Understanding the Excretory and Urinary Systems
Posted on Nov 16, 2024 in Biology
Excretory System
The excretory system is responsible for removing toxins and wastes from our body.
The excretory system consists of the urinary tract, lungs, and skin.
The excretory system should be added to the large intestine or colon, waste that accumulates in the feces to be excreted through the anus.
Urinary System
The excretory system is a set of organs responsible for the elimination of nitrogenous waste products of metabolism known as urine, in the form of urea and creatinine. Its architecture consists of structures that filter body fluids.
The urinary system is embryologically and anatomically closely related to the reproductive system, so that both systems are called the urogenital system.
The basic unit is the nephron.
Components of the Urinary System
Composition of the Urinary System
It consists of two main parts:
The secretory organs that are the kidneys, which produce urine and carry out other functions.
Excretory Pathways
Excretory organs, which collect urine and expel it outside. This consists of a set of organs that are:
The ureters carry urine from the kidneys to the bladder.
The urinary bladder is a container that collects the urine.
The urethra is a tube that carries urine to the outside, being short in length in women and longer in men.
Kidneys
Histoanatomy of the Kidneys
The initial part and most important is responsible for the filtration of certain tissues and fluids, and the elimination of toxins.
The kidneys are two bean-shaped organs, the size of a clenched fist, and dark red in color, located in the retroperitoneum on the posterior abdominal wall on both sides of the spine.
They weigh about 150 g and reach dimensions of up to 3 × 6 × 12 cm (thickness, width, and length), although there is a decrease in size as one ages.
The left kidney is usually slightly lower than the right (1.5 cm) because the latter is pushed up by the liver.
The lateral border is convex and the medial is concave. On it are the renal hilum, which connects with the renal sinus, a cavity in which the calyces lie.
Each kidney contains thousands of nephrons, which are the functional units responsible for filtering the blood and producing urine.
Each kidney is surrounded by three layers of tissue:
Renal capsule
Perirenal fat
Renal fascia
Regulatory and Excretory Functions of the Kidney
Filter the blood and separate it from impurities, toxic substances, and nutrients to clean and return to circulation.
Reabsorb water, minerals, and nutrients.
Produce urine, which is one way to remove harmful substances from the body.
Regulate the osmolarity of body fluids (blood) volume.
Regulatory Functions of the Kidney
Regulation of electrolyte balance
Regulation of acid-base balance
The production and excretion of hormones that regulate blood pressure, including renin, via the renin-angiotensin system.
The production of other substances important for metabolism, such as calcitriol (the active form of vitamin D), prostaglandins, and erythropoietin (a substance that stimulates red blood cell production in the bone marrow).
Internal Anatomy of the Kidney
The renal cortex: a yellowish color and located on the periphery.
The renal medulla: has a thickness twice that of the cortex and contains clear red pyramid-shaped structures called renal pyramids, which are separated by renal columns.
The renal medullary pyramids are between 8 and 18 cone-shaped structures that have a striated appearance due to the presence of tubules and blood vessels aligned and straight.
The renal papillae are distributed in each minor calyx, funnel-shaped, with 8 to 18 minor calyces, and 2 or 3 major calyces.
Through these structures, urine is stored before being transported into the renal pelvis.
The Nephron
It is the structural and functional renal unit where urine is formed. Each nephron begins with a blind end widened and invaginated by a tuft of capillaries, forming a small rounded structure called the glomerulus or renal corpuscle.
From there, it has two parts called the proximal convoluted tubule and the distal tubule segment through a thin segment known as Henle’s loop.
Glomerulus Microarchitecture:
There are an average of 1,500,000 glomeruli in each kidney, all charged with carrying out the fully vascularized functional processes of the kidney.
The afferent arteriole contains juxtaglomerular cells that secrete renin.
Nephron: Structural and Functional Unit
The ureters carry urine from the kidneys to the bladder.
The urinary bladder is a receptacle where urine collects.
The urethra is the tube that carries urine to the outside, being short in length in women and longer in men, called the penile urethra.
Ureters
Two small tubes, one from each kidney, measuring about 40 cm long and 0.3 cm thick.
Carry urine formed in the kidneys to the urinary bladder.
Bladder
A membranous sac formed by muscle fibers, capable of storing up to 500 ml, thanks to its elasticity.
When the bladder contains about 300 ml, the urge to urinate is felt, and urine is expelled to the exterior in a voluntary act through the urethra.
Urethra
It is a ring of striated muscle that controls the release of substances from the bladder and can be opened and closed at will.
The urethra in women is shorter and carries only urine, while in men it is longer and runs through the penis, also leading the semen.
Urinary System: Male / Female
Micturition: Bladder Eliminates Content
The bladder is a storage organ that supports only up to a certain amount of urine before evacuating. At this time, a series of mechanisms are set in motion to achieve micturition. Here, the main stakeholders are the muscles of the bladder wall, as well as those on the floor of the pelvis.
When the bladder reaches its threshold muscle storage (approximately between 200 and 300 cm³), stretching a series of nerve receptors in its wall send impulses to the spinal cord.
By reflex (micturition reflex), signals are sent back that tell the internal sphincter of the bladder (muscular ring located between the bladder and urethra) to relax. In parallel, our brain receives indications that trigger the urge to urinate.
Urination
Between sensation and voiding, the same process occurs that we handle consciously.
Although the muscles of the bladder walls are not under voluntary control, those below them on the floor of the pelvis are.
Thanks to them, we can control the emptying of the bladder, providing a certain amount of time between the desire we feel to urinate and the timing of urination.
Urine Production
Urinary Tract: The Journey of Urine
The journey of urine goes from the renal papillae to the minor calyces and then to the major calyces, renal pelvis, and ureter, through the bladder, where it serves as a reservoir for urine, with a normal capacity of 500 ml, reaching its maximum capacity of 1 liter.
The bladder expels urine through the urethra, reaching a speed of 30 to 35 km/h when the bladder is at average capacity, and when at its maximum reservoir, it is expelled at about 50 km/h.
Passing through the penile urethra (in men), it should be mentioned that urine is expelled more quickly, reaching its maximum height of 75 km/h, due to the structure of the urethra.
Diseases of the Urinary System
Urinary Incontinence
Urethral Pain
Cystitis
Urolithiasis
Pyelonephritis
Polycystic Kidney Disease
Glomerulonephritis
Diabetic Nephropathy
Acute Renal Failure
Urinary Incontinence
It is the loss of voluntary control during urination. It occurs due to weakened pelvic muscles that help in the evacuation of urine. There are varying degrees of incontinence, from those produced by specific situations (stress, cough, laugh) letting out a small amount of urine, to those that relate to total loss of urinary control (in people with paralysis or the elderly).
Urethral Pain
Urethritis has painful manifestations during urination and erection, indicating severe inflammation of the urethra; the pain is usually related to urination.
Dysuria: Investigate if this condition occurs at the start of the stream, at the end, or during the act of urination.
Edema typically occurs on the eyelids, and swelling of the extremities is more common early in the day; these are signs of kidney disease of any cause, acute or chronic.
Bladder Pain
The patient complains of pain when urinating, and at the end, there is a spasmodic pain in the distal urethra. Bladder pain usually has a burning sensation and projects to the suprapubic area or lower abdomen.
Cystitis
Cystitis is the acute or chronic inflammation of the urinary bladder, with or without an infection.
The most common symptoms are increased frequency of urination and the presence of turbidity in the urine.
This form of cystitis is called acute bacterial cystitis. It affects people of all ages, but especially women of childbearing age or the elderly of both sexes.
The most common cause of cystitis is infection with gram-negative bacteria; cystitis occurs when bacteria first colonize the bladder (bacteriuria) and then produce an inflammatory response in the bladder mucosa.
Kidney Stones
These small stones can form in both the kidney and renal pelvis in the presence of deposits of calcium oxalate crystals in the urine.
Their appearance is associated with an increased level of blood calcium, parathyroid gland disorder, or excess uric acid, caused by improper diet or excessive alcohol consumption.
Kidney Stones: Treatment
When they are small, they can be evacuated safely; if they are larger in size, they produce great pain, known as renal colic.
If they are too large to be expelled naturally, surgery or lithotripsy may be required, a treatment based on shock waves to pulverize the stones.
Glomerulonephritis
It is caused by a streptococcal infection and directly affects the glomeruli and their function. As a result, these structures become inflamed, decreasing their ability to filter urine.
Its symptoms include the appearance of foamy urine, hematuria (blood in urine), and morning inflammation of the face, hands, feet, and abdomen.
If left untreated, it often leads to acute renal failure.
Diabetic Nephropathy
It is a typical complication of diabetes mellitus, in which renal damage occurs. It affects the smaller blood vessels of the kidneys. Similarly, it affects the appearance of the glomeruli, as they thicken and eventually become destroyed.
It often leads to chronic kidney failure or kidney failure. One of the most notable indicators of this disease is the presence of major protein in the urine (which accumulates abnormally).
Pyelonephritis
This corresponds to a bacterial infection that affects both kidneys and the ureters. Usually, this starts in the bladder and ascends to the other organs, resulting from reflux of urine (vesicoureteral reflux). It causes inflammation of the affected structures, especially the renal pelvis.
Numerous white spots for microfoci fester in the renal cortex.
Polycystic Kidney Disease
It is an inherited disorder characterized by the presence of multiple cysts in the kidney. These are usually of different sizes, with an appearance similar to that of a cluster of grapes, gradually increasing the size of the kidney and altering its function. This disease has a high mortality rate during the first year of life.
Renal Failure
This corresponds to a disorder that directly affects the cleaning work done by the kidneys. It occurs when these organs stop functioning properly, effectively decreasing the filtrate produced in the renal glomeruli.
Therefore, one of the first indicators of this disease is the increase in blood levels of urea and creatinine. When we face a rapid decline in renal function, it leads to acute renal failure, whereas if the work of the kidneys is affected progressively, it corresponds to chronic renal failure.
Among its causes include poor blood supply to the kidneys, injuries to these organs, and obstruction of urine flow, among others.
Acute Renal Failure
Causes:
Some kidney problems happen quickly, like an accident that causes kidney damage.
The loss of a significant amount of blood can cause sudden kidney failure.
Some drugs or poisons can cause the kidneys to stop working.
Consequences:
Acute renal failure can lead to permanent loss of kidney function. However, if the kidneys do not suffer serious injury, this failure may be addressed by surgery.
In most cases, surgery involves a kidney transplant, replacing the damaged kidney with a healthy one.
Kidney Disease
The kidneys are so important that if they fail, a person can die in a few days from intoxication with their own waste. A person can live with one kidney if they take good care of it. Today, kidney transplants are performed with great success, along with a procedure called hemodialysis, which serves to replace kidney function when it malfunctions, while waiting for a transplant.
Artificial Purification
There is an artificial mechanism capable of performing similar work to that of the kidneys, known as dialysis. This is used mainly when there is acute or chronic renal failure.
It purifies the blood through a machine, passing it through a semipermeable membrane housed in a network of tubes and immersed in a special solution called dialysate. Once the blood flow begins, the membrane captures smaller molecules, such as waste products and urea, which remain in the dialysate, ready to be eliminated, while larger molecules (such as blood cells and plasma proteins) are retained and returned to the blood.
Currently, there are two types of dialysis: hemodialysis and peritoneal dialysis, differentiated by the type of membrane used in waste collection.
Peritoneal Dialysis
Peritoneal dialysis is characterized by using a semipermeable membrane of the human body itself: the peritoneum.
The serous layer, which lines the walls of the abdominal and pelvic cavity, is capable of filtering the blood during the procedure; the waste products pass from the capillaries (lining the peritoneal cavity) into the dialysate fluid.
The patient inserts a cannula in the lower abdomen, where liquid is injected to capture waste substances.
Over several hours, the solution carries waste from the blood vessels in the peritoneal membrane.
Peritoneal dialysis, compared with hemodialysis, has an efficiency of about 1/8 in terms of change in concentration of solutes in the blood and 1/4 in the elimination of liquids.
Hemodialysis
Hemodialysis involves accessing a blood conduit (performed through an operation to create an arteriovenous fistula, joining an artery and a vein) at the height of the arm, which will be connected to a specialized machine for filtering the blood. The machine cleans the blood in the dialysate solution and then returns it free of toxic waste.
Vascular Access
To perform hemodialysis, the patient requires vascular access to take blood to the dialysis machine.
If vascular access is done by installing a thin tube, it is temporarily inserted into a central vein (jugular, subclavian, or femoral artery), called a catheter.
If done permanently, it involves a minor surgical procedure usually in the wrist with local anesthetic, which joins an artery with a large vein, called an arteriovenous fistula.
Hemodialysis Patient
Questions
How long do the kidneys take to filter the blood throughout the body? About five minutes.
What is urgency? It corresponds to the ineffective and painful effort to defecate or urinate.
What is the diameter of a renal corpuscle? It fluctuates between 150 and 250 microns.
How many liters of urine per day are produced by an adult? Under normal conditions, about 1.5 liters.
What is enuresis? It corresponds to the wetting in children or adults.
