Physiology Flashcards
WHAT IS HOMEOSTASIS
Maintenance of nearly constant conditions in the internal environment.
what is internal environment
extracellular fluid or interstitial fluid
difference between ICF and ECF
ECF
14 L
Large amount of Sodium, chloride and bicabonate ions.
Oxygen and carbon dioxide.
Nutrients: Glucose, fatty acids and amino acids.
ICF
28 L
Potassium, magnesium and phosphate
why is ECF called internal environment
ECF has ions & nutrients needed by the cells to maintain cell life.
All cells live in essentially the same environment (ECF).
ECF = internal environment / milieu interieur
Cell growth & functions depend on proper concentration of components of internal environment (oxygen, glucose, different ions, amino acids, fatty substances etc..
how many times the blood circulate in one minute
At rest:
1 rotation / minute.
Extreme activity:
6 rotations / minute
define feedforward
term used for responses made in anticipation of a change
define feedback and name its type
Refers to responses made after change has been detected
Types of feedback systems
Negative
Positive
what are examples of negative feedback
Higher conc. of CO2 in ECF Increase in pulmonary ventilation more expiration of CO2 decrease in CO2 conc. in ECF.
High blood pressure series of reactions lower pressure OR
Low blood pressure series of reactions higher pressure.
Both the effects are negative to the initiating stimulus.
Thus homeostasis is maintained to prevent excess or deficiency of substances internal environment (ECF) is kept constant.
give example of positive feedback resulting in death
Normal heart pumps 5L/min.
2L Bled person poor pumping, less arterial pressure, less coronary flow weak heart less pumping, further less coronary flow more weak heart death.
Conclusion: Initiating stimulus causes more of the same (positive feed back).
Mild positive feedback may not lead to death, if overcome by negative feedback control (e.g., if person bled 1L Control mechanisms recovery).
describe positive feedback as part of a negative feedback mechanism
Rupture of blood vessel formation of clot activation of clotting factors / enzymes within the clot.
Some of these enzymes activate enzymes of adjacent blood more blood clotting till plugging of hole bleeding stops.
Sometimes unwanted clots formation atherosclerotic plaque in coronary artery acute heart attack.
describe positive feedback mechanism associated with childbirth
Strong uterine contractions during childbirth baby’s head pushed through cervix stretch of cervix signals through uterine muscle body of uterus more powerful contractions more stretch to cervix more stronger contractions.
If strong enough baby is born.
If not strong enough contractions die out restart after few days.
describe and relate feedforward control and adaptive response
When there is not enough time for afferent signals (from periphery to brain) & efferent nerve signals (from brain to periphery) sensory nerve signals from moving parts apprise the brain, whether movement is performed correctly (FEED FORWARD CONTROL)
If not brain corrects feed forward signals in the next attempt of muscle contraction.
If further correction is required done in subsequent contractions (ADAPTIVE CONTROL / DELAYED NEGATIVE FEEDBACK).
describe cytoskeleton nd its components
Cytoskeleton, a system of fibers that not only maintains the structure of the cell but also permits it to change shape and move.
Microtubules
Intermediate filaments
Microfilaments
describe the structure of microtubules in cell
Uniform in size and straight.
25nm in diameter and several micrometers in length.
Wall of microtubules consists of individual filamentous structures made of protein tubulin.
what are the functions of microtubules
They are considered to be a framework that determines the shape of the cell.
They are involved in transport of macromolecules in the cell’s interior.
Several cell organelles are derived from special assemblies of microtubules.
Cilia, flagella, basal bodies and centrioles have groups of microtubules arranged in a special fashion.
Mitotic spindles are also composed of microtubules
describe strcuture and function of microfilaments
Microfilaments represent the active or mobile part of cytoskeleton.
These are the thinnest, ranging in diameter from 6 to 7 nm.
Composed of protein actin, myosin, as well as tropomyosin and other proteins.
Actin filaments are made of globular actin molecules, called G-actin.
They help generate movement (muscle contraction, cell division and cell locomotion) and provide mechanical support to cell.
describe types and function of intermediate filaments
Found in parts of cells subject to mechanical stress, help stabilize the position of organelles such as nucleus & help attach cells to one another.
Keratin filaments, present in epithelial cells.
Neurofilaments, present in axons, dendrites.
Glial filaments, present in astrocyte.
Heterogenous filaments, e.g., desmin and vimentin filaments.
what are the functions of cytoskeleton
Plays an important role in maintaining the cell shape.
Cytoskeletal fibers stabilize the positions of organelles.
Cytoskeleton helps transport materials into the cell and within cytoplasm.
Fibers of cytoskeleton connect with protein fibers in the extracellular space, linking cells to each other and to support material outside the cells.
Cytoskeleton enables cell movement
describe structure and structural components of cilia
Cilia are short, hair like structures projecting from the cell surface like the bristles of brush.
Surface of cilium is continuation of cell membrane, and its core contains nine pairs of microtubules surrounding a central pair.
Multiple protein arms composed of protein dynein, having ATPase activity, project from tubules.
Microtubules terminate just inside the cell at basal body. Or cilium is an outgrowth of basal body.
Basal body is similar in structure to centriole.
what are the functions of cilia
Cilia beat rythmically back and forth
Ciliary movement creates currents that sweep fluids or secretions across the cell surface.
Ciliary movement is a whip like movement that occurs in only 2 places in human body: on the inner surfaces of respiratory airways and on the inner surfaces of uterine tubes (fallopian tubes).
In resp. airways, movement of cilia causes a layer of mucus to move towards pharynx.
In uterine tubes, it moves ovum towards uterus.
what are functions and functional elements of flagellum
Function of flagellum is to push the cell through fluid with wave like movements, just as undulating contractions of a snake’s body.
Axoneme is the term applied to axial structure of cilia and flagella, and is the essential motile element.
There are 2 conditions for continuous beating of axoneme: presence of ATP and appropriate ionic conditions, especially calcium and magnesium
describe ameboid movement
It means movement of an entire cell in relation to its surroundings. For example, movement of WBC’s through tissues.
This movement begins with protrusion of pseudopodium from one end of the cell and attaches to a new area of tissue.
Remaining cell is pulled toward pseudopodium.
what is the mechanism of ameboid movement
It results from formation of new cell membrane continuously at the leading edge of pseudopodium and continuous absorption of membrane in remaining parts of cell.
Attachment of pseudopodium to surrounding tissues occurs while remaining cell is pulled forwards towards the point of attachment.
Attachment is caused by receptors present in exocytotic vesicles.
Vesicles become part of pseudopodial membrane and they open to exterior.
This exposes the receptors which now attach to surrounding tissues.
At the opposite end of cell, receptors pull away from their ligands, forming endocytotic vesicles.
These vesicles move toward pseudopodial end, where they are used to form new membrane for pseudopodium.
Energy is required for all this mechanism.
Protein actin is present in cytoplasm of all cells.
Actin network binds with another protein, myosin thus causing contraction.
Whole process is energized by ATP.
what is the intercellular gap between epithelium and other closely packed tissues
20nm
define cell junctions and their function
Acell junction(orintercellularbridge) is a type of structure that exists within the tissue of some multicellular organisms, such as animals.
Cell junctionsconsist of multiprotein complexes that provide contact between neighboringcellsor between acelland the extracellular matrix
what are the forces that hold cells together
Mutual force of cohesion.
Cell junctions: specialized structural arrangements present at various sites.
describe classification of cell junctions on the basis of shape and contact area
1) Limited extent:
e. g., MACULA (spot / punctate area)
2) Around entire cell:
e. g., ZONULA (belt / girdle like)
describe classification of cell junctions on the basis of relative closeness ad nature of cell contact
1) No intercellular space, cell membranes in contact / fused:
e. g., OCCLUDENS.
2) Intercellular space is 20-25 nm wide & dense granular material in intercellular space & on cytoplasmic surfaces of adjacent cell membranes:
e. g., ADHERENS.
3) Very narrow intercellular space = 3nm:
e. g., GAP junctions
what the types of cell junctions
Macula Adherens (Desmosome or Spot
Desmosome).
2) Zonula Adherens (Belt Desmosome).
3) Zonula Occludens (Tight Junction).
4) Gap Junction (Nexus).
describe the structure of macula adherens
Location: Between epithelial cells, on lateral cell interfaces with their long axes perpendicular to basement membrane of epithelium.
Shape: Small discoid structures.
Intercellular gap: 25 nm
Adhesive glycoprotein: Desmocollin
Intra-cytoplasmic densities: Attachment plaques beneath plasma membranes of adjacent cells.
Intermediate filaments: Are inserted into attachment plaque or make hairpin loops & turn back into cytoplasm.
describe the function and structure of Hemi-desmosomes
Location: between certain epithelial cells & basal lamina.
Shape: like half a desmosome on epithelial plasma membrane only. Sometimes basal lamina facing the hemi-desmosome is thickened.
Function: To bind the epithelial cells to basal lamina.
describe the structure and location of zonula adherens
Arrangement: as a girdle / belt around each cell that is joined.
Intercellular gap: Normal width (20 nm).
Bridging of gap: No bridge of filaments, though filaments & submembrane cytoplasmic densities are present.
Location: among epithelial cells, fibroblasts & smooth muscle cells.
describe the structure, function and location of zonula occludens
Arrangement: like a girdle.
Intercellular gap: No gap due to apparent fusion of plasma membranes of adjacent cells.
Location: intestinal mucosa & urinary bladder mucosa.
Function: important sealing effect (prevent the change in chemical composition of urine).
describe the structure, function of gap junctions
Intercellular gap: 2-3 nm only. It is traversed by hollow tube-like structures.
Function: permeable to colloidal substances without entering the ECF . Provide communication channels between adjacent cells. Also role in spread of electric impulse from one cell (smooth / cardiac cell) to another.
Desmosomes Vs Nexus:
Nexus usually form limited attachment plaques like
desmosomes, but sometimes more extensive.
Connexons: hexagonal arrays of protein units. Six subunits surrounding a channel.
Regulators of diameter of channels:
Increase in Ca2+ concentration causes the subunits to slide together, reducing the diameter of the channel.
Diameter may also be regulated by pH and voltage
describe the structure of gap junction
Each connexon is made up of six subunits.
Each connexon in the membrane of one cell lines up with a connexon in the membrane of the neighboring cell
forming a channel through which substances can pass from one cell to another without entering the ECF
where are gap junctions located
Cardiac & smooth muscles,
Liver, kidney, thyroid, pancreas, adrenals,
Urinary bladder,
Nervous system (between neurons & between glial cells),
Skin.
what is junctional complex
describe its structure and location
Series of cell junctions between adjacent epithelial cells = junctional complex.
Location: small
intestinal mucosa.
Comprises of:
Zonula occludens + zonula adherens + macula adherens.
what are the functions of glycocalyx
Negative charge of glycocalyx repels other negative charges.
Glycocalyx of some cells attaches to glycocalyx of other cells, thus attaching them together.
Many CHO act as receptors for binding hormones. This attachment with hormones activates attached internal proteins thus activating a cascade of intracellular enzymes.
Some carbohydrates enter into immune reactions.
Repels other negative charged objects
Attaches Glycocalyx of other cells
Act as receptor substances for binding hormones such as Insulin
Involved in some immune reactions (Infections)
Defense against cancer
Embryonic development
Fertilization
describe myelinogenesis
Formation of myelin sheath around the axon.
In peripheral nerve, it starts at 4th I.U month.
It is completed in 2nd year after birth.
Myelin sheath is produced by layers of Schwann cells.
Outermost layer of Schwann cells remain as neurilemma / Sheath of Schwann.
Cytoplasm of Schwann cells is not deposited.
what is the general classification of nerves in guyton
use book bitch
during nerve degeneration changes take place at which levels
) nerve cell body / soma.
2) central stump (nerve fiber central to the site
of lesion) / retrograde degeneration.
3) changes in distal stump (wallarian degeneration).
describe changes in nerve soma during degeneration
Nerve cell body swells
chromatolysis (dissolution of Nissl granules)
nucleus pushed aside
Mitochondria, golgi apparatus, ribosomes & lysosomes 🡪 structural changes.
If axon is cut quite close to cell body 🡪 cell may die.
describe changes taking place in central stump during degeneration
Degenerated area usually extends upwards up to 1 or 2 nodes or more.
Degeneration 🡪 repair soon follows.
describe changes that take place in distal stump during nerve degeneration
Axon & myelin sheath completely degenerate (secondary / Wallerian degeneration).
Simultaneous degeneration throughout length of nerve fiber.
Changes appear in 24 hrs & complete in 3 wks.
Continued conduction for 3 days post injury.
After 5th day all function is stopped.
what are the histological changes that take place during nerve degenerations
Axoplasm 🡪 breaks up into short segments.
Swelling of neurofibrils 🡪 become tortuous & disappear after sometime.
Within few days, space containing axoplasm shows only a little debris.
Myelin sheath disintegrates 🡪 fat droplets appear (8th to 32nd day).
Lecithin molecules present in myelin sheath 🡪 completely hydrolyzed to glycerol, fatty acids, phosphoric acid & choline 🡪 removed by increased number of macrophages (appearing as foam cells due to their high lipid content) or by blood stream.
Endoneurium remains intact within endoneurial tubes.
Schwann cells proliferate & their increased number along with fibrous tissue 🡪 false neuroma. (True neuroma in regeneration)
discuss stages of nerve regeneration
If slight axon injury or injury away from cell body 🡪 nerve cell body shows signs of repair. Nissl granules reappear. Nucleus resumes central position. Nucleolus moves to periphery of nucleus. Full recovery may take 3-6 months.
At the onset of repair 🡪 axon in the central end of cut fiber elongates 🡪 large number of fibrils (up to 50) 🡪 enter the periphery of endoneurial tubes 🡪 only 1 fibril survives 🡪 tubes with fibrils are slowly surrounded by myelin sheath by activity of Schwann cells.
discuss mechanism of regeneration
Less understood.
Factors believed to be responsible:
Neurotrophic stimuli (? Chemical in nature)
what are neurtrophins and their functions
A number of proteins necessary for survival and growth of neurons
Some are isolated from muscles / other structures innervated by neurons
Others are produced by astrocytes
These proteins bind to receptors at neuron endings 🡪 internalized 🡪 transported by retrograde transport 🡪 neuronal cell body 🡪 produce proteins for 🡪 neuronal development, growth & survival.
Other neurotrophins: produced in neurons 🡪 transported in anterograde fashion 🡪 nerve ending 🡪 maintain the integrity of postsynaptic neuron.
what are the different neurotrophins and their receptors
Nerve growth factor
(NGF)
trk A
Brain-derived neurotrophic factor (BDNF)
trk B
Neurotrophin 3 (NT-3) trk C, less on trk A and trk B
Neurotrophin 4/5 (NT-4/5)
trk B
