Ch. 26 Urinary system: urine formation by kidneys

The kidney’s main function is to maintain homeostasis. What are the 6 ways this occurs?

1. Excretion of metabolic waste (urea, uric acid, creatinine (from muscle creatine), bilirubin, hormones, “foreign “stuff”: drugs, toxins, food additives”)

2. Water and electrolyte balance

3. pH balance by eliminating acids

4. Regulation of calcitriol - essential for normal calcium deposition and reabsorption in the GI tract

5. Gluconeogenesis - after prolonged fasting

6. RBC production regulation - stimulated by hypoxia

The kidneys maintain homeostasis with water and electrolyte balance. What is the goal or result of this?

a. regulate arterial pressure

b. regulate venous pressure

c. regulate filration rate

d. all of the above

a. regulate arterial pressure

• with sodium and renin to angiotensin II

T/F: Gluconeogensis can occur at the kidney but only after prolonged fasting or starvation

true - processes faster than the liver too

Explain the regulation of erythrocyte production

• O2 will be delivered to the kidneys

• where it stimulates the secretion of erythropoietin (EPO). EPO then promotes the production of red blood cells in the bone marrow, increasing oxygen transport in the blood.

• cycle repeats

*stimulated by hypoxia because EPO creates RBC when oxygen carrying hemoglobin levels are low

How does kidney disease affect the regulation of EPO production?

patient will become anemic because of inability to create RBC because O2 delivery is needed to the kidneys to start EPO production

How does urine travel to the ureter?

a. Major calyx, minor calyx, renal pelvis

b. Minor calyx, renal pelvis, major calyx

c. renal pelvis, minor calyx, major calyx

d. minor calyx, major calyx, renal pelvis

d. minor calyx, major calyx, renal pelvis

________ filters blood by removing metabolic wastes while extracting much of its water content

renal system

1. functional unit of the kidney

2. tiny sac-like structure where blood is delivered and INITIALLY FILTERED

1. nephron

2. renal corpuscle

Afferent arteriole vs efferent arteriole

• afferent a - carries blood toward the corpuscle to be filtered

• efferent a - carries non-filtered portion of blood away from the corpuscle

Define the following

1. Glomerulus

2. Bowman’s (glomerular capsule)

3. Podocyte

1. Glomerulus - specialized capillary that filters blood

2. Bowman’s (glomerular capsule) - outer layer of the corpuscle and site of filtration

3. Podocyte - specialized cells that prevent large molecules such as proteins from exiting filtrate

T/F: the glomerulus is a capillary

true

What is the site of filtration?

a. Glomerulus

b. Bowman’s capsule

c. Nephron

d. Podocyte

b. Bowman’s capsule

Why is there no venous system in the renal system?

1. blood does not go back to the heart

2. no gas diffusion occurs so O2 is still present in the blood

What 4 actions is the nephron responsible for?

1. filtration - to create filtrate

2. reabsorption - back into the blood

3. secretion

4. excretion - elimination of urine

Give the steps of the filtration pathway

1. renal corpuscle (glomerulus and bowman’s capsule (site of filtration))

2. Proximal convoluted tubule - for reabsorption and secretion

3. loop of henle - reabsorption alllowing urine to be concentrated here

4. macula densa cells - touch the glomerulus and sense Na+ levels

5. Distal convulated tubule - reabsorption and secretion

6. collection duct - some reabsorption

7. renal pelvis

8. ureter

_____ is the portion of the tubules that loops back very close to the corpuscle

distal convoluted tubule

Describe the loop of henle

• has a descending limb and an ascending limb

• together these segments concentrate urine by extracting water from filtrate

What are the two types of nephrons in the kidneys and what differentiates them?

• Cortical nephron

  • located deep in the cortex

  • short loop of henle

• Juxtamedullary nephron

  • near the medulla

  • long loop of henle and concentrates urine

The Kidneys are delicate organs that filter blood and produce urine.

1. How many nephrons are in each kidney?

2. How many glomerulus are designated to each nephron?

3. How do nephrons hold up with age?

4. Are they (kidneys) able to regenerate?

1. about 800,000 to 1,200,000 nephrons

2. 1 glomerulus per nephron

3. 10% decrease in nephron function every 10 years after 40 y/0

   1. by age 80, 40% fewer functioning nephrons that at 40 y/o

4. unable to regenerate but the nephrons are able to adjust

Smooth muscle chamber with a body (rugae) and a neck is known as the _____

bladder

Why are the rugae in the bladder important?

allow the bladder to expand as it fills with urine

Which of the following are false about the bladder?

a. Lower part of the neck of the bladder is called the posterior urethra

b. the smooth muscle of the bladder is known as the detrussor muscle

c. the bladder’s trigone consists of rugae to aide in expanding as it fills with urine

d. electrical pathways are responsible for the bladder to contract as a unit or all at once with gap junctions

c. the bladder’s trigone consists of rugae to aide in expanding as it fills with urine

• no rugae in trigone

Why are the ureters in the trigone angled and not entering the trigone directly superiorly?

To prevent backflow of urine into the ureters when the bladder contracts.

T/F: Micturition is not a reflex

false - it is a reflex because brain integration is not required

Explain how the bladder empties with the input of spinal reflexes

The bladder will continue to fill until the spinal reflex is initiated but can be overrided by the cortex and brain stem

• the internal sphincter which is smooth muscle will hold the urine in the bladder

  • involuntary action

• the external sphincter is made of skeletal muscle and is under voluntary control

  • innervated by the pudendal nerve

• Autonomic spinal reflex

  • sympathetic stimuli will inhibit contraction (fight/flight)

  • parasympathetic stimulation (S2-S4) causes contraction because the body has relaxed

    • stretch sensation in the bladder will allow sensory and motor nerve fibers on the bladder to release urine as the muscle contracts

Give a quick step by step overview of how the micturition reflex occurs at the parasympathetic level

1. the reflex is controlled by the PNS at S2-S4

2. stretch receptors in the bladder wall detect filling

3. sigals are sent to the spinal cord causing:

   1. detrusor muscle to contract

   2. internal urethral sphincter to relax, allowing urine to flow from the bladder and the external sphincter will release the urine voluntarily when appropriate

What can occur with extreme bladder filling or overdistention?

The afferent signals from the bladder stretch receptors become so strong they:

• overrride the voluntary control of the brain

• engage spinal reflex without brain input

• causes reflex inhibition of the external sphincter, relaxing it involuntarily ad urination occurs

Explain the relationship between volume in the bladder and pressure in the bladder

The pressure in the bladder will not change from 150 to 300 ml because the bladder is expanding. At 300 ml the bladder will begin to contract as urine enters the bladder and as contractions increase, pressure increases because the urge to urinate will increase.

Bladder smooth muscle tone keeps pressure steady up to ______ ml

a. 500 ml

b. 300 ml

c. 150 ml

a. 100 ml

b. 300 ml

How does damage to sensory nerve fibers affect micturition?

• atonic bladder occurs where pressure in the bladder does not change

• therefore, stretch can’t be detected, reflex can’t be initiated, bladder fills to capacity and then overflows known as overflow incontinence

• occurs in T2D with damage to the nerves = no sensation

how does damage to the sacral region of the spine affect micturition?

• causes an “automatic bladder”

• reflex is intact but is exaggerated and spastic = frequent urination

how does damage to the brain above the pons affect micturition?

• individual loses ability of voluntary control of bladder leading to involuntary and frequent urination

  • urge to urinate is present but unable to supress it because the brain can no longer inhibit the reflex

The kidneys are not supposed to filter protein. How can it be detected and what does it signify?

• found by detecting protein in the urine

• signifies kidney damage

How can you control the volume of GFR?

Pressure

• pressure added to the efferent arteriole will increase filtrate

• pressure added to the afferent arteriole will decrease filtrate

Absorption and Secretion

1. If entered into the kidneys, what can we expected to be filtered and excreted?

2. When do we see excretion < filtration?

3. What elements do we see to not be excreted?

4. Only excretion occurs with which elements?

1. inulin and creatinine

2. Na, Cl, water - partial reabsorption from the tubules into the blood

3. Amino acids (building blocks) and glucose (energy) - body needs these to function so we don’t want them to be removed

4. organic acids and bases are not reabsorbed

What elements do we commonly see being secreted after filtration?

• drugs

• potassium

• toxins

• H+ ions (acidity)

• penicillin

T/F: reabsorption is more important than secretion

true

Which nutrients are greatly absorbed? (Hint: 5 answers)

a. K+

b. Na+

c. Cl-

d. proteins

e. glucose

f. amino acids

g. bicarbonate

h. hydrogen

Na+, Cl-, glucose, amino acids, and bicarbonate

• K and H are secreted

Review chart