urinary tract: part 2

The micturation reflex occurs in a series of steps.

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urinary bladder

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internal urethral sphincter

At the neck of the urinary bladder an involuntary "internal urethral sphincter" is formed by the smooth muscle that encircles the urethral opening

step 2

Impulses within the parasympathetic division of the autonomic nervous system travel to both the internal urethral sphincter and the detrusor muscle

step 5

In addition to the squeezing action of the detrusor muscle on the volume of the urinary bladder, the expulsion of urine is facilitated by contraction of muscles in the abdominal wall and expiratory muscles

position of urinary bladder in females

In females the urinary bladder is anterioinferior to the uterus and directly anterior to the vagina

position of the urinary bladder in males

In males, the urinary bladder is anterior to the rectum and superior to the prostate gland.

function of the trigone?

It functions as a funnel to direct urine into the urethra as the bladder wall contracts to evacuate the stored urine.

what is the median umbilical ligament a remnant of?

It is a remnant of the embryonic structure called the "urachus", which extends from the superior part of the bladder to the umbilicus. This will be discussed more later.

function of the para innervation

Nerve fibers from this region relax the internal urethral sphincter so that urine can pass through and stimulate contraction of the detrusor muscle. - Thus, the parasympathetic fibers stimulate micturation.

outer adventitia

The "adventitia" is the outermost layer of loose connective tissue of the urinary bladder

location and structure of the mucosa

The "mucosa" lines the bladder lumen; it is formed by stretchable epithelium

muscularis

The "muscularis" consists of three layers of smooth muscle collectively called the "detrusor (Latin for "to drive away") muscle"

location and structure of the submucosa

The "submucosa" lies immediately external to the mucosa and is formed by dense irregular connective tissue that supports the urinary bladder wall

structure and function of the urinary bladder

The "urinary bladder" is an expandable, muscular container that serves as a reservoir for urine.

location of the urinary bladder

The bladder is positioned immediately posterior to the pubic symphysis

para or symp innervation of the urinary bladder?

The bladder is supplied by both parasympathetic and sympathetic nerve fibers of the autonomic nervous system

location of the "neck" of the bladder

The constricted "neck" of the bladder is located inferiorly and connected with the urethra.

micturation

The expulsion of urine from the bladder is called "urination" or "micturation" (Latin for "to desire to make water")

location of the para fibers

The parasympathetic fibers come from the micturation reflex center located in the spinal cord segments S2-S4.

does the parietal peritoneum cover the whole urinary bladder?

The parietal peritoneum covers only the superior surface of the urinary bladder (and in this superior region, the parietal peritoneum plus the connective tissue forms a serosa

step 4

The person's conscious decision to urinate causes relaxation of the external urethral sphincter.

step 3

The smooth muscle in the internal urethral sphincter relaxes and the smooth muscle in the detrusor muscle contracts.

location of the symp fibers

The sympathetic fibers are from the T11-L2 segments of the spinal cord

is the trigone mobile?

The trigone remains immovable as the urinary bladder fills and evacuates

assoc of the urinary bladder with the peritoneum

The urinary bladder is a retroperitoneal organ since only its superior surface is covered with the parietal peritoneum

function of the symp innervation

These fibers cause contraction of the internal urethral sphincter and inhibit contraction of the detrusor muscle. - Thus, the sympathetic fibers inhibit micturation.

when is step 1 achieved?

This process will be initially triggered when the urinary bladder contains about 250 milliliters of urine.

step 6

Upon emptying of the urinary bladder, the detrusor muscle relaxes and the neurons of the micturation reflex center are inactivated.

where do the ureters enter the urinary bladder?

Ureters enter the posterolateral wall of the urinary bladder through the oblique "ureteral openings".

what initiates micturation?

Urination is initiated by a complex sequence of events called the "micturation reflex".

blood drain from the urinary bladder

Venous blood drain into the internal iliac veins.

shape of urinary bladder when empty vs full

When empty, the urinary bladder exhibits an upside-down pyramidal shape and when it is full it distends superiorly until it assumes an oval shape

step 1

When the bladder fills with urine and becomes distended, stretch receptors in the bladder wall are activated and they signal the micturation center.

does the mucosa always have rugae?

Within the trigone region the mucosa is smooth, thick, and lacking rugae

function of the mucosa

accommodates the shape changes occurring with distension, and by a highly vascularized lamina propria that supports the mucosa

location and function of the urinary bladder

A fibrous, cordlike "median umbilical ligament" extends toward the umbilicus from its origin on the anterosuperior border of the urinary bladder to secure the bladder in place.

trigone

A posteroinferior triangular area of the urinary bladder wall, called the "trigone" (Greek for "triangle"), is formed by imaginary lines connecting the two ureteral openings and the urethral opening.

mucosal folds

Additionally, mucosal folds, called "rugae" (Latin for "wrinkles"), allow for even greater distention.

blood supply to urinary bladder

Arterial blood vessels from the internal iliac artery extend to the urinary bladder and penetrate its wall from branches of the internal iliac artery.

There are four tunics that form the wall of the bladder.

inner: mucosa submucosa muscularis adventitia :outer