Urinary System Flashcards
State the seven major functions of the
kidneys.
- Excretion of metabolic waste products
* Urea, creatinine, bilirubin, hydrogen - Excretion of foreign chemicals
* Drugs, toxins, pesticides, food additives - Secretion, metabolism & excretion of hormones
* Erythropoetin
* 1,25 dihydroxycholecalciferol (Vitamin D)
* Renin
* Most peptide hormones - Regulation of acid-base balance
- Gluconeogenesis
* Glucose synthesis from amino acids - Control of arterial pressure
- Regulation of water & electrolyte excretion
Describe the mechanism of moving urine from kidneys into bladder
Urine formed in the nephron collects into the renal pelvis of the kidney .
Urine then travels down the ureter due to gravity but
aided by peristalsis into the bladder, acheived by smooth muscle.the pacemaker activity of the smooth muscle in the ureters also contain
mechanosensitive channels that increase the rate of depolarization when they encounter stretch.
Micturition Reflex (At Rest)
Internal sphincter is
contracted (passively)
* External sphincter is
contracted (skeletal
muscle)
* Toxic discharge of
somatic motor neuron
* Higher CNS input, also
Micturation
Stretch receptors on
bladder send afferent
signal to the spinal cord;
leads to:
* Parasympathetic neurons
activating bladder muscle
* Bladder smooth
muscle contracts,
pulling internal
sphincter open
* Inhibition of somatic motor
neuron
* External sphincter
relaxed
* Can be inhibited by CNS
Explain the process of urination and the micturition reflex
the bladder is innervated by the sympathetic nervous system only to control blood flow to the bladder.
The parasympathetic nervous system innervates the bladder, the neck, and the sphincters (Md: somatic motor neuron]
At rest, the internal sphincter is contracted passively and the external sphincter is contracted through skeletal muscle by toxic APs down the somatic motor neuron.
During the micturition reflex, stretch receptors on the bladder send afferent signals to the spinal cord.
This will lead to parasympathetic motor neurons activating the bladder smooth muscle, causing contraction + opening of the internal sphincter.
It also leads to inhibition of the somatic motor neuron l
pudendal) to relax the external sphincter
Excretion
Filtration-Reabsorption+Secretion
Filtration
- Somewhat variable
- Not selective (except for proteins)
- Averages 20% of renal plasma flow
- Takes place at
glomerulus - Substances must
cross filtration
membrane - Glomerular filtrate
composition is about
the same as plasma,
except for large
proteins
Reabsorption
Highly variable and selective
* Most electrolytes (e.g. Na+, K+, Cl-) and nutritional
substances (e.g. glucose) are almost completely
reabsorbed
* Most waste products (e.g. urea) are poorly reabsorbed
Secretion
- Highly variable and selective
- Important for rapidly excreting some waste products (e.g. H+),
foreign substances (including drugs), and toxins
Define filtration , reabsorption,
and secretion .
Filtration is the process the Bowman’s capsule uses to remove waste from the blood. It is somewhat variable and not selective, except concerning proteins. ~ 20% of renal plasma flow is filtered, the remaining 80% continues to the peritubular capillaries.
Reabsorption is the process of putting some components of solute in the nephron back into the blood. It uses energy that is highly variable and selective. Most electrolytes Na+,k+, and nutrients (glucose) as almost completely reabsorbed.
Most waste products are not reabsorbed at all.
Secretion is the process of components of blood being put into the nephron. It is highly selective and variable and uses energy for action. Secretion is important for rapidly excreting waste products.
Glomerular Filtration Rate (GFR)
GFR = 125 ml/min = 180 liters/day
* Plasma volume is filtered 60 times per day
* Filtration fraction (GFR / Renal Plasma
Flow)
= 0.2 (i.e. 20% of plasma is filtered)
Filtration Coefficient of
Glomerular Capillaries
- Kf describes permeability
- In glomerular capillaries, Kf = GFR/NFP
- Normally not highly variable
Using normal values:
Kf = 125ml/min / 10 mmHg
= 12.5ml/min/mmHg
Bowman’s Capsule
Hydrostatic Pressure (PBC)
Normally changes as a function of GFR
* Affected by
* Tubular Obstruction
* Kidney stones
* Tubular necrosis
* Urinary tract obstruction
* Prostrate hypertrophy
* Cancer
Glomerular Capillary Osmotic
Pressure (Pi G)
Affected by
* Arterial plasma oncotic pressure (Pi A)
* increase in Pi A causes increase Pi G
* Filtration fraction (FF)
* increase in FF causes increase Pi G
Glomerular Hydrostatic Pressure (PG)
- Influenced by
- arterial pressure (effect is buffered by
autoregulation) - afferent arteriolar resistance
- efferent arteriolar resistance
- PG is GFR determinant most subject
to physiological control
Renal Blood Flow (RBF)
Kidneys get ~22% of
CO
* To maintain GFR
* Much more than O2 or
nutrient demand
* Kidneys consume ~2X
as much O2 as brain
(per gram weight)
Determinants of RBF
RBF = P / R
* P = renal artery pressure – renal vein pressure
* R = total renal vascular resistance
* Sum of resistances of all renal vessels
Control of GFR and RBF
Neuralhormonal/Paracrine
1. Sympathetic Nervous System
2. Angiotensin II
3. Endothelin
4. Prostaglandins
5. Endothelial-Derived Nitric Oxide
* Local/intrinsic
Sympathetic Nervous System/
catecholamines
(strong innervation)
Increase in RA + Increase RE -> decrease in GFR & decrease in RBF
Endothelin
(released by damaged vessels)
Increase in RA + Increase RE –> decrease in GFR & decrease in RBF
Angiotensin II
(helps prevent GFR)
Increase RE <——-> GFR & decrease in RBF
Prostaglandins/Bradykinin
Decrease in RA + Decrease RE -> Increase in GFR & Increase in RBF
Endothelial-Derived Nitric Oxide (EDRF)
Decrease in RA + Decrease RE -> Increase in GFR & Increase in RBF
Local Control of GFR and RBF
Autoregulation of GFR and RBF
* Myogenic regulation
* Macula densa feedback (tubuloglomerular)
* Angiotensin II
Reabsorption Rate
Filtration Rate – Excretion Rate
Filtration Rate
GFR x Plasma Concentration
Excretion rate
Urine Concentration s x V
(V = urine flow rate)
