Module 4: Renal PHGY Flashcards
how is homeostasis in the renal sys controlled
- Controlled by the kidneys
- Responsible for regulation of electrolyte composition, volume, osmolarity, and ph.
- Kidneys work to eliminate all the waste products from bodily metabolism with the exception of carbon dioxide removed via respiration
Describe the major structures of a juxtamedullary nephron and discuss the importance of each section with respect to reabsorption and secretion
- Renal Corpuscle: Filters blood and collects filtrate
- Proximal Convoluted Tubule (PCT): Reabsorbs essential substances like glucose and ions, and secretes waste products
- Loop of Henle: Establishes concentration gradient in the medulla, enabling water reabsorption
- Distal Convoluted Tubule (DCT): fine-tunes reabsorption and secretion processes initiated earlier
- Collecting duct: Responds to hormones to regulate water reabsorption and urine concentration, and maintains acid-base balance
Describe blood flow through the kidneys and its physiological importance in the generation of urine
Blood Flow:
1. Renal Artery Entry: Oxygenated blood enters each kidney through the renal artery.
2. Afferent Arterioles: Branch off the renal artery to form the glomerular capillaries within the renal corpuscle.
3. Glomerular Filtration: Blood pressure forces fluid and solutes from the glomerular capillaries into Bowman’s capsule, forming filtrate.
4. Efferent Arterioles: Carry blood away from the glomerulus, leading to two pathways:
- Peritubular Capillaries: Surround the renal tubules for reabsorption and secretion.
- Vasa Recta: Form long, hairpin-like capillaries around the loop of Henle, maintaining osmotic gradient in the medulla.
5. Renal Vein Exit: Filtered blood exits the kidney via the renal vein, carrying reabsorbed substances and wastes.
6. Urine Formation: Filtrate undergoes reabsorption (essential substances reclaimed) and secretion (additional substances added) throughout the nephron, resulting in concentrated urine.
Importance:
- Filtration: Removes waste products and excess substances from the blood, maintaining internal environment balance.
- Reabsorption: Retrieves essential substances like glucose, ions, and water, conserving body resources.
- Secretion: Excretes waste products and regulates electrolyte and acid-base balance.
- Concentration Gradient: Establishes osmotic gradient in the medulla, crucial for water reabsorption and concentration of urine.
- Blood Pressure Regulation: Renin-angiotensin-aldosterone system and other mechanisms adjust blood volume and pressure.
Using your knowledge of osmotic gradients, describe how the kidney can make urine either more dilute or more concentrated than other bodily fluids
The kidney regulates urine concentration through osmotic gradients. By adjusting the reabsorption of water and solutes along the renal tubules, it can produce urine that is either more dilute or more concentrated than other bodily fluids. This process involves creating and maintaining osmotic gradients in the renal medulla, primarily through countercurrent mechanisms in the loop of Henle. Hormonal regulation, such as antidiuretic hormone (ADH), also plays a crucial role in modulating water reabsorption and urine concentration. Overall, the kidney’s ability to manipulate osmotic gradients allows for precise control of urine concentration, essential for maintaining fluid and electrolyte balance in the body.
Using dehydration as an example, describe the physiological responses and processes that occur in order to reduce water loss through urine production
- Dehydration Detection:
Osmoreceptors and baroreceptors detect decreased blood volume and increased osmolality. - Release of ADH:
Hypothalamus signals pituitary gland to release ADH into bloodstream. - Increased Water Reabsorption:
ADH increases collecting duct permeability, promoting water reabsorption.
Aquaporin channels facilitate water movement from ducts to interstitium. - Concentration of Urine:
Reabsorbed water reduces urine volume, making it more concentrated.
Helps conserve water in the body. - Thirst Mechanism Activation:
Dehydration triggers thirst, prompting fluid intake. - RAAS Activation:
Renin-Angiotensin-Aldosterone System may activate to enhance sodium and water retention.
Importance:
Maintains fluid balance, blood pressure, and electrolyte levels during dehydration, aiding overall homeostasis.
Identify the major fluid compartments and describe how they are interrelated
Fluid within cells, constituting about 2/3 of total body water.
Contains electrolytes, proteins, and other solutes necessary for cellular function.
Extracellular Fluid (ECF):
Fluid outside cells, comprising interstitial fluid, plasma, and transcellular fluid.
Interstitial fluid: Surrounds cells, exchanges nutrients and waste with blood.
Plasma: Fluid portion of blood, carries nutrients, hormones, and waste products.
Transcellular fluid: Small, specialized compartments like cerebrospinal fluid, synovial fluid, and digestive juices.
Fluid Movement: Exchange occurs between compartments via osmosis, diffusion, and active transport.
Homeostasis: Fluid balance is maintained through intricate regulatory mechanisms.
Blood Pressure Regulation: ECF volume influences blood pressure, impacting fluid movement between compartments.
Nutrient Distribution: Plasma transports nutrients to cells, while waste products are removed via interstitial fluid.
Cellular Function: ICF provides the environment for cellular metabolism and signaling.
Osmotic Regulation: Electrolyte concentrations in ECF and ICF are regulated to prevent osmotic imbalances.
Hormonal Control: Hormones like ADH and aldosterone regulate fluid balance by affecting water reabsorption in the kidneys.
Compare and contrast short-term vs long-term control of the extracellular fluid
Short-term Control:
Rapid Response: Acts within minutes to hours.
Mechanisms:
Neural Regulation: Baroreceptors in blood vessels detect changes in blood pressure, signaling the nervous system to adjust.
Hormonal Regulation: Rapid release of hormones like ADH (vasopressin) and aldosterone in response to changes in blood pressure or osmolality.
Effects:
ADH increases water reabsorption in the kidneys, reducing urine output and conserving water.
Aldosterone enhances sodium and water reabsorption, promoting blood volume and pressure.
Long-term Control:
Gradual Adjustment: Occurs over days to weeks.
Mechanisms:
Renal Regulation: Kidneys play a central role in long-term fluid balance through processes like reabsorption, secretion, and filtration.
Thirst Mechanism: Controlled by osmoreceptors in the hypothalamus, prompting fluid intake to restore hydration.
Effects:
Renal mechanisms adjust over time to maintain fluid and electrolyte balance.
Thirst mechanism prompts increased fluid intake to replenish lost fluids and restore homeostasis.
Describe the differences between isotonic, hypertonic, and hypotonic, and how cells in each of these solutions would be affected
Isotonic:
Same solute concentration as cell cytoplasm.
No net water movement.
Cells maintain normal shape and volume.
Hypertonic:
Higher solute concentration than cell cytoplasm.
Water moves out of cells.
Cells shrink or undergo crenation/plasmolysis.
Hypotonic:
Lower solute concentration than cell cytoplasm.
Water moves into cells.
Cells swell or undergo lysis/turgor pressure.
Effects on Cells:
Isotonic: No change.
Hypertonic: Cells shrink.
Hypotonic: Cells swell.
Describe the pathways involved in the regulation of water balance in terms of intake and output
Intake Pathways:
Thirst Mechanism:
Triggered by increased plasma osmolality or decreased blood volume.
Stimulates the sensation of thirst, prompting individuals to drink fluids to restore hydration.
Regulated by osmoreceptors in the hypothalamus.
Output Pathways:
Renal Regulation:
Filtration: Blood is filtered in the kidneys, producing urine.
Reabsorption: Essential substances like water, ions, and nutrients are reabsorbed from the filtrate back into the bloodstream.
Secretion: Additional substances, such as waste products and excess ions, are secreted from the bloodstream into the filtrate for excretion.
Hormonal Regulation:
Antidiuretic Hormone (ADH):
Released by the pituitary gland in response to dehydration or increased plasma osmolality.
Increases water reabsorption in the kidneys, reducing urine output and conserving water.
Aldosterone:
Released by the adrenal glands in response to low blood pressure or low blood volume.
Enhances sodium reabsorption in the kidneys, indirectly affecting water reabsorption and blood volume.
Thirst Mechanism:
Regulates fluid intake in response to changes in fluid output and hydration status.
ICF
Intracellular Fluid
Fluid within cells
Comprises 2/3rds of total body fluid
ECF
Extracellular Fluid
Fluid surrounding the cells (plasma, interstitial fluid, lymph, and transcellular fluid
Comprises 1/3rd of total body fluid
what do barriers btwn body-fluid compartments do
They limit the movement of water and solutes between the various compartments
plasma-interstitial fluid
Separated by the blood vessel wall
Plasma and interstitial fluid are identical (except plasma proteins)
2 barriers btwn bodu-fluid compartments
- plasma-interstitial fluid
- ICF and ECF
- plasma membrane barrier
- intracellular contains proteins that do not exchange with extracellular
- greater [c] of K+ in ICF
- greater [c] of Na+ in ECF
overall umbrella def for ECF volume and osmolarity
Overall control of fluid balance is dependent upon regulating the ECF
ECF volume
is closely regulated to maintain blood pressure (salt-balance is important for long-term regulation)
ECF Osmolarity
is closely regulated to prevent swelling and shrinkage of cells
To maintain fluid balance, the extracellular volume and osmolarity is regulated closely
Short-term ECF volume control
- Only temporary and can compensate for fairly minor changes in ECF volumes
- Baroreceptor reflex
- Fluid shifts
baroreceptor reflex
Baroreceptor Reflex is mechanoreceptors that are located in the carotid artery and the aortic arch, and they detect changes in arterial blood pressure, the autonomic NS then affects the heart and blood vessels
The baroreceptor reflex regulates blood pressure
When pressure falls too low, cardiac output and total peripheral resistance will increase to raise blood pressure
When blood pressure rises above normal, both decrease to reduce blood pressure
Fluid Shifts
a decrease in plasma volume can temporarily be compensated for by a shift of the fluids out of interstitial compartment to the plasma, the opposite is also true, as an increase in plasma volume can cause fluid to shift to the interstitial compartment
Long term ECF volume control
Kidneys and thirst mechanism (control of urine output)
Describe the Control of Salt
1) describe sodium and how it is controlled
Sodium, and the anions that are associated with it (mainly chloride) accounts for more than 90% of the ECF’s solutes
When salt is transported across a membrane, water follows due to osmosis
Control salt=ECF volume is controlled
To maintain salt balance (salt input=salt output)
describe salt input
is dependent on dietary salt, replace salt loss through feces and sweat (0.5g/day)
describe salt output
excess salt must be eliminated (feces, sweat and kidneys)
describe hypotonicity + causes
Associated with overhydration, or excess of free H20
Causes
Renal Failure (can’t produce concentrated urine)
Rapid water ingestion (kidneys can’t deal with it quick enough)
Over secretion of vasopressin (promotes water retention)
describe hypertonicity and causes
Associated with dehydration
Causes
Insufficient water intake, not drinking enough
Diabetes insipidus, vasopressin deficiency
Excessive water loss from exercise, vomiting, or diarrhoea
describe isotonic
- Has an equal osmolarity to that of normal body fluids
- Isotonic fluids are injected into blood plasma within the veins (1/5th of ECF)
- When isotonic fluids are injected into the ECF compartments, the ECF volume increases, but the concentration of the ECF remains unchanged (remains isotonic)
- There will be no fluid shift between compartments because ECF and ICF are still in osmotic equilibrium (cells would not shrink nor swell)
- Isotonic fluid loss, is confined to the ECF, with no corresponding fluid loss from the ICF.
Regulation of Water Balance (describe this)
- Hypothalamus, near the vasopressin-secreting cells and thirst centre, there is hypothalamic osmoreceptors (which monitor osmolality of fluid around them)
- If osmolality increases, so does vasopressin secretion and thirst
- Vasopressin acts on the kidneys to increase water reabsorption
Thirst stimulates the intake of water - If it becomes hypotonic, then vasopressin secretion and thirst are not stimulated.
- Large losses of ECF volume also impact these pathways (Left atrial volume receptors) monitor pressure of blood in left atrium, they are activated with more than 7% loss of ECF volume and blood pressure, they also stimulate vasopressin and thirst
describe the roles of the kidneys
Filtration: Removes waste products, toxins, and excess ions from the bloodstream.
Fluid and Electrolyte Balance: Regulates body fluid volume and composition by reabsorbing water and electrolytes.
Excretion of Waste: Eliminates waste products like urea, creatinine, and uric acid through urine.
Acid-Base Balance: Maintains pH levels by excreting or retaining hydrogen and bicarbonate ions.
Hormone Production:
Renin: Regulates blood pressure.
Erythropoietin (EPO): Stimulates red blood cell production.
Calcitriol (Active Vitamin D): Regulates calcium and phosphate levels.
Blood Pressure Regulation: Controls blood volume and vascular resistance to maintain optimal blood pressure.
describe the major structural components of a nephron
Renal Corpuscle:
Glomerulus: Network of capillaries where blood filtration occurs.
Bowman’s Capsule: Surrounds the glomerulus, collecting filtrate from blood.
Renal Tubule:
Proximal Convoluted Tubule (PCT): Initial segment for reabsorption and secretion.
Loop of Henle: Descending and ascending limbs involved in water and ion reabsorption.
Distal Convoluted Tubule (DCT): Fine-tunes reabsorption and secretion processes.
Collecting Duct: Collects tubular fluid from multiple nephrons, regulates water reabsorption.
describe the basic renal processes involved in urine excretion
Filtration:
Occurs in the renal corpuscle.
Blood pressure forces fluid and solutes from the glomerulus into Bowman’s capsule, forming filtrate.
Reabsorption:
Takes place in the renal tubules.
Essential substances like water, ions, and nutrients are reabsorbed from the tubular fluid back into the bloodstream.
Proximal Convoluted Tubule (PCT) is a major site for reabsorption.
Secretion:
Occurs in the renal tubules.
Additional substances, such as waste products and excess ions, are actively transported from the bloodstream into the tubular fluid for excretion.
Distal Convoluted Tubule (DCT) and collecting ducts are involved in secretion.
Concentration:
Involves the loop of Henle and collecting ducts.
Establishes a concentration gradient in the medulla, allowing for water reabsorption and concentration of urine.
Hypothalamus regulates water reabsorption via Antidiuretic Hormone (ADH).
Excretion:
Final step where urine is excreted from the body.
Urine, containing waste products and excess substances, exits the kidneys via the ureters, bladder, and urethra.
The kidneys are controlled by…
Both neural and endocrine inputs
functions of the kidneys
Maintain water balance in the body
Maintain body fluid osmolarity
Maintain proper plasma volume
Help maintain acid-base balance
Regulates ECF solutes (NA, K, Cl, Ca, PO4)
Excretes wastes of metabolism
Excretes foreign compounds ingested
Produces erythropoietin
Produces renin
Activated Vitamin D
describe the structure of the kidney
Bean shaped organ
10cm in length
An adrenal gland on top of the kidney
Outside of the kidney is the renal cortex
Inner part is renal medulla
Renal pelvis is at the core of the kidney (urine empties)
Urine channeled to the ureter
Functional unit of the kidney is the nephron (blood is filtered to produce urine and reabsorb fluids and molecules
describe the vascular component of the nephron
- Glomerulus (ball-like capillary), is where water and solutes are filtered from plasma
- Blood enters the kidney via the renal artery, and this subdivides into afferent arterioles (each supplies a nephron)
- Leaving the nephron are efferent arterioles, which transport unfiltered blood from the glomerulus (arterial blood enters and leaves with no oxygen extracted)
- Capillaries of the nephron, efferent arterioles subdivide into capillaries, the peritubular capillaries deliver oxygen to renal tissues
describe the tubular component of the nephron
(Begins with) Bowmans capsule, encircles the glomerulus to collect filtered fluid
Fluid then passes into the proximal tubule within the renal cortex
Loop of Henle forms a hairpin loop that dips down into the renal medulla
The descending limb of loop of Henle travels from the cortex to the medulla back to the cortex
Ascending limb of loop of Henle passes through a fork of the afferent and efferent arteries in a region called juxtaglomerular apparatus.
Tubule coils again and is called the distal tubule (within the cortex)
The distal tubule empties into a collecting duct, which travels deep into the medulla and drains in the renal pelvis
what are the 2 types of nephrons
- Cortical Nephrons- lie in the outer layer of the cortex (secretory and regulatory functions)
- Juxtamedullary Nephrons - inner layer of cortex (concentration and dilution of urine function) and they form hairpin loops called vasa recta
What is glomerular filtration (GF)
20% of blood flowing through the glomerular capsule is foltered in Bowmans capsule
what is tubular reabsorption (TR)
As filtrate flows through the tubules, important substances are returned to the peritubular capillaries by the process of tubular reabsorption
Tubular Secretion (TS)
Second route for substances in the blood to enter renal tubules
Selective transfer of substances from the peritubular capillaries into the tubules (remaining 80%)
Describe the forces that regulate glomerular filtration
Hydrostatic Pressure in Glomerular Capillaries (PGC):
Blood pressure within the glomerular capillaries.
Forces fluid and solutes out of the blood into Bowman’s capsule.
Hydrostatic Pressure in Bowman’s Capsule (PBS):
Pressure exerted by the filtrate in Bowman’s capsule.
Opposes filtration by pushing fluid back into the capillaries.
Osmotic Pressure in Glomerular Capillaries (πGC):
Created by proteins (e.g., albumin) in the blood.
Draws water back into the capillaries, opposing filtration.
Filtration Pressure (Net Filtration Pressure, NFP):
NFP = PGC - (PBS + πGC).
Represents the overall pressure gradient driving filtration.
Positive NFP favors filtration, while negative NFP opposes it.
Describe how glomerular filtration is regulated by the body, both intrinsically and extrinsically
Intrinsic Regulation:
Myogenic Mechanism:
Description: Autoregulatory response to changes in blood pressure.
Process: Increased blood pressure stretches afferent arterioles, triggering smooth muscle contraction and vasoconstriction to maintain a steady glomerular filtration rate (GFR).
Purpose: Protects glomeruli from damage due to excessive pressure.
Tubuloglomerular Feedback (TGF):
Description: Feedback mechanism involving the juxtaglomerular apparatus.
Process: Macula densa cells in the DCT sense changes in tubular fluid composition, particularly NaCl levels. Increased NaCl concentration triggers vasoconstriction of afferent arterioles, reducing GFR.
Purpose: Maintains a stable flow of filtrate to prevent electrolyte imbalances.
Extrinsic Regulation:
Sympathetic Nervous System (SNS):
Description: Neural regulation of renal blood flow.
Process: Activation of the SNS leads to vasoconstriction of both afferent and efferent arterioles, reducing GFR and renal blood flow.
Purpose: Redirects blood flow to vital organs during times of stress or low blood pressure.
Hormonal Regulation:
Description: Hormones control renal blood flow and GFR.
Example: Angiotensin II, released in response to low blood pressure or low sodium levels, constricts arterioles, increasing blood pressure and GFR.
Purpose: Maintains blood pressure and fluid balance.
