Chapter 18 Urinary System Flashcards
Metabolic Waste Products
Potentially harmful substances to the body
* Must be eliminated
* Of no further use
* Can be harmful if allowed to accumulate
*Examples
* Carbon dioxide and water
* Nitrogenous wastes, primarily urea
*Bile salts and pigments
*Various salts
Routes for Waste Product Elimination
Respiratory system
* Carbon dioxide, water vapor
Sweat glands
* Water, salts, urea
Digestive system
*Bile salts, pigments
Urinary system
* Urea, salts, water, other soluble waste products
The Urinary System
Single most important route for removal of waste products
* Removes nearly all soluble waste from blood
* Transports soluble waste out of the body
Major route for elimination of excess water
Parts of the Urinary System
Kidneys (2)
Ureters (2)
Urinary bladder (1)
Urethra (1)
Microscopic Anatomy of Kidney
Nephron
1 million nephrons per kidney
Nephron = basic
functional unit
* Number varies with size
of the animal
* Composed of:
* Renal corpuscle
*Proximal convoluted
tubule (PCT)
* Loop of Henle
* Distal convoluted
tubule (DCT)
Kidney Functions
Production of urine to facilitate elimination of metabolic waste materials
Maintenance of homeostasis through:
*Blood filtration, reabsorption, secretion
* Fluid balance regulation
*Antidiuretic hormone (ADH) -decreases urination, aldosterone
*Acid-base balance regulation
*Production of hormones
*Erythropoietin, prostaglandins
*Blood pressure regulation
The Kidneys Anatomy
Located in dorsal abdominal area
*Ventral to first few lumbar vertebrae
* On either side of first few lumbar vertebrae
Retroperitoneal to the abdominal cavity
Surrounded by layer of peri-renal fat
Right kidney more cranial than left (except pigs)
Gross Anatomy of Kidneys
Renal cortex-
* Most of urine is formed
Renal medulla
* Mostly collecting ducts that’s moving urine to Renal Pelvis
Calyx
Fibrous connective tissue capsule
Hilus: indented area on medial side
* Ureters, nerves, blood and lymph vessels enter and leave
Renal pelvis: funnel-shaped area inside hilus
Trace a Urea Molecule through the urinary system
- Aorta
- Right and left renal arteries
- Branch of the renal artery
- Afferent arteriole
- Renal corpuscle
- proximal convoluted tubule (reabsorption)
- Loop of Henle
- Distal convoluted tubule (secretion)
- Collecting duct (urine)
- Renal Pelvis
- Ureter
- urethra
Nephron
Structural and functional unit of the kidney
Glomerelus
A network of capillaries, inside the kidney, where the the blood is filtered
3 steps to urine formation
- Pressure filtration - Glomerulus
- Selective reabsorption - proximal convoluted tubule
*sodium, h2o, glucose - Tubular secretion- Distal convoluted tubule
Renal Corpuscle
*Located in renal cortex Glomerulus surrounded by Bowman’s capsule
*Filters blood in first stage of urine production: glomerular
filtrate
Proximal Convoluted Tubule (PCT)
Continuation of capsular space of Bowman’s capsule
Reabsorption and secretion functions
Glomerular filtrate now called tubular filtrate
Loop of Henle
Continues from PCT, descends in medulla, makes a U-turn, and heads back into cortex
Ascending wall becomes thicker again
Distal Convoluted Tubule (DCT)
Continuation of ascending loop of Henle
DCTs from all nephrons in the kidney empty into collecting ducts
*Empty into renal pelvis
*Primary site of ADH action, and regulation of potassium and acid/base balance
Urine Formation Process
Filtration – glomerulus
Reabsorption – PCT
* Na+
* H2O
* Glucose, amino acids
* Other nutrients
Secretion – DCT
*Ammonium
* H+
*Some antibiotics
Nerve Supply to the Kidney
Primarily from sympathetic portion of the autonomic nervous system
* Not essential for kidney function
Sympathetic stimulation causes vasoconstriction of renal vessels
* Temporarily decreases urine function
Blood Supply to the Kidney
*Renal artery enters at hilus
*Subdivides to become series of afferent glomerular arterioles
*Afferent glomerular arterioles carry blood to renal corpuscle
*Glomerular capillaries filter some plasma out of the blood: glomerular filtrate 7,4pH
*Peritubular capillaries
*Oxygen transfer to cells of nephron
*Tubular reabsorption and tubular secretion occur at this level
The Ureters
Tubes that exit the kidney and then connect to the urinary bladder
Continuation of the renal pelvis
Trigone: Arrangement of openings of ureters into bladder and opening from bladder into urethra
Each ureter leaves its kidney at the hilus
Composed of 3 layers:
* Outer fibrous layer
* Middle muscular layer
—Smooth muscle propels urine by peristalsis
*Inner epithelial layer
—Allows ureters to stretch when urine passes
through
Calyx
The periphery of the renal pelvis is interrupted by cuplike projections
Ureters physiology
Enter bladder at an oblique angle
Openings collapse when bladder is full
*Prevent backup of urine into ureters
The Urinary Bladder
*Stores urine as it is produced
*Releases urine periodically from the body
*The wall of the urinary bladder contains smooth muscle bundles that run lengthwise, obliquely, and in a circular direction collectively called the detrusor muscle
* Neck of bladder has circular sphincter muscles- voluntary control.
Renal Artery Blood Pressure
120/80
Anatomy of the Urinary Bladder
Size and position vary depending on amount of
urine it contains
* Transitional epithelium stretches as bladder fills
with urine
* Detrusor muscle contracts to expel urine
Circular sphincter muscles around neck of bladder
*Provides voluntary control over urination process
2 parts:
-Muscular sac
-Neck
Function of the Urinary Bladder
Collect urine
*Kidneys constantly produce urine
Store urine
Release urine
Uresis
Other terms-Urination, Micturition
Expulsion of urine from the urinary bladder into the urethra for elimination from the body
2-3 steps in process:
* Urine accumulation
* Muscle contraction
*Sphincter muscle control
Control of Urination
Urine accumulation
*Bladder constantly accumulates urine
*Stretch receptors in bladder wall are activated
*Pressure of filling bladder reaches certain trigger point
Muscle contraction
*Spinal reflex is activated
* Motor impulse sent to detrusor muscle
*Smooth muscle in bladder wall contracts
*Bladder emptied if animal is not housebroken
Urinary Sphincter muscle control
*Voluntary control of sphincter around neck of bladder offers temporary control of urination
* The fuller the bladder, the more pressure on the sphincter muscle
*Eventually the sphincter muscle relaxes
* Urine is released
The Urethra
*Continuation of the neck of the bladder
*Carries urine from bladder to the external environment
* Runs through pelvic canal
Comparative Anatomy of the Urethra
Female urethra
*Shorter and straighter
* Opens on floor (ventral portion) of vestibule of the vulva
* Lined with transitional epithelium which allows it to expand
Male urethra
* Longer and curved
* Runs along the ventral aspect of the penis
* Lined with transitional epithelium which allows it to expand
Male Urethra
- Longer and curved
- Has both urinary and reproductive functions
– Goes through the prostrate gland - Carries urine or semen
Canine Female Urethra
*Shorter, straighter, wider in diameter
**Strictly a urinary function
* Carries only urine
Filtration of Blood
In Glomerulus
Glomerular capillaries contain many large fenestrations in capillary endothelium
* Fenestrations not large enough to allow blood cells or large proteins to pass through
High blood pressure in the glomerular capillaries forces some plasma out of the capillaries and into the capsular space of Bowman’s capsule
Glomerular filtration rate (GFR): how fast plasma is filtered through glomerulus
Reabsorption (urinary)–
In Proximal Convoluted Tubule - in PCT
Substances to be reabsorbed pass out of the tubular lumen through or between tubular epithelial cells
Substances to be reabsorbed then enter interstitial fluid and pass through endothelium into peritubular capillaries
Sodium and Glucose Reabsorption (kidneys)
Sodium in tubular filtrate attaches to carrier protein that moves it into the cytoplasm of the PCT epithelial cell
Glucose and amino acids attach to same carrier protein and follow sodium into the cell by passive transport (sodium co-transport)
Reabsorption of Other Minerals (Kidneys)
Potassium and calcium reabsorbed in the PCT, ascending loop of Henle, and DCT
* Calcium moves under influence of Vitamin D, PTH, and calcitonin
Magnesium reabsorbed from PCT, ascending loop of Henle, and the collecting duct
*PTH increases its reabsorption
A WET BED
Functions of the kidney:
Acid/base balance
Water removal
Erythropoiesis
Toxin Removal
Blood pressure control
Electrolyte balance
D (vitamin) activation
Secretion (kidney) –
Primarily occurs in the DCT (distal convoluted tubule)
Hydrogen, potassium, and ammonia are eliminated by secretion
Some medications are also eliminated from the body by secretion
Urine pH
Plasma pH – 7.4
Glomerular filtrate pH – 7.4
Urine pH – “It depends”
* Carnivores - less than 7
* Herbivores - greater than 7
Urine Volume Regulation
Urine volume is determined by amount of water contained in tubular filtrate when it reaches the renal pelvis
Controlled by actions of 2 hormones
* Antidiuretic hormone (ADH)
*If absent, polyuria results
*Aldosterone - regulating sodium
Regulation of Blood Pressure
Kidneys help maintain homeostasis by their role in regulating blood pressure
* Renin-angiotensin-aldosterone system responds when blood pressure falls
* Renin is released, and splits enzyme angiotensin
*Increased amounts of sodium and water reabsorbed back into bloodstream, causing an increase in blood volume
*As blood volume increases, so does blood pressure
Glomerular filtration
*Filtration of blood occurs in the renal corpuscle.
*glomerular capillaries found between two arterioles have a high blood pressure.
*high blood pressure forces some of the plasma out of the capillaries
– into the capsular space of Bowman’s capsule.
– transfer of plasma out of the glomerular capillaries is helped by the presence of many fenestrations
– The fluid that leaves through these fenestrations is called the glomerular filtrate
— is similar to plasma except that it contains virtually no proteins.
–Larger molecules that cannot fit through the fenestrations will stay in the bloodstream.
Renal threshold
*The nephron has a specific reabsorptive capability for each substance, known as the renal threshold.
*The renal threshold varies between species.
*A substance that isn’t reabsorbed travels through
the remainder of the nephron, enters the collecting ducts, and will result in a lack of homeostasis
glycosuria
glucose in urine
Polyuria
(PU) – Production of an excessive volume of urine
Polydipsia
(PD) – excessive thirst; drinking increased amounts of water to
balance the amount of water in the body
Urolithiasis
an abnormal condition characterized by the presence of urinary tract stones; can occur anywhere in the urinary system
Uremia
– urine in the blood. Refers to a buildup of waste material, especially urea, in the blood because of insufficient removal by the kidneys
Urine production
The amount of urine produced depends on the flow of blood through the kidneys.
*Approximately ¼ of total cardiac output passes through the kidneys every minute.
–In other words, in 4-5 min, the animal’s total blood volume will have passed through the renal circulation.
▪ Approximately 90% of the renal blood flow directs itself outward into the cortex and glomerular tufts to bto be filtered. ▪The remaining 10% perfuses and nourishes the kidney tissue
ADH
plays the most important role in regulating urine volume.
*acts on DCT and collecting ducts to promote water reabsorption and prevent water loss from the body.
Aldosterone
*Increases reabsorption of sodium into the bloodstream in the DCT and the collecting duct.
*This causes an osmotic imbalance and encourages water to follow the sodium out of the tubular filtrate and into the blood
▪ The hitch is that water cannot move out of the DCT and collecting ducts unless sufficient ADH control is present
