BIO 161 Study Guide - Final Guide: Distal Convoluted Tubule, Proximal Tubule, Urethral Sphincters
1
URINARY SYSTEM
What are the Functions of the Urinary System? Main function: to regulate to volume,
pressure, and composition of the blood
1. Excretion of metabolic wastes
- Urea
o Ammonia = end product of protein breakdown
▪ Very toxic to cells
▪ Combines with CO2 to form urea
• Less toxic, but still needs to be removed (by kidneys)
o Uric acid = end product of nucleic acid breakdown
▪ Toxic to cells
▪ Limited solubility in blood
• If too much, precipitates out = gout
o Creatinine = from creatinine phosphate breakdown
2. Maintains fluid balance in the body
- Important for blood pressure regulation
3. Maintains proper acid-base balance
- Monitors and controls blood pH
o Secretes H+
o Reabsorbs bicarbonate
4. Produces erythropoietin (kidneys)
- Erythropoietin – enzyme produced when oxygen in blood is low
o Stimulates RBC production in response
5. Transforms vitamin D into its active form
- Promotes absorption and use of calcium and phosphorous
6. Removes some foreign compounds
- Like drugs, food additives, pesticides, etc.
What are the Organs of the Urinary System and what are their functions?
- 2 kidneys
o Structure: Fist-sized, reddish, bean shaped organs in abdominal cavity
o Function: produce urine
- 2 Ureters
o Structure: muscular tube
o Function: connects urine to bladder
- Urinary bladder
o Structure: hollow, expandable, muscular organ
o Function: stores urine, contraction expels urine into urethra
- Urethra
o Structure: muscular tube
o Function: carries urine from bladder out of body
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2
What is the urination reflex, what does it involve?
- Urination reflex: occurs in response to stretch receptors; sends action potentials
to reflex arc
o If time is right, voluntarily relax external urethral sphincter (skeletal muscle)
o If not, consciously prevent relaxation of external urethral sphincter and
store urine
What is urinary incontinence and what are the possible causes?
- Urinary incontinence: inability to control the relaxation of external urethral
sphincter
- Causes
o Men: damage to external urethral sphincter
o Women: damage, childbirth
o Both men and women: infections, aging, overactive or spastic bladder
o Young children: nervous connections not developed
What is the function of the kidney?
- Function: to regulate the makeup (ions, water, nitrogenous wastes, drugs,
toxins) of the extracellular fluid (interstitial fluid and the plasma)
o Filters the blood
o Forms urine (metabolic wastes, water, ions, and other small soluble
compounds)
What are the renal cortex and the renal medulla? What is the Renal Pelvis?
- Renal cortex: outer portion of the kidney; granular portion that dips down between
the renal medulla
- Renal medulla: cone-shaped tissue masses called renal pyramids
- Renal pelvis: hollow chamber in the kidney that lies inside the renal medulla nad
receives freshly prepared urine from the collecting ducts
What is a Nephron? What does it do? What is the renal corpuscle? What is a renal tubule?
- Nephron: functional unit of the kidney; smallest unit capable of forming urine;
microscopic (1-2 million/kidney) → extracts filtrate from the blood (filters blood);
takes back what body needs, concentrates wastes into small volume of urine
- Renal corpuscle: blood filtering component of nephron; where filtrate is formed
- Rena tubule: site of filtrate processing (reabsorption and secretion); microscopic
tube
Afferent and efferent arterioles?, The peritubular capillaries?, What are their functions?
- Afferent arterioles: carries blood to glomerulus
- Efferent arterioles: carries blood out of glomerulus
- Peritubular capillaries: surround renal tubule
o Blood from the efferent arteriole travels through these capillary networks
and into a venule that travels to the renal vein
-
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3
What is the path that blood takes through the kidneys? Renal artery → afferent arteriole →
glomerulus → efferent arteriole → peritubular capillaries → venules → exits through the
renal vein
What are the Glomerular (Bowman’s) Capsule, the proximal convoluted tubule, the loop of the
nephron (Henle), the distal convoluted tubule, the collecting duct?
- Glomerulus: a knot of capillaries inside the glomerular capsule
- Bowman’s/Glomerular capsule: double walled cup that surrounds the glomerulus
at the beginning of the nephron; outer layer composed of squamous epithelial
cells; inner layer made up of podocytes
- Proximal convoluted tubule: highly coiled region of a nephron near the glomerular
capsule, where tubular reabsorption takes place
- Loop of Henle: portion of the nephron lying between the proximal convoluted
tubule and the distal convoluted tubule that functions in water reabsorption
- Distal convoluted tubule: final portion of a nephron that joins with a collecting
duct; associated with tubular secretion
- Collecting duct: duct within the kidney that receives fluid from several nephrons;
the reabsorption of water occurs here
-
What are podocytes?
- Podocytes: have long, cytoplasmic extensions; cling to capillary walls of
glomerulus and leave pores that allow easy passage of small molecules from the
glomerulus to the instead of the glomerular capsule
What are the Three Urine-forming Processes performed by the nephron?
1. Glomerular Filtration
2. Tubular Reabsorption
3. Tubular Secretion
What is Glomerular Filtration, where does it occur, how does it occur, and what is the result of
the process?
- Glomerular filtration: movement of small molecules from the glomerulus into the
glomerular capsule due to the action of blood pressure
o occurs in glomerulus
o driven by blood pressure
Where do the filtered substances start, where do they end up, and how do they get there?
o fluid and dissolved substances are squeezed through (capillary
endothelium, basement membrane, podocytes)
▪ water and small molecules get out
▪ cell and plasma proteins don’t
o filtered fluid is called: glomerular filtrate
o aside from size, glomerular filtration is non-selective (any solutes small
enough can get through)
o approximately 20% of plasma is filtered as it passes through glomerulus
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Document Summary
Main function: to regulate to volume, pressure, and composition of the blood. If too much, precipitates out = gout: creatinine = from creatinine phosphate breakdown, maintains fluid balance in the body. Important for blood pressure regulation: maintains proper acid-base balance. Monitors and controls blood ph: secretes h, reabsorbs bicarbonate, produces erythropoietin (kidneys) Erythropoietin enzyme produced when oxygen in blood is low: stimulates rbc production in response, transforms vitamin d into its active form. Promotes absorption and use of calcium and phosphorous: removes some foreign compounds. 2 kidneys: structure: fist-sized, reddish, bean shaped organs in abdominal cavity, function: produce urine. 2 ureters: structure: muscular tube, function: connects urine to bladder. Urinary bladder: structure: hollow, expandable, muscular organ, function: stores urine, contraction expels urine into urethra. Urethra: structure: muscular tube, function: carries urine from bladder out of body. Urination reflex: occurs in response to stretch receptors; sends action potentials to reflex arc.
