AEHBY Task 4 Cheatsheet

AEHBY TASK 4 CHEATSHEET

Chapter 5: The Circulatory System 5.1 Structure of the Blood The blood consists of a liquid matrix and formed cellular elements:

• Plasma (approx. 55%): The liquid portion that transports nutrients, wastes, hormones, proteins, and antibodies throughout the body.
• Formed Elements (approx. 45%):
  • Erythrocytes (Red Blood Cells): Flattened, biconcave cells that lack a nucleus. This shape increases flexibility and allows more room for haemoglobin to transport oxygen. They live for around 120 days.
  • Leucocytes (White Blood Cells): Larger than red blood cells but make up only 1% of blood. They are crucial for protecting the body from infection. Examples: Neutrophils, Monocytes/Macrophages, Lymphocytes.
  • Thrombocytes (Platelets): Small cell fragments used for the coagulation of blood. They adhere to injured blood vessels to form scaffolding. 5.2 Transport of Gases
• Oxygen (O₂): Because oxygen is not very water-soluble, only 3% travels in the plasma. The remaining 97% combines with haemoglobin to form a weak bond called Oxyhaemoglobin (HbO₂). High O₂ concentration in the lungs forces this combination, while low O₂ in body cells causes it to break down and release oxygen into tissues.
• Carbon Dioxide (CO₂): Transported in three main ways:
  • 7-8% is dissolved directly in the plasma.
  • 22% combines with globin to form Carbaminohaemoglobin.
  • 70% reacts with water to form Carbonic Acid (H₂CO₃), which then ionises into hydrogen ions (H⁺) and Bicarbonate ions (HCO₃⁻). 5.2 Blood Clotting & Blood Vessels When a blood vessel is damaged, four processes stop blood loss and prevent infection:
• Vasoconstriction: Artery wall muscles constrict immediately to reduce blood flow.
• Platelet Plug: Platelets stick to the rough damaged surface, attracting more platelets to build a temporary plug.
• Coagulation: For serious injuries, clotting factors form threads of an insoluble protein called fibrin. This web traps blood cells and platelets to form a clot (thrombus).
• Clot Retraction: The fibrin threads contract, pulling the damaged edges together and squeezing out fluid (serum). The clot dries into a protective scab. 5.2 The Heart & Circulation
• Heart Structure: Enclosed by the pericardium (a membrane preventing overstretching) and composed of cardiac muscle. A wall called the septum separates the left and right sides.
• Chambers: Two top Atria (receive blood) and two bottom Ventricles (pump blood). The left ventricle has a thicker wall because it pumps blood around the entire body.
• Valves: * Atrioventricular valves: Located between the atria and ventricles, held by chordae tendineae.
  • Semilunar valves: Located in arteries leaving the heart, preventing backflow into the ventricles.
• Blood Sequence: Deoxygenated blood enters the Right Atrium via the Vena Cava → Right Ventricle → Pulmonary Artery to the lungs. Oxygenated blood returns via the Pulmonary Veins → Left Atrium → Left Ventricle → Aorta to the body.
• Cardiac Output = Stroke Volume x Heart Rate. 5.3 Blood Groups and Transfusions
• ABO System: Determined by the presence or absence of Antigen A and Antigen B on red blood cells. Your plasma contains antibodies against non-self antigens (e.g., Type A blood contains Anti-B antibodies). If incompatible blood is mixed, red blood cells will clump together (agglutinate).
• Rh System: Rh-positive people have Rh antigens; Rh-negative people lack them and will produce Anti-Rh antibodies if exposed to Rh-positive blood.
• Transfusion Types:
  • Whole Blood: Used for severe blood loss.
  • Red Cell Concentrates: Plasma/WBCs removed; used for heart disease or severe anaemia.
  • Cryoprecipitate: Thawed frozen plasma; treats severe bleeding and haemophilia.
  • Immunoglobulins: Extracted antibodies for patients lacking specific immunity (e.g., tetanus).
  • Autologous: The patient’s own blood is collected weeks before surgery to eliminate disease transmission risks. 5.4 The Lymphatic System
• Functions: Collects fluid that escapes blood capillaries and returns it to the circulatory system; acts as an internal defence against disease; transports dietary lipids.
• Lymph Vessels: Originate as blind-ended tubes. They are more permeable than blood capillaries and have more valves. The system has no pump; lymph is pushed upwards by skeletal muscle contractions, smooth muscle, and breathing movements.
• Lymph Nodes: Bean-shaped bodies containing lymphoid tissue. Afferent vessels carry unfiltered lymph into the node. Here, macrophages destroy foreign particles and bacteria via phagocytosis. Filtered lymph exits via Efferent vessels. Chapter 7: The Excretory System 7.1 & 7.2 The Organs, Liver, and Skin
• Excretory Organs: Lungs (excrete CO₂), Sweat glands (secrete water), Alimentary canal (passes bile pigments), and Kidneys (maintain body fluid concentrations).
• Skin: Secretes about 500 mL of water daily, containing dissolved sodium chloride, lactic acid, and urea.
• The Liver & Deamination: The liver processes chemicals into safer forms. Through Deamination, enzymes strip the amino group (NH₂) from excess amino acids. This forms highly toxic Ammonia (NH₃), which the liver immediately converts into less toxic Urea to be excreted safely by the kidneys. 7.3 The Kidneys & Urine Production
• Kidney Structure: Outer Renal Cortex, inner Renal Medulla (containing renal pyramids), and the concave Renal Pelvis that funnels urine into the ureter.
• Nephrons: The functional units (approx. 1.2 million per kidney). They consist of a Renal Corpuscle (Glomerulus + Glomerular/Bowman’s Capsule) and a Renal Tubule (Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule, Collecting Duct).
• Production of Urine (The 3 Steps):
  • Glomerular Filtration: High blood pressure in the glomerulus forces fluid through two single layers of flat cells into the capsule. Why high pressure? The efferent arteriole leaving the glomerulus has a narrower diameter than the afferent arteriole entering it.
  • Selective Reabsorption: The renal tubules return vital substances (water, glucose, amino acids) back into the peritubular capillaries. Maximised by the long tubule length and massive surface area.
  • Tubular Secretion: The blood actively adds unwanted materials (potassium, hydrogen ions, creatinine) into the filtrate to maintain strict blood pH (7.4-7.5). 7.4 Effects of Lifestyle on Excretion
• Kidney Stones: Solid crystals that build up when urine becomes too concentrated; can painfully block the ureter, bladder, or urethra.
• Kidney Failure: Occurs when glomeruli lose filtration ability (often linked to diabetes, high blood pressure, or lifestyle factors). Excessive proteins and red blood cells leak out into the urine, causing fluid accumulation and swelling in tissues.
• Dialysis (Artificial Filtration):
  • Peritoneal Dialysis: A catheter pumps fluid (free of wastes) into the abdominal cavity. Wastes naturally diffuse from the rich blood supply of the peritoneum into this fluid, which is then drained.
  • Haemodialysis: Blood is hooked to an artificial machine and passed through thousands of fine tubes surrounded by fluid. Wastes diffuse out of the blood; required ~3 times a week for 4-5 hours.

High-Yield Exam Essentials & Crucial Sequences

1. The Complete Blood Vessel Sequence You must know the exact pathway blood takes when leaving and returning to the heart.

• Leaving the Heart (Oxygenated): Aorta → Arteries → Arterioles → Capillaries (where oxygen exchange occurs).
• Returning to the Heart (Deoxygenated): Capillaries → Venules → Veins → Superior & Inferior Vena Cava → Right Atrium.
• Exception: The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, and the pulmonary veins carry oxygenated blood from the lungs to the left atrium.

2. Comparing Arteries and Veins

• Arteries: Carry blood away from the heart. They have thick, muscular, and elastic walls to stretch and accommodate high-pressure blood pumped directly from the ventricles. They do not have valves.
• Veins: Carry blood towards the heart. Blood pressure here is low and constant, so their walls are much thinner and non-muscular. Because of this low pressure, veins contain valves to prevent the backflow of blood.

3. Maximizing Urine Formation in the Kidney The structure of the kidney and nephrons is perfectly adapted to maximize efficiency. Memorize these structural adaptations:

• Filtration Surface Area: The glomerulus is a heavily knotted network of capillaries, massively increasing the surface area for filtration.
• High Pressure System: The efferent arteriole (leading out) has a smaller diameter than the afferent arteriole (leading in), which creates a high-pressure environment forcing fluid out of the blood.
• Minimal Barrier: Filtrate only needs to pass through two single cell layers (one from the capillary wall, one from the glomerular capsule).
• Reabsorption Surface Area: Each tubule has two sets of highly coiled convolutions and a long Loop of Henle to provide massive surface area for reabsorption. Additionally, the cells lining the Proximal Convoluted Tubule (PCT) are ciliated for even more surface area.
• Active Transport Energy: The PCT cells contain increased mitochondria to supply the energy needed for the active transport of nutrients back into the blood.

4. Composition of Urine & Waste Origins Normal urine is mostly water containing dissolved wastes. Know where these specific wastes come from:

• Urea: Produced in the liver via deamination of excess amino acids.
• Uric Acid: Produced by the metabolism of purines (which come from the breakdown of nucleic acids like DNA when cells die).
• Creatinine: Produced in muscles from the breakdown of creatine phosphate (an energy-rich molecule).

5. Crucial Excretory Definitions Do not mix these up on a multiple-choice section:

• Excretion: The removal of the wastes of metabolism from the body (e.g., sweating urea, exhaling CO₂).
• Elimination: The removal of substances that were never part of metabolism (e.g., undigested food/bacteria).
• Secretion: The process where cells release useful substances for the body to use (e.g., hormones, digestive enzymes).
• Defecation: The specific elimination of faeces from the body.