Grade 11 Biology: Human Excretion

• Excretion in humans is covered in Module 3 of Grade 11 IEB Biology

Module Timeline Breakdown

• Week 1: Functions and components of the human excretory system, structure and function of the kidney and nephron, and the internal structure of a kidney and nephron.
• Week 2: Main processes of the human excretory system, health issues, and module evaluation.

Module Objectives

• Understand how the excretory system works.
• Identify and describe the different disorders of the excretory system.
• Describe how dialysis works.
• Discuss kidney transplants.
• You should be able to list the parts of the excretory system and describe the function of each
• Draw, label and interpret the diagrams of the excretory system.
• Identify the structure and roles of a kidney and nephron.
• Describe the main renal processes in the excretory system.
• Differentiate between filtration, reabsorption and secretion in renal processes.

Excretory Organs and Products

• Kidney excretes urea, uric acid, creatinine, drugs, hormones, poisons and CO2 which come from the breakdown of amino acids and nucleic acids
• The Lungs excrete CO2, water, and heat, which come from cellular respiration.
• Skin excretes water, salts, urea, and heat, which come from metabolism.
• The Colon excretes bile pigments & cholesterol, originating from the breakdown of RBCs and bile salts

Components and Functions of the Urinary System

• Inferior vena cava carries purified deoxygenated blood back to the heart.
• Kidneys filter nitrogenous waste out of the blood and regulate water and salt balance via osmoregulation.
• Aorta carries oxygenated blood with nitrogenous waste to all parts of the body.
• Motor nerves stimulate contraction of the bladder wall.
• Renal artery carries oxygen and nitrogenous waste to the kidney.
• Adrenal gland secretes aldosterone.
• Renal vein carries purified blood to the inferior vena cava.
• Ureter carries urine to the bladder.
• The bladder stores urine.
• Sphincter muscle controls the flow of urine.
• Urethra carries urine to the exterior.

Urinary System vs. Excretory System

• The urinary system is a part of the excretory system.
• The excretory system removes any excretory products , but the the urinarysSystem removes excretory products, especially nitrogenous wastes like urea, uric acid, and creatinine, via the kidneys.
• Kidneys are responsible for osmoregulation, pH regulation, and sodium regulation.

Internal Structure of the Kidney

• Renal capsule protects the kidney and prevents infections in the surrounding area.
• Cortex is the reddish area made up of renal corpuscles.
• Medulla is the reddish-brown area made up of 8-12 cone-shaped pyramids.
• A pyramid is made up of collecting ducts.
• Calyx is a short duct, part of the pelvis, that collects urine from the collecting ducts.
• Renal sinus is the space between the calyces.
• Papilla is the tip of each pyramid, fits into calyx.
• Renal pelvis allows urine to drain from the calyces into an enlarged upper end of the ureter.
• The renal artery carries blood with high urea content into the kidney.
• The renal vein carries blood with low urea content out of the kidney.
• The ureter carries urine from the pelvis to the bladder for storage.

Microscopic Structure of the Kidney

• The nephron is the functional unit of the kidney and is composed of the renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

Processes in the Nephrons

• Glomerular filtration: Substances are filtered from the blood at the renal corpuscle.
• Tubular reabsorption: Useful substances are taken back between the proximal convoluted tubule and collecting duct.
• Tubular excretion: Substances are added to the nephron at the proximal and distal convoluted tubules.

Renal Corpuscle

• Glomerulus is a capillary network with a single cell thick layer with pores.
• Bowman's capsule is the start of the nephron and its inner wall is made of specialized cells called podocytes.
• The renal corpuscle is composed of the glomerulus and Bowman's capsule, and glomerular filtration occurs there.
• The afferent arteriole is wider than the efferent arteriole. This leads to a pressure build up which forces substances into the Bowman's capsule.