Renal 8

Question 1

What does renin do when it’s secreted?

Answer 1

Renin turns angiotensiogen to angiotensin 1

- Liver makes angiotensiogen, releases it to blood. 
- When we detect decrease in blood pressure and increased plama concentration
- Angiotension 1 then turned to angiotension 2 in the lungs and in vasculature (by angiogensin converting enzyme ACE), ACE1. 
- ACE converts A1 to A2 
- A2 has a lot of targets (adrenal, kidney, brain), potent vasocontrictor, responds to reduced blood pressure. (restores blood pressure) 

1. Increased cardiac output (cardio control center) 
2. Arterioles (efferent and afferent in glom) are vasocontricted (both). Reduce blood going to the kidney. Change amount of filtration (filtration fraction will go up), promotes sodium reabsorption, more water reabsorption. 
3. Hypothalamus releases AVP from posterior pituitary to help reabsorb water via aquaporins and 
4. Hypothalamus induce thirst. 
5. Adrenal cortex: increases aldosterone secretion to increase sodium reabsorption 

A2 restores water volume and restore normal blood pressure

Question 2

How do we respond when our blood volume changes?

Answer 2

Increased blood volume and decreased blood volume very similar responses.

- Renin
- Sympathetic activity
- Antiogensin 2
- Molecules released from cardiac tissue and brain 

Increased blood volume
- Decrease Renin
Decrease Renin in increased blood volume (tubuloglomerular feedback, increased dosium to macula densia, decreases renin release), less angiotensin 2, decreased aldosterone, no angiotensin 2, no thirst drive, no AVP release, increases our excretion of sodium and water, reducing reabsorption in the collecting duct.
Mostly in collecting duct regulation happens.

Question 3

How is urine delivered to the bladder?

Answer 3

Fluid that has left collecting duct
- can’t modify anymore

Duct of Bellini
Major and minor calyces (little parts before the renal pelvis)
Main part: renal pelvis

Drain from all nephrons to central renal pelvis.

- Urine drains down ureter and is delivered to the bladder. 
- Peristalsis helps move urine towards the bladder. Pushes urine against the pressure gradient. (even if its getting full)

Question 4

What is the anatomy of the bladder?

Answer 4

Ureters: deliver to the bladder bottom

Bladder: stores urine different layers
1. Transitional epithelial cells on inside of bladder (allows for stretching of storage space
2. Smooth muscles (detrusor muscle), electrical coupling (similar to heart tissue’s gap junctions). Allows us to contract bladder to pee.
3. Bladder neck: funnel, between body and urethra. Has detrusor and elastic fibers
Two sphincters
A. Internal: smooth mucles, tonic contraction (no voluntary control)
B. External sphincter: urigenital diaphragm, skeletal muscle, voluntary control.

Body/Fundus
Bladder

Question 5

How is urine stored? (mechanism so you don’t have to pee all the time)

Answer 5

Contractility.
- Wall will be contracted in relaxed state (empty)
○ Tonic contraction
- As urine is delivered to the bladder, the volume increases but pressure does NOT increase (or very minimal)
- The bladder is relaxed so that it can expand to accommodate. Storeage space without increasing pressure immediately.
- Balance of sympathetic and parasympathetic activity.
○ Sympathetic stimulation
○ Parasympathetic inhibiton.
§ This allows for expansion/relaxion of detrosor muscle.
When you pass volume (400ml or 20 pressure) then you have the mitration reflex, signal to us that we need to pee .

Question 6

How is the bladder innervatd?

Answer 6

Involuntary

1. Sympathhetic: hypogastric, allow bladder wall and internal sphincter to expand. 
2. Parasympathetic: pelvic nerves  to innervate bladder neck and posterior urethra

Voluntary
3. Somatic motor nerves - Pudendal nerves, innervate external sphincters. How we voluntarily override mitrition so that we pee on demand

Question 7

What is the micturition Reflexx?

Answer 7

Micturition reflex
About 400 ml

Once you reach 400, that pressure goes up pretty steeply.

Stretch receptors found in the wall of the bladder.

Activated in response to that increased stretch, pressure.
Sends signal to spinal cord to bladder and to internal sphincter. Promote bladder wall contraction, push urine towards environment, relaxation of internal sphincter.

(also effects bladder wall)

That’s micturition.
External sphincter relaxation now needs to be voluntarily controlled.

Question 8

Describe micturition?

Answer 8

Filling
Progression relaxation that expands so no reflex yet.

Voiding:
- Intravsiculal pressure rises, micturation reflex occurs
- Once its been initiated, voiding can occur (supraspinal control and voluntary)
- Voluntary control can be overridden
○ Barringtons nucleus (pons) makes you pee overriding your inhibition when it becomes dangerous.
○ Hypothalamus and cerebrum oppose voiding as intravesicular pressure rises up. (voluntary control over when we wanna pee)
= in healthy people, micturition occurs only when inhibitory cortical control is suppressed.
Voiding empties bladder completely.