Urinary Flashcards
List the main functions of the kidneys
○ Eliminate plasma waste substances
○ Salvage essential compounds from filtrate
○ Regulate ion levels
○ Maintain osmolality
○ Regulate plasma volume (& blood pressure)
○ Hormone production
○ Kidney – v. vascularised, 25% cardiac output, converts 20% of plasma to filtrate
Describe the components of the urinary system and its general topographic anatomy
○ Upper urinary tract – kidney & ureter (drains from kidney into bladder)
○ Lower urinary tract – bladder & urethra (tube that voids in penis/vestibulum)
○ Kidney – abdominal cavity, asymmetric (R cranial to L)
§ Renal artery – from aorta
○ Renal vein – to vena cava
Describe the gross internal structure of the kidney and ureter
○ Renal parenchyma – outer cortex & inner medulla, pelvis
(subdivided end of ureter)
○ Renal fibrous capsule – surround entire kidney
○ Medulla – subdivided into renal pyramids, apex surrounded by funnels
○ Papilla – apex where urine drains into pelvis (urine collection)
○ Nephrons – functional units
List the subunits of the nephron
○ Bowman’s Capsule - Cortex
○ PCT - Cortex
○ Descending Limb – outer & inner medulla (start in cortex)
○ Loop of Henle – Inner medulla
○ Ascending Limb – outer & inner medulla (end in cortex)
○ DCT - Cortex
○ Collecting Duct – cortex – inner medulla (to bladder)
Describe the structure of the renal corpuscle
○ 1st nephron component – glomerulus (capillary tuft) surrounded by Bowman’s capsule
○ Glomerulus - indents bowman’s capsule = specialised epithelium walling the capsule
○ Podocytes - specialised epithelial cells, line internal wall that sit adjacent to capillary endothelium
○ Capillary endothelium - line external wall, sit adjacent to podocytes
○ Afferent arteriole - supply glomerular tuft (arterial blood that perfuses of capillary network), glomerulus capillaries have fenestrated endothelium
○ Efferent arteriole – carries blood away from glomerulus
○ Mesangeal cells - within & outside glomerulus
○ PCT & DCT sit adjacent to glomerulus
Describe the process of filtration in the renal corpuscle
○ Three layers = filter
§ Endothelial cells (line glomerular capillaries)
· Restricts blood cells
§ Glomerular basement membrane - main filtration barrier
(collagen & glycoprotein -ve charged matrix)
§ Podocyte visceral epithelial lining (of bowman’s capsule)
· Restricts med-size proteins & phagocytose macromolecules
○ Net filtration pressure
§ Generates filtrate in bowman’s capsule
§ Pushes solvents/solutes in or out of filtrate
§ Caused by: Hydrostatic & oncotic pressure
Briefly describe the function of the proximal convoluted tubule
○ Reabsorb water (osmosis)
○ Solutes are either
§ reabsorbed from filtrate (glucose, amino acids, most Na+, Cl-, HCO3-)
§ secreted into filtrate
○ paracellular route – via conc./electrical gradient (flux between cells)
○ transcellular route – via active transport
(move across cells from 1 place to another)
- Describe the four basic membrane transport mechanisms (Diffusion)
§ Powered by random movement of molecules in a solution.
§ Net movement is from high concentration to low
§ Does not saturate.
§ Diffusion of different substances do not interfere with each other (no comp)
§ Net flux (amount of movement) is proportional to the concentration difference and the permeability of any barrier
§ Substances can cross cell membranes by diffusion if they can dissolve in the membrane (lipid = hydrophobic)
§ Diffusion can occur through tight junctions
§ Osmosis - diffusion of water down its concentration gradient is
- Describe the four basic membrane transport mechanisms (facilitated diffusion)
§ Proteins act as carriers or pores to permit flux of substances that cannot diffuse directly through a membrane
§ Movement is still passive (like diffusion), from high concentration to low Occurs across cell membranes only
§ Saturates due to limit of available carrier protein
§ Related substances can compete for the same carrier or pore
§ Transport max ( TM ) Max rate of transport (fully saturated)
- Describe the four basic membrane transport mechanisms (primary active transport)
§ Proteins in the membrane can act as pumps
§ Move ions or small molecules from low conc. to high conc. (up gradients)
§ Require cellular energy (ATP)
§ Saturates due to limit of available protein pump
§ Example: Na-K ATPase
□ present in nearly every cell in the body.
□ Pumps 3 Na ions out in exchange for 2 K ions pumped in (cost 1 ATP)
§ Other pumps include the Ca-ATPase, and the H-ATPase
- Describe the four basic membrane transport mechanisms (secondary active transport)
§ Uses proteins similar to those for facilitated diffusion
§ Couples the movement of several different molecules in each cycle
§ Can saturate due to limit of available protein
§ Co-transport moves 2+ molecules in the same direction across membrane
§ Counter transport moves molecules in opposite directions
§ Normal active transport (Na-KATPase) makes a strong Na gradient and powers many secondary active transport mechanisms
§ Example: Na-Glucose co-transport
Describe the exchange processes that occur in PCT & Loop of Henle
○ Proximal convoluted tubule
§ Sodium reabsorb = Cl follows = 65% water following NaCl
§ Paracellular reabsorption of sodium – via diffusion
§ Transcellular reabsorption of sodium – by ATPase pump (active transport)
§ Cells secrete into lumen – metabolites & xenobiotics
○ Loop of Henle § Descending Limb □ Absorb 20% water □ Impermeable to electrolytes § Ascending Limb □ Absorb electrolytes (Na+, K+, Cl-) □ Impermeable to water § Ion & water fluxes = increase osmotic gradient in medulla □ Gradient used to reabsorb water in collecting duct
Describe the exchange processes that occur in: DCT & Late tubule/collecting duct
○ Distal convoluted tubule
§ Small Na+ reabsorbed (Cl- is co-transported)
§ Ca2+ reabsorption via parathyroid hormone
§ Impermeable to water
○ Late tubule & Collecting duct
§ K+ & H+ actively secreted (inc. when more Na+ is actively reabsorbed)
§ Small levels of Na+ reabsorbed (4%)
§ Aldosterone – hormone increase Na+ absorption & K+ excretion
○ Water – only reabsorb if ADH is present
Discuss the kidney’s role in regulating plasma osmolality and sodium balance
§ Plasma osmolality too low = net movement of water into cells
§ Plasma osmolality too high = net movement of water out of cells
§ Too low OR high = cell function is compromised
§ Kidney function to maintain plasma osmolality within narrow limits
§ 1% variation in plasma osmolality = trigger a corrective response via kidneys
○ The corrective response is achieved by varying the amount of water reabsorbed by the collecting ducts
- Disscuss the kidney’s contriution to the endocrine systems (ADH - antidiuretic hormone)
§ Regulate water balance
§ Secreted when plasma osmolality inc. (too many solutes, not enough water)
§ ADH allows water to diffuse out of DCT & collecting duct (inc. urine conc.) & back into the body (inc. water retention)
□ Process
® ADH bind to membrane receptor
® activates cAMP 2ndary messenger signal
® storage vesicles form AQP2 water pores into apical membrane
□ water reabsorbed via
® collecting duct cell –> medullary interstitial fluid –> vasa recta
(body)
§ Vasoconstrictor in blood vessels (inc. blood pressure & volume) when a dec. blood pressure is sensed by baroreceptors
