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Anatomy and Physiology > Urinary System > Flashcards

Urinary System Flashcards

1
Q

Functions of the Urinary System

A

Kidneys dispose of waste products in urine

  • Nitrogenous wastes (excrete liquid waste)
  • Toxins
  • Drugs
  • Excess ions
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2
Q

Regulatory Functions of Kidneys

A

▪ Produce renin to maintain blood pressure and volume by controlling volume of water
▪ Regulate pH and osmolarity of blood by controlling concentration of various ions in blood
▪ Produce erythropoietin and renin to stimulate red blood cell production
▪ Convert vitamin D to its active form

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3
Q

Location of Kidneys

A

▪ The kidneys are situated against the dorsal body wall in a retroperitoneal position (behind the parietal peritoneum)
▪ Peritoneum – membrane which lines the abdominal cavity
▪ The kidneys are situated at the level of the T12 to L3 vertebrae
▪ The right kidney is slightly lower than the left (because of position of the liver)

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4
Q

Kidney Structure

A

▪ An adult kidney is about 12 cm (5 in) long and 6 cm (2.5 in) wide
▪ Convex lateral edge, concave medial surface

▪ Renal hilum
- A medial indentation where several structures enter or exit the kidney (ureters, renal blood vessels, and nerves)

▪ An adrenal gland sits atop each kidney
▪ Two lowest ribs protects kidneys from blows from behind

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5
Q

Three Protective Layers that Enclose the Kidney

A

▪ Fibrous capsule encloses each kidney
▪ Perirenal fat capsule surrounds the kidney and cushions against blows
▪ Renal fascia is the most superficial layer that anchors the kidney and adrenal gland to surrounding structures

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6
Q

Three Regions Revealed in a Longitudinal Section

A
  1. Renal cortex—darker outer region
  2. Renal medulla—deeper region divided in to renal (medullary) pyramids (triangular regions of tissue in medulla)
    Renal columns—inward extensions of cortex like tissue that separate the pyramids
  3. Renal pelvis—medial region that is a flat, funnel shaped tube, deepest part of kidney
    ▪ Calyces form cup-shaped “drains” that enclose the renal pyramids
    ▪ Calyces collect urine and send it to the renal pelvis, on to the ureter, and to the urinary bladder for storage
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7
Q

Blood Supply

A

▪ One-quarter of the total blood supply of the body passes through the kidneys each minute
▪ 20-22% of the blood pumped by heart under resting conditions goes to kidneys
▪ Renal artery provides each kidney with arterial blood supply
▪ Renal artery approached hilum and divides into segmental arteries → interlobar arteries (travel through medulla to cortex) → arcuate arteries (at junction between medulla and cortex) → cortical radiate arteries (supplies renal cortex)

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8
Q

Venous Blood Flow

A

▪ Arterial supply in reverse
▪ Cortical radiate veins → arcuate veins → interlobar veins → renal vein
▪ There are no segmental veins
▪ Renal vein returns blood to the inferior vena cava

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9
Q

Nephrons

A

▪ Structural and functional units of the kidneys
▪ Each kidney contains over a million nephrons

▪ Each nephron has its own blood supply and creates urine which passes through collecting duct to the renal pelvis consists of two main structures

  1. Renal corpuscle
  2. Renal tubule
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10
Q

Renal Corpuscle Consists of: Glomerulus

A
  1. Glomerulus, a knot of capillaries made of podocytes. Blood enters through afferent arteriole and exits through efferent arteriole
    - Podocytes (foot processes that cling to the glomerulus)
    - Filtration slits create a porous membrane – ideal for filtration
    - As blood passes through the capillaries, lot of the plasma leaks through the endothelial cells of the capillaries (which are leaky).
    - As blood passes It then leaks through the filtration slits of the surrounding podocytes into the glomerular capsule.
    - After processing, this becomes urine.
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11
Q

Renal Corpuscle Consists of: Glomerular (Bowman’s Capsule)

A
  • Cup-shaped structure that surrounds the glomerulus
  • First part of the renal tubule
  • Has an inner and outer surface
    o Between the area, there is a hollow space called glomerular capsular space
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12
Q

Renal Tubule

A

▪ Extends from glomerular capsule and ends when it empties into the collecting duct
▪ From the glomerular (Bowman’s) capsule, the subdivisions of the renal tubule are:
1. Proximal convoluted tubule (PCT)
2. Nephron loop (loop of Henle)
3. Distal convoluted tubule (DCT)

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13
Q

Steps of Fluid Flow Through Renal Tube

A
  1. Proximal convoluted tubule begins at glomerular capsules.
  2. Fluid in these capsules passes into the PCT.
  3. Fluid then enters nephron loop (descending and then ascending limb). Descending and lower part of the ascending limb have thinner walls than PCT and DCT.
  4. When fluid reaches thick part of ascending limb, it enters the DCT.
  5. Fluid that reaches the end of DCT, enters the collecting duct.
  6. Each collecting duct receive fluid from various nephrons. It merges into larger ducts and ultimately drains into hollow renal pelvis
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14
Q

Cortical Nephrons

A

▪ Located entirely in the cortex

▪ Include most nephrons, short nephron loops (penetrate slightly into medulla)

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15
Q

Juxtamedullary Nephrons

A

▪ Found at the cortex-medulla junction
▪ Nephron loop dips deep into the medulla
▪ Collecting ducts collect urine from both types of nephrons, through the renal pyramids, to the calyces, and then to the renal pelvis.
▪ Produces highly concentrated urine.

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16
Q

Nephron: 2 Capillary Beds

A
  1. Glomerulus

2. Peritubular capillary bed

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17
Q

Glomerulus

A

Fed and drained by arterioles
▪ Afferent arteriole—arises from a cortical radiate artery and feeds the glomerulus
▪ Efferent arteriole—receives blood that has passed through the glomerulus and has a larger diameter
Specialized for filtration (unique as both drained and fed by arterioles)

High pressure forces fluid and small solutes out of blood and into the glomerular capsule

Most of these are reclaimed by renal tubule cells and returned to blood in peritubular capillary beds

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18
Q

Peritubular Capillary Beds

A

▪ Arise from the efferent arteriole of the glomerulus
▪ Low-pressure, porous capillaries
▪ Adapted for absorption instead of filtration
▪ Cling close to the renal tubule to receive solutes and water from tubule cells
▪ Drain into the interlobar veins leaving the cortex

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19
Q

Urine Formation

A

Urine formation is the result of three processes:

  1. Glomerular filtration
  2. Tubular reabsorption
  3. Tubular secretion

Filtration occurs at renal corpuscle, where water and small dissolved molecules diffuse or spread into the glomerular capsule.

Water, ion and glucose are later reabsorbed into the capillaries from the tubules

Some waste molecules and ions are secreted from the capillaries and into the tubules and collecting ducts

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20
Q

Glomerular Filtration

A

▪ The glomerulus is a filter

▪ Filtration is a nonselective passive process

Water and solutes smaller than proteins are forced through glomerular capillary walls

▪ Proteins and blood cells are normally too large to pass through the filtration membrane

▪ Once in the capsule, fluid is called filtrate

▪ Filtrate leaves via the renal tubule

To reach the glomerular capsular space, the water and fluid must cross the endothelial cells, basement membrane and podocytes of the glomerular capsule. Collectively known as filtration membrane.

Cannot cross the membrane due to being too large in size – red and white blood cells, large and medium sized proteins including albumin

Can cross membrane – water, glucose, urea (metabolism waste product), sodium, potassium, chloride, amino acids

Glomerular filtration rate – normal value for 125ml/min for male and 105ml/min for females

Driving force for this filtration is pressure.

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21
Q

Hydrostatic Pressure

A
  • Occurs as a result of blood being pushed into the afferent arteriole.
  • Pushes blood from high to low pressure.
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22
Q

Osmotic Pressure

A
  • Created by the presence of dissolved substances in water.

- High osmotic pressure pulls in water from low osmotic pressure areas.

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23
Q

Kidneys: Hydrostatic and Osmotic Pressure

A
  • In healthy kidneys, hydrostatic pressure exceeds osmotic pressure.
  • So, slightly more water and dissolved substances are pushed out of the glomerular capillaries and into the glomerular capsule space than pulled back in.
  • There is a small net filtration of fluid out of the glomerular capillaries –> becomes lymphatic fluid.
24
Q

Kidneys: Filtrate

A
  • Filtrate will be formed as long as systemic blood pressure is normal
  • If arterial blood pressure is too low, filtrate formation stops because glomerular pressure will be too low to form filtrate
25
Q

Tubular Resorption

A
  • Begins as soon as filtrate enters PCT
  • Tubule cells are transporters taking up needed substances from filtrate and then passing them out to extracellular space from which they are absorbed into the peritubular capillary blood.
  • Some reabsorption is done passively. Eg. Water passes by osmosis
  • Active transport most common – require ATP, membrane carriers and are very selective
  • The peritubular capillaries reabsorb useful substances from the renal tubule cells, such as: ▪ Water ▪ Glucose ▪ Amino acids ▪ Ions
  • Some reabsorption is passive; most is active (ATP)
  • Most reabsorption occurs in the proximal convoluted tube (DCT and collecting duct are still active)
26
Q

Tubular Secretion

A

▪ Reabsorption in reverse

Some materials move from the blood of the peritubular capillaries into the renal tubules to be eliminated in filtrate
▪ Hydrogen and potassium ions
▪ Creatinine

Secretion is important for:
▪ Getting rid of substances not already in the filtrate ▪ Removing drugs and excess ions
▪ Maintaining acid-base balance of blood (pH)

  • Materials left in the renal tubule move toward the ureter
27
Q

Nitrogenous Waste

A
  • Nitrogenous waste products are poorly reabsorbed, if at all
  • Tend to remain in the filtrate and are excreted from the body in the urine in high concentrations
  • Urea—end product of protein breakdown (when amino acids are used to form energy)
  • Uric acid—results from nucleic acid metabolism
  • Creatinine—associated with creatine metabolism in muscle tissue
  • In 24 hours, filter between 50 to 100 liters of blood plasma through the glomeluar into the tubules which process the filtrate by taking and adding substances about 1.0 to 1.8 liters of urine are produced
28
Q

Urine and Filtrate are Different

A
  • Filtrate contains everything that blood plasma does (except proteins).
  • As filtrate has reached collecting ducts it has lost almost all of its nutrients and water
  • Urine is what remains after the filtrate has lost most of its water, nutrients, and necessary ions through reabsorption
  • Urine contains nitrogenous wastes and substances that are not needed
29
Q

Urine Characteristics

A

▪ Clear and pale to deep yellow in colour

▪ Yellow colour is normal and due to the pigment urochrome (from the destruction of hemoglobin) and solutes

▪ Dilute urine is a pale, straw colour

▪ Sterile at the time of formation

▪ Slightly aromatic, but smells like ammonia with time

▪ Slightly acidic (pH of 6)

▪ Weighs more than distilled water (due to contained nutrients)

▪ Specific gravity of 1.001 to 1.035. Low when excessive fluid is drank/ chronic renal failure. High concentration – inadequate fluid intake, kidney inflammation

30
Q

Solutes Found in Urine

A

▪ Sodium and potassium ions
▪ Urea, uric acid, creatinine
▪ Ammonia
▪ Bicarbonate ions

31
Q

Solutes Not Found in Urine

A 
▪ Glucose 
▪ Blood proteins
▪ Red blood cells 
▪ Hemoglobin 
▪ WBCs (pus) 
▪ Bile
32
Q

Ureter

A

Slender tubes 25–30 cm (10–12 inches) attaching the kidney to the urinary bladder:

  • Continuous with the renal pelvis
  • Enter the posterior aspect of the urinary bladder
  • Run behind the peritoneum

▪ Peristalsis aids gravity in urine transport

  • Each kidney is connected by ureter to the bladder.
  • Renal pelvis connects to the hollow ureter
  • Lined with epithelium and contains smooth muscles in its wall
33
Q

Urinary Bladder

A

▪ Smooth, collapsible, muscular sac situated posterior to the pubic symphysis

▪ Stores urine temporarily

▪ Sits on the floor of the pelvic cavity in front of vagina and uterus in females

Trigone—triangular region of the urinary bladder base based on three openings
▪ Two openings from the ureters (ureteral orifices)
▪ One opening to the urethra (internal urethral orifice)

▪ In males, the prostate surrounds the neck of the urinary bladder

34
Q

Walls of the Urinary Bladder

A
  • Three layers of smooth muscle collectively called the detrusor muscle
  • Mucosa made of transitional epithelium
    ▪ Walls are thick and folded in an empty urinary bladder
    ▪ Urinary bladder can expand significantly without increasing internal pressure
  • Capacity of the urinary bladder
    ▪ A moderately full bladder is about 5 inches long and holds about 500 ml of urine
    ▪ Capable of holding twice that amount of urine

As urine accumulates, the bladder rise superiorly and muscular walls stretches, epithelial walls thins.
- This allows storage of urine without substantially increasing internal pressure

Formed continuously by kidney and stored in the bladder until release is convenient

35
Q

Urethra

A

▪ Thin-walled tube that carries urine from the urinary bladder to the outside of the body by peristalsis

36
Q

Urethra: Functions

A

▪ Females—carries only urine
▪ Males—carries urine and sperm (never at the same time)

Release of urine is controlled by two sphincters
1. Internal urethral sphincter
▪ Involuntary and made of smooth muscle – keeps urethra closed if urine isn’t passed

  1. External urethral sphincter
    ▪ Voluntary and made of skeletal muscle
37
Q

Urethra: Length

A

▪ In females: 3 to 4 cm (1.5 inches long)

▪ In males: 20 cm (8 inches long)

38
Q

Urethra: Location

A

Females
- External opening is anterior to the vaginal opening

Males

  • Travels through the prostate and penis
  • Prostatic urethra –> Membranous urethra –> Spongy urethra
39
Q

Micturition

A

▪ Voiding, or emptying of the urinary bladder
▪ Two sphincters control the release of urine, the internal urethral sphincter and external urethral sphincter
▪ Bladder collects urine to 200 ml
▪ Stretch receptors transmit impulses to the sacral region of the spinal cord
▪ Impulses travel back to the bladder via the pelvic splanchnic nerves to cause bladder contractions
▪ When contractions become stronger, urine is forced past the involuntary internal sphincter into the upper urethra
▪ Urge to void (empty bladder) is felt
▪ The external sphincter is voluntarily controlled, so micturition can usually be delayed (eventually occurs if convenient or not)

40
Q

Fluid, Electrolyte and Acid-Base Balance

A

Blood composition depends on three factors:

  1. Diet
  2. Cellular metabolism
  3. Urine output

Kidneys have four roles in maintaining blood composition:

  1. Excreting nitrogen-containing wastes
  2. Maintaining water balance of the blood
  3. Maintaining electrolyte balance of the blood
  4. Ensuring proper blood pH

Normal amount of water in the human body :

  • Young adult females = 50% (large amount of body fat, less muscle)
  • Young adult males = 60%
  • Babies = 75%
  • The elderly = 45%

Water is necessary for many body functions, and levels must be maintained

41
Q

Three Main Fluid Compartments: Water

A
  1. Intracellular fluid (ICF) 40% of body weight
    ▪ Fluid inside living cells
    ▪ Accounts for two-thirds of body fluid
  2. Extracellular fluid (ECF)
    ▪ Fluids outside cells; includes blood plasma, interstitial fluid (IF), lymph, and transcellular fluid (CSF, humours of the eyes, etc.,)
  3. Plasma (blood) is ECF, but accounts for 3L of total body water.
    ▪ Links external and internal environments
42
Q

Link Between Electrolytes and Water

A

The link between water and electrolytes:
▪ Electrolytes are charged particles (ions) that conduct electrical current in an aqueous solution
▪ Sodium, potassium, and calcium ions are electrolytes are also important to body homeostasis

43
Q

Regulation of Water Intake and Output

A

▪ Water intake must equal water output if the body is to remain properly hydrated

Sources for water intake
▪ Ingested foods and fluids
▪ Water produced from metabolic processes (10%)
▪ Thirst mechanism is the driving force for water intake

If large volumes are lost, kidneys compensate by losing less urine to retain fluid volume

44
Q

Thirst Mechanism

A

▪ Osmoreceptors are sensitive cells in the hypothalamus that become more active in reaction to small changes in plasma solute concentration

▪ When activated, the thirst center in the hypothalamus is notified

▪ A dry mouth due to decreased saliva also promotes the thirst mechanism

▪ When less fluid leaves the blood stream, less saliva is produced, reinforcing thirst response

▪ Also reinforced when blood volume or pressure declines

▪ Both reinforce the drive to drink

▪ As well as regulating fluid volume, kidneys are responsible for ensuring correct concentrations of electrolytes are present in extra and intracellular fluids

▪ Hormones are primarily responsible for reabsorption of water and electrolytes by the kidneys

45
Q

Antidiuretic Hormone

A

▪ Prevents excessive water loss in the urine and increases water reabsorption

▪ ADH targets the kidney’s collecting ducts

▪ When blood volume drops- arterial pressure drops which reduces filtrate volume or solute content in renal tubules.
▪ In addition, hypothalamic osmoreceptors becomes more active and nerve impulses are sent to posterior pituitary to release ADH.

▪ Blood volume increases due to increase water absorption.

▪ ADH is released continuously unless solute concentration of blood drops too low.
▪ Activity of osmoreceptors decreases and excess water is allowed to leave in the urine.

46
Q

Maintaining Electrolyte Balance

A

▪ Small changes in electrolyte concentrations cause water to move from one fluid compartment to another
- Movement alters blood volume, blood pressure and impairs activity of excitable cells (nerve, muscle cells)

▪ A second hormone, aldosterone, helps regulate blood composition and blood volume by acting on the kidney

▪ For each sodium ion reabsorbed, a chloride ion follows, and a potassium ion is secreted into the filtrate
o Sodium – electrolyte most important for osmotic water flow (when blood ion concentration is low, water leaves the blood and enters tissue –> causes edema or swelling)

▪ Water follows salt: when sodium is reabsorbed, water follows it passively back into the blood –> blood volume and pressure increase

47
Q

Renin-Angiotensin Mechanism

A

▪ Most important trigger for aldosterone release

▪ Mediated by the juxtaglomerular (JG) apparatus of the renal tubules

▪ When cells of the JG apparatus are stimulated by low blood pressure in efferent arteriole , the enzyme renin is released into blood

▪ Renin catalyzes reactions that produce angiotensin II

▪ Angiotensin II causes vasoconstriction and aldosterone release (through stimulation of adrenal cortex)

▪ Result is increase in blood volume and blood pressure

48
Q

Maintaining Acid-Base Balance of Blood

A

Blood pH must remain between 7.35 and 7.45 to maintain homeostasis and allow cells to function properly
▪ Alkalosis—pH above 7.45
▪ Acidosis—pH below 7.35
▪ Physiological acidosis—pH between 7.0 and 7.35

▪ Although small amounts of acidic substances are from food, hydrogen ions originate from biproducts of cellular metabolism –> continuously adds substances to blood which disturb acid-base balance

▪ Kidneys play greatest role in maintaining acid-base balance

Other acid-base controlling systems:
▪ Blood buffers
▪ Respiration (eliminating CO2)

Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrations
▪ Bind to H+ when pH drops
▪ Release H+ when pH rises

49
Q

Three Major Chemical Buffer Systems

A
  1. Bicarbonate buffer system
  2. Phosphate buffer system
  3. Protein buffer system
    - All work together –> If hydrogen ion concentration changes in one compartment, it changes in the others as well. Therefore, any abnormal pH is resisted by the entire buffering system
50
Q

Respiratory Mechanisms

A

▪ Respiratory rate can rise and fall depending on changing blood pH to retain CO2 (decreasing the blood pH) or remove CO2 (increasing the blood pH)

  • When C02 enters blood from tissues, most enters the RBCs and is converted to bicarbonate ions for transport in the plasma
  • C02 is expelled from lungs at same rate it is formed in tissues.
  • Therefore, hydrogen ions released when C02 is loaded into blood are not allowed to accumulate as they are tied up in water, when C02 is unloaded from the lungs
  • Under normal conditions –> hydrogen ions produced by C02 have essentially no effect on blood pH
  • However, when C02 accumulates in blood (during restricted breathing) more hydrogen ions are released to blood via metabolic processes –> chemoreceptors in respiratory control centres in brain are activated –> breathing rate and depth increase –> excess hydrogen ions are removed as more C02 is removed from the lungs
  • When blood pH rises –> respiratory centre is depressed –> respiratory rate and depth decrease –> C02 and hydrogen ions accumulate in blood –> blood pH is restored to the normal range
51
Q

Renal Mechanisms

A
  • Chemical buffers can tie up excess acids or bases temporarily but cannot eliminate them from the body
  • Although lungs can eliminate carbonic acid by removing C02, only kidneys can remove other acids generated during metabolism
  • Only kidneys can regulate pH of alkaline substances. Therefore, although they act slowly and require hours or days to change blood pH –> provide most effect way to regulate acid and base balance

When blood pH rises:
▪ Bicarbonate ions are excreted
▪ Hydrogen ions are retained by kidney tubules (most effective)

When blood pH falls:
▪ Bicarbonate ions are reabsorbed and generated
▪ Hydrogen ions are secreted

Urine pH varies from 4.5 to 8.0
- Reflects ability of kidneys to excrete basic or acid ions to maintain blood pH homeostasis

52
Q

Diabetes Mellitus

A
  • A condition in which urine output is abnormally elevated due to large amount of glucose
  • Develops when body fails to produce insulin or when body cells fail to respond to insulin
  • Glucose is usually filtered by the glomerulus and fully reabsorbed in the Renal Tubules, however, too much enters tubules and tubules cannot reabsorb all the glucose
  • Urine has sweet smell
  • Excess glucose creates osmotic pressure and leads to less water reabsorption and more urine production
  • Long term – may lead to kidney damage or diabetic neuropathy which can lead to renal failure or chronic kidney disease
53
Q

Diabetes Insipidus

A
  • Characterised by the production of large amounts of urine that is highly diluted

Caused by failure of the pituitary gland to produce ADH
o Little or no water is reabsorbed if kidney cannot respond to ADH

54
Q

Chronic Kidney Disease

A
  • Developed slowly and can lead to renal failure (less than 15ml – most severe stage)
    o Need kidney transplant or receive renal dialysis
  • Most commonly caused by diabetes mellitus or high blood pressure
  • Associated with a long term decrease in glomerular filtration rate
55
Q

Kidney Stone

A
  • A solid crystalline mass that forms in the urine
  • Made from calcium containing compounds or magnesium or uric acid
  • Greater fluid intake increases flow rate of urine and reduces the chance of crystallisation
56
Q

Urinary Tract Infections

A
  • Usually caused by bacteria that enter the urethra at its outside opening
  • More common in women due to shorter urethra
  • Bacteria can more easily lead the bladder
  • Can travel up the urethra and infect the kidney

Anatomy and Physiology (14 decks)

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