NEET MDS Lessons
Physiology
An anti-diruetic is a substance that decreases urine volume, and ADH is the primary example of it within the body. ADH is a hormone secreted from the posterior pituitary gland in response to increased plasma osmolarity (i.e., increased ion concentration in the blood), which is generally due to an increased concentration of ions relative to the volume of plasma, or decreased plasma volume.
The increased plasma osmolarity is sensed by osmoreceptors in the hypothalamus, which will stimulate the posterior pituitary gland to release ADH. ADH will then act on the nephrons of the kidneys to cause a decrease in plasma osmolarity and an increase in urine osmolarity.
ADH increases the permeability to water of the distal convoluted tubule and collecting duct, which are normally impermeable to water. This effect causes increased water reabsorption and retention and decreases the volume of urine produced relative to its ion content.
After ADH acts on the nephron to decrease plasma osmolarity (and leads to increased blood volume) and increase urine osmolarity, the osmoreceptors in the hypothalamus will inactivate, and ADH secretion will end. Due to this response, ADH secretion is considered to be a form of negative feedback.
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.
Proteinuria—Protein content in urine, often due to leaky or damaged glomeruli.
Oliguria—An abnormally small amount of urine, often due to shock or kidney damage.
Polyuria—An abnormally large amount of urine, often caused by diabetes.
Dysuria—Painful or uncomfortable urination, often from urinary tract infections.
Hematuria—Red blood cells in urine, from infection or injury.
Glycosuria—Glucose in urine, due to excess plasma glucose in diabetes, beyond the amount able to be reabsorbed in the proximal convoluted tubule.
Hormones are carried by the blood throughout the entire body, yet they affect only certain cells. The specific cells that respond to a given hormone have receptor sites for that hormone.
This is sort of a lock and key mechanism. If the key fits the lock, then the door will open. If a hormone fits the receptor site, then there will be an effect. If a hormone and a receptor site do not match, then there is no reaction. All of the cells that have receptor sites for a given hormone make up the target tissue for that hormone. In some cases, the target tissue is localized in a single gland or organ. In other cases, the target tissue is diffuse and scattered throughout the body so that many areas are affected.
Hormones bring about their characteristic effects on target cells by modifying cellular activity. Cells in a target tissue have receptor sites for specific hormones. Receptor sites may be located on the surface of the cell membrane or in the interior of the cell.
In general those protein hormones are unable to diffuse through the cell membrane and react with receptor sites on the surface of the cell. The hormone receptor reaction on the cell membrane activates an enzyme within the membrane, called adenyl cyclase, which diffuses into the cytoplasm. Within the cell, adenyl cyclase catalyzes or starts the process of removal of phosphates from ATP to produce cyclic adenosine monophosphate or c AMP. This c AMP activates enzymes within the cytoplasm that alter or change the cellular activity. The protein hormone, which reacts at the cell membrane, is called the first messenger. c Amp that brings about the action attributed to the hormone is called the second messenger. This type of action is relatively rapid because the precursors are already present and they just needed to be activated in some way.
Biological Functions are Extremely Sensitive to pH
- H+ and OH- ions get special attention because they are very reactive
- Substance which donates H+ ions to solution = acid
- Substance which donates OH- ions to solution = base
- Because we deal with H ions over a very wide range of concentration, physiologists have devised a logarithmic unit, pH, to deal with it
- pH = - log [H+]
- [H+] is the H ion concentration in moles/liter
- Because of the way it is defined a high pH indicates low H ion and a low pH indicates high H ion- it takes a while to get used to the strange definition
- Also because of the way it is defined, a change of 1 pH unit means a 10X change in the concentration of H ions
- If pH changes by 2 units the H+ concentration changes by 10 X 10 = 100 times
- Human blood pH is 7.4
- Blood pH above 7.4 = alkalosis
- Blood pH below 7.4 = acidosis
- Body must get rid of ~15 moles of potential acid/day (mostly CO2)
- CO2 reacts with water to form carbonic acid (H2CO3)
- Done mostly by lungs & kidney
- In neutralization H+ and OH- react to form water
- If the pH changes charges on molecules also change, especially charges on proteins
- This changes the reactivity of proteins such as enzymes
- Large pH changes occur as food passes through the intestines.
Each hormone in the body is unique. Each one is different in it's chemical composition, structure, and action. With respect to their chemical structure, hormones may be classified into three groups: amines, proteins, and steroids.
Amines- these simple hormones are structural variation of the amino acid tyrosine. This group includes thyroxine from the thyroid gland and epinephrine and norepinephrine from the adrenal medulla.
Proteins- these hormones are chains of amino acids. Insulin from the pancreas, growth hormone from the anterior pituitary gland, and calcitonin from the thyroid gland are all proteins. Short chains of amino acids are called peptides. Antidiuretic hormone and oxytocin, synthesized by the hypothalamus, are peptide hormones.
Steroids- cholesterol is the precursor for the steroid hormones, which include cortisol and aldosterone from the adrenal cortex, estrogen and progesterone from the ovaries, and testosterone from the testes.
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) .