The Renal System & Water, Electrolyte and Acid-Base Balance Flashcards
(27 cards)
Urinary System
Main Organs:
1) Kidneys – Filter blood, remove waste, regulate fluid and electrolyte balance, and produce urine.
2) Ureters – Transport urine from kidneys to the bladder.
3) Bladder – Stores urine.
4) Urethra – Excretes urine from the bladder out of the body
Functions:
- Filtration: Kidneys filter blood to remove waste, excess substances, and toxins.
- Reabsorption: Nutrients and water are reabsorbed back into the blood.
- Excretion: Waste products like urea are excreted in the form of urine
- Regulation: Maintains fluid balance, electrolyte balance, and blood pressure.
Kidney Function
- Excretes organic waste (e.g., urea, ammonia, uric acid,..)
- Regulates blood volume and arterial blood pressure
- Regulates the concentration of ions in blood (Na+, Cl-, K+, Ca2+, etc)
- Regulates extracellular pH at physiological range (7.35-7.45)
- A physiological system that filters 180L of blood per day
- Production of 1-2L urine a day
Kidney and renal capsule
Kidney:
- Main organ of the urinary system, responsible for filtering blood, removing waste, and maintaining fluid and electrolyte balance.
- Contains nephrons, the functional units of the kidney that filter blood and produce urine.
Renal Capsule:
- Outer layer of the kidney, a tough, fibrous membrane that protects the kidney from physical damage and infection.
- Encapsulates the kidney, giving it its shape
Glomeruli and renal blood vessels
Glomeruli:
- Clusters of capillaries within the nephrons in the kidneys.
- Filter blood to initiate urine formation, allowing water, ions, and waste to pass into the Bowman’s capsule.
- Blood pressure in the glomerulus forces small molecules out of the blood into the filtration system
Renal Blood Vessels:
- Renal artery brings oxygenated blood to the kidneys.
- Blood flows into smaller vessels and reaches the glomerulus.
- After filtration, the blood exits via the renal vein, carrying away filtered blood.
Athletes with Single Kidney
Exercise is still recommended but there is a need to protect the single kidney. Combat sports are not recommended
General Structure of the Nephron
- The nephron is the functional unit of the kidney, responsible for filtering blood and producing urine
1) Renal Corpuscle:
- Glomerulus: Filters blood
- Bowman’s Capsule: Collects filtrate
2) Renal Tubule:
- Proximal Convoluted Tubule (PCT): Reabsorbs water, ions, nutrients.
- Loop of Henle: Concentrates urine.
- Distal Convoluted Tubule (DCT): Fine-tunes filtrate composition.
- Collecting Duct: Transports urine to renal pelvis.
Capillary Beds of the Nephron
1) Glomerular Capillaries (Glomerulus):
- Site of filtration; blood pressure forces plasma, waste, and small molecules into Bowman’s capsule to form filtrate
2) Peritubular Capillaries:
- Surround the renal tubules (PCT, DCT)
- Reabsorb water and solutes back into the bloodstream from the filtrate
3) Vasa Recta:
- Specialized capillaries that surround the Loop of Henle
- Maintain osmotic gradient for water reabsorption
Three Processes Contributing to Urine Formation
1) Glomerular filtration
2) Tubular reabsorption
3) Tubular secretion
1) Glomerular Filtration
- Movement of fluid, derived from blood flowing through the glomerulus, across filtration membrane
- Filtrate: water, small molecules, ions that can pass through membrane
- Renal blood flow rate: 1.2 L/min, 72 L/h or 1728 L/day
- Filtration fraction: part of plasma that is filtered into lumen of Bowman’s capsules; average 20%
- Glomerular filtration rate (GFR): amount of filtrate produced each minute in all glomeruli combined. 125 mL/min or 7.5 L/h or 180 L/day
- Average urine production/day: 1-2 L. Thus, 99% of filtrate must be reabsorbed
2) Tubular Reabsorption of Water in Response to Reabsorption of Na+ and Cl-
1) Na⁺ and Cl⁻ Reabsorption:
- Na⁺ and Cl⁻ are actively reabsorbed from the filtrate in the proximal convoluted tubule (PCT) and loop of Henle
- This creates an osmotic gradient in the surrounding interstitial fluid
2) Water Reabsorption:
- Water follows Na⁺ and Cl⁻ by osmosis due to the osmotic gradient created by their reabsorption
- Most of the water is reabsorbed in the PCT and descending loop of Henle, with additional water reabsorption occurring in the distal convoluted tubule (DCT) and collecting duct under the influence of antidiuretic hormone (ADH)
3) Tubular Secretion of K+ in Response to
Reabsorption of Na+
1) Na⁺ Reabsorption:
- Na⁺ is reabsorbed from the filtrate into the bloodstream, primarily in the proximal convoluted tubule (PCT) and loop of Henle
2) K⁺ Secretion:
- In response to Na⁺ reabsorption, K⁺ is secreted from the blood into the distal convoluted tubule (DCT) and collecting duct
- This process is influenced by aldosterone, which increases Na⁺ reabsorption and promotes K⁺ secretion
3) Purpose:
- Helps maintain the balance of electrolytes (Na⁺ and K⁺) and acid-base homeostasis.
Regulation of Glomerular Filtration Rate
- Sympathetic stimulation: leads to release of
noradrenaline (NA; also called norepinephrine,
NE) - NA constricts small arteries and arterioles
- Decrease renal blood flow and thus filtrate formation
- During intense exercise: the intense
sympathetic stimulation leads to an increase
in the rate of filtrate formation a few ml/min
Urine Concentration Mechanism
When large volume of water consumed:
- Eliminate excess without losing large amounts of electrolytes
- Response is that kidneys produce large
volume of dilute urine
When drinking water not available:
- Kidneys produce small volume of concentrated urine
- Removes waste and prevents rapid
dehydration
Urine Concentration Mechanisms
1) Countercurrent Multiplier (Loop of Henle):
- Descending loop: Reabsorbs water.
- Ascending loop: Reabsorbs Na⁺ and Cl⁻, but not water.
2) Vasa Recta:
- Maintains osmotic gradient by carrying away water and solutes.
3) Antidiuretic Hormone (ADH):
- Increases water reabsorption in the DCT and collecting duct, producing concentrated urine.
Regulation of Urine Concentration and Volume: Renin/Angiotensin/Aldosterone Mechanism
1) Renin Release:
- Triggered by low blood pressure or low sodium levels
- Released by the juxtaglomerular cells in the kidneys
2) Angiotensin II Formation:
- Renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by the enzyme ACE (angiotensin-converting enzyme)
3) Effects of Angiotensin II:
- Constriction of blood vessels increases blood pressure
- Stimulates aldosterone release from the adrenal glands
4) Aldosterone Action:
- Promotes Na⁺ reabsorption in the distal convoluted tubule (DCT) and collecting duct, which also increases water reabsorption
- Results in increased blood volume and blood pressure, as well as concentrated urine
The Antidiuretic Hormone (ADH) Mechanism
1) ADH Release:
- Released by the posterior pituitary in response to high blood osmolarity or low blood volume
2) Action on Kidneys:
- ADH increases the permeability of the distal convoluted tubule (DCT) and collecting ducts to water
- This allows more water to be reabsorbed back into the bloodstream
3) Result:
- Concentrated urine is produced
- Helps to conserve water, increasing blood volume and lowering blood osmolarity
Urine Formation
1) Filtration:
- Occurs in the glomerulus; blood is filtered to remove waste, excess ions, and water, forming glomerular filtrate
2) Reabsorption:
- Water, nutrients, and ions are reabsorbed from the filtrate back into the blood in the proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting ducts.
3) Secretion:
- Waste products (like K⁺, H⁺, and drugs) are secreted from the blood into the filtrate in the DCT and collecting ducts
4) Excretion:
- The final product, urine, is excreted from the kidneys, stored in the bladder, and expelled from the body via the urethra
Urine Excretion Via Micturition Reflex
1) Bladder Filling:
- As the bladder fills with urine, stretch receptors in the bladder wall are activated.
2) Micturition Reflex:
- Stretch receptors send signals to the spinal cord and then to the brain
- The parasympathetic nervous system triggers the contraction of the detrusor muscle in the bladder.
3) Sphincter Control:
- The internal urethral sphincter relaxes, allowing urine to enter the urethra
- The external urethral sphincter is under voluntary control, allowing conscious control of urination
4) Urine Excretion:
- When the external sphincter relaxes, urine is expelled from the bladder through the urethra
Water, Electrolyte and Acid-Base
Balance
- Major fluid compartments of the body
- Dominant cations (+) and anions (-) (ions)
- Body fluid osmolality
- The mechanisms that regulate extracellular and intracellular fluid volume
- Mechanisms of acid-base balance
Water Content in the Human Body
Total body water = ~45L or ~60% of body weight
Ion Concentration in Fluid Compartments
1) Intracellular Fluid (ICF):
- Main ions: K⁺ (potassium), phosphate ions
- High concentration of K⁺ inside cells, with low levels of Na⁺
2) Extracellular Fluid (ECF):
- Main ions: Na⁺ (sodium), Cl⁻ (chloride), bicarbonate (HCO₃⁻)
- High concentration of Na⁺ and Cl⁻ outside cells, with low levels of K⁺
3) Interstitial Fluid:
- A type of ECF, located between cells, containing Na⁺ and Cl⁻
4) Plasma:
- The liquid part of blood, also a type of ECF, with high Na⁺ and Cl⁻ concentrations
Net Movement of Fluids Between Compartments
1) Fluid Movement:
- Osmosis and hydrostatic pressure drive the movement of fluids between compartments
2) Capillary Filtration:
- Hydrostatic pressure in capillaries forces fluid out into the interstitial space (between cells)
3) Reabsorption:
- Osmotic pressure created by plasma proteins (mainly albumin) pulls fluid back into the capillaries from the interstitial space
4) Lymphatic System:
- Collects excess fluid from the interstitial space and returns it to the circulatory system
5) Factors Affecting Fluid Movement:
- Blood pressure, osmolarity, and protein concentration in blood and interstitial fluid determine how much fluid moves between compartments
Daily Water Balance
Greater water losses with physical activity due to thermoregulatory sweating 500-4000 mL/day
Cellular Fluid Changes
1) Hypertonic Environment:
- Higher solute concentration outside the cell.
- Water moves out of the cell → cell shrinks (crenation)
2) Hypotonic Environment:
- Lower solute concentration outside the cell
- Water moves into the cell → cell swells and may burst (lysis)
3) Isotonic Environment:
- Equal solute concentration inside and outside
- No net water movement → cell remains stable
