Bio307 - Ch. 19 - Kidneys

Urine

dynamically controlled fluid that has a a concentration changed depending on the body's water retention needs

Ureter

smooth muscle tube carrying urine, connects kidneys to the urinary bladder

Urinary Bladder

triangular shaped hollow organ in the lower abdomen, held by ligaments to other organs and pelvic bones

walls relax/expand to store urine

walls flatten and contract to empty urine through the urethra

Urethra

allows urine to pass outside of the body

brain signals for the bladder muscles to tighten, which squeezes urine out of the bladder

sphincter muscles relax, allows urine to exit bladder through the urethra

Renal

refers to anything dealing with kidney function

renal arteries branch off of the abdomen, supply blood to the kidney

renal veins carry blood from the kidneys to the inferior vena cava

Cortex

outside layer or covering of many body organs, so the renal cortex is the outer layer of the kidney

Medulla

inner part of the kidney, visible in a cross section

Nephron

the functional unit of the kidney, a microscopic tubule which makes up an outer cortex and an inner medulla

Glomerulus

ball-like network, a capillary bed where blood flows from the afferent arteriole

Filtrate

a filtered fluid that passes into the lumen of the nephron

Filtration: movement of the fluid from blood into the lumen of the nephron

(Glomerular) Filtration

the first step in making urine, kidney filters excess fluid and waste products out of the blood into urine collecting tubules of the kidney

(Tubular) Reabsorption

movement of filtered materials from the tubule to the blood

(Tubular) Secretion

movement of selected molecules from blood to tubules

Excretion

separation or throwing off of waste product from cells to tissues of a plant or animal

Glomerular Filtration Rate (GFR)

volume of fluid (GFR) that filters into Bowman's capsule per unit time

(Renal) Clearance

excretion rate / concentration of substance in plasma

Micturition

act of urinating, which is a spinal reflex subject to conscious and unconscious control

Major Functions of the Kidney

1: Regulation of extracellular fluid volume and blood pressure
2: Regulation of osmolarity
3: Ion balance maintained
4: Homeostatic regulation of pH
5: Excretion of waste
6: Produce hormones

"Story" of Filtrate through the major sections of the nephron

1) Glomerulus/Bowman's Capsule: protein-free plasma flows from capillaries to the capsule
2) Proximal Tubule: Unregulated isosmotic reabsorption of nutrients (ex: glucose, amino acids), ions, water

3) Loop on Henle: Ions are reabsorbed
(Descending Limb): permeable to water
(Ascending Limb): permeable to ions


4) Distal nephron (distal tubule + collecting duct): regulated reabsorption of ions and water for salt water balance and pH homeostasis

Generally, what categories of substances are typically completely reabsorbed from the kidney and which are selectively reabsorbed, depending on need:

Energy molecules are COMPLETELY reabsorbed (dont want to pee out ur glucose)

Na+ and H2O as needed

Glucose, amino acids are completely reabsorbed

Mechanism of Tubular Reabsorption

a) draw/explain major mechanisms by which Na+, Cl-, water, glucose reabsorbed

b) why a change in one parameter affects another

(how does having fewer Na+/K+ pumps affect water reabsorption)

a) SGLT (cotransport) of glucose/Na+
(sodium-linked reabsorption pathway)

b) Na+/K+ primary active transport pump impacts Na+/Glucose, secondary active transport pathway affected

having less transporters slows diffusion due to a smaller gradient (piggybacking)

Recognize that saturation of transporters limits reabsorption:

explain the role of saturation in diabetes mellitus

glucose transporters reach a fully saturated state, not allowing any more substrate to be absorbed

(glucose concentration surpasses renal threshold so any extra is excreted)

Several substances that are commonly secreted into kidney tubule (tubular secretion)

penicillin

PAH (para-aminohippurate)

urea

GFR remains relatively constant through normal changes in posture or through renal autoregulation

constriction of afferent restricts blood leading to glomerulus

constriction of efferent restricts blood from leaving the glomerulus

explain how knowing a substance's clearance compared to the GFR tells you whether its secreted or reabsorbed (net)

clearance rate = GFR - neither reabsorbed nor secreted

Clearance of X > GFR: net secretion of X

Clearance of X < GFR: net reabsorption of X