Lesson Notes By Weeks and Term v5 - Grade 10
Organs and systems of the human body – Week 5 focus
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Organs and systems of the human body – Week 5 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Life Sciences
Class: Grade 10
Term: 2nd Term
Week: 5
Theme: General lesson support
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This week, we delve into the fascinating world of the human body, focusing specifically on the excretory system and its crucial role in maintaining homeostasis. Understanding how our bodies eliminate waste is not just academic; it directly impacts our health, well-being, and even our ability to participate fully in daily life. For example, kidney problems are increasingly prevalent in South Africa, linked to factors like diabetes and hypertension. Learning about the excretory system empowers you to make informed choices about your health and understand the importance of medical interventions when necessary.
2.1 The Excretory System: An Overview The excretory system is responsible for removing metabolic waste products from the body. These waste products are toxic and must be eliminated to maintain a stable internal environment (homeostasis). The primary organs involved are the kidneys, ureters, bladder, and urethra. The skin and lungs also play a role in excretion, albeit to a lesser extent. 2.2 Organs of the Excretory System Kidneys: These bean-shaped organs are located in the abdominal cavity, one on each side of the spine. They are the primary filters of the blood. Each kidney contains millions of tiny filtering units called nephrons.
Structure: Each kidney has an outer cortex, an inner medulla, and a central renal pelvis. The nephrons extend from the cortex into the medulla. Blood enters the kidney through the renal artery and exits through the renal vein.
Function: The kidneys filter waste products, excess salts, and water from the blood. They also regulate blood pressure, pH balance, and red blood cell production.
Ureters: These are tubes that carry urine from the kidneys to the bladder. Peristaltic contractions of the ureter walls push the urine along.
Bladder: This is a muscular sac that stores urine. The bladder can expand to hold up to 500 ml of urine.
Urethra: This is a tube that carries urine from the bladder to the outside of the body. The urethra is longer in males than in females.
Skin: The skin helps excrete waste products such as water, salts, and urea through sweat glands. Sweat also plays a role in thermoregulation (temperature control).
Lungs: The lungs excrete carbon dioxide, a waste product of cellular respiration, when we breathe out. 2.3 The Nephron: The Functional Unit of the Kidney The nephron is the microscopic structural and functional unit of the kidney.
Each nephron consists of: Glomerulus: A network of capillaries where filtration occurs. Blood pressure forces water, salts, glucose, amino acids, and urea from the blood into Bowman's capsule. Blood cells and large proteins remain in the blood.
Bowman's Capsule: A cup-shaped structure that surrounds the glomerulus and collects the filtrate.
Proximal Convoluted Tubule (PCT): Reabsorption of glucose, amino acids, salts, and water occurs here. These substances are returned to the bloodstream.
Loop of Henle: This U-shaped structure helps to concentrate the urine. Water is reabsorbed in the descending limb, and salts are reabsorbed in the ascending limb. This creates a concentration gradient in the medulla of the kidney.
Distal Convoluted Tubule (DCT): Further reabsorption of water and salts occurs here, regulated by hormones such as ADH (antidiuretic hormone) and aldosterone.
Collecting Duct: Several nephrons empty into a single collecting duct, which carries urine to the renal pelvis. The collecting duct is also involved in water reabsorption, controlled by ADH. 2.4 Urine Formation: A Three-Step Process Filtration: Occurs in the glomerulus. Blood pressure forces small molecules (water, salts, glucose, amino acids, urea) from the blood into Bowman's capsule, forming the filtrate.
Reabsorption: Occurs in the PCT, Loop of Henle, DCT, and collecting duct. Useful substances (glucose, amino acids, salts, water) are selectively reabsorbed from the filtrate back into the blood. This process is vital to prevent the loss of essential nutrients.
Secretion: Occurs in the DCT. Waste products (drugs, toxins, excess ions) are actively secreted from the blood into the filtrate. This helps to remove substances that were not filtered initially. 2.5 Osmoregulation and pH Balance Osmoregulation: The kidneys regulate the water balance in the body by controlling the amount of water reabsorbed from the filtrate. ADH, released by the pituitary gland, increases water reabsorption in the collecting duct, resulting in more concentrated urine. When the body is dehydrated, more ADH is released, and less urine is produced. When the body is overhydrated, less ADH is released, and more dilute urine is produced. pH Balance: The kidneys help maintain blood pH by excreting excess acids or bases in the urine. They also reabsorb bicarbonate ions, which act as a buffer to neutralize acids in the blood. 2.6 Common Kidney Disorders in South Africa Kidney Stones: These are hard deposits of minerals and salts that form inside the kidneys. They can cause severe pain as they pass through the urinary tract. Risk factors include dehydration, diet, and family history. In South Africa, kidney stones are a relatively common problem.
Kidney Failure (Renal Failure): This occurs when the kidneys lose their ability to filter waste products from the blood. Causes include diabetes, hypertension, glomerulonephritis (inflammation of the glomeruli), and polycystic kidney disease. Kidney failure can lead to a buildup of toxins in the body and can be life-threatening. Dialysis or kidney transplantation may be necessary.