Ch 10 Part 1 Flashcards
Excretion
Disposal of Waste. Generally refers to the Kidneys - although the liver, large intestine, and skin are involved.
Liver
Deals with large hydrophobic waste products that the kidney cannot attend. Releases waste into bile.
Synthesizes urea which is a carrier of excess nitrogen (from protein breakdown). Important because free ammonia is toxic.
Colon
ie. The large intestine.
Reabsorbs water and ions. Does not typically excrete, rather recycles components of waste.
Although can excrete excess ions if necessary using active transport.
Skin
Produces sweat which releases water, ions, and urea.
Although excretion of waste is only a secondary role of sweating.
Kidneys
Excretion of hydrophilic waste. Ex. Urea, sodium, bicarbonate, water.
Maintain constant solute concentration and pH.
Maintain constant fluid volume.
Important to think of the kidney as a regulator of optimal levels, not simply a passive reservoir for waste excretion.
Kidney processes (General)
3 Step Process:
FILTRATION - pressurized blood flows over a filter leaving cells and proteins in blood, while removing water and small molecules into RENAL TUBE. Water and molecules become known as FILTRATE –> urine.
SELECTIVE REABSORPTION - recycle useful products like glucose, water, and aa.
SECRETION - Addition of substances to the filtrate, which can increase the rate at which substances are eliminated from the blood (osmosis mediated)
Ends with - CONCENTRATION and DILUTION - decision to produce dilute or concentrated urine. Anything in renal tube is excreted.
Artery and Veins supplying Kidney
Inferior Vena Cava and Abdominal Aorta.
See pg. 369 for details.
Blood in the kindey
Enters via the renal artery and purified blood leaves via the renal vein.
Urine leaving Kidneys
Leaves via a URETER that empties into the urinary bladder
Urinary Sphincters
Internal Sphincter - made of smooth involuntary muscle. Relaxes when the bladder is full.
External Sphincter - made of skeletal voluntary muscle. Person decides when to urinate.
Regions of the Kidney
Cortex - outer region
Medulla - inner region
Medullary Pyramids - Pyramid striations in the medulla as a result of collecting ducts. Urine empties from collecting ducts and leaves at the tip of a pyramid known as PAPILLAE.
Calyx (Calyces) - a space in which urine empties
RENAL PELVIS - formed by convergence of Calyces
Pg. 370
Functional Unit of a Kidney
Nephron
Nephron Components
Two components:
Bowmans Capsule - a rounded region surrounding capillaries, where filtration takes place.
Renal tube - a coiled structure, that receives filtrate from capillaries and empties into collecting duct.
Blood vessels surrounding the Nephron
Arterial blood is carried toward the capillaries of capsule for filtration.
Blood vessels also surround the tubule to carry filtered blood and reabsorbed substances away from tubule.
Kidney Filtration
Renal artery flows into afferent arteriole which branches into the GLOMERULUS (ball of capillaries).
Blood then flows in efferent arteriole. Constriction here results in high pressure in the glomerulus causing blood plasma (fluid) to leak out of capillaries.
Fluid flows through the GLOMERULAR BASEMENT MEMBRANE before entering BOWMAN’s CAPSULE.
Lume of Bowman capsule is continuous with rest of tubule/renal tube.
Kidney Selective Reabsorption
Filtrate molecules that can be recycled are taken from the filtrate, often by active transport, and carried by PERITUBULAR CAPILLARIES –> venules –> renal vein.
Most selective reabsorption occurs near the PROXIMAL CONVOLUTED TUBULE (PCT), which is closest to Bowman’s Capsule. Absorbs selectively - as much as it can, but only of specific things.
A lot of water absorption occurs here, up to 70% of filtrate is reabsorbed. Overall urine is really dictated by small fluxes more distally in the nephron.
Note: 5% of our blood that is circulating is passing through glomerulus, so majority needs to be reabsorbed.
How much glucose is typically reabsorbed by the PCT?
Roughly 100%
Kidney Secretion
Movement of substances into filtrate (typically by active transport).
A back up method to the glomerulus that ensures elimination of specific things. Primary method to excrete drugs and toxins.
Occurs along the entire tubule, but majority in the DCT and collecting duct.
Kidney Concentration and Dilution
Distal Nephron (DCT + collecting duct) - location of urine adjustment for volume and osmolarity.
Controlled by ADH and aldosterone.
Function of ADH in Kidney
Also known as Vasopressin.
During dehydration, blood fluid levels are low with high solute concentration. NEED to create SMALL AMOUNTS OF CONCENTRATED URINE. These conditions released ADH which prevent DIURESIS (water loss in the urine) by increasing water reabsorption in Distal Nephron by making it permeable to water.
If well hydrated, no ADH secreted.
Note that the Distal Nephron is normally impermeable to water - the first tissue I am aware of that is impermeable to water!
Aldosterone in Kidney
Released in response to low blood pressure, by adrenal cortex.
Increases reabsorption of Na+ by distal nephron.
Increases plasma osmolarity. Increases thirst and water retention –> raises BP.
Aldosterone release can also be stimulated by low blood osmolarity, low blood volume, angiotensin II.
Note that ADH and Aldosterone both increase BP and work together.
Aldosterone is released first, increases blood osmolarity, causing release of ADH.
Where are Bowman’s capsule and PCT located in the broader kidney?
Renal cortex
More detailed structures of nephron
PCT empties into the LOOP of HENLE (which dips down into renal medulla); the part that dips down into medulla is the DESCENDING LIMB OF THE LOOP OF HENLE (thin, squamous epithelial tissue), while the part that returns out to the cortex is the ASCENDING LIMB (thick cuboidal epithelial cells - more active).
Loop of Henle becomes the DCT, DCT empties into collecting duct.
Ion active transport
For Cl-; Na+; K+ - Occurs in the ascending limb of the loop of Henle, but there is also passive return of K+.
In the Collecting duct there is secretion of potassium and hydrogen ions as well as reabsorbtion of Na in response to Aldosterone (DCT and cortical region of collecting duct)
pg. 375
