Enjoy these detailed notes, directly from the Ontario Secondary School Grade 12 Curriculum, focussing on SBI4U! These extensively detailed notes should help you if you're studying for an exam or just love biology! Good luck!
Homeostasis Test Notes 2017-05-12
Hassan Alibhai Page HH1
Homeostasis: Introduction
• The physiological state of the body in which internals are kept within a suitable environmental
range for practical use.
• A dynamic process, adjusted for changing external conditions in the interstitial fluid (the fluid
surrounding body cells)
◦ Maintains internal temperature, pH, and hormone levels
• Homeostatic Control Systems:
◦ Sensor (Monitor): Detects the change in the environment
◦ Integrator (Brain): Compares existing conditions to ideal ones and decides how to react
◦ Effector (Regulator): An action that is able to return the body to a normal, ideal state
• Feedback
◦ Negative: described above, the body regulates an uncomfortable situation
◦ Positive: body takes change in a positive manner, does not restore homeostasis (breastfeed)
Water Balance
• To maintain homeostasis, cells regulate their ionic balance and pH balance, in addition to their
osmotic concentration.
• Therefore, certain ions and toxic compounds, such as the metabolites of nitrogenous compounds
like amino acids and nucleic acids, must be eliminated.
◦ This happens through the process of urination,
where toxic liquids and solids are removed
◦ In mammals, the chemical itself is urea
Kidneys
• The primary organ of the excretory system is the kidney, of which there are two
• In essence, the two kidneys filter blood, resulting in the removal of waste fluid that excite the
body as urine
• The functional units of the kidney are called nephrons
, Homeostasis Test Notes 2017-05-12
Hassan Alibhai Page HH2
Nephrons: The Functional Unit of Kidneys
The behaviour of ions during urine
filtration is displayed below to give
context to the nephron anatomy. It
is discussed in detail next page.
Part of Nephron Function
Bowman’s capsule A small folded structure in the human kidney that encircles the
glomerulus
Glomerulus A network of capillaries within the Bowman’s capsule that performs
the first step in the filtration of blood
Afferent Arteriole A vessel that supplies blood to the nephrons in the human kidney
Efferent Arteriole A vessel that carries away filtered blood from the nephrons in the
human kidney
Peritubular Capillaries A net of capillaries in the nephrons that reabsorb essential ions and
minerals from filtered blood
Proximal Convoluted Tubule The duct portion of a nephron that connects the Bowman’s capsule to
the loop of Henle
Loop of Henle The U-shaped part of the duct that connects the proximal convoluted
tubule to the distal convoluted tubule
distal convoluted tubule The duct portion of a nephron that connects the loop of Henle to the
ducts that lead to the renal pelvis
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