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By the end of this section, you will be able to:
  • Identify the ureters, urinary bladder, and urethra, as well as their location, structure, histology, and function
  • Compare and contrast male and female urethras
  • Describe the micturition reflex
  • Describe voluntary and involuntary neural control of micturition

Rather than start with urine formation, this section will start with urine excretion. Urine is a fluid of variable composition that requires specialized structures to remove it from the body safely and efficiently. Blood is filtered, and the filtrate is transformed into urine at a relatively constant rate throughout the day. This processed liquid is stored until a convenient time for excretion. All structures involved in the transport and storage of the urine are large enough to be visible to the naked eye. This transport and storage system not only stores the waste, but it protects the tissues from damage due to the wide range of pH and osmolarity of the urine, prevents infection by foreign organisms, and for the male, provides reproductive functions.

Urethra

The urethra    transports urine from the bladder to the outside of the body for disposal. The urethra is the only urologic organ that shows any significant anatomic difference between males and females; all other urine transport structures are identical ( [link] ).

Female and male urethras

The top panel of this figure shows the organs in the female urinary system.
The urethra transports urine from the bladder to the outside of the body. This image shows (a) a female urethra and (b) a male urethra.

The urethra in both males and females begins inferior and central to the two ureteral openings forming the three points of a triangular-shaped area at the base of the bladder called the trigone    (Greek tri- = “triangle” and the root of the word “trigonometry”). The urethra tracks posterior and inferior to the pubic symphysis (see [link] a ). In both males and females, the proximal urethra is lined by transitional epithelium, whereas the terminal portion is a nonkeratinized, stratified squamous epithelium. In the male, pseudostratified columnar epithelium lines the urethra between these two cell types. Voiding is regulated by an involuntary autonomic nervous system-controlled internal urinary sphincter    , consisting of smooth muscle and voluntary skeletal muscle that forms the external urinary sphincter    below it.

Female urethra

The external urethral orifice is embedded in the anterior vaginal wall inferior to the clitoris, superior to the vaginal opening (introitus), and medial to the labia minora. Its short length, about 4 cm, is less of a barrier to fecal bacteria than the longer male urethra and the best explanation for the greater incidence of UTI in women. Voluntary control of the external urethral sphincter is a function of the pudendal nerve. It arises in the sacral region of the spinal cord, traveling via the S2–S4 nerves of the sacral plexus.

Male urethra

The male urethra passes through the prostate gland immediately inferior to the bladder before passing below the pubic symphysis (see [link] b ). The length of the male urethra varies between men but averages 20 cm in length. It is divided into four regions: the preprostatic urethra, the prostatic urethra, the membranous urethra, and the spongy or penile urethra. The preprostatic urethra is very short and incorporated into the bladder wall. The prostatic urethra passes through the prostate gland. During sexual intercourse, it receives sperm via the ejaculatory ducts and secretions from the seminal vesicles. Paired Cowper’s glands (bulbourethral glands) produce and secrete mucus into the urethra to buffer urethral pH during sexual stimulation. The mucus neutralizes the usually acidic environment and lubricates the urethra, decreasing the resistance to ejaculation. The membranous urethra passes through the deep muscles of the perineum, where it is invested by the overlying urethral sphincters. The spongy urethra exits at the tip (external urethral orifice) of the penis after passing through the corpus spongiosum. Mucous glands are found along much of the length of the urethra and protect the urethra from extremes of urine pH. Innervation is the same in both males and females.

Questions & Answers

where is heart located
medical Reply
thoracic cavity
Ashley
1
Noor
between which line
medical
where is the thorax located at?
angel
heart located between T5-T8
Biplav
thorax is the area between the base of neck to the diaphragm
Biplav
The heart is placed Obliquely behind the body of the sternum and adjoining part of the costal cartilages, so that 1/3 of its lies to the right and 2/3 to the left of the median plane
Manisha
The heart lies in the thoracic cavity in the mediastinum (the space between the lungs) . It lies obliquely, a little more to the left than the right. Presents the base above and the apex below. The apex is 9cm to the left of the midline at the level of the 5th intercostal space
Bashraba
why does a person's complexion change when he relocates to another cold environment & tends to become more light skinned, does this mean the distribution of melanin to the surface of the skin changes ?
Ferrel Reply
what is Aponeurosis
Komolika Reply
aponerosis is modifications of deep fascia of the skin.. it generally covers the muscles Or tendons within it
niyati
A sheet of parly white fibrous tissue that takes the place of tendon in flat muscles having a wide area of attachment
mishra
what is the difference between sex and gender?
Hridya Reply
Those are synonyms
Ferrel
What is Physiology?
Nancy Reply
The study of functions of the human body.
Evans
study of human body
obaidullah
The biochemical study of any organism (eg. different systems) is called Physiology.
Doctor
which category of bone is among the most numerous in the skeleton?
DAMSON Reply
what is a nutrition ?
Jitu Reply
Nutrition is the process of providing or obtaining the food necessary for health and growth.
Gloria
Nutrition is the process of taking food and using it for growth , repair and metabolism ...
Om
how many parts of bone
Amir Reply
know the meaning of both messages
Amir
what is the name of suture that is present between frontal. parietal. occipetal ...
Amir
what is the name of suture that is present between frontal. parietal. occipetal ...
Amir
Coronal suture present between frontal and parietal bone and lambdoid suture present between parietal and occipital bone ...
Om
Squamous suture
Ferrel
& where is the squamous suture ?
Ferrel
what is meant by synovial joint? and what is this role
Fozia
type of joint that is found between bones that move against each other. it's function is to prevent bone friction
Ferrel
epinephrine is the true meaning of epi
Michele Reply
what does the word 'epi' means
Melex Reply
good evening, my question is what are function of metal in human body like aluminum?
Yosef Reply
please want you to help me in understanding digestive system
Hamidu Reply
this is muscular system?
Patel Reply
bruh moment
Viana
It is an organ system consisting of skeletal ,smooth and cardiac muscles
mishra
im too retarded to be here
Viana
naww Viana, I know it's hard to absorb info, I'm having the same issue, but keep practising, chin up.
Katarina
what is the question
Amir
to have a better understanding as to how our human bodies function. the knowledge we gain can improve our quality of life. Without our study of anatomy how could a doctor know what prescription to give us when our bodies is being attacked by a bacteria? We wouldn't!
Robin Reply
discuss nervers system in human being life.
Allen Reply
neuralgia what is other name of it
Muniba

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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