Renal Physiology Flashcards
What are the main renal functions?
Filtering waste
Balancing fluids
Regulating blood pressure
Managing acid-base levels
Supporting RBC production
How does the renal system filtrate waste?
Remove waste products - like urea and creatine and toxins from blood
Blood enters the kidney through the renal artery, where the nephron filters it removing these by products by cellular metabolism
The clean blood exits back into circulation while the waste forms urine
Why is the filtration critical?
As accumulating toxins can lead to systemic issues, affecting organ function and potentially leading to symptoms like confusion and weakness
How does the renal system sort out fluid balance?
By adjusting the amount of water reabsorbed or excreted kidneys maintain a delicate balance of bodily fluids, ensuring cell operate in an optimal environment
Hormones like antidiuretic hormone (ADH) signal kidneys to retain water during dehydration, while excess fluid prompts increased urination
Why is fluid balance essential?
In cases of dehydration or fluid overload, where imbalances can disrupt cell function, leading to potential cardiac or neurological complications
How does the renal system regulate blood pressure?
Through the renin-angiotensin-aldosterone system (RASS) kidneys detect changes in blood flow and secrete renin which triggers reactions that constrict blood vessels and increase fluid retention, thereby raising blood pressure
Why is BPR vital?
In shock and LPB cases, as it helps stabilise the patient through prolonged activation can lead to hypertension and renal strain
Why is acid-base balance essential?
Kidney’s regulate the body’s PH excreting hydrogen ions and reabsorbing bicarbonate ions
This buffer system ensures that blood pH remains in the narrow range of 7.35 - 7.45, preventing harmful shifts towards acidosis or alkalosis
Why is acid base balance crucial?
As deviations in pH impact enzymatic and metabolic functions. In conditions like DKA the kidneys response helps mitigate acid build-up
What happens during Erythropoiesis (RBC production)?
When O2 levels are low, kidneys release erythropoietin, a hormone that stimulates bone marrow to produce more RBC, this improving oxygen-carrying capacity
Why is Erythropoiesis important?
Important in CKD, where reduced erythropoietin levels can lead to anemia, impacting a patients energy levels and overall health
What are the components of the renal system?
Two kidneys
Two ureters
Bladder
Urethra
Working together for blood filtration and waste excretion
Kidney overview in the renal system
Bean shaped organs located either side of the spine, just below the rib cage
Act as the bodys natural filtration system filtrating around 180L of blood daily to remove waste and excess fluids
Each kidneys houses about a million nephrons, which are the functional units that process blood from urine
What are the Ureters within the renal system?
Narrow, muscular tubes (around 25-30cm long) that connect each kidneys to the bladder. Urine flows down the peristaltic waves, preventing backflow and allowing for the safe transport of urine to the bladder
The ureters are equipped with one-way valves where they enter the bladder, ensuring urine does not enter to the kidneys, which could lead to infection or kidney damage.
What is the bladder in the renal system?
A hollow, muscular organ located in the pelvis, serving as a temporary storage reservoir for urine. It can hold around 400-600ml of urine before signalling the need to urinate.
The bladders walls are lined with layers of muscle that stretch and contract
When full, sensory signals are sent to the brain prompting urge to urinate.
This functionality is essential for controlled and voluntary urination.
What is the Urethra in the renal system?
The tube expels urine from the bladder out of the body.
In males, it also carrier semen and is longer (around 20cm)
In females, is shorter (around 4cm) which makes females more susceptible to UTIs due to bacteria’s shorter travel distance
The urethra sphincter muscle controls urine release, preventing involuntary leakage and maintain continence
What is the renal cortex and medulla?
The outer later, or cortex, contains the glomeruli and is responsible for initial blood filtration.
The medulla, organised into pyramid-shaped regions, contains the tubules that modify the filtrate into urine.
What are the Nephron Units?
Each kidney contains about 1 million nephrons, which are the functional filtration units.
These nephrons filter blood, remove waste, and balance fluids and electrolytes through a series of filtration and reabsorption process
Each nephron has two main parts:
Renal corpuscle - for filtration
Renal tubule - for modification of filtrate
What is the blood supply in the kidney?
Blood flows into each kidney through the renal artery, which branches off from aorta.
Within the kidney, the artery further branches into smaller arterioles that deliver blood to the nephrons. After filtration, the blood exists via the renal vein, which connect to the inferior vena cava, returning clean blood to circulation
What is the structure of the nephron?
Each nephron consists of two main parts: the renal corpuscle and the renal tubule
What is the Renal Corpuscle?
Composed of the glomerulus (a network of capillaries) and Bowman’s capsule, which captures the filtrate that becomes urine.
Blood enters the glomerulus through the afferent arteriole, where pressure forces plasma out, filtering out large proteins and cells
What is the Renal Tubule?
- Includes the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.
Each segments play a role in selectively reabsorbing water, ions, and nutrients while excreting waste products. This process refines the initial filtrate into urine.
How is blood supplied to the nephron?
Blood enters via the afferent arteriole and is filtered in the glomerulus.
Post-filtration, the blood exits through the efferent arteriole and travels through the peritubular capillaries, allowing for reabsorption and secretion of various substances along the tubule.
What are Podocytes?
Specialised cells in Bowman’s capsule that wrap around capillaries of the glomerulus, forming filtration slits that control passes into the nephron.
Podocytes play a critical role in filtering plasma, ensuring only the correct substances enter the nephron.
What is the filtration begin?
The renal corpuscle is where filtration begins, and includes the Glomerulus (a bundle of capillaries) and a Bowman capsule.
The glomerulus is encompassed by renal cells from the bowman capsule, known as Podocytes
The renal tubule is comprised of a proximal convoluted tubule, the nephron loop and the distal convoluted tubule.
The renal tubule is surrounded by Tubular capillaries this allows for absorption and re-absorption to occur.
The proximal and distal convoluted tubule are tightly coiled to give the nephron an increased ability to process filtrate.
What is the Afferent Arteriole?
Carries unfiltered blood from the renal artery to the glomerulus. The pressure in this arteriole facilitates filtration as blood flows into the capillary bed.
What is the Glomerulus?
A network of tiny capillaries where initial filtration occurs.
Dur to high pressure, plasma filters out into Bowman’s capsule, while larger cells and proteins remain in the bloodstream.
What is Efferent and Peritubular Capillaries?
Blood leaves the glomerulus via the efferent arteriole, then flows through peritubular capillaries surrounding the nephron tubules.
Here, reabsorption of water, nutrients, and ions occurs before blood returns to circulation via the renal vein.
What is a Podocyte?
The cells within the Bowman’s capsule, that surround the glomerulus controlling what enters the nephron
What is the structure and function of a Podocyte?
Specialised cells with extensions that wrap around glomerular capillaries, forming a barrier with filtration slits.
These slits prevent large molecules, like proteins and blood cells from entering the filtrate
What are Podocytes role in filtration?
Adjust the size of the filtration slits in response to changes in blood pressure or kidney function, allowing for fine control of filtration.
Damage to podocytes can lead to proteinuria (urine in the protein), a sign of kidney dysfunction.
What is Glomerular Filtration Barrier?
Composed of fenestrated endothelial cells, the glomerular basement membrane, and the podocyte foot processes
What is the filtration process?
Substances in the blood are filtered based on their size, charge, and molecular weight, allowing water, ions, and small molecules to pass through
What is selective permeability?
The filtration barrier is selectively permeable, preventing the passage of larger molecules, such as proteins and maintaining the body’s fluid balance
What are the three main processes involved in the filtration of blood, ad the formation of urine?
- Filtration
- Selective reabsorption
- Secretion
What is the filtration process in regards to the blood and production of urine?
Blood enters the glomerulus under high pressure, forcing water, ions and small molecules through the filtration membrane into Bowman’s capsule
What is selective reabsorption in regards to the filtration of blood and production of urine?
As filtrate passes through the nephron tubules, essential substances like glucose, ions, and water are reabsorbed back into the bloodstream based on the body’s needs.
What is tubular secretion in regards to the filtration of blood and production of urine?
Final adjustments occur, where additional waste products (excess hydrogen or potassium for example) are secreted into the filtrate before it exists as urine
What is the pressure gradient in regards to filtration?
Filtration is driven by a pressure difference between the glomerulus and Bowman’s capsule.
Blood pressure within the glomerulus is relatively high, creating a pressure gradient that forces plasma through filtration barrier into Bowman’s capsule.
The gradient relies on the kidney’s receiving a significant portion of cardiac output, ensuring a continuous blood supply that maintains this pressure.
What is the definition of Glomerular Filtration Rate?
The volume of filtrate produced by both kidney’s each minute, a key indicator of renal function. GFR reflects how efficiently kidneys filter blood and is used to assess kidney health.
How is an estimated GFR tested?
Estimated based on blood tests (for example, creatinine levels) to evaluate kidney performance.
An abnormal eGFR suggests possible kidney dysfunction, which may require further investigation or intervention.
During selective reabsorption, what is the hormonal influence?
Hormones like aldosterone, and antidiuretic hormone (ADH) regulate reabsorption, adjusting BP and fluid balance.
ADH for example increases water reabsorption in dehydration
What does the hormone ADH do?
Increases water reabsorption in the distal tubule.
By increasing water reabsorption, ADH helps concentrate urine, reduce water loss and maintain BP.
When BP becomes too concentrated, ADH release increases to dilute it; conversely, when hydration levels are high, ADH secretion decreases.
What does the hormone ANP do? (Atrial Natriuretic Peptide)
Lowers BP by promoting sodium and water excretion.
By promoting sodium and water exception, ANP helps lower blood volume and BP acting as a natural diuretic
Particularly active in condition of high BP, serving to counterbalance the effects of ADH and aldosterone to prevent fluid overload.
What does the hormone Aldosterone do?
Boosts Na+ and water reabsorption, K+ excretion
By retaining sodium and water, aldosterone helps elevate blood volume and BP.
This hormone is active in situations where BP needs to be restored, such as during hypovolemia or low sodium states
What is the purpose of Tubular Secretion?
Crucial process that removes substances from the bloodstream that were not effectively filtered out in the glomerulus.
Some substances like drugs or excess ions pass quickly through the glomerulus and require additional filtering to be fully excreted.
This process allows the body to eliminate foreign materials, metabolic by-products and other excess substances.
What examples of Secreted Substances that may have to use tubular secretion?
Drugs
Hydrogen Ions
In relation to drugs that go through Tubular Secretion, why does this happen?
Many meds such as penicillin and aspirin, do not remain in the glomerulus long enough to complete filtration.
Through tubular secretion, these drugs are transferred from the blood into the filtrate within the convoluted tubules, enhancing their removal from the body.
In relation to Hydrogen Ions that go through Tubular Secretion, why does this happen?
Secretion of H+ ions is critical for pH regulation.
When blood becomes too acidic, kidneys secrete more H+ ions into the filtrate to restore acid-base balance.
Conversely, when blood pH is too high (alkaline) the kidneys reduce H+ secretion to retain more acid.
What is the mechanism of secretion of tubular secretion?
Process primarily occurs in the proximal and distal convoluted tubules where peritubular capillaries surrounding the tubules transfer unwanted substance into the tubule.
Specialised transport proteins actively move these substances into the filtrate, ensuring their elimination in urine.
What is tubular secretion role in waste management?
Tubular secretion allows the body to fine-tune the excretion of substances not fully removed by glomerular filtration
Its especially important in maintaining electrolyte and pH balance as well as in removing waste products and drugs that need further filtering after the initial filtration stage.
What is the autoregulation mechanism of autoregulation?
The kidneys have an intrinsic ability to regulate their own blood flow, independent of systemic blood pressure fluctuations.
This process, called autoregulation, ensures that renal blood flow and glomerular filtration remain stable across a systolic blood pressure range of 80-200mmHg
What is the Myogenic response?
When BP rises, the afferent arteriole (the artery bringing blood into the glomerulus) constricts to prevent excessive blood flow, protecting the delicate nephron structures from high pressure.
Conversely, when BP drops, the afferent arteriole dilates to maintain adequate blood flow and filtration
What is Tubuloglomerular feedback?
Specialised cells in the nephron, particularly in the juxtaglomerular apparatus, sense changes in filtrate flow and sodium levels.
If flow or sodium concentration drops, these cells trigger mechanisms to increase blood flow to the glomerulus, maintaining filtration.
When is autoregulation effective and when does it fail?
Autoregulation is effective only within a BP range of 80-200 mmHg.
When SBP falls below, 80mmHg, autoregulation fails, and blood flow to the kidneys decreases significantly.
This leads to reduced glomerular filtration, causing waste and toxins to accumulate in the bloodstream.
What can prolonged hypotension result in?
Acute Kidney Injury (AKI) due to ischemia (insufficient oxygen supply), as renal cells are highly sensitive to oxygen deprivation.
This condition can cause significant harm to the patient, leading to symptoms such as confusion, nausea, and fatigue due to toxin build up.
What does the juxtaglomerular complex help to do and what does it consist of?
Helps to regulate blood pressure and glomerular filtration rate (GFR).
It consists of macula densa cells, extraglomerular mesangial cells and juxtaglomerular cells.
What is the location and structure of the Juxtaglomerular Complex?
The JGC is found between the distal convoluted tubule and the afferent arteriole of each nephron.
It plays a crucial role in sensing and responding to changes in BP and sodium concentration, maintaining kidney function and overall BP stability.
What are the Macula Densa Cells?
These cells are located in the distal convoluted tubule, adjacent to the glomerulus.
They detect Na+ and Cl- levels in filtrate,
In states of hypovolemia or hypotension the cells sense reduce Na+ and Cl- levels.
They then send a signal to juxtaglomerular cells to initiate a response.
What are the Extraglomerular Mesangial Cells?
These cells act as intermediaries, relating the signal from the macula densa cells to the juxtaglomerular cells.
They serve as a ‘messenger system’ within the JGC, ensuring communication between the detection and response phases of blood pressure regulation.
What are the Juxtaglomerular Cells?
Located in the wall of the afferent arteriole, juxtaglomerular cells receive signals from the macula densa and extraglomerular mesangial cells.
They are responsible for monitoring BP direct and in response to low BP release the enzyme renin into the bloodstream.
What is renin release and function?
When BP drops, renin is released by the juxtaglomerular cells.
Renin initiates a chain reaction, known as the renin-angiotensin-aldosterone system (RAAS) to increase BP
What is Na+ reabsorption in relation to renin?
Renin promoted sodium reabsorption in the kidneys.
Since water follows sodium, this action increases blood volume, contributing to an increase in BP.
What is vasoconstriction in relation to renin?
Renin also triggers the production of angiotensin II, a powerful vasoconstrictor, which narrows blood vessels to raise blood pressure.
What is the urine formation in the Nephron?
Begins in the Proximal Convoluted Tubule:
- Filtrate, which will become urine, starts in the proximal convoluted tubule, where initial processing of waste and reabsorption of nutrients occur
Pathway through the Nephron:
- As the filtrate moves through the Loop of Henle and into the distal convoluted tubule, the concentration of urine adjust based on the body’s needs.
- The concentration is primarily determined by sodium levels, as sodium reabsorption affects water reabsorption, making the urine more or less concentrated.
What is the Pathway of Urine Out of the Kidney?
Collecting Duct to Ureter:
- From the distal tubule, urine flows into the collecting duct, which transports it to the kidneys calyces.
- Minor calyces drain into major calyces, eventually pooling into the renal pelvis
Peristalsis in the Ureter:
- From the renal pelvis, urine enters the ureter.
- Peristalsis - rhythmic contractions of smooth muscles in the ureter walls - propels urine downward toward the bladder
- The active movement prevents backflow and allows urine to flow consistently even when lying down.
What are the stretch receptors in the bladder?
The bladders walls contain stretch receptors that sense increasing fluid volume.
As urine fills the bladder, these receptors send nerve signals to the cerebral cortex, creating conscious sensation of needing to urinate.
What is the brain-controlled micturition reflex?
When the brain decide its appropriate to void, it sends impulses down the spinal cord to trigger two actions:
Relaxation of the Internal Ureteral Sphincter:
- This sphincter opens, allowing urine to pass toward the urethra.
Contraction of the Detrusor Muscle:
- The detrusor muscle in the bladder wall contracts, expelling urine through the urethra and out the body.
What is Micturition?
This process of the bladder emptying is called micturition.
In infant, micturition is involuntary as the detrusor muscle constriction is reflexive.
As children grow, they develop the cognitive ability to control urination, achieving voluntary bladder control.
