Unit 2: Physiology

Question 1

Outline the roles of sensory receptors in mammals in converting different forms of energy into nerve impulses

Answer 1

Sensory receptors are the specialised part of sensory neurones that allow external stimuli to be detected.
The types of sensory receptors (and their stimuli) include: Mechanoreceptors(physical force), Thermoreceptors(temperature), Chemoreceptors(dissolved chemicals), nociceptors(pain), proprioceptors(positional information)

Question 2

Describe, with the aid of diagrams, the structure and functions of sensory and motor neurones

Answer 2

Motor neurons: motor neurones in animals are part of the central nervous system and they connect to muscles, glands and organs throughout the body. Transmit impulses from spinal cord to skeletal muscles to control movement. Lower motor neurones: travel from spinal cord to muscle. Upper motor neurones: travel between the brain and spinal cord. Are multipolar(one axon and several dendrites).
Sensory Neurons: activated by sensory input from the environment. Most sensory neurons are pseudo-unipolar, which means they have only one axon split into two branches

Question 3

Describe and explain how the resting potential is established and maintained

Answer 3

Potassium concentration is higher in the cell, while sodium is higher outside the cell. This gradient is maintained by a sodium-potassium pump(which uses ATP to maintain this gradient). These concentration gradients are a form of chemical energy.

Question 4

Describe and explain how an action potential is generated

Answer 4

If sodium ions influx, more sodium channels open as they are voltage gated. This temporarily changes the membrane potential significantly. Once initiated an AP has a magnitude independent of the strength of the stimulus. AP are an all or none response. If a large enough stimulus is present an action potential is generated. AP has constant magnitude and regenerates the same potential in adjacent areas of the membrane. AP can therefore spread along axons/dendrites for long distance communication

Question 5

Describe and explain how an action potential is transmitted in a myelinated neuron, with reference to the roles of voltage-gated sodium ion and potassium ion channels

Answer 5

The sodium inflow in the rising AP phase creates a current that depolarises the adjacent region. This process is repeated until the end of the axon/dendrite. Magnitude will be the same at every location. The zone immediately behind the AP is in the refractor period so APs can’t go backward

Question 6

Outline the significance of the frequency of impulse transmission

Answer 6

AP has a constant magnitude but a neuron can produce hundreds of APs a second. The information about the environment is encoded in frequency not amplitude. Strong stimulus= more frequent AP. Small stimulus=less frequent AP

Question 7

Outline the role of neurotransmitters in the transmission of action potentials

Answer 7

A neurotransmitter molecule can bind to different types of receptors that can excite or inhibit the postsynaptic cell. Neurotransmitter signalling is terminated by several methods: simple diffusion away from the membrane, recapture by the presynaptic neurone(allows recycling), enzymatic hydrolysis

Question 8

Outline the role of synapses in the nervous system

Answer 8

Neurotransmitters often bind to ligand-gated ion channels. This opens channels that allow specific ions across the postsynaptic membrane. Two outcomes from this process: Excitatory postsynaptic potential(K+ and Na+ acts to bring membrane potential to threshold), and Inhibitory postsynaptic potential(Cl- act to do the opposite).

Question 9

Show understanding of the difference in structural features of the brain in various animals

Answer 9

Chordata and Echinodermata: Brain and largely dorsally localised nerve cord
Arthropoda, Nematoda, Annelida, Mollusca: brain and largely ventrally localised nerve cord
Platyhelminthes: Nerve ring and nerve cord
Cnidaria: Diffuse nerve net
Porifera: no nerve cells

Question 10

Demonstrate understanding of the role of the central nervous system in disease

Answer 10

Alzheimer’s: neurodegenerative disease, causing loss of neurons in the brain. Starts in the hippocampus and spreads in a predictable pattern to other regions of the brain. 70% of cases of dementia. Affects first memory and ability to perform task and movements, followed by decline of behavioural, social and verbal skills.
Parkinson’s: neurodegenerative disease, caused by neuronal loss in an area of the midbrain, the substantia nigra. Causes movement disorder and is characterised by tremors and muscular rigidity. Proteins aggregate into Lewy bodies in neurons. Eventually leads to dopamine reduction.

Question 11

Compare and contrast the structure and function of myelinated and non-myelinated neurons

Answer 11

Lipid-rich substance surrounding the axons to insulate them. Casing made of oligodendrocytes and Schwann cells extensions. Myelin wraps the nerve in segments, with gaps called Nodes of Ranvier. Myelin increases the speed at which electrical impulses travel along the axon by forcing them to ‘jump’ from one node of Ranvier to another. ‘Fuelling station’ for the axon after the generation of electrical impulses. Coordinates the transport of cytoskeletal proteins and organelles. Demyelination is the hallmark of multiple sclerosis and other neuro-degenerative diseases. Similar structure found in some invertebrates(shrimps, annelid worms).

Question 12

Interpret graphs of the voltage changes taking place during the generation and transmission of an action potential

Answer 12

Resting potential: -70 mV membrane potential
Threshold: -45mV membrane potential
Strong depolarizing stimulus: 0-3 seconds increases from resting to threshold.
Action potential: +35 mV membrane potential. 3-4 seconds increases from threshold to action potential.
4-6 seconds: decrease back down to resting potential

Question 13

Understand the term ‘endocrinology’ and why animals and humans need an endocrine system

Answer 13

Endocrine system: Hormones are chemical signalling molecules that travel through the blood and reach every part of the body but only target cells have receptors that allow them to respond.
Why: Required for effective cell-cell communication in large, complex multicellular organisms. Monitor and coordinate internal environment and make appropriate adaptive changes. Regulate growth, development, reproduction, senescence. Enable you to respond and adapt to changes in external environment.

Question 14

Define the term hormone and explain the different types

Answer 14

A chemical messenger produced and secreted by a specialized endocrine gland that is transported in the bloodstream to a distant target organ/cell where it elicits a physiological response.
Proteins: Growth hormone(hydrophilic)
Cholesterol Derivates: Steroids and Vitamin D(Hydrophobic)
Modified Amino Acids: Adrenaline(hydrophilic) and Thyroid hormones(hydrophobic)

Question 15

Understand the concepts of hormone regulation and hormone action

Answer 15

Hormone action: Affect growth, development, metabolic activity and function of tissues. May be stimulatory or inhibitory. May act on several tissues or just one specific target tissue- major difference between endocrine and nervous system. Responsive tissues must have specific receptors for that hormone.
home regulation: By physiological changes(blood glucose regulates insulin and glucagon release from pancreas), by endogenous rhythms(ultradian-cycles in minutes: GnRH pulses(90-120 min.)), by feedback mechanisms(mostly negative(maintains homeostasis) but some positive(much less common))

Question 16

Be able to give an explanation of the pituitary gland and give an example of a system that the pituitary regulates

Answer 16

Pituitary Gland: ‘Conductor of he Endocrine Orchestra’. Organizes appropriate hormonal responses to stimuli from higher centres of brain in response to external or internal environmental changes.
Systems: Growth, Metabolism, Stress response, reproduction, lactation, water and salt balance, birth, and feeding behaviour.

Question 17

Be able to give a basic explanation of the regulation of glucose levels in man

Answer 17

Insulin: Go(glucose uptake in muscle and adipose tissue, glycolysis, glycogen synthesis, protein synthesis, and uptake of ions). Stop(proteolysis, ketogenesis, lipolysis, glycogenolysis, gluconeogenesis).
Insulin and glucagon act reciprocally. Insulin=fed state. Glucagon=fasted state

Question 18

Explain the need for transport systems in multicellular animals

Answer 18

Link exchange surfaces with cells throughout the body. Small molecules move between cells and their surroundings by diffusion. Diffusion is only efficient over small distances because the time it takes to diffuse is proportional to the square of the distance. The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of waste.

Question 19

Describe the different types of circulatory systems

Answer 19

Open: Hemolymph in sinuses surrounding organs. Open veins.
Closed: Interstitial fluid. Small branch vessels in each organ.
Single: one way all around. Ventricle, Artery, Gill capillaries, Systemic capillaries, vein, atrium.
Double: Two way. Right ventricle, lung capillaries, Left atrium, Left ventricle, systemic capillaries, right atrium.

Question 20

Explain the structure and functions of arteries, arterioles, capillaries, venules and veins

Answer 20

Artery: Endothelium, smooth muscle, connective tissue, arteriole
Capillary: Endothelium, Basal Lamina. Are only slightly wider than a red blood cell. Have thin walls to facilitate the exchange of materials. Capillaries in major organs are usually filled to capacity. Exchange between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries. The difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end. Most blood proteins and all blood cells are too large to pass through the endothelium.
Vein: Venule, Connective tissue, Smooth muscle, Endothelium

Question 21

Relate the external and internal structure of the mammalian heart to its function

Answer 21

Atrioventricular valves: separate each atrium and ventricle
Semilunar valves: control blood flow to the aorta and the pulmonary artery.
1. Atrial and ventricular diastole(relax). Both relaxed blood flows into the atria and ventricles.
2.Atrial systole(contracts) and ventricular diastole(relax). Atria contracts blood flows into the relaxed ventricles.
3. Ventricular systole(contracts) and atrial diastole(relax). Ventricle contracts blood exits, atria relaxed blood enters.

Question 22

Describe the cardiac cycle

Answer 22

Blood begins its flow with the right ventricle pumping blood to the lungs via the pulmonary arteries. In the lungs, the blood loads O2 and unloads CO2. Oxygen-rich blood from the lungs enters the heart at the left atrium via the pulmonary veins. It is pumped through the aorta to the body tissues by the left ventricle. The aorta provides blood to the heart through the coronary arteries. Blood returns to the heart through the superior vena cava(head, neck, and forelimbs) and inferior vena cava(trunk and hind limbs). The superior and inferior vena cava flow into the right atrium.

Question 23

Describe how heart action is initiated and coordinated

Answer 23

With each heartbeat, an electrical signal travels from the top of the heart to the bottom, causing the heart to contract and pump blood. the cardiac electrical system causes the heart to contract in a coordinated manner, maximizing the efficiency of the beating heart.

Question 24

Describe structure of the blood

Answer 24

Blood in vertebrates is a connective tissue consisting of several kinds of cells suspended in a liquid matrix called plasma. The cellular elements occupy about 45% of the volume of blood.
Red blood cells: (erythrocytes) transport O2.
White blood cells: (leukocytes) function in defence
Platelets: fragments of cells that are involved in clotting

Question 25

Describe lung structure and function

Answer 25

From mouth to diaphragm: Pharynx, Larynx, Trachea, primary bronchus, Secondary bronchus, Tertiary bronchus, Respiratory bronchiole, Alveoli(pulmonary venule, Pulmonary arteriole, Alveolar duct, Alveolar sac, Capillary), Diaphragm.
Tissues release oxygen to body cells as the oxygen pressure in the tissues is lower(the hight carbon dioxide levels in the tissues lowers the pH, and the binding of haemoglobin to carbon dioxide facilitating the release of oxygen).

Question 26

Explain the role of haemoglobin in transporting oxygen and carbon dioxide

Answer 26

Haemoglobin picks up oxygen because of the increased oxygen pressure in the capillaries of the lungs.

Question 27

Define the term excretion

Answer 27

Process that rids the body of nitrogenous metabolites

Question 28

Explain the importance of removing metabolic wastes

Answer 28

Removing metabolic wastes(excretion) is important to maintain homeostasis. If waste products are not excreted, they can build up in the body, which would disrupt homeostasis.

Question 29

Describe the histology and structure of the liver

Answer 29

Front: Right lobe, Gallbladder; Round ligament, Coronary ligament, Falciform ligament; Left lobe.
Back: Right lobe, Hilus, Gallbladder, common bile duct, Quadrate lobe, Hepatic artery proper, Hepatic portal vein, Inferior vena cava, Left hepatic vein, caudate lobe; Left lobe.

Question 30

Describe the formation of urea in the liver

Answer 30

The urea cycle or ornithine cycle converts excess ammonia into urea in the mitochondria of liver cells. The urea forms, then enters the blood stream, is filtered by the kidneys and is ultimately excreted in the urine.

Question 31

Describe the roles of the liver in detoxification

Answer 31

Ornithine cycle: urea is synthesised by the liver
Drugs and Poisons: substances that are not normally present in the body are known as xenobiotics. Liver is responsible for neutralizing xenobiotics- modifying chemical constitution(biotransformation). The liver also plays an important role in inactivation and excretion of hormones such as steroids.

Question 32

Describe the histology and structure of the kidney

Answer 32

Central to homeostasis- dispose metabolic waste and control fluid composition. Diverse excretory systems are variations on a tubular theme. This involves four key processes- filtration, reabsorption, secretion and excretion. Animals produce fluid waste called urine.
Kidneys consist of numerous tubules that are arranged in a highly organised manner. Function in both osmoregulation and excretion.

Question 33

Describe the structure of a nephron and its associated blood vessels

Answer 33

Functional unit of the vertebrate kidney. Each nephron is made up of several components: glomerulus(Larger diameter of the afferent arteriole than the efferent arteriole causes an increase in blood pressure. Filtrate produced contains water, salts, glucose, amino acids, vitamins, nitrogenous waste, and other smaller molecules.), bowman’s capsule(porous capillaries and specialized cells of the Bowman’s capsule are permeable to water and small solutes, but not blood cells or larger molecules. High hydrostatic pressure forces small molecules from the blood across the Bowman’s capsule and into the renal tubules.), proximal tube(reabsorption is critical for the recapture of ions, water and valuable nutrients. Maintaining pH balance, some toxic materials are actively secreted into the filtrate), loop of henle(aquaporin proteins make the transport epithelium freely permeable to water. Interstitial fluid is hyperosmotic to the filtrate which increases from cortex to medulla. Transport epithelium studded with ion not water channels. Two specialized regions: thin and thick segment), distal tube(regulating K+ and NaCl concentration of body fluids. Maintaining pH balance), collecting duct(carries filtrate through medulla to the renal pelvis. formation of urine. Reabsorption of water and nearly all sugars, amino acids and vitamins).

Question 34

Describe/explain the production of urine

Answer 34

Filtration, reabsorption and secretion. Check notes for nephrons.

Question 35

Explain the control of water content of the blood

Answer 35

Osmoregulation- Process by which animals control solute concentration and balance water gain and loss