Urinary System, Fluid & Electrolyte Balance, and Acid-Base Balance

Flashcards covering the urinary system, nephron structures, steps of urine formation, RAAS regulation, micturition reflexes, urine characteristics, fluid compartments, and acid-base balance mechanisms.

What organ structures and counts comprise the urinary system according to the lecture notes?

Kidneys (2), ureters (2), urinary bladder (4), and urethra (1).

What are the major functions of the kidneys?

Regulating blood volume and electrolytes, regulating acid-base balance, excreting nitrogenous waste, regulating blood pressure, regulating RBC production (Erythropoietin), and regulating blood glucose.

What is the structural role of the renal capsule?

It is a tough, fibrous outer covering that protects the kidney.

What is the renal cortex and what process takes place there?

It is the outer layer of the kidney containing nephrons, where filtration occurs.

What is the structure and function of the renal medulla?

It is the inner region of the kidney consisting of renal pyramids that help transport urine from nephrons to the renal pelvis.

What is the function of Bowman's capsule within the nephron?

It encases the glomerulus and initiates the filtration of blood.

What is the function of the Proximal Convoluted Tubule (PCT)?

It reabsorbs nutrients, water, and electrolytes back into the blood.

What is the key function of the Loop of Henle and its components?

It has descending and ascending limbs and is crucial for concentrating urine by reabsorbing water and salts.

What are the primary functions of the Distal Convoluted Tubule (DCT)?

It regulates ion exchange and pH balance.

What is the role of the Collecting Duct in urine formation?

It serves as the final site for urine concentration before urine is transported to the renal pelvis.

What are the three main steps of urine formation?

Filtration, Reabsorption, and Secretion.

What occurs during the filtration stage of urine formation?

Water and dissolved substances move from blood in the glomerulus to the glomerular capsule.

What specific substances and percentages are typical during tubular reabsorption?

Up to $99JSON_PERCENT_ESCAPED$ of water, sodium, and chloride, and $100JSON_PERCENT_ESCAPED$ of glucose and other small organic molecules are returned to the blood.

Which substances are actively moved from blood into the renal tubules during tubular secretion?

Hydrogen ions ($H^+$), potassium ions ($K^+$), and certain drugs.

Where is Antidiuretic Hormone (ADH) secreted and how does it alter urine volume?

It is secreted by the posterior pituitary, increases water reabsorption in the collecting ducts, and reduces urine volume as a "water-retaining hormone".

Where is aldosterone secreted and what is its physiological action?

It is secreted by the adrenal cortex, increases sodium and water reabsorption, and reduces urine volume as a "salt + water retaining hormone".

What triggers the Renin-Angiotensin-Aldosterone System (RAAS)?

It is triggered by low blood pressure or low blood volume.

What sequence of steps occurs in the RAAS pathway when low blood pressure is detected?

Juxtaglomerular cells in the kidney detect low blood pressure and release renin, which converts angiotensinogen to angiotensin I. Angiotensin-converting enzyme (ACE) then converts angiotensin I to angiotensin II.

How does angiotensin II act to restore normal blood volume and pressure?

It causes arteriolar constriction to increase blood pressure, stimulates aldosterone secretion from the adrenal gland (promoting $H_2O$ retention), and stimulates ADH production.

How is urine moved through the ureters to the urinary bladder?

Urine drains from collecting ducts to the renal pelvis and down the ureters, where thick muscular walls produce peristaltic movements.

What anatomical features characterize the urinary bladder structure and lining?

It lies in the pelvis behind the pubic symphysis, has elastic involuntary muscle lined with transitional epithelium and mucous membrane, and features rugae when empty that stretch smooth when full.

What is the trigone of the urinary bladder and why do ureters enter at an angle?

The trigone is a smooth triangular area between the ureters and urethral opening. Ureters enter the bladder wall at an angle to prevent backflow.

How do female and male urethras differ in length and function?

The female urethra is shorter ($4\,\text{cm}$) and serves the urinary system only. The male urethra is longer ($20\,\text{cm}$) and serves both the urinary and reproductive systems.

Which two sphincters control micturition and what are their control types?

The internal urethral sphincter (involuntary) and the external urethral sphincter (voluntary).

What bladder volumes trigger the urge to void and increased internal pressure?

The urge to void starts around $150\,\text{mL}$, and the bladder holds $300-400\,\text{mL}$ before pressure increases.

Which region of the spinal cord mediates the emptying reflex for urination?

Spinal cord levels $S2-S4$.

What are the definitions of anuria, oliguria, and polyuria?

Anuria is the absence of urine; oliguria is a scanty (small/insufficient) amount of urine; polyuria is an unusually large amount of urine.

What are the standard reference values for urine blood tests (creatinine and BUN), pH, and specific gravity?

Creatinine is $0.5-1.2\,\text{mg/dL}$; BUN is $10-20\,\text{mg/dL}$; urine pH is $4.6-8.0$ (average $6.0$); urine specific gravity standard range is $1.005-1.030$ (overall normal range $1.002$ very dilute to $1.040$ very concentrated).

What is the general chemical composition of urine?

Urine consists of $95\%$ water and $5\%$ dissolved solids/gases.

What are the two major fluid compartments in the body and their main electrolytes?

Intracellular Fluid (ICF, largest volume inside cells, main ion Potassium) and Extracellular Fluid (ECF, fluid outside cells including plasma, interstitial fluid, lymph, and transcellular fluids, main ion Sodium).

What is the normal pH range of blood, and how are acidosis and alkalosis defined?

Normal blood pH is $7.35-7.45$; acidosis is a blood pH $< 7.35$; alkalosis is a blood pH $> 7.45$.

What are the three lines of defense for maintaining body acid-base balance?

1st line of defense: Buffers (prevent sharp changes in $H^+$ concentration); 2nd line of defense: Respiration/Lungs ($CO_2$ regulation); 3rd line of defense: Kidneys (regulate $H^+$ ions and create new molecules like bicarbonate, $HCO_3^-$).