renal arteries?
the 2 branches of the abdominal aorta that supply the kidneys
What is the renal hilus?
a location where renal arteries enter the kidney and renal veins exit the kidney
Where are most abdominal organs located?
they are enclosed within the peritoneum
What is the capsule?
a tough, fibrous connective tissue that surrounds the outside of the kidney
What is the renal cortex?
a reddish brown outer layer of the kidney
What is the renal medulla?
the inner region of the kidney
What is the renal pyramid?
a triangular shaped division of the medulla of the kidney – also aka papillae
What do collecting ducts do?
several nephrons share a collecting duct which serve to carry urine to the renal pelvis; originate at the tips of papillae
Where do collecting ducts drain to?
minor calyces
The convergence of minor calyces form what?
2-3 major calyces
Where do major calyces drain to?
the renal pelvis
Polylobed vs monolobed
monolobed means there is one lobe on the kidney (ex. pigs, sheep, horses, dogs an cats) whereas polylobed means there are multiple (ex. chicken or cattle)
What are nephrons?
the functional unit of the kidney (over a million of them in the kidney)
What is the renal corpuscle composed of?
bowmans capsule and the glomerulus
What is bowmans capsule?
a spherical structure at the inflow end of the renal tubules (where urine is formed)
What is the glomerulus?
a network of capillaries that bring blood to the nephron
What are renal tubules?
a system of tubes into which filtered fluid in the nephron flows
What occurs at the renal corpuscle?
where blood is filtered and where filtrate originates
What is the proximal tubule?
In the vertebrate kidney, the portion of a nephron immediately downstream from Bowman’s capsule that conveys and helps refine filtrate.
What is the proximal convoluted tubule?
first section of the renal tubule that the blood flows through; reabsorption of water, ions, and all organic nutrients
What is the proximal straight tubule?
commonly referred to as the thick descending limb of the loop of henle, descends into the medulla
What is the loop of henle?
section of the nephron tubule that conserves water and minimizes the volume of urine
What is the descending limb?
the limb of the loop of Henle that carries fluid from the cortex towards the medulla of the kidney
What is the thin ascending limb?
receives concentrated fluid from descending limb and allows diffusion of Na+ and Cl- into the interstitial fluid
What is the thick ascending limb?
impermeable to water, active solute transport
What is the distal convoluted tubule?
between the loop of Henle and the collecting duct; selective reabsorption and secretion occur here, most notably to regulate reabsorption of water and sodium
What is the collecting duct?
a segment of the nephron that returns water form the filtrate to the bloodstream.
What is the juxtamedullary nephron?
accounts for 15-20% of the nephrons. long loop of henle extending into medulla, responsible for medullary osmotic gradient, important in conserving water and reabsorption
What is the cortical nephron?
accounts for 80-85% of nephrons; in mammals and birds, a nephron with a short loop of Henle located almost entirely in the renal cortex
What is the juxtaglomerular apparatus?
produces substances involved in the control of kidney function; consists of the macula densa and juxtaglomerular cells
What is the macula densa?
it senses NaCl and releases prostaglandin or renin
What are juxtaglomerular cells?
aka granular cells, these produce renin
What is the renal sinus?
space within kidney that is adjacent to renal medulla, contains calyces and renal pelvis
What are segmental arteries?
branches of renal artery after it passes through the hilum
What are interlobar arteries?
segmental arteries further divide into these arteries which supply blood to the arcuate arteries
What are arcuate arteries?
small vessels found at the base of the renal pyramids; appear as echogenic structures
What are interlobular arteries?
branches off of the arcuate arteries which ascend into the cortex, giving off afferent arterioles
What are afferent arterioles?
the small blood vessels approaching the glomerulus (proximal part of the nephron); split from interlobular arteries
What are glomerular capillary beds?
branch from afferent arterioles and form a network
What are efferent arterioles?
the small blood vessels exiting the glomerulus. at this point blood has completed its filtration in the glomerulus.
What do efferent arterioles give rise to?
2 capillary beds: peritubular capillaries and the vasa recta
What is responsible for reasorption in the loop of henle and where does it come from?
the vasa recta – branches from the efferent arteriole
What is responsible for reabsorption in the distal convoluted tubule and where does it come from/
the peritubular capillaries, branch from the efferent arteriole
What are interlobular veins?
reuniting of the vasa recta and drain into arcuate veins
What are arcuate veins?
receive blood that drains from the interlobular veins and feeds into the interlobar veins
What are the interlobar veins?
receive blood that drains from the arcuate veins before feeding into the renal veins
What are renal veins?
removes deoxygenated blood from the kidneys
What 3 exchange processes occur within the renal nephrons?
glomerular filtration, reabsorption and secretion
What is glomerular filtration?
from the glomerulus to bowmans capsule
What is reabsorption?
from the tubules to the peritubular capillaries (tubules back into the plasma)
What is secretion?
from peritubular capillaries to tubules (same transport mechanism and barriers as for reabsorption)
What is excretion?
from the tubules out of the body
Where does the bulk flow of plasma occur?
from glomerular capillaries to renal bowmans capsule
What do starling forces do?
they drive filtration at the renal corpuscle
How much glomerular filtration occurs? (blood filtered)
125mL/min or 180L/day
What 3 barriers must. the glomerular filtrate cross to enter the bowman’s capsule?
- capillary endothelial cell layer
- epithelial cell layer
- barement membrane
What does the basement membrane do?
it prevents filtration of proteins in glomerular capillaries
What 4 starling forces play roles in glomerular filtration?
glomerular capillary hydrostatic pressure (Pgc), Bowmans capsule oncotic pressure (Pibc), bowmans capsule hydrostatic pressure (Pbc) and glomerular oncotic pressure (Pigc)
What is the glomerular filtration pressure?
the sum of starling forces in the renal corpuscle
What is the glomerular capillary hydrostatic presssure (Pgc)?
high due to resistance of efferent arteriole (60mmHg) and favours filtration
What is the bowmans capsule oncotic pressure (Pibc)?
low due to lack of protein in filtrate (0mmHg), favours filtration
What is bowmans capsule hydrostatic pressure (Pbc)?
relatively high due to large volume of filtrate inclosed space (15mmHg), opposes filtration
What is the glomerular oncotic pressure (Pigc)?
higher than in systemic capillaries due to plasma proteins in smaller volume of plasma (29mmHg), opposes filtration
What are the net pressures favouring and opposing filtration at the renal corpuscle?
favouring: 60mmHg
opposing: 44mmHg
Total = 16mmHg
What is the rate of renal plasma flow?
625mL/min
What is the filtration fraction?
the fraction of blood plasma in the afferent arterioles of the kidneys that comes glomerular filtrate (20%)
What is the proximal tubule?
the primary location in which reabsorption, unregulatd movement of solute and water from tubules into peritubular capillaries takes place
Is reabsorption regulated or unregulated?
unregulated
Where does reabsorption often occur?
in the proximal convoluted tubule (little bit in distal convoluted tubule)
What are the 2 barriers for reabsorption?
epithelial cells of renal tubules an endothelial cells of capillaries
Which way does the apical membrane face?
faces the lumen
Which way does the basolateral membrane face?
faces the interstitial fluid and is indirectly in contact with the blood
As X and Y get reabsorbed, what occurs>
they increase the osmolarity of the plasma
To be passively reabsorbed by diffusion, what must a substance be able to permeate?
the plasma membrane of the capillary and tubule endothelium
Which 5 things are actively transported?
K, H, choline, creatinine and penicilin
What do intercalated cells do?
regulate absoprtion of acids from nephrons
What do principle cells do?
regulate the reabsorption of water
What does the proximal convoluted tubule (PCT) do?
consists of simple cuboidal epithelial cells with prominent brush borders of microvilli; enables mass unregulated absorption
What 2 sections of the loop of henle consist of simple squamous epithelial cells
descending and thin ascending
Which section of the loop of henle consists of simple cuboidal to low columnar epithelial cells?
the thick ascending limb
Which section consists of simple cuboidal epithelial cells with small invaginations?
the distal convoluted tubule
What is the location of nonregulated reabsorption?
the proximal tubule (70% water and sodium and 100% glucose reabsorption)
What is the location of regulated reabsorption and secretion?
the collecting duct and distal tubule
What is the location of water conservation?
the loop of henle
What is the mass reabsorber?
proximal tubule – brush border provides a larger SA
Water reabsorption is regulated by what?
ADH
What does paracellular transport mean?
through junctions between adjacent cells
What do leaky tight junctions do?
they enable paracellular transport in proximal tubules
What barrier is transport regulated in the distal tubule and collecting duct?
the epithelium
What do tight junctions do?
limit paracellular transport in the distal tubule and collecting duct
What 3 factors that the amount excreted depends on?
filtered load, reabsorption rate, secretion rate
What is the amount of substance excreted = to?
amount filtered + amount secreted - amount reabsorbed
Whats another term for urination?
micturition
Where does urine get formed?
in the renal tubules
What collects urine and passes it to the ureter?
the renal pelvis
What is the ureter?
the tube that carries urine from the kidney to the urinary bladder
What does the bladder do?
stores urine until excretion
What does detrusor muscle do?
compresses the urinary bladder and expels urine through the urethra; powered via parasympathetic innervation (parasympathetic innervation causes contration, VV)
What is the internal urethral sphincter?
a circular muscle innervated by the sympathetic neurons that prevents leakage
What holds urine in the bladder?
voluntary skeletal muscle in the external urethral sphincter
What is the opening of the urethra to the outside called
the external urethral orifice
What is the pelvic floor?
a muscular base of the abdomen attached to the pelvis
What is micturition reflex?
relaxation of the urethral sphincter in response to increased pressure in the bladder
