Physiology I Past Paper (2024/2025) PDF

Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Transport across cell membrane (Types of permeation) 1- Passive (no carrier & no energy)...

Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Transport across cell membrane (Types of permeation) 1- Passive (no carrier & no energy) ✔ the concentration gradient across a membrane separating two body Driving force compartments Movement ✔ A region of high concentration to one of lower concentration. Carrier no ✔ Is not saturable. Character ✔ Shows a low structural specificity. ✔ The vast majority of drugs gain access to the body by this mechanism Lipid soluble drugs Water soluble drugs Ex. Readily move across most Penetrate the cell membrane through biologic membranes due to aqueous channels or pores. their solubility in the In plasma membrane there are aqueous membrane bilayers. channels = porins = pores 2- Facilitated diffusion (carrier & no energy) Sort of passive that need carrier but not energy (Ex: Large molecular weight drug) Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I 3- Active (carrier & energy) ✔ It is capable of moving drugs against a concentration gradient that Driving force the process shows saturation kinetics for the carrier Movement Active transport is energy-dependent and involves (ATP) Carrier Yes - specific carrier proteins "ferry" ‫ معدية‬- need structural similarity Character ✔it is saturable process (energy may lost, carrier may be occupied) ✔ A few drugs that closely resemble the structure of naturally occurring Ex. metabolites Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I 4- Phagocytosis→ This type of drug delivery transports drugs of large size across the cell membrane. Endocytosis Exocytosis ✔ Engulfment of a drug molecule by ✔ reverse of endocytosis (cells use exocytosis to the cell membrane and transport into secrete substances out of the cell through a the cell by pinching off the drug-filled similar process of vesicle formation) vesicle. ✔ Vitamin B12 ✔ Insulin in granules moves till cell membrane → fusion → rupture → exocytosis. ✔ Norepinephrine is stored in membrane- bound vesicles in the nerve terminal and is released by exocytosis. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Physiology  The study of the functions of the human body (the mechanisms by which the various organs and tissues carry out their specific activities) in order for the body to function normally. The internal environment must be regulated to become relatively constant. Why? Homeostasis Role of Systems in homeostasis Homeo → (human cell) Different body systems (except reproductive system) share in maintaining homeostasis. For example: Stasis → ▪ The gastrointestinal tract → digest food to provide the body  Tendency to maintain with nutrients. constant environmental ▪ The respiratory system → obtains oxygen and removes condition of the cell. carbon dioxide. Many variables such as: ▪ The cardiovascular system → transports all these materials body temperature, blood and others from one part of the body to another. pressure, blood glucose, ▪ The urinary system→ eliminates wastes products and plays a oxygen, carbon dioxide role in regulation of blood volume and blood pressure. content Regulation  The activities of body system are regulated by two systems (maestro) 1- The nervous system. 2- The endocrine system. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Nervous system I. Central Nervous system Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I I. Central Nervous system 1) Brain *The brain constitutes about one-fifth of the body weight and lies within the cranial cavity. 1. Cerebrum (cerebral cortex). Parts 2. Cerebellum. 3. The brain stem [Midbrain - Pons- Medulla oblongata.]  The brain receives about 15% of the cardiac output (COP), Blood approximately 750 ml of blood per minute.  Blood flow in the brain has its own circulation called circulus arteriosus. flow  Keeps blood flow to the brain constant by adjusting the diameter of the arterioles By Vasoconstriction and Vasodilation Membranes covering the brain and spinal cord (the meanings) Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I For Protection (avoid friction with bone) and also offer nutrient and O2 to brain Purpose and spinal cord  brain and spinal cord surrounded by Meninges, Position  lying between the skull and the brain and between the vertebrae and the spinal cord i) Dura matter. Names ii) Arachnoid matter. iii) pia matter (order from skull to brain) [subdural space] subarachnoid space, potential space separate Space separate between the arachnoid and pia Spaces between the Dura and maters ➔ containing cerebrospinal fluid. which arachnoid maters present in ventricle Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Blood Brain Barrier (BBB) ❖ barrier between cerebral capillary blood and the CSF. Anatomy  CSF fills the ventricles and the subarachnoid space. ❖ It consists of the endothelial cells of the cerebral capillaries and the choroid plexus epithelium. 1. Maintains a constant environment for neurons in the CNS. 2. protects the brain from endogenous or exogenous toxins. 3. prevents the escape of neurotransmitters from their functional sites in the CNS into the general circulation. Function 4. Drugs penetrate the blood–brain barrier to varying degrees.  For example, nonionized (lipid-soluble) drugs cross more readily than ionized (water-soluble) drugs.  Inflammation, irradiation, and tumors may destroy the blood–brain barrier and permit entry into the brain of substances that are usually excluded (e.g., antibiotics, radiolabeled markers). Ventricles of the brain Within the brain there are four irregular shaped cavities or ventricles, containing cerebrospinal fluid (CSF). * They are 1) Right and left lateral ventricles. 2) Third ventricle. 3) Fourth ventricle. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Cerebrospinal fluid 1. Acts as a Cushion and shock absorber between the brain and the cranial bones. 2. Supports and protects the brain and spinal cord. 3. Maintains a uniform pressure around these delicate structures. Shape of organ ➔ is kept by pressure ➔help in function.‫وجود ضغط ثابت مهم للوظيفة‬ 4. there may be interchange of substances between CSF & nerve cells, such as nutrients and waste products. Parts of the brain 1. Cerebrum =Cerebral cortex  responsible for difference of human from higher animal Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I For description purposes each hemisphere of the cerebrum is divided into lobes which Parts take the names of the bones of the cranium under which they lie ➔ frontal. Parietal. Temporal. Occipital. 1. Mental Involved in memory, intelligence, sense of responsibility, activities thinking, reasoning, moral sense and learning are attributed to the higher centers. Function 2. Sensory including the perception of pain, temperature, touch, perception sight, hearing, taste and smell 3. Initiation and Of skeletal (voluntary) muscle contraction control 2.Diencephalon Function * It connects the cerebrum with the midbrain. * It consists of several structures; the most important structures are the Structure thalamus and the hypothalamus. Thalamus Hypothalamus. (Classification of Input) A) Controls the output of hormones from both lobes of the 1. Processing of some emotions pituitary gland. and complex reflexes. B) Other functions 2. It relays and redistributes 1- Thirst and water balance. impulses from most parts of the 2-Autonomic nervous system. brain to the cerebral cortex. 3- Body temperature 4- Sexual behavior 5- Appetite and satiety 6- Biological clocks or circadian rhythms, 7- Emotional reactions, e.g. pleasure, fear & rage. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I 3- Medulla oblongata The vital centers, consisting of groups of cells associated with autonomic reflex activity, lie in its deeper structure. (Any shock may cause death) * These are the: 1- Cardiac Centre Regulate heart rate & cardiac output. 2- Respiratory center. Regulate respiratory rate 3- Vasomotor center. Regulate Blood pressure & diameter of blood vessels 4- Reflex centers of vomiting, coughing, sneezing, and swallowing. Cough ➔ due to exclusion of foreign body also sneezing 4-Cerebellum 1- Controls and coordinates the movements of various groups of muscles ensuring smooth, even, concise, precise actions. (GIT need to contract as one unit) 2- It coordinates activities associated with the maintenance of the balance and equilibrium of the body.  Damage to the cerebellum results in clumsy uncoordinated muscular movement, staggering gait and inability to carry out smooth, steady, precise movement. (Parkinsonism) Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Neurons (nerve cells) Nervous system Consists of a vast number of cells ➔ called neurons [supported by a special type of connective tissue, neuroglia] Each neuron a) Cell body and its processes. consists of b) One axon. c) Many dendrites Nerves  Bundles of axons bound together, distributed all over the body Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Characters of neurons 1) Synthesis chemical energy (ATP) only from glucose [Unlike many other cells] ➔ (↓ glucose cause Attentional deficiency) 2) Cannot divide. 3) They need a continuous supply of oxygen and glucose for survival. 4) Irritability and conductivity: Conductivity Irritability  Ability to transmit an impulse.  Ability to initiate nerve impulses in response to stimuli  Source of stimuli Outside the body Inside the body e.g., touch and light waves e.g., change in the concentration of CO2 in blood ➔ alters respiration (a thought may result in voluntary movement.) " trough chemoreceptor" ➔ (response to both electrical & Chemical stimuli) Types of stimulation Electrical Chemical  in that motor neurons and  in the transmission of impulses between one neuron and the next or sensory nerve endings between a neuron and an effector organ. initiate nerve impulses.  Ex: CO2 ➔ HCO3 ➔ change PH of blood ➔ this is considering chemical stimuli Synaptic transmission ✓ site at which the impulse is transmitted from one cell to the next, neuron may terminate on a muscle cell, glandular cell, or another neuron. presynaptic neuron post synaptic neuron transmits the impulse toward transmits the impulse away from the synapse. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Types 1) Electrical synapse presynaptic neuron and the postsynaptic neuron are in direct contact. allow current to flow from one excitable cell to the next via low resistance pathways between the cells called gap junctions.  Gap junctions are found in cardiac muscle and in some types of smooth muscle.  account for the very fast conduction in these tissues.  For example, rapid cell-to-cell conduction occurs in cardiac ventricular muscle, uterus bladder ➔ allowing cells in these tissues to be activated simultaneously and ensuring that contraction occurs in a coordinated manner. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I 2) Chemical synapse presynaptic neuron and the postsynaptic neuron are not in direct contact ➔ Synaptic cleft but separated by a narrow (0.01 to 0.02 mm) space called synaptic cleft. Chemical substance synthesized in the nerve ending in nerve knob, stored in Neurotransmitter nerve ending & released from presynaptic neuron➔ diffuse across synaptic cleft➔ bind to specific receptors on post synaptic nerves 1- Passive diffusion of neurotransmitter away from the synaptic cleft. 2- Destruction of neurotransmitter by enzymes located in the synaptic Inactivation cleft or in the plasma membrane of presynaptic or postsynaptic /Removal neurons. 3- Active reuptake of neurotransmitter into the synaptic knob of presynaptic neuron for reuse or enzymatic destruction. The arrival of an action potential at the axon terminal causes voltage- gated Ca++ channels to open.  in conc. Of Ca++ ions in the intracellular fluid facilitates exocytosis of Mechanism of action the neurotransmitter into the synaptic cleft. at a chemical Binding of the neurotransmitter to its specific receptor on the synapse postsynaptic neuron alters the permeability of the membrane to one or more ions ➔ causing a change in the membrane potential and generation of a graded potential in this neuron. neurotransmission across chemical synapses is unidirectional (from In contrast to presynaptic cell to postsynaptic cell). electrical synapses The synaptic delay is the time required for the multiple steps in chemical neurotransmission to occur. Synapses may be excitatory or inhibitory. Type of synapses Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Excitatory Postsynaptic Potentials Inhibitory Postsynaptic Potentials synaptic inputs ➔ depolarize the postsynaptic  synaptic inputs ➔ hyperpolarize the postsynaptic cell, bringing the membrane potential closer cell, taking the membrane potential away from to threshold and closer to firing an action threshold and farther from firing an action potential. potential. EPSPs are produced by opening Na+ and K+  IPSPs are produced by opening Cl− channels. channels, The membrane potential is driven to a value  The membrane potential is driven toward the Cl− approximately halfway between the equilibrium potential (approximately −90 mV), equilibrium potentials for Na+ and K+, or 0 which is a hyperpolarized state. mV, which is a depolarized state. Excitatory neurotransmitters:  Inhibitory neurotransmitters are γ-aminobutyric ACh, norepinephrine, epinephrine, dopamine, acid (GABA) and glycine. glutamate, and serotonin Membrane Potential & Action Potential Membrane Potential  Intracellular fluid (ICF) & extracellular fluid (ECF) are electrically neutral solutions  containing an equal number of positively and negatively charged ions.  In a non-stimulated (resting) cell: a slight accumulation of -ve charges on the internal surface of the plasma membrane is attracted to an equal number of +ve charges on the external surface  polarized. This separation of charge across the plasma membrane is called the membrane potential  measured in mV (millivolt)  The membrane potential value takes –ve or +ve signs according to the predominant charge on the internal surface of the cell membrane.  Nerve cells and muscles are the main cells that depend on the membrane potential in their function. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Resting Membrane Potential ▪ The resting membrane potential is ≈ –70 mV. ▪ The development of this potential depends on the distribution and permeability of three ions: Sodium (Na+) Potassium (K+) Anions (A-) Chloride (CI-) greater concentrations Greater concentration Large anionic proteins found greater concentration in ECF in ICF only within the cell in ECF ▪ Under resting conditions: most mammalian plasma membranes are ≈ 50 to 75 times more permeable to K+ than to Na+ - Anions are impermeable at all times. How is the resting membrane potential generated & maintained? ▪ When the membrane become permeable, the movement of Na+ and K+ ions in & out of the cell depends on two factors: Concentration gradient Electrical gradient Under normal resting conditions: Na+ ions & K+ ions are permeable. Since K+ is more permeable than Na+  a large number of K+ ions diffuse outward and a very small number of Na+ ions diffuse inward down their concentration gradients. The balance of these two opposing effects results in a typical neuron resting membrane potential of –70 mV  Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I 1) When the membrane is permeable only to Na+ 2) When the membrane is permeable only to K+ o K+ ions initially diffuse out of the cell down their concentration gradient  Na+ ions initially diffuse into the cell down their concentration [from higher concentration to lower concentration]  excess +ve gradient  excess +ve ions accumulates in the ICF along the internal ions accumulate in the ECF along the external surface of the plasma surface of the plasma membrane. membrane.  An excess of -ve impermeable extracellular anion (Cl–), remains o The impermeable A– ions remain inside the cell  attracted to these outside the cell along the external surface of the plasma membrane. positive charges, along the internal surface of the plasma membrane  This creates a +ve membrane potential  negative membrane potential [the inside of the cell is negative relative to the outside o As the positively charged K+ ions continue to diffuse outward  an As the Na+ ions continue to diffuse inward, an electrical gradient electrical gradient begins to develop & excess (+) charges are develops. accumulated on the external surface.  repel any additional K+ ions The (+) charges accumulated in the ICF begin to repel any o At this point, K+ ions not only diffuse outward down their additional Na+ ions & oppose the further movement of (+) charges concentration gradient, but also diffuse into the cell down their electrical inward. gradient the force moving Na+ ions inward down their concentration gradient The force that moved K+ ions inward balances the force that moved is balanced by the force moving Na+ ions outward down their K+ ions outward  no further net diffusion of K+. electrical gradient  no further net diffusion of sodium o The membrane potential at this point has reached the equilibrium o The membrane potential at this point reached the equilibrium potential for Na+ (ENa+)  +60 Mv potential for K+ (EK+)  –90 mV Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I The Action Potential  At the resting membrane potential (–70 mV)  most ion channels are in their resting state (closed but capable of opening)  When the neuron is stimulated  the activation gates of the voltage-gated Na+ channels open  permitting the influx of Na+ ions  further depolarization toward threshold  At the threshold potential  all voltage-gated Na+ channels are open  the “spike” of the action potential  Approximately 1m sec after the activation gates open  the inactivation gates of the Na+ channels close; in addition, the activation gates of the K+ channels open, resulting in the repolarization of the neuron.  The increase in K+ ion permeability results in the after-hyperpolarization [the cell is in its relative refractory period (RRP)] The absolute refractory period (ARP) begins when the voltage-gated Na+ channels become activated & continues through the inactivation phase. During this time  no further Na+ ion influx & no new action potentials can be generated. Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Na+ – K+ pump ▪ For each molecule of ATP expended by the pump  3 Na+ ions are pumped out of the cell & 2 K+ ions are pumped into the cell. ▪ Role of the pump  It maintains the concentration differences for Na+ & K+ by accumulating Na+ ions outside and K+ ions inside the cell  indirect role in the resting membrane potential generation. Depolarization: A decrease in the potential difference between the inside & outside of the cell. Hyperpolarization: An increase in the potential difference between the inside and outside of the cell. Repolarization: Returning to the resting membrane potential from either direction. Conduction of the action potential along neuronal axon Factors Influencing Conduction Speed of action potential: Large diameter axons provide a low resistance to current flow within the 1- Axon diameter: axon  speeds up conduction.  Wraps around vertebrate axons  prevents current leak out of the cells (Acts like an insulator). 2- Myelin sheath  However, portions of the axons lack the myelin sheath, and these are called Nodes of Ranvier.  Contain high concentration of Na+ channels (Action potential generated here). Faculty of oral and dental surgery 2024/2025 Level 1 Physiology I Conduction in Myelinated Axon Conduction in an Unmyelinated Axon (Saltatory conduction).  Depolarization jumps from one Node of  Cable spread of depolarization with Ranvier to another since current is unable influx of Na+  depolarizes the adjacent to flow through myelin. region membrane  propagating the  Conduction rate is rapid. AP.  Conduction rate is slow: AP must be produced at every fraction of micrometer. ▪ Occurs in nerves that innervate skeletal ▪ Occurs in nerve fibers carrying less muscle so that movements can be done important information, such as those rapidly. regulating slow digestive processes Multiple Sclerosis  In patients with multiple sclerosis, neurons in the brain, spinal cord & optic nerve are demyelinated.  The loss of myelin  slows down the conduction of APs  muscle weakness, numbness, fatigue, difficulty with walking & loss of vision.