Cell and general physiology

Question 1

Name the major components of the intracellular fluid

Answer 1

• Water
• Potassium
• Magnesium
• Phosphate

Question 2

What are the major components of the extracellular fluid

Answer 2

• Water
• Sodium
• Chloride
• Bicarbonate
• Nutrients
  
  • Oxygen
  • Glucose
  • Amino acids
  • Fatty acids
• Waste products
  
  • eg. carbon dioxide

Question 3

In broad terms, describe the major functions performed by the various organ systems to maintain homeostasis

Answer 3

• Lungs:
  
  • Provide oxygen to the extracellular fluid
  • Remove carbon dioxide
• Kidneys:
  
  • Maintain ion concentrations - potassium, sodium etc
  • Maintain acid/base balance
  • Monitoring and maintenance of extracellular fluid volume
  • Soluble waste removal
• Gastrointestinal tract
  
  • Provision and absorption of nutrients
  • Insoluble waste removal
• Liver
  
  • Metabolism of drugs/chemicals
  • Excretion of wastes via the bile

Question 4

Extracellular fluid transport

Discuss the mixing of the extracellular fluid components within the blood vessels and the interstitial spaces

Answer 4

• Blood is transported through the arteries to capilliaries and back via veins to the heart
• Mixing of the extracellular fluid component occurs within the capilliary beds
• Capiliaries are permeable to most of the blood plasma components - except plasma proteins
• Fluid and dissolved constituents move back and forth between the capiliaries and the interstitial spaces.
  
  • This movement is in large part driven by kinetic motion of the molecules
• Capiliaries are in close contact with almost all cells in the body
  
  • Thus diffusion of almost any substance can occur within seconds
• This diffusion ensures constant mixing and homogeneity of the intravascular and extravascular extra-cellular fluid.

Question 5

Regulation of Body Functions

Describe the major components of the nervous system and how they contribute to homeostasis maintenance

Answer 5

• Sensory input, central NS (integrative), motor output
• Autonomic Nervous System

Sensory:

• Receptors in the skin and the special sensory organs monitor the surrounding environment

CNS:

• Integrates sensory inputs
• Stores information
• Generates thoughts and creates ambition
• Determines reactions in response to various sensations

Motor:

• Performs the movements as determined or desired by the CNS
• Localised reactive movements are also performed

Autonomic:

• Operates at a subconscious level
• Controls the function of internal organs including the heart, GIT and secretion from the various glands

Question 6

List various hormone systems and their effect on homeostasis

Answer 6

1. Thyroid
   
   • Regulates cellular metabolism - rate of chemical reactions
2. Insulin
   
   • Regulates glucose metabolism and helps maintain glucose homeostasis
3. Adrenocortical hormones
   
   • Aldosterone: Regulate sodium and potassium balance
   • Cortisol: regulates protein metabolism
4. Parathyroid hormone
   
   • Tightly regulates blood calcium and phosphate

Question 7

What are the major components of the immune system

How does the immune system contribute to maintenance of homeostasis

Answer 7

• White blood cells
• Tissue cells derived from white blood cells
• Thymus
• Lymph nodes
• Lymphatics

The immune system provides a mechanism to:

1. Distinguish self and foreign (and potentially harmful) substances
2. Destroy, neutralise or remove foreign substances

Question 8

How does the integumentary system contribute to homeostasis?

Answer 8

• Protection of the body from the outside world
• Water balance - primarily preventioni of water loss
• Regulation of body temperature
  
  • Sweating to assist with cooling
  • Air-trapping to help limit temperature loss / regulate the skin surface environment
• Can contribute to waste excretion

Question 9

Discuss the basic control mechanism of oxygen levels in the extracellular fluid

Answer 9

• Oxygen concnetration in the ECF largely relies on the composition and characteristics of haemoglobin
• Haemoglbin has a high affinity for oxygen
• Hb combines with oxygen within the lungs
  
  • The heart serves to pump both de-oxygenated and oxygenated blood around the body
• Hb releases oxygen in the capiliary beds and into the tissue fluid when there is low oxygen concentration
  
  • The oxygen passes along a diffusion gradient determined largely by the metabolic rate of the tissue
  • Diffusion alone does not account for the degree of oxygen transport into the tissue bed
  • The tissue bed serves as an oxygen sink
  • Oxygen diffuses through arteriolar and venule walls as well as at the level of the capillary.

Question 10

Briefly describe the control mechanisms to ensure carbon dioxide homeostasis and removal.

Answer 10

• Carbon dioxide is a major end-product of oxidative reactions within cells
• Carbon dioxide readily diffuses from the tissue extracellular fluid into the plasma
• Increased CO2 in the plasma activates the respiratory centre
  
  • Increases respiration effort and tidal volume
• CO2 diffuses into the alveolar spaces within the lungs down a diffusion gradient.
• Respiratory efforts expel excessive carbon dioxide into the environment.

Question 11

Describe the baroreceptor reflex and how it serves to regular arterial blood pressure.

Answer 11

• Barorecptors are specialised nerve receptors that respond to arterial wall stretch
• Baroreceptors are located in the carotid arteries and the aortic trunk
• With increased arterial pressure, there is increased baroreceptor stimulation
  
  • Increased nerve impulses are transmitted to the vasomotor centre of the medulla oblongata
  • Increased inputs leads to a decrease in the number of impulses transmitted to the sympathetic nervous system
  • Reduced SNS activation leads to a reduced heart rate and peripheral vasodilation
• Conversely, reduced blood pressure leads to reduced stimulation of the baroreceptors, reduced inhibition of the vasomotor centre and increased stimulation of the SNS

Question 12

Describe the nature of homeostatic control systems

Answer 12

• The majority of control systems act by negative feeback
  
  • Eg. high carbone diaxoide concentration leads to increased respiration with an end goal of reducing carbon dioxide - a result negative to the initial abnormality within the system
• Negative feedback acts to return a parameter towards normal when it becomes either deficient or excessive
• The degree to which a control system operates is referred to as the gain
  
  • ​The gain refers to the ability of the body system to correct for an error (Gain = correction/error)

Question 13

Describe and provide examples of positive feedback mechanisms

Answer 13

• Positive feedback occurs when the inciting stimulus contributes to more of the original stimulus.
  
  • A damaged blood vessel initiates the coagulation cascade. Stimulation of the local clotting factors causes amplification of the clotting process and further activation of local coagulation enzymes / proteins.
  • Generation of a nerve signal: stimulation causes slight sodium leagage into the nerve cell. This alters the cell memprane potential and further sodium channels are opened and further sodium influx. This creates an action potential which generates an electrical current. This current initiates additional action potentials in adjacent nerves

Question 14

Describe the basic cell structure

Answer 14

• Nucleus and cytoplasm are the two major components
• The nucleus is surrounded by the nuclear membrane
• The cytoplasm is contained by the cell membrane (or plasma membrane)
• The cell is made up of different substances collectively called the protoplasm
• The protoplasm contains
  
  • Water
  • Electrolytes
  • Proteins
  • Lipids
  • Carbohydrates

Question 15

Describe the components and basic structure of the cell membrane

Describe the major functions of the various components of the cell membrane

Answer 15

• 55% protein, 25% phospholipid, 13% cholesterol, 4% other lipids, 3% carbohydrates
• Phospholipid bilayer with hydrophoic ends attached to each other centrally, hydrophilic ends contact the intra- and extra-cellular fluid
• Cholesterol molecules are essentially dissolved within the bilayer.
  
  • Cholesterol composition largely controls the degree of permeability/impermeability to water soluble components.
  • Cholesterol controls the fluidity of the cell membrane
• Integral (trans-membrane) and Peripheral cell membrane proteins
  
  • Integral proteins provide pores through which water and water-soluble substances can diffuse
  • Also can act as carrier proteins for active transport against the diffusion gradient
  • Integreal proteins can act as receptors for water-soluble peptides / hormones which acan then activate secondary messengers within the cell.
  • Peripheral cell membrane proteins function almost exclusively as enzymes that alter transport of substances through the pores

Question 16

Describe the structure and role of cell membrane carbohydrates

Answer 16

Structures:

• The majority of cell membrane carbohydrates are in the form of glycoproteins or glycolipds
• Proteoglycans are mainly carbohydrates bound to small proteins
  
  • These are attached loosely to the cell surface
• The outer surface of the cell has a “loose’ carbohydrate coat called the glycocalyx

Functions:

1. Negative electrical charge to repel adjacent cells / objects
2. Glycocalyx attached to adjacent glycocalyx - cell to cell adhesion
3. Many carbohydrates act as receptors
4. Some carbohydrates are important for immune reactions

Question 17

Describe the various processes by which nutrients and molecules can move into a cell.

Answer 17

• Passive Diffusion
  
  • Lipids move directly through the membrane
  • Many electrolytes pass through “pores” that may require activation or only allow certain molecules through

Active transport

• Pinocytosis - tiny vesicles that engulf most large macromolecules. Eg. most proteins. Form in coated pits on the cell surface
• Phagocytosis - large vesicles form to engulf larger particles. Only certain cells have the ability to perform phagocytosis. Eg. Macrophages, neutrophils.

Question 18

Describe the process of phagocytosis

Answer 18

• Bacterium or particle is opsinized by antibodies
• Antibodies bind to receptors on the phagocyte cell surface
• Membrane edges surrounding the particle evaginate to surround the particle
• More and more membrane receptors attach to the particle ligands - “zipper like” motion
• Actin and contractile elements in the cytoplasm contract pushing the vesicle inwards
• Contractile proteins pinch off the stalk leaving the phagocytic vesicle free within the cytoplasm

Question 19

Descirbe the process by which the contents of an endocytotic vesicle is digested

Answer 19

• Pinocytosis or phagocytosis results in the formation of an intra-cytoplasmic vesicle.
• Almost immediately, lysosomes attach to the vesicle surface
• Hydrolases are released into the vesicle
• Hydrolases break down the components of the vesicle
  
  • Hydrolysis of proteins, carbohydrates and lipids results in the products of digestion
    
    • glucose, amino acids, phosphates
• Digestion products can then diffuse through the vesicle membrane into the cytoplasm
• The residual body represents the indigestible substances - released from the cell via exocytosis

Question 20

Note the action of lysosomes in the presence of cell damage

Answer 20

• When a cell is damaged (heat, cold, trauma, chemicals) lysosomes can rupture
• The ruptured lysosome releases hydrolases into the cytoplasm directly which starts the process of cell digestion
• If there is minor damage, small numbers of lysosomes are damages only and cell repair can ensue.
• If there is major damage and many lysosomes are ruptured, autolysis of the cell occurs

Question 21

What three bactericidal agents are contained within lysosomes?

Briefly note the role of each

Answer 21

1. Lysozyme
   
   • Dissolves the cell wall
2. Lysoferrin
   
   • Binds iron and other substances necessary for bacterial growth
3. Acid pH of ~5.0
   
   • Activates hydrolases
   • Inactivates bacterial metabolic systems

Question 22

Descirbe the processes that occur within the endoplasmic reticulum

Answer 22

• Protein is synthesised in the rough ER
• Lipids and cholesterol are synthesised in the smooth ER
  
  • rapidly incorporated into the smooth ER lipid bilayer
  • vesciles continually break off and migrate to the golgi apparatus
• Provides the enzymes for glycogen breakdown
• Provision of a vast number of enzymes capable of detoxification
  
  • coagulation, oxidation, hydrolysis and conjugation with glucuronic acid

Question 23

Describe the processes and functions of the golgi apparatus

Answer 23

• Further processing of substances already formed in the ER
• Carbohydrate moeities are added to the formed proteins
• The ER secretions are concentrated and packaged into secretory vesicles
• Synthesis of certain carbohydrates
  
  • large polysaccharide polymers bound with small amounts of protein such as hyaluronic acid and chondroitin sulfate

Question 24

Broad strokes of the citric acid cycle

Answer 24

• Glucose, fatty acids and amino acids are taken into the cell.
• Pyruvic acid from glucose and acetoacetic acid from FA and AA
  
  • Both eventually converted into acetyl CoA
• Acetyl CoA enters the citric acid cycle
  
  • Acetyl CoA is split into component parts - hydrogen atoms and carbon dioxide
    
    • Carbon dioxide diffuses out of the cell
    • Hydrogen atoms are converted to hydrogen ions
    • H ions combine with oxygen to release energy
• ADP is converted to ATP and H combines with oxygen to produce water.

Question 25

What are the three major categories of cellular function that utilse ATP

Answer 25

1. **Transport** of substances through membranes 2. **Synthesis** of chemical compounds 3. **Mechanical work**

Question 26

Briefly list the events that allow cellular ameboid movement

Answer 26

* A pseudopodium protrudes from one end of the cell. * Pseudopodium partially attaches to new tissue area * New cell membrane is formed at the pseudopodium by attachment release of exocytic vesicles * Old cell membrane is recycled and receptors disengaged by the formation of endocytic vesicles at the "tail" end * Ecocytic vesicles can contain receptors that bind to the adjacent tissue * Actin is present within the cytoplasm and forms a filamentous network. * Actin binds with myosin and contraction of the filaments can occur * Chemotaxis is the major means of control of ameboid movement. * Chemical mediators cause membrane changes leading to the development of pseudopodia

Question 27

List the cells that exhibit ameboid movement

Answer 27

1. While blood cells - to migrate out of blood vessels * Neutrophils * macrophages 2. Fibroblasts * to migrate and move to areas of damage 3. Embryonic cells * migration occurs during foetal growth 4. Cancer cells * Especially sarcomas * Major mechanism for progression to metastasis.

Question 28

What are the major locations of cilia within the body? What is the structure and function of the cilia?

Answer 28

1. Cilia are location primarily within the respiratory tract and fallopian tubes * Cilia are composed of 11 microtubes - 9 in pairs around the outside and 2 single tubules centrally. These tubules are supported and bound together by a complex of protein cross links * Cilia function by beating in a co-ordinated whip like motion to move fluid on the cell surface * Towards the pharynx in the respiratory tract and towards the uterine body in the female reproductive tract

Question 29

Describe the knows aspects of ciliary movement

Answer 29

1. The microtubules are all linked together by protein cross links - the structure is called the axoneme 2. Cilia can still function without the cell membrane 3. ATP must be available for function 4. Appropriate ionic conditions must exist * Especially calcium and magnesium 5. Mictotubes on the front edge of the cilium crawl out / slide towards the cilia tip causing bending 6. Multiple protein arms composed of *dynein* project from each double tubule * These dynein arms have ATPase enzyme activity 7. The central cilia may be responsible for an electrochemical signal - when not present, cilia do not beat

Question 30

Discuss the structure and action of primary (sensory) cilia

Answer 30

* Primary cilia are non-motile and generally solitary on each cell * They are thought to act as a sensory antennae * Sense chemical and mechanical signals * Transduction of sensory signals to initiate multiple cellular effects. * May be driven in part by changes in intra-cellular calcium signalling * Defects in signalling by primary cilia in renal tubular cells is thought to contribute to polycystic kidney disease

Question 31

What are the basic DNA building blocks

Answer 31

1. deoxyribose 2. Phosphoric acid 3. Nitrogenous bases * guanine * cytosine * adenine * thymine 4. Weak hydrogen bonds between bases hold the two strands together

Question 32

What are the RNA building blocks?

Answer 32

* Ribose * Phosphoric acid * Nucleic acids * Pyrimidines * Uracil and cytosine * Purines * Guanine and adenine * Weak hydrogen bonds

Question 33

Briefly describe the process of transcription

Answer 33

* RNA polymerase attaches to a promoter sequence of DNA nucleotides * Attaching of RNA polymerase leads to unwinding of ~ 2 coils of the DNA * New activated RNA nucleotides are added as RNA polymerase moves along the single DNA strand * RNA polymerase breaks away phosphate radicals from the RNA nucleotides to liberate energy * This energy is used to form a bond between the remaining phosphate at adjacent ribose * Weak hydrogen bonds are formed between the DNA strand and forming RNA * RNA elongation continues until RNA polymerase encounters a STOP codon (chain-terminating sequence) * Weak hydrogen RNA-DNA bond breaks as the DNA-DNA bond has a greater affinity * RNA is released into the cytoplasm

Question 34

Briefly describe the process of translation

Answer 34

* mRNA moves from the nucleus through the cytoplasm to the ribosomes on the rough endoplasmic reticulum * The mRNA moves through the ribosome with each codon encoding for a specific amino acid. * Transfer RNA (tRNA) transports the amino acids to the ribosome for addition into protein molecules * Chemical reactions take place within the ribosome to bond the growing amino acid chain into a single protein molecule * A STOP codon passing through the ribosome signals the end of the protein molecule and it is freed into the cytoplasm

Question 35

Briefly note the components of gene expression

Answer 35

1. The specific sequence of the individual DNA 2. Information from the DNA is used to produce vast arrays of RNA * RNA has numerous forms that may promote (mRNA), assist (tRNA) or regulate (miRNA) protein synthesis 3. The over-arching process of RNA and protein synthesis is referred to as gene expression 4. The process of gene expression directly affects the phenotype as its final effect

Question 36

List the various control mechanisms that modulate and regulate gene expression

Answer 36

1. Basal promoter (TATAAA bases - TATA box) * Binding of RNA polymerase is necessary for initiation of transcription 2. Upstream promoter * Several binding sites for both positive and negative transcription factors 3. Enhancers * Regions of DNA that can bind transcription factors * May be remote from the gene they act on - even on a different chromosome 4. Insulators * Gene sequences that provide a barrier against transcriptional influences from surrounding genes 5. Control points exist apart from RNA transcription also * RNA processing can be regulated * Translation by the ribosaome can be influenced * Enzymes can influence many levels of gene expression 6. Transcription factors can control the DNA structure thus making it available or unavailable for transcription to occur

Question 37

Briefly describe the mechanism and role of enzyme regulation on gene expression

Answer 37

1. Enzyme inhibition * The synthesised enzyme (almost always) binds back with the first enzyme in a sequence, blocking activity * Intermediary enzymes thus do not build up * An example of negative feedback * This mechanism helps control intracellular concentrations of multiple amino acids, purines, pyrimidines, vitamins and other substances 2. Enzyme activation * Normally inactive enzymes are activated in certain circumstanses * eg. cAMP (produced by ATP breakdown) increases cause activation of the glycogen splitting enzyme phosphorylase - leads to gluocse molecule liberation for energy generation and increase of ATP stores

Question 38

List the steps in DNA replication

Answer 38

* DNA helicase starts to "un-zip" and a replication fork is formed * RNA primers attached to the 3' end of the leading strand * DNA polymerase binds to the leading strand and creates a new strand via elongation * This strand is continuous * Multiple primers attach to the 5' (lagging strand) which are several bases apart * DNA polymerase then adds pieces of DNA called *Okazaki fragments* * DNA ligase joins the Okazaki fragments to form a continuous strand * Exonuclease removes the RNA primers * Another exonuclease "proofreads" the DNA

Question 39

List the phases of mitosis

Answer 39

​Mitosis commences AFTER chromosomal duplication has occurred * Prophase * Chromosomes become condensed into well defined strands * Prometaphase * Multiple microtubules from the aster attach to the chromatids at the centromere * Tubules then pull one chromatid of each pair to each pole of the cell * Metaphase * The two asters are pushed farther apart * The chromatids are pulled tightly to the cell centre to form the equatorial plate * Anaphase * The two sets of chromatids are pulled apart toward each mitotic aster * Telophase * Mitotic apparatus dissipates * New nuclear membrane forms from endoplasmic reticulum * Cell pinches in two via contraction of a ring of microfilaments

Question 40

Note the mechanisms by which cell growth can be regulated and controlled

Answer 40

1. Growth factors * Derived from somewhere remote from the cell/tissue * Can be derived from adjacent connective tissue or a hormone derived from a remote organ 2. Growth stops when the cells have run out of space for growth 3. Cell secretions (own cells) can inhibit cell growth * negative feedback control

Question 41

What are proto-oncogenes? How may they contribute to the development of cancer?

Answer 41

* A proto-oncogene is a gene that could become an oncogene through mutation or increased activation * Most proto-oncogenes encode for proteins that regulate cell growth, adhesion or differentiation * Mutated or activated proto-oncogenes can contribute to increased or unregulated cell division, production of protein that alters the micro-environment in favour of cell growth or avoid apoptosis

Question 42

What are anti-oncogenes and how might they contribute to the development of cancer

Answer 42

* Anti-oncogenes are also called tumour suppressor genes * They help to suppress the activation of specific oncogenes - thus they can help to control cell growth, adhesion and protein production * Loss or inactivation of tumour suppressor genes due to mutation can allow activation of oncogenes

Question 43

Describe the cellular mechanisms that help prevent the development of cancer from cellular mutations

Answer 43

1. Most mutated cells have less survival capabilities than normal cells 2. Most mutated cells have intact feedback controls preventing excessive growth 3. The immune system can detect many mutated cells (or the products they produce) and target them for destruction * Abnormal proteins trigger either antibody production opsinization 4. Multiple mutations or activation of multiple oncogenes is necessary for the development of most cancerous cells

Question 44

List the 5 major risk factors for the development of cancerous cells

Answer 44

* Ionizing radiation exposure * Exposure to carcinogens (chemicals that can cause mutations and cancer) * Physical irritants * Hereditary tendency * Likely various mutations in oncogenes are already present within the genome * Oncoviruses * DNA virus inserts directly into a chromosome * RNA virus carrying reverse transcriptase causes DNA to be generated from RNA which is then inserted into the genome

Question 45

List some of the characteristics that are unique to cancerous cells

Answer 45

1. Abnormal growth * Not bound by normal growth limis * may need less factors to grow * reduced response to inhibitors of growth 2. Less adhesive than normal cells * This allows for movement between normal tissue barriers including tissue planes, entering lymphatics and blood vessels 3. Production of angiogenic factors * Increases blood vessel growth and therefore provision of nutrients