Urinary anatomy

• Function of the urinary system is the removal of unwanted material and maintain homeostasis by regulating the content of the blood plasma
• Organs of the urinary system include the kidneys, ureters, bladder, and urethra
• The kidneys are located in the abdominopelvic cavity against the posterior wall of the abdomen. They are oval in shape, like a bean with a concave notch called the hilum
• The internal structure of the kidney is separated into the cortex (outer region) and medulla (inner region)
• The medulla of the kidney contains the renal pyramids. The base faces the cortex and the tip (papillae) faces the hilum. The papillae have openings which excrete urine into the renal pelvis
• Kidneys are highly vascular organs since they process the blood before returning it to the circulation. The major blood vessels of the kidneys are the renal vein and renal artery
• The renal artery brings blood into each kidney. It branches out into lobar and interlobular arteries and then into afferent arterioles with carry the blood to the nephron.
• The renal vein is responsible for removing the blood from the kidneys
• Ureters are two tubes which connect the kidneys to the bladder. They also act as a valve when the bladder is full. The wall of the ureters are made up of the mucosa, smooth muscle and fibrous layer
• Male vs female:

  In females ureter are close to the cervix and ovaries

  In males ureters are close to the prostate gland
• The urinary bladder is a muscular bag located in front of the rectum, anterior to the vagina for women and on top of the prostate for men.
• The urinary bladder serves as reservoir for urine and expels urine from the body
• The wall of the bladder is made up of the mucosa, submucosa, smooth muscle (detrusor muscle) and the serosa
• Many folds in the mucosa layer in the urinary bladder make it possible for the bladder to distend so it can contain more liquid. The opening on the floor of the bladder connects to the urethra.
• The urethra is a small tube lined with mucous membrane. It runs from the bladder to the exterior of the body
• Location of the urethra

  Males: center of the prostate gland, through the penis and into the urinary meatus

  Females: behind the pubic symphysis and ends in the external urinary meatus
• Urination (micturition) begins with involuntary contractions of the detrusor muscle. As the bladder fills with urine, the contractions become more intense
• Urination occurs due to the relaxation of internal urethral sphincters in the bladder. Volunary urination occurs due to the contraction of the external urethral sphincters as well as the skeletal muscles of the pelvic floor
• The nephron is the functional unit of the kidney. It is divided into the renal corpuscle (glomerulus and bowman’s capsule) and the renal tubules (PCT, loop of Henle and DCT)
• The glomerulus is a capillary network made up of an outer layer of epithelial cells with pores. Their porosity allows the filtration of blood which enters the glomerulus through the afferent arteriole
• The Bowman’s capsule surrounds the glomerulus. It has slits and openings to filter out large molecules
• The glomerular filtration capsular membrane is found between the glomerulus and Bowman’s capsule. It allows the filtration to be efficient
• The renal tubule is a winding hollow tube which starts after the renal corpuscule and ends before the collecting ducts. It is divided into the PCT, loop of Henle and DCT
• The proximal convoluted tubule (PCT) is located close to the Bowman’s capsule. It shows one layer of epithelial cells with a brush border formed by thousands of microvilli
• The loop of Henle consists of the descending limb and ascending limb. The length of the loops is related to the production of highly concentrated or diluted urine.
• The distal convoluted tubule conducts filtrate out of the nephron into the collecting duct, which is formed by the joining of several nephrons where urine is collected
• When blood leaves the nephron, the afferent arteriole enters the peritubular capillaries, joins the vasa recta and goes into the interlobular veins until the blood goes back to the heart