Biology Flashcards
5 types of tissue
Muscle
> Located in muscles
> > Skeletal (voluntarily contractable)
> > Smooth (involuntarily like vessels and GI)
> > > Can hold contraction for a very long time (tonic control)
> > Cardiac
Nervous
> Located in all part of the nervous system
> Contain neurons
Connective (bindweefsel)
> Located around organs and vessels, to support, protect and form them
> Provides a medium for diffusion
Epithelium (dekweefsel)
> Located at most of the surfaces inside and outside the body
> E.g. skin, cornea, gut
> Very tight so allows almost no diffusion
> Gets energy from nearby connective tissue
Mineralized (hard tissue)
> Located in bones, enamel (glazuur) and dentin (tandbeen)
What is a mole (NL: mol)
A mole is a constant: 6,022*10^23 particles
An osmole is the amount of particles after solvation. 1 mol/L NaCl will be 2 Osmol/L in water because the NaCl splits into 2 particles Na and Cl ions.
What is tissue (NL: weefsel)
Group of cells having the same origin, structure and function in the body (e.g. muscle tissue). Organs are made up of several different kinds of tissue.
Describe the synapse
A synapse consists of
- Pre-synapse: the terminal of an axon
- Synapse cleft: space between pre- and post-synapse
- Post-synapse: the receiving cell
The pre-synapse is at the end of an axon. When it receives an action-potential, it opens Ca++ gates, which in turn activate the release of neurotransmitter vesicles into the cleft.
The post-synapse (which can be the dendrytes of another neuron, or a muscle cell for example) has receptors for the neurotransmitter. The result will be a graded potential, one of two types:
> Excitatory postsynaptic potential (EPSP): depolarization
> Inhibitory postsynaptic potential (IPSP): hyperpolarization
If the post-synapse is another neuron, it needs to reach a threshold to fire an action potential itself. Therefore, it is as if it sums the inputs it gets from the dendrites, where EPSP are positive and IPSP are negative, and the location (closer to the initial segment) gives a higher weight.
After the release, the synapse takes care to remove/degrade the neuro-transmitter so the cell can react to a next potential action potential
Two chemical types of synapses:
> Cholinergic
> Adrenergic
Somatosation
Receptors in skin, muscles and bones that detect pain, temperature, touch, pressure and proprioception (spatial information)
Endocrine system
The endocrinic glands deliver their hormones to the blood directly (no special ducts).
It regulates
- Sodium/water balance
- Calcium balance
- Energy balance
- Stress
- Growth & development
- Reproduction
The concentration controls the strength of the stimulus and is best controlled at the source (the endocrinic gland). But also the delivery can be controlled, because it depends on
- Perfusion rate
- Blood flow
- Degradation (excretion by liver/kidney)
Pathology in endocrinology occurs because there is too much hormone, too little hormone or receptor insensitivity.
Senses
> Somatosensation
- Touch/pressure
- Mechanoreceptors
- Pain
- Nociceptors (responds to chemicals of damaged cells and immune cells)
- Temperature
- Thermoreceptors (ion channels that respond at a particular temperature)
- Some chemicals open these channels as well (ex. menthol opens cold, capsaicin/ethanol open hot)
- Proprioception
- Stretch receptors (channels that are gated by stretch)
> Special senses
- - Vision
- - - Retina contains photoreceptors that convert light into electrical signal (phototransduction)
- - - - There are rods (many-rods-to-1-ganglion, low-resolution but highly sensitive; used at very dark conditions. Positioned at the outer edges of the retina, ~90million) and cones (1-to-1-ganglion, so high resolution; can differentiate color. Positioned in the center of the retina, ~6million)
- - - - We have only 3 types of cones to detect all colors: R, G, B. The combination of their amount of activation tells the Nervous system the correct color
- - - The lense controls the focus: ciliary muscles around the lense can contract to come closer to each other and therbey they release tension on the zonular fibers which are ligaments running to the lense. The lense will be rounded: focus on near object (you can feel this happening when you look at something nearby)
- - Hearing (Auditory system)
- - - Inside the ear, vibrating ear reaches the eardrum. The eardrum will vibrate as well and the vibration is amplified by 3 bones (malleus, incus, stapes) which in turn vibrate the cochlea: a shell like comparment containing 2 fluid comparments (scala vestibuli, scala tympani). Between these compartments lies the Organ of Corti which contain hairs that will vibrate for a certain pitch; the further away, the higher the pitch. These hair cells release action potentials (of which the strength correlates with the volume of the sound) onto axons that form the cochlear nerve
- - Vestibular system (Equilibrium)
- - - The inner ear contains 3 orthogonal semicircular canals that respond to head rotation (angular acceleration like nodding/shaking). At the ends of the semicircular canals there are regions called ampullae, which contain a capula. This gelatinous component is like a plant in the fluid (endolymph) - because of inertia the capula moves out of its resting position slowly and delayed when accelerated (so with constant speed (a=0) it is back at its resting position)
- - - It also contains 2 otolith organs that respond to horizontal(utricle)/vertical(saccule) movement (linear accelearation like elevator drop and body leans). These organs again consists of hair cells, but now they are surrounded by gel with a heavy layer of CaCO3 crystals on top. Because these crystals are heavy, gravity pulls on them when the body moves and in turn they pull on the gel which is sensed by the hairs.
- - Taste/smell
- - - Both are done by chemoreceptors
- - - Taste is done by taste receptors which have little taste pores on the tongue. Because they are so small, food needs to be dissolved into liquid first before it’s able to pass through and be tasted (this happens thanks to saliva). There are 5 types of taste receptors (sweet (sugars), sour (H+ ions), salt (Na+ and K+ ions), bitter (plant alkaloids) and umami (glutamate)).
- - - Smell is done by olfactory receptors in the nasal cavity. There are ~400 types that can distinguish 10.000 odors.
Visceral (visceral = inside the body) stimuli
- - pH, O2, glucose levels in blood
- - Osmolarity
Sensation: the sensory information reaching the brain
Perception: the interpretation of sensation by the CNS
Adaptation: sensitivity will decrease over time with the same sensation (to be able to filter all the sensory input and to focus)
Ganglia are clusters of neuron, usually found near to senses and in the spine. They combine sensory input to more meaningful information.
Cell differentiation
The process of a cell changing from one type to another
What are the 11 organ systems?
Circulatory system > Cardiovascular (heart, blood, blood vessels) - Transport nutrients > Lymphatic (lymph, lymph vessels) - Immune response > Endocrine system (Endocrine glands, adrenals) - Communication by hormones Raspiratory system (Pharynx, larynx, bronchi, lungs, diaphragm) - Breathing Digestive system - Breakdown food for absorption by the body > Gastrointestinal tract (mouth, esophagus, stomach, gut, rectum) > Accessory organs of digestion (tongue, salivary glands, pancreas, liver, gallbladder) Reproductive system (sex organs) - Reproduction Renal system (kidneys, ureters, bladder, urethra) - Removal of waste product from the body Nervous system (brain, spinal cord, peripheral nervous system) - Collect and transfer of information Integumentary system (skin, hair, fat, nails) - Protect body from losing water and damage from outside Skeletal system (bones, cartilage, ligaments, tendons) - Body support Muscle system (skeletal, smooth and cardiac muscles) - Provides motion and heat
What is an organ?
A collection of tissues joined in a structural unit to serve a common function.
Synonyms: Viscus, offal (from butchered animals), guts, innards
Describe the different fluids inside the human body
Fluid inside the human body is either stored inside cells or outside cells. 60% of the total body weight is fluid
Intracellular fluid (ICF) - inside the cells (about 2/3 of total body fluid weight)
> Mostly cytosol (the fluid of the cytoplasm)
> Contains proteins
> High K, low Na
Extracellular fluid (ECF) - oustide the cells (about 1/3 of total body fluid weight)
80% Surrouding cells (IS): Interstitial fluid
18% Inside vessels (IV): Blood plasma and Lymph
- > Contains proteins
2% Transceullar fluid: Cerebrospinal (hersenvocht), eyes, joints
> High Na, low K
There is an equilibrium inside each of these compartments; for example IS and IV can exchange substance without barrier and energy cost. However, between the compartments it’s different.
Exchange of ions between ICF and ECF is done by ATPases. This is a group of enzymes that can use ATP to transport ions through the cell membrane. For every 3 Na that goes out, 2 K comes back in.
Osmosis
The diffusion of a fluid through a semipermeable membrane.
For example, equal amounts of water in ICF and ECF, but a higher amount of sodium in the ECF. So the concentration of water in the ECF is lower. The cell membrane is permeable for water but not for sodium. So to reach equilibrium (of concentration! volume can be different), water will diffuse (via aquaporins) from ICF to ECF.
Molarity = #mole / volume Osmolarity = #osmoles / volume Osmolality = #osmoles / mass Tonicity = #non-permeable-osmoles / volume
The body is in homestatis with ~300 mOsM (milli-osmoles). Putting the cell in a solution that is
- <300 mOsM, that solution is hyposmotic to the cell
- =300 mOsM, that solution is isosmotic to the cell
- > 300 mOsM, that solution is hyperosmotic to the cell
Insulin
A peptide hormone.
The prohormone consists of insluin and c-peptide
Protein/peptide-hormones
Protein/peptide-hormones are 1 of 3 types of hormones. Properties:
- Amino-acid based
- Water soluble (thus also in blood, don’t need a carrier)
- Short half-life
- Target cells need receptors on the cell membrane. They stick out of the membrane on both ends. When the hormone binds to the receptor on the outside, the inside is activated in a way that results in metabolic changes in the cell
They are always 3 amino-acids or larger and are made up of > Protein molecules - - Shorter amino acid-chains > Peptide molecules - - Longer amino acid chains
P/P-Hormones are synthesized inside the cell and prepared in vesicles. This means they can be released fast because they are pre-created.
- mRNA has the transcription for the amino-acid chain
- The amino-acid chain is synthesized by the RER and is called a preprohormone
- Enzymes in the RER remove the ‘signal peptide’ part. Now we have a prohormone
- The prohormone enters the Golgi where it is packed in a secretory vesicle (a wrap for stuff that needs to go outside the sell)
- Enzymes inside the vesicles cleave the prohormones into hormones
- The vesicle stays within the cell until there is a secretagogue (release signal)
- The vesicles are secreted into the blood and the hormones are released
Once secreted, the hormone is active
Homeostasis
The primary work of all organs trying to keep the consituents of the ECF constant (in relative amounts).
If homeostasis can not be maintained, the body becomes ill.
Sensors report to the brain about current values of the ECF. The brain has setpoints that decide if there should be acted upon the new values. If so, it sends a stimulus to the body which will react and try to reestablish the homeostasis.
For example, if you eat salty food, the brain will be alarmed and make you thirsty. You drink water which will end up in the ECF (just like the sodium did) and the concentration is stable again. Internal changes can happen as well - for example, an illness response can be to raise the SETPOINT in the brain to 40C
In extreme cases where homeostasis can not be maintained, the body will make trade-offs and prioritize brain and heart.
Steroid/thyroid hormone
Steroid hormones are created in the adrenals, gonads or placenta.
They are lipid soluble, so:
- They can not be prepared in the cell because they would float through the membrane outside of the cell
- Hence they are created on demand (slower)
- They need a carrier protein (created in liver) to be transported in the blood
- They are derivatives of cholestorol
- They have nuclear receptors, inside the cell instead of on the membrane. This is because they can float through the membrane. Here they can change the activity of the DNA, changing future protein synthesis (slow response)
Sometimes they are converted even further at the target cell (for example testostorone to DHT)
Homeostatic control
To restabilize the homestasis after something has changed, cells have to be informed of the change so they can act upon it. There are multiple ways such a signal can be sent:
Locally:
> Paracrine: A neighbor cell releases a chemical
> Autocrine: The cell itself releases a chemical
> Nexus (gap junction): Two cells are interconnected physically
Over distance (by reflex):
> Endocrine: Releases chemical to blood
- - Very low concentration because it dilutes in blood. Target cells need to have a very high affinity receptor
- - Slow, can take hours for hormone to reach destination
> Neuron: Releases chemical to synapse
- - Very high concentration because it is released in a tiny space: the synapse. Target cells have a very low affinity receptor
- - Fast, within seconds
Receiving the signal is done by receptors on the cell. The sensitvity of a cell to a hormone in the plasma is determined by affinity, number of receptors, saturation (how many receptors are already in use) and competition (a receptor that is already bound by another hormone).
A cell can inactivate it´s hormone response by sequestration (removing the receptor from the cell surface) or degradation (remove it completely from the cell). This is the case with Diabetes type II, where skeletal muscle becomes insenstive to insulin
What is a neuron?
A nerve cell. Consists of:
- Cell body
- Dendrites (Attach to the cell body and receive information. Can be hundreds)
- Initial segment (Where the axon attaches to the neuron)
- Axon (A tail that takes information Away from the neuron)
- Axon terminals (Branches at the other end of the axon)
What is the difference between a positive and a negative feedback loop
NEGATIVE FEEDBACK LOOP:
Any process where the output acts on the input with the result of stabilizing. For example:
1. Eating -> Glucose level rises
2. High glucose is a stimulus for insulin release
3. Insulin in the blood enables skeletal muscles to take up glucose
4. Glucose level is brought back down again
POSITIVE FEEDBACK LOOP:
Any process where the output acts on the input with the result of augmentation. Obviously, this means accelerated growth which in all cases have to be stopped by another, negative, feedback loop.
A positive feedback can be generated by a cell that increases its receptors for the chemical as result of the chemical; or by the cell releasing a chemical that stimulates more of the original chemical
What are glial cells?
Glial cells belong to the nervous system but are not neurons. They
- Maintain homeostasis
- Form myelin
- Provide support/protection for neurons
MACROGLIAL CELLS
> Some types of Glial cells wrap themselves arround axons of neurons with myelin (myelination), to insulate them and help them better propagate electrical signals. Between these wraps you have ‘Nodes of Ranvier’ where the Na+ can come in. Because of the wraps there is one action potential per node instead of many: the signal propagates faster.
- - In the CNS they are called Oligodendrocytes (multiple portions of axon per cell)
- - In the PNS they are called Schwann cells (one portion of axon per cell)
> Astrocytes support the CNS neurons metabolically.
MICROGLIAL CELLS
They are macrophages (immune cells) that protect the CNS
Membrane potential
Cells keep an electric potential between the in- and outside. This is created by the K/Na-pump where the inside of the cell becomes more negative.
Functions of such a potential:
> To provide a gradient for transport
> To let ions cross the membrane and thereby generate a current for signaling
There are two forces working: chemical gradient and electrical gradient.
If we look at Na+ only, because of the pump there is more on the outside. Hence the chemical gradient wants it to enter the cell, but it will reach equilibrium at about +60mV. At this point the inside of the cell is too electrically positive for more Na+ to enter.
The same story holds for K+, which will reach -90mV because the pump takes all these positive ions out of the cell but the electrical gradient wants them to come back.
The actual potential is thus somewhere between -90mV and +60mV, and it is decided by the pump and how many ‘leak’ channels are open. A normal resting potential is about -40mV (because the pump works harder than the leak channels)
A cell at resting potential is called polarized. If it gets more negative, it’s hyperpolarizing. When it gets less negative, it’s depolarizing. When it becomes positive, it is said to overshoot.
ACTION POTENTIAL
Ligand gated channels can cause a Graded potential:
- Some chemical opens the gate
- Na+ comes in and quickly depolarizes the resting potential
- The Na+ dilutes and the gate gets closed, so the interior of the cell repolarizes
However, if the depolarization is big enough, it can cause voltage-gated ion channels to open up - causing an Action potential:
- The ion channels open up
- Na+ ions flow into the cell causing the interior potential to overshoot to Na-equilibrium
- K+ ion channels open up as well, causing hyperpolarization to K-equilibrium
- Na channels close because of the polarized cell interior
- K channels close because of the polarized cell interior
- The resting potential is restored by normal K/Na-pump
Thicker axons, or those which are myelinated, propagate the potential much faster
What is vasoconstriction?
Vessels are surrounded by smooth muscles which can be contracted by the SNS. The opposite of contraction is vasodilation.
The contraction is tonic, meaning the force can be varied continously and be held for a very long time with little energy expenditure (as opposed to phasic contraction, which rapidly alternates contraction and releaxtion)
Describe the various nervous systems
Central Nervous System (CNS)
- Brain and spinal cord
Peripheral Nervous System (PNS)
- - Nerves
- - They use acetylcholine as neuro-transmitter
> Somatic Nervous System (SoNS)
- - Afferent nerves relay sensory input to the brain
- - Efferent nerves control sketal muscles voluntarily
- - One axon from CNS to the skeletal muscle
> Autonomic Nervous System
- - Regulated by Hypothalamus
- - Acts unconsciously
> > Sympathetic Nervous System (SNS)
- - - Fight-or-flight response
- - - Maintain homeostasis
- - - Two axons, second one uses norepipherine with adrenergic receptor
- - - Sometimes one axon, to adrenal gland which releases epipherine
> > Parasympathetic Nervous System (PSNS)
- - - Rest-and-digest, feed-and-breed
- - - Two axons, second one uses ACh as well but with muscarinic receptor
- - SNS and PSNS work in an antagonistic manner
> Enteric Nervous System
- - Acts on GI tract, unconsciously
Growth hormone
Activated by Ghreline (empty stomach), when going to sleep (fasted period). Therefore, growth hormone has a high peak right after you go to sleep and stays elevated during sleep.
When cortisol in the morning increases glucose even further, the high glucose then shuts off growth hormone
