Urinary System / Portage Learning A&P2, Module 7

urinary system organs

2 kidneys

2 ureters

1 urinary bladder

1 urethra

Membranous urethera

Within the urogenital diaphragm

kidney (shape, weight, location)

bean shaped / size of soup can, about 5oz / located between T12-L3 vertebrae and are protected by the rib cage / right is slightly lower than the left b/c of the liver above it

adrenal glands

a pair of endocrine glands that sit just above the kidneys and secrete hormones (epinephrine and norepinephrine) that help arouse the body in times of stress.

renal hilus (hilum)

a notch located near center of medial concave side of the kidney / the passageway to renal sinus for vessels and ureter

3 layers of kidney tissue (outermost to innermost)

renal fascia (outer, fibrous connective tissue, keeps kidney in place), adipose capsule (middle, fatty layer protects kidney from trauma), renal capsule (inner layer of protective tissue projects kidney from injury + infection)

3 regions of kidney (outermost to innermost)

cortex, medulla, renal pelvis

renal pelvis (of kidney)

central collecting region in the kidney, extensions of the pelvis (calyces) collect urine and drain continuously into pelvis and then into ureter

kidney blood supply chain

Abdominal aorta -> renal artery -> segmental artery -> lobar artery -> interlobar artery -> arcuate artery -> interlobular artery -> afferent arteriole -> glomerular capillaries / filtration / efferent arteriole -> peritubular capillaries (deoxygenated) or vasa recta -> interlobular vein -> arcuate vein ->interlobar vein -> renal vein which exits kidney

Input from the _______ adjusts the diameter of the renal arteries thereby regulating renal blood flow.

sympathetic nervous system

Ureters

Thin muscular tubes that carry urine from the kidneys to the bladder.

ureterovesical valves

sphincters located where the ureters enter the bladder, prevent urine from flowing back toward the kidney

trigone of bladder

triangular region at the base of the urinary bladder between the openings of the two ureters and the urethra

urinary bladder (location)

the male bladder lies in front of the rectrum + just behind the pubic symphysis / the female bladder sits below uterus, in front of vagina

ureteral orifices

The opening of a ureter into the urinary bladder

3 layers of ureter wall (outermost to innermost)

outer fibrous connective tissue layer / middle muscular layer, uses peristaltic waves to carry urine to bladder / inner layer made of transitional epithelium, continuous with kidney's lining, becomes stratified epithelium towards exit

3 layers of bladder wall (outermost to innermost)

outer fibrous connective tissue layer / middle detrusor muscle layer / inner mucosal layer made of transitional epithelium specialized to enable cellular expansion to absorb fluid

Describe the bladder when it is full and when it is empty.

When filled with urine, the bladder swells and becomes pear-shaped, raising in the abdominal cavity / It collapses into a pyramid shape when empty

2 sphincters of the bladder

Internal Urethral Sphincter (involuntary controlled) + External Urethral Sphincter (voluntary controlled)

transitional epithelium location

lines the ureters, bladder, and part of the urethra, specialized to enable cellular expansion to absorb fluid

Differences between male and female urethra:

Female is shorter and only carries urine. Male is longer and carries urine and semen

3 regions of male urethra

prostatic urethra, membranous urethra, spongy (penile) urethra

nephron

Functional and structural unit of the kidney, function of the nephron is to control the concentration of water and soluble materials by filtering the blood, reabsorbing needed materials and excreting the rest as urine.

nephron (functions)

• Controls concentration of water and soluble materials

• Eliminates waste from blood

• regulation of blood pressure, pH, blood volume and electrolyte balance.

renal tubule consists of

proximal convoluted tubule, loop of henle, distal convoluted tubule

glomerulus

A ball of capillaries surrounded by Bowman's capsule in the nephron

glomerulus capsule (renal corpuscle)

composed of the glomerulus, a network of tiny blood capillaries surrounded by the glomerular (Bowman's) capsule, a double-walled simple squamous epithelial cup

What causes water and solutes to leave the glomerulus?

• The afferent arteriole, which is fed by the interlobular artery, is much larger in diameter than the efferent arteriole.

• The difference in diameter causes an extremely high blood pressure in the glomerular capillaries, forcing water and solutes out of the blood, thus making filtration possible.

• Water and solutes leave the glomerulus, enter the glomerular capsule, and subsequently flow into the renal tubule.

filtrate

water and solutes that have been filtered through the glomerulus and entered the glomerular capsule (Bowman's capsule)

________are found in the cortex region of the kidney, except for a portion of their loop of Henle which extends into the medulla. ______pass deeply into the medulla because of their location and their longer loops of Henle.

Cortical nephrons / Juxtamedullary nephrons

proximal convuluted tubule (PCT)

first coiled section of the renal tubule, specialized to reabsorb water and many solutes from the glomerular filtrate and secrete unwanted substances

Loop of Henle

second section of renal tubule, initial descending limb that allows water loss followed by ascending limb that allows salt loss

distal convuluted tubule (DCT)

last coiled section of renal tubule, allows for hormonal controlled reabsorption of water and solutes, mostly responsible for secretion of unwanted substances

Filtrate is considered urine once it:

reaches the renal pelvis

fenestrations

are small openings in the capillary endothelium that allow the passage of water, solutes, and small proteins.

What are the three types of capillaries associated with nephrons and their function?

1. Glomerular Capillaries, highly coiled capillary beds formed from afferent arteriole, leaving as efferent arteriole, specialized for filtration because of porosity and high pressure

2. Peritubular capillaries, closely follow renal tubules and drain into interlobular vein, adapted for reabsorption because of porosity and low pressure

3. Vasa Recta, follows loop of Henle in juxtamedullary nephrons of the medulla

micturition

urination, the act of emptying the bladder

incontinence

inability to control urination

urine retention

inability to empty the bladder

How many times a day does the kidney filter through the blood plasma?

60 times each day, using 25% of the resting body energy to excrete waste as urine

About how many gallons are filtered vs. excreted as urine?

About 47 gallons of glomerular filtrate containing the water, nutrients, and essential ions are removed daily from the blood plasma. By the time filtrate enters the collecting ducts, it contains about only 0.5 gallons of urine, with the other 99% being returned to the blood.

3 steps of urine formation

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

What is Blood hydrostatic pressure (HP)?

the amount of pressure found inside the blood in the capillaries, driving fluids out of the glomerular capillary (rises with BP)

What is Colloid osmotic pressure (COP)?

aka oncotic pressure, the movement of fluid from the interstitial fluid back into the capillaries dependent on the amount of proteins in the plasma (normal range 25-32mmHg

Capsular Pressure (CP)

It also opposes blood hydrostatic pressure and drives fluid back into the glomerular capillaries.

Net Filtration Pressure (NFP)

the difference between net hydrostatic pressure and net osmotic pressure when entering the PCT (difference between outgoing forces and incoming forces at the glomerulus)

What prevents blood cells from leaving the glomerular capillaries?

The size of the capillary fenestrations prevents passage of blood cells and most blood proteins from leaving across the filter.

Glomerular Filtration Rate (GFR)

the amount of blood filtered by the glomerulus over time (normal GFR is 120-125mL/min or 180 L/day)

What causes an increase in the GFR? a decrease?

GFR is increased by arterial blood pressure in the kidneys. Decreased by an increase in glomerular osmotic pressure most often caused by dehydration.

What happens if the GFR is too slow? too fast?

If flow is too slow, nearly all the filtrate is reabsorbed, including most of the wastes that should be exerted. If flow is too fast, the needed substances cannot be adequately reabsorbed.

What are the three mechanisms that regulate renal flow?

Renal Autoregulation / Nervous System Controls / Renin-Angiotensin-Aldosterone (RAA)

Renal Autoregulation of GFR

Under normal circulstances, the kidneys themselves regulate GFR by controlling the diameter of the afferent and efferent arterioles.

Nervous System Control of the GFR

Nervous system takes over regulation by narrowing afferent arteriole diameter, the adrenal glands secrete epinephrine which decreases renal blood flow and therefore decreases GFR

renin-angiotensin-aldosterone system (RAA)

Decreased blood pressure causes the juxtaglomerular cells of kidneys to secrete renin which converts angiotensinogen (inactive) to angiotensin I (active) which is then converted into angiotensin II by angiotensin-converting enzyme (ACE) / Angiotensin II stimulates the adrenal cortex to secrete aldosterone which causes renal tubules to reabsorb more sodium ions and increased blood pressure/ Once blood pressure is restored, there is a decreased drive to stimulate renin release

Angiotensinogen

a pre-enzyme produced by the liver and freely circulates in the blood (is converted to angiotensin 1 and then angiotensin 2 to trigger thirst mechanism during RAA)

When blood pressure drops, the enzyme ____ is released by the juxtaglomerular (JG) cells of the nephron.

renin

In the ____, angiotensin I is converted to ____. (during RAA)

lungs, angiotensin II

Once circulating angiotensin II reaches the adrenal cortex, it causes the release of the hormone ____. (during RAA)

aldosterone

Tubular reabsorption

process of reclaiming water and solutes from the filtrate and returning them to the blood, and may be a passive or active process

True or false: all reabsorption occurs in the renal tubules by diffusion.

False: Some ions require active transport.

Where does the greatest amount of renal tubular reabsorption occur?

in the cells of the PCT (all glucose and amino acids are reabsorbed here in addition to most of the water and other ions)

About what percentage of Na+ is reabsorbed in the PCT? The loop of Henle? The DCT?

PCT - 65%

Loop of Henle - 25%

DCT - 10%

What is secretion and where does it occur?

opposite of reabsorption, is the last chance to dump any unwanted items into the filtrate (urea, drugs, potassium ions) ONLY at the DCT

What is countercurrent flow?

the movement of fluids in opposite directions through adjacent channels (in the nephron, filtrate flows one way through tubules while blood flows opposite way through blood vessels)

When an osmotic gradient is isosmotic, what does this mean?

the fluid outside and inside have the same osmotic concentrations

What is the concentration of the filtrate in the PCT vs. the bottom of the loop of Henle?

filtrate entering the PCT is around 300 mOsm/L and increases to about 1200 mOsm/L when it reaches the bottom of the loop of Henle.

True or False: The descending and ascending regions of the loop of Henle have the same reabsorption characteristics.

False

True or False: The concentration of urea is relatively low in the distal convoluted tubule and the cortex regions of the collecting ducts because the tubules in the cortex are permeable to it.

False. The concentration of urea is high in the DCT and cortex regions of collecting ducts b/c tubules in cortex are impermeable to urea.

ADH is secreted by the

posterior pituitary gland

Describe the action of ADH.

ADH is released in response to dehydration or a hemorrhage. ADH inhibits urine output by increasing number of channels in the cells of collecting ducts which allows water to pass easily from the filtrate and move into the interstitial space.

Aldosterone

Hormone that is secreted by the adrenal cortex under control of RAA system and stimulates the kidney to retain sodium ions and water which increases blood volume and blood pressure as needed.

What are diuretics?

chemicals that act on the nephron to increase urinary output (decrease Na+ reabsorption therefore less water is absorbed from filtrate, opposite of ADH)

How do the cardiovascular baroreceptors control the nephron?

If blood volume/pressure rises, baroreceptors inhibit sympathetic nervous system signals to the kidney, dilating the afferent arterioles that carry blood to glomerulus, which causes a dramatic decrease in filtration rate, increasing water and Na+ output, which reduces blood volume quickly to normalize pressure.

Characteristics of Urine

color: clear, pale to deep yellow / aroma: slightly aromatic upon excretion / pH: 4.5-8.0 / 95% water and 5% solutes

Water is found in what two main compartments?

Intracellular Fluid and Extracellular Fluid

Describe the impact of weak acids on a solution.

Weaker acids don't significantly contribute to pH because in this form, H+ is tightly bound and cannot dissociate to become free H+

What is the normal pH of arterial blood?

7.35-7.45

What is the principal method through which acids enter the human body?

Cellular Metabolism

Anion

A negatively charged ion (ie. bicarbonate ion HCO3-)

Cation

A positively charged ion (ie. Ammonium NH4+)

What are the three major chemical buffer systems in the body?

Bicarbonate buffer system for interstitial and plasma fluids; Phosphate buffer system in the urine and intracellular; The protein system is the main buffer of the intracellular fluid.

The bicarbonate buffer system is composed of _____and _____.

weak carbonic acid (H2CO3) and bicarbonate ion (HCO3-)

How does the respiratory center control pH?

Removes carbon dioxide from the blood and adds oxygen to the blood by controlling the respiratory rate in response to the level of carbon dioxide (and pH) detected in the blood.

What happens to cause hyperventilation? hypoventilation?

Hyperventilation is an increase in the respiratory rate caused by a low blood pH. Hypoventilation is a decrease in respiratory rate due to an elevated pH.

Which system has the largest impact on the level of pH in the blood?

Renal Control Mechanisms

Severe acidosis

blood pH drops below 7.0 and CNS is depressed causing coma and imminent death

Severe alkalosis

blood pH rises above 7.8 and CNS is markedly excited causing extreme nervousness, muscle contraction, convulsion, and death due to cessation of breathing.

What are the normal blood serum levels? (for pH, PCO2, HCO3-)

pH: 7.35-7.45 / PCO2: 35-45 mm / HCO3-: 22-26 mEq/L

respiratory acidosis

low blood pH due to hypoventilation (shallow breathing) and high CO2 (PCO2>45mm)

respiratory alkalosis

high blood pH due to hyperventilation (excessive breathing) and low CO2 pressure (PCO2<35mm).

metabolic acidosis

low pH with normal CO2 levels and low HCO3- concentration. (caused by buildup of acidic metabolic products, diabetic ketosis, or extreme diarrhea)

metabolic alkalosis

high pH with normal CO2 levels and high HCO2- concentration (caused by vomiting, antacids, and constipation.