lecture 13 bio142

osmolarity gradient within kidney

low solutes in the cortex, high in the medulla

afferent arterioles

carry blood to glomerulus

efferent arterioles

carry blood from glomerulus

glomerulus is

a network of capillaries

glomerular or bowman’s capsule

filters blood into filtrate

descending limb special characterisitc

has aquaporin -1 AQP

a countercurrent mechanism is one where fluid

in separate structures flows in opposite directions relative to one another. This is achieved due to MEDULLARY concentration gradient. As the fluids pass by each other, materials can be exchanged between fluids.

in the nephron loop, the filtrate is concentrated in the descending limb (water exits nephron) and then

diluted in the ascending limb (solutes exit nephron)

in the arterioles of the kidney (vasa recta), the osmolarity of the blood

does not change appreciable due to its low pressure and slow flow

contents (water, solutes, glucose) that diffuse out of the nephron loop

is returned to the general circulation by way of the vasa recta

nephron pathway

1. Glomerulus

2. PCT

3. descending loop of henle

4. ascending loop of henle

5. DCT

6. collecting duct

Glomerus

filters small solutes from the blood

proximal convoluted tubule

reabsorbs ions, water, and nutrients; removes toxins and adjusts filtrate pH

descending loop of henle

aquaporins allow water to pass from the filtrate into the interstitial fluid

ascending loop of henle

reabsorbs Na+ and Cl- from the filtrate into the interstitial fluid

distal convoluted tubule

selectively secretes and absorbs different ions to maintain blood pH and electrolyte balance

collecting duct

reabsorbs solutes and water from filtrate

urinary tract infections UTI

an infection of the urinary system, which includes the kidneys, ureters, bladder and urethra

UTIs are more common in women due to

a shorter distance between the anus and external urethra orifice, both make it easier for bacteria to infiltrate the urethra. Also common in children under 5

Prevention of UTI

drink lots of water (Some evidence for cranberry juice), wipe front to back, empty bladder after sex

treatment of UTI

often treated with 2 weeks of antibiotics

complications untreated UTIs can be devestating

pyelonephritis can cause long lasting kidney damage , reducing GFR, and potential spread of infection to blood stream

symptoms of UTI

problems peeing, fever, chills, cloudy foul smelling and/or dark pee,, pain in your flank, abdomen, pelvic area, or lower back, pain while peeing, pain during sex

a diuretic

is a drug that increases the amount of urine your body produces, which helps get rid of excess salt and water. AKA water pills

antidiuretic hormone (aka vasopressin)

is given to constrict blood vessels and increase water reabsorption as a means to increase BP

hypertension & kidney function are closely linked

uncontrolled hypertension can damage the kidneys, and kidney disease can lead to or worsen hyper tension, creating harmful cycle

hypertension and diabetes mellitus are the most common cause of

kidney failure, sugar in blood also damages kidney tubules

positive pathway of high bp & kidney function

high bp destroys nephrons, nephroclerosis (blood vessels in kidney becomes hardened) → kidneys dont excrete sodium, dont excrete other waste like uric acid, further reduction of GFR → sodium retention increases bp, waste products in blood damage vessels, further elevation of BP

how high blood glucose damages kidneys

1. more glucose filtered

2. proximal tubule works harder

3. sodium reabsorbtion increases

4. distal nephron misreads signal

5. glomerular hyperfiltration

6. structural damage over time
   over time these changes lead to the scarring of glomeruli, loss of nephrons, and decreased GFR which becomes chronic kidney disease

sodium glucose transport proteins (SGLTs)

are membrane proteins that cotransport glucose and sodium into cells, with SGLT2 being the primary renal glucose reasbsorber

SGLT2 inhibitors provide significant benefits including

reducing blood sugar, lowering BP, and protecting against kidney and heart failure, regardless of diabetes status

micturtion reflex

activates when your body needs to urinate

the flow of urine from the kidney to the urinary bladder through the ureter is relatively continuous.

The urinary bladder acts as a reservoir for urine until it can be eliminated, it can be eliminated quickly at appropriate time and place.

urination is called micturition, and the micturition reflex is active when the

urinary bladder wall stretches as urine fills the bladder

micturition reflex under parasympathetic regulation steps

1. urine filling urinary bladder stimulates stretch receptors, producing APs

2. APs are carried by sensory neurons to spinal cord by pelvic neurons

3. In spinal cord, parasympathetic neurons are activated stimulating smooth muscle of the urinary bladder (detrusor muscle) to contract. Also, somatic motor neurons are inhibited causing relaxation of the skeletal muscles of the urethral sphincter

4. APs carried by sensory neurons from 1 also ascend to brain (pons and cerebellum)

5. micturition reflex integrated in the spinal cord is automatic (i.e happens in brain dead patients, babies, and quadriplegics) However the brain can control this circuit by inhibiting parasympathetic neurons and stimulating the contraction of the urethral specter from step 3

6. The brain voluntarily controls the external; sphincter through somatic motor neurons, causing constriction as you “hold it” OR relaxation when it is time to urinate

more glucose filtered

high blood glucose levels leads to excess glucose being filtered at the glomerulus

proximal tubule works harder

the proximal tubule reabsorbs more glucose, increasing workload and stress on the cells

sodium reabsorption increases

glucose reabsorption pulls more Na+ back into the blood

distal nephron misreads signal

Less Na+ reaches the distal nephron, so it senses low filtration

glomerular hyperfiltration

pressure and blood flow in the glomerulus increase

structural damage overtime

high pressure damages the filtration barrier, leading to leaks and scarring