kidney homeostatic regulation

• The metabolic waste of humans chiefly includes nitrogenous wastes such as urea, creatinine, ammonium, and uric acid
• Creatinine


  Results from the metabolism of a high-energy phosphate reserve in muscles called creatine
• Men have generally higher creatinine levels than women
• Blood volume


  The average adult has a blood volume of approximately five liters (1.3 gal), accounting for about eight percent (8%) of the human body weight
• Sodium chloride


  Attracts water enabling it to stay in the blood and so maintain blood volume
• If you ingest too much sodium chloride

  More water is reabsorbed, thus increasing blood volume
• Greater blood volume


  Requires more effort from the heart to pump blood, increasing the pressure in the arteries
• Renin-Angiotensin-Aldosterone System (RAAS)


  1. Macula densa cells stimulate juxtaglomerular cells to release renin

  2. Renin triggers a series of reactions that lead to the splitting of angiotensin

  3. Angiotensin II has many effects including constricting arterioles, increasing sodium reabsorption, triggering the release of aldosterone, and decreasing the sensitivity of the baroreceptor reflex

  4. Aldosterone causes the distal convoluted tubules and collecting ducts to permit the passage of more potassium ions and absorb more sodium ions

  
• Renin-Angiotensin-Aldosterone System


  An example of negative feedback, where a drop in blood volume and blood pressure stimulates the release of renin to eventually produce angiotensin II, which acts to raise the blood pressure and blood volume to normal

  
• Antidiuretic hormone (ADH)


  • binds to hypothalamus
  • when blood osmolarity rises, ADH levels increase, signaling distal tubules and collecting ducts to become more permeable to water by temporarily increasing the number of aquaporins, to let water diffusion levels rise

  
• Although ADH and RAA systems bring about the same effect, that is maintaining blood volume and pressure, they are coordinated in their activity

  
• Our urinary system processes and excretes wastes in our blood in the form of urine
• It works in coordination with other organ systems like the cardiovascular system, endocrine system, nervous system, and to some extent, with the integumentary system
• Organs of the urinary system have to constantly perform close monitoring of bodily processes to maintain homeostasis
• Keeping normal levels of solute concentration, blood volume, and blood pressure depends on hormonal circuits that comprise the renin-angiotensin-aldosterone system, the antidiuretic hormone, and atrial natriuretic peptide

  
• Along with these are still other hormonal regulatory pathways which generally work to help our body work at its finest
• Excessive salt and fluid loss, like when someone had an injury and incurred a major wound, blood volume will be reduced without increasing blood osmolarity
• This event will not affect ADH release but will trigger the RAA system to respond by increasing sodium and water reabsorption
• The effect of ADH is limited to increasing water reabsorption in the kidneys to address high levels of blood osmolarity
• The RAA system assists in maintaining body fluid osmolarity in normal levels by stimulating sodium reabsorption
• ANP inhibits the release of renin and so inhibits the functions of angiotensin II