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PSL205 Basic Human Physiology > Midterm > Flashcards

Midterm Flashcards

1
Q

Types of Tissues

A
  1. Nerves - transmits signal for communication; Receive from receptors and transmit to muscles and glands
  2. Muscle - Specialized to contract (voluntary or involuntary)
  3. Epithelium - Sheet like layer of cells that line the external body surfaces, hollow-bodied tubes, as well as organs
  4. Connective - Characterized by extracellular matrix; Anchors and links structures of the body
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2
Q

Negative Feedback System

A

Primary mechanism that keeps a variable close to a particular value or set point In the body, made up of

(1) Sensor - which detects changes in internal environment
(2) Regulatory Center - activates effector
(3) Effector - Reverses the change and brings condition back to normal
(4) Reversal inhibits the sesnor

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3
Q

Thermoregulation

A
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4
Q

Plasma Membrane

A

Phospholipid Bilayer - Basic structure of membrane and provides barrier for passage of water soluble molecules between ECF and ICF; also provides fluidity

Cholesterol adds to fluidity and interferes with hydrohobic things, prevents crystallization of phospholipids, and decreases permeability of membrane to water

Integral Membrane Proteins have hydrophilic and hydrophobic parts; some are transmembrane proteins acting as channels or as carrier proteins

Peripheral Membrane Proteins are generally located on the inside (cytoskeletal) and are easily removed from the barrier

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5
Q

Cell to Cell Adhesions

A

Cell Adhesion Molecules

Specialized Junctions

  1. Tight Junctions - common in epithelial tissue specialized for molecular transport; occludins (integral membrane proteins) fuse adjacent cells to form nearly impermeable barrier so solutes must cross membrane into cell to travel in between adjacent cells
  2. Desmosomes - Filamental Junctions between cells that are common in cells that are subject to mechanical stress (heart or uterus)
  3. Gap Junctions - Connexins (membrane proteins) link cytosol of adjacent cells allowing for movement of small molecules/ions between cells common in cells that need to contract as unit (smooth and cardiac muscle)
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6
Q

Types of Passive Diffusion

A
  1. Simple Diffusion
  • No membrane proteins are needed
  • Transport is through the bilipid layer
  • Rate depends on magnitude of driving force and membrane permeability
  1. Facilitated Diffusion
  • Passive transport through a carrier
  • Carrier Characteristics: Transmembrane protein with binding sites for specific particles that binds to one side at a time
  • Rate depends on rate of transport of each carrier, number of carrier proteins, and concentration gradient
  1. Diffusion Through Channels
  • Passive transport through a channel
  • Channel Characteristics: Transmembrane protein that functions like a passageway or pore; substance specific
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7
Q

Secondary Active Transport

A
  • Energy released from ion diffusion
  • Energy drives a pump
  • Diffusion results from previous active transport of ion
  • Ex. Contransport - Sodium linked glucose pump –> diffusion of sodium down its concentration gradient provides energy that pumps glucose into the cell
  • Ex. Countertransport - Sodium linked proton pump –> diffusion of sodium down its concentration gradient provides energy to actively pump H+ out of the cell
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8
Q

Transport via Compartments

A
  • Transport of macromolecules
  • Uses membrane compartments
    1. Endocytosis - inward pinching of membrane to create vesicles; phagocytosis, pinocytosis, receptor-mediated transport
    2. Secretory Vesicles
    3. Exocytosis - partial or complete fusion of vesicles for bulk transport from inside to outside
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9
Q

Glial Cells

A
  1. Astrocytes - numerous functions
  2. Ependymal Cells - line cavities
  3. Microglia - phagocytes
  4. Oligodendrocytes - form myelin in CNS
  5. Schwann Cells - form myelin in PNS
    - Compose 90% of CNS
    - Astrocyte feet terminate at the blood vessels
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10
Q

Na+/K+ Pump

A
  • 20% of resting membrane potential directly due to Na/K-ATPase
  • Elecrogenic 3 sodium out, 2 potassium in
  • 80% indirectly due
  • Produces concentration gradients
  • K+ chemical driving force is out of the cell and as it diffuses out of the cell pushing potassium out of the cell, making the inside more negative and causing the electrical driving force to pull it back into the cell until the cell finally reached equilibrium
  • Na+ has chemical driving force bringing it in and electrical driving force pushing it out
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11
Q

Voltage-Gated Sodium Channel

A

-Activation Gate

  • Voltage dependent
  • Opens at threshold and depolarization
  • Positive feedback

-Inactivation Gate

  • Voltage and time dependent
  • Close and open during depolarization
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12
Q

Frequency Coding

A

Strength of stimulus is measured by the frequency of coding - intensity of a stimulus is coded by the frequency of AP

Degree of depolarization of axon hillock is signaled by the frequency of APs

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13
Q

Communication Across a Synapse

A
  1. Terminal depolarized, opening VG calcium channels (synaptic delay - 0.5-5 ms between arrival of AP and change in postsynaptic Vm caused by changes in [Ca] and release of NT)
  2. Calcium enters the cell causing the vesicles to move towards the wall
  3. Cascade of vesicles towards wall
  4. Exocytosis
  5. Reaction of NT in postsynaptic neuron

NT Removal

  1. Breakdown of NT by enzyme (degredation)
  2. Presynaptic reuptake
  3. Diffusion
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14
Q

Summation

A
  • Adding effects of graded potentials
  • IPSPs and EPSPs are graded potentials and can be summed
  • Types of summation
  • Temporal - one synapse through time
  • Spatial - several synapses same time
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15
Q

Acetylcholine

A
  • CNS and PNS
  • Acetyl CoA + choline –(choline acetyl transferase)–> ACh + CoA
  • Synthesized in the cytosol of axon terminal
  • ACh –(acetylcholinesterase)–> acetate + choline
  • degredation occurs in synaptic cleft
  • Nicotinic (ionotropic) and Muscarinic (metabotropic) receptors
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16
Q

Biogenic Amines

A
  • Derived from amino acids
  • Catecholamines - derived from tyrosine
  • Dopamine
  • Norepinephrine
  • Epinephrine
  • Serotonin - derived from tryptophan
  • Histamine - derived from histidine
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17
Q

Serotonin

A
  • Derived from tryptophan
  • CNS transmitter mostly located in the brainstem
  • Functions to regulate sleep and emotions
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18
Q

Histamine

A
  • Derived from histidine
  • CNS NT located in hypothalamus
  • Known for pancreatic actions and modulation of sleep
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19
Q

Amino Acid Neurotransmitters

A

-Excitatory

  • Aspartate
  • Gluatmate

-Inhibitory

  • Glycine
  • GABA
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20
Q

Neuropeptides

A
  • Endogenous opioids - enkephalins + endorphins
  • TRH
  • Vasopressin (ADH)
  • Oxytocin
  • Substance P
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21
Q

Astrocytes

A
  • Development of neural connections
  • Remove NT from synaptic cleft
  • Communicate to neurons through chemical messengers
  • Maintain normal electrolyte composition of ISF in CNS
  • Protect neurons against toxic substances and oxidative stress
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22
Q

Microglia

A
  • Protect CNS from foreign matter through phagocytosis
  • bacteria/dead or injured cells
  • Protect CNS from oxidative stress
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23
Q

Physical Support of CNS

A

Bone

  • Cranium and vertebrae

Cranial and Spinal Meninges

  • Dura mater - very tough
  • Arachnoid mater - more delicate
  • Pia mater - lies right along the brain

Cerebrospinal Fluid and BBB in the subarachnoid space

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24
Q

Cerebral Spinal Fluid

A
  • Extracellular fluid of CNS that is secreted by ependymal cells of the choroid plexus and functions to cushion the brain
  • CSF provides communication between ventricles and subarachnoid space, and eventually drains back into normal circulation to be recycled
  • The ventricles are filled with CSF and bring the CSF to the central canal, which goes down the spinal cord
  • Circulation: Choroid plexus of third ventricle produces CSF and circulates around subarachnoid space and eventually into the arachnoid villi and drains into venus circulation
  • Production: Total volume is about 125-150 mL, and the choroid plexus produces 400-500 mL/day –> it is recycled 3 times a day
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25
Q

Spinal Cord

A
  • Cylinder of nerve tissue that is continuous with the brain and surrounded by vertebral column
  • Origin of spinal nerves (31 pairs), which each serve a particular dermatome (sensory region of the skin)
  • 8 Cranial
  • 12 Thoracic
  • 5 Lumbar
  • 5 Sacral
  • 1 Coccygeal
  • Afferent axons enter through the dorsal root ganglion and terminate in the dorsal horn
  • Efferent axons originate in the **ventral horn **and are held in the ventral root before going off to target
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26
Q

Brainstem

A

-Connects forebrain and cerbellum to spinal cord

  • midbrain connects to forebrain
  • pons connect to cerebellum
  • medulla connects to spinal cord

-Processing center for 10/12 cranial nerves

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27
Q

Lobes of Cerebrum

A
  1. Frontal - control motor movements, judgement, and foresight
  2. Parietal - somatic sensations and higher level logical reasoning
  3. Occipital - vision
  4. Temporal - audition, hearing and language
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28
Q

Topographical Organization

A
  • Areas mapped according to function
  • Primary motor cortex - motor homunculus - sits just in front of the central sulcus
  • Primary somatosensory cortex - sensory homunculus - sits just behind the central sulcus
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29
Q

Learning

A
  • Hippocampus important
  • Associative learning (Pavlovian)
  • Non-associative learning
  • Habituation: Decrease in response to a repeated stimulus
  • Sensitization: Increas in response to a repeated stimulus
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30
Q

Endocrine System

A
  • Communication and coordination system (between endocrine cells and their target cells)
  • Consists of glands or groups of cells that secrete hormones and the target cells responsive to them
  • Hormones wirelessly communicate via the bloodstream to reach most cell types over long distances (as compared to the nervous system which uses NTs to communicate via synapses to neurons, glands and muscles)
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31
Q

Regulation via Endocrine System

A
  • Metabolism
  • Growth and development
  • Reproduction
  • Responses to stress
  • Water and electrolyte balance
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32
Q

Endocrine System Malfunction

A
  • Diabetes mellitus
  • Cushing’s disease
  • Addison’s disease
  • Osteoporosis
  • Hyperthyroidism
  • Hypothyroidism
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33
Q

Hormones: Chemical Properties

A
  1. Hydrophobic = Lipophilic –> steroid and thyroid hormones travel in blood bound to carrier proteins; free hormone diffuses into the cell
  2. Hydrophilic = Lipophobic –> proteins and catecholamines travel freely in the blood and do not penetrate the cell
34
Q

Hydrophobic Hormone Signaling

A

Signal Transduction - How a cell converts a signal to another across a membrane

1a) Hormone binds with nuclear receptor and forms a hormone-receptor complex (HRC)
1b) Hormone binds with cytoplasmic receptor and forms HRC complex that then enters the nucleus
2) HRC binds to DNA at hormone response element (HRE)
3) Binding of HRC to HRE activates (or deactivates) gene, which affects transcription of mRNA and ultimately increases/decreases synthesis of protein coded by gene
4) mRNA moves into cytoplasm
5) mRNA translated by ribosomes to yield protein

35
Q

Hydrophilic Hormone Signaling

A

G-protein linked receptor

  1. Hormone binds to G-protein linked receptor
  2. G protein subunit dissociates to activate adenylate cyclase
  3. AC catalyzes conversion of ATP to cAMP
  4. cAMP activates protein kinase A
  5. PK activates protein
  6. Activated protein provokes cellular response
36
Q

Pituitary Gland

A

-Offshoot (scrotum) of the hypothalamus that consists of two sections

  • Anterior pituitary (adenohypophysis)
  • Posterior pituitary (neurohypophysis) - relay station that secretes hormones to the target cells via systemic circulation

-Both the supraoptic (secretes oxytocin) and paraventricular (secretes antidiuretic hormone, ADH/vasopressin) nuclei have termination in the posterior pituitary right next to a blood supply that allows for the direct entry into the blood supply to reach the rest of the body

37
Q

Growth Hormone

A
  • Growth Hormone Releasing Hormone (GHRH) in the hypothalamus stimulates the endocrine cells of the anterior pituitary to secrete GH to the liver and cells throughout the body
  • Can be inihibited by GH Inhibiting Hormone (GHIH), aka somatostatin
  • Can be mediated by somatomedins in liver
  • Major factor of growth spurts (human growth curve)
  • Action: Promotes growth by promoting hypertrophy to increase cell size and hyperplasia to increase cell number
  • Promotes linear growth in children (via long bone elongation) and maintains body mass/lean body mass in adults
  • Also increases fuels for growth by promoting glycolysis and glucose for energy so that actions can occur
38
Q

Long Bone Anatomy

A
  • Epiphyseal Plate is the site of linear growth and made of cartilage
  • Linear height increases due to increasing height of epiphyseal plate
  • GH stimulates hypertrophy and hyperplasia –> chondrocytes increase in size and number to increase the height of the plate –> chondrocytes adjacent to shaft die and are replaced with bones –> long bone elongation
39
Q

Thyroid Hormones

A
  • Thyrotropin Release Hormone (TRH) in hypothalamus promotes secretion of Thyroid Stimulating Hormone (TSH) from anterior pituitary, which stimulates release of thyroid hormones in the thyroid gland (specifically T3 and T4)
  • Negative feedback loop exists –> TSH and T3/T4 can inhibit further secretion of TRH
  • T3 and T4 are amine, hydrophobic hormones
40
Q

Thyroid Gland Histology

A
  • Colloid contains components necessary to synthesize TH: thyrogobulin , enzymes and iodine
  • All are synthesized by follicular cells, expept iodine, which is transported into the cell by the follicular cells
  • Thyrogobulin is the glycoprotein precursor of T3/T4 and contains lots of tyrosine
  • T3: Triiodothyronine; T4: Tetraiodothyronine (thyroxine)
41
Q

Thyroid Hormone Synthesis and Secretion

A
  1. Tyrosine residues iodinated
  2. Coupling of MIT (monoiodotyrosine) and DIT (diiodotyrosine)
  • T3: DIT + MIT
  • T4: 2 DIT
  1. Storage in colloid (can be up to 3 months long)
  2. TSH activates cAMP
  3. Uptake of iodonated thyrogobulin into follicular cells
  4. Phagosome fuses with lysosome; lysosomal enzymes break bonds and release free T3 and T4
  5. T3 and T4 released into follicular cell freely thanks to hydrophobicity
  6. T3 and T4 diffuse into blood steam
42
Q

Actions of T3 and T4

A
  • Regulate basal metabolic rate (rate of energy expenditure of a person at rest)
  • Calorigenic effect: Increase in heat due to increase in thyroid hormones leading to increase in BMR
  • Necessary for normal growth
  • Essential for normal brain development and normal brain functioning in adults
  • Promote increased energy mobilization when in excess AND increased energy storage when in deficiency
  • Increase number of beta adrenergic receptors
43
Q

Adrenal Glands

A
  • Made up of two functionally distinct portions
    1. Cortex, which secretes adrenocorticoids
  • Mineralocorticoids - present in zona glomerulosa (aldosterone)
  • Glucocorticoids - present in zona fasiculata and zona reticularis (cortisol)
  • Sex hormones - present in zona fasiculata and zona reticularis (androgens)
  1. Medulla, which releases catecholamines
44
Q

Hypothalamic-Pituitary-Adrenal Axis

A
  • Stress/circadian rhythym acts in the hypothalamus to increase CRH (corticotropin releasing hormone) secretion –> increase in ACTH (adrenocorticotropin hormone) secretion in anterior pituitary –> increase in cortisol secretion in adrenal cortex
  • Ways to Activate
    1. Stress - cortisol levels are a direct measure of stress; someone good at dealing with stress has lesser activation of the HPA axis
    2. Time of day - peak in the morning and goes down throughout the day
45
Q

Glucocorticoids Actions

A
  • Promote energy metabolism
  • Required for GH secretion
  • Maintain vessel responsiveness to catecholamines
  • Adaptive stress response
  • Clinically: Inhibit inflammation and allergic responses (low dose); immune suppression (high dose)
46
Q

Abnormal Glucocorticoid Secretion

A

Cushing’s Syndrome (hypersecretion)

  • Weight gain - due to inhibition of glucose uptake causing insulin secretion in increase and store more fat
  • Most common identifier - get fat in the buffalo hump and trunk (abs)
  • Hyperglycemia - increasing responsiveness of vasculature to vasoconstricting stimuli
  • Infections
  • Hypertension
  • Protein depletion –> wasting away of tissue

Addison’s Disease (hyposecretion)

  • May be predicted by actions of hormones (cortisol and aldosterone)
  • Weight loss, loss of appetite, fatigue, and salt craving (due to loss in urine from low aldosterone)
  • Elevated blood potassium levels due to low aldosterone with serious effects on heart
47
Q

Calcium Regulation

A
  • Three hormones control Ca2+ levels
    1. Parathyroid Hormone
    2. Calcitonin
    3. Calcitriol (Vit D3 derivative, aka )
  • Three target sites for control of Ca2+ levels
    1. Bone
    2. Kidneys
    3. Digestive Tract
48
Q

Calcium: Functions

A

-Important component of bone and teeth

  • Bone is the main reservoid of calcium (99%) as hydroxyapetite, which allows for bones to withstand compressive forces
  • Osteoblasts in the bone add to bone, which allows for bones to withstand tensile forces
  • Osteoclasts resorb bones and liberate calcium when needed
  • Exocytosis of chemical messengers
  • Stimulates muscle contraction
  • Increases contractility of heart and blood vessels
  • Essential for normal blood clotting (coagulation cascade)
49
Q

Parathyroid Hormone

A
  • Peptide-type, hydrophilic hormone that releases in response to low blood calcium levels
  • Bones
  • Stimulates osteoclast activity to release calcium (indirect)
  • Kidneys
  • Stimulates thick ascending limb (loop of Henle) and distal tubule
  • Free calcium is freely filtered at glomerulus of kidneys and come out in tubular filtrate to be excreted as urine; 99% of calcium will be reabsorbed into blood stream, 70% occurs in proximal tubule, 20% in thick ascending limb of loop of Henle, 10% in distal tubule
  • Digestive Tract
  • Small increase indirectly by stimulating calcitriol in kidneys
50
Q

Calcitriol

A
  • Steroid-type, hydrophobic hormone that increases calcium absorption at the digestive tract and kidneys
  • Also known as 1,25-(OH2)D3
  • Can be formed from sunlight (skin) or through diet (GI tract)
  • Vitamin D3 is converted to 25-OH D3 in liver and then to 1,25-(OH2)D3 in the kidneys
51
Q

Calcitonin

A
  • Peptide-type, hydrophilic hormone
  • Stimulates bone deposition to reduce blood calcium levels
  • Increases excretion of calcium at the kidneys
  • Made by cells in the thyroid gland that are between follicles
52
Q

Osteoporosis

A
  • Decreased bone mass leading to bone fragility and increased fracture risk
  • Risk factors:
  • Post menopausal (estrogen deficiency)
  • Lack of exercise
  • Calcium, Vit D deficient diet
  • Current cigarette smoking
  • Biophosphates are the most popular way to treat by helping stimulate osteoblasts
  • Diagnosed using bone density testing: associated bone density reading of less than 0.65 g/cm2 is considered to be osteoporosis
53
Q

Carbohydrate Metabolism

A
  • Carbs are broken down in the digestive system and travel as monosaccharides
  • Glucose is transported into the cell by glucose transporters
  • Once in the cell, glucose can be used immediately for energy (2) or used in other metabolic processes (3) or converted to glycogen for storage (4)
  • Glycogen can then be broken down to make glucose (5)
  • Glycogen is stored in the liver and muscle, but only liver glycogen can be broken down into transportable glucose
54
Q

Lipid Metabolism

A

Triglycerides are broken down by bile acids and pancreatic enzymes transported as lipoproteins

At the target cells, they leave the glycoproteins by

  1. Lipoprotein lipases, which are found on the inner surface of capillaries (esp in adipose)
  2. Fatty acids are taken up by cells and used (3) or stored for later (4) as triglycerides
  3. Triglycerides are broken down for energy - fatty acids can be used or sent off in the blood stream (6)
55
Q

Absorptive vs. Post-Absotive States

A

Absorptive

  • Energy stored
  • Anabolic reactions
  • Primary fuel: Glucose

Post-Absorptive

  • Energy stores broken down
  • Catabolic reactions
  • Primary fuel: Fatty acids
56
Q

Absorptive vs. Post-Absotive States: Carbs

A

Absorptive

  • Glucose primary fuel
  • Glycogen synthesis and storage
  • Conversion of excess glucose to triglyerides and storage in fat

Post-Absorptive

  • Glycogen breakdown and depletion (glycogenolysis)
  • Glucose synthesized via gluconeogenesis (in the liver)
57
Q

Absorptive vs. Post-Absotive States: Lipids

A

Absorptive

-Triglyceride synthesis (lipogenesis in adipose) and storage

Post-Absorptive

  • Triglyceride breakdown (lipolysis)
  • Fatty acids primary fuel
  • Partial oxidation of fats produces ketones
58
Q

Absorptive vs. Post-Absotive States: Proteins

A

Absorptive

  • Protein synthesis
  • Conversion of excess AAs to triglycerides and storage as fat

Post-Absorptive

  • Protein breakdown
  • Amino acids used for gluconeogenesis (only under extreme conditions)
59
Q

Pancreas

A
  • Made up of a head and a tail
  • Isles of Langerthans of the endocrine pancreas secrete insulin and glucagon (hydrophilic, peptide-type hormones)
60
Q

Insulin Secretion

A

Insulin (secreted by beta cells in pancreas) is the most important hormone for absorptive state because it acts to decrease blood glucose

GLUT4 - insulin can eiher trigger new synthesis or bring them to the surface –> lowers blood glucose by bringing it into the cell and using it for energy

61
Q

Insulin Actions

A

Most Tissues

  • Increase glucose uptake (except in brain, liver and exercisng muscle), amino acid uptake, and protein synthesis
  • Decrease protein breakdown

Adipose Tissue

  • Increase fatty acid and triglyceride synthesis
  • Decrease lipolysis

Liver and Muscle

  • Increase glycogen synthesis
  • Decrease glycogenolysis

Liver

  • Increase fatty acid and triglyceride synthesis
  • Decrease gluconeogenesis

=>OVERALL promoting decrease of blood glucose

62
Q

Glucagon Secretion

A
63
Q

Glucagon Actions

A

Liver

  • Increase glycogenolysis, gluconeogenesis, ketone synthesis, protein breakdown
  • Decrease glycogen synthesis and protein synthesis

Adipose Tissue

  • Increase lipolysis
  • Decrease triglyceride synthesis
64
Q

Diabetes Mellitus

A

Type I Insulin-Dependent Diabetes

-Insulin secretion is reduced or absent due to an autoimmune response killing pancreatic beta cells

Type II Non-Insulin-Dependent Diabetes

  • Defect in target cell responsiveness to insulin (insulin resistance)
  • Risk factors: Obesity, age, pre-diabetes, and family history

Long Term Complications

  • Large vessel disease –> stroke, heart attack, heart failure
  • Small vessel disease vessel weakening and breakage –> kidney failure, neuropathy and retinopathy
65
Q

Neuromuscular Junction

A
  • Efferent neurons of the somatic nervous system are motor neurons
  • NMJ is the synapse between a motor neuron and a muscle fibre
  • All motor neurons release ACh and all synapses are excitatory
  • Activity of motor neuron depends on summation of EPSPs/IPSPs
    1. AP arrives are terminal button
    2. VG Ca2+ channels open
    3. Calcium enters cell triggering release of ACh
    4. ACh diffuses across cleft and binds to nicotinic receptors on the motor end plate
    5. ACh triggers opening of channels for small cations (sodium and potassium)
    6. Net movement of positive charge in –> depolarization
    7. Causes AP in muscle cell
    8. AP spreads through muscle causing contraction
66
Q

Crossbridge Cycle

A
  • How muscles generate force via actin (thin filaments) and myosin (thick filaments)
  • Myosin head undergoes conformation changes swiveling back and forth
  • High energy form - high affinity for actin
  • Low energy form - low affinity for actin
  • Relies on ATP hydrolysis
    1. Binding of myosin to actin
    2. Power stroke - myosin head moves propelling thin filament toward centre of the muscle
    3. Rigor (myosin in low energy form) - ADP is released and new ATP binds to myosin head
    4. Unbinding of myosin and actin
    5. Cocking of the myosin head (myosin in high energy form)
67
Q

Excitation-Contraction Coupling

A

Skeletal Muscles

  • Sequence of events whereby an AP in the sarcolemma causes contraction
  • Dependent on neural input from motor neuron
  • Requires calcium release
    1. ACh releasef from terminal and binds to nAChR on motor end plate, triggering AP in muscle cell
    2. AP propogates along sarcolemma and down T tubules
    3. AP triggers calcium release from SR
    4. Ca2+ binds to troponin, exposing myosin-binding sites
    5. Crossbridge cycle begins (muscle fibre contracts)
    6. Ca2+ actively transported back into lumen of SR following AP
    7. Tropomyosin blocks myosin binding sites (muscle fibre relaxes)

Cardiac Muscles

-Summation cannot occur because by time the AP reaches the heart, it has already relaxed by time the refactory period if over

68
Q

Twitch Contraction

A
  • Contraction produced in a muscle fibre in response to a single AP
  • All-or-nothing event for a given muscle fibre at rest
  • Can be defined for a given muscle fibre or a whole muscle level
    1. Latent Period: Muscle excited but nothing has happened yet
    2. Contraction Phase: IC calcium high enough and force is happening
    3. Relaxation Phase: Calcium being pumped back into SR and IC falls so fewer crossbridges can form
69
Q

Summation and Tetanus

A
  • Summation occurs when a muscle is stimulated repetitively such that additional AP arrive before twitches can be completed, the twitches become superimposed on one another, yielding a force greater than that of a single twitch
  • Tetanus is a peak of stimulation that only occurs in skeletal muscles - occurs when calcium levels are high enough to saturate troponin so all myosin binding sites are exposed
  • unfused tetanus - force demonstrates small oscillations with breif periods of relaxation bewteen peaks
  • fused tetanus - complete saturation with a plateau
70
Q

Blood Vessels

A
  • Vasculature
  • Arteries: Relatively large, branching vessels that conduct blood away from the heart; carry oxygenated blood (aorta is the most important one)
  • Arterioles: Small branching vessels with high resistnace
  • Capillaries: Site of exchange between blood and tissue
  • Venules: Small converging vessels
  • Veins: Relatively large converging vessels that conduct blood to the heart; carry deoxygenated blood (vena cava is most important one)
71
Q

Anatomy of the Heart

A
  • Four chambers: two atria and two ventricles
  • Interventricular septum separates the blood in the right and left heart
  • Ventricles are much larger than the atria and make up most of the heart
  • need to generate great pressure that pushes blood away from the heart to the arteries
  • atria only needs to pump blood to the ventricles, which is much closer
72
Q

Rules of the Heart

A
  1. Blood goes IN through the atrium and OUT through the ventricle
  2. Blood only flows in one direction (atria –> ventricle –> artery)
  3. Left heart supplies blood to the systemic circuit through the aorta. Right heart supplies blood to the pulmonary circuit through the pulmonary artery.
73
Q

Oxygenation of Blood

A
  • Exchange between blood and tissue takes place in capillaries
  • Pulmonary Capillaries
  • Blood entering lungs = deoxygenated blood
  • Oxygen diffuses from tissue to blood
  • Blood leaving lungs = oxygenated blood

-Systemic Capillaries

  • Blood entering tissues = oxygenated blood
  • Oxygen diffuses from blood to tissue
  • Blood leaving tissues = deoxygenated blood, which returns to the pulmonary circuit to get reoxygenated
74
Q

Path of Blood Flow

A
  1. Blood becomes deoxygenated in the body and travels back to the heart in the vena cava, bringing it to the right atrium
  2. Blood travels through the bicuspid valve to the right ventricle
  3. Blood travels to the pulmonary artery and ends up in the lungs to oxygenate the blood
  4. Oxygenated blood goes to the left heart (left atrium)
  5. Pumps to the left ventricle and pumps it through the aorta to the rest of the body
75
Q

Heart Valves

A

-Atrioventricular Valves (AV Valves) separate atria and ventricles

  • Right AV valve - tricupsid
  • Left AV valve - bicuspid (mitral)
  • Papillary muscles and chordae tendinae keep the AV valves from everting

-Semilunar Valves separate ventricles and arteries

  • Aortic valve
  • Pulmonary Valve
76
Q

Atrioventricular Valve Action

A

When the ventricles are relaxed, blood enters the atria, pushing the AV valve cusps down into the ventricles, opening the valves

When the ventricles contract, blood presses up against the AV valve cusps, forcing the valves closed. Contraction of the papillary muscles tightens the chordae tendineae, preventing the valve cusps from being pushed into the atria

77
Q

Conduction System

A
  • Autorhythmic cells generate little or no contraction force; initiate and conduct APs that trigger contraction
  • Pacemaker Cells
  • Spontaneously depolarizing membrane potentials to generate APs
  • Coordinate and provide rhythm to heartbeat
  • Sinoatrial node - pacemaker of the heart
    • Upper right atrium where it joins superior vena cava
    • Heart beat almost always comes frmo APs here
    • Always beats the AV node to the punch because it has a higher beat frequency and so the AV node can’t go off during refractory period
  • AV node

-Conduction Fibres

  • Rapidly conduct APs initiated by pacemaker cells to myocardium
  • Conduction velocity = 4 meters/second
  • Ordinary muscle fibres, CV = 0.4 meters/second

-Impulse goes from SA to AV node and the AV node transmits AP less rapidly before moving to the ventricles (0.1 sec delay) to allow for atria to fully contract before going on

78
Q

Pacemaker Cells

A
  • Autorhythmic cells have pacemaker potentials
  • Spontaneous depolarizations caused by closing K+ channels and opening two types of channels
    1. Funny channels: sodium and potassium bring about net depolarization
    1. Calcium channels bring about further depolarization
  1. Pacemaker Potential: funny channels open and allow a slow depolarization (close when about 5 mV below threshold); voltage gated T-type Ca2+ channels bring polarization up to threshold
  2. Rapid Depolarization: L-type Ca2+ channels open causing rapid depolarization and AP to initiate
  3. Action Potential
  4. Repolarization: Potassium channels open allowing positive charges to leak out of the cell
79
Q

Contractile Cell Action Potential

A

Phase 0 - Rapid Depolarization: Increased permeability to sodium

Phase 1 - Small Repolarization: Decreased permeability to sodium

  • Not rapid because (1) closing of VG potassium channels and (2) opening of L type calcium channels

Phase 2 - Plateau: Increased permeability to calcium, decreased permeability to postassium

Phase 3 - Repolarization: Increased permeability to potassium, decreased permeability to calcium

  • Permeabilty of potassium increases causing efflux to increase
  • Calcium channels begind closing so less calcium can enter the cell

Phase 4 - Resting Potential: Resting membrane potential

80
Q

Electrocardiogram

A
  • External measure of electrical activity of the heart
  • Non-invasive technique used to test for clinical abnormalities regarding conduction of electrical signls in the heart
  • Body = conductor
  • Distance and amplitude of spread depends on size of potentials and synchronicity of potentials from other cells
  • Heart electrical activity - synchronized
  • Electrical events cause mechanical events, so precede mechanical events
  • P wave precedes atrial contraction (atrial depolarization)
  • QRS complex precedes ventricular contraction (ventricular depolarization and atrial repolarization)
  • T wave precedes ventricular relaxation

-Arrhythmias

  • Sinus rhythm - pace generated by SA node
  • Abnormal rates shown
    • Tachycardia = fast rhythm
    • Bradycardia = slow rhythm

-Ventricular Fibrillation

  • Loss of coordination of electrical activity of heart
  • Death can ensue within minutes unless corrected

PSL205 Basic Human Physiology (2 decks)

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