Flashcards in Chapter 16 Deck (55)
How is the urinary system closely associated with the reproductive system
- Shared embryonic development
- together termed urogenital system
What are the 6 principle organs of the urinary system
2 kidneys, 2 ureters, bladder and urethra
What are the functions of the kidneys?
1) Filter blood, separate wastes and excrete them, and return useful material to the bloodstream.
2) regulate blood volume and pressure by eliminating or conserving water as necessary
3) Regulate the osmolarity of body fluids by controlling the relative amounts of water and solutes eliminated.
4) Secrete enzyme "renin" which activates hormonal mechanisms that control blood pressure and electrolyte balance
5) Secrete hormone "erythropoietin" which stimulates the production o red blood cells and thus supports the oxygen-carrying capacity of the blood
6) Carry out the final step in synthesizing hormone "Calcitriol" and thereby contributing to calcium homeostasis
7) Detoxify some drugs
What is Excretion?
Process of separating wastes from body fluids and eliminating them
What is "waste"?
Any substance that is useless or present in excess of the body's needs
What is a Metabolic Waste?
Waste substance produced by the body
e.g. a by-product of ATP production or protein catabolism
What other systems besides the urinary system excrete wastes?
- Respiratory excretes CO2
- Digestive and Integumentary system excretes water and salts
What are some Nitrogenous wastes?
- Urea --> makes up 50%; converted from ammonia in the liver, carried in blood plasma to kidneys, filtered into urine and excreted
- Uric Acid --> Produced by catabolism of nucleic acids
- Creatine --> Produced by catabolism of creatine phosphate.
What are the 4 stages of Urine formation?
1) Glomerular Filtration --> Creates a plasma-like filtrate of the blood
2) Tubular reabsorption --> Removes useful solutes from the tubular fluid and returns them to the blood
3) Tubular secretion --> Removes additional wastes from the blood, adds them to the tubular fluid.
4) Water Conservation --> Removes water from the urine and returns it to blood; concentrates wastes
What are the 3 layers of the filtration membrane?
1) Endothelium of the Capillary --> glomerulus with fenestrated capillaries; penetrated by large filtration pores; small enough to exclude RBC's
2) Basement Membrane --> Mesh of Glycoproteins. Holds back most proteins
3) Filtration Slits --> Created by podocytes of capsule; bulbous cell bodies with several thick arms; arms with numerous extensions, "foot processes"; Wrap around capillaries and lace together
How much higher is blood pressure in the glomerular capillaries than in most other capillaries?
60 mm Hg
Which is bigger the afferent or efferent arteriole in the glomerular capillaries?
Afferent which results in increased blood pressure
What are the 2 forces that oppose blood pressure in glomerulus?
1) Fluid pressure in the capsular space
2) Osmotic pressure of the blood
What does higher blood pressure in the glomeruli do to the kidneys?
Makes them especially vulnerable to hypertension which can have devastating effects on renal function. Hypertension ruptures glomerular capillaries and leads to scarring of the kidneys (nephrosclerosis). It promotes atherosclerosis of the renal blood vessels and thus diminishes renal blood supply. Over time, Hypertension often leads to renal failure.
What is the GFR?
Glomerular Filtration Rate -- the amount of filtrate formed per minute by 2 kidneys
What happens if the GFR is too high?
Fluid flows through the renal tubules too rapidly for them to reabsorb the usual amount of water and solutes. Urine output rises and creates a threat of dehydration and electrolyte depletion.
What happens if the GFR is too low?
Fluid flows sluggishly through the tubules and they reabsorb wastes that should be eliminated in the urine.
How is GFR regulated by hormonal chain reactions?
When Blood pressure drops, sympathetic nerves stimulate the kidneys to secrete enzyme "Renin" which converts Angiotensiongen (a blood plasma protein) into Angiotensin I. Angiotensin-converting enzyme converts this to Angiotensin II (a hormone that acts in several ways to restore fluid volume and blood pressure)
What are Some effects of Angiotensin II?
- Makes one thirsty and encourages water intake
- Stimulates adrenal cortex to secrete aldosterone which promotes retention of sodium and water.
- Stimulates Pituitary to secrete ADH which promotes water retention
- It is a Potent Vasoconstrictor meaning it constricts efferent more than afferent arteriole of nephron and sustains glomerular pressure when blood pressure is low.
What is Renal Autoregulation?
- Also known as local control, it refers to the ability of the nephrons to adjust their own blood flow and GFR even without external control
- Enables nephrons to maintain a relatively stable GFR in spite of changes in arterial blood pressure.
What are the 2 mechanisms of Autoregulation?
1) Myogenic Mechanism --> Smooth muscle has a tendency to contract when stretched. A rise in arterial blood pressure stretches the afferent arteriole. In response, the arteriole contracts and prevents blood flow into the glomerulus from changing much. When blood pressure falls, the afferent arteriole relaxes and allows blood to flow more easily into the glomerulus. GFR remains fairly stable.
2) Tubuloglomerular Feedback --> Involves communication between the glomerulus and renal tubule through a complex of structures called the juxtaglomerular apparatus.
What are the 2 special cell types which occur in the Juxtaglomerular apparatus?
1) Macula Densa Cells --> Epithelia cells at the end of nephron loop facing arterioles
2) Juxtaglomerular Cells (JG) --> Enlarged smooth cells located in afferent arteriole across from the macula. Dilate or constrict when stimulated by macula. Secrete Renin.
What are the Substances reabsorbed by PCT?
- Na, Cl, K, Mg and phosphate ions
- Glucose --> normally all reabsorbed
- Nitrogenous Wastes --> Some urea reabsorbed with water.
- Water --> absorbs 2/3 of total reabsorbed water.
What is the Transport Maximum (Tm)?
If all the transporters are occupied as solute molecules pass though, we reach this point where no more solute can be reabsorbed and the excess passes through the tubule and into the urine.
What is Glycosuria?
At any blood glucose level above 220 mg/dL or so, glucose is filtered faster than the renal tubule can reabsorb it and the excess passes in the urine.
What is the primary function of the nephron loop?
Generate an osmotic gradient that enables the collecting duct to concentrate the urine and conserve water, but in addition, the loop reabsorbs water and salts.
The thin segment of the nephron loop is permeable to water but not to ________?
As tubular fluid flows down the descending limb, about how much water is reabsorbed and returned to the bloodstream?
The Cells in the Thick segment of the ascending limb are actively engaged in _______?
Salt reabsorption but are impermeable to water.
What is considered the most important function of the nephron loop?
Supporting the work of the collecting ducts.
What are the hormones that effect the DCT?
1) Aldosterone --> "Salt-retaining hormone" secreted by adrenal cortex when blood pressure or Na falls or K rises; Stimulates ascending loop, DCT, and collecting duct to reabsorb more NaCl and secrete more K; reduces urine volume and K in blood; retention of salt and water, increasing Blood pressure
2) Natriuretic Peptides --> Secreted by the heart in response to high blood pressure. their effect is to increase excretion of salt and water in the urine, thus reducing blood volume and pressure.
What is Tubular Secretion?
Process in which the renal tubule extracts chemicals from blood of the peritubular capillaries and secretes them into the tubular flux.
How is Tubular secretion important?
1) Acid-Base balance through secretion of varying proportions of Hydrogen to bicarbonate (HCO3) ions
2) Waste removal through extracting urea, uric acid, bile acids, and ammonia from the blood
3) Clearance of drugs and contaminants from the body, such as morphine, penicillin, and aspirin. Drug dosage set to keep pace with clearance.
Where does the Collecting Ducts begin?
When Urine first enters the collecting ducts it it _________?
Isotonic with blood plasma -- 300 Milliosmoles per liter
By the time urine leaves the lower end of the collecting duct it can be up to 4X as concentrated making it ____________?
Hypotonic to the blood plasma
What 2 facts enable the collecting duct to produce Hypotonic urine?
1) The osmolarity of the tissue fluid surrounding the collecting duct is 4X as high in the lower medulla as it is in the cortex
2) The medullary portion of the CD is more permeable to water than to solutes
What does it mean that the Nephron loop acts as a "Countercurrent Multiplier"?
It continually recaptures salt and returns it to the deep medullary tissue. It is called "multiplier" because it multiplies the salinity deep in the medulla and a "countercurrent" mechanism because it is based on fluid flowing in opposite directions in the descending and ascending limbs of the loop.
What would happen without the Countercurrent Multiplier?
The CD would be unable to absorb water and produce such concentrated urine
What happens during dehydration?
- High blood osmolarity stimulates the release of ADH from the posterior pituitary gland.
- The ADH induces the cells of the CD to synthesize "Aquaporins (Water-Channeling Proteins) and install them in the plasma membrane, so more water can pass through the epithelium.
- More water is reabsorbed and is carried away by the surrounding blood capillaries. Urine output is consequently reduced and its osmolarity can be as high as 1,200 mOsm/L
What happens during Hydration?
- ADH secretion is inhibited and the aquaporins are removed and less water is reabsorbed.
- The cortical portion of the CD reabsorbs NaCl but the CD is less permeable to water.
- More water passes through as abundant, dilute urine, with an osmolarity as low as 50. This response is called "Water Diuresis."
What aids in the prevention of Urine leakage?
1) Sympathetic Nervous System --> Issues nerve fibers from the spinal cord to the detrusor to relax that muscle, preventing bladder contraction and fibers to the internal urethral sphincter to contract that muscle and hold the urine in.
2) External Urethral Sphincter --> Innervated by somatic rather than sympathetic motor nerve fibers. They also hold the sphincter closed.
What is Micturition?
- The act of urinating
- Initiated by an autonomic spinal micturition reflex.
a) Filling of bladder
b) Excites stretch receptors on bladder walls
c) Sends signals to spinal cord
d) Returns signal to bladder via parasympathetic nerve
e) Contracts detrusor
f) Relaxes internal urethral sphincter
- In young children, results in bladder emptying
How is Micturition inhibited?
- Normally with Voluntary control
- Stretch signals from bladder ascend the spinal cord to a nucleus in the pons called the "Micturition Center." This nucleus integrates information about bladder tension with info from other brain centers such as the cerebral cortex.
- If urination is desired, signals descend from the pons to inhibit the spinal somatic neurons that keep the external urethral sphincter constricted. The sphincter then relaxes and micturition proceeds.
How much urine does an average adult produce?
1-2 Liters per day
What is it called when there is a urine output in excess of 2L a day?
Diuresis or polyuria
What is it called when there is a low urine output?
What is the pH of Urine?
From 4.5 to 8.2, usually about 6.0, mildly acidic
What is Uremia?
Dangerously high nitrogenous wastes in blood. Usually indicates kidney failure
Variation in Urine Color depends on ________?
What causes the yellow color in urine?
Pigment from hemoglobin breaks down
Pyuria indicates _____?
What is Hematuria?
Blood in the urine. May be due to a urinary tract infection, trauma, or kidney stones
What is the chemical composition of Urine?
95% water and 5% solutes by volume (Urea, Creatinine, Ammonia, Chloride, Sodium, and Potassium)