ANHB1102 Lecture Notes - Lecture 16: Internal Sphincter Muscle Of Urethra, Urethral Sphincters, Renal Pelvis
25 May 2018
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Course
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Urinary System:
Function of Urinary System:
-Homeostasis
-Water balance
-Electrolyte balance
-Removal of nitrogenous wastes
-Removal of toxins
-Blood pH balance
-excrete H+ ions
-reabsorb HCO3-
-Maintain blood pH = 7.4
-Blood pressure regulation (renin)
-Red blood cell production (erythropoietin)
Osmoregulation:
-All animals balance the gain and loss of water and dissolved
solutes
-E.g Na+ Cl- K+ Ca 2+ HCO3-
-Water gain:
-Food, drink (consumed), metabolic water (produced)
-Water loss:
-Urinating, defecating, evaporation (breathing, sweating)
-Osmosis:
-The net flow of water from one side of a selectively permeable
membrane to the other
-Direction of movement = higher concentration of water
molecules (less dissolved matter) to the side with the lower
water concentration (more dissolved matter) (DOWN the
water concentration gradient)
-Solute particles draw water away from the other side
-Kidney = certain cells regulate the rate of urinary water loss by
adding or removing aquaporins
The Kidney:
-Plays a major role in conserving water and regulates the osmotic pressure of
blood
-Fluid intake is HIGH = kidneys excrete dilute urine, saving sales and excreting
water
-Fluid intake is LOW = kidneys conserve water by forming concentrated urine
-Can concentrate urine ~ x4 blood osmotic concentration
-Enables excretion of waste with minimal water loss
Excretion of Nitrogenous Wastes:
-Ammonia (NH3):
-Too toxic to be stored in the body
-Does not diffuse readily into air
-Highly soluble in water
-Diffuses rapidly across cell membrane
-Animal surrounded by water - NH3 readily diffuses out of its
cells
-Must be transported and excreted in large volumes of very
dilute solutions
-Urea:
-Highly soluble in water
-100,00 times less toxic than NH3
-Can be stored in a concentrated solution
-Water required for disposal
-Uric Acid:
-More complex molecule
-Relatively non-toxic
-Largely insoluble in water
-Excreting uric acid minimises water loss
-Requires more energy
-Energy cost balanced by savings in body water
Gross Anatomy of the Urinary System:
The Kidney:
The Ureters:
-Urine enters the ureters from the renal pelvis
-Stretches the ureters
-Contraction of ureter muscle wall
-Peristaltic wave
-Draws urine from the renal pelvis down to the bladder
-Urine enters the bladder from below
The Urinary Bladder:
-Bladder:
-Muscular sac located on floor of pelvic cavity
-Capacity ~ 500mL
-As the bladder fills; it expands superiorly, rug flatten, epithelium
thins from 5-6 layers to 2-3
-Muscularis (muscle wall):
-3 layers of smooth muscle
-Rugae present - allow for stretching
-Mucosa:
-Lined with transitional epithelium
-Highly distensible
The Urethra:
-Conveys urine out of the body
-Internal urethral sphincter:
-Thickening of the muscle of the bladder (smooth
muscle)
-Under involuntary control
-Compresses the urethra and retains during in the
bladder
-External urethral sphincter:
-Muscles of pelvic floor (skeletal muscle)
-Provides voluntary control over the urethra
Neural Control of Micturition:
-Micturition: the act of urinating
-Bladder filling:
-Stretch receptors in bladder wall
-Signals travel to the sacral spinal cord
-Motor nerves contract the muscle of the bladder and relax
internal urethral sphincter
-Voluntary control:
-Input from stretch receptors travels to brain, if timely to
urinate;
-Motor signals to muscle of bladder wall to contract
-Relaxation of the internal urethral sphincter
-Motor signals from brain control the external urethral
sphincter
Gross Anatomy of the Kidney:
-Basic functional unit of the kidney is the nephron
-Each nephron consists of a folded tube and associated
blood vessels
-Nephrons extract a filtrate from the blood and refine the
filtrate into much smaller amount of urine
The Nephron:
-Each kidney has ~ 1.2 million nephrons
-Renal corpuscle = glomerous + Bowman’s capsule
-Filters the blood plasma
-Renal tubule:
-Converts filtrate into urine
1. Proximal convoluted tubule
2. Loop of Henle
3. Distal convoluted tubule
Brain
Document Summary
All animals balance the gain and loss of water and dissolved solutes. E. g na+ cl- k+ ca 2+ hco3- The net ow of water from one side of a selectively permeable membrane to the other. Direction of movement = higher concentration of water molecules (less dissolved matter) to the side with the lower water concentration (more dissolved matter) (down the water concentration gradient) Solute particles draw water away from the other side. Kidney = certain cells regulate the rate of urinary water loss by adding or removing aquaporins. Plays a major role in conserving water and regulates the osmotic pressure of blood. Fluid intake is high = kidneys excrete dilute urine, saving sales and excreting water. Fluid intake is low = kidneys conserve water by forming concentrated urine. Can concentrate urine ~ x4 blood osmotic concentration. Enables excretion of waste with minimal water loss. Too toxic to be stored in the body.
