Human Excretory System: Functions and Health Maintenance
Understanding the Human Excretory System
What is Excretion?
Excretion is the elimination from the body of waste substances resulting from cellular activity. Although excretion takes place in various parts of the human body (the liver expels substances from hemoglobin degradation to the intestine, the lungs remove CO2 from cellular metabolism, and the sweat glands excrete sweat onto the skin), most of this function is carried out by the excretory system.
Components of the Urinary System
The Ureters
These are two ducts, one coming out of each kidney, that carry urine to the bladder.
The Urinary Bladder
A hollow, muscular organ where urine is stored until it is expelled to the outside.
The Urethra
A canal that connects the bladder with the outside of the body. Urine exits the body through it during urination. The output of urine is controlled by the voluntary relaxation of a muscle, the sphincter.
The Kidneys: Structure and Function
Kidneys filter blood, changing its composition as it is processed within them, to finally become urine.
Kidney Anatomy
The kidneys are covered with a thin, resistant membrane called the capsule, which is shiny and dark brown. Through the middle of its front side enters the renal artery, and leaving are the renal vein and the ureter. In a longitudinal section, a kidney shows a clear outer zone, the renal cortex, and an inner, darker zone, the renal medulla, from which some extensions reach into the cortex (medullary rays). In the medulla, there are a number of renal pyramids, whose vertices or papillae are the areas through which urine pours into the renal pelvis, a funnel-shaped cavity that narrows into a tube called the ureter.
Sweat Glands and Excretion
Sweat glands are located within the skin, surrounded by capillaries. They filter waste material transported by the blood, which is then excreted as sweat.
How Kidneys Function: The Nephron
The kidney maintains the constant chemical composition of the blood and regulates water loss through urine. This involves the nephrons.
Nephron Parts
Key components include the Malpighian corpuscle (containing the glomerulus and Bowman’s capsule) and the renal tubule.
Stages of Urine Formation
The nephron operates in 3 stages:
- Filtration: This occurs as blood passes through the glomerulus. Small substances pass from the blood into the renal tubule.
- Reabsorption of Useful Substances: Essential substances like glucose, amino acids, and over 90% of water are reabsorbed back into the blood from the tubule.
- Secretion of Waste Substances: Waste products, such as urea, are actively transported from the capillaries into the renal tubule. This process continues along the entire tubule, concentrating the remaining fluid into urine. This urine is then drained into a collecting duct, common to several nephrons, which leads to the renal pelvis.
As a result of this process, the blood that leaves the kidneys via the renal veins is cleansed of waste products.
Associated Health Conditions
Common related health issues include:
- Cardiovascular Diseases
- Respiratory Diseases
Preventing Kidney and Related Diseases
How can you prevent these diseases?
Control Risk Factors
- Monitor and control hypertension with frequent and regular blood pressure measurements.
- Change eating habits; avoid tobacco use and excessive alcohol consumption.
- Control diseases such as diabetes and obesity.
- Be aware of any family history of heart disease or kidney failure.
Adopt Healthy Lifestyles
- Reduce the consumption of fats and proteins; increase consumption of legumes, vegetables, and fruits.
- Reduce salt intake.
- Avoid alcohol and other toxic substances.
- Avoid tobacco use and exposure to secondhand smoke.
- Lose weight if overweight.
- Engage in a regular exercise program. A healthy habit is to walk for 30 minutes daily.