Phys V

What are the major functions of the respiratory system? Where do each of these take place?

• Gas exchange-In the alveoli

• Ventilation (Breathing / Air Movement)-Diaphragm and intercostal muscles of the chest wall

• Air Conditioning (Warming and Moistening)- Nasal cavity, mouth, and upper airways

• Air Filtration and Defense-Nasal hairs, cilia and mucus lining the trachea and bronchi, and epiglottis

• Sound Production (Phonation / Speaking)-In the larynx

What are the two parts of the respiratory cycle? How many liters of air flow in and out of the lungs per minute (at rest)?

Inspiration (inhaling air into the lungs) and expiration (exhaling air out of the lungs). At rest, approximately 6 liters of air flow in and out of the lungs per minute.

What parts of the body make up the upper respiratory tract? Conducting zone? Respiratory zone?

• Nose and Nasal Cavity

• Paranasal Sinuses

• Pharynx (Throat)

• Larynx (Voice Box

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• Nose, Pharynx, and Larynx

• Trachea (Windpipe)

• Bronchi (Main, lobar, and segmental)

• Terminal Bronchioles

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• Respiratory Bronchioles

• Alveolar Ducts

• Alveolar Sacs

• Alveoli

Where is the site of gas exchange?

The alveoli

How do the arteries (blood) interact with the respiratory zone? Be able to describe the arrangement of the vessels and airways.

1. The Structural Arrangement

• Parallel Branching: Pulmonary arteries branch side-by-side along the entire airway tree.

• Capillary Basket: At the respiratory zone, arterioles split into a massive meshwork of capillaries that completely wrap around each alveolus like a sheet.

2. The Functional Interaction

• Pulmonary Arteries: Bring deoxygenated (high CO₂) blood from the right heart into the alveolar capillary beds.

• The Exchange: O₂ diffuses into the blood; CO₂ diffuses out into the alveolus to be exhaled.

• Pulmonary Veins: Collect the freshly oxygenated blood from the capillaries and send it to the left heart for the body.

Describe how ventilation occurs during normal (rest) breathing

The movement of air into and out of the lungs driven by pressure gradients created by muscle contraction and lung elasticity.

Define ventilation. What is the basic equation of bulk flow?

Ventilation is the mechanical process of moving air into and out of the lungs (breathing) to facilitate gas exchange between the atmosphere and the alveoli.

F=ΔP/R

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F=Flow rate

ΔP=Pressure Gradient

R=Resistance

How do alveolar and atmospheric pressure affect air flow?

Air always flows from high pressure to low pressure. Atmospheric pressure stays constant at 760 mmHg; the body changes Alveolar pressure to breathe

Where does ventilation take place? Where are O2 and CO2 exchanged with the

environment? With the cells? Transported?

1. Ventilation: Takes place in the Airways & Lungs. Moves air in/out.

2. Exchange with Environment: Takes place across the Respiratory Membrane (Alveoli ⇄ Pulmonary Capillaries).

3. Gas Transport: Takes place in the Bloodstream via Hemoglobin and Bicarbonate

4. Exchange with Cells: Takes place across Systemic Capillaries (Blood ⇄ Body Tissues/Cells).

What is Boyle’s Law? How does this apply to volume changes during inspiration and expiration?

The pressure of a given mass of gas is inversely proportional to its volume at a constant temperature.

This means if you increase the volume of a closed container, the gas molecules spread out, and the pressure drops. If you decrease the volume the molecules compress, and the pressure spikes.

What is transpulmonary pressure? Chest wall pressure? At rest, what do these add up to?

The inflating force that holds the lungs open. Must always be positive (otherwise, the lung collapses).

The force acting on the ribs. It is negative at rest, reflecting the chest wall's natural urge to spring outward

They add up to exactly 0 mmHg-Meaning: The lung's inward collapse force perfectly balances the chest's outward spring force. No air flows.

Describe the lung mechanics during inspiration and expiration

Lung mechanics rely on Boyle’s Law=gas pressure is inversely proportional to volume (as volume increases, pressure decreases, and vice versa). Air flows down a pressure gradient from high to low pressure.

Describe alveolar, intrapleural, and transpulmonary pressure changes during a

normal respiratory cycle. When is the diaphragm contracting during these events?

• During a normal respiratory cycle, they change in a coordinated sequence as the thoracic volume expands and recoils, while the diaphragm actively contracts only during the entire inspiratory phase.

During “normal” respiration which muscle contract to cause inspiration and expiration?

The Diaphragm and External Intercostal Muscles

During “maximal” respiration which muscle contract to cause inspiration and expiration?

The Diaphragm, External Intercostal Muscles, Sternocleidomastoid, Scalenes Pectoralis Minor

What do surfactants do to the alveoli? Which cells produce these?

-Reduces Surface Tension, Prevents Alveolar Collapse, Increases Lung Compliance

-Type II Alveolar Cells (also known as Type II Pneumocytes)

Describe the respiratory volumes measured in adults

The amount of air inhaled, exhaled, and stored in the lungs during different phases of the breathing cycle

What is tidal volume? Vital capacity? Dead space? Total lung capacity?

• The volume of air that moves in and out of the lungs during a single, normal quiet breath. (Average: ~500 mL)

• The maximum amount of air a person can forcefully exhale after taking the deepest breath possible. ( ~4,500 – 4,800 mL)

• Air that is inhaled but does not participate in gas exchange because it remains trapped in the conducting pathway ( ~150 mL)

• The absolute maximum volume of air the lungs can hold after a maximal inhalation. ( ~6,000 mL)

What is a “normal” tidal volume values for a college-age male at rest? What is the maximum breath volume values that can be exerted by the lungs during intense exercise?

-500 mL

-4.5 to 5.0 Liters (4,500 – 5,000 mL) for a young adult male. During maximal exercise, tidal volume will scale up significantly to utilize up to 50–60% of this total vital capacity per breath

What is a “normal” dead space volume? What would happen if dead space reached 0 mL?

For a healthy adult is approximately 150 mL

• Lung Collapse, Massive Infections, Suffocation

Describe the partial pressure of gases monitored in the human body

-PaO2 measures the pressure of oxygen dissolved directly in arterial blood and dictates how well oxygen moves from the lungs into the bloodstream.

-PaCO2 measures dissolved carbon dioxide in the blood and serves as the primary marker for alveolar ventilation and acid-base balance

What is the partial pressure of O2 in the air? CO2?

Partial Pressure of Oxygen: ~160 mmHg

Partial Pressure of Carbon Dioxide: ~0.3 mmHg

What are the partial pressures of O2 and CO2 in the arteries? Veins? By how much do they change at the capillaries?

• Systemic Arteries:

  • O2= 100 mmHg

  • CO2= 40 mmHg

• Systemic Veins:

  • O2= 40 mmHg

  • CO2= 46 mmHg

• Net Capillary Shift:

  • O2 drops by 60 mmHg (leaves blood).

  • CO2 rises by 6 mmHg (enters blood).

How does hyperventilation affect partial pressure of O2 and CO2 in the alveoli Hypoventilation?

—Alveolar PCO2: ⬇ Decreases significantly (drops below 40 mmHg)

—Alveolar PO2: ⬆ Increases slightly (climbs toward ~120–140 mmHg)

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—Alveolar PCO2: ⬆ Increases significantly (rises above 40 mmHg).

—Alveolar PO2: ⬇ Decreases significantly (drops below 100 mmHg).

What is hemoglobin? What is a heme made of? What molecules can heme bind to?

• Hemoglobin: Protein with 4 globin chains, each holding 1 heme group.

• Heme Composition: Made of a central Iron ion encased in a carbon/nitrogen porphyrin ring.

• Heme Binds directly to:

  1. O2

  2. CO

  3. NO (Nitric oxide)

Describe how the brain regulates respiration.

Primarily through the brainstem (the medulla oblongata and pons), which drives involuntary breathing

Describe how hemoglobin increases the oxygen carrying capacity of blood

Binding oxygen molecules to iron-containing heme groups inside red blood cells

How much O2 is bound to hemoglobin relative (percentage) to the plasma?

-98.5% of total O2

-Plasma 1.5% of total O2

Explain how hemoglobin affect the overall O2 available in the blood.

Hemoglobin drastically increases the total oxygen available in the blood by acting as an enormous biochemical reservoir.

What are variables that can affect how Hemoglobin’s affinity to O2? What is anemia (different from being anemic)?

• Carbon Dioxide : An increase in local CO2 shifts the curve to the right (decreasing affinity) by binding directly to the globin chains.

• Acidity / pH (The Bohr Effect): An increase in hydrogen ions which drops pH shifts the curve to the right (decreasing affinity).

• Temperature: An increase in temperature shifts the curve to the right (decreasing affinity) because thermal energy physically disrupts the bond between oxygen and the heme group.

• 2,3-Bisphosphoglycerate (2,3-BPG): This metabolic byproduct is produced by red blood cells under low-oxygen conditions. Increased 2,3-BPG binds to hemoglobin (decreasing affinity).

During normal breathing, is this a voluntary or involuntary motor response? Elevated

(exercise) breathing?

• Normal Breathing: Strictly Involuntary.

• Exercise Breathing: Primarily Involuntary. Driven by metabolic demands. Chemoreceptors detect rising CO₂ and acid, automatically forcing the brain stem to speed up breathing

What are the two main components of the medullary respiratory center? Where is

this found in the brain? What do each group do?

Located inside the medulla oblongata

1. Dorsal Respiratory Group (DRG): Controls normal, quiet inspiration.

2. Ventral Respiratory Group (VRG): Controls forced or maximal breathing (exercise, coughing).

Where are the apneustic and pneumotaxic center found? What do they modulate?

Located inside the pons, they act as a fine-tuning system that coordinates and smooths out the transitions between breathing in and breathing out.

Where are the chemoreceptors found in the circulatory system that detect CO2 concentration?

1. Peripheral Chemoreceptors (In the blood vessels)

2. Central Chemoreceptors (In the brain)

What happens when partial pressure of O2 is low?

A condition known as hypoxia—the body triggers a coordinated chain of neural, chemical, and physical responses to protect vital organs and restore oxygen delivery

What happens when Arterial pressure of O2 is low? Increase of non-CO2 acids?

Cells do not get enough oxygen to produce energy through normal aerobic metabolism,

Leads to an increase in non-CO2 acids—specifically lactic acid (lactic acidosis)

What are the five general functions of the kidney? How does an increase of water affect blood osmolarity?

Waste excretion, fluid balance regulation, electrolyte balance, blood pressure regulation, and hormone production

How does an increase in sodium affect blood osmolarity? What is the set point of blood osmolarity?

-275-295mOsm/L

-Increases blood osmolarity, raising the concentration of solutes in your bloodstream.

Describe how the plasma is turned into filtrate

-Glomerular filtration.

-Occurs within the renal corpuscle of the nephron by using high blood pressure to force water and small solutes through a three-layered physical sieve.

At the glomerulus, how does the blood become filtered? What leaves the blood?

Which regions does the fluid enter? Which tube does the filtered fluid enter?

What happens at that location to the fluid?

-Glomerular filtration, Water, glucose, amino acids, vitamins, urea, uric acid, and electrolytes

-Bowman’s capsule (the cup-like sack surrounding the glomerulus) > proximal convoluted tubule (PCT)

-The PCT responsible for massive tubular reabsorption. In this location, the cells lining the tube immediately go to work to salvage valuable nutrients before they can be lost in urine

What is the difference between a cortical and juxtamedullary nephron? Where are the juxtamedullary apparatus located?

-Their location in the kidney and the length of their loops of Henle,(Jux being longer) which dictates how effectively they can concentrate urine.

-At the point of contact between the afferent arteriole and the distal convoluted tubule of the very same nephron.

Describe the differences between: a) Glomerular filtration, b) Tubular secretion, c) Tubular reabsorption, d) Urine excretion. Where does each occur?

Formula: Excretion = Filtration – Reabsorption + Secretion

• 1. Glomerular Filtration

  • Direction: Blood to Nephron Lumen

  • Location: Renal Corpuscle (Glomerulus to Bowman’s Capsule)

  • Core Action: Blood pressure pushes water and small solutes out; filters out cells and large proteins.

• 2. Tubular Reabsorption

  • Direction: Nephron Lumen to Blood

  • Location: Entire tubule (predominantly the Proximal Convoluted Tubule)

  • Core Action: Selective reclamation of valuable water, nutrients, and electrolytes back into circulation.

• 3. Tubular Secretion

  • Direction: Blood to Nephron Lumen

  • Location: Mainly Proximal Convoluted Tubule, Distal Convoluted Tubule, and Collecting Duct

  • Core Action: Active transport backup to intentionally dump extra toxins, drugs, hydrogen ions, and potassium into the urine.

• 4. Urine Excretion

  • Direction: Nephron to Out of Body

  • Location: Exits Collecting Ducts to Renal Pelvis, Ureters, Bladder, and Urethra

  • Core Action: Elimination of the finalized urine waste fluid from the body.

On average, how much water is filtered at the glomerulus in one day? How much of the water filtered is reabsorbed at the tubules? Sodium? Glucose? Urea?

-180L per day

-Water=180L / 178.5L

-Na+=25,200mEq / 25,000mEq

-Glucose=180g / 180g

-Urea=50g / 25g

Describe how products in the filtrate are reabsorbed and secreted at the tubules

The cells lining the renal tubules use a mix of active (energy-requiring) and passive (concentration-driven) transport to move substances between the filtrate (tubule lumen) and the blood (peritubular capillaries).

What is primary and secondary transport? Which cost energy (ATP)?

Primary transport uses energy source directly, while secondary transport relies on an established concentration gradient created by primary transport.

-Primary Active Transport

Describe the organization of the tubular epithelium

The renal tubule wall is made of a single layer of epithelial cells resting on a basement membrane. This barrier separates the filtrate inside the tubule lumen from the interstitial fluid and blood vessels outside.

What is co-transportation? How does sodium typically play a role in this? What type of diffusion does this permit?

-A form of secondary active transport where a membrane protein moves two or more different substances in the same direction across a cell membrane at the same time.

-Serves as the primary power source for co-transportation allows for Secondary Active Transport (specifically carrier-mediated transport)

What is Transport Maximum (Tm)? How does the condition glucosuria apply to Tm?

-The maximum rate (measured in mg/min) at which a specific solute can be actively reabsorbed or secreted by the renal tubules.

-Once the Tm is crossed, the excess glucose cannot be reabsorbed. It remains in the tubule fluid and is excreted in the urine, a condition called glucosuria (commonly seen in uncontrolled diabetes mellitus).

How are ions like potassium and hydrogen secreted from the blood into the tubules? What other products are secreted from the blood into the tubules?

-Sodium-hydrogen antiporters (counter-transport), and in the distal tubule/collecting duct by primary active transport ATP pumps

-The sodium-potassium pump moves K+ from the blood into the tubule cell, and K+ then leaks down its gradient into the filtrate through specialized ion channels

-Metabolic Wastes, Organic Ions, Exogenous Chemicals (Foreign substances)

What is the concept “division of labor”? How are absorption and filtration rates controlled? Why must the GFR remain high?

-Different anatomical regions of the nephron are specialized to perform distinct tasks rather than the entire tubule doing the same job.

-Filtration Rate (GFR) Control: Regulated by adjusting the diameter of the afferent and efferent arterioles to alter glomerular blood pressure. High GFR means the body's entire blood plasma volume is filtered and cleaned

-Absorption Rate Control: Regulated primarily in the distal nephron by hormones that change membrane permeability.

What is the general equation of renal clearance? What is the “normal” renal clearance of glucose?

• Formula: C = (U x V) / P

  • C = Clearance rate of a specific substance (mL/min)

  • U = Concentration of the substance in urine (mg/mL)

  • V = Urine flow rate (mL/min)

  • P = Concentration of the substance in blood plasma (mg/mL)

• 0 mL/min, In a healthy individual, 100% of the filtered glucose is actively reabsorbed by the proximal convoluted tubule back into the bloodstream.

What is inulin? What property of inulin at the tubules is important in determining renal clearance, thus GFR?

-A naturally occurring carbohydrate plant polysaccharide (fructose polymer) that is not synthesized or broken down by the human body. It must be infused intravenously to be used in renal function tests.

-Because 100% of the inulin that enters the filtrate ends up exactly in the final urine, its renal clearance rate is mathematically identical to the Glomerular Filtration Rate (GFR). Tubule cells lack any transport proteins to reclaim it, and possess no mechanisms to pump more of it in.

Describe the process of micturition

-The physical process of emptying the urinary bladder.

• Phase 1: Bladder Filling and Detection

  • Urine continuously drains into the bladder @ 150 to 200 mL of urine, stretch receptors in the wall are activated, sending sensory nerve impulses up the spinal cord.

  • Phase 2: The Involuntary Reflex (Spinal Cord)

  • The spinal reflex arcs back to cause the detrusor muscle to rhythmically contract and the involuntary internal urethral sphincter (smooth muscle at the bladder neck) relaxes and opens.

• Phase 3: Voluntary Brain Regulation

  • The brain recognizes the urge to urinate.

  • If the timing is inappropriate, the cerebral cortex sends inhibitory signals to keep the external urethral sphincter tightly closed.

  • When ready to urinate, the brain stops these inhibitory signals, allowing voluntary relaxation of the external urethral sphincter. The detrusor muscle contracts with full force, and urine is pushed out of the body through the urethra.

After the urine leaves the collect ducts, how does it travel to the urinary bladder?

-Peristalsis: The walls of the ureters contain smooth muscle that contracts in rhythmic, wave-like motions (peristalsis) to actively pump urine into the bladder.

1. Minor and Major Calyces: The fluid drains into small cup-like structures (minor calyces) which merge into larger ones (major calyces).

2. Renal Pelvis: The major calyces funnel the urine into a single, large funnel-shaped cavity called the renal pelvis.

3. Ureters: The renal pelvis narrows into the ureter, a long, slender muscular tube that drops down to connect to the posterior wall of the urinary bladder.

What are the three muscles that help control micturition?

1. Detrusor Muscle

2. Internal Urethral Sphincter

3. External Urethral Sphincter

As the bladder fills with urine, which receptors relay information to the CNS?

-Mechanoreceptors

(specifically called stretch receptors).

• Embedded deep within the muscular wall (detrusor muscle) and the mucosal lining of the urinary bladder.

Describe how both divisions of the autonomic nervous system (sympathetic and parasympathetic), and the somatic nervous system are all (3 divisions) needed to complete micturition once the bladder is full.

Completing micturition requires a coordinated shift from the storage phase (sympathetic dominance) to the emptying phase (parasympathetic and somatic activation).

Describe the basic regulation of ions and water.

-The body maintains water and ion homeostasis by matching intake (diet) with output (primarily renal excretion) through negative feedback loops that monitor blood osmolarity and blood volume

What is insensible water loss? What are other losses of water experienced by the body?

-Water loss that occurs continuously and automatically without a person consciously noticing or feeling it. It cannot be easily measured or regulated by the body.

-Sweat, Feces

Lungs (Respiration): Water vapor lost as dry air is inhaled, humidified by the respiratory tract, and exhaled out of the body.

Skin (Evaporation): Water diffusing directly through the skin cells and evaporating, completely separate from active sweating.

What is the average intake of water in an adult per day? Output? Sources?

Total Intake must equal Total Output to maintain homeostasis, typically averaging around 2,500 mL (2.5 liters) per day.

• Ingested Liquids, Moisture in Food, Metabolic Water

On average, how much sodium chloride should we be intaking? Sources of output?

-2,300 mg of sodium per day

-Sweat, Feces, Urine

Describe the reabsorption mechanism of sodium in the proximal tubule cells.

The PCT reabsorbs roughly 65% of all filtered sodium. This movement occurs across two distinct cellular boundaries and is entirely powered by cellular energy.

Describe what products are co-transported with sodium.

Glucose, Amino Acids, Phosphate Ions, Lactate and Pyruvate, Water-Soluble Vitamins, Chloride and Potassium

How is the cotransport of products (example: glucose) facilitated in the cells?

The cell acts like a waterwheel, using a constant downhill flow of sodium to drag other passengers (like glucose or amino acids) uphill into the cell.

How is the Sodium gradient maintained in the cells. Where is energy used in this system?

Maintained by the Sodium-Potassium ATPase pump. Energy is consumed directly and exclusively at the basolateral Na+/K+ pump through Primary Active Transport

Describe sodium and chlorine exchange in the loop of Henle (ascending limb)

The thick ascending limb reabsorbs about 25% of filtered sodium and chloride. Unlike other parts of the nephron, this region is completely impermeable to water, allowing it to pump out salt while leaving water behind

Describe what products are co-transported with sodium.

In the Proximal Convoluted Tubule (PCT):

• Glucose

• Amino Acids

• Phosphate Ions

• Vitamins

In the Thick Ascending Limb of the Loop of Henle:

• Chloride and Potassium

In the Distal Convoluted Tubule (DCT):

• Chloride

How is the cotransport of chlorine facilitated in the cells?

Is driven indirectly by the energy of the basolateral Sodium-Potassium pump. By pairing negatively charged chloride with positively charged sodium, the cell maintains electrical balance while reclaiming salt.

Describe sodium and potassium exchange in the cortical collecting duct cells

The exchange happens exclusively in Principal cells, which make up the majority of the epithelial lining in the cortical collecting duct.

• 1. Set up the Cell: A pump on the back wall of the cell uses energy to throw sodium out into the blood and pull potassium inside. This leaves the cell empty of sodium but packed with potassium.

• 2. Reabsorb Sodium: Sodium from the urine slides into the empty cell through front-door channels (ENaC).

• 3. Secret Potassium: Because positive sodium just left the urine, it creates a negative pull that sucks potassium out of the packed cell and into the urine through exit channels (ROMK)

How is the cotransport of potassium facilitated in the cells?

This specific co-transport occurs across the apical membrane of epithelial cells in the Thick Ascending Limb of the Loop of Henle.

Describe water reabsorption in the tubules

by osmosis (passive transport). It follows the osmotic gradient created by the active pumping of solutes, particularly sodium. Water slips through the cell membranes via specialized channel proteins called aquaporins.

How does water move into the blood? How is it transported? To what affect?

-Water is drawn into the peritubular capillaries and vasa recta via bulk flow, driven by Starling forces physical and osmotic pressures that govern the movement of fluid across capillary walls between the bloodstream and the surrounding tissue.

-Crosses the capillary walls passively through specialized water channels called Aquaporin-1 proteins and through the tiny slits between the endothelial capillary cells

-Regulates Blood Volume and Pressure, Restores Blood Osmolarity

What are aquaporins? What roles do they play?

Aquaporins are a family of specialized, pore-forming membrane proteins that act as "plumbing systems" for cells, allowing water molecules to flow through cell membranes rapidly in single file while blocking ions and other solutes.

How does vasopressin (ADH) affect aquaporins?

Vasopressin (also known as Antidiuretic Hormone or ADH) controls water reabsorption in the kidneys by regulating water channels called aquaporins (specifically AQP2 in the renal collecting ducts)

Describe the countercurrent multiplier system

The mechanism the kidneys use to create a hyperosmotic (highly concentrated) medullary interstitium, which allows the body to excrete concentrated urine and conserve water. This process occurs entirely within the Loop of Henle of juxtamedullary nephrons

What is obligatory water loss? What does it mean that the urine is concentrated? Hypoosmotic?

-The minimum volume of urine the kidneys must excrete each day to rid the body of metabolic waste products and ingested toxins

-When urine is concentrated (hyperosmotic), it means the urine contains a high amount of solutes and a low amount of water.

-When urine is hypoosmotic (dilute), it means the urine contains a low amount of solutes and a high amount of water.

How does the loop of Henle function? What regions (limbs) reabsorb water? NaCl?

-Establish a hyperosmotic vertical gradient in the renal medulla, which allows the kidney to concentrate or dilute urine as needed. It does this by selectively separating water reabsorption from solute reabsorption across its different anatomical segments.

-Descending Limb (Thin Descending Limb)

• Reabsorbs: Water only.

-Ascending Limb (Thin & Thick Ascending Limbs)

Reabsorbs: NaCl only

What is the osmolarity of the filtrate at the vasa recta? What does this osmolarity gradient achieve in the medulla? Why is this gradient crucial for urine concentration?

1. Vasa Recta Blood: Ranges from 300 > 1200 > 325 mOsm/L, passively matching the tissue to preserve the gradient without washing it out.

2. Medullary Gradient Achieves: A hyperosmotic tissue environment composed of concentrated NaCl and urea.

3. Crucial Role: Acts as the osmotic engine that pulls water out of the collecting ducts via aquaporins, concentrating urine up to 1200 mOsm/L.

Describe the countercurrent multiplier system

the mechanism the kidneys use to create a hyperosmotic (highly concentrated) vertical gradient in the renal medullary interstitium. This gradient is what ultimately allows the body to excrete concentrated urine and conserve water

Describe the responses of the feedback loop stimulated with increase in sodium and water loss?

It triggers a coordinated negative feedback loop to restore blood volume, maintain blood pressure, and conserve remaining fluid and electrolytes.

This system primarily acts through two major neurohormonal axes: the Renin-Angiotensin-Aldosterone System (RAAS) and Vasopressin (ADH) secretion.

Describe the responses of the feedback loop stimulated with renin stimulation. Also called RAS-system

The Renin-Angiotensin-Aldosterone System (RAAS)—is a highly coordinated hormonal negative feedback loop designed to regulate blood volume, arterial blood pressure, and systemic sodium balance.

When the kidneys release renin, it sets off a chemical cascade that alters systemic vascular resistance and renal transport mechanisms to restore homeostasis.

How does the osmolarity of the filtrate change as it moves through the tubules

1. Entering the Loop (~300 mOsm/L)

2. Moving Down the Descending Limb (300 > 1200 mOsm/L)

3. Moving Up the Ascending Limb (1200> 100 mOsm/L)

4. Exiting the Loop (~100 mOsm/L):