Physiology Flashcards
What is urine?
Remaining water and solutes after the kidneys have filtered the blood plasma
What are 3 things that allow urine to move through the ureters to the bladder?
What prevents backflow?
- Peristaltic waves
- Hydrostatic pressure
- Gravity
No backflow = physiological sphinter (bladder filling compresses opening)
What is the input to:
- The prostatic urethra
- The spongy urethra
Prostatic = urine, secretions from prostate containing sperm, and things to neutralize acidity and contribute to sperm motility/viability
Spongy = urine, mucus, things to neutralize acidity
What is the job of the pontine micturition center? Where does it get its input?
Job = regulaiton of micturition and relaxation of urethral sphincter
Input = bladder, medial frontal cortex, insular cortex, hypothalamus, periaqueductal gray
Explain the micturition reflex
- Urine volume exceeds 200-400mL and we sense fullness
- We decide that we will allow urination and relax the pelvic floor muscles
- Stetch receptors send an AP to the spinal micturition center
- The spinal micturition center inhibits motor neuons of the external sphinter and sends a PNS impulse to the urinary bladder and internal sphincter for bladder contraction and sphincter relaxation
- Urination occurs.
What is in the fluid the prostate secretes into the prostatic urethra?
- Semen (30% of total)
- Spermatozoa
- Seminal vesicle fluid
What is the renal blood flow? (L/min)
1.2 L/min
What are 8 main functions of the kidneys?
- Regulate water and electrolyte balance
- Regulate body fluid volume
- Regulate blood osmolarity/electrolyte concentration
- Regulate blood pH
- Regulate arterial blood pressure
- Produce hormones (calcitriol, erythropoietin)
- Regulate blood glucose
- Excrete waste (ammonia, urea, bilirubin) and foreign substances from the body
What are the 3 processes involved in the formation of urine by the nephron? Define each:
- Glomerular filtraiton = movement of water and most solutes from blood plasma to Bowman’s capusle and renal tubule
- Tubular reabsorption = reabsorption of 99% of water/solutes from the renal tubule back into the blood (peritubular capillaries/vasa recta)
- Tubular secretion = secretion of wastes, drugs, and excess ions back into the fluid from the blood (peritubular capillaries/vasa recta)
- How much fluid is filtered by the renal corpuscle a day?
- How much fluid is excreted in urine a day?
- What is the glomerular filtration rate in mL/min?
- How much blood flows through the kidney in a minute? What % becomes filtrate?
- 150 L in females and 180 L in men
- 1-2 L
- 105 mL/min in females and 125 mL/min in men
- About 1L/min; About 20%
What is the filtration fraction?
The fraction of blood plasma in afferent arterioles that becomes glomerular filtrate (usually 16-20%)
What are 2 ways that filtration prevents proteins from making it into the filtrate?
- Endothelial cell fenestration size
- Negative charge of the basal lamina between capillary endothelium and podocytes
What is able to make it through the podocyte’s slit membrane?
Water, glucose, vitamins, amino acids, small plasma proteins, ammonia, urea, and ions
What 3 forces determine what the net filtration pressure will be?
- Glomerular blood hydrostatic pressure (~55mmHg)
- Capsular hydrostatic pressure (~15mmHg)
- Blood colloid osmotic pressure (~30mmHg)
NFP = 10mmHg
What are 6 ways the body regulates glomerular filtration rate?
- Myogenic mechanism = afferent arteriole stretching leads to vasoconstriction of the afferent arteriole (via prostaglandins/decreased NO)
- Tubuloglomerular feedback = increased Na/Cl/water delivery in macula densa causes decreased NO release from JGA and thus vasoconstriction
- Macula densa = decreased Na/Cl/water delivery in macula densa causes them to release prostaglandins which causes vasodilation of the afferent arteriole
- Epinephrine binding to alpha 1 receptors causes afferent arteriole vasoconstriction
- Angiotensin II causes vasoconstriction of afferent and efferent arteriole
- ANP = stretch of teh atria leads to relaxation of mesangial cells and increased filtration
What part of the nephron has the biggest role in reabsorption?
What solutes are reabsorbed in the nephron?
What are 2 routes of reabsorption?
Proximal convoluted tubule
Glucose, amino acids, urea, sodium, potassium, calcium, chloride, bicarbonate, phosphate, small proteins/peptides
Paracellular reabsorption (between cells) or transcellular reabsorption (passive, primary active, secondary active)
What part of the nephron has the biggest role in secretion?
What solutes are secreted in the nephron?
Distal tubule and collecting ducts
Creatinine, certain drugs, hydrogen, potassium, ammonium
What does the proximal convoluted tubule reabsorb (and in what percentages?)
What does the proximal convoluted tubule secrete?
- Water, Na+ and K+ = 65-70%
- Glucose and amino acids = 100%
- Cl- and urea = 50%
- HCO3- = 80-90%
- Ca++, Mg++, HPO4- = variable
Secrete = H+, NH4+
Explain the role of sodium in establishing solute movement in the PCT
Sodium is pumped into the interstitium via ATPase powered Na+/K+ pump
This creates a concentration gradient that pulls sodium into the cell from the lumen.
Using symporters, this energy also pulls in 2 glucose, amino acids, phosphate, and citrate. It also pulls out Na+
Explain how the proximal convoluted tubule deals with hydrogen and bicarbonate?
- HCO3- is filtered into the tubule
- In the PCT, H+ is secreted into the lumen
- H+ and HCO3- join to form H2O and CO2. The H2O is excreted and the CO2 is absorbed. If there is excess H+ it is excreted. If there is excess HCO3- it is excreted
- CO2 once in the cell reacts with H2O in the cell to form HCO3- and H+. HCO3- enters the blood while H+ enters the lumen.
- Production of HCO3- can also occur when glutamine is metabolized to NH4+ and HCO3-. The NH4+ is excreted and the HCO3- enters the blood
- How much of our body’s fluids are ICF vs. ECF?
- Of the ECF, how much fluid is interstitial vs. plasma?
- Where else is our body’s fluids located?
- ICF = 2/3, ECF = 1/3
- Interstitial = 80% of ECF, plasma = 20% of ECF
- Lymph, CSF, synovial fluid, aqueous humor, vitreous body, endolymph, perilymph, pleural fluid, peritoneal fluid, pericardial fluid
What percent of our body is fluid (vs. solid)
55% in women and 60% in men
How is water gained in our body versus lost?
Gained = drink liquids, eat moist food, aerobic respiration, dehydration synthesis
Lost = kidney excretion, perspiration, sweat, exhalation, feces, menstrual flow
How does our body ativate the thirst center in the hypothalamus?
- Increased blood osmolarity detected by hypothalamic osmoreceptors
- Angiotensin II from kidney’s sensing low BP –> siganls hypothalamus
- Baroreceptors in heart/vessels sensing BP –> signals hypothalamus
- Decreased salivary flow sensed by neurons in the mouth –> signals hypothalamus

































