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NEET MDS Synopsis - Lecture Notes
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📖 Physiology

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The Parathyroid Glands

Physiology

The Parathyroid Glands

The parathyroid glands are 4 tiny structures embedded in the rear surface of the thyroid gland. They secrete parathyroid hormone (PTH) a polypeptide of 84 amino acids. PTH increases the concentration of Ca2+ in the blood in three ways. PTH promotes

  • release of Ca2+ from the huge reservoir in the bones. (99% of the calcium in the body is incorporated in our bones.)
  • reabsorption of Ca2+ from the fluid in the tubules in the kidneys
  • absorption of Ca2+ from the contents of the intestine (this action is mediated by calcitriol, the active form of vitamin D.)

PTH also regulates the level of phosphate in the blood. Secretion of PTH reduces the efficiency with which phosphate is reclaimed in the proximal tubules of the kidney causing a drop in the phosphate concentration of the blood.

Hyperparathyroidism

Elevate the level of PTH causing a rise in the level of blood Ca2+ .Calcium may be withdrawn from the bones that they become brittle and break.

 Patients with this disorder have high levels of Ca2+ in their blood and excrete small amounts of Ca2+ in their urine. This causes hyperparathyroidism.

Hypoparathyroidism

This disorder have low levels of Ca2+ in their blood and excrete large amounts of Ca2+ in their urine.

Heart sounds

Physiology

Heart sounds


Heart sounds are a result of beating heart and resultant blood flow . that could be detected by a stethoscope during auscultation . Auscultation is a part of physical examination that doctors have to practice them perfectly.
Before discussion the origin and nature of the heart sounds we have to distinguish between the heart sounds and hurt murmurs. Heart murmurs are pathological noises that results from abnormal blood flow in the heart or blood vessels.
Physiologically , blood flow has a laminar pattern , which means that blood flows in form of layers , where the central layer is the most rapid . Laminar blood flow could be turned into turbulent one .

Turbulent blood flow is a result of stenotic ( narrowed ) valves or blood vessels , insufficient valves , roughened vessels` wall or endocardium ,  and many diseases . The turbulent blood flow causes noisy murmurs inside or outside the heart.

Heart sounds ( especially first and second sounds ) are mainly a result of closure of the valves of the heart . While the third sound is a result of vibration of ventricular wall and the leaflets of the opened AV valves after rapid inflow of blood from the atria to ventricles . 

Third heart sound is physiologic in children but pathological in adults.

The four heart sound is a result of the atrial systole and vibration of the AV valves , due to blood rush during atrial systole . It is inaudible neither in adults nor in children . It is just detectable by the phonocardiogram .


Characteristic of heart sounds :

1. First heart sound  (S1 , lub ) : a soft and low pitch sound, caused by closure of AV valves.Usually has two components ( M1( mitral ) and T1 ( tricuspid ). Normally M1 preceads T1.

2. Second heart sound ( S2 , dub) : sharp and high pitch sound . caused by closure of semilunar valves. It also has two components A2 ( aortic) and P2 ( pulmonary) . A2 preceads P2.

3. Third heart sound (S3) : low pitched sound.

4. Fourth heart sound ( S4) very low pitched sound.

As we notice : the first three sounds are related to ventricular activity , while the fourth heart sound is related to atrial activity.
Closure of valves is not the direct cause for heart sounds , but sharp blocking of blood of backward returning of blood by the closing valve is the direct cause.
 

Autonomic Nervous System

Physiology

  • The Autonomic Nervous System (ANS) Controls the Body's Internal Environment in a Coordinated Manner

  • The ANS helps control the heart rate, blood pressure, digestion, respiration, blood pH and other bodily functions through a series of complex reflex actions
  • These controls are done automatically, below the conscious level
  • To exert this control the activities of many different organs must be coordinated so they work to accomplish the same goal
  • In the ANS there are 2 nerves between the central nervous system (CNS) and the organ. The nerve cell bodies for the second nerve are organized into ganglia:
    • CNS -> Preganglionic nerve -> Ganglion -> Postganglionic nerve -> Organ
  • At each junction neurotransmitters are released and carry the signal to the next nerve or organ.

  • The ANS has 2 Divisions, Sympathetic and Parasympathetic

     

  • Comparison of the 2 systems:

  •  

    Anatomical
    Location

     Preganglionic
    Fibers

     Postganglionic
    Fibers

     Transmitter
    (Ganglia)

     Transmitter
    (Organs)

     Sympathetic

     Thoracic/
    Lumbar

     Short

    Long

    ACh

    NE

     Parasympathetic

     Cranial/
    Sacral

     Long

    Short

    ACh

    ACh

     

    The Sympathetic is the "Fight or Flight" Branch of the ANS

  • Emergency situations, where the body needs a sudden burst of energy, are handled by the sympathetic system
  • The sympathetic system increases cardiac output and pulmonary ventilation, routes blood to the muscles, raises blood glucose and slows down digestion, kidney filtration and other functions not needed during emergencies
  • Whole sympathetic system tends to "go off" together
  • In a controlled environment the sympathetic system is not required for life, but it is essential for any stressful situation

  • The Parasympathetic is the Rest and Digest Branch of the ANS

  • The parasympathetic system promotes normal maintenance of the body- acquiring building blocks and energy from food and getting rid of the wastes
  • It promotes secretions and mobility of different parts of the digestive tract.
  • Also involved in urination, defecation.
  • Does not "go off" together; activities initiated when appropriate
  • The vagus nerve (cranial number 10) is the chief parasympathetic nerve
  • Other cranial parasympathetic nerves are: III (oculomotor), VII (facial) and IX (glossopharyngeal)

  • The Hypothalamus Has Central Control of the ANS

  • The hypothalamus is involved in the coordination of ANS responses,
  • One section of the hypothalamus seems to control many of the "fight or flight" responses; another section favors "rest and digest" activities

  • The Adrenal Medulla is an Extension of the Sympathetic Nervous System

  • The adrenal medulla behaves like a combined autonomic ganglion and postsynaptic sympathetic nerve (see diagram above)
  • Releases both norepinephrine and epinephrine in emergency situations
    • Releases a mixture of epinephrine (E = 80%) and norepinephrine (NE = 20%)
    • Epinephrine = adrenaline
  • This action is under control of the hypothalamus

  • Sympathetic & Parasympathetic Systems

  • Usually (but not always) both sympathetic and parasympathetic nerves go to an organ and have opposite effects
  • You can predict about 90% of the sympathetic and parasympathetic responses using the 2 phrases: "Fight or Flight" and "Rest and Digest".
  • Special cases:
    • Occasionally the 2 systems work together: in sexual intercourse the parasympathetic promotes erection and the sympathetic produces ejaculation
    • Eye: the sympathetic response is dilation and relaxation of the ciliary muscle for far vision (parasympathetic does the opposite)
    • Urination: the parasympathetic system relaxes the sphincter muscle and promotes contraction of muscles of the bladder wall -> urination (sympathetic blocks urination)
    • Defecation: the parasympathetic system causes relaxation of the anal sphincter and stimulates colon and rectum to contract -> defecation (sympathetic blocks defecation)

  •  Organ

     Parasympathetic Response
    "Rest and Digest"

     Sympathetic Response
    "Fight or Flight"

     Heart
    (baroreceptor reflex)

    Decreased heart rate
    Cardiac output decreases

    Increased rate and strength of contraction
    Cardiac output increases

     Lung Bronchioles

     Constriction

    Dilation

     Liver Glycogen

    No effect

     Glycogen breakdown
    Blood glucose increases

     Fat Tissue

     No effect

    Breakdown of fat
    Blood fatty acids increase

     Basal Metabolism

     No effect

     Increases ~ 2X

     Stomach

     Increased secretion of HCl & digestive enzymes
    Increased motility

    Decreased secretion
    Decreased motility

     Intestine

     Increased secretion of HCl & digestive enzymes
    Increased motility

     Decreased secretion
    Decreased motility

     Urinary bladder

     Relaxes sphincter
    Detrusor muscle contracts
    Urination promoted

    Constricts sphincter
    Relaxes detrusor
    Urination inhibited

     Rectum

     Relaxes sphincter
    Contracts wall muscles
    Defecation promoted

     Constricts sphincter
    Relaxes wall muscles
    Defecation inhibited

     Eye

     Iris constricts
    Adjusts for near vision

    Iris dilates
    Adjusts for far vision

     Male Sex Organs

     Promotes erection

     Promotes ejaculation

     

Clinical Physiology CVS

Physiology

Clinical Physiology 

Heart Failure : Heart failure is inability of the heart to pump the enough amount of blood needed to sustain the needs of organism .
It is usually called congestive heart failure ( CHF) .

To understand the pathophysiology  of the heart failure ,  lets compare it with the physiology of the cardiac output :
Cardiac output =Heart rate X stroke volume

Stroke volume is determined by three determinants : Preload ( venous return ) , contractility , and afterload    (peripheral resistance ) . Any disorder of these factors will reduce the ability of the heart to pump blood .

Preload : Any factor that decrease the venous return , either by decreasing the intravenous pressure or increasing the intraatrial pressure will lead to heart failure .

Contractility : Reducing the power of contraction such as in  myocarditis , cardiomyopathy , preicardial tamponade ..etc , will lead to heart failure .

Afterload : Any factor that may increase the peripheral resistance such as hypertension , valvular diseases of the heart may cause heart failure.

Pathophysiology : When the heart needs to contract more to meet the increased demand , compensatory mechanisms start to develope to enhance the power of contractility  . One of these mechanism is increasing heart rate , which will worsen the situation because this will increase the demands of the myocardial cells themselves . The other one is hypertrophy of the cardiac muscle which may compensate the failure temporarily but then the hypertrophy will be an additional load as the fibers became stiff  .

The stroke volume will be reduced , the intraventricular pressure will increase and consequently the intraatrial pressure and then the venous pressure . This will lead to decrease reabsorption of water from the interstitium ( see microcirculation) and then leads to developing of edema ( Pulmonary edema if the failure is left , and systemic edema if the failure is right) .