Unit 2 Biology Revision - Homeostasis, Nervous and Endocrine Control, Thermoregulation, Osmoregulation, Excretion, Infectious Disease, and Immunity

Comprehensive vocabulary flashcards covering nervous and endocrine regulation, action potentials, thermoregulation, osmoregulation, nephron anatomy, disease classifications, virulence factors, and immune responses.

Homeostasis

The process of maintaining stable internal conditions within tightly regulated physiological tolerance limits despite fluctuations in external or internal environments.

Chemoreceptor

A type of sensory receptor that detects chemical substances, such as those involved in taste and smell.

Thermoreceptor

A sensory receptor that detects temperature changes, such as heat and cold.

Mechanoreceptor

A sensory receptor that detects mechanical pressure or distortion, including touch, vibration, and stretch.

Photoreceptor

A sensory receptor that detects light, such as visual stimuli in the eyes.

Nociceptor

A sensory receptor that detects pain or harmful stimuli, such as extreme heat, mechanical damage, or chemical irritation.

Dendrites

Structures of a neuron that receive incoming signals (neurotransmitters) from other neurons and carry them towards the cell body.

Soma (Cell Body)

The region of a neuron that integrates incoming signals and maintains normal cell functions, including metabolism and protein synthesis.

Axon

The nerve fiber that transmits electrical impulses (action potentials) away from the soma towards other neurons, muscles, or glands.

Myelin Sheath

An insulating layer surrounding the axon that speeds up electrical signal conduction and prevents signal loss.

Nodes of Ranvier

Gaps in the myelin sheath that allow saltatory conduction, where action potentials jump from node to node to greatly increase transmission speed.

Axon Terminal

The specialized structure at the end of an axon that releases neurotransmitters into the synaptic cleft to communicate with the next cell.

Resting Potential

The state where a neuron is polarised with a negative charge inside and a positive charge outside, maintained by the $\text{Na}^+/\text{K}^+$ pump.

Depolarisation

The phase of an action potential where a stimulus opens $\text{Na}^+$ channels, allowing sodium ions to flow into the neuron and making the inside more positive.

Repolarisation

The phase of an action potential where $\text{K}^+$ channels open, allowing potassium ions to flow out of the cell and restoring the negative internal charge.

Hyperpolarisation

The state where the neuron's membrane potential temporarily becomes more negative than the resting potential due to $\text{K}^+$ channels remaining open too long.

Upregulation

An increase in the number of receptors displayed on a target cell, making the cell more sensitive to a specific signal or hormone.

Downregulation

A decrease in the number of receptors displayed on a target cell, making the cell less sensitive to a specific signal or hormone.

Brown Adipose Tissue

Specialized fat containing many fat droplets and mitochondria that generates heat through non-shivering thermogenesis.

Kleptothermy

A behavioural thermoregulatory response in which animals huddle together to share body heat.

Hibernation

A long-term state of inactivity and decreased metabolic rate associated with redirection of blood flow in animals during winter.

Aestivation

Prolonged torpor in response to high environmental temperatures and low water availability to conserve water and energy.

Torpor

A short-term state of decreased physiological activity in an animal, usually with a reduced body temperature and metabolic rate as a result of cold conditions.

Vasomotor Control

Physiological mechanisms adjusting blood vessel diameter, where vasodilation increases heat loss and vasoconstriction reduces heat loss.

Osmoregulators

Animals that maintain a constant internal osmotic environment in spite of changes in their external environment.

Osmoconformers

Animals whose body fluids are in osmotic balance with their surrounding environment.

Antidiuretic Hormone (ADH)

A hormone secreted by the pituitary gland that increases the permeability of the distal convoluted tubule and collecting ducts in the kidney, promoting water reabsorption.

Glomerulus

A network of capillaries with thin walls that allow smaller molecules, wastes, and fluid to pass into the nephron tubule while retaining larger molecules such as proteins and blood cells.

Bowman's Capsule

A double-walled sac surrounding the glomerulus that creates a urinary space through which filtrate enters the nephron.

Proximal Tubule

The segment of the nephron responsible for reabsorbing approximately $65\%$ of the filtered load and most glucose, amino acids, solutes, and low molecular weight proteins.

Loop of Henle

A U-shaped tube in the nephron that reabsorbs water and $\text{NaCl}$ from filtrate, conserving water and producing highly concentrated urine.

Distal Tubule

The section of the nephron involved in regulating water, electrolyte, and hydrogen-ion balance.

Collecting Tubule

The tubular structure in the kidney responsible for transporting urine and facilitating water reabsorption.

Infectious Disease

A disease that can be transmitted from one person to another and is caused by pathogenic micro-organisms such as bacteria, viruses, fungi, or parasites.

Non-Infectious Disease

A disease that cannot be spread through person-to-person contact and is caused by factors such as genetics, malnutrition, environment, and lifestyle.

Pathogenesis

The process by which an infection leads to disease.

Adherence Factors

Molecules or structures, such as pili, that allow pathogens to attach to host cells and tissues.

Invasion Factors

Mechanisms or molecules, such as tissue-degrading enzymes, that enable pathogens to enter and spread within host tissues.

Capsules

Polysaccharide layers surrounding the cell walls of certain bacteria that act as protective barriers to help pathogens evade host phagocytosis.

Toxins

Poisonous substances produced by pathogens, such as exotoxins, that cause direct damage to host tissues and organs.

Complement System

A group of immune proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens via opsonization, inflammation, and membrane lysis.

Humoral Response

The branch of adaptive immunity involving B lymphocytes and antibodies that neutralize and clump pathogens in extracellular fluids.

Cell-Mediated Response

The branch of adaptive immunity driven by T lymphocytes, such as Killer T cells, which identify foreign antigens on host cells and instruct infected cells to undergo apoptosis.

Active Immunity

Immunity produced when the body actively responds to an antigen by producing its own antibodies and memory cells.

Passive Immunity

Immunity acquired when a person receives pre-formed antibodies to a disease rather than producing them through their own immune system.

Dendritic Cells

Antigen-presenting cells that collect samples of pathogens from infection sites and travel to the lymphatic system to activate specific T-helper and Killer T cells.