NEET MDS Lessons
Physiology
Reflexes
A reflex is a direct connection between stimulus and response, which does not require conscious thought. There are voluntary and involuntary reflexes.
The Stretch Reflex:
The stretch reflex in its simplest form involves only 2 neurons, and is therefore sometimes called a 2-neuron reflex. The two neurons are a sensory and a motor neuron. The sensory neuron is stimulated by stretch (extension) of a muscle. Stretch of a muscle normally happens when its antagonist contracts, or artificially when its tendon is stretched, as in the knee jerk reflex. Muscles contain receptors called muscle spindles. These receptors respond to the muscles's stretch. They send stimuli back to the spinal cord through a sensory neuron which connects directly to a motor neuron serving the same muscle. This causes the muscle to contract, reversing the stretch. The stretch reflex is important in helping to coordinate normal movements in which antagonistic muscles are contracted and relaxed in sequence, and in keeping the muscle from overstretching.
Since at the time of the muscle stretch its antagonist was contracting, in order to avoid damage it must be inhibited or tuned off in the reflex. So an additional connection through an interneuron sends an inhibitory pathway to the antagonist of the stretched muscle - this is called reciprocal inhibition.
The Deep Tendon Reflex:
Tendon receptors respond to the contraction of a muscle. Their function, like that of stretch reflexes, is the coordination of muscles and body movements. The deep tendon reflex involves sensory neurons, interneurons, and motor neurons. The response reverses the original stimulus therefore causing relaxation of the muscle stimulated. In order to facilitate that the reflex sends excitatory stimuli to the antagonists causing them to contract - reciprocal activation.
The stretch and tendon reflexes complement one another. When one muscle is stretching and stimulating the stretch reflex, its antagonist is contracting and stimulating the tendon reflex. The two reflexes cause the same responses thus enhancing one another.
The Crossed Extensor Reflex -
The crossed extensor reflex is just a withdrawal reflex on one side with the addition of inhibitory pathways needed to maintain balance and coordination. For example, you step on a nail with your right foot as you are walking along. This will initiate a withdrawal of your right leg. Since your quadriceps muscles, the extensors, were contracting to place your foot forward, they will now be inhibited and the flexors, the hamstrings will now be excited on your right leg. But in order to maintain your balance and not fall down your left leg, which was flexing, will now be extended to plant your left foot (e.g. crossed extensor). So on the left leg the flexor muscles which were contracting will be inhibited, and the extensor muscles will be excited
HEART DISORDERS
- Pump failure => Alters pressure (flow) =>alters oxygen carrying capacity.
- Renin release (Juxtaglomerular cells) Kidney
- Converts Angiotensinogen => Angiotensin I
- In lungs Angiotensin I Converted => Angiotensin II
- Angiotensin II = powerful vasoconstrictor (raises pressure, increases afterload)
- stimulates thirst
- stimulates adrenal cortex to release Aldosterone
(Sodium retention, potassium loss) - stimulates kidney directly to reabsorb Sodium
- releases ADH from Posterior Pituitary
- Myocardial Infarction
- Myocardial Cells die from lack of Oxygen
- Adjacent vessels (collateral) dilate to compensate
- Intracellular Enzymes leak from dying cells (Necrosis)
- Creatine Kinase CK (Creatine Phosphokinase) 3 forms
- One isoenzyme = exclusively Heart (MB)
- CK-MB blood levels found 2-5 hrs, peak in 24 hrs
- Lactic Dehydrogenase found 6-10 hours after. points less clearly to infarction
- Serum glutamic oxaloacetic transaminase (SGOT)
- Found 6 hrs after infarction, peaks 24-48 hrs at 2 to 15 times normal,
- SGOT returns to normal after 3-4 days
- Creatine Kinase CK (Creatine Phosphokinase) 3 forms
- Myocardium weakens = Decreased CO & SV (severe - death)
- Infarct heal by fibrous repair
- Hypertrophy of undamaged myocardial cells
- Increased contractility to restore normal CO
- Improved by exercise program
- Prognosis
- 10% uncomplicated recovery
- 20% Suddenly fatal
- Rest MI not fatal immediately, 15% will die from related causes
- Congenital heart disease (Affect oxygenation of blood)
- Septal defects
- Ductus arteriosus
- Valvular heart disease
- Stenosis = cusps, fibrotic & thickened, Sometimes fused, can not open
- Regurgitation = cusps, retracted, Do not close, blood moves backwards
Red Blood Cells (erythrocytes)
- Women average about 4.8 million of these cells per cubic millimeter (mm3; which is the same as a microliter [µl]) of blood.
- Men average about 5.4 x 106 per µl.
- These values can vary over quite a range depending on such factors as health and altitude.
- RBC precursors mature in the bone marrow closely attached to a macrophage.
- They manufacture hemoglobin until it accounts for some 90% of the dry weight of the cell.
- The nucleus is squeezed out of the cell and is ingested by the macrophage.
RBC have characteristic biconcave shape
Thus RBCs are terminally differentiated; that is, they can never divide. They live about 120 days and then are ingested by phagocytic cells in the liver and spleen. Most of the iron in their hemoglobin is reclaimed for reuse. The remainder of the heme portion of the molecule is degraded into bile pigments and excreted by the liver. Some 3 million RBCs die and are scavenged by the liver each second.
Red blood cells are responsible for the transport of oxygen and carbon dioxide.
HEART DISORDERS
- Pump failure => Alters pressure (flow) =>alters oxygen carrying capacity.
- Renin release (Juxtaglomerular cells) Kidney
- Converts Angiotensinogen => Angiotensin I
- In lungs Angiotensin I Converted => Angiotensin II
- Angiotensin II = powerful vasoconstrictor (raises pressure, increases afterload)
- stimulates thirst
- stimulates adrenal cortex to release Aldosterone
(Sodium retention, potassium loss) - stimulates kidney directly to reabsorb Sodium
- releases ADH from Posterior Pituitary
- Myocardial Infarction
- Myocardial Cells die from lack of Oxygen
- Adjacent vessels (collateral) dilate to compensate
- Intracellular Enzymes leak from dying cells (Necrosis)
- Creatine Kinase CK (Creatine Phosphokinase) 3 forms
- One isoenzyme = exclusively Heart (MB)
- CK-MB blood levels found 2-5 hrs, peak in 24 hrs
- Lactic Dehydrogenase found 6-10 hours after. points less clearly to infarction
- Serum glutamic oxaloacetic transaminase (SGOT)
- Found 6 hrs after infarction, peaks 24-48 hrs at 2 to 15 times normal,
- SGOT returns to normal after 3-4 days
- Creatine Kinase CK (Creatine Phosphokinase) 3 forms
- Myocardium weakens = Decreased CO & SV (severe - death)
- Infarct heal by fibrous repair
- Hypertrophy of undamaged myocardial cells
- Increased contractility to restore normal CO
- Improved by exercise program
- Prognosis
- 10% uncomplicated recovery
- 20% Suddenly fatal
- Rest MI not fatal immediately, 15% will die from related causes
- Congenital heart disease (Affect oxygenation of blood)
- Septal defects
- Ductus arteriosus
- Valvular heart disease
- Stenosis = cusps, fibrotic & thickened, Sometimes fused, can not open
- Regurgitation = cusps, retracted, Do not close, blood moves backwards
Serum Lipids
|
LIPID |
Typical values (mg/dl) |
Desirable (mg/dl) |
|
Cholesterol (total) |
170–210 |
<200 |
|
LDL cholesterol |
60–140 |
<100 |
|
HDL cholesterol |
35–85 |
>40 |
|
Triglycerides |
40–160 |
<160 |
- Total cholesterol is the sum of
- HDL cholesterol
- LDL cholesterol and
- 20% of the triglyceride value
- Note that
- high LDL values are bad, but
- high HDL values are good.
- Using the various values, one can calculate a
cardiac risk ratio = total cholesterol divided by HDL cholesterol - A cardiac risk ratio greater than 7 is considered a warning.
Levels of Organization:
CHEMICAL LEVEL - includes all chemical substances necessary for life (see, for example, a small portion - a heme group - of a hemoglobin molecule); together form the next higher level
CELLULAR LEVEL - cells are the basic structural and functional units of the human body & there are many different types of cells (e.g., muscle, nerve, blood)
TISSUE LEVEL - a tissue is a group of cells that perform a specific function and the basic types of tissues in the human body include epithelial, muscle, nervous, and connective tissues
ORGAN LEVEL - an organ consists of 2 or more tissues that perform a particular function (e.g., heart, liver, stomach)
SYSTEM LEVEL - an association of organs that have a common function; the major systems in the human body include digestive, nervous, endocrine, circulatory, respiratory, urinary, and reproductive.
There are two types of cells that make up all living things on earth: prokaryotic and eukaryotic. Prokaryotic cells, like bacteria, have no 'nucleus', while eukaryotic cells, like those of the human body, do.
The Nervous System Has Peripheral and Central Units
- The central nervous system (CNS) is the brain and spinal column
- The peripheral nervous system (PNS) consists of nerves outside of the CNS
- There are 31 pairs of spinal nerves (mixed motor & sensory)
- There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)
The pattern of innervation plotted on the skin is called a dermatome
The Nervous System Has Peripheral and Central Units
- The central nervous system (CNS) is the brain and spinal column
- The peripheral nervous system (PNS) consists of nerves outside of the CNS
- There are 31 pairs of spinal nerves (mixed motor & sensory)
- There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)
The pattern of innervation plotted on the skin is called a dermatome