Urinary Physiology Overview

The movement of substances across cell membranes that requires energy from ATP hydrolysis. Carrier proteins use energy to move substances against their concentration gradient.

The movement of substances across cell membranes that utilizes the energy released from the movement of another substance down its concentration gradient.

A type of secondary active transport where two substances move in the same direction across the membrane.

A type of secondary active transport where two substances move in opposite directions across the membrane.

The movement of substances across cell membranes without requiring energy. The driving force is the concentration gradient, chemical gradient, electrical gradient, or a combination of these.

The kidneys maintain a constant environment within the body by removing waste products from the blood, regulating electrolyte balance, and maintaining proper blood acidity.

The kidneys produce hormones like renin, erythropoietin, and active vitamin D, which regulate crucial processes like blood pressure, red blood cell production, and calcium levels.

The formation of urine involves three main steps: glomerular filtration, where blood is filtered in the kidney; tubular reabsorption, where essential substances are reabsorbed back into the blood; and tubular secretion, where additional waste products are added to the urine.

Almost all of the blood that enters the kidneys passes through the glomeruli, tiny structures where filtration takes place. This circulation involves two capillary networks, the glomeruli and the peritubular capillaries.

The efferent arteriole, a vessel carrying blood away from the glomerulus, is also considered a 'portal artery' because it leads to another capillary bed. This is unique in the body.

The glomerular capillaries are the only capillaries in the body that empty into arterioles, not venules, which is crucial for maintaining high pressure for filtration.

The portal renal system facilitates filtration within the glomerular capillaries and reabsorption/secretion within the peritubular capillaries, making it an efficient system for regulating blood composition.

The kidneys receive a large amount of blood, about 1/4 of the heart's output per minute, to ensure efficient filtration and maintain homeostasis. However, this high flow is not due to high oxygen consumption by the kidneys, but rather their filtering properties.

The myogenic mechanism is an intrinsic property of afferent arterioles that helps regulate glomerular filtration rate (GFR). It responds to changes in arterial pressure by contracting or relaxing the afferent arteriole to maintain a stable GFR.

The tubuloglomerular feedback mechanism involves the macula densa cells in the distal tubule, which sense changes in NaCl concentration in the tubular fluid. This feedback loop regulates GFR by affecting the tone of the afferent arteriole.

When arterial pressure increases, the afferent arterioles stretch, triggering a reflex contraction to reduce blood flow into the glomerulus. This helps maintain a stable GFR by preventing excessive filtration.

When arterial pressure decreases, the afferent arterioles relax, allowing more blood flow into the glomerulus. This increases filtration rate, helping to maintain a stable GFR.

The macula densa is a specialized group of cells in the distal tubule that senses the concentration of NaCl in the tubular fluid. It plays a key role in regulating GFR through the tubuloglomerular feedback mechanism.

When blood pressure is low, the macula densa detects a decrease in NaCl delivery and releases vasodilatory substances like nitric oxide (NO) to widen the afferent arteriole, increasing GFR.

When blood pressure is high, the macula densa detects an increase in NaCl delivery and releases vasoconstrictor substances like ATP and adenosine to narrow the afferent arteriole, decreasing GFR.

When blood pressure is low, the macula densa stimulates the juxtaglomerular (JG) cells to release renin. Renin activates the renin-angiotensin system, leading to angiotensin II production, which constricts efferent arterioles, increasing glomerular pressure and restoring GFR.

Renal blood flow (RBF) is relatively constant over a range of arterial pressures (70-160 mmHg). This autoregulation is mainly achieved by the myogenic and tubuloglomerular feedback mechanisms.

If prolonged low arterial pressure persists for more than 10-20 minutes, blood flow autoregulation becomes less effective, leading to a decline in renal function.

The relationship between bladder volume and internal pressure, measured during bladder filling.

The initial phase of bladder filling where pressure increases moderately with volume. This occurs up to 50 ml.

The middle phase of bladder filling where pressure remains almost constant even with increased volume. This occurs from 50 ml to 300 ml.

The relaxed state of bladder smooth muscles during the high compliance phase. It is controlled by the sympathetic nervous system.

The final phase of bladder filling where a steep increase in pressure happens with additional volume. This occurs above 400 ml.

The involuntary reflex triggered by bladder distension, leading to urination. It's initiated by stretch receptors in the bladder wall, particularly around the neck.

The muscle responsible for emptying the bladder, it's tonically inhibited (relaxed) during bladder filling.

The feeling of wanting to urinate, usually felt at around 150 ml of bladder volume. It is often easily suppressed.

A solution containing a weak acid and its conjugate base. It resists major pH changes upon addition of small amounts of acid or base.

The process by which the kidneys generate new bicarbonate ions (HCO3-) to replenish those lost in buffering strong acids produced in the body.

The bicarbonate buffer system is the primary defense against strong acids produced in the body. This system utilizes bicarbonate ions (HCO3-) to neutralize H+ ions.

The process of maintaining the pH of body fluids within a narrow range, typically around 7.35-7.45. It is crucial for proper cellular function and overall health.

When the body produces strong acids, the bicarbonate buffer system consumes HCO3- to neutralize them. The kidneys then generate new HCO3- to replace those lost.

A major buffer system in the body, composed of bicarbonate (HCO3-) and carbonic acid (H2CO3). It helps neutralize excess acids and bases in the blood and other bodily fluids.

The kidneys excrete excess H+ ions by combining them with non-bicarbonate buffers like ammonia and phosphate.

A large protein found in red blood cells that plays a crucial role in oxygen transport. It also acts as a buffer in the blood, helping to regulate pH.

A buffer system composed of a mixture of acidic phosphate (H2PO4-) and alkaline phosphate (HPO42-). It is more effective in the intracellular fluid (ICF) than the extracellular fluid (ECF).

Ammonia (NH3) is a highly effective buffer for H+ ions in the kidneys. It is synthesized and secreted into the tubular lumen, where it reacts with H+ to form ammonium ions (NH4+).

The process of regulating the pH of the blood by controlling the partial pressure of CO2 (PCO2) in arterial blood.

Ammonium ions (NH4+) are weakly acidic and readily excreted in urine. Their formation allows for the excretion of H+ while preserving blood pH stability.

The process of eliminating excess acid or base from the body via the kidneys. The kidneys regulate the pH of the blood by filtering and excreting waste products, including H+ ions.

The formation of ammonium ions (NH4+) consumes H+ and leads to the generation of new bicarbonate ions (HCO3-), which are reabsorbed into the blood.

The amount of ammonia (NH3) produced and secreted by the kidneys increases in acidic conditions (acidosis) and decreases in alkaline conditions (alkalosis).

A condition where the blood is too acidic, often due to an imbalance in the bicarbonate buffer system. Symptoms can include headaches, confusion, and rapid breathing.