OCR (A) Biology A-level Topic 5.1: Communication and homeostasis Notes

Flashcards on Communication and Homeostasis, covering cell signaling, homeostasis mechanisms, thermoregulation, excretion, kidney function, hormonal and neuronal communication, and muscle contraction.

Cell signalling

Communication between cells in the form of electrical signals carried by neurones or chemical signals with the help of hormones.

Neuronal Cell Signalling

Faster and short term cell signalling.

Chemical Cell Signalling

Slower and long term cell signalling.

Endocrine signalling

Long distance signalling, where the signalling molecule is carried by the circulatory system.

Paracrine signalling

Signalling which occurs between cells which are in close proximity to each other and occurs directly or with the help of extracellular fluid.

Autocrine signalling

Signalling where the cell releases signals to stimulate its own receptors thus triggering a response within itself.

Homeostasis

Ensures that a constant internal environment is maintained despite changes in the external environment.

Negative feedback

Counteracts any change in internal conditions to restore optimum conditions.

Positive feedback

Increase the original change in the conditions.

Ectotherm

An organism which regulates its body temperature with the help of external source.

Endotherm

An organism able to maintain a constant body temperature, independent of the external temperature.

Excretion

Removal of metabolic waste.

Liver's role in excretion

Breaks down harmful substances and toxic waste, converting them into less harmful forms for excretion.

Deamination

Removal of the amino group from excess amino acids, leading to formation of ammonia and organic acids.

Hepatocytes

Converts ammonia to urea by the addition of carbon dioxide in the ornithine cycle.

Kidney function

Blood enters the kidney through the renal artery, waste products are filtered out as it passes through capillaries, selective reabsorption occurs, and filtered blood exits through the renal vein.

Ultrafiltration

Waste products are filtered out of the blood as it passes through the capillaries and into the long tubules.

Selective reabsorption

Useful substances such as amino acids, glucose, vitamins are reabsorbed back through the tubules in the medulla.

Afferent

Blood arrives at the Glomerulus through the _ arteriole.

Efferent

Blood leaves the glomerulus through the _ arteriole.

Selective Reabsorption

Occurs in the proximal convoluted tubule (PCT), where 100% of glucose and amino acids are reabsorbed.

Loop of Henle

Produces a low water potential in the medulla of the kidney by acting as a countercurrent multiplier to produce concentration gradients.

Control of blood water potential

Osmoreceptors in the hypothalamus control the water potential of the blood, and antidiuretic hormone (ADH) is released to increase water reabsorption.

ADH

It makes walls of DCT and collecting duct more permeable to water therefore increasing the reabsorption of water from the tubules into the blood.

Kidney failure

Triggered by kidney infections or high blood pressure, leading to inefficient filtration and reabsorption.

Renal dialysis

Filtration of the blood with the help of a machine containing dialysis fluid to remove waste products, excess water, and ions.

Haemodialysis

Removes blood from the body and pumps it through a machine where the blood is run in countercurrent flow alongside dialysis fluid.

Peritoneal dialysis

Dialysis fluid is put into the body cavity so that exchange can happen across the body’s own peritoneal membrane.

Kidney transplant

Replaces the damaged kidney and reverses kidney failure symptoms.

Urine samples

Used in diagnostic tests, such as pregnancy testing with monoclonal antibodies to detect human chorionic gonadotropin.

Neurones

Coordinating communication within the nervous system.

Motor neurones

Transmit electrical impulses from the central nervous system to muscles and glands in the body.

Sensory neurones

Transmit impulses from receptors to the central nervous system.

Relay Neurones

Located within the central nervous system, are involved in transmitting the electrical impulses from sensory neurones to motor neurones.

Saltatory Conduction

Increases the speed at which the electrical potential is carried with the help of myelin sheath.

Synapses

Junctions between two neurones.

Receptors

Cells specialised for detection of stimuli.

Pacinian corpuscles

Convert mechanical energy into electrical energy.

Hormones

Signalling molecules secreted by ductless endocrine glands directly into the blood.

Adrenal glands

Located above the kidneys and composed of an outer adrenal cortex surrounding the inner adrenal medulla.

Adrenal medulla

Secretes adrenaline in response to danger, stress, or excitement for the fight or flight response.

Adrenal cortex

Produces mineralocorticoids and glucocorticoids.

Pancreas

The _ functions in both an endocrine and exocrine way.

Islets of Langerhans

Secrete insulin from beta cells and glucagon from alpha cells directly into the blood.

Type I diabetes

An autoimmune disease where the beta cells are destroyed by the body, leading to insufficient insulin production.

Type II diabetes

A result of cells becoming less responsive to insulin.

Tropisms

Directional growth responses of plants.

Phototropism

Growth response to light, with shoots exhibiting positive phototropism and roots exhibiting negative phototropism.

Geotropism

Growth response to gravity, with roots exhibiting positive geotropism and shoots exhibiting negative geotropism.

Auxins

Plant growth regulators that promote cell elongation.

Leaf abscission

Dropping of leaves controlled by auxin, ethene, and cytokinins.

Apical dominance

Phenomenon where the growth of side shoots does not take place during shoot growth, controlled by auxin, abscisic acid, and cytokinins.

Mammalian nervous system

Consists of the brain and spinal cord (the central nervous system) and the sensory and motor neurones (the peripheral nervous system).

Autonomic nervous system

Consists of sympathetic and parasympathetic systems, which are antagonistic systems with opposing effects.

Cerebrum

Largest part of the brain involved in controlling vision, thinking, learning, emotions, and voluntary control.

Cerebellum

Located underneath the cerebrum, plays an important role in coordinating muscle movements and balance.

Hypothalamus

Located just beneath the middle part of the brain, involved in thermoregulation and hormone production.

Medulla oblongata

Located at the base of the brain, controls vital body processes such as breathing, heart rate, and blood pressure.

Sinoatrial node (SAN)

Initiates a wave of electrical stimulation causing the atria to contract, acting as the pacemaker of the heart.

Tendons

Non-elastic tissue which connects muscles to bones.

Ligaments

Elastic tissue that joins bones together and determines the amount of movement possible at a joint.

Skeletal muscles

Muscles attached to bones, arranged in antagonistic pairs.

Antagonistic muscle pairs

Pairs of muscles which pull in opposite directions, such as flexors and extensors.

Sarcolemma

When an action potential arrives at the these channels open and so depolarization occurs.

Slow twitch fibres

Specialised for slow contractions and are adapted to long periods of exercise.

Fast twitch fibres

Adapted for rapid release of energy during intense exercise.