The Hypothalamus, Pituitary Glands and Hormones! And not the Sex Pheromone Variety…

The Hypothalamus and the pituitary gland are super important in regulating the hormone release from one other gland in the body.
The Hypothalamus is the link between the Endocrine and Nervous System, It also controls the Pituitary Gland through 9 releasing and inhibiting hormones. Together the Pituitary Gland and the Hypothalamus regulate all aspects of growth, development, metabolism and homeostasis. The Pituitary Gland secretes several hormones that the Hypothalamus generates (synthesises).

For example the Pituitary Gland and the hypothalamus are involved in Thyroid Function.
The Hypothalamus produces TRH  – Thyrotropin releasing Hormones when the thyroid hormone level drops in the body. This causes the secretion of TSH – Thyroid stimulating Hormone from the Pituitary Gland. This causes the Thyroid to produe more T3 and T4 Hormones which raise the level in the blood – The Pituitary Gland will then lower the amount of TSH in the blood.


ADH – Antidiuretic Hormone – Vasopressin

ADH is produced in the Hypothalamus and released in the posterior pituitary (Posterior Lobe/Neurophypophysis) as a response to dehydration.

Antidiuretic Hormone stimulates water reabsorption by the kidneys and arteriolar constriction. General Function is vasopressin – conserving water. ADH (is released) kicks in during dehydration –  decreases urine production and sweating and increases blood pressure as a result of vasoconstriction. ADH is controlled by the osmotic pressure in the blood. And during over hydration ADH is inhibited.

Dehydration:

  1. Hypothalamic osmoreceptors are stimulated by High Blood Osmotic pressure
  2. Osmoreceptors activate the neurosecretory cells that synthesis and release ADH
  3. Nerve impulses free ADH from axon terminals in the Pituitary Gland into the bloodstream
  4. Kidneys retain more water – decreases urine volume, Sweat Glands decrease water loss and Arterioles constrict – increased BP

Overhydration:

  1. Low Blood Osmotic Pressure inhibits hypothalamic osmoreceptors
  2. Then this impacts on the ADH secretion as osmoreceptors are inhibited
  3. Which effects, sweat, urine and blood pressure.

Flight or Fight?

The Autonomic Nervous System usually operates without conscious control, it is regulated by the hypothalamus and the brain stem. The efferent parts of the ANS are divided into the Sympathetic and the Parasympathetic. Some organs in the body receive impulses from both of these, this is called dual innervation.

The Sympathetic system takes over in any physical or mental stress, for example;

  • exercise,
  • embarrassment,
  • excitement
  • and emergency.

It is accompanied by the body getting ready to implement the fight or flight response, this means:

  • dilation of pupils
  • increase of heart rate and blood pressure
  • decrease in blood flow to nonessential organs (e.g. focus away from digesting food)
  • increase in blood flow to skeletal & cardiac muscle
  • airways dilate & respiratory rate increases
  • and blood glucose level increase

I can identify a few times when the fight or flight response kicked in,

A few weeks ago two men tried to break into the secure building I live in at 3am, my body was flooded with adrenaline and cortisol even though I knew I was safe. I could feel my heart racing and suddenly had such amazing energy even though I had just been woken up at 3 am by breaking tiles. I went out and started to yell at them, and ended up man handling one of them, not realising that I felt somewhat stronger than usual, I ended up piercing the skin when I grabbed one guy by the arm which I didn’t notice until after the fiasco.

On reflection,  I wouldn’t actually be threatening to two very intoxicated big burly men. It took around an hour for my body to calm down afterwards and I felt like I really needed to go for a run or do something to expel all the excess energy.

Learned Reflexes Vs Innate Reflexes

What is the difference between innate reflexes and learned reflexes?

An Innate Reflex is one that you have no choice over, it is a natural unlearned response to a stimulus, for example the pupil in the eye ball resizing in adjustment to light or a knee jerk in response to getting hit by a hammer, or goose bumps in the cold.
 Learned Reflexes are association related. For example, beginning to salivate when smelling food, or the sound of a bell as seen in studied.

While both forms of reflexes show success to survival, the innate reflexes, like the gag reflex to stop you from choking, are life essential, or the automatic response to jerk away from items that are too hot or to drop them in our attempt to remove ourselves from the exposure to pain.

Neurons – A briefing – Anatomy and Physiology



Neurons, yay! These little guys respond to electrical excitement! Don’t they just sound like the life of the party? They respond to a change in the environment ( but it has to be powerful enough to start the ball rolling on action potential), this is called a stimulus, and then turn that response into action potential! Action potential is a nerve impulse – an electrical charge that moves all the way along the surface of the membrane of a neuron!
How the hell does it move? Easy! The movement of Na and K, ions, between the interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane. A nerve impulse travels at the same quick speed through the journey. Some Neurons are really short, and some are super long! like form your waste to your ankle.

Neurons are made up of three parts:

  1. Cell Body (Perikaryon or Soma) contains a nucleus surrounded by cytoplasm
  2. Dendrites (like little trees, there is usually multiple dendrites and only one axon) are the part that receives the signal, the plasma membranes contain reception sites for binding the chemical messages from other cells. Dendrites are usually short but with lot of branches.
  3. Axon (or since there is only one of them usually per neuron – Axis) of a neuron starts the outgoing nerve impulse towards another neuron, gland cell or muscle fibre. An axon is long and thin cylinder shaped, it joins to the cell body at the cone shape (axon hillock), the closes to this part of the axon is called the initial segment. The nerve impulse starts between the axon hillock and the initial segment, this is called the trigger zone. The cytoplasm of the axon, axoplasm, is covered by plasma membranes – axolemma, a bit like a husk. The communication between neurons occurs in the synapse

Now for the interesting bit:

Structural Classification of Neurons:

  • Multipolar neurons: these have lots of dendrites and one axon, mainly the neurons of the brain and spinal cord and all motor neurones fit in this category.
  • Bipolar neurons: one dendrite and one axon, found mainly in the eye, ear and olfactory area of the brain
  • Unipolar Neurons: have some dendrites and one axon that have fused together to become a single process. These ones detect the feeling sensations : touch, pressure, pain or thermal. These can be found in the spinal cord.
    There are is also a functional classification for these neurons too*

Anatomy and Physiology – Bones – Osteoporosis

So to many of us, the idea of getting old sucks, but what about getting Osteoporosis?

 

Osteoporosis is a condition that makes bone brittle.

 

Getting old and being a female is a risk in itself, but having low bone mass – osteopenia, puts the risk for osteoporosis higher. Low bone mass can result in bones breaking due to regular lifestyle wear and tear. It is an interesting note to look at hip replacement failure – there is a higher incidence in patients who are younger since they are generally more physically active.

The effects of of this condition is largely due to a depletion of calcium in the body, it is important to consider the thyroid function. Osteoporosis effects the whole body, not just hips or knees. The Spine can be effected and Osteoporosis can be in play when you see a larger range of elderly people hunched over or through the stereotypical idea that people get shorter as they age – which can be due to osteoporosis.

How might osteoporosis impact on the life of an elderly person?

We all generalise that as people age, they become more frail, but with osteoporosis this is really the case. A simple fall or knock could result in some serious damage being done. Everyday activities can result in a one way trip to hospital, providing they can even make it to a phone if they live alone.

For example if an elderly woman lives alone  and is suffering from Osteoporosis, if she falls and that results in a bone breakage, there may be no way for her to call for help and may become trapped at one end of the house with no way to get assistance. It can really cause a lot of anxiety in sufferers and cause fear to be left alone. Unfortunately this occurs too regularly where an elderly person will suffer a bone breakage and become unable to call for assistance, leaving them reliant on someone to check in on them to alert the hospital and health care services. This is a form of alienation, which can aggravate anxiety and depression in the elderly who may become to feel uncomfortable being alone and performing routine everyday tasks.

Anatomy and Physiology – Apical Surface Structure Adaptation of Epithelial Cells For Different Functions – Pseudo Stratified Columnar Epithelium

Cells have adaptions to perform functions…. WHAT?

Get To Know What The Hell I’m Talking About:

  • Epithelial Cells cover EVERYTHING, well not really, but it does cover the body surface and lines the hollow organs as well as forming ducts and some other pretty cool things, it can be put into two types: Covering and Lining Epithelium (skin, lining of the blood vessels, ducts and tracts – GI, Urinary, Reproductive and Respiratory) and Glandular Epithelium – thyroid, adrenal and sweat glands .
  • Epithelial Cells are very closely packed and cell junctions make sure that they are securely attached. There is no blood vessels so everything moves by diffusion. Here there is also a super high mitotic rate.
  • These epithelial cells sit on the basement membrane : the  Apical – free surface (top) and the basal surface against the basement membrane (bottom).
    They are classified by their arrangement: Simple(One cell thick), Stratified (two or more layers thick) or Pseudo Stratified (not all the cells reach apical surface but they are touching the basement membrane – nuclei are located at different levels )
    They are also classified by their shape of the surface cells:
    Squamous – flat, Cuboidal – cube shaped, columnar – like columns, transitional – varied shape.

Now that we are on a flat playing field and we all have the basic basic knowledge we can talk further about the cells adaptation for function. While as interesting as it is to know about cell mutations in the body due to adaption, we better save that for another day and focus on The adaption of cells to perform a designated function.

Let’s look at Pseudo Stratified Epithelium –  Ciliated and Columnar :

Epithelial Cells have adapted their surface shape to meet the requirements to perform their function. Pseudo Stratified Epithelium has the nuclei at different levels and appears multi layered and only have the appearance of multiple layers unlike stratified epithelium – which isa actually layered for two or more. These cells are at varied lengths, so not all cells reach apical surface, and those that do will either secrete mucus – goblet cells or have cilia – to sweep away mucus in the Ciliated Columnar Pseudo Stratified Epithelium.  Columnar Cells – protect underlying tissue and are specialised with secretion and absorption (mainly non ciliated columnar) and often have microvilli or cilia.
Ciliated Columnar Pseudo Stratified Epithelium can be found in the respiratory system as well as the epidermis and male urethra. Due to it’s location in the respiratory tract the epithelial cells are adapted so that they can get rid of the foreign particles that get swept in with inhalation.

How Viruses Take Over Our Cells In Order To Replicate – Anatomy and Physiology

Why are viruses so freaking cool?

If you ignore the reputation they have about making people sick, they are by far the coolest thing you will come across in Microbiology. The word virus means venom or poison (Lee and Bishop, 2013).
Viruses are selective as all get out, they are specific to animals, plants and bacteria, and to narrow it down even further, they usually are species specific, but some aren’t, so keep that in mind (Cough*Bird Flu*Cough).

Lets start with the characteristics of Viruses:

  • They are the smallest infectious agents known, ranging from a diameter of 20nm to 400nm. You need an electronic microscope to be able to see them.
  • They lack enzymes necessary for metabolism, and due to their lacking of important enzymes, they can’t even synthesis complex molecules. This is why they need a living host, and there they will replicate inside a host cell. It is  inside the host cell that they ‘hijack’ the metabolic machinery.

Viruses take over our cell reproduction in our DNA in order to replicate. During replication, the host cells often get damaged resulting in cell death. (Lee and Bishop, 2013).

Viruses are categorised by shape and structure. They only produce one type of nucleic acid which holds their genetic code, this can be single stranded RNA, double stranded RNA, single stranded DNA, double stranded DNA. Due to the small size of viruses they can’t not carry the equipment needed, this is where a living host cell is required.

How do Viruses take over our cells in order to replicate?

The Lytic Phase:

  • A virus attaches to a host
  • The virus either enter the cell or injects genetic instructions for the host enzymes to make a new virus.
  • A new virus is assembled
  • The virus busts out of the host cell = killing the cell
  • Moves on to Infect a new cell.

They Attach and Enter:
The capsid’s proteins can have antigenic properties, which means that they will produce a corresponding antibody to the immune system – enabling the virus to attach and enter the host cell. A bit like a lock key fit. Whether or not a virus attaches is dependent on the attachment site on the surface of the host cell.
Some viruses have an envelope surrounding them, which have a lipid bilayer, on this lipid bilayer, there are proteins and glycoproteins that happen to look like spikes. These ‘spikes’ help the virus attach. For example in the Influenza virus, the ‘spikes’ to the surface receptors on the cells of the respiratory epithelium.  These proteins on the surface of the virus bind to the receptor molecules on the surface (plasma membrane) of the host cell if they correspond.

Replication, Assembly and the Infective Process:
The Virus has genes which will code for enzymes required for replication – in order to start infection. When a host cell is infected, the virus will ensure that the cell will produce viral protein and genetic material from it’s ‘hijacked’ equipment through nucleic acid transcription. The actual replication process is dependent on whether the nucleic acid of the virus is single or double stranded, or, DNA or RNA.
The new virus will be made inside the cell and when ready to go out and infect other cells, it will burst the cell, killing it. Up until this point the host cell will still be functioning, just at a very reduced rate, this is because the virus needs to make all the parts necessary before destroying the host cell.

*The envelope can be easily damaged and some viruses don’t have one, these are called naked viruses, and are generally more resistant to environmental changes.*

Our DNA contains the ‘blue-print’ for over 100,000 different proteins AND it contains genes that are just for us! So we should really consider how cool our DNA is too. I mean, can you believe that it knows the code for so many things??

All information was taken from Lee and Bishop’s textbook ‘Microbiology and Infection Control for Health Professionals‘, 5th edition, 2013 and  Introduction to the Viruses by the University of Berkley.

For Further Info check out this youtube video : Entry of a Virus into the Host Cell