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)

 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 ?

Don't forget about the age old question of What is a mosque?

 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?

Thoracic Cavity

 ↳ Keep in mind: Diaphragm during relaxation ⇒

dome-shaped

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

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

∙ ↳ Lungs will be stretched due to the surface tension  

between the  

 pleural membranes ⇒ cause the clinging on lungs We also discuss several other topics like What is the purpose of the treasury dept in the federal government?

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

 No resistance due to cartilage rings around the airways If you want to learn more check out What is the meaning of pareto improvement in economics?

∙ 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 Don't forget about the age old question of What are the standard integration formulas?

∙ 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 leave

 Occurs when the tissues are unable to overcome the effects of  the injuring agent Don't forget about the age old question of Which manner of articulation refers to the restriction of airflow in the oral cavity thus causing turbulence and noise?

∙ 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

∙ 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