UNIT 9 - URINARY SYSTEM Flashcards
Kidney
Two bean shaped organs about the size of a fist located against the posterior back wall (right peritoneal) where the right kidney is lower than the left. It is covered by a fibrous capsule composed of dense irregular connective tissue
Renal fat pad
Shock absorbing layer of adipose layer that covers the capsule of kidney
Functions of the kidney (8)
- Maintaining ACID-base balance
- Maintaining WATER balance
- ELECTROLYTE balance
- TOXIN removal (urea, uric acid)
- BLOOD pressure control
- Making ERYTHROPOIETIN
- Vitamin D metabolism
- = A WET BED
Paired ureters
Transports urine from the kidneys to the bladder
Urinary bladder
Provides a temporary storage reservoir for urine (approx. 700-800mL)
Urethra
Transports urine from the bladder out of the body
Male urethra
Passes through the prostate gland located immediately inferior (below) bladder and also serves as the duct where semen is discharged
Female urethra
Short in length (4cm) which is the reason why many women get UTI’s
Layers of the kidney (3)
- Renal cortex
- Renal medulla
- Renal pelvis
Renal cortex
Outer layer of the kidney that filters blood
Renal medulla
Inner layer of the kidney that contains renal pyramids where urine formation takes place
Renal pelvis
Hollow portion in the middle of each kidney collect urine as its produced
Path of urine drainage (6)
- Collecting duct
- Minor calyx
- Major calyx
- Renal pelvis
- Ureter
- Urinary bladder
Collecting duct:
Consists of a series of tubules and ducts that connect nephrons to minor calyx or directly to renal pelvis
Blood supply of kidney
1/4 (1200mL) of systemic cardiac output flows through the kidneys each minute and the entire blood volume of the body is filtered by the kidneys 60 times a day
Pathway of blood through renal blood vessels (15)
- Aorta
- Renal artery
- Segmental artery
- Interlobar artery
- Arcuate artery
- Cortical radiate artery
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Peritubular capillaries
- Cortical radilate vein
- Arcuate vein
- Interlobar vein
- Renal vein
- Inferior vena cava
Nephron
Basic structural and functional unit of the kidney and consists of a million filtering units on the kidney; has a vascular & tubular component
Vascular components of nephron (5)
- Renal arteries & arterioles
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Peritubular capillary
Tubular components of nephron (5)
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle; descending limb & ascending limb
- Distal convoluted tubule
- Collecting ducts
3 basic systems in urine formation:
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Glomerular filtration
Use of passive pressure to force fluids and solutes into Bowman’s capsule
Bowman’s capsule
Two walled pouch that covers the glomerulus and filters all blood components except blood cells and most proteins
Reasons why glomerular filtration is efficient (3)
- Filtration membrane is thin & very permeable
- Glomerular blood pressure is higher than that in Bowman’s capsule
- Glomerular capillaries present a large surface area
Tubular reabsorption
Process by which about 99% water and most solutes are removed from the tubular fluid and returned to blood stream (160L a day), can be active transport, facilitated, or simple diffusion based on size
Why is tubular reabsorption called reabsorption and not absorption
Because these substances have been absorbed previously, usually in the intestines
Tubular reabsorption breakdown (4)
- 65% reabsorption in proximal convoluted tubule
- 16% reabsorption in limb of Henle
- 10-15% reabsorption in distal convoluted tubule
- 5-9% in collecting duct
What is reabsorbed along the length of the nephron (generally) (6):
- Water
- Salts (Na+, CL-)
- Bicarbonate ion (HCO3-)
- Ions (Ca2+, K+)
- Urea 50%
- Glucose and amino acids (only in PCT)
What is reabsorbed along the length of the nephron (PCT) (5)
- Water
- Salt
- Bicarbonate ion
- Glucose
- Amino acids
Loop of Henle
Long U-shaped loop that carries filtered fluid down to medulla and back to cortex to reabsorb water and salts
Descending limb (downward path)
Absorbtion water = fluid more concentrated
Ascending limb (upwards path)
Absorbtion of salt = fluid less concentrated
Thicker portion of ascending limb
Region that actively pumps out salt to make medulla even saltier
Result of loop of Henle
By the end of the loop, reabsorption of both water and salt has occurred so that the filtrate at the very end of loop is diluted
Important hormones for reabsorption at the distal convoluted tubule (2):
- Aldosterone: Water, NaCl
- Parathyroid hormone: Calcium
Important hormones for reabsorption at the collecting duct (2):
- ADH: Water
- Aldosterone: Urea, NaCl
Tubular secretion
Process of transporting solutes into the renal tubule to be excreted in the urine
Importance of tubular secretion (4)
- Disposing of substances not already in filtrate
- Eliminating undesirable substances (eg. Urea, uric acid)
- Ridding the body of excess potassium ions
- Controlling blood pH
Water
Reabsorbed throughout nephron, secreted through collecting duct
Sodium
Reabsorbed throughout PCT & ascending limb , secreted through DCT & collecting duct
Potassium
Reabsorbed though PCT & ascending limb, secreted through DCT & collecting duct
Hydrogen ion
Secreted through PCT & collecting duct
Bicarbonate ions
Reabsorbed through PCT & DCT
Glucose
Reabsorbed in PCT
Urea
Reabsorbed in PCT & collecting duct, secreted in ascending limb
Chemical compositions of urine
Urine is made of 95% water and 5% solutes (urea, sodium, chloride, potassium, phosphate, sulfate, calcium, magnesium, bicarbonate)
Urea
Nitrogenous waste product formed in the liver as a result of protein metabolism
Uric acid
Waste product formed during the breakdown of nucleic acids
Factors that affect urination (voiding) (9)
- Food/fluid intake + loss
- Temperature
- Humidity
- Body temperature
- General health
- Stress
- Activity
- Life style
- Medication
Average amount of urine per day
1 to 2L per day
Average amount of urine per hour
Output of 50-60mL per hour is normal, an output of less than 30mL per hour could indicate kidney failure
Specific gravity
Measures density of a substance in comparison to density of water
Urine pH average
Range is 5.0-7.8 and variations are closely related to diet as well as factors such as high altitude, fasting, and exercise (high protein = acidic, high vegetable diet = basic)
2 most important hormones regulating urine volume and composition
ADH and aldosterone
Diuresis
Physiological process by which urine production in the kidneys is increased
ADH
Produced by the hypothalamus, released by the posterior pituitary gland and affects the ability of kidney to reabsorb water
Stimulation for ADH
Increased plasma osmolarity, fall in blood volume
Results of ADH action (4)
- Blood volume increases
- Blood osmolarity falls
- Urine volume decreases
- Urine solute concentration increases
Juxtaglomerular cells
Specialized smooth muscle cells mainly in walls of afferent arterioles that deliver blood to glomerulus and synthesize, store, and secrete enzyme renin
Renin
Regulates blood pressure
Aldosterone
Hormone released by adrenal glands that help regulate blood pressure by managing levels of sodium and potassium in blood
Angiotensin II
Stimulates adrenal cortex to release aldosterone
Stimulation of aldosterone
Blood volume decrease, decrease in blood Na+, and increase in plasma K+ directly on adrenal cortex
Blood pressure decrease regulation
Renin –> angiotensin II –> aldosterone
Results of aldosterone action (3)
- Reabsorption of Na+ and Cl-
- Water reabsorption
- Secretion of K+ and H+ in collecting ducts
Aldosterone effects on blood
Increased volume, increased Na+, reduced K+, and increased pH (basic)
Aldosterone effect on urine
Reduced volume, reduced Na+, Increased K+ and increased H+
ADH and aldosterone both increase water reabsorption but how are they different
ADH responds to increase in blood osmolarity, and aldosterone responds to decrease in blood pressure/volume
Micturition reflex
Bladder to bladder contraction reflex
Process of micturition reflex (5)
- When bladder is full, stretch receptors signal micturition centre in sacral spinal cord to trigger micturition reflex
- Reflex signal is sent to smooth muscle in bladder wall and internal sphincter
- Bladder wall contracts and internal sphincter relaxes
- External sphincter (skeletal muscle) also relaxes
- Voiding results
Nervous control of micturition
We can sense the bladder being full before the reflex actually occurs and adults can consciously keep external sphincter contracted even when the reflex occurs which keeps the internal sphincter contracted = no urination
How much urine does it take for micturition to occur
500ml to 600ml and greater
