Importance of Bicarbonate and Kidney Function

• Bicarbonate Role in Blood:

  • Bicarbonate is a crucial buffer in blood regulation, primarily managed by the kidneys which can reabsorb or filter out bicarbonate as needed.

  • It's important for maintaining blood pressure and volume, especially when the body needs to conserve water.

Hormonal Regulation in Kidneys

• Calcitriol:

  • Hormone made from Vitamin D3 in the kidneys under the influence of parathyroid hormone;

  • Increases absorption of calcium from food, raising blood calcium levels.

• Erythropoietin (EPO):

  • Stimulates red blood cell production, impacting oxygen transport.

• Osmolarity:

  • Refers to the concentration of solutes in blood; controlled by kidneys crucially.

Kidney Anatomy and Structure

• Location:

  • Kidneys positioned between the 12th thoracic and 3rd lumbar vertebrae, considered retroperitoneal.

• Nephroptosis:

  • Condition where a kidney becomes displaced due to lack of support from peritoneum, often effecting urine flow.

• Kidney Structure:

  • Consists of an outer layer (renal capsule) and adipose tissue surrounding them for protection and support.

  • Hilum:

  • Area where blood vessels (renal artery, vein) and ureters enter and exit.

  • Renal pyramids and columns comprise the medulla and cortex, respectively.

The Nephron

• Functional Unit:

  • Each kidney contains ~1 million nephrons, responsible for urine formation through filtration, reabsorption, and secretion.

• Collecting Ducts and Urine Formation:

  • Collecting ducts receive urine from multiple nephrons and refine it further.

  • Fine tuning of urine occurs here regarding water and ionic balance.

Effective Filtration Processes in Kidneys

• Three Key Processes:

  1. Filtration:

  • At Bowman's capsule, driven by glomerular blood hydrostatic pressure; roughly 16-20% of plasma volume is filtered into Bowman's space.

  1. Reabsorption:

  • Process where useful substances (glucose, amino acids) are reabsorbed, primarily in the proximal convoluted tubule (PCT) and later segments.

  • The majority of water is also reabsorbed here, maintaining osmolarity similar to plasma initially.

  1. Secretion:

  • Additional waste products (e.g., drugs) are secreted into tubules, particularly in the distal convoluted tubule and collecting ducts.

Regulation of GFR & Blood Pressure in Kidneys

• Juxtaglomerular Apparatus & Autoregulation:

  • Helps regulate blood pressure and glomerular filtration rate (GFR) using myogenic mechanisms (vasoconstriction in response to stretch) and metabolic signals (macula densa cells sensing fluid volume and composition).

• Hormonal Influences:

  • Renin-Angiotensin-Aldosterone System (RAAS):

    • Activated by low blood perfusion, ultimately raises blood pressure by retaining sodium and water.

  • Atrial Natriuretic Peptide (ANP):

    • Released by the heart increases urine output and lowers blood pressure by inhibiting sodium reabsorption.

Significance of Hormones in Kidney Function

• ADH (Antidiuretic Hormone):

  • Saves water by promoting reabsorption along the collecting ducts – essential for water conservation especially during dehydration.

• Aldosterone:

  • Promotes sodium reabsorption and indirectly causes water retention, influencing blood volume and pressure.

Urine Composition and Kidney Health

• Glucose and Protein in Urine:

  • Presence indicates potential issues (e.g., uncontrolled diabetes, kidney damage).

  • Normally filtered glucose is wholly reabsorbed; if overflow occurs (e.g., high blood glucose), it spills into urine.

Summary of Main Functions**

• Kidneys coordinate complex functions vital for fluid, electrolyte, and pH balance;

• Key role in blood filtration, waste removal, and regulation of critical hormones to maintain homeostasis and overall health.