Introduction
Human physiology is a crucial area of study within the International Baccalaureate (IB) Biology syllabus. It encompasses various systems of the human body, their functions, and how they interact to maintain homeostasis. This study note document will delve into the detailed aspects of human physiology, specifically focusing on digestion and absorption, the blood system, defense against infectious diseases, gas exchange, neurons and synapses, and hormones, homeostasis, and reproduction.
6.1 Digestion & Absorption
The Digestive System
The digestive system is responsible for breaking down food into nutrients, which the body uses for energy, growth, and cell repair.
Key Components:
- Mouth: Begins mechanical digestion through chewing and chemical digestion through enzymes in saliva.
- Esophagus: Transports food to the stomach using peristalsis.
- Stomach: Uses acid and enzymes to further break down food.
- Small Intestine: Main site for digestion and absorption of nutrients.
- Large Intestine: Absorbs water and forms feces.
- Rectum and Anus: Expel waste from the body.
Digestion Process
- Mechanical Digestion: Physical breakdown of food (e.g., chewing).
- Chemical Digestion: Enzymatic breakdown of macromolecules into smaller molecules (e.g., amylase breaking down starch into maltose).
Absorption
Absorption occurs primarily in the small intestine, where nutrients pass through the lining of the intestine into the blood.
Key Structures:
- Villi and Microvilli: Increase the surface area for absorption.
- Capillaries: Transport absorbed nutrients to the bloodstream.
- Lacteals: Absorb fats and transport them to the lymphatic system.
Example:
Example Calculation: If a person consumes 100 grams of carbohydrates, and the efficiency of carbohydrate absorption is 90%, then the amount of carbohydrates absorbed is: $$ 100 , \text{g} \times 0.90 = 90 , \text{g} $$
6.2 The Blood System
Components of Blood
- Red Blood Cells (Erythrocytes): Transport oxygen using hemoglobin.
- White Blood Cells (Leukocytes): Play a role in immune response.
- Platelets: Involved in blood clotting.
- Plasma: Liquid component that carries cells, nutrients, hormones, and waste products.
Blood Vessels
- Arteries: Carry blood away from the heart; thick-walled to handle high pressure.
- Veins: Carry blood to the heart; have valves to prevent backflow.
- Capillaries: Microscopic vessels where gas and nutrient exchange occurs.
The Heart
The heart pumps blood through two main circuits:
- Pulmonary Circulation: Carries blood to the lungs for gas exchange.
- Systemic Circulation: Delivers oxygenated blood to the rest of the body.
Cardiac Cycle:
- Systole: Contraction phase, pumping blood out of the heart.
- Diastole: Relaxation phase, allowing the heart to fill with blood.
Note:
The heart rate is regulated by the sinoatrial (SA) node, also known as the pacemaker of the heart.
6.3 Defence Against Infectious Disease
The Immune System
Skin
The skin acts as a physical barrier to pathogens.
Blood Clotting
Platelets and clotting factors work together to form a clot and prevent pathogen entry.
White Blood Cells
- Phagocytes: Engulf and digest pathogens.
- Lymphocytes: Produce antibodies and memory cells for specific immune responses.
Antibiotics
Antibiotics are substances that kill or inhibit the growth of bacteria.
Common Mistake:
Common Mistake: Antibiotics are effective against bacteria but not viruses.
Antibiotic Resistance
Overuse and misuse of antibiotics have led to the development of antibiotic-resistant bacteria.
6.4 Gas Exchange
Function & Structures
Key Structures:
- Trachea: Windpipe that conducts air to the lungs.
- Bronchi and Bronchioles: Branching airways that lead to alveoli.
- Alveoli: Tiny air sacs where gas exchange occurs.
Mechanism of Ventilation
Inhalation:
- Diaphragm contracts and moves downward.
- Rib cage expands.
- Air pressure in the thoracic cavity decreases, drawing air into the lungs.
Exhalation:
- Diaphragm relaxes and moves upward.
- Rib cage contracts.
- Air pressure in the thoracic cavity increases, pushing air out of the lungs.
Lung Diseases
Common lung diseases include asthma, bronchitis, and emphysema.
Tip:
Tip: Regular exercise can improve lung function and efficiency.
6.5 Neurones & Synapses
Structure of Neurons
- Dendrites: Receive signals from other neurons.
- Cell Body: Contains the nucleus and organelles.
- Axon: Transmits electrical impulses.
- Myelin Sheath: Insulates the axon and speeds up signal transmission.
- Synaptic Terminals: Release neurotransmitters to communicate with other neurons.
Synaptic Transmission
- Action Potential: Electrical impulse travels down the axon.
- Neurotransmitter Release: Vesicles release neurotransmitters into the synaptic cleft.
- Receptor Binding: Neurotransmitters bind to receptors on the post-synaptic neuron, continuing the signal.
Note:
Synaptic transmission is essential for all neural communication, including reflexes and voluntary movements.
6.6 Hormones, Homeostasis & Reproduction
6.6.1 Hormones
Hormones are chemical messengers released by endocrine glands and travel through the bloodstream to target organs.
Examples:
- Insulin: Regulates blood glucose levels.
- Adrenaline: Prepares the body for 'fight or flight' response.
6.6.2 Hormones Continued
Endocrine Glands:
- Pituitary Gland: Master gland controlling other endocrine glands.
- Thyroid Gland: Regulates metabolism.
- Adrenal Glands: Produce adrenaline and cortisol.
6.6.3 Reproduction: Background
Human reproduction involves the formation of gametes, fertilization, and development of the embryo.
6.6.4 Reproduction: Sex Determination in Males
Key Structures:
- Testes: Produce sperm and testosterone.
- Penis: Delivers sperm into the female reproductive tract.
6.6.5 Reproduction: Sex Determination in Females
Key Structures:
- Ovaries: Produce eggs and hormones (estrogen and progesterone).
- Uterus: Supports the developing embryo.
6.6.6 Skills: Reproduction Diagrams
Diagrams:
- Male reproductive system
- Female reproductive system
- Fertilization process
Note:
Understanding these diagrams is crucial for visualizing the processes involved in human reproduction.
Conclusion
Human physiology is a complex but fascinating subject that covers various systems and their interactions to maintain homeostasis and support life. From digestion and absorption to the intricate workings of the nervous and endocrine systems, each component plays a vital role in the overall functioning of the human body. Understanding these concepts is essential for a comprehensive grasp of biology in the IB syllabus.