Lecture 44 - Urinary System Overview Flashcards
What is the urinary system responsible for and what are the 3 pathways of the urinary system?
It is responsible for the production, storage, and elimination of urine
- The kidneys filter blood, producing urine
- Urine is moved through the urinary system and is temporarily stored in the bladder
- Urine is excreted by urination/micturition
Where is urine produced and where is it stored?
Urine is produced in the kidneys and is stored in the bladder before elimination
What does urine contain?
Mostly water, ions, and wastes (especially nitrogenous compounds)
What is the typical range of daily urine production for a healthy adult?
~1.4L in a typical day
What coordination is required for micturition (urination)?
It relies on the coordination of bladder and urethral sphincter muscles through the autonomic and somatic nervous systems
What is the capacity of the bladder and how does it empty?
The typical capacity is around 0.5L. The urge to urinate occurs when the bladder is ~50% full
To empty the bladder, the 2 urethral sphincters must relax and the detrusor must contract, expelling urine through the urethra
Name 4 functions of the kidney
- Removing wastes and toxins from blood (without removing nutrients)
- Regulating plasma ion concentrations
- Regulating blood pH
- Regulating blood volume and blood pressure
These functions are meant for body fluid homeostasis
Is the kidney a primary or secondary endocrine organ?
Secondary
How does the kidney act as a target of other endocrine organs?
Hormones made by the kidney can act on the kidney and/or on other organ systems to regulate ion and fluid homeostasis in the body
The kidney also responds to hormones made by other organs
Name the 3 hormones that the kidney produces
- Calcitriol
- Erythropoietin (EPO)
- Renin
What is the function of calcitriol? Where is it secreted and where does it act on?
It regulates calcium intake and retention.
It’s secreted from the proximal tubule cells in response to the parathyroid hormone (PTH) signalling when plasma [Ca2+] is low
It acts through receptors in both the digestive tract and kidney to promote the absorption (and reabsorption) of Ca2+
What is the function of erythropoietin (EPO)? Where is it secreted and where does it act on?
Stimulates RBC production
It’s secreted by intertubular fibroblasts (EPCs; EPO-producing cells) within kidney tissue in response to tissue hypoxia
EPO acts on bone marrow to enhance erythrocyte (RBC) production, leading to increases in blood volume (and hematocrit)
What is the function of renin? Where is it secreted and what does it activate?
It regulates other hormones which control blood pressure and plasma volume
It’s secreted by cells within the juxtaglomerular apparatus (JGA) in response to decreased pressure in kidney arterioles
It activates the RAAS, leading to increased blood pressure (through vasoconstriction) and increased blood volume (through intake and reabsorption)
What is the functional unit of the kidney? Describe where it’s located in the kidney and its structure
Nephron; it begins at the glomerulus within the renal cortex. Each one has a glomerulus, where blood is initially filtered, and a complex renal tubule where the filtrate is processed
Name the specific location where blood is filtered and explain the process
Blood is filtered at glomerular capillaries to create filtrate, which then enters the nephron and flows through its lumen and into the collecting duct
What happens to remaining (unfiltered) blood?
It flows through capillaries around the nephron
What is filtration?
It refers to the movement of fluid through small pores in response to pressure differences
If higher pressure is inside the vessel, fluid is pushed out the vessel (bulk flow), along with any solutes small enough to filter through the available gaps
What affects the composition of urine?
The interactions between renal tubules, interstitial fluid, and peritubular capillaries. The complex patterns of reabsorption of water and solutes (and extra secretion of certain solutes) that occur throughout the nephron and ultimately sculpt the filtrate into the final product (urine)
What makes the composition of urine highly variable? Name the 2 processes
It is because some aspects of nephron function are under hormonal regulation
- Obligatory processes - always present; cannot be modified
- Facultative processes - not always present; regulated by hormones (especially ADH and aldosterone). Facultative reabsorption means urine can vary in volume and composition, depending on homeostatic requirements
What is renal failure? Name 3 symptoms
A life-threatening condition that occurs when kidney function is compromised. Some symptoms are:
- Reduced urine production
- Oedema
- Fatigue
Name 4 possible triggers for renal failure
- Clot in a renal artery or vein
- Physical damage to kidney tissue
- (Nephro-)toxins (from certain drugs or breakdown of other body tissues)
- Kidney stones blocking a ureter
What happens when kidney filtration slows, stops, or reabsorption processes are disrupted?
Metabolic wastes, excess ions, and water will be retained in the plasma
How can kidney failure be managed?
Using haemodialysis. It allows waste products and excess ions to be removed from the patient’s blood. This process typically takes 3-4 hours and must be repeated 3x per week
How does dialysis work?
It relies on passive diffusion across a selectively permeable membrane. The membrane permits ions and small organic molecules to pass, but restricts the movement of large molecules, especially plasma proteins
What is the composition of dialysis fluid designed to do?
It’s meant to prevent the loss of nutrients and key ions from plasma. Its adjusted to meet each individual patient’s specific needs
