Physio Oral (essays)

Role of lysosomes

• Vesicular structure formed by Golgi apparatus

• Contains digestive enzymes hydrolases which degrade proteins

Role of peroxisomes

• Contain digestive enzyme oxidase

• Breaks down H2O2 (harmful to cell) into H2O by catalases

• It degrades fatty acids

What are the different types of cell junctions

Junction	Main Function	Cytoskeleton Attached
1. Tight junction (Zonula occludens)	Seals adjacent cells together, preventing leakage of substances between cells	Actin filaments
2. Adherens junction (Zonula adherens)	Strong cell-to-cell adhesion; joins actin filaments of neighboring cells	Actin filaments
3. Desmosome (Macula adherens)	Strong mechanical attachment between cells; resists stretching forces Found in epithelia (e.g. skin)	Intermediate filaments (keratin)
4. Hemidesmosome	Anchors epithelial cells to the basal lamina (basement membrane)	Intermediate filaments (keratin)
5. Gap junction (Nexus)	Intercellular channels allows passage btw. cells of ions and small molecules	No major cytoskeletal attachment

• Tight junctions: Prevent paracellular movement of substances.

• Adherens junctions: Connect actin cytoskeletons of adjacent cells.

• Desmosomes: Connect intermediate filaments of adjacent cells.

• Hemidesmosomes: Connect intermediate filaments to the basal lamina.

• Gap junctions: Allow passage of ions and small molecules between neighboring cells.

What are the types of signaling (intercellular)

1. Endocrine signaling - secretes substances into the bloodstream and affects the target cells in different parts of the body

2. Paracrine signaling - secretes substances that act on adjacent cells

3. Autocrine signaling - cell affects itself

4. Juxtacrine signaling - contact dependent à a ligand on one surface binds to a receptor on the other cell surface

Is cell membrane polar or non-polar? Why?

• POLAR

• induces electric potential difference permeable to several different ions

• Depends on conc. inside and outside of memb.

What are the 3 states of membrane for osmosis?

1. Isotonic - normal conc. of solute and water

2. Hypotonic - Little solute and big water conc —> bursts

3. Hypertonic - conc. of solute is too high —> shrinks

What are the 2 types of hormonal regulation ?

Hormonal

• not-well addressed

• slow

• hormones released form endocrine and exocrine glands

• long-term response

Neural

• well-addressed

• fast

• based on reflexes of CNS and ANS

• give short term response

What are the 2 feedback systems ?

Negative feedback

• Response opposes the original stimulus and returns variable toward its normal value

• Characteristics:

  • Most common homeostatic mechanism

  • Stabilizes the internal environment

  • Reduces deviation from the set point

  Examples

  1. Blood glucose regulation

     • ↑ Glucose → insulin release → ↓ glucose

  2. Thermoregulation

     • ↑ Temperature → sweating

     • ↓ Temperature → shivering

  3. Blood pressure regulation

     • ↑ Blood pressure → vasodilation → ↓ pressure

Positive feedback

• This amplifies the original stimulus and causes further deviation from the normal value

• Characteristics:

  • Less common

  • Continues until a specific event is completed

  Examples

  1. Childbirth

     • Cervical stretching → oxytocin release → stronger contractions → more stretching

  2. Blood clotting

     • Activated clotting factors stimulate activation of additional clotting factors

  3. Action Potential Generation

     • Depolarization opens sodium channels → further depolarization

What are the 3 basic components of the homeostatic regulatory system?

1. Receptor (Sensor)

Detects changes in the internal or external environment.

Examples:

• Thermoreceptors —> detect changes in temp. of internal + external environment, vasodilation/vasoconstriction

• Chemoreceptors —> chemical changes in blood and fluids

• Baroreceptors

2. Control Center (Integrating Center)

• Receives information from receptors

• Compares it with the normal value (set point)

• Determines the appropriate response

Examples:

• Hypothalamus

• Brainstem

• Endocrine glands

3. Effector

Produces the corrective response.

Examples:

• Muscles

• Glands

• Blood vessels

Homeostatic Sequence

Stimulus → Receptor → Control Center → Effector → Response

Homeostatic regulatory systems

Skeletal system

• Supports posture and movement

• Mineral reservoir (Ca 2+ and phosphate)

• Blood cell formation

Cardiovascular system

• Transport of nutrients, gases and hormones

• Regulate BP

Lymphatic system

• Returns excess tissue fluid

• Immunity

• Fat absorption

Respiratory system

Digestive system

Urinary system

• Excretes waste

• Regulates water and electrolyte balance

Reproductive system

• Maintains reproductive function

• Produces sex hormones

Immune system

Muscular system

• Produces movement

• Generates heat thru contraction

Integumentary system

• Protects against pathogens

• Regulated temp

• Maintains temp and ion balance

Levels of physiological regulation

• Intracellular level —> gene expression, enzyme activity, metabolism, osmotic balance

• Tissue level

• Organ level

• Organ system level

• Organismal level

What are the types of regulation

Proportional regulation

The response is proportional to the size of the change.

Example: CO₂ and breathing

• Normal CO₂ → normal breathing

• Slightly ↑ CO₂ → slightly faster breathing

• Very ↑ CO₂ → much faster breathing

Differential regulation

• The body responds to the rate of change, not just the value itself

• Example: Baroreceptor reflex

  Imagine blood pressure falls:

  Case 1

  BP drops from 120 → 110 mmHg slowly over hours.

  The body doesn't panic.

  Case 2

  BP drops from 120 → 80 mmHg in 5 seconds.

  The body reacts immediately:

  • ↑ Heart rate

  • ↑ Vasoconstriction

  The actual BP value matters less than how quickly it changed.

  Memory: Differential = speed of change.

Integral regulation

The body takes into account the accumulated error over time.

Example: Blood volume

Suppose you lose a little blood.

For 5 minutes:

• Not a huge response.

For several hours:

• Kidneys retain water.

• ADH secretion increases.

• Aldosterone increases.

The body is responding because the deviation has been present for a long time.

What is the difference btw. irritability and excitability?

Irritability

• Ability of the cell to react to stimuli from external or internal environment by increase or decrease of its activity

• Stimuli may be mechanical, chemical, electrical, or thermal

• Stimuli differ in intensity, duration and rate of application

Excitability

• Ability of specialised cells to respond to change in environment (irritation)

• Does this by changing their membrane potential and generating an action potential when the stimulus reaches a threshold value

What are the excitable tissues ?

• Motor neuron —> longest to cause action potential

• Skeletal muscle —> shortest to cause action potential

• Heart muscle —> contraction of muscle cells

• Endocrine cells —> produces and releases hormones

What is membrane potential ?

• The electrical difference between the inside and outside of the cell membrane

• Voltage diff. across cell memb. due to differences in ion conc.

What is resting memb. potential ?

• Electrochemical gradient that exists when cell is not transmitting a signal

• Typically -70mV in neurons

• Muscle cells may have values btw. -70 to -90 mV

• This means inside of cell = negatively charged relative to outside

Action potential process/steps

Put Pic From Ipad !!!!!!!!!!!!!!

1. Resting state

• Memb. potential -70mV

• To every 3 Na+ flowing out of cell, 2 k+ flow inside

• More +ve charges outside, memb. potential is -ve

2. Depolarisation

• If stimulus reaches threshold of -55 mV = action potential

• Voltage-gated channels open = Na+ flow inside

• POSITIVE FEEDBACK - more voltage-gated channels open leading to memb. potential rising to 30 mV

3. Repolarisation

• Sodium channels close

• Voltage gated potassium channels open —> K+ out cell

• Voltage-gated channels for K+ open causing flow of K+ out of cell

• Memb. potential becomes -ve

4. Hyperpolarisation

• As the K+ voltage-gated channels take a long time to close

• membrane may become temporarily more negative than the resting potential, producing a phase called hyperpolarization

What are the different types of ion channels and pumps?

1. Voltage-gated channels

• Open/close in response to changes in memb. potential

2. Ligand-gated channels

• Open/close in response to binding of a specific molecule

3. Ion pumps

• Use energy (ATP)

• actively transport ions against conc. gradient (Na+/k+ ATPase pump)

• embedded in cell memb., help to maintain and alter ionic balance

How can excitability be measured ? What are the parameters?

• Hoorweg-Weiss strength-duration relationship

Rheobase

The minimum stimulus intensity capable of producing excitation.

Utilization Time

The minimum duration required for a rheobase-strength stimulus to excite tissue.

Chronaxie

The minimum duration required for a stimulus with twice the rheobase intensity to produce excitation.

Liability

The maximum number of impulses a tissue can transmit per second.

What are the 2 diff. types of synapses?

Electrical

• Consist of gap junctions that create v. narrow space of abt. 2.5 nm btw. adjacent cells

• Signal transmission depends on VOLTAGE GATED ion channels —> open + close depending on memb. potential

• Allow direct passage of ions from one cell to another = extremely rapid transmission w. virtually no synaptic delay

• Conduction = BIDIRECTIONAL (impulse travels 2 ways)

• Mainly muscles cells —> synchronized activity is required

• Depolarisation = increase in memb. potential

• Higher conduction velocity, greater no. of cells can be excited simultaneously

Chemical

• Most common in nervous system.

• Characterized by synaptic cleft of 20-30nm btw. presynaptic + postsynaptic cells

• UNIDIRECTIONAL

• neurotransmitters released from presynaptic neuron and act ONLY on receptors of postsynaptic memb.

• Physiological delay of - 0.3-0.5 ms

• Chemical synapses exhibit plasticity —> strength can increase or decrease depending on activity

• Can be excitatory or inhibitory

• According to location —> conventional synapses (axodendritic, axosomatic, and axoaxonic), which are generally excitatory, and non-conventional synapses (dendrodendritic, dendroaxonic, and dendrosomatic)

• Transmission only occurs thru ligand-gated ion channels —> open when a neurotransmitter binds to its receptor, allows specific ions to pass thru memb. and alter excitability of postsynaptic cell

Types of postsynaptic channel receptors

Ionotropic

Metabotropic

Types of ionotropic receptors

• N-cholinoreceptors

• Glutamate

• Glycine

• GABA receptors

Types of metabotropic

• G protein-coupled receptors —>

• Alpha and Beta adrenoreceptors

• M-cholinoreceptors

Inhibitory postsynaptic potentials are due to:

• GABA

• Glycine

• Serotonin

Excitatory postsynaptic potentials are due to:

• Glutamate

• norepinephrine

• Epinephrine

• Cl- channels

• K+ channels

• Na+ channels

K+ channels

Na/K or Na/K/Ca channels

Na channels

What are the 2 classifications of reflexes according to how they’re formed

• Unconditioned

• Conditioned

What are unconditioned reflexes

• Innate, inherited responses that don’t require learning

• Permanent reflex arc

• need adequate stimulus

What are conditioned reflexes?

• acquired during life through life via learning and experience

• No fixed reflex arc

• Temporary reflexes

• elicited by stimuli that acquire signal significance through repeated association with another stimulus.