Chapter 22: Physiology of the Respiratory  System 

What are the factors influencing external + internal respiration?

 Respiratory System: Physiology

 Pressure

 Intrapulmonary Pressure: pressure in the lungs (aka Intra-alveolar  pressure)

o Equals the Atmospheric Pressure: 760 mm Hg

 Intrapleural Pressure: pressure in the pleural cavity

o Less than Atmospheric Pressure: 756 mm Hg (–4 mm Hg)

∙ Fluid in pleural cavity is the reason the membranes can slide across one another (need a big force to separate them) Don't forget about the age old question of What is a mosque?

 Surface Tension 

∙ Kept negative

 If more than atmospheric pressure  alveoli would collapse  lungs collapse

 Lymphatics drain the fluid in pleural space

What is oxygen-hemoglobin dissociation curve ?

 Pulmonary Ventilation (breathing process)

 ↳ ventilating the alveoli  

 Breathing Process:

o Volume Change  Pressure Changes  Facilitate Breathing (pressure  gradient)

 2 Major Phases

1) Inspiration (inhalation)

∙ Active Process – consuming energy (ATP)

 Contraction of skeletal muscles

 Diaphragm

o Location: separates the Thoracic Cavity from the  

Abdominal Cavity

o Activated by nerve impulses form the somatic NS  

o Becomes flat; moves downward

∙ Increases the height (or vertical dimension) of the  

What is hypercapnia?

If you want to learn more check out What is the meaning of adjacent nodes?

Thoracic Cavity

 ↳ Keep in mind: Diaphragm during relaxation ⇒

dome-shaped

 External Intercostal Muscles 

o Location: between (individual) ribs  

o Ribcage moves outward

∙ Increases the diameter (width)

∙ Promotes the ↑ of volume in the Thoracic Cavity; ↑ of  

volume in Lungs If you want to learn more check out What is the purpose of the treasury dept in the federal government?

∙ ↳ Lungs will be stretched due to the surface tension  

between the  

 pleural membranes ⇒ cause the clinging on lungs

to thoracic  

 cavity wall

 Pressure (intra-alveoli) in lungs decreases less than atmospheric  pressure in a short-time

 Air enters from area of high pressure

o Air from outside the lungs move inside

∙ Lasts for about 2 seconds

2) Expiration (exhalation)

∙ Passive Process

 Relaxation (elastic recoiling of lung) + recoiling of skeletal  

muscles

 Diaphragm returns to dome-shape; ↓ height of lungs

 Intercostal Muscles ↓ diameter of lungs

 Automatic recoiling of the lungs:

 Promotes ↓ volume in lungs and ↑ in pressure  

o Generates Pressure Gradient

∙ High pressure in lungs moves outside to the  

environment

 Factors Influencing Breathing Process

1. Airway Resistance

 NOT a significant factor!

o There are only certain points at which there are problems in airway  resistance

∙ Trachea and the Primary + Secondary Bronchi If you want to learn more check out What is the meaning of equality in economics?

 No resistance due to cartilage rings around the airways

∙ Tertiary Bronchi ⇒ ONLY point where airway resistance could occur;  irregular plates in the wall

∙ Bronchioles ⇒ smooth muscle layer; no cartilage = should have  resistance, WRONG!

 Airway resistance (< 1 ml in diameter)

 Branches out so extensively; makes up for small diameter

o Surface Area is huge ⇒ NO resistance

∙ Terminal Bronchioles

 Extensive branches provide a huge cross-sectional area which  makes up for the small diameter = No resistance

∙ Respiratory Bronchioles or Alveoli Ducts

 Gas exchange occurs here

 Resistance is not the driving force; diffusion is

2. Compliance of Lung

 Degree of stretch-ability (↑ stretch = ↑ compliance)

o Under Healthy Conditions ⇒ very high stretch-ability

o Under Disease

∙ Chronic Inflammation: inflammation that may have a rapid or slow  onset but is persistent and resistant to leaveWe also discuss several other topics like What are the standard integration formulas?

 Occurs when the tissues are unable to overcome the effects of  the injuring agent

∙ Fibrosis: changing elastic tissue of lungs into fibrous tissue

 Formation of scar tissue

 Fibrous is made of tough fibrous connective tissue (dense  

collagen replacing elastic)

 Influencing the stretch ability leads to ↓ in compliance of  

lungs

 Compliance of the lung also depends on Compliance of the Thoracic  Cavity

o Abnormality in bone of ribcage leads to ↓ in compliance of thoracic  cavity = ↓ in compliance of lungs

3. Surface Tension of Fluid in Alveoli

  Assumption Case! 

o If the fluid on the internal wall of alveolus was pure water it would  collapse due to hydrogen bonding of water molecules (makes alveolus  assume the smallest size)

∙ This condition doesn’t happen due to the synthesis and release of  Surfactant (lipo-protein)

 Fluid is partly water, other particles, and surfactant

 Synthesized by Type II Alveolar Cells (cuboidal) which prevents  cohesiveness of water molecules We also discuss several other topics like How do we perceive speech accurately?

∙ Occurs in premature babies

 Babies born before the end of pregnancy (8 weeks before)

 Placed on ventilators because they have Infant Respiratory  

Distress Syndrome (IRDS)

o Have the complete respiratory system but synthesis of  

surfactant takes place after 7 months

∙ Babies are exposed to the collapse of alveoli due to  

surface tension

 External + Internal Respiration

 Both are gas exchange process; meaning diffusions of O2 and CO2  External Respiration: process in which gas exchange at the level of the  lungs (pulmonary gas exchange)

o Called external due to exchange of gases when source of O2 is from the external environment + exhalation of CO2 into environment

o Diffusion of O2: From alveolus through respiratory membrane into  capillaries

o Diffusion of CO2: From blood of capillaries into alveolus goes outward  during exhalation

 Internal Respiration: process of capillary gas exchange at the level of the  tissue

o Partial pressures and diffusion gradients are reversed from external  respiration

∙ Diffusion of O2: from blood into tissues

∙ Diffusion of CO2: from tissue into blood

 Factors Influencing External + Internal Respiration

1. Partial Pressure Gradient (concentration gradient for gases) o Relative amount of the gases

∙ External Resp.

 Oxygen

 O2 in Alveoli = 104 mm Hg

 O2 in Blood Returning from Tissue = 40 mm Hg

o Creates a partial pressure gradient  

∙ About 64 mm Hg

∙ O2 in alveolus is higher; it moves from alveolus into  

blood in capillary

 Carbon Dioxide

 In Alveoli = 40 mm Hg

 In blood returning from Tissue = 45 mm Hg

o Partial pressure is only about 5 mm Hg

 Although the difference of PP is drastic between O2 and CO2 the  same amount of gases are exchanged

 CO2 seems less, but the is that CO2 is 20x more soluble in  plasma and alveolar fluid than O2

∙ Internal Resp.

 Oxygen

 In Blood Entering Tissue = 100 mm Hg

 In Tissue = less than 40 mm Hg

o PP is about of less than 60 mm Hg

∙ O2 moves rapidly from blood into tissues; at the same  

time CO2 moves quickly from tissues into blood

∙ Gas exchange between blood and tissue takes place  

by simple diffusion 

2. Thickness + Surface Area of Respiratory Membrane

o Resp. Membrane is extremely thin; efficient in gas exchange ∙ Inflammation due to Ammonia  formation of edema  increases  thickness of surface membrane

o Surface Area

∙ Huge # of Alveoli = Huge amount of Surface Area

 Emphysema: complete destruction of alveoli wall

 No respiratory membrane ⇒ promotes problem in gas  

exchange

 In healthy people = 90 m2 (40x greater than surface area of skin) 3. Transport of Gases

o Transport of Oxygen

∙ Oxygen: gas binding to hemoglobin

 Not soluble in plasma; 1.5% of dissolved oxygen travels in  hemoglobin

∙ Hemoglobin: made of 4 polypeptide chains, each with a heme group which has one iron atom (area where O2 binds; MAX = 4)

 Binding is reversible! Unbinds when O2 is needed

 First O2 Bind ⇒ promotes the change of shape to allow the  other O2 molecules to bind to the hemoglobin at a fast rate  First O2 Unbind ⇒ promotes change of shape to allow the rest of O2 to unbind as well

∙ Association between Oxygen + Hemoglobin

 Partially Saturated: Hemoglobin < 4 O2 molecules binded  Fully Saturated: Hemoglobin has all 4 O2 binded

∙ Percent O2 Saturation of Hemoglobin

 Local Partial Pressure

 In the Lungs

o PP= 100 – 104 mm Hg

∙ 98% O2 saturation

 In the Tissue

o PP = 40 mm Hg (After one complete systemic circulation) ∙ 75% saturation

o Blood in the veins to the heart

∙ Still has O2 in case it is needed anywhere else

∙ ↳ Even at high altitude there is still 95% O2 saturation  ↳ Important to note! Oxygen-hemoglobin Dissociation Curve ⇒ how much O2 is going to unbind from the hemoglobin; how  much oxygen will be used/released

 Partial Pressure of CO2

 Increase in CO2 = ↑ Hydrogen Ion = ↓ pH (Acidosis)

o Promotes the change in shape of hemoglobin

∙ Facilitating the unbinding of O2 = ↓ Saturation  

 ► At 40 mm Hg (level of tissue) there is now 60% O2

saturation,  

 instead of the usual 75% at the level of tissue

 ↳ More O2 is being released

o Bohr Effect: the phenomena that O2is released where it is  needed

∙ ↑ in CO2 occurs at the level of the tissue which is were  more O2 is needed (for exercise and such)

 Decrease in CO2 = ↓Hydrogen Ion = ↑ pH

o More O2 in being binded; less O2 is being released

 Temperature

 Increase of body temperature at Tissues  

o PP = 40 mm Hg

∙ Almost 50% (normal conditions = 75%)

      ► ↑ Release of O2

 Production of Organic Compound = 2,3-bisphosphoglycerate  Occurs during the rise of body tempt.

 Influences the affinity of O2 and hemoglobin

o Transport of Carbon Dioxide

∙ More routes are available for the transport of CO2

 Through Plasma (7-10%)

 CO2 is more soluble in the plasma = ↑ percentage will be  dissolved during transport

 Carbamino-hemoglobin (20%)

 CO2 binded to hemoglobin

 Bicarbonate Ion (70%)

∙ At the Level of the Tissues

 CO2 moves from the tissues into the blood

 Once in blood, CO2 moves to RBC where it will be hydrated  (by water present in RBC)

o Takes place at a fast rate; catalyzed by Carbonic  

Anhydrase

∙ Leads to production od Carbonic Acid (weak acid)

► Breaks into Bicarbonate ion and Hydrogen ion

 ↳ BC ion leaves RBC to plasma (to get to the lungs)

 ↳ Cl- enters RBC through Chloride Shift to keep  

medium of RBC in  

 normal conditions  

 ↳ Hydrogen ion (in RBC) influences the shape of  

hemoglobin  

 (which contains O2)

 ↳ Promotes the release of O2 (Bohr Effect!)

∙ At the Level of the Lungs

 CO2 moves from blood into lungs to be exhaled out of the body  Returns Bicarbonate back to the plasma ⇒ Reverse Chloride  Shift 

 Hydrogen releases from the hemoglobin because of the  entrance of O2

o Hydrogen + Bicarbonate ions will react together to turn  back into Carbonic Acid

∙ Carbonic Anhydrase is used to reverse the Carbonic  

Acid back into CO2 and water (H2O in RBC)

∙ ► CO2 can now be pushed into alveolus to be exhaled  

out of body

4. Neural Mechanisms (for control of breathing) – Summary  o Medullary Centers 

∙ Located in the Medulla Oblagata + Pons

∙ Consists of 2 Groups

 Ventral Respiratory Group (VRG) 

 Cluster of nerves

o Contains rhythm generators whose output drives  

respiration

∙ No pacemakers!

 Made of Expiratory and Inspiratory Neurons  

o Work to together in Mutual Inhibition ⇒ one is activated  while the other is inhibited

∙ Sends impulses to the inspiratory muscles (external  

intercostals and diaphragm)

 Dorsal Respiratory Group (DRG) 

 Cluster of nerves  

o Integrates peripheral sensory input

o Modifies the rhythms generated by the VRG

 Posterior to ventral

o Pontine Respiratory Center 

∙ Located in the Pons of the brainstem

 Superior to Medullary Centers

∙ Interact with the Medullary Respiratory Centers to smoothen the  respiratory pattern

 Control of Breathing by Neural Mechanisms – Further Explained  Ventral Respiratory Group

 Contains inspiratory + expiratory neuronal networks

 Impulses sent by the Phrenic Nerve (to Diaphragm) and the Intercostal  Nerve

o Activation of Intercostal Nerve promotes the inspiration phase ∙ Activates contraction of inspiratory muscles

 Inhalation takes place for 2 secs.  

 Impulses stop from inspiratory + Activation of expiration  

neurons occur

o Intercostal + diaphragm go into relaxation ⇒ Expiratory  

Phase (3 secs.)

∙ Impulses through Phrenic + Intercostal activate once  

again causing activation of inspiration + inhibition of  

expiration

 >> Leads to 12 -16 sec. cycle

 Dorsal Respiration Group

 Responsible for integrating information

o Receives information form chemoreceptors

o Relays info to the VRG

 Located a bit posterior to the VRG

 Pontine Respiratory Center

 Similar to DRG

o Integrates info relaying into DRG and VRG

 Responsible for smooth transition between inspiration + expiration  Controls breathing during sleep + exercise

 Neural + Chemical Influences on Brain Stem Respiratory Centers  Control of breathing rate

 Control of Gases

 Negative Feedback Mechanism

o Receptors senses a change of gases in arterial blood (blood going to  the brain/out of left ventricle and into tissues)

∙ Chemoreceptors

 Central Chemoreceptors 

 In brain, mainly the brainstem

 Peripheral Chemoreceptors

 Located in arteries

o Close to baroreceptors which sense change in BP

o Close to the Aortic Arch

 Located in the Ceratoid Artery

o Blood entering the brain

∙ CO2 ⇒ most important stimulus that promotes a change in  breathing rate

 Hypercapnia: Increase of CO2 in Arterial Blood (Normal CO2 = 40 mm Hg) o Change in breathing rate occurs once CO2 goes up 5 mm Hg ∙ Almost doubles the breathing rate

∙ Blood goes into the brain where the Blood Brain Barrier is  (continuous capillary with no intercellular clefts)

 CO2 will be able to diffuse through the BBB into the  

cerebrospinal fluid (aka fluid of the brain)

 CO2 will react with water to produce Carbonic Acid, leading to Bicarbonate + Hydrogen Ion

o Hydrogen Ion ⇒ Acidosis ⇒ disturbance of metabolic  

activity

∙ No buffer in the brain like the hemoglobin in RBCs

∙ Influences Central Chemoreceptors

 >>Breathing rate is increased to get rid of H+ 

(therefore CO20

 >>Impulses is sent to the Medullary Center →

Muscles →  

 Increase in Breathing Rate

 >Expels more CO2, getting rid of H+ 

 Hypoxia: O2 Deprivation

o O2 saturation should go way below 60 mm Hg

∙ At the tissue (40 mm Hg) there is still 75% O2 saturation  Change in breathing rate will NOT change until way under 60  mm Hg

o Negative Mechanism = Same as Hypercapnia

∙ Only difference is that the Peripheral Chemoreceptors receive the  impulse instead of the Central Chemoreceptors

 Brain goes numb due to O2 deprivation, therefore the central  chemoreceptors are numb

 Acidosis: Increase of Hydrogen Ions (↓ pH)

o Influences Peripheral Chemoreceptors

o ↑ H+ in blood and reaches the BBB but does NOT diffuse ∙ The BBB is not permeable to Hydrogen (not lipid-soluble)  Not going to be a major factor in changing the Breathing Rate o Conditions such as Diabetes could also increase H+ ⇒ increasing CO2

Chapter 25: The Urinary System 

 Organs

 Kidneys 

 Bean-shaped organs

 Functions:

o Formation of Urine

o Control of blood pressure (in long term mechanism)

 Right Kidney is a bit lower/inferior to the Left Kidney

o The liver is right above/superior the right kidney

 In the presence of endocrine glands

o Adrenal Glands (hats, sit atop the kidneys)

 3 Major Regions

o Cortex 

∙ Outer region

∙ Consists of the nephrons

 Functional & structural units of kidney

 Responsible for the formation of urine

 1 million nephrons are found here

o Renal Medulla 

∙ Made of triangular-shaped structures called Renal Pyramids

 Base of pyramid faces the cortex

 Tip faces the Renal Pelvis

 Each has a striped appearance due to permeable collecting  ducts that drain the nephrons

 Papilla of Pyramid: finger-like projecting structures

o Where all collecting ducts fuse together

o Urine goes from Papilla to Renal Pelvis

∙ Papilla of Renal Medulla → Minor Calyx (cup-shape) →

Major Calyx → Renal Pelvis → Ureter → Urethra → Out  

of Body

o Renal Pelvis 

∙ Broadened top part of the ureter  

 Funnel shaped

 Where the kidney tubules drain 

 Renal Column = extends from cortex into all 3 regions 

 Renal Lobe = 2 renal columns surrounded by renal pyramid 

o Average of 7-8 lobes in each kidney 

 Ureters 

 Tubes from kidneys to Urethra 

 Urethra 

 Expels urine to outside the body 

 Functional + Structural Unit of Kidney: The Nephron 

 Made of 2 Major Portions

 Renal Corpuscle 

o Made of Glomerulus and Glomerular Capsule

∙ Glomerulus:  

 Network of fenestrated capillaries

 Allows fluid to pass; prevents plasma proteins from exiting

 Responsible for filtration of blood

∙ Glomerular Capsule 

 Aka “Bowman’s Capsule”

 Beginning part of the renal corpuscle

 Surrounds Glomerulus

 Leads to the Renal Tubule

 Renal Tubule 

o 3 Areas

∙ Proximal Convoluted Tubule

∙ Loop of Henle or the Nephron Loop

∙ Distal Convoluted Tubule

 Distal & Proximal describes their position to the Renal Corpuscle  Leads to the Collecting Ducts which is not part of the Renal  Tubule

 Physiology of Nephron

 Renal Corpuscle 

 Located in the Cortex

 Part of Nephron Loop is located in the Medulla

o Glomerulus Capsule 

∙ Double-layered Membrane

 Parietal Layer of Glomerulus Capsule 

 External + single layer of simple squamous

o Does NOT have to do with filtration

 Visceral Layer of Glomerulus Capsule 

 The parietal layer when it turns inferiorly

 Adheres to the Glomerulus

 Internal layer made of modified epithelial cells called  

Podocytes

o Contain cytoplasmic extensions to cling to Glomerular  

Capillaries called Foot Processes

∙ Foot Processes interdigitate ⇒ they leave gaps or  

Filtration Slits 

∙ Extremely important in formation of urine

 Renal Tubule 

 Made of single layer of epithelial but changes in accordance to the  different regions

o Proximal Convoluted Tubule 

∙ Simple Cuboidal epithelial cells

 Abundances in microvilli on the epical surface of the epithelial  cells

 Epical Surface = surface facing the lumen (or inside of the  cell)

o Region where reclaiming of the material from lumen  

through the cells back into the blood occurs (Reabsorbing  

occurs)

∙ Huge # of microvilli = increases the surface area

 Makes up the Brush Border

o Increases absorption  

o Loop of Henle 

∙ Descending Limb

 Cuboidal epithelial cells with microvilli (Thick Descending Limb)  Lower portion turns into Simple Squamous epithelial cells  (Thin Descending Limb)

o Same epithelial in the actual loop

∙ Ascending Limb

 1st Portion (turning up) = Simple Squamous epithelial (Thin  Ascending Limb)

 2nd Portion (going up) = Cuboidal epithelial (Thick Ascending  Limb)

o Distal Convoluted Tubule 

∙ Cuboidal epithelial

∙ Not abundant in microvilli

∙ Region that secretes material from blood into urine to be able to  excrete wastes

 Collecting Ducts 

 Contains 2 Types of Cells

o Principal Cell 

∙ More abundant of the two

∙ Simple Squamous

∙ Contains NO microvilli

∙ Associated with Sodium-Water Balance

o Intercalated Cell 

∙ Simple Cuboidal  

∙ Abundant in microvilli

∙ Associated with Acid-Base Balance

 Nephron Capillary Beds

 2 Types

o Glomerulus Capillary 

∙ Anatomical + Psychological exception

∙ Drained by efferent arteriole

 Makes it an exception ⇒ arterioles are usually drained by  venules!

 Arterioles have high pressure; meaning high resistance;  

therefore, high blood pressure

 Average BP is 26 mm Hg; in the Glomerulus Capillary BP is 55 mm Hg

o Higher BP ables it to push the fluid out to the Glomerulus  

to produce urine

 Efferent arteriole has a smaller diameter than the afferent  

arteriole

o Increases the resistance ⇒ ability to push fluid out

 Leads to generation of other capillary bed

o Peritubular Capillary 

∙ Tiny capillaries that travel alongside nephrons  

 Allows reabsorption and secretion between blood and the inner  lumen of the nephron 

∙ Branched off of efferent arteriole

 Leads to the Cortical Nephron

 85% of kidney nephrons

 Nephron Loop is shorter

 Glomerulus is further away from the Corticormedullary  

Junction 

 Leads to the Juxtamedullary Nephron

 Vasa Recta = the long capillaries running vertical + parallel  to Henle’s Loop

o Part of the Juxtaglomerular Complex

 Juxtaglomerular Complex 

 Region/contact between Ascending Limb of the Nephron + the Afferent  Arteriole of the Peritubular Capillary

 Involved in blood pressure regulation via the release of Renin and the  autoregulation of Glomerular Filtration Rate

o Contains different types of cells

∙ Macula Densa Cells 

 Modified (tall) Cuboidal epithelial cells from the Ascending Limb  Chemoreceptors = senses chemicals in the filtrate

 Mainly senses sodium chloride present in the filtrate

∙ Granular Cells 

 Aka Juxtaglomerular Cells

 Belong to the Afferent Arteriole

 Smooth muscle cells; modified to be larger

 Contain granules

 Contains the enzyme Renin

o Promotes vasoconstriction

 Mechanoreceptors!

∙ Extra-glomerular Mesangial Cells 

 Located between Macula Densa cells + Granular Cells

 Contain gap junctions

 Provides the ability to communicate signals between the  

Macula + Granular cells

 Physiology of the Kidney

 3 Processes + the excretion of urine

 Glomerular Filtration

o Filtration of fluid derived from the plasma (except blood cells + plasma  proteins)

 Reabsorption 

o In Proximal Convoluted Tubule (all over the Renal Tubule)

o Selective reclaiming of certain substances from filtrate back into blood; back to venous blood

 Tubular Secretion 

o Selective secretion of material

∙ From blood through epithelial cell to urine to be excreted

 Filtrate is not the same as urine

 Filtrate: plasma without blood cells or plasma proteins

 Urine: everything not needed in filtrate; waste

 Filtration

 Passive process

 Increase of blood pressure in the glomerulus leads to movement of filtrate  3 Layered Filtration Membrane (in glomerulus)

 Glomerular Capillary Endothelium (epithelial)

o Fenestrated

∙ Allows passage of all material except blood cells through the  Filtration Slit that provides a place of exchange between the  

podocytes and glomerular capillary

 Basement Membrane 

o Fused membranes of the podocyte and glomerular capillary

o Physical barrier

∙ No proteins present here!

o Made of negatively charged glycoproteins

∙ Electrically repels the negatively charged plasma proteins in the  capillary

 Electrical Repulsion occurs!

 Major reason for maintaining plasma proteins

 Foot Processes of Podocyte of Glomerular Capsule

o Finger-like projections of Podocytes that wrap around the glomerular  capillaries  

o Contain filtration slits between the foot processes

∙ Slit Diaphragm 

 Thin membranes that extend across the filtration slits

 Catch and stop any macromolecules that manage to get by  

the basement membrane

 Made of Mesangial Cells

o Modified smooth muscle cells

∙ Can contract + controls surface area

o Engulf proteins that escape the filtration membrane

∙ Substances < 3 mm can pass

∙ Substances > 5 mm cannot pass

 Factors Affecting Glomerulus Filtration Rate

 Outward + Inward Pressures

 Outward Pressure 

o Promotes filtration

∙ Hydrostatic Pressure of Glomerulus (HPGC) = Blood Pressure in  Glomerulus = 55 mm Hg

 Extremely high because its drained by arterioles

 The efferent arteriole is also smaller in diameter compared to the afferent arteriole

 Reabsorption does not occur in Glomerular Capillary!  

(Glomerulus)

 Filtration occurs across (unlike blood capillaries)

 HP is the single force responsible for filtration

 There are no proteins present

o No Colloid Osmotic Pressure in the Glomerulus (OPGC)

o Outward Pressure = HP in Glomerulus + OP in Glomerulus = 55 mm Hg  Inward Pressure 

o Opposes filtration

∙ Colloid Osmotic Pressure in Glomerular Capsule (OPCS) = 30 mm Hg  Proteins are present in the blood of the glomerulus

 Provides opposing force because proteins attract water

∙ Capsular Hydrostatic Pressure  

 Fluid in the glomerular capsule, not the blood

 Confined to a small space; HP in capsule (HPCS) = 15 mm Hg o Inward Pressure = HP in Glomer. Capsule + OP in Glomer. Capsule = 45 mm Hg

 NFP: Winning Force

 Net-Filtration Pressure (NFP) = Outward Pressure – Inward Pressure  = HPGC – (HPCS + OPGC)

 = 55 – (15 + 30)

 = 10 mm Hg

 Due to the blood in the Glomerulus (capillary)  

o ↑ BP in Glomerulus = ↑ Net Filtration Pressure

∙ Filtration rate is dependent on the NFP  

 Glomerular Filtration Rate (GFR)

 Amount/volume of filtrate formed in a minute = 120 mm per min. (180 L  per day)

o Directly proportional to:  

∙ Surface Area for filtration

 Surface area is almost = to the surface area of your skin!

∙ Permeability of filtration membrane

 About 1000x more permeable than blood capillaries

 Due to the fenestrations

∙ NFP

 Most controllable + Most important factor

 Dependent on blood pressure

 Adjustment in diameter of Afferent arteriole helps control the  blood pressure

o Changes the HP in Glomer. Capillary = changes in NFP =  

change in GFR

 Vasoconstriction  

 ↓

 ↓ Diameter

 ↓

 ↓ Blood Flow

 ↓

 ↓ Blood Pressure in the Glomerulus (HP)

 ↓

 ↓ Net Filtration Rate (NFP)

 ↓

 ↓ Glomerular Filtration Rate (GFR)

∙ Therefore, a decrease in urine output = the  

conservation of water

 ↳ Maintains the blood volume and blood pressure

o Extreme changes in blood pressure leads to Extrinsic  

Mechanisms

 Extrinsic Mechanisms 

 Occurs when BP is < 80 mm Hg and > 180 mm Hg  

o EX: Hypovolemic Shock 

∙ Extrinsic takes over Intrinsic

 Drastic decrease in systemic pressure is sensed by the  

baroreceptors

 Activates the Cardio-Exhibitory Center which leads to  

Vasoconstriction

o Activates Granular cells of Juxtaglomerular Apparatus to  

release Renin

o Activates Sympathetic NS to release Renin as well

∙ Renin: enzyme that catalyzes plasma proteins to  

create Angiotensinogen and Angiotensin II 

 ↳ Which promote further vasoconstriction

∙ Renin also activates the Adrenal Glands

 ↳ Releases Aldosterone to promote the reabsorption

of Sodium of  

 urine back to the blood

 ↳ Sodium attracts water

 ↳ ↑BV = ↑SV = ↑CO = ↑BP = ↑NFR =  

↑GFR