D4.1 - Overview of Excretory System

Excretory System Overview

• The excretory system's basic function is to regulate the volume and composition of body fluids. It removes waste and reuses needed substances.
• Waste is any substance produced by the body in excess of its needs.
• Excretion is the process of separating wastes from body fluids and eliminating them.
• Respiratory system excretes CO2.
• Skin excretes water, salts, and urea.
• Digestive system excretes water, salts, and lipids.
• Feces is not a process of excretion.

Organs of the Excretory System

• Kidneys: Located in the lower back, they can function with just one.
• Ureters: Muscular tubes that carry urine from the kidneys to the bladder. Urine is moved through the ureters by peristalsis, a rhythmic muscle contraction. The flow of urine is controlled by a sphincter, a ring of muscle at the base of the bladder.
• Urethra: Tube that carries urine from the bladder out of the body.

Importance of Kidneys

• Body cells break down complex compounds into smaller ones, some of which can be toxic.
• The liver removes the amine group from proteins, forming ammonia.
• The liver combines ammonia with CO2 to form urea.
• Kidneys filter out urea and uric acid from the blood. Urea and uric acid contain ammonia, which is harmful to the body.

Urinary System

• Renal arteries, branches of the aorta, enter the kidneys. "Renal" refers to the kidneys.
• Wastes are filtered from the blood in the kidneys and sent to the bladder via the urethra.
• The urinary sphincter at the base of the bladder releases urine into the urethra when it is time to void.

Bladder Volume

• When the bladder contains 200 mL of urine, it signals the brain to empty.
• 400 mL signals a more urgent need to urinate.
• 600 mL causes involuntary emptying of the bladder.

The Kidney (Internal Anatomy)

• The kidney has three regions: cortex, medulla, and pelvis.

The Kidney (Tissue)

• The kidney's tissue is divided into the outer renal cortex and inner renal medulla.
• Renal pelvis is a hollow chamber that connects the kidney to the ureter.
• Nephrons are microscopic structures within the kidney, embedded in the cortex and medulla, responsible for filtering blood and producing urine.
• Nephrons are organized into a Filter, Tube, and Duct.

Nephron Diagram

• The diagram shows the various components of a nephron. Components include Bowman's Capsule, glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting duct (renal cortex and renal medulla)

Three Regions of Nephron

• Filter: Bowman's capsule and a filtration device (glomerulus) filter fluid from the blood. The filtered fluid, now known as filtrate, enters Bowman's capsule.
• Tube: The filtrate travels through tubules (proximal tubule, loop of Henle, distal tubule) where useful substances are reabsorbed and waste products are secreted.
• Duct: The collecting duct reclaims water and other substances, leaving urine to be excreted.